Pulse or digital communications – Transceivers
Patent
1994-02-18
1998-10-27
Coles, Edward L.
Pulse or digital communications
Transceivers
375221, 375228, 455 88, H04B 138, H04B 140
Patent
active
058286950
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a radio system, and in particular, though not exclusively, to a radio system for mobile radio using Quadrature Amplitude Modulation (QAM) as a modulation scheme.
BACKGROUND OF THE INVENTION
QAM transmissions over Rayleigh fading mobile radio channels are subjected to error bursts due to deep fades, even when the channel signal-to-noise ratio (SNR) is high. This leads to the notion of varying the number of modulation levels according to the integrity of the channel, so that when the transmissions are not subject to fading the number of modulations levels could be increased by increasing the number of QAM constellation points, and when fading occurs the number of constellation points could be reduced to a value which provides an acceptable bit error rate (BER). If the required BER and switch levels are specified accordingly, variable data throughput results. Alternatively, if throughput is kept reasonably constant a variable BER is obtained.
One approach, known from U.S. Pat. No. 4,495,619 (Acampora), is to have a variable rate system and some method of informing the transmitter at one end of the radio link of the quality of the link as perceived by the receiver at the other end of the link. The transmitter can then respond by changing the number of QAM levels according to the quality criteria adopted. Successful variable rate transmission requires that the fast fading channel changes slowly compared to a number of symbol periods. If this condition is not met, then the frequent transmission of quality control information will significantly increase the bandwidth requirements of the system.
SUMMARY OF THE INVENTION
The present invention seeks to provide a radio system in which transmissions are adapted to transmission conditions.
According to a first aspect the invention provides a radio system comprising a pair of stations at least one of which has a radio transceiver having: assessment of the received signals; modulation scheme having a plurality of modulation states; the selected modulation state; and other station an indication of the selected modulation state.
According to a second aspect the invention provides a radio transceiver for the transmission of digital signals characterised in that the number of binary digits encoded onto each symbol for transmission is varied according to measured received signal strength, the measured bit error rate (BER) or some combination of these.
According to a third aspect the invention provides a radio transceiver characterised in that the received signal strength is averaged over a predetermined time period and the number of bits/symbols to be used in forthcoming transmissions is determined according to this average.
According to a fourth aspect the invention provides a radio transceiver characterised in that errors in received decoded digital signals are identified using an error detection system, and the number of bits/symbol to be used in forthcoming transmissions is based on the number and distribution of the errors detected.
In radio systems wherein the radio communication is bi-directional but instantaneously uni-directional, the data being placed in packets or blocks, the initial symbols in each block may be reserved for signalling the number of bits/symbol to be used in the block.
According to a fifth aspect the invention provides a a mobile radio system for operation over radio channels with fast fading wherein the number of modulation levels is varied at a rate commensurate with the fast fading.
According to a sixth aspect the invention provides a radio transceiver comprising: assessment of the received signals; having a plurality of modulation states; the selected modulation state; and indication of the selected modulation state.
To reduce the problem of fast fading the data rate could be increased, allowing the transmission of more symbols before the channel changes significantly. The slower the mobile travels, the slower the fading rate and the lower the signalling rate required for adapting t
REFERENCES:
patent: 4462105 (1984-07-01), Wagner et al.
patent: 4495619 (1985-01-01), Acampora
patent: 4677625 (1987-06-01), Betts et al.
patent: 4780883 (1988-10-01), O'Connor et al.
patent: 4797898 (1989-01-01), Martinez
patent: 4852090 (1989-07-01), Borth
patent: 4888792 (1989-12-01), Yagi et al.
patent: 4899367 (1990-02-01), Sampei
patent: 4903324 (1990-02-01), Warnagiris
patent: 4937844 (1990-06-01), Kao
patent: 4945549 (1990-07-01), Simon et al.
patent: 4956851 (1990-09-01), Wolensky et al.
patent: 5054036 (1991-10-01), Brownlie et al.
patent: 5063571 (1991-11-01), Vancraeynest
patent: 5117423 (1992-05-01), Shepherd et al.
patent: 5123008 (1992-06-01), Beesley
patent: 5134635 (1992-07-01), Hong et al.
patent: 5150384 (1992-09-01), Cahill
patent: 5170413 (1992-12-01), Hess et al.
patent: 5210770 (1993-05-01), Rice
patent: 5222247 (1993-06-01), Breeden
patent: 5233629 (1993-08-01), Paik et al.
patent: 5263052 (1993-11-01), Borth et al.
patent: 5276686 (1994-01-01), Ito
patent: 5282222 (1994-01-01), Fattouche et al.
patent: 5289459 (1994-02-01), Browlie
patent: 5363408 (1994-11-01), Paik et al.
Proceedings of the 1988 IEEE Military Communications Conference, 23-26 Oct. 1988, San Diego, pp. 933-937.
IBM Technical Disclosure Bulletin, vol. 23, No. 2, Jul. 1980, pp. 641-643.
Wireless 90, Jul. 16-17, 1990, Marlborough Inn, Calgary, Alberta, Canada "Deploying Peronsal Communication Networks" by Raymond Steele, pp. 1-8.
British Telecommunications public limited company
Coles Edward L.
Nguyen Madeleine A-V
LandOfFree
QAM system in which the constellation is modified in accordance does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with QAM system in which the constellation is modified in accordance , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and QAM system in which the constellation is modified in accordance will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1619976