Mobile station operating in an analog mode and for subsequent handoff to another system

• US 5,509,035 A
• Filed: 01/31/1995
• Issued: 04/16/1996
• Est. Priority Date: 04/14/1993
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Teidemann, Edward G. Jr., Holcman, Alejandro R.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Le, Amanda T.
• Application Number:
  US08/383,555
• Time in Patent Office: 441 Days
• Field of Search: 375/200, 375/205, 375/208, 375/354, 375/355, 375/356, 375/357, 375/358, 375/362, 375/367, 370/103, 370/105, 370/107, 370/108, 455/33.2, 455/49.1, 455/51.1, 455/54.1, 455/54.2, 455/56.1, 379/58-60
• US Class Current: 375/356
• CPC Class Codes: H04B 1/70758 Multimode search, i.e. using multiple search strategies
• CPC Class Codes: H04B 7/2681 Synchronisation of a mobile station with one base station
• 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 7/043 Pseudo-noise [PN] codes variable during transmission synchronisation of spread spectrum receivers H04B1/69
• CPC Class Codes: H04L 7/08 the synchronisation signals recurring cyclically
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time
• CPC Class Codes: H04W 56/0075 based on arrival time vs. expected arrival time

Abstract

A method of mobile station synchronization to a system time, wherein the time alignment is attained while the mobile station operates in analog mode. The mobile stations transmits a periodic signal, each period of which has a leading edge. The base station detects the leading edge of the periodic signal and compares it to an indication of system time. The base station generates an error message for the mobile station indicating an update to the phase of the periodic signal. When the mobile station and the base station are time aligned, the base station may send a message indicating the absolute time at some future leading edge of the periodic signal thereby eliminating ambiguities of time due to the finite time required to receive the message.

Claims

1. In a communication system including a mobile station and a base station, a method of time aligning a mobile station to a predetermined system time provided by a base station comprising the steps of:

providing by said mobile station during periodic intervals a periodic timing signal in a first direction over a communication channel, said periodic intervals being of a duration related to a digital mode modulation period of said communication system, each period of said periodic timing signal having a leading edge;

detecting at said base station one of the leading edges;

providing at said base station a series of periodic indications of said predetermined system time;

comparing in time one of said leading edges to one of said periodic indications;

generating from the comparison an error signal;

imparting to said mobile station by said base station, in a second direction over said communication channel, an indication of an error corresponding to said error signal; and

delaying at said mobile station a next leading edge of said periodic timing signal in response to said indication of an error corresponding to said error signal.

2. The method of claim 1 further comprising the step of informing said mobile station by said base station of an absolute time of day corresponding to the leading edge of said periodic timing signal occurring at a future time.

3. The method of claim 1 wherein said step of delaying includes the step of adjusting a timing device within said mobile station in response to said indication of an error corresponding to said error signal.

4. The method of claim 3 further including the step of switching said mobile station from operation in an analog mode to operation in a digital mode upon said mobile station timing device becoming aligned with said predetermined system time.

5. The method of claim 1 further including the step of providing by said mobile station, during selected intervals between each of the leading edges of said periodic timing signal, a data packet to said base station in said first direction over said communication channel.

6. A time-alignment system for synchronizing timing within a mobile station to a predetermined system time provided by a base station, said time-alignment system comprising:

a mobile station transmitter for providing during periodic intervals a periodic signal in a first direction over a communication channel, said periodic intervals being of a duration related to a system digital mode modulation period;

a base station receiver for detecting at said base station a beginning of a first period within said periodic signal;

a timing generator for providing at said base station a series of periodic indications of said predetermined system time;

a comparator for comparing in time said beginning of said first period to one of said periodic indications, said comparator generating from the comparison an error signal;

a base station transmitter for conveying to said mobile station by said base station, in a second direction over said communication channel, an indication of an error corresponding to said error signal; and

a timing adjustment circuit at said mobile station for adjusting timing of said mobile station transmitter in response to said indication of an error corresponding to said error signal, thereby synchronizing timing of a digital modulation sequence used in said mobile station to said predetermined system time.

