A channel estimation based opportunistic scheduling scheme in wireless bidirectional networks

The applicability of analog network coding (ANC) to a wireless network is constrained by several limitations: 1) some ANC schemes demand fine-grained frame-level synchronization, which cannot be practically achieved in a wireless network; 2) others support only a specific type of modulation or require equal frame size in concurrent transmissions. In this paper, a new ANC scheme, called restriction-free analog network coding (RANC), is developed to eliminate the above limitations. It incorporates several function blocks, including frame boundary detection, joint channel estimation, waveform recovery, circular channel estimation, and frequency offset estimation, to support random concurrent transmissions with arbitrary frame sizes in a wireless network with various linear modulation schemes. To demonstrate the distinguished features of RANC, two network applications are studied. In the first application, RANC is applied to support a new relaying scheme called multi-way relaying, which significantly improves the spectrum efficiency as compared to two-way relaying. In the second application, RANC enables random-access-based ANC in an ad hoc network where flow compensation can be gracefully exploited to further improve the throughput performance. RANC and its network applications are implemented and evaluated on universal software radio peripheral (USRP) software radio platforms. Extensive experiments confirm that all function blocks of RANC work effectively without being constrained by the above limitations. The overall performance of RANC is shown to approach the ideal case of interference-free communications. The results of experiments in a real network setup demonstrate that RANC significantly outperforms existing ANC schemes and achieves constraint-free ANC in wireless networks.

This study deals with the performance analysis of time division broadcast (TDBC) protocol with channel estimation errors. The tight lower bounds for individual and system outage probabilities are first presented in closed-form. It is shown that the presence of channel estimation error causes outage probability to maintain a fixed level even when a noiseless channel is adopted. Simulation results validate the accuracy of our analytical results. Furthermore, comparison of signal-to-noise ratio (SNR) gap ratio shows that TDBC protocol is less sensitive to the effect of channel estimate error than analog network coding (ANC) protocol.

Packet scheduling is investigated for the downlink of a multiple-input multiple-output (MIMO) cellular system. The conventional round robin scheduling (RRS) scheme does not utilize the benefits of multiuser environments, although it provides fair channel access chance to users. We propose an antenna-assisted round robin scheduling (AA-RRS) scheme to improve the conventional RRS scheme. The AA-RRS scheme provides fair channel access chance to users as the RRS scheme, whereas it increases the system capacity through the effective use of multiple antennas in achieving a diversity effect from multiple users. Computer simulations are conducted to compare the RRS and AA-RRS schemes in terms of the expected and outage capacities. It is shown that the AA-RRS scheme provides significant capacity gain over the RRS scheme, especially in terms of the outage capacity. We also discuss the effects of power control, signal-to-noise ratio (SNR), and spatial correlation on the system capacities.

Opportunistic relay selection (RS) is an efficient method to obtain diversity gain in analogue network coding (ANC) protocol with multiple relays. However, in networks with mobile relays, the channel state information (CSI) used in the RS procedure becomes outdated because of the time-varying nature of fading channels, which severely deteriorates the system performance. In this study, the authors study the RS strategy which aims to optimise the outage performance of the ANC protocol with multiple mobile relays. RS schemes for two different cases are designed, that is, (i) the scheme with only the outdated CSI during the RS procedure, and (ii) the scheme with both the outdated CSI and the statistical knowledge of channels during the RS procedure. The closed-form expressions of the outage probabilities as well as the asymptotic expressions are analytically derived for the proposed schemes, and moreover, the achievable diversities are analysed based on the asymptotic expressions. Simulation results are presented to evaluate the performances while validate the theoretical analyses for the proposed schemes.

Analog network coding (ANC) and time division broadcasting (TDBC)are two major protocols used in bidirectional cooperative networks with half-duplex terminals. Most previous work on those two protocols was based on the assumption that there was no direct channel between the two sources. In this paper, we remove this limitation and investigate both protocols in a general bidirectional cooperative network with a direct channel between the two sources. Lower bounds on the outage probabilities of the two protocols are derived first. These lower bounds are very close to the exact outage probabilities in the whole signal-to-noise ratio (SNR) range irrespective of the values of channel variances. Based on the lower bounds, the finite-SNR diversity-multiplexing tradeoffs (DMTs) of the ANC and TDBC protocols are obtained. These tradeoffs establish a framework which enables us to make a comprehensive comparison between both protocols.

