1,721,115 research outputs found
A Framework for Routing and Congestion Control for Multicast Information Flows
Full text linkWe propose a new multipurpose multicast routing and schedulingalgorithm (MMRS). The routing policy load balances amongstvarious possible routes between the source and the destinations,relying its decisions on the message queue lengths at thesource node. The scheduling amongst various sessionssharing links is devised such that the flow of a sessiondepends on the congestion of the next hop links. MMRSis throughput optimal and computationally simple.The algorithm can be implemented in a distributed,asynchronous manner. It has several parameters which can besuitably modified to control the end-to-end delay, packet lossin a topology specific manner. These parameters can be adjustedto offer limited priorities to some desired sessions. MMRS is expectedto play a significant role in end-to-end congestion controlin the multicast scenario
Carrier Assignment Algorithms in Wireless Broadband Networks with Channel Adaptation
Full text linkWireless broadband access is an appealing solution to the projected trend towards reliable and easily deployable high-speed connections. In order to enhance system capacity and tolerate volatility of the wireless medium, sophisticated adaptation techniques are required. In this paper, we consider the problem of efficient resource allocation with adaptive modulation techniques in a multi-carrier wireless cellular system. We identify the inherent complexity of the problem and propose a heuristic algorithm for carrier frequency assignment to users, based on channel quality. The algorithm leads to an efficient allocation, in the sense that each user is assigned to a carrier and occupies the least number of channels (timeslots). Simulation results show that the algorithm leads to high link utilization and low blocking rate for a wide range of traffic loads and interference levels
A Unified Framework for Handover Prediction and Resource Allocation in Non-Geostationary Mobile Satellite Networks
Full text linkEfficient satellite resource management and allocation techniques aim at providing reliable real-time service, taking into consideration the scarcity of resources and the large number of handovers. This paper presents algorithms and modules for accurate satellite and beam handover prediction at the SBS. The call is assigned to that path which provides the highest preference factor. Several alternative solutions for path selection are proposed and evaluated in terms of time consumption and computational intensity
The Impact of Space Division Multiplexing on Resource Allocation: A Unified Approach
Full text linkRecent advances in the area of wireless communications have revealed the emerging need for efficient wireless access in personal, local and wide area networks. Space division multiple access (SDMA) with smart antennas at the base station is recognized as a promising means of increasing system capacity and supporting rate-demanding services. However, the existence of SDMA at the physical layer raises significant issues at higher layers. In this paper, we attempt to capture the impact of SDMA on channel allocation at the media access control (MAC) layer. This impact obtains different forms in TDMA, CDMA and OFDMA access schemes, due to the different cochannel and inter-channel interference instances, as well as the different effect of corresponding channels (time slots, codes or subcarrier frequencies) on user channel characteristics. We follow a unified approach for these multiple access schemes and propose heuristic algorithms to allocate channels to users and adjust down-link beamforming vectors and transmission powers, with the objective to increase achievable system rate and provide QoS to users in the form of minimum rate guarantees. We consider the class of greedy algorithms, based on criteria such as minimum induced or received interference and minimum signal-to-interference ratio (SIR), as well as the class of SIR balancing algorithms. Our results indicate that this cross-layer approach yields significant performance benefits and that SIR balancing algorithms achieves the best performance
Fair Allocation of Discrete Bandwidth Layers in Multicast Networks
Full text linkWe study fairness when receivers in a multicast network can not subscribeto fractional layers. This case arises whenthe source hierarchically encodes its signal and the hierarchical structureis predetermined. Unlike the case of the fractional layer allocation,which has been studied extensively in a previous work, bandwidth canbe allocated in discrete chunks only. Fairness issues becomevastly different. Computation of lexicographically optimal rateallocation becomes NP-hard in this case, while lexicographicallyoptimal rate allocation is polynomial complexity computablewhen fractional layers can be allocated. Furthermore, maxmin fair rate vector may not exist in this case.We introducea new notion of fairness, maximal fairness.We propose a polynomialcomplexity algorithm for computation of maximally fair ratesallocated to various source-destination pairs. Even though, maximal fairnessis a weaker notion of fairness, itcoincides with lexicographic optimality and maxmin fairness, when maxmin fair rate allocation exists. So the algorithmfor computing maximally fair rate allocation computes maxmin fairrate allocation, when the latter exists
Distributed Algorithms for Computation of Fair Rates in Multirate Multicast Trees
Full text linkWe study fairness in arbitrary networks with multicast capabilities.Multicast traffic in internet and ATM provides a motivationfor studying these networks. A study of fairness in multicastnetworks poses several interesting problems e.g., the issueof {it intra-session} fairness in addition to thatof {it inter-session} fairness in unicastnetworks. We develop a mathematical frameworkto model the fair allocation of bandwidth in multicast networkswith minimum and maximum rate constraints. We presentdistributed algorithms for computation of maxmin fair ratesallocated to various source-destination pairs
Channel State-Adaptive Techniques for Throughput Enhancement in Wireless Broadband Networks
