20 research outputs found
Performance evaluation of an improved PRMA protocol for low earth orbit mobile communication systems
Performance Evaluation of an Improved PRMA Protocol for Low Earth Orbit Mobile Communication Systems
EQUILIBRIUM ANALYSIS AND CONTROL FOR DESIGN OF PACKET RESERVATION MULTIPLE ACCESS PROTOCOLS
The Packet Reservation Multiple Access (PRMA) protocol and its variants
have been considered as possible access schemes for communication media for indoor communications, terrestrial communications and satellite communications. Most recently, PRMA (and its variants) has been considered for applications such as beyond third generation and/or fourth generation communication systems, cooperative communication, and multimedia communication in dynamic environments.
In this dissertation, equilibrium behavior of general voice and/or data systems employing PRMA are studied along with means for control of this behavior. The main objective is to determine conditions guaranteeing a unique equilibrium for these systems, as multistability can result in an unacceptable user experience. Systems considered include voice systems, voice and data systems, and voice systems
with high propagation delay (these are studied both for an error-free channel and a random error channel). Also, various control schemes are introduced and their effect on these system is analyzed at equilibrium. Control schemes considered include a price based control, state estimation-based control, and control using multiple transmission power and capture. For each type of control, the effect of the control on the equilibrium structure of the system is studied, in the spirit of the methodology of bifurcation control. In bifurcation control, the number and nature of steady state solutions of a system are managed by appropriate design of system control laws. Several sufficient conditions for uniqueness of operating points of the PRMA systems under the studied control schemes is determined. Numerical analysis of the equilibrium equations of the systems is provided to support the analytical studies. The equilibrium behavior of voice systems and voice-data systems employing frame-based PRMA is also studied. Effects of price based control on these systems is analyzed. Further, the price based control studied in conjunction with the PRMA systems is extended to a finite buffer finite user slotted ALOHA system, and the equilibrium behavior of the system is studied using a tagged user approach.
Among the contributions of the dissertation are analytical sufficient conditions guaranteeing a unique equilibrium point for the various classes of systems studied, control law designs that result in improved system capacity, and extensive numerical studies including comparisons with two previously proposed approaches. Analysis is
also given proving the Markovian nature of the system's stochastic dynamics (under some basic assumptions) and the existence of a unique stationary probability law
Satellite-3G Hybrid Networks: Impact of ACM and ARQ on TCP Performance
The adoption of satellite systems in providing broadband transmissions to mobile users such as trains, buses and vans is expected to be an interesting solution. The scenario we considered refers to a hybrid network architecture, where a geostationary satellite forward link and a terrestrial 3G return link are used in order to exploit both the high bandwidth of a satellite channel and the lower propagation delay of a terrestrial path. The resulting round-trip delay is much shorter than that one experienced by using both the forward and return link via satellite. This is particularly appealing for overcoming the TCP efficiency degradation in high delay-bandwidth product and error prone channels. In this hybrid scenario, we used simulation results to compare the goodput of four of the most popular TCP variants, in the presence of a GOOD-BAD satellite channel, as the one experienced by mobile users. We applied an Adaptive Coding and Modulation (ACM) technique as well, and studied its impact on TCP efficiency, when used both alone and in cooperation with an Automatic Repeat reQuest (ARQ) scheme of the Selective Repeat (SR) type with low persistency. Results obtained indicate that this hybrid architecture is advantageous for TCP transmissions in terms of average goodput, and that ACM is effective only if it is jointly used with ARQ schemes
System level performance of ATM transmission over a DS-CDMA satellite link.
PhDAbstract not availableEuropean Space Agenc
Satellite-3G Hybrid Networks: Impact of ACM and ARQ on TCP Performance
The adoption of satellite systems in providing broadband transmissions to mobile users such as trains, buses and vans is expected to be an interesting solution. The scenariowe considered refers to a hybrid network architecture, where a geostationary satellite forward link and a terrestrial 3G return link are used in order to exploit both the high bandwidth of a satellite channel and the lower propagation delay of a terrestrial path. The resulting round-trip delay is much shorter than that one experienced by using both the forward and return link via satellite. This is particularly appealing for overcoming the TCP efficiency degradation in high delay-bandwidth product and error prone channels. In this hybrid scenario, we used simulation results to compare the goodput of four of the most popular TCP variants, in the presence of a GOOD-BAD satellite channel, as the one experienced by mobile users. We applied an AdaptiveCoding and Modulation (ACM) technique as well, and studied its impact on TCP efficiency, when used both alone and in cooperation with an Automatic Repeat reQuest (ARQ) scheme of the Selective Repeat (SR) type with low persistency. Results obtained indicate that this hybrid architecture is advantageous for TCP transmissions in terms of average goodput, and that ACM is effective only if it is jointly used with ARQ schemes
Protocols for voice/data integration in a CDMA packet radio network.
