Satellite-switched Time-division Multiple Access Research Articles

A branch and price algorithm for the SS/TDMA problem with cardinality constraint

In this paper, we consider a square n×n traffic matrix D and a satellite having l≤n receiving and transmitting antennas. Transmissions are allowed by interconnecting pairs of receiving–transmitting antennas, through an on-board switch. We also assume that no preemption of the communications is allowed, and that changing the configuration of the switch requires a negligible time. We ask for a set of switch configurations that minimizes the total time occurring for transmitting the entire traffic matrix. In the literature, an exact method has been already proposed for the SS/TDMA optimization problem without cardinality constraint (i.e. for instances having l=n), but only heuristics have been proposed for the general case. In this paper, from a known MILP formulation we derive an extended formulation, and we use a column generation method to obtain its LP-relaxation. We address the derived pricing problem through a polynomial time algorithm based on solvers for the k-cardinality assignment problem. We insert this lower bound method in a two-phase branch and price algorithm in order to obtain the optimal solutions. To compare our new exact method with the one proposed in literature to solve the SS/TDMA optimization problem without cardinality constraint, we extend this older method to consider the cardinality constraint. The final computational experiments, comparing our new method with other already known methods, show the efficiency of our algorithms. Scope and purposeSatellites are the commonly used devices to wirelessly connect two distant earth points. Since satellites are very expansive devices, it is important to schedule the communications requests in an efficient manner. A satellite receives transmissions requests between pairs of earth stations, and these requests can be described by a traffic matrix. One method used in practice to satisfy these requests is called Satellite-Switched Time-Division-Multiple-Access (SS/TDMA) which requires to partition the traffic matrix entries in sets called frames and to transmit the elements of each different frame in a single time slot. Each frame must contain at most one communication involving the same earth station and the number of its nonzero entries must be at most equal to the number of satellite antennas. Since a satellite has to complete the transmission of a frame before starting the transmission of the next one, each frame is associated with a completion time equal to the maximum transmission time of its entries. A crucial decision, to minimize the total satellite used time, is how to partition the given traffic matrix. Our aim is to provide an effective exact algorithm for finding optimal solutions to the SS/TDMA problem and to compare it with other methods already known in the literature.

Performance evaluation of a satellite-switched variable-frame TDMA system

In satellite-switched time-division multiple access (SS/TDMA) systems, the demand assignment control is a suitable scheme for the bursty packets to enhance the capacity efficiency. In the system, by applying the demand assignment scheme, the minimum transmission time could be achieved by the efficient time slot assignment algorithm. According to a given traffic matrix, the minimum transmission time cannot exceed the fixed TDMA frame duration. The spare time may be left at the end of the TDMA frame as the growth space for the future needs. To increase the system efficiency, the spare time could be reduced. In this paper, a demand assignment protocol with a variable frame is proposed for the system. The Markov chain model is applied to analyze the system performance on throughput, balking probability and packet delay. Performance comparison with the previous presented protocol, the proposed protocol could show a simple control technique and the efficient performance results in the system. It is a suitable candidate to be employed in the satellite networks to provide communication between the satellite and earth stations.

Scheduling Satellite-Switched Time-Division Multiple Access With General Switching Modes

Based on network circulation formulation, the existence of feasible beam-to-beam switching modes for a satellite-switched time-division multiple access system is completely and transparently proved, where simultaneous transmissions on several carriers in each spot-beam are configured. Showing the linear independence of all but one augmented switching modes, a new bound of mn+2 is obtained on the number of switching modes, where m and n are the number of up-link and down-link beams, respectively. The time complexity for finding the whole sequence of switching modes and for finding the initial switching mode are improved to O(m/sup 2/n/sup 2/) and O(min(/spl radic/K,(m+n)/sup 2/3/)mn), respectively. Practical implementation considerations are discussed.

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.

A unified algorithmic framework for variable-rate TDM switching assignments

A unified algorithmic framework for time-optimal transmission scheduling is obtained for satellite-switched time-division multiple access systems with M uplink and N downlink beams. System capability may vary from the basic configuration of one carrier per beam to complex configurations of variable number of carriers for each beam and variable transmission rate for each beam. The computational complexity for time-optimal transmission scheduling remains strongly polynomial at O(M/sup 2/N/sup 2/) and the number of switching configurations is at most MN+1 for all system configurations considered.

