umts bronze study raeference

WCDMA Physical Layer L1 The WCDMA-based Physical Layer is used to transmit data over the air, it implements the following WCDMA functions: Medium Access Control MAC Layer L2 The MAC La

UMTS Reference for

RF Engineers

and RNC Engineers

Version 1.0 November 10, 2008

All rights reserved No part of this book shall be reproduced or transmitted by any means, electronic, mechanical, photocopying, recording or otherwise, without the express written consent from Award Solutions, Inc

Table of Contents

1.0 Scope of the Document 1

2.0 Introduction of UMTS 1

3.0 GSM/GPRS/EDGE Evolution to UMTS 1

4.0 UMTS Releases 2

Release 99 2

Release 4 2

Release 5 2

Release 6 2

Release 7 2

Release 8 2

5.0 The UMTS Core Network 3

MSC/VLR 3

Home Location Register (HLR) 3

SGSN 3

GGSN 3

6.0 The UTRAN 3

RNC 4

Node B 4

7.0 UMTS Interfaces 4

Access Stratum (AS) 4

Non Access Stratum (NAS) 4

Uu Interface 5

Iu Interface 5

Iub Interface- “The Backhaul” 5

Iur Interface 5

8.0 UE-UTRAN Protocol Stack 5

WCDMA Physical Layer (L1) 5

Medium Access Control (MAC) Layer (L2) 5

Radio Link Control (RLC) Layer (L2) 6

Radio Resource Control (RRC) Layer (L3-Control) 6

Packet Data Convergence Protocol (PDCP) Layer (L3-Data Traffic) 7

9.0 WCDMA 7

Forward Error Correction (FEC) Coders 7

Orthogonal Variable Spreading Factor (OVSF) Codes 7

Scrambling Codes 8

Data Rate Computation 8

10.0 Channels 9

Logical Channels 9

Transport Channels 9

Physical Channels 10

DL Dedicated Physical Channel 10

UL Dedicated Physical Channel 11

Modulation Schemes 11

11.0 Power Control 12

Eb/No 12

Ec/Io 12

Power Control in UMTS R99 12

Open Loop Power Control 12

Closed Loop Power Control 12

12.0 RRC Connection and RRC States 13

RRC Idle Mode 13

RRC Connected Mode 13

CELL_DCH sub-state 14

CELL_FACH sub-state 14

CELL_PCH sub-state 14

URA_PCH sub-state 14

13.0 UE Power Up and Initial Cell Selection 15

Synchronization 15

14.0 Voice Calls 15

Registration Procedure 15

Voice Call Setup 15

Channels for a Voice Call 16

15.0 R99 Data Calls 16

Attach Procedure 16

R99 Data Call Setup 16

Channels for a R99 Data Call 17

PDP Contexts 17

16.0 Handovers and Measurements 17

Soft Handovers 17

Hard Handovers 18

Measurements 18

Measurement Control and Measurement Reports 19

17.0 HSDPA Concepts 21

18.0 HSDPA Channels 21

High Speed – Downlink Shared Channel (HS-DSCH) 21

High Speed – Physical Downlink Shared Channel (HS-PDSCH) 22

High Speed - Shared Control Channel (HS-SCCH) 22

High Speed - Dedicated Physical Control Channel (HS-DPCCH) 23

19.0 HSDPA Traffic Operations 24

Basis for CQI Reporting 24

HSDPA DL Scheduler 25

HSDPA Hybrid ARQ 25

20.0 HSUPA Concepts 27

Rise over Thermal (ROT) Threshold: 27

21.0 HSUPA Channels 27

Enhanced Dedicated Channel (E-DCH) 27

Enhanced Dedicated Physical Data Channel (E-DPDCH) 28

Enhanced Dedicated Physical Control Channel (E-DPCCH) 28

E-DCH Absolute Grant Channel (E-AGCH) 28

E-DCH Relative Grant Channel (E-RGCH) 28

E-DCH HARQ Indicator Channel (E-HICH) 29

22.0 HSUPA Traffic Operations 30

Scheduling Request 30

Grants 30

HSUPA Hybrid ARQ 31

23.0 HSPA Data Calls 32

Attach Procedure 32

HSPA Data Call Setup 32

Channels for a HSPA Data Call 32

24.0 Acronyms 34

1.0 Scope of the Document

This document is a quick reference for RF Engineers and RNC Engineers for UMTS Release 99 (R99), Release 5 (R5) HSDPA and Release 6 (R6) HSUPA concepts and terms It provides a summary of the important ideas and concepts in the courses which are part of the Bronze curriculum for RF Engineers and RNC Engineers at AT&T The courses are:

1 FOT110 - Evolution from GSM to UMTS (eLearning)

2 FOT120 – Overview of UMTS (eLearning)

3 FOT121 – UMTS/WCDMA Air Interface Fundamentals (eLearning)

4 FOT123 – UMTS Signaling (eLearning)

5 AOT101 – HSDPA (R5) Overview (eLearning)

6 AOT103 – HSUPA (R6) Overview (eLearning)

7 ATN301 – UMTS Radio Network Protocols and Signaling (Instructor Lead Training)

8 ATN302 – HSPA Protocols and Signaling (Instructor Lead Training)

It is intended to serve two purposes:

• Serve as a quick reference document on the job for UMTS concepts and terms

• Assist RF Engineers and RNC Engineers to prepare for their Bronze Assessment Test

This document is designed to be used as a supplementary reference to the courses listed above and not as a stand-alone document

