Tesi Doc Maja

POLITECNICO DI MILANO Polo Territoriale di Como

Scuola di Ingegneria dell'Informazione

Corso di Laurea Magistrale in Ingegneria Informatica

SMARTPHONES ANALYSIS ESTIMATING RNC UNIT LOAD

Relatore: Prof. Antonio Capone

Tesi di Laurea di: Maja Lazarovska 764510

ANNO ACCADEMICO 2011-2012

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Contents Motivazione ...................................................................................................................... iii Motivation ......................................................................................................................... iv Acknowledgements ........................................................................................................... v Abbreviations ................................................................................................................... vi 1 Introduction ............................................................................................................... 1 2 UMTS Architecture ................................................................................................... 3

2.1 UTRAN Architecture .......................................................................................... 5 2.2 UTRAN Interfaces and Signaling ....................................................................... 7

3 Transport Channels ................................................................................................. 10 3.1 Dedicated Transport Channel ........................................................................... 10 3.2 Common Transport Channels ........................................................................... 10

4 HSPA and HSPA+ ................................................................................................... 12 4.1 HSDPA ............................................................................................................. 12 4.2 HSUPA ............................................................................................................. 14 4.3 HSPA+ .............................................................................................................. 16

5 Radio Resource Management ................................................................................. 21 5.1 RRC Connection States..................................................................................... 24

6 Smartphones ............................................................................................................ 26 6.1 Understanding smartphones behavior ............................................................... 27

6.1.1 Always-On-Line Applications ...................................................................... 31 6.1.2 Always-On-Line PDP Context ..................................................................... 32 6.1.3 Fast Dormancy .............................................................................................. 35

7 Radio Network Controller ...................................................................................... 39 7.1 NSN RNC2600 ................................................................................................. 42

7.1.1 Hardware Characteristics .............................................................................. 42 7.1.2 Software Characteristics ............................................................................... 45

7.2 Huawei BSC6900.............................................................................................. 45 7.2.1 Hardware Characteristics .............................................................................. 46 7.2.2 Software Characteristics ............................................................................... 47

8 Estimation of the Unit Loads .................................................................................. 48 8.1 Key Performance Indicators ............................................................................. 48 8.2 NSN Units ......................................................................................................... 50

8.2.1 ICSU Model .................................................................................................. 50 8.2.2 DMPG Model................................................................................................ 57

8.3 Huawei Units .................................................................................................... 61

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8.3.1 SPU Model .................................................................................................... 61 8.3.2 DPU Model ................................................................................................... 64

8.4 Review .............................................................................................................. 67 9 Future Work ............................................................................................................ 68 10 Conclusion ................................................................................................................ 69 References ........................................................................................................................ 71

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Motivazione La popolarit crescente delle tecnologie e delle applicazioni mobili sta attirando giorno per giorno gli utenti che sfruttano sempre pi i nuovi servizi a banda larga in mobilit che nelle loro vite, il loro lavoro e il loro modo di comunicare e di interagire con i loro amici, familiari e colleghi. La richiesta di unalta qualit del servizio sta quindi aumentando, e un miglioramento delle tecnologie mobili necessario per ispirare e motivare nuove idee che potrebbero migliorare il nostro modo di comunicare e il nostro modo di accedere alle informazioni disponibili su Internet. Questo ha spinto i fornitori di apparati e gli operatori ad accelerare alcune evoluzioni nella rete radiomobile per soddisfare le esigenze dei loro clienti. Il consumo dei dati mobili ha iniziato a crescere molto velocemente, spingendo gli operatori ad gestire una notevole mole di dati, generata principalmente dagli utenti connessi tramite laptop. Con l'arrivo degli smartphone, gli operatori in un primo tempo hanno ritenuto sufficiente la prestazione in quanto questi nuovi utenti generavano dei volumi decisamente pi contenuti di traffico dati (circa un sesto di quella dei laptop). Dopo poco per emerso un nuovo collo di bottiglia, infatti il gran numero di applicazioni always-on-line ha cambiato le condizioni la congestione della rete. Tutte le connessioni generate da questi applicativi infatti, instant messaging, modifica dello stato di Facebook, ricevere una nuova email, portano piccole quantit di dati, ma molto traffico di segnalazione che apre e chiude la sessione di dati. Con limplementazione delle reti WCDMA, il traffico dati stato attivato, ma anche la qualit della voce stata migliorata. Con la sola Release 99, stata offerta dagli operatori la velocit massima di 384 kbps. Implementando levoluzione di HSPA, le velocit hanno raggiunto dei valori fino a 14,4 Mbps e 42 Mbps con HSPA +. Quindi, la velocit non un problema, ma cosa dire della segnalazione?

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Motivation The growing popularity of mobile technologies and applications is attracting day by day users that are looking for new mobile broadband services that interweave their lives, their work, and the way they communicate and interact with their friends, family and colleagues. Thus, the demand of a new quality of experiences is rising and an improvement on the mobile technologies is needed inspiring and motivating new ideas that might improve the way we communicate and the way we access the information available on the Internet. This has put the vendors and the operators into an urgent position to make some changes in the network in order to satisfy the need of their customers. Mobile data consumption started to grow really fast, leading the broadband operators to a task to provide enough data capacity for the laptop users. After the arrival of the smartphones, the operators were happy with their performance in terms of data traffic generation (about one-sixth of the laptops). But, the great number of always-on-line applications is what makes the congestion in the network. All this small connections to the network for instant messaging, changing Facebook status, receiving a new email, are carrying small amounts of data, but so much signaling traffic that opens and closes the data session. With the deployment of the WCDMA networks, data was enabled, but also the voice quality was improved. A speed of maximum 384 kbps for laptop users was offered by the operators. Deploying HSPA on the top of it, rates reached up to 14.4 Mbps and now reaching amazing 42 Mbps with HSPA+. So, the speed is not an issue, but what about the signaling?

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Acknowledgements I would like to express my deepest gratitude to my supervisor Luisa Venturini, from whom I have learned a lot, for her patient guidance and enthusiastic encouragement during my six months in Vodafone Italy. I am also particularly grateful to Lucia Levi, who has always been glad to share her knowledge with me, and whose valuable suggestions and advices, not only professional, have been a great help. Moreover, I would like to thank the employees in Vodafone Italy for their willingness to give me a part of their time so generously and for their assistance during my internship. My grateful thanks are extended to prof. Antonio Capone as well, for accepting to be the academic supervisor of this thesis and for giving useful critiques of my work. Finally, I wish to thank my parents and my sister for their endless support and encouragement throughout my studies without which these two years abroad would have been really hard.

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Abbreviations ACK ACKnowledgement ALCAP Access Link Control Application Part AMC Adaptive Modulation and Coding AMR Adaptive Multi Rate ARQ Automatic Repeat-reQuest, BC BroadCast BCH Broadcast Channel BHCA Busy Hour Call Attempts BSC Base Station Controller CBC Cell Broadcast Center CN Core Network C-NBAP Common NBAP CPC Continuous Packet Connectivity CPCH Common Packet Channel CQI Channel Quality Indicator CRNC Controlling RNC CS Circuit Switch DCH Dedicated Channel DL DownLink DMCU Data and Macro Diversity Combining Unit DMPG Data and Macro Diversity Processor Group D-NBAP Dedicated NBAP DPCCH Dedicated Physical Control Channel DPCH Dedicated Physical Channel DPDCH Dedicated Physical Data Channel DRNC Drift RNC DRX Downlink Discontinuous Reception DSCH Downlink Shared Channel DTX Uplink Discontinuous Transmission E-AGCH E-DCH Absolute Grant Channel E-DCH Enhanced DCH E-DPCCH Enhanced DPCCH E-DPDCH Enhanced DPDCH E-HICH E-DCH HARQ Indication Channel EPR Extended Processing Rack EPS Extended Processing Subrack ERGCH E-DCH Relative Grant Channel FACH Forward Access Channel F-DPCH Fractional DPCH FP Frame Protocol GGSN Gateway GPRS Support Node GMSC Gateway MSC GPRS General Packet Radio Service

