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Multi-hop relaying is an economically efficient architecture for coverage extension and throughput enhancement in future wireless networks. OFDM, on the other hand, is a spectrally efficient physical layer modulation technique for broadband transmission. As a natural consequence of combining OFDM with multi-hop relaying, the allocation of per-hop subcarrier power and perhop transmission time is crucial in optimizing the network performance. This paper is concerned with the end-to-end information outage in an OFDM based linear relay network. Our goal is to find an optimal power and time adaptation policy to minimize the outage probability under a long-term total power constraint. We solve the problem in two steps. First, for any given channel realization, we derive the minimum short-term power required to meet a target transmission rate. We show that it can be obtained through two nested bisection loops. To reduce computational complexity and signalling overhead, we also propose a sub-optimal algorithm. In the second step, we determine a power threshold to control the transmission on-off so that the long-term total power constraint is satisfied. Numerical examples are provided to illustrate the performance of the proposed power and time adaptation schemes with respect to other resource adaptation schemes. Index TermsOFDM, relay networks, outage probability, resource allocation, end-to-end rate.

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The IEEE standard 802.16x based broadband wireless Lots of multicast routing protocols are proposed for ad-hoc access is a promising technology to provide wireless broadband wireless networks. One category is called tree-based protocols connectivity. Besides Point to Multi-Point mode, a mechanism to (e.g. MAODV, ABAM, ADMR [3,4,5]) running on the similar create multi-hop network through Mesh mode is defined for the network topology as WiMax mesh network, in which there frequency spectrum band 2-11 GHz. The standard only defines unicast transmission under mesh mode, but does not specify exists only a single path for a source-receiver pair. Tree based multicast transmission scheme. This paper proposes a novel multicast protocols can be further divided into two types: multicast mechanism in WiMax mesh network by building a high source-tree-based and share-tree-based. In source-tree-based efficient multicast tree with utilization of scheduling messages multicast protocols, the tree is rooted at the source and each defined in the standard. An easy-to-implement tree construction session has its own multicast tree, whereas in shared-treealgorithm is presented based on the adjustment of the centralized based multicast protocols, a single tree is shared by all the routing tree. Simulation results show the proposed multicast sources within the multicast group. However, because of mechanism improves transmission efficiency and reduces group frequent topology changing in ad-hoc network, flooding latency over the traditional way to fulfill multicast by multiple message exchanging will be generated during the process of unicast transmissions.constructing and maintaining a multicast tree. Time durationIndex terms: WiMax, multicast, centralized scheduling,802.16to finish constructing may vary a lot under topology updating.Multicast routing protocol is independent of any specific I. Introduction unicast routing protocol to reduce the packet overhead and dependency[6], which is a common principle to design a IEEE 802.16 series standards based WiMax (Worldwide multicast routing protocol in ad-hoc networks. Interoperability for Microwave Access) networks provides In this paper, a multicast tree construction mechanism is multiple services for the broadband wireless access (BWA) proposed based on the unicast routing tree in WiMax mesh network. In addition to single-hop PMP (Point-to-Multipoint) network, therefore the feature of periodical updating and operation, specifications of Mesh mode were integrated into synchronization of routing tree will be inherited so that there the standard of IEEE 802. [1], which can be is no need to define new messages for multicast. At the same considered as a new approach to implement wireless mesh time, the broadcasting feature of omni-directional antenna is network (WIMN) [2]. The capability of self-organization in used to improve the transmission efficiency. Thus a global WMNs reduces the complexity of network deployment and unicast and partial broadcast are integrated into a unified maintenanc...

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We study the end-to-end resource allocation in an OFDM based multi-hop network consisting of a one-dimensional chain of nodes including a source, a destination, and multiple relays. The problem is to maximize the end-to-end average transmission rate under a long-term total power constraint by adapting the transmission power on each subcarrier over each hop and the transmission time used by each hop in every time frame. The solution to the problem is derived by decomposing it into two subproblems: short-term time and power allocation given an arbitrary total power constraint for each channel realization, and total power distribution over all channel realizations. We show that the optimal solution has the following features: the power allocation on subcarriers over each hop has the water-filling structure and a higher water level is given to the hop with relatively poor channel condition; meanwhile, the fraction of transmission time allocated to each hop is adjusted to keep the instantaneous rates over all hops equal. To tradeoff between performance, computational complexity and signalling overhead, three suboptimal resource allocation algorithms are also proposed. Numerical results are illustrated under different network settings and channel environments.

In this paper we consider the topology aggregation problem in hierarchical ASON networks. Usually, the requirement of scalability and security of the network is fulfilled by domain division. The relevant information exchanged among domains will be greatly increased for large scale networks. The topology aggregation aims at reducing the amount of link state information without losing accuracy for routing calculation. We propose to apply a bidirectional shuffle-net model to topology abstraction procedure, which can significantly reduce the size of link state information. A genetic algorithm is utilized to construct the optimal mapping relationship between shuffle-net and aggregated topology for accuracy purpose. Simulation shows that the proposed scheme has good performance compared with symmetric-star approach and heuristic shuffle-net algorithm.