Method and apparatus for using synchronous CDMA in a mobile environment

• US 7,151,944 B2
• Filed: 09/27/2001
• Issued: 12/19/2006
• Est. Priority Date: 09/27/2001
• Status: Expired due to Fees

• Current Assignee: Blackberry Limited
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Hashem, Bassam M, Steer, David G, Matyas, Robert
• Primary Examiner(s): Ramakrishnaiah, Melur
• Application Number:
  US09/965,272
• Publication Number:
  US 20030058833A1
• Time in Patent Office: 1,909 Days
• Field of Search: 455/502, 455/422.1, 455/65, 370/342, 370/335, 370/441, 375/130, 375/140
• US Class Current: 455/502
• CPC Class Codes: H04B 1/7113 Determination of path profile
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 7/2662 Arrangements for Wireless System Synchronisation
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time

Abstract

The present invention relates to a method and apparatus for reducing interference arising from signal propagation delay in multipath signal environments in wireless communication systems. The present invention provides a method of operating a mobile communications base station which receives multipath components of signals from a number of high mobility subscriber terminals, the method comprising: for each subscriber terminal signal received, determining a best signal component; determining the difference in time between reception of said best signal component and a reference time; transmitting to said terminal a transmission timing offset in order to receive said best component at substantially said reference time.

Claims

1. A method of operating a mobile communications base station which receives signals from a number of high mobility subscriber terminals, each of said subscriber terminal signals comprising a number of multipath components, the method comprising:

for each subscriber terminal signal received, determining a best signal component;

wherein for each determination of a best signal component, the method comprises the steps of;

determining a difference in time between reception of said best signal component and a reference time; and

transmitting to said terminal a transmission timing offset value calculated at said base station in order to receive said best signal component at substantially said reference time, said transmission timing offset value comprising said difference in time between reception of said best signal component and said reference time.

2. A method as claimed in claim 1 wherein said offset is in the form of a regular layer 1 timing alignment command having two or more offset absolute magnitude settings.

3. A method as claimed in claim 2 wherein the magnitude settings a minimum setting of 1 microsecond.

4. A method as claimed in claim 1 wherein the best signal component is determined as that having the highest average value of a predetermined signal parameter over a predetermined time.

5. A method as claimed in claim 4 wherein the predetermined signal parameter is signal strength.

6. A method as claimed in claim 4 wherein the average value of said predetermined parameter for a number of signal components over a shortened predetermined period are stored, and wherein in the event of fast fading of the best signal component the signal component having the next highest average value over said shortened period is determined as the best signal component.

7. A method as claimed in claim 4 further comprising determining a new said best component only if said average value is a predetermined threshold above a current best component.

8. A method as claimed in claim 7 further comprising determining a new said best component only if said difference in time is above a predetermined threshold offset.

9. A mobile communications base station which receives signals from a number of high mobility subscriber terminals, each of said subscriber terminal signals comprising a number of multipath components, the base station comprising:

means for determining a best signal component for each received subscriber terminal signal;

means for determining a difference in time between reception of said best signal component and a reference time;

means for transmitting to each said subscriber terminal a transmission timing offset value calculated at the base station in order to receive said best signal component at substantially said reference time, said transmission timing offset value comprising said difference in time between reception of said best signal component and said reference time;

wherein said time difference determining means is arranged to determine a time difference and said timing offset transmitting means is arranged to transmit a timing offset value for each determination of a best signal component by the best signal component determining means.

10. A base station as claimed in claim 9 wherein said offset is in the form of a regular layer 1 timing alignment command having two or more offset absolute magnitude settings.

11. A base station as claimed in claim 10 wherein the magnitude settings include a minimum setting of 1 microsecond.

12. A base station as claimed in claim 9 wherein the best signal component is determined as that having the highest average value of a predetermined signal parameter over a predetermined time.

13. A base station as claimed in claim 12 wherein the average value of said predetermined parameter for a number of signal components over a shortened predetermined period are stored, and wherein in the event of fast fading of the best signal component the signal component having the next highest average value over said shortened period is determined as the best signal component.

14. A method of operating a high mobility subscriber terminal comprising:

determining a transmission timing offset value calculated at a base station and transmitted from said base station to said subscriber terminal, said transmission timing offset value comprising a difference in time between reception of a best signal component of a multi-path signal transmitted from said subscriber terminal to said base station and a reference time;

adjusting the transmission timing of said terminal according to said offset value in order that said best signal component transmitted by said subscriber terminal is received at said base station at substantially said reference time;

wherein said offset is in the form of a regular layer 1 timing alignment command having two or more absolute magnitude settings.

15. A method as claimed in claim 14 wherein the magnitude settings include a minimum setting of 1 microsecond.

16. A high mobility terminal for use in a mobile communications system, the terminal comprising:

means for determining a transmission timing offset value calculated at a base station and transmitted from said base station to said subscriber terminal, said transmission timing offset value comprising a difference in time between reception of a best signal component of a multi-path signal transmitted from said subscriber terminal to said base station and a reference time;

means for adjusting the transmission timing of said terminal according to said offset value in order that said best signal component transmitted by said subscriber terminal is received at said base station at substantially said reference time;

wherein said offset is in the form of a regular layer 1 timing alignment command having two or more absolute magnitude settings.

17. A high mobility terminal as claimed in claim 16 wherein the magnitude settings include a minimum setting of 1 microsecond.

18. A mobile communications system having a number of high mobility terminals and a base station which receives signals from said terminals;

each of said subscriber terminal signals comprising a number of multipath components, the base station comprising;

means for determining a best signal component for each received subscriber terminal signal;

means for determining a difference in time between reception of said best signal component and a reference time;

means for transmitting to each said subscriber terminal a transmission timing offset value calculated at the base station in order to receive said best signal component at substantially said reference time, said transmission timing offset value comprising said difference in time between reception of said best signal component and said reference time;

wherein said time difference determining means is arranged to determine a time difference and said timing offset transmitting means is arranged to transmit a timing offset value for each determination of a best signal component by the best signal component determining means for each subscriber terminal;

and each subscriber terminal comprises;

means for determining a transmission timing offset value transmitted from the base station; and

means for adjusting the transmission timing of said terminal according to said offset value.