MAC Protocol For Wireless LANs Research Articles

G-DCF: Improving System Spectral Efficiency through Concurrent Transmissions in Wireless LANs

This paper presents G-DCF, a MAC protocol for wireless LANs that can improve system spectral efficiency of wireless LANs by allowing more concurrent transmissions. The 802.11 DCF creates exposed terminals which are nodes that can transmit successfully but are blocked by carrier sensing. More potential exposed terminals are created when APs are densely placed, limiting spatial reuse of channels and thus system throughput. In order to allow concurrent transmissions from exposed terminals, G-DCF establishes groups in the network. Members of a group are nodes located within the carrier sense range of each other but can transmit packets concurrently. Whenever one member of a group wins the channel and transmits its packet, other nodes in the group also start transmission, triggered by the group ID included in the preamble. Contention window is adjusted according to the group size for fair share of the channel. Performance evaluations show that G-DCF can significantly improve system throughput and fairness over 802.11 DCF, especially when the APs are densely deployed.

Multi-channel cooperative MAC protocol for wireless LANs

Traditional IEEE 802.11-based wireless LANs use only a single channel in order to ensure the connectivity of networks, although multi-channel capability is available to provide higher network throughput by allowing simultaneous multiple transmissions that do not interfere with each other. However, using multiple channels results in several new challenges: finding the receiver, scheduling the next transmission, and balancing the load among channels. This paper proposes a novel and efficient control-channel-based, multi-channel mechanism that uses a single transceiver. Simulation results indicate that the proposed mechanism effectively exploits all available data channels with multiple packet transmissions, provides high network throughput, and requires a low overhead. For example, when we have 13 channels with a 54Mbps data rate, the proposed mechanism provides 349Mbps throughput, while the IEEE 802.11 MAC with a single channel achieves only 13Mbps throughput.

A link-adapted fragment and rate matching (FaRM) MAC protocol for wireless LANs

The paper proposes a fragment and rate matching (FaRM) MAC protocol for wireless LANs to resist the frequent change of channel quality so as to increase network throughput. In wireless transmissions, channel quality varies with time. The FaRM protocol estimates channel quality by detecting current signal-to-noise ratio (SNR) through frame exchanges. A finite state Markov chain (FSMC) is utilised to predict the variation in the channel conditions during the next frame transmission. According to the results obtained from the FSMC, the FaRM protocol enables the sender to dynamically select an appropriate transmission rate as well as an acceptable fragment length to transmit, such that the reliability and time of this transmission can be improved. As a result, the FaRM protocol can not only obtain better network throughput through the selection of the high transmission rate, but it can also increase the successful transmission rate by the determination of a suitable fragment length. Simulation results show that the FaRM protocol has better performance, higher transmission reliability, and lower transmission delay by FaRM in comparison to the related work.

A novel multi-channel MAC protocol with directional antenna for enhancing spatial reuse and bandwidth utilization in WLANs

This paper aims at developing an efficient MAC protocol for wireless LAN by considering multi-channel and directional antennae. Extending IEEE 802.11 to a multi-channel environment not only exploits the bandwidth utilization but also reduces the degree of contentions. Involving directional antennae in designing multi-channel MAC protocol additionally increases the spatial reuse, allowing more parallel communications. This study proposes an efficient Multi-Channel MAC protocol with a Directional Antenna (MCDA) for WLAN. Since each station is only equipped with a single antenna, communicating pairs that progress their communications on data channels cannot maintain the channel usage information which is only obtained from the control channel, raising the channel collision problem. The proposed protocol adopts the channel switch sequence (CSS) mechanism to cope with the channel collision problem and to reduce message exchange overhead for switching channels. According to the state management, MCDA then controls directional antenna transmitting data on a selected channel to exploit the opportunities of spatial reuse, and to maintain fairness among communicating pairs. Simulation results show that the proposed MCDA protocol maintains the fairness and significantly improves bandwidth utilization and throughput.

Performance Analysis of IEEE 802.11 DCF under Nonsaturation Condition

Carrier sense multiple access with collision avoidance (CSMA/CA) methods are considered to be attractive MAC protocols for wireless LANs. IEEE 802.11 distributed coordination function (DCF) is a random channel access scheme based on CSMA/CA method and the binary slotted exponential backoff procedure to reduce the packet collision. In this paper, we propose a new analytical model for a nonsaturated IEEE 802.11 DCF network and evaluate its performance. We verify our model using simulations and show that our results agree with the simulations.

