Hybrid/Automatic Repeat Request Schemes For Wideband Mobile Communication Systems

The future wideband mobile communication system will support fast wireless access to Internet for users. As we known, TCP (Transport Control Protocol) is tuned to perform well in wired networks where bit error rates are very low and packet loss occurs mostly because of congestion. However, when it is used over wireless channels which are characterized by high frame error rates (FER), the performance of TCP is severely affected. Therefore, most researches are focused on how to improve the wireless TCP performance. In addition, the future wideband mobile communication system will employ new transmission techniques to improve transmission quality and efficiency, such as OFDM, MIMO and AMC. In order to keep the reliability of data, another hot research is about the combination of new techniques and hybrid automatic repeat request. Thus, the main task of this thesis is to research the scheme to improve wireless TCP performance and the new HARQ schemes for wideband mobile communication system equipped with new transmission techniques. The main contributions of this thesis include: In the research about the schemes to improve wireless TCP, first, an adaptive selective repeat ARQ (ASR-ARQ) is proposed and it can adaptively adjust the retransmission number of every frame belonging to one packet. The general expressions for packet error rate and transmission delay introduced by ASR-ARQ are derived. Compared with the conventional SR ARQ scheme, the ASR ARQ scheme can achieve smaller packet error rate (PER) while just a little longer delay. At the same time, the effects of ASR-ARQ as the link layer ARQ on TCP is analyzed and evaluated. The effects of the wireless link layer parameters, maximum allowed retransmission number and wired link parameters on TCP throughput are also analyzed. The results show that the ASR-ARQ greatly improves the TCP throughput compared with conventional SR ARQ. Second, an analysis model for RLP/MAC two-layer retransmission scheme is proposed, in which the n-channel stop-and wait ARQ protocoland selective repeat ARQ protocol are used respectively in MAC layer and the RLP layer. In this model, all kinds of delay involved in the system are considered. Through the analysis, the general expressions of PER and transmission delay in this scheme are achieved. The effects of soft combining at MAC layer on PER and transmission delay are also analyzed. The results show that two-layer retransmission scheme can achieve smaller PER and shorter transmission delay compared with the single RLP layer ARQ scheme. In addition, in the research about the combination of HARQ and multiple input multiple output (MIMO) system, two basic kinds of HARQ, namely MMARQ and MSARQ, are evaluated firstly. Then another two HARQ schemes are proposed. One scheme is to combine the Chase Combining HARQ with antenna permutation for different transmission times, and here it is named MIMO Antenna Permutation HARQ (MIMO-AP-HARQ). In low mobile speed environments, the different transmission attempts through the antenna permutation are combined by maximum ratio combining at the receiver. Thus, the combined signal can achieve the time and spatial diversity gain. Compared with the scheme of Chase Combining without antenna permutation, the MIMO-AP-HARQ scheme can greatly decrease the block error rate (BLER) at low mobile speed. However, this schemeworks hardly at high mobile speed environments. The other scheme is to combine the Chase Combining (CC) with transmit antenna selection technique, and here we name it SV-AS-CC (Singular Value Antenna Selection Chase Combining). In this scheme, the antenna selection algorithm is based on minimum error rate and thus maximum minimum singular value of channel matrix. As we know, the bit error rate is decreasing with the transmit antenna number reducing, however the channel capacity is also decreased. For high reliability required services, it is worth to get high reliability at the cost of long transmission delay. It is the reason to combine the antenna selection with HARQ. The simulation results show that the HARQ with antenna selection can greatly decrease the BLER while no throughput decreases. Finally, the research about the HARQ scheme for multiple subcarriers system is focused on the comparison of the maximum ratio combining frequency diversity ARQ (MRC-ARQ) and other three HARQ (HARQ-I, HARQ-II, HARQ-III) schemes using convolutional code as forward error correction (FEC). The results show that the MRC-ARQ can achieve good accumulative correct packet reception rate (ACPRR) performance than other three schemes in low mobile environments. However, in high mobile speed environments, the HARQ-III scheme can...