Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2000-06-14
2001-11-13
Pham, Chi (Department: 2734)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S232000, C342S379000
Reexamination Certificate
active
06317467
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radar receivers. More specifically, the present invention relates to beamforming and interference cancellation systems used in high performance digital radar receivers.
2. Description of the Related Art
Sophisticated high performance military and commercial digital radar receivers detect and process signals in complicated environments that include broadband clutter, interference sources (intentional and unintentional), echoes, and receiver noise. These receivers perform some or all of the following functions: synthesis of in-phase (I) and quadrature (Q) components from high-speed sampled signals, formation of video filters, notch DC components, decimation of data, provision of channel-to-channel equalization, digital range correlation, beam steering and interference cancellation.
Currently, these tasks are performed by Hilbert filters, digital video filters, equalization filters, discrete Fourier transform filters, decimating filters, convolvers, correlators, and general purpose cascadable FIR filters implemented in commercial off-the-shelf hardware (COTS) and customized hardware in embedded systems.
Unfortunately, digital radar receivers implemented in accordance with conventional teachings often require several hundred signal processing chips. As a result, conventional digital radar receivers are typically heavy, bulky, and expensive to develop and manufacture. In addition, these receivers typically consume considerable power and generate much heat.
Hence, there was a need in the art for a unique receiver architecture that would be highly flexible, scalable, and reconfigurable that could perform the numerous functions mentioned above. The need in the art was addressed by copending application entitled GENERAL PURPOSE FILTER, filed Jun. 14, 2000, by L. C. Cox et al. (Atty. Docket No. PD R98027-1), the teachings of which are incorporated by reference. This application disclosed and claimed a signal processor design including a plurality of filters which were selectively interconnected to provide a variety of digital signal processing functions. In the illustrative embodiment, each filter was adapted to multiply input data by a coefficient. Specifically, each filter was adapted to multiply input data by coefficients to form digital products which were combined to accumulate the sum of the products. The coefficients are provided by a microprocessor and configure the logic to a particular function, such as a general purpose filter, a Hilbert filter, a finite impulse response filter, an equalizer, a convolver, a correlator, or an application specific integrated circuit by way of example. When interconnected in accordance with the teachings provided therein, these circuits may be used to provide a digital receiver.
The digital receiver would comprise a plurality of general purpose filters constructed in accordance with the referenced teachings. Each filter would have a plurality of filter banks, switching circuitry to interconnect the filter banks, and programmability provided by an external processor. The processor would configure the filter banks, to provide a delay element, a first decimating filter and a first equalizer in a first channel of a first general purpose filter and a Hilbert transform, a second decimating filter and a second equalizer in a second channel of the first general purpose filter. A first range correlator would be provided in a first channel of a second general purpose filter and a second range correlator would be provided in a second channel of a second general purpose filter. The first channel of the first general purpose filter would be connected to the first channel of the second general purpose filter and the second channel of the first general purpose filter would be connected to the second channel of the second general purpose filter.
An external processor would program the general purpose filter to configure the filter banks to simultaneously provide the functions found in most digital receivers (e.g., Hilbert transforms, video filters, equalizers, range correlation, and general purpose video filters).
The versatile, flexible and reusable features of the general purpose filter architecture allows analog and digital receivers to be built using a single chip type. Accordingly, the receivers would be much smaller and lighter in weight then conventional systems and have lower associated power dissipation, thermal heating, and development and manufacturing cost.
While the teachings of the referenced patent application substantially addressed the need in the art, a need remains for a system and technique for implementing beamforming and interference cancellation in a digital radar receiver using a general purpose filter architecture.
SUMMARY OF THE INVENTION
The need in the art is addressed by the beamforming system of the present invention. In a most general sense, the inventive beamforming system includes a multiplier stage for providing a plurality of steered signal terms, each term being a product of an input signal term and a steering signal term. A filter is provided for multiplying the steered signal terms by a plurality of respective filter weights to provide a plurality of weighted products. The weighted products are summed to provide an outer beam directionally responsive to the steering signal. A microprocessor provides the steering signal terms and the filter weights in response to the input signal and/or user input.
In a specific implementation, the multiplier stage includes a plurality of multipliers. Each multiplier being configured to multiply one of the input signal terms with a respective one of the steering signal terms to provide a respective one of the steered signal terms. In the preferred embodiment, the filter is a reconfigurable, general purpose matched filter configured to multiply a plurality of delayed representations of a respective one of the steered signal terms by a plurality of the weights to provide a plurality of intermediate weighted product terms. The filter further includes a summing circuit for accumulating the intermediate weighted product terms to provide a respective one of the plurality of weighted products.
In the illustrative embodiment, the filter includes the first plurality of multipliers and a plurality of channels, one for each quadrant of the associated antenna. Each channel includes a plurality of multipliers and delay elements configured to provide the intermediate weighted product terms.
The inventive beamforming system cancels unwanted interference, while forming a beam to allow a desired signal to be received with a maximum signal-to-interference-plus-noise ratio (SINR). Through a data-capture RAM, the system allows interference samples to be collected and passed to a microprocessor to calculate the optimum filter weights. The received beam may be steered to any desired direction to form an optimal space-time adaptive matched filter.
REFERENCES:
patent: 4959653 (1990-09-01), Ganz
patent: 5473333 (1995-12-01), Chiba et al.
patent: 5510796 (1996-04-01), Applebaum
patent: 5689528 (1997-11-01), Tsujimoto
patent: 5926135 (1999-07-01), Minkoff
patent: 5952965 (1999-09-01), Kowalski
Baker Robert M.
Cox Lloyd C.
Freeman Stephen
Gramlich Gary A.
Krim Jordan A.
Benman William J.
Lenzen, Jr. Glenn H.
Pham Chi
Phu Phuong
Raufer Colin M.
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