A General Multibeam Satellite Switching Algorithm

In this paper we consider an SS/TDMA system withMuplink beams,Ndownlink beams, andKconnection points. We first assume that the downlink is α times faster than the uplink, and a simple time multiplexing scheme is employed. An optimal time slot assignment algorithm for anyM, N,alpha, andK,1 leq K leq min (M, alphaN), and for any traffic matrix is presented, where optimality means achieving the minimal possible total transmission time for the given traffic matrix. The number of switching matrices generated by the algorithm never exceedsMN + Kalpha + 1. Extensive simulation results on randomly generated matrices are carried out, showing that the average number of switching matrices generated is substantially lower than the upper bound. The case when the uplink is faster than the downlink is also considered.     

An Optimum Time Slot Assignment Algorithm for an SS/TDMA System with Variable Number of Transponders

In this paper we consider an SS/TDMA system withMuplink beams,Ndownlink beams, andK, 1 leq K leq min (M, N)transponders. An optimal time slot assignment algorithm for anyM, N, K,and any traffic matrix is presented, where optimality means achieving the minimal possible total duration for the given traffic matrix. The number of switching matrices generated by the algorithm is bounded above byN^{2} - N + 1forK = M = NandMN + K + 1otherwise. Extensive simulation results on randomly generated matrices are carried out, showing that the average number of switching matrices generated is substantially lower than the bounds.     

Simulation and analysis of software defined cognitive frequency hopping multi beam satellite system

Traditional multi-beam satellites cannot adapt to the changing traffic because of the fixed bandwidth and cannot adjust dynamically for the traffic load.In the future,the multi-beam broadband satellite system must have great flexibility and can be dynamically adjusted according to the change of the traffic flow.Beam hopping for multi-beam broadband satellite network system has been proposed to improve the traditional multi-beam broadband satellite network system performance,whose principle is to assign different beams to different time slots,rather than the allocation of bandwidth,so that in each time slot,the entire available bandwidth is allocated to each beam,and the time window is periodically applied to the beam selection system ,in the full band hopping mode,the band can be selected optimally in the duration of each beam to meet user transmission bandwidth and delay requirements.With the development of cognitive radio technology,cognitive beam hopping for multi-beam satellite system can further improve the efficiency of spectrum utilization,to meet the growing shortage of spectrum resources,to achieve large-capacity high-bandwidth broadband satellite network system,and to support the rising user service capacity and the transmission efficiency of user services under different load conditions.In addition,software definition technology is also used in satellite networks,which could achieve effective management of satellite resources to improve the utilization of satellite resources.In this paper,the principle of software-defined cognitive hopping multi-beam broadband satellite network system is discussed.The spectrum utilization efficiency and throughput are analyzed,which can be used as a reference for broadband satellite network system design.     

The input admittance of the rectangular cavity-backed slot antenna

The input admittance of the rectangular cavity-backed slot antenna is investigated. The slot is assumed narrow so that the voltage distribution in its aperture is sinusoidal. Equations which represent the input admittance of this slot, backed by a rectangular cavity in which a single propagating wave is assumed to exist, are given. Calculations based on these representations are compared to available measured data. As the depth of the cavity increased the resonant frequency decreased and the bandwidth became narrower. Input admittance curves as a function of electrical slot length are also presented for several size cavities.     

Slot allocation strategies for delay sensitive traffic support in asynchronous ad hoc wireless networks

