Symbol-level selective decode-forward relaying for uncoordinated dense wireless networks

We consider in this paper, a spectrum sharing cognitive radio system with a ratio selection scheme; where one out of N independent-and-identically-distributed transmit antennas is selected such that the ratio of the secondary transmitter (ST) to the secondary receiver (SR) channel gain to the interference from the ST to the primary receiver (PR) channel gain is maximized. Although previous works considered perfect, outdated, or partial channel state information at the transmitter, we stress that using such assumptions may lead to a feedback overhead for updating the SR with the ST-PR interference channel estimation. Considering only statistical knowledge of the ST-PR channel gain, we investigate a ratio selection scheme using a mean value (MV)-based power allocation strategy referred to as MV-based scheme. We first provide the exact statistics in terms of probability density function and cumulative distribution function of the secondary channel gain as well as of the interference channel gain. Furthermore, we derive exact cumulative density function of the received signal-to-noise ratio at the SR where the ST uses a power allocation based on instantaneous perfect channel state information (CSI) referred to as CSI-based scheme. These statistics are then used to derive exact closed form expressions of the outage probability, symbol error rate, and ergodic capacity of the secondary system when the interference channel from the primary transmitter (PT) to the SR is ignored. Furthermore, an asymptotical analysis is also carried out for the MV-based scheme as well as for the CSI-based scheme to derive the generalized diversity gain for each. Subsequently, we address the performance analysis based on exact statistics of the combined signal-to-interference-plus-noise ratio at the SR of the more challenging case; when the PT-SR interference channel is considered. Numerical results in a Rayleigh fading environment manifest that the MV-based scheme outperforms the CSI-based scheme provided that a low interference power constraint is deployed, implying that the MV-based scheme is more suitable for practical systems.

In this paper cooperation among users at the physical layer level is studied for the downlink. Distributed space time linear dispersion codes are proposed for the cooperative strategies amplify and forward (AF) and decode forward (DF), assuming no channel state knowledge at the transmitter. Both AF and DF strategies are evaluated in a cellular multiuser realistic scenario based on TDMA access, considering cellular reuse of the relay slot. Different configurations regarding the number of antennas at the relay and destination nodes are considered. The maximum achievable rate of cooperative schemes implemented by means of space time linear dispersion codes is compared with the theoretical capacity of the cooperative channel. Finally an analysis in terms of BER is given for different schemes.

We apply the concept of artificial and controlled interference in a two-hop relay network with an untrusted relay, aiming at enhancing the wireless communication secrecy between the source and the destination node. In order to shield the square quadrature amplitude-modulated (QAM) signals transmitted from the source node to the relay, the destination node designs and transmits artificial noise (AN) symbols to jam the relay reception. The objective of our considered AN design is to degrade the error probability performance at the untrusted relay, for different types of channel state information (CSI) at the destination. By considering perfect knowledge of the instantaneous CSI of the source-to-relay and relay-to-destination links, we first present an analytical expression for the symbol error rate (SER) performance at the relay. Based on the assumption of an average power constraint at the destination node, we then derive the optimal phase and power distribution of the AN that maximizes the SER at the relay. Furthermore, we obtain the optimal AN design for the case where only statistical CSI is available at the destination node. For both cases, our study reveals that the Gaussian distribution is generally not optimal to generate AN symbols. The presented AN design takes into account practical parameters for the communication links, such as QAM signaling and maximum likelihood decoding.

A channel estimation based opportunistic scheduling scheme in wireless bidirectional networks

We propose using cooperative relaying technique in spectrum-sharing systems to more effectively and efficiently use the available transmission resources, such as power, rate and bandwidth, while adhering to the spectrum-sharing resource requirements of the licensed (primary) user. Specifically, we consider that the secondary user of the spectrum is assisted by a decode-and-forward (DF) relay to help in the communication between its source and destination nodes. In this context, we obtain the end-to-end performance of the proposed spectrum-sharing cooperative relaying system in terms of the average symbol error rate (SER) of the secondary's communication under appropriate constraints on the interference power at the primary receiver. We further analyze our theoretical results through simulations and comparisons illustrating the SER performance of the proposed spectrum-sharing cooperative system for different operating scenarios.

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

Using multiple terminals each of which is equipped with multiple antennas to relay messages is a promising technique to improve the capacity of wireless networks. In this paper, we propose two relay schemes for multiple-input and multiple-output (MIMO) wireless networks: 1) ZF-P-QR scheme: it conducts zero forcing (ZF) processing on the backward channel and QR decomposition (QRD) on the forward channel in conjunction with phase control, and 2) QR-P-ZF scheme: it conducts QRD on the backward channel and ZF on the forward channel in conjunction with phase control. The ergodic capacities of the proposed schemes are compared to those of previously proposed relay schemes, as well as that of direct communication under path-loss environments with various relay node configurations. It's shown that the ZF-P-QR and the QR-P-ZF schemes outperform the previously proposed relay schemes when the relay nodes are located close to the source and destination nodes, respectively. It is also found out that the relay schemes can achieve higher capacity than direct communication when the source and destination nodes are in non line of sight propagation environments and are separated by large distances.

