Method and a system for silence removal in a voice signal transported through a communication network

• US 5,870,397 A
• Filed: 08/06/1996
• Issued: 02/09/1999
• Est. Priority Date: 07/24/1995
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Pucci, Bernard, Chauffour, Pascal, Richter, Gerard, Duault, Maurice
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): RAO, SEEMA SRINIVAS
• Application Number:
  US08/695,280
• Time in Patent Office: 917 Days
• Field of Search: 370/386, 370/389, 370/433, 370/434, 370/435, 370/437, 370/442, 370/458, 370/459, 370/461, 370/465, 370/490, 370/498, 370/528, 370/468, 370/522, 704/219
• US Class Current: 370/435
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• CPC Class Codes: H04B 1/46 by voice-frequency signals; by pilot signals
• CPC Class Codes: H04L 2012/5616 Terminal equipment, e.g. codecs, synch.
• CPC Class Codes: H04L 2012/5647 Cell loss
• CPC Class Codes: H04L 2012/5652 Cell construction, e.g. including header, packetisation, depacketisation, assembly, reassembly
• CPC Class Codes: H04L 2012/5671 Support of voice
• CPC Class Codes: H04Q 11/0478 Provisions for broadband connections
• CPC Class Codes: H04Q 2213/13034 A/D conversion, code compression/expansion
• CPC Class Codes: H04Q 2213/13056 Routines, finite state machines
• CPC Class Codes: H04Q 2213/13166 Fault prevention
• CPC Class Codes: H04Q 2213/13201 Change-over of service during connection
• CPC Class Codes: H04Q 2213/13216 Code signals, frame structure
• CPC Class Codes: H04Q 2213/1329 Asynchronous transfer mode, ATM

Abstract

A method and an apparatus for removing the silence from the digitalized voice signals conveyed through packets or cells switching networks. The silence samples are neither packetized nor sent over the network but are regenerated at the output of the network. The silence samples generated are white noise samples, where the level is adapted to the background noise of the silence samples received at the input node of the network. For long periods of silence, the white noise level is periodically refreshed to be adapted to the last silence samples received at the input node of the network. The method provides also a control of packet or cell loss. The method uses are not control packets; in the later case, it can be used for ATM networks with AAL1. The method is implemented as a program executed in a Digital Signal Processor located on adapter cards dedicated to voice processing in the network access nodes.

Claims

1. A method for transporting a stream of packets between a transmitting side and receiving side through a communication network, said stream including voice packets corresponding to detected speech periods and silence packets corresponding to detected silence periods, characterized in that it comprises:

at the transmitting side, detecting the ends of speech periods, transmitting voice packets corresponding to the speech periods followed, for a first period of time after the end of each speech period, by silence packets, calculating following the end of a speech period, a white noise level corresponding to the background noise of at least one following silence packet and transmitting to the receiving side, a control packet including said white noise level,

at the receiving side, receiving the voice, silence and control packets, reading the white noise level in the control packet, and reconstituting said stream by interleaving between the voice packets received from the transmitting side, received white noise packets.

2. The method according to claim 1 characterized in that it comprises at the receiving side:

if no packet is received and if the last received packet is not a control packet, repeating in the packet stream reconstituted by the receiving side, the last received packet at least once.

3. The method according to claim 1 characterized in that it comprises at the receiving side:

if no packet is received and no end of speech is detected, repeating in the packet stream reconstituted by the receiving side, the last received packet at least once.

4. The method according to claim 2, characterized in that it comprises at the transmitting side,

starting a timer having a second period of time at the end of the first period,

when the timer is expired and if no voice packets are to be transmitted, calculating a new white noise level corresponding to the background noise of silence period and sending a new corresponding control packet which is used by the receiving side for generating refreshed white noise packets.

5. The method according to claim 3 characterized in that it comprises:

at the transmitting side;

starting a timer having a second period of time at the end of the first period,

when the timer is expired and if no voice packets are to be transmitted, sending a burst of silence packets and at the receiving side,

receiving the burst of silence packets and calculating a new white noise level which is used for generating refreshed white noise packets.

6. The method according to any one of claim 5, characterized in that it comprises:

calculating with a linear interpolation algorithm and for a third period of time, the progressive values of the next white noise packets to be generated.

7. A system for transporting a stream of packets between a transmitting side and a receiving side through a communication network, said stream including voice packets corresponding to speech periods and silence packets corresponding to silence periods, said system comprising:

a transmission system including

a voice activity detector for detecting voice periods and silence periods, control logic for transmitting voice packets representing voice periods and, for a first period of time following the end of voice packets, silence packets representing silence periods following the represented voice periods,

a background noise calculator for calculating, following the end of a voice period, a white noise level corresponding to the background noise of one or more of the silence packets representing the silence period following the voice period,

a control packet generator for generating control packets including the white noise level, and

a transmitter for transmitting voice packets, silence packets and control packets to a receiver system; and

a receiver system including;

receiver circuitry for receiving transmitted voice, silence and control packets, background noise logic for receiving white noise level values carried in received control packets and for generating white noise level packets, and signal reassembly logic for reconstituting voice activity detected at the transmission system by interleaving generated white noise packets with received voice packets.

8. For use in a communications network carrying a stream of packets representing voice activity, a transmission system comprising:

a voice activity detector for detecting voice periods and silence periods;

a packet generator for generating voice packets representing periods of detected voice and silence packets representing periods of detected silence;

control logic for transmitting voice packets and, for a first period of time following the end of voice packets, silence packets;

a background noise calculator for calculating following the end of a voice period, a white noise level corresponding to the background noise of one or more of the silence packets representing the silence period following the voice period;

a control packet generator for generating one or more control packets carrying the calculated white noise level; and

a transmitter for transmitting voice packets, silence packets and control packets into the communications network.

9. For use in a voice communications network, a method of generating a stream of packets representing voice activity, said method comprising the steps of:

detecting periods of speech and periods of silence;

generating voice packets representing periods of detected speech and silence packets representing periods of detected silence;

transmitting generated voice packets and, for a first period of time following the end of voice packets, generated silence packets;

calculating following the end of the voice packets, a white noise level corresponding to the background noise of one or more of the silence packets representing the period of silence following the period of voice activity;

generating one or more control packets carrying the calculated white noise level; and

transmitting voice packets, silence packets and control packets into the voice communication network.