Wireless communications using ad hoc networks are receiving an increasing interest. The most attractive feature of ad hoc networks is the flexibility. The network is set up by a number of units in an ad hoc manner, without the need of any fixed infrastructure. Communication links are established between two units if the signal strength is sufficiently high. As not all pairs of nodes can establish direct links, the traffic between two units may have to be relayed through other units. This is known as the multi-hop functionality.

While several approaches have been proposed in literature for improving the performance of wireless packet data networks, a recent class of approaches has focused on improving the underlying wireless network model itself. Several of such approaches have shown that using peer-to-peer communication, a mode of communication used typically in ad-hoc wireless networks, can result in performance improvement in terms of both throughput and energy consumption. However, the true impact of using the ad-hoc network model in wireless packet data networks has neither been comprehensively studied, nor characterized. In this paper, we investigate the benefits of using an ad-hoc network model in cellular wireless packet data networks. We find that while the ad-hoc network model has significantly better spatial reuse characteristics, the improved spatial reuse does not translate into better throughput performance. Furthermore, although considerable improvement is seen in energy consumption performance, we observe that using the ad-hoc network model as-is might actually degrade the throughput performance of the network. We identify and discuss the reasons behind these observations. Finally, using the insights gained through our performance evaluations, we discuss strawman versions of three techniques which when used in tandem with the ad-hoc network model result in better throughput, energy consumption, fairness, and mobility-resilience characteristics. Through our simulation results, we motivate that using the ad-hoc network model in conventional wireless packet data networks is a promising approach when the network model is complemented with appropriate mechanisms. 1.

In the Code Division Multiple Access (CDMA) framework, collisions that can occur in wireless networks are eliminated by assigning orthogonal codes to stations, a problem equivalent to that of coloring graphs associated to the physical network.

Time division multiple access (TDMA) based medium access control (MAC) protocols provide QoS with guaranteed access to wireless channel. However, in multihop wireless networks, these protocols may introduce delay when packets are forwarded from an inbound link to an outbound link on a node. Delay occurs if the outbound link is scheduled to transmit before the inbound link. The total round trip delay can be quite large since it accumulates at every hop in the path. This paper presents a method that finds schedules with minimum round trip scheduling delay.

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Spatial reuse TDMA is an access scheme for multi-hop radio networks. The idea is to increase capacity by letting several radio terminals use the same time slot when possible. A time slot can be shared when the radio units are geographically separated such that small interference is obtained. STDMA schedules can assign transmission rights to nodes or alternatively assign transmission rights to links, i.e. transmitter/receiver pairs. Here we compare these two methods and determine which one is preferable. We show that only the connectivity of the network and the input traffic load of the network is needed in order to determine whether node or link assignment is preferable. I. INTRODUCTION We consider a radio network where a number of radio units are spread out in some terrain and where the mobility demands are moderate. If the received signal power is sufficient in relation to noise and interferences, it is assumed that any two radio units can communicate, i.e., establish a link. In a ...

A diversity of possible communication assumptions complicates the study of algorithms and lower bounds for radio networks. We address this problem by defining an Abstract MAC Layer. This service provides reliable local broadcast communication, with timing guarantees stated in terms of a collection of abstract delay functions applied to the relevant contention. Algorithm designers can analyze their algorithms in terms of these functions, independently of specific channel behavior. Concrete implementations of the Abstract MAC Layer over basic radio network models generate concrete definitions for these delay functions, automatically adapting bounds proven for the abstract service to bounds for the specific radio network under consideration. To illustrate this approach, we use the Abstract MAC Layer to study the new problem of Multi-Message Broadcast, a generalization of standard single-message broadcast, in which any number of messages arrive at any processes at any times. We present and analyze two algorithms for Multi-Message Broadcast in static networks: a simple greedy algorithm and one that uses regional leaders. We indicate how these results can be extended to mobile networks.

The design of an e#cient Medium Access Control (MAC) is challenging in ad-hoc networks where users can enter, leave or move inside the network without any need for prior configuration. The existing topology-unaware TDMA-based schemes are capable of providing a minimum guaranteed throughput by considering a deterministic policy for the utilization of the assigned scheduling time slots. In an earlier work, a probabilistic policy that utilizes the non-assigned slots according to an access probability, common for all nodes in the network, was proposed. The achievable throughput for a specific transmission under this policy was analyzed. In this work, the system throughput is studied and the conditions under which the system throughput under the probabilistic policy is higher than that under the deterministic policy are established. In addition, the value for the access probability that maximizes the system throughput is determined analytically, as well as simplified lower and upper bounds that depend only on a topology density metric. Since the analysis of the system throughput is shown to be di#cult or impossible in the general case an approximation is introduced whose accuracy is investigated. Simulation results show that the approximate analysis successfully determines the range of values for the access probability for which the system throughput under the probabilistic policy is not only higher than that under the deterministic, but it is also close to the maximum.

Abstract-We propose an efficient centralized scheduling algorithm in IEEE 802.16 based Wireless Mesh Networks (WMN) to provide high qualified wireless multimedia services. Our algorithm takes special attention on the relay function of the mesh nodes in a transmission tree which is seldom studied in previous research. Some important design metrics, such as fairness, channel utilization and transmission delay are considered in this scheduling algorithm. IEEE 802.16 employs TDMA and the selection policy for scheduled links in a time slot will definitely impact the system performance. We evaluated the proposed algorithm with four selection criteria through extensive simulations and the results are instrumental for improving the performance of IEEE 802.16 based WMNs in terms of link scheduling. I.

An ad hoc network can be set up by a number of units without the need of any permanent infrastructure. Two units establish a communication link, if the channel quality is sufficiently high. As not all pairs of units can establish direct links, the traffic between two units may have to be relayed through other units. This is known as the multi-hop functionality. In military command and control systems, ad hoc networks are also referred to as multi-hop radio networks. Spatial TDMA (STDMA) is a scheme for access control in ad hoc networks. STDMA improves TDMA by allowing simultaneous transmission of multiple units. In this paper, we study the problem of STDMA scheduling, where the objective is to find minimum-length schedules. Previous work for this problem has focused on heuristics, whose performance is difficult to analyze when optimal solutions are not known. We develop novel mathematical programming formulations for this problem, and present a column generation solution method. Our numerical experiments show that the method generates a very tight bound to the optimal schedule length, and thereby enables optimal or near-optimal solutions. The column generation method can be used to provide benchmarks when evaluating other scheduling algorithms. In particular, we use the bound obtained in the column generation method to evaluate a simple greedy algorithm that is suitable for distributed implementations.