Cooperative Wireless Research Articles

Cooperation and distributed optimization for the unreliable wireless game with indirect reciprocity

Cooperation in packet forwarding among users and operators of a distributed wireless network has been widely studied.However, because of the limited computational resources, users in wireless communication do not prefer to cooperate with others unless cooperation may improve their own performance.Therefore, the key problem in cooperation enforcement must be solved first to enable a wireless network to be efficient.Yet, most of the existing game-theoretic cooperation stimulation approaches assume that the interactions between any pair of players (users) are long-lasting.In this paper, we apply game theory to optimize the communication efficiency of a distributed wireless network with finite number of interactions between any pair of players.Based on the mechanism of indirect reciprocity, we theoretically analyze the optimal action rule with the method of dynamic programming,and derive the approximate threshold of benefit-to-cost ratio to achieve the optimal action rule.Furthermore, we adopt the replicator dynamics to assess the evolutionary stability of the optimal action rule against the perturbation effect.Numerical illustrations verify the performance of the proposed method on wireless cooperation.

Outage analysis in two‐way communication with RF energy harvesting relay and co‐channel interference

AbstractThe study of relays with the scope of energy harvesting (EH) looks interesting as a means of enabling sustainable, wireless communication without the need to recharge or replace the battery driving the relays. However, the reliability of such communication systems becomes an important design challenge when such relays scavenge energy from the information bearing radio‐frequency signals received from the source, using the technique of simultaneous wireless information and power transfer (SWIPT). To this aim, this work studies bidirectional communication in a decode‐and‐forward (DF) relay–assisted cooperative wireless network in the presence of co‐channel interference (CCI). In order to quantify the reliability of the bidirectional communication systems, a closed‐form expression for the outage probability of the system is derived for both power splitting (PS) and time switching (TS) modes of operation of the relay. Simulation results are used to validate the accuracy of our analytical results and illustrate the dependence of the outage probability on various system parameters, like PS factor, TS factor and distance of the relay from both of the users. The results of performance comparison between PS relaying (PSR) and TS relaying (TSR) schemes are also presented. Besides, simulation results are also used to illustrate the spectral efficiency and the energy efficiency of the proposed system. The results show that, in terms of both spectral efficiency and energy efficiency, the two‐way communication system in the presence of moderate CCI power, performs better than the similar system without CCI. Additionally, it is also found that PSR is superior to TSR protocol in terms of peak energy efficiency.

Cooperative Jamming for Secure Communication With Finite Alphabet Inputs

This letter considers cooperative jamming to secure communication in the presence of multiple eavesdroppers with finite alphabet inputs. Considering the global constraint, the joint design of artificial noise covariance matrices and power allocation between the source and the relays is studied. Specifically, we transformed the problem of artificial noise design into a semi-definite programming problem, which is efficiently solved by standard optimization method. Besides, the power allocation between the source and relays is derived by utilizing the relationship between mutual information and minimum mean square error. Furthermore, a two-step algorithm is developed to enhance the achievable secrecy rate of cooperative jamming wireless network. Numerical examples demonstrate the proposed algorithm achieves a significant gain over the conventional counterparts in terms of secrecy rate.

POLYPHONY: Scheduling-Free Cooperative Signal Recovery in Enterprise Wireless Networks

Recent years have seen major innovations in cooperative wireless networks. Despite the fact that throughput gains have been achieved in packet recovery, hardly any of these technologies could effectively decode signals when the number of signal sources is greater than available antennas in each AP. Thus, conventional cooperative methods rely on adaptive scheduling for interference-free data packets. Deploying scheduling-free cooperative signal recovery requires prompt processing with low overheads. Yet potentially, the concurrent client transmissions could overwhelm any single AP, i.e., the number of concurrent transmissions are more than that of antennas. This paper presents the first step towards breaking this stalemate, by enabling symbol alignment and constellation reinforcement instead of relying on scheduling. We present POLYPHONY, a scheduling-free cooperative design, where decoding process could be coordinated without over-the-air scheduling, and coupled signals are decoded promptly after deep cooperations. We implement POLYPHONY prototype with GNURadio/USRP platform, and deploy it with a 16-node enterprise network. Particularly, we demonstrate how it manages the complex interactions with scheduling-free signal enforcement, and enables a beyond node-DoF (Degree of Freedom) decoding with AP coordinations. Furthermore, we show how the cooperative decoding process improves radio access among clients. Our results demonstrate a gain of nearly 200 percent for network throughput, which is a significant improvement for heavy contending networks.

