Diversity-multiplexing Tradeoff Research Articles

Diversity-multiplexing tradeoff for cooperative MIMO radar and communications system

In this paper, multiple-input multiple-output (MIMO) integrated radar and communications (IRC) system is studied, where the radar and communications parts work cooperatively, leading to a hybrid active-passive (HAP) MIMO radar and a radar-aided (RA) MIMO communications subsystems. To unify the performance metric for both subsystems, the diversity gain and multiplexing gain are derived for the RA MIMO communications and the HAP MIMO radar subsystems, based on which the tradeoff between the diversity and multiplexing gains is analyzed theoretically for each of the subsystems. The obtained diversity gain and multiplexing gain can facilitate the design and optimization of the IRC system. Employing these two unified performance metrics, the IRC system antenna number assignment is formulated as a multi-objective optimization problem, and the Pareto solutions are provided. The correctness of theoretical analysis is verified by simulations. Our results can provide useful guidance for system designers.

An Information-Theoretic Characterization of MIMO-FAS: Optimization, Diversity-Multiplexing Tradeoff and q-Outage Capacity

An Information-Theoretic Characterization of MIMO-FAS: Optimization, Diversity-Multiplexing Tradeoff and <i>q</i>-Outage Capacity

Selective-Fading Multiple-Access MIMO Channels: Diversity-MultiplexingTradeoff and Dominant Outage Event Regions

We establish the optimal diversity-multiplexing (DM) tradeoff for coherent selective-fading multiple-access MIMO channels and provide corresponding code design criteria. As a byproduct, on the conceptual level, we find an interesting relation between the DM tradeoff framework and the notion of dominant error event regions, first introduced in the AWGN case by Gallager, IEEE Trans. IT, 1985. This relation allows us to accurately characterize the error mechanisms in MIMO fading multiple-access channels. In particular, we find that, for a given rate tuple, the maximum achievable diversity order is determined by a single outage event that dominates the total error probability exponentially in SNR. Finally, we examine the distributed space-time code construction proposed by Badr and Belfiore, Int. Zurich Seminar on Commun., 2008, using the code design criteria derived in the present paper.

Finite SNR Diversity-Multiplexing Trade-off in Hybrid ABCom/RCom-Assisted NOMA Networks

Finite SNR Diversity-Multiplexing Trade-off in Hybrid ABCom/RCom-Assisted NOMA Networks

Impartial Cooperation in SWIPT-Assisted NOMA Systems With Random User Distribution

Impartial cooperation is considered in simultaneous wireless information and power transfer (SWIPT)-assisted downlink non-orthogonal multiple access (NOMA) systems with random user distribution. Unlike conventional SWIPT-assisted cooperative NOMA transmissions, we consider random user locations and investigate a transmission model in which both the near and far users of a NOMA system can serve as energy harvesting relays and forward information to each other. To assess the impact of user placement on the system performance, three user pairing schemes are designed. Closed-form expressions for the outage probability, diversity order, diversity-multiplexing trade-off (DMT), and system throughput are derived under different user location distributions, revealing that the novel SWIPT-assisted impartial cooperative NOMA improves these metrics of the near user, and does not degrade those of the far user, compared with the conventional schemes. Numerical results validate our analysis and confirm that our approach is more efficient in resource utilization, as compared to existing schemes.

Outage and DMT Analysis of Partition-Based Schemes for RIS-Aided MIMO Fading Channels

In this paper, we investigate the performance of multiple-input multiple-output (MIMO) fading channels assisted by a reconfigurable intelligent surface (RIS), through the employment of partition-based RIS schemes. The proposed schemes are implemented without requiring any channel state information knowledge at the transmitter side; this characteristic makes them attractive for practical applications. In particular, the RIS elements are partitioned into sub-surfaces, which are periodically modified in an efficient way to assist the communication. Under this framework, we propose two low-complexity partition-based schemes, where each sub-surface is adjusted by following an amplitude-based or a phase-based approach. Specifically, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">activate-reflect</i> (AR) scheme activates each sub-surface consecutively, by changing the reflection amplitude of the corresponding elements. On the other hand, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">flip-reflect</i> (FR) scheme adjusts periodically the phase shift of the elements at each sub-surface. Through the sequential reconfiguration of each sub-surface, an equivalent parallel channel in the time domain is produced. We analyze the performance of each scheme in terms of outage probability and provide expressions for the achieved diversity-multiplexing tradeoff. Our results show that the asymptotic performance of the considered network under the partition-based schemes can be significantly enhanced in terms of diversity gain compared to the conventional case, where a single partition is considered. Moreover, the FR scheme always achieves the maximum multiplexing gain, while for the AR scheme this maximum gain can be achieved only under certain conditions with respect to the number of elements in each sub-surface.

