A hybrid multi-channel MAC protocol for wireless ad hoc networks

In a regular wireless ad hoc network, the Medium Access Control (MAC) protocol coordinates channel access among nodes, and the throughput of the network is limited by the bandwidth of a single channel. The multi-channel MAC protocols can exploit multiple channels to achieve high network throughput by enabling more concurrent transmissions. In this paper, we propose a hybrid and adaptive protocol, called H-MMAC, which utilizes multi-channel resources more efficiently than other multi-channel MAC protocols. The main idea is to adopt the IEEE 802.11 Power Saving Mechanism and to allow nodes to transmit data packets while other nodes try to negotiate the data channel during the Ad hoc Traffic Indication Message window based on the network traffic load. The analytical and simulation results show that the proposed H-MMAC protocol improves the network performance significantly in terms of the aggregate throughput, average delay, fairness and energy efficiency.     

Distributed semi-synchronous channel coordination for multi-channel wireless networks

In multi-channel wireless networks, multi-channel diversity can increase the number of concurrent transmissions and thus improve the throughput performance as data transmission on a wireless channel does not interfere with transmissions on the other non-overlapping channels. However, multi-channel coordination may cause severe performance degradation due to hidden terminals, missing receivers, or broadcast deafness problems if the channel usage information is not properly shared among the neighboring nodes. In this paper, we devise a semi-synchronous multi-channel coordination protocol that enables wireless nodes to: (i) efficiently exchange channel and coordination information, and (ii) reduce the overhead of channel switchings. In the proposed protocol, a rendezvous interval is set up in a distributed manner depending on the traffic rate and pattern, and each node independently switches its channel when it can complete its transmissions and then returns to the control channel within the rendezvous interval. This approach makes all nodes return to the control channel at almost the same time without incurring a severe synchronization overhead. Through subsequent analyses and simulation studies, we show that the proposed protocol effectively reduces the number of channel switchings, thereby achieving higher throughput in various multi-channel networking environments.     

Planning the Reassignment of Frequencies in Fiber-Wireless Access Networks

FiWi architectures have been proposed as efficient solutions to provide high bandwidth and ubiquity at access network areas. In multi-radio and multi-channel FiWi scenarios an effective frequency assignment should be done to radios so that higher throughput and low delay can be obtained and the best of such architectures is achieved. However, traffic conditions change over time meaning that radio channel reconfigurations can be done to improve network performance. In this article a methodology for FiWi frequency reassignment planning is proposed, together with two algorithms, that avoids service disruption and attempts to increase throughput, reduce delay and increase the overall QoS perceived by users. Results show that the RBR algorithm is the one able to better exploit channel reconfigurations, increasing parallel transmissions and reducing time division required by nodes at the transmission area of each other.     

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.     

Load-aware channel hopping protocol design for mobile ad hoc networks

Using multiple channels in wireless networks improves spatial reuse and reduces collision probability and thus enhances network throughput. Designing a multi-channel MAC protocol is challenging because multi-channel-specific issues such as channel assignment, the multi-channel hidden terminal problem, and the missing receiver problem, must be solved. Most existing multi-channel MAC protocols suffer from either higher hardware cost or poor throughput. Some channel hopping multi-channel protocols achieve pretty good performance in certain situations but fail to adjust their channel hopping mechanisms according to varied traffic loads. In this paper, we propose a load-aware channel hopping MAC protocol (LACH) that solves all the multi-channel-specific problems mentioned above.LACH enables nodes to dynamically adjust their schedules based on their traffic loads. In addition to load awareness, LACH has several other attractive features: (1) Each node is equipped with a single half-duplex transceiver. (2) Each node’s initial hopping sequence is generated by its ID. Knowing the neighbor nodes’ IDs, a node can calculate its neighbors’ initial channel hopping sequences without control packet exchanges. (3) Nodes can be evenly distributed among available channels. Through performance analysis, simulations, and real system implementation, we verify that LACH is a promising protocol suitable for a network with time-varied traffic loads.     