2.0 Introduction of UMTS

Second Generation (2G) cellular wireless systems, like GSM/GPRS/EDGE, introduced the use of digital radio techniques that employ digital transmission mechanisms, including digitized compressed speech signals, for wireless mobile telephony and low speed packet data services Since the original intent of 2G systems was the delivery of high quality voice services, 2G systems can only provide low data rate packet radio services In particular, GPRS/EDGE is an enhancement to GSM which adds a second domain to the existing circuit-switched domain of the GSM core network; specifically, a packet domain of routers is added to GSM’s circuit-switched core network Though the packet-switched domain provides direct access to the Internet, the user’s access is constrained by the existing 2G radio technologies, which are highly optimized for circuit-switched voice services Overcoming this 2G limitation was one of the driving factors for 3rd Generation (3G) cellular wireless systems Third generation (3G) cellular networks profoundly transform the radio access network to remove the 2G radio technology’s constraints imposed on so-called 2.5G systems (GPRS/EDGE), while leaving the dual-domain 2.5G core network intact The key feature of 3G wireless systems is the concurrent support of both circuit-switched voice, and higher-rate packet data speeds that support a wide variety of packet data services We call this wireless multimedia mobile network the UMTS (Universal Mobile Telecommunication System), which we declare

to be a 3G Wireless System with the following key characteristics:

• Theoretical Downlink (DL) and Uplink (UL) data rates as high as 2 Mbps in R99

• Practical DL and UL data rates in the range of 100 kbps – 384 kbps in R99

• Support of circuit-switched voice, packet-switched data, and SMS

• Support of concurrent services (simultaneous voice and data calls on a UE for instance)

• Defined by the 3rd Generation Partnership Project (3GPP)

3.0 GSM/GPRS/EDGE Evolution to UMTS

The GSM core network (GSM PLMN) provides voice and SMS services The GPRS core network (GPRS PLMN) provides packet data services Both kinds of services share the existing 2G, GSM-based radio technologies, which delivers either service in a non-concurrent way, i.e one service or the other, but not both at the same time The GSM Radio Access Network (RAN) includes the Base Station Controller (BSC) which controls several Base Transceiver Subsystem (BTS) and which also referred to as the “cell site” There is no support for concurrent services in this kind of 2.5G network

• The Radio Access Network (RAN), the GSM RAN, connects to the two core networks, or what we call a

“dual-domain” core network

• The GSM RAN connects to the GSM PLMN, which is the legacy circuit-switched domain, through the A Interface between the BSC and MSC

• The GSM RAN connects to the GPRS PLMN, the newer packet-switched domain, using the Gb Interface between the BSC and SGSN

• The BSC connects to the BTS, or its BTSs, using the Abis Interface(s) within the RAN

• There is no interface defined to connect two BSCs within the RAN

4.0 UMTS Releases

UMTS Releases are listed in the chronological order of their formulations:

Release 99

The first release of UMTS is called Release 99 which has the following characteristics:

• Deploys the UMTS Terrestrial Radio Access Network (UTRAN) which is the UMTS-specific RAN

• Uses a Wideband Code Division Multiple Access (WCDMA) air interface

• Frequency Division Duplex (FDD) is the most commonly deployed mode of the WCDMA interface

• FDD deployment requires a total of 10 MHz of spectrum: 5 MHz for the DL and another 5 MHz for the UL

• Supports voice, packet data, SMS and multimedia services, and supports these as concurrent services

• Uses the GSM PLMN for voice services; the Circuit Switched Core Network (CS-CN)

• Uses the GPRS PLMN for packet data services the Packet Switched Core Network (PS-CN)

• UTRAN uses Asynchronous Transfer Mode (ATM) and Internet Protocol (IP) for transport services

• The mobile station and all its associated hardware is called the User Equipment (UE) in UMTS

Release 4

UMTS Release 4 (R4) introduces a new and important

feature in the CS-CN with the introduction of Media

Gateways (MGW) and MSC servers

• The MSC is replaced by MSC servers and some

Media Gateways

• MSC Servers implement the control, billing, call

processing, mobility management and Visitor

Location Register (VLR) related functions as well

as facilities for controlling its MGWs

• The MGW is responsible for processing and

switching user traffic (media) as well the

conversions between different formats of traffic

(e.g., AMR to PCM)

Release 5

UMTS Release 5 introduces High Speed Downlink Packet Access (HSDPA) as a UTRAN feature

• Enhances and builds on the R99 UTRAN while still requiring the R99 capabilities

• Theoretical Downlink (DL) data rates as high as 14 Mbps; UL data rates are the same as in R99

• Practical DL data rates depend on the HSDPA Category of the UE

IP Multimedia Subsystem (IMS) is also introduced in R5 as a new core network feature

Release 6

UMTS Release 6 introduces High Speed Uplink Packet Access (HSUPA), as a UTRAN feature

• Enhances and builds on the R99/R5 UTRAN while still requiring the R99 capabilities

• Theoretical Uplink (UL) data rates as high as 5.76 Mbps; DL data rates are the same as in R5

• Practical UL data rates depend on the HSUPA Category of the UE

5.0 The UMTS Core Network

The Release 99 UMTS network includes the UTRAN, the CS-CN/GSM PLMN and the PS-CN/GPRS PLMN/UMTS PLMN as shown in the picture below

