The Space-Time Block Codes In MIMO Systems

The multiple-input-multiple-output (MIMO) technology is an important breakthrough in the area of wireless communication. The capacity and frequency efficiency of communication systems can be improved by this technology without extra frequency bandwidths and transmitted power. MIMO is the key technology of the new generation mobile communication systems. Space-time coding technology is a coding technology based on MIMO systems. It not only can achieve the high spectrum efficiency in the wireless transmission, but also has the powerful ability to exterminate multi-paths fading. So it can greatly improve the quality of communication service and the capacity of the communication systems. Space-time block codes (STBC) is one of the space-time coding schemes. STBC becomes the widest researched and implied coding scheme in space-time codes, because it has the advantages such as the simple construction, low decoding complexity and good performance.During the encoding and decoding process of STBC, the channel state information (CSI) can be unknown at the transmitter, but it must be estimated correctly at the receiver. The main research work in this paper is to discuss some new encoding and decoding algorithms of STBC on the conditions of changing the knowledge of CSI at transmitter or receiver. A lot simulation of those algorithms has been done. The analyses from theory and simulation are also appeared in this paper. The new algorithms are at below:(1) Space-time block codes with partial feedback It is an encoding and decoding algorithm that modified by the partial feedback of CSI at the transmitter under the condition that the receiver can get the correct CSI. Because of the feedback, the performance of this algorithm is better than traditional STBC. Two methods are researched: one is the power weight feedback, in which the value of the weight is determined by channel fading;another one is phase feedback, that is a method using the feedback to adjust the phase of the transmit signals in order to achieve the best receive. It is mentionable that the data rate can be improved by the second method, and it can be increased to 1 whatever the number of transmit antennas are. The influence on the performance by the numbers of feedback is analyzed from the simulation and theory.(2) Differential space-time block codes It is an encoding and decoding algorithm that utilizes the differential scheme within the STBC, and both the transmitter and receiver have no CSI. It could be fit for the fast changing communication condition. There are two differential algorithms researched in this paper, and both the two-rransmit-antennas system and multiple-transmit-antennas systems are discussed.