TCP performance over wireless MIMO channels with ARQ and packet combining

Multiple-input multiple-output (MIMO) wireless communication systems that employ multiple transmit and receive antennas can provide very high-rate data transmissions without increase in bandwidth or transmit power. For this reason, MIMO technologies are considered as a key ingredient in the next generation wireless systems, where provision of reliable data services for TCP/IP applications such as wireless multimedia or Internet is of extreme importance. However, while the performance of TCP has been extensively studied over different wireless links, little attention has been paid to the impact of MIMO systems on TCP. This paper provides an investigation on the performance of modern TCP systems when used over wireless channels that employ MIMO technologies. In particular, we focus on two representative categories of MIMO systems, namely, the BLAST systems and the space-time block coding (STBC) systems, and how the ARQ and packet combining techniques impact on the overall TCP performance. We show that, from the TCP throughput standpoint, a more reliable channel may be preferred over a higher spectral efficient but less reliable channel, especially under low SNR conditions. We also study the effect of antenna correlation on the TCP throughput under various conditions.     

An 802.11 MAC layer covert channel

For extremely sensitive applications, it may be advantageous for users to transmit certain types of data covertly over the network. This provides an additional layer of security to that provided by the different layers of the protocol stack. In this paper we present a covert side channel that uses the 802.11 MAC rate switching protocol. The covert channel provides a general method to hide communications within currently deployed 802.11 LANs. The technique uses a one‐time password (OTP) algorithm to ensure high‐entropy randomness of the covert messages. We investigate how the covert side channel affects network throughput under various rate‐switching conditions with UDP‐based and TCP‐based application traffic. We also investigate the covertness of the covert side channel using standardized entropy. The theoretical analysis shows that the maximum covert channel bandwidth is 60 bps. The simulation results show that the impact on network throughput is minimal and increases slightly as the covert channel bandwidth increases. We further show that the channel has 100% accuracy with minimal impact on rate switching entropy for scenarios where rate switching normally occurs. Finally, we present two applications for the covert channel: covert authentication and covert WiFi botnets. Copyright © 2010 John Wiley & Sons, Ltd.     

GATE,a game theory approach on traffic volume aware channel width adaptation for WBAN medical applications

Traditional single channel communication in Wireless Sensor Networks (WSN) offers limited network throughput due to frequent interferences and congestion caused by concurrent transmissions in the same neighborhood. On the one hand, successful packet delivery requires mostly multiple retransmissions because of frequent collisions which also uses much battery. On the other hand, concurrent transmissions over multiple channels not only offer better network throughput and delays, but also reduce power consumption as packet collisions are minimized or eliminated depending upon the efficiency of the concerned channel assignment scheme. This may ensure QoS requirements of transmissions demanding high bandwidth and those that are delay sensitive such as in the case of wireless body area networks. In this paper, we consider a multiple channel wireless body area networks and propose GATE, a theoretical game approach to adapt the channel bandwidth to the volume traffic requirement. In this way, medical video and audio traffics which are likely to be much bandwidth consumer are mainly considered using their priority classes. The simulation results show good performances of the proposed system in terms of increasing throughput and significantly reducing delay and energy consumption.     

RIM-MAC：一种适用于水下传感网接收者发起的多会话MAC协议

声通信是水下传感网的主要通信方式之一,但是它具有长延迟和低带宽的特点,这是水下传感网MAC（media access control）协议研究面临的主要挑战。为提高网络吞吐量,提出了一种接收者发起的多会话MAC协议（RIM-MAC）。它利用接收者发起会话,通过一次会话的4次握手完成所有邻居数据分组的传输,有效地减少握手次数。同时利用侦听到的本地信息（邻居延迟图和邻居的传输调度）避免信道冲突并发起多个会话,这解决了长传播延迟带来的信道利用率低的问题。RIM-MAC通过增强节点间并行传输的能力,在接收者和发送者两端提高时空复用率,与经典水下MAC协议比,网络吞吐量提高了至少36%。除此之外,基于自适应数据轮询策略提出了一种网络负载公平算法（FTA）,它保证了网络中竞争节点间的信道访问的公平性。仿真实验表明,在长传播延迟的场景下,RIM-MAC取得了比典型的水下传感网MAC协议更好的吞吐量性能。     