Thesis (Ph.D.)-University of Natal, Durban, 1999.Wireless cellular communications is witnessing a rapid growth in, and demand for,
improved technology and range of information types and services. Future third
generation cellular networks are expected to provide mobile users with ubiquitous
wireless access to a global backbone architecture that carries a wide variety of electronic
services. This thesis examines the topic of multiple access protocols and models
suitable for modem third-generation wireless networks.
The major part of this thesis is based on a proposed Medium Access Control (MAC)
protocol for a Code Division Multiple Access (CDMA) data packet radio network, as
CDMA technology is proving to be a promising and attractive approach for spectrally
efficient, economical and high quality digital communications wireless networks. The
proposed MAC policy considers a novel dual CDMA threshold model based on the
Multiple Access Interference (MAl) capacity of the system. This protocol is then
extended to accommodate a mixed voice/data traffic network in which variable length
data messages share a common CDMA channel with voice users, and where the voice
activity factor of human speech is exploited to improve the data network performance.
For the protocol evaluation, the expected voice call blocking probability, expected data
throughput and expected data message delay are considered, for both a perfect channel
and a correlated Rayleigh fading channel. In particular, it is shown that a significant
performance enhancement can be made over existing admission policies through the
implementation of a novel, dynamic, load-dependent blocking threshold in conjunction
with a fixed CDMA multiple access threshold that is based on the maximum acceptable
level of MAl
Design of a medium access protocol and scheduling algorithm for multimedia traffic over a DVB-RCS satellite link using a cross-layer approach.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.Satellite networks provide an alternative to terrestrial networks where cost and lack of infrastructure are driving parameters. For a satellite network to be cost effective one needs to be able to increase the efficiency of the network: this is accomplished by focusing on the parameters that affect the performance of the system and improving on them where possible. The factors affecting the network performance include the capacity, the propagation delay, the protocol used, and the channel error rate, among others. There are various ways to implement a satellite network depending on the satellite orbit, the architecture used, the access technique used, the radio interfaces used, etc.
This thesis work describes the chosen satellite standard, Digital Video Broadcasting – Return Channel via Satellite (DVB-RCS) and the associated Medium Access Control (MAC) protocols.
Two protocols were designed and investigated under ideal channel conditions, these being the Combined Free/Demand Assigned Multiple Access with Piggy Backing – Packet Dropping (CF/DAMA-PB-PD) protocol; and the Combined Free/Demand Assigned Multiple Access with Piggy Backing – Prioritised Earliest Deadline First (CF/DAMA-PB-PEDF) protocol, both derived from the Combined Free/Demand Assigned Multiple Access with Piggy Backing (CF/DAMA-PB) protocol.
The multimedia traffic models for voice, video and web classes are described, validated through simulations and presented; these provide the heterogeneous
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traffic required for evaluating the performance of the satellite system implemented and the designed protocols. Under the multimedia traffic, CF/DAMA-PB-PD was shown to excel in average packet delay reduction while reducing the overall system throughput. The CF/DAMA-PB-PEDF does not contribute to an improvement over the CF/DAMA-PB-PD protocol.
The effects of a non-ideal channel on the CF/DAMA-PB-PD protocol was investigated and presented along with the design of three MAC protocols that take the channel characteristics into account to improve on the system performance. The cross-layer interactions, more specifically the interaction between the physical and data–link layers, were used, investigated and presented. The channel state information in terms of signal-to-noise ratio (SNR) was used to improve the system performance.
The five protocols evaluated under non-ideal channel conditions were the CF/DAMA-PB, CF/DAMA-PB-PD, CF/DAMA-PB-BSNRF, CF/DAMA-PB-DD and the CF/DAMA-PB-BSNRF+DD. The best overall performance, both in average packet delay while maintaining good QoS levels and throughput was shown to be that of the CF/DAMA-PB-DD protocol