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GSM Global System for Mobile communications GTP GPRS Tunneling Protocol HARQ Hybrid ARQ HC High Capacity HLR Home Location Register HS-DSCH High Speed DSCH HSDPA High Speed Downlink Packet Access HS-DPCCH High Speed Dedicated Physical Control Channel HS-PDSCH High Speed Physical Downlink Shared Channel HS-SCCH High Speed Shared Control Channel HSPA High Speed Packet Access HSUPA High Speed Uplink Packet Access ICSU Interface Control and Signaling Unit IP Internet Protocol KPI Key Performance Indicator LMU Location Measurement Unit MAC Media Access Control ME Mobile Equipment MIMO Multiple Input Multiple Output MPR Main Processing Rack MPS Main Processing Subrack MSC Mobile Services Switching Center NACK Negative ACK NAS Non Access Stratum NAT Network Address Translator NBAP Node B Application Part NPGEP Network Processor Gigabit Ethernet Protected NRT Non-Real Time NSN Nokia Siemens Networks OM Operation and Maintenance OS Operating System OSS Operations Support System PCH Paging Channel PDCP Packet Data Convergence Protocol PDU Packet Data Unit PDP Packet Data Protocol PLMN Public Land Mobile Network PS Packet Switch QAM Quadrature Amplitude Modulation QoS Quality of Service RAB Radio Access Bearer RACH Random Access Channel RAN Radio Access Network RANAP RAN Application Part RAT Radio Access Technology RLC Radio Link Control

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RNC Radio Network Controller RNS Radio Network Subsystem RNSAP Radio Network Subsystem Application Part RRC Radio Resource Control RRM Radio Resource Management SF Spreading Factor SGSN Serving GPRS Support Node SHO Soft HandOver SMLC Serving Mobile Location Center SRNC Serving RNC SRNS Serving Radio Network Subsystem SRVCC Single Radio Voice Call Continuity SRVCC TCP Transmission Control Protocol TTI Transmission Time Interval UE User Equipment UMTS Universal Mobile Telecommunications System UL UpLink URA UTRAN Registration Area USIM UMTS Subscriber Identity Module UTRAN UMTS Terrestrial Radio Access Network VHC Very High Capacity VIK Vodafone Internet Key VLR Visitor Location Register VoIP Voice over IP WCDMA Wideband Code Division Multiple Access

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1 Introduction Led by the huge demand of the smartphones on the market and by the desire to offer a better quality to the customers, the main idea of this thesis is to provide a model that will estimate the behavior of the network that changes as the number of smartphones constantly grows, and in this way to provide useful information for the network planning in the future. The unexpected behavior in a 3G network is mostly due to the great amount of signaling traffic generated by the large number of smartphones connected to the network. This signaling is fully utilizing the resources of the main network elements and in this way cutting their chance to take care of the data traffic. The RNCs and the SGSNs are the central nodes that must process both the data traffic and the signaling traffic, so if one of these network elements is overloaded with the transfer of the signalizations, the managing of the data traffic would be interfered and the resources could not be properly assigned. Thus, the throughput is lowered, the response time is longer, and the quality of the voice is also getting worse. In this thesis work we will focus on the radio part of the network, having the RNC as the main node that should be prevented from congestion. One important task of the radio resource management is to ensure that the system is not overloaded and that it will remain stable. Thus, having models for estimating the load of the RNCs for the traffic in both the user (data traffic) and control plane (signaling traffic) would help the system to be planned properly and would provide exceptional overload situations. In the beginning, in chapter 2, a general overview will be given about the UMTS architecture explaining the functionalities of every part. More attention will be paid at the UTRAN part which is from greatest importance for this thesis since it consist the air interfaces and the signalization. The components of the UTRAN will be described together with their roles in the network. The functions of each interface and signaling protocol will be presented as well.

Introduction

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In chapter 3, a description of the transport channels will be given, which are used to carry the information over the air interfaces. The characteristics of both the dedicated and shared channels will be reviewed as well as their main functionalities. In the following chapter 4, an overview of HSPA and HSPA+ will be presented. The features and the improvements of HSDPA and HSUPA will be discussed and their operational principles will be illustrated. Furthermore, the fundaments of HSPA+ will be explained. All the main characteristics of this technology and its extensions will be shown. It will be discussed how HSPA+ managed to improve the performance of HSPA by the deployment of some new significant features. After understanding how HSPA/HSPA+ work in general and how this has changed the user experience, in chapter 5 it will be explained how the management of the radio resources has also changed. The new roles of the network elements and the new protocols will be presented. Also the modes and the connected states in which the UE can operate will be discussed. Further, the behavior of the smartphones will be elaborated in chapter 6. It will be shown why and how their presence in the network has brought an inevitable need of changes. Different applications and different types of smartphones will be reviewed and their effect on the network will be given, showing the problems that they cause. Also some proposed improvements will be discussed. What will be presented in chapter 7 is a general idea of a RNC and its importance in the network. Also a description of the NSN RNC2600 and Huawei BSC6900 will be given, since RNCs of this type was considered for building the models. The main parts regarding their architecture will be described. After finding out how RNCs work, in the next chapter 8, the usefulness of the KPIs for evaluating the network will be described and the elaboration of the estimation models from both of the vendors will be presented. The development of the model will be given followed by explanation of each step, as well as the conclusion of all the work giving the results obtained. In the end, chapters 9 and 10, the future work will be discussed and a conclusion of the thesis will be given accordingly.

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2 UMTS Architecture The Universal Mobile Telecommunications System (UMTS) is a 3G mobile cellular system which consists of elements that have a defined functionality and are defined at logical level. Based on similar functions that they perform, the elements are grouped into Radio Access Network (RAN) or UMTS Terrestrial RAN (UTRAN) that handles all the functions that are related to the radio part, and the Core Network (CN) which handles the switching and the routing of the calls and the data to external networks. The last part of the system is the UE. [23] The elements of the UMTS network can also be divided into sub-networks and grouped based on these features. This is possible since several elements can be of the same type. Each sub-network can be operational either on its own or together with other sub-networks and it is distinguishable by an unique identity. Such sub-network is called UMTS Public Land Mobile Network (PLMN). The figure 2.1 shows the elements of the PLMN as well as the interfaces. From specification and standardization point of view, the UE and the UTRAN have completely new protocols due to the new WCDMA radio technology, while the CN is adopted from GSM.

Figure 2.1. Network elements in PLMN

UMTS Architecture

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The UE has two parts: Mobile Equipment (ME) is the terminal used for radio communication over the Uu

interface. UMTS Subscriber Identity Module (USIM) is a smartcard which keeps the users

identity and performs authentication algorithms. It has the authentication and encryption keys stored.

The UTRAN also has two elements:

Node B is the node that communicates directly with the handset. Radio Network Controller (RNC) is the element that manages the radio resources.

It controls the Node Bs that are in its domain. In the CN, these are the main elements:

Home Location Register (HLR) is a database with the users service profile which consists of information about allowed and forbidden services. This information stays stored as long as the subscription is active.

Mobile Services Switching Centre/Visitor Location Register (MSC/VLR) serves the UE in its current position. The MSC is used to switch the CS transitions, while the VLR has a copy of the visiting users service profile that are in its location area.

Gateway MSC (GMSC) is a gateway between two networks for CS services. When the mobile switches networks during a call, the call has to pass through the GMSC.

Serving General Packet Radio Service (GPRS) Support Node (SGSN) is typically used for PS services with similar functionalities to MSC/VLR.

Gateway GPRS Support Node (GGSN) has a function similar to GMSC but for PS services.

The external networks can be grouped as:

CS networks provide circuit-switched connections. PS networks provide connections for packet data.

Speaking of the interfaces, these are the main open interfaces:

Cu interface is the electrical interface between the USIM and the ME. Uu interface is the radio interface through which the UE communicates with the

Node B.

UMTS Architecture

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Iu interface connects UTRAN to CN. Iur interface allows soft handover between RNCs from different manufacturers. Iub interface is the connection between a Node B and a RNC.

2.1 UTRAN Architecture The UTRAN is the part of the UMTS network that is of highest concern in this thesis work, therefore it will be described in details. UTRAN is a group of one or more Radio Network Sub-Systems (RNSs), where a RNS consists of one RNC and one ore more Node Bs. If there is more than one RNC, they are connected through the Iur interface among them; while the connection with the Node B is via the Iub interface. Radio Network Controller The RNC handles the control of the radio resources of the UTRAN. It interfaces the CN and terminates the RRC protocol as well. According to the logical functions of the RNC, three types can be considered:

Controlling RNC (CRNC); Serving RNC (SRNC); Drift RNC (DRNC).

If there is only one Node B that is connected to a certain RNC, this RNC is a CRNC of that Node B. It is responsible to control the load and the congestion of the cells used by the mobile, as well as for the admission control and code allocation. The SRNC terminates the Iu link for user data transfer and also the corresponding RAN application part (RANAP) signaling to/from the CN. It performs L2 processing of the data to and from the radio interface. The RRM operations, like RAB parameters mapping, handover decision etc, are also a role of the SRNC. The DRNC is in any RNC. It performs transparent routing between the Iub and Iur interfaces, except when the UE uses a common or shared transport channel.

UMTS Architecture

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Node B The Node performs the air interface L1 processing, such as channel coding and interleaving, rate adaptation, spreading etc. Some of the RRM operations are also performed by the Node B like inner loop power control. The protocol structures for the UTRAN terrestrial interfaces are divided into horizontal layers and vertical planes. The main layers are the Radio Network Layer and the Transport Network Layer.

