Method to indicate synchronization lock of a remote station with a base station

• US 5,943,375 A
• Filed: 02/06/1997
• Issued: 08/24/1999
• Est. Priority Date: 02/06/1997
• Status: Expired due to Term

• Current Assignee: Clearwire Ip Holdings LLC (Deutsche Telekom AG)
• Original Assignee: AT&T Wireless Services Incorporated (AT&T, Inc.)
• Inventors: Veintimilla, Gregory J.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): PARK, ALBERT C
• Application Number:
  US08/796,492
• Time in Patent Office: 929 Days
• Field of Search: 375/364, 375/362, 375/207, 375/356, 375/354, 375/355, 375/209, 375/206, 375/208, 375/202, 375/201, 370/513, 370/503, 370/342, 370/343, 370/330, 370/350, 370/344, 370/480
• US Class Current: 375/355
• CPC Class Codes: H04B 1/69 Spread spectrum techniques
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2659 Coarse or integer frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 5/0016 Time-frequency-code
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 56/0085 detecting a given structure in the signal
• CPC Class Codes: H04W 92/10 between terminal device and access point, i.e. wireless air interface

Abstract

A method for a wireless discrete tone communications system, synchronizes the remote station to the base station. The method begins with the step of generating a clock signal at the base station. The base station then derives a synchronization symbol pattern from the base station clock signal and spreads the it with spreading codes that distributes the symbol pattern over a plurality of discrete tones, forming a discrete tone signal. The base station then transmits the spread signal to the remote station. The remote station generates a first clock signal and samples the discrete tones using the remote station first clock signal, forming a first sampled signal. Then the remote station applies the first sampled signal to a matched filter bank, forming a frequency error signal. The method then adjusts a frequency of the remote station first clock signal using the frequency error signal, forming a second clock signal. Then the remote station samples the discrete tones using the remote station second clock signal, forming a second sampled signal. Then the remote station despreads the second sampled signal with despreading codes to extract the synchronization symbol pattern. Then the remote station compares the extracted synchronization symbol pattern with a reference symbol pattern at the remote station. If the comparing step is successful, then the remote station selectively processes traffic signals received from the base station using the second clock signal. If the comparing step is not successful, then the remote station selectively adjusts a time offset value of the remote station second clock signal forming a third clock signal. The remote station then samples the discrete tones using the remote station third clock signal, forming a third sampled signal. The remote station then despreads the third sampled signal with despreading codes to form a second extraction of the synchronization symbol pattern. The remote station then compares the second extraction of the synchronization symbol pattern with the reference symbol pattern at the remote station. If the step of comparing the second extraction is successful, then the remote station selectively processes traffic signals received from the base station using the third clock signal.

Claims

1. A method of synchronizing a remote station to a base station in a bandwidth efficient communication system, comprising the steps of:

generating a clock signal at the base station;

deriving a synchronization symbol pattern from said base station clock signal;

spreading said synchronization symbol pattern at the base station with spreading codes that distributes the synchronization symbol pattern over a plurality of discrete tones, forming a spread signal;

transmitting the spread signal from the base station;

receiving the spread signal at the remote station;

generating a first clock signal at the remote station;

sampling said discrete tones at the remote station using said remote station first clock signal, forming a first sampled signal;

applying said first sampled signal to a matched filter, forming frequency error signal;

using said frequency error signal, forming a second clock signal;

sampling said discrete tones at the remote station using said remote station second clock signal, forming a second sampled signal;

selectively adjusting a time offset value of said remote station second clock signal forming a third clock signal;

sampling said discrete tones at the remote station using said remote station third clock signal, forming a third sampled signal;

despreading said third sampled signal at the remote station with despreading codes to form an extraction of said synchronization symbol pattern;

comparing said extraction of said synchronization symbol pattern with a reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said third clock signal, if said step of comparing said extraction is successful.

