Abstract Here, the authors consider the uplink of a cellular massive multiple‐input multiple‐output (MIMO) system with maximum ratio combiner (MRC) at base stations (BSs). To achieve a better QoS provisioning, users in the cells employ link adaptation using adaptive modulation and coding (AMC) in conjunction with packet retransmission. The authors present a cross‐layer approach for the AMC design exploiting the time variation feature of MIMO wireless channels. At first, a fast AMC (FAMC) scheme is proposed to adapt the fast small‐scale fading of the wireless channel based on the instantaneous channel state information. Since the fast fading is asymptotically averaged out due to the channel hardening property of massive MIMO system, we then suggest a slow AMC (SAMC) scheme which adjusts the adaptation parameters based on only the large‐scale channel fading statistics including shadow fading and pass loss of the channel. The SAMC substantially reduces the feedback rate and implementation cost because of using a larger coherence time compared to that of the FAMC. For the proposed schemes, the probability density function of signal‐to‐interference‐plus‐noise ratio (SINR) for MRC receivers at BSs is analytically derived and verified by simulation. Also, closed‐form expressions are presented for the throughput and packet error outage of the system. Index Terms—Massive MIMO, MRC, AMC, ARQ, Performance analysis.

This study presents a novel idea for information hiding at the physical layer level in order to securely transmit confidential cognitive radio data in cooperative relaying systems. Considering a cognitive radio network in which the secondary user cooperates with the primary system in relaying its data, in the proposed model, confidential cognitive information is hidden into the primary signal as a low‐power noise at a symbol level such that it would be invisible by malicious users. The new hiding algorithm can be utilised along with any standard relaying scheme as long as the primary information signal is used as the cover data without significant degradation of the primary system performance. In the presence of cognitive data hiding, both the frame error rate and throughput performance of the primary and secondary systems are derived analytically for well‐known relaying schemes such as fixed and incremental relaying protocols, when a selection‐combining rule is utilised at the primary receiver for symbol detection. Using simulation results the correctness of the proposed theoretical analysis is verified. Moreover, using numerical results the existing tradeoff between the hiding cognitive capacity of the proposed model and the performance degradation of the primary system is highlighted.

In this paper, we consider an underlay cognitive radio paradigm with a primary packet system which implements automatic repeat request (ARQ)-based error control. We propose cognitive transmission strategies which provision for minimum primary quality of service (QoS) requirements. The proposed strategies take advantage of opportunities that arise during ARQ retransmissions of the primary system at the link layer, and adapt channel fading variations by employing adaptive modulation and coding (AMC) and power control at the physical layer. In this cross-layer formulation, the cognitive throughput is optimized subject to 1) a packet-loss-rate (PLR) constraint on the cognitive link, and 2) a minimum required throughput and a PLR constraint on the primary link. We first derive analytical expressions for the link-layer throughput of the cognitive link defined in terms of the data rate successfully received at the receiver side. Next, we present optimized AMC and power control schemes for the cognitive transmitter. Numerical results show significant improvement in terms of the cognitive throughput and PLR performance. Namely, when the cognitive transmitter employs both power and rate control the throughput-maximizing strategy is determined based on a tradeoff between the primary PLR and delay (in terms of the number of retransmission rounds) QoS metrics.

The effective capacity (EC) for a wireless system expresses the maximum arrival source rate that the system can transmit over the wireless channel by fulfilling certain probabilistic delay constraints. This paper presents an EC analysis for a relay-assisted cooperative protocol exploiting adaptive transmission at physical and data-link layers. In the considered model, a source employs adaptive modulation and coding (AMC) in conjunction with a cooperative ARQ protocol, to transmit delay-constrained traffic to the destination node. To achieve adaptive cooperative diversity, a relay node, also equipped with AMC, performs cooperation when it decodes the source packet correctly and the destination requested a packet retransmission. We derive a tight closed-form upper-bound expression for the EC of the queue service process at the source node when wireless links are subject to time-correlated fading. To this end, a Markov model for the relay channel is used. We also present a cross-layer approach to delay-aware AMC design for the relay channel which provides the maximum system throughput subject to a probabilistic delay constraint. The numerical and simulation results show that the proposed adaptive cooperative protocol can dramatically improve the EC and the system throughput over time-correlated fading channels when compared to a direct transmission system.

