Code division multiple access transmitter and receiver

Details Code division multiple access transmitter and receiver Code division multiple access transmitter and receiver

1999-04-26

2001-12-04

Corrielus, Jean (Department: 2631)

Multiplex communications

Communication over free space

Combining or distributing information via code word channels...

C375S135000, C375S136000, C375S142000, C375S146000, C375S150000, C370S335000

Reexamination Certificate

active

06327257

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a code division multiple access transmitter comprising a modulation stage followed by an up-converter, and to a code division multiple access receiver comprising reciprocally a down converter followed by a demodulation stage. This invention may have important applications in relation with the future mobile communications standards which will use code-division multiple access modulation techniques for all types of channel.
2. Description of Related Art
Spread spectrum transmission techniques, implemented for over thirty years in the field of military communications, may also be of interest for use in mobile radio applications. According to the basic principle of these techniques, a signal is spread over a frequency bandwidth that is much wider than the minimum bandwidth required to transmit the signal. More precisely, the idea behind spread spectrum is to transform a signal with a given bandwidth into a noise-like signal of much larger bandwidth: hence the total power transmitted when a spread spectrum technique is used (this power is assumed to be the same as that in the original signal) is spread over 10 to 1000 times the original bandwidth, while its power spectral density is correspondingly reduced by the same amount. This feature gives to a spread spectrum signal the characteristic of causing little interference to a narrow-band user.
This frequency-spreading characteristic offers a transmitted signal the possibility of using CDMA (code-division multiple access), particularly in order to support simultaneous digital communication among a large community of relatively uncoordinated users. The CDMA multiplexing technique is described for instance in the document “Overview of multicarrier CDMA”, by S. Hara and R. Prasad, IEEE Communications Magazine, December 1997, pp. 126-133. In fact, a CDMA system is a spread spectrum system in which, in order to share the same bandwidth, the users are assigned different spreading codes (generated by a pseudo-noise generator and determined by code parameters such as a chip length T and a code length N) in order to spread their signals over a bandwidth much wider than their transmitted data bandwidth, a specific signature sequence being assigned to each user to ensure signal separability.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to propose a CDMA transmitter based on a new principle of modulation.
To this end the invention relates to a CDMA transmitter such as defined in the preamble of the description and which is moreover characterized in that said modulation stage itself comprises in series at least a data-to-frequency offset converter, a frequency synthesizer controlled by said converter and a code generator.
In a particular embodiment of said transmitter, the code generator is periodically initialized by an initialization module by means of which at least one code period without any frequency offset is provided each P code periods.
An other object of the invention is to propose a corresponding CDMA receiver allowing to demodulate signals generated by such a CDMA transmitter.
To this end the invention relates to a CDMA receiver such as defined in the preamble of the description and which is characterized in that said demodulation stage receives a signal that has been modulated by a modulation stage, comprising at least a data-to-frequency offset converter, a frequency synthesizer controlled by said converter and a code generator, and comprises a demodulation branch and calibration branch, said demodulation branch comprising correlation means, for detecting said frequency offsets, and decision means, for yielding the corresponding demodulated data, and said calibration branch being provided for a periodical frequency control of the reference code generator of said receiver before data demodulation.
In the case the code generator of the transmitter has been periodically initialized so that at least one code period without any frequency offset is provided each P code periods, any offset detected at the receiving side can then be considered as a wrong one that does not correspond to input data.


REFERENCES:
patent: 4639932 (1987-01-01), Nakagawa
patent: 5128957 (1992-07-01), Nakagawa
patent: 5150377 (1992-09-01), Vannucci
patent: 5748623 (1998-05-01), Sawahashi et al.
patent: WO 94/29970 (1994-12-01), None
By S. Hara & R. Prasad, “Overview of Multicarrier CDMA”, IEEE Communications Magazine, Dec. 1997, pp. 126-133.

Affiliated with

Also associated with

Rating

Code division multiple access transmitter and receiver does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Code division multiple access transmitter and receiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Code division multiple access transmitter and receiver will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2578706