Apparatus for noise removal during the silence periods in the discontinuous transmission of speech signals to a mobile unit

• US 5,553,192 A
• Filed: 10/12/1993
• Issued: 09/03/1996
• Est. Priority Date: 10/12/1992
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Hayata, Toshihiro
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): Sartori, Michael A.
• Application Number:
  US08/133,864
• Time in Patent Office: 1,057 Days
• Field of Search: 395/2, 395/2.1, 395/2.17, 395/2.23, 395/2.24, 395/2.28, 395/2.29, 395/2.35, 395/2.37, 395/2.42, 395/2.67, 395/2.71, 395/273, 381/41, 381/46, 381/47, 381/51
• US Class Current: 704/228
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10

Abstract

The disclosure is to eliminate discomforting background noise regenerated at a receive side (viz., a base station) in a mobile radio communications system wherein discontinuous transmission (DTX) is utilized. When speech pause is detected at the receive side, synthesis filter coefficients are produced using a background noise code which has been transmitted from a mobile unit. Subsequently, a Q value of the synthesis filter is measured using the above-mentioned synthesis filter coefficients. If the Q value is larger than a threshold level, each of the filter coefficients is lowered by a predetermined value. Thus, the regenerated discomforting background noise can effectively be reduced.

Claims

1. An arrangement for demodulating speech code sequences discontinuously transmitted from a mobile unit and for demodulating background noise code sequences transmitted from said mobile unit while said speech code sequences pause, said arrangement receiving speech pause/start indicators, said arrangement comprising:

first means for generating synthesis filter coefficients using either of said speech code sequence or said background noise code sequence;

second means for synthesizing either of speech signals or background noise signals using said synthesis filter coefficients;

third means for discriminating speech pause and speech start using said speech pause/start indicators;

fourth means for estimating Q value of said second means using said synthesis filter coefficients and generating an estimated Q value if said third means discriminates said speech pause; and

fifth means for generating reduced synthesis filter coefficients by reducing said synthesis filter coefficients if said estimated Q value is larger than a threshold level, said fifth means supplying said second means with said reduced synthesis filter coefficients.

2. An arrangement as claimed in claim 1, further including a comparator which is coupled to compare said estimated Q value with said threshold level, said comparator issuing a control signal indicative of a result of comparison, said fifth means being responsive to said control signal.

3. An arrangement as claimed in claim 1, further including a memory for storing said reduced synthesis filter coefficients, said reduced synthesis filter coefficients stored in said memory being applied to said second means at a predetermined time interval until being updated.