01 HSPA System Overview in UMTS Network

HSPA System Overview

Objective

At the end of the module the participant will be able to:

• Describe UMTS network and Radio Access Network.

• Explain aspects of UMTS Release 99 air interface.

• Briefly introduce HSPA system and key elements of HSPA.

Content

• UMTS evolution and HSPA

• UMTS Release 99 environment– Network

– Air Interface

• HSDPA introduction and advantages

• HSUPA introduction and advantages

HSPA or HSxPA

Consists of:

• HSDPA = High Speed Downlink Packet Access– Introduced in Release 5

– Up to 14.4 Mbps in downlink

• HSUPA = High Speed Uplink Packet Access– Introduced in Release 6

– Up to 5.76 Mbps in uplink

Future enhancements to HSPA will lead to even higher data rates.

Rel 99 ( = Rel 3)

Rel 4 Rel 5 Rel 98 (EGPRS)

RAN

CORE

UTRANQoS

HSDPA

VoIPMGW

QoSIMS

Rel 6

HSUPA

Evolution of UMTS

UMTS Release 99 Environment

Core Network: Same as GSM/GPRS/EDGE

Radio Access Network:

• User Equipment (UE) = Mobile phone + USIM

• Node B – Base station supporting WCDMA

• Radio Network Controller (RNC) – Controller in 3G RAN

Unlike 2G, Iur interface exists between neighbor RNCs.

UMTS Network

Circuit-switchedand IN network

Internet

IntranetISP

Node B Node BB

3G access

network

Packet-switchednetwork

Management System

Node BIur

IuCS

IuPSIub

E

Gn Gi

RNC

GGSN

GMSC PSTN

IN

RNC

MSC

SGSN

3G Core network

UE

Uu

HLR

UMTS Release 99 Air Interface

• Large 5 MHz bandwidth.

• FDD: Simultaneous transmit and receive using different band.

• CDMA– Spreading: creating signal through unique user code to create multiple

bandwidth.

– Despreading: reobtaining original signal by correlating signal with user code.

Frequency Time PN code

FDMATDMACDMA

frequency f

time t

power

TS 1TS 2

TS 3

TDMA

frequency f

time t

power

1 2 3

FDMA

frequency f

time t

power

123

CDMAMultiplexmethod

BS & MS with commonknow-how regarding:

P

P P

For coordinating limited frequency resources to different users

-1

User data:100

0 01

T Bit

Spreading code:0110

+1

+1

-1

+1

-1

Coded signal T chip

t

t

t

SF = 4

0 0 0 0 0 01 1 1 1 1 1

0 0 0 01 1 1 11 10 0

Spreading

CodeGenerator

WidebandModulation

CarrierGenerator

De-Spreading

CodeGenerator

De-Modulation

RB

AirInterface

RB

RC

Timesynchronization

RB: Bit RateRC: Chip RatefT: Carrier frequency

RCfT

bits chips symbol

Transmitter Receiver

Cch,1,0 = (1)c

(c , c)

(c , -c)

SF = 1 SF = 2 SF = 4 SF = 8

Cch ,2,0 = (1,1)

Cch ,2,1 = (1,-1)

Cch ,4,0 = (1,1,1,1)

Cch ,4,1 = (1,1,-1,-1)

Cch ,4,2 = (1,-1,1,-1)

Cch ,4,3 = (1,-1,-1,1)

Cch ,8,0 = (1 , 1 , 1 , 1 , 1 , 1 , 1 , 1)

Cch ,8,1 = (1 , 1 , 1 , 1 , -1 , -1 , -1 , -1)

Cch , 8,2 = (1 , 1 , -1 , -1 , 1 , 1 , -1 ,-1)

Cch ,8,3 = (1 , 1 , -1 , -1 , -1 , -1 , 1 , 1)

Cch , 8,4 = (1 , -1 , 1 , -1 , 1 , -1 , 1 , -1)

Cch ,8,5 = (1 , -1 , 1 , -1 , -1 , 1 , -1 , 1)

Cch ,8,6 = (1 , -1 , -1 , 1 , 1 , -1 , -1 , 1)

Cch ,8,7 = (1 , -1 , -1 , 1 , -1 , 1 , 1 , -1)

Code Tree in UMTS Air Interface

Role of Channelization and Scrambling Code in Downlink Direction

• Channelization codes distinguish user within a cell.

