Haiming Wang

Leakage-Aware Energy-Efficient Beamforming for Heterogeneous Multicell Multiuser Systems

Energy-efficient communications has attracted much interest in the research of 5G cellular systems. In this paper, we study energy-efficient coordinated beamforming design for heterogeneous multicell multiuser downlink systems. The considered problem is formulated as maximizing the weighted sum per-cell energy efficiencies (WSPEEMax) subject to predefined per-user target rate demands, maximum leakage interference power constraints, and per-BS transmit power constraints. This formulation is more general than the conventional EE optimization problem and provides a unified way to consider the EE of heterogeneous networks. However, it is hard to tackle due to the weighted sum-of-ratios form of the objective function and the non-convex nature of per-user target rate constraints. To address it, we propose to first transform the original problem into a polynomial form optimization by introducing some auxiliary variables and then further reveal their equivalence in finding the solution. Then, an efficient block coordinate ascent optimization algorithm is developed to solve the equivalent problem by exploiting the concave nature of the considered problem with respect to each optimization variable. To further improve the network EE, we also develop an energy-efficient transmission method for each small-cell network. Finally, extensive numerical results are provided to verify the effectiveness of the proposed schemes and show that both the EE and spectral efficiency (SE) of heterogeneous network can be significantly improved by energy-efficient coordinated multiple-input multiple-output (MIMO) transmission.

Performance analysis of two-way relaying satellite mobile communication

In this paper, a two-way relaying GEO satellite communication scheme is proposed, which significantly reduces the transmission delay as compared to conventional satellite communication strategy. The outage probability of this scheme under Ricean channel model is further analyzed, and a theoretical expression is found. Simulation results show that the derived expression of outage probability is consistent with the numerical results. The BER performances of the proposed scheme under different Ricean factors are also investigated.

Preamble-Based Channel Estimation for Amplify-and-Forward OFDM Relay Networks

In this paper, we address the preamble-based channel estimation problem for orthogonal frequency-division multiplexing (OFDM) systems using multiple amplify-and-forward (AF) relays. We first establish a linear minimum mean-square-error (LMMSE) channel estimator which directly estimates the overall channels from the source to the destination. Then, based on the assumption that the channel correlations between the relays are unknown at the source terminal, a suboptimal training sequence and precoding matrices in closed form are designed to approach the optimal estimation performance at low-complexity.

Duality Based Energy-Efficient Beamforming Design for Multiuser Downlink Systems

In this letter, we consider energy efficient beamforming for the broadcast multiple antenna channel. The optimization problem is formulated as maximizing the ratio of the achievable sum-rate to the total power consumption subject to given power and SINR constraints, which is non-convex and hard to tackle. In contrast to existing approaches, we first derive a virtual uplink problem that is dual to the primal downlink problem, which extends the conventional uplink-downlink duality into energy efficiency region. Owing to the fact that the optimal receive beamforming vectors in the uplink have analytical solutions, we then propose an efficient algorithm to solve the dual problem and convert its solution to the primal problem. Our complexity analysis shows that the proposed algorithm has much lower complexity than the existing solutions. Numerical results finally confirm the effectiveness of our proposed algorithm and illustrate its advantage over the conventional approaches.

Coordinated multi-cell beamforming scheme using uplink-downlink max-min SINR duality

In this paper, a new analytical expression of the max-min SINR duality between the multi-cell downlink and the virtual uplink subject to per-BS power constraints is firstly given. Based on that, a hierarchical iterative scheme is proposed to solve the virtual uplink optimization problem. The uplink solution is then converted to achieve the solution to the multi-cell downlink beamforming problem. Simulation results show that, in contrast to existing multi-cell beamforming schemes, the proposed scheme achieves better performance in terms of both the worst-user rate and the rate per energy.

