Interaction between radio link level truncated ARQ, and TCP in multi-rate wireless networks: a cross-layer performance analysis

A complete queueing model for radio link layer performance analysis is developed assuming adaptive modulation and coding (AMC) at the physical layer and truncated automatic repeat request (ARQ)-based error control at the link layer. From the model, queue length distribution and average queueing delay can be calculated. The average queueing delay is then used to estimate transmission control protocol (TCP) throughput performance using a fixed-point approach. Using the model, we are able to choose signal-to-noise ratio thresholds of different transmission modes for AMC at the physical layer for different persistence levels of ARQ at the link layer so that TCP throughput is maximized. We observe that channel correlation negatively impacts the TCP throughput performance. Also, throughput enhancement of TCP NewReno over TCP Reno is observed to be non-negligible only if no ARQ-based error recovery is employed at the link layer.     

Quality of service for multimedia traffic using cross-layer design

Quality-of-service (QoS) guarantees are critical for the transmission of multimedia traffic over mobile wireless networks. Currently, wireless networks provide QoS guarantees using the legacy layered protocol architecture where each layer provides a separate, independent solution, with its own optimised adaptation and protection mechanisms. Cross-layer design has been proposed as a methodology to extend that paradigm in wireless links where there is interdependence between the layers and hence opportunity for information sharing. Recently, cross-layer adaptation mechanisms have been proposed which attempt to solve the QoS provisioning problem. However, most of these mechanisms only use the lower (physical and data link) layers and the possibility of using higher protocol layers remains unexplored. As a result, restrictions are placed on the system which introduces functional and efficiency limitations. Here, one such limitation is highlighted, namely the inability to insert more than one class of traffic in a physical layer frame. A physical and application layer cross-layer adaptation mechanism is then proposed, which overcomes this limitation. The performance results of the scheme show that the cross-layer mechanism can be efficiently applied for the purpose of providing QoS guarantees for multimedia traffic.     

一种能处理无线链路拥塞的TCP/ARQ改进算法

采用链路层自动请求重传（ARQ）方法来对分组差错进行恢复，并对传统的TCP／ARQ算法加以改进，加入了在无线链路拥塞情况下的自适应拥塞避免算法。仿真结果表明，这种能处理无线链路拥塞的TCP／ARQ算法对于提高无线网络的吞吐量非常有效。     

Differentiated cooperative multiple access for multimedia communications over fading wireless networks

The quality of service (QoS) support for multimedia communications faces a big challenge in a fading wireless network. On one hand, conventional automatic repeat request (ARQ) schemes are not effective for small-scale fading channels with correlated errors due to consecutive retransmission failures. On the other hand, large-scale fading due to propagation loss or shadowing severely limits transmission range. A novel differentiated cooperative medium access control (MAC) protocol, called DC-MAC, is proposed to enhance the QoS support for multimedia communications while supporting service differentiation based on the IEEE 802.11e architecture. By enabling cooperative ARQ, the retransmission is initiated from an appropriate transmission queue of an appropriate relay node instead of the original source. Since unnecessary and useless retransmissions may intensify the node contention and degrade the system performance contrarily, a novel negative acknowledgement feedback mechanism is introduced for loss distinguishing and channel estimation such that cooperative retransmission will be employed only when necessary and only by competent nodes. Extensive simulations are conducted on the OPNET platform to analyse the performances of DC-MAC under both small-scale and large-scale fading. Simulation results show that the proposed scheme significantly improves the performances of both multimedia applications and best-effort data applications in terms of throughput, delay and coverage with moderate user contention.     

Throughput fairness and efficiency of link adaptation techniques in wireless networks

Link adaptation techniques aim to maximise the quality of service and resource utilisation in wireless networks. However, fairness must be taken into consideration, particularly, in low-mobility environments where the channel dynamic variation is small. The authors propose and analyse three link adaptation techniques [using joint power control (PC) and adaptive coding and modulation (ACM)] for fairness enhancement. In the first technique, called aggregate throughput maximisation with fairness constraint, the authors formulate the fairness problem as a constrained optimisation problem where the authors try to maximise the aggregate throughput subject to the throughput fairness constraint. In order to solve the optimisation problem, the authors convert the constrained optimisation problem to an unconstrained optimisation one using the penalty method. Then, the unconstrained optimisation problem is solved using the steepest descent technique. The second techniques, called individual throughput balancing, tries to equalise the individual throughput by using a higher throughput level for disadvantaged users and using a lower throughput level for advantaged users. Finally, the third technique, called adaptive virtual maximum power constraint, uses virtual maximum power cap, which is lower than the real maximum power cap. The virtual maximum power cap of each user is variable and it adapts based on the user's individual throughput to compensate disadvantaged users. The authors analyse the three proposed techniques in terms of the throughput fairness and the throughput efficiency and compare them with three basic link adaptation techniques (PC, ACM, and joint PC and ACM). The three proposed techniques are shown to be able to enhance the fairness with different degrees and with different levels of aggregate throughput degradation.     

