SEMINAR REPORT ON WIDEBAND CODE-DIVISION MULTIPLE ACCESS(WCDMA) DEPARTMENT OF ELECTRONICS AND COMMUNICATIONSUBMITTED TO: SUBMITTED BY:MRS. MEENAKSHI AWSATHI SABAL KUMARSR.ASSTT. PROFESSOR EC-B(3RD YEAR)
CONTENTINTRODUCTION :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 Channelization Scrambling code codeChannel QPSKdata Channel Chip rate Chip rate bit rate (always 3.84 Mchips/s)
SPREADING PRINCIPLEDirect Sequence Spreading - Code Division Multiple Access (DS-CDMA) Separates users through different codes Codes are used for two purposes: Differentiate channels/users Spreading the data over the entire bandwidth t MS 1 MS 2Code MS 3 • WCDMA (5 MHz) f • IS-95 (1.25 MHz) 5 MHz • CDMA2000 (1.25, 3.75 MHz)
SPREADING CODESSpreading code = Scrambling code + Channelization codeScrambling codes Separates different mobiles (in uplink) Separates different cells (in downlink)Channelization codes Separates different channels that are transmitted on the same scrambling code Orthogonal Variable Spreading Factor (OVSF) codes Period depends on data rate
CHANNELIZATION CODES Channelization Codes have different length depending on the bit rate In the Downlink, Channelization Codes are used to distinguish between data (and control) channels coming from the same RBS CC3, CC4 CC1, CC2 CC5, CC6, CC7 In the Uplink, Channelization Codes are used to distinguish between data (and control) channels from the same UE CC1, CC2 CC1 , CC2, CC3 CC1, CC2, CC3, CC4
SCRAMBLING CODES 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 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) Cell “1” transmits using SC1 SC1 SC1 SC3 SC4 Cell “2” transmits using SC2 SC2 SC2 SC5 SC6
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 Without PC received UE1 power levels would UE2 be unequal UE3 UE1 UE2 In theory with PC UE1 UE2 UE3 received power levels would be equal UE3
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 HandoversWCDMA handovers can be categorized into three different types which support different handover modes Intra-frequency handover WCDMA handover within the same frequency and system. Soft, softer and hard handover supported Inter-frequency handover Handover between different frequencies but within the same system. Only hard handover supported Inter-system handover Handover to the another system, e.g. from WCDMA to GSM. Only hard handover supported
WCDMA Handovers Soft handover Handover between different base stations Connected simultaneously to multiple base stations The transition between them should be seamless Downlink: 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 UE: USER EQUIPMENT required that only one of them receives the transmission BS:BASE STATION correctly
WCDMA Handovers Softer handover SECTOR B Handover within the coverage area of one base station but between different sectors UE1 Procedure similar to soft handover BS 2 Hard handover The source is released first and then new one is added Short interruption time 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 : 5MHZ DUPLEX MODE : FDD and TDD CHIP RATE : 3.84Mbps FRAME LENTH : 10ms SPREADING 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 WCDMASERVICE FLEXIBILITYSPECTRUM EFFICIENCYCAPACITY AND COVERAGEEVERRY CONNECTION CAN PROVIDE MULTIPLE SERVICENETWORK SCALE ECONOMICSOUTSTANDING VOICE CAPABILITY