Re: [STDS-802-16] [PREAMBLE] - Technical discussion on preamble structure and sequence design

[bcihm <bcihm@LGE.COM>]

Dear Anand Dabak and all,

 

I think that initial symbol timing acquisition can be done using symmetric structure of preamble.

Because the preamble is generally real-valued, its IFFT version in time domain has symmetric structure inherently.

 

For example, if Nfft=8 and preamble consists of only real, then samples in time domain within a symbol duration are symmetric as follows:

 

[ a  b  c  d   e   d*   c*  b* ]

 

The samples around 'e' are conjugated symmetric and this property can be used for acquisition of symbol timing.

The symmetric structure is more usefull to finding correlation peak than CP based method because the symmetric part has length of (Nfft/2-1) longer than CP.

 

 

 

And I think this inherent symmetric structure is more useful than repetitive structure.

For example, let's consider a repetitive structure as following:

 

[ a  b  c  d   a   b     c    d  ]

 

The correlation at sample 'a' is |a|^2 + |b|^2+ |c|^2+|d|^2  and that at sample 'b' is  |b|^2+ |c|^2+|d|^2 + ax*.

This means that it is hard to discriminate the peak among correlations over several positions.

However, in the symmetric structure, the correlation at sample 'e' is |b|^2+ |c|^2+|d|^2 and that at sample 'd*' is ec* + db* + cx.

This means that it is easy to discriminate the peak among correlations over several positions.

 

 

In summary, it is enough for acquisition of symbol timing to use the inherent symmetric structure obtained without any manipulation to preamble structure in my opinion.

 

 

 

Best Regards

 

Bin-Chul Ihm

LGE

 

----- Original Message -----

From: owner-stds-802-16@listserv.ieee.org

To: STDS-802-16@listserv.ieee.org

Sent: Thursday, August 12, 2004 5:29 AM

Subject: [STDS-802-16] [PREAMBLE] - Technical discussion on preamble structure amd sequence design

Dear All,

This mail is a followup to yesterday's conference call:

 

In order to help us in evaulating the performance of the existing preamble and compare it against any changes, we would like to know the simulation scenarion that needs to be assumed (eg. a 19 cell model) and the procedure for the initial acquisition (after power on of mobile).

 

Specifically, we want to know whether one can assume that initial symbol timing acquisition is done using CP correlation of the OFDM symbols and that the preamble is used only for Frame timing. If this is a valid assumption, has any one run any simulations using the CP technique to measure its reliability? If so can they share their results with the group?

 

In case the CP base symbol timing is not reliable, we have to perform a time correlation against the preamble sequence itself for initial symbol timing acquisition – in this case, we are concerned with the correlator complexity which could be potentially large as we have to do these correlation operations per ADC output sample. So, in this case we would like to suggest that we look at alternative preamble structures and sequences to reduce the complexity (and in turn power consumption) of the mobile for initial symbol timing acquisition.

Anand Dabak
Texas Instruments