ABSTRACT
Wireless Networks (WNs) require effective wireless access to network resources. The rapid advancement in wireless technology and protocol development has facilitated ex- tensive usability of WNs. Each station of a WN requires channel access for communi- cation. Contention-based approach is one of the most accepted channel access in WNs.
However, frame collision remains one of the fundamental problems in channel access of Contention-based Wireless Networks (CWNs). Collision is managed by sacrificing network performance, but is not fully avoidable yet. The primary reason of this ineffi- ciency is the shared nature and distributed access control of wireless channel. In their current forms, CWNs suffer from limited throughput, higher channel access delay, unfair resource provisioning, and security threat. They cannot meet users’ demands, such as real-time and reliable file sharing, differentiated quality-of-service, and secured commu- nication. Motivated by these problems, in this dissertation, we explore an alternative design of collision management scheme that can effectively address these challenges.
This dissertation broadly studies two types of collisions – unintentional and inten- tional, and proposes solutions for them. When multiple stations simultaneously trans- mit their data frames, the receiving station might experience unintentional collision.
On the other hand, the receiver might experience intentional collision when an adver- sary collides its own frame with legitimate communications. In the first scenario, we consider the IEEE 802.11 and 802.11e Wireless LANs, whereas we consider an energy- constrained CWN such as underwater sensor network for the second one. We show the existence of packet-centric unfairness in the existing IEEE 802.11 DCF MAC protocol usingpacket-centric analysis(PCA). We design asemi-distributed backoff (SDB) scheme for avoiding successive collisions. We exploit the inaccessible time slots for designing the anomalous transmission (ANT) scheme, which reduces the average channel access de- lay of a station. The delay-aware distributed dynamic adaptation of contention window (D2D) scheme jointly optimizes the saturation throughput and channel access delay in runtime. Finally, we propose a cumulative sum-based controllable reactive jamming de- tection (CURD) scheme for successful detection of intentional collisions due to reactive jamming. Nevertheless, we theoretically analyze the proposed schemes for establishing their respective performance improvements in CWNs.
The contributions of this dissertation are multi-fold. First, it shows through packet- centric analysis the scope of performance improvement of the DCF protocol. Second, the work proposes a seamlessly integrable backoff algorithm for providing guaranteed
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channel access to loss-sensitive applications by avoiding successive collisions. The pro- posed scheme is capable of providing optimal backoff counters, and, thus, reduces idle channel overhead. Third, the idle channel overhead is further reduced by exploiting the inaccessible time slots in the channel access processes. Fourth, the work further shows the joint performance improvement of saturation throughput and channel access delay in runtime. Finally, it allows the system to detect reactive jamming, one of the causes of intentional collisions. In brief, this dissertation analyzes the DCF protocol from packet- centric viewpoint followed by the design and analysis of four schemes for mitigating the impact of both intentional and unintentional collisions in CWNs.
Keywords: Wireless networks, Distributed coordination function, Contention-based channel access, Backoff algorithm, Frame collision, Reactive jamming, Collision avoid- ance, Performance analysis, Differentiated service.
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