The GSM PLMN provides traditional voice services and

SMS The GPRS/UMTS PLMN provides packet data

services The UTRAN is composed of the Radio Network

Controller (RNC) which controls one or more Node B’s

• The UTRAN connects to the two core networks

• The UTRAN connects to the GSM PLMN using the

Iu Interface between the RNC and MSC

• The UTRAN connects to the GPRS PLMN using the

Iu Interface between the RNC and SGSN

• The Iu Interfaces perform the functions of both

the GSM A Interface and GPRS Gb Interface

The GSM PLMN provides connectivity to the 3G UTRAN via

the evolved 3G MSC/VLR, while the GPRS/UMTS PLMN

provides connectivity to the 3G UTRAN via the evolved 3G

Serving GPRS Support Node (SGSN)

MSC/VLR

• The MSC anchors voice calls and provides SMS

• The MSC performs switching, mobility management, authentication, Quality of Service (QoS) approval and billing for all the UEs in its geographical area

• The MSC assigns a Temporary Mobile Subscriber Identifier (TMSI) to each UE to identify and track it

• The MSC is responsible for one or more Location Areas (LA)

• The VLR is the local database associated with each MSC

• The VLR updates the HLR whenever subscribers attach to the MSC so the HLR knows the UEs location down to the MSC/VLR level

Home Location Register (HLR)

• The HLR maintains a common UE subscription database for both CS and PS domains

• The HLR maintains separate location information for the two domains

• The HLR uses the International Mobile Subscriber Identity (IMSI) to track UE profiles

• The SGSN assigns a Packet TMSI (P-TMSI) to each UE to identify and track it

• The SGSN is responsible for one or more Routing Areas (RA)

• The SGSN connects to the Gateway GPRS Support Node (GGSN)

• The SGSN updates the HLR whenever subscribers attach to it so the HLR knows the UEs location down to the SGSN level

GGSN

• The GGSN is the gateway from the operator’s core network, specifically the PS-CN, to any of the external

IP networks to which it provides connectivity

• The GGSN assigns IP addresses as required to UEs desiring packet-switched services

6.0 The UTRAN

The UTRAN consists of one or more Radio Network Subsystems (RNS) The RNC is the master of the RNS A Node B is the radio transmission and reception unit within an RNS

The UTRAN provides one unified set of radio bearers for

both the PS domain and the CS domain These radio

bearers carry bursty traffic for the packet-switched

domain and delay sensitive voice traffic for the

circuit-switched domain The UTRAN provides some distribution

functionality to the two domains In doing so, the UTRAN

provides the UE with access to the basic services the two

core networks provide, and provides both kinds of access

concurrently, if desired, with equal ease Unlike the case

with 2G and 2.5G, the UTRAN’s radio bearers are not

exclusively optimized for any service in particular; they

can be dynamically configured for any kind of service

RNC

The RNC handles all aspects of radio resource

management within the RNS The RNC interfaces with both the MSC and SGSN, each through their own Iu interfaces, to route signaling and traffic to/from the UE

Some RNC functions include:

• Manage all radio resources and enforce QoS, which includes but is not limited to

o Allocation of DL and UL OVSF Codes for UEs in UMTS R99

o Allocation of UL Scrambling Codes for UEs

and reception duties for multiple sectors (or logical cells)

within a cell (or coverage area)

Some Node B functions include:

• Implement WCDMA functions: digital coding,

interleaving, spreading, scrambling, modulation

• Power Control

• Handling of logical cells

• Node Bs are responsible for one or more cells (or

sectors) on one or more radio carriers

7.0 UMTS Interfaces

UMTS defines open interfaces between all components

Each interface defines a set of protocols for exchanging

traffic and signaling information

Access Stratum (AS)

This is a functional layer in the UMTS protocol stack between the RNC and the UE that serves both traffic and signaling AS signaling is used for establishment, modification and release Radio Links and associated functions These functions are very specific to the UTRAN and its technologies

Non Access Stratum (NAS)

This is a functional layer in the UMTS protocol stack between the Core Network and the UE that serves both traffic and signaling NAS signaling is used for Mobility Management, Connection Management and Session

Management functions These functions (authentication for instance) are independent of the radio access network and its technologies

Uu Interface

• The interface between the UTRAN and the UE is known as the Uu Interface

• The Uu is a WCDMA-based air interface that allows the UE to connect to the UTRAN via code channels

• RRC (Radio Resource Control) is the main signaling protocol on the Uu Interface

Iu Interface

• Each of the interfaces between the RNC and the two domains in the core network is known as the Iu Interface

• The Iu Interface between the RNC and SGSN is called the Iu-PS Interface

• The Iu Interface between the RNC and MSC is called the Iu-CS Interface

• Radio Access Network Application Part (RANAP) is the signaling protocol on the Iu Interface

• The Iu Interface is can be deployed with ATM at Layer 2 or with IP at Layer 3

• The Core Networks use their Iu Interfaces to request radio resources from the UTRAN

• The Iu Interface is used to carry UE traffic between the UTRAN and Core Networks

Iub Interface- “The Backhaul”

• The interface between the Node B and its RNC is known as the Iub Interface

• The Iub Interface is an open interface, which is in sharp contrast to the somewhat proprietary Abis interface in GSM

• Node B Application Part (NBAP) is the messaging protocol on the Iub Interface

• The Iub Interface is can be deployed with ATM at Layer 2 or with IP at Layer 3

• The Iub Interface is used to carry common and dedicated signaling and user traffic

Iur Interface

• The interface between two RNC’s is known as the Iur Interface

• The Iur Interface is an open interface which has no equivalent whatever in GSM/GPRS

• Radio Network Subsystem Application Part (RNSAP) is the signaling protocol on the Iur Interface

• Iur Interface is can be deployed with ATM at Layer 2 or IP at Layer 3

• The Iur Interface is used to carry common and dedicated signaling and traffic between RNCs

• It allows certain mobility procedures such as soft handovers between different RNSs

• It is an optional Interface

8.0 UE-UTRAN Protocol Stack

The UE-UTRAN Interface protocols are implemented on the UE, Node B and the RNC There are five participating protocols (WCDMA-Physical, MAC, RLC, RRC, and PDCP)

involving two functional layers (AS and NAS)

WCDMA Physical Layer (L1)

The WCDMA-based Physical Layer is used to transmit data

over the air, it implements the following WCDMA functions:

Medium Access Control (MAC) Layer (L2)

The MAC Layer is an elaborate traffic cop type of function that organizes multiple users and services in the WCDMA-Physical Layer As such MAC is responsible for the following functions:

• Logical to Transport Channel Multiplexing

• Priority Handling

• Identification of UEs on Common Transport Channels

• Ciphering (in Transparent Mode RLC)

• Transport Channel type switching

• Selection of the appropriate Transport Format for each Transport Channel

Radio Link Control (RLC) Layer (L2)

The RLC Layer hides the high error rates inherent in the WCDMA-Physical Layer from the layers above it (RRC, PDCP and user voice bits. As such RLC is responsible for the following functions, some of which may be absent in certain RLC modes of operation:

• Segmentation/Reassembly

• Concatenation

• Padding

• Error correction (retransmissions in acknowledged mode)

• Transfer of user data in transparent, unacknowledged, or acknowledged mode as defined by QoS settings

• In-sequence delivery of upper layer PDUs (in acknowledged mode)

• Unacknowledged Mode (UM) – sequenced but not guaranteed delivery (no ARQ) This mode of the RLC is used for signaling connections and real-time packet data connections

• Transparent Mode (TM) – no RLC overhead at all This mode of the RLC is used for voice connections

Radio Resource Control (RRC) Layer (L3-Control)

The RRC Layer is complicated control plane protocol that includes messages that carry all the parameters needed

to set up, modify, and release layer 2 and layer 1 protocol elements and entities As such RRC is responsible for the following functions:

• Radio Resource Management

• Setup, Reconfiguration and Release of Radio Bearers

• Configuring other layers below it

• Carrying as payload higher layer signaling messages (MM, CM, SM)

• Interfaces with the core network protocols

• Broadcast System Information

• RRC Signaling (measurements, handovers, cell updates)

RRC messages are exchanged when calls are setup/released, handovers occur or reconfigurations are done Some RRC messages (their direction) used during call setup and soft handover are:

• RRC Connection Request (UL)

• RRC Connection Setup (DL)

• RRC Connection Setup Complete (UL)

• Initial Direct Transfer (UL)

• Direct Transfer (UL and DL)

• Security Mode Command (DL)

• Security Mode Complete (UL)

• Radio Bearer Setup (DL)

• Radio Bearer Setup Complete (UL)

• Radio Bearer Reconfiguration (DL)

• Radio Bearer Reconfiguration Complete (UL)

• Measurement Control (DL)

• Measurement Report (UL)

• Active Set Update (DL)

• Active Set Update Complete (UL)

Packet Data Convergence Protocol (PDCP) Layer (L3-Data Traffic)

PDCP only applies to the L3 user plane protocol for IP traffic As such PDCP is responsible for the following functions:

• Provides header compression services for IP datagrams

Forward Error Correction (FEC) Coders

• First step in physical layer processing is to

protect the data (bits) against errors that

might occur in the radio link

• This process is called Forward Error

Correction (FEC) which is achieved with

Convolutional Coders and Turbo Coders

• The 0s and 1s that emerge after this

processing are called “symbols” The channel

coder transforms bits into a somewhat larger

number of symbols, which “symbolize” or

represent the bits in a redundant way that

“protects” the bits from the hazards of the

radio channel

• The higher the rate of protection (the more added redundancy) the lower the effective user data rate and vice-versa

• Since they a somewhat slow in decoding, Turbo Coders are used for Packet Data traffic

• Convolutional Coders are faster than Turbo Coders, and are used for Voice traffic and signaling

• Additional protection of the payload’s bits is provided by means of CRC (Cyclic Redundancy Codes), Block Interleaving and some Repetition techniques

• UMTS supports ½ Convolutional, 1/3 Convolutional, 1/3 Turbo Coders The fraction refers to the “rate” of channel coding: “½” rate means 2 symbols emerge from the channel coder for each bit admitted to it

Orthogonal Variable Spreading Factor (OVSF) Codes

• The second step in physical layer processing has two functions:

1 Spread the channel encoded symbols to a much higher chip rate sufficient to make the signal occupy the wide bandwidth allocated for it The WCDMA chip rate in UMTS is 3.84 Million cchips per second (Mcps) The 0s and 1s that occur after spreading are called Chips, because they

“chop up” symbols into a specified number of chips, thus representing each coded symbol on the air with a known chip sequence

2 Identify the receiver of the WCDMA radio frame by an assigned chipping sequence Multiple frames can occupy the same bandwidth at the same time merely by assigning unique chipping codes (spreading codes) to each of them

• These spreading codes are called Channelization Codes, since they are assigned as if they were channels, and have the property of being orthogonal with each other Being “orthogonal” means they do not normally interfere with each other; the receiver cannot easily confuse one of these orthogonal codes with any one of the others

• In WCDMA these channelization codes are called OVSF Codes, (Orthogonal Variable Spreading Factor Codes)

