摘要:
To find frequency slots over which a cognitive radio can send an opportunistic transmission, a wideband spectrum is searched with a lower resolution to identify bandwidth slices having low or no signal levels. The identified bandwidth slices are searched with a higher resolution candidate frequency slices are selected as those bandwidth slices having least signal levels after the higher resolution searching, and ranked from lowest signal level to highest. A spectrum detection algorithm is executed on the selected candidate frequency slices in the order of the rank until it is decided that one of them has sufficiently free spectrum. A transmission is then opportunistically sent on the decided candidate frequency slice. Ongoing to the searching, intermittent signals are detected and a band about them is searched with the lower resolution to determine if the band about the detected intermittent signal is an identified bandwidth slice. Various techniques are shown for how the fine search is conducted.
摘要:
Described is an apparatus that includes a frequency source and a plurality of time domain direct digital synthesizers each having an input connected to an output of the frequency source and an output providing an output frequency signal. A particular time domain direct digital synthesizer includes a sigma-delta modulator that functions as a second order multi-stage noise shaping sigma-delta modulator. In one exemplary embodiment sigma-delta modulator outputs provide a unitary-weighted word used to switch certain unit capacitors that comprise part of a delay modulator to produce a time-varying delay having a time-averaged value that directly corresponds to a binary value appearing on a plurality of phase accumulator outputs.
摘要:
Described is an apparatus that includes a frequency source and a plurality of time domain direct digital synthesizers each having an input connected to an output of the frequency source and an output providing an output frequency signal. A particular time domain direct digital synthesizer includes a sigma-delta modulator that functions as a second order multi-stage noise shaping sigma-delta modulator. In one exemplary embodiment sigma-delta modulator outputs provide a unitary-weighted word used to switch certain unit capacitors that comprise part of a delay modulator to produce a time-varying delay having a time-averaged value that directly corresponds to a binary value appearing on a plurality of phase accumulator outputs.
摘要:
Electrical circuit (300, 500, 800, 900) has an input (301, 501, 801, 802, 901, 902) and an output (311, 502, OUT, I-OUT, Q-OUT). The circuit samples an input signal coupled to the input having a certain input frequency and converts the input signal into a certain output frequency at the output, the output frequency being lower than the input frequency. It comprises a first sampler circuit (302, 510, 803, 910) coupled to the input, a second sampler circuit (303, 520, 804, 920) coupled to the input, a buffering component (309, 509, 809, 903, 904) coupled to the output and buffer switching means (305-307, 514, 515, 811-818, 914, 915, 924, 925, 934, 935, 944, 945, 954, 955, 964, 965, 974, 975, 984, 985). The buffer switching means are arranged to respond to a buffering command (fs/N, A, B) by coupling said first sampler circuit and said second sampler circuit to said buffering component.
摘要:
The invention pertains to a method and corrector (IC6) for correcting an error in a parallel analog-to-digital conversion. Such a correctable error is caused by uncertainties in the reading of the states of parallel comparing elements (IC1, IC2, IC3, IC4) in the converter, said uncertainties being brought about by nonideality, such as non-simultaneous state latching. This error is corrected using a nonlinear cellular neural network preferably such that the real level of the phenomenon compared by means of comparing elements (IC1, IC2, IC3, IC4) is estimated by estimating the states corresponding to correct reading of the comparing elements (IC1, IC2, IC3, IC4) read temporally or otherwise erroneously.
摘要:
A delta-sigma modulator for converting an analog input signal into a digital output signal comprises a modulator input (501) and a first analog to digital converter (504) coupled to the modulator input (501). The first analog to digital converter has a first analog input and a first digital output. The delta-sigma modulator further comprises an error quantization unit (505, 506, 507) coupled to the first digital output for determining the quantization error caused by the first analog to digital converter (504). Additionally it comprises first signal combining means (508, 708, 802) for combining the outputs of the first analog to digital converter and said error quantization unit to form the digital output signal.