In this paper, switch-and-stay combining (SSC) is considered in two-way relay systems with amplify-and-forward (AF) relays, among which one is activated to assist the information exchange between two sources. We assume that the two-way relay system operates in the analog network coding (ANC) protocol where the communication can only be achieved through the active relay without the direct link. The outage probability and the average bit error rate (BER) for Rayleigh fading channels are studied. In particular, we derive closed-form lower bounds for the outage probability and the average BER, which is tight for different fading conditions. Moreover, we present asymptotic analysis for both the outage probability and the average BER at high signal-to-noise ratio (SNR) region. It is shown that SSC can achieve the full diversity order in two-way relay systems with proper switching thresholds. Numerical and simulation results are also provided to verify the theoretical study.

There has been a growing interest in analog network coding, which can improve system throughput and spectrum efficiency significantly in wireless systems. Two-way relay scenario is considered in this paper, where the base station (BS) and the relay are both equipped with multiple antennas, and each of K user equipments (UEs) in the cell has a single antenna. An advanced multi-user scheduling scheme is proposed for the analog network coded two-way relay channel, where UEs and BS exchange information via the relay node during two time slots. Because each UE with single antenna has poor transmission and reception capability, the scheduling scheme is carefully designed to decrease multi-user interference and optimize beamforming gain from BS to relay. Analytical results of sum rate and outage probability have been developed to demonstrate that the multi-user diversity gain can be achieved by the proposed scheme. Meanwhile, the user fairness of the proposed scheme is on the same order as that of round robin (RR), and the computation complexity only increases linearly with the number of users in the serving cell. Monte-Carlo simulation is conducted to exhibit the performance gains from the proposed scheduling scheme. Results show that the proposed channel correlation based user selection scheme outperforms existing traditional scheduling schemes significantly, even when the cellular user payload is low.

In this letter, an AGV based relay selection mechanism is developed to ensure relays reporting true information in wireless relay networks. The source selects relays based on the channel state information (CSI) of relay-destination links. Selfish relays may report fake CSI in order to obtain a better chance of being selected, whereas the source is not able to tell the reported in real or in false. In the proposed scheme, a relay node receives some payoffs from the destination with respect to the achievable data rate and also some compensations from the others in terms of the reported CSI of all relays. This mechanism not only enforces truth-telling upon relay nodes with maximum payoff but also ensures fairness among them. The equilibrium of payoff is attained when relay nodes report their true CSI. Simulation results demonstrate the theoretical solutions.

The Modulation Scheme with Unknown CSI for Analog Network Coding in Multi-Antenna Relay Channel

In this paper we investigate the impact of a Relay Node (RN) placement plan on a heterogeneous wireless network called Hybrid Wireless Network with dedicated delay nodes (HWN*) in terms of system capacity, transmission delay and Quality of Service (QoS). A novel HWN* Heuristic RN Placement (HHRP) algorithm, which considers RN assistance & support for radio resource sharing such as inter-network traffic balancing, TD/CDMA soft handover, routing and user mobility has been implemented. A system level simulation is used to quantify the benefits of HWN* using HHRP algorithm over HWN* with other RN placement plans and multi-hop cellular networks. I. INTRODUCTION A heterogeneous wireless network refers to a wireless net- work that is comprised of wireless nodes with different radio access technologies or equipment with different operating systems. For example, it can be a wireless sensor network including bluetooth based radio access and zigbee 802.15.4 based radio access or a hybrid wireless network including cellular access and 802.11b/g based radio access. Specifi- cally for a hybrid wireless network, the increase of cellular communication intensity results in a reduction in cell size, thus much denser clusters are required resulting in increased infrastructure cost and system complexity. Meanwhile, the bursty nature of communication traffic and path loss results in traffic prediction difficulty. A solution must be found to provide effective resource management, congestion control and routing. The hybrid wireless network which incorporates cellular and MANET interfaced RELAY nodes, provides a practical approach for this. Nevertheless, the dedicated relay infrastructure approach can be also be adapted to the emerging wireless sensor network in order to maintain node connectivity, support sensor data aggregation and optimise power consump- tion.