• OVSF codes can have variable lengths, affording variable spreading factors to the underlying coded symbols For a fixed radio bandwidth and chip rate, the faster the symbol rate, the shorter the OVSF code; the slower the coded symbol rate, the longer the OVSF code

• Because of their mutual orthogonality, transmission to multiple users over the same channel is possible

• In UMTS R99, the allowed range of OVSF code lengths in the DL is - 4 bits through 512 bits

• In UMTS R99, the allowed range of OVSF code lengths in the UL is - 4 bits through 256 bits

• Length of the OVSF codes is also called the Spreading Factor (SF) of the code

• The Processing Gain is defined as “chip rate / data rate”; the longer the OVSF code applied to a coded symbol, each of which represents a payload bit, the grater the processing gain The greater the processing gain, the more “over-represented” a bit appears to be on the air with its spreading code, and the easier it is for a receiver to recover the bit in the presence of noise

• The process of spreading a signal with a sequence of bits known to both sides of the radio channel is a well-established method for enabling communicating devices to operate at very low noise margins

• The higher the spreading factor of the OVSF code the lower the user data rate and vice-versa

• The higher the spreading factor of the OVSF code the greater the processing gain and vice-versa

• The higher the processing gain achieved through spreading the lower the power requirement for a transmission to achieve a certain QoS, and vice-versa

• OVSF Codes in WCDMA are managed and constructed using OVSF Code Trees Each transmitter (base or mobile) gets an entire OVSF Tree for its use

• Every WCDMA Channel uses a different OVSF Code

• A Cell gets a complete OVSF Code Tree to share among all the UEs in that Cell for the DL

• A UE gets a complete OVSF Code Tree to share among all the channels that the UE will use for the UL

• If a Cell runs out of DL OVSF Codes – call blocking and handover blocking will occur

• In UMTS R99, OVSF Codes are assigned to a UE at Call Setup, re-assigned at Reconfiguration and allocated at Call Release

• These secondary transmitter identification codes are called Scrambling Codes or Gold Codes

• The UMTS DL supports 512 different Scrambling Codes that uniquely identify a Cell These are downlink Cell-Specific Scrambling Codes and the planning of these codes is required at network deployment time

• The UMTS UL provides 224 (16,777,216) Scrambling Codes that uniquely identify a UE in the uplink

• Since scrambling codes run at the same rate as their underlying OVSF codes, 3.84 Mcps, scrambling does not change the rate of the information being transmitted; they have a unity spreading factor (SF = 1), and they offer no processing gain

Data Rate Computation

Basic equation used to calculate the WCDMA air interface physical layer user data rate, is the following:

User Data Rate x Coding Rate x Spreading Factor = 3,840,000 x Modulation Factor

• In the equation above

o User Data Rate is the data rate for the user connection in each direction on the air interface

o Coding Rate is the inverse of the rate of channel coding

o Spreading Factor is the length of the OVSF Code assigned for the user connection

o Modulation Factor is the number of bits a modulation symbol represents

• Using a 7.5 kbps user data rate as an example to calculate the spreading factor required:

o User Data = 7.5 kbps

o FEC = ½ Convolutional Coder – thus the Coding Rate = 2

o QPSK Modulation – thus the Modulation Factor = 2 (Used in the DL)

o Spreading Factor = (3,840,000 * 2)/(7,500 * 2) = 512

o This calculation does not take into account the physical channel overhead needed for a bearer path

o This calculation does not take into account the bandwidth needed for RRC messages

• Using a 7.5 kbps user data rate as an example to calculate the spreading factor required:

o User Data = 7.5 kbps

o FEC = ½ Convolutional Coder – thus the Coding Rate = 2

o Offset-QPSK/BPSK Modulation – thus the Modulation Factor = 1 (Used in the UL)

o Spreading Factor = (3,840,000 * 1)/(7,500 * 2) = 256

o This calculation does not take into account the physical channel overhead needed for a bearer path

• This calculation does not take into account the bandwidth needed for RRC messages

• 12.2 kbps AMR voice call uses – 128 bit OVSF code in the DL and 64 bit OVSF code in the UL

• 384 kbps RAB (Radio Access Bearer) uses an 8 bit OVSF code in the DL and a 4 bit OVSF code in the UL

o Type of Control information

o RLC Mode (TM, UM, AM)

• Some R99 Logical Channels are:

o Broadcast Control Channel (BCCH)

o Paging Control Channel (PCCH)

o Common Control Channel (CCCH)

o Dedicated Control Channel (DCCH)

o Dedicated Traffic Channel (DTCH)

Transport Channels

• The Transport Channel defines the services

provided by the physical layer to the upper layers,

or the manner in which information has to be moved over the air The manner of transmission is closely related to the service

• The Transport Channel is a new concept introduced for the UTRAN

• Data is exchanged over Transport Channels (between the MAC and Physical layers) in units of Transport Blocks

• Transport Blocks arrive at the Physical Layer once every TTI (Transmission Time Interval) Each Transport Channel has its own TTI setting

• The TTI has 4 settings: 10 ms, 20 ms, 40 ms or 80 ms

• Variable rates are supported by changing the number of Transport Blocks per TTI over time, and changing the number of bits per Transport Block over time

• Transport Channels were not defined for the GSM/GPRS/EDGE RAN

• The Transport Channel indicates the METHOD and CHARACTERISTICS of the information transfer and answers the question “HOW is information being transported?” These are things like:

o Protection Level defined by the QoS of the specific service

o FEC Codes (1/2 Convolutional, 1/ Convolutional, 1/3 Turbo)

o Cyclic Redundancy Code (CRC) (8, 12, 16, 20 bit CRCs)

o Repetition/Puncturing/Interleaving

o Block Error Rate (BLER)

