Baseband signal processor for a microwave radio receiver
First Claim
1. In a digital radio transmission system having a source of binary digital information for transport in bursts from origin to destination, a signal source using that information to generate a bandwidth limited baseband binary waveform, a first transmitting transducer to linearly modulate that information bearing waveform upon a radio frequency carrier which is then amplified and applied to a first radio antenna which radiates the radio frequency energy containing carrier and information, a fading and time dispersive medium over which that radiated radio frequency carrier energy is transferred between source and destination, a second antenna capturing a fraction of that radiated energy, a second receiving transducer connected to said second antenna which demodulates the captured radiated energy and recovers the baseband waveform modulated at the transmitter except as modified by distortion in the transmission medium, and a signal processor to recover the original binary information from said recovered baseband waveform, said signal processor including means for block coding the transmitted digital stream into symbols of 7, 11 or 13 sub-bits, recognition means for detecting particular significant patterns of sub-bits within said symbols, said recognition means including an analog delay line tapped at regular intervals corresponding to the time duration of one sub-bit of said symbols, means for algebraically and linearly summing the signal levels at a number of consecutive taps to detect correlation between received and expected sub-bit patterns, and means for the selection of one or the other of opposed polarities at each tap which represents the expected polarity of the corresponding sub-bit at the collection points of a voltage or current summing network, the improvement comprising:
- means for the use of only the Barker pattern for the synchronization of sub-bit and symbol clocks at the beginning of each burst;
means for the transfer of further data by use of one-of-four patterns to carry two-bits of data information per symbol, or one-of-N patterns where N equals the decimal representation of the number of bits per symbol when three or more bits per symbol are coded; and
means for limiting sub-bit patterns within said symbols to those where there is a three sub-bit window in which there is no cross-correlation between allowed and possible patterns.
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Accused Products
Abstract
A baseband signal processor within a radio receiver provides a design which does not materially increase the size and weight or decrease the battery life of the host equipment. A passive analog delay line is used for correlation by analog summing. The time discrimination function of spread spectrum is retained, and is used for one dimension of the diversity operation. A further analog integration technique is used to sum the data symbol energy received over a time interval corresponding to the delay differences of multiple radio paths. The input signal for the signal processor is an NRZ binary analog baseband waveform that is shaped for a minimal bandwidth transmission medium, but modified by the distortions which result from radio propagation. The output of the signal processor is the data content presented as clean logic-level states with lines for data and bit clock.
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Citations
13 Claims
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1. In a digital radio transmission system having a source of binary digital information for transport in bursts from origin to destination, a signal source using that information to generate a bandwidth limited baseband binary waveform, a first transmitting transducer to linearly modulate that information bearing waveform upon a radio frequency carrier which is then amplified and applied to a first radio antenna which radiates the radio frequency energy containing carrier and information, a fading and time dispersive medium over which that radiated radio frequency carrier energy is transferred between source and destination, a second antenna capturing a fraction of that radiated energy, a second receiving transducer connected to said second antenna which demodulates the captured radiated energy and recovers the baseband waveform modulated at the transmitter except as modified by distortion in the transmission medium, and a signal processor to recover the original binary information from said recovered baseband waveform, said signal processor including means for block coding the transmitted digital stream into symbols of 7, 11 or 13 sub-bits, recognition means for detecting particular significant patterns of sub-bits within said symbols, said recognition means including an analog delay line tapped at regular intervals corresponding to the time duration of one sub-bit of said symbols, means for algebraically and linearly summing the signal levels at a number of consecutive taps to detect correlation between received and expected sub-bit patterns, and means for the selection of one or the other of opposed polarities at each tap which represents the expected polarity of the corresponding sub-bit at the collection points of a voltage or current summing network, the improvement comprising:
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means for the use of only the Barker pattern for the synchronization of sub-bit and symbol clocks at the beginning of each burst; means for the transfer of further data by use of one-of-four patterns to carry two-bits of data information per symbol, or one-of-N patterns where N equals the decimal representation of the number of bits per symbol when three or more bits per symbol are coded; and means for limiting sub-bit patterns within said symbols to those where there is a three sub-bit window in which there is no cross-correlation between allowed and possible patterns. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification