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stds-802-16-mobile: OFDMA DL and UL pilot carrier allocation



Dear members,

I'm a graduate student of the University of Lecce (Italy): I'm doing a research about the TCP performance in the wireless environment.

In this moment I'm making a Matlab implementation of the OFDMA physical layer for 802.16e. My problem is the UL pilot carrier allocation.
In Std. 802.16a-2003 pilot carriers are handled as subcarriers of a specific subchannel (for every subchannel), so (logical) pilot carriers are allocated using the described in 8.5.6.2 permutations (e.g. in 8.5.6.2.1). In this way, in every OFDM symbol, physical pilot carriers are allocated as they are illustrated in ftp://193.204.78.98/pubblica/Mino/base.gif.
Otherwise DL, in this way UL physical pilot carriers are not distributed uniformly in used spectra, but they are gathered together in particular zones of spectra. I'm thinking this allocation is bad for correct channel estimation operations !!!
If channel estimation operations are run "for subchannel" performance does not change, because of great physical "frequency-distance" between two consecutive pilot carriers compared as little logical "frequency-distance" of Figure 128bb in Std.802.16a-2003.

Could you tell me if I'm making a mistake or my observation is correct?

Could you tell me how channel estimator should operate (for hole OFDM symbol or for single subchannel)?

What are the news for 802.16e?

Comments and suggestions are well wanted.
Thanks in advance.

Best regards.

Cosimo Palazzo (Università degli Studi di Lecce - Italy)