• The Coded Composite Transport Channel (CCTrCH) is the function/procedure by which multiple transport channels are multiplexed into a single physical channel

• Some R99 Transport Channels:

• The Physical Channel indicates the two ends of the information transfer and answers the question ,

“WHO is the information being transported for? These are things like:

o OVSF Code

o Scrambling Code

• In UMTS, the WCDMA radio frame is 10 msec long (38400 chips)

• A radio frame is divided into 15 slots

• Each slot is 0.667 msec long (2560 chips)

• In GSM/GPRS the Physical Channel was identified by time slot and frequency The UMTS equivalent is the OVSF code, the OFSF code’s SF and the scrambling code

Acronym Physical CH Direction OVSF/SF Information carried

PCCPCH Primary Common Control Physical Channel DL C 256,1 Broadcast

SCCPCH Secondary Common Control Physical Channel DL 128 Paging, Control, Traffic

DPDCH Dedicated Physical Data Channel DL, UL Variable User Data (Traffic, RRC, NAS)

DPCCH Dedicated Physical Control Channel DL, UL Variable TFCI, TPC, Pilot (Physical Control) PRACH Physical Random Access Channel UL 128 Preamble, Control (RRC)

P-SCH Primary Synchronization Channel DL None Primary Sync Code

S-SCH Secondary Synchronization Channel DL None Secondary Sync Sequence

AICH Acquisition Indicator Channel DL 256 PRACH Acquisition Indication

DL Dedicated Physical Channel

The frame structure of the DL Dedicated Physical Channel (DPCH) is shown The DPCH consists of two channels:

sub-• DL Dedicated Physical Control Channel (DPCCH)

• DL Dedicated Physical Data Channel (DPDCH)

The DPCCH carries Physical Layer control information:

• Pilot Bits are used as a reference for all DL power control

• Power Control bits (TPC) are used to send UL power control commands to the UE

• The UE needs the Transport Format Combination

Indicator (TFCI) bits in order to understand how to

decode the accompanying DPDCH:

o Channel Encoding

o Interleaving

o Bit rate

o Transport Channel to Physical Channel mapping

The DPDCH carries the Physical Layer data:

• User Traffic (Voice, IP packets etc.)

• RRC messages

• NAS messages (MM, CM, SM messages)

The DPCCH and DPDCH are time-multiplexed in a 10 msec

frame using a single OVSF code

UL Dedicated Physical Channel

The frame structure of the UL Dedicated Physical Channel (DPCH) is shown The DPCH consists of two channels:

sub-• DL Dedicated Physical Control Channel (DPCCH)

• DL Dedicated Physical Data Channel (DPDCH)

The DPCCH carries Physical Layer control information:

• Pilot Bits are used as a reference for all UL power control

• Power Control bits (TPC) are used to send DL power control commands to the Node B

• The Node B receiver needs the Transport Format

Combination Indicator (TFCI) bits to figure out

how to decode he accompanying DPDCH:

o Channel Encoding

o Interleaving

o Bit rate

o Transport Channel to Physical Channel mapping

• Feedback Information (not used)

The DPDCH carries the Physical Layer data:

• User Traffic (Voice, IP packets etc.)

• RRC messages

• NAS messages

The DPCCH and DPDCH are code-multiplexed in 10 msec

frames using multiple OVSF codes

Modulation Schemes

The UL and the DL use two different modulation schemes The reason for this is the remarkable difference in the overall signal we see in the UL and DL In particular, the Node B typically makes transmissions to many UEs, but the UE makes only its own transmissions to the Node B But the UE’s uplink transmissions consist of DPCCH control channel which always has a spreading factor of 256 (requiring relatively little power to be heard by the Node B thanks to all the processing gain), but the DPDCH can have a very small spreading factor when the data rate is high WE get around the uniqueness of the uplink with an intricate combination of (a.) assigning OVSF spreading according to the given spreading factors, (b.) the Node B automatically knowing these relationships in advance without having to agree upon them through signaling, (c.) adjusting the relative amplitudes of the I and

Q chip streams with the spreading factors, and (d.) applying the uplink scrambling code (selected by the RNC) at the last multiplication stage in the form of complex scrambling code that consists of two real chip sequences

• In the light of the strict uplink modulation requirements, UMTS R99 uses Offset-QPSK Modulation/BPSK Modulation (1 bit is represented by each modulation symbol) on the UL OQPSK, or Offset-QPSK, is a version of QPSK in which the transmitted signal has no amplitude modulation The incoming signal is divided in the modulator into two portions, I and Q, which are then transmitted as shifted streams with a half symbol duration This means that the UL requires half the SF for the same throughput that the DL can provide

• UMTS R99 uses Modulation (2 bits are represented by each modulation symbol) on the DL

