Time Slot Assignment Problem Research Articles

Multi-objective faculty course timeslot assignment problem for tutorial and laboratory courses

Multi-objective faculty course timeslot assignment problem for tutorial and laboratory courses

Research on Resource Allocation Algorithm for Satellite Uplink to Provide Differentiated QoS Support

Broadband satellite systems are built to serve different user groups ranging from enterprise and military users to common personal users, with various kinds of services calling for dissimilar quality of service (QoS). Obviously, the satellite systems are expected to distinguish the specific type of an incoming service request as well as the importance of its owner in order to perform an efficient assignment of valuable resources. In this article, the uplink resource management challenge in a multifrequency-time-division multiple access satellite system is addressed where provisioning the discriminated QoS is of vital importance. Having taken both user priority and service type into account, a differentiated QoS support principle conforming to the digital video broadcast - second generation DVB interactive satellite system (DVB-RCS2) standard is put forward, based on which the uplink timeslot assignment problem is formulated.The NP-hardness of the problem is proved, and a differentiated QoS resource allocation scheme is designed, decoupling the problem into the coarse-level of resource allocation and fine-level of timeslot assignment. The former stage involves the constant rate assignment, bandwidth adjustment, QoS degradation and user scheduling, among which the subproblem of user scheduling is an integer nonlinear program. To tackle the issue, the problem is first innovatively converted to an integer linear program, and is then modeled as the multiple-choice multiple knapsack (MCMK) problem. Furthermore, an MCMK algorithm is presented to give the optimal solution to the user scheduling problem, after which the timeslot assignment is investigated in the second phase to generate the terminal burst time plan table for return channel satellite terminals.

Multi-Objective Faculty Course Timeslot Assignment Problem for Tutorial and Laboratory Courses

Multi-Objective Faculty Course Timeslot Assignment Problem for Tutorial and Laboratory Courses

Polynomial Time Algorithm for Satellite Communications Scheduling Problem with Capacity Constrainted Transponder

This paper deals with the capacity constrained time slot assignment problem(CTSAP) that a satellite switches to traffic between m × n ground stations using on-board k ≤ min{m,n} , k-transponders switching modes in SS/TDMA time-division technology. There was no polynomial time algorithm to solve the optimal solution thus this problem classified by NP-hard. This paper suggests a heuristic algorithm with O(mn) time complexity to solve the optimal solution for this problem. Firstly, the proposed algorithm selects maximum packet lengths of (mn/c) combination and transmits the cut of minimum packet length in each switching mode(MSMC). In the case of last switching mode with inefficient transmission, we applies a compensation strategy to obtain the minimum number of switching modes and the minimum makespan. The proposed algorithm finds optimal solution in polynomial time for all of the experimental data.

Polynomial Time Algorithm for Multi-Beam SS/TDMA Satellite Communications Scheduling Problem with Frequency-Hopping Ground Stations

The time slot assignment problem (TSAP) or Satellite Communications scheduling problem (SCSP) for a satellite performs <TEX>$n{\times}n$</TEX> ground station data traffic switching has been known NP-hard problem. This paper suggests <TEX>$O(n^2)$</TEX> time complexity algorithm for TSAP of a satellite that performs <TEX>$n^2{\times}n^2$</TEX> ground station data traffic switching. This problem is more difficult than <TEX>$n{\times}n$</TEX> TSAP as NP-hard problem. Firstly, we compute the average traffic for n-transponder's basic coverage zone and applies ground station exchange method that swap the ground stations until all of the transponders have a average value as possible. Nextly, we transform the D matrix to <TEX>$D_{LB}$</TEX> traffic matrix that sum of rows and columns all of transponders have LB. Finally, we select the maximum traffic of row and column in <TEX>$D_{LB}$</TEX>, then decide the duration of kth switch mode to minimum traffic from selected values. The proposed algorithm can be get the optimal solution for experimental data.

