32 0890-8044/08/$25.00 © 2008 IEEE n a wireless mesh network (WMN) [1] end users are provided with wireless broadband connectivity by means of a predefined system hierarchy. The end terminals, also referred to as mesh clients (MCs), are connected to special nodes, called mesh routers (MRs). These nodes do not generate traffic, since they are simply meant to relay the packets of their MCs. Additionally, some MRs, called mesh access points (MAPs), can be provided with cabled connection, and can therefore act as gateways toward the Internet. A MAP is also wirelessly interconnected to every other MR in a multihop fashion. In contrast, an MC can interact only with the MR to which it is connected. MRs form what is usually referred to as the backbone of the WMN, which can physically cover a large region using wireless multihop communication.A possible realization of a WMN is depicted in Fig. 1. This structure offers a good cost/benefit balance, since it almost entirely avoids cable setup. For this reason, it is deemed applicable in rural areas as well as dense residential or business areas, where the deployment of wireline networks may be too expensive or difficult because of physical obstacles.The first hop from any MC to its related MR is often assumed to employ widespread cost-effective radio technologies (e.g., IEEE 802.11 [2]). The multihop communication among MRs is an open issue and involves several challenges related to different layers of the protocol stack. On one hand, the creation of low-interference high-rate paths to the MAPs is key to achieve good rates at each MR. On the other hand, the link layer needs to schedule packets over multiple links in order to achieve good transmission parallelism and possibly forward more data toward the MAPs at the same time. Finding the optimal path toward an MAP and scheduling links so as to maximize the transmission parallelism are traditionally performed by the routing algorithm running at the network layer and by the medium access control (MAC) protocol at the link layer, respectively. However, in a multihop wireless network, the routing algorithm needs to deal with link scheduling. If predefined routes (e.g., based on a shortest path criterion) are used, any scheduling algorithm will be forced to activate only the links belonging to that route. The combined result may be suboptimal in the sense that not all available network resources are utilized. In [3] the authors addressed the question of combining optimal link scheduling with suboptimal routing and vice versa, and pointed out that these tasks affect each other, and their optimality is strongly coupled. This is mainly due to the broadcast nature of the wireless medium, which combines the advantage of allowing each MR to communicate with multiple MRs through a single network interface with the disadvantage that simultaneous transmissions from different MRs may interfere with each other. Therefore, the main conclusion of [3] is that interference awareness available at the link layer must be exploited at the routing ...
IEEE 802.16 mesh does not include support to traffic flows with strict Quality of Service requirements. In this paper, we propose an End-to-end Bandwidth Reservation Protocol (EBRP) in the backhaul of a Wireless Mesh Network using IEEE 802.16 mesh. The distinctive feature of EBRP is that it is carried out at the Medium Access Control (MAC) layer. Therefore, EBRP not only makes the resource reservation process extremely rapid, it also allows the available resources to be allocated efficiently by exploiting technology specific iinformation available at the MAC. We present EBRP as part of a framework which also includes the support for performing distributed Call Admission Control (CAC). Preliminary simulations results obtained with VoIP traffic and nodes arranged in a grid topology are presented to show the effectiveness of EBRP, with ideal CAC computation
IEEE 802.16 is a recent standard for Broadband Wireless Access networks, which includes a mesh mode operation for distributed channel access of peering nodes. In accordance with the IEEE 802.16 MAC protocol, time is partitioned into frames of fixed duration, each one divided into two sub-frames, for control and data transmission, respectively. Slots in the control sub-frame are used by nodes to negotiate the schedule of transmissions in data subframes, and are accessed by means of a collision-free distributed procedure, namely the mesh election procedure. In this paper, we analyze the performance of the mesh election procedure by means of extensive simulations, and identify the system configuration parameters that have the most impact on the performance of control message transmission. The analysis is carried out under the assumption that the wireless link is error-free.
IEEE 802.16 is a recent IEEE standard for broadband wireless access networks. In IEEE 802.16 networks, the Medium Access Control ( MAC) protocol is centralized and explicitly supports quality of service ( QoS). That is to say, access to the medium by a number of Subscriber Stations ( SSs) is centrally controlled by one Base Station ( BS), which is responsible for allocating bandwidth to several MAC connections in order to provide them with the negotiated QoS guarantees. However, although the network can be operated in Frequency Division Duplex ( FDD) mode ( that is, transmissions from the BS ( downlink) and SSs ( uplink) occur on separate frequency channels), the standard supports SSs with half- duplex capabilities. This means that they are equipped with a single radio transceiver which can be used either to transmit in the uplink direction or to receive in the downlink direction. This may severely hamper the capacity to support QoS. Therefore, in order to allocate bandwidth, an IEEE 802.16 BS has to solve two related issues: 1) how it can schedule bandwidth grants to SSs in order to meet the QoS requirements of their connections and 2) how it can coordinate the uplink and downlink scheduled grants so as to support half- duplex capabilities. In this paper, we derive sufficient conditions for a set of scheduled grants to be allocated so that the transmission of each half- duplex SS does not overlap with its reception. Based on this, we propose a grant allocation algorithm, namely, the Half- Duplex Allocation ( HDA) algorithm, which always produces a feasible grant allocation provided that the sufficient conditions are met. HDA has a computation complexity of O(n), where n is the number of grants to be allocated. Finally, we show that the definition of HDA allows us to address the two issues mentioned above by following a pipeline approach. This is when scheduling and allocation are implemented by separate and independently running algorithms, which are just loosely coupled with each other. We show via extensive simulations that the performance of SSs with half- duplex capabilities, in terms of the delay of real- time and non- real- time interactive traffic, using HDA almost perfectly matches that of full- duplex SSs, whereas an alternative approach, based on the static partitioning of half- duplex SSs into separate groups, which are allocated alternately, is shown to degrade the performance
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