On the diversity-multiplexing trade-off of hybrid diamond relay channels

The diversity-multiplexing trade-off (DMT) of a diamond relay channel in a quasi-static slow Rayleigh fading environment is studied, where one of the relays operates in half-duplex mode while the other one is full-duplex; hence, the term hybrid is used to refer to this channel. DMT is a known powerful tool that captures the inherent tension between the reliability and the transmission rate in a wireless communication network at high signal-to-noise ratios (SNR). In this study, we have assumed that the average SNRs of different links vary at different rates, each represented by an exponent at high SNR. These average SNR exponents are categorized into two different classes: In Class I, both of the relays are placed either in close proximity to the source or in close proximity to the destination, whereas in Class II one of the relays is closer to the source while the other one is closer to the destination. Subsequently, for Class I and for a special symmetric case of Class II, an explicit expression of the DMT of the static quantize-map-and-forward (SQMF) strategy and the optimal static schedule in the half-duplex relay, are derived. The non-symmetric case of Class II can numerically be studied using the optimization problem provided in the paper for any given parameters. As a corollary, our analysis shows that for Class I, the SQMF strategy in the proposed hybrid diamond relay channel reaches the ideal full-duplex DMT upper bound if the degrees of freedom provided by the path through the full-duplex relay is greater than or equal to that provided by the path through the half-duplex relay, or if the degrees of freedom provided by the former is less than that provided by the latter, but still large enough to support the desired multiplexing gain.

Tradeoff Between Diversity and Multiplexing Gains in Block Fading Optical Wireless Channels

The diversity-multiplexing tradeoff (DMT) provides a fundamental performance metric for different multiple-input multiple-output (MIMO) schemes in wireless communications. In this paper, we explore the block fading optical wireless communication (OWC) channels and characterize the DMT in the presence of both optical peak- and average-power constraints. Three different fading distributions are considered, which reflect different channel conditions. In each channel condition, we obtain the optimal DMT when the block length is sufficiently large, and we also derive the lower and upper bounds of the DMT curve when the block length is small. These results are dramatically different from the existing DMT results in radio-frequency (RF) channels. These differences may be due to the fact that the optical input signal is real and bounded, while its RF counterpart is usually complex and unbounded.

A Novel Cooperative NOMA Coding for Uplink MTC Networks

In this paper we consider machine-type communications (MTC) in 5G cellular networks for internet-of-thing (IoT) applications, where a large number of MTC devices simultaneously communicate with a base station (BS) over an uplink channel. To overcome the resource-constrained nature of the MTC nodes, we introduce a novel cooperative non-orthogonal multiple access (NOMA) coding scheme for supporting multi-user uplink transmissions with low complexity and signaling overhead, where the assumption of no feedback link hence no channel state information (CSI) available at the transmitting MTC nodes is taken. To gain deep understanding of its performance, we derive close-form analytical expressions on outage probability and diversity-multiplexing tradeoff (DMT) curve in the asymptotic regime of high signal-to-noise ratio (SNR), and optimize the end-to-end performance in terms of the exponential decay rate of expected distortion (ED). The asymptotic analytical result can be translated into a significant SNR gains of practical implementations with general SNR values, which is further confirmed via extensive simulation.

Modeling of a Vehicle-to-Vehicle Based Visible Light Communication System Under Shadowing and Investigation of the Diversity-Multiplexing Tradeoff

In this research, we propose a novel vehicle-to-vehicle (V2V) visible light communications (VLC)-based system model under <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">shadowing.</i> Shadowing significantly affects the path loss, which arises due to the blockage of the line-of-sight path, on the VLC link performance. Moreover, we analyze the performance of the considered system using the diversity-multiplexing tradeoff (DMT) metric. Note that DMT provides an optimal tradeoff between the diversity gain and the multiplexing gain. Further, DMT provides the operating points which play a significant role in the design of the communication system. In this research, we first model the V2V-VLC system based on the probabilistic behavior of the shadowing, followed by analyzing the corresponding DMT. In addition, we investigate the optimal DMT for a practical transmission scenario, where there is a possibility that the VLC link may experience an outage. Furthermore, we investigate the system performance under the atmospheric turbulence conditions. Finally, the entire study and the subsequent analysis is acknowledged by means of useful remarks and interesting observations that have not been previously identified in the literature.

Outage Probability and Finite-SNR DMT Analysis for IRS-Aided MIMO Systems: How Large IRSs Need to be?

