Diversity-multiplexing Tradeoff Performance Research Articles

Diversity-Multiplexing Tradeoff of Multi-Layer Scattering MIMO Channels

Multi-layer (or multi-cluster) scattering Multiple-Input Multiple-Output (MIMO) channels are considered in the framework of the diversity-multiplexing tradeoff (DMT). This MIMO channel model finds application in indoor networks, typical of 5G architectures, in which the signal propagates from the transmitter to the receiver through the walls and floors of a building (represented by scattering layers). These results extend the seminal work by Zheng and Tse from the independent identically distributed (iid) Rayleigh fading MIMO channel to a channel matrix which is the product of iid Rayleigh fading matrix components. It is worth noting that the resulting product channel matrix elements are not independent. It is shown that the presence of multiple scattering layers eventually degrades the DMT performance of a MIMO channel by an amount depending only on the least three dimensions of the matrices characterizing the product channel matrix.

Impartial SWIPT-Assisted User Cooperation Schemes

In this paper, an impartial simultaneous wireless information and power transfer (SWIPT)-assisted cooperation mechanism is proposed for a non-orthogonal multiple access (NOMA) downlink scenario. The key idea of the proposed impartial user cooperation mechanism (IUCM) is that not only the cell-center user but also the cell-edge user applies the power-splitting architecture and utilizes the harvested energy to forward the other user's information. Analytical results show that the proposed IUCM outperforms the traditional partial cooperation mechanism in terms of outage probability, diversity order and diversity-multiplexing trade-off (DMT). For comparison, the proposed IUCM is further incorporated into an orthogonal frequency-division multiple access (OFDMA) framework, which is shown to preserve the same diversity order, while has a worse but more flexible DMT performance compared with the IUCM in the NOMA framework. Furthermore, a classic non-linear energy harvesting model is introduced, based on which the outage probability, diversity order and DMT performance of the proposed IUCM and the conventional mechanism are analyzed. Finally, representative numerical results are given to validate our theoretical analysis.

Diversity-Multiplexing Tradeoff for MIMO-FSO System Under Different Transmission Scenarios With Limited Quantized Feedback

The diversity-multiplexing tradeoff (DMT) in a multiple-input multiple-output (MIMO) free-space optical (FSO) communication with limited channel state information at the transmitter (CSIT) is investigated. Using the limited CSIT based power and rate control strategy, we optimally allocate the power among the good and bad channels in such a fashion that the DMT performance of the system enhances significantly unlike the no-CSIT based MIMO-FSO DMT. In this way, a new limited CSIT based technique/model with optimal power and rate control strategy is proposed to enhance the DMT performance. The optimal DMT is studied for two different transmission scenarios: single-rate and adaptive-rate transmission. It is shown that how the optimal DMT is influenced when the concept of minimum guaranteed multiplexing gain in the forward link is taken into account. It is illustrated that power control based on the feedback plays a vital role in attaining the optimal DMT, and rate adaptation is significant in obtaining a high diversity gain, especially at high rates. Moreover, the analysis of upper and lower bounds on the optimal DMT is done by giving useful insights. Furthermore, a novel study based on the optimal tradeoff between the degrees of freedom and the number of transmit apertures in a coherent MIMO-FSO channel is also done. To validate the results of the proposed model, we compare the derived results with the no-CSIT based MIMO-FSO DMT. It is observed that the proposed technique/model outperforms the no-CSIT based MIMO-FSO DMT.

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.

Diversity-multiplexing Tradeoff of Opportunistic Relaying Coded Cooperation and Distributed Space-time Coding Coded Cooperation

In this paper, we analyze the diversity-multiplexing tradeoff (DMT) performance of opportunistic relaying coded cooperation (ORCC) and distributed space-time coding coded cooperation (DSTCCC) with arbitrary number of relays. Exact DMT curves are derived for two scenarios, i.e., when the source is included in cooperation (denoted by S1) or not (denoted by S2), by formulating the problem as linear optimization problem. The DMT curves of ORCC and DSTCCC are found to be identical for S1 (or S2), and S1 has better DMT performance than S2. Numerical results are provided to illustrate the analysis as well.

