22,918 research outputs found
Zipper - a Duplex Method for VDSL based on DMT
We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise source
Radio frequency optimization of a Global System for Mobile (GSM) network
Includes bibliographical references
Factors Affecting QoS in Tanzania Cellular Networks
Quality of service in cellular communication system is a topic that recently
has raised much interest for many researchers. This paper presents the findings
obtained from the study on factors affecting QoS in Tanzania cellular networks.
The study was carried out in Dodoma Municipal, Tanzania. The study employed
cross sectional research design. Information was gathered from structured
questionnaire of 240 subscribers during the study of quality of service for the
four leading cellular networks in Tanzania. Both qualitative and quantitative
data from field survey were collected and analyzed using Statistical Package
for Social Sciences and Excel software. The study findings show that the major
factors that degrade QoS in Tanzania cellular networks are inadequate network
infrastructure, lack of fairness from service providers and little efforts
taken by the government in enforcing the national agreed standards. Other
factors are lack of reliable end to end systems, geographical terrain, low
quality handsets, poor government monitoring on standards and lack of
subscriber skills and training.Comment: 7 Page
Markov Models of Statistical Multiplexing of Telephone Dialogue with Packet Switching
Existing methods of analysis of voice transmission
by packet switching were designed mainly with respect to a
Poisson stream of input packets, for which the probability of
an active packet on each input port of the router is a constant
value in time. This assumption is not always valid, since the
formation of speech packets during a dialogue is a nonstationary
process, in which case mathematical modeling
becomes an effective method of analysis, through which
necessary estimates of a network node being designed for
packet transmission of speech may be obtained. This paper
presents the result of analysis of mathematical models of
Markov chain based speech packet sources vis-Ă -vis the
peculiarities of telephone dialogue models. The derived models
can be employed in the design and development of methods of
statistical multiplexing of packet switching network nodes
Mobile radio alternative systems study, executive summary
Present day mobile communication technologies, systems and equipment are described from background in evaluating the concepts generated in the study. Average propagation ranges are calculated for terrestrial installations in each of seven physiographic areas of the contiguous states to determine the number of installations that would be required for nationwide coverage. Four system concepts are defined and analyzed to determine how well terrestrial systems can fulfill the requirements at acceptable costs
Capacity analysis of reservation-based random access for broadband wireless access networks
Abstract—In this paper we propose a novel model for the capacity analysis on the reservation-based random multiple access system, which can be applied to the medium access control protocol of the emerging WiMAX technology. In such a wireless broadband access system, in order to support QoS, the channel time is divided into consecutive frames, where each frame consists of some consequent mini-slots for the transmission of requests, used for the bandwidth reservation, and consequent slots for the actual data packet transmission. Three main outcomes are obtained: first, the upper and lower bounds of the capacity are derived for the considered system. Second, we found through the mathematical analysis that the transmission rate of reservationbased multiple access protocol is maximized, when the ratio between the number of mini-slots and that of the slots per frame is equal to the reciprocal of the random multiple access algorithm’s transmission rate. Third, in the case of WiMAX networks with a large number of subscribers, our analysis takes into account both the capacity and the mean packet delay criteria and suggests to keep such a ratio constant and independent of application-level data traffic arrival rate
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