Fei Zesong

Shaping gain by non-uniform QAM constellation with binary turbo coded modulation

A non-uniform signal constellation can be used to obtain shaping gain. One typical way to design non-uniform constellation is make the output signal follow a Gaussian distribution by using equally like signals with unequal spacing. However, for binary turbo coded modulation (BTCM) with M-QAM system, this non-uniform constellation design criteria can be modified based on different impacts of various turbo encoded hits sequence on BER performance. In this paper, author points out that shaping gain for M-QAM with BTCM can be achieved integrated with optimization of mapping rule, performance of the proposed scheme outperforms over BTCM with uniform constellation, especially under low and moderate SNR region. Meanwhile, the effects of code rate, order of QAM constellation on shaping gain are investigated. Numeral results are provided to support the proposed scheme and analysis. The proposed scheme can be applied to high rate data service with hybrid ARQ, such as HSDPA system.

Improved binary turbo coded modulation with 16QAM in HSDPA

High speed downlink packet access (HSPDA) is proposed as the evolution of WCDMA recently, aiming at providing higher downlink transmission rate with peak rate about 8-10 Mbps. Turbo code combined with high order modulation can provide bandwidth efficient transmission with substantial coding gain over traditional trellis coded modulation (TCM). In this paper, author evaluates the feasibility of the application of binary turbo coded modulation (BTCM) with 16QAM in HSPDA. Some improvements of interleaver design according to label mapping are proposed to enhance the performance. And the impact of rate matching functionality on the performance of BTCM is analyzed. Simulation results show that the improved BTCM scheme with 16QAM can be implemented with low code rate and outperform the conventional scheme.

Resource allocation for physical layer security in heterogeneous network with hidden eavesdropper

The tremendous performance gain of heterogeneous networks (HetNets) is at the cost of complicated resource allocation. Considering information security, the resource allocation for HetNets becomes much more challenging and this is the focus of this paper. In this paper, the eavesdropper is hidden from the macro base stations. To relax the unpractical assumption on the channel state information on eavesdropper, a localization based algorithm is first given. Then a joint resource allocation algorithm is proposed in our work, which simultaneously considers physical layer security, cross-tier interference and joint optimization of power and subcarriers under fairness requirements. It is revealed in our work that the considered optimization problem can be efficiently solved relying on convex optimization theory and the Lagrangian dual decomposition method is exploited to solve the considered problem effectively. Moreover, in each iteration the closed-form optimal resource allocation solutions can be obtained based on the Karush-Kuhn-Tucker (KKT) conditions. Finally, the simulation results are given to show the performance advantages of the proposed algorithm.

Rate-Compatible Schemes for Link Adapted LDPC Codes in IEEE 802.16e Standard

IEEE P802.16e standard specifies the construction of low-density parity-check (LDPC) codes with four different code rates, i.e. 1/2, 2/3, 3/4, 5/6, and totally six parity check matrices. However, such a coarse coding rate granularity cannot provide comparable link adaptation performance comparing to turbo codes in HSDPA. In another aspect, more mother codes lead to much higher complexity of encoder implementation due to individual parity check matrices. To reach a balance between the implementation complexity and the fine granularity in link adaptation, this paper investigates the performance of the rate-compatible (RC) scheme, with targeted coding rate varying from 0.1 to 0.9, based on different sets of mother LDPC codes. As a summary, this paper proposes an instruction of mother codes selection and RC schemes for different targeted coding rates, which makes the link adaptation of LDPC codes very convenient for WiMAX systems.

Type II Hybrid-ARQ Schemes of LDPC Codes Based on Information-Nulling Rate-Compatible Algorithm

In this paper, information nulling (IN) type II HARQ protocol with low-density parity-check (LDPC) codes is presented. Incremental redundancy is created from partial null versions of the original information data using the same encoder/decoder structure. In comparison to the conventional rate-compatible type II HARQ schemes, the decoder architecture always operates at the highest code rate, thus efficiently exploiting the decoder hardware. The performance analysis shows that the proportion of un-nulled information-bits influences the performance significantly, and the performance of the IN-HARQ system does not increase monotonically as the proportion increases. An improved IN-HARQ scheme is designed with variable proportion values of different retransmission, and some preliminary results have been derived to make sure the optimum proportion of un-nulled information-bits. Another IN-HARQ scheme is presented by combining interleaving and IN-HARQ protocol, which provides additional performance gain of interleaving to the original IN-HARQ scheme

