Multichannel CSMA Research Articles

Temporal starvation in multi-channel CSMA networks

In this paper we consider a stochastic model for a frequencyagile CSMA protocol for wireless networks where multiple orthogonal frequency channels are available. Even when the possible interference on the different channels is described by different conflict graphs, we show that the network dynamics can be equivalently described as that of a single-channel CSMA algorithm on an appropriate virtual network. Our focus is on the asymptotic regime in which the network nodes try to activate aggressively in order to achieve maximum throughput. Of particular interest is the scenario where the number of available channels is not sufficient for all nodes of the network to be simultaneously active and the well-studied temporal starvation issues of the single-channel CSMA dynamics persist. For most networks we expect that a larger number of available channels should alleviate these temporal starvation issues. However, we prove that the aggregate throughput is a non-increasing function of the number of available channels. To investigate this trade-off that emerges between aggregate throughput and temporal starvation phenomena, we propose an analytical framework to study the transient dynamics of multi-channel CSMA networks by means of first hitting times. Our analysis further reveals that the mixing time of the activity process does not always correctly characterize the temporal starvation in the multi-channel scenario and often leads to pessimistic performance estimates.

Temporal starvation in multi-channel CSMA networks: an analytical framework

In this paper, we consider a stochastic model for a frequency-agile CSMA protocol for wireless networks where multiple orthogonal frequency channels are available. Even when the possible interference on the different channels is described by different conflict graphs, we show that the network dynamics can be equivalently described as that of a single-channel CSMA algorithm on an appropriate virtual network. Our focus is on the asymptotic regime in which the network nodes try to activate aggressively in order to achieve maximum throughput. Of particular interest is the scenario where the number of available channels is not sufficient for all nodes of the network to be simultaneously active and the well-studied temporal starvation issues of the single-channel CSMA dynamics persist. For most networks, we expect that a larger number of available channels should alleviate these temporal starvation issues. However, we prove that the aggregate throughput is a non-increasing function of the number of available channels. To investigate this trade-off that emerges between aggregate throughput and temporal starvation phenomena, we propose an analytic framework to study the transient dynamics of multi-channel CSMA networks by means of first hitting times. Our analysis further reveals that the mixing time of the activity process does not always correctly characterize the temporal starvation in the multi-channel scenario and often leads to pessimistic performance estimates.

Distributed Gateway Selection for M2M Communication in Cognitive 5G Networks

M2M communication is an important component for future wireless networks. M2M systems consist of a large number of devices that can operate with minimum or no human intervention. However, spectrum demand rises exponentially with the increase in the number of connected devices. Cognitive 5G networks are key to address the issue of spectrum scarcity. Further, use of multiple gateways in cognitive 5G networks for M2M communication can increase system throughput, coverage, and energy efficiency. Nevertheless, using multiple gateways for the secondary M2M devices may cause interference to the primary M2M devices. Existing gateway selection protocols for cognitive M2M communication mostly use single channel CSMA, and thus are not efficient in terms of reducing the interference. Thus, in this article, we propose a DGAP based on multi-channel CSMA for M2M communication in 5G networks. Further, we propose a Lo-DGAP, where each gateway transmits only the worst primary M2M device information rather than transmitting all neighboring primary M2M device information. The proposed Lo-DGAP increases the throughput of the system by reducing the message header payload and is also energy- efficient. Simulation results demonstrate the effectiveness of the proposed schemes in terms of network lifetime and energy consumption.

An Efficient Time Slot Acquisition on the Hybrid TDMA/CSMA Multichannel MAC in VANETs

The multichannel MACs increase the throughput and reduce the collision probability compared to the single-channel MACs. However, coordination of multiple nodes across multichannels is nontrivial. Recently, a multichannel MAC, called HER-MAC, uses both TDMA and CSMA schemes to improve reliability in broadcasting safety messages and efficiency in service channel utilization. Nevertheless, HER-MAC suffers a high collision probability for a large number of vehicle nodes. In this letter, we propose a hybrid TDMA/CSMA multichannel MAC protocol for VANETs that allows efficient broadcasting of messages and increases throughput on the control channel. Furthermore, our proposed MAC eliminates unnecessary control packet such as HELLO and SWITCH packets in HER-MAC. Analysis and simulation results show that the proposed MAC can provide faster time slot acquisition on the control channel than HER-MAC.

