Cross-Layer Optimization of MAC and Network Coding in Wireless Queueing Tandem Networks

In wireless networks, throughput optimization is an essential performance objective that cannot be adequately characterized by a single criterion (such as the minimum transmitted or sum-delivered throughput) and should be specified over all source-destination pairs as a rate region. For a simple and yet fundamental model of tandem networks, a cross-layer optimization framework is formulated to derive the maximum throughput region for saturated multicast traffic. The contents of network flows are specified through network coding (or plain routing) in network layer and the throughput rates are jointly optimized in medium access control layer over fixed set of conflict-free transmission schedules (or optimized over transmission probabilities in random access). If the network model incorporates bursty sources and allows packet queues to empty, the objective is to specify the stability region as the set of maximum throughput rates that can be sustained with finite packet delay. Dynamic queue management strategies are used to expand the stability region toward the maximum throughput region. Network coding improves throughput rates over plain routing and achieves the largest gains for broadcast communication and intermediate network sizes. Throughput optimization imposes fundamental tradeoffs with transmission and processing energy costs such that the throughput-optimal operation is not necessarily energy efficient.     

Optimized multipath network coding in lossy wireless networks

Network coding has been a prominent approach to a series of problems that used to be considered intractable with traditional transmission paradigms. Recent work on network coding includes a substantial number of optimization based protocols, but mostly for wireline multicast networks. In this paper, we consider maximizing the benefits of network coding for unicast sessions in lossy wireless environments. We propose Optimized Multipath Network Coding (OMNC), a rate control protocol that dramatically improves the throughput of lossy wireless networks. OMNC employs multiple paths to push coded packets to the destination, and uses the broadcast MAC to deliver packets between neighboring nodes. The coding and broadcast rate is allocated to transmitters by a distributed optimization algorithm that maximizes the advantage of network coding while avoiding congestion. With extensive experiments on an emulation testbed, we find that OMNC achieves more than two-fold throughput increase on average compared to traditional best path routing, and significant improvement over existing multipath routing protocols with network coding. The performance improvement is notable not only for one unicast session, but also when multiple concurrent unicast sessions coexist in the network.     

Medium access control protocols for wireless mobile ad hoc networks: issues and approaches

In this article, a comprehensive survey of the medium access control (MAC) approaches for wireless mobile ad hoc networks is presented. The complexity in MAC design for wireless ad hoc networks arises due to node mobility, radio link vulnerability and the lack of central coordination. A series of studies on MAC design has been conducted in the literature to improve medium access performance in different aspects as identified by the different performance metrics. Tradeoffs among the different performance metrics (such as between throughput and fairness) dictate the design of a suitable MAC protocol. We compare the different proposed MAC approaches, identify their problems and discuss the possible remedies. The interactions among the MAC and the higher layer protocols such as routing and transport layer protocols are discussed and some interesting research issues are also identified. Copyright © 2003 John Wiley & Sons, Ltd.     

A joint scheduling,power control,and routing algorithm for ad hoc wireless networks

In wireless networks there is strong coupling among the traditional layers of the architecture, and these interactions cannot be ignored. One example is the interaction between routing in the network layer and access control in the MAC layer. Another one is the coupling between power control in the physical layer and scheduling in the MAC layer. In this paper, we assume a TDMA-based wireless ad hoc network and provide a centralized algorithm of joint power control, scheduling, and routing. Simulation results show the improvement of the network performance, in terms of throughput, delay, and power consumption, through use of the joint algorithm. Energy efficiency is another important aspect of ad hoc networking, and is considered in our algorithm. Our simulation also shows the trade-off between energy consumption and network throughput or delay performance.     

Energy efficient multi-channel media access control for dense wireless ad hoc and sensor networks

Traditional single-channel MAC protocols for wireless ad hoc and sensor networks favor energy-efficiency over throughput. More recent multi-channel MAC protocols display higher throughput but less energy efficiency. In this article we propose NAMAC, a negotiator-based multi-channel MAC protocol in which specially designated nodes called negotiators maintain the sleeping and communication schedules of nodes within their communication ranges in static wireless ad hoc and sensor networks. Negotiators facilitate the assignation of channels and coordination of communications windows, thus allowing individual nodes to sleep and save energy. We formally define the problem of finding the optimal set of negotiators (i.e., minimizing the number of selected negotiators while maximizing the coverage of the negotiators) and prove that the problem is NP-Complete. Accordingly, we propose a greedy negotiator-election algorithm as part of NAMAC. In addition, we prove the correctness of NAMAC through a rigorous model checking and analyze various characteristics of NAMAC—the throughput of NAMAC, impact of negotiators on network capacity, and storage and computational overhead. Simulation results show that NAMAC, at high network loads, consumes 36 % less energy while providing 25 % more throughput than comparable state-of-art multi-channel MAC protocols for ad hoc networks. Additionally, we propose a lightweight version of NAMAC and show that it outperforms (55 % higher throughput with 36 % less energy) state-of-art MAC protocols for wireless sensor networks.     

Delay Aware Link Scheduling for Multi-Hop TDMA Wireless Networks

Time division multiple access (TDMA) based medium access control (MAC) protocols can provide QoS with guaranteed access to the wireless channel. However, in multi-hop wireless networks, these protocols may introduce scheduling delay if, on the same path, an outbound link on a router is scheduled to transmit before an inbound link on that router. The total scheduling delay can be quite large since it accumulates at every hop on a path. This paper presents a method that finds conflict-free TDMA schedules with minimum scheduling delay. We show that the scheduling delay can be interpreted as a cost, in terms of transmission order of the links, collected over a cycle in the conflict graph. We use this observation to formulate an optimization, which finds a transmission order with the min-max delay across a set of multiple paths. The min-max delay optimization is NP-complete since the transmission order of links is a vector of binary integer variables. We devise an algorithm that finds the transmission order with the minimum delay on overlay tree topologies and use it with a modified Bellman-Ford algorithm, to find minimum delay schedules in polynomial time. The simulation results in 802.16 mesh networks confirm that the proposed algorithm can find effective min-max delay schedules.     

High throughput route selection in multi-rate wireless mesh networks

Most existing Ad-hoc routing protocols use the shortest path algorithm with a hop count metric to select paths. It is appropriate in single-rate wireless networks, but has a tendency to select paths containing long-distance links that have low data rates and reduced reliability in multi-rate networks. This article introduces a high throughput routing algorithm utilizing the multi-rate capability and some mesh characteristics in wireless fidelity （WiFi） mesh networks. It uses the medium access control （MAC） transmission time as the routing metric, which is estimated by the information passed up from the physical layer. When the proposed algorithm is adopted, the Ad-hoc on-demand distance vector （AODV） routing can be improved as high throughput AODV （HT-AODV）. Simulation results show that HT-AODV is capable of establishing a route that has high data-rate, short end-to-end delay and great network throughput.     

Fair coding for inter‐session network coding in wireless mesh networks

Because of the broadcast and overhearing capability of wireless networks, network coding can greatly improve throughput in wireless networks. However, our investigation of existing inter‐session network coding protocols found that the short‐term unfairness that existed in 802.11‐based medium access control (MAC) protocols actually decreases the coding opportunity, which in turn compromises the throughput gain of network coding. To alleviate the negative impact of this unfairness, we propose a coding‐aware cross‐layer heuristic approach to optimize the coordination of network coding and MAC layer protocol, named FairCoding, which can significantly increase coding opportunities for inter‐session network coding through a fair short‐term traffic allocation for different coding flows. Experiment evaluation shows that the proposed mechanism can bring more coding opportunities and improve the total throughput of wireless mesh networks by up to 20%, compared with the coding mechanism, without considering the negative impact of the short‐term unfairness. Copyright © 2015 John Wiley & Sons, Ltd.     

A two stage approach for channel transmission rate aware scheduling in directional mmWave WPANs

Millimeter wave (mmWave) communications in 60 GHz band have become a hot topic in wireless communications. New medium access control (MAC) protocols are needed because of the fundamental differences between mmWave communications and existing other communication systems. In mmWave wireless personal area networks, the channel transmission rates of links vary significantly because of the difference in the distance between nodes, the accuracy of beamforming, and the existence of obstructions. Owning to the directivity of mmWave links, spatial reuse should be exploited to improve network capacity. In this paper, we develop a channel transmission rate aware directional MAC protocol, termed RDMAC, in which both the multirate capability of links and spatial reuse are exploited to improve network performance. RDMAC has two stages. The first stage measures the channel transmission rates of links, and a heuristic algorithm is proposed to compute near‐optimal measurement schedules with respect to the total number of measurements. The second stage accommodates the traffic demand of links, and a heuristic transmission scheduling algorithm is proposed to compute near‐optimal transmission schedules with respect to the total transmission time. Simulations under various traffic modes show that compared with existing protocols, RDMAC has lower network latency, higher network throughput, and also a good fairness performance. Copyright © 2014 John Wiley & Sons, Ltd.     

Topology-Independent Link Activation Scheduling Schemes for Mobile CDMA Ad Hoc Networks

In this paper, we study medium access control (MAC) protocols with quality-of-service (QoS) support, that is, topology-independent link activation transmission scheduling, for mobile code-division multiple-access (CDMA) ad hoc networks. QoS provisioning for each communication link is guaranteed without the need to adopt transmission schedules in mobile environments. An interference model, which captures the difference between transmission and interference ranges, is considered. Under this interference model, an approach to guaranteeing conflict-free transmission slots in each frame (QoS provisioning) for each communication link is proposed. Compared with the previously known method, superior performance is obtained. We then present a topology-independent link activation scheduling framework based on the theory of group-divisible (GD) designs. By the mathematical properties of GD designs, the proposed framework guarantees conflict-free transmission slots in each frame for each communication link, without the overhead due to the recomputation of transmission schedules when the network topology changes. With the proposed framework, we study and evaluate one series of GD design constructions. Based on the results derived, topology-independent link activation scheduling algorithms are then presented. The proposed schemes are designed for different objectives: maximizing the minimum system throughput and/or minimizing the schedule frame length. Numerical results show that the proposed algorithms outperform previously known schemes. The average performance of the proposed schemes is also derived.     

Bounds and parameter optimization of medium access control coding for wireless ad hoc and sensor networks

The use of codes to schedule transmissions is an attractive technique able to guarantee a non-zero throughput medium access performance for the nodes of a wireless ad hoc or sensor network regardless of network topology variations. Some authors refer to this technique as topology-transparent scheduling. In this paper, we use the term MAC coding in order to emphasize the exclusive use of codes to achieve topology-transparency within the MAC sub-layer. We present a new upper bound expression on the guaranteed throughput achievable by any linear code used in a MAC coding context. This bound proves to be tighter than the one obtained when the minimum distance of the code is equal to its length. Additionally, we derive new and simple closed analytical expressions for the parameters of maximum distance separable codes that maximize the minimum, average, or joint minimum-average throughput of MAC coding. The optimization methods presented here are also applicable to other codes with available analytical expressions for their minimum distance and distance distribution. Finally, we present system-level simulation results of MAC coding on static and dynamic topologies with mobility and including wireless channel errors. Throughput simulation results are compared with their corresponding analytical expressions and to a random scheduling approach. The results show agreement with analysis and confirm the robustness of MAC coding in maintaining minimum levels of performance with good average performance and graceful degradation.     

Distributed Sequential Access MAC Protocol for Single-Hop Wireless Networks

Medium access control overhead is the primary reason for low throughput in wireless networks. Performing blind contentions, contentions without any information of other contenders, and exchanging control message are time-consuming control operations. In this study, we propose a new MAC protocol called distributed sequential access MAC (DSA-MAC) which provides the transmission order without any explicit control operations. It may induce very light control overhead; therefore, compared to existing wireless MAC protocols, DSA-MAC can remarkably enhance network throughput.     

Middleman covert channel establishment based on MORE routing protocol using network coding in ad hoc networks

Covert channels have been recently the subject of the study in both creation and countermeasure aspects. There are many different ways to embed the covert data in network standards and protocols, especially in wireless networks. MORE (MAC‐independent opportunistic routing) is an opportunistic routing protocol which uses networks coding to enhance routing performance by reducing the repetitions. This protocol can be a suitable medium for covert channel establishment. A middleman covert channel establishment method is proposed in this paper over MORE routing protocol and with the use of network coding. Hidden data are transferred through packet's payload bytes. Covert sender manipulates coding mechanism by calculating packets' coefficients instead of random selection. The proposed covert channel provides the average throughput of 218 and 231 bps, using two different data length approaches which is relatively a good comparing to the previous network layer covert channels. The proposed covert channel is also a covert storage channel and cannot be removed or restricted. Effect of different network characteristics on the proposed method's capacity and security is investigated by a simulation study, and the results are discussed.     

Design of multichannel MAC protocols for wireless ad hoc networks

Medium access control (MAC) protocols coordinate channel access between wireless stations, and they significantly affect the network throughput of wireless ad hoc networks. MAC protocols that are based on a multichannel model can increase the throughput by enabling more simultaneous transmission pairs in the network. In this paper, we comprehensively compare different design methods for multichannel MAC protocols. We classify existing protocols into different categories according to the channel negotiation strategies they employ. The common problems that may be encountered in multichannel design are discussed. We then propose a hybrid protocol that combines the advantages of the two methods of a common control channel and a common control period. The simulation results show that our proposed protocol can significantly outperform two representative protocols. Copyright © 2008 John Wiley & Sons, Ltd.     