LT Codes with Limited Feedback

Rate less codes, such as LT codes, are a class of widely used practical forward error correcting codes. However, conventional LT codes do not make use of feedback information. In addition, owing to the selection of the symbols randomly, conventional LT codes have large redundancy. In this paper, LT codes with limited feedback are investigated. We use several acknowledgment bits to inform the transmitter the most useful symbol for decoding at the receiver side. Transmitter retransmits an input symbol after each feedback to reduce redundancy. Simulation results show that the proposed LT codes can reduce the redundancy significantly and the performance of bit error rate outperform the conventional LT codes.

Joint linear processing design for distributed two-way Amplify-and-Forward MIMO relaying networks

Linear transceiver designs are investigated for distributed two-way relaying networks, which aim at minimising the Weighted Mean Square Error (WMSE) of data detections. The forwarding matrices at relays and equalization matrices at destinations are jointly optimised. To overcome the challenging limitations introduced by individual power constraints, a Semi-Definite Relaxation (SDR) called element-wise relaxation is proposed, which can transform the original optimization problem into a standard convex optimization problem. In this research, two-way relaying is understood from a pure signal processing perspective which can potentially simplify the theoretical analysis. Finally, simulation results are used for assessing the performance advantage of the proposed algorithm.

Distributed resource allocation in ultra-dense networks via belief propagation

Ultra-dense networking is widely accepted as a promising enabling technology to realize high power and spectrum efficient communications in future 5G communication systems. Although joint resource allocation schemes promise huge performance improvement at the cost of cooperation among base stations, the large numbers of user equipment and base station make jointly optimizing the available resource very challenging and even prohibitive. How to decompose the resource allocation problem is a critical issue. In this paper, we exploit factor graphs to design a distributed resource allocation algorithm for ultra dense networks, which consists of power allocation, subcarrier allocation and cell association. The proposed factor graph based distributed algorithm can decompose the joint optimization problem of resource allocation into a series of low complexity subproblems with much lower dimensionality, and the original optimization problem can be efficiently solved via solving these subproblems iteratively. In addition, based on the proposed algorithm the amounts of exchanging information overhead between the resulting subprob-lems are also reduced. The proposed distributed algorithm can be understood as solving largely dimensional optimization problem in a soft manner, which is much preferred in practical scenarios. Finally,the performance of the proposed low complexity distributed algorithm is evaluated by several numerical results.

A Type-II Hybrid ARQ Scheme Based on Rate-compatible LDPC Code

Rate-compatible code is a typical way to achieve high forward error correction (ARQ/FEC) systems in packet data transmission. This paper focuses on the construction of efficient rate-compatible low density parity check (RC-LDPC) codes in a flexible way. A special technique to get rate compatible LDPC codes called extending without code-rate threshold is presented in comparison to the results in Zhu Miao et al. (2005), with code-rate threshold. Based on the improved scheme, a type-II hybrid ARQ scheme is presented in the paper, which is greatly flexible and results in good performance. The throughput performances of different full incremental redundancy (FIR) schemes depend on the length of retransmitted incremental redundancy (IR) substantially. Furthermore, performance comparison between full incremental redundancy (FIR) based on this rate-compatible structure and chase combing (CC) protocols has been investigated

Combining Eigen-Beamforming and Space-Time Block Coding with Equal Power Allocation

A wireless transmission scheme combining eigen-beamforming and space-time block coding (STBC) is proposed and the transmission performances are investigated under both the uncorrelated and correlated transmit antennas, separately. By minimizing the upper bound of the symbol error rate, the design of eigen-beamforming could provide the diversity order. Besides the careful power allocation for the common beamforming, this paper shows that the transmission power can be simply allocated equally to every beams to achieve the transmit diversity when the eigen-beamforming is combined with STBC. Numerical simulation results show that the transmit diversity of STBC can be further improved by eigen-beamforming with equal power allocation.