The One-persistent Multichannel CSMA Protocol with Monitoring Functions Based on Conflict Resolution Algorithm in WSN

In the Wireless Sensor Network, a new MAC protocol: one-persistent CSMA protocol with monitoring functions and multichannel mechanism for Wireless Sensor Network based on conflict resolution algorithm is proposed. Protocol from the system throughput, collision rate, better service quality for higher priority and other aspects improve the traditional CSMA system to perfect the controllability of the system, making the system more stable for the big data, better adapted to different business. The average cycle method is used to derive rigorous mathematical expressions of specific relevant parameters. Using MATLAB simulation tool for the accuracy of the agreement is demonstrated.

Research on Time Division Multi-channel p-Persistent CSMA Based on Binary Trees Conflict Resolution Mechanism

Research on Time Division Multi-channel p-Persistent CSMA Based on Binary Trees Conflict Resolution Mechanism

Research on the Multi-channel P-persistent CSMA Protocol with Monitoring Function

Research on the Multi-channel P-persistent CSMA Protocol with Monitoring Function

CogMAC+: A decentralized MAC protocol for opportunistic spectrum access in cognitive wireless networks

The rapidly increasing number of wireless applications are making the wireless spectrum scarcity a serious problem. Cognitive MAC protocols have emerged as a promising solution to address this issue by opportunistically allowing secondary users to utilize unused licensed bands, and enabling spectrum co-existence of multiple secondary networks. In this paper, we present CogMAC+, a decentralized multichannel MAC protocol, which is based on multichannel preamble reservation scheme and CSMA principle. It achieves parallel transmissions for multiple secondary users by enabling them to estimate the duration of channel occupancy of each other. In order to achieve the optimal sensing schedule, it allows secondary users to dynamically access channels according to the channel occupancy of primary users and other secondary networks. Moreover, CogMAC+ uses an adaptive energy detection scheme to dynamically set the energy detection threshold according to the carrier sensing status, the false positive detection ratio and the estimated noise level. CogMAC+ has been verified and evaluated empirically in a software defined radio testbed with realistic spectrum occupancies of licensed users. Our experimental performance evaluation indicates that CogMAC+ is able to carry out reliable parallel communication in multiple channels even in a severely interfered environment.

Multichannel CSMA Based MAC Scheme for Unsaturated Cognitive Radio Networks: Performance Study of the Opportunity and Contention Window

In cognitive radio networks, secondary users (SUs) opportunistically utilize the spectrum without harmful interruption to the primary users (PUs). In this article, the overlay medium access control (MAC) scheme is considered in which SU uses the spectrum portion which is not utilized by PU. The imperfect sensing is considered at SU network (SUN) to detect PU's transmission. In the SUN, carrier sense multiple access protocol with contention window (CW) is used to minimize the collisions between SUs and PUs. Multichannel decentralized MAC protocol is investigated to analyse the throughput and examine the impact of various arrival rates of PUs (opportunities) and SUs, number of SUs, number of channels, and CWs. Numerical results verify various events and demonstrate the performance of the proposed MAC protocol under imperfect sensing conditions.

Opportunistic multi-channel CSMA protocol for OFDMA systems

In this letter, we present an opportunistic multichannel CSMA protocol for OFDMA systems in frequency-selective fading channel. In order to opportunistically exploit the frequency selectivity, an OFDM-based single-channel CSMA protocol can employ water-filling power allocation as it allows a single station to utilize the whole frequency bandwidth at each time instant. In contrast, the proposed OFDMA-based multichannel CSMA protocol achieves the multi-user diversity gain by arranging multiple stations to transmit on their favorable sub-channels simultaneously. The proposed protocol is designed as an opportunistic version of the original multi-channel CSMA protocol, which was proposed in our previous work, and adopts a channel-adaptive backoff (or transmission probability control) algorithm, enabling each station to attempt data transmission on its high-SNR sub-channel with a high probability. The opportunistic multi-channel CSMA turns out to improve the total data rate significantly over the opportunistic single-channel CSMA, and to achieve almost full multi-user diversity gain despite the distributed operation.