Aiming at improving the QoS performance over fading channels, this paper presents an analysis of the effective capacity for a relay-assisted communication system which utilizes a cooperative packet retransmission protocol at the link-layer in conjunction with AMC-based multi-rate transmission at the physical layer. In the considered model, a source (S) node employs AMC to transmit delay-constrained packet traffic to the destination (D) node. To achieve adaptive cooperative diversity, a relay node, also equipped with AMC, forwards the packet received from node S to node D if it was able to decode the source packet correctly and node D requested a packet retransmission. For this protocol we derive a closed-form expression for the effective capacity of the queue service process at node S. Numerical results reveal that the proposed cooperative protocol can dramatically increase the effective capacity with respect to a direct transmission system with AMC.

This paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocols in wireless networks, which employ adaptive modulation and coding (AMC) in conjunction with adaptive cooperative diversity and are subject to time-correlated fading channels. We first consider a point-to-point scenario, i.e., non-cooperative HARQ with AMC. Utilizing a Markov channel model which accounts for the temporal correlation in the successive transmission of incremental redundancy by the HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional code family. Next, we consider a cooperative HARQ (CHARQ) scheme in which a relay node, also equipped with AMC, retransmits redundancy packets when it is able to decode the source information packet correctly. For this scenario, we also derive the throughput and packet loss performance. Finally, we present a cross-layer AMC design approach which takes into account the hybrid ARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocols leads to a substantial throughput gain. While the performance of the AMC with HARQ protocol is strongly affected by the channel correlation, the CHARQ protocol provides noticeable performance gains over correlated fading channels as well.

This paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocol in wireless networks which employ adaptive modulation and coding (AMC) at the physical layer and are subject to time-correlated fading channels. Utilizing a Markov channel model which accounts for the temporal correlation in successive parity transmissions by the adaptive rate HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional (RCPC) code family. As an application, we then present a cross-layer AMC design which takes into account the performance gain of the HARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocol leads to a substantial throughput gain, but the channel correlation strongly diminishes the performance of the HARQ protocol in terms of throughput and packet loss rate.

An optimisation framework for wireless link adaptation which maximises the system throughput subject to a packet-level quality of service (QoS) constraint is presented. The authors consider joint adaptive variation of the transmitted power level, transmission data rate and packet-error-rate (PER) at the physical layer to improve the throughput performance of the selective-repeat automatic repeat request (SR-ARQ) protocol over block-fading channels. Specifically, for discrete-rate coded M-QAM schemes, the authors present a power and rate adaptation algorithm that guarantees a target PER constraint. The proposed framework also facilitates optimising the throughput performance for delay constrained wireless applications, which imposes a limit on the number of retransmissions for the ARQ. In particular, a link adaptation scheme is presented, which guarantees a target packet-loss rate (PLR) when a truncated SR ARQ protocol at the data-link layer is employed. Numerical results indicate that the proposed adaptation schemes compared with other adaptive schemes noticeably enhance the system throughput. Also, in the case of truncated ARQ, the results illustrate a fundamental trade-off between the delay and PLR QoS metrics achieved at the maximum throughput performance.