Intelligent reflecting surfaces (IRSs) are promising enablers for high-capacity wireless communication systems by constructing favorable channels between the transmitter and receiver. However, general, accurate, and tractable outage probability analysis for IRS-aided multiple-input-multiple-output (MIMO) systems is not available in the literature. In this paper, we first characterize the distribution of the mutual information (MI) for IRS-aided MIMO systems by capitalizing on large random matrix theory (RMT). Based on this result, a closed-form approximation for the outage probability is derived and a gradient-based algorithm is proposed to minimize the outage probability with statistical channel state information (CSI). We also investigate the diversity-multiplexing tradeoff (DMT) with finite signal-to-noise ratio (SNR). Based on these theoretical results, we further study the impact of the IRS size on system performance. In the high SNR regime, we provide closed-form expressions for the ergodic mutual information (EMI) and outage probability as a function of the IRS size, which analytically reveal that the benefit of increasing the IRS size saturates quickly. Simulation results validate the accuracy of the theoretical analysis and confirm the increasing cost to improve system performance by deploying larger IRSs. For example, for an IRS-aided MIMO system with 20 antennas at both the transmitter and receiver, we need to double the size of the IRS to increase the throughput from 90% to 95% of its maximum value.

A Markov Chain Approach for Myopic Multi-Hop Relaying: Outage and Diversity Analysis

In this paper, a cooperative protocol is investigated for a multi-hop network consisting of relays with buffers of finite size, which may operate in different communication modes. The protocol is based on the myopic decode-and-forward strategy, where each node of the network cooperates with a limited number of neighboring nodes for the transmission of the signals. Each relay stores in its buffer the messages that were successfully decoded, in order to forward them through the appropriate channel links, based on its supported communication modes. A complete theoretical framework is investigated that models the evolution of the buffers and the transitions at the operations of each relay as a state Markov chain (MC). We analyze the performance of the proposed protocol in terms of outage probability and derive an expression for the achieved diversity-multiplexing tradeoff, by using the state transition matrix and the related steady state of the MC. Our results show that the proposed protocol outperforms the conventional multi-hop relaying scheme and the system's outage probability as well as the achieved diversity order depend on the degree of cooperation among neighboring nodes and the communication model that is considered for every relay of the network.

Backscatter Cooperation in NOMA Communications Systems

In this paper, a backscatter cooperation (BC) scheme is proposed for non-orthogonal multiple access (NOMA) downlink transmission. The key idea is to backscatter the surplus power of the received downlink signals at one user to enhance the reception of the user who cannot recover its information. To evaluate the performance of the proposed BC-NOMA scheme, three benchmark schemes are introduced, which include the non-cooperation (NC)-NOMA scheme, the conventional relaying (CR)-NOMA scheme, and the incremental relaying (IR)-NOMA scheme. For all these schemes, the outage performance, the expected rate, and the diversity-multiplexing trade-off (DMT) performance are analyzed. Additionally, the optimal power allocation to maximize the expected rate of the BC-NOMA scheme in the high signal-to-noise ratio region is derived. The theoretical results show that the proposed BC-NOMA can enhance both transmission reliability (outage performance) and transmission effectiveness (expected rate) compared with NC-NOMA. Furthermore, representative numerical results are presented to validate the theoretical results. It is shown that unlike the two relaying-based cooperative schemes (CR/IR-NOMA), which improve the outage performance at the cost of transmission rate, the proposed BC-NOMA scheme can enhance the transmission reliability without impairing the spectrum efficiency, which makes backscattering an appealing solution to cooperative NOMA downlinks.

DMT analysis and optimal scheduling for FSO relaying communications

In this paper, two-hop parallel N-relay networks are considered and the diversity-multiplexing tradeoff (DMT) is derived over Gamma-Gamma free-space optical (FSO) channels with identical average received signal to noise rations in all links. In the derivations, both local and global channel state information (CSI) are investigated. In the local CSI case, the node only knows its incoming link conditions, while in the global CSI case, the nodes are aware of all the CSIs in the network. The listening and transmitting times at the relays as variables in the DMT derivation are further considered which are later used to optimize the performance of the network. It is demonstrated that the optimal DMT is obtained with the static quantize map and forward (SQMF) and dynamic quantize map and forward (DQMF) strategies for different ranges of the multiplexing gain. In addition, the optimal schedule of relays in the DQMF strategy is determined as a function of the local channel conditions in the relays.