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.

A note on scheduling problems arising in satellite communications

We present a brief overview of recent results on scheduling in Time Division Multiple Access (TDMA) satellite communications systems which augment those included in a recent survey. These results address problems arising in Satellite Switched TDMA (SS/TDMA) systems and SS/TDMA systems with intersatellite links, as well as generalizations and relatives of these problems. They also have application in other areas, for example, I/O in parallel computers.

SS/TDMA scheduling for satellite clusters

The authors present a novel approach to the optimal time-slot assignment problem for a general satellite-switched time-division multiple-access (SS/TDMA) satellite cluster with intersatellite links (ISLs) interconnection. The proposed allocation algorithm accounts for the following: systems with any number of satellites; each satellite covers an arbitrary number of zones; no onboard buffering at the satellites; and ISLs with arbitrary capacities. They present an analogy between the satellite cluster scheduling problem and the modified openshop scheduling problem. Using this analogy the authors introduce a heuristic algorithm and an optimal branch-and-bound algorithm. They investigate the performance of the proposed heuristic both by theoretical bounds and by comparing the simulation results produced by the heuristic with the optimal results. In all cases the heuristic algorithm results are within 10% of the optimum. >

Efficient algorithms for SS/TDMA scheduling

Efficient scheduling algorithms for the slot assignment problem in a satellite-switched time-division multiple-access (SS/TDMA) system are presented. This problem is translated into a modified open-shop scheduling problem, allowing the use of known optimal algorithms. Their complexity is expressed as a function of the following parameters: the number of nonzero entries in the demand matrix, the number of uplinks, and the number of downlinks. According to the values of these parameters, the algorithm with the lowest computational complexity can be adopted. Although the computational complexity of previously published algorithms is drastically reduced, simulation results show that the results are close to previously presented solutions in terms of the assignment duration and the number of switching matrices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Burst scheduling algorithms for SS/TDMA systems

Efficient algorithms that generate a detailed operation plan for satellite-switched time-division multiple access (SS/TDMA) systems are proposed. A burst time plan generation problem is analyzed and two algorithms for burst scheduling are presented. The first method is an algorithm based upon a bin pack problem. The other algorithm schedules new bursts while reassigning already scheduled bursts by a single machine scheduling model. These algorithms are shown to be applicable to practical systems operating with transponder hopping and multidestination bursts. Simulation results for a number of example problems are presented. >

A Polynomial Time Optimal Algorithm for Satellite-Switched Time-Division Multiple Access Satellite Communications with General Switching Modes

The Satellite-Switched Time-Division Multiple Access (SS /TDMA) is a technique effectively used in wideband communication satellites. A very important problem for SS/TDMA systems is the proper communications scheduling over the satellite equipment. This problem is equivalent to decomposing a given traffic matrix T into a positive linear combination of $( 0,1 )$-matrices satisfying additional technology-dependant constraints. The sum of the multiplying constants represents the time taken by the satellite to handle the communications and must be minimum in order to achieve an efficient use of the equipment. A polynomial time optimal algorithm for the SS/TDMA scheduling problem for systems with variable bandwidth beams and restricted multiplexing and demultiplexing is presented. As a corollary of the presented results, another generalization of the classical Birkhoff-von Neumann Theorem is established.

Approximate performance analysis and simulation study for variable-channel-per-burst SS-TDMA

An analysis is presented of the traffic performance of a variable-channel-per-burst (VCPB) satellite-switched time-division multiple access (SS-TDMA) that dynamically reconfigures traffic bursts. An SS-TDMA system with an onboard baseband switch is used as the VCPB application system. Bursts are assigned to each earth station one-by-one. Idle channels of other bursts are transferred to a burst having an insufficient number of idle channels by reconfiguration on a call-by-call basis. The VCPB is suited to SS-TDMA systems with relatively few earth stations. VCPB traffic performance depends on the reconfiguration strategy. The effects on traffic performance caused by reallotting idle channels to all bursts in every reconfiguration are described. An approximate formula for the reconfiguration probability from the loss probability of fixed-channel-per-burst TDMA weighted by the binomial distribution for the number of channels in each burst is derived.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Maximum zeros scheduling for satellite switch TDMA

A scheduling technique suitable for pre-assignment in satellite switched time division multiple access (SS-TDMA) systems is presented. As many uninterrupted bursts as are feasible are transmitted per configuration of the switch matrix. For small switch matrices (up to 6 × 6) this technique usually requires fewer reconfigurations than previous methods.

