Lajos L. Hanzo

Admission control schemes for 802.11-based multi-hop mobile ad hoc networks: a survey

Mobile ad hoc networks (MANETs) promise unique communication opportunities. The IEEE 802.11 standard has allowed affordable MANETs to be realised. However, providing quality of service (QoS) assurances to MANET applications is difficult due to the unreliable wireless channel, the lack of centralised control, contention for channel access and node mobility. One of the most crucial components of a system for providing QoS assurances is admission control (AC). It is the job of the AC mechanism to estimate the state of the networks resources and thereby to decide which application data sessions can be admitted without promising more resources than are available and thus violating previously made guarantees. Unfortunately, due to the aforementioned difficulties, estimating the network resources and maintaining QoS guarantees are non-trivial tasks. Accordingly, a large body of work has been published on AC protocols for addressing these issues. However, as far as it is possible to tell, no wide-ranging survey of these approaches exists at the time of writing. This paper thus aims to provide a comprehensive survey of the salient unicast AC schemes designed for IEEE 802.11- based multi-hop MANETs, which were published in the peer-reviewed open literature during the period 2000-2007. The relevant considerations for the design of such protocols are discussed and several methods of classifying the schemes found in the literature are proposed. A brief outline of the operation, reaction to route failures, as well as the strengths and weaknesses of each protocol is given. This enables patterns in the design and trends in the development of AC protocols to be identified. Finally, directions for possible future work are provided.

Quality of Service Routing and Admission Control for Mobile Ad-hoc Networks with a Contention-based MAC Layer

In mobile ad hoc networks (MANETs), accurate throughput-constrained quality of service (QoS) routing and admission control have proven difficult to achieve, mainly due to node mobility and contention for channel access. In this paper we propose a solution to those problems, utilising the dynamic source routing (DSR) protocol for basic routing. Our design considers the throughput requirements of data sessions and how these are affected by protocol overheads and contention between nodes. Furthermore, in contrast to previous work, the time wasted at the MAC layer by collisions and channel access delays, is also considered. Simulation results show that in a stationary scenario with high offered load, and at the cost of increased routing overhead, our protocol more than doubles session completion rate (SCR) and reduces average packet delay by a factor of seven compared to classic DSR. Even in a highly mobile scenario, it can double SCR and cut average packet delay to a third

Throughput Assurances Through Admission Control for Multi-Hop MANETs

In multi-hop mobile ad hoc networks (MANETs) it is difficult to provide throughput guarantees due to the lack of central co-ordination, mutual contention between nodes, collisions, node mobility and an error-prone wireless channel. Existing QoS-aware admission control protocols for multi-hop MANETs either ignore the effect of collisions, or do not consider the increase in collision rate upon traffic admission. However, we have found that such effects have a significant impact on the achievable throughput. In this work we therefore present a novel low-complexity passive observation-based admission control scheme for ensuring that sessions throughput requirements are upheld in a contention-based, collision-prone multi-hop MANET. We show, via simulations, that in large networks, even at offered traffic loads greatly exceeding the network capacity, at least 88% of admitted sessions maintain their desired throughput throughout their duration. For all traffic loads, average packet delay and packet loss ratio remain below 55 ms and 1% respectively.

Connectivity-Related Properties of Mobile Nodes Obeying the Random Walk and Random Waypoint Mobility Models

This paper independently derives the probability of any pair of uniformly-distributed nodes to be within transmission range of each other in a square-shaped area. It then explores, via simulation, some new applications of this expression. The applications are relevant for scenarios where node mobility is governed by the popular random walk or random waypoint mobility models (RWkMM and RWPMM). Under the RWPMM with pausing, at any time, some nodes will be mobile and some stationary. The positions of mobile nodes are drawn from a nonuniform distribution, while a uniform distribution applies to the stationary nodes. In various forms of the RWkMM, the node spatial distribution is uniform in its steady state. The studied applications include calculating the expected node degree and the node isolation probability. Simulation results show that the considered model is able to predict these connectivity-related properties near-perfectly under a paused RWPMM and with all mobility scenarios under the RWk with reflection model. With the RWPMM, the accuracy decreases as the fraction of time the nodes spend moving increases. However, it is still generally better than the simple pir2/A disk-covering model, which is often employed for calculating network connectivity-related properties in ad hoc networks. Further application of the considered methods is exemplified by calculation of an accurate upper bound on the per-node transmission capacity for contention-based networks, when the nodes are uniformly distributed.

Adaptive Soft-Decision Aided Differential Modulation for Cooperative Uplink Transmission Relying on Radio-Over-Fiber Backhaul

A novel adaptive turbo-coded soft-decision aided differential detection (ATSDD) scheme is proposed for cooperative uplink wireless and Radio-over-fiber (ROF) transmission in a Fractional Frequency Reuse (FFR) based multicell, multiuser system. More specifically, the ATSDD scheme is employed by the Mobile Station (MS) for reliably conveying the source bits to a pair of Remote Antennas (RAs) by appropriately adjusting the modulation mode according to the near-instantaneous wireless and ROF channel conditions. The ATSDD switching thresholds are specifically adjusted for ensuring that the Bit Error Ratio (BER) remains below 10^(-5). We also investigated the effect of phase-rotations, which is routinely inflicted by practical imperfect ROF links. We demonstrate that our ATSDD scheme increases the overall throughput.

Classic QAM Modems for Bandlimited AWGN Channels

This chapter contains sections titled: Introduction Trellis Coding Principles V.29 Modem V.32 Modem V.33 Modem Summary

Timing Recovery for Fading Channels

This chapter contains sections titled: Introduction Times-two Clock Recovery for QAM Basic Early-Late Clock Recovery for Star 16-QAM Modified Early-Late Clock Recovery for QAM Clock Recovery in the Presence of ISI Early-Late Clock Recovery Implementation Details Carrier Recovery Summary

Coded Modulation Assisted Channel Equalised Systems

This chapter contains sections titled: Introduction Intersymbol Interference Decision Feedback Equaliser Decision Feedback Equaliser Aided Adaptive Coded Modulation Radial Basis Function-Based Equalisation Turbo Equalisation Using Symbol-Based MAP Decoder RBF Assisted Turbo Equalisation of Coded Modulation Schemes In-phase/Quadrature-phase Turbo Equalisation RBF Assisted Reduced Complexity In-phase and Quadrature-phase Turbo Equalisation of Coded Modulation Schemes Summary