Figure 2.2. Protocol model for UTRAN interfaces

The vertical plane is divided into Control and User Plane. The control plane is used for all the signaling part. It includes the application protocol and the signaling bearer for the transport of the application protocol messages. The control plane in the transport network layer is used for all the signaling in the transport layer and it doesnt include any radio network layer information. The transport network control plane allows complete independence to the application protocol in the radio network control plane from the technology selected for the data bearer in the user plane.

UMTS Architecture

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The user plane is in charge of transporting all the information sent and received by the user like coded voice or packets. The data streams and the data bearers for the data streams are included in the user plane. In the transport network user plane are the data bearers in the user plane and the signaling bearers for the application protocol. During real-time operation, the data bearers in the transport network user plane are directly controlled by the transport network control plane.

2.2 UTRAN Interfaces and Signaling The Iu interface, as mentioned before, is the connection between UTRAN and CN. It is an open interface whose role is to deal with switching, routing and service control. The Iu has two different instances for CS and PS services, and also an additional third instance for BC (Broadcast) has been deployed for Cell Broadcast Services. The main signaling protocol in Iu is the RANAP (Radio Access Network Application Part) protocol. It contains all the control information intended for the radio network layer. RANAP has many functions:

Relocation and SRNS Relocation handles SRNS relocation from one RNS to another without changing the radio resources, and hard handover;

Inter-RNS hard handover for relocation of the SRNS functionality from one RNS to another and changing the radio resources;

RAB management, RAB Setup, modification of the characteristics of a existing RAB, clearing an existing RAB, including the RAN-initiated case;

Iu release releases all the resources related to a specified UE; Reporting unsuccessfully transmitted data; Common ID management identification of the UE is sent to the UTRAN to

allow coordinated paging from two different CN; Paging CN pages an UE which is in Idle state for a service request; Management of tracing the CN is asking to the UTRAN to record all the activity

in a given connection between some UE and the UTRAN; UE-CN signaling transfer transparent transfer of UE-CN signaling messages; Transfer of the first UE message from UTRAN to UE - initiates the signaling

connection for the Iu; Direct transfer transfer of all the signaling messages over the Iu both in

downlink and uplink;

UMTS Architecture

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Security rode control to set the ciphering or integrity checking on or off; Management of overload a simple mechanism is applied to control the load over

Iu; Reset used in error situations to reset the CN or the UTRAN side of the Iu; Location reporting.

The Iur Interface (RNCRNC Interface) was initially designed to support the soft handover between two RNCs, but later on more features were added. The signaling protocol in the Iur interface, the RNSAP (Radio Network Subsystem Application Part) protocol has four different groups of procedures i.e. four modes due to the four different functionalities connected to the Iur interface. The modes, followed by the main functions are listed below.

Iur1: Support of the Basic Inter-RNC Mobility Support of SRNC relocation; Support of inter-RNC cell and UTRAN registration area update; Support of inter-RNC packet paging; Reporting of protocol errors.

Iur2: Support of Dedicated Channel Traffic

Establishment, modification and release of the dedicated and shared channel in the DRNC due to handovers in the dedicated channel state;

Setup and release of dedicated transport connections across the Iur interface

Transfer of DCH Transport Blocks between SRNC and DRNC; Management of the radio links in the DRNS, via dedicated measurement

report procedures, power setting procedures and compress mode control procedures.

Iur3: Support of Common Channel Traffic

Setup and release of the transport connection over Iur for common streams;

Flow control between the MAC-d and MAC-c; Splitting of the MAC layer between the SRNC (MAC-d) and the DRNC

(MAC-c). The scheduling for downlink data transmission is performed in the DRNC.

UMTS Architecture

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Iur4: Support of Global Resource Management Transfer of cell information and measurements between two RNCs; Transfer of positioning parameters between controller; Transfer of Node B timing information between two RNCs.

The Iub Interface (RNCNode B Interface) i.e. the NBAP (Node B Application Part) signaling can be divided in two important components:

Common NBAP (C-NBAP), which defines the signaling procedures across the common signaling link, controls the overall Node B functionality: Setup of the first radio link of one UE and selection of the traffic termination

point; Cell configuration; Handling of the RACH/FACH/CPCH and PCH channels; Initialization and reporting of Cell or Node B specific measurement; Location Measurement Unit (LMU) control; Fault management.

Dedicated NBAP (D-NBAP), for the signaling in the dedicated signaling link,

controls radio links for a specific UE: Addition, release and reconfiguration of radio links for one UE context; Handling of dedicated and shared channels; Handling of softer combining; Initialization and reporting of radio-link-specific measurement; Radio-link fault management.

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3 Transport Channels The data in the UMTS Terrestrial Radio Network that are generated at higher layers are being carried over the air by transport channels that are mapped on certain physical channels at the physical layer, which should be able to support variable bit-rate transport channels so that bandwidth-on-demand services could be offered.

3.1 Dedicated Transport Channel The Dedicated Channel (DCH) is the only dedicated transport channel which handles information transfer for a particular UE, both the actual data, such as speech, and the higher layer control information, like handover commands or measurement reports. This content on the DCH cannot be seen by the physical layer, thus they have the same treatment. With the WCDMA, there is no need of separate transport channel since variable bit rate is supported as well as service multiplexing. Some of the characteristics of DCH are:

- Shorter TTI, leading to faster link adaptation; - HARQ (forward error correction added to error detection) with incremented

redundancy, leading to more effective transfer; - Power control; - Soft handover support; - Spreading code assigned per user; - Max DL data rate: 384 kbps.

3.2 Common Transport Channels There are six different common transport channel types. They dont have soft handover, but some of them have fast power control.

Transport Channels

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Broadcast Channel (BCH) transports information that is specific for the UTRA or for some specific cell, such as random access codes and slots, or types of transmit diversity methods. In order to reach all the users in an area, this channel is transmitted with high power.

Forward Access Channel (FACH) is a downlink transport channel which brings

control information to the UE registered on the system, and can also be used for transmitting packets. These are the characteristics of the FACH:

- No power control; - Common spreading code; - There might be more than one FACH per cell; - Low data rate: 30 kbps.

Paging Channel (PCH) is a downlink transport channel carrying the data

important for the paging procedure, meaning the information when the network tries to start a communication with the UE. The same paging message can be sent in up to hundred cells. The terminals have to be able to receive the paging information in the whole cell area.

Random Access Channel (RACH) is an uplink transport channel which carries

control information from the UE, and it can also be used to transmit small data packets. The whole cell area has to hear the RACH, meaning that the practical data rates have to be low.

Downlink Shared Channel (DSCH) is carrying dedicated user data and/or control

information and it can be shared by several users. It is similar to FACH with the difference that it uses fast power control and variable bit rate. It is not needed to be heart in the whole cell area. It is always associated with a downlink DCH. DSCH was further replaced with HSDPA, which will be discussed in the next chapter.

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4 HSPA and HSPA+ High Speed Packet Access (HSPA) is the enhancement of the performances of the WCDMA technology. With HSPA higher rates in both downlink and uplink can be reached, 14 Mbps and 5.76 Mbps respectively. The latency is smaller and system capacity is increased while the production cost is reduced. It consists of two mobile telephony protocols, HSDPA and HSUPA.

4.1 HSDPA The intention of the design of the High Speed Downlink Packet Access (HSDPA) was to increase the packet data throughput by using fast layer 1 retransmission and transmission combining, and using fast link adaptation under the control of the Node B. For HSDPA, a new transport channel was added, High Speed Downlink Shared Channel (HS-DSCH) which carries the user data in the downlink direction. The HS-DSCH has some differences with respect to the Release 99 channels. The TTI is significantly shorter, 2 ms (three slots), which achieves a short round-trip delay for the retransmissions between the UE and Node B. The peak data rate is increased up to 10 Mbps by adding a higher order modulation scheme, 16 QAM, and lower encoding redundancy. The, SF is always 16, it is fixed, and also multi-code transmission and code multiplexing is allowed. Maximum of 15 codes can be allocated.

Figure 4.1. Channels for HSDPA operation in Release 5

HSPA and HSPA+

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HS-DSCH was implemented with the introduction of three new physical channels:

The High Speed Shared Control Channel (HS-SCCH) tells to the user that the data will be sent on the HS-DSCH. It carries the necessary control information to enable decoding of the data on HS-DSCH and to perform the possible physical layer combining of the data sent on HS-DSCH in case of retransmission or a packet with an error. A number of HS-SCCHs should be allocated that correspond to the maximum number of users that will be code-multiplexed. It is not necessary to transmit the HS-SCCH if there is no data on the HS-DSCH.

