updated lte link budget reference

src/lte/test/reference/lte_link_budget.m

@@ -1,18 +1,27 @@
+clear all;
+close all;
+
 ## LTE from theory to practice
 ## Table 22.7 Reference sensitivity.
 
-
 f = 2160e6;  # carrier freq Hz, EARFCN = 500 (downlink)
-n = -107.5 # noise power dBm, corresponds to 5 MHz BW
+nrbs = 25; # tx bandwdith configuration in number of RBs
+bw = nrbs * 180000; # bandwidth in Hz, note that this is smaller than
+		    # the nominal Channel Bandwdith, see TS 36.101 fig 5.6-1
+kT = -174; # noise PSD in dBm / Hz
+n = kT + 10*log10(bw);  # noise power dBm
 p = 30;  # tx power dBm
-nf = 5; # receiver noise figure in dB
+txPsd = p - 10*log10(bw); # power / bandwidth in linear units
+nf = 9; # receiver noise figure in dB
 
 d = logspace (0,5,100);
 g = 10.*log10 (gain_freespace(d,f)); # propagation gain in dB
-snr = p + g - n - nf ; #dB
+
+snr = p + g - n - nf; # dB
+##snr = txPsd + g - kT - nf ; # dB
 
 
-semilogx (d, snr);
+semilogx (d, snr, ";friis;");
 xlabel ("distance (m)");
 ylabel ("SNR (dB)");
 title ("LTE link budget");