3 research outputs found
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.link_to_subscribed_fulltex
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Satellite multiple access protocols for land mobile terminals. A study of the multiple access environment for land mobile satellite terminals, including the design analysis and simulation of a suitable protocol and the evaluation of its performance in a U.K. system.
This thesis is a study of multiple access schemes for satellite land
mobile systems that provide a domestic or regional service to a large
number of small terminals.
Three orbit options are studied, namely the geostationary, elliptical
(Molniya) and inclined circular orbits. These are investigated for
various mobile applications and the choice of the Molniya orbit is
justified for a U. K. system.
Frequency, Time and Code Division Multiple Access (FDMA, TDMA and
CDMA) are studied and their relative merits in the mobile environment
are highlighted. A hybrid TDMA/FDMA structure is suggested for a
large system.
Reservation ALOHA schemes are appraised in a TDMA environment and an
adaptive reservation multiple access protocol is proposed and analysed
for a wide range of mobile communication traffic profiles. The system
can cope with short and long data messages as well as voice calls.
Various protocol options are presented and a target system having
100,000 users is considered. Analyses are presented for the steady
state of protocols employing pure and slotted ALOHA and for the
stabilty of the slotted variant, while simulation techniques were
employed to validate the steady state analysis of the slotted ALOHA
protocol and to analyse the stability problem of the pure ALOHA
version.
An innovative technique is put forward to integrate the reservation
and the acquisition processes. It employs the geographical spread of
the users to form part of the random delay in P-ALOHA.
Finally an economic feasibility study is performed for the spacesegment.
For costs of capital (r) less than 23 % the discounted
payback period is less than the project's lifetime (10 years). At r-
8% the payback period is about 5.6 years, while the internal-rate-of-return
is 22.2 %. The net present value at the end of the projects
lifetime is £M 70 at r-8%
Second-generation mobile satellite system. A conceptual design and trade-off study
In recent years, interest has grown in the mobile satellite (MSAT) system, a satellite-based communications system capable of providing integrated voice and data services to a large number of users. To explore the potential of a commercial mobile satellite system (MSS) beyond the horizon of the first generation, using technologies of the 1990's and to assist MSAT-X in directing its efforts, a conceptual design has been performed for a second-generation system to be launched around the mid-1990's. The design goal is to maximize the number of satellite channels and/or minimize the overall life-cycle cost, subject to the constraint of utilizing a commercial satellite bus with minimum modifications. To provide an optimal design, a series of trade-offs are performed, including antenna sizing, feed configurations, and interference analysis. Interference is a serious problem for MSAT and often an overlapping feed design is required to reduce interbeam interference. The trade-off studies will show that a simple non-overlapping feed is sufficient for the second-generation system, thus avoiding the need for the complicated beam-forming network that is associated with the overlapping feed designs. In addition, a system that operates at L-band, an alternative frequency band that is being considered by some for possible MSAT applications, is also presented