Unified Performance Analysis of MIMO Mixed RF/FSO Relaying System

This paper investigates the asymmetric dual–hop multiple input multiple output (MIMO) mixed radio frequency (RF)/free space optical (FSO) decode–and–forward (DF) relaying system. This kind of system can utilize two different fading characteristic channels to reduce the possibility of the system falling into deep fading. In addition, each link of the system adopts MIMO technology to mitigate the disadvantages of fading. In this paper, the closed form expressions of the outage probability, bit error rate (BER) and average ergodic capacity are derived. The approximate expression of the system outage probability considering the pointing error is also derived. Additionally, asymptotic performance for diversity order and diversity–multiplexing tradeoff (DMT) of the system is analyzed and discussed, which provides direct theoretical basis for practical engineering design.

DMT analysis and optimal scheduling for two-hop parallel relay networks

Two-hop parallel networks with half-duplex relays over quasi-static Rayleigh fading channels are considered. Assuming relays have only local channel state information, optimal communication schemes for these networks in terms of the diversity multiplexing trade-off (DMT) are obtained. It is shown that the dynamic quantize-map-and-forward (DQMF) and the static quantize-map-and-forward (SQMF) communication strategies achieve the optimal DMT at different ranges of the multiplexing gain. In the DQMF scheme, a relay sets its transmitting/listening times according to the instantaneous source-relay channel condition. However, in the SQMF scheme, a relay sets its transmitting/listening times to be a constant independent of the instantaneous source-relay channel gain. Essentially, we calculate the DMT of the network under the general setting for arbitrary average signal-to-noise ratios over links and it is shown that the DMT of the proposed schemes matches the upper bounds. Moreover, the optimal transmitting/listening times of the half-duplex relays as functions of the instantaneous channel realizations are derived for different communication strategies in the general setting. Finally, various simulation scenarios are considered and the DMT of the proposed schemes and the dynamic decode and forward communication strategy are compared.

Optimal PHY Configuration in Wireless Networks

In this work, we study the optimal configuration of the physical layer in wireless networks by means of Semi-Markov Decision Process (SMDP) modeling. In particular, assume the physical layer is characterized by a set of potential operating points, with each point corresponding to a rate and reliability pair; for example, these pairs might be obtained through a now-standard diversity-multiplexing tradeoff characterization. Given the current network state (e.g., buffer occupancies), a Decision Maker (DM) needs to dynamically decide which operating point to use. The SMDP problem formulation allows us to choose from these points. A solution to the SMDP problem is an optimal selection of operating points, which is expressed by a decision rule as a function of the number of packets in the source’s finite queue, the channel state, and the size of the packet to be transmitted. We derive a general solution to the SMDP which covers various model configurations, packet size distributions and channel dynamics. For the specific case of exponential transmission times, we analytically prove the optimal policy has a threshold structure. Numerical results validate this finding, as well as depict muti-threshold policies for time varying channels such as the Gilbert-Elliott channel.

Incremental Decode-and-Forward Protocols for D2D Communication: A Diversity-Multiplexing-Tradeoff Perspective

We propose a slotted incremental decode-and-forward (SIDF) and a non-slotted incremental decode-and-forward (NIDF) protocol for device-to-device communication. Different from previous incremental protocols in literature, a user only spend a portion of its temporal degrees of freedom to help its partner, enabling improved bandwidth efficiency. We derive the diversity-multiplexing tradeoffs (DMTs), and show that NIDF achieves the DMT upper bound whereas SIDF is slightly away from the upper bound at the medium multiplexing gain region. We also show how the DMT optimizing resource allocation factor varies for different multiplexing gains. Numerical outage probability results are shown to line up with the theoretical DMT analysis, and improved bandwidth efficiency over the existing incremental amplify-forward is demonstrated.

Half-duplex multiple-relay multiple-antenna diamond networks with perfect full-duplex performance

Diversity-multiplexing tradeoff (DMT) of a full-duplex diamond network where the inter-relay interference (IRI) is suppressed, global channel state information (CSI) is available in all nodes, and perfect self-interference cancellation (SIC) technique is used, which we call it the perfect full-duplex diamond network, is an upper bound for the DMT of the equivalent half-duplex diamond network, i.e., the perfect full-duplex diamond network outperforms the half-duplex case. Nevertheless, the implementation of the perfect full-duplex diamond network is a high-cost operation and requires significant hardware changes in current systems. The main question addressed in this paper is: under which condition (or perhaps conditions) does a prevalent half-duplex diamond network provide the same performance as the perfect full-duplex one? In this regard, first, we calculate the DMT of a perfect full-duplex multiple-relay and multiple-antenna (MRMA) symmetric diamond network. Then, we demonstrate that for the same network but with half-duplex relays, when the number of antennas in relays satisfies a specific condition, there exists a fixed listen-transmit schedule combined with quantize-map-and-forward (QMF) relaying to achieve the optimal DMT. Also, we attain a lower bound for the total number of antennas of the MRMA symmetric diamond network to achieve the optimal DMT.

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.