Network Coded Cooperation System Research Articles

Network-Coded Cooperative Systems in Cognitive Radio Networks

We study the performance of a network-coded cooperative (NCC) system in an underlay cognitive radio network (CRN). The primary network (PN) consists of a single transmitter-receiver pair, and the secondary network (SN) is an NCC system with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> users, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> relays, and a single destination. The relays employ decode-and-forward (DF) protocol and use network coding (NC). We study the performance of the SN under two types of power constraints: i) the combined peak interference power constraint on the PN and maximum transmit power constraint at the SN; and ii) the single peak interference power constraint on the PN. For the SN, an exact closed-form expression and an asymptotically tight end-to-end outage probability are derived, and the diversity order and coding gain are quantified. Compared to the existing literature, the proposed CRN NCC has four main distinguishable features: i) it applies to general CRN NCC network settings with an arbitrary number of users and relays; ii) it considers general relay selection mechanism and independent and non-identically distributed (i.n.i.d.) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Nakagami-m$ </tex-math></inline-formula> fading channels; iii) it assumes secondary-to-primary and primary-to-secondary interference links; and iv) it provides a generalization of previous work and includes existing results in the literature as special cases.

Network-Coded Cooperative Systems With Generalized User-Relay Selection

We consider a network-coded cooperative (NCC) system that consists of N ≥ 2 sources, M ≥ 1 decode- and-forward (DF) relays, and a single destination. The relays perform network coding (NC) on the received sources' symbols using maximum distance separable (MDS) codes. For this system, we propose the most generalized user-relay selection (GURS) scheme in the literature that selects any arbitrary subsets of K users and any arbitrary subsets of L relays subject to practical constraints such as load balancing conditions and scheduling policy. Our analytical results and design guidelines generalize and subsume all existing results as special cases. To this end, we derive a new closed-form outage probability (OP) expression, assuming non-identically and independently distributed (n.i.i.d.) Rayleigh fading channels. The asymptotic outage expression at high signal-to-noise ratio (SNR) regime is further derived, based on which, the achievable diversity order and coding gain are quantified. The theoretical derivations are also validated through Monte-Carlo simulation.

Energy-Efficiency of Selective Relaying in a MIMO Network-Coded Cooperative System

We evaluate the outage probability and the energy efficiency (EE) of a network composed of multiple sources, multiple relays and a single common destination, all of them provided with multiple antennas. More specifically, we resort to the network-coded cooperative (NCC) technique with multiple relay selection (MRS) and compare the EE of the network when operating under two combining techniques at the receiver, namely selection combining (SC) and maximum ratio combining (MRC). Our analysis, which adopts a realistic energy consumption model that encompasses the circuitry consumption, shows that MRC, which is optimal from the reliability perspective, may be outperformed by SC in terms of EE. Moreover, we also provide some insights about the number of relays that must be selected to maximize the EE. Finally, numerical results are presented and confirm the mathematical analysis.

Multiple relay‐based Reed–Muller network‐coded cooperation for wireless communication system

This research article proposes a multiple relay-based Reed–Muller network-coded cooperative (MR-RMNCC) scheme for wireless communication. In the MR-RMNCC scheme, Hadamard transform construction is adopted to build Reed–Muller (RM) codes that effectively achieve network coded-cooperation among multiple sources and multiple relays over slow and fast Rayleigh fading channels. In any network coded-cooperative system, a proper encoding strategy at the relay nodes is vital for achieving an optimum code construction at the destination node. Therefore, the authors have proposed an efficient message bit selection algorithm at relay-2 that optimally selects the message bits. The supremacy of the message bit selection algorithm is demonstrated by Monte–Carlo simulation. Furthermore, the performance bound for average error-probability is also derived for the MR-RMNCC scheme that validates its simulated bit-error-rate performance over a fast Rayleigh fading channel. At the destination node, the MR-RMNCC scheme is jointly decoded by two different decoding strategies, i.e. joint soft maximum likelihood decoding and joint majority logic decoding. Monte–Carlo simulations suggest that the MR-RMNCC scheme not only provides a significant bit-error-rate performance gain over its corresponding coded non-cooperative scheme but also to the existing state-of-the-art RM network-coded cooperative scheme under identical conditions.

