This letter proposes a robust joint linear precoding scheme based on the minimum mean squared error (MMSE) criterion for amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay broadcast systems with limited feedback, where only the quantized channel direction information (CDI) of the forward channel is available for the base station (BS) and the relay station (RS). The proposed scheme employs an iterative algorithm which alternately optimizes the BS and RS precoders to jointly minimize the expected MSE conditioned on the quantized CDI.

A new approach to low-complexity rate allocation scheme in closed loop MIMO-OFDM system is proposed. The new scheme utilizes ordered statistics of channel matrix's singular values to simplify the ideal scheme which uses water filling in both frequency and space domain. Unlike the conventional simplified algorithm called FFC [1] ("frequency flat constraint"), the proposed scheme has no restrictions of the numbers of antennas. The improvement of SNR gain with this new scheme is about 0.8 dB in 2-antenna systems with a little more complexity than FFC.

This letter investigates a subchannel and power allocation (SPA) algorithm which maximizes the throughput of a user under the constraints of total transmit power and fair subchannel occupation among relay nodes. The proposed algorithm reduces computational complexity from exponential to linear in the number of subchannels at the expense of a small performance loss.

In this letter, we propose an efficient relay antenna selection algorithm for the amplify and forward (AF) two-way multiple-input multiple-output (MIMO) relay systems with analogue network coding (ANC). The proposed algorithm greedily selects the additional receive-transmit antenna pair that provides the maximum sum-rate. An iterative computation method is also designed to evaluate the sum-rate efficiently.

In this paper, we propose an ICI mitigation method for MIMO OFDM using turbo detection technique. In order to reduce the computational complexity, we present a method for dividing the received frequency-domain signals into subbands and the manner of division varies with each iteration, joint soft ICI cancellation and decoding is then performed on each subband. To perform iterative ICI mitigation, the estimation of the time-variant channel using a great quantity of pilot tones is needed, which results in poor spectral efficiency. We then propose a method to reduce the required scatter pilot tones, which is differentially-modulated-pilot scheme. Moreover, the estimation can be constructed based on EM-type algorithms to further reduce the computational complexity. Finally, the results of computer simulations demonstrate that the proposal can provide significant performance improvement.

In this letter, we propose a novel antenna selection algorithm for amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay systems with Zero-Forcing (ZF) processing applied both at the source node and at the destination node. We obtain the optimum antenna selection criterion by deriving an iterative closed-form expression for capacity maximization.

In this letter, we develop a two-step receive antenna selection method to maximize channel capacity. Different from previous work, we first derive a lower bound on capacity based on Hadamard inequality and arithmetic-geometric mean inequality, which is then used to iteratively drop the worst-performing antennas according to their measure. The recursive nature of this method helps to largely reduce the computational complexity.

The conventional semi-orthogonal user pairing algorithm in uplink virtual MIMO systems can be used to improve the total system throughput but it usually fails to maintain good throughput performance for users experiencing relatively poor channel conditions. A novel user paring algorithm is presented in this paper to solve this fairness issue. Based on our analysis of the MMSE receiver, a new criterion called “inverse selection” is proposed for use in conjunction with the semi-orthogonal user selection. Simulation results show that the proposed algorithm can significantly improve the throughput of users with poor channel condition at only a small reduction of the overall throughput.

This paper addresses the problem of channel estimation for multiple-input and multiple-output orthogonal frequency division multiplexing (MIMO-OFDM)-based wireless networks with frequency-reuse. Firstly, the optimal time-domain training sequences are derived for the multiple cells with the same frequency group and a set of suitable sequences are also presented for practical implementation. Secondly, a low complexity iterative algorithm is combined with the time domain channel estimation to suppress the co-channel interferences (CCIs). The channel estimation method is applied to synchronous and asynchronous cellular and the MSE performance of the estimator is also analyzed. Simulation results demonstrate that the presented channel estimation approach can substantially suppress CCIs and outperform the conventional LS MIMO-OFDM channel estimation over multipath fading channels in multicell environments.

In this letter, we propose an antenna selection single frequency network precoding (AS-SFNP) scheme for downlink cooperative multiple-input multiple-output (MIMO) systems, which efficiently improves system capacity with low feedback overhead and low complexity.

In this letter, we study cell cooperation in the downlink OFDMA cellular networks. The proposed cooperation scheme is based on fractional frequency reuse (FFR), where a cooperation group consists of three sector antennas from three adjacent cells and the subchannels of each cooperation group are allocated coordinately to users. Simulation results demonstrate the effectiveness of the proposed schemes in terms of throughput and fairness.

In this letter,we design a special preamble composed of two OFDM training blocks with different numbers of identical parts. Based on the designed preamble, we propose a method to estimate frequency offset utilizing initial estimates from the two OFDM training symbols. By elaborately selecting the numbers of identical parts for the two training blocks, the proposed estimator provides a much larger estimate range than conventional estimators using identical parts. Computer simulations show that the proposed estimator exhibits superior estimate performance, while maintaining low computational complexity.

In this paper, a practical adaptive TuCM scheme is proposed, and its adaptive method is described. With some hardware considerations, a suboptimal optimization algorithm which shows that the number of fading regions is variable is put forward. The proposed adaptive TuCM comes within 3 dB of fading channel capacity, exhibits about 3 dB power gain over conventional adaptive TCM, and is easy to realize by hardware. Considering delay and channel estimation error, the BER performance of adaptive TuCM is analyzed and simulated. In the performance analysis, the method of data fitting is applied to obtain the BER expression for TuCM, and a fitting mathematical model is proposed. Results show that adaptive TuCM is very sensitive to delay and channel estimation error. To alleviate these problems, we proposed an improved power adaptation that can make adaptive TuCM practical.

We introduce a novel power allocation scheme for decode-and-forward relaying system with partial channel state (CSI) information, i.e., the source knows full CSI of source-relay link but only statistical CSI of source-destination and relay-destination links. Our objective is to minimize the outage probability by jointly allocating the transmit power between the source and relays. To avoid exhaustive search, the MAOP scheme and the MMS scheme are proposed to approach the optimal allocation in the high and low signal-to-noise ratio regimes, respectively.

A multi-user space-time block coding (STBCa) system is a multi-access system where co-channel users employ space-time block codes (STBC). In this paper, we aimed at the design of efficient zero-forcing (ZF) receivers, especially ZF iterative interference cancellation (IC) receivers, for multi-user {G2, G3, G4} STBC systems with an arbitrary number of users, based on the identification of algebraic properties existing in the systems. First, we identify some algebraic properties for {G2, G3, G4} STBC systems. Then, utilizing these algebraic properties, we further expose two significative properties, called "ZF output uncorrelated property" and "ZF output equal Post-detection SNR property" respectively, for least-squares (LS) ZF receivers in multi-user {G2, G3, G4} STBC systems by detailed proofs. Based on the two properties, a novel LS ZF user-ordered successive interference cancellation (ZF UOSIC) detection algorithm is proposed subsequently. Finally, simulation results show that ZF UOSIC is superior to the conventional ZF IC and maximum-likelihood (ML) algorithms and the non-ordered ZF user-based SIC (ZF USIC) algorithm due to adopting iterative IC and optimal ordering among users, and has very close performance to the ZF symbol-ordered SIC but with lower complexity due to the fewer iterative times.