In this paper, we introduce a MAC scheme that reduces the probability of collision and also uses frame aggregation to improve the efficiency. The scheme we propose is called Group-based MAC (GMAC). Our scheme divides the contending stations into groups. Out of each group, only one station will contend. This station is called the leader of the group. Since fewer stations are contending, the probability of collision is reduced.
Group gains access to the channel, it reserves time for all the stations in its group via an RTS/CTS exchange with the AP. The leader also transmits the schedule of the group. Hence, the other stations in the group do not need to contend and do not need to transmit RTS/CTS. This reduction in control frames increases the throughput of the MAC scheme.
The stations in a group rely on the RTS frame transmitted by the leader. They also rely on hearing each other’s transmissions. Hence, the condition is that a group should be free of hidden nodes. All the stations in the group should be able to hear each other’s transmissions. Accordingly, the stations in a group should be in close proximity. Our scheme provides performance gain over the standard’s DCF since it has a lower probability of collision.
Our scheme also uses aggregation of data frames and the Block- ACK mechanism. We evaluate the performance of our scheme with analytic and simulation results. We compare our scheme to the 802.11n standard’s DCF and to other schemes from the literature. The simulation results show that our scheme provides a significant increase in throughput. Our scheme also has one of the lowest collision rates. The results also show that our scheme has good delay characteristics and provides a high fairness to the users. Group-Based Medium Access Control for IEEE 802.11n Wireless LANs
EXISTING SYSTEM:
Previous designing an efficient Medium Access Control (MAC) protocol and Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol, and the IEEE 802.11 MAC protocol that uses the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol, are first studied. They are analyzed using a new analytical approach proposed in this thesis. The new approach is based on the idea that the service process of a MAC protocol can be modeled by a Phase-Type (PH) distribution. This way, the arrival process as well as the service process of the actual protocol can be described by a certain multidimensional continuous time Markov chain over the traditional approach for performance analyses of MAC protocols are that: (i) it provides a unified model for the analysis of MAC protocols; (ii) it significantly simplifies the analytical model of a MAC protocol which makes it possible to include a more complex and realistic traffic model with compromising the protocol details; (iii) vast knowledge is available on the analysis of a continuous time Markov chain, which allows for more insight to the performance of a MAC protocol. Extensive demonstrations of the use of the approach on performance analyses of MAC protocols are provided, some of which conducte d under realistic bursty traffic conditions.
PROPOSED SYSTEM:
We propose a Group-based MAC (GMAC) scheme that reduces the probability of collision and also uses frame aggregation to improve the efficiency. The contending stations are divided into groups. Each group has one station that is the group leader. Only the leader stations contend, hence, reducing the probability of a collision. We evaluate the performance of our scheme with analytic and simulation results. The results show that GMAC achieves a high throughput, high fairness, low delay and maintains a high performance with high data rates.
We use is that the contending stations, which are the leaders, include in the polling frame the value of the Back-Off (BO) timer that they will use in the next contention. This mechanism was proposed in and to allow the contending stations to know each other’s BO timers. In GMAC, the BO timer of the leader is transmitted in the field “Backoff for Next Contention” in the polling frame. This field is used by the stations in the leader’s group to detect if the leader has left the network gets access to the channel by winning the contention, it reserves time for itself and for all the stations in its group via an RTS/CTS exchange with the AP. All the stations in the WLAN (such as other groups) hear the CTS and refrain from transmission. The reserved time is dedicated for the current group.