SS/TDMA Satellite Communications withk-Permutation Switching Modes

The Satellite-Switched Time-Division Multiple Access (SS/TDMA) scheme has been one of the most effective techniques designed to allocate the communication bandwidth provided by communication satellites. The scheduling problem for SS/TDMA corresponds to finding a positive linear combination of a predefined set of (0,1)-matrices which covers a given traffic matrix ${\bf T}$ such that the sum of the multiplying constants used in the linear combination is minimum. In this paper, an algorithm is given to solve the optimization problem using a result which is a generalization of a theorem by Birkhoff and von Neumann. The case of k-permutation matrices is first addressed. The result is then further extended to more general sets of (0, 1)-matrices.

Real‐time configurable SS/TDMA equipment for second generation french telecommunications satellite project

AbstractThis paper describes new on‐board equipment built around a microprocessor and controlled by earth through a specialized link. It drives in real‐time a 4 × 4 microwave switch matrix (MSM) for operation in satellite‐switched time division multiple access (SS/TDMA). The system is designed to evaluate SS/TDMA performances when (i) frame and multiframe durations are changed, (ii) the switch states sequence which controls the MSM is updated in real‐time. Another specific feature of this versatile equipment is the possibility to modify upon earth request the program run by the microprocessor to be able to carry out further experiments.

Integration and testing of an SS-TDMA 120 Mbit/s regenerative repeater for advanced communications satellites at K-band

The paper deals with a test campaign performed on a regenerative repeater with an onboard baseband switching matrix (BBSM), able to set up a satellite-switched, time-division multiple-access (SS-TDMA) system. We first address the optimisation of the transmission channel (filters, TWTA back-off etc. ) on the basis of BER measurements, and then examine some functional tests including a TDMA terminal as a traffic terminal simulator.

A Wide-Band Satellite Microwave Switch Matrix for SS/TDMA Communications

A lightweight, broad-band, 8 × 8 crossbar microwave switch matrix (MSM) has been developed for satellite-switched timedivision multiple-access (SS/TDMA) operation anywhere in the 6 GHz up-link and/or 4 GHz down-link bands. The nearly transparent performance characteristics in the 3.5-6.5 GHz band, for any of the highly flexible interconnect possibilities, have been facilitated by the design of a low-power-consuming resistively matched PIN diode switch. Broad-band push-pull connectors are used to simplify assembly and disassembly of this modular three-dimensional matrix. The switch control electronics (SCE) circuits have been implemented as custom-designed LSI chips for integration within the MSM input distribution networks. Design considerations and performance characteristics of the satellite switch matrix are presented.

SS/TDMA Time Slot Assignment with Restricted Switching Modes

The time-slot assignment problem for a satellite-switched time-division multiple access system where only a restricted set of all possible switching modes is to be used is studied. An efficient algorithm for finding an optimal assignment is proposed. Also, methods for selecting restricted sets of switching modes are presented.

Issues in Terrestrial/Satellite Network Synchronization

This paper examines the key issues involved in choosing synchronization techniques applicable to both terrestrial and satellite switching networks. The terrestrial networks considered involve circuit switching, message switching, packet switching, and other integrated voice/data nodal configurations. The satellite networks considered involve time-division multiple access (TDMA) systems and their associated synchronization problems. Peculiar problems associated with satelliteswitched TDMA (SS/TDMA) network synchronization are also addressed. Finally, the issues involved in synchronizing integrated satellite/terrestrial networks are addressed. Emphasis will be placed on assessing the state of the art of current terrestial/satellite synchronization technology and projecting future trends.

Analysis of a switch matrix for an SS/TDMA system

Time slot scheduling problem for a satellite switched/time-division multiple access (SS/TDMA) system is discussed and an algorithm called Greedy Algorithm is presented. This algorithm guarantees a most efficient utilization of a frame period with n2- n (n is the number of beams) number of switchings at most. Another problem discussed in this paper is the choice of the type of microwave switch matrix to be put on board the satellite. A switch-matrix structure called rearrangeable multistage matrix is shown to have high reliability and low-insertion-loss characteristics. Also brief discussions are made on the experimental results of an engineering model SS/TDMA system.