2. A method of synchronizing a remote station to a base station in a bandwidth efficient communication system, comprising the steps of:

generating a clock signal at the base station;

deriving a synchronization symbol pattern from said base station clock signal;

spreading said synchronization symbol pattern at the base station with spreading codes that distributes the synchronization symbol pattern over a plurality of discrete tones, forming a spread signal;

transmitting the spread signal from the base station;

receiving the spread signal at the remote station;

generating a first clock signal at the remote station;

sampling said discrete tones at the remote station using said remote station first clock signal, forming a first sampled signal;

applying said first sampled signal to a matched filter, forming frequency error signal;

using said frequency error signal, forming a second clock signal;

sampling said discrete tones at the remote station using said remote station second clock signal, forming a second sampled signal;

selectively adjusting said frequency of said remote station second clock signal, forming a third clock signal, if said comparing step is not successful;

sampling said discrete tones at the remote station using said remote station third clock signal, forming a third sampled signal;

despreading said third sampled signal at the remote station with despreading codes to form an extraction of said synchronization symbol pattern;

comparing said extraction of said synchronization symbol pattern with a reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said third clock signal, if said step of comparing said extraction is successful.

3. The method of synchronizing a remote station to a base station in a bandwidth efficient communication system of claim 2, further comprising the steps of:

selectively adjusting a time offset value of said remote station third clock signal forming a fourth clock signal, if said step of comparing said extraction is not successful;

sampling said discrete tones at the remote station using said remote station fourth clock signal, forming a fourth sampled signal;

despreading said fourth sampled signal at the remote station with despreading codes to form a next extraction of said synchronization symbol pattern;

comparing said next extraction of said synchronization symbol pattern with said reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said fourth clock signal, if said step of comparing said next extraction is successful.

4. A method of synchronizing a remote station to a base station in a bandwidth efficient communication system, comprising the steps of:

generating a clock signal at the base station;

deriving a synchronization symbol pattern from said base station clock signal;

spreading said synchronization symbol pattern at the base station with spreading codes that distributes the synchronization symbol pattern over a plurality of discrete tones, forming a spread signal;

transmitting the spread signal from the base station;

receiving the spread signal at the remote station;

generating a first clock signal at the remote station;

sampling said discrete tones at the remote station using said remote station first clock signal, forming a first sampled signal;

applying said first sampled signal to a matched filter, forming frequency error signal;

using said frequency error signal, forming a second clock signal;

sampling said discrete tones at the remote station using said remote station second clock signal, forming a second sampled signal;

selectively sampling said discrete tones at the remote station using said remote station second clock signal, forming a second sampled signal, if said comparing step is not successful;

applying said second sampled signal to a matched filter bank, forming a second frequency error signal;

adjusting a frequency of said remote station second clock signal using said second frequency error signal, forming a third clock signal;

sampling said discrete tones at the remote station using said remote station third clock signal, forming a third sampled signal;

despreading said third sampled signal at the remote station with despreading codes forming an extraction of said synchronization symbol pattern;

comparing said extraction of said synchronization symbol pattern with a reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said third clock signal, if said step of comparing said extraction is successful.

5. The method of synchronizing a remote station to a base station in a bandwidth efficient communication system of claim 4, further comprising the steps of:

selectively adjusting a time offset value of said remote station third clock signal forming a fourth clock signal, if said step of comparing said extraction is not successful;

sampling said discrete tones at the remote station using said remote station fourth clock signal, forming a fourth sampled signal;

despreading said fourth sampled signal at the remote station with despreading codes to form a next extraction of said synchronization symbol pattern;

comparing said next extraction of said synchronization symbol pattern with said reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said fourth clock signal, if said step of comparing said next extraction is successful.

6. The method of synchronizing a remote station to a base station in a bandwidth efficient communication system of claim 5, wherein said base station and said remote station are part of a wireless discrete tone communications system.

7. A method of synchronizing a remote station to a base station in a wireless discrete tone communications system, comprising the steps of:

generating a clock signal at the base station;

deriving a synchronization symbol pattern from said base station clock signal;

spreading said synchronization symbol pattern at the base station with spreading codes that distributes the synchronization symbol pattern over a plurality of discrete tones, forming a spread signal;

transmitting the spread signal from the base station and receiving the spread signal at the remote station;

generating a first clock signal at the remote station;

sampling said discrete tones at the remote station using said remote station first clock signal, forming a first sampled signal;

forming a frequency error signal from said first sampled signal;

adjusting a frequency of said remote station first clock signal using said frequency error signal, forming a second clock signal;

sampling said discrete tones at the remote station using said remote station second clock signal, forming a second sampled signal;

despreading said second sampled signal at the remote station with despreading codes to extract said synchronization symbol pattern;

comparing said extracted synchronization symbol pattern with a reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said second clock signal, if said comparing step is successful.

