Pulse or digital communications – Repeaters – Testing
Patent
1995-11-22
1998-02-17
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
375343, 375349, 370320, 370342, 370479, 455 523, 455 65, H04B 1500
Patent
active
057198993
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multiple access digital transmission system comprising at least one transmitter for transmitting at least one modulated datastream, and at least one receiver for receiving a transmitted signal, which comprises the modulated datastreams, via a transmission channel, the receiver comprising receiving means having resolving means for resolving at least one path for at least one multipath received modulated datastream, and having channel estimation means, which are coupled to the resolving means, for estimating channel path delays in the received modulated datastreams. Such a transmission system can be a mobile radio multiple access system based upon direct-sequence spread spectrum techniques or the like, or other transmission systems using similar techniques.
The present invention further relates to a radio base station and to a receiver for use in such a system.
2. Description of the Related Art
Spread spectrum systems are well-known since long and have been described in numerous articles and handbooks, such as in a basic article describing a system implementing a direct-sequence spread spectrum system, "A Communication Technique for Multipath Channels", R. Price et at., Proc. of the IRE Vol. 46, March 1958, pp. 555-570, a tutorial article "Theory of Spread-Spectrum Communications--A Tutorial", R. L. Pickholtz et at, IEEE Tr. on Comm., Vol. COM-30, No. 5, May 1982, pp. 855-884, and a handbook "Digital Communications", J. Proakis, McGraw-Hill, 1989, Chapters 7 and 8. In Chapter 7, pp. 702-799 of said handbook digital signalling over fading multipath channels is described as is the case in a mobile radio system, in Chapter 7, pp. 719-739 a so-called RAKE receiver is described implementing diversity for multipath spread spectrum receivers, and in Chapter 8 spread-spectrum receivers, especially pp. 802-804, describing direct-sequence spread spectrum, pp. 831-836 describing PN sequences for DS SS, pp. 862-864, describing a sync acquisition phase for DS SS, and pp. 868-872, describing sync tracking for DS SS. In this respect it is to be noticed that synchronisation of a DS SS receiver to a DS SS transmitter has to be very accurate, i.e. within a fraction of a so-called chip in the tracking phase. In practical systems, the acquisition and tracking phases may not be quite distinguishable.
From the U.S. Pat. No. 5,099,493 a DS-SS (Direct Sequence-Spread Spectrum) Receiver is known with separate integrated signal estimator-and-demodulator arrangements for processing DS-SS channels. A common error signal is formed as the difference between the received signal and the sum of reconstructed signals estimated by the estimator-and-demodulator units. Each reconstructed signal is also fed back to the input of the corresponding estimator-and-demodulator unit. This approach does not exploit efficiently the fact that the channel parameters vary slowly as compared to the bit period. Due to the immediate feedback the channel estimates are sub-optimal Furthermore, the U.S. Pat. No. 5,099,493 is not directed to multipath signal path resolving, and the shown analog COSTAS-loops are not particularly suitable for digital receivers.
A multiple access digital transmission system of the above kind is known from the European Patent No. 0 361 299. In said patent a multiple access direct-sequence spread spectrum system or CDMA (Code Division Multiple Access) mobile radio system is disclosed. In such a mobile radio system the transmission channel between mobile radio station and a base station, having a multipath behaviour, is apt to give fadings due to the fact that such a multipath behaviour is time variant. I.e., signals arriving at the base station via various paths of different phase shifts and different length and thus giving rise to different path delays may cancel each other almost completely. In order to counter such situations, the system disclosed in said patent applies wide band signals and channel estimation for estimating channel path delays
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Thielecke, "A State Space Multiuser Detector for CDMA Systems", IEEE Int. Conference on Comm., ICC '93, Geneva, Switzerland, May 23-26, 1993, vol. 3, pp. 1762-1767.
Granzow Wolfgang
Thielecke Jorn
Chin Stephen
Le Amanda T.
Schaier Arthur G.
U.S. Philips Corporation
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