Gangming Lv

Distributed Space-Time Code for Asynchronous Two-Way Wireless Relay Networks Under Frequency-Selective Channels

In this paper, we consider asynchronous two-way wireless relay networks with amplify-and-forward protocol (AFTWRN), where the distributed space-time code (DSTC) is utilized without synchronization among relays to assist the communication between two terminals. We analyze the pairwise error probability (PEP) behavior of DSTC for AF-TWRN under frequency-selective channels. From our analysis, it is seen that of the paths from one terminal to relays and from relays to another terminal, those with smaller diversity order result in an overall system performance bottleneck. Considering both the timing errors among relays and the multipath fading, we then propose a family of distributed convolutional space-time codes (DCSTC) for AF-TWRN such that the full diversity order can be achieved. Finally, various numerical examples are provided to corroborate the analytical studies.

A Distributed Power Allocation Algorithm with Inter-Cell Interference Coordination for Multi-Cell OFDMA Systems

Inter-cell interference is a serious problem in multi-cell OFDMA systems. In this paper, an iterative interference price based power allocation algorithm with inter-cell interference coordination is proposed for downlink multi-cell OFDMA systems. In the algorithm, each base station announces a price for interference and performs power allocation based on the price information received from other base stations with the objective of maximizing the net utility of the local cell. Through price information updating and transmit power reallocation in every iteration, the algorithm can intelligently coordinate the inter-cell interference in the system. Besides, the algorithm can be implemented distributedly with price information shared among neighboring cells. Considering the heavy feedback overhead from the users to the base stations, a simplified algorithm which considers only the major interference is also proposed. Simulation results show that when the inter-cell interference is serious, the proposed algorithms can effectively increase the transmission rate compared with iterative water-filling.

Relay Selection for Lifetime Extension in Amplify-And-Forward Cooperative Networks

Prolonging lifetime is of paramount importance for an energy-constrained wireless network to ensure uninterrupted information exchange. Cooperative communication technology, which can achieve high energy-efficiency by exploiting spatial diversity of distributed nodes, has become an attractive way for lifetime extension of wireless networks. In this paper, a novel relay selection method is developed for lifetime extension in an Amplify-and-Forward (AF) cooperative network where the transmission power is subject to a signal-to-noise ratio (SNR) requirement at the destination. In the proposed method firstly the average transmission power for every relay to forward the message is derived through the knowledge of channel statistics and then a utility function is designed to introduce it into the relay selection procedure so as to offer a relay more opportunity to be selected when its required transmission power is lower than usual. Simulation results show that the proposed method achieves improved performance in extending the lifetime by both reducing the average transmission power and lowering the residual battery energy.

High diversity downlink two-cell coordination with low backhaul load

In this study, the authors present a novel low backhaul load cooperative transmission framework for the two-cell multiple-input–single-output systems. In this framework, the neighbouring two base stations (BSs) take turns to transmit data in two consecutive slots. In each slot, only one BS is active, transmitting the preprocessed data symbols of both its own serving user and the cooperative user in neighbouring cell, and sharing its preprocessed data symbols to the other cooperative BS for next transmission. Linear constellation spreading is utilised for preprocessing which helps the system to exploit the macro-diversity without reducing the multiplexing gain. Besides, zero-forcing beamforming is applied in each transmission slot so as to cancel the multiuser interference. In this way, the inter-cell links become beneficial rather than detrimental. Pairwise error probability analysis demonstrates that the multi-cell spatial diversity gain can be achieved for each data stream. Both theoretical analysis and simulation results confirm that the proposed scheme outperforms the existing relevant strategies with less channel estimation overhead. It is shown that because of the higher diversity order it achieved, the proposed scheme can significantly improve the error performance in a distributed manner while maintaining the same multiplexing gain.

Distributed Space-Time Trellis Code for Asynchronous MIMO Relays over Frequency-Selective Channels

In most cooperative communications works, perfect synchronization among relay nodes is assumed. However, this assumption is not realistic due to the distributed nature of each relay node. In this paper, we consider the downlink in a MIMO cellular network utilizing two-hop transmission protocols with fixed infrastructure relay stations (RS) to enhance coverage and data rates. We propose a family of distributed space-time trellis code (DSTTC) for two RSs without the synchronization assumption. It is shown that the construction of the proposed DSTTCs is equivalent to using the generator matrices that have full row rank regardless of sub-matrices shifting problem, where a sub-matrix corresponds to the generator matrix of a RS under frequency-selective channels. Finally, various numerical examples are provided to verify the analytical studies.

