Mingjun Dai

Linear Network Coding Strategies for the Multiple Access Relay Channel with Packet Erasures

The multiple access relay channel (MARC) where multiple users send independent information to a single destination aided by a single relay under large-scale path loss and slow fading is investigated. At the beginning, the users take turns to transmit their packets. The relay is not aware of the erasure status of each packet at the destination but has the knowledge of the average signal-to-noise-ratio (SNR) of every communication link. With this knowledge, the relay applies network coded retransmission on the overheard packets so as to maximize the expected total number of recovered packets or minimize the average packet loss rate at the destination. Several network coding (NC) strategies at the relay are designed. In particular, for the case where the relay is given only one time slot for retransmission, an optimal NC construction is derived. For the multiple-slot case, three sub-optimal schemes are investigated, namely network coding with maximum distance separable (MDS) code (NC-MDS), the worst-user-first (WUF) scheme and a hybrid of NC-MDS and WUF. We prove that NC-MDS and WUF are asymptotically optimal in the high and low SNR regimes, respectively. A lower bound on the average packet loss rate has been derived. Numerical studies show that, in a cellular system, the hybrid scheme offers significant performance gain over a number of existing schemes in a wide range of SNR. We also observe that performance curves of both WUF and the hybrid scheme touch the derived lower bound in the low SNR regime.

Survey on cooperative strategies for wireless relay channels

Cooperative communication has the potential of providing better throughput and reliability to wireless systems when compared with direct communication. To realise the potential gain, it is important to design cooperative strategies for some representative scenarios. This survey deals with three basic wireless relay channels, namely, the parallel relay channel, the multiple-access relay channel and the broadcast relay channel. For the first channel, which models a single unicast connection, various forwarding strategies are studied. For the second and third channels, which model, respectively, the uplink and downlink scenarios with multiple unicast connections; network codes that exploit the possibility of coding among the connections are studied. The common aim pertaining to the studies of all these three channels is to use the limited radio resource in the most efficient way. Beside the aforementioned conventional works, studies that have state-of-the-art assumptions for relay networks, including outdated channel state information at the transmitter, full duplex relay and practical rateless-coded cooperation, are also extensively reviewed. Copyright

Data Dissemination With Side Information and Feedback

Index coding (IC), which can be regarded as a special class of network coding, deals with the problem of sending a number of packets to a group of receivers, each of which requests one packet and may have some other packets in its cache. This paper generalizes the IC problem in that both the packet requested by a receiver and the packets in its cache can be linear combinations of the packets. To minimize the number of transmissions required, a heuristic algorithm based on the idea of partitioning the users into coding groups is designed. To realize this idea, a polynomial time algorithm to determine whether a set of users form a coding group over the binary field or a field with a size larger than the number of users is constructed. For users that form a coding group, the corresponding encoding vector can be also found. A lower bound is derived in order to evaluate the performance of the heuristic algorithm. Numerical results show that the number of transmissions required by the heuristic algorithm and the lower bound both grow roughly linearly with the number of users, and the heuristic algorithm outperforms some benchmark algorithms.

Achieving high diversity and multiplexing gains in the asynchronous parallel relay network

A single source-destination pair communicating via a layer of parallel relay nodes under quasi-static slow fading environment is investigated. The time delays from the source to the destination via different relays are assumed to be different. For such an asynchronous environment, a new transmission scheme is constructed so as to achieve better diversity-multiplexing tradeoff (DMT). More specifically, both the source and the destination adopts orthogonal frequency division multiplexing technique to solve the asynchronous problem; the relays cooperatively apply the distributed generalised complex orthogonal design, a form of orthogonal space–time coding, for high-rate transmission. Each relay is assumed to use the adaptive amplify-and-forward relaying strategy. To optimise its outage performance, a distributed on-off power control rule applied to the relays is analytically derived and is proved to yield full spatial diversity order. Compared with an existing protocol, our proposed scheme is shown to achieve the same DMT when there are four relay nodes and better DMT when there are more. Besides, the DMT gap between our scheme and the existing one increases with the number of relay nodes. Copyright

Broadcasting with coded side information

In the original index coding problem, each user has a set of uncoded packets as side information, and wants to decode some other packets from the source node. The source node aims at satisfying the demands of all users as quickly as possible. With linear network coding, this is accomplished by broadcasting linear combinations of the source packets over some finite field. Since the broadcast is performed over a wireless channel, a user may overhear some coded packets that are not intended to him/her. This motivates a generalization of the index coding problem to the case where linearly coded packets are used as side information. We show that this generalized linear index coding problem is equivalent to solving a system of multi-variable polynomial equations. A heuristic solution is constructed and is applied to the broadcast relay channel.

Diamond relay network under Rayleigh fading: On-off power control and outage-capacity bound

The achievable outage probability of the diamond relay network under Rayleigh fading is investigated. Two existing transmission protocols are considered, namely, the Alamouti-Coded Amplify-and-Forward (ACAF) and the Alamouti-Coded Decode-and-Forward (ACDF). For ACAF, a distributed optimal power control rule for the two relays is analytically derived. Simulation results show that with this power control rule, the diversity gain of ACAF increases from one to two, and its performance approaches that of ACDF in the high signal-to-noise ratio (SNR) regime. For ACDF, a performance bound is analytically obtained: for any outage probability e, its SNR offset is bounded above by 3 dB and its e-outage rate is within 1 bit of the e-outage capacity of the diamond relay network.

A distributed on-off amplify-and-forward protocol for the fading parallel relay channel

A single source-destination pair communicating via a layer of two parallel relay nodes under slow fading is considered. The bit error rate (BER) performance of Alamouti-Coded Amplify-and-Forward (ACAF) transmission protocol under different power control strategies is investigated. The optimal power control rule is analytically derived and two distributed approximations to this rule are proposed. The optimal rule reveals an interesting fact: The transmission of each relay is on-off in nature. Simulation results show that our proposed distributed approximations improve the BER performance significantly.

Distributed Beamforming in MISO SWIPT System

In previous works on simultaneous wireless information and power transfer (SWIPT) multiple-input single-output (MISO) system with multiple users, beamforming requires all the transmitters know the channel state information (CSI) of the whole system. We relax it so that it is a practical assumption: Each transmitter only knows its own CSI to all the receivers, combined with individual power constraints at transmitters and signal-to-interference-plus-noise ratio (SINR) constraints at information receivers. The objective is to maximize the total harvested energy at the energy receivers. An improved version of the alternating direction method of multipliers is proposed. In particular, we split an optimization problem with nonconvex constraints into iterations of several singular value decomposition (SVD) problems and prove the convergence. Simulation results show that our algorithm achieves less computational complexity and control channel budget with acceptable performance degradation when compared with a centralized solution.

Achieving the Outage Capacity of the Diamond Relay Network to Within One Bit and Even Less

A new forwarding strategy is proposed for the wireless diamond relay network under slow fading. The key feature is that it can adaptively switch between decode-forward and compress-forward according to the instantaneous received signal strength. It has four control parameters, which can be optimized by an alternating optimization procedure. Its outage performance is compared with two lower bounds. Analytically, it is proven to achieve the outage capacity to within 1 bit and within 50% for any signal-to-noise ratio (SNR). Empirically, it is shown to be nearly optimal for some fading scenarios.

Incorporating D2D to Current Cellular Communication System

A device-to-device (D2D) group works as relay nodes to aid the information delivery from a source to a destination in cellular communication network. Within this system, we propose a communication mechanism to aid traditional cellular communication and correspondingly borrow some channel resource from traditional cellular communication system for D2D communication. On one side, to aid cellular communication, we propose a modified Alamouti scheme which does not modify the operation at the base station. This makes our proposed scheme consistent with previous cellular communication system. On the other side, there are many competitive D2D groups that want to potentially utilize the borrowed channel resource from traditional cellular system for delivering their own information. We model this competition as a game and utilize game theory technique to solve this competition problem.