In this paper, we consider the problem of transmission of a delay-sensitive and bursty traffic source over a time-varying Nakagami-m fading channel in a cross-layer optimization framework. Aiming at minimizing the packet delay due to queuing at the data link layer, we present power and rate adaptation policies for coded M-QAM modulation schemes, which guarantee a prescribed channel packet error rate constraint. This is also equivalent to minimizing the system packet loss rate. The proposed adaptation policies are derived both for block and correlated channel fading scenarios. To enable the transmission policy design, we use a statistical model to characterize the packet delay derived from a known result of large deviations theory. Considering the error resolution capability of the automatic repeat request protocol, we then provide the appropriate analytical tools to incorporate the effect of packet retransmission in the proposed optimization framework for transmission policy design. The results show that the proposed adaptation policies compared to others adaptive solutions, significantly improve the delay and throughput performance for delay-sensitive bursty traffic over time-varying fading channels.

In this paper, we consider the problem of transmission of a bursty data-packet traffic over MIMO space-time diversity fading channels. Aiming at minimizing the packet loss probability due to buffer overflow at the data link layer, we propose a cross-layer analytical framework for transmission policy design which directly satisfies a packet error rate (PER) constraint at the physical layer. Particularly, we present a power and rate adaptation policy for coded M-QAM modulation schemes that are implemented in conjunction with a MIMO diversity system. To enable the transmission policy design, we use a statistical model to characterize the buffer overflow derived from a large deviations result. Numerical results demonstrate that the proposed adaptation policy significantly improves the packet-loss performance for bursty data traffic over MIMO fading channels, when compared to others adaptive solutions.

In this paper, we consider the problem of transmitting a delay-sensitive and bursty traffic over a time- varying MIMO Nakagami-ra fading channel, and optimize the delay performance of packet queuing at the data link layer. We use a statistical model to characterize the packet delay derived from a known large deviations result, and allows for analytical insights into transmission policy design. We derive power and rate adaptation policies for coded M-QAM modulation schemes that are implemented in conjunction with a MIMO diversity system; such that the packet delay probability is minimized subject to a prescribed channel packet error rate constraint. This is also equivalent to minimizing the system packet loss rate. The proposed adaptation policies depend not only on channel conditions but also on the quality of service performance at the data link layer. Numerical results show that the proposed cross- layer adaptation policies significantly improve the delay performance for delay-sensitive bursty traffic over MIMO fading channels, when compared to others adaptive solutions.

In this paper, we consider a deadline constrained traffic and analyze the joint effects of packet queuing and adaptive modulation (AM) for packet transmission in MIMO systems. We present a general analytical procedure, and derive the achievable delay-bound violation probability, the packet loss rate, and the average throughput of AM in MIMO wireless links employing orthogonal space time block coding (STBC) over Nakagami fading channels. In the proposed analytical procedure, we use statistical delay-bound for deadline constrained traffic based on the effective bandwidth theory. Based on our performance analysis, we propose a cross-layer design, which selects the optimal target packet error rate of AM at the physical layer, to minimize the packet loss rate and maximize the average throughput, when combined with packet queuing at the data link layer. Numerical results demonstrate that the system performance depends on various parameters, and show the performance gain due to cross-layer design. We also discuss briefly possible applications of our proposed modeling to quality of service guarantee in multiuser scenarios.

Adaptive modulation and coding (AMC) and automatic repeat request (ARQ) protocol are powerful techniques for improving the spectral efficiency (SE) or the error performance in wireless packet networks over fading channels. In this paper, we first consider a discrete-rate M-QAM based AMC scheme and propose a variable power transmission scheme for transmission of packets over block-fading wireless channels. Considering the error-correcting capability of the truncated-ARQ, which depends on the maximum number of retransmissions (Nr), we then optimize the AMC and power control schemes that guarantee the required packet loss rate (PLR) performance while satisfying an average transmit power constraint. Numerical results reveal that in wireless packet systems with limited packet length, the proposed link adaptation algorithm improves the system performance in terms of the SE and the PLR However, this improvement depends on the target PLR and NrWhen the target PLR is sufficiently small, this improvement will be observed in terms of the SE for small Nphowever, in the larger target PLR, the improvement will only be observed in terms of the achievable PLR.