296 research outputs found
Proactive TCP mechanism to improve Handover performance in Mobile Satellite and Terrestrial Networks
Emerging standardization of Geo Mobile Radio (GMR-1) for satellite system is
having strong resemblance to terrestrial GSM (Global System for Mobile
communications) at the upper protocol layers and TCP (Transmission Control
Protocol) is one of them. This space segment technology as well as terrestrial
technology, is characterized by periodic variations in communication properties
and coverage causing the termination of ongoing call as connections of Mobile
Nodes (MN) alter stochastically. Although provisions are made to provide
efficient communication infrastructure this hybrid space and terrestrial
networks must ensure the end-to-end network performance so that MN can move
seamlessly among these networks. However from connectivity point of view
current TCP performance has not been engineered for mobility events in
multi-radio MN. Traditionally, TCP has applied a set of congestion control
algorithms (slow-start, congestion avoidance, fast retransmit, fast recovery)
to probe the currently available bandwidth on the connection path. These
algorithms need several round-trip times to find the correct transmission rate
(i.e. congestion window), and adapt to sudden changes connectivity due to
handover. While there are protocols to maintain the connection continuity on
mobility events, such as Mobile IP (MIP) and Host Identity Protocol (HIP), TCP
performance engineering has had less attention. TCP is implemented as a
separate component in an operating system, and is therefore often unaware of
the mobility events or the nature of multi-radios' communication. This paper
aims to improve TCP communication performance in Mobile satellite and
terrestrial networks.Comment: 5 pages, 2 figure
On Channel Sharing Policies in LEO Mobile Satellite Systems
We consider a low earth orbit (LEO) mobile satellite system with "satellite-fixed" cells that accommodates new and handover calls of different service-classes. We provide an analytical framework for the efficient calculation of call blocking and handover failure probabilities under two channel sharing policies, namely the fixed channel reservation and the threshold call admission policies. Simulation results verify the accuracy of the proposed formulas. Furthermore, we discuss the applicability of the policies in software-defined LEO satellites
Performance evaluation of an improved PRMA protocol for low earth orbit mobile communication systems
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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%
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