The High Speed Dedicated Physical Control Channel (HS-DPCCH) transports

acknowledgement information (both ACK and NACK) uplink to reflect the results of the CRC check, and the current channel quality indicator (CQI) downlink, to indicate the estimated transport block size, modulation type and number of parallel codes that can be received correctly.

The High Speed Physical Downlink Shared Channel (HS-PDSCH) is mapped to

the HS-DSCH which carries the actual data. The illustration of the HSDPA functionalities is given in figure 4.2. For each active HSDPA user, the channel quality is estimated by the Node B regarding the power control, ACK/NACK ratio and the user feedback. Then, scheduling and link adaptation takes place.

Figure 4.2. General operation principle of HSDPA and associated channels

HSPA and HSPA+

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The fundamental features of WCDMA, variable spreading factor and fast power control do not exist anymore with HSDPA. On that expense, adaptive modulation and coding (AMC), extensive multi-code operation and a fast and spectrally efficient retransmission strategy (HARQ) were added. Another change is that the scheduling decisions are given to the Node B. HSDPA enables a scheduling such that most of the cell capacity is allocated to one user for a very short time, if requested, when there are good conditions. With the packet combining diversity gain is achieved as well as an improvement of the decoding efficiency, since the received data packets are stored and then they are combined with the new transmission. Summed up, these are the main improvement in HSDPA:

- Data rate up to 14.4 Mbps; - Shared channel transmission; - No fast power control; - No variable spreading codes (only SF=16); - No soft handover; - Time and code multiplexing; - Adaptive modulation and coding, leading to rate control; - Fast retransmission/scheduling; - Short TTI = 2ms; - The same set of codes and power is time shared among multiple users (up

to 15 codes).

4.2 HSUPA HSUPA was introduced to deliver similar favors for the uplink as the HSDPA did for the downlink. So the improvements were made mainly to make the uplink packet data performance better by using HARQ and Node B controlled scheduling. From the Release 99 uplink channels, only DCH and RACH were kept in Release 5 and onwards. Since RACH is usable only in Cell_FACH state for sending limited amount of data, the only channel discussed will be DCH, known as E-DCH. The Enhanced Dedicated Channel (E-DCH) is used for any type of service. Conversely from HSDPA, E-DCH has dynamically variable spreading factor, uses power control and can supports soft handover. The main things for increasing the packet data throughput are the extensive multi-code operation together with the Node B scheduling, and the fast

HSPA and HSPA+

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HARQ. The fast scheduling allows the interference budget as well as the network resources to be shared dynamically, meaning baseband processing capacity and Iub transmission resources.

Figure 4.3. General operation principle of HSUPA

In the Figure 4.3 the general functionality is shown. Based on the feedback sent by each of the active HSUPA users, the Node B estimates the data rate that is needed for transmission. After that, the scheduler in the Node B provides the scheduling algorithm and the user prioritization scheme. Then, the retransmissions take place. HSUPA was implemented with introducing five new physical channels:

The Enhanced DPDCH (E-DPDCH) carries the user data in the uplink direction. Because of the uplink range, unlike in the case of HSDPA, there are two values for the TTI, 10 ms and 2 ms. The same as in Release 99, BPSK modulation is used. When up to four parallel code channels are used, E-DPDCH reaches peak rate of 5.76 Mbps.

The Enhanced DPCCH (E-DPCCH) carries in the uplink the E-DPDCH-related

rate information, retransmission information and the information to be used by the Node B for scheduling control.

The E-DCH Hybrid ARQ (HARQ) Indicator Channel (E-HICH) carries

information in the downlink direction indicating if a packet has been correctly received on a particular Node B. One code channel is being shared by multiple users in order to save code space

HSPA and HSPA+

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The E-DCH Absolute Grant Channel (E-AGCH) and E-DCH Relative Grant Channel (ERGCH) carry the Node B scheduling control information in order to control the uplink transmission rate.

4.3 HSPA+ The objective of HSPA+ is to improve the HSPA based radio networks regarding to spectrum efficiency, peak data rate and latency. HSPA+ enhances the performance of HSPA networks, and having the increased demand for high-performance mobile broadband services with the new data applications, it enables wireless operators to continue satisfying these data needs in the most economical way, as HSPA+ doubles the data capacity compared to HSPA Release 6. [7] There are many important features that will be presented further on to make it clear why HSPA+ made an evolution in the radio network. The first very significant feature is the deployment of the MIMO technology, which represents a system with multiple input and multiple output signals. That means that there are multiple antennas both at the transmitter and the receiver side so that the spatial dimension of the radio channel is efficiently used. In the downlink, the introduction of MIMO increases the throughput and the data rate, which theoretically reaches up to 28 Mbps. Uplink MIMO is not supported. [9]

Figure 4.4. Evolution with MIMO

HSPA and HSPA+

17

Second, HSPA+ uses higher order modulation. The possibility of using 64QAM in downlink and 16QAM in uplink, leads to pick data rates of 21 Mbps and 11.5 Mbps respectively. What optimizes the support of the packet data services in the high speed network is the Continuous Packet Connectivity (CPC). The connections of the packet data users has to be maintained since large number of users, which stay connected longer period of time, are being supported in a cell, although these users may only occasionally have active periods of transmissions. Thus, to minimize the latency, connection termination and re-establishment must be avoided. The maintaining means that the control channels in both uplink and downlink have to be supported which leads to augmentation of overhead; the uplink control channels (DPCCH and HS-DPCCH) contribute to the overall uplink noise raise, while the downlink control channel (HS-SCCH) causes increased battery consumption. So, one of the aims of CPC is to reduce the overhead. [8] Some of the features that are introduced to resolve this issue are:

Uplink Discontinuous Transmission (DTX) allows the UE to stop the transmission on DPCCH if there is no activity on E-DCH or HS-DPCCH.

E-DCH Tx start time restrictions allows the Node B to restrict the points of

transmission for a certain UE, meaning that the UE can transmit only on pre-defined instants.

Downlink Discontinuous Reception (DRX) allows the network to limit the

number of subframes in which the UE has to monitor the HS-SCCH, for finding out the possible downlink data allocations, in order to reduce the battery consumption of the UE.

HS-SCCH less operation for small packet services.

HS-SCCH orders they tell to the UE if DRX, DTX or HS-SCCH less operation

should be enabled or disabled.

New Uplink DPCCH slot format contains only six pilot bits and four TPC bits.

HSPA and HSPA+

18

Enhanced Fractional DPCH (F-DPCH) allows code sharing between HSDPA data users.

Further on, in order to support the high data rates that were enabled from MIMO and higher order modulation, some layer 2 modifications in downlink were also inevitable, including both the MAC and the RLC protocol. Namely, in HSPA+, flexible RLC PDU sizes are supported and multiplexing of data belonging to several priority queues into one TTI is allowed.

Figure 4.5. Flexible RLC PDU size operation HSPA+ has also introduced an enhanced Cell_FACH state (downlink). Not like the release 99, where the FACH mapped on S-SSPCH was used for small packets, now the HS-DSCH on HS-PDSCH in Cell_FACH state is preferred. This increases the data rate in Cell_FACH state and also the signaling delays of the control messages are reduced because of the shorter TTI. The improvements that were mentioned till now were considering the Release 7. In release 8 there are some more features added. To increase the throughput of the user even more when the radio conditions are very well, the combination of 64QAM and MIMO was introduced. This allows maximum rate of even 42Mbps.

HSPA and HSPA+

19

Next, CS over HSPA is allowed. Namely, we are not talking about VoIP, but circuit telephony with a wireless IP transport. Both AMR and AMR wideband is supported. To provide even better user experience in the cell, allowing a dual cell HSDPA operation gives a chance of network recourse pooling which helps a lot in the cases when some techniques (e.g. MIMO) cannot be used. The two cells belong to the same Node B and are on adjacent carriers. Both work in the same frequency band.

Figure 4.6. Dual Cell HSDPA operation As an analogy to the downlink, similar changes were done in the uplink as well. Namely, Layer 2 improvements in uplink were also made; flexible RLC PDU sizes are supported as well as segmentation/reassembly was allowed. Also, enhanced uplink for Cell_FACH state was introduced. For this feature to be supported, a new common transport channel E-DCH was specified which is used for transmitting in uplink. This channel is shared between UE who have individual codes. Furthermore, Release 8 introduces HS-DSCH DRX reception in Cell_FACH which gives an improvement in terms of battery consumption when there is infrequent small packet data services. Another feature is the HSPA VoIP to WCDMA/GSM CS continuity, allowing an efficient way of switching from a VoIP call to a WCDMA or GSM CS call while the UE is in a connected mode. For this reason, a Single Radio Voice Call Continuity (SRVCC) mechanism was specified which handles session transfers of the voice component within a PS bearer to the CS domain.

