Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2002-09-30
2004-06-01
Pham, Chi (Department: 2667)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C370S441000
Reexamination Certificate
active
06744749
ABSTRACT:
REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT
The present invention is related to the following Applications for Patent in the U.S. Patent & Trademark Office:
“Method And Apparatus For Pilot Estimation Using Suboptimum Expectation Maximization” by Farrokh Abrishamkar et al., having Attorney Docket No. 020123, filed concurrently herewith and assigned to the assignee hereof;
“Method And Apparatus For Pilot Estimation Using A Prediction Error Method With A Kalman Filter And Pseudo-Linear Regression”, by Farrokh Abrishamkar et al., having Attorney Docket No. 020201, filed concurrently herewith and assigned to the assignee hereof;
“Method And Apparatus For Pilot Estimation Using A Prediction Error Method With A Kalman Filter And A Gauss-Newton Algorithm,” by Farrokh Abrishamkar et al., having Attorney Docket No. 020205, filed concurrently herewith and assigned to the assignee hereof; and
“Method And Apparatus For Pilot Estimation Using An Adaptive Prediction Error Method With a Kalman Filter and A Gauss-Newton Algorithm,” by Farrokh Abrishamkar et al., having Attorney Docket No. 020232, filed concurrently herewith and assigned to the assignee hereof.
FIELD
The present invention relates to wireless communication systems generally and specifically, to methods and apparatus for estimating a pilot signal in a code division multiple access system.
BACKGROUND
In a wireless radiotelephone communication system, many users communicate over a wireless channel. The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems.
The CDMA technique has many advantages. An exemplary CDMA system is described in U.S. Pat. No. 4,901,307, entitled “Spread Spectrum Multiple Access Communication System Using Satellite Or Terrestrial Repeaters”, issued Feb. 13, 1990, assigned to the assignee of the present invention, and incorporated herein by reference. An exemplary CDMA system is further described in U.S. Pat. No. 5,103,459, entitled “System And Method For Generating Signal Waveforms In A CDMA Cellular Telephone System”, issued Apr. 7, 1992, assigned to the assignee of the present invention, and incorporated herein by reference.
In each of the above patents, the use of a forward-link (base station to mobile station) pilot signal is disclosed. In a typical CDMA wireless communication system, such as that described in EIA/TIA IS-95, the pilot signal is a “beacon” transmitting a constant data value and spread with the same pseudonoise (PN) sequences used by the traffic bearing signals. The pilot signal is typically covered with the all-zero Walsh sequence. During initial system acquisition, the mobile station searches through PN offsets to locate a base station's pilot signal. Once it has acquired the pilot signal, it can then derive a stable phase and magnitude reference for coherent demodulation, such as that described in U.S. Pat. No. 5,764,687 entitled “Mobile Demodulator Architecture For A Spread Spectrum Multiple Access Communication System,” issued Jun. 9, 1998, assigned to the assignee of the present invention, and incorporated herein by reference.
Recently, third-generation (3G) wireless radiotelephone communication systems have been proposed in which a reverse-link (mobile station to base station) pilot channel is used. For example, in the currently proposed cdma2000 standard, the mobile station transmits a Reverse Link Pilot Channel (R-PICH) that the base station uses for initial acquisition, time tracking, rake-receiver coherent reference recovery, and power control measurements.
Pilot signals can be affected by noise, fading and other factors. As a result, a received pilot signal may be degraded and different than the originally transmitted pilot signal. Information contained in the pilot signal may be lost because of noise, fading and other factors.
There is a need, therefore, to process the pilot signal to counter the effects of noise, fading and other signal-degrading factors.
REFERENCES:
patent: 4901307 (1990-02-01), Gilhousen et al.
patent: 5101501 (1992-03-01), Gilhousen et al.
patent: 5103459 (1992-04-01), Gilhousen et al.
patent: 5740208 (1998-04-01), Hulbert et al.
patent: 5764687 (1998-06-01), Easton
Baltersee J. et al: “Performance Analysis of Phasor Estimation Algorithms For A FDD-UMTS Rake Receiver”, IEEE, vol. 2, Sep. 6, 2000, pp. 476-478, figures 1,3.
Abrishamkar Farrokh
Butler Brian K.
Lin Yu-Chuan G.
Brown Charles D.
Ly Anh-Vu H
Pauley Nicholas J.
Pham Chi
Qualcomm Incorporated
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