SEMINAR REPORT ON

WIDEBAND CODE-DIVISION MULTIPLE ACCESS(WCDMA)

DEPARTMENT OF ELECTRONICS AND COMMUNICATION

SUBMITTED TO: SUBMITTED BY: MRS. MEENAKSHI AWSATHI SABAL KUMAR SR.ASSTT. PROFESSOR EC-B(3RD YEAR)

CONTENT

INTRODUCTION :WCDMABASICS OF WCDMASPECIFICATIONSGENRATION OF WCDMASPREADING PRINCIPLECODESPOWER CONTROLWCDMA HANDOVERSADVANTAGES OF WCDMACURRENT WCDMA MARKET

WCDMA

WCDMA: A high speed 3G mobile wireless technology with capacity to offer higher data rate than CDMA.

WCDMA has the capacity to easily handle bandwidth-intensive applications such as video, data, and image transmission necessary for mobile internet services.

WCDMA was adopted as a standard by the International Mobile Telecommunications-2000 (IMT 2000) with the intention to create a global standard for real time multimedia services and international roaming.

WCDMA is direct spread technology, which means that it will spread its transmissions over a wide, 5MHz carrier.

WCDMA is the leading 3G wireless standard in the world today.

BASICS OF THE WCDMA

WCDMA users share same radio resources whereas TDMA or FDMA users have their own radio resources allocated.

User signals are differentiated based on codes.

GENERATION OF WCDMA

Channel data

Channel data

Channelization code

Channelization code

Scrambling code

Scrambling code

Channel bit rate

Chip rate Chip rate(always 3.84 Mchips/s)

QPSK

Separates users through different codes Codes are used for two purposes:

Differentiate channels/users Spreading the data over the entire bandwidth

f

Code

t

MS 1MS 2MS 3

5 MHz

• WCDMA (5 MHz)

• IS-95 (1.25 MHz)

• CDMA2000 (1.25, 3.75 MHz)

SPREADING PRINCIPLE

Direct Sequence Spreading - Code Division Multiple Access (DS-CDMA)

SPREADING CODES

Spreading code = Scrambling code + Channelization code

Scrambling codes Separates different mobiles (in uplink) Separates different cells (in downlink)

Channelization codesSeparates different channels that are transmitted on the same scrambling codeOrthogonal Variable Spreading Factor (OVSF) codesPeriod depends on data rate

CHANNELIZATION CODES

CC1, CC2CC3, CC4

CC5, CC6, CC7

CC1 , CC2, CC3CC1, CC2

CC1, CC2, CC3, CC4

In the Uplink, Channelization Codes are used to distinguish between data (and control) channels from the same UE

In the Downlink, Channelization Codes are used to distinguish between data (and control) channels coming from the same RBS

Channelization Codes have different length depending on the bit rate

After the Channelization Codes, the data stream is multiplied by a special code to distinguish between different transmitters.

Scrambling codes are not orthogonal so they do not need to be synchronized

The separation of scrambling codes is proportional to the code length – longer codes, better separation (but not 100%)

Scrambling codes are 38400 chips long

SCRAMBLING CODES

SCRAMBLING CODES

In the Downlink, the Scrambling Codes are used to distinguish each cell (assigned by operator – SC planning)

In the Uplink, the Scrambling Codes are used to distinguish each UE (assigned by network)

SC3 SC4

SC5 SC6

SC1 SC1

Cell “1” transmits using SC1

SC2 SC2

Cell “2” transmits using SC2

POWER CONTROL IN WCDMA

The purpose of power control (PC) is to ensure that each user receives and transmits just enough energy to prevent:Blocking of distant users (near-far-effect)Exceeding reasonable interference levels

UE1UE2

UE3

UE1

UE2

UE3

UE1 UE2 UE3

Without PC received power levels would

be unequal

In theory with PC received power levels

would be equal

Power control can be divided into two parts:

Open loop power control (fast power control)

Used to compensate e.g. free-space loss in the beginning of the call Based on distance attenuation

Closed loop power control (slow power control) Used to eliminate the effect of fast fading Applied 1500 times per second

Closed loop power control can also be divided into two parts: Inner loop power control

Measures the signal levels and compares this to the target value and if the value is higher than target then power is lowered otherwise power is increased

Outer loop power control Adjusts the target value for inner loop power control Can be used to control e.g. the Quality of Service (QOS)

Example of inner loop power control behavior:

With higher velocities channel fading is more rapid and 1500 Hz power control may not be sufficient

WCDMA Handovers

WCDMA handovers can be categorized into three different types which support different handover modesIntra-frequency handover

WCDMA handover within the same frequency and system. Soft, softer and hard handover supported

Inter-frequency handoverHandover between different frequencies but within the same

system. Only hard handover supportedInter-system handover

Handover to the another system, e.g. from WCDMA to GSM. Only hard handover supported

WCDMA Handovers

Soft handoverHandover between different base

stations Connected simultaneously to

multiple base stations The transition between them

should be seamlessDownlink: Several Node BS

transmit the same signal to the UE which combines the transmissions

Uplink: Several Node BS receive the UE transmissions and it is required that only one of them receives the transmission correctly

UE: USER EQUIPMENT

BS:BASE STATION

WCDMA Handovers

Softer handover

Handover within the coverage area of one base station but between different sectors

Procedure similar to soft handover

Hard handover

The source is released first and then new one is added

Short interruption time

UE1

BS 2

SECTOR B

SECTOR A CELLS

CURRENT WCDMA MARKETS

GSM+WCDMA share currently over 86%.Around 260 WCDMA networks in over 105 countries. CDMA share decreasing every year.More than 340 million WCDMA subscriber.

WCDMA SPECIFICATIONS

CHANNAL BANDWIDH : 5MHZDUPLEX MODE : FDD and TDD CHIP RATE : 3.84MbpsFRAME LENTH : 10msSPREADING MODULATION BALANCED QPSK(DOWNLINK) DUAL CHANNEL QPSK(UPLINK)DATA MODULATION : QPSK (DOWNLINK) BPSK(UPLINK)CHANNEL CODING : CONVOLUTIONAL and TURBO

CODES COHERENT DETECTION : USER DEDICATED TIME

MULTIPLEXED PILOT

HANDOVER : SOFT HANDOVER and FREQUENCY HANDOVER

ADVANTAGES OF WCDMA

SERVICE FLEXIBILITY

SPECTRUM EFFICIENCY

CAPACITY AND COVERAGE

EVERRY CONNECTION CAN PROVIDE MULTIPLE SERVICE

NETWORK SCALE ECONOMICS

OUTSTANDING VOICE CAPABILITY

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