Pulse or digital communications – Receivers
Patent
1997-03-18
2000-03-07
Ghebretinsae, Temesghen
Pulse or digital communications
Receivers
341139, H04L 2706
Patent
active
060350016
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and to an arrange- ment for extending the dynamic range of a signal receiver in a digital signal transmission system, i.e. for enhancing the ability of the receiver to reproduce correctly signals of different strengths.
BACKGROUND ART
In the transmission of signals between a transmitter and a receiver, such as voice signals, it is necessary for the receiver to have a certain dynamic range in order for the signals to be correctly reproduced. Signal strengths can vary markedly when received by the receiver, and a wide dynamic range contributes towards better signal reproduction in the receiver. For instance, U.S. Pat. No. 5,276,685 teaches a method of adapting the strength of an incoming signal to the receiver to the ability of the receiver to receive the signal, so-called automatic gain control. When the strength of the signal received by the receiver is greater than an upper limit value of the dynamic range of the receiver, the signal is attenuated. When the strength of the signal received by the receiver is beneath a lower limit value of the dynamic range of the receiver, the signal is amplified. One drawback with the method taught by the U.S. patent resides in the requirement of such complicated equipment in addition to the equipment normally available in the receiver. This additional equipment adds to the cost. Problems also occur when the strength of the received signal varies very abruptly. U.S. Pat. No. 4,893,316 teaches another method of extending the dynamic range. The patent describes dithering. By dithering is meant briefly the application of known noise to a signal which is too weak to be detected. The signal superimposes the noise. The signal can be detected by amplifying the total signal and filtering-out the known noise. The drawback with dithering lies in the requirement of components as dither generators and de-generators, which also add to the cost. The dynamic range can also be extended by extending the number of quantizing levels and using a 13-bit A/D-converter instead of a 12-bit converter. An increase in the number of bits results in more quantizing levels, which enables an extended dynamic range to be reproduced correctly. However, A/D-converters that have such extended properties also add to the costs and may be difficult to achieve.
DISCLOSURE OF THE INVENTION
A signal receiver of a digital system receives an analog signal after the signal has first passed through a certain analog signal processing stage. The signal is then digitalized so as to enable the digital information in the signal to be extracted. The problem relating to the dynamic range is solved by allowing an extended dynamic range over and above a normal limit value during the analog signal processing stage. The amplitude of the signal is then restricted in the digitalizing process. This digitalized signal contains amplitude information that would have been lost if the signal had already been restricted in the analog signal processing stage. The present invention also relates to an arrangement for implementing the aforesaid method.
A prime object of the present invention is to obtain amplitude information from the signal even when the signal is stronger than said limit value.
Another object is to enhance the transmission of information when the transmitted signal is subjected to serious disturbances and interference.
A further object is to improve signal processing in a receiver-mounted equalizer.
The aforesaid analog signal processing stage involves restricting the amplitude of the received signal in accordance with the extended dynamic range and filtering the signal through a low-pass filter. When signal transmission takes place on a high-carrier frequency, the signal processing stage is preceded by mixing down a received high-frequency signal with a synthesizing frequency so as to obtain an intermediate frequency signal. The low-pass filtered signal is applied to an analog/digital converter, which is overextended by the low-pass filtered signal. The si
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Eklund Johan
Melander Patrik
Burd Kevin M
Ghebretinsae Temesghen
Telefonaktiebolaget LM Ericsson
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