Economical synchronization system for asynchronous transfer mode mobile communication network without dependence on external system

• US 6,477,183 B1
• Filed: 11/10/1998
• Issued: 11/05/2002
• Est. Priority Date: 11/11/1997
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Yamamoto, Masatoshi
• Primary Examiner(s): Ngo, Ricky
• Assistant Examiner(s): TRAN, PHUC H
• Application Number:
  US09/189,635
• Time in Patent Office: 1,456 Days
• Field of Search: 370/324, 370/328, 370/331, 370/335, 370/336, 370/338, 370/350, 370/395, 370/503, 370/508, 370/252, 370/519, 370/329, 370/395.1, 370/340, 455/13.2, 455/502, 455/503, 455/524
• US Class Current: 370/508
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 2012/5674 Synchronisation, timing recovery or alignment

Abstract

An asynchronous transfer mode network includes a high-level station and a mobile station in a boundary zone between service cells of wireless base stations connected to the high-level station through asynchronous transfer mode channels, wherein the high level station transmits a control message through the asynchronous transfer mode channels and the wireless base stations to the mobile station and receives response messages from the mobile station through the wireless base stations and the asynchronous transfer mode channels, and determines a difference between transmission time lags along the asynchronous transfer mode channels so as to make built-in clocks provided for the wireless base stations synchronous with one another.

Claims

1. An asynchronous transfer mode network comprising:

a plurality of low-level stations communicable with at least one mobile station in a boundary zone between service cells of said plurality of low-level stations;

a high-level station communicable with said plurality of low-level stations through respective asynchronous transfer mode channels; and

a synchronization system including

a plurality of clocks each respectively associated with a corresponding one of said high-level station and said low-level stations, and each clock independently indicating a current time,

a message transmitting unit associated with said high-level station and concurrently transmitting a control message from said high-level station to said plurality of low-level stations through said asynchronous transfer mode channels,

a plurality of message relaying units each respectively associated with a corresponding one of said plurality of low-level stations, for replaying said control message from one of said plurality of low-level stations of said at least one mobile station, each message relaying unit respectively receiving a first response message respectively supplied from said at least one mobile station to said plurality of low-level stations and respectively transmitting a second response message from said plurality of low-level stations through said asynchronous transfer mode channels to said high-level station,

for each mobile station of said at least one mobile station, a first message generator associated with the corresponding mobile station and respectively transmitting said first response messages to said plurality of message relaying units after said at least one mobile station receives said control message,

a plurality of second message generators each respectively connected to a corresponding one of said plurality of message relaying units and respectively producing said second response message, each second response message representative of the current time indicated by the clock associated with the corresponding one of said plurality of low-level stations and a first message exchange period between said corresponding one of said plurality of low-level stations and said at least one mobile station, and

a timing regulator connected to said message transmitting unit and determining a difference between transmitting time lags along said asynchronous transfer mode channels on the basis of said second response messages and a plurality of second message exchange periods between said high-level station and said at least one mobile station through said low-level stations for supplying a piece of control information representative of said difference between said transmitting time lags to said plurality of low-level stations.

2. The asynchronous transfer mode network as set forth in claim 1, in which each of said first message exchange periods is represented by a first lapse of time between the arrival time of said control message at said corresponding one of said plurality of low-level stations and the arrival time of the respective first response message and each of said plurality of second message exchange periods is represented by a second lapse of time between the time of transmission of said control message and the time of arrival of a respective one of said plurality of second response messages at said high-level station through one of said asynchronous transfer mode channels.

3. The asynchronous transfer mode network as set forth in claim 2, in which a difference in arrival times of said plurality of first response messages respectively at said plurality of low-level stations is corrected in a manner as if said at least one mobile station is equally spaced from said plurality of low-level stations.

4. The asynchronous transfer mode network as set forth in claim 1, in which said difference between said transmission time lags include a first time difference arising from a signal transmission from said high-level station to said plurality of low-level stations respectively along said asynchronous transfer mode channels and a second difference arising from respective signal transmissions from said plurality of low-level stations to said high-level station.

