Method and apparatus for radio system cochannel interference suppression
First Claim
1. In a radio communication system in which significant signal reception and demodulation is possible at one station from plural signal sources having the same nominal frequency, but only one of such sources is assigned for communication with such station and each source signal has modulated thereon a unique tone for that source as well as other frequencies, the system being characterized in that there are provided,a filter in the station for separating a band of frequencies, including the tones, from substantially all other frequencies in a received and demodulated source signal,a circuit for producing at least one reference frequency tone,a circuit for producing a digital signal to indicate the relative frequency spectrum positions of the separated tone signal from the filter and of the reference tone, anda circuit, responsive to the digital signal, for indicating whether or not the separated tone signal is the correct tone.
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Accused Products
Abstract
In a radio communication system of the cellular type wherein sets of communication channels are reused in different adjacent sets of cell areas within a common mobile communication service area, each cell base station utilizing a given set of channels in common with other base stations is assigned a different supervisory tone to be modulated on all of its channels. Any mobile unit receiving such channel transponds the modulated supervisory tone and sends it back to the base station. At each base station the transmitted and received supervisory tones for any given channel are compared to produce an indication of whether or not the sending mobile unit is actually communicating on the transmitted channel of the same base station. At each mobile unit, reference tones are generated which are spectrally located between adjacent ones of the possible supervisory tones for the mobile communication area, and the spectral position of a received tone with respect to the reference tones is determined. Signals representing that determination are translated into a digital character corresponding to the name of the received tone, and that name is compared with the name of the tone for the mobile unit'"'"'s assigned channel. A name mismatch is utilized to quiet the mobile unit receiver for the duration of the mismatch. In addition, if that duration exceeds a predetermined interval, the mobile unit controller is actuated to initiate the dropping of communication on the assigned channel.
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Citations
12 Claims
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1. In a radio communication system in which significant signal reception and demodulation is possible at one station from plural signal sources having the same nominal frequency, but only one of such sources is assigned for communication with such station and each source signal has modulated thereon a unique tone for that source as well as other frequencies, the system being characterized in that there are provided,
a filter in the station for separating a band of frequencies, including the tones, from substantially all other frequencies in a received and demodulated source signal, a circuit for producing at least one reference frequency tone, a circuit for producing a digital signal to indicate the relative frequency spectrum positions of the separated tone signal from the filter and of the reference tone, and a circuit, responsive to the digital signal, for indicating whether or not the separated tone signal is the correct tone.
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2. In a radio communication system,
means for receiving a plurality of signals having the same nominal frequency and having different tones modulated thereon, only one of said signals being desired for communication with said receiving means, said receiving means providing at an output thereof one of said plurality of signals, means coupled to said receiving means output for selecting a sufficient band of signal frequencies to include all of said tones of the tone signal modulation to produce thereby a selected tone which is the one of said tones modulated on said one of said plurality of signals, means for generating at least one reference tone, and means, responsive to said selected tone signal in the output of said selecting means and to said reference tone, for producing a digital signal indicating the relative frequency spectral position of the selected tone signal with respect to said reference tone.
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11. A radio communication system of the cellular type wherein plural cell sets are assigned the same set of communication frequency channels and the cell-channel assignment pattern in each set is such that cells with the same channel assignments are at least a predetermined minimum distance apart so that interference-limited radio communication can be effected between a base station of any one of said cells and mobile radio stations in such cell, each of said cells which is within a potential interference range of another cell, and utilizing the same channel assignment, is assigned a tone which is different from a correspondingly assigned tone of said another cell and which is provided for modulation on its channel carrier frequencies by its base station, and said system comprises
in each base station and each mobile station, means for selecting said assigned tones received at such station on a predetermined channel, and means for evaluating the correctness of the selected tone with respect to the tone assigned for the station by comparing the selected tone to at least one reference tone, said evaluating means comprises in a base station, means for comparing the assigned tone provided in the base station for modulation, as the reference, to the selected tone, and means for indicating whether or not there is a frequency difference in excess of a predetermined threshold between such tones, and said evaluating means comprises in a mobile unit means for generating at least one reference tone which is different from any of said assigned tones, and means for indicating the relative frequency spectrum positions of the last-mentioned reference and selected tones.
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12. In a radio communication system in which signal reception is possible at one station from plural signal sources having the same nominal frequency but only one of such sources is assigned for communication with such station and each such source signal has modulated thereon a unique tone for that source as well as other frequencies, a method for verifying reception of said one source signal comprising the steps of
separating a band of frequencies, including the tones, from substantially all other frequencies in a received source signal, producing at least one reference frequency tone, producing a digital signal to indicate the relative frequency spectrum positions of a dominant one of the separated tones and of the reference tone, and determining in response to said digital signal whether or not the dominant tone is the correct tone.
Specification