Multi-source Multi-relay Networks Research Articles

A Tutorial on Lossy Forwarding Cooperative Relaying

Lossy decode-and-forward (DF) relaying, also referred to as lossy forwarding (LF), can significantly enhance the transmission reliability and expand the communication coverage at the cost of a small increase in computational effort compared to its DF counterpart. Furthermore, it can further simplify the operations at the relay nodes by removing the error-detecting operation, e.g., cyclic redundancy check, which is used in the conventional DF systems. Due to these advantages, LF has been intensively investigated with the aim of its applications to various cooperative communication networks with different topologies. This paper offers a comprehensive literature review on the LF relaying strategy and makes comparisons between LF and DF. Five basic exemplifying scenarios are taken into consideration. These are the three-node network, the single-source multi-relay network with direct source-to-destination link, the multiple access relay channel, the two-way relay network, and the general multi-source multi-relay network. The paper includes not only theoretical performance limit analyses, but also performance evaluation by employing low-complexity accumulator aided turbo codes at the sources and relays as well as joint decoding at the destination. As expected, the performance enhancement in terms of outage probability, frame error rate, and $ {\epsilon }$ -outage achievable rate by LF over DF is significant, which is demonstrated in all the exemplifying scenarios in the literatures. Hence LF has a great potential to be applied to future 5G wireless communication networks, e.g., device-to-device, vehicle-to-vehicle, and machine-type communications, which are composed of the aforementioned exemplifying scenarios.

A Design of Overlapped Chunked Code over Compute-and-Forward for Multi-Source Multi-Relay Networks.

This paper investigates the design of overlapped chunked codes (OCC) for multi-source multi-relay networks where a physical-layer network coding approach, compute-and-forward (CF) based on nested lattice codes (NLC), is applied for the simultaneous transmissions from the sources to the relays. This code is called OCC/CF. In this paper, OCC is applied before NLC before transmitting for each source. Random linear network coding is applied within each chunk. A decodability condition to design OCC/CF is provided. In addition, an OCC with a contiguously overlapping, but non-rounded-end fashion is employed for the design, which is done by using the probability distributions of the number of innovative codeword combinations and the probability distribution of the participation factor of each source to the codeword combinations received for a chunk transmission. An estimation is done to select an allocation, i.e., the number of innovative blocks per chunk and the number of blocks taken from the previous chunk for all sources, that is expected to provide the desired performance. From the numerical results, the design overhead of OCC/CF is low when the probability distribution of the participation factor of each source is dense at the chunk size for each source.

Improved Bounds on the Decoding Failure Probability of Network Coding Over Multi-Source Multi-Relay Networks

This paper considers a multi-source multi-relay network, in which relay nodes employ a coding scheme based on random linear network coding on source packets and generate coded packets. If a destination node collects enough coded packets, it can recover the packets of all source nodes. The links between source-to-relay nodes and relay-to-destination nodes are modeled as packet erasure channels. Improved bounds on the probability of decoding failure are presented, which are markedly close to simulation results and notably better than previous bounds. Examples demonstrate the tightness and usefulness of the new bounds over the old bounds.

Low-Complexity Compute-and-Forward Techniques for Multisource Multirelay Networks

Compute-and-forward (CF this method is referred to as “blind C&F” and an algorithm is proposed which guarantees that each relay chooses the best integer vector that contains information from at least m source nodes. In the second algorithm that is described as “partially coordinated C&F,” we assume that partial cooperation between the relay nodes and propose to exchange a single variable with which the relays are sorted for transmission. The performance of the proposed algorithm is nearly equivalent with optimal relaying, which requires significant overhead signaling.

Blind Compute-and-Forward

Compute-and-forward (C&F) is a promising new approach to interference management, enjoying several advantages over other information-theoretic schemes. C&F usually requires channel state information (CSI) at the receivers so that an “optimal” scaling factor can be computed for the purposes of decoding. In this paper, a blind C&F scheme—i.e., one not requiring CSI—is developed. Rather than attempting to compute the optimal scaling factor, this new scheme seeks one or more “good” scalars, i.e., scalars that allow correct decoding despite possibly being suboptimal. The region of all such good scalars is characterized. To find a good scalar, a computationally efficient scheme is proposed which involves error-detection, a hierarchically organized list, as well as a use of the smoothing lemma from lattice theory. Simulation results show that our blind C&F scheme achieves—for a class of nested lattice codes—the same throughput as its CSI-enabled counterpart at the expense of, approximately, a two-fold increase in computational complexity in the high-throughput region. Moreover, our blind C&F scheme can be applied to multisource multirelay networks with a good performance/complexity tradeoff.

