By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then design two schemes that are practically realisable, decentralised approximations of this optimal scheme and operate with different amounts of sensing information. We achieve this by (1) introducing learning algorithms that can substantially speed up convergence to collision free operation; (2) developing a decentralised schedule length adaptation scheme that provides long-run fair (uniform) access to the medium while maintaining collision-free access for arbitrary numbers of stations.
ZC is proposed in @cite_17 . We can regard ZC as being similar to L-BEB in that on success it effectively chooses a fixed backoff. On failure, however, a station looks at the occupancy of slots in the previous schedule. The station chooses uniformly between the slot it failed on previously and the slots that were idle in the last schedule. By avoiding other busy slots, which other stations have reserved', ZC finds a collision-free allocation more quickly than other schemes.
@cite_17
2143747785 1484545291 90489852 2129374252
This paper proposes a semi-random backoff (SRB) method that enables resource reservation in contention-based wireless LANs. The proposed SRB is fundamentally different from traditional random backoff methods because it provides an easy migration path from random backoffs to deterministic slot assignments. The central idea of the SRB is for the wireless station to set its backoff counter to a deterministic value upon a successful packet transmission. This deterministic value will allow the station to reuse the time-slot in consecutive backoff cycles. When multiple stations with successful packet transmissions reuse their respective time-slots, the collision probability is reduced, and the channel achieves the equivalence of resource reservation. In case of a failed packet transmission, a station will revert to the standard random backoff method and probe for a new available time-slot. The proposed SRB method can be readily applied to both 802.11 DCF and 802.11e EDCA networks with minimum modification to the existing DCF EDCA implementations. Theoretical analysis and simulation results validate the superior performance of the SRB for small-scale and heavily loaded wireless LANs. When combined with an adaptive mechanism and a persistent backoff process, SRB can also be effective for large-scale and lightly loaded wireless networks. This paper proposes and analyzes a distributed MAC protocol that achieves zero collision with no control message exchange nor synchronization. ZC (ZeroCollision) is neither reservation-based nor dynamic TDMA; the protocol supports variable-length packets and does not lose efficiency when some of the stations do not transmit. At the same time, ZC is not a CSMA; in its steady state, it is completely collision-free. The stations transmit repeatedly in a round-robin order once the convergence state is reached. If some stations skip their turn, their transmissions are replaced by idle @math -second mini-slots that enable the other stations to keep track of their order. Because of its short medium access delay and its efficiency, the protocol supports both real-time and elastic applications. The protocol allows for nodes leaving and joining the network; it can allocate more throughput to specific nodes (such as an access point). The protocol is robust against carrier sensing errors or clock drift. While collision avoidance is guaranteed in a single collision domain, it is not the case in a multiple collision one. However, experiments show ZC supports a comparable amount of goodput to CSMA in a multiple collision domain environment. The paper presents an analysis and extensive simulations of the protocol, confirming that ZC outperforms both CSMA and TDMA at high and low load. Abstract —Random access protocols have been the mechanismof choice for most WLANs, thanks to their simplicity anddistributed nature. Nevertheless, these advantages come at theprice of sub-optimal channel utilization because of empty slotsand collisions. In previous random access protocols, the stationstransmit on the channel without any clue of other stations’intentions to transmit. In this article we provide a framework tostudy the efﬁciency of channel access protocols. This frameworkis used to analyze the efﬁciency of the Binary Exponential Backoffmechanism and the maximum achievable efﬁciency that can beobtained from any completely random access protocol. Then wepropose Learning-BEB (L-BEB).L-BEB is exactly the same as legacy BEB, with one exception:L-BEB chooses a deterministic backoff value after a successfultransmission. We call this value the virtual frame size ( V ). Thissubtle modiﬁcation signiﬁcantly reduces the number of collisions.It can be observed that, as the system runs, the number of colli-sions is progressively reduced. Thus we conclude that the systemlearns. Further, if the number of contending stations is equal orlower than The IEEE 802.11 standard for wireless local area networks (WLANs) employs a medium access control (MAC), called distributed coordination function (DCF), which is based on carrier sense multiple access with collision avoidance (CSMA CA). The collision avoidance mechanism utilizes the random backoff prior to each frame transmission attempt. The random nature of the backoff reduces the collision probability, but cannot completely eliminate collisions. It is known that the throughput performance of the 802.11 WLAN is significantly compromised as the number of stations increases. In this paper, we propose a novel distributed reservation-based MAC protocol, called early backoff announcement (EBA), which is backward compatible with the legacy DCF. Under EBA, a station announces its future backoff information in terms of the number of backoff slots via the MAC header of its frame being transmitted. All the stations receiving the information avoid collisions by excluding the same backoff duration when selecting their future backoff value. Through extensive simulations, EBA is found to achieve a significant increase in the throughput performance as well as a higher degree of fairness compared to the 802.11 DCF.