In this paper, we investigate a two-way relaying power line communication (PLC) network with analog network coding. We focus on the analysis of the system outage probability, symbol error rate, and average capacity. Specifically, we first derive the probability density function (PDF) of the received signal-to-noise ratio (SNR) with a closed form, by exploiting the statistical properties of the PLC channel. Then with the help of this PDF, we develop the outage probability, symbol error rate, and average capacity with closed forms, based on the Hermite polynomial. Simulations show that the derived analytical results are consistent with those by Monte Carlo simulation.

In this paper, the optimum tradeoff between diversity and multiplexing gains in a two-user quasi-static Rayleigh fading interference channel (IC) is studied. The diversity and multiplexing gains are two basic performance measures in wireless networks which characterize the transmission reliability and the data rate, respectively. It would be of interest to investigate the optimal tradeoff between these two measures. First, we develop a coding scheme for the two-user quasi-static Rayleigh fading Gaussian IC with interference level α := log INR/log SNR ≥ 1. Then, for this coding scheme the achievable diversity-multiplexing tradeoff (DMT) is characterized. Our achievable DMT coincides with its outer bound. In the low and high rate regions (to be defined later), the proposed coding scheme is a one-level Gaussian code, independent of the channel state information (CSI). In the middle rate region (to be defined later), the proposed coding scheme, depending on the partial CSI, can be a one-level or a two-level Gaussian code. We show that the relevant partial CSI can be represented by only one bit determined by the absolute value of the channel gain. In the middle rate region, we assume that the single-bit partial CSI for all the four channel gains of the Gaussian IC are available at both transmitters.

Interference alignment (IA) is an effective method that can eliminate interferences in wireless networks, and has been applied to spectrum sharing in cognitive radio (CR) networks recently. However, the availability of perfect network channel state information (CSI) is necessary for most existing IA schemes, which is not practical in general due to the realistic communication scenarios and deployment challenges. In this paper, we apply IA to cognitive relay networks under CSI mismatch where the variance of the CSI measurement error depends on signal-to-noise ratio (SNR). An adaptive Max-SINR IA algorithm has been introduced to improve the performance of the secondary network by using the knowledge of CSI error variance. Finally, we analyze the performance of the secondary network in terms of the end-to-end equivalent transmission rate and outage probability. Simulation results indicate that our proposed adaptive Max-SINR IA scheme can greatly improve the performance of the secondary network.

Blockchain technology is finding applications in wireless networks, in particular vehicular networks, for the purposes of establishing trust. A certain set of network resources in terms of communication and computation requirements is also necessary for successful blockchain deployment. Moreover, heterogeneity in wireless networks and changing radio conditions at the physical layer, make it even more challenging to guarantee steady block generation latency. In this work, we study the possible denial of blockchain service attacks where malicious nodes threaten to slow down the block generation latency. We propose a novel Proof-of-Communication-Capability (PoCC) authentication framework that acts as a defense against communication capability spoofing over wireless networks. Our PoCC authentication framework utilizes physical properties such as distance between nodes, channel state information (CSI), and communication puzzle latency to establish the communication capabilities of nodes in the wireless network. Results from a simulated AV network under three different variations of the proposed PoCC framework are encouraging and demonstrate that such attacks can be effectively mitigated.

Providing secure communication between the wireless networks is a major issue. Particularly, providing confidentiality is the major concern in the multiple relay assisted wireless networks. Generally, conventional cryptography methods are being adapted to provide various security services. But the conventional encryption techniques cannot be always used in wireless devices, where the resources such as power and energy are limited. However, physical layer security is a recently emerging technique to provide security in wireless networks. In this work, a novel physical layer security scheme for orthogonal frequency division multiplexing (OFDM) with joint relay selection, and subcarrier mapping is proposed to improve the secrecy rate. To improve the systems secrecy rate, the proposed technique selects the optimal relay from among the available N relays for subcarrier mapping. The best channel gain between source and relay is mapped with the best channel gain between relay and destination in subcarrier mapping. In order to improve the secrecy rate further, the optimum power allocation is performed to allocate the power for subcarriers at the source node and relay node. Simulation results show that the proposed method outperforms existing method in terms of secrecy and confidentiality. Also the proposed method provides good secrecy rate even at low transmitted power with nearby eavesdropper.KeywordsPhysical layer securityRelay selectionSubcarrier mappingPower allocationRelay-aided OFDM systemSecrecy rate