7. The system of claim 6 wherein said base station transmitter operates to adjust timing of said beginning of said first period of said periodic signal in order to convey absolute time of day information to said mobile station.

8. The system of claim 6 wherein said timing adjustment circuit includes an interval timer, said interval timer being incremented in response to said indication of an error signal.

9. The system of claim 6 further including a mobile station controller disposed to switch said mobile station from operation in an analog mode to operation in a digital mode upon said mobile station transmitter becoming synchronized to said predetermined system time.

10. In a communication system including a mobile station and a base station, a time-alignment system for synchronizing timing within a mobile station to a predetermined system time provided by a base station, said mobile station being operative in an analog mode and in a digital mode, said time-alignment system comprising:

a mobile station transmitter for providing during periodic intervals by said mobile station a periodic timing signal during operation of said mobile station in said analog mode, said periodic intervals each being of a duration related to a period of an encoding sequence of said communication system;

a base station receiver for detecting at said base station a beginning of a first period within said periodic timing signal;

a timing generator for providing at said base station a series of periodic indications of said predetermined system time;

a comparator for comparing in time said beginning of said first period to one of said periodic indications, said comparator generating from the comparison an error signal;

a base station transmitter for imparting to said mobile station an indication of an error corresponding to said error signal; and

a timing adjustment circuit for delaying transmission by said mobile station transmitter a next period of said periodic timing signal in response to said indication of an error corresponding to said error signal in order to synchronize said digital mode operation of said mobile station to said predetermined system time.

11. The system of claim 10 further comprising means for informing said mobile station by said base station of an absolute time of day corresponding to the occurrence of said beginning of said first period of said periodic timing signal.

12. The system of claim 10 wherein said timing adjustment circuit operates to adjust a timing device within said mobile station in response to said indication of an error corresponding to said error signal, said timing device being disposed to provide timing information during operation in said digital mode.

13. The system of claim 10 further including a mobile station controller for switching said mobile station from operation in said analog mode to operation in said digital mode upon said mobile station becoming synchronized to said predetermined system time.

14. The system of claim 10 wherein said mobile station transmitter operates to provide, during selected intervals between each period of said periodic timing signal, analog data to said base station.

15. A method of time aligning a mobile station to a predetermined system time provided by a base station, said mobile station being disposed to operate in analog and digital modes, comprising the steps of:

providing during periodic intervals by said mobile station a periodic timing signal during operation of said mobile station in said analog mode, said periodic intervals being of a duration related to a mobile station digital mode modulation period, each period of said periodic timing signal having a leading edge;

detecting at said base station one of the leading edges;

providing at said base station a series of periodic indications of said predetermined system time;

comparing in time one of said leading edges to one of said periodic indications;

generating from the comparison an error signal;

imparting to said mobile station by said base station an indication of an error corresponding to said error signal; and

delaying at said mobile station a next leading edge of said periodic timing signal in response to said indication of an error corresponding to said error signal thereby synchronizing said digital mode operation of said mobile station to said predetermined system time.

16. The method of claim 15 further including the step of informing said mobile station by said base station of an absolute time of day corresponding to the leading edge of said periodic timing signal occurring at a future time.

17. The method of claim 15 wherein said step of delaying includes the step of adjusting a timing device within said mobile station in response to said indication of an error corresponding to said error signal, said timing device being disposed to provide timing information during operation in said digital mode.

18. The method of claim 15 further including the step of switching said mobile station from operation in said analog mode to operation in said digital mode upon said mobile station becoming to said predetermined system time.

19. The method of claim 15 further including the step of providing by said mobile station, during selected intervals between each of the leading edges of said periodic timing signal, analog data to said base station.

