Zhiqiang He

Performance of Dual-Hop Transmissions with Fixed Gain Relays over Generalized-K Fading Channels

We present the end-to-end performance of dual-hop wireless communication systems with non-regenerative fixed gain relays operating over independent not necessarily identically Generalized-K (KG) fading channels. New closed-form expressions are derived for the moments of the end-to-end signal-to-noise ratio (SNR), while the corresponding moment-generating function (MGF) is accurately approximated with the aid of Pade approximants theory. Useful performance criteria are studied; the average end-to-end SNR and the amount of fading, which are expressed in closed form, the average bit-error probability for several coherent, noncoherent, and multilevel modulation schemes, and the outage probability, which are both accurately approximated using the well-known MGF approach. Furthermore, novel closed-form expression is obtained for the gain of semi-blind relays over KG fading channels. The proposed mathematical analysis is complemented by various performance evaluation results, which demonstrate the accuracy of the theoretical approach.

Performance Evaluation of LTE MBMS Baseline

MBMS is an efficient means to provide multimedia services by sharing common radio channels among a group of users. This paper presents performance evaluation of MBMS in LTE framework by a simulator set up according to 3GPP standard. A general comparison is first made among point-to-point (p-t-p), point-to-multipoint (p-t-m) and single frequency network (SFN), which shows that p-t-m with feedback is more efficient than p-t-p, and SFN can lead to remarkable performance enhancement. We also elaborate the packet scheduling process of p-t-m with feedback scheme, which involves sector-specific adaptive modulation coding (AMC) and hybrid automatic repeat request (HARQ), and then investigate the gain provided by them. It is shown that with moderate user number, fast AMC and HARQ can give 25% and 70% throughput gain respectively. However, this gain decreases with user number.

A novel OFDM channel estimation method based on Kalman filtering and distributed compressed sensing

Channel estimation is important for coherent detection in orthogonal frequency-division multiplexing (OFDM) systems. Current frequency-domain Kalman filtering (FDKF) channel tracking method requires a large number of pilots, which reduces the spectral efficiency of the system and increases the complexity. In this paper, in order to solve this problem, a new channel estimation method based on the recent methodology of distributed compressed sensing (DCS) and FDKF is proposed. By exploiting the sparse attribute of OFDM channels and introducing DCS, the number of pilots could be reduced greatly, which means more resources are saved for data transmission. Moreover, simulations indicate the proposed method achieves a better performance than conventional FDKF and least square (LS) method.

Sub-Sampling Framework of Distributed Video Coding

Distributed video coding (DVC) has recently been proposed to reduce the complexity of the encoder, whereas it suffers from the sampling cost of huge amount of image data. To relax such sampling burden, this paper develops a novel sub-sampling distributed video coding (SuDVC) by utilizing compressive sensing (CS) technique. Due to the inherent sparsity in video sources, the video frames are compressively sampled at the encoder. On the other hand, by exploiting the correlation between CS measurements and side information and by performing sparsity recovery, the video frames are recovered at the decoder. When compared with the traditional fully-sampling equivalence, SuDVC enjoys the reduction of transmission rate, the reduction of implementation complexity and the robustness to channel losses, which are verified in the simulations.

System performance evaluation of distributed antennas based CoMP in LTE-Advanced

In this paper, we have summarized our analysis about distributed antennas based CoMP in LTE-Advanced and evaluated the system spectrum efficiency in three scenarios. From the results, we can see the proposed scheme achieves a higher throughput compared with centralized antennas based system. The location of antennas closed to sector center leads to the optimal system performance. With the change in the number and location of the antennas, the antennas tend to be scattered placement. The method of clustering, algorithm of antennas selection, and multi-antennas per sector, are worthy of further research.

Pilot-aided channel estimation method based on compressed sensing and Kalman filtering in OFDM systems

In this paper, by combining CS and TDKF, we propose a novel channel estimation scheme for OFDM time-variant channels. Compared with conventional TDKF method, our scheme is more practical as it need not to know the delays of multipath previously. Numerical results proved that compared with LS method, both the MSE and the BER performance are improved in our scheme.

Impact of control channel constraints on downlink performance comparison of MIMO transmission schemes in 3GPP LTE

In spite of the significant performance gain that multiple-input multiple-output (MIMO) transmission can provide in wireless communication, the use of MIMO in realistic systems will lead to large control signaling overhead. Performance comparison of different transmission schemes should consider the control channel (CC) constraints. In this paper, we first build the model of CC for downlink MIMO transmission, which is an extension of previous work in [1], and then we introduce the concept of CC operation point and propose a principle that performance comparison should be with same CC operation point. Three transmission schemes defined in 3GPP long term evolution (LTE), 1×2 maximum ratio combining (MRC), 2×2 open-loop transmit diversity (OLTD), and 2×2 closed-loop spatial multiplexing (CLSM), are compared through system level simulations, and results show that to keep CC operation point constant, the requirements on CC resource are different, which will further influence the spectral efficiency of the transmission schemes.

Opportunistic Packet Scheduling in OFDM Distributed Antenna Systems

Opportunistic packet scheduling optimization problem in orthogonal frequency division multiplexing (OFDM) distributed antenna systems (DAS) is investigated by this paper. Physical-layer channel state information (CSI) and wireless links requirements for bit error rate are taken into account during problem formulation. The optimization aim is to minimize packet loss rate (PLR) subject to limited wireless resource, which is characterized by power, subcarrier, antenna et al. According to the characteristics of users packet queues as well as CSI, the proposed algorithm adaptively allocates wireless resource to users to exploit as much spatial and multiuser diversity as possible. Simulation results show the proposed algorithm achieves the lowest PLR in all compared algorithms. Further more, the proposed circular DAS significantly outperforms co-located antenna systems (CAS) due to distributed antenna deployment.

List Sphere Decoding Combined with Linear Detection-Based Iterative Soft Interference Cancellation Via Exit Chart

Iterative list sphere decoding (LSD) can achieve near capacity on a multiple-antenna channel, however, with a rather high complexity. In order to reduce the complexity, in this paper, linear detection-based iterative soft interference cancellation (ISIC) instead of LSD is applied at the second and later iterations. We propose to exploit extrinsic information transfer (EXIT) chart analysis to select a specific ISIC to alleviate large performance degradation. Here MF-based and MMSE-base iterative soft interference cancellations (ISIC) are selected to be combined with the LSD. Simulation shows that the iterative combined detections have little signal-to-noise ratio (SNR) loss and a much lower complexity in comparison with iterative LSD

Recursive encoding of spatially coupled LDPC codes with arbitrary rates

Spatially coupled LDPC codes have attracted much attention due to the promising performance. Recursive encoding with low delay and low complexity has been proposed in the literature for selected node degrees. To realize the recursive encoding of spatially coupled LDPC codes with arbitrary rates, we propose in this paper a modified structure of the parity-check matrix and implement the encoding using a shift-register regardless of the node degrees. By rearranging the edge connections, the parity bits at each coupling position can be jointly determined by the information bits at the current position and the encoded bits at former positions. Performance analysis in terms of design rate and density evolution has been provided. It can be observed that the modified code structure leads to a better belief-propagation threshold. Finite-length simulation results are provided, which verify the theoretical analysis.