A Joint Routing and Time-Slot Assignment Algorithm for Multi-Hop Cognitive Radio Networks with Primary-User Protection

Cognitive radio has recently emerged as a promising technology to improve the utilization efficiency of the radio spectrum. In cognitive radio networks, secondary users (SUs) must avoid causing any harmful interference to primary users (PUs) and transparently utilize the licensed spectrum bands. In this paper, we study the PUprotection issue in multi-hop cognitive radio networks. In such networks, secondary users carefully select paths and time slots to reduce the interference to PUs. We formulate the routing and time-slot assignment problem into a mixed integer linear programming (MILP). To solve the MILP which is NP-Hard in general, we propose an algorithm named RSAA (Routing and Slot Assignment Algorithm). By relaxing the integral constraints of the MILP, RSAA first solves the max flow from the source to the destination. Based on the max flow, RSAA constructs a new network topology. On the new topology, RSAA uses branch and bound method to get the near optimal assignment of time slots and paths. The theoretical analyses show that the complexity of our proposed algorithm is O(N^4). Also, simulation results demonstrate that our proposed algorithm can obtain near-optimal throughputs for SUs.

Study on the problem of routing, wavelength, and time-slot assignment towards optical time-slot switching technology

Conventional optical burst switching (OBS) is incapable of providing connection-oriented service, and burst loss is more likely to occur with increasing of traffic load due to its inherent architecture where the burst size is variable. In this paper, we propose and evaluate the optical time-slot switching technology, in which the fixed-size time-slot is adopted as the basic switching granularity, and switching is done in the time domain, rather than the wavelength domain. Also, we prove that time-slot switching has an equivalent function to eliminate data conflict relative to wavelength converter. Subsequently, the routing, wavelength, and time-slot assignment problem is studied in this paper. An adaptive weight function is introduced to the routing and wavelength selection algorithm, then several useful approaches, such as the train approach, wagon approach and p-distribution approach, are presented for time-slot assignment and scheduling. The results show that our scheme can perform better than conventional OBS in the aspect of blocking performance, quality of service, and class of service.

Study on Dynamic Routing, Wavelength and Timeslot Assignment Algorithm in WDM-TDM Optical Networks

In order to improve the wavelength utilization in WDM networks, multiple traffic connections can be allowed to share the capacity of a wavelength via TDM technology. The resultant network is a WDM-TDM optical network, where the Routing, Wavelength and Timeslot Assignment (RWTA) problem is the key for setting up traffic connections. In this paper, the dynamic RWTA problem is studied, a Most-Used Based RWTA algorithm (MUB) and an Enhanced MUB algorithm (EMUB) are proposed, and their performances are evaluated through computer simulation. The results show that the EMUB algorithm outperforms the MUB algorithm, and improves the resource utilization of WDM-TDM optical network.

A Real-Time Algorithm for Timeslot Assignment in ISM System with DVB-RCS

This paper considers a timeslot assignment problem in an interactive satellite multimedia (ISM) system with digital video broadcast-return channel via satellite (DVB-RCS). The timeslot assignment problem is formulated as a binary integer programming to maximize the overall weighted throughput and is shown to be NP-hard. Thus, three real-time heuristic algorithms including ratio-based, packet-size (PS)-based, and transmission gain (TG)-based are derived, and some computational experiments are made. Considering the results, the ratio-based heuristic algorithm is demonstrated to be the most effective and efficient. We propose adapting the ratio-based heuristic algorithm to the timeslot assignment problem to greatly improve the ISM system utilization.

A multiobjective faculty–course–time slot assignment problem with preferences

A faculty–course–time slot assignment problem is studied. The multiobjective 0-1 linear programming model considering both the administration’s and instructors’ preferences is developed and a demonstrative example is included. Both modeling and solving such problems are difficult tasks due to the size, the varied nature, and conflicting objectives of the problems. The difficulty increases because the individuals involved in the problem may have different preferences related to the instructors, courses, and time slots. The Analytic Hierarchy Process (AHP) and Analytic Network Process (ANP) are used to weigh different and conflicting objectives. These weights are used in different scalarization approaches. The scalarized problems are solved using a standard optimization package, and solutions corresponding to the AHP and ANP weights are compared.

Routing and Time-Slot Assignment in Optical TDM Networks

Optical time-division multiplexing (O-TDM) networks can provide a finer bandwidth granularity than wavelength-division multiplexing networks, and will play an important role in future all-optical networks. Since optical buffers are expensive, a small buffer size will be the characteristic of O-TDM systems. This paper analyzes the problem of routing and time-slot assignment in O-TDM networks. The results lead to the proposal of a Dijkstra-like shortest-path routing scheme that intends to maximize the performance of an optical network with a small number of optical buffers. Performance evaluation of the proposed scheme is also presented.

