Method and apparatus for timing correction in communications systems

• US 20040192201A1
• Filed: 03/12/2004
• Published: 09/30/2004
• Est. Priority Date: 03/05/1999
• Status: Active Grant

• Current Assignee: Inmarsat Global Limited (Inmarsat PLC)
• Original Assignee: Inmarsat Ltd (Inmarsat PLC)
• Inventors: Mudge, David Denis, Febvre, Paul, Jones, Edward Arthur, Fines, Panagiotis
• Granted Patent: US 7,532,891 B2
• Time in Patent Office: Days
• US Class Current: 455/13.2
• CPC Class Codes: H04B 7/2125 Synchronisation
• CPC Class Codes: H04B 7/2643 using time-division multiple access [TDMA] H04B7/2615, H04B7/2618 take precedence
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time
• CPC Class Codes: H04W 56/0085 detecting a given structure in the signal

Abstract

In a wireless communications system, transceivers transmit short bursts to a base station, which determines timing corrections from the time of receipt of the burst and transmits the timing corrections to the respective transceivers. In one aspect, the base station indicates to the transceivers a plurality of time slots, each transceiver selects one of the time slots at random, formats a burst including an Indicator of the selected time slot and transmits the burst in that slot. In another aspect, the base station transmits to each transceiver a timing uncertainty value, which determines how the timing correction will be modified by the tranceiver as the interval since last receiving a timing correction increases. Data bursts are transmitted in a format comprising a first unique word, a content field and a second unique word, in that order. The bursts are transmitted in a TDMA channel format which can accommodate both short and long bursts in a block format of constant periodicity.

Claims

1. A method of controlling the transmission timing of a wireless transceiver in a wireless communications system, including:

receiving a burst transmission from the transceiver on a time-slotted channel, the burst transmission including a time slot indication indicating a time slot within which the burst was transmitted;

calculating from the timing of reception of said burst transmission a timing correction value for the transceiver so as to synchronise the transmission timing of said transceiver with a reference timing; and

transmitting said timing correction value to the transceiver.

2. A method as claimed in claim 1, further including, prior to said receiving step:

transmitting to the transceiver a time slot allocation indicating a plurality of slots in the channel;

wherein the time slot indication indicates one of said time slots.

3. A method as claimed in claim 1 or claim 2, wherein said plurality of time slots form a sequential block having a total length greater than the maximum variation in propagation delay in said wireless communications system.

23. Apparatus arranged to perform the method of any one of claims 1 to 10, 16 to 19 or 21.

4. A method of controlling the transmission timing of a wireless transceiver in a wireless communications system, including:

selecting a time slot in a time-slotted channel;

transmitting from the transceiver a burst transmission in said selected time slot, the transmission including a time slot indication indicating the selected time slot;

receiving at the transceiver a timing correction value derived from the timing of the burst transmission; and

adjusting the timing of a subsequent transmission by the transceiver according to said timing correction value.

5. A method as claimed in claim 4, further including:

receiving at the transceiver a time slot allocation indicating a plurality of time slots in the channel;

wherein the selected time slot is selected from said plurality of time slots.

6. A method as claimed in claim 4 or 5, wherein said selected time slot is selected randomly or pseudo-randomly.

7. A method of controlling the transmission timing of a wireless transceiver in a wireless communications system, including:

transmitting a burst transmission from the transceiver;

receiving at the transceiver a timing correction value; and

controlling a subsequent transmission by the transceiver according to the timing correction value and according to a timing uncertainty value as a function of time elapsed since reception of the timing correction value.

8. A method us claimed in claim 7, wherein the timing uncertainty value is determined by a timing uncertainty rate received by the transceiver.

9. A method as claimed in claim 7 or claim 8, wherein if the timing uncertainty value exceeds a predetermined limit, the transceiver is inhibited from transmission in a time slot allocated to that transceiver until a further timing correction value is received.

10. A method of controlling the transmission timing of a transceiver in a wireless communications system, including:

transmitting to said transceiver a channel allocation signal indicating a channel dedicated that transceiver and not available to other transceivers in said system;

receiving from said transceiver a transmission substantially in the dedicated channel allocation;

detecting a timing error in said transmission; and

transmitting to said one of said transceivers a timing correction signal dependent on said timing error, for correction of the transmission timing of said transceiver.

11. A wireless link signal comprising a data burst including in temporal sequence:

an initial predetermined synchronisation sequence;

a data field carrying the data content of the burst; and

a final predetermined synchronisation sequence.

13. A signal as claimed in claim 11 or 12, wherein the burst includes an initial preamble preceding the first synchronisation sequence.

14. A signal as claimed in any one of claims 11 to 13, wherein the burst is transmitted in a time-slotted channel.

15. A signal as claimed in claim 14, wherein the channel comprises a plurality of slots sequentially separated by a guard band, wherein the length of the guard band is less than the maximum relative timing error between transmissions in adjacent time slots.

16. A method of transmitting a signal over a wireless link comprising transmitting a signal as claimed in any one of claims 11 to 15.

17. A method of receiving a signal over a wireless link, comprising receiving a signal as claimed in any one of claims 11 to 15.

12. A wireless link signal comprising a data burst including in temporal sequence:

an first predetermined synchronisation sequence;

a data field carrying substantially all of the data content of the burst; and

a second predetermined synchronisation sequence.

18. A method of transmitting data over a wireless communications link, comprising:

detecting a timing reference signal;

receiving a timing slot allocation over the wireless communications link;

and transmitting said data according to said timing reference signal and said timing slot allocation, in a time-slotted channel having a format including periodic blocks of constant length each occupied by either one long burst or an integral number of short bursts of equal length.

19. A method of controlling the transmission of data over a time-divided multiple access channel of a wireless communications link, comprising:

determining an allocation scheme of said channel to each of a plurality of transceivers, and transmitting said allocation scheme to said transceivers,

whereby said transceivers transmit data in said channel with a format including periodic blocks of constant length each occupied by either one long burst or an integral number of short bursts of equal length.

20. A wireless link signal having a format including periodic blocks of constant length each occupied by either one long burst or an integral number of short bursts of equal length.

21. A method of transmitting data over a wireless communications link, comprising:

transmitting the data in one or more short bursts and/or one or more long bursts, the short bursts comprising 112 modulated data symbols and having a total length of approximately 5 ms, and the long bursts comprising 596 data symbols and having a total length of approximately 20 ms.

22. A signal comprising a burst transmission having a total length of approximately either 5 or 20 ms and comprising 112 or 596 data symbols respectively.

24. A method substantially as herein described with reference to FIGS. 7, 8a and 8b of the accompanying drawings.

25. A signal substantially as herein described with reference to FIG. 5 or FIG. 6 of the accompanying drawings.