Generalized CSMA/CA for OFDMA systems: protocol design, throughput analysis, and implementation issues

In this paper, we present a multi-channel carrier sense multiple access with collision avoidance (CSMA/CA) protocol for orthogonal frequency division multiple access (OFDMA) systems. The CSMA/CA system in conventional single-channel operation has the advantage of not requiring the signaling for bandwidth request and allocation over the scheduled access system but it sacrifices system efficiency significantly. We overcome the system efficiency limitation by exploiting the OFDMA system features that multiple stations can transmit simultaneously on different sub-channels, and the stations can obtain the channel information of all the sub-channels at each time instant. The OFDMA-based multi-channel CSMA/CA protocol is designed to enable the stations to contend with each other for channel access both in time and frequency domains through a two-dimensional backoff scheme. The protocol takes a generalized form of the conventional single-channel CSMA/CA protocol: It allows to segment the channel bandwidth into multiple narrow-band random access channels and adjust the transmission probability according to the multi-channel activity in a flexible manner. For throughput analysis, we devise a multi-channel p-persistent CSMA protocol that can emulate the multi-channel CSMA/CA protocol and then analyze its saturated throughput. The simulation and analysis results reveal that the proposed system performs far better than the single-channel CSMA/CA system while using the same total bandwidth and even close to the scheduled access system. Further, we examine how stringent time synchronization is required among the constituent stations in implementing of the OFDMA-based multi-channel CSMA/CA system.

Adaptive cross-layer MAC design for improved energy-efficiency in multi-channel wireless sensor networks

We present a novel cross-layer design for improving energy efficiency in a wireless sensor network that utilizes a multi-channel non-persistent CSMA MAC protocol with adaptive MQAM modulation at the physical layer. Cross-layer interactions are achieved through joint, traffic-dependent adaptation of the backoff probability at the MAC layer and the modulation order at the physical layer. The joint optimization of the backoff probability and the modulation order is conducted subject to a constraint on the packet retransmission delay. Such an optimization is shown to produce a significant improvement in the per-bit energy requirement for successful packet delivery. Our analytical findings are verified through numerical results and computer simulations.

Comparison of a distributed dynamic channel assignment scheme with multichannel CSMA in a terrestrial radio environment

The comparison is explored between call-oriented distributed channel assignment strategies used in UFDMA, DECT, and PACS-UB, and packet-oriented multichannel CSMA. Analysis is developed for a UFDMA call-oriented scenario for channel sense delays, which are either fixed or increase according to the number of channels in the allocation. It is shown that when the channel sense delay becomes a large fraction of the call length, thus causing a long vulnerable period, this becomes the limiting factor on the call unsuccessful probability performance. Simulation is used to validate the analysis and it is shown that there is excellent agreement over a wide range of channel sense delays. Possible solutions for reducing the effects of channel sensing delay are also considered.

Cellular mobile packet radio using multiple-channel CSMA

One way to increase frequency spectrum utilisation in a mobile communication system is to divide the geographical region spatially into a number of cells, each of which contains a base station. Each base station is assigned a set of channels, and the users in the neighbourhood of a base station can transmit their messages to the base station. Several protocols governing the access to the base station channels are available. The paper considers multichannel CSMA schemes embedded in a spatially celluar communication environment. Several alternative ways of organising the system resources, layout and protocol are considered. The complexity of the system is progressively increased, culminating in the general case: each base station is assigned a set of Cachannels and users access any one of the k nearest base stations with multichannel CSMA protocol. The performance characteristics of the system—normalised delay against system bandwidth utilisation—are given in terms of the system parameters. The several configurations considered are compared based on the delay, band-width utilisation and interference rejection characteristics.