Supporting real‐time traffic in ad hoc wireless networks is considered as a challenging problem. Existing bandwidth reservation mechanisms assume a TDMA environment where achieving time synchronisation is expensive in terms of resources. Heuristics that exist for slot allocation schemes assume a CDMA over TDMA model in order to alleviate the presence of hidden terminals. Slot allocation strategies in the presence of hidden terminals assume significance in a single channel system for supporting delay sensitive traffic. In this paper, we propose three heuristics for the slot allocation process in asynchronou single channel multihop wireless networks in the presence of hidden terminals. The heuristics we propose are the early fit reservation (EFR), minimum bandwidth‐based reservation (MBR) and position‐based hybrid reservation (PHR). The EFR heuristic assigns bandwidth link‐by‐link in the forward path. The MBR heuristic allocates bandwidth to the links in the increasing order of free conn‐slots. The PHR heuristic assigns bandwidth for every link proportional to its position in the path. Simulation studies show that EFR performs better in terms of delay characteristics. MBR provides better call blocking performance at the cost of high end‐to‐end delay. PHR provides a better delay performance compared to MBR and better call blocking performance comparedto EFR. Copyright © 2004 John Wiley & Sons, Ltd.     

Optimal Bandwidth Allocation in a Delay Channel

In this paper, we consider the problem of allocating bandwidth to two queues with arbitrary arrival processes, so as to minimize the total expected packet holding cost over a finite or infinite horizon. Bandwidth is in the form of time slots in a time-division multiple-access schedule. Allocation decisions are made based on one-step delayed queue backlog information. In addition, the allocation is done in batches, in that a queue can be assigned any number of slots not exceeding the total number in a batch. We show for a two queue system that if the holding cost as a function of the packet backlog in the system is nondecreasing, supermodular, and superconvex, then: 1) the value function at each slot will also satisfy these properties; 2) the optimal policy for assigning a single slot is of the threshold type; and 3) optimally allocating$M$slots at a time can be achieved by repeatedly using a policy that assigns each slot optimally given the previous allocations. Thus, the problem of finding the optimal allocation strategy for a batch of slots reduces to that of optimally allocating a single slot, which is conceptually much easier to obtain. These results are applied to the case of linear and equal holding costs, and we also present a special case where the above results extend to more than two queues.     

Rain granularity effects on bandwidth demand for faded DVB‐RCS systems

Broadband satellite communication networks, operating at Ka band and above, play a vital role in today's worldwide telecommunication infrastructure. The problem, however, is that rain can be the most dominant impairment factor for radio propagation above 10 GHz. This paper studies bandwidth and time slot allocation problem for rain faded DVB‐RCS satellite networks. We investigate how using finer rain granularity can improve bandwidth utilization in DVB‐RCS return links. The paper presents a mathematical model to calculate the bandwidth on demand. We formulate the radio resource allocation as an optimization problem and propose a novel algorithm for dynamic carrier bandwidth and time slots allocation, which works with constant bit rate type of traffic. We provide theoretical analysis for the time slot allocation problem and show that the proposed algorithm achieves optimal results. The algorithm is evaluated using a MATLAB simulation with historical rain data for the UK. Copyright © 2014 John Wiley & Sons, Ltd.     

Adaptive digital access protocol: a MAC protocol for multiservicebroadband access networks

The authors describe a protocol that can adapt to the changing demands of a mix of synchronous transfer mode (STM) and asynchronous transfer mode (ATM) applications and efficiently allocate bandwidth to a variety of bursty traffic sources. In the case of a hybrid fiber-coaxial (HFC) network, the protocol resides in customer premises equipment (CPE) and a common head-end/central-office (HE/CO) controller. A medium-access control (MAC) processor provides for dividing the time domain for a given digital bitstream into successive frames, each with multiple STM and ATM time slots. Within the STM region of a frame, variable-length time slots are allocated to calls (e.g., telephony, video telephony) requiring different amounts of bandwidth. In the upstream channels, a contention access signaling time slot is also provided in the STM region for call control and setup requests. Within the ATM region, fixed-length time slots accommodate one individual ATM cell. These ATM time slots may be reserved for a user for either the duration of a call or a burst of successive ATM cells, or shared via a contention process. At least one contention time slot is available for signaling messages related to ATM call control and setup requests. The MAC-layer protocol, its relation to circuit- and ATM-amenable applications, and its performance with respect to throughput, latency, and bandwidth efficiency for several service scenarios are examined     