5. The asynchronous transfer mode network as set forth in claim 4, in which said first time difference is determined on the basis of a difference between said first message exchange periods corresponding to said plurality of low-level stations, and said second time difference is determined on the basis of a difference between said plurality of second message exchange periods and said first time difference.

6. The asynchronous transfer mode network as set forth in claim 5, in which each of said first message exchange periods is represented by a first lapse of time between arrival of said control message at said corresponding one of said plurality of low-level stations and arrival of said respective first response message, and each of said plurality of second message exchange periods is represented by a second lapse of time between the transmission of said control message and arrival of a respective one of said plurality of second response messages at said high-level station through said asynchronous transfer mode channels.

7. The asynchronous transfer mode network as set forth in claim 6, in which said first time difference is determined through a first subtraction between the respective first lapses of time.

8. The asynchronous transfer mode network as set forth in claim 7, in which said second time difference is determined through a second subtraction between the respective second lapses of time and a third subtraction between the difference of said first subtraction and the difference of said second subtraction.

9. The asynchronous transfer mode network as set forth in claim 1, in which said plurality of low-level stations communicate with said at least one mobile station by using a time division multiple access technology.

10. A synchronizing system comprising:

a high-level station including

a message transmission unit,

a measuring unit for measuring a response time period, and

a built-in clock;

a plurality of wireless base stations each including

a respective message relaying unit,

a respective measuring unit for measuring a respective response time period, and

a respective built-in clock;

a mobile station including a message response unit; and

an asynchronous transfer mode network for communication between at least said high-level station and said plurality of wireless base stations,

wherein when said mobile station is communicable with said plurality of wireless base stations, transmission time periods are measured between said high-level station and said plurality of wireless base stations, and a difference between the measured transmission time periods is accounted for, if necessary.

15. The synchronizing system according to claim 10, wherein the difference in transmission time periods is resolved in the plurality of base stations.

16. The synchronizing system according to claim 15, wherein the difference in transmission time periods is resolved by resetting at least one of the respective built-in clocks in the plurality of base stations.

17. The synchronizing system according to claim 10, wherein the base stations become synchronized with each other upon accounting for the transmission time period difference.

18. The synchronizing system according to claim 10, wherein the measured transmission time period between said high-level station and each of said plurality of wireless base stations encompasses a transmission time period between said mobile station and the respective wireless base station.

19. The synchronizing system according to claim 10, wherein the measured transmission time period between said high-level station and each of said plurality of wireless base stations includes a transmission time period between said mobile station and the respective wireless base station as well as a round trip transmission time between said respective wireless base station and said high-level station.

11. A method of synchronizing base stations in an ATM mobile communication network when a mobile station is in a boundary condition between adjacent base stations, comprising:

sending a first control signal from a high-level station to a plurality of base stations;

relaying the first control signal to the mobile station from one of the plurality of base stations;

after receiving the control signal, transmitting a first response message from the mobile station to the plurality of base stations;

at each base station, sending a second response message to the high-level station after receiving the response message;

at the high-level station, calculating a time lag of each base station based on the second response messages received from each of the base stations and the corresponding arrival times thereof; and

transmitting, from the high-level station, a second control message to the plurality of base stations to synchronize the base stations.

12. The method of synchronizing base stations according to claim 11, wherein the first control signal is relayed to the mobile station from a base station among the plurality of base stations which first receives the first control signal from the high-level station.

13. The method of synchronizing base stations according to claim 11, wherein each second response message sent to the high-level station from a corresponding base station contains information of the arrival time of the first response message from the mobile station at the respective base station, and the lapse of time between the time of arrival of the first control message from the high-level station at the respective base station and the time of arrival of the first response message from the mobile station.

14. The method of synchronizing base stations according to claim 11, wherein the time lag of each base station is calculated by determining a first difference between the arrival times of the second response messages in the high-level station, and a second difference between the lapses of time contained in the received second response messages, and then subtracting the second difference from the first difference.