A space-time block coded orthogonal frequency division multiple access (STBC-OFDMA) scheme based on combination of user grouping (UG) and frequency reuse (FR) is proposed for WiMAX uplink transmission where each user employs an STBC scheme. First, a direction-of-arrival (DOA)-based intra-cell UG model is combined with the idea of inter-cell FR so as to produce a UGFR-STBC-OFDMA uplink access scheme which satisfies with both UG constraints and the inter-cell FR planning. Furthermore, a Capons beamforming-based receiver with a smart antenna array is proposed for directional reception of signals coming from different user groups as well as multiple access interference (MAI) suppression at the base station. Both theoretical analysis and simulation results show that the proposed uplink access scheme not only achieves a well-behaved tradeoff in ideal average spectral efficiency, bit error rate (BER) and computational complexity, but also suppresses inter-cell interferences without power control, compared with some conventional schemes for uplink transmission.

The authors propose a resource allocation algorithm for orthogonal frequency division multiplexing (OFDM) system to provide QoS guarantee for multicast and unicast service concurrently. The optimization objective is to maximize the sum rate of the unicast users under the constraints of power and the minimal rate requirements of multicast service, which can be solved by traditional two-step approach. To decrease the complexity, a greedy-based approach is proposed. According to theoretical analysis and simulation results, the performance of the proposed algorithm is close to the two-step approach meanwhile the complexity is effectively decreased. In summary, the proposed algorithm can balance the performance and complexity well and is suitable to be applied to the practical scenario.

The authors propose a pseudo-noise (PN) sequence-based carrier frequency offset (CFO) estimation algorithmfor multiuser OFDMuplink. In the proposed algorithm, a PN sequence and its circular-shifting versions are considered as training sequences for different users, and then channel parameters with CFO factors from each user to a central base station can be estimatedby virtue of autocorrelation characteristic of the PN sequence. Finally all users’CFO estimates can be acquired simultaneously by calculating channel phase-angle difference between two training periods. The simulation result shows that the proposed algorithm achieves better estimation performance.

In order to improve the performance of the MMSE (minimum mean squared error) turbo equalizer further, the MMSE turbo equalization with partial prior information is proposed. The partial prior information equals to the sumof the whole extrinsic information and the partial prior information of the MAP(maximum a posteriori probability) decoder. The simulation results show that the performance of the MMSE turbo equalizer with partial prior information is much better than the performance of the conventional MMSE turbo equalization and is very close to the performance of the MAPturbo equalizer which is the optimal turbo equalizer for minimizing the bit error rate (BER) and the frame error rate (FER).

The decoding algorithm is investigated and an improved architecture for the decoders is presented. The architecture makes variable nodes and check nodes work for two different code words at the same time. And the architecture is not only fit for full-parallel LDPC decoders but also fit for the semi-parallel decoders which are mostly used in the practical communication systems. Asemi-parallel LDPC decoder with code length equal to 1008bits is implemented based on this architecture on FPGA platform. Synthesize results show that the improved architecture can improve the efficiency of the logic cells. And the throughputs of information bits attain 45 Mbps which is twice of the throughputs of the decoder without the improved architecture.

LDPC-SPC codes is introduced. LDPC-SPC codes choose LDPC codes as horizontal codes and single parity check (SPC) codes as vertical codes. Some decoding algorithms are also given, including algorithms based on hard decision and soft decision. By these algorithms, each bit of every LDPC code can get extrinsic messages from other LDPC code words to help LDPC decoder decode successfully. Based on the LDPC code which is half rate and 8064 bits long, a LDPC-SPC code is constructed. Simulation results show that the LDPC-SPC codes can lower the error floor of the LDPC codes and have better BER (Bit Error Ratio) performance. When BER is 10-7, the performance of the LDPC-SPC codes is 0.3 dB better than the LDPC codes.

The multiple access control (MAC) protocol in broadband satellite access network is investigated. A novel combined dynamic allocation multi-access scheme is proposed, which is based on the chaotic prediction of self-similar traffic. The OPNET simulation system is developed for comparing the performance of different schemes. Simulation results indicate that the novel scheme has better performance when the traffic data exhibit self-similarity. The superiority of centralized access control with satellite onboard processing (OBP) is also proved.

The Time-Hopping Pulse Position Modulation (TH-PPM) is one of the most popular approaches for IR-UWB multi-user systems, and a lot of research efforts have been devoted on its performance analysis. In several latest literature, a method of numerical computation of MAI characteristic function was carried out to derive precision analytical error performance, which, however, still showed a few inconvenient limitation on the system configuration. To overcome this shortage, the corresponding MAI model is enhanced in this paper, and the multi-access BER performance expression is also derived based on this modified model. Finally, Monte-Carlo simulations are carried out to verify the analytical results.

A PN (Pseudo Noise) based Channel Estimation (CE) algorithm using circular correlation is proposed, and is implemented in Single Carrier Frequency Domain Equalization (SC-FDE) system. The new CE algorithm is compared to typical frequency-domain algorithms, and it is found that new algorithm has lowest complexity and acceptable performance. A no-guard-interval PNA-SC-FDE (PN Assisted SC-FDE) system is studied and a simpler receiving procedure for interference-canceling based receiver is proposed. Simulation shows that the performance of receiver with interference-canceling and new CE algorithm can approach the performance of receiver with perfect CSI (Channel State Information).

This paper focuses on the appliance of multiuser detection algorithm based on belief propagation (BP) in MIMO systems with M-QAM(Quadrature Amplitude Modulation) modulation scheme. Because of the characteristics of M-QAM modulation, this paper introduces a preprocess to eliminate the correlation between the elements of receiving signal vector, proposes to take a conditional probability vector as the measurement of “belief” of transmitting signal, deduces the corresponding formulae of belief-updating and thus constructs the BP-Based MUD algorithms in MIMO systems with M-QAM modulation scheme. The algorithm proposed in this paper has a computation complexity proportional to the square of transmitting antenna number while it outperforms the conventional linear MMSE multiuser detector. Simulation results are given to prove this.

For the detected error words by the LDPC decoder, the characteristics of code bits reliability information is investigated. An efficient novel hybrid automatic repeat request (HARQ) scheme is proposed for system coded with Low-Density Parity Check (LDPC) codes. Compared with the Reliability-based hybrid ARQ (RB-HARQ), the new HARQ scheme outperforms the RB-HARQ in consideration of the bit transmission power for the requesting messages in the backward transmission channel. Simulation results show that the new H-ARQ scheme is more practical than RB-HARQ.