A Stochastic Geometry Analysis of Large-Scale Cooperative Wireless Networks Powered by Energy Harvesting

Energy harvesting is an emerging technology for enabling green, sustainable, and autonomous wireless networks. In this paper, a large-scale wireless network with energy harvesting transmitters is considered, where a group of transmitters forms a cluster to cooperatively serve a desired receiver amid interference and noise. To characterize the link-level performance, closed-form expressions are derived for the transmission success probability at a receiver in terms of key parameters such as node densities, energy harvesting parameters, channel parameters, and cluster size, for a given cluster geometry. The analysis is further extended to characterize a network-level performance metric, capturing the tradeoff between link quality and the fraction of receivers served. Numerical simulations validate the accuracy of the analytical model. Several useful insights are provided. For example, while more cooperation helps improve the link-level performance, the network-level performance might degrade with the cluster size. Numerical results show that a small cluster size (typically 3 or smaller) optimizes the network-level performance. Furthermore, substantial performance can be extracted with a relatively small energy buffer. Moreover, the utility of having a large energy buffer increases with the energy harvesting rate as well as with the cluster size in sufficiently dense networks.

Network Coding for Video Distortion Reduction in Device-to-Device Communications

In this paper, we study the problem of distributing a real-time video sequence to a group of partially connected cooperative wireless devices using instantly decodable network coding (IDNC). In such a scenario, the coding conflicts occur to service multiple devices with an immediately decodable packet, and the transmission conflicts occur from simultaneous transmissions of multiple devices. To avoid these conflicts, we introduce a novel IDNC graph that represents all feasible coding and transmission conflict-free decisions in one unified framework. Moreover, a real-time video sequence has a hard deadline and unequal importance of video packets. Using these video characteristics and the new IDNC graph, we formulate the problem of minimizing the mean video distortion before the deadline as a finite horizon Markov decision process (MDP) problem. However, the backward induction algorithm that finds the optimal policy of the MDP formulation has high modeling and computational complexities. To reduce these complexities, we further design a two-stage maximal independent set selection algorithm, which can efficiently reduce the mean video distortion before the deadline. Simulation results over a real video sequence show that our proposed IDNC algorithms improve the received video quality compared with the existing IDNC algorithms.

A Multi-relay Cooperative Communication Using Space Time Spatial Phase Coding Based on OFDM

Among schemes to obtain diversity gain, space-time block code (STBC) and spatial phase coding (SPC) have been widely studied for the cooperative wireless relaying system. However, conventional STBC has a problem that cannot deal with change in the number of relays due to low throughput. In this paper, we propose a SPC that multi-relay transmission is possible and a space-time spatial phase coding (STSPC) using the proposed SPC scheme and STBC. The STSPC scheme provides improved bit error rate performance and full rate.

A queueing system for modeling cooperative wireless networks with coupled relay nodes and synchronized packet arrivals

In this work we analyze a novel queueing system for modeling cooperative wireless networks. We consider a network of three saturated source users, say a central and two background users, two relay nodes and a common destination node. When the central user fails to transmit a packet directly to the destination, it forwards a copy of the blocked packet at both relay nodes in order to exploit the spatial diversity they provide. Moreover, each relay node receives also blocked packets from a dedicated background user. Relay nodes assist source users by retransmitting their blocked packets to the destination. Due to the complex interdependence among relays, and the wireless interference, the retransmission rate of a relay is affected by the state of the other. We consider a three-dimensional Markov process, investigate its stability, and study its steady-state performance using the theory of boundary value problems. Explicit expressions for the expected delay in the symmetrical model, and a generalization to N>2 relay nodes are also given. Numerical examples are obtained and show insights into the system performance.