A Real-Time Algorithm for Timeslot Assignment in Multirate Return Channels of Interactive Satellite Multimedia Networks

Since the digital video broadcast-return channel via satellite (DVB-RCS) standard was released in 2000, developing an interactive satellite multimedia (ISM) network has become a hot issue. In order to provide high-speed multimedia services using a DVB-RCS system, it is important to efficiently and dynamically assign the timeslots to a number of terminals according to their various demands. Also, it is imperative to improve the degradation of link quality due to rain-fade attenuation in Ka-band satellite communications. As a result, multirate superframe structures should be implemented for a relatively low data rate at the cost of stable connection to terminals in rain-fade regions and a relatively high data rate to terminals in clear-sky regions. Timeslot scheduling in this environment is studied in this paper. We mathematically formulate the timeslot assignment problem as a nonlinear integer programming problem and develop an efficient real-time solution algorithm. Extensive simulation results show that our algorithm successfully finds a feasible solution with optimality gap less than 0.05% within about 5 ms at Pentium III PC. We believe that our algorithm can be utilized as a guideline in developing real-time timeslot assignment algorithms for ISM networks.

Bandwidth guaranteed call admission in TDMA/CDMA ad hoc wireless networks

This paper first studied the timeslot assignment problem in time division multiple access/code division multiple access (TDMA/CDMA) wireless ad hoc networks. Given a path P, we prove that a timeslot assignment providing one unit of bandwidth on P can be found in O(∣ P∣) time if such an assignment exists. The results have been extended to the case that P can provide two units of bandwidth. Based on the timeslot assignment for the special cases, an efficient slot assignment algorithm with O(∣P∣ 2 k) is proposed for general cases, where k is the number of slots in a TDMA frame. Then, the timeslot assignment algorithm is integrated into a quality of service (QoS) call admission scheme for QoS call requests. Extensive simulations are conducted and the results have demonstrated the superior performance of our method.

Throughput-maximizing timeslot scheduling for interactive satellite multiclass services

We develop an efficient method for optimal timeslot scheduling in an interactive satellite multimedia network. We formulate the timeslot assignment problem as a binary integer programming (BIP) problem, where the throughput is maximized, and decompose this BIP problem into two sub-problems. With this decomposition, we promote the computational efficiency in finding the optimal solution of the original BIP problem.

An integer programming approach to the time slot assignment problem in SS/TDMA systems with intersatellite links

We consider the time slot assignment problem (TSAP) in a cluster of satellite-switched time-division multiple-access (SS/TDMA) satellite system with intersatellite links (ISL). The problem is known to be NP-complete. In this paper, we consider TSAP as a graph coloring problem on a bipartite multigraph which is constructed from the traffic requirements. We give an integer programming (IP) model for TSAP and propose an algorithm based on the column generation technique. Computational results using randomly generated data are reported.

An adaptive time slot assignment algorithm for variable bandwidth switching systems

In this paper, we consider an optimal (i.e., minimum scheduling length) time slot assignment (for short, TSA) problem in variable bandwidth switching systems. In previous studies, the interdependencies between two consecutive switching configurations were neglected. However, it is highly probable that the amount of change between the switching configurations will be small. Therefore, it is unnecessary to schedule all traffic for each configuration if we preserve the previous switching configuration and update the switching configuration appropriately according to changes in traffic demand. The adaptive TSA algorithm proposed in this paper employs such an idea and reduces the computational burden of finding switching configurations. The computational complexity of the proposed algorithm and simulation results are reported. The results show that our algorithm is more efficient than existing optimal TSA algorithms. Scope and purpose In a satellite-switched time division multiple access (SS/TDMA) system, the satellite has a number of spot beam antennas covering geographically distributed zones and a solid-state RF switch to provide connections between the various uplink and downlink beams with different bandwidths depending on traffic rates of corresponding covering zones. A TDMA frame is divided into several time slots, and each slot has a switching configuration permitting a certain amount of traffic to be transmitted. The objective of the system is to ensure that all traffic in a given traffic matrix can be transmitted without conflict within the TDMA frame and to accomplish this with maximum transponder utilization.

