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COMBINATION OF CDMA AND OFDM FOR DATA TRANSMISIION OVER FIDER
Valentin S. Speransky, Moscow Technical University of Communications and Informatics, Moscow, Russia
Stepan V. Abramov, FSUE «STC «Orion», Moscow, Russia
Oleg I. Klintsov, FSUE «STC «Orion», Moscow, Russia, oklintsov@mail.ru
Abstract
For broadband data transfer over optical, fiber OFDM technology is applied. On the other hand in optical subscriber networks, it is advisable code demultiplexing of subscribers to provide high interference immunity to narrow-band and impulse noises and low interference noise level. In this work we consider combination of CDMA multichannel data transmission and OFDM in optical subscriber network. It allows using the advantages of both technologies. In turn data transmission over fiber supplies long reach up to thousand kilometers. The structure chart of the CDMA-OFDM transmission system over fiber is described. Incoming transmitted subscribers’ data are received by multichannel signal shaper according to the subscriber number. Each channel consists of OFDM signal shaper followed by pseudorandom sequence multiplier. Individual sequence (at the same time the address) is assign to every subscriber. It is comfortable to choose the length of sequence equal to a number of OFDM frequencies.
Pseudorandom code sequences should possess good auto and è joint correlation properties, i.e. have low level sideband peaks, determining nonorthogonality noise and therefore the interference noise level, being along with noise the main problem in reception process. Interface combines channels. Then, they come to light modulator together with carrier frequency laser reference signal. Received modulated optical signal is fed to fiber optic link (feeder). Data sink comprises optical band-pass filter, indicating received signals band, photodetector converting optical signal into radio signal. On amplification, radio signal comes into multichannel pseudorandom sequence decoder, estimating subscribers sequence, and OFDM data signal demodulators. Received data is sent to subscribers. In addition, the diagrams of BER in regard to the number of active subscribers are given.
Keywords: code demultiplexing, OFDM, optical network termination (ONT), fiber, data, pseudo-random sequence, bit error.
References
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Information about authors:
Valentin S. Speransky, MTSc, professor MTUCI, Moscow Technical University of Communications and Informatics, Moscow, Russia
Stepan V. Abramov, MTSc, head of a department FSUE «STC «Orion», Moscow, Russia
Oleg I. Klintsov, MTSc, deputy of a head of a department FSUE «STC «Orion», Moscow, Russia