Auction-Based Pricing Schemes for Distributed Partner Selection in Cooperative Wireless Networks

In autonomous wireless networks, distributed and efficient partner selection is critical for fully realizing the benefits of cooperative communications. However, the selfish nodes in the networks bring catastrophe for partner selection when implementing cooperative transmissions. In order to stimulate cooperation and achieve distributed partner selection for such systems, an auction-based pricing scheme that considering efficiency and fairness is proposed in this paper. Two most prevalent auction forms, i.e., the second-price auction and the first-price auction, are both considered and analyzed in the single- and multiple-relay networks. In the single-relay scenario, the Nash equilibrium strategy for each auction is characterized, based on which the expected payoff and revenue for the source and relay are derived, respectively. Conclusions show that the same expected payoff is charged for the source with different auction schemes, and so is the expected revenue for the relay. Nonetheless, things are different in the multi-relay networks. With the linear 0–1 integer programming models, it is concluded that the first-price auction is more efficient than the second-price auction. Numerical results and analysis present that the proposed auction scheme efficiently solve the noncooperation issues of selfish nodes in autonomous wireless networks.

Relay Selection in Adaptive Buffer-Aided Space-Time Coding with TAS for Cooperative Wireless Networks

In this work, we propose an adaptive buffer-aided space-time coding scheme for cooperative wireless networks. A maximum likelihood receiver and adjustable code vectors are considered subject to a power constraint with an amplify-and forward cooperation strategy. Each relay is equipped with a buffer and is capable of storing the received symbols before forwarding them to the destination. We also present an adaptive relay selection and a new hybrid relay selection protocol, in which the instantaneous signal to noise ratio in each link is calculated and compared at the destination. The transmit antenna selection (TAS) is adopted at the destination where a single transmit antenna at the transmitter and relay that maximizes the instantaneous received signal-to-noise ratio is selected for further transmissions to improve the performance of co-operative network. A stochastic gradient algorithm is then developed to compute the parameters of the adjustable code vector with reduced computational complexity. Simulation results show that the proposed buffer-aided schemes with TAS obtain performance gains over existing schemes.

Optimization and Analysis of Wireless Powered Multi-Antenna Cooperative Systems

In this paper, we consider a three-node cooperative wireless powered communication system consisting of a multi-antenna hybrid access point (H-AP) and a single-antenna relay and a single-antenna user. The energy constrained relay and user first harvest energy in the downlink and then the relay assists the user using the harvested power for information transmission in the uplink. The optimal energy beamforming vector and the time split between harvest and cooperation are investigated. To reduce the computational complexity, suboptimal designs are also studied, where closed-form expressions are derived for the energy beamforming vector and the time split. For comparison purposes, we also present a detailed performance analysis in terms of the achievable outage probability and the average throughput of an intuitive energy beamforming scheme, where the H-AP directs all the energy towards the user. The findings of the paper suggest that implementing multiple antennas at the H-AP can significantly improve the system performance, and the closed-form suboptimal energy beamforming vector and time split yields near optimal performance. Also, for the intuitive beamforming scheme, a diversity order of N+1/2 can be achieved, where N is the number of antennas at the H-AP.

