A bandwidth-efficient and fair CSMA/TDMA based multichannel MAC scheme for V2V communications

In the overlay medium access control (MAC) of cognitive radio networks, secondary user (SU) uses the spectrum portion which is assigned to primary user (PU), when PU is not using this spectrum at that time. In this article, a multiuser overlay MAC protocol is considered in which PUs and SUs are using time division multiple access and carrier sense multiple access (CSMA) MAC schemes, respectively. Firstly, new frame format and algorithm for the proposed MAC protocol are described, then the analytical modelling of this protocol is explained. In the SU network, Markov chain model along with the CSMA protocol is used for better utilization of the opportunity from the PU network (PUN). Channel utilization and probability of success are also derived and analyzed for this protocol with respect to idle time, collision (failure) time, various spectrum opportunities from PUN, number of SUs, and their fairness. This MAC scheme provides the optimal solution for channel utilization under a constraint on the probability of collisions. Numerical results are also provided to validate analysis of proposed MAC protocol and to investigate the performance behaviour of the optimal solution.

In this paper we propose a decentralized medium access control (MAC) scheme to coordinate the access of multiple transmitters adopting a multi-packet reception (MPR) physical (PHY) layer. MPR receivers are able to decode multiple transmissions, and depending on the technique adopted at the PHY-layer, there is an optimal number of simultaneous transmissions that maximize the number of packets successfully decoded in a simultaneous way. The proposed MAC scheme admits an MPR PHY-layer and is divided in two stages. In the first one the nodes indicate their willingness to transmit, while in the second one they jointly transmit. Adopting a generic model for the PHY-layer, we characterize the throughput achieved by the proposed MAC when both MAC and PHY layers are considered. The formal characterization of the throughput is then used to optimize the duration of the first stage of the MAC scheme in order to optimize the throughput. In this way, the number of transmitters is regulated to optimize the cross-layer operation, taking into consideration the features of the MPR PHY-layer and the maximum performance achieved with the proposed MAC design. Several results obtained through simulation are presented, which validate the numerical results obtained with the proposed characterization. The proposed scheme is a first step to develop MAC protocols specifically designed to distributed MPR systems that operate in a cross-layer and improve the exploitation of current and future MPR techniques proposed for the PHY-layer.

Provisioning of high throughput in wireless mesh networks (WMNs) is a challenging issue for medium access control (MAC) protocol. This is due to not only some difficult problems present in such networks such as the hidden and exposed terminal problems but also the fact that a WMN is often used as a backbone network requiring more reliable and efficient performance. Note that multi-channel based MAC protocols were proposed in the literature to handle the hidden and exposed terminal problems in multi-hop wireless ad hoc networks. Here this approach is advocated for WMNs since many literature studies show that it can much outperform the singlechannel based MAC protocols but at the expense of increased implementation complexity, which however should be acceptable in backbone WMNs. However, most existing multi-channel based MAC protocols use dedicated control channels (DCC). DCCs not only causes channel wastage but also may become a performance bottlenecks, both of which are undesirable for WMNs. In this paper, we discuss a new MAC scheme which does not use any DCCs and only requires one transceiver per node for the implementation. The simulation studies show that this scheme can outperform the one using DCCs especially in the case of heavy traffic loads.

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Full-duplex MAC protocol using buffer status reports during unused uplink periods in WLAN

This paper proposes a location-assisted random medium access control (MAC) scheme for distributed vehicular ad hoc networks (VANETs). Consider a vehicular network with a wireless bandwidth of M orthogonal channels that shared by multiple vehicles. Efficient distributed channel access mechanism should be used to improve the bandwidth utilization. We observe that each vehicle has a unique location, which could be exploited as a key information to identify its access channel. Motivated by this observation, we design a location-to-channel (L2C) randomized mapping approach. In the approach, each vehicle will access to the channels with optimal location-dependent probabilities. The simulation results are presented to demonstrate the performance of this MAC scheme by comparing it to the general random MAC scheme. It is shown that the average collision probability of channel access is clearly reduced and the average throughput of the channel is significantly enhanced.

