Hanwen Luo

Joint MMSE Transceiver Design in Non-Regenerative MIMO Relay Systems

In this letter, we address the problem of transceiver design in a non-regenerative MIMO relay system, where linear processing is applied at both the relay and destination to jointly minimize the mean-squared error (MSE) of symbol estimations. Under average power constraint at the relay station, we show that the optimal relay-precoder always loads power across channel eigenvectors and then decomposes the equivalent MIMO channel into a set of parallel SISO channels. Simulation results demonstrate that our method outperforms other relaying schemes in terms of both BER and MSE.

MMSE Based Greedy Antenna Selection Scheme for AF MIMO Relay Systems

We propose a greedy minimum mean squared error (MMSE)-based antenna selection algorithm for amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay systems. Assuming equal-power allocation across the multi-stream data, we derive a closed form expression for the mean squared error (MSE) resulted from adding each additional antenna pair. Based on this result, we iteratively select the antenna-pairs at the relay nodes to minimize the MSE. Simulation results show that our algorithm greatly outperforms the existing schemes.

Linear Relaying Scheme for MIMO Relay System With QoS Requirements

In this letter, we address the problem of fulfilling quality-of-service (QoS) requirements in a multiple-input multiple-output (MIMO) relay system, where a set of target signal-to-noise ratios (SNRs) should be attained on different substreams. By solving a two-step optimization problem, we obtain a power-efficient relaying scheme that can make the SNR requirements asymptotically fulfilled. A simple relay selection method is also proposed such that the relay-power consumption can be largely reduced when there is a large number of relays.

Dynamic Subchannel and Power Allocation in OFDMA-Based DF Cooperative Relay Networks

This paper focuses on subchannel and power allocation problem in OFDMA-based decode-and-forward (DF) cooperative relay networks. The objective of this problem is to maximize the total data rate under the constraints of joint total transmission power and subchannels occupation, while maintaining the maximum fairness among multiple relay nodes. We transform this mixed integer programming problem to a standard convex optimization one through Lagrangian relaxation method. Accordingly, the optimal solution can be achieved by using Karush-Kuhn-Tucker (KKT) conditions. In addition, we propose two suboptimal subchannel allocation schemes with and without subchannel permutation (SP), which reduce significantly the computational complexity with small performance loss. The simulation results show that the performance of the proposed suboptimal algorithms with SP approaches asymptotically that of the optimal algorithm and with the increment of the number of relay nodes.

Efficient Relay Beamforming Design With SIC Detection for Dual-Hop MIMO Relay Networks

In this paper, we consider a dual-hop multiple-input-multiple-output (MIMO) relay wireless network, in which a source-destination pair, which are both equipped with multiple antennas, communicates through a large number of half-duplex amplify-and-forward (AF) relay terminals. Two novel linear beamforming schemes based on the matched filter and regularized zero-forcing precoding techniques are proposed for the MIMO relay system. We focus on the linear process at the relay nodes and design the new relay beamformers by utilizing the channel-state information (CSI) of both backward and forward channels. The proposed beamforming designs are based on the QR decomposition filter at the destination node, which performs successive interference cancellation to achieve the maximum spatial-multiplexing gain. Simulation results demonstrate that the proposed beamformers that fulfil both the intranode array gain and distributed array gain outperform other relaying schemes under different system parameters in terms of the ergodic capacity.

A novel direct waveform synthesis technique with carrier frequency programmable

The technique of direct waveform synthesis (DWS) is analyzed based on the technique of direct digital synthesis (DDS). The digital modulated waveforms are created by lookup tables (LUT) which contain waveform samples precomputed using the DWS technique. A novel DWS technique is proposed whose carrier frequency is programmable compared to the current one. Furthermore, the effect of memory versus computation is performed. The simulation results show that it is an efficient scheme to implement the software radio modulation for the DWS technique especially the novel technique of DWS with carrier frequency programmability.

Cooperative data dissemination in cellular-VANET heterogeneous wireless networks

Vehicular Ad hoc Networks(VANETs) enable plenty of important applications for vehicles, such as accident prevention and traffic jam avoidance. However, VANETs can hardly provide reliable connectivity between vehicles, which makes data dissemination of the aforementioned applications extremely difficult. Compared with VANETs, 3GPP cellular networks(e.g., LTE), offer much more reliable connectivity. Furthermore, cellular networks ensures timely dissemination in large scales due to the broadcast nature. In this paper, we deploy a cellular-VANET heterogeneous network achitecture to realize efficient data dissemination. In the heterogeneous networks, a part of vehicles are selected as mobile gateways to connect the two kind of networks. Later, we apply the coalition game theory to stimulate vehicles to join coalitions which can maximize the efficient data rate. The simulation results show that, by following the protocol, maximin overall effective data rate can be achieved.

Joint Power Allocation and Scheduling of Multi-Antenna OFDM System in Broadcast Channel

This paper considers the general multiuser down-link scheduling problem and power minimization with multiuser rate constraints. We present joint user selection algorithms for DPC, ZF-DPC, ZFBF and TDMA for multi-antenna OFDM system in broadcast channels, and we also present a practical waterfilling solution in this paper. By the selected users with the consideration of fairness, we derive the power optimization algorithm with multiuser rate constraints. Simulation results show that the presented user scheduling algorithms and power minimization algorithms can achieve good power performance. Meanwhile, simulation results also show that the scheduling algorithm can guarantee fairness.

A novel CQI calculation scheme in LTE\LTE-A systems

We propose a novel Channel Quality Indicator (CQI) calculation scheme in LTELTE-A systems. SNR-CQI mapping scheme, as well as SINR-CQI mapping scheme, is extensively studied in previous works. However, these kinds of CQI mapping schemes always provide imprecise results in fading channels, since all of them ignore the channel quality degeneration caused by other factors. In this paper, we further improve CQI calculation by considering the impact of multipath delay spread. The calculation scheme is presented in details. In order to guarantee the converge of CQI calculation, a Block Error Ratio (BLER) based converge algorithm is proposed. Simulations show that our calculation scheme can select CQIs more precisely, and achieve better throughput performance than traditional schemes. Furthermore, our scheme converges much faster than previous schemes.

Transceiver Design for AF MIMO Two-Way Relay Systems with Imperfect Channel Estimation

We address the transceiver design problem for amplify-and-forward (AF) MIMO two-way relay systems with imperfect channel estimation. Since only estimated channel state information (CSI) is available, the self-interference (SI) cannot be completely canceled at destination nodes. With both channel estimation errors and residual self-interference considered, we propose two robust schemes to minimize the average sum mean squared error (MSE). % averaged over channel uncertainties., In the iterative scheme, the relay precoder and destination receivers are alternately optimized until convergence. In the constrained structure scheme, a specific structure is imposed on the relay precoder to reduce complexity. By solving a relaxed optimization problem, we derive a closed-form solution for the constrained structure precoder. Simulation results show that the proposed iterative scheme provides better robustness against channel uncertainties than the non-robust iterative scheme, and the constrained structure scheme achieves close performance with the proposed iterative scheme.