A Hybrid Adaptive Wireless Channel Access Protocol for Multimedia Personal Communication Systems

This paper proposes a new medium access protocol (MAC) protocol for futurewireless multimedia personal communication systems, denoted hybrid andadaptive multiple access control (HAMAC) protocol. The HAMAC protocolintegrates fixed assignment TDMA protocol, reservation-based protocols, andcontention-based protocols into a single wireless network so as tosimultaneously and efficiently support various classes of traffic such asconstant-bit-rate (CBR), variable-bit-rate (VBR), and available-bit-rate (ABR)traffic. In particular, the HAMAC protocol uses a novel preservationslot technique to overcome the packet contention overhead in packetreservation multiple access (PRMA) like protocols, while keeping mostisochronous service features of TDMA protocols to serve voice and CBR trafficstreams. A preservation slot is a very short slot which is used torepresent a CBR connection when the traffic in the CBR connection is in asilent period in which there is no meaningful data to transmit. Due to thevery short length of the preservation slot, it only takes minimalportion of the bandwidth pre-allocated to the CBR connection, so that theremaining bandwidth can be freed for other connections to use. When the CBRsource becomes active again, the preservation slot is replaced bynormal data slots without any reservation operation, extra delay, orsignificant bandwidth loss. Consequently, the guaranteed service andsimplified signaling features of TDMA protocols, together with the adaptivebandwidth allocation features of PRMA-like protocols, are both realized in theHAMAC protocol. We have analyzed the performance of the HAMAC protocol usingextensive simulations. The results show that the HAMAC protocol can achievevery low loss rates for various multimedia traffic with stringent quality ofservice (QoS) requirements and outperforms state-of-the-art PRMA-likeprotocols. As a result, the HAMAC protocol appears to be a good candidate forfuture generation multimedia personal communication systems.     

Adaptive channel selection and slot length configuration in cognitive radio

This paper investigates the channel selection and slot time configuration in a cognitive radio network with a number of potential channels. Each channel alternates between ON state (i.e., the primary user is using the channel) and OFF state (i.e., the primary user does not use the channel), and the state evolution process is modeled as a continuous‐time Markov process. The traffic parameters (the transition rates) of the Markov process also evolve with time, modeled as a discrete‐time Markov process. A secondary user adopts a slotted structure with dynamic slot length. At each slot, the secondary user needs to determine which channel to sense and, if the channel is sensed idle, how long the slot length should be. Considering both the amount of data that the secondary user can transmit and the duration when the secondary user interferes with primary activities, a reward definition is given. Based on the reward definition, an adaptive channel selection and slot length configuration method is proposed, which includes a reward maximization procedure to maximize the achieved reward and an update procedure for the channel state belief vector and traffic parameter state belief vector. Numerical results are given to demonstrate the effectiveness and features of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.     

The transmission capacity of multibeam communication satellites

The transmission capacity which can be provided by a geosynchronous multiple-beam satellite employing frequency reuse is studied. Like all communication channels, satellite capacity is limited by available power, transmission bandwidth, and noise. In addition, factors peculiar to satellite links include cochannel interference among neighboring beams, channel nonlinearity, nonuniformly distributed traffic, and for satellites operating at frequencies above 10-GHz, rain attenuation. The effects of these factors upon the capacity of a satellite system are examined in detail. Results for a 12/14-GHz system with assumed satellite parameters compatible with a space shuttle launch and small 5 m earth station antennas show that a capacity of about 30 Gbit/s can be provided if the unavailability due to rain outage is no greater than 0.1 percent, and that about 10 Gbit/s can be provided for an unavailability no greater than 0.01 percent. Efficient utilization of the geosynchronous arc is also explored, and current trends in communication satellites are discussed.     