Power efficient ultra-wideband based wireless communication for wireless body area network applications

Traditional algorithms for Media Access Control (MAC) in Mobile Ad Hoc Networks (MANET) such as CSMA-CA allow only a single user to transmit at a given time. This means that the sum throughput in a MANET cannot increase to service additional users. Such MAC protocols disregard the possibility that by utilizing multiple antenna processing to handle interference intelligently at the Physical layer (PHY), many concurrent user transmissions can co-exist. Previous works have proposed altered versions of CSMA-CA that allow multi user operation but may not necessarily be able to coexist with an existing IEEE 802:11 based network. This paper proposes a Concurrent CSMA MAC protocol that is completely compatible with traditional CSMA based MAC and follows the same timing structure allowing co-existence of both protocols. Specifically, in Concurrent CSMA after a primary user has captured the channel, secondary users listen to the RTS/CTS handshake and form a beamnull towards the primary receiver. Hence secondary users can communicate concurrently with minimal increase in interference to the primary receiver. Simulations show that the proposed PHY and MAC scheme is able to achieve 2 to 3 times the network spectral efficiency of CSMA with a single antenna and this improvement factor is sustained as the network scales in size. Further the proposed scheme allows the network spectral efficiency (sum throughput per unit bandwidth) to scale with users and improves upon a previous promising approach which uses Interference Alignment.

Recent advances in interference cancellation and signal-processing techniques can enable full-duplex radios and multipacket reception (MPR), which will have significant impact on medium access control (MAC) schemes. In this paper, we propose a MAC scheme in unmanned aerial vehicle (UAV) ad-hoc networks with full-duplex radios and MPR. To efficiently handle the highly mobile environment of a UAV ad-hoc network, a token-based technique is used to update information in the network as well. The MAC schemes in the presence of perfect and imperfect channel state information (CSI) are formulated as a combinatorial optimization problem and a discrete stochastic optimization problem, respectively. Simulation results show the effectiveness of the proposed MAC.

Since cognitive wireless network (CRN) has the characteristic of secondary use, it can enable the device to dynamically access available spectrum without interference to primary users (PUs), which can effectively alleviate contradiction between the lack of spectrum resources and the growing demand for wireless access. However, Medium Access Control (MAC) protocol as CRN core components, can achieve competition access of the licensed spectrum and coordination control, which will maximize spectrum utilization efficiency and network throughput. The contribution of this survey is threefold. First, we analyze the characteristics of the existed multi- channel MAC protocol in CRN; Second, according to the different ways of spectrum access in CRNs, the multi-channel MAC protocols are classified into time-slotted based MAC protocol, control channel based MAC protocol and hybrid MAC protocol, and the paper emphatically analyzed the advantages and disadvantages of these multi-channel MAC protocols; Finally, the paper explores the difficulties and the challenges of multi-channel MAC protocols design in cognitive wireless network.

In this paper, we propose a cognitive radio based Medium Access Control (MAC) protocol for packet scheduling in wireless networks. Cognitive MAC protocols allow a class of users, called secondary users, to identify the unused frequency spectrum and to communicate without interfering with the primary users. In our proposed MAC protocol, each secondary user is equipped with two transceivers. One of the transceivers is used for control messages while the other periodically senses and dynamically utilizes the unused data channel. The secondary users report the status of channels on control channel and negotiate on the selected data channel itself for onward data transmission. Each channel is used by different set of secondary users. Contrary to existing protocols, data transmission takes place in the time slot in which spectrum opportunity is found. We develop a new analytical model, while taking into account the backoff mechanism. Our simulation results show that throughput increases with the increase in the number of channels.

