UMTS System Architecture, Protocols

(Module 2)

by,

Usman Qureshi

SINA- Feb 2014

UTRAN Logical Architecture

WCDMA Network Architecture

InterfacesOpen Interfaces:The function of the Network Elements have been clearly specified by the 3GPP.Their internal implementation issues are open for the manufacturerAll the interfaces have been defined in such a detailed level that the equipment at the endpoints can be from different manufacturers.“Open Interfaces” aim at motivating competition between manufacturers.

Physical implementation of Iu interfaces:Each Iu Interface may be implemented on any physical connection using any transport technology, mainly on E1 (cable), STM1 (Optic fiber) and micro-waves.ATM will be provided in the 3GPP R4 release and IP is foreseen for the 3GPP R6.

RNC: Radio Network Controller

Main Functions of this Intelligent part of UTRAN System includes; Radio resource management (code allocation, Power Control, congestion control, admission control) Call management for the users Connection to CS and PS Core Network Radio mobility management

Node-B

A Node-B can be considered, as first approximation, like a transcoder between the data received by antennas and the data in the ATM cell on the Iub. Radio transmission and reception handling Involved in the mobility management Involved in the power control Modulation / Demodulation Closed loop power control

An RNS (Radio Network Subsystem) contains one RNC (Radio Network Controller) and at least one Node-B.

Multiple Access Technology

Multiple Access Techniques

Defect

1. Simple Implementation 1. Frequency Reuse

2. privacy

1. Need synchronized of frame

1. Reduction the interference

2. Diversity Hand-over

3. Privacy

1. Sophisticated power control for mobile

1.Privacy

Advantages

FDMA

TDMA

CDMA

AMPS, TACS

GSM, PDC

IS95,W-CDMA

Disadvantages

Multiple Access Techniques

FDMA/TDMA CDMA

Frequency is different in each sector.

Frequency is same.

Need for

frequency plan (Frequency ReuseFrequency Reuse)

No need for frequency plan

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FDMA/TDMA CDMA

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CDMA Concept

UMTS Bandwidth

UMTS BandwidthChannel SpacingThe nominal channel spacing is 5 MHz, but this can be adjusted to optimize performance in a particular deployment scenario.

Channel RasterThe channel raster is 200 KHz, which means that the center frequency must be an integer multiple of 200 KHz.

Channel NumberThe carrier frequency is designated by the UTRA Absolute Radio Frequency Channel Number (UARFCN), where

Fcenter = UARFCN * 200 KHz

WCDMA – Wideband & codes

Carrier Spacing & Carrier Spacing Raster

The nominal carrier spacing for UMTS is 5 MHz It is possible to move the centre frequency of the carrier on a 200 kHz raster We can have carrier spacings between 4.2MHz and 5.8MHz This may be set within the license conditions, or to the operators discretion

Characteristics of CDMA System

High Spectral Efficiency– Frequency multiplex coefficient is 1.

Soft capacity– Quality– Coverage– Interference

Self-interference system– A UE transmission power is interference for another UE.

Characteristics of CDMA SystemIn CDMA system, mutual interference between users or cells is permitted, so adjacent cells can be distributed with same frequency. That is why the spectrum efficiency is very high and the capacity is also very large in CDMA system. But it also causes self-interference, if the interference is out of control, the capacity and quality of CDMA system will be worse, so many technologies were invented to control the interference, and it is not easy.The second feature of CDMA is security. After spreading, the narrowband signal of the user will be changed to broadband signal, is close to noise, only people who use the same spreading code can revert it. Of course, it causes the other shortcoming: more frequency band needed.The third feature of CDMA is soft capacity. Because all of the carrier resource (the main resource is power) is “shared” by all of the users, if some user occupy more power, it will cause the capacity lower. Soft capacity will cause network planning more complex, emulation is necessary.

Protocols in UTRAN

The Iu protocolsUsed to exchange data (traffic and signaling) between RNCs, Node Bs and the Core Network.The Radio protocolsUsed to process the data sent on the air and for the signaling between UTRAN and the UEsImportant Radio ProtocolsRRC: Radio Resource ControlRLC: Radio Link Control MAC: Medium Access Control

UMTS Signaling Protocol Stack

Radio Channels, Protocols & Network Elements

Radio Channels, Protocols & Network Elements

The radio protocols are responsible for exchanges of signaling and user data between the UE and the UTRAN over the Uu interface.

User plane protocols These are the protocols implementing the actual Radio Access Bearer (RAB) service, i.e. carrying user data through the access stratum (EXAMPLES 1,2 and 4).

Control plane protocolsThese are the protocols for controlling the radio access bearers and the connection between the UE and the network from different aspects including requesting the service, controlling different transmission resources, handover & streamlining etc...Also a mechanism for transparent transfer of Non Access Stratum (NAS) messages is included.

Radio protocol stack

The radio protocols are responsible for exchanges of signaling and user data between the UE and the UTRAN over the Uu interfaceThe radio protocols are layered into:the RRC protocol located in RNC* and UEthe RLC protocol located in RNC* and UEthe MAC protocol located in RNC* and UE the physical layer (on the air interface) located in Node-B and UE

Radio Resource Control (RRC)

The RRC functions are:Call management RRC connection establishment/release (initial access) Radio Bearer establishment/release/reconfiguration (in the control plane and in the user plane) Transport and Physical Channels reconfigurationRadio mobility managementHandover (soft and hard)Cell and URA update Paging procedureMeasurements control (UTRAN side) and reporting (UE side)Outer Loop Power Control Control of radio channel ciphering and deciphering

Radio Link Control (RLC)

RLC main functions includes:RLC Connection Establishment/Release in 3 configuration modes: transparent data transfer (TM): without adding any protocol information unacknowledged data transfer (UM): without guaranteeing delivery to the peer entity (but can detect transmission errors) acknowledged data transfer (AM): with guaranteeing delivery to the peer entity. The AM mode provides reliable link (error detection and recovery, in-sequence delivery, duplicate detection, flow Control, ARQ mechanisms)

Medium Access Control (MAC)

Data transfer: MAC provides unacknowledged data transfer without segmentationMultiplexing of logical channels (possible only if they require the same QoS)Mapping between Logical Channels and Transport ChannelsSelection of appropriate Transport Format for each Transport Channel depending on instantaneous source rate.Priority handling/Scheduling according to priorities given by upper layers: - between data flows of one UE - between different UEsPriority handling/Scheduling is done through Transport Format Combination (TFC) selectionReporting of monitoring to RRCCiphering for RLC transparent data (if not performed in RLC)

The Physical Layer

Physical layer main functions: Multiplexing/de-multiplexing of transport channels on CCTrCH (Coded Composite Transport Channel) even if the transport channels require different QoS. Mapping of CCTrCH on physical channels Spreading/de-spreading and modulation/demodulation of physical channels RF processing Frequency and time (chip, bit, slot, frame) synchronization Measurements and indication to higher layers (e.g. FER, SIR, interference power, transmit power, etc.) Open loop and Inner loop power control Macro-diversity distribution/combining and soft handover execution

UMTS Global Services

A Radio Bearer is the service provided by a protocol entity (i.e. RLC protocol) for transfer of data between UE and UTRAN.Radio bearers are the highest level of bearer services exchanged between UTRAN and UERadio bearers are mapped successively on logical channels, transport channels and physical channels (Radio Physical Bearer Service on the figure)

Radio Access Bearers

The RAB provides confidential transport of signaling and user data between UE and CN with the appropriate QoS.

UMTS Modulation - QPSK

UMTS Modulation – 16 QAM

Quadrature Amplitude Modulation