11.0 Power Control

Eb/No

Energy per Bit over Noise Energy per Hertz (Eb/No) only applies to dedicated channels carrying information Eb/No is measured after de-spreading, and is classically defined as the ratio of Energy per Bit (Eb) to the Spectral Noise Density (No) Like the C/N (the carrier to noise ratio) of analog systems, Eb/No is a measure of signal to noise ratio for a digital communication system It is measured at the input to a receiver and is used as the basic measurement of how strong the signal is There are published charts and curves for the different forms of modulation (BPSK, QPSK, QAM, etc.) which give the theoretical bit error rates versus Eb/No for all the modulation types These reflect the best performance that can be achieved across a digital link with a given amount of RF power Eb/No is a fundamental tool for predicting the performance of a digital link; given a type of modulation,

we know what error rates to expect for a certain Eb/No

Ec/Io

Energy per Chip over all the Interference Energy per Hertz applies only to the CPICH (Common Pilot Channel) It’s a ratio that expresses the pilot strength Suppose, for example the Ec/Io equals “0.25” This means that 25%

of the energy in the total bandwidth is due to the pilot If

you prefer, you can express this in decibels, which in this

case is -20log10(.25) which equals 12.04

Power Control in UMTS R99

Ec/Io and Eb/No are elements of power control and

interference management in UMTS There are two types

of Power Control in UMTS R99:

• Open Loop

• Closed Loop

Open Loop Power Control

Open Loop Power Control is used when the UE wants to

transmit a message on the PRACH (Physical Random

Access Channel)

• It is typically used only once during call setup and

never again as long as the UE is in the Cell_DCH

sub-state of the CONNECTED Mode

The UE determines the transmit power to use for the message (RRC Connection Request) it places on the PRACH for itself based on the calculation described below This is Open Loop Power Control

Initial UE Transmit Power = CPICH Transmit Power – CPICH_RSCP + UL Interference + Constant Value

In the equation above

• CPICH Transmit Power is the power with which the CPICH (Common Pilot Channel) is being transmitted and is provided by the Node B on the Broadcast Channel

• CPICH_RSCP is the CPICH Received Signal Code Power (this is measured by the UE)

• UL Interference is the uplink interference value provided by the Node B on the Broadcast Channel

• Constant Value is an adjustment provided to the UE by the Node B on the Broadcast Channel

Closed Loop Power Control

Closed Loop Power Control is used when the UE is in the Cell_DCH sub-state of the CONNECTED Mode and is symmetrical between the DL (Downlink) and the UL (Uplink) There are two elements to closed loop power control: the Inner Loop and the Outer Loop

• Inner Closed Loop Power Control runs at 1500 times a second (1500 Hertz)

• Outer Closed Loop Power Control occurs at 50 to 100 times a second

• All Power measurement/comparisons on dedicated channels use the Pilot Bits’ power on the DPCCH (Dedicated Physical Control Channel) as the REFERENCE

• The Inner Closed Loop tracks (at a 1500 Hertz

rate) an Eb/No target established by the Outer

Closed Loop (updated at 50 - 100 Hertz)

• The Outer Closed Loop changes the Eb/No target,

for the Inner Closed Loop, based on the current

BLER (Block Error Rate) which compared with a

BLER target specified in the QoS for the service

• The Inner Loop “chases” the Outer Loop target

• Primary purpose of Power Control is to Maximize

Capacity using Link Adaptation

• DL Power Control helps with maximizing Cell

capacity

• UL Power Control helps solve the Near-Far

problem in a cell

• The Inner Closed Loop only has power up and

power down commands; there is no “stay the

same” command in the Inner Loop

• It is possible to slow down the rate of the Inner Closed Loop and the options are based on whether it is for the UL or the DL UMTS deployments commonly use the default value of 1500 times a second

• When the UE or Node B receives a TPC command (Transmit Power Control) it changes the power of its transmission by a “Step Size” amount UMTS deployments commonly use the default value of 1 dB (decibel)

12.0 RRC Connection and RRC States

RRC can be in one of two states (Idle or Connected), and while in the connected state the UE can be in one of four sub-states (Cell_DCH, Cell_FACH, Cell_PCH, or URA_PCH)

RRC Idle Mode

Some key characteristics of the UEs RRC Idle Mode are:

• UE has no Radio/UTRAN resources allocated for it

• UE is listening to the Broadcast Channel of a Cell

• UE can perform measurements and does Cell

Reselection on its own

• Core Network has assigned a TMSI/P-TMSI to the

UE

• Core Network has created a VLR/MM Context for

the UE and is tracking the location of the UE

• UE is responsible for updating the Core Network

using Location Area Updates/Routing Area

Updates with its cell reselections

RRC Connected Mode

An RRC Connection is a logical signaling connection

between a UE and the RNC and must be setup before the UE can get any kind of service from the network The RRC Connection setup procedure is initiated by the UE and is typically released by the RNC A UE with an RRC Connection is said to be in the RRC Connected Mode which has the following characteristics:

• RNC has created a Context for the UE and has assigned it a U-RNTI

• UE has an RRC connection with its Serving RNC

• RNC is tracking the UE at the Cell/URA level

• UE is responsible for updating the RNC using Cell Update/URA Update

• UE may or may not have a dedicated connection to the UTRAN depending on the state of the UE

• UE can only have one RRC Connection/SRNC at any time

• The RRC Connected Mode has 4 sub-states, and the SRNC decides when to move the UE in/out of these states

o Cell_DCH

o Cell_FACH

o Cell_PCH

o URA_PCH

• The RRC Connection has 4 Signaling Radio Bearers (SRBs)

o SRB #1 – unreliable UE-RNC messages

o SRB #2 – reliable UE-RNC messages

o SRB #3 – reliable UE-CN messages

o SRB #4 – reliable SMS information

CELL_DCH sub-state

In the Cell_DCH sub-state:

• UE has dedicated radio resources (DCH) and is considered to be in the traditional “in a call” state

o DL
DCCH/DCH/DPCH

o UL
DCCH/DCH/DPDCH

• UE can transmit/receive data on the UL and DL

• Mobility is managed by the RNC via Soft Handovers

• UE typically enters this sub-state at the RRC

Connection setup phase

CELL_FACH sub-state

In the Cell_FACH sub-state:

