Distributed Switch-and-stay Combining Research Articles

When distributed switch-and-stay combining meets buffer in IoT relaying networks

This paper studies the IoT relaying networks, where one decode-and-forward (DF) relay equipped with a buffer helps determine whether to receive the data from the source or send the data to the destination. Moderate shadowing environments are considered and the source can also communicate with the destination through the direct link. Although the opportunistic selection (OS) technique can select one better branch among the direct and buffer-aided relay branches, it requires to estimate the channel parameters of two branches, and the branch switching may occur frequently. To deal with these disadvantages, we employ the distributed switch-and-stay combining (DSSC) technique for the buffer-aided relay network, in which the same branch goes on being employed until the current branch cannot support the data transmission no longer. In this protocol, the branch switching depends on the buffer state and the state transition in the buffer is also affected by the branch switching. For this communication scenario where the buffer meets the DSSC, we study the system performance by deriving the analytical outage probability and the asymptotic expression with high regime of transmit power. From the asymptotic expression, we find that DSSC can effectively exploit the system spatio-temporal resources and it obtains the same performance of the OS with ease of implementation. Moreover, the system performance improves with the buffer size. We finally provide some simulation and numerical results to demonstrate the merits of the DSSC-based buffer-aided IoT relaying networks.

Full-duplex distributed switch-and-stay energy harvesting selection relaying networks with imperfect CSI: Design and outage analysis

We analyze the effect of distributed switch and stay combining (DSSC) technique and imperfect channel state information (CSI) in the scenario, where the communication between the source and the destination is conducted through either the direct transmission or with the help of the best relay among K full-duplex energy harvesting relays by using partial relay selection. To activate such communication, at the destination, we apply DSSC technique, which is considered as an effective method to achieve spatial diversity in a distributed manner with low processing complexity and compatibility to resource-constrained wireless networks. Considering two popular relaying protocols, i.e., decode-and-forward (DF) and amplify-and-forward (AF), the performance analysis in terms of outage probability (OP) is carried out. Numerical results show that imperfect CSI has a negative impact on system performance. Besides that, our DSSC-full duplex selection relaying (FDSSCSR) system achieves a better performance in terms of outage probability than that of the DSSC-half duplex selection relaying (HDSSCSR) and the full duplex/half duplex dual hop relaying with partial relay selection (FD/HDDRPRS) systems. Simulation results are conducted to verify the correctness of our analysis.

Performance of Distributed Switch-and-Stay Combining for Cognitive Relay Networks with Primary Transceiver

This paper investigated cognitive relay networks with practical distributed switch-and-stay combining (DSSC) protocol when considering the primary transmitter’s interference to secondary network. The closed-form expressions for the outage probability is derived, the correctness of the analysis is validated by Monte Carlo simulations and readily allows us to evaluate the impact of the key system parameters on the performance. The analytical results reveal that the proposed DSSC scheme has optimal switch threshold, and it is not the threshold SNR for the outage, which is true for the model without the interference from primary transmitter, and increasing the switching threshold do not always improve the system performance. The asymptotic analysis also reveals that the outage diversity only achieves one, which is also different from the traditional relay network with DSSC protocol.

Full-duplex distributed switch-and-stay networks with wireless energy harvesting: design and outage analysis

Distributed switch and stay combining (DSSC) has been considered as an effective technique to achieve spatial diversity in a distributed manner with low processing complexity. In this paper, we incorporate DSSC into a full-duplex dual hop relaying system, where two energy-constrained relay nodes assist the information transmission from the source to the destination using energy wirelessly harvested from the source. By applying DSSC at the destination, this efficient technique not only improves performance of full-duplex relaying systems and increases the system diversity but also reduces the implementation and hardware complexity at the destination. We obtain tight approximate expression for outage probability in the case of using decode-and-forward (DF) relaying protocol and analytical expression for outage probability in the case of using amplify-and-forward (AF) relaying protocol. Numerical results show that our DSSC full-duplex relaying with wireless information and power transfer (WIPT) system achieves the full spatial diversity and has a better performance in terms of outage probability than that of the DSSC half-duplex relaying and conventional full-duplex relaying with WIPT system.

