Multi-Hop Bi-Directional Relay Transmission Schemes Using Amplify-and-Forward and Analog Network Coding

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.

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.

High speed integrated RF–VLC data communication system: Performance constraints and capacity considerations

This paper evaluates the impact of using outdated channel estimates in a multiuser Amplify-and-Forward (AF) relay network, under Nakagami-m fading. Both variable gain AF and fixed gain AF schemes are considered. Expressions for the system's outage probability and the average bit error rate (BER) are derived. Since the expressions are barely tractable, we also present approximations for the high signal-to-noise ratio (SNR) regime. By doing so we characterize the impact of network parameters such as the number of relays, correlation between the delayed and current channel state information, chosen user rank and SNR imbalance on the performance degradation.

This paper studies the performance of a half-duplex (HD) two-way relay (TWR) in power line communication (PLC) over a log-normal fading channel with impulsive noise. We consider the two common relaying protocols: amplify-and-forward (AF) and decode-and-forward (DF). For the DF relaying, we apply physical-layer network coding (PNC) and analog-network coding (ANC) to the PLC TWR. We derive analytic expressions for the average sum capacity and the outage probability of the system. The Monte Carlo simulations are provided throughout to validate our analysis. The analytical results show a tight approximation to the simulation results. We compare the one-way relay (OWR) to the TWR and show that the HD spectral efficiency loss incurred by the OWR can be sufficiently mitigated in PLC. However, the outage probability of the TWR is inferior to that of the OWR. To enhance the outage performance of the PLC TWR, we implement a hybrid PLC/wireless (HPW) system, where all nodes are equipped with the PLC and wireless capabilities. Data transmission occurs over the two parallel links. The diversity in the transmission allows the TWR to improve its outage performance in the AF and DF protocols. The impact of the impulsive noise, inherent to the PLC channels, is also highlighted in the simulation results. It is shown that the impulsive noise severely impairs system performance.

The two-way relaying scheme is a network coding scheme which provides efficient utilization of spectrum. The performance of a two-way relaying scheme based on analog network coding (ANC) can be evaluated in context of many parameters such as overall symbol error rate (OSER), overall outage probability (OOP) and ergodic sum rate (ESR). In this paper we analyse the OSER over Nakagami-m fading channels for analog network coding scheme. The variation of OSER with respect to signal to noise ratio (SNR) has been observed for various factors such as fading parameter, modulation scheme used and number of antennas at the source and destination terminal. The threshold range of SNR for a tolerable value of OSER of 0.001 is computed as 20 to 25 dB. The results demonstrate the necessity of high SNR in two way relaying scheme for tolerable OSER. Further the analysis may be useful for selection of various physical layer parameters in design of communication networks.

In this paper, the error performance analysis of an amplify-and-forward (AF) relay-aided cooperative multi-antenna system using spatial modulation (SM) over Rayleigh channels is presented. The SM is a simple and spectral efficient modulation technique that can increase the data rate by using input data bits to select a transmit antenna to send a constellation point. The relay transmission deploying SM not only can enhance the coverage and but also can improve the spectral efficiency. In the performance analysis, the overall average bit error rate (BER), which is related to the error probability of an antenna index detection ( $P_{a}$ ) and the error probability of symbol detection ( $P_{d}$ ) given transmit antenna index, is analyzed. With the derivation of the probability density function and the moment generating function of output signal-to-noise ratio (SNR), closed-form expressions of $P_{a}$ and $P_{d}$ are obtained to compute the overall BER. With the obtained BER expression, asymptotical BER expressions are derived to reveal the BER performance of the system at high SNR. By minimizing the asymptotical BER, a suboptimal power allocation (PA) scheme is developed. The diversity gain is analyzed at high SNR. The results indicate that the cooperative AF-SM can achieve full diversity order. Simulation results verify the effectiveness of the theoretical BER analysis, and the cooperative AF-SM with PA scheme outperforms upon the equal PA scheme.

We propose an mobile-to-mobile (M2M) communication system employing analog network coding (ANC) with fixed gain amplify-and-forward (AF) scheme on relay, and investigate performance of the system for the case of imperfect self-interference cancellation proceeded by the the receiver. For this purpose, first we find the expression of end-to-end signal-to-interference-noise-ratio (E2E-SINR) at the receiver. Then, we derive the closed form expression of the cumulative density function (CDF) of E2E-SINR for the fast fading cascaded Rayleigh channel conditions. Using this CDF, we obtain the closed-form expression of outage probability. Finally, we verify the analytic results by comparing with computer simulations. Our results show that the outage probability increases when the success of the self-interference cancellation by the receiver decreases. Also it is shown that the increasing cascading degree of the channels decreases the outage performance of the system.

New, exact closed-form expressions are derived for the probability density function (PDF) and the cumulative distribution function (CDF) of the instantaneous end-to-end signal-to-noise ratio (SNR) of amplify-and-forward (AF) relaying systems with “full” selection diversity. The direct path, from the source to the destination, as well as multiple dual-hop paths, through intermediate relays, are considered in the selection set. The selection process follows a maximum SNR policy, such that the path of the maximum end-to-end SNR is used as the communication link, whether this path is the direct path or one of the dual-hop paths. The derived expressions are used to obtain the first exact results for the average error probability and the outage probability of such AF relaying systems. The results are verified through simulations for identically distributed as well as non-identically distributed Nakagami-m fading links. The system performance is compared to that of conventional wireless systems which use only the direct link between the source and the destination for communication. The system performance is compared also to that of an opportunistic dual-hop AF system with maximum end-to-end SNR relay selection that excludes the direct path from the selection set. Results show that the full selection system performance is superior to those in the comparison. For example, in the case of Nakagami-m fading links with m = 4 and N = 2 candidate intermediate relays, an average error probability of 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> in the case of AF relaying with full selection, occurs at 4.06 dB less than it occurs in the case of only direct transmission and at 0.95 dB less than it occurs in the case of maximum end-to-end SNR relay selection that excludes the direct path from selection. Results show also that the system provides diversity gain, proportional to the selection set size, N +1.