Full text linkWireless broadband access is becoming increasingly popular in the telecommunications market due to the projected demand for flexible and easily deployable high-speed connections. In order to adhere to the volatility of the wireless medium, the adoption of sophisticated adaptation techniques is required. In this paper, we investigate the problem of enhancing channel throughput by performing resource assignment and reuse with adaptation of physical layer parameters. We propose an algorithm to allocate channels to users with different rate requirements, while appropriately adjusting the modulation level and transmission power, based on instantaneous channel quality. Our algorithm constructs the cochannel set of users in a sequential manner, by utilizing a criterion which is based on the induced and received amounts of interference for a user and the contribution in throughput increase. Although illustrated in the context of TDMA/TDD, the proposed technique can be applied in systems which support different multiple access and signaling schemes with orthogonal channels (e.g. OFDMA, CDMA). Our results indicate a considerable increase in throughput per utilized channel under such adaptive techniques
Performance issues of Bluetooth scatternets and other asynchronous TDMA ad hoc networks
Full text linkIn this paper we address a practical performance issue arising inwireless ad hoc networks using time division multiple access(TDMA). This issue relates to the degradation of the networkability to allocate bandwidth when the usual assumption ofsystem-wide slot synchronicity does not hold.The problem is investigated for the case of Bluetooth, a newpromising TDMA wireless technology that enables the formation ofad hoc networks called scatternets. A scatternet does not supporta global slot synchronization mechanism. Instead, nodes aregrouped in multiple channels called piconets and each piconet usesa different time slot reference provided by a node designated asmaster. Traffic forwarding between piconets is performed in a timedivision fashion by bridge nodes that are aware of the timereferences of the piconets they participate in. Due to theinherent lack of global synchronicity, slots are wasted whenbridges switch piconet time references. This translates to abandwidth loss compared to an ideally synchronized scatternet.While the existence of this asynchronicity overhead has beenreported in previous work, there has been no effort to minimize itor even evaluate its possible extent. Nevertheless, these issuesare very important for the deployment of practical TDMA-based adhoc networks.We consider a scatternet that allocates bandwidth to its linksusing an asynchronous periodic conflict-free TDMA schedule. Inthis setting the asynchronicity overhead is manifested as anincrease in the minimum period required to realize a demandallocation when compared to a perfectly synchronized system.We first derive a general upper bound on the overhead of anyscatternet and demand allocation. Then we consider the problem ofminimizing the overhead given a scatternet configuration anddemand allocation on its links. We cast this as a combinatorialoptimization problem and propose two algorithms for its solution.The first algorithm reaches the optimal solution using exhaustivesearch. However this approach can be computationally prohibitivefor large problem sizes. To this end, we introduce a secondpractical heuristic algorithm of polynomial complexity. Usingsimulations, the heuristic is shown to perform very well forproblem sizes where the optimal can be computed. For large problemsizes we use the heuristic to investigate the effect of thevarious system parameters on the generated overhead and evaluateits performance with respect to the derived general upper bound
Adaptive Channel Allocation for OFDM-Based Smart Antenna Systems with Limited Transceiver Resources
Full text linkSmart antennas constitute perhaps the most promising means of increasing capacity in wireless systems by allowing intra-cell channel reuse by several users. The employment of smart antennas at the physical layer raises significant issues in medium access control (MAC) layer. In this paper, we study the impact of smart antennas on MAC layer channel allocation in the presence of limited transceiver resources, where a transceiver is a communication unit that is used to set up a distinct beam. The problem is addressed in the context of Orthogonal Frequency Division Multiplexing (OFDM), which is the predominantly proposed signaling scheme for wireless broadband access. Since a beam can only serve users in different subcarriers, the problems of subcarrier and transceiver assignment are coupled. We propose heuristic algorithms to allocate channels to users, adjust beamforming vectors and assign users and channels in beams, with the objective to increase system throughput and provide QoS to users in the form of minimum rate guarantees. Our criteria for resource assignment and beam formation are based on spatial separability properties of users, beam vector cross-correlations and induced interference to the system. This unified cross-layer approach is shown to yield significant throughput benefits
Designing Broadcast Schedules for Information Dissemination through Broadcasting
Full text linkBroadcast data delivery is encountered in many applications where there is a need to disseminate information to a large user community in a wireless asymmetric communication environment. In this paper, we consider the problem of scheduling the data broadcast such that the access latency experienced by the users is low. In a push-based system, where the users cannot place requests directly to the server and the broadcast schedule should be determined based solely on the access probabilities, we formulate a deterministic dynamic optimization problem, the solution of which provides the optimal broadcast schedule. Properties of the optimal solution are obtained and then we propose a suboptimal dynamic policy which achieves mean access latency close to the lower bound. The policy has low complexity, it is adaptive to changing access statistics, and is easily generalizable to multiple broadcast channels. In a pull-based system where the users may place requests about information items directly to the server, the scheduling can be based on the number of pending requests for each item. Suboptimal policies with good performance are obtained in this case as well. Finally, it is demonstrated by a numerical study that as the request generation rate increases, the achievable performance of the pull- and push- based systems becomes almost identical
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