Using Moment Generating Function for Performance Analysis in Non-Regenerative Cooperative Relay Networks with Max-Min Relay Selection

Power Line Carrier (PLC) and micropower wireless are two mainstream local communication technologies for low-voltage electricity information acquisition system, the cooperation- and complementarity between which-represent the future development trend. Aiming at the high outage probability deficiency- of traditional PLC and micropower wireless cooperative communications and the insufficient utilization of channel diversity gains, an Adaptive Relay Selection (ARS) based PLC and wireless multi-channel cooperative communication method is proposed. When the quality of the PLC link between the source node and the destination node is poor, the data of the source node is first sent to the potential relay node through the micropower wireless channel. Then, based on the channel quality of the PLC link between the relay node and the destination node, as well as the channel capacity between the source node and the relay node, the relay node and relay mode can be confirmed. Thus, a virtual Multi-Input Multi-Output (MIMO) PLC array can be constructed between the relay node and the destination node, and the system reliability can be improved by using distributed space-timecoding scheme. Simulation results show that, compared with traditional methods, ARS can significantly reduce the outage probability of the relay system, and reduce the transmission error rate via transmission diversity gains of multiple relay nodes.

Relaying is one of the latest technologies developed for next generation wireless networks. The purpose of relays in these networks is to increase the coverage and bitrates for cell edge users. Thus they are considered for Next generation wireless communication systems like Wi-Max (IEEE 802.16m), 3GPP LTE-Advanced (4G) and 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> Generation wireless networks to provide considerable increase in data throughput than the previous wireless communication systems. Reduction in deployment cost and easy to utilize are other promising features of these technologies. The objective of this paper is to understand the existing relay techniques, both cooperative and non-cooperative and outline the advantages of Relay implementation. Reduction in transmission power requirement for Simple Relay is shown in comparison with the conventional direct transmission, using Matlab simulation. Also SER (Symbol error rate) is calculated at the receiver for no relay and relay scenario (Amplify & Forward Relay) using Matlab to show the improvement using Relay node. Finally the benefits of Cooperative relaying is outlined using Matlab simulation.

&lt;p&gt;Relaying is one of the latest communication technologies developed for wireless networks like WiMAX, LTE Advanced and 5G Ultra Reliable Low Latency Communication (URLLC) networks to provide coverage extension as well as higher bitrates for cell edge users. Thus they are included in the design of next generation wireless communication systems to provide performance improvement in terms of coverage and capacity over their predecessors. Other promising features of this technology include easy to implement and reduction in deployment cost. The objective of this paper is to analyze both cooperative and non-cooperative relaying techniques in the Infinite Block length regime and findout the benefits of Relay implementation. A single Amplify and Forward (A&amp;amp;F) Relay is used for this purpose. Reduction in power requirement for Simple Relay is shown in comparison to the direct transmission, using experimental analysis with Matlab simulation. SER (Symbol error rate) is calculated at the receiver for no relay, simple Relay and Cooperative Relaying scenario to show the improvements of cooperative Relaying implementation.The performance enhancement of the Relay is then carried out using Particle Swam Optimization (PSO) optimization technique where allocation of power between Base station and Relay Node is effectively distributed for optimum performance.&lt;/p&gt;

Region based cooperative routing in underwater wireless sensor networks

Transmit antenna selection is a promising technique to simplify hardware and computational complexity of MIMO wireless communication systems. In this paper, we derive expressions for outage probability and bit error rate of two-hop relaying systems incorporated with transmit antenna selection at source and relay node. A closed form expression for outage probability and an infinite expression for bit error rate are derived for two hop cooperative communication system for BPSK modulation scheme. In the analysis, received signals are assumed to be collection of signals received as a result of multiple reflections having a line of sight component. Such channels can be well approximated by к-μ fading distribution which is generalized assumption to model fading channels with a dominant or line of sight component. To analyze the performance of the system at high SNR conditions, the expression of asymptotic BER is also derived in closed form from the expression for exact BER. The transmit antenna is selected at the source and relay nodes such that the received signal to noise ratio at the destination node is maximized. Maximal ratio combining is considered at the relay and destination nodes. The bit error rate results obtained from analytical expressions and Monte Carlo simulations are plotted for different values of fading parameters, к and μ. The analytical results are found to be in close agreement with simulation results.

A novel three-hop cooperative diversity system model is proposed in this paper comparing to conventional dual-hop cooperative systems, assuming all terminals have only one antenna for size limitation. This system model avoids complex relay selection criterions and data forwarding strategies which are necessary for conventional cooperative systems to optimize their performance. Both source node and destination node request free nodes around them to perform as virtual antenna arrays based on the simplest selection criterion, and then a virtual multiple-input multiple-output (MIMO) system is constructed. Different from the systems reported in literatures, signals from source node need three hops before arriving at destination. We show that if channels between destination node and its virtual antennas are better than channels between source and destination, symbol error rate (SER) of this virtual MIMO system can approximate the performance of actual MIMO system.

In this paper, the outage probability (OP) and symbol error rate (SER) performance of an intelligent reflecting surface (IRS) aided wireless power transfer wireless system in the Rayleigh fading channel are discussed. In the considered system, energy source (ES) sends radio frequency (RF) signals to the source node with the help of IRS. Source harvests energy from the RF signals sent by ES and uses the harvested energy to communicate with the destination node. Specifically, we consider two phase adjustment situations in the IRS, i.e., perfect phase and one-bit phase. The expressions on the OP and SER for the two cases are derived. The effects of the number of reflecting elements, transfer power, energy conversion efficiency, and phase error are investigated to shed lights on the system design. Finally, Numerical results and Monte-Carlo simulations are provided to verify the correctness of the theoretical analysis.