Dynamic Decode-and-forward Protocol Research Articles

RF Energy Harvesting Based Multiple Access Relay Systems: A DMT Perspective

A multiple-access relay system, where the relay node is powered by radio frequency radiation is analyzed in this paper. Specifically, the focus is on the time-switching-based scheme in which the intermediate relay switches between the energy harvesting (EH), information decoding (ID), and the information re-transmission (TX). For this system, we have characterized the diversity-multiplexing trade-off (DMT) for two variants of the EH-based dynamic decode-and-forward (DDF) protocols: without feedback (EH-DDF) and with limited feedback (EH-DDF-LF). Analysis of the protocols reveals that the diversity gain of EH-DDF scheme is inferior to that of the traditional non-EH-based DDF protocol. Furthermore, the impact of energy harvesting duration on the DMT performance has been extensively investigated. Consequently, it is observed that the achievable diversity gain of the EH-DDF improves with the reduction in energy harvesting interval. However, there exists a performance difference between the classical non-EH-based DDF and EH-DDF even for the minute harvest duration. On the other hand, in the case of EH-DDF-LF, the performance approaches the diversity upper bound in the high multiplexing gain regime. Finally, a detailed comparison of the proposed EH-based schemes has been presented.

Dynamic Decode‐and‐Forward Relaying with Partial CSIT and Optimal Time Allocation

A Dynamic decode-and-forward (DDF) relaying protocol with partial Channel state information at the transmitter (CSIT) for a three-node half-duplex single-antenna network, which consists of a single source destination pair and a relay, is proposed. A Diversity multiplexing trade off (DMT) analysis is presented, in which the DMT of the proposed protocol is derived in a closed form and an adaptive time allocation strategy is also developed to achieve the optimal performance. It is shown that time allocation with partial CSIT significantly improves the achievable DMT for DDF relaying. Moreover, unlike the existing DDF protocol with CSIT, which is performed with the assumption of long-term power constraint, the proposed protocol can be generalized to the practical scenarios where a strict short-term power constraint is often imposed on, due to the environmental safety and interference prevention.

The Performance of Systems Featuring Dynamic Decode-and-Forward and Network Coding

We constructed a single-relay-station cooperative communications system, featuring integration between the dynamic decode-and-forward (DDF) protocol and network coding (NC) to examine the outage probabilities in the Rayleigh, Rician, and Nakagami fading channels. In addition, the diversity-multiplexing tradeoff of the system was analyzed to examine improvements for system performance through integrating these two technologies. Through simulations and analyses, we discovered that the systems featuring NC had lower outage probability and greater diversity gain, and consequently, greater system reliability compared to the ordinary system featuring only the DDF protocol. However, because we added a final phase for the transmission of network coded signals, the system showed lower multiplexing gain compared to the system featuring only the DDF. Users should adopt this system based on their needs. For example, in situations that have higher requirements for reliability and lower requirements for multiplexing gain, users can adopt a DDF-NC cooperative communications system.

Diversity-Multiplexing Trade-off in Adaptive Two-Way Relaying

Resource allocation for symmetric half-duplex bidirectional relaying networks is considered. Various decode-and-forward (DF) based relaying strategies that efficiently exploit quantized channel state information (CSI) at the transmitters (CSIT) are investigated. Adapting the number of channel uses for each relaying phase and allocating transmit power based on limited CSIT is shown to result in a significant improvement in the diversity-multiplexing trade-off (DMT). Without a direct link between the sources, power control is instrumental to efficiently exploit CSI feedback from sources to relay, resulting in superior performance that matches corresponding upper bounds in certain cases. With direct links between the sources, it is shown that DF two-way relaying does not suffer from a diversity loss when the multiplexing gain is high, a significant improvement over the dynamic DF protocol for one-way relaying. The best DMT is achieved when each source broadcasts partial CSI to the other nodes in the network, allowing them to adapt their transmit powers.

Macro and Micro Diversity Behaviors of Practical Dynamic Decode and Forward Relaying Schemes

In this paper, we propose a practical implementation of the Dynamic Decode and Forward (DDF) protocol based on rateless codes and HARQ. We define the macro diversity order of a transmission from several intermittent sources to a single destination. Considering finite symbol alphabet used by the different sources, upper bounds on the achievable macro diversity order are derived. We analyse the diversity behavior of several relaying schemes for the DDF protocol, and we propose the Patching technique to increase both the macro and the micro diversity orders. The coverage gain for the open-loop transmission case and the spectral efficiency gain for the closed loop transmission case are illustrated by simulation results.

Opportunistic Buffered Decode-Wait-and-Forward (OBDWF) Protocol for Mobile Wireless Relay Networks

In this paper, we propose an opportunistic buffered decode-wait-and-forward (OBDWF) protocol to exploit both relay buffering and relay mobility to enhance the system throughput and the end-to-end packet delay under bursty arrivals. We consider a point-to-point communication link assisted by K mobile relays. We illustrate that the OBDWF protocol could achieve a better throughput and delay performance compared with existing baseline systems such as the conventional dynamic decode-and-forward (DDF) and amplified-and-forward (AF) protocol. In addition to simulation performance, we also derived closed-form asymptotic throughput and delay expressions of the OBDWF protocol. Specifically, the proposed OBDWF protocol achieves an asymptotic throughput ΘL(\log_2 K) with ΘL(1) total transmit power in the relay network. This is a significant gain compared with the best known performance in conventional protocols (ΘL(\log_2 K) throughput with ΘL(K) total transmit power). With bursty arrivals, we show that both the stability region and average delay of the proposed OBDWF protocol can achieve order-wise performance gain ΘL(K) compared with conventional DDF protocol.