Multi-channel support for DMAC in WSNs

Currently most wireless sensor network applications assume the presence of single-channel medium access control (MAC) protocols. However, lower sensing range result in dense networks, single-channel MAC protocols may be inadequate due to higher demand for the limited bandwidth. In this paper we proposed a method of multi-channel support for DMAC in Wireless sensor networks (WSNs). The channel assignment method is based on local information of nodes. Our multi-channel DMAC protocol implement channel distribution before message collecting from source nodes to sink node and made broadcasting possible in DMAC. Analysis and simulation result displays this multi-channel protocol obviously decreases the latency without increasing energy consumption.     

On a joint temporal-spatial multi-channel assignment and routing scheme in resource-constrained wireless mesh networks

Use of multiple orthogonal channels can significantly improve network throughput of multi-hop wireless mesh networks (WMNs). In these WMNs where multiple channels are available, channel assignment is done either in a centralized manner, which unfortunately shows a poor scalability with respect to the increase of network size, or in a distributed manner, where at least one channel has to be dedicated for exchanging necessary control messages or time synchronization has to be utilized for managing the duration of data packet transmission, causing excessive system overhead and waste of bandwidth resource. In this paper, we first formulate multi-channel assignment as a NP-hard optimization problem. Then a distributed, heuristic temporal-spatial multi-channel assignment and routing scheme is proposed, assuming every wireless node in the network is equipped with a single-radio interface. Here the gateway node is set to use all the channels sequentially in a round-robin fashion. This temporal scheme ensures all the nodes that need to directly communicate with the gateway node shall have a fair access to it. For those non-gateway nodes, a spatial scheme where channels are assigned based on their neighbors’ channel usage is adopted to exploit parallel communications and avoid channel interference among nodes. Furthermore, since the routing factors, including channel usage of neighbor nodes, node hop count, node memory size, and node communication history, are all considered along with the channel assignment, network performance, measured by packet delivery latency, channel usage ratio, and memory usage ratio, tends to be considerably enhanced. The simulation results have confirmed that, compared with a couple of well-known multi-channel assignment schemes, such as LCM [21] and ROMA [15], the proposed scheme shows substantial improvement in network throughput with a very modest collision level. In addition, the proposed scheme is highly scalable as the algorithm complexity is only linearly dependent on the total number of channels that are available in the network and the number of neighbors that a network node directly connects to.     

Transmission scheduling in a multi‐channel wireless network with bidirectional relaying links

Using network coding in a wireless network can potentially improve the network throughput. On the other hand, it increases the complexity of resource allocations as the quality of one transmission is affected by the link conditions of the transmitter to multiple receivers. In this work, we study time slot scheduling and channel allocations jointly for a network with bidirectional relaying links, where the two end nodes of each link can exchange data through a relay node. Two scenarios are considered when the relay node forwards packets to the end nodes. In the first scenario, the relay node always forwards network‐coded packets to both end nodes simultaneously; in the second scenario, the relay node opportunistically uses network coding for two‐way relaying and traditional one‐way relaying. For each scenario, an optimization problem is first formulated for maximizing the total network throughput. The optimum scheduling is not causal because it requires future information of channel conditions. We then propose heuristic scheduling schemes. The slot‐based scheduling maximizes the total transmission rate of all the nodes at each time slot, and the node‐based scheduling schedules transmissions based on achievable transmission rates of individual nodes at different channels. The node‐based one has lower complexity than the slot‐based one. Our results indicate that although the node‐based scheduling achieves slightly lower throughput than the slot‐based one, both the proposed scheduling schemes are very effective in the sense that the difference between their throughput and the optimum scheduling is relatively small in different network settings. Copyright © 2015 John Wiley & Sons, Ltd.     

