Hi Colby, I don't understand why compute RSSI need an IIR filter? as I know the rssi can be compute like that: (sample[0]*sample[0]+...sample[i]*sample[i]) / (i+1)
Regards! On Thu, Aug 4, 2011 at 2:44 PM, Colby Boyer <colby.bo...@gmail.com> wrote: > On Wed, Aug 3, 2011 at 6:30 PM, Page Jack <jack.page...@gmail.com> wrote: > >> the code below is in sdr_lib/rssi.v I don't understand especially this >> line: rssi_int <= #1 rssi_int + abs_adc - rssi_int[25:10]; >> >> wire [11:0] abs_adc = adc[11] ? ~adc : adc; >> >> reg [25:0] rssi_int; >> always @(posedge clock) >> if(reset | ~enable) >> rssi_int <= #1 26'd0; >> else >> rssi_int <= #1 rssi_int + abs_adc - rssi_int[25:10]; >> >> assign rssi = rssi_int[25:10]; >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> > It appears to be a clever way to implement a single pole IIR filter. Josh? > > If you recall an IIR is defined as y[n] = (1-alpha) * y[n-1] + x[n] > > Since multiplier are expensive in hardware, lets use a multiples of two so > you can bit shift, then add and subtract. :D In this case alpha is 2^-10 > > --Colby >
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