Adaptive Mobile Access Protocol (AMAP) for the Message Service of a Land Mobile Satellite Experiment (MSAT-X)

This paper describes a feasibility study of the adaptive mobile access protocol (AMAP) for MSAT-X, a proposed experimental mobile satellite communication network. The mobiles are dispersed over a wide geographical area and the channel data rate is limited due to the size and cost limitations of mobile antennas. AMAP is a reservation based multiple-access scheme. The available bandwidth is divided into subchannels, which are divided into reservation and message channels. The ALOHA multiple-access scheme is employed in the reservation channels, while the message channels are demand assigned. AMAP adaptively reallocates the reservation and message channels to optimize system performance. It has been shown that if messages are generated at a rate of one message per hour, AMAP can support approximately 2000 active users per 2400 bit/s channel with an average delay of 1.4 s.     

UHF频段陆地卫星移动通信业务多径效应测量

UHF测段陆地卫星移动业务多径实验于1999年6月至8月间利用日本GMS140E气象卫星为信标,分别在河南郑州至开封高速公路、林州至上党方向公路以及石家庄至阳泉高速公路段进行。地面接收系统和数据处理设备安置于汽车上。此项实验的目的是为地面卫星移动通信系统的设计提供重要的信道参数。本文给出了不同环境下多径效应的累计分布特性以及相应的预测模型。     

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     

Slotted ALOHA multiple access and error control coding for land mobile satellite networks

This paper considers a satellite network with data messages being transmitted by land mobile users according to slotted Aloha multiple access. The mobile communication links suffering from multipath fading and signal shadowing are modelled as Gilbert-Elliott channels. FEC block coding is used to correct transmission errors. The maximum achievable information throughput and the mean packet delay are derived from a combined analysis of the multiple access and FEC/ARQ protocol. The results show that the additional overhead necessary for FEC is outweighed by the benefit in throughput and delay. Finally, the capture effect and its consequences are discussed.     

A near-optimum MAC protocol based on the distributed queueingrandom access protocol (DQRAP) for a CDMA mobile communication system

This paper presents and analyzes a new near-optimum medium access control (MAC) protocol. The proposed access scheme is suitable for a CDMA mobile communication environment, and keeps under control and upper bounded the number of simultaneous transmissions. It has a delay performance approaching that of an ideal optimum M/M/K system, where K is the number of spreading codes being used (maximum number of simultaneous transmissions). The protocol is a free random access protocol when the traffic load is light, and switches smoothly and automatically to a reservation protocol when traffic load becomes heavier. It is based on distributed queues and a collision resolution algorithm. Moreover, a physical receiver structure is proposed and analyzed in order to preserve the robustness of the protocol in a wireless link. The results obtained show that the protocol outperforms other well known medium access protocols in terms of stability and delay, even when taking into account the loss caused by channel propagation conditions     

A statistical model for a land mobile satellite link

A statistical model for a land mobile satellite link is described. The model assumes that the amplitude of the line-of-sight component under foliage attenuation (shadowing) is lognormally distributed and the received multipath interference has a Rayleigh distribution. Expressions for the level crossing rate and average fade duration are given. Comparison between results calculated from the model and from measurements show reasonably good agreement. The model should be useful for designing communications systems and for simulating propagation effects in the laboratory.     

Efficient estimators for the land mobile satellite channel

A novel class of adpative Kalman channel estimators (AKCEs) for low-data-rate signalling via the land mobile satellite (LMS) channel is presented in this paper. The proposed technique is based on a scheme known as the ‘parallel processing algorithm’ and assumes a discrete Gauss–Markov extension of the LMS channel model. Three different approaches compared against the non-adaptive filter show an improved estimation error variance under various environmental conditions. Trading off computational complexity and performance, the derived maximum a posteriori (MAP) approach has been found to be best applicable. © 1998 John Wiley & Sons, Ltd.     

