Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

[STDS-802-16] choice of wimax physical layer parameters ?



Dear All,

Does any one have any idea why wimax forum have commonly chosen parameter below ? (Table 1 of http://www.wimaxforum.org/news/downloads/Mobile_WiMAX_Part1_Overview_and_Performance.pdf )

BW                         : 10MHz
Sampling frequency: 11.2 MHz
FFT                        : 1024
cyclic prefix            : 128

The set of parameter above does not work well for mandatory convolutional coding in ITU Vehicular B channel model, where ITU Veh-B happens quite often. The cyclic prefix is 11428 ns length while the channel impulse response of ITU Veh B is longer than that ! For your reference, the channel impulse response of ITU Vehicular B model is below

Relative delay (ns)  |    Average power (dB)
0                            |    -2.5
300                        |     0
8900                      |    -12.8
12900                    |    -10.0
17100                    |    - 25.2
20000                    |    -16.0

As you can see, the relative delay is longer than 128 * ( 1/11.2e6 ) = 11428 ns (cyclic prefix) of the chosen parameter above ! This confuse me a lot, enlighten me please ? Many thanks.

Regards,
Arthur.