Medium access control and network planning in wireless networks

Wireless Local Area Networks (WLANs) and Wireless Metropolitan Area Networks (WMANs) are two of the main technologies in wireless data networks. WLANs have a short range and aim at providing connectivity to end users. On the other hand, WMANs have a long range and aim at serving as a backbone network and also at serving end users. In this dissertation, we consider the problem of Medium Access Control (MAC) in WLANs and the placement of Relay Stations (RSs) in WMANs. We propose a MAC scheme for WLANs in which stations contend by using jams on the channel. We present analytic and simulation results to find the optimal parameters of the scheme and measure its performance. Our scheme has a low collision rate and delay and a high throughput and fairness performance. Secondly, we present a MAC scheme for the latest generation of WLANs which have very high data rates. In this scheme, we divide the stations into groups and only one station from each group contends to the channel. We also use frame aggregation to reduce the overhead. We present analytic and simulation results which show that our scheme provides a small collision rate and, hence, achieves a high throughput. The results also show that our scheme provides a delay performance that is suitable for real-time applications and also has a high level of fairness. Finally, we consider the problem of placing Relay Stations (RSs) in WMANs. We consider the Worldwide Interoperability for Microwave Access (WIMAX) technology. The RSs are used to increase the capacity of the network and to extend its range. We present an optimization formulation that places RSs in the WiMAX network to serve a number of customers with a pre-defined bit rate. Our solution also provides fault-tolerance by allowing one RS to fail at a given time so that the performance to the users remains at a predictable level. The goal of our solution is to meet the demands of the users, provide fault-tolerance and minimize the number of RSs used

Medium access control with physical-layer-assisted link differentiation

In this paper, we develop medium access control (MAC) schemes for both contention and contention-free accesses over wireless local area networks and give performance analysis of these MAC protocols. User detection and multirate adaptation (MRA) modules are proposed in the physical layer (PHY) to assist link differentiation. With these two modules, for contention accesses, a new distributed queuing MAC protocol (PALD-DQMP) is proposed. Based on different users' channel states, PALD-DQMP makes use of a distributed queuing system to schedule transmissions. To support multimedia transmissions, an enhanced PALD-DQMP (E-PALD-DQMP) is designed by providing two-level optimized transmission scheduling for four access categories, thus eliminating both external and internal collisions among mobile stations. For contention-free accesses, based on the same PHY-assisted link differentiation provided by the two modules, a new multipolling MAC protocol (PALD-MPMP) is proposed, which not only reduces the polling overhead but also prioritizes transmissions according to their delay requirements. Performance analysis and simulation results show that our proposed protocols outperform the standard MAC protocols for both delay-sensitive and best-effort traffics. All these improvements are mainly attributed to the awareness of cross-layer channel state information and the consequent MRA scheme. © 2008 IEEE.published_or_final_versio

Optimizing frequency domain contention in wireless network

Wireless communication became popular in the last decades, giving the mobility to the users. However with increased number of users and contention, network efficiency can hardly keep up with user needs. This thesis focuses on a new frequency domain contention technique called FICA. In FICA, the channel is assumed to be using Orthogonal Frequency Division Multiplex (OFDM) with multiple sub-carriers. We investigated the use of multiple channels and multiple access points (APs) in the design. First we investigated having one channel that is divided into number of sub-carriers, it shows good result, but only for limited number of users. Therefore we worked on the second scenario of having several sub-channels and each sub-channel is divided into a number of sub-carriers to communicate through one AP. And for efficient result nodes contend on the contention band and winner nodes will have the chance to send their data through the transmission band. In real world, networks have more than one AP, for that reason we investigate the third scenario, which is having more than one AP. In this setup, the result showed significant outcome, that we can divide the channel into several sub-channels to serve more than one AP and hash an ID for each AP. We further investigated optimal number of ID bits that are used to represent the hashed receiver IDs. We summarize the results as following: 1) it is possible to divide the channel bandwidth into several sub-channels that is divided into several sub-carriers to serve large number of users. 2) node contention should be partitioned into contention band and transmission band to reduce the overhead that the contending node cause when contending on the whole channel. 3) AP ID is required when the network has more than one AP. 4) number of sub-carriers in the contention band has to increase at least to the double for higher efficiency, since more AP on the network would make the channel more loaded. 5) AP ID can be anything between 20-40 bits. Decreasing the ID to less than 40bits did not affect the throughput and efficiency of the channel

High Throughput MAC Protocol Using Sequential Collision Resolution and Outband Signalling

AbstractSince the release of the IEEE 802.11 standard, several efforts have been made to improve its performance. By using collision resolution together with collision detection in wireless networks, the time spent on collision can be reduced, thus improving system throughput. In this paper, collision detection is initiated by the receiver and a Sequential Collision Resolution mechanism is proposed where preferential access is given to all the colliding packets. Extensive simulations are carried out to evaluate the performance of this collision resolution protocol and a higher system throughput and lower delay is obtained