Reed-Solomon codes for land mobile satellite channels

The performance of Reed-Solomon codes is determined for land mobile satellite communications where a shadowed Rician channel model is used. An effective coding/interleaving scheme is proposed which uses the multipath fading and shadowing statistics of the channel.<>     

Modelling the land mobile satellite channel: a review

The use of satellite systems in the implementation of third-generation mobile communication systems obviously involves a propagation environment for the signal different from that in the conventional terrestrial first- and second-generation systems. The propagation conditions and phenomena met with are embraced by the expression `land mobile satellite (LMS) channel'. This paper reviews the studies of the LMS channel reported in the literature. The various models are classified and compared in such a way that their similarities and differences are apparent     

Adaptive predistortion of COFDM signals for a mobile satellite channel

In this paper, we consider the optimization of the performance of QPSK and 16‐QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non‐linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non‐linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non‐linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10^?3 when compared to QPSK COFDM without the predistortion scheme and 16‐QAM COFDM provides a gain of 0.5 dB output back‐off and 1.2 dB signal to noise ratio at a BER of 3×10^?5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10^?4 for QPSK and 16‐QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

一种移动终端协议栈的消息处理方法研究

为了降低移动终端协议栈中消息编解码的复杂度,丰富消息的处理方式,以及在消息的传递过程中,不考虑使用何种方式进行传输,通过对消息的结构进行精心的设计以及对消息编解码操作进行封装,为承载信令提供丰富的接口(消息内容的编码和解码),研究出一种移动终端协议栈的处理消息方法。实际应用证实,这种方法使得消息的处理更加简单、灵活、可靠、清晰,使得消息在层与层之间的传递更加便利、灵活、高效。     

Digital transmission through a land mobile satellite channel

An analytical derivation of the probability of bit error noncoherent frequency-shift keying (FSK) and coherent phase-shift keying (PSK) signals transmitted through a land-mobile satellite channel is described. The channel characteristics used in the analysis are based on a recently developed model which includes the combined effects of fading and shadowing. Analytical expressions for the probability of bit error of FSK and coherent phase-shift keying (CPSK) signals are obtained. The results show that large amounts of signal-to-noise ratio (SNR) are required to compensate for the combined effect of fading and shadowing. An analytical expression for the irreducible probability of bit error of a CPSK signal due to phase variations caused by fading and shadowing is derived. The results described should be useful in the design of land mobile satellite communication systems     

The design and implementation of a private message service for mobile computers

Even as wireless networks create the potential for access to information from mobile platforms, they pose a problem for privacy. In order to retrieve messages, users must periodically poll the network. The information that the user must give to the network could potentially be used to track that user. However, the movements of the user can also be used to hide the user's location if the protocols for sending and retrieving messages are carefully designed. We have developed a replicated memory service which allows users to read from memory without revealing which memory locations they are reading. Unlike previous protocols, our protocol is efficient in its use of computation and bandwidth. In this paper, we will show how this protocol can be used in conjunction with existing privacy preserving protocols to allow a user of a mobile computer to maintain privacy despite active attacks.The work reported was supported by ARPA/ONR grant N00014-92-J-1866 and a grant by Siemens Corp. The views expressed herein are those of the authors and do not represent the opinions of ARPA/ONR or Siemens Corp.This paper is a revised and extended version of Preserving Privacy in a Network of Mobile Computers presented at the 1995 IEEE Symposium on Security and Privacy.     

Idle-signal casting multiple access with collision detection (ICMA-CD) for land mobile radio

A population of mobile terminals communicating with a central station over a packet-switched multiple-access radio channel is investigated. In land mobile radio communication, in which terminals cannot sense the carrier transmitted from other terminals (either because they are out-of-range or obstructed), a central controlled multiple access system in which a central station broadcasts idle/busy information of the access channel is used for multiplexing the packets from the terminals. Idle-signal casting multiple access (ICMA), which is a practical application of this central controlled system, has been used in the Nippon Telegraph and Telephone Public Corp. (NTT) mobile phone system for some years. ICMA-CD, which is an advanced ICMA scheme characterized by collision detection and evaluates its improved throughput, channel capacity and loss probability in a mobile radio fading environment with restrictions on retransmission, is proposed. It is clarified that ICMA-CD is suitable for the mobile multiple access scheme, especially in the case where packet detection delay and collision recovery time are short and offered traffic is heavy.     

