Multiplex communications – Duplex – Transmit/receive interaction control
Reexamination Certificate
1998-03-12
2001-09-11
Vu, Huy D. (Department: 2663)
Multiplex communications
Duplex
Transmit/receive interaction control
C375S349000, C455S063300, C455S278100
Reexamination Certificate
active
06289004
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wireless digital communication systems. More particularly, the present invention relates to an adaptive interference canceler included within telecommunication base stations and uses at least one auxiliary antenna in conjunction with a primary antenna for increasing the capacity of the telecommunication system by substantially reducing interference produced by one or more known interference sources proximate to the base station.
2. Description of the Prior Art
Over the last decade consumers have become accustomed to the convenience of wireless communication systems. This has resulted in a tremendous increase in the demand for wireless telephones, wireless data transmission and wireless access to the Internet. The amount of available RF spectrum for any particular system is often quite limited due to government regulation and spectrum allotments.
CDMA communication systems have shown promise in the effort to provide efficient utilization of the RF spectrum. At least one brand of CDMA systems, Broadband Code Division Multiple Access™ or B-CDMA™ communication systems available from InterDigital Communications Corporation, permit many communications to be transmitted over the same bandwidth, thereby increasing the capacity of the allotted RF spectrum. In B-CDMA™ communication systems, a data signal at the transmitter is mixed with a pseudorandom “spreading code” to spread the information signal across the entire transmission bandwidth or spectrum employed by the communication system. Afterwards, the spread spectrum signal is modulated with an RF carrier signal for transmission. A receiver receives the transmitted RF carrier signal and down converts the signal to a spread baseband signal. The spread data signal is despread by mixing the locally generated pseudorandom spreading code with the spread signal.
In order to detect the information embedded in a received signal, a receiver must use the same pseudorandom spreading code that was used to spread the signal. Signals which are not encoded with the pseudorandom code of the receiver appear as background noise to the receiver. However, signal frequencies within the transmission bandwidth contribute to the overall background noise making it difficult for receivers to properly detect and receive signals. A subscriber may increase the power of his transmitted signal to compensate, but overpowering interferes with the reception of other communication channels sharing the same communication bandwidth.
The allocated transmission bandwidths of many CDMA communication systems approach or share frequencies with other communication systems, such as microwave relaying or cellular communication systems. These systems may present interference signals which can greatly exceed the power of the CDMA communication signals in specific regions of the transmission bandwidth.
Applicants have recognized the need to decrease the amount of interference from identified manmade interferers in order to efficiently increase the allocated spectrum capacity of a CDMA communication system.
SUMMARY OF THE INVENTION
The present invention provides an improved base station which cancels the effects of known fixed interference sources to produce a signal substantially free from the interference sources.
In one embodiment, an antenna system in conjunction with a base station is deployed at a location with one or more known interference sources. The antenna system includes a main antenna for receiving signals from other communication stations and at least one directional antenna directed toward an interference source. The main and directional antennas are coupled to an adaptive canceler, which weights signals received by the directional antennas and sums the weighted signals to produce a cancellation signal. The adaptive canceler subtracts the cancellation signal from the signals received by the main antenna to provide an output signal substantially free from the interference generated by the one or more known interference sources. The adaptive canceler may use a plurality of feedback loops to implement a least mean square (LMS) algorithm to properly weight the directional antenna signals.
Accordingly, it is an object of the present invention to decrease the amount of interference produced from manmade interference sources that is processed as a received CDMA communication signal.
Other advantages may become apparent to those skilled in the art after reading the detailed description of the preferred embodiment.
REFERENCES:
patent: 4644359 (1987-02-01), Katagi et al.
patent: 5694134 (1997-12-01), Barnes
patent: 3223598 (1991-05-01), None
patent: 0684660 (1995-11-01), None
Mesecher David K.
Ozluturk Fatih M.
InterDigital Technology Corporation
Volpe and Koenig P.C.
Vu Huy D.
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