Efficient Utilization of Available Channels in Dynamic Spectrum Access Networks

In case of dynamic spectrum access networks, how to efficiently utilize the dynamically available bandwidth is very important to enhance the performance of the networks. In this paper, we propose an Error Adaptive MAC protocol which adaptively changes its transmission mode according to the channel status. Using the cognitive radio technology, additional channels are assumed to be randomly available for data transmission. When the channel error rate is relatively high, those additional channels are utilized for error recovery; otherwise, the extra channels can be used to increase the throughput if the wireless medium is stable and reliable. We formulate an analytical model to study the dynamics of our adaptive MAC protocol, and using simulation, show our proposed method can significantly enhance the throughput of dynamic spectrum access networks.     

Cooperative Strategies and Achievable Rate for Tree Networks With Optimal Spatial Reuse

In this paper, a low-complexity cooperative protocol that significantly increases the average throughput of multihop upstream transmissions for wireless tree networks is developed and analyzed. A system in which transmissions are assigned to nodes in a collision free, spatial time division fashion is considered. The suggested protocol exploits the broadcast nature of wireless networks where the communication channel is shared between multiple adjacent nodes within interference range. For any upstream end-to-end flow in the tree, each intermediate node receives information from both one-hop and two-hop neighbors and transmits only sufficient information such that the next upstream one-hop neighbor will be able to decode the packet. This approach can be viewed as the generalization of the classical three node relay channel for end-to-end flows in which each intermediate node becomes successively source, relay and destination. The achievable rate for any regular tree network is derived and an optimal schedule that realizes this rate in most cases is proposed. Our protocol is shown to dramatically outperform the conventional scheme where intermediate nodes simply forward the packets hop by hop. At high signal-to-noise ratio (SNR), it yields approximately 66% throughput gain for practical scenarios.     

Distributed power control over multiple channels for ad hoc wireless networks

In this paper, we investigate the deficiency of uncontrolled asymmetrical transmission power over multiple channels in ad hoc environments. We further propose a novel distributed transmission power control protocol called the distributed power level (DPL) protocol for multi‐channel ad hoc networks without requiring clock synchronization. Specifically, different transmission power levels are assigned to different channels, and nodes search for an idle channel on the basis of the received power so that the maximum allowable power of the preferred data channel is larger than or equal to the received power. If the most preferred channel of the least maximum power is busy, the nodes are able to select the next channel and so forth. As a result, interference is reduced over channels because the nodes that require higher transmission power are separated from interfering with the nodes that require lower transmission power. Two transmission power control modes are introduced for DPL: symmetrical and asymmetrical. For the symmetrical DPL protocol (mode), nodes transmit at the same power level assigned to the selected channel. On the other hand, for the asymmetrical DPL protocol, nodes are allowed to transmit at a lower or equal power level that is assigned to the selected channel. Extensive ns‐2‐based simulation results are presented to demonstrate that the proposed protocols can enhance the network throughput compared with the existing uncontrolled asymmetrical transmission power protocol. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance Analysis of a Bandwidth Guaranteed Medium Access Control Protocol for WDM Local Networks

In this paper, we propose and analyze a bandwidth guaranteed medium access control protocol for broadcast-and-select WDM local networks with a star topology. The proposed protocol is based on a combination of contention and dedicated reservation mechanisms for time slotted WDM networks. Every node accesses the data channel by transmitting request packets in minislots on a separate control channel. There are two types of minislots; dedicated minislots and contention minislots. Nodes requiring bandwidth guarantees, called guaranteed nodes, use dedicated minislots that are assigned by the centralized control node. The remaining nodes, called random-access nodes, share contention minislots using a distributed random access mechanism. The dedicated minislots can guarantee a minimum bandwidth for the guaranteed nodes. The contention minislots enable on-demand services at the optical layer and achieve good fairness for the remaining bandwidth. Here, the data channels are dynamically assigned to the minislots successfully returned on a first-come-first-served (FCFS) basis. This protocol can combine the best of centralized and distributed access protocols such as simplicity, efficiency, and flexibility. We analyze the maximum throughput and verify the results by simulation.     