Cognitive Radio (CR) exploits underutilized licensed spectrums to improve its bandwidth availability. Using CR technology, a node is able to adapt its transmission and reception radio parameters including channel frequency dynamically according to local spectrum availability. For channel access between wireless nodes, a cognitive Medium Access Control (MAC) protocol is necessary to coordinate the CRs. Multi-channel MAC protocol extensions have been proposed in IEEE802.11 to enable a node to operate in multiple channels in order to improve network-wide throughput. These multi-channel MAC protocols have several functions that can be leveraged by cognitive MAC protocols due to their similarities in certain aspects, though the CR has an additional requirement to cope with the existence of licensed users that have higher authority over the channels. Current research in cognitive MAC protocols assumes the availability of a common control channel at all times, which is an approach in the multi-channel MAC protocols. This approach has certain hardware requirements that may not be readily available at CR nodes. Hence, other approached may be necessary. In this paper, various types of multi-channel MAC protocols are reviewed, followed by discussion of their merits and demerits in multi-channel environments. The purpose is to show the additional functionalities and challenges that each multi-channel MAC protocol has to offer and address in order to operate in multihop CR networks. By providing discussion on possible technology leverage from multi-channel to cognitive MAC protocols, we aim to establish a foundation for further research and discussion.

The directional medium access control (MAC) protocol improves the throughput of mobile ad hoc networks but has a deafness problem and requires location information for neighboring nodes. In the dual-channel directional MAC protocol [12], the use of omnidirectional packets does not require the exact location of destination node. In this letter, we propose a tone dual-channel MAC protocol with directional antennas to improve the throughput of mobile ad hoc networks. In the proposed MAC protocol, we use a directional CTS and an out-of-band directional DATA tone with a new blocking algorithm to improve the spatial reuse. We confirm the throughput performance of the proposed MAC protocol by computer simulations using the Qualnet simulator.

This work introduces a Medium Access Control (MAC) protocol designed to allow a group of underwater robots that share a wireless communication channel to effectively communicate with each other. The goal of the Underwater Multirobot Cooperative Intervention MAC (UMCI-MAC) protocol presented in this work is to minimize the end to end delay and the jitter. The access to the medium in UMCI-MAC follows a Time Division Multiple Access (TDMA) strategy which is arbitrated by a master, which also has the capability to prioritize the transmission of some nodes over the rest of the network. Two experiments have been carried out with a team of four Autonomous Underwater Vehicles (AUV) in order to compare this protocol with Aloha-CS and S-FAMA MAC protocols used in Underwater Wireless Sensor Networks (UWSN). In the first experiment, the communications and the AUVs have been simulated using UWSim-NET. The objective of this experiment was to evaluate all three protocols in terms of delay, jitter, efficiency, collisions and throughput depending on the size of the data packet and the rate of packet delivery in the application layer for each robot. The results of this experiment proved that UMCI-MAC successfully avoids packet collisions and outperforms the other two protocols in terms of delay, jitter and efficiency. The second experiment consisted of a Hardware In The Loop (HIL) teleoperation of a team of four robots. One of the AUVs was a real BlueROV in a water tank, while the remaining AUVs and the communications were simulated with UWSim-NET. It demonstrates the impact of the MAC protocols in underwater acoustic links. Of the three MAC protocols evaluated in this work, UMCI-MAC was the only one which succeeded in the proposed teleoperation experiment. Thus demonstrating its suitability as a communications protocol in underwater cooperative robotics.

Most of the existing Medium Access Control (MAC) protocols for ad hoc networks involve the use of a single wireless channel as the transmission medium. Throughput of a single channel MAC protocol is li-mited by the bandwidth of a single channel. Use of multiple channels helps to alleviate this problem. One of the existing methodologies towards using multiple channels in a MAC protocol for ad-hoc networks is to assign one channel as the control channel and the rest as data channels. However, dedicating one channel completely for control messages leads to a poor utili-zation of the available bandwidth. In this paper, we propose a Control-channel-Reuse-based Multiple-channel MAC (CRM-MAC) protocol in ad-hoc net-works which identifies mechanisms to improve the bandwidth utilization. The proposed protocol derives from an existing multi-channel MAC solution called Dynamic Channel Assignment (DCA). We demonstrate the improvement in our proposed protocol over DCA through extensive simulations.