Cross-layer queuing analysis on multihop relaying networks with adaptive modulation and coding

Multihop relaying is one of the promising techniques in future generation wireless networks. The adaptive modulation and coding (AMC) mechanisms can be applied in order to increase the spectral efficiency of wireless multihop networks. However, most of these mechanisms concentrate on the physical layer without taking the queuing effects at the data link layer into account, whose performances are overestimated. Therefore the cross-layer analytical framework is presented in analysing the quality-of-service (QoS) performances of the decode-and-forward (DF) relaying wireless networks, where the AMC is employed at the physical layer under the conditions of unsaturated traffic and finite-length queue at the data link layer. Considering the characteristics of DF relaying protocol at the physical layer, the authors first propose modelling a two-hop DF relaying wireless channel with AMC as an equivalent Finite State Markov Chain (FSMC) in queuing analysis. Then, the performances in terms of queuing delay, packet loss rate and average throughput are derived. The numerical results show that the proposed analytical method can be efficiently applied for studying the issues including the relay deployment and the cross-layer design in the multihop relaying networks.     

Joint rate and power adaptation for radio resource management in uplink wideband code division multiple access systems

The benefits of adaptive joint power control and rate allocation for uplink transmission in a wideband code division multiple access cellular system are investigated. Closed-loop power control (CLPC), to adaptively adjust the transmit power, has the effect of maintaining a target signal-to-interference ratio and bit error rate (BER) performance. On the other hand, rate adaptation requires less transmit power, although the BER performance may be poorer. The authors differentiate the power update interval from the data rate update interval, analyse and evaluate the performance of two joint rate/power adaptation algorithms in a fading environment: optimal spreading factor-power control (OSF-PC) and greedy rate packing-power control (GRP-PC). Numerical results show that GRP-PC exhibits superior throughput performance compared with other three adaptation schemes. CLPC alone exhibits throughput and BER performances comparable to those of the OSF-PC scheme, but consumes a significantly higher amount of transmit power. Rate adaptation only is not efficient in enhancing throughput, but its power consumption is minimal.     

A cross-layer adaptive algorithm for multimedia QoS fairness in WLAN environments using neural networks

The authors address the problem of providing fair multimedia quality-of-service (QoS) in IEEE 802.11 distributed co-ordination function-based wireless local area networks in the infrastructure mode where mobile hosts experience heterogeneous channel conditions due to mobility and fading effects. It was observed that unequal link qualities can pose significant unfairness of channel sharing, which may thereby lead to the degradation of multimedia QoS performed in adverse conditions. A cross-layer adaptation scheme that provides fair QoS by online adjusting the multidimensional medium access control layer backoff parameters in accordance with the application-layer QoS requirements as well as the physical-layer channel conditions was proposed. The solution is based on an optimisation approach, which utilises neural networks to learn the cross-layer function. Simulation results demonstrate that the proposed adaptation scheme can tackle heterogeneous channel conditions and random joining (or leaving) of hosts to achieve fair QoS in terms of throughput and packet delay.     

Fairness and throughput enhancement based resource allocation scheme for underlay cognitive radio networks

Acquiring good throughput and diminishing interference to primary users (PU) are the main objectives for secondary users in a cognitive radio (CR) network. This paper proposes a centralized subcarrier and power allocation scheme for underlay multi-user orthogonal frequency division multiplexing considering the rate loss and the interference those the PU can tolerate. The main purpose of the proposed scheme is to efficiently distribute the available subcarriers among cognitive users to enhance both the fairness and the throughput performance of the cognitive network while maintaining the QoS of primary users. Simulation results show that the proposed scheme achieves a significantly higher CR network throughput than that of the conventional interference power constraint (IPC) based schemes and provides a significantly enhanced fairness performance. Also, contrary to the conventional IPC based schemes, the proposed scheme is able to significantly increase the achieved throughput as the number of CR users increases.     