20. In a cellular communication system including a mobile station in communication with a base station, said mobile station being operative in both analog and digital modes, a method of synchronizing said digital mode operation of said mobile station to a predetermined system time provided by said base station, said method comprising the steps of:

transmitting during periodic intervals from said mobile station to said base station a periodic signal, said periodic signal being of a phase related to timing of said digital mode operation of said mobile station and said periodic intervals being of a duration related to a period of a digital modulation sequence of said system;

detecting, at said base station, said phase of said periodic signal and generating an error signal by comparing the detected phase to a reference signal derived from said predetermined system time; and

adjusting said phase of said periodic signal in accordance with said error signal so as to align timing of said digital modulation sequence to said predetermined system time.

21. The method of claim 20 wherein each period of said periodic signal includes a leading edge, and wherein said step of adjusting said phase includes the step of delaying at said mobile station leading edges of said periodic signal in accordance with said error signal.

22. The method of claim 21 wherein said step of delaying includes the step of adjusting a timing device within said mobile station on the basis of said error signal, said timing device governing said timing of said digital mode operation of said mobile station.

23. In a cellular communication system including a mobile station in communication with a base station, said mobile station being operative in both analog and digital modes, a time-alignment system for synchronizing said digital mode operation of said mobile station to a predetermined system time provided by said base station, said time-alignment system comprising:

a mobile station transmitter for transmitting during periodic intervals from said mobile station to said base station a periodic signal, said periodic signal being of a phase related to timing of said digital mode operation of said mobile station and said periodic intervals being of a duration related to a period of a digital modulation sequence of said system;

a base station receiver for detecting, at said base station, said phase of said periodic signal and for generating an error signal by comparing the detected phase to a reference signal derived from said predetermined system time; and

a timing adjustment circuit for adjusting said phase of said periodic signal in accordance with said error signal so as to align timing of said digital modulation sequence of said mobile station to said predetermined system time.

24. The time-alignment system of claim 23 wherein each period of said periodic signal includes a leading edge, and wherein said timing adjustment circuit operates to delay at said mobile station leading edges of said periodic signal in accordance with said error signal.

25. The time-alignment system of claim 24 wherein said timing adjustment circuit operates to adjust timing of a timing device within said mobile station on the basis of said error signal, said timing device governing said digital mode operation of said mobile station.

26. In a cellular communication system including a mobile station and a base station in communication over a communication channel, a time-alignment system for synchronizing a timing device within said mobile station to a predetermined system time provided by said base station, said time-alignment system comprising:

a mobile station transmitter for transmitting during periodic intervals from said mobile station to said base station in a first direction over said communication channel a periodic signal, said periodic signal being of a phase determined by said timing device wherein said periodic intervals are of a duration related to a period of a digital modulation sequence of said system;

a base station receiver for detecting, at said base station, said phase of said periodic signal and for generating an error signal by comparing the detected phase to a reference signal derived from said predetermined system time; and

a base station transmitter for providing to said mobile station a timing adjustment signal indicative of the results of the comparison in a second direction over said communication channel, said mobile station including a timing adjustment circuit for adjusting said timing device on the basis of said timing adjustment signal.

27. In a system including a remote station in communication with a base station, said remote station being operative in both analog and digital modes, a method of facilitating handoff of operation of said remote station in said analog mode to operation of said remote station in said digital mode, said method comprising the steps of:

transmitting during periodic intervals from said remote station to said base station a periodic signal, said periodic signal being of a phase determined by timing of said digital mode operation of said remote station and said periodic intervals being of a duration related to a period of a digital modulation sequence used in said remote station;

detecting, at said base station, said phase of said periodic signal and generating an error signal by comparing the detected phase to a reference signal derived from a predetermined system time;

adjusting said phase of said periodic signal in accordance with said error signal so as to align said timing of said digital modulation sequence with said predetermined system time; and

switching operation of said remote station from said analog mode to said digital mode upon said timing of said digital mode of operation becoming aligned with said predetermined system time.