High performance static and dynamic cooperative communication protocols for the half duplex fading relay channel

Two novel communication protocols for the quasistatic coherent fading relay channel are proposed and analyzed under the diversity-multiplexing tradeoff framework. Both these protocols satisfy the half-duplex constraint and fall under the class of decode and forward (DF) protocols, wherein the relay node attempts to decode the source signal and if successful transmits the re-encoded signal. The first protocol is a static DF protocol where the relay waits for a fixed, channel independent duration before attempting to decode. It is shown that it achieves a tradeoff curve that uniformly improves upon those of the previously best known static half-duplex protocols, which are the NAF protocol and the STC3 protocol. Our second protocol is a dynamic DF protocol where the relay waits for a dynamic, channel dependent duration before attempting to decode and it is shown to achieve a tradeoff curve that uniformly improves upon the previously proposed half-duplex dynamic DF protocol.

On the Diversity Gain of AF and DF Relaying With Noisy CSI at the Source Transmitter

The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel state information at the source transmitter (CSIT) is studied, with a focus on the asymptotically high signal-to-noise ratio (SNR) regime. A novel upper bound on the diversity-multiplexing tradeoff (DMT) is derived, taking into account the quality of the CSIT. It is shown that from a DMT perspective, the decode-and-forward (DF) protocol is strictly optimal over a certain range of the multiplexing gains. When the quality of the CSIT is sufficiently high, the DMT performance of the DF protocol with noisy CSIT equals that of the dynamic DF protocol shifted above by a constant diversity gain, which depends only on the quality of the CSIT about the source-destination link. When the quality of the CSIT reduces, DF relaying is still DMT-optimal, but only over a smaller range of the multiplexing gains. In an intermediate range of the multiplexing gains, nonorthogonal schemes provide some additional gains when the CSIT quality is sufficiently low. It is also shown that the DMT of the amplify-and-forward (AF) protocol is offset by a constant term depending on the quality of the CSIT of the source-destination link only.

Coding and Decoding for the Dynamic Decode and Forward Relay Protocol

We study the dynamic decode-and-forward (DDF) protocol for a single half-duplex relay, single-antenna channel with quasi-static fading. The DDF protocol is well known and has been analyzed in terms of the diversity-multiplexing tradeoff (DMT) in the infinite block length limit. We characterize the finite block length DMT and give new explicit code constructions. The finite block length analysis illuminates a few key aspects that have been neglected in the previous literature: 1) we show that one dominating cause of degradation with respect to the infinite block length regime is the event of decoding error at the relay; 2) we explicitly take into account the fact that the destination does not generally know a priori the relay decision time at which the relay switches from listening to transmit mode. Both of the above problems can be tackled by a careful design of the decoding algorithm. In particular, we introduce a decision rejection criterion at the relay based on Forney's decision rule (a variant of the Neyman-Pearson rule), such that the relay triggers transmission only when its decision is reliable. Also, we show that a receiver based on the generalized likelihood ratio test (GLRT) rule that jointly decodes the relay decision time and the information message achieves the optimal DMT. Our results show that no cyclic redundancy check (CRC) for error detection or additional protocol overhead to communicate the decision time are needed for DDF. Finally, we investigate the use of minimum mean-squared error generalized decision feedback equalizer (MMSE-GDFE) lattice decoding at both the relay and the destination, and show that it provides near-optimal performance at moderate complexity.

On the Achievable Diversity–Multiplexing Tradeoff in Half-Duplex Cooperative Channels

We propose novel cooperative transmission protocols for delay-limited coherent fading channels consisting of N (half-duplex and single-antenna) partners and one cell site. In our work, we differentiate between the relay, cooperative broadcast (down-link), and cooperative multiple-access (CMA) (up-link) channels. The proposed protocols are evaluated using Zheng-Tse diversity-multiplexing tradeoff. For the relay channel, we investigate two classes of cooperation schemes; namely, amplify and forward (AF) protocols and decode and forward (DF) protocols. For the first class, we establish an upper bound on the achievable diversity-multiplexing tradeoff with a single relay. We then construct a new AF protocol that achieves this upper bound. The proposed algorithm is then extended to the general case with (N-1) relays where it is shown to outperform the space-time coded protocol of Laneman and Wornell without requiring decoding/encoding at the relays. For the class of DF protocols, we develop a dynamic decode and forward (DDF) protocol that achieves the optimal tradeoff for multiplexing gains 0lesrles1/N. Furthermore, with a single relay, the DDF protocol is shown to dominate the class of AF protocols for all multiplexing gains. The superiority of the DDF protocol is shown to be more significant in the cooperative broadcast channel. The situation is reversed in the CMA channel where we propose a new AF protocol that achieves the optimal tradeoff for all multiplexing gains. A distinguishing feature of the proposed protocols in the three scenarios is that they do not rely on orthogonal subspaces, allowing for a more efficient use of resources. In fact, using our results one can argue that the suboptimality of previously proposed protocols stems from their use of orthogonal subspaces rather than the half-duplex constraint.