Diversity–Multiplexing Tradeoff of Asynchronous Decode-and-Forward Cooperative Networks

The diversity-multiplexing tradeoff (DMT) of a general two-hop asynchronous cooperative network is examined for orthogonal and nonorthogonal selection decode-and-forward relaying protocols. The transmitter nodes send pulse amplitude modulation signals, in which information symbols are linearly modulated by a shaping waveform to be sent to the destination. We consider two different cases of band-limited and time-limited shaping waveforms. In each case, the DMT performance of the asynchronous and synchronous networks is compared. It is proved that in the band-limited system scenario, the asynchronism does not incur any performance loss, and the same DMT as that of the corresponding synchronous network is obtained for both protocols. In the time-limited-system scenario, the bandwidth is expanded for high values of signal-to-noise ratio. In this scenario, it is observed that only asynchronous signaling is able to exploit the extra degrees of freedom of the channel. The asynchronous network in this scenario provides better DMT performances for both protocols throughout the range of the multiplexing gain.

Optimal diversity multiplexing tradeoff for opportunistic relaying coded cooperation protocols with quantised channel state information feedback

A cooperative multiple relay system is considered in this study which exploit opportunistic relaying (OR)-based protocol with coded cooperation approach. For the considered system, the optimal diversity multiplexing tradeoff (DMT) is determined in different scenarios including either considering the source node as a potential relay or not. The study is then extended to the case where the quantised channel state information (QCSI) feedback is considered. In particular, an OR-based protocol with QCSI at the source node is presented. It is shown that the QCSI feedback linearly improves the DMT performance. In addition, it is proved that the role of QCSI feedback to improve DMT performance is higher than that of cooperative relays.

Diversity–Multiplexing Tradeoff Analysis of AF Two-Way Relaying Channel With Hybrid ARQ Over Rayleigh Fading Channels

This paper investigates the diversity–multiplexing tradeoff (DMT) performance of the two-way relaying channel (TWRC) with hybrid automatic repeat request (HARQ) in Rayleigh fading channels. We focus on the amplify-and-forward (AF) mode and the scenario without a direct link. Two implementation schemes for the TWRC with retransmission are presented. In one scheme (Scheme I), the source does not immediately transmit new message in the next round after its message is decoded successfully. It waits until the message of the other source is also successfully decoded via retransmission, and then, the two sources transmit new message simultaneously. In the other scheme (Scheme II), the source immediately transmits new message after its message is successfully decoded, regardless of the transmission state of the other source. To calculate the DMT of Scheme I, we first propose both lower and upper bounds on its outage probability. The exact DMT is then derived in closed form based on these bounds. Furthermore, the DMT of Scheme II is obtained. The DMT results reveal that both schemes achieve the same DMT performance, and reliability (i.e., diversity) could be enhanced by leveraging on transmission delay (i.e., retransmission).

Power Efficient Relay Selection and Diversity-Multiplexing Tradeoff in Two-way Relaying Networks

Two-way amplify-and-forward (AF) relaying networks have been widely studied because of its simplicity and high spectral efficiency. In this paper, we investigate the relay selection problem and the diversity-multiplexing tradeoff (DMT) for two-way AF relaying systems over independent flat Rayleigh fading channels. We first derive the closed-form expression of the minimum total transmit power under the predefined data rate requirements. Based on the minimum total transmit power, we propose a simple relay selection which only requires user-relay channel state information (CSI). We proved that the proposed relay selection scheme can achieve the same DMT performance as obtained by the popular outage-optimal two-way opportunistic relaying scheme. Simulation results demonstrate that the proposed scheme can significantly decrease the power consumption compared with random relay selection and other schemes.

Outage Probability and DMT Performance of Underlay Cognitive Networks with Incremental DF and AF Relaying over Nakagami-m Fading Channels

This letter studies the outage performance of cognitive radio systems with incremental decode-and-forward (DF) and amplify-and-forward (AF) relaying in a Nakagami-m fading environment. The outage behavior and diversity-multiplexing tradeoff (DMT) are investigated. These results indicate that the DMT is irrelevant to the primary user and the secondary system can achieve the full diversity order. Simulation results substantiate the accuracy of our analysis. The presented method/steps for performance evaluation are applicable to other fading channels.

Naïve Decode-and-Forward Relay Achieves Optimal DMT for Cooperative Underwater Communication

Diversity-multiplexing tradeoff (DMT) characterizes the fundamental relationship between the diversity gain in terms of outage probability and the multiplexing gain as the normalized rate parameter r, where the limiting transmission rate is given by rlog SNR (here, SNR denote the received signal-to-noise ratio). In this paper, we analyze the DMT and outage performance of an underwater network with a cooperative relay. Since over an acoustic channel, the propagation delay is commonly considerably higher than the processing delay, the existing transmission protocols need to be explained accordingly. For this underwater network, we briefly describe two well-known relay transmissions: decode-and-forward (DF) and amplifyand-forward (AF). As our main result, we then show that an instantaneous DF relay scheme achieves the same DMT curve as that of multiple-input single-output channels and thus guarantees the DMT optimality, while using an instantaneous AF relay leads at most only to the DMT for the direct transmission with no cooperation. To validate our analysis, computer simulations are performed in terms of outage probability.

