Based On Linear Diffusion Theory Of Space-time Coding

Digital communication exploiting Multiple-Input Multiple-Output (MIMO) wireless channels has been considered as one of the most significant technical breakthroughs in modern communications. Wireless systems that employ multiple antennas provide a higher bit rates compared with the Single-Input Single-Output (SISO) systems. Space-Time Processing (STP) is the core concept of MIMO systems. By Space-Time Coding (STC) multiple antennas can exploit a rich wireless scattering environment and benefit from the multipath fading nature of the wireless channel. STC technology is mainly classified into two categories. One class is rate-oriented code that is based on data multiplexing. This class is designed for improving the attainable spectral efficiency of the system by transmitting different signal streams independently over each of the transmit antennas and employing proper interference cancelation to separate the different transmitted signals at the receiver side, hence resulting in Nt symbols per channel used. The other class is BER-oriented code that is based on spatial diversity. Multiple antennas are used to transmit and receive appropriately encoded replicas of the same information sequence in order to reduce the probability of severely attenuation and hence to obtain an improved BER performance. The spectral efficiency of this class cannot exceed one symbol per channel used. In this paper we mainly focus on the BER-oriented code also called diversity technology scheme, and carry on innovative research in the following aspects.1. Adaptive full-rate full-diversity and linear decoding of space-time block codingWhen complex signal constellation and more than two transmit antennas are considered, it is impossible to obtain a kind of STBC with orthogonality and full-rate simultaneously. We propose a closed-loop adaptive STBC scheme which chooses the optimal matrix from the group according to current channel state information can obtain rate of one and linear maximum likelihood (ML) decoding. At the same time due to a linear decoder, we can calculate the post-SNR, thus maintaining compatibility with post-SNR based technologies, such as Adaptive Modulation and Coding (AMC), Exponential Effective SIR Mapping (EESM) and so on. Simulation results show that both BER performance and decoding complexity are superior to existing schemes.2. Adaptive space-time block coding in the retransmissionFor the problem of transmitting STBC in a MIMO system for Hybrid Automatic Repeat reQuest (HARQ), we propose an scheme that the STBC matrix of the retransmission can be changed adaptively according the channel state, enabling the combined STBC's optimal performance and linear ML decoding complexity. The simulation results show that the proposed scheme not only in BER performance is superior to the traditional Chase combining (CC) and Incremental Redundancy (IR), but in decoding complexity that has essentially advantage.3. Simplified sphere decoding algorithm for the multi-layer STBCWe design a simplified sphere decoder (SD) algorithm for the multi-layer STBC. This SD algorithm reduces the decoding complexity without any loss of performance, and has increasingly advantages as the signal constellation level increasing. Simulation results show that the decoding complexity of the proposed algorithm is lower than the existing simplified SD algorithm.4. The adaptive relay forward method for hierarchical dataIn a relay cooperative system, we propose an adaptive relay forward method for data operations with different priorities. According to the channel qualities of eNB, relay node and user equipment, this scheme tries its best to transmit the low priority data under the premise of the correct transmission of high priority data, hence result in system throughput improvement. Simulation results show that the throughput of the proposed relay forwarding method is superior to the traditional fixed forwarding scheme.