On-demand routing and channel assignment in multi-channel mobile ad hoc networks

The capacity of mobile ad hoc networks is constrained by the intra-flow interference introduced by adjacent nodes on the same path, and inter-flow interference generated by nodes from neighboring paths. By assigning orthogonal channels to neighboring nodes, one can minimize both types of interferences and allow concurrent transmissions within the neighborhood, thus improving the throughput and delay performance of the ad hoc network. In this paper, we present three novel distributed channel assignment protocols for multi-channel mobile ad hoc networks. The proposed protocols combine channel assignment with distributed on-demand routing, and only assign channels to active nodes. They are shown to require fewer channels and exhibit lower communication, computation, and storage complexity, compared with existing approaches. Through simulation studies, we show that the proposed protocols can effectively increase throughput and reduce delay, as compared to several existing schemes, thus providing an effective solution to the low capacity problem in multi-hop wireless networks.     

Downlink scheduling with guarantees on the probability of short-term throughput

We consider the problem of scheduling multiple transmissions on the downlink of a wireless network with performance guarantees in the form of the probabilities that short term throughputs exceed user specified thresholds. Many interactive data applications have some degree of a latency requirement, and measure performance by throughput over a relatively short time interval. We refer to the fraction of time such user throughput reaches a predefined rate threshold or higher as tail probability. The problem is formulated as maximizing the minimum ratio of tail probability to the user specified probability threshold. We present necessary and sufficient optimality conditions for the case in which the time interval of interest is consistent with the time scale of channel variation. An online algorithm is proposed which can achieve the optimality. For the case in which the time interval of interest is large compared to the time scale of channel variation, we develop an online algorithm which attempts to maximize the minimum normalized tail probability by taking the advantage of channel variation over users and over time. Simulation results demonstrate that the proposed algorithm can achieve better performance than other algorithms such as the proportional fair algorithm and the Max C/I algorithm.     

Design of an enhanced access point to optimize TCP performance in Wi-Fi hotspot networks

In the last years, the number of Wi-Fi hotspots at public venues has undergone a substantial growth, promoting the WLAN technologies as the ubiquitous solution to provide high-speed wireless connectivity in public areas. However, the adoption of a random access CSMA-based paradigm for the 802.11 MAC protocol makes difficult to ensure high throughput and a fair allocation of radio resources in 802.11-based WLANs. In this paper we evaluate extensively via simulations the interaction between the flow control mechanisms implemented at the TCP layer and the contention avoidance techniques used at the 802.11 MAC layer. We conducted our study considering initially M wireless stations performing downloads from the Internet. From our results, we observed that the TCP downlink throughput is not limited by the collision events, but by the inability of the MAC protocol to assign a higher chance of accessing the channel to the base station. We propose a simple and easy to implement modification of the base station’s behavior with the purpose of increasing the TCP throughput reducing useless MAC protocol overheads. With our scheme, the base station is allowed to transmit periodically bursts of data frames towards the mobile hosts. We design a resource allocation protocol aimed at maximizing the success probability of the uplink transmissions by dynamically adapting the burst length to the collision probability estimated by the base station. By its design, our scheme is also beneficial to achieve a fairer allocation of the channel bandwidth among the downlink and uplink flows, and among TCP and UDP flows. Simulation results confirm both the improvement in the TCP downlink throughput and the reduction of system unfairness.