| In the past ten years, we have witnessed the unprecedented growth of high speed wireless communication links which support voice, video, E-mail and web browsing, etc that have been widely applied. Providing the reliable link is challenging, and in a high-speed wireless application system the challenges include the poverty of the available broadband, the strictly limited of launch power, hardware complexity and the cost requirements, etc. With the new wireless spectrum scarcity and the steady growth in the number of new wireless application system wireless applications or the expansion of the wireless application how to support these applications become a significant problem. Multi-input multi-output systems (Multi-Input Multi-Output, MIMO) came into being. Multi-input multi-output (MIMO) as the key technology of the future wireless communication can effectively restrain multipath fading, extend channel capacity, considerably increase data rate and transmission reliability, improve spectrum efficiency, the system capacity and the cost.Space-time coding is not only an important content of the multiple-input multiple-output (MIMO) technology but also the hot spot of the today’s wireless communication field. Using the space-time codes (STC) is a viable and effective method that can achieve MIMO wireless channel capacity. Space-time coding is a coding technology used for many antennas. This coding can produce the airspace and temporal correlation between the signals that are transmitted by many antennas and every time period. In order to reduce the effects of multipath-fading, space-diversity uses multi-transmitting antenna and multi-receiving antenna (multiple independent channel) to process signals separately. The space-time correlation can make receiver overcome MIMO channel decline and reduce emission error. Algebra space-time codes is developed on the basis of the space-time block code and space-time hierarchy code, and it makes many space-time coding scheme as its expressions. Algebra space-time code is the general expression form of the space-time code. Researches of this paper are as following:(1) the principle of cooperation is analyzed, and studies the influence of cooperative diversity in space-time codes and the advantages in the multiple-input multiple-output (MIMO) transmission. Through the simulation we confirmed using cooperation technology can reduce the error rate and improve the performances.(2)The sphere decoding based on distributed space-time code is studied including the principle of the sphere decoding, derivation and simulation results. The simulation is based on the QAM modulation pattern. Simulation results showed that whatever the antenna multiple-input multiple-output (MIMO) system number, the performance of maximum likelihood decoding is best in performance, and two norm sphere decoding losses a few dB. In simulation time the maximum likelihood decoding spends more time than two norm sphere decoding. So using two norm sphere-decoding to reach maximum likelihood decoding is better.(3) The distributed space-time code based on algebra theory in cooperative systems discussed in this paper is linear, but it doesn’t satisfy the design criterion of orthogonal and quasi orthogonal space-time code. First the collaborative channel model is established and then design the distributed space-time block codes which base on the model of two transmit antennas and two receive antennas. The sphere decoding method is adopted. In the final the traditional code, the cooperative code, based on algebra theory code and based on algebra theory cooperative code are simulated on performance. Simulation result show that the distributed space-time code based on algebra theory in cooperative systems can reduce the bit error rate and improve system performance.(4) Quaternion is presented to use in the distributed space-time code technology. The simulation shows that this technology can improve the performance of the system and reduce the error rate of the system. |
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