INTRODUCTION
Broadband wireless access for evolving mobile internet and multimedia services are driving a surge of research on future wireless communication systems, which have to be highly spectral efficient in order to support multi-user access and high data rates. Therefore, MC-CDMA formed by combining orthogonal frequency division multiplexing (OFDM) with code division multiple accesses (CDMA) became significant research topics.The former is well suited for high data rate applications in frequency selective fading channels and the later is a multiplexing technique where number of users is simultaneously available to access a channel. With its capability of synchronous transmission, MC-CDMA is suitable for downlink of cellular communication systems. High data rate MC-CDMA systems can additionally employ MIMO techniques, e.g., Alamouti codes and STBC .Data transmission involves spreading operations which are carried out by short channelisation code and long scrambling code.
Short channelisation code helps in separating the signals of different users present within the cell and long scrambling code mitigates the effects of interference produced by users belonging to other cells. However, the scrambling codes are generally not orthogonalised among cells. Therefore, since the signals from other cells cannot be orthogonalised to the signals of its own cell, multi-cell interference exists. In high data rate transmission system over frequency selective fading channel, multi-cell interference results in degradation of bit-error rate (BER) and this characteristic affects the performance of MCCDMA systems. Site diversity technique has been proposed for realizing CDMA and OFDM systems to minimize multi-cell interference. Site diversity system transmits encoded signals from several base stations and these signals are combined at the receiver with decoding operation. This method does not have inter-cell interference. Scrambling codes are assigned to each base station to maintain orthogonality among the signals between the cells and reduces interference among them. The same technique is applied to MC-CDMA system.
In this project STBC and DSTBC with multiple antennas are used in the base stations and also exploiting several base stations the site diversity is obtained.Moreover, by using various combining techniques the performance of the system is analyzed.
Broadband wireless access for evolving mobile internet and multimedia services are driving a surge of research on future wireless communication systems, which have to be highly spectral efficient in order to support multi-user access and high data rates. Therefore, MC-CDMA formed by combining orthogonal frequency division multiplexing (OFDM) with code division multiple accesses (CDMA) became significant research topics.The former is well suited for high data rate applications in frequency selective fading channels and the later is a multiplexing technique where number of users is simultaneously available to access a channel. With its capability of synchronous transmission, MC-CDMA is suitable for downlink of cellular communication systems. High data rate MC-CDMA systems can additionally employ MIMO techniques, e.g., Alamouti codes and STBC .Data transmission involves spreading operations which are carried out by short channelisation code and long scrambling code.
Short channelisation code helps in separating the signals of different users present within the cell and long scrambling code mitigates the effects of interference produced by users belonging to other cells. However, the scrambling codes are generally not orthogonalised among cells. Therefore, since the signals from other cells cannot be orthogonalised to the signals of its own cell, multi-cell interference exists. In high data rate transmission system over frequency selective fading channel, multi-cell interference results in degradation of bit-error rate (BER) and this characteristic affects the performance of MCCDMA systems. Site diversity technique has been proposed for realizing CDMA and OFDM systems to minimize multi-cell interference. Site diversity system transmits encoded signals from several base stations and these signals are combined at the receiver with decoding operation. This method does not have inter-cell interference. Scrambling codes are assigned to each base station to maintain orthogonality among the signals between the cells and reduces interference among them. The same technique is applied to MC-CDMA system.
In this project STBC and DSTBC with multiple antennas are used in the base stations and also exploiting several base stations the site diversity is obtained.Moreover, by using various combining techniques the performance of the system is analyzed.
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