Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-06-26
2001-03-06
Hunter, Daniel S. (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S067700, C455S575100
Reexamination Certificate
active
06198940
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile radiophone apparatus, and more particularly to a digital mobile radiophone apparatus including a highly efficient voice encoder in which an input analogue voice signal is quantized through an A/D conversion and features of the quantized voice signal are extracted to convert the signal to codes of a smaller data quantity.
2. Description of the Related Art
In a highly efficient voice-encoding technique for voice signals in a digital mobile radiophone apparatus, after an input signal such as a voice is quantized through an A/D conversion, the quantized signal is divided into fixed units along the time axis and a group of plural quantization samples is encoded together. For encoding, there are methods such as linear estimation analysis in which calculation is performed by using a parameter representing a feature in time of the voice signal as a coefficient for filtering (refer to “DIGITAL MOBILE RADIOPHONE SYSTEM STANDARD RCR-STD-27B”, p.515, issued by, a foundation, Denpa System Kaihatu Center, for instance).
By the way, the analogue voice signal input to the mobile radiophone apparatus is quantized through the A/D conversion and then input to the highly efficient voice encoder. But the amplitude data quantized through the A/D conversion are input to the highly efficient voice encoder as they are, in general.
FIG. 1
is a block diagram showing a conventional mobile radiophone apparatus
2
in a digital communication system, in respect of conversion an analogue voice signal input as a voltage amplitude to highly efficient voice codes and conversion of highly efficient voice codes to an analogue voice signal.
As shown in
FIG. 1
, an analogue voice input to a microphone
25
of the digital mobile radiophone apparatus
2
is input to an A/D converter
21
as a voltage amplitude, converted to quantized data representing the voltage amplitude in the A/D converter
21
, and then input to a highly efficient voice encoder
22
. The highly efficient voice encoder
22
extracts their features in time from the quantized data representing the voltage amplitude, performs highly efficient voice-encoding, and then sends out the encoded codes to a transmitter
28
as transmission voice codes. The transmission voice codes are modulated in the transmitter
28
and then transmitted through an antenna
29
to a base station.
On the other hand, modulated highly efficient voice codes received from the base station through the antenna
29
of the digital mobile radiophone apparatus
2
are demodulated in a receiver
27
and then input to a highly efficient voice decoder
23
. The highly efficient voice decoder
23
decodes the codes to quantized data representing a voltage amplitude and then sends out them to a D/A converter
24
. The data are converted to the voltage amplitude in the D/A converter
24
and then output through a speaker
26
as an analogue voice.
As described above, in the conventional highly efficient voice-encoding method in the mobile radiophone apparatus, because the quantized data A/D-converted are input to the highly efficient voice encoder as they are, the amplitude of the voice signal is small. In the case of a little variation of the quantization samples, there is such problem that faithfulness to the original input voice signal decreases upon decoding the voice-encoded data. This is because calculation error upon performing highly efficient voice-encoding is large owing to a small quantity of information included by the input voice signal or the like in the case of a little variation of the samples.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a mobile radiophone apparatus in which a voice can be decoded more faithfully to the original voice upon decoding with a calculation error upon performing highly efficient voice-encoding even in case of a small amplitude of an input voice signal in a digital mobile radiophone apparatus.
For attaining the above object, according to the present invention, a mobile radiophone apparatus including an A/D converter for outputting an input analogue voice signal as quantized data and a highly efficient voice encoder for extracting features of the quantized data output at said A/D converter and converting the data to codes of a smaller data quantity by a fixed time unit to output the codes, is characterized by comprising a transmitting system in which the number of quantization bits in said A/D converter is established to be larger than the number of quantization bits possible to be input to said highly efficient voice encoder and a converter is provided for converting the number of bits of the quantized data output at said A/D converter to the number of quantization bits possible to be input to said highly efficient voice encoder as an amplitude value as large as possible by the fixed time unit to output the converted data to said highly efficient voice encoder and the conversion parameter for the quantized data in said converter is transmitted in addition to the codes output at said highly efficient voice encoder, and a receiving system in which codes output at said highly efficient voice encoder are received and then decoded to quantized data in a highly efficient voice decoder and then said quantized data are converted to the number of quantization bits output at said A/D converter on the basis of said conversion parameter and then converted to an analogue signal in a D/A converter to be output as a voice.
As described above, because the conversion method of the number of quantization bits is changed by unit time in accordance with the amplitude of the quantized data and the quantized data are input to the highly efficient voice encoder by unit time as large values as possible, the calculation error can be reduced upon highly efficient voice-encoding.
Besides, in the above construction of the mobile radiophone apparatus, if the above conversion parameter employs the shift quantity of the number of bits obtained by the manner that the quantized data output at the above A/D converter are referred by unit time and the number of the effective figures of quantization bits possible to be input to the above highly efficient voice encoder is subtracted from the maximum number of bits in the unit time, the calculation with the conversion parameter becomes relatively easy and it becomes possible easily to carry out the present invention because the conversion can easily be performed since it is merely bit-shifting based on the shift quantity.
REFERENCES:
patent: 3789392 (1974-01-01), Candiani
patent: 4852090 (1989-07-01), Borth
patent: 5005150 (1991-04-01), Dent et al.
patent: 5066952 (1991-11-01), Koerner
patent: 5353374 (1994-10-01), Wilson et al.
patent: 5790941 (1998-08-01), Peponides
patent: 54-33013 (1979-03-01), None
patent: 60-54538 (1985-03-01), None
patent: 1-248711 (1989-10-01), None
Hunter Daniel S.
NEC Corporation
Nguyen Thuan T.
Young & Thompson
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