Relay Selection in Network-Coded Cooperative MIMO Systems

Network-coded cooperation (NCC) has recently gained interest as it improves the network throughput in multi-source cooperative systems. NCC has been studied for single-antenna terminals only. Employing multiple-input multiple-output (MIMO) techniques can significantly improve the performance of NCC systems. Furthermore, the existing relay selection (RS) strategies for NCC utilize the “max-min” end-to-end (E2E) criterion. This selection strategy (called Strategy $\mathcal {A}$ ) is complicated even for a network with single-antenna terminals as it requires global channel state information (CSI). This requirement makes it hard to implement RS-based NCC. To counter this issue, we introduce a new RS strategy (Strategy $\mathcal {B}$ ), which utilizes only the local CSI (not global CSI), significantly reducing the signaling overhead without sacrificing the performance. The performance of MIMO-NCC under Strategies $\mathcal {A}$ and $\mathcal {B}$ is studied over independent and non-identically distributed (i.n.i.d.) Rayleigh fading channels. Relays and the destination are equipped with multiple antennas, whereas sources have a single antenna. The exact outage probability expressions of the system under consideration are derived. The asymptotic outage expressions are further provided to obtain valuable insights into the practical system-design parameters such as the diversity order and coding gain. Furthermore, numerical results are provided in support of the analytical results.

Multiuser Diversity in Network-Coded Cooperation: Outage and Diversity Analysis

In this letter, we study multiuser diversity (MUD) in network-coded cooperation (NCC) systems. Specifically, we propose a two-step user-relay selection mechanism that selects subsets of users and relays to exploit both MUD and cooperative diversity in a multiuser multirelay NCC system. Assuming independent but not necessarily identically distributed Rayleigh fading channels, we derive closed-form expressions for the system outage probability. We further obtain asymptotic outage expressions to quantify the diversity order as a function of different system parameters. Our results demonstrate the superiority (diversity gains) of the proposed MUD-based NCC compared with NCC schemes without MUD. Monte-Carlo simulations are also presented to verify the accuracy of our theoretical findings.

Optimal Power Allocation for Multi-User Linear Network Coded Cooperation System

Linear network coded cooperation (LNCC), which deeply integrates cooperative communications and linear network coding, has been proposed to increase spectrum efficiency in wireless communications. However, the issue of optimal power allocation (OPA) for multi-user LNCC systems still remains open. This paper studies the OPA problems for a multi-user two-slot LNCC system which works in a many-to-one pattern. We first analyze and present the tight approximation of the outage probability of the multi-user LNCC system by fully considering the effect of path loss, the effectiveness of which is validated by Monte Carlo simulations. On the basis of the theoretical analyses on outage performance, we further investigate the OPA strategies for multi-user LNCC systems. Two OPA strategies under different optimization criteria, i.e., minimizing the total outage probability and jointly minimizing the outage probabilities for each user under the constraint of total power available, are proposed by utilizing genetic algorithms. To the best of our best knowledge, this is the first work on OPA for multi-user LNCC systems. Numerical results demonstrate that the proposed OPA strategies do achieve the OPA and improve the system’s performance.

Generalized Relay Selection for Network-Coded Cooperation Systems

We investigate the outage probability and diversity gain of generalized relay selection (GRS) for network-coded cooperation systems where ${N}$ sources use ${M}$ relays to communicate with a single destination. Although it is common to select a set of the relays with the highest signal-to-noise ratios (SNRs), reasons such as load balancing, scheduling, and others may force the selection of different relays. Thus, it is important to quantify and analyze the performance of any arbitrary selection of ${L}$ relays out of ${M}$ (also known as GRS). We show that the full diversity gain of ${d={M}+1}$ is only persevered when ${L} \ge {N}$ and the set of selected relays includes ${N}$ highest SNR relays.