• UE has no dedicated resources and communicates

with the RNC on common channels (RACH and FACH)

• Used mostly for packet data services

• UE sends Cell Update messages to the RNC

CELL_PCH sub-state

In the Cell_PCH sub-state:

• UE has no dedicated resources and communicates with the RNC on common channels (RACH and FACH)

o DL
DCCH/FACH/SCCPCH

o UL
DCCH/RACH/PRACH

• UE monitors the PICH and PCH for network-initiated operations

• UE conserves battery power while still in the RRC Connected Mode

• UE must update the RNC upon cell reselection and periodically as well

• UE sends Cell Update messages to the RNC

URA_PCH sub-state

In the URA_PCH sub-state:

• UE has no dedicated resources and communicates with the RNC on common channels (RACH and FACH)

o DL
DCCH/FACH/SCCPCH

o UL
DCCH/RACH/PRACH

• UE monitors the PICH and PCH for network initiated operations

• UE conserves battery power while still in the RRC Connected Mode

• UE must update the RNC upon URA reselection and periodically as well

• UE sends URA Update messages to the RNC, but these messages occur at a much lower frequency than Cell Updates

13.0 UE Power Up and Initial Cell Selection

Synchronization

When the UE powers up it achieves synchronization with a Node B’s DL transmissions by performing the following

in the order indicated here:

1 First, it achieves Slot Synchronization by listening to the transmissions of the Primary Synchronization Channel (P-SCH)

2 Second, it achieves Frame Synchronization by

listening to the transmissions of the Secondary

Synchronization Channel (S-SCH)

3 Besides assisting with achieving Frame

Synchronization, the Secondary Synchronization

Sequence on the S-SCH employs an “alphabet” of

codes that indicate Scrambling Code Group of the

cell for the UE so that the UE does not have to try

all 512 scrambling codes to discover the cell’s

scrambling code The 512 possible DL scrambling

codes are partitioned into 64 groups of 8 codes

each, and the UE need only try the 8 scrambling

codes in the group “spelled out” by the sequence of

codes on the S-SCH

4 Third, the UE determines the DL Scrambling Code

the Cell, from eight possibilities, by listening to the CPICH which is scrambled with the cell’s assigned scrambling code

5 Fourth and finally, the UE can decode the PCCPCH and listen to all the System Information Blocks (SIBs) being transmitted on the Broadcast Channel embedded in the PCCPCH

The UE is now ready to initiate an RRC Connection Setup so that it can Register with the MSC and Attach to the SGSN

• MSC creates a VLR entry for the UE and informs the HLR of the UEs location

• MSC assigns the UE a TMSI

Voice Call Setup

From the perspective of the UTRAN, a typical voice call setup has the several important phases illustrated in the picture The phases are:

• RRC Connection Establishment (Signaling Radio

Bearers)

o The UE is typically assigned dedicated channel

resources during this phase to get the UE off

open loop power control and onto closed loop

power controlled radio resources

o DL – 128 bit OVSF code is assigned

o UL – 64 bit OVSF code is assigned

o DL – DCCH/DCH/DPCH

o UL – DCCH/DCH/DPDCH-DPCCH

• Service Request from the UE for the Core Network

• Iu Signaling Connection Establishment

• Authentication by the MSC

• Security (Ciphering/Integrity)

• Radio Bearer Establishment

o Logical and Transport Channels to carry voice traffic are setup during this phase

o These channels are mapped to the same Physical Channels which were setup during the RRC Connection establishment

Channels for a Voice Call

The final view of all the channels used for a voice call are

shown in the picture For each direction we have:

• Voice Class A Bits – 1 DTCH/DCH channel set

• Voice Class B Bits – 1 DTCH/DCH channel set

• Voice Class C Bits – 1 DTCH/DCH channel set

• SRB #1 – 1 DCCH channel

• SRB #2 – 1 DCCH channel

• SRB #3 – 1 DCCH channel

• SRB #4 – 1 DCCH channel

• 1 DCH for all the SRBs

• 1 DPCH for all the channels shown above

• Total of 7 Logical Channels (one for each of the A, B, and C categories of voice bits and four more for each of the SRBs), 4 Transport Channels (three for each of the A, B, and C categories of voice bits and one more for all the SRBs), 1 Physical Channel (the DPCH)

15.0 R99 Data Calls

Data “calls” are actually data “sessions” between the UE and a router (the UE’s SGSN) They are set up in a way reminiscent of voice calls, but the details are different in some important ways As it is with voice calls, one must register for services before they can be provided

Attach Procedure

• The UMTS UE attaches to the SGSN using an Attach procedure, which is the equivalent of the Registration procedure for circuit-switched voice

• SGSN authenticates the UE

• SGSN creates a MM context for the UE with which it can track the UE

• SGSN assigns a P-TMSI to the UE

R99 Data Call Setup

From the perspective of the UTRAN, a typical R99 data call

setup has the several important phases as illustrated in

the picture The phases are:

• RRC Connection Establishment (SRBs)

o The UE is typically assigned dedicated channel

resources during this phase to get the UE off

open loop power control and onto power

controlled radio resources

o DL – 128 bit OVSF code is assigned

o UL – 64 bit OVSF code is assigned

o DL – DCCH/DCH/DPCH

o UL – DCCH/DCH/DPDCH-DPCCH

• Service Request from the UE

• Iu Signaling Connection Establishment