Power-Constrained Secrecy Rate Maximization for Joint Relay and Jammer Selection Assisted Wireless Networks

In this paper, we examine the physical layer security for cooperative wireless networks with multiple intermediate nodes, where the decode-and-forward protocol is considered. We propose a new joint relay and jammer selection (JRJS) scheme for protecting wireless communications against eavesdropping, where an intermediate node is selected as the relay for the sake of forwarding the source signal to the destination and meanwhile, the remaining intermediate nodes are employed to act as friendly jammers, which broadcast the artificial noise for disturbing the eavesdropper. We further investigate the power allocation among the source, relay and friendly jammers for maximizing the secrecy rate of proposed JRJS scheme, and derive a closed-form sub-optimal solution. Specifically, all the intermediate nodes, which successfully decode the source signal, are considered as relay candidates. For each candidate, we derive the sub-optimal closed-form power allocation solution and obtain the secrecy rate result of the corresponding JRJS scheme. Then, the candidate, which is capable of achieving the highest secrecy rate, is selected as the relay. Two assumptions about the channel state information (CSI), namely the full CSI (FCSI) and partial CSI (PCSI), are considered. Simulation results show that the proposed JRJS scheme outperforms the conventional pure relay selection, pure jamming, and generalized singular-value-decomposition-based beamforming schemes in terms of secrecy rate. Additionally, the proposed FCSI-based power allocation and PCSI-based power allocation schemes both achieve higher secrecy rates than the equal power allocation scheme.

OUTAGE ANALYSIS OF LOW-LATENCY COOPERATIVE WIRELESS NETWORKS WITH THRESHOLD-BASED PROTOCOL OVER COMPOSITE FADING

This paper studies a low-latency decode-and-forward cooperative wireless network subject to composite fading. Assuming temporally correlated channel between cooperating nodes and maximal ratio combining at the destination, outage probability (OP) performance is investigated and novel OP expressions are derived when nodes apply a threshold-based protocol for internode communication. The effects of network dimension, multipath fading and shadowing severity parameters, correlation coefficients and average uplink and internode signal-to-noise ratios on OP are discussed.

Study of Power Consumption in a Cooperative Wireless Network

A cooperative wireless network is defined to be a network where nodes cooperate in routing and/or improving thequality of transmission of each other’s packets [1]-[5]. Thecooperation is especially useful when the channel between a pair of nodes (source and destination) is in a deep shadow-fading state. In this situation increasing the power level may either not resolve the problem or be too power consuming, while generating interference for other receivers on the same channel. A cooperating node, which has good propagation channels to both the source and the destination, may be used to relay the packets between them. This paper presents the comparison of theaverage amounts of power consumed by nodes in a standard wireless network that uses single-hop transmission and a cooperative wireless network that uses two-hop transmission. It is shown that under certain conditions the ratio of the average power consumptions in the two networks, when N cooperating nodes on average are available for each node, can be approximated by k ln N + q. The constants k and q are related to the propagation channel. For a Nakagami fading channel with parameter m, k =1/ lnm and q=1, while for a shadowing channel with standard deviation σdB, k =σdB/ √ π and q = 0.23σdBdB.

Partner Selection Based on Optimal Power Allocation for Lifetime Maximization in Cooperative Networks

This paper investigates the joint partner selection and power allocation problem for two different network power management policies, i.e, group lifetime maximization (GLM) and minimum weighted total power (MWTP), with the aim of lifetime maximization in symbol error rate (SER)-constrained pairwise cooperative wireless networks. With the optimal power allocation solution derived according to each policy, we show that the optimal partner selection can be obtained using the bottleneck matching (BM) algorithm and the maximum weighted matching (MWM) algorithm for GLM and MWTP policies, respectively. Since partner selection with the BM algorithm is not power efficient, we propose a novel minimum BM (MBM) algorithm to solve the optimal partner selection problem for the GLM policy. We further propose a suboptimal partner selection (SPS) algorithm for these policies with lower time complexity, compared with the optimal partner selection schemes. Simulation results demonstrate that the proposed partner selection and power allocation strategies based on the GLM policy have better network lifetime performance over the strategies based on the MWTP policy and achieve significant network lifetime improvement over conventional strategies of minimizing the total power per transmission, with and without an equal power constraint. Compared to the MBM and SPS algorithms, partner selection based on the BM algorithm for the GLM policy has inferior network lifetime performance at a low update interval. We show that partner selection based on the MBM algorithm achieves maximum network lifetime performance and that partner selection with the SPS algorithm performs very close to it.

