Frame synchronization system among multiple radio base stations for TDMA digital mobile communications system

• US 5,293,380 A
• Filed: 12/27/1990
• Issued: 03/08/1994
• Est. Priority Date: 12/27/1989
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kondo, Seiji
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): MARCELO, MELVIN C
• Application Number:
  US07/634,894
• Time in Patent Office: 1,167 Days
• Field of Search: 370/95.1, 370/95.3, 370/108, 370/107, 370/106, 370/105.1, 370/17, 370/100.1, 370/104.1, 370/105.4, 370/105.5, 455/33, 455/13.2, 455/33.1, 455/33.2, 455/33.3, 455/33.4, 455/56.1, 455/54.1, 379/59, 379/60, 379/63
• US Class Current: 370/337
• CPC Class Codes: H04B 7/2684 Synchronisation of a mobile station with more than one base station
• CPC Class Codes: H04B 7/2696 Over the air autonomous synchronisation, e.g. by monitoring network activity H04B7/2693 takes precedence
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation

Abstract

A TDMA digital mobile communications system prevents TDMA frame synchronization from being asynchronous among radio base stations when a communication held by a mobile station is handed over from one service area to another. A control station sends a reset pulse for TDMA frame synchronization to the radio base stations each being situated in a particular service area over communications cables. In response, the radio base stations each generates a TDMA frame. The control station has a synchronous signal generator for generating the reset pulse while each radio base station has a time delay adjustment unit for adjusting the time delay of the reset pulse. The synchronous signal generator and the time delay adjustment units of the individual radio base stations perform measurement and setting such that a reset signal has the same time delay between the control station and all of the radio base stations. Hence, regarding a TDMA signal which the mobile station receives, TDMA frame synchronization is immediately set up at the time of hand-over and thereby prevents a voice signal from being interrupted.

Claims

1. A TDMA digital mobile communications system comprising a control station, a plurality of radio base stations each being located in respective one of service areas which are governed by said control station and each comprising a TDMA frame generator, and a plurality of mobile stations each being movable in said service areas while interchanging digital signals with said radio base stations located in said service areas by using a given time slot, said system further comprising:

synchronous signal generating means placed in or in the vicinity of said control station for transmitting a reset pulse to said base stations for resetting their TDMA frame generators;

delaying means for delaying said transmitted reset pulse by a predetermined period of time, and inputting said delayed reset pulse to associated one of said radio base stations; and

means for applying said reset pulse inputted from said delaying means to associated one of said TDMA frame generators;

wherein a time delay assigned to each of said delaying means varies with a distance between said radio base station and said control station and is selected such that said reset pulse delayed by all of said radio base stations is inputted to all of said radio base stations at the same time; and

wherein said delaying means comprises returning means for receiving said reset pulse and returning said reset pulse as a return pulse to said synchronous signal generating means, and wherein said synchronous signal generating means comprises time delay determining means for detecting a first time when said return pulse is received and, on the basis of a period of time defined by a second time when said reset pulse is transmitted and said first time when said reset pulse is received, determining a time delay of said reset pulse.

2. A TDMA digital mobile communications system comprising a control station, a plurality of radio base stations each being located in respective one of service areas which are governed by said control station and each comprising a TDMA frame generator, and a plurality of mobile stations each being movable in said service areas while interchanging digital signals with said radio base stations located in said service areas by using a given time slot, said system further comprising:

synchronous signal generating means placed in or in the vicinity of said control station for transmitting a reset pulse to said base stations for resetting their TDMA frame generators;

delaying means for delaying said transmitted reset pulse by a predetermined period of time, and inputting said delayed reset pulse to associated one of said radio base stations; and

means for applying said reset pulse inputted from said delaying means to associated one of said TDMA frame generators; and

wherein said synchronous signal generating means comprises;

signal generator means for generating a clock;

first counter means for dividing a frequency of said clock to generate said reset pulse having a period of one TDMA frame and transmitting said reset pulse to said delaying means;

second counter means reset by said reset pulse fed from said first counter means for measuring a period of time until a return pulse of said reset pulse transmitted from said delaying means arrives by using said clock; and

latch circuit means for latching said period of time measured by said second counter means.

3. A TDMA digital mobile communications system comprising a control station, a plurality of radio base stations each being located in respective one of service areas which are governed by said control station and each comprising a TDMA frame generator, and a plurality of mobile stations each being movable in said service areas while interchanging digital signals with said radio base stations located in said service areas by using a given time slot, said system further comprising:

synchronous signal generating means placed in or in the vicinity of said control station for transmitting a reset pulse to said base stations for resetting their TDMA frame generators;

delaying means for delaying said transmitted reset pulse by a predetermined period of time, and inputting said delayed reset pulse to associated one of said radio base stations; and

means for applying said reset pulse inputted from said delaying means to associated one of said TDMA frame generators;

wherein a time delay assigned to each of said delaying means varies with a distance between said radio base station and said control station and is selected such that said reset pulse delayed by all of said radio base stations is inputted to all of said radio base stations at the same time; and

wherein said delaying means comprises;

latch circuit means to which a set time delay is written via a set input terminal thereof;

flip-flop means having a set input terminal for receiving said reset pulse;

signal generator means for generating a clock;

counter means reset by an output of said flip-flop means for counting time by using said clock signal; and

comparator means for comparing the output of said latch circuit means and the output of said counter means and, when said outputs coincide, outputting a reset pulse while feeding said reset pulse to said flip-flop means as a reset pulse and to said radio base station as an output.

4. A TDMA digital mobile radio communications system comprising:

a control station;

synchronous signal generator means situated near or in said control station;

a first and a second radio base station; and

a first and a second time delay units situated near or in said first and second radio base stations, respectively;

said synchronous signal generator comprising;

signal generator means for generating a clock;

first counter means for dividing a frequency of said clock signal to generate a reset pulse having a period of one TDMA frame;

second counter means reset by said reset pulse outputted by said first counter means for measuring a period of time from said resetting to arrival of a return pulse of said reset pulse by using said clock; and

latch circuit means for latching said period of time measured by said second counter means;

said first and second time delay units each comprising;

latch circuit means to which a set time delay is written via a set input terminal thereof;

flip-flop means having a set input terminal for receiving a pulse signal;

signal generator means for generating a clock;

third counter means reset by an output of said flip-flop means for counting time by using said clock; and

comparator means for comparing the output of said latch circuit means and the output of said third counter means and, when said outputs coincide, outputting a delayed pulse signal by delaying said pulse signal by said set time delay and feeding said delayed pulse signal to said flip-flop means as a reset pulse and to said radio base station as an output pulse.

5. A system as claimed in claim 4, wherein said reset pulse generated by said synchronous signal generator means is applied to said set input terminal of said flip-flop means over a communications cable, said output pulse produced by delaying said reset pulse being applied to said synchronous signal generator means over said communications cable.

6. A method of synchronizing Time Division Multiple Access (TDMA) frames transmitted to a mobile station from a plurality of base stations which are connected to a control station, comprising the steps of:

transmitting a first reset pulse from said control station to said base stations;

delaying the transmitted first reset pulse at said base stations by predetermined periods of time, respectively; and

adjusting the transmission timings of said TDMA frames in response to the delayed reset pulses, respectively, to synchronize the TDMA frames;

further comprising the steps of;

transmitting a second reset pulse from said control station to said base stations;

returning the transmitted second reset pulse from respective base stations to said control station;

responsive to the returned second reset pulses, calculating delay times for which said second reset pulse propagates between said control station and said base stations, respectively, to produce measured time periods; and

supplying said measured time periods to said base stations, respectively, as said predetermined periods of time.