Hi Colby, I know cheaper in hardware, but now I don't understand how using IIR filter can compute the RSSI?
On Fri, Aug 5, 2011 at 9:18 AM, Colby Boyer <colby.bo...@gmail.com> wrote: > Cheaper in hardware. You only need one adder. > > > On Thu, Aug 4, 2011 at 6:13 PM, Page Jack <jack.page...@gmail.com> wrote: > >> 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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