VSAT communications networks-an overview

The very-small-aperture-terminal (VSAT) fixed satellite communication network is a star network in which many dispersed micro terminals attempt to send data in a packet form through a random access/time-division multiple-access (RA/TDMA) satellite channel with transmission delay. The basic concept of the VSAT and its service potential are discussed. Two classes of traffic are addressed, namely business-oriented low-rate-data traffic and bulk data traffic of corporate networks. Satellite access, throughput, and delay are considered. The size of the network population that can be served in an RA/TDMA environment is calculated. User protocols are examined. A typical VSAT business scenario is described     

Performance analysis of integrated-services load-adaptive/TDMA satellite networks

A load-adaptive/TDMA multiple-access communications system which serves to interconnect broad-band multimedia packet streams is considered. In particular, the use of a satellite backbone communications link whose channels are dynamically assigned to network stations is investigated. Each station supports packetized voice and data message streams. Incoming streams to a station are statistically multiplexed by the station across the backbone channels currently allocated to this station. To enhance the multiplexing process, a variable bit-rate packet-voice encoding scheme is also employed. Stations periodically issue requests for backbone channel allocations, based upon their estimated loading status. We introduce two distinct multiple-access algorithms for allocating the shared backbone channels to the stations. We develop analytical methods for the analysis and design of such integrated multiplexing/multiple-access networks. Performance measures include voice and data packet delays and packet blocking probabilities. Voice stream performance is also characterized by the average number of bits per sample used by the voice encoding scheme. The effects of the propagation delay across the backbone link are especially demonstrated. Also illustrated are the performance improvements attained due to the use of the load-adaptive/TDMA scheme. Under the example of the ’all-voice’ traffic loading, an LA/TDMA scheme exhibits no obvious performance improvement over a fix-assigned scheme. However, as the burstiness of the traffic loading increases in the example of the ’data-voice’ traffic loading, a significant amount of improvement (36 per cent bandwidth savings) is realized by a LA/TDMA scheme.     

SBS TDMA-DA system with VAC and DAC

This paper describes many of the design considerations involved in developlng the demand assignment (DA) subsystem of the TDMA satellite communication system for Satellite Business Systems. Each earth station has a satellite communications controller (SCC) which requests capacity to meet current voice and data traffic demands. A central reference station frequently reallocates capacity based on the requests of all the earth stations in a network. To minimize the amount of satellite capacity required, the SCC has a circuit-switching capability for voice calls as well as for digital data calls. Furthermore, the SCC employs voice activity, compression (VAC) and data activity cornpression (DAC), In which the amount of capacity requested is based on measured average speech activity as well as the number of off-hook voice ports and the number of off-hook data ports. Data calls are queued on a first-come, first-served basis when capacity is not immediateiy available. The reference station distributes excess capacity according to a nonlinear table lookup procedure so that the voice call blocking probability is equalized across the network. The DA system makes much more efficient use of satellite transmission capacity than a design with fixed-capacity trunk routes.     

Packet CDMA versus dynamic TDMA for multiple access in anintegrated voice/data PCN

A comparative evaluation of dynamic time-division multiple access (TDMA) and spread-spectrum packet code-division multiple access (CDMA) approaches to multiple access in an integrated voice/data personal communications network (PCN) environment are presented. After briefly outlining a cellular packet-switching architecture for voice/data PCN systems, dynamic TDMA and packet CDMA protocols appropriate for such traffic scenarios are described. Simulation-based network models which have been developed for performance evaluation of these competing access techniques are then outlined. These models are exercised with example integrated voice/data traffic models to obtain comparative system performance measures such as channel utilization, voice blocking probability, and data delay. Operating points based on typical performance constraints such as voice blocking probability 0.01 (for TDMA), voice packet loss rate 10^-3 (for CDMA), and data delay 250 ms are obtained, and results are presented     

The RRA‐ISA multiple access protocol with and without simple priority schemes for real‐time and data traffic in wireless cellular systems

A multiple access protocol, based on a Reservation Random Access (RRA) scheme, is derived for a wireless cellular network carrying real-time and data traffic. Given a TDMA framed channel and a cellular structure, the aim of the protocol is that of maximizing the one-step throughput over an entire frame. This is achieved by deciding on the access rights at the cell base station, which then broadcasts this information at the beginning of the frame. The decision is made on the basis of binary channel feedback information (collision/no collision) over the previous frames, as well as of long term averages of packet generation rates at the mobile stations, assuming independence in the presence of packets at the latter. The resulting protocol has therefore been termed Independent Stations Algorithm (ISA), and the overall scheme RRA-ISA. As in other RRA protocols, time constrained (e.g., voice) traffic operates in a dynamic reservation mode, by contending for a slot in the frame with the first packet of a burst, and then keeping the eventually accessed slot for the duration of the burst; packets of the time constrained traffic unable to access a slot within a maximum delay are dropped from the input buffer. No such constraint is imposed on data traffic. Together with the “basic” version of the access algorithm, three other variants are presented, which exploit three simple different priority schemes in the RRA-ISA “basic” structure, in order to give a prominence to the voice service. The aim of these variants is to improve the performance in terms of the maximum number of stations acceptable in the system, by slightly increasing the data packets delay. All the proposed schemes are analyzed by simulation in the presence of voice and data traffic. Several comparisons show a relevant performance improvement (in terms of data delay and maximum number of voice stations acceptable within a cell) over other protocols that use ALOHA as a reservation mechanism (RRA-ALOHA or PRMA schemes). This revised version was published online in June 2006 with corrections to the Cover Date.     

