Study Comparison of WCDMA and OFDM

Wideband Code Division Multiple Access (WCDMA) is one of the main technologies for the implementation of third-generation (3G) cellular systems. It is based on radio access technique proposed by ETSI Alpha group and the specifications was finalised 1999. WCDMA is also known as UMTS and has been adopted as a standard by the ITU under the name “IMT-2000 direct spread”. The implementation of WCDMA will be a technical challenge because of its complexity and versatility. The complexity of WCDMA systems can be viewed from different angles: the complexity of each single algorithm, the complexity of the overall system and the computational complexity of a receiver. In WCDMA interface different users can simultaneously transmit at different data rates and data rates can even vary in time. WCDMA increases data transmission rates in GSM systems by using the CDMA air interface instead of TDMA. WCDMA is based on CDMA and is the technology used in UMTS. WCDMA is the dominating 3G technology, providing higher capacity for voice and data and higher data rates. The gradual evolution from today’s systems is driven by demand for capacity, which is required by new and faster data based mobile services. WCDMA enables better use of available spectrum and more cost-efficient network solutions. The operator can gradually evolve from GSM to WCDMA, protecting investments by re-using the GSM core network and 2G/2.5G services.Orthogonal Frequency Division Multiplexing (OFDM) – technique for increasing the amount of information that can be carried over a wireless network uses an FDM modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of crosstalk in signal transmissions. 802.11a WLAN, 802.16 and WiMAX technologies use OFDM. It’s also used in the ETSI’s HiperLAN/2 standard. In addition, Japan’s Mobile Multimedia Access Communications (MMAC) WLAN broadband mobile technology uses OFDM. In frequency-division multiplexing, multiple signals, or carriers, are sent simultaneously over different frequencies between two points. However, FDM has an inherent problem: Wireless signals can travel multiple paths from transmitter to receiver (by bouncing off buildings, mountains and even passing airplanes); receivers can have trouble sorting all the resulting data out. Orthogonal FDM deals with this multipath problem by splitting carriers into smaller subcarriers, and then broadcasting those simultaneously. This reduces multipath distortion and reduces RF interference allowing for greater throughput.In this paper we have discussed about these two methods of third generation radio transmission system which are WCDMA and OFDM with various aspects. In between these two radio transmission technique, a better choice will be investigated.

1. Introduction
1.1 Motivation
1.2 Evolution Of Cellular System
2. Cellular Communication Review
9.2.1 First Generation System
9.2.2 Second Generation System
9.2.3 Third Generation System
9.2.4 Forth Generation System
3. Multiple Access Technique
9.2.5 Frequency Division Multiple Access
9.2.6 Time Division Multiple Access
9.2.7 Code Division Multiple Access
3.3.1 CDMA Process Gain
3.3.2 CDMA Design Consideration
3.3.3 CDMA Forward Link Encoding
3.3.4 CDMA Reverse Link Encoding
4. Wideband CDMA
9.2.8 CDMA Key Features
9.2.9 WCDMA Specifications
9.2.10 Carrier Spacing and Deployment Scenario
5. WCDMA Physical layer
9.2.11 Physical Channel Structure
5.1.1 Uplink Spreading and Modulation
5.1.2 Downlink Spreading and Modulation
5.2 Uplink Frame Structure
5.3 Downlink Frame Structure
5.4 Uplink Spreading Codes
5.5 Uplink Scrambling Codes
5.6 Downlink Scrambling Codes
5.7 Summary Of the WCDMA Modulation
6. Multi-rate User Data Transmission
9.2.12 Transport Format Detection
9.2.13 Channel Coding
6.2.1 Error Detection
6.2.2 Error Correction
7. Air Interface Procedures
9.2.14 Cell Search Operation
9.2.15 Handover
7.2.1 Inter-frequency Handovers
7.2.2 Handover Between GSM and WCDMA
7.3 Power Control
7.4 Uplink Synchronization Transmission Scheme
7.5 Packet Data
8. Performance Enhancing Schemes
9.2.16 Adaptive Antennas
9.2.17 Transmission Diversity Schemes
9.2.18 Advanced Receiver Structure
9. Orthogonal Frequency Division Multiplexing
9.2.19 Advantages Of OFDM
9.2.20 OFDM Principles
9.2.21 Frequency Division Orthogonal
9.3 OFDM Transmission
9.4 OFDM Generation
9.5 Adding a Guard Period To OFDM
9.6 Interference
10. OFDM System: An Overview
9.7 System Model
10.1.1 Cyclic Extension Of OFDM Symbol
11. Conclusion

Author: Moyamer Chowdhury, Aminul Alam

Source: Blekinge Institute of Technology

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