Germany : Bitrate flexible code division multiplex for atm access.
The main objective of FLEXIMACS is to investigate and develop a synchronous code division multiple access (S-CDMA) technique, which allows flexible bitrate assignment and quality of service for the individual user in an ATM based multipoint to point access network supporting both high capacitance and high robustness against interference and noise. The project will identify applicable S-CDMA flexibilization schemes and investigate appropriate solutions for the minimisation of multiple access interference (MAI) and for media access control (MAC) protocols regarding their efficiency, delay and flexibility. Based on the identified and defined alternative approaches and algorithms, a preferred overall system solution will be selected in terms of granularity, complexity, flexibility, performance and cost.
Broadband access systems of the immediate future will have to use existing wired networks, such as cable television (CATV) networks, or emerging wireless techniques, e.g. microwave and mm-wave radio, to bridge the last mile to the user and offer rapid, flexible and economical access to new services. ATM is an appropriate transport technique to integrate services of different bitrate and quality requirements onto a single digital access link and to provide interoperability of technologies as different as wireline and wireless final drop on a single access node.
An access system with a shared medium, such as a hybrid fiber coax (HFC) cluster or a radio cell, needs a multiple access scheme in the upstream direction to manage the traffic of a number of simultaneous users. Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA) as well as hybrids of these are being considered. Both frequency and time division multiplexing are mature telecommunication technologies, but are sensitive to ingress noise and interference. CDMA on the other hand is based on spread spectrum technology, which has been used in military communication for decades because of its resistance to jamming and eavesdropping, and has distinct advantages in media subject to ingress noise. In a coax system within the designated uplink band of 5-40 MHz, the ingress consists mainly of impulse noise, narrow band signals such as short wave and amateur radio. In a cellular radio system, intercell interference and co-located systems are the dominant sources. In addition, CDMA offers a certain degree of privacy through individual user individual codes and provides flexibility for system evolution as the demand for capacity and services grows.
A CDMA system has two possible operational modes. In asynchronous mode, the spreading sequences of different channels are arbitrary in phase. Here, the spreading gain is partly consumed by multiple access interference, since the codes are not exact
2013 Al Bawaba (Albawaba.com)
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|Date:||Feb 4, 2013|
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