Terminal‐Assisted Hybrid MAC Protocol for Differentiated QoS Guarantee in TDMA‐Based Broadband Access Networks

This paper presents a terminal‐assisted frame‐based packet reservation multiple access (TAF‐PRMA) protocol, which optimizes random access control between heterogeneous traffic aiming at more efficient voice/data integrated services in dynamic reservation TDMA‐based broadband access networks. In order to achieve a differentiated quality‐of‐service (QoS) guarantee for individual service plus maximal system resource utilization, TAF‐PRMA independently controls the random access parameters such as the lengths of the access regions dedicated to respective service traffic and the corresponding permission probabilities, on a frame‐by‐frame basis. In addition, we have adopted a terminal‐assisted random access mechanism where the voice terminal readjusts a global permission probability from the central controller in order to handle the ‘fair access’ issue resulting from distributed queuing problems inherent in the access network. Our extensive simulation results indicate that TAF‐PRMA achieves significant improvements in terms of voice capacity, delay, and fairness over most of the existing medium access control (MAC) schemes for integrated services.     

Block Reservation Time Division Multiple Access (BRTDMA) Protocol for a High Capacity Wireless Network

Next generation high capacity wireless networks need to support various types of traffic, including voice, video and data, each of which have different Quality of Service (QoS) requirements for successful transmission. This paper presents an advanced reservation packet access protocol BRTDMA (Block Reservation Time Division Multiple Access) that can accommodate voice and data traffic with equal efficiency in a wireless network. The proposed BRTDMA protocol has been designed to operate in a dynamic fashion by allocating resources according to the QoS criteria of voice and data traffic. Most of the existing reservation protocols offers reservation to voice traffic while data packets are transmitted using contention mode. In this paper we propose a block reservation technique to reserve transmission slots for data traffic for a short duration, which minimizes the speech packet loss and reduce the end-to-end delay for wireless data traffic. The optimum block reservation length for data traffic has been studied in a cellular mobile radio environment using a simulation model. Simulation results show that the BRTDMA protocol offers higher traffic capacity than standard PRMA protocol for integrated voice and data traffic and offers flexibility in accommodating multimedia traffic.     

Novel satellite digital video TDMA system for business videocommunications

The authors propose a satellite video signal transmission system that uses a time division multiple access (TDMA) scheme for digital video signal transmission and a code division multiple access (CDMA) scheme for voice signal transmission from a video signal reception-only earth station (backward voice signal transmission). The adoption of a TDMA scheme makes it possible to transmit video signals from various places and to communicate in multipoint-to-(multi)point mode. For backward voice channel transmission from video signal reception-only earth stations, a superposed CDMA voice signal transmission over TDMA video signals by using the same transponder is proposed. The employment of high coding gain forward error correction and development of a cochannel interference cancellation technique have made it possible for the proposed system to transmit a practical number of voice channels. The performance of the proposed system has been experimentally evaluated and the results show the proposed scheme can transmit about 20 CDMA voice channels simultaneously     

Link-level connection control schemes in a high-speed satellitedata network: a performance comparison

The author makes a performance comparison between a connection-oriented (CO) logical link control (LLC) protocol and a connectionless (CL) LLC protocol in a high-speed satellite packet network with the time-division-multiple-access (TDMA)-reservation multiple-access protocol. In particular, the way that the channel transmission rate affects the performance of the two LLC protocols is examined. The most suitable LLC protocol for any given system environment is determined. The comparison indicates that the CL-LLC protocol has more advantages over the CO-LLC protocol as the channel transmission rate increases and that the suitable region for the CL-LLC protocol becomes wider as the receiver-buffer capacity increases and as the network load decreases     

Estimation of the efficiency of bandwidth request piggybacking to data packets in the wireless network controlled by the IEEE 802.16 protocol

A data transmission process of the centralized wireless network controlled by IEEE 802.16 protocol, in which a set of subscriber stations utilizes the common channel to transmit data to the base station, is discussed. The developed analytical model makes it possible to investigate the efficiency of upstream traffic transmission, including channel reservation using the random multiple access algorithm and packet sending with allowance for bandwidth request piggybacking onto data. The analytical estimates of packet registration and service durations are presented.     

