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diff --git a/gr-sounder/README b/gr-sounder/README new file mode 100644 index 0000000000..ef495f1e8c --- /dev/null +++ b/gr-sounder/README @@ -0,0 +1,61 @@ +This is a work-in-progress implementation of a m-sequence based channel +sounder for GNU Radio and the USRP. + +At present, only the transmitter is implemented. When completed, you +will be able to place the sounder transmitter at one location, the +sounder receiver at another location, then determine in real-time the +channel impulse and frequency response between them. + +The sounder uses a custom FPGA bitstream that is able to generate and +receive a sounder waveform across a full 32 MHz wide swath of RF spectrum; +the waveform generation and impulse response processing occur in logic in +the USRP FPGA and not in the host PC. This avoids the USB throughput +bottleneck entirely. Unfortunately, there is still roll-off in the AD9862 +digital up-converter interpolation filter that impacts the outer 20% of +bandwidth, but this can be compensated for by measuring and subtracting +out this response during calibration. + +The sounder is based on sending a maximal-length PN code modulated as BPSK +with the supplied center frequency, with a chip-rate of 32 MHz. The +receiver (partially implemented at this time but not working yet) correlates +the received signal across all phases of the PN code and outputs an impulse +response vector. As auto-correlation of an m-sequence is near zero for +any relative phase shift, the actual measured energy at a particular +phase shift is related to the impulse response for that time delay. This +is the same principle used in spread-spectrum RAKE receivers such as are +used with GPS and CDMA. + +The transmitter and receiver are designed to work only with the board in +side A. This may be a standalone LFTX/LFRX or an RFX daughterboard. + +To use, the following script is installed into $prefix/bin: + +usage: usrp_sounder.py [options] + +options: + -h, --help show this help message and exit + -f FREQ, --frequency=FREQ + set frequency to FREQ in Hz, default is 0.0 + -t, --transmit enable sounding transmitter + -r, --receive enable sounding receiver + -d DEGREE, --degree=DEGREE + set souding sequence degree (len=2^degree-1), default + is 16 + -n SAMPLES, --samples=SAMPLES + number of samples to capture on receive, default is + infinite + -l, --loopback enable digital loopback, default is disabled + +To use with an LFTX board, set the center frequency to 16M: + +$ usrp_sounder.py -f 16M -t + +You can vary the m-sequence degree between 1 and 16, which will create +sequence lengths between 1 (DC) and 65535 (1.023 us). This will affect +how frequently the receiver can calculate impulse response vectors (to be +documented as the receiver is completed.) + +Johnathan Corgan +Corgan Enterprises LLC +jcorgan@corganenterprises.com +4/25/07 |