HSPA and HSPA+

20

The last thing worth to be mentioned is the serving cell change enhancement. Basically there is a target cell pre-configuration which allows the network by using the HS-SCCH to send the serving HS-DSCH cell change command also to the target cell.

Figure 4.7. Enhanced serving HS-DSCH cell change procedure

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5 Radio Resource Management Moving to HSDPA and HSUPA not only the user experience was changed, but also the managing of the radio resources has undergone some changes. The role of a scheduler was taken from the RNC and given to the Node B, using adaptive coding and modulation which leads to an effective rate control. Also the retransmission task was transferred from the RNC to the Node B, introducing HARQ. Another change that was not having soft handovers for HSDPA data, so there is no more need of utilizing multiple Iub and Iur interfaces. The roles of each element in the UMTS network are given in the figure below.

Figure 5.1. HSDPA and HSUPA RRM architecture in Release 6

The architecture can be divided in user and control plane. The control plane handles the user data in terms of Erlangs and Mbps, while the control plane is handling all the signaling related to configuring the channels, mobility management etc. The radio link control RLC is the one that manages the segmentation and retransmission for both the user and control data. [5] Three different modes of RLC are applicable:

Transparent mode: not applicable when HSDPA/HSUPA is used; used for AMR speech

Radio Resource Management

22

Unacknowledged mode: when there are no retransmissions; in the case of VoIP. Acknowledged mode: when there are ensured retransmission, required all the

packets to be delivered.

In the HSDPA user plane a new protocol entity was introduced, MAC-hs (for high speed) which is in charge of the scheduling and the priority handling. With HSUPA there is new MAC entity as well, MAC-es/e, based on the control information from the RNC and the capacity request from the UE. The main task of the new MAC-es is to ensure that the packets received in different Node Bs, in the case of soft handover to be provided in the correct order. Conversely, in the HSUPA the RLC layer doesnt succeed to deliver the packets correctly after an excess of the maximum number of retransmissions.

Figure 5.2. HSDPA flow control on the Iub interface

Speaking of the air interfaces, the buffering in the Node B, together with the scheduler, allows a pick rate as high as the terminal and the Node be are capable to reach, keeping the maximum bit rate over the Iub/Iup with retaining the QoS parameters received by the packet core. This also requires flow control, to keep the buffer from overflow. This way the user gets more resources under good radio conditions. In the previous image the flow control is shown.


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As mentioned before, for all the network elements as well as for the UE, HSDPA/HSUPA caused a lot of changes. Summed up, the new functionalities added due to the use of HSDPA are:

RNC HSDPA radio resource and mobility management; HSDPA Iub traffic management; Larger data volume.

Node B

Data buffering; ARQ handling; Feedback decoding; Flow control; Downlink scheduling; 16QAM modulation.

UE

ARQ handling with soft value buffer; Feedback generation and transmission; 16QAM demodulation.

Similarly, these are the new functionalities caused by the use of HSUPA:

RNC HSUPA radio resource and mobility management; HSUPA Iub capacity allocation; Larger uplink data volume; Packet re-ordering.

Node B

ARQ handling with soft value buffer; Feedback encoding; Uplink scheduling against; interference/baseband/Iub capacity.


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UE ARQ handling; TX power and buffer status feedback; generation and transmission; Multicode transmission; Uplink scheduling.

The major part of the control signaling between UE and UTRAN is radio resource control (RRC) messages which are carrying all the necessary parameters to set up, modify and release layer 2 and layer 1 protocol entities. They also carry all higher layer signaling messages like mobility management, connection management, session management. Also the mobility of the UE while it is connected is controlled by the RRC signaling (measurements, handovers, cell updates).

5.1 RRC Connection States The UE can operate in two modes, Idle and connected. While it is in connected mode, the UE can be found in different service states which define the physical channels that are used by the UE. The main RRC states and the transitions between them can be seen in the following image.

Figure 6.3. UE modes and RRC states in connected mode In the Idle mode, when the UE is switched on, it contacts a PLMN and chooses a suitable cell and tunes to its control channel. It does not communicate to the network, but it does listen to for certain broadcast messages. In this state the phone is not consuming any resources and it consumes minimum amount of power. The UE stays in this mode until it


25

requests a RRC connection. The UTRAN can only address all the UEs in a cell or all the UEs that are monitoring. In the Cell_DCH state, the UE is allocated a dedicated physical channel and the UE is known by its serving RNC. According to the measurement control information that was sent to the UE from the RNC, the UE sends measurement reports for the measurements it performs. The UE consumes the most resources from the network in this mode, both RNC processing and air interfaces, but also the battery waist is at highest level. In the Cell_FACH state, there is no dedicated physical channel assigned to the EU, instead, RACHs and FACHs are used for carrying both signaling messages and small data. So, the phone communicates with the network by shared channel and the RNC knows the location of the phone. The UE performs cell reselection, and in order to inform the RNC about its location on a cell level, it sends Cell Update message to the RNC. Thus, the UE uses the network resources in terms of the capacity of the air interfaces and also in terms of RNC processing power. In this state small bits of data can be transmitted at a relatively low rate. Whats more, the UE shares the forward and access channels with other devices meaning that the amount of data that can be processed depends on the load of the common channel. In Cell_FACH the power consumption is much higher. In the Cell_PCH state, the serving RNC knows where the UE is located in the network, but the UE can only be reached via PCH, whose monitoring is performed with a discontinuous reception (DRX) functionality which saves the battery of the UE. The UE listens to the BCH for some critical information, but since it is a shared channel, an additional phone in Cell_PCH state doesnt have any impact on the network, so the there is small current consumption. The URA_PCH state is very similar to the Cell_PCH with the difference that the UE tells its location to the SRNC only if the UTRAN Registration Area (URA) changes, and not after every reselection. This is similar to the Cell Update procedure and its called URA Update Procedure. A cell can belong to one or more URAs, so the UE performs URA Update Procedure just when the UE cannot find the latest URA identification from the list of URAs read from the BCH. If the RRC connection experiences failure or the RRC connection is released, the UE returns to the Idle mode.

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6 Smartphones The number of the smart devices is constantly growing and it is a lot higher than the active mobile broadband-enabled laptops. According to the Nokia Siemens Network experts, by the year 2015 over 85% of the traffic in the mobile networks worldwide will be generated by mobile data, 49% of which will be via handheld devices. [17] Therefore, it is pretty logical the operators and vendors to turn their attention to the smartphones and do some analysis in this field in order to provide good quality of the service to the customers. We did an investigation about this issue in the Vodafone network for the last one and a half year, and the numbers show a rapid growth of the smartphones, while the number of the Vodafone Internet Keys (VIKs) doesnt change much.

VIK Smartphone

Figure 6.1. Growth of VIKs and smartphones in the last one and a half year

The rapidly increasing number of smartphones in the network has given a great challenge to the operators. Thus, todays network should not only satisfy the laptop users that require high data traffic, but also to make the smartphone users happy who are keen on establishing lots of connections per day. Some market researches show that an average smartphone consumes only 10% of the data traffic that a laptop does. So, the throughput is no longer the challenge, but there is a new aspect the operators have to focus on the number of simultaneous connections.

Smartphones

27

In the beginning when the number of smartphones in the network was relatively low, operators didnt experience any problem and there was nothing to worry about. But, as soon as the number of smartphones started to constantly increase, the customers started to complain about the poor data performance and the poor battery life. Why would this be happening? Apparently because laptops and smartphones have a different behavior in the network.

6.1 Understanding smartphones behavior Using the smartphones, two kinds of traffic are generated in the network. There is the data traffic that is carrying the information interesting for the user, and the signaling traffic, the language that all the network elements use. The later is the one that the smartphones are generating more and the one that the networks were not built to handle. Having in mind that the smartphone trend is still going to rise, a shift of the attention should be expected from volume and throughput to connections and signaling. We tried to see how the smartphones and the laptops are behaving in the network of Vodafone Italy from the side of the both types of traffic starting from 2010 onwards. The results have proved our expectations. Since the smartphones are usually connected 24 hours a day, they generate more control plane traffic to keep the applications alive and therefore it is more likely to have a big amount of smartphones active in the network (see image 6.2). But in the same time all of them carry a small amount of data (see image 6.3).

