8 Jan
2011
8 Jan
'11
8 a.m.
Bit rate duration is determined from physical channel throughput for
particular modulation schema. GMSK modulation is used with constant BT
= 0.3, where B is the 3dB bandwidth of the theoretical Gaussian
filter and T is duration of input data bit. Knowing B, we calculate
1/T = 1625/6 ksymb/s or approximately 270.833 ksymb/s. From here bit
duration is 3.69.. μ s.
Voice signal is processed in time intervals of 20ms = s/50. For that
period of time throughput is [(1625/6) x (1000/50)] symbols. Because
this number is fractional, let look at 6 times longer time interval.
For time interval 120ms throughput is [1625 x 20] symbols or [13 x 125
x 20] symbols or [26 x 1250] symbols or [26 x 8 x 156.25] symbols.