question about fixed Wimax

[jskhalid]

Hi , i have a question about Wimax , i am wondering , that in 802.16d ( fixed wimax ) for two channel bandwith 3.5 & 7 Mhz there is the same FFT 256 carriers , but with 7 Mhz we can get double troughput than the 3.5 Mhz ? , how can we have this if the number of subcarriers are the same??


BR

[firstmaxim]

In WiMAX we have 'subcarrier spacing', which is the distance between two adjacent physical OFDM carriers. The value is calculated by deltaf = (sampling freq)/ (FFT size).

From the value of delta f, the useful symbol time Tb can be computed using Tb = 1 / delta f. To this we will add the guard period Tg. So total symbol period Ts= Tb + Tg. The throughput per subcarrier is the reciprocal of Ts.

Now, coming to your question, on why the througput is different for different bandwidths, although the carriers are constant in WiMAX. You can see from highlighted equation that Tb is small, if subcarrier spacing is large (which is the case with larger bandwidths). This results in a higher throughput per carrier.

Regards.

[jskhalid]

Hi , thx you for your help , i understand now , i have another question , this time about wimax mobile , there is a paramters called permbase , what is this term reffering too, as i know , there is 3 DL permutation scheme in wimax PUSC & FUSC & FFR , but some documents says that there is 32 permbase?, so is there 32 PUSC permbase ??, if i am correct, what are these permutation??, i will apreciate if someone can give a documents explaining this.......


BR

[calvin]

Hi,

If you refer the 802.16e standard, permbase is used to randomize the subcarriers in the subchannel. different permbase is used to create subchannels with different subcarriers to avoid interference at cell edge etc.

In standard you will get the algorithm used to randomise the subcarriers also.

regards,