A Smart TCP Acknowledgment Approach for Multihop Wireless Networks

Reliable data transfer is one of the most difficult tasks to be accomplished in multihop wireless networks. Traditional transport protocols like TCP face severe performance degradation over multihop networks given the noisy nature of wireless media as well as unstable connectivity conditions in place. The success of TCP in wired networks motivates its extension to wireless networks. A crucial challenge faced by TCP over these networks is how to operate smoothly with the 802.11 wireless MAC protocol which also implements a retransmission mechanism at link level in addition to short RTS/CTS control frames for avoiding collisions. These features render TCP acknowledgments (ACK) transmission quite costly. Data and ACK packets cause similar medium access overheads despite the much smaller size of the ACKs. In this paper, we further evaluate our dynamic adaptive strategy for reducing ACK-induced overhead and consequent collisions. Our approach resembles the sender side's congestion control. The receiver is self-adaptive by delaying more ACKs under nonconstrained channels and less otherwise. This improves not only throughput but also power consumption. Simulation evaluations exhibit significant improvement in several scenarios     

无线Mesh网中实时数据业务仿真与分析

无线Mesh网络是一种架构式多跳无线网络,具有结构灵活、快速部署、自组织和自愈合等优点,具有广泛的应用前景。通过采用ns-2仿真软件对基于IEEE 802.11 MAC协议和AODV路由协议的无线Mesh网中实时数据业务的数据传输进行建模与仿真,分析了Mesh网络中数据流经过的传输跳数与吞吐率的关系,以及MAC层RTS/CTS、重传次数以及MAC层和路由层相互作用对无线Mesh网中实时数据业务性能的影响,指出了提高无线Mesh网中实时数据业务性能的所需要的改进方向。     

Evaluating a cross-layer approach for routing in Wireless Mesh Networks

Routing in Wireless Mesh Networks is challenging due to the unreliable characteristics of the wireless medium. Traditional routing paradigms are not able to propose an efficient solution to this problem. Further, Gupta et al. demonstrated that the average throughput capacity per node of a wireless multi-hop network decreases as 1/n, where n is the number of nodes in the network. Recent studies have shown that a cross-layer approach is a promising solution to get closer to the theoretic throughput capacity bound. Cross-layer solutions have been already proposed either for specific TDMA/CDMA networks or for power-efficient routing protocols. These proposals are strongly MAC dependent, or suffer from targeting a steady state offering the best trade-off performance. In this paper, the problem we tackle in a more general context, disregarding the specific MAC and Physical layers technologies, can be formulated as follows: How to design a routing algorithm able to increase the average throughput capacity experienced by Wireless Mesh Networks? Starting from a theoretic result, we analyze the gain that a cross-layer approach can deliver, the metrics suitable to improve throughput capacity, and the power control policy that reduces interference. We take a MAC independent approach, focusing on the general characteristics of wireless links, targeting the improvement of throughput capacity in Wireless Mesh Networks. Our proposal performs path selection and power optimization based on three metrics, namely physical transmission rate, interference, and packet error rate. Performances are thoroughly analyzed and evaluated by extensive simulations, with both TCP and UDP traffic, and compared to other multi-hop routing protocols. For both kind of traffic, the simple heuristic we propose here allows to double the average throughput the network is able to route.     

A modified medium access control algorithm for systems with iterative decoding

Efficient transmission methods for fading radio channels often require an iterative decoder. This is for example the case for systems using turbo codes. Receiver decoder iterations could potentially lead to a latency problem which impacts the performance of the medium access control protocol. In this paper, we present modifications based on the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol to accommodate the increased latency in the iterative processing. One area of applications is wireless local area networks (WLANs) with high data rate. The simulation results performed in the IEEE 802.11a WLAN environment by replacing the 802:11a's convolutional coding with turbo coding demonstrate that the proposed algorithm provides a throughput gain over the conventional method.     

Cooperative Protocols Design for Wireless Ad-Hoc Networks with Multi-hop Routing

Wireless ad-hoc networks can experience significant performance degradation under fading channels. Spatial diversity has been shown to be an effective way of combating wireless fading with the multiple-input multiple-output (MIMO) technique by transmitting correlated information through multiple antennas. The virtual MIMO technique, which allows multiple wireless stations with single antenna to form a virtual transmission array, is shown to be a viable solution from several recent studies. In this paper, we propose a complete system framework for wireless ad-hoc networks utilizing two different cooperative relaying techniques at the physical layer: the repetition coding and the space-time coding. In the data link layer, two medium access control protocols are proposed to accommodate the corresponding physical layer cooperative diversity schemes. In the network layer, diversity-aware routing protocols are proposed to determine the routing path and the relaying topology. Simulations with both constant bit rate and TCP (transmission control protocol) traffic show significant performance gains of the proposed cooperative relaying schemes.     

High throughput reactive routing in multi-rate ad hoc networks

A reactive routing algorithm for multi-rate ad hoc wireless networks is proposed. It enhances the AODV protocol and achieves higher throughput by utilising the multi-rate capability of the underlying wireless channel via the MAC delay routing metric. Simulations show that the protocol leads to a significant throughput increase over traditional ad hoc routing protocols.