Extended sliding frame R-Aloha: Medium access control (MAC) protocol for mobile networks

Proliferation of mobile communication devices necessitates a reliable and efficient medium access control (MAC) protocol. In this paper, A MAC protocol, called extended sliding frame reservation Aloha (ESFRA), based on sliding frame R-Aloha (SFRA) is proposed for network access technique. ESFRA is particularly designed to solve the mobile hidden station (MHS) problem in a mobile ad hoc network (MANET) by including relative locations of transmitting stations in the packet frame information header. The MHS problem is unique in mobile networks and occurs if a mobile station enters in a collision free zone of any ongoing communication and disturbs this communication with its transmission. In addition to the MHS problem, ESFRA simultaneously solves hidden station, exposed station, and neighborhood capture problems typically observed in wireless networks. A Markov model of ESFRA is developed and provided here to estimate throughput, delay and collision probabilities of the proposed protocol. The Markov modeling is extended to the analysis of SFRA and IEEE 802.11 to compare these competing MAC protocols with ESFRA. The analysis shows that ESFRA decreases frame transmission delay, increases throughput, and reduces collision probabilities compared to IEEE 802.11 and SFRA. ESFRA improves the network throughput 28 percent compared to that of IEEE 802.11, and 33 percent compared to that of SFRA. The improved performance is obtained at the expense of the synchronization compared to IEEE 802.11, but there is virtually no extra cost compared to SFRA.     

Euteltracs: the European mobile satellite service

Euteltracs is Europe's first commercially operated mobile satellite service. Under the overall network operation of Eutelsat, the European Telecommunications Satellite Organisation, Euteltracs provides an integrated message exchange and position-reporting service for the European transportation industry with the aim of increasing cost-effectiveness, radically improving efficiency and security and enhancing business flexibility. This paper describes the architecture of the system and the message exchange and position-reporting service, and gives an overview of the commercial deployment of Euteltracs and of the current regulatory situation for its operation within Europe. It also provides an insight into some new applications for Euteltracs outside of its original target market, including specialised aeronautical and maritime services     

A dynamic reservation protocol for LEO mobile satellite systems

In this paper, we propose a dynamic reservation protocol for the low earth orbit (LEO) mobile satellite system. Based on an analytical model, the dynamic reservation protocol enhances system performance by dynamically varying both the access probability and reservation bandwidth. To implement the protocol, a novel contention-pattern-analysis method is proposed to estimate the number of contending terminals at the start of a frame. The reservation protocol is employed to integrate connection-oriented and connectionless traffic over a satellite channel. Simulation and theoretical results are presented to analyze the performance of the protocol and illustrate its benefits.     

介质独立信息服务的匿名访问协议

针对异构网络环境下介质独立信息服务(MIIS)的匿名访问需求,提出了一种MIIS匿名访问协议.协议中用户和信息服务器在家乡网络服务器的辅助下,既能实现双向认证,也能保护用户的隐私性.提出的协议与已有协议相比具有较好的性能,并且在CK模型下是可证明安全的.     

A packet media access protocol for mobile networks*

In this paper, we propose and analyze a packet time division multiple access protocol for the media access control (mac) sublayer of a radio interface suitable to be implemented in the third generation of mobile networks. This protocol is considered to be adequate for future personal communications networks that should interwork with the broadband-isdn. The protocol is designed to work in a microcell environment employing low power terminals, and to support a wide spectrum of services with both asynchronous and isochronous traffic profiles and different bandwidth requirements.     

A microstrip array feed for land mobile satellite reflectorantennas

A circularly polarized feed array for a spacecraft reflector antenna is described that was constructed by using linearly polarized microstrip elements. The array has seven subarrays which form a single cluster as part of a large overlapping cluster reflector feed array. Each of the seven subarrays consists of four linearly polarized microstrip elements. The array achieved a better than 0.8-dB axial ratio at the array pattern peak and better then 3 dB antenna gain to 20° from the peak, across a 7.5% frequency bandwidth. A teardrop-shaped feed probe was used to achieve wideband input impedance matching for the relatively thick microstrip substrate. The low impedance and axial ratio bandwidths were achieved using a relatively thick honeycomb substrate with the impedance-matching feed probes