Figure 6.2. Peak PDP context per month for smartphones

and laptops in Vodafone Italy

2010

2011

2012

PeakPDPContext/monthDonglesanddatacardSmartphone

Smartphones

28

2010

2011

2012

MlnMbyte/month

DonglesanddatacardSmartphone

Figure 6.3. MB per month for smartphones and laptops in Vodafone Italy

Focusing only on the laptop users experience, since they were the common high-speed mobile data customers till recently, operators and manufacturers have optimized the network performance in terms of latency, browsing time, downlink or uplink throughput, but not in terms battery life, for instance. Laptops tend to be plugged to the power line when they are being used, so battery consumption wasnt an issue. With the smartphones arrival on the market, instead, a completely new behavior appears on stage. Customers usually used their smartphones to stay in touch with friends through social networks, to search through the internet browser for the best restaurant for dinner in their closest surrounding, to check the weather forecast for planning a trip. Even without customer awareness, the terminal itself performs a lot of signaling transactions to check for a new email, or updates form the social networks or application installed. Even if the laptops generate high quantity of data volume while staying continuously connect for a long time, they produce small amount of signaling. While smartphones, on the other hand, create huge signaling flows by checking the network periodically for updates and also due to embedded features like fast dormancy, but creating relatively low data volumes. We wanted to study the traffic share between the smartphones and laptops in Vodafone Italy, in terms of both data and signaling. The results that we obtained are shown in the following chart. It can be seen that the data traffic volume from the smartphones is only around 20%, while the one from the datacards is four times higher. On the contrary, the result is the other way around when speaking about the signaling traffic.

Smartphones

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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

TbyteVolumes PeakPDPContext

Shareofdatavolumesanddataconnectionsbetweensmartphonesanddatacard

Smartphone Datacard

Figure 6.4. Data and signaling traffic volumes Nowadays, the smartphone customers want to use a large variety of applications like instant messaging, Facebook, Twitter, Skype and other pretty popular applications. The statistics says that out of 500 million active Facebook users, 200 million are accessing Facebook from their mobile and they are twice as active. It is common that a user is logged in simultaneously on multiple social network services and exactly all these applications that are enjoyable for the customers are generating signaling overloads which affects all the users in the network not only the ones generating them. Due to this fact, some of the network elements could have a decreased throughput because of the increased signaling. What is of great challenge are the hot spots, meaning lots of users concentrated in a small area for some particular happening. When speaking about this variety of applications present on the market, what we found interesting was to see which are the applications that are generating highest traffic volumes in Vodafone Italy. This is shown in the following figure. As the pie chat shows, the audio and video streaming and the browsing are the biggest data generators, while the applications that are mostly favored by the smartphone users, namely the social networking like Facebook and the instant messaging such as Whatsapp, are taking very small percentage from the pie chart for data volume while generating lots of signaling.

Smartphones

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StreamingVideo&Audio

Browsing

FileTransfer&P2P

Store

Social(Facebook&Twitter)

Minor&Other(SSL)

Mail Maps&FlickrIMApp(Facebook&

WhatsApp)

StreamingVideo&AudioBrowsing

FileTransfer&P2PStore

Social(Facebook&Twitter)Minor&Other(SSL)Mail

Maps&FlickrIMApp(Facebook&WhatsApp)Cloud

VOIP

Games

Figure 6.5. Data traffic share from different applications

These applications generate small amount of data (ex. an usual IM has 1-2kB of data), but any time that a message or update is done, there is signaling traffic equal to the one needed to set up or break a voice call or larger data session. Moreover, the IM sessions, consisting of back and forth messages, sometimes involve group of friends which leads to a multiplicative effect from the signaling point of view. The IMS chat and other persistent TCP based application like Push Mail apply periodic exchange of messages between client and server so that the TCP connection is kept alive. When the user runs multiple applications of this kind on his smartphone, it is really very difficult to predict the overall periodicity of message exchange between network and smartphone and the timer depends on the application synchronization needs. This should be solved with the HSPA+ DRX feature mentioned before.[2] Moreover, the mobile online gaming is becoming more and more popular. The users that are attached to Internet gaming are now able to play the same games on their smartphone that has a processor powerful enough to support that. This is another huge signaling generator. From one side, the laptop gaming has more ads, leading to even higher data traffic, around two times the one from the smartphones. And from another side, the laptop gaming uses far less individual data connections, generating around one tenth of the signaling provided by the smarphone gaming.

Smartphones

31

6.1.1 Always-On-Line Applications With the smartphones the users want to access the Internet and to get up-to-date information anywhere and everywhere they want. Consequently this requires always-on-line connection between the client and the server. For this connection to be maintained, frequent periodical heartbeat packets have to be send. These packets are called keep-alive messages that are used to keep the TCP connection when there are no messages to be exchanged between the network and the smartphone. They are short and frequent and are one of the main components of the background traffic. They consist of nearly 150 bytes data and 6-7s connection time, but the amount of signaling traffic that is being generated is large. These messages occur any time the application is active, which for most applications means the whole day. The main interaction technologies are listed below. [4]

Pull/Polling the initial request for data is done by the client and then the server gives a respond to it immediately

Long-polling the client ask for information from the server who keeps the

request open until there is some information available

Push when there is any new information the server notifies the client directly Mostly, the mobile application use polling, but the same application can be implemented with different technology on different platforms and have different heartbeat characteristics. This is shown in the table 6.1 (source: Huawei Smart Lab).

Table 6.1. Interaction technologies used for different applications on different platform

Platform Application Pull/Polling Longpolling PushiPhone Twitter 50s/205s

Facebook 5to60s APNS 10~15min

HTCAndroid Twitter 5min Facebook 30m/1H/2H/4H/Never GoogleTalk 40to60min

NokiaSymbian

Nimbuzz 2min39s Messaging 5to30min

Smartphones

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Being the most popular application among users and generating lots of keep-alive messages to provide the status updates as they occur, we wanted to see what is going on in the network (Vodafone Italy) in the case of running a social network application, from both data and signaling point of view. What we obtained was the following chart (image 6.6). When speaking about data volume (expressed in TB), there is two times higher traffic in favor of the datacards. On the contrary, in the case of the signaling, around five times more signaling traffic is generated from the smartphones.

TbyteVolumes PeakPDPContext

DatavolumeandconnectionsforSocialNetworkapplication

Smartphone Datacard

Figure 6.6. Data traffic and signaling generated for smartphones and laptops when using a social network application

6.1.2 Always-On-Line PDP Context Having always-on-line application obviously requires always-on-line PDP context, which contains the subscriber's session information when the subscriber has an active session. The always-on-line PDP context means that there are less PDP activation attempts, but there is a high possibility of more Iu signaling traffic like paging, service request and Iu release. It also requires from the network to have more IP addresses since one IP address could be taken for a longer period. The keep-alive messages help this issue because of the presence of the NATs (Network Address Translators). The NAT keeps track of the active connections and it is connected to a limited number of public IP addresses and translates

Smartphones

33

the local IP addresses to a public address. This way, the network can provide data services to large number of users through small number of public addresses. When speaking about the data volume per PDP context, in the network of Vodafone Italy, when we compared the smartphone traffic to the traffic generated by the laptop users, it turned out that the number of MBs per PDP context from the laptops is around nine times the MBs from the smartphones, but the amount of signaling per transferred MB that the smartphones generate is much higher.

Smartphone Datacard

VolumeperPDPContext

Smartphone Datacard

ConnectionperMbyte

Figure 6.7. Data traffic per PDP context and signaling traffic per MB

for smartphones and laptops Different types of smartphones behave differently in term of how do they perform the GPRS attach (the connection procedure that the UE performs in order to be able to use the GPRS services), the PDP context activation (for establishing a logical connection with the required QoS from the UE to the GGSN) and the PDP context deactivation (for deleting a particular logical connection between the UE and the GGSN).

Table 62. GPRS attach and PDP context activation for different kinds of OS

GPRSAttach PDPContextActivationOS PowerOn Triggeredbyapp Poweron TriggeredbyappiPhone3.0 Y YiPhone4.0 Y YAndroid Y Y WM Y Y

Smartphones

34

From the Table 6.2 (source: Huawei Smart Lab) it can be noticed that once a smartphone based on Android is on, it immediately attaches to the GPRS network and activates a PDP context. On the other hand, an iPhone attaches only to the GPRS network once its power is on, while the PDP context is activated by launching the application. However, if push notifications are enabled, the PDP context can be activated in case push talk starts in the background. Speaking of windows mobile OS, event the GPRS attach is triggered by the application, when the browser is opened or when the user sends MMS.

Table 6.3. PDP deactivation by MS for different OS

OS Appquit Screenlock PowerofiPhone3.0 Y YiPhone4.0 Y Y YAndroid YWM Y

Regarding the PDP context deactivation, it usually occurs if the smartphone is turned off. It can also be triggered by application quit or by screen lock. The table 6.3 above (source: Huawei Smart Lab) shows the case for different OS.

Table 6.4. PDP deactivation by CN for different OS

OS Deactivationaccept Deactivationignore ReactivatePDPafterdeactivation

iPhone3.0 YiPhone4.0 YAndroid YWM Y

In case there is a network failure, the PDP context can be deactivated by the Core Network. The Table 6.4 (source: Huawei Smart Lab) shows that the WM accepts the deactivation normally, while the iPhone and the Android re-activate the PDP context immediately after.