A Cooperative Wireless Sensor Network for Indoor Industrial Monitoring

Industrial wireless sensor networks are getting popular for indoor monitoring of heavy machinery and large factories to make a reliable decision on the state of machines in a certain area of interest. However, the indoor wireless communication channel is not always reliable, and observations of some sensors cannot be reported successfully to the base station. In order to deal with this problem, we propose a cooperative WSN scheme by introducing a novel cooperation mechanism and a medium access control protocol. The proposed scheme effectively increases the probability of correct decision about the state of the machine, reduces the probability of false alarms at a given signal level, and reduces the overall energy consumption as compared to noncooperative schemes. We also present a closed-form expression for the symbol-error rate analysis of the proposed scheme, which shows that our proposed scheme achieves full diversity order offered by the cooperation scheme.

SRT analysis of relay selection in the presence of multiple co‐channel interferers

In this study, a cooperative wireless network is studied based on physical-layer security, where multiple co-channel interferers exist at relays, the destination and eavesdropper. Under the influence of multiple co-channel interferers, the tradeoff between the security and reliability of wireless communications against eavesdropping attacks is analysed in terms of the intercept probability (IP) and the outage probability (OP). The exact closed-form expressions for the IP and OP are derived for the direct transmission (DT) and the relay selection (RS) schemes over Rayleigh fading channels. The theoretical analysis is validated by numerical results. It is shown that the increase of the number of relays and (or) the number of co-channel interferers can efficiently improve the security-reliability tradeoff (SRT). Moreover, the RS strategy can achieve a higher SRT performance compared with the DT strategy.

New Trends in Wireless LAN and Cooperative Wireless LAN Technology

New Trends in Wireless LAN and Cooperative Wireless LAN Technology

Adaptive Secure Transmission for Physical Layer Security in Cooperative Wireless Networks

We investigate the physical layer security in cooperative wireless networks where a source (Alice) transmits a confidential message to a destination (Bob) with the help of a cooperative node (Charlie), in the presence of an eavesdropper (Eve). Cooperative transmission is explored to secure communication between Alice and Bob, while ensuring the desired quality of service (QoS) at Charlie’s receiver. We provide a transmit design for outage constrained secrecy rate maximization, taking both security and QoS constraints into account. Unlike the conventional cooperative security that adopts a fixed transmission scheme, we propose a mechanism for transmit strategy adaptation with security protection. Specifically, the proposed cooperative transmission is replaced by a cooperative jamming scheme if either security or QoS constraint is not satisfied. Numerical results confirm that our design enables dynamic transmission, and thus is flexible and environment-adaptive.

Finite-SNR Diversity-Multiplexing Tradeoff for Network Coded Cooperative OFDMA Systems

Network-coded cooperation (NCC) is an effective method to improve the throughput efficiency in cooperative wireless networks. The combined use of orthogonal frequency division multiplexing (OFDM) with NCC has been further studied in the literature to exploit the multipath diversity gains. In this paper, we consider orthogonal frequency division multiple access (OFDMA), an extension of OFDM to a multiuser system where subsets of carriers are assigned to different users. We first derive a closed-form expression for the outage probability of NCC-OFDMA over Rician fading channels and then present the asymptotical and finite-SNR DMT expressions. Our results provide insight into the performance mechanisms under practical SNR regime of NCC-OFDMA systems and demonstrate that NCC-OFDMA is able to fully exploit both frequency and spatial diversity. We also show that the derived finite-SNR DMT converges to an asymptotical one as expected. Furthermore, special cases for our derived analytical expressions are presented, to show that the derived expression is a generalized case of the related the state of the art results. Simulation results are further presented to verify our theoretical analyses.