Performance of Turbo Coded Ofdm in Wireless Local Area Network (Wlan)

Topics: Forward error correction, Error detection and correction, Wireless Pages: 5 (1312 words) Published: December 18, 2012

List of Abbreviations

GSM Global System for mobile communications GPRS General Packet Radio System
EDGE Enhanced Data rates for Global Evolution IEEE Institute of Electrical and Electronics Engineers MC-CDMA Multiple-Carrier Code Division Multiplex

W-CDMA Wideband-Code Division Multiple Access
OFDMA Orthogonal Frequency Division Multiple Access 3G Third generation, mobile multimedia communications WLAN Wireless Local Area Network

PAN Personal Area Network
HIPERLAN high-performance radio local area network FEC forward error control
BER Bit-Error Rate
AWGN Additive White Gaussian Noise

1. Background information
Wireless and mobile communications is one of the fastest growing areas of modern life. It has an enormous impact on almost every aspect of our daily lives. A world of ubiquitous wireless devices is emerging, from wireless sensors and tags to mobile terminals. There are a number of wireless systems and networks in operation such as GSM, GPRS, EDGE, UMTS, IEEE 802.11, and Bluetooth, and several multiple access techniques including MC-CDMA, W-CDMA, and OFDM are used. Long-range cellular communication encompasses the evolution from GSM to 3G systems. It aims to achieve full mobility and global roaming for individual links maximizing system capacity. In short-range wireless networking and wireless connectivity, WLAN or PAN covers local hot spot areas for very high data rate asymmetric individual links (e.g. IEEE 802.11, HIPERLAN). Also fixed wireless local loops provide wireless access from street to home for broadband internet and multimedia services.[1] Wireless communications channels are far more hostile as opposed to wire alternatives, and the need for mobility proves especially challenging for reliable communications. Hence to overcome multipath fading and Inter ISI, in convolutional single carrier systems equalizers are used. But it increases the system complexity. Another approach is to use a multicarrier modulation technique such as OFDM, where the data stream to be transmitted is divided into several lower rate data streams each being modulated on a subcarrier. To avoid ISI, a small interval, known as the guard time interval, is inserted into OFDM symbols. The length of the guard time interval is chosen to exceed the channel delay spread. Therefore, OFDM can combat the multipath fading and eliminate ISI almost completely and also it has an advantage of efficient spectral usage by allowing overlapping in the frequency domain.[2] In high speed wireless communications there is a growing need to quickly transmit information wirelessly and accurately, for this reason OFDM is a suitable candidate for high data rate transmission with FEC methods over wireless channels. Therefore, to reduce error rate in transmitting digital data we use error correcting Codes in the design of digital transmission systems. Turbo Codes have been widely considered to be the most powerful error control code of practical importance. This thesis work will be done to increase the system throughput while maintaining system performance under a desired BER of a working OFDM system by adding turbo coding. The use of turbo coding and power allocation in OFDM is useful to the desired performance at higher data rates. Simulation will be done over AWGN and Rayleigh fading channel using MATLAB software. 2.Statement of the problem

In high speed wireless communications, OFDM has become a popular modulation scheme. Besides there is a growing need to quickly transmit information wirelessly and accurately. In Such networks there is...
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