Distributed truncated ARQ protocol for cooperative diversity networks

Automatic repeat request (ARQ) retransmission in user cooperative networks, which use amplify-and-forward as a relaying strategy is dealt with. In contrast to the conventional environments, where the source responds in a retransmission demand, in cooperative systems this requirement can also be satisfied by a relay node. In addition, if a relay node can be selected according to the instantaneous channel conditions, the source is not always the optimal responder. The problem under consideration here is to find the retransmission combination which optimises the performance under a given delay quality-of-service constraint. It will be shown that the optimal combination depends on the number of available relays, the total number of retransmissions and the average signal-to-noise ratio. We provide an analytical framework for the definition of the optimal combination in function of these three system parameters. Since the practical ad hoc networks are not centralised and do not have an external control, a distributed truncated ARQ protocol is further proposed to apply the decided retransmission combination.     

Cross-layer design for block subchannel allocation and admission control in the IEEE 802.16 OFDMA networks

The flexibility of orthogonal frequency-division multiple access (OFDMA) technology necessitates a compromise between spectrum efficiency and quality of service (QoS) in IEEE 802.16 broadband wireless networks. This article proposes a complete solution with the nice feature of adaptive modulation and a coding scheme to provide both delay and loss rate guarantees for real-time services. The proposed method first determines the subframe boundary according to the current downlink and uplink backlogs. To comply with the IEEE 802.16 standard, the proposed method then groups contiguous subchannels and allocates them to proper connections based on the current loss rate and available modulation and coding schemes for each connection. By modeling the aggregated required subchannels as a Gaussian distribution, this study develops a simple admission control algorithm by checking if there are enough resources for a new connection. Simulation results show that the proposed solution can provide QoS guarantee with high spectrum efficiency.     

一种新的基于移动预测的MANET路由协议

移动自组网是一种由一系列可以自由移动的节点主机聚集而成的一个临时性动态网络。它没有固定基站，也没有作为控制管理中心的节点主机，由于其拓扑的动态性，其路由协议与其他传统网络有很大的区别。为了能更有效地移动自组网中实现数据的传送，本文提出了一种基于移动预测下的MANET路由协议，该协议综合考虑了传输路径的延时和稳定性，选择在延时限制下平均拥有最稳特性的传输路径，模拟结果表明，这种方法比基于移动预测量稳路径路由协议的传输时延要短，传送成功概率要高，而控制开销却相关不大。     

Quality of service supporting downlink scheduling scheme in worldwide interoperability for microwave access wireless access systems

IEEE 802.16 is a standardisation for a broadband wireless access in metropolitan area networks (MAN). Since the IEEE 802.16 standard defines the concrete quality of service (QoS) requirement, a scheduling scheme is necessary to achieve the QoS requirement. Many scheduling schemes are proposed with the purpose of throughput optimisation and fairness enhancement, however, few scheduling schemes support the delay requirement. In this study, the authors propose a new scheduling scheme reflecting the delay requirement. Specifically, the authors add the delay requirement term in the proportional fair scheduling scheme and the scheduling parameters are optimised with respect to the QoS requirement. Therefore the QoS requirement is achieved without the excessive resource consumption.     

Adaptive RS codes for message delivery over an encrypted mobile network

The authors present a hybrid automatic repeat request technique using adaptive Reed-Solomon (RS) codes with packet erasure. This technique suits the transport layer in tactical mobile wireless networks with type I encryption, where encryption erasures the entire Internet protocol packet. The novelty of the presented technique is the multifaceted optimisation of Reed-Solomon codes at the transport layer for delivery assurance, speed of service (SoS) and network throughput. With this technique, the transport layer in tactical networks can meet the stringent requirements of quality of service imposed by the tactical network user, even under adverse conditions. These requirements define a high level of reliability (delivery assurance), a specific SoS and optimum use of the limited bandwidth (BW) of the wireless network, where the probability of packet erasure can be very high. The provided probabilistic analysis shows that focusing on network throughput alone will result in violating SoS and delivery assurance requirements. On the other hand, focusing on SoS and delivery assurance requirements can result in poor network throughput. The multifaceted optimisation technique, which utilises hybrid ARQ for message delivery, is described using a homogeneous Markov chain.     

Adaptive bandwidth sharing mechanism for quality of service administration in infrastructure wireless networks

In infrastructure wireless networks, the wireless hop can be considered as another hop of the transmission path. With the rapid growth of wireless traffics, the future wireless network is expected to provide services for heterogeneous data traffics with different quality of service (QoS) requirements. Most proposed schemes do not have adaptive mechanisms to deal with the environment changes. In real situation, bandwidths, error rates and loss rates of wireless links vary frequently. We will base on the differentiated service model and propose a wireless differentiation (WD) scheme for user datagram protocol (UDP) flows and a wireless differentiation with prioritised ACK scheme for connections with transmission control protocol (TCP) flows. Both schemes provide QoS support for IEEE 802.11b and do not change the basic access mechanism of IEEE 802.11b.     