System performance evaluation for millimeter wave wireless communication

This paper evaluates the link-level performance of millimeter wave (mmWave) wireless communication system operating on 39.5 GHz frequency band. A frame structure based on the long term evolution (LTE) is proposed, including resource allocation and reference signal pattern. Some key parameters are carefully set to adapt to the mmWave frequency. Simulation results validate that the performance of mmWave communication system satisfies the requirements of great throughput and high reliability.

Coordinated Multicell Precoding for Weighted Sum Rate Maximization with Per-Cell EE Constraints

Spectral efficiency (SE) and energy efficiency (EE) are both essential in future wireless communications. To improve the system performance on these two metrics, in this paper we consider the weighted sum rate maximization (WSRMax) problem subject to per-cell EE constraints and per-BS transmit power constraints in multicell multiuser downlink systems. This problem is difficult in its original form due to the introduction of new EE constraints. We first reveal that the original problem can be transformed into an equivalent parameterized polynomial form by introducing some auxiliary variables. By exploiting the concavity property with respect to each variable in the equivalent problem, an efficient block coordinate ascent algorithm is then proposed with guaranteed convergence property. Numerical results show that compared with the conventional WSRMax algorithm, in addition to fulfilling the EE requirement of each cell, our algorithm achieves a better system EE performance at the cost of a slight sum rate performance loss at a certain region and offers a new insight on the SE-EE tradeoff in wireless communication systems.

Performance analysis of symbol interleaving for next generation mm-Wave MIMO WLAN

Interleaving, as an important module of wireless communication system, is used to resist burst errors caused by frequency-selective fading. Low Density Parity Check Code (LDPC) tone mapping would be adopted for Orthogonal Frequency Division Multiplexing (OFDM) systems in IEEE 802.11aj (45GHz). In this paper, an optimal symbol interleaving parameter selecting (OSIPS) algorithm is proposed to get the optimal interleaving parameter. Based on this algorithm, the optimal tone mapping distance for conventional bandwidth based tone mapping (BTM) mechanism is obtained. This paper also presents two adaptive tone mapping mechanisms, including spatial streams based adaptive tone mapping (SSATM) and MCS based adaptive tone mapping (MATM). Adopting the tone mapping distance selected by OSIPS algorithm can bring the best packet error rate gain (up to 4dB) for BTM. And SSATM and MATM perform better than BTM, especially for small number of spatial streams and low MCS.

Energy-efficient coordinated precoding for multicell system with transceiver impairments

Mutlicell coordinated multiple-input multiple-output (MIMO) transmission that ignores hardware impairment of transceivers will usually suffer severe performance degrade. To reduce the impact of hardware impairments, in this paper we focus on investigating coordinated precoding design for the multicell system by taking the transceivers impairments into account. The optimization problem is formulated based on a general model of residual impairment, which is hard to solve due to the high coupling of optimization variables and has more drawback than the conventional problem without transceiver impairments. To address it, we first transform the primal problem into an equivalent but more tractable form by exploiting the relationship between the achievable rate and the MMSE receiver, then we propose to solve it using block coordinate ascent method and develop an iterative algorithm. It is proved that our algorithm is guaranteed to converged to a stable point. Finally, numerical results shown that substantial gain over traditional energy-efficient transmission scheme can be achieved, especially in the high signal-to-noise ratio (SNR) regime.

Multicell coordinated beamforming for WSRM with imperfect CSI at both transceiver sides

This paper considers a coordinated robust design of beamforming and power allocation under per-BS power constraints in a multicell multiuser downlink network with only imperfect channel state information (CSI) is available at both base stations (BS) and mobile users (MU). Our goal is to maximize the weighted sum rate while taking imperfect CSI into account. Due to the intractability of the original formulation, we firstly provide a lower bound optimization problem and then establish the uplink and downlink duality for imperfect CSI. The robust beamformer is obtained by exploiting jointly the minimum mean square errors receivers and convex approximation method based on some separable and linear monotone properties. Numerical results are provided to validate the effectiveness of our beamforming design.