Code distribution multiple access communication system with user

Details Code distribution multiple access communication system with user Code distribution multiple access communication system with user

1991-05-30

1994-07-05

Chin, Stephen

Pulse or digital communications

Spread spectrum

Direct sequence

370 18, H04L 700

Patent

active

053274679

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a code distribution multiple access communication system in which the transmission carrier is activated by the user voice.
The bandwidth available for mobile satellite services is limited so that the available number of channels for service is insufficient to absorb the traffic of the community of potential users. The major problem is the system efficiency in terms of information transmitted vs. used frequency bandwidth for a given signal-to-noise ratio.
The code distribution multiple access system while demonstrating interesting advantages, was applied heretofore to satellite mobile communication for data transmission only and this because of the long acquisition time combined with the poor spectral efficiency of the system.
It has been proposed recently to increase the communication channel efficiency of a CDMA mobile communication system by using carrier activation by the user voice, said technique resulting in reducing the average number of contemporary users and consequently reducing the interference levels between communication channels ("Comparison of CDMA and FDMA for the Mobilestar System" by I. M. Jacobs et al, Proceedings of the Mobile Satellite Conference, Pasadena, Calif., May 3-5, 1988).
Said document discusses the theoretical advantages of the proposed techniques but it does not show how the system can operate nor does it disclose any solution to operate the system in a non-continuous mode so as to maintain the spread spectrum acquisition time compatible with the real-time speech communication needs. The aforementioned document does neither suggests any solution for controlling the call blocking.
The object of the present invention is to solve said practical problems and to improve the CDMA system efficiency so as to make it possible to transmit not only data but also voice via satellite.
In accordance with the invention there is now provided a process for achieving the synchronization between a user terminal and a master control station in a code distribution multiple access communication system With a carrier activated by the user voice at the user terminal, wherein the synchronization in the forward link is achieved by transmitting a master code (MC) with the same clock frequency and the same carrier as the communication signals, the master code (MC) is transmitted uninterruptedly and with a higher power level than the return link signals, and the user voice activated carrier for the speech transmission is interrupted during speech pauses.
The user voice is compressed by a voice processor and subdivided into two data streams according to the hierarchical coding principle.
The present invention has also for an object, a code distribution multiple access satellite communication system in which each user terminal comprises a code acquisition and tracking device adapted to receive the master code and to control a code generator that is arranged to produce a local replica of the user code used for the link to be established.
The present invention solves the synchronization problems in satellite communication systems by using the technique of voice activation of the transmission carrier. The blocking probability is reduced by adopting a hierarchical coding with a minimum complexity increase on the mobile terminal. The advantage of the invention is that it solves the synchronization problems posed by the use of voice activation in a CDMA communication system and this feature is obtained with a reduced additional hardware. Thanks to the proposed solution, the invention makes it possible to operate a satellite mobile communication system with a better efficiency, a lower interference level and a better quality of service than an equivalent frequency distribution multiple access system.
The invention applies not only to a mobile communication system but also to any communication system in which the synchronization is a challenging problem. For instance, we may mention a Satellite Relay System and a Satellite Communication System using Small Fixed Terminals. In such

REFERENCES:
patent: 4494228 (1985-01-01), Gutleber
patent: 4559633 (1985-12-01), Kan et al.
patent: 4688210 (1987-08-01), Eizenhofer et al.
patent: 4882579 (1989-11-01), Siwiak
Viola, et al. "Variable Rate Speech Coder Matching The Needs of Traffic Reconfigurability" Oct. 1985, Int'l. Astronautical Federation.
Jacobs, et al. "Comparison of CDMA and FDMA for the Mobilestar System", May 1988, pp. 303-308.
Atal, et al. "A New Model of LPC Excitation for Producing Natural-Sounding Speech at Low Bit Rates", 1982 Proceedings IEEE ICASP, pp. 614-617.

Affiliated with

Also associated with

Rating

Code distribution multiple access communication system with user 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 distribution multiple access communication system with user, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Code distribution multiple access communication system with user will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-802366