Method and apparatus for a carrier frequency control in a wireless communication system

• US 6,603,958 B1
• Filed: 02/09/2000
• Issued: 08/05/2003
• Est. Priority Date: 02/09/2000
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Gao, Shiwei, Zhang, Genzao G., Wu, Kuang-Tsan
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): SHARMA, SUJATHA R
• Application Number:
  US09/500,458
• Time in Patent Office: 1,273 Days
• Field of Search: 455/255, 455/257-60, 455/266, 455/316, 455/119, 455/69
• US Class Current: 455/63.1
• CPC Class Codes: H04L 2027/002 using feedback from a remote receiver
• CPC Class Codes: H04L 2027/0022 using the carrier of the associated receiver of a transceiver
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

The invention provides a frequency control method and apparatus for efficiently controlling in a wireless system the carrier frequency of a received signal transmitted over a radio link to counteract carrier frequency drifts in the received signal and hence maintain link connectivity. In a preferred embodiment, the invention provides upstream and downstream carrier frequency control in a broadband wireless access (BWA) time division multiplex access (TDMA) system formed of a base transceiver station (BTS) and multiple customer premises equipment (CPE) units. At each of the CPE units, the CPE upstream carrier frequency is preemptively adjusted based on downstream carrier frequency measurements to counteract carrier frequency variations in the upstream carrier frequency. For downstream communications, the BTS periodically polls all active CPE units to obtain downstream frequency offset estimates, calculate a frequency correction offset and adjust the downstream carrier frequency accordingly.

Claims

1. A method of providing a carrier frequency control in a wireless communications network for at least one first signal respectively produced for transmission in at least one first station at a first carrier frequency and transmitted from the at least one first station to a second station having a defined carrier frequency acquisition range, the method comprising:

receiving in each of the at least one first station a second signal transmitted from the second station;

producing in each of the at least one first station the second signal received at a respective second carrier frequency;

estimating in each of the at least one first station a respective carrier frequency offset between the corresponding second carrier frequency and an expected carrier frequency;

preemptively shifting in each of the at least one first station the first carrier frequency based on the respective carrier frequency offset estimated for maintaining the first signal within the defined carrier acquisition range of the second station;

at the second station, polling the at least one first station to request carrier frequency offset estimates;

at each of the at least one first station where a poll request is received, reporting the respective carrier frequency offset estimate to the second station;

at the second station, receiving the respective carrier frequency offset estimates reported;

based on the carrier frequency offset estimates received, calculating in the second station a frequency adjustment; and

applying in the second station the frequency adjustment calculated to shift a third carrier frequency at which the second signal is produced so as to minimize carrier frequency variations in the second signal.

2. The method of claim 1 wherein estimating in each of the at least one first station a respective carrier frequency offset between the corresponding second carrier frequency and an expected carrier frequency comprises in each of the at least one first station:

digitizing the second signal received to produce digital samples of the second signal;

acquiring the second carrier frequency; and

estimating the corresponding carrier frequency offset between the acquired second carrier frequency and the expected carrier frequency.

3. The method of claim 2 wherein acquiring the second carrier frequency in each of the at least one first station is done with a respective frequency sweep carrier recovery loop (CRL).

4. The method of claim 1 wherein preemptively shifting in each of the at least one first station the first carrier frequency based on the respective carrier frequency offset estimated comprises in each of the at least one first station subtracting the respective carrier frequency offset estimated from the corresponding first carrier frequency so as to maintain the first carrier frequency within the defined carrier acquisition range of the second station.

5. The method of claim 1 wherein the first and second carrier frequencies are intermediate carrier frequencies.

6. The method of claim 5 further comprising in each of the at least one first station up-converting the respective first signal from the corresponding preemptively shifted first intermediate carrier frequency to a first radio carrier frequency for transmission to the second station.

7. The method of claim 6 wherein receiving in each of the at least one first station a second signal transmitted from the second station comprises receiving in each of the at least one first station the second signal at a second radio carrier frequency, and wherein producing in each of the at least one first station the second signal received at a respective second carrier frequency comprises down-converting in each of the at least one first station the second signal received from the second radio carrier frequency to the respective second intermediate carrier frequency.

8. The method of claim 7 wherein a single local oscillator is used in each of the at least one first stations for up-converting the respective first signal and for down-converting the second signal.

9. The method of claim 8 wherein prior to being transmitted to the at least one first station, the second signal is up-converted in the second station from the third carrier frequency to the second radio carrier frequency, the method further comprising:

receiving in the second station the at least one first signal transmitted at the first radio carrier frequency; and

down-converting in the second station the at least one first signal received from the first radio carrier frequency to a fourth intermediate carrier frequency.

10. The method of claim 9 wherein a single local oscillator is used in the second station for up-converting the second signal and for down-converting the plurality of first signals received.

11. The method of claim 1 wherein applying in the second station the frequency adjustment calculated is done to facilitate carrier acquisition of the second signal at each of the at least one first station.

12. The method of claim 1 wherein the second station is a base transceiver station, each of the at least one first station is a customer premises equipment unit, and wherein the first and the second signals are upstream and downstream signals respectively.

13. The method of claim 1 wherein the wireless communication network is a broadband wireless access (BWA) time division multiple access (TDMA) network.

14. The method of claim 1 wherein for polling the at least one first station to obtain carrier frequency offset estimates, messages are exchanged between the second station and each of the at least one first station based on the international telecommunications union (ITU) R112 local multipoint distribution service (LMDS) protocol.