Round-Robin Relaying With Diversity in Amplify-and-Forward Multisource Cooperative Communications

In this paper, a round-robin-based relay protocol dubbed round-robin relaying with source selection protocol (R3SSP) is proposed to achieve full cooperative diversity in multisource cooperative communication networks. In R3SSP, all the sources transmit their individual information in turn. The relays then forward the messages of some specific sources in a fixed order according to the limited feedback information. Compared with traditional relay selection-based protocols, R3SSP is based on round-robin relaying, thus avoiding relay selection and requiring no specific channel state information feedback. R3SSP can therefore be implemented with lower complexity. Furthermore, the exact and asymptotic expressions of the outage probability are derived. The diversity-multiplexing tradeoff (DMT) performance is also analyzed. Theoretical analysis shows that R3SSP achieves full cooperative diversity and provides better DMT performance than relay selection-based protocols in a system where the number of sources is higher than that of the relays. Based on the DMT analysis, we further propose an adaptive relay activation scheme that is capable of achieving higher DMT by dynamically selecting the number of relays to be activated in the entire network. Simulation results also verify the validity and superiority of R3SSP.

Improving the DMT Performance for MIMO Communication With Linear Receivers

Multiple-input-multiple-output (MIMO) linear receivers are often of more practical interest than maximum-likelihood (ML) receivers due to their low decoding complexity but at the cost of worse diversity gain performance. Such a statement on performance loss is due to the assumption of using an independent identically distributed complex Gaussian vector as channel input. By removing this assumption, we find that the diversity performance of MIMO linear receivers can be significantly improved. In an extreme case, it can be the same as that of ML receivers. Specifically, in this paper, we investigate the diversity-multiplexing tradeoff (DMT) performance of MIMO linear receivers with colored and possibly degenerate Gaussian channel inputs. By varying the rank of the covariance matrix of the channel input vector and by allowing temporal coding across multiple channel uses, we show that the MIMO linear receiver can achieve a much better DMT performance than the currently known one. Explicit optimal code constructions are provided, along with simulation results, to justify the above findings. For the case of (2 × 2) and (3 × 3) MIMO linear receivers, simulation results show that the newly proposed codes provide significant gains of 10 and 12.08 dB in E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at bit error rate 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> compared to the conventional schemes, respectively.

A multi-relay-selection scheme with cyclic delay diversity

In our proposed multi-relay-selection scheme with cyclic delay diversity (CDD), relays with spectral efficiency above a threshold are chosen to forward information, and a distinct cyclic shift is assigned to each selected relay. We derive an approximate expression of the end-to-end mutual information for the proposed scheme. We further analyze the outage probability and diversity-multiplexing tradeoff (DMT) performance. Numerical results show that the proposed scheme can realize full diversity and achieve the same outage probability and DMT performance as that of the selection cooperation scheme without the need for feedback information and strict synchronization among relays.

Decode‐and‐forward two‐way relaying protocol with one retransmission

SUMMARYThis paper investigates the decode‐and‐forward two‐way relaying channel without direct link and proposes a protocol based on the physical‐layer network coding (PNC) protocol. The proposed protocol (termed ORT) introduces one retransmission into PNC, aiming at enhancing its outage performance. To manifest the merits of ORT, we compare it with PNC and the time‐division broadcast (TDBC) protocol, in terms of outage performance, expected rate, and diversity‐multiplexing tradeoff (DMT). Firstly, we derive the outage probability of the three protocols and then the expected rate. Secondly, asymptotic analysis is conducted to shed light on the diversity and coding gains. Finally, the DMT is obtained for the three protocols. The numerical results reveal the following: (i) that ORT performs better than PNC in both outage and expected rate performance when the nodes transmit with different powers. However, it has the same DMT performance with PNC; (ii) that ORT possesses improved DMT performance over TDBC whereas its expected rate is only better than the latter at medium to high signal‐to‐noise ratio. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Opportunistic Distributed Space-Time Coding for Decode-and-Forward Cooperation Systems

