Multiple Access Schemes for Packet Switching in Radio Channels : An Overview

• For almost a century circuit switching has dominated communication / networks. It was not until the beginning of the 70's as switching cost dropped below communication (bandwidth) costs making packet switching networks feasable. For modern computer communications, circuit switching 1s very wasteful, especially over long distances. This is due to the fact that the datastream from computers and terminals is very bursty, with peak to average ratios up to 2000 to | [5]. If, in a circuit switching environment a high bandwidth channel is used to ensure low delay, this channel will be idle most of ~the time. If we instead use a channel with a bandwidth corresponding to the ~average transmission rate, we will get intolerable delays. The above dilemma arises because the users access the channels randomly. We have no way to tell when the channel will be used, so we assign one channel capable of handling peak rates all the time. This is of course wasteful.The packet-switching solution to the situation above is based on the law of large numbers, stating that the sum of all demands from a large number of users will fluctuate very little. around its average. This is usually called statistical load averaging. The implication is clear -we should use a single wideband channel, dynamically shared among the users. This has been utilized in packet-switched computer networks. The datastream is divided into packets. When a packet is ready for transmission, it is allocated some time-slot (possibly after some queuing delay) on the shared channel. The allocation of suitable time-slots is here done by the network facilities.In recent years the use of packet switching in radio channels has been proposed and implemented. 8oth ground radio and satellite channel s have been utilized for packet switching. The radio medium offers several advantages for these applications....

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TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Signalbehandling (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Signal Processing (hsv//eng)

NATURVETENSKAP  -- Data- och informationsvetenskap (hsv//swe)

NATURAL SCIENCES  -- Computer and Information Sciences (hsv//eng)

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