Smartphones

35

6.1.3 Fast Dormancy In order to extend the life of the battery of the smartphones, the feature that was proposed was Fast Dormancy. This way, the UE forces the network to break the data connection once the user has downloaded what he wanted, and than the UE goes back to Idle state. Since the UE is not spending longer periods in Active state, the battery life is improved. Conversely, the network doesnt have so much benefit from this. Being in Active state for short periods means that of the user wants to connect again for sending data it has to start a whole new connection from the Idle state. This significantly increases the signaling traffic which wastes the network resources and could be that less number of smartphones will be able to connect. Using the basic form of fast dormancy i.e. switching constantly form Idle to Active and than back to Idle again, the Android devices cause higher signaling traffic than other devices. On the other hand, starting from iOS4.1 iPhone started to use a modified version of Fast Dormancy which keeps the phone connected as long as the backlight is on supposing that if it is on, the user is looking at the phone and could send a data request any time. To solve the problem of the huge signaling loads that was introduced by the smartphones, the RNC vendors started using a paging channel or Cell_PCH state in the networks in order to avoid frequent connection setups i.e. they prefer to change the UE state into PCH rather than Idle. When the UE is about to return in Idle state after having made a data connection, 30 signaling messages are required. While if the handset is kept in PCH mode between active connections, which keeps the Iu connection and the RAB unreleased, it requires only 12 signaling messages for the round trip. This way the connection times are becoming shorter, for establishing a new connections only half a second is needed. The UE is no longer held in Active state for long period which also saves the battery life. [20]

Smartphones

36

Figure 6.8. Difference between disabled and enabled Cell_PCH

Although this sounds like a perfect solution for latency, battery life and signaling, there is one problem Fast Dormancy. The handsets that have this feature enabled are forced to go back to Idle between data connections. Nokia Siemens Networks have proved that having the Cell_PCH enabled in the radio equipment and a disabled Fast Dormancy feature in the handsets, the signaling can be reduced from 30-50% and also the capacity needed in the SGSN can be cut in half. Some analysis were done by the Signal Processing Group, LLC about the RRC state transition changes and the battery consumption, parallel in two networks, one of them with Cell_PCH enabled and the other without. From the results stated in table 6.5 it can be observed that enabling the Cell_PCH the signaling traffic has been reduced significantly. [18] For IM messaging, the Cell_PCH enabled network used Cell_FACH to send and receive messages. Since the transition changes between Cell_PCH and Cell_FACH require less signaling messages as stated before, there was a significant reduction of the signaling load. This way also the capacity for other voice and data users was freed.

Smartphones

37

With the tracking application that allows friends to find each other GPS was used for location to be identified. In both of the networks the UEs required Cell_DCH state to send and receive the updates. However, in the Cell_PCH enabled network, the UE returned to this mode after each message and stayed in the same mode until next message was send or received.

Table 6.5. Signaling traffic with and without Cell_PCH state enabled

Application Observedmsg Estimatedunobservedmsg

Payload Currentrequirement

PCH noPCH PCH noPCH PCH noPCH PCH noPCHIMmessage 208 294 30 174 12kB 12kB 291mA 388mATrackingapp 199 318 58 200 90kB 92kB 172mA 221mADownload 153 182 48 90 5.8MB 5.8MB / /Browsing 286 339 64 210 328kB 328kB 366mA 464mAMail 73 88 44 60 65kB 71kB / /Maps 138 160 32 60 43.1kB 32.6kB / /YouTube 107 107 34 50 12.3MB 12.3MB / /SkypeVideoCall 105 109 32 60 2.6MB 2.6MB / /IncomingVoiceCall 44 62 20 20 / / / /

When a downloading of a large file takes place, in this case 5.8MB, there are few RRC state transitions, so there is no large amount of signaling traffic. That is why there are no meaningful differences between the two networks. In the case of web browsing, loading of 10 pages was observed. Looking at the table, very good results were obtained. There was a 36% reduction of the signaling messages (including the unobserved ones) and 21% lower power consumption. In the Cell_PCH enabled network, the UE remained in this mode during the time between receiving and sending an email. While the in the second network, the UE was switching to Idle and then returning to Cell_DCH this way generating significantly more signalization. What was interesting in the test of using the maps on the phone was that there was very low data traffic generated, only when the user searches for the desired landmark. And

Smartphones

38

also there was small amount of signaling traffic. The UE remained in Cell_PCH the entire test, in the first network, and returned to Cell_DCH only at the end. Speaking of watching videos on YouTube, one would assume that the UE would enter Cell_DCH when the video is selected and stay there until the video is downloaded. And this is correct. That is why small signaling traffic was generated and the results are rather equivalent for a meaningful amount of data. For Skype video call as well, there is relatively big amount of data and thus the results are pretty equivalent. The test of the incoming voice call was added, although it has nothing to do with data, from a simple reason to see how an UE behaves when it receives a voice call. The results should be the same in theory, the behavior was the same for both networks, transition from Cell_FACH to Cell_DCH and then back to Idle. The number of signaling messages could have been measured higher for the Cell_PCH disabled network because the ringing time was longer. 3GPP came up with an idea of Network Controlled Fast Dormancy, also known as Release 8 Fast Dormancy. With this feature the smartphones are more flexible meaning that they can exploit the Cell_PCH on the networks that has it enabled or they can adjust to Fast Dormancy on the vendors that dont have the Cell_PCH supported. What happens is that on the part where Cell_PCH is used both battery life and signaling traffic are optimized, while on the other part that has no Cell_PCH at least the battery life is improved by using the Fast Dormancy, but causing lots of signaling.

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7 Radio Network Controller The Radio Network Controller (RNC) is a key element within UTRAN which controls all the radio resources of UTRAN. However, each RNC controls only resources under its control. There are multiple RNCs in UTRAN and as such, control of radio resources is done with a distributed architecture. As mentioned before, the RNC can have three logical roles:

Controlling RNC (CRNC) responsible for the Node Bs and all cells belonging to it. When a UE wants to access the system, it sends a message for access to a Node B which forwards this message onto its CRNC.

Serving RNC (SRNC) terminates the mobile link layer communications and it is

responsible for admission control which assures that radio resources are allocated to the user up to the availability to the network.

Drift RNC (DRNC) the place where the mobiles physical layer communications

terminates. If there is no soft handover activity is in progress, a Drift RNC may also be the Serving RNC.

Speaking of the functionality, we are thinking of the Radio Resource Management (RRM) which was discussed in chapter 5. Namely, the RNC manages the allocation of the channels so that the transport of the real traffic and the signaling can take place simultaneously. The functions of the RNC can be divided into two groups, network based and connection based. The network based functions are further divided into:

Event based functions that are preformed when required. This group consists of the admission control and the packet scheduling. With the admission control the stability is maintained and it is used for the required capacity of the RAN to be achieved. While the packet scheduling manages the scheduling of the radio resources for the NRT radio bearers.

Radio Network Controller

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Continuous functions that are performed constantly. This kind of a function is the load control which should ensure that there will be no overload in the system. If at some point the system is overloaded, it has to return the system in the normal state as defined in as short time as possible.

On the other hand, the connection based functions take place whenever a radio link is assigned to a connection. Here falls the power control and the handover control. With the power control should be ensured that the power requirements are kept for the transmission. It also takes care of maintaining the SIR targets by keeping the lowest interference possible and providing good connection quality. The handover control provides support for the soft handovers. It can be both RNC controlled and UE initiated.

Figure 7.1. RNC functions

As stated previously, the RNC communicates with the network elements in both the RAN and the CN through various interfaces.

Iub Interface connection between the Node B and the RNC. Iur Interface connects two RNCs and it manages the soft handovers. It is an

open interface. Iu-CS Interface connects the RNC with the Core Network. Usually terminates

in the MSC via the Media Gateway. It supports circuit switched traffic.

ACPS

LC

HCPC

AC AdmissionControlPSPacketSchedulerLCLoadControlPCPowerControlHCHandoverControl


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Iu-PS Interface connects the RNC with the Core Network. Usually terminates in the SGSN. It supports packet switched traffic.

Iu-BC Interface - connects the RNC with the Core Network, more specifically with the Cell Broadcast Center (CBC).

Iu-PC Interface interface between the RNC and the Stand Alone SMLC (Serving Mobile Location Center). It provides GPS information to the RNC about the UE positioning.

Network Management Interface connects the RNC to the Operation Support System. It uses TCP/IP.

