Kuang Jingming

High speed all digital symbol timing recovery based on FPGA

This paper presents an all digital timing recovery scheme for high speed modem. Compared to the conventional schemes, which use a VCO to drive A/D sampling clock, the new scheme based on interpolation filter is easy to simulate and implement. In the case which oversampling rate is slightly larger than 2, the new scheme can also give precise timing recovery. So this scheme is very suitable for high symbol rate situation. Firstly, the theory of the asynchronous symbol timing recovery is presented. Then, an implementation scheme of all digital timing recovery is proposed. As a key component, interpolation filter and timing controller are analyzed. Finally, based on the Xilinx Virtex II series FPGA xc2v1000-5, an all digital QPSK timing recovery scheme is implemented. Simulation and hardware test results show that the new scheme can efficiently be used when the symbol rate is up to 45 Msps.

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.

Enhanced HARQ Schemes Based on LDPC Coded Irregular Modulation

The bit-interleaved coded irregular modulation (BICIM) was initially proposed for convolutional code and turbo code cases, which applies different signal constellations and mappings within one codeword. We firstly extend this idea to irregular LDPC codes and present an optimized mapping rule for LDPC coded irregular modulation according to the code degree distribution. Furthermore, we apply this optimized LDPC coded irregular modulation to chase combing (CC) HARQ and propose two enhanced HARQ schemes. The improved schemes can efficiently reduce the reliability variances of bits after soft combining. Simulation results show that they can not only achieve better BER performance but also provide a throughput performance enhancement.

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.

Software simulation in GSM environment of Federal standard 1016 CELP vocoder

The working performance of the Federal standard 1016 CELP (4.8 kbps) vocoder in GSM environment is discussed, and compared with that of the VSELP vocoder of standard GSM half-rate traffic channel. The conclusions through results analysis and comparison are helpful to propel the development of a low-bit-rate speech coder in the next generation digital mobile communication system.