Comparison of time slot allocation strategies for CDMA/TDD systems

The traffic (load) asymmetry between uplink and downlink is a remarkable traffic characteristic in cellular mobile multimedia communications. The code division multiple access system with time division duplex mode (CDMA/TDD system), adopting unbalanced slot allocation between uplink and downlink, is a good solution for this traffic asymmetry. However, the level of traffic asymmetry may be significantly different from cell to cell. In this paper, we investigate a slot allocation strategy (DA strategy), by which each cell has its own slot allocation according to the level of traffic asymmetry. We compute the system capacity with DA strategy and find out the optimal slot allocation for the system. We also compare the maximum capacity to that with another strategy (SA strategy), by which all cells have the same slot allocation. As a result, this paper shows that the system with DA strategy outperforms the system with SA strategy in the aspect of capacity     

Distributed timeslot allocation with crossed slots in CDMA‐TDD systems

Code division multiple access system with time division duplex (CDMA‐TDD) is a promising solution to cope with traffic asymmetry of downlink (DL) and uplink (UL) in multimedia services. When a rate of asymmetry is different in each cell, CDMA‐TDD system may employ crossed slots, where a timeslot is used for different links in cells. However, it may suffer from base station (BS)‐to‐BS and mobile station (MS)‐to‐MS interference problem. Zone division scheme is an efficient way to tackle the crossed slot interference by dividing a cell into inner and outer zones and restricting communication in crossed slots only to inner zone. In this paper, we propose distributed crossed slot resource allocation with zone division in multi‐cell CDMA‐TDD system. Two conditions for crossed slot resource allocation are defined and the bound on the size of inner zone is analyzed mathematically based on the conditions. Relationship between the capacity of crossed slot and the size of inner zone is also analyzed. Then, numerical results of the mathematical analysis are presented; showing that the proposed crossed slot allocation is effective for traffic asymmetry problem. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectral Efficiency of Dynamic Time Division Duplex Fixed Wireless Cellular System for Asymmetric and Dynamic Multimedia Traffic

We analyze spectral efficiency of dynamic time division duplex in a fixed wireless cellular network. Conventionally, spectral efficiency has been analyzed for static and fully loaded systems. In this paper, we investigate how asymmetric and dynamic traffic affect the spectral efficiency of Time-Division-Duplex (TDD) systems. Recently, dynamic TDD (D-TDD) has gained much attention as an efficient duplex scheme for high-speed data communications, because adaptive switching ability enables the system to obtain statistical multiplexing gain by exploiting dynamic and asymmetric data traffic. However, it has been noted that a rather strong co-channel interference can be present due to adaptive switching in a cellular network that uses frequency reuse. Thus, benefits of dynamic TDD may not be justifiable unless a proper countermeasure is employed. To suppress the effect of strong co-channel interference, we employ time slot allocation (TSA) strategy along with sector antenna layouts, as proposed in our previous work Jeong and Kavehrad (IEEE and Transactions on communication, Vol. 50, no.10 pp. 1627–1636, 2002). We note that higher spectral efficiency is obtained in D-TDD systems by employing TSA strategy. We also evaluated spectral efficiency of D-TDD system employing adaptive modulation, assuming that traffic is delay tolerant. It is observed that five times higher spectral efficiency can be obtained by employing adaptive modulation. The effect of variance of ratio of offered load on uplink and downlink is also evaluated. Our computer simulation results show that spectral efficiency of D-TDD system with time slot allocation algorithm is more than that of static TDD (S-TDD) over a large range of traffic variation. In conclusion, D-TDD system can take advantage of statistical multiplexing gain of dynamic traffic by adaptively positioning the boundary to the varying traffic bandwidth in its two-way transmissions when TSA strategy is employed for suppression of strong co-channel interference.     