8. The method of synchronizing a remote station to a base station in a wireless discrete tone communications system of claim 7, further comprising the steps of:

selectively adjusting a time offset value of said remote station second clock signal forming a third clock signal, if said comparing step is not successful;

sampling said discrete tones at the remote station using said remote station third clock signal, forming a third sampled signal;

despreading said third sampled signal at the remote station with despreading codes to form a second extraction of said synchronization symbol pattern;

comparing said second extraction of said synchronization symbol pattern with said reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said third clock signal, if said step of comparing said second extraction is successful.

9. The method of synchronizing a remote station to a base station in a wireless discrete tone communications system of claim 7, further comprising the steps of:

selectively sampling said discrete tones at the remote station using said remote station second clock signal, forming a second sampled signal, if said comparing step is not successful;

forming a second frequency error signal from said second sampled;

adjusting a frequency of said remote station second clock signal using said second frequency error signal, forming a third clock signal;

sampling said discrete tones at the remote station using said remote station third clock signal, forming a third sampled signal;

despreading said third sampled signal at the remote station with despreading codes forming a second extraction of said synchronization symbol pattern;

comparing said second extraction of said synchronization symbol pattern with said reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said third clock signal, if said step of comparing said second extraction is successful.

10. The method of synchronizing a remote station to a base station in a bandwidth efficient communication system of claim 9, further comprising the steps of:

selectively adjusting a time offset value of said remote station third clock signal forming a fourth clock signal, if said step of comparing said second extraction is not successful;

sampling said discrete tones at the remote station using said remote station fourth clock signal, forming a fourth sampled signal;

despreading said fourth sampled signal at the remote station with despreading codes to form a third extraction of said synchronization symbol pattern;

comparing said third extraction of said synchronization symbol pattern with said reference symbol pattern at the remote station; and

selectively processing traffic signals received from the base station using said fourth clock signal, if said step of comparing said third extraction is successful.

11. A method of synchronizing a remote station to a base station in a wireless discrete tone communications system to enable communication of data traffic, comprising the steps of:

generating a clock signal at the base station;

deriving a synchronization symbol pattern from said base station clock signal;

spatially spreading said synchronization symbol pattern at the base station with spreading codes that distributes the synchronization symbol pattern over a plurality of discrete tones, forming a spread signal;

including traffic data in the spread signal by spatially spreading the traffic data the base station said spreading codes to distribute the traffic data over a plurality of discrete tones

transmitting the spread signal from the base station and receiving the spread signal at the remote station;

generating a first clock signal at the remote station;

sampling said discrete tones at the remote station using said remote station first clock signal, forming a first sampled signal;

forming a frequency error signal from said first sampled signal;

adjusting a frequency of said remote station first clock signal using said frequency error signal, forming a second clock signal;

sampling said discrete tones at the remote station using said remote station second clock signal, forming a second sampled signal;

despreading said second sampled signal at the remote station with despreading codes to extract said synchronization symbol pattern;

comparing said extracted synchronization symbol pattern with a reference symbol pattern at the remote station; and

despreading said traffic data with said despreading codes to extract said traffic data from said spread signal using said second clock signal, and outputting said traffic data if said comparing step is successful.

12. The method of synchronizing a remote station to a base station in a wireless discrete tone communications system to enable communication of data traffic of claim 11, further comprising the steps of:

selectively adjusting a time offset value of said remote station second clock signal forming a third clock signal, if said comparing step is not successful;

sampling said discrete tones at the remote station using said remote station third clock signal, forming a third sampled signal;

despreading said third sampled signal at the remote station with despreading codes to form a second extraction of said synchronization symbol pattern;

comparing said second extraction of said synchronization symbol pattern with said reference symbol pattern at the remote station; and

despreading said traffic data with said despreading codes to extract said traffic data from said spread signal using said second clock signal, and outputting said traffic data if said step of comparing said second extraction is successful.