Multiplex communications – Generalized orthogonal or special mathematical techniques – Fourier transform
Patent
1995-05-12
1997-10-21
Kizou, Hassan
Multiplex communications
Generalized orthogonal or special mathematical techniques
Fourier transform
370208, 370536, 370329, 375260, H04J 1100, H04J 304, H04Q 700
Patent
active
056803885
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for dynamic allocation of multiple carrier-wave channels for multiple access by frequency division multiplexing and transmitter arrangements and receiver arrangements for carrying out the method. The invention is especially intended to be applied to mobile telecommunication systems. The invention provides a number of mobile units with the possibility for flexible data speed and continuous transmission. On the fixed side, the number of transmitters and receivers can be minimized by utilizing broadband receivers which serve several mobile units.
PRIOR ART
In mobile telecommunication systems, it is generally desirable to be able to provide a variable transmission speed in the different connections in order to be able to utilize the accessible frequency band as effectively as possible. In general, the system is provided with a frequency band with fixed width at a certain frequency.
There are a number of known ways to control the utilization of the frequency band, for example TDMA, FDMA, CDMA and hybrids of these.
Time division multiple access (TDMA) involves transmitting and receiving being divided into time gaps. Each channel has its predetermined time gap and the transmission speed can be varied by changing the length of the time gap. A disadvantage is that the system only uses one frequency at a time. TDMA is also sensitive to time dispersion due to the high channel data speed.
Frequency division multiple access (FDMA) involves the frequency band being divided into frequency bands with one transmitter/receiver in each narrow band with a carrier wave in the centre of the frequency bands. If it is attempted to increase the data speed by widening the carrier wave, interference is produced in adjacent frequency bands, which is naturally a disadvantage. Moreover, it is uneconomical to have one transmitter for each frequency bands, which makes for a large number of transmitters.
Code division multiple access (CDMA) involves all channels using the same frequency band but being distinguished by each mobile unit having its own unique code key with which the data sequence is coded. CDMA gives rise to very complex receivers and also requires control of the transmitted power.
SUMMARY OF THE INVENTION
The present invention is mostly related to FDMA in that a wider frequency band is divided into a number of subbands with a modulated carrier wave in each subband. To vary the transmission speed, a user will be able to allocate as many subbands as he needs for covering his data clock requirement. It should also be possible to vary this allocation of subbands with time. Instead of having one transmitter/receiver in each subband, however, broadband transmitters/receivers are used which handle transmission over the entire accessible band.
Thus, the present invention provides a method for dynamic allocation of multiple carrier-wave channels where the bit stream or bits streams which will be transmitted are subjected to conversion from serial form to parallel form with a number of outputs, each parallel output is allocated a frequency band with a defined subcarrier wave, each subcarrier wave is subjected to symbol coding by being modulated by the respective parallel bit stream in order to provide a number of parallel symbols or parallel subcarrier waves. The parallel symbols are converted by inverse discrete Fourier transform to a sequence in the time domain, which sequence is D/A-converted to provide a baseband signal. The baseband signal is RF-modulated with a frequency at the centre of the overall accessible frequency band. Thus, a single broadband transmitter handles the transmission of all channels. At the receiver end, the RF signal is demodulated to the baseband, the baseband signal is A/D-converted and the sample is frequency-demultiplexed by discrete Fourier transform which recreates the signal in frequency bands. Suitable frequency bands are selected taking into account the respective user and the signals in these frequency bands are symbol-decoded
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Bnimoussa A.
Kizou Hassan
Telia AB
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