Optimal scheduling in cdma packet radio networks

Scope and Purpose—A packet radio network provides flexible data communication services among a large number of geographically distributed and mobile users (nodes). Organizing the multiple channel access in packet radio networks is a well known and widely discussed area. The time division multiple access (TDMA) technology has been popularly used and has been studied extensively. On the other hand, the development of the code division multiple access (CDMA) technology raises a new question in this field. In CDMA packet radio networks the channels can be realized by different orthogonal codes and the simultaneous reception of several packets is possible through the use of orthogonal codes. The multiple reception capacity provides an opportunity for significantly increasing system throughput. In this paper, we suggest an efficient heuristic algorithm for scheduling in CDMA packet radio networks. We consider the time slot assignment problem in a CDMA packet radio network. Unlike the classical TDMA packet radio networks, a CDMA packet radio network can provide each node with a multiple reception capacity using orthogonal codes. This multiple reception capacity of each node presents a new challenge for channel access protocols. Also we consider non-uniform traffic demand over nodes which has become important due to the increase of subscribers and the introduction of personal communication system (PCS). We present an algorithm for a general system where the number of nodes and the reception capacity can be any positive integers and the traffic demand can be non-uniform. Computational tests show that our algorithm generates excellent solutions in most cases.

A new parallel algorithm for time-slot assignment in hierarchical switching systems

The time-slot assignment (TSA) problem in a TDM switching system is to find a conflict-free assignment of traffic-units to slots such that the frame-length is minimized. In this paper, we develop a new parallel algorithm for the TSA problem in hierarchical switching systems (HSS). To design the parallel algorithm, we first reduce the TSA problem to the problem of routing permutations in three-stage Clos networks; we also show how this reduction can be achieved in polylogarithmic time using a polynomial number of processors on the EREW PRAM model. Once this reduction is achieved, we use existing parallel algorithms in literature to route permutations in Clos networks. The overall time-complexity of our parallel algorithm is O(log/sup 3/ X) using O(MX) processors, where X=max{M, L}, M is the number of inputs of the HSS, and L is the length of the time-slot assignment. This result is a significant improvement upon the earlier parallel algorithms, which require O(M/sup 2/ log M log L) time and O(ML) processors to solve the TSA problem.

Polynomial time optimal algorithms for time slot assignment of variable bandwidth systems

Considers the optimal (i.e., minimum length) time slot assignment problem for variable bandwidth switching systems. Existing algorithms for this problem are known to be pseudo-polynomial. The practical question of finding a fast optimal algorithm, as well as the theoretical question of whether the above problem is NP-complete were left open. The authors present a technique to show polynomial time complexity of some time slot assignment algorithms. Such a technique applies to an algorithm proposed by Chalasani and Varma in 1991 (called the CV algorithm), as well as to a network flow based optimal algorithm, proposed in the present paper for the first time. The CV algorithm and the one proposed are slightly different. Thus, the authors give an answer to both the above questions, by establishing that the problem is in P, and by showing effective algorithms for it.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Efficient time-slot assignment algorithms for SS/TDMA systems with variable-bandwidth beams

In this paper, we present efficient sequential and parallel algorithms for computation of time-slot assignments in SS/TDMA (satellite-switched/time-division multiple-access) systems with variable-bandwidth beams. These algorithms are based on modeling the time-slot assignment (TSA) problem as a network-flow problem. Our sequential algorithm, in general, has a better time-complexity than a previous algorithm due to Gopal, et al. (1982) and generates fewer switching matrices. If M (N) is the number of uplink (downlink) beams, L is the length of any optimal TSA, and /spl alpha/ is the maximum bandwidth of an uplink or downlink beam, our sequential algorithm takes O((M+N)/sup 3/min(MN/spl alpha/,L)) time to compute an optimal TSA when the traffic-handling capacity of the satellite is of the same order as the total bandwidth of the links. Our parallel algorithm uses L/2 processors and has a time-complexity of O((M+N)/sup 3/logL) on a PRAM model of parallel computation. We then generalize this algorithm to P/spl les/L/2 processors and describe an efficient implementation of the algorithm on a hypercube multiprocessor with P processors. A massively-parallel version of the algorithm runs in O((M+N)/sup 2/log(M+N)logL) time on (M+N)L/2 processors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>