Research On Key Techniques In Wireless Communications Of Reliable And High Data Rate

It is well known that communication system achieve much higher transmit power utilization efficiency and spectral efficiency within limited bandwidth, consequently ensure reliable Quality of Service (QoS) by exploiting three-Dimension informatioms of wireless channel in space, time, and frequency, and tightly combining with Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input Multiple Output (MIMO), Space Time Codes (STCs), Adaptive resource allocations, Automatic Repeat reQuest (ARQ), and Beam Forming (BF) techniques. In this dissertation, The problems how to achieve much higher data rates and reliability of links with low complexity in the future military wireless communication system are investigated from the system design point of view. The main highlights of innovation are as follows:(1) In order to achieve reliable and high data rate digital transmission over fading channels with low decoding complexity, we first investigate design method for full-rate and full-diversity space-time block code (STBC). This code design approach is based on coordinate interleaved orthogonal designs (CIODs), A STBC with low maximum likelihood (ML) decoding complexity for the 2×2 MIMO quasi-static Rayleigh flat fading channel is proposed. and then, According to the aforementioned code design theory and comprehend, we further introduce this excellent CIOD method into practical system design, and combine trellis coded modulation (TCM) and STBC, A trellis code STBC MIMO-OFDM is proposed which offer high diversities, The simulation results show that the codeword error rate (CER) performances of this system is excellent than that of the benchmark systems.(2) In order to achieve the objective of optimal throughput in practicality wireless communication network, we investigate network optimization problems in the case of single user. First, we research the resource allocation problems in SISO-OFDM system, then expand to MIMO-OFDM. But transmitter cann't exploit full channel state information (FCSI-T) in practice, we adopt suboptimum linear prefiltering technique, in which different pre-filtering coefficients can be applied to form a transmit beam. A power allocation algorithm is proposed, in which adaptive MIMO channel at transmitter side. In order to settle the maximization problem of BER-besed on subcarrier in coded MIMO-OFDM system, A optimum MIMO greedy power allocation algorithm and suboptimum greedy power allocation algorithm are proposed, and then, we modifiy this optimum MIMO greedy power allocation algorithm into adaptive Packet Error Rate (PER) algorithm. The simulate results show that the performances of these adaptive algorithms are prominent.(3) In contemporary communication system, general transmission modes design is based on uniform bits and power allocations, the system performance have a potential to be improved. Hence, we investigate adaptive resource allocation based on maximum throughput of HARQ OFDM network with the full channel state information (FCSI-TR) at both receiver and receiver sides. In order to settle adaptive bits and power allocation problem, A bits and power allocation algorithm is proposed for coded adaptive ARQ retransmission protocol in OFDM system. We deduce the throughput respectively when stop-and-wait (SAW), goback-N (GBN), and selective-repeat (SR) ARQ protocol is used. Different strategies for solving the discrete bit and power allocation problem are proposed. The main results are as followings:the water-filling solution with adequate SNR gap value (or equivalently target BER) is equal to the solution to the relaxed problem, which is near-optimal in terms of throughput while having lower complexity. the throughput show a trade-off between the bit rate and BER criteria. Jointly maximizing the bit rate for a target BER (whose solution is the water-filling solution) can maximise the throughput, and adjust the target BER. we choose this target BER, or equivalently the SNR gap value. Analytically results show that this SNR gap value depends on the convolutional code, the frame length, the ARQ protocol type, the available power, and the harmonic and geometric mean of the subcarrier gains.(4) Traditional Hybrid Automatic Repeat reQuest (HARQ) protocols cann't effectively exploit additional dimensions for spatial diversity provided by multiple antenna system. In order to settle this problem, Alamouti-based H-ARQ transmission scheme is proposed to increases reliability of wireless links for a MIMO system in a slowly varying channel. This technique increases the efficiency of HARQ packet transmission by exploiting both the spatial and time diversity of the MIMO channel. It uses the full diversity of Alamouti STC and the added gain of the packet combining scheme to provide reliable communication. We analysis the PER of space-time coded MIMO-HARQ, and derive the expression of a multi-dimension pairwise error probability (PWEP) for the Alamouti-based HARQ protocol. The simulation results show that this scheme outperforms traditional Chase Combining (CC), and we reveal the gain of ARQ feedback in space-time coded MIMO systems. The gains of Alamouti-based HARQ are not only from PER but also from the receiver soft-output ML detection complexity.(5) The most of reports about beamforming in multiuser MIMO downlink is only based on the assumption, in which full channel state information at the transmitter (CSI-T), It is impossible in practical terms. Consider the case of partial channel state information at the transmitter (PCSI-T) in multiuser MIMO downlink, and in order to reduce the control overhead and signal processing complexity in multiuser MIMO-OFDM systems, two suboptimum transmission schemes are proposed:(Ⅰ) A per-cluster user selection scheme for limited feedback multiuser MIMO-OFDM downlink with optimized cluster size, which obtain a very close approximation for the sum rate of the system; (Ⅱ) A per-antenna selection scheme on each subcarrier, which using spatial multiplexing transmission and post-processing SNR feedback value from users with zero forcing (ZF) linear processors. The performance of these two spatial multiplexing transmission strategies with low complexity is simulated and compared.(6) In multi-cell multi-antennas networks, the uplink training for the channel estimate at the base station in one cell is usually jammed by users from other cells, which leads to loss of orthogonality of pilots, so that the channel estimate quality suffers tremendous losses due to the use of non-orthogonality pilots. In order to mitigate the reduction of achievable rates caused by damaged pilots, A multi-cell MMSE precoding is proposed which depend on the pilots assigned to the users, this precoding technique effectively reduce intra/inter-cell interference, and increase the system performance. The simulation results show that this precoding method preponderate over ZF and two-way pilots precoding method.