rfid_datacapture: forward_link_limit.py Source File

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00001 import numpy as np, math
00002 import pylab as pl
00003 
00004 SENSITIVITY = -80 # dBm
00005 THRESHOLD = -18 # dBm
00006 
00007 # P^inc_rdr = P_rdr + 2*alpha > SENSITIVITY  (1)
00008 # P^inc_tag = P_rdr +   alpha > THRESHOLD    (2)
00009 
00010 # crossover = (1) - (2)
00011 
00012 crossover_alpha = SENSITIVITY - THRESHOLD
00013 crossover_Prdr = THRESHOLD - crossover_alpha
00014 
00015 # alpha > 0.5 * (SENSITIVITY - Prdr)   (3)
00016 # alpha >        THRESHOLD   - Prdr    (4)
00017 
00018 print 'Crossover Point:\n\talpha: %2.2f\n\tPrdr: %2.2f' % (crossover_alpha, crossover_Prdr)
00019 
00020 prdr = np.linspace( 0, 50 )
00021 # alpha = np.linspace( -47, -30 )
00022 alpha_3 = 0.5 * ( SENSITIVITY - prdr )
00023 alpha_4 =         THRESHOLD   - prdr
00024 
00025 f = pl.figure( figsize=(12,6) )
00026 pl.axes([0.1,0.1,0.65,0.8])
00027 
00028 f3 = pl.plot( prdr, alpha_3, 'g', linewidth = 3.0 )
00029 pl.hold( True )
00030 f4 = pl.plot( prdr, alpha_4, 'r', linewidth = 3.0 )
00031 # x_min, x_max, y_min, y_max = pl.axis()
00032 # pl.axis([-47,-30,y_min,y_max])
00033 
00034 pl.legend((f3,f4),
00035           ('$P^{inc}_{rdr}$ > %d dBm' % (SENSITIVITY), '$P^{inc}_{tag}$ > %d dBm' % (THRESHOLD)),
00036           loc=(1.03,0.2))
00037 pl.xlabel( '$P_{rdr}$ (dBm)' )
00038 pl.ylabel( '$\\alpha$ (dBm)' )
00039 pl.savefig('forward_link_limit.png')
00040 pl.show()
00041 
00042 
00043