Packet error rate analysis of decode-and-forward free-space optical cooperative networks in the presence of random link blockage

This paper analyses end-to-end packet error rate (PER) of a free-space optical decode-and-forward cooperative network over a gamma–gamma atmospheric turbulence channel in the presence of temporary random link blockage. Closed-form analytical expressions for PER are derived for the cases with and without transmission links being prone to blockage. Two cooperation protocols (denoted as ‘selfish’ and ‘pilot-adaptive’) are presented and compared, where the latter accounts for the presence of blockage and adapts transmission power. The influence of scintillation, link distance, average transmitted signal power, network topology and probability of an uplink and/or internode link being blocked are discussed when the destination applies equal gain combining. The results show that link blockage caused by obstacles can degrade system performance, causing an unavoidable PER floor. The implementation of the pilot-adaptive protocol improves performance when compared to the selfish protocol, diminishing internode link blockage and lowering the PER floor, especially for larger networks.     

一种支持多跳无线网QoS业务的MAC层接入协议

提供一定的服务质量保证(QoS)是多跳无线网络研究中的热点和难点,本文基于TDMA/FDMA机制提出了一种支持多信道多跳无线网络话音级QoS业务的MAC层接入协议RA/SRN。该协议以RBRP协议思想为基础,针对无线信道中隐藏、暴露终端造成的信道利用率降低和分组冲突问题进行改进设计,减小了信道冲突概率,提高了信道利用率,降低了信道接入时延,为网络层QoS路由协议提供了良好的支持。     

Game-theoretic medium access control protocol for wireless sensor networks

In the traditional medium access control (MAC) protocols for wireless sensor networks (WSNs), energy consumption is traded for throughput and delay. However, in future WSNs, throughput and delay performance had better not be sacrificed for energy conservation. Here first, an incompletely cooperative game-theoretic heuristic-based constraint optimisation framework is introduced to achieve the goals of throughput, delay and energy conservation simultaneously. Then a simplified game-theoretic MAC (G-MAC) protocol is presented, which can be easily implemented in WSNs. Simulation results show that compared with two typical MAC protocols for WSNs, sensor MAC and timeout MAC, G-MAC can increase system throughput, and decrease delay and packet-loss-rate, while maintaining relatively low energy consumption.     

Integrated quality-of-service differentiation over IEEE 802.11 wireless LANs

The fundamental medium access control mechanism in IEEE 802.11 wireless LANs (WLANs)-distributed coordination function (DCF) only supports the best-effort service and does not support quality-of-service (QoS) differentiation. Enhanced distributed channel access (EDCA) in IEEE 802.11e supports delay differentiation. A new approach, EDCA+ , is proposed to enhance QoS over WLANs. It simultaneously achieves bandwidth, delay and jitter differentiation by distinguishing the minimum contention window, the maximum backoff stage or persistent factor and packet-loss rate differentiation by distinguishing the retry limit. Analytical models are proposed to analyse the performance of EDCA+ in terms of throughput, bandwidth, delay, jitter and packet-loss rate. Extensive simulations are also carried out to evaluate the accuracy of the proposed performance models and to compare the performance of DCF, EDCA and EDCA+. The simulation results show that EDCA+ performs better than DCF and EDCA in ensuring integrated QoS, and that the proposed analytical models are valid.     

Combined methodology for measurement of available bandwidth and link capacity in wired packet networks

Accurate measurement of network parameters such as available bandwidth (ABW), link capacity, delay, packet loss and jitter are used to support and monitor several network functions, for example traffic engineering, quality-of-service (QoS) routing, end-to-end transport performance optimisation and link capacity planning. However, proactive network measurement schemes can impact both the data traffic and the measurement process itself, affecting the accuracy of the estimation if a significant amount of probe traffic is injected into the network. In this work, the authors propose two measurement schemes, one for measuring ABW and the other for measuring link capacity, both of them use a combination of data probe packets and Internet control messaging protocol (ICMP) packets. Our schemes perform ABW and link-capacity measurements in a short time and with a small amount of probe traffic. The authors show a performance study of our measurement schemes and compare their accuracy to those of other existing measurement schemes and also show that the proposed schemes achieve shorter convergence time than other existing schemes and high accuracy.