Radio communication system with controlled voice code switching

• US 5,513,211 A
• Filed: 05/25/1994
• Issued: 04/30/1996
• Est. Priority Date: 09/02/1991
• Status: Expired due to Term

• Current Assignee: Nippon Telegraph and Telephone Corporation, NTT Mobile Communications Network Inc. (Nippon Telegraph and Telephone Corporation)
• Original Assignee: Nippon Telegraph and Telephone Corporation, NTT Mobile Communications Network Inc. (Nippon Telegraph and Telephone Corporation)
• Inventors: Yamamoto, Kouji, Yabusaki, Masami, Uebayashi, Shinji
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): PHAN, HAI
• Application Number:
  US08/249,077
• Time in Patent Office: 706 Days
• Field of Search: 379/58, 379/59, 379/90, 379/258, 379/230, 455/53.1, 455/54.1, 455/38.1, 455/14, 375/377, 375/242, 375/243, 375/219
• US Class Current: 375/219
• CPC Class Codes: H04L 5/1415 using control lines

Abstract

A radio communication system operates between two radio terminals, and/or between a radio terminal and a fixed terminal through a network. In the present disclosure, the switching of codec-release mode and codec mode in the network is controlled by using a specific control line which is installed in addition to a speech line. Thus, when a radio terminal communicates with another radio terminal through a network, no codec is used in the network, and so, speech distortion and signal delay are not deteriorated due to signal conversion by using a codec.

Claims

1. A radio communication system comprising;

a plurality of radio terminals which operate with a first voice coding system,

a network coupled with said plurality of radio terminals through a plurality of radio links, said network having a plurality of base stations for coupling the network with said plurality of radio terminals through said plurality of radio links, a plurality of exchange stations, each having an exchange switch coupled with a corresponding base station of said plurality of base stations and also with fixed terminals of a fixed network operating with a second voice coding system, for exchanging calls between terminals, and a plurality of codecs coupled between said plurality of base stations and said fixed network for converting voice coding systems between said first voice coding system and said second voice coding system, each of said voice coding systems having voice carrying lines that carry voice signals represented by a plurality of voice-representative digital bits,

said network including a plurality of selectors for switching respective codecs between a codec release mode and a codec mode, a plurality of control circuits for controlling the switching by said selectors, and a control line, separate from voice carrying lines of said voice coding systems, coupled between said control circuits in different exchange stations for control of said control circuits during operation on said voice carrying lines, such that said selectors are operative to select a codec release mode when a radio terminal communicates with another radio terminal through said network, and to select a codec mode for conversion between said first voice coding system and said second voice coding system when a radio terminal communicates with a fixed terminal/such that none of the digital bits on the voice carrying lines is used for switching between codec release mode and codec mode, and the digital bit resolution on said voice carrying lines is retained without deterioration by the switching.

2. A radio communication system according to claim 1, wherein said selectors are implemented by said exchange switches.

3. A radio communication system according to claim 1, wherein said control circuits are operative to control said codecs such that when two radio terminals communicate with each other, a codec in an originating side is first in codec mode, and switched to codec release mode after a response for ringing by a destination terminal is acknowledged, and a codec in a destination side is in codec release mode when a destination terminal is recognized by said control circuits as a radio terminal.