Due to the market demands, current communication systems evolve rapidly from existing 4G standard to a future 5G, that implies higher capacity and flexibility. In 4G systems the orthogonal frequency-division multiplexing (OFDM) modulation and multiple-input multiple-output (MIMO) technique are used to enable higher rates for mobile users, while in 5G it is expected to further increase the performances by using a significantly higher number of antennas (massive MIMO) and cooperative relays for solving the problem of coverage and capacity at the cell border. In this work, massive multiuser MIMO OFDM (MV-MIMO) systems, with 10 to 100 antennas are used, without relay nodes, to evaluate the bit error rate (BER) as a function of the Signal to Noise Ratio (SNR). Then, the system is further developed, by introducing amplify-and-forward (AF) relays as intermediaries between the transmitter and the receiver to see if the performances are improved.

In this paper, we propose and analyze a multihop transmission scheme based on detect-and-forward (DF) relay protocol and network coding (NC) for two-way relay channels. In this scheme, the odd relays perform hard detection and then forward the detected signals to the next hop, whereas the even relays perform NC on the detected signals from the two adjacent nodes and broadcast them to the next hop. By separating the network into multiple two-hop subsystems, we develop closed-form expressions for bit error rate (BER) in flat Rayleigh fading channels. Our results are given as both lower bound and asymptotic expression based on an accurate upper bound of the end-to-end signal-to-noise ratio (SNR). It is shown that the proposed scheme has the same asymptotic BER performance and a much higher throughput compared with the conventional bidirectional relay scheme based on four transmission phases. Therefore, the proposed scheme is efficient for practical wireless applications. Simulation results are provided to validate the analysis.

We propose a new secure underwater acoustic communication scheme designed to let a user (Alice) transmit a confidential message to another user (Bob) in the presence of an eavesdropper (Eve). A typical approach in conventional wireless physical-layer security is to rely on a friendly jammer to jam Eve through artificial noise (AN). Instead, for the first time, we propose a secure underwater communication scheme that relies on cooperative friendly jamming through CDMA-based analog network coding (ANC). The cooperative friendly jammer transmits information using the same spreading code used in the legitimate Alice-Bob link. The information transmitted by the cooperative jammer is known a priori to Bob, but not to Eve. Although the jammer's packet will also interfere at Bob, we show that after jointly estimating the two multipath-affected channels, Bob can suppress the interfering packet and decode Alice's packet, while Eve cannot. We also formulate the problem of joint optimal selection of friendly jammer and power allocation (for Alice and the jammer) that minimize Eve's capability of intercepting the signal while guaranteeing a predefined level of quality of service (QoS) for Bob. The proposed scheme is implemented in a testbed based on Teledyne Benthos Telesonar SM-975 underwater modems and tested extensively in Lake LaSalle at the University at Buffalo. Experiments and simulations demonstrate that, for a given energy budget, the proposed scheme can guarantee much higher bit error rate (BER) at Eve, while creating minimal BER disturbance at Bob, compared to the AN-aided approach.

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

This paper introduces a cooperative orthogonal frequency division multiplexing (CO-OFDM) based on amplify and forward (AF) relay and utilizing a fast low complexity T-transform as a subcarriers modulation scheme. The proposed cooperative system is developed by changing the modulation/demodulation algorithms which significantly enhanced the immunity of the system to deep notches of the multipath channels. Thereafter, the paper presents a mathematical analytic model for the proposed amplify and forward CO-T-OFDM scheme. The use of T-transform in the transceiver of the proposed system enhances the signal diversity. Therefore, the presented AF cooperative system is efficient in enhancing the signal diversity, mitigating the effects of multipath fading channels and achieving more reliable bit-error-rate (BER) performance than the state-of-the-art cooperative system. It also moderates the peaks power of the signal. The BER of the developed AF cooperative system is evaluated by Monte Carlo simulation over frequency-selective multipath channels when AF relay is used, and compared with the BER performance of the standard AF cooperative system. The results show that the developed AF cooperative technology achieves better BER than the classic CO-OFDM under different transmission scenarios.

Radio channel is characterized by a multipath propagation that is suitable for application of network coding (NC) to improve the network capacity. In particular, physical layer network coding (PNC) scheme is known to double the network capacity of bi-directional communication between pairs of end users assisted by a relay terminal in a Gaussian channel. Recently, analog network coding (ANC) has been proposed with a simpler implementation complexity in comparison with PNC scheme, but the same achievable network capacity. On the other hand, an important question is how much the channel capacity is improved over a conventional point-to-point communication in a frequency-selective fading channel. In this paper, we present the ergodic channel capacity analysis of bi-directional transmission with analog network coding in a frequency-selective fading channel. The channel capacity expression for transmission with frequency domain equalization (FDE) is derived based on the Gaussian approximation of the inter-symbol interference (ISI) after FDE.