A Token Based Code Division Multiple Access Mac Protocol For Wireless Ad Hoc Networks

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2009Ad Hoc ağlarında en mühim konulardan biri MAC protokol tasarımıdır. Bilindiği gibi, MAC protokollerin başlıca fonksiyonu, olabilecek çarpışmaları mümkün olduğunca azaltmak ve uygun kanal kullanımını sağlamaktır. Ayrıca MAC protokoller adil olmalı ve düğümlerin önceliklerine göre kanal erişim sırasını ayarlamalıdır. Gerçek zaman iletişimlerini sağlamak için en uygun olan protokoller jeton yöntemine dayanmaktadır. Bu tip protokollerde paket gecikmeleri deterministiktir ve olabilecek en büyük paket gecikmeleri tahmin edilebilmektedir. Bu çalışmada ileri sürülen MAC protokol de bir çok MAC protokol gibi jeton yöntemine dayanmaktadır, fakat bu çalışmada jeton CDMA kodlarını ağda paylaştırmak için kullanılmaktadır. CDMA özelliği protokole, ağda aynı anda birden çok yayın yapabilmesini sağlamaktadır. Önerilen protokol literatürde adı geçen protokolle karşılaştırılmıştır ve simulasyon sonuçları, önerilen protokolün paket gecikmelerini azaltmakta ve kanal kullanımını artırmakta olduğunu göstermiştir.MAC protocols are very important issues in wireless ad hoc networks. As known, its primary function is to minimize the collisions and achieve reasonable channel utilization. Also MAC protocols must support fairness and prioritized access to the medium. Token based MAC schemes are more suitable for real time communications due to the fact that the packet delay is highly deterministic and upper bound of latency is predictable. The proposed work in this thesis is based on a token passing scheme as many studies have proposed till now, but the difference is that this MAC scheme is based on a token passing scheme with the incorporation of a Code Division Multiple Access (CDMA) unlike others. The protocol is able to support multiple, simultaneous transmissions with it is unique CDMA feature. Nodes are equipped with only one transceiver. The performance of proposed MAC protocol is compared with MAC protocols that have appeared in the literature by simulations. Simulation results show that proposed MAC scheme is effective in decreasing the packet delay and increasing the channel utilization.Yüksek LisansM.Sc

Cross-Layer Design for Medium Access Control in CDMA Ad Hoc Networks

<p/> <p>A medium access control (MAC) protocol for spread-spectrum ad hoc networks with dynamic channel allocation (DCA) is presented. DCA can support large systems with a smaller number of channels by dynamically assigning channels only when a node has a packet to transmit. The protocol extends cross layer, with the scheduling at the MAC, and assignment of channels at the physical layer by means of a query. It is shown that DCA is collision-free under ideal conditions. By assigning channels dynamically, DCA offers improved throughput normalized by available bandwidth. Analytical results are presented for the performance of the query detection and the throughput for a fully connected network.</p

Hybrid token-CDMA MAC protocol for wireless networks.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.Ad hoc networks are commonly known to implement IEEE 802.11 standard as their medium access control (MAC) protocol. It is well known that token passing MAC schemes outperform carrier-sense-multiple-access (CSMA) schemes, therefore, token passing MAC protocols have gained popularity in recent years. In recent years, the research extends the concept of token passing ' scheme to wireless settings since they have the potential of achieving higher channel utilization than CSMA type schemes. In this thesis, a hybrid Token-CDMA MAC protocol that is based on a token passing scheme with the incorporation of code division multiple access (CDMA) is introduced. Using a dynamic code distribution algorithm and a modified leaky-bucket policing system, the hybrid protocol is able to provide both Quality of Service (QoS) and high network resource utilization, while ensuring the stability of a network. This thesis begins with the introduction of a new MAC protocol based on a token-passing strategy. The input traffic model used in the simulation is a two-state Markov Modulated Poisson Process (MMPP). The data rate QoS is enforced by implementing a modified leaky bucket mechanism in the proposed MAC scheme. The simulation also takes into account channel link errors caused by the wireless link by implementing a multi-layered Gilbert-Elliot model. The performance of the proposed MAC scheme is examined by simulation, and compared to the performance of other MAC protocols published in the literature. Simulation results demonstrate that the proposed hybrid MAC scheme is effective in decreasing packet delay and significantly shortens the length of the queue. The thesis continues with the discussion of the analytical model for the hybrid Token CDMA protocol. The proposed MAC scheme is analytically modelled as a multiserver multiqueue (MSMQ) system with a gated service discipline. The analytical model is categorized into three sections viz. the vacation model, the input model and the buffer model. The throughput and delay performance are then computed and shown to closely match the simulation results. Lastly, cross-layer optimization between the physical (PHY) and MAC layers for the hybrid token-CDMA scheme is discussed. The proposed joint PHY -MAC approach is based on the interaction between the two layers in order to enable the stations to dynamically adjust the transmission parameters resulting in reduced mutual interference and optimum system performance