Figure 7.2. RNC interfaces


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7.1 NSN RNC2600 The NSN RNC2600 is based on the IPA2800 platform which is suitable for very high throughput real-time media processing and transmission. [11]

7.1.1 Hardware Characteristics The RNC2600 can have three different hardware configuration steps:

Step 1, RNC2600/900 1 cabinet with all the sub racks fully equipped; Step 2, RNC2600/1450 2 cabinets; the first one with all the sub racks fully

equipped, and the second one with the first two sub racks fully equipped; Step 3, RNC2600/2600 2 cabinets, both of them with all the sub racks fully

equipped.

Figure 7.3. RNC2600 capacity steps In this thesis work, only Step 1 and Step 3 will be discussed further on since these are the configuration steps used by Vodafone Italy. The RNC2600 capacity licensing is based on the actual traffic. The parameters that are used are Iub PS data throughput in Mbps, AMR capacity in Erlang and number of required carriers.


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Each type of RNC has different values in terms of supported services. This includes number of subscribers, number of supported call attempts (CS and PS), Erlangs, MB, number of carriers, number of Node Bs connected and RRC subscribers. These values can obviously vary since many factors affect the behavior of a RNC. For instance, the maximum number of subscribers that can be handled by a RNC2600 is affected by the subscribers that are performing a soft handover procedure. By optimizing the handover control parameters and the power control parameters this effect could be minimized. Furthermore, the number of Node Bs that a RNC can control is dependent on the Iub configuration. A RNC cabinet is consisted of four subracks that contain a number of plug-in units which represent a piece of hardware used for a certain function by adding the appropriate software. Thus, these plug-in units are called functional unites and are divided in the following groups:

Computing units and their storage units; Signal processing units; Switching and multiplexing units; Network interface units; O&M server and its storage units.

The units that are most important for this thesis work are ICSU, DMPG and NPGEP and will be the ones described below. The Interface Control and Signaling Unit (ICSU) has the task to perform the RNC functions connected to the signaling to the other network elements. Namely, it takes care of the control plane. It also handles functions RRM functions. Form the signaling point of view it takes care of:

NBAP signaling (over Iub); RNSAP signaling (over Iur); RANAP signaling (over Iu); RRC signaling (between UE and RNC); ALCAP signaling (for AAL2 connections).


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As for the radio resource management, it is involved in: Admission control; Handover control; Load control; Packet scheduling; Management of radio resources; Management of transport resources.

ICSU has N+1 redundancy, meaning that there is one more spare board. The Data and Macro Diversity Processor Group (DMPG) is an integral part of the Data and Macro Diversity Combining Unit (DMCU) which is a signal processing unit in charge of the user plane. The main functionalities are:

Macrodiversity combining the DMCU combines the signals from different base stations choosing the best quality transport blocks into a new signal;

Outer loop power control the quality of the uplink signal is monitored and if it is not good enough a command is send to the base station to increase the SIR value;

Frame protocol processing; MAC protocol processing; Ciphering (encryption) in UMTS the ciphering is between the UE and the

SRNC; RLC protocol processing; PDCP protocol processing; HSPA-related processing.

DMPG has SN+ redundancy which means that there is no spare unit. The Network Processor Gigabit Ethernet Protected (NPGEP) unit is a network interface unit which offers IP over two Gigabit Ethernet interfaces. It also performs header translation, O&M, traffic management, performance monitoring and performance data collection. The NPGEP is the board that decides whether to send the traffic to the ICSU or to the DMPG. It has 2N redundancy meaning hot standby, establishing a fault-tolerant default gateway.


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7.1.2 Software Characteristics The NSN RNCs have two different software releases, Ru20 and Ru30. Most of the features are related to the capacity. [1][25]

Table 7.1. Ru20 and Ru30 Features

Ru20 Ru30o HSDPA64QAMo MIMO28Mbpso DualCellHSDPA42Mbpso FlexibleRLCinDLo CSVoiceoverHSPAo FractionalDPCHo CPCo HSUPA2mso HSUPA5,8Mbpso HSPA72UsersperCello 24kbpsPagingChannelo FastL1Synchronizationo DirectResourceAllocationforHSPAo PowerSavingModeforBTSo LTEInterworking

o HSUPADLPCHPowerControlo HSUPAInterferenceCancellationReceivero HSUPA16QAMo HSUPAInterFrequencyHandovero FrequencyDomainEqualizationo DualCellHSUPA23Mbpso DualCellHSDPAwithMIMO84Mbpso UEDRXinCell_FACHo FlexibleRLCinULo MIMO42Mbpso HighSpeedCell_FACHo HSPA128UsersperCello FastDormancyo MultiBandLoadBalancingo LTEPSHandoverandSRVCCo DualBandHSDPA42Mbps

7.2 Huawei BSC6900 The BSC6900 is an important network element of Huawei Single RAN solution. It supports the leading multiple radio access technologies (RATs), IP transmission mode and has a modular design. The BSC6900 can be flexibly configured as required in different networks. The BSC6900 satisfies the mobile network requirements for very high capacity, high integration, high performance and low power consumption. With the same hardware it is possible to set up a Base Station Controller (BSC), thus the name. [13]


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7.2.1 Hardware Characteristics The BSC6900 UMTS cabinet is classified into Main Processing Rack (MPR) (1 MPS, 0 2 EPSs) and Extended Processing Rack (EPR) (1 3 EPSs). The subracks are classified into Main Processing Subrack (MPS) and Extended Processing Subrack (EPS). The MPS performs centralized switching and provides service paths for other subracks. It also provides the service processing interface, OM interface, and system clock interface. There can be only one MPS. The EPS performs the functions of user plane processing and signaling control. There can be 0-5 EPSs. One MPS is minimum configuration while one MPS and five EPSs is the maximum configuration. The BSC6900 UMTS has a modular design. The resource utilization is enhanced and also the system reliability since the subracks are fully interconnected and have distributed resource pools to manage the service processing units. The backplane is universal and every slot is common to different types of boards so that different functions can be performed. In this way, the universality and future evolution capability of the hardware platform are improved. The BSC6900 has the following types of boards:

Interface processing boards; OM boards; Switching processing boards; Signaling processing boards; Service processing boards; Clock processing boards.

Figure 7.4. Boards in MPS and EPS respectively


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The boards that are important for us are the SPU and the DPU boards. As the name is indicating, the Signal Processing Unit (SPU) is in charge of processing high-layer signaling of the Uu, Iu, Iur, and Iub interfaces, which consists of call control plane, managing various resources necessary for service setup and establishing signaling and service connections, Node B management, cell management, NBAP management and transmission management. It has 1+1 back up mode, which means that if a faulty board is detected, the system re-establishes the transmission of the ongoing services on the standby board by adopting an active/standby switchover. It uses pooling for the call control plane, meaning grouping of resources. For the other tasks pooling is not used. The board responsible for the user plane processing is the Data Processing Unit (DPU). This includes call user plane and cell common channel. It doesnt have any back up, it has a N pool design, meaning that load-sharing is performed in the resource pool. Based on the load it supports call processing sharing. Also, if damaged active channel is detected, transmission of the ongoing services on the standby channel is enabled by an active/standby switchover.

7.2.2 Software Characteristics Depending on the RAN features and services that are supported, there were two different releases present in the Vodafone Italy Network: RAN12.0 and RAN13.0. The RAN12.0 release is implemented according to the 3GPP Release 8 specifications, while RAN13.0 corresponds to the Release 9. In the following table the most important features are given. Recently, all the RNCs were upgraded to RAN13.0.

Table 7.2. RAN12.0 and RAN13.0 Features

RAN12.0 RAN13.0o Uplinklayer2improvementso Downlink64QAM+MIMOo DualcellHSDPAo Uplink16QAMo InterferenceCancelationo FrequencyDomainEqualization

o HSPA+Downlink84Mbpsperusero DualcellHSDPA+MIMOo EDPCCHBoostingo PSServiceRedirectionfromUMTStoLTEo UplinkEnhancedCell_FACHo FlexibleHSPA+TechnologySelectiono EnhancedDRX

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8 Estimation of the Unit Loads After understanding how a smartphone behaves in the network, in order to provide good end-to-end service for the smartphone users, the networks have to act smart also. As it was mentioned, the RNC is the most important node in the UTRAN, since it must process both the data traffic and the signaling traffic. If in some case the RNC reaches overload situation because of the signalization, there would be difficulties in managing of the data traffic and could happen that the resources are not properly assigned. This means that the throughput gets lower, the response time longer and the quality of the voice is worse. Thus, the RNC should be the main objective for investigation in order to increase the performance of the network. Having the RNC dimensioned to manage certain amount of Erlangs and Mbps and to support certain number of signaling procedures, with the rising number of smartphones and the traffic that they generate, there is a need to monitor the behavior of the units that manage both user and control plane. The goal is to maximize the broadband experience and to ensure efficient and congestion-free connection. For this reason,

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