In this paper, we consider a decode-and-forward (DF) cooperation system consisting of two cooperative users in sending their information to a common destination, for which the distributed space-time coding (DSTC) is applied in an opportunistic manner, called opportunistic DSTC (O-DSTC), depending on whether the two users succeed in decoding each other's information or not. We propose two O-DSTC schemes for the full-duplex and half-duplex relaying scenarios, which are, respectively, referred to as the full-duplex and half-duplex-based O-DSTC. We evaluate the outage performance of the proposed O-DSTC as well as the conventional selective DF (S-DF) cooperation and fixed DSTC (F-DSTC) schemes. Numerical results show that the O-DSTC outperforms the conventional S-DF and F-DSTC schemes considering both full-duplex and half-duplex. In addition, we develop the diversity-multiplexing tradeoff (DMT) of the proposed O-DSTC, conventional S-DF and F-DSTC schemes by considering the two cooperative users with different data rates (also known as different multiplexing gains). We show that, for both the full-duplex and half-duplex modes, the proposed O-DSTC strictly outperforms the conventional S-DF and F-DSTC in terms of DMT. It is also shown that, in the full-duplex-based O-DSTC scheme, the diversity gain obtained by any of the two cooperative users not only depends on its own multiplexing gain, but also relates to its partner's multiplexing gain. By jointly considering the two users' DMT, the full-duplex-based O-DSTC scheme can achieve the optimal diversity gain when the two users are with the same multiplexing gain. For the half-duplex-based O-DSTC scheme, the DMT performance of the two users are independent of each other, which differs from the full-duplex-based O-DSTC scheme where mutual dependence exists between the cooperative users in terms of DMT.

Low-complexity distributed relay selection for two-way AF relaying networks

Presented is a low-complexity distributed two-way amplify-and-forward (AF) relay selection scheme, in which the optimal relay can be selected only by comparing the received power at the relay separately from two users, is easy to implement and has potential to find wide application in practical two-way relaying systems. It is proved that the proposed relay selection scheme can achieve the same diversity-multiplexing trade-off performance as obtained by the popular outage-optimal two-way relaying selection scheme. Simulation results validate the analysis.

DMT Optimal Cooperative Protocols with Destination-Based Selection of the Best Relay

We design a cooperative protocol in the context of wireless mesh networks in order to increase the reliability of wireless links. Destination terminals ask for cooperation when they fail in decoding data frames transmitted by source terminals. In that case, each destination terminal D calls a specific relay terminal B with a signaling frame to help its transmission with source terminal S. To select appropriate relays, destination terminals maintain tables of relay terminals, one for each possible source address. These tables are constituted by passively overhearing ongoing transmissions. Hence, when cooperation is needed between S and D, and when a relay B is found by terminal D in the relay table associated with terminal S, the destination terminal sends a negative acknowledgment frame that contains the address of B. When the best relay B has successfully decoded the source message, it sends a copy of the data frame to D using a selective decode-and-forward transmission scheme. The on-demand approach allows maximization of the spatial multiplexing gain and the cooperation of the best relay allows maximization of the spatial diversity order. Hence, the proposed protocol achieves optimal diversity-multiplexing trade-off performance. Moreover, this performance is achieved through a collision-free selection process.

Diversity-Multiplexing Tradeoff Analysis of Coded Multi-User Relay Networks

We study the impact of multiple access strategies on the diversity-multiplexing tradeoff (DMT) performance in wireless multi-user relay networks. The networks contain multiple independent sources, multiple half-duplex decode-and-forward (DF) relays, and one common destination. Instead of separately retransmitting each source message, the relays employ a class of spectrally efficient finite field network codes to assist the sources. It is shown that fully orthogonal or fully non-orthogonal transmission among sources/relays does not necessarily provide optimized DMT performance. We propose a novel transmission protocol that divides the sources and relays into individual clusters. The nodes within one cluster transmit non-orthogonally while the transmissions of different clusters span orthogonal channels. We provide the method to calculate the achievable DMT for each clustering strategy. The network DMT performance can thus be optimized by properly clustering the multiple sources and relays.

Approaching the Optimal Diversity-Multiplexing Tradeoff in a Four-node Cooperative Network

A novel cooperative diversity transmission protocol is proposed for a four-node network, in which a single-antenna source communicates with an N-antenna destination with the help of two K-antenna half-duplex decode-and-forward (DF) relays. The proposed shifted successive DF relaying (SSDFR) protocol asymptotically achieves the optimal diversity-multiplexing tradeoff (DMT) the system can provide. The resulting DMT performance does not require complex coding strategies at the relays, extremely strong or weak inter-relay channel conditions, or feedback from the destination to the source, which highlights the advantages of the proposed protocol over state of the art techniques.