Hybrid Automatic Repeat Request Protocols For Next Genearation Communications Systems

Multiple-Input Multiple-Output (MIMO) technology can increase the capacity greatly and is regarded as a significant breakthrough in the development of wireless communication technologies. And MIMO systems adopt channel coding, adaptive transmission and other techniques to improve the reliability. Howerver, since the wireless circumstance is terrible, Hybrid Automatic Repeat reQuest (HARQ) can increase the point-to-point reliability further.MIMO-HARQ systems combine the MIMO technology and HARQ protocol, and can increase the system reliability greatly. But validity and reliability are in contradiction with each other. In information theory aspect, MIMO-HARQ systems can tradeoff validity and reliability.The thesis mainly researches into the detection and adaptive transmission of MIMO-HARQ systems, a novel encoder & decoder structure of adaptive scheme for HARQ protocol, and the MIMO channel estimation with spatial correlation.The main innovations and contributions in this thesis can be summarized as follows:Firstly, we investigate two classical MIMO channel model, and based on training sequence the thesis presents a novel MIMO channelestimation with spatial correlation.Secondly, a joint detection and combining scheme in MIMO-HARQ systems is proposed. Since previous transmission information ought to be fully utilized in retransmission detection in MIMO-HARQ systems, detection schemes are not the same as the traditional MIMO detection schemes. In other words, detection processing should be combined with combining processing in MIMO-HARQ systems. The joint detection and combining scheme does detection while doing combining. So, the total equivalent signal-to-noise ratio of one antenna is the sum of the equivalent SNR on the antenna at each retransmission. The undetected antenna which has the biggest total equivalent SNR will be picked for detection. This detection order is better than the traditional MIMO detection order, since it helps to reduce the error propagation possibility.Thirdly, three adaptive HARQ schemes in MIMO-HARQ systems where the transmitters know the channel state information are presented. The main idea is to adjust transmission parameters under the constant transmit power to optimize transmission performance, including antenna permutation and power allocation. These three schemes are named as sorted adaptive scheme, local optimization adaptive scheme and global optimization adaptive scheme, respectively. Sorted adaptive scheme makes full use of degree of freedom of antennas permutation. The sub-streams of bad performance at previous transmission should be allocated to sub-channels which have large singular values at each retransmission. In order to optimize the current transmission performance, local optimization adaptive transmission scheme adjusts current retransmission sub-streams order and allocated power on each transmit antenna. Global optimization adaptive transmission scheme is an optimization problem based on all channels experienced by one data frame. This scheme should predict the transmission times for each transmit frame and then optimize the performance of data frame after the predicted transmission times. Simulations results show that this scheme can obtain the best throughput performance with much higher computation complexity than other two schemes, and can only applied under very slow fading MIMO channels and accurate channel prediction conditions.Fourthly, we design a hybrid encoder & decoder structure for adaptive HARQ protocol. The hybrid encoder, composed of two recursive systematic convolutional (RSC) encoders, realizes the function of encoding the turbo codes and convolutional codes as FEC. The hybrid decoder, composed of two maximum a posteriori (MAP) decoders, realizes the function of decoding the corresponding channel codes. The hybrid encoder & decoder save the hardware resource and realize the RCPT codes and RCPC codes. What's more, this adaptive HARQ protocol chooses the different coding codes and different puncture modes based on the feedback information and the service's delay sensitivity.At last, we present a nearly invariable transfer delay (NITD) HARQ protocol. Different from the traditional HARQ protocols, the presented protocol guarantee that the transmitter sends the new data frame without intermittence, whether the former transmitted data frame is error free or not. If the transmitted frame is decoded in error, the retransmitted data frame includes the information of former transmitted frame and that of previous transmitted frame. To keep the length of data frame constant, code rate of retransmission will increased. If the channel condition is bad beyond given threshold, the process of this protocol is the same as that of tradition of HARQ protocols and the receiver only sends the information which is decoded with error.