Clear channel assessment (CCA) for UWB communications system
Clear channel assessment (CCA) is a very important issue in Ultra-Wideband (UWB) systems. An effective CCA mechanism will have a large impact on the overall throughput of the communications system. It is disclosed methods and circuits to carry out CCA determinations exploiting the structure of the pulse signal either by using a moving average or by performing a cross-correlation with a locally generated signal.
1. A method of clear channel assessment with respect to a communications medium expected to sometimes carry a specified communications signal, comprising:
attempting reception of the specified communications signal to produce a received signal;
deriving the envelope of the received signal from the received signal;
cross-correlating the envelope of the received signal with a locally-generated signal to obtain a cross-correlation result;
combining multiple cross-correlations results to obtain a combined cross-correlation result;
comparing the combined cross-correlation result to a threshold; and
based on said comparing, producing a clear channel assessment result,
wherein cross-correlating the envelope of the received signal with the locally-generated signal to obtain the cross-correlation result comprises cross-correlating the envelope of the received signal with a rectangular wave or a sine wave, wherein the specified communications signal is a multi-band OFDM ultra-wideband signal, and wherein the rectangular wave or the sine wave has a frequency that is equal to a symbol rate of the multi-band OFDM ultra-wideband signal.
2. The method of claim 1 , wherein combining the multiple cross-correlations results to obtain the combined cross-correlation result comprises averaging the multiple cross-correlations results to obtain the combined cross-correlation result.
3. A method of clear channel assessment with respect to a communications medium expected to sometimes carry a specified communications signal, comprising:
attempting reception of the specified communications signal to produce a received signal;
determining a moving average power of the received signal to produce a moving average output signal;
performing peak detection with respect to the moving average output signal, including determining whether a suspected peak value is valid; and
depending on a number of valid peaks detected, producing a clear channel assessment result,
wherein the method comprises cross-correlating the envelope of the received signal with a rectangular wave or a sine wave, wherein the specified communications signal is a multi-band OFDM ultra-wideband signal, and wherein the rectangular wave or the sine wave has a frequency that is equal to a symbol rate of the multi-band OFDM ultra-wideband signal.
4. Apparatus for clear channel assessment with respect to a communications medium expected to sometimes carry a specified communications signal, comprising:
means for attempting reception of the specified communications signal to produce a received signal;
means for deriving the envelope of the received signal from the received signal;
means for cross-correlating the envelope of the received signal with a locally-generated signal to obtain a cross-correlation result;
means for combining multiple cross-correlations results to obtain a combined cross-correlation result;
means for comparing the combined cross-correlation result to a threshold; and
means for, based on said comparing, producing a clear channel assessment result,
wherein means for cross-correlating the envelope of the received signal with the locally-generated signal to obtain the cross-correlation result is configured to cross-correlate the envelope of the received signal with a rectangular wave or a sine wave, wherein the specified communications signal is a multi-band OFDM ultra-wideband signal, and wherein the rectangular wave or the sine wave has a frequency that is equal to a symbol rate of the multi-band OFDM ultra-wideband signal.
5. The apparatus of claim 4 , wherein means for combining the multiple cross-correlations results to obtain the combined cross-correlation result is configured to average the multiple cross-correlations results to obtain the combined cross-correlation result.
6. Apparatus for clear channel assessment with respect to a communications medium expected to sometimes carry a specified communications signal, comprising:
means for attempting reception of the specified communications signal to produce a received signal;
means for determining a moving average power of the received signal to produce a moving average output signal;
means for performing peak detection with respect to the moving average output signal, including determining whether a suspected peak value is valid; and
means for, depending on a number of valid peaks detected, producing a clear channel assessment result,
wherein the apparatus further comprises means for cross-correlating the envelope of the received signal with a rectangular wave or a sine wave, wherein the specified communications signal is a multi-band OFDM ultra-wideband signal, and wherein the rectangular wave or the sine wave has a frequency that is equal to a symbol rate of the multi-band OFDM ultra-wideband signal.