• Each cell has the same channelization code tree – two users in different cells can have the same channelization code assigned.

• Therefore the different cells must be characterized by a Scrambling code.

Code 3

Code 3Code 2

Code 1

Code 2

Code 1

Code Comparison between Uplink and Downlink

Uplink Downlink

Scrambling Codes User separation Cell separation

Channelisation CodesData and control channels

from same UEUsers within a cell

Available

Channelisation Codes

FDD

4, 8, 16, 32, 64, 128, 2564, 8, 16, 32, 64, 128, 256,

512

Spreading Code Channelisation Code x Scrambling Code

In the uplink direction the user signals are not synchronised due to time delay.

In case of different time delays Channelization Codes are not orthogonal any more.

Scrambling Codes: High autocorrelation if synchronized, almost zero correlation between different codes even if unsynchronized.

Chann. Code = (1,-1,-1,1)

Chann. Code = (1,1,-1,-1)

T=0

1 1 -1 -1 1 1 -1 -1 1 1 -1 -1

1 -1 -1 1 1 -1 -1 1 1 -1 -1 1

Delay

t

Role of Scrambling Code in Uplink Direction

Reserved forsignaling

2 voiceconnections

7 dataconnections

3.4 kbps

SF=64

SF=8

SF=16

SF=32

SF=4

12.2 kbps

384 kbps

SF=128

SF=256

144 kbps

64 kbps

OVSF Code Tree Usage

2560 chipsTimeslot TS

2/3 ms

Frame TS#0 TS#i TS#14••• •••

10 ms

f#1 f#i f#72••• •••Superframe

720 ms

1/3,840,000 s 0.2604 s

Chip Shortest information unit in CDMA

(of the spreading code)

Periodic repetition ofcontrol information (e.g. TPC)

Shortest transmission durationand data rate adaption

Counting period for:• Definition of physical channels• Handover to GSM (120 ms frame)

Chip, Timeslot, Frame, Superframe

HSDPA

• Introduced in Release 5.• Can coexist with non-HSDPA in the same cell.• Improve downlink direction. Uplink still relies on Rel '99.

Advantages:• Higher data rate: up to 14.4 Mbps with practical rate 10.8

Mbps.• Reduce latency:

– especially with TCP Slow Start and Congestion Avoidance.– Retransmission and HARQ in Node B.

• Spectral efficiency: TTI=2ms schedule of shared channels.

TCP Window Size

8,760

congestion occurs

receiver’s window seize

cwnd

slow start threshold, start value = 65535

slow start threshold, readjusted value

readjustment

of slow start

thresholdthird phase:

congestion voidance,

linear growth

second phase:

slow start,

eponential growthfirst phase:

slow start,

exponential growth

Rel‘99 DCH

RNC RNC

Packet

Node B

Packet

Retransmission

L1 ACK / NACK

RLC ACK / NACK

Retransmission

Retransmission Cycle in HSDPA

Rel‘5 HS-DSCH

HSDPA Scheduling

10 msDedicated DCH

SharedHS-DSCH Big shared pipe

Time

Code

HSDPA

wasted bandwidth!

2 ms

inefficient usage!

Rel '99

HSUPA

• Introduced in Release 6.

• Improve uplink direction. Rely on HSDPA in downlink.

Advantages:

• Higher data rate: up to 5.76 Mbps with practical rate 1.44 Mbps in first version.

• Reduce latency: retransmission request by Node B.

• Increased coverage and capacity: efficient handling of uplink interference problem.

Improved Performance with HSUPA

User data rate

Round trip time, delays

Cell throughput

Coverage

20 – 100% improvement depending on the channel conditions

Round trip time approximately 50 milliseconds

Cell throughput improved by 20 – 50%

Coverage gain 0.5 – 1.5dB