Generalized anti-eavesdropping space-time network coding for cooperative communications

Physical (PHY) layer security has recently become a hot issue in wireless communication. In this paper, an approach to a generalized anti-eavesdropping space-time network coding (GAE-STNC) for cooperative communications is proposed to achieve the physical layer security and overcome the problem of imperfect synchronization while still guaranteeing full diversity. Based on the assumption of channel reciprocity, the basic idea is to exploit the channel state information (CSI) between the legitimate transmitters and the receiver, which is used to generate the secret key. With this secret key, the transmitters introduce pseudo random interferences by adding an anti-eavesdropping matrix to the initial system. Since the eavesdroppers channel is typically independent of the legitimate channel, the channel between the legitimate transmitters-receiver pair, the signal received by the eavesdropper is interfered. While the receiver can effectively decode the signal by utilizing the global CSI, the eavesdroppers can not decode the received signal correctly. Then, two specific schemes derived from the GAE-STNC are proposed. Numerical analysis and simulation results are presented to illustrate the proposed GAE-STNC schemes.

A hybrid clustering approach in Coordinated Multi-Point transmission system

Coordinated Multi-Point transmission technology which can improve cell edge spectral efficiency and meet the demand of high-speed transmission is one of the key technologies of LTE-Advanced. In this work, we propose a hybrid cell clustering approach in coordinated multi-point transmission system which is more efficient and practical. First, we divide a cell into three sectors: the intra-cell sector, the intra-cluster sector and the inter-cluster sector. Users in these three sectors are designed to utilize the non-coordinated approach, the static coordinated approach, and the dynamic coordinated approach, respectively. Second, we propose a method to identify the users type in order to choose the best coordinated approach. Finally, we give a resource scheduling method to suit the novel clustering approach. Simulations show that, compared with static clustering and dynamic clustering, our proposed hybrid clustering algorithm can achieve the highest cell edge spectral efficiency.

A low complexity heuristic adaptive resource llocation algorithm for multiuser OFDM under rate constraints

Power minimization problem under minimum rate constraint for each user is studied in this paper for multiuser OFDM systems. By thoroughly analyzing the necessary conditions for the optimum solution of the resource allocation problem, we deduce a heuristic Lagrange relaxation (LR) based resource allocation algorithm. Different from existing LR schemes which obtain Lagrange multipliers through exhaustive search, we use the estimations of the Lagrange multipliers to guide the resource allocation and then revise the estimations according to the allocation result. By repeating the process the algorithm can achieve a good resource allocation strategy with a low complexity. Numerical results show that the proposed low complexity algorithm offers comparable performance with the exhaustive search algorithm and outperforms existing low complexity algorithms.

Analysis and Design of Distributed Space-Time Trellis Code With Asynchronous Amplify-and-Forward Relaying

In this paper, we study the asynchronous cooperative diversity schemes employing the amplify-and-forward (AF) protocols over the frequency-selective channel. We consider three time-division-multiple-access (TDMA) based cooperation protocols and derive the corresponding pairwise error probabilities (PEP). From our analysis, it is seen that of the paths from the source to relays and from relays to the destination, those with smaller diversity order result in the bottleneck for the overall system performance. We propose a new type of the distributed space-time trellis code (DSTTC) that can achieve full diversity for the asynchronous transmission by utilizing a specifically designed generator matrix. The optimal DSTTCs with the minimum memory order are found by the exhaustive computer search. Finally, various numerical examples are provided to corroborate the analytical studies.

L1/2-Regularization Based Antenna Selection for RF-Chain Limited Massive MIMO Systems

Massive Multi-input Multi-output (MIMO) technique shows great potentials in improving energy and spectral efficiency while suffers high costs of the requirement for large amount of radio frequency (RF) chains. In this paper, we develop an