A new approach to the design of MAC protocols for wireless LANs: combining QoS guarantee with power saving

An alternative WLAN protocol which could be adapted in the HCF access scheme defined by IEEE 802.11e, in place of the HCCA mechanism, is introduced. LEPOAC-QG (low energy priority oriented adaptive control with QoS guarantee) is a centralized access mechanism that supports low energy consumption, guarantees QoS for all types of multimedia network applications, enhances the parameterized traffic with priorities, and supports time division access. It instantly negotiates the quality levels of the traffic streams trying to support multiple streams with best possible quality. LEPOAC-QG, compared with HCCA, exhibits generally superior performance.

A new approach to the design of MAC protocols for wireless LANs: combining QoS guarantee with power saving

An alternative WLAN protocol which could be adapted in the HCF access scheme defined by IEEE 802.11e, in place of the HCCA mechanism, is introduced. LEPOAC-QG (low energy priority oriented adaptive control with QoS guarantee) is a centralized access mechanism that supports low energy consumption, guarantees QoS for all types of multimedia network applications, enhances the parameterized traffic with priorities, and supports time division access. It instantly negotiates the quality levels of the traffic streams trying to support multiple streams with best possible quality. LEPOAC-QG, compared with HCCA, exhibits generally superior performance.

Proportional Service Differentiation in Wireless LANs Using Spacing-based Channel Occupancy Regulation

In this paper, we propose Spacing-based Channel Occupancy Regulation (SCORE) MAC protocol for wireless LANs that provides proportional service differentiation in terms of normalized throughput. As shown by our system model and simulation study, SCORE provides consistent, scalable and adjustable proportional differentiation for any network size, any service class distribution, any node data rate and any packet size. Compared to state-of-the-art prioritized service differentiation schemes like Enhanced Distributed Coordination Function (EDCF), SCORE can quantitatively control the channel sharing between different service classes. Moreover, SCORE obtains significant performance improvements in terms of higher network throughput, higher transmission efficiency, lower medium access delay and lower delay jitter.

Two-step multipolling MAC protocol for wireless LANs

The IEEE 802.11 standard defines two coordination functions: distributed coordination function (DCF) and point coordination function (PCF). These coordination functions coordinate the shared wireless medium. The PCF uses a centralized polling-based channel access method to support time-bounded services. To design an efficient polling scheme, the point coordinator (PC) needs to obtain information about the current transmission status and channel condition for each station. To reduce overhead caused by polling frames, it is better to poll all stations using one polling frame containing the transmission schedule. In this paper, we propose an efficient polling scheme, referred to as two-step multipolling (TS-MP), for the PCF in wireless local area networks (WLANs). In this new scheme, we propose to use two multipolling frames with different purposes. The first frame is broadcast to collect information such as the numbers of pending frames and the physical-layer transmission rates for the communication links among all stations. The second frame contains a polling sequence for data transmissions designed based on the collected information. This frame is broadcast to all stations. Extensive simulation studies show that TS-MP not only overcomes the aforementioned deficiencies, but also help to implement rate adaptation over time-varying wireless channel.

Carrier-sense-assisted adaptive learning MAC protocols for distributed wireless LANs

SUMMARY A Carrier-sense-assisted adaptive learning MAC protocol for wireless LANs, capable of operating efficiently in bursty traffic wireless networks with unreliable channel feedback, is introduced. According to the proposed protocol, the mobile station that is granted permission to transmit is selected by means of learning automata. At each station, the learning automaton takes into account the network feedback information in order to update the choice probability of each mobile station. The proposed protocol utilizes carrier sensing in order to reduce the collisions that are caused by different decisions at the various mobile stations due to the unreliable channel feedback. Simulation results show satisfactory performance of the proposed protocol compared to similar MAC protocols. Copyright # 2005 John Wiley & Sons, Ltd.

Throughput analysis of novel CDMA-based MAC protocolfor wireless LANs

A new throughput analysis for a novel slotted CDMA-based medium-access-control protocol, with a channel-load sensing feature, for wireless LANs is presented. Numerical results are shown of throughput against offered-load, and it is shown that the proposed protocol offers considerable throughput improvement when compared with ALOHA DS/SSMA (‘random-access’ CDMA).