Shenji Luan

To obtain efficient channel codes with high power efficiency at moderate signal-to-noise ratios (SNRs), an efficient high-rate protograph quasi-cyclic (QC) low-density parity-check (LDPC) codes is optimally constructed. By an optimized protograph template, the code framework is firstly produced by the extensions of the variable nodes. By enlarging the dimension of the sub-matrices related to the protograph framework, the base QC matrix template is generated with required code rate and length by the extrinsic information transfer (EXIT) chart for better decoding threshold. Then, the elements in the base matrix are split with even smaller square sub-matrices of the same row and column weights. In this procedure, a progressive-edge-growth (PEG) algorithm is employed to find the optimized positions of the QC sub-matrices to obtain larger girth for better error floor performance. Moreover, an asymptotic weight distribution (AWD) is employed to keep a low-code-error floor for the code. Also the circulant offsets in all QC sub-matrices are optimally searched by a QC oriented nested loop approximated cycle extrinsic message degree (QC-NLACE) algorithm, which improves the relationship of the unavoidable loops in the code’s Tanner graph to cut the error floor. Simulation results show that the codes produced by the proposed method show quite good bit-error-rate (BER) performance. In addition, they exhibit good properties of high spectrum efficiency brought by the high code rate, and the low complexity by the short code length. Moreover, a series of different rate-compatible LDPC codes can be generated from the same protograph framework with some variable node extensions, which significantly eases the code design. Therefore, the proposed code construction can be efficiently applied in the optimal construction of high-rate and short-length rate-compatible QC-LDPC codes with a high data rate and rational complexity, which makes the codes extremely suited for use in new-generation power-constrained wireless communications.

Restricted target wake time (R-TWT) is designed to prioritize latency-sensitive traffic within a basic service set (BSS). However, when transmissions from overlapping BSSs (OBSSs) overlap with the R-TWT service period (SP), the resulting interference may still disrupt latency sensitive traffic. The IEEE 802.11bn amendment addresses this issue by introducing coordinated R-TWT (CR-TWT), which mandates neighboring BSSs using the same primary channel to remain silent, thereby extending SP protection. While nonoverlapping R-TWT schedules guarantee protection, they may not satisfy the stringent timing requirements of delay-sensitive traffic. Conversely, allowing concurrent transmissions among multiaccess points (Multi-APs) in the same SP through spatial reuse can be beneficial. This poses challenges since spatial reuse typically requires a centralized coordinator to collect received signal strength indicator (RSSI) information and compute the optimal transmit power of involved access points (APs), incurring significant signaling overhead. Meanwhile, the traffic identifier (TID) is critical for negotiating R-TWT SPs, as Multi-APs can use this information to prioritize high-priority latency-sensitive traffic. These considerations motivate our proposal of distributed CR-TWT (DCR-TWT), which incorporates TID prioritization and formulates weighted data rate maximization as a convex optimization problem. In DCR-TWT, each AP independently solves its local optimization problem to determine whether to transmit within the SP and its corresponding optimal transmit power, greatly reducing signaling overhead. We evaluate the performance of CR-TWT and DCR-TWT using a full physical layer model coupled with a simplified medium access control (MAC) layer model. An adaptive modulation and coding scheme (MCS) selection mechanism is devised to enhance simulation realism. Results show that DCR-TWT outperforms CR-TWT by achieving more than two times the weighted data rate, a significant reduction in the packet error rate and the packet transmission latency. Furthermore, we identify a limitation in DCR-TWT: excessive scheduling for concurrent transmissions. This overscheduling results in up to 30% of cases failing to meet the minimum signal-to-interference-plus-noise ratio (SINR) threshold. To overcome this, we propose enhanced DCR-TWT (EDCR-TWT), which excludes BSSs causing difficulties in the convergence of the convex optimization problem. Experimental results demonstrate a significant improvement: the proportion of cases below the minimum SINR threshold decreases from 30% to below 10% under EDCR-TWT. A comparative analysis reveals that EDCR-TWT outperforms prior work in both weighted data rate and packet error rate.

To eliminate inter-symbol interferences (ISI) caused by nonlinear group delay effect in high-speed broadband satellite sensor networks, an efficient parallel adaptive blind equalization of improved block constant modulus algorithm (IBCMA) with decision-directed (DD) mode (IBCMA-DD) is proposed with block minimum mean square error (MMSE) criterion. First, nonlinear group delay models are introduced in satellite channels. Second, the criterion of the classical Godard’s constant modulus algorithm (CMA) is derived in the block vector form as the IBCMA for satellite signals with inter-symbol interference (ISI) caused by the above satellite channels. In the IBCMA, stochastic gradient descent and block minimum mean square error are adopted to reduce excess errors in equalization by adjusting block tap-weight vectors adaptively. Finally, the IBCMA is combined with the DD mode of equalization to both accelerate the parallel blind equalization with low complexity and improve the spectrum efficiency without any training data to occupy unnecessary bandwidth. Simulation results indicate that the proposed IBCMA-DD equalization possesses good performance in approaching ideal non-ISI transmissions. It achieves good bit error rate (BER) performance just within 0.3 dB of the theoretic performance under high signal-to-noise ratios (SNRs), even at satellite group delay channels by high-power nonlinear broadband filters. Therefore, it obtains excellent equalization under severely deteriorated group delay channels in broadband satellite sensor networks with high data rate.

To improve the reliability and efficiency in cooperative communications, a power optimized single relay selection scheme is proposed by increasing the diversity effort with an improved link-adaptive-regenerative (ILAR) protocol. The protocol determines the forwarding power of a relay node by comparing the signal-to-noise ratio (SNR) at both sides of the node; thus it improves the power efficiency. Moreover, it also proposes a single relay selection strategy to maximize the instantaneous SNR product, which ensures the approximate best channel link quality for good relay forwarding. And the system adjusts the forwarding power in real time and also selects the best relay node participated in the cooperative forwarding. In addition, the cooperation in the protocol is analyzed and the approximate expression of the bit-error-rate (BER) and the outage probability at high SNRs are also derived. Simulation results indicate that the BER and outage probability of the relay selection scheme by the ILAR protocol outperform other contrast schemes of current existing protocols. At BER of 10⁻², the proposed scheme with ILAR protocol outperforms those of the decoded-and-forward (DF), the selected DF (SDF), and the amplify-and-forward (AF) protocols by 3.5, 3.5 and 7 dB, respectively. Moreover, the outage probability of the relay system decreases with the growth of the relay number. Therefore, the proposed relay selection scheme with ILAR strategies can be properly used in cooperative communications for good reliability and high power efficiency.