C-PRMA: a centralized packet reservation multiple access for localwireless communications

Packet-switched technology has been demonstrated as effective in cellular radio systems with short propagation delay, not only for data, but also for voice transmission. In fact, packet voice can efficiently exploit speech on-off activity to improve bandwidth utilization over time division multiple access (TDMA). Such an approach has been first suggested in the packet reservation multiple-access (PRMA) technique, an adaptation of the reservation ALOHA protocol to the cellular environment. However, being PRMA-based on a fixed frame scheme, it cannot thoroughly take advantage of the very short propagation delays encountered in microcellular systems that allow, for instance, the immediate retransmission of packets lost because of the interference noise from adjacent cells. We present the centralized PRMA, a natural enhancement of PRMA, in which the base station (BS) plays a central role in scheduling the transmissions of mobile stations (MSs). As a consequence, the transmission scheduling is very flexible and can account for the different traffic rate and delay constraints that emerge from voice and data integration. A packet retransmission policy to recover corrupted packets can be implemented and operated efficiently to provide an acceptable grade of service, even in a very noisy environment. The simulation results presented show the quantitative improvements of the centralized packet reservation multiple-access (C-PRMA) performance with respect to PRMA     

Packet Voice on a Local Area Network with Round Robin Service

In this paper, we propose a combined voice/data protocol suitable for multiple access broadcast networks that provide round robin service to the stations. Such networks are well suited to the integration of voice and data since they guarantee bounded delay and provide high utilization even for high bandwidth channels. Using one such network proposal-namely Expressnet-as a representative scheme, we examine the characteristics of the service that voice traffic experiences under the voice/data protocol. We show that the access protocol is able to utilize the channel efficiently to support a large population of voice sources while maintaining low packet delay and guaranteeing some prespecified minimum bandwidth for data traffic. In addition, we show the advantages of silence suppression, i.e., discarding speech that constitutes silent periods, and we examine the cost of overloading the network in terms of the amount of speech discarded.     

ETPS-MAC: Energy Traffic Priority Scheduling-based QoS-aware MAC protocol for hierarchical WSNs

The evolution of the wireless sensor network (WSN) in recent years has reached its greatest heights and applications are increasing day by day, one such application is Smart Monitoring Systems (SMSs) which is in vision of implementation in every urban and rural areas. The implementation of WSN architecture in SMS needs an intelligent scheduling mechanism that efficiently handles the dynamic traffic load without sacrificing the energy efficiency of network. This paper presents a centralized TDMA scheduling based medium access control (MAC) protocol, called Energy Traffic Priority Scheduling MAC (ETPS-MAC) that accommodates variable traffic load while maintaining Quality-of-Service (QoS) assurance in hierarchical WSNs. The ETPS-MAC protocol employs priority scheduling algorithm which considers two factors for assigning priority, the energy factor and the traffic load factor to avoid packet buffering and maintains minimum data packet delay in case of high traffic load. Moreover, a novel rank-based clustering mechanism in FPS-QMAC protocol prolongs the network lifetime by minimizing the distance between the cluster head (CH) and the base station (BS). Both analytical and simulation models demonstrate the superiority of the ETPS-MAC protocol in terms of energy consumption, transmission delay, data throughput and message complexity when compared with the existing TDMA based MAC protocols.     

A Medium Access Control Protocol for Real Time Video over High Latency Satellite Channels

We report the results of extensive simulation work on a new satellite medium access control (MAC) protocol for medium quality interactive video. This MAC protocol uses combined random access/demand assigned multiple access (RA/DAMA). The underlying multiple access physical layer is time division multiple access (TDMA). The RA/DAMA MAC seeks to adaptively minimize the delay of each network layer (nl) packet that arrives to the output queue by transmitting packets on either a collision free demand assigned channel or on a collision possible random access channel. Combined with this dual channel transmission method is a new technique for acquiring demand assigned bandwidth, called a packet flow rate metric (PFRM). This metric seeks to track the slow time behavior of video traffic, leading to a significant reduction in the amount of DAMA signaling. All simulations were conducted using SMACS, the Satellite Medium Access Control Simulator [4], a simulation tool built into ns-2.0 (network simulator version 2) [10]. This simulation tool allowed us to evaluate our MAC protocol using an actual 2 hour long video trace rather than a parametric video traffic generator. Our results show that if light packet loss is tolerable (less than 3%), then significantly lower delays and higher link utilization can be achieved.     