Mapping and Scheduling for Circuit‐Switched Network‐on‐Chip Architecture

Network‐on‐chip (NoC) architecture provides a high‐performance communication infrastructure for system‐on‐chip designs. Circuit‐switched networks guarantee transmission latency and throughput; hence, they are suitable for NoC architecture with real‐time traffic. In this paper, we propose an efficient integrated scheme which automatically maps application tasks onto NoC tiles, establishes communication circuits, and allocates a proper bandwidth for each circuit. Simulation results show that the average waiting times of packets in a switch in 6×6, 8×8, and 10×10 mesh NoC networks are 0.59, 0.62, and 0.61, respectively. The latency of circuits is significantly decreased. Furthermore, the buffer of a switch in NoC only needs to accommodate the data of one time slot. The cost of the switch in the circuit‐switched network can be reduced using our scheme. Our design provides an effective solution for a critical step in NoC design.     

A Variable Slot Length TDMA Protocol for Personal Communication Systems

We present a new TDMA-based scheme intended for carrying traffic withdiverse QoS requirements in mobile environments, e.g.,Personal Communication Systems (PCS).In contrast to mostother TDMA protocols for mobile applications, instead oftrying to fit the offered traffic to the slot size, our solution adaptsthe slot size to the offered traffic.This feature is combined with a dynamic and responsive bandwidth scheduler.As demonstrated by our performance studies, the proposedscheme is more flexible and incurs lower bandwidth overhead than otherTDMA-based solutions.     

A polynomial form for logarithms modulo a prime (Corresp.)

An explicit polynomial form for logarithm functions modulo a prime p is given; the coefficients have a surprisingly simple form. It follows that any polynomial that represents a logarithm modulophas at leastp - 2nonzero coefficients and is therefore highly inefficient to use as a computational method.     

The no slot wasting bandwidth balancing mechanism for dual busarchitectures

A bandwidth balancing (BWB) mechanism has been added to the distributed queueing algorithm of the distributed-queue dual bus (DQDB) network. BWB can provide the requested throughputs by lightly loaded stations and evenly distribute the remaining channel bandwidth among overloaded stations. However, its operation requires the wastage of channel slots. The authors introduce a new bandwidth balancing mechanism for DQDB. The operation of the new mechanism requires one additional bit in the access control field (ACF) of the slot but has the advantage of exhibiting a similar behavior with the current BWB mechanism of DQDB without wasting any channel slots. For this reason, it can converge faster to the steady state in which fair bandwidth allocation is achieved. The authors investigate the throughput and delay performance of the proposed mechanism under one traffic class and examine its capacity to support multiple priority classes of traffic. They also compare its performance with the corresponding performance of the BWB mechanism of DQDB     

Dynamic bandwidth recycle algorithm for OVSF–CDMA systems

This paper presents a dynamic bandwidth recycle algorithm in the downlink of a WCDMA system using orthogonal variable spreading factor codes (OVSF). It consists of a bandwidth recycle algorithm and a bandwidth reservation algorithm. The bandwidth recycle algorithm is used to recycle bandwidth from current serviced connections when the system does not have enough available bandwidth to support a bandwidth request. The bandwidth reservation algorithm is used to reduce transmission delay caused by suddenly increasing bandwidth requests. Four traffic classes, conversational, streaming, interactive, and background classes, defined by universal mobile telecommunication system (UMTS) are considered. Simulation results show that the bandwidth utilization and block rate are improved, the bandwidth guaranteed to conversational and streaming classes are protected, and the delay time of interactive and background classes are kept under an acceptable value even when the traffic load is heavy. Copyright © 2005 John Wiley & Sons, Ltd.     

Broadband circularly polarised hexagonal slot antenna excited by a tapered microstrip feeder

In this article, a broadband circularly polarised slot antenna fed by a single microstrip line is implemented. The proposed antenna is composed of an unequilateral hexagonal slot to implement circular polarisation and tapered microstrip feeding line to enhance the impedance bandwidth. A conducting reflector is also employed to enhance the antenna gain. The proposed antenna, 60 mm × 60 mm × 18.12 mm in size, was fabricated and tested. The measured??10 dB reflection bandwidth and 3 dB axial ratio bandwidth were 48.9% and 17%, respectively. The measured gain of the fabricated antenna ranged from 5.4 dBi to 6 dBi within an axial ratio bandwidth of 3 dB.