Detection And Design Of Code Division Multiple Access Signals

Future high-speed wireless communication requires transmission technique enabling high spectral efficiency with garanteed performance. This thesis studies this basic communication problem in the framework of single-carrier and multicarrier code division multiple access (CDMA). The thesis explores a new valid multiuser detection method and a signal transmission scheme, and studies the principle of improving the spectral efficiency when multiuser detection is employed.The thesis first proposes a novel group single interference cancellation to upgrade the system bit error rate (BER) in single-carrier long code CDMA system. The number of supported users can be one fourth more than that of the conventional method. Then, the BER of multicarrier CDMA with convolutional coding is analyzed, and the clear relation between free distance and BER or spectral efficiency is given. To improve the performance of multicarrier CDMA, a multi-carrier antennal selection scheme is proposed based on space time block coding, and it is shown that the system with the new scheme can provide at least 2dB signal to noise ratio gain.To be able to completely evaluate a system in terms of spectral efficiency, the thesis then extracts the mathematical model of the previously considered system, and analyzes the spectral efficiency of CDMA when matched filter (MF) or linear minimum mean square error (MMSE) front end is used. The theoretical results based on random matrix theory can be employed to analyze the relation between spectral efficiency, loading factor, signal to noise ratio, the number of receive antennas, and the number of transmit antennas in multi-carrier CDMA. Then the spectral efficiencies of multi-carrier system, single-carrier system, and orthogonal system are compared. The basic conclusion is that multi-carrier system can provide spectral efficiency about twice of that of single-carrier system. The spectral efficiency of multi-carrier system is higher that that of orthogonal system when the number of receive antennas is large enough. The thesis also proposes a distributed antenna structure, and it is shown that it can provide almost the same spectral efficiency with co-located antenna structure when taking the advantage of decreasing the number of placed antennas.Then an example is provided to illustrate how to optimize the single-carrier multicell CDMA system design parameters. The thesis also studies the following basic problems about spectral efficiency, the tradeoff between coding and spreading, the effect of pilot insertion on the spectral efficiency, and the effect of modulation. It is shown that when linear MMSE front end is used and the bit signal to noise ratio is high enough, more bandwidth expansion must be allocated to spreading than coding. The spectral efficiency with pilot symbol insertion is higher than that with continuous pilot signals. Higher level modulation must not provide higher spectral efficiency in un-coded CDMA system.