A tutorial on network coded cooperation

Network Coding (NC) can significantly help increase the efficient use of network resources. However, directly applying NC to wireless networks is not an effective design solution. Wireless channels are prone to bit errors due to fading, possibly generating erroneous decisions at the relay nodes while applying NC. Furthermore, the broadcast nature of wireless channels may provide a direct communication link between source and destination nodes. In order to combat fading channel impairments, and also to exploit the inherent spatial diversity provided through the direct link, network coded cooperation (NCC) techniques should be incorporated to the NC systems for wireless networks. This tutorial provides an overview of the state-of-the-art in the NCC systems, combining the powerful tools of NC and cooperative communication, in order to increase data transmission rates and robustness of multiple source wireless networks.

Energy Consumption in Network-coded Cooperation System with Feedback Method of Base Station

For the case of low energy efficiency in network coding cooperative system, a feedback method of the base station is presented, At the end of the first slot, the feedback information from the Base Station (BS) is used to perform opportunistic network coding. Simulation results reveal that in the two user network coding cooperative system, the proportion of energy saved can be almost fifty percent with no increment to the system outage probability.

Energy Efficiency of Network Coded Cooperative Communications in Nakagami-$m$ Fading

In this letter, we evaluate the energy efficiency of a wireless network-coded cooperative system where multiple nodes cooperatively transmit their information to a common destination. The energy consumption of the transmission and reception circuits is taken into account. It is shown that network coding can provide significant energy savings compared to direct transmission and traditional cooperation techniques. We consider a Nakagami- m fading model, so that the influence of a line-of-sight is also investigated. The optimal number of users that minimizes the energy consumption is obtained analytically, and confirmed by numerical results. Using this number to organize the nodes in clusters can provide considerable energy savings and decrease the network encoding/decoding complexity.

Delay Statistics for ARQ Protocols over Network-Coded Cooperative Networks

This paper presents a queuing analysis method for automatic repeat request (ARQ) in network-coded cooperative transmission networks with dynamic radio link adaptation. An equivalent Nakagami-m channel model is derived for the network-coded cooperative system and a Finite State Markov Chain (FSMC) is modeled for conducting queuing analysis of packet transmission. Finally, the matrix geometry method is used to get the steady state probability distribution and delay statistics. Numerical results show that as the network coding method reduces the feedback delay, the corresponding total delay has a relatively decrease.

Joint Optimal Threshold-Based Relaying and ML Detection in Network-Coded Two-Way Relay Channels

In this paper, we address the problem of joint optimal threshold-based relaying and maximum likelihood (ML) detection in network-coded cooperative systems. The purpose of using threshold-based relaying is to circumvent the impact of error propagation, which could lead to degrading the system diversity. For simplicity, we consider a simple network comprising two source nodes and one relay node. The relay operates in the decode-and-forward (DF) mode and employs binary network coding. The communication between the two source nodes is bidirectional, resulting in a two-way relay channel. We assume binary phase shift keying (BPSK) signaling. For a given log-likelihood ratio (LLR)-based threshold used at the relay, we derive the ML detector at the destination assuming that the destination has full knowledge of the locations of the blocked bits at the relay. We then derive an expression for the corresponding end-to-end (E2E) bit error rate (BER) performance, which is used to find the optimal threshold. We also derive two practical discontinuous transmission detectors at the destination for the purpose of identifying whether the relay is forwarding or not. The performance of one of the detectors is similar to that when the destination knows the locations of the blocked bits, whereas the performance of the other detector suffers some performance degradation. We present several numerical examples that illustrate the efficacy of the proposed scheme as compared to existing schemes.

On Relay Assignment in Network-Coded Cooperative Systems

We consider in this paper relay assignment for cooperative systems with multiple two-way relay channels. The nodes corresponding to one two-way relay channel (henceforth referred to as pair) communicate with each other through a relay. The relays use network coding to simultaneously transmit the signals corresponding to the pairs they are assigned to. We propose two relay assignment schemes. One scheme considers all possible relay assignment permutations and selects the one that yields the best performance, and the other one considers only a subset of these permutations and selects the best one. The advantage of the latter is that it results in a significant reduction in computational complexity, in addition to making the analysis more tractable. We analyze the performance of these schemes over asymmetric independent Rayleigh fading channels. We also consider semi-symmetric and symmetric channels as special cases. We derive closed-form expressions for the end-to-end bit error rate performance for all scenarios and show that the full diversity order is achieved, which is the number of available relays. We present several examples to verify the theoretical results.