Opportunistic Relay Selection for Secrecy Enhancement in Cooperative Networks

In this paper, we present a comprehensive investigation on the secrecy performance of opportunistic relay selection systems employing the decode-and-forward protocol over Rayleigh fading channels. Considering a practical setting where direct link between the source node (Alice) and the destination node (Bob) is available, we study the secrecy performance of three different diversity combining schemes, namely, maximum ratio combining (MRC), distributed selection combining (DSC), and distributed switch-and-stay combining (DSSC). Throughout the analysis, we consider two different scenarios based on the availability of the eavesdropper's channel state information (CSI), i.e., Scenario A, where the eavesdropper's CSI is not available at Alice and the relay, and Scenario B, where Alice and the relay have knowledge about the eavesdropper's CSI. For Scenario A, we derive exact closed-form expressions for secrecy outage probability and simple asymptotic approximations for the secrecy outage probability, which enable the characterization of the achievable secrecy diversity order and coding gains. For Scenario B, we derive closed-form expressions for the achievable secrecy rates. For both scenarios, we investigate the impact of feedback delay (outdated CSI) on the secrecy performance wherein exact and asymptotic secrecy outage probability and closed-form expressions of the secrecy achievable rates are obtained. Our analytical findings suggest that both the MRC and DSC schemes achieve the maximum diversity order of K+1 where K is the number of relays. In addition, the feedback delay has a significant impact on the achievable secrecy performance by reducing the achievable diversity order to two.

Distributed switch and stay combining with partial relay selection and signal space diversity

Spatial diversity schemes are often used to extract additional performance from wireless communication systems. Incorporating the partial relay selection (PRS) protocol into a distributed switch-and-stay combining (DSSC) cooperative communication network gives the benefit of diversity while simplifying hardware, processing and feedback requirements. Because only a single relay is ever active, the destination employs no combiner; the best relay is chosen based on first-hop relay conditions. However, achieved performance is worse than other distributed protocols, such as distributed selection combining (DSC). In this study, signal space diversity (SSD) is added to the DSSC–PRS system to provide further diversity and error performance gains, at the expense of necessitating a maximum-likelihood detector with increased complexity at the receiver. Analytical results are presented in the form of a lower bound based on the minimum distance lower bound for SSD systems and are verified with simulation. The DSSC–PRS–SSD system shows an improvement of 5 dB at a symbol error rate of 10 − 4 as well as a clear diversity order improvement. Spectral efficiency of the new system with SSD is slightly decreased at low signal-to-noise ratios, but is still an improvement over other distributed schemes, such as DSC.

Distributed Two-Way Switch and Stay Combining with a Single Amplify-and-Forward Relay

This letter considers a two-phase two-way relay network (TWRN) consisting of two sources and a single amplify-and-forward (AF) relay. In order to efficiently exploit the direct link between sources for achieving full diversity order, we propose to utilize a distributed switch and stay combining (DSSC) in the two-phase TWRN. In DSSC, one branch out of the direct and relay branches is activated, and the branch switching occurs when the minimum end-to-end signal-to-noise ratio (SNR) of bidirectional communication falls below a preset threshold. We analyze the system performance over Rayleigh fading channels, by deriving the lower bounds and asymptotic expressions for the outage probability and symbol error rate (SER). It is shown that the DSSC preserves the same spectral efficiency as pure analogy network coding (ANC) protocol, while can concurrently achieve full diversity order as the optimal selection (OS) with less channel estimation complexity and lower switching rate. Numerical and simulation results demonstrate the proposed studies.

Selective Cooperative Relaying over Time-Varying Channels

In selective cooperative relaying only a single relay out of the set of available relays is activated, hence the available power and bandwidth resources are efficiently utilized. However, implementing selective cooperative relaying in time-varying channels may cause frequent relay switchings that deteriorate the overall performance. In this paper, we study the rate at which a relay switching occurs in selective cooperative relaying applications in time-varying fading channels. In particular, we derive closed-form expressions for the relay switching rate (measured in Hz) for opportunistic relaying (OR) and distributed switch and stay combining (DSSC). Additionally, expressions for the average relay activation time for both of the considered schemes are also provided, reflecting the average time that a selected relay remains active until a switching occurs. Numerical results manifest that DSSC yields considerably lower relay switching rates than OR, along with larger average relay activation times, rendering it a better candidate for implementation of relay selection in fast fading environments.

Distributed Switch and Stay Combining (DSSC) with a Single Decode and Forward Relay

A distributed version of switch and stay combining is proposed for relaying systems that utilize a single decode and forward relay. The performance analysis of such system is presented, along with that of a simplified version of the so-called incremental relaying protocol. Numerical results show that these systems achieve the beneficial effects of diversity, although they do not employ any diversity combiner at the destination terminal