A Bandwidth Reservation Multiple Access Protocol for Wireless ATM Local Networks

A bandwidth reservation multiple access scheme(BRMA) is proposed to resolve contention and assignbandwidth among multiple users trying to gain access toa common channel such as in mobile users contending for resources in an ATM-based cellular networkor a wireless local area network (LAN) with shortpropagation delays. The protocol is best suited tosupport variable-bit-rate (VBR) traffic that exhibits high temporal fluctuations. Each mobile user isconnected end-to-end to another user over virtualchannels via the base station that is connected to thewired ATM B-ISDN network. The channel capacity is modeled as a time frame with a fixed duration.Each frame starts with minislots, to resolve contentionand reserve bandwidth, followed by data-transmissionslots. Every contending user places a request for data slots in one of the minislots. If therequest is granted by the base station through adownlink broadcast channel, the user then startstransmission in the assigned slot(s). The number ofassigned slots varies according to the required qualityof service (QoS), such as delay and packet lossprobability. A speech activity detector is utilized inorder to indicate the talkspurts to avoid wastingbandwidth. Due to its asynchronous nature, BRMA is ratherinsensitive to the burstiness of the traffic. Since theassignment of the minislots is deterministic, therequest channels are contention-free and the data channels are collision-free. Hence, in spite ofthe overhead (minislots) in each frame, BRMA provideshigher throughput than Packet Reservation MultipleAccess (PRMA) for the same QoS, especially for high-speed systems. A better delay performance is alsoachieved for data traffic compared to Slotted Alohareservation-type protocol PRMA. In addition, BRMAperforms better in terms of bandwidth efficiency thanthe conventional TDMA or the Dynamic TDMA, wherespeech activity detectors are very difficult toimplement.     

卫星数据接收站中网络协议的应用

卫星信号通过数据接收站传送到地面网络再分发给不同的用户。数据接收站将承担陆地观测卫星的接收任务,并继续承担国外相关卫星的接收、处理与分发的任务。延时长信道的传输速率受限降低了TCP协议拥塞控制和流量恢复策略的性能。主要讨论了卫星数据接收站采用组播的方式与数据存储或其他数据管理分系统互连,并通过TCP/IP协议与中心站互通。     

Delay and throughput characteristics of TH, CDMA, TDMA, and hybridnetworks for multipath faded data transmission channels

The new concepts of adaptive time hopping and variable frame code division (CDMA) multiple access are introduced. By a unified analysis, the probabilities of bit and packet errors in multipath fading environment for five time division (TDMA), code division, and time hopping (TH) related multiaccess networks are obtained; namely, TDMA, CDMA, CDMA/TDMA, Adaptive CDMA/TH, and variable frame CDMA/TDMA networks. The delay and useful throughputs of the five systems are also evaluated for data and voice traffic. All systems compared have the same channel power and bandwidth and support the same traffic. Though implementation issues are not covered, CDMA systems are put at a disadvantage (compared to cellular-type FDMA networks, for example) by ignoring such inherent advantages as voice silence utilizations and automatic frequency reuse. Nontheless, two CDMA systems outperform TDMA systems at low and medium input traffics     

VMcMAC: Voice Call Support over Wireless Multi-Channel MAC Protocol

This paper presents a new scheme to support voice calls over a wireless multi-channel MAC protocol (VMcMAC). We increase the voice capacity of wireless networks by reducing protocol overhead and interference between voice traffic and data traffic. Voice calls are allocated to specific reserved channels in a distributed TDMA fashion. Each voice node visits the voice channel with a fixed frequency and then transmits a voice frame without sending control messages. Simulation results show a significant improvement in the voice capacity of wireless ad-hoc networks     

Cognitive medium access control protocols for secondary users sharing a common channel with time division multiple access primary users

The unused time slots in a primary time division multiple access (TDMA) network are regarded as the potential channel access opportunities for secondary users (SUs) in cognitive radio (CR). In this paper, we investigate the medium access control protocols that enable SUs to access a common TDMA channel with primary users (PUs). The primary traffic is assumed to follow a Bernoulli random process. A two‐state Markov chain is used to model the secondary traffic, and two different scenarios are considered. The first scenario assumes that the secondary packet arrivals are independent and follow a Bernoulli random process and a cognitive carrier sensing multiple access (Cog‐CSMA) protocol is proposed. A Rayleigh fading channel is considered in evaluating Cog‐CSMA, and its throughput expression is derived in this paper. The second scenario assumes that the packet arrivals follow a correlated packet arrival process and a cognitive packet reservation multiple access (Cog‐PRMA) protocol is proposed. A Markov chain is used to model the different system states in Cog‐PRMA and derive the throughput. Numerical results show that the Cog‐CSMA and Cog‐PRMA protocols achieve the objective of supporting secondary transmissions in a TDMA network without interfering the PUs' transmissions and improve the network bandwidth utilization. Copyright © 2012 John Wiley & Sons, Ltd.