| 3G systems have been evolving to offer the users enhanced data communication capability. The 3.5G systems which allow around 14Mbps peak data transmissions have been under rapid deployment over the world. The 3.9G or 3G LTE systems will appear in a few years to achieve much faster, 50-100Mbps peak data transmissions. However, this data rate is not sufficient and the broadband wireless technology which allows higher than 1Gbps downlink and 100Mbps uplink peak data transmissions with extremely low transmit power are necessary in the 4G mobile communication systems.The wireless channel for such broadband transmissions is severely frequency-selective. Frequency-domain wireless signal processing (i.e. frequency-domain equalization (FDE)) and antenna diversity may play an important role in achieving a good signal transmission performance. For the uplink (from mobile to base-station (BS)) transmission, since different users'signals are asynchronously received via different fading channels and therefore the multiple access interference (MAI) occurs which limits the uplink capacity. The use of 2-dimensional (2D) block spreading can be applied to solve the MAI problem for multi-user uplink transmission. Meanwhile, the spectrum is limitation for such high-speed transmission. ITU allocated the spectrum for 4G systems in Dec. 2007, and the global use spectrum is 3.4~3.6GHz. So the available bandwidth in global frequency band is 200 MHz only. This must be shared by several operators, and the spectrum efficiency should be larger than 5bps/Hz. Particular attention has been paid to multi-input/multi-output (MIMO) multiplexing (SDM) to significantly increase the throughput without expanding the signal bandwidth. Besides the broadband wireless signal processing, another practically important issue exists, which is a significant reduction of transmit power. Cooperative communications is a possible solution to this issue.The research of this paper is based on the theory of 2D, meanwhile take into consider the code resource allocation for 2D system in chapter 2, MIMO diversity and multiplexing in chapter 3, the remained MAI and channel estimation in Chapter 4, and cooperative communications in chapter 5.As code resource assignment is the basic problem for 2D system, thus we will discuss this problem in Chapter 2, which includes four sections. At beginning, an adaptive code assignment algorithm for multi-user/multi-rate transmission in CDMA system is discussed. After that, further discussion is given to the 2D uplink multi-user/multi-rate transmissions. A code reuse algorithm is also considered to improve the code reuse efficiency for 2D system when users are transmitted in multi-cell case. At last, we discuss the combination analysis of the code assignment algorithms when multi-user/ multi-cell/multi-rate transmission is considered.To further improve the bit error rate (BER) performance and increase the spectrum efficiency of 2D system, it is the main work for Chapter 3. Taking into account the advantages of antenna diversity, a combination of 2D with different antenna diversity technology (i.e. cyclic-delay transmit diversity (CDTD), space-time transmit diversity (STTD), space-time cyclic delay transmit diversity (STCDTD)) is discussed in the first section of chapter 3. In the second section of chapter 3, we will discuss the situations when 2D joint with MIMO-SDM.In fact, the block de-spreading of 2D is based on the assumption that the channel gain is slow fading, thus remained MAI will exist and partly destroy the BER performance especially antenna diversity is used. Therefore, some signal detection methods are considered in chapter 4 to solve this problem. The above discussions are based on the ideal channel estimation, however the channel state information is unknown. Thus, channel estimation is a very important problem for wireless transmission, and the estimation results will affect the BER performance significantly. A joint of unscented Kalman filter (UKF) and minimum mean square error (MMSE) channel estimation is discussed in the second part of chapter 4, and the applications of the proposed algorithm to 2-antenna STTD system and 2D system are also presented respectively.Above all, the discussions are based on cellular system, and in chapter 5, we will use 2D multi-user virtual MIMO in cooperative communications. Some interesting topics will be introduced in this chapter. At beginning, a virtual cellular netork (VCN) model is givn; then how to select a suitable cooperative user (cluster-head) for the VCN is considered; while three clusting algorithms are introduced one by one, they are stability weighted clustering algorithm (SWCA), fariness weighted clustering algorithm (FWCA) and adaptive weighted clustering algortim (AWCA). Simulation results show that the AWCA provides the best performances. At last, 2D block spread CDMA relay using virtual 4-Antenna STCDTD is given.
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