Communications: electrical – Audible indication – Percussion-type sound producer
Patent
1984-06-13
1986-03-11
Hix, L. T.
Communications: electrical
Audible indication
Percussion-type sound producer
358 13, 358 23, H04N 7133
Patent
active
045757097
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to signal encoding-decoding apparatus, provided in a communications system, and comprising an encoder for encoding information signals prior to transmission and a decoder for decoding the received transmissions. In particular, but not exclusively, the invention relates to appartus used to encode and decode colour television signals broadcast via a direct broadcast by satellite (DBS) service.
A characteristic feature of television DBS systems is the very low signal levels involved both due to the power limitations placed on the satellite transporter and due to the relatively small size of the receiving antenna (particularly in domestic situations). As a result, the signal to noise, (SNR) ratio is generally high leading to poor picture quality at the receiver.
It is an object of the present invention to provide apparatus for encoding and decoding television signals, and other information signals in a manner reducing the effect of noise on picture quality.
SUMMARY OF THE INVENTION
Accordingly, in one aspect the present invention, provides encoding-decoding apparatus in which the encoder comprises: sequentially and to represent each sample by the combination of a baselevel signal BLS indicative of a coarse level quantisation of the sample, and a difference signal DS providing a high resolution measurement of the difference between the actual sampled signal level and the quantisation level represented by the BLS signal, and DS signals into a composite modulation output that is divided into a succession of modulation time intervals MTI and includes, at least when considered over a number of MTI, both coarsely-quantised BLS-related components, hereafter referred to as Q symbols, and high-resolution DS-related components hereafter referred to as A symbols, each symbol being mono-valued and occupying one MTI, output to modulate said carrier signal respectively with a coarsely quantised first modulation indicative of said BLS signals and with a high resolution second modulation indicative of said DS signals; demodulate said first and second modulations to produce a composite demodulated output with Q symbol and A symbol components indicative of the corresponding symbols of the encoder composite modulation output, demodulated output and to provide therefrom signals corresponding to the BLS and DS signals of the encoder; and provided by the decoder signal-organising means to reproduce the information-signal samples in their original sequence.
It can be seen that the encoding-decoding apparatus of the invention combines the advantages of digital and analog transmission by dividing each sample into a coarsely quantised BLS signal and a high resolution DS signal.
The advantage that accrue due to digital transmission are: limited impairment due to noise; the straightforward implementation of time division multiplexing; and the possibility of encryption which may be required for a subscriber type of service. The transmission of an analog component ensures bandwidth efficiency and a demodulated signal to noise ratio that improves as the transmission signal to noise ratio is increased.
Regarding the signal to noise ratio of the apparatus, assuming no transmission errors, the BLS components of the information signals are faithfully reproduced noise free. As for the DS components which produce the fine detail information, although these components are not received noise free, the effects of this noise is limited to low level.
DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a generalised block diagram showing the main functional blocks of encoding - decoding apparatus embodying the invention;
FIG. 2 is an amplitude-time diagram for a waveform W showing quantisation levels used to encode samples of the waveform;
FIG. 3 is a modulation diagram illustrating the various possible phase states of a carrier phase-modulated by one form of encoder of the apparatus;
FIG. 4 is a modulation
REFERENCES:
patent: 3277462 (1966-10-01), Sekimoto
patent: 3723879 (1973-03-01), Kaul et al.
patent: 4023199 (1977-05-01), Netravali et al.
General Electric Company
Gray David M.
Hix L. T,.
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