Telecommunications – Receiver or analog modulated signal frequency converter – Squelch
Reexamination Certificate
1998-11-03
2001-09-18
Nguyen, Lee (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Squelch
C455S222000, C455S501000, C455S296000, C375S346000
Reexamination Certificate
active
06292654
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to field programmable radio frequency communications systems and more particularly to a field programmable digital noise reduction circuits therefor.
Descriptions of the various components of the system are contained in co-pending patent applications owned by the assignee hereof and filed concurrently herewith, specifically: U.S. patent application Ser. No. 09/184714, entitled “Reconfigurable Radio System Architecture And Method Therefor”; U.S. patent application Ser. No. 09/184,716, entitled “A Control System For Controlling the Processing Data of a First In First Out Memory and Method Therefor”; U.S. patent application Ser. No. 09/184,910, entitled “Configurable Circuits for Field Programmable Radio Frequency Communications Equipment and Methods Therefor”; U.S. patent application Ser. No. 09/184,710, entitled “A System For Accelerating the Reconfiguration of a Transceiver and Method Therefor”; U.S. patent application Ser. No. 09/184,709, entitled “A Field Programmable Radio Frequency Communications Equipment Including A Configurable IF Circuit, And Method Therefore”; U.S. patent application Ser. No. 09/184,711, entitled “A Field Programmable Modulator-Demodulator Arrangement For Radio Frequency Communications Equipment, And Method Therefor”; U.S. patent application Ser. No. 09/184,712, entitled “TCM Revisiting System and Method”; U.S. patent application Ser. No. 09/184,941, entitled “Least Squares Phase Fit As Frequency Estimate”; U.S. patent application Ser. No. 09/184,715, entitled “Polar Computation of Branch Metrics For TCM”; U.S. patent application Ser. No. 09/184,746, entitled “Efficient Modified Viterbi Decoder”; U.S. patent application Ser. No. 09/184,713, entitled “Receiver For a Reconfigurable Radio System and Method Therefore”; each of which is incorporated herein by reference.
In the use of radio frequency equipment for communications, there is a need for a large variety of types communication devices, such as receivers, transmitters and transceivers that are able to operate with a large variety of communications schemes, or waveforms such as, AM, AME, A
3
E, H
3
E, J
3
E, CW, SSB, M-PSK, QAM, ASK, angular modulation, including FM, PM, FSK, CMP, MSK, CPFSK etc., as well a need of being able to process the signals within the communications devices, such as by filtering, gain control, impulse noise rejection, etc. To achieve this in the past, a plurality of different dedicated pieces of equipment was required, such as, receivers, transmitters and transceivers, each designed to operate with separate communication schemes or waveforms, or a limited group of schemes or waveforms. Hence it would be desirous to have a configurable type of radio frequency communications equipment that is readily field programmable to function as a transmitter and receiver and to be able to be programmed to function with any of the above mentioned communications schemes or waveforms.
An important building block for a configurable type transceiver is a configurable digital intermediate frequency (IF) transmitter and receiver signal processing circuit that can be field programmed to provide the receiver demodulation functions and transmitter modulator functions and also corresponding waveform filtering and shaping. When configured in the receiver mode of operation, it would be desirable to include a noise reduction or blanking circuit that would be readily adaptable for use when receiving either voice or data signals.
Radio frequency receivers are susceptible to a variety of noise signal that may appear in the radio frequency spectrum, particularly to noise created by lightening and ignition systems. This is particularly important in data reception where the noise levels override the signal and erroneous data may be inserted into the transmission. Radio frequency noise can be considered as wideband signals including a wide range of frequencies, while information signals can be considered as narrow band signals having a limited and controlled range of frequencies. Noise (usually in the form of impulses) can also be consider to be of short duration as compared to the ongoing duration of the information signals. Although noise impulses are of short duration, radio frequency receiver include a number of filter circuits, that as part of the filtering process, tend to stretch the duration of noise impulse. Hence, in order to provide effective noise reduction or blanking, the impact of the filters on the noise impulse duration, is needed to be taken into consideration when determining the blanking duration
Short term averaging circuits and long term averaging circuit have in the prior art been used to provide measures of noise and information signal. When using the averaging systems of the prior art in digital type noise reduction or blanking circuits, such circuits require digital multiplication type functions. Digital multiply function require a lot of hardware in implementation to cover the expected dynamic range of magnitudes and frequencies involved in averaging the noise and signals. It would be desirable if a digital averaging arrangement could be provided to cover the dynamic ranges needed while minimizing the use of multiply functions and thereby reduce the complexities and costs involved in such averaging circuits.
It is therefor an object of this invention to provide a new and improved noise reduction circuits for digital communication systems.
It is also an object of this invention to provide a new and improved noise reduction circuits for digital radio frequency receivers.
It is also an object of this invention to provide a new and improved noise reduction circuits for digital radio frequency receivers that can be readily configured by the user in the field to conform with the characteristics of the receiver.
It is also an object of this invention to provide a new and improved noise reduction circuits for digital field configurable radio frequency receivers that can be readily configured by the user in the field to conform with the configuration of the receiver.
Is also an object of this invention to provide a new, improved and simplified noise reduction circuit for digital communications systems.
These and other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains form a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.
REFERENCES:
patent: 4293736 (1981-10-01), Ogita
patent: 4327446 (1982-04-01), Deressler
patent: 4637067 (1987-01-01), Steinberger
patent: 5459750 (1995-10-01), Hiotakakos et al.
patent: 5537675 (1996-07-01), Bond
patent: 5712872 (1998-01-01), Hawkins et al.
patent: 5890059 (1999-03-01), Shoemaker et al.
Crawford Douglas C.
Hessel Clifford
Kreeger Michael E.
Mackey Christopher D.
Marks Scott E.
Carter, Ledyard & Milburn
Harris Corporation
Nguyen Lee
Nguyen Simon
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