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


Hello Arthur,

   The major reason is that ITU-Vehicular B is not suitable for the cell planning considered in Mobile WiMax.
Recall that the delay spread of channel depends on the cell size, the height of antennas and so on. The
precise analysis on the delay spread might be provided by others. However, I would like to draw your attention
on Table 7 (page 31) of the PDF file your referred. Please note that the distance between BS to BS is only 2.8 Km.
Acutally, per information on field trial for 16e, the cell radius is only around 1 Km. For such a cell size, the delay
spread of channel could not be larger than 10 usec.

ITU-Vehicular B might be popular for GSM/3G system due to the larger cell size but not for Mobile WiMax. For example,
in the current Mobile WiMax Radio Comformance Test (MRCT) MS-09 (sensitivity), only three channel models are considered:
AWGN, ITU-Pedestrian B at 3 Km/Hr mobilty and ITU-Vehicular A at 60 Km/Hr mobility. FYI.

Best regards,
  Lepidus.



Arthur Liew <geniusbb@GMAIL.COM>

2006/10/14 01:29 AM
請回信 給 Arthur Liew

       
        收件人：      STDS-802-16@listserv.ieee.org
               
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        主旨：          [SPAM] [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.



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