Compute-and-Forward: Optimization Over Multisource–Multirelay Networks

In this paper, we investigate a multisource multicast network with the aid of an arbitrary number of relays, where it is assumed that no direct link is available at each S-D pair. The aim is to find the fundamental limit on the maximal common multicast throughput of all source nodes if resource allocations are available. A transmission protocol employing the relaying strategy, i.e., compute-and-forward (CPF), is proposed. We also adjust the methods in the literature to obtain the integer network-constructed coefficient matrix (i.e., a naive method, a local optimal method, and a global optimal method) to fit the general topology with an arbitrary number of relays. Three transmission scenarios are addressed. The first scenario is delay-stringent transmission, where each message must be delivered within one slot. The second scenario is delay-tolerant transmission where no delay constraint is imposed. The associated optimization problems to maximize the short- and long-term common multicast throughputs are formulated and solved, and the optimal allocation of power and time slots are presented. The third case (a general $N$ -slot-delay-tolerant scenario) is also discussed, and a suboptimal algorithm is presented. Performance comparisons show that the CPF strategy outperforms conventional decode-and-forward (DF) strategy. It is also shown in the simulation that with more relays, the CPF strategy performs even better due to the increased diversity. Finally, by simulation, it is observed that, with CPF, the $N$ -slot-delay-constraint case can perform close to that of the delay-tolerant case in terms of throughput, given that $N$ is relatively large.

Cooperative Power Allocation Based on Multi-Objective Intelligent Optimization for Multi-Source Multi-Relay Networks

Cooperative Power Allocation Based on Multi-Objective Intelligent Optimization for Multi-Source Multi-Relay Networks

Combining cooperative diversity and network coding in uplink multi-source multi-relay networks

In this paper, a new scheme of combining cooperative diversity with network coding is proposed for wireless uplink multi-source multi-relay networks. The existing network-coded cooperative scheme always conducts network coding operation at relays in moderate-to-high signal-to-noise ratio region. Distinct from it, the proposed scheme determines either a direct cooperative mode or a network-coded cooperative mode at relays according to the channel qualities of the broadcast phase. Compared with the existing network-coded cooperative scheme, the proposed scheme achieves a performance gain in terms of both diversity order and system ergodic capacity without extra bandwidth resource consumption. Both theoretical analysis and simulations verify the validity and superiority of the proposed cooperative scheme.

Performance analysis of multi‐source multi‐relay wireless networks with co‐channel interference

The performance of multi-source multi-relay wireless networks based on a joint source-relay-selection scheme is investigated over Rayleigh interference-limited fading channels. The tight lower bound and asymptotic expressions for the outage probability are derived and the diversity order of the system with/without co-channel interference is further discussed. Simulation results are presented to demonstrate the validity of the theoretical analysis.

Combining Cooperative Diversity and Multiuser Diversity: A Fair Scheduling Scheme for Multi-Source Multi-Relay Networks

In this letter, we propose a round-robin (RR) based fair scheduling scheme (RRFS) to achieve both cooperative diversity (CD) and multiuser diversity (MUD) in multi-source, multi-relay amplify-and-forward (AF) cooperative networks. Different from traditional schemes in multiuser scenarios which only allow the best source to transmit and cause transmission unfairness, all the sources transmit in a RR fashion first in RRFS. In order to achieve both kinds of diversity in the relay phase, we then exploit a joint source-relay selection strategy which selects the best relay to help the worst source's transmission in each relay time slot. Therefore, RRFS brings MUD benefit to cooperation communication systems while maintaining transmission fairness.

Diversity Exploitation in Multi-Source Cooperations with Multiple Antennas at the Destination

In amplify-and-forward (AF) based multi-source multi-relay cooperative networks, system diversity will be restricted by the channels of the forwarding hop in the absence of direct source-destination links in Rayleigh fading. In this letter, we dedicate to solve this bottleneck by deploying multiple antennas at the destination. By analyzing the outage bounds and diversity order of the system, we make a conclusion that both forms of diversity, cooperative diversity and multiuser diversity, can be fully exploited when the number of antennas is not less than the number of sources.

On the Combination of Cooperative Diversity and Multiuser Diversity in Multi-Source Multi-Relay Wireless Networks

This letter presents an analysis of the combined use of cooperative diversity and multiuser diversity (MUD) in multi-source multi-relay networks. A joint selection scheme, which selects the best source-relay pair to access the channel, is proposed. The main contribution of our work is the derivation of the exact and asymptotic expressions for the outage probability of the system with amplify-and-forward (AF) protocol. From these expressions it is indicated that the total diversity order of M +N can be achieved, where M and N are the number of source nodes and relay nodes, respectively. Based on the outage probability in high signal-to-noise-ratio (SNR) region, the optimum power allocation scheme is also given to improve the system performance.

A comprehensive study of repetition-coded protocols in multi-user multi-relay networks

The diversity-multiplexing tradeoff (DMT) performances of novel decode-and-forward (DF) relaying protocols for multi-source multi-relay cooperative networks are studied in this paper. For a strong-interference scenario and an isolated-relay scenario, the proposed protocols significantly improve diversity performance over direct source-destination transmissions by using a simple repetition coding strategy in relays. This is in addition to enhancing the multiplexing performance over standard DF protocols, which usually suffer from the half-duplex limitation at relays. Although the DMT performance of DF based relaying protocols is limited by the quality of source relay links in principle, adaptive forms of the proposed protocols at the relays can transmit/not transmit according to source relay transmissions and still provide link reliability and spectral efficiency advantages in general source-relay channel conditions.