In wireless communications, radio
propagation can be modeled effectively with a
1/dn transmit power rolloff (usually, n = 2 for
short distance and n = 4 for longer distance). For
successful transmissions, the signal-to-noise ratio
(SNR) received at a host nj should be greater
than a specified predetection threshold yj. This
threshold yj is closely related to the bit error rate
(BER) of the received signal. For successful
transmissions from a host ni to nj, the SNR at
host nj should satisfy the following equation: