Dear
Jiho Jang and all,
I
agree that the computational complexity required in the correlation algorithm
using symmetric pattern is higher than that of using repetitive pattern.
However, the peak value among correlation values from the algorithm using the
repetitive pattern is vague so that multiple candidates for fine synchronization
appear. As a result, a lot of additional correlation process with time domain
version of preamble PN sequence are required to find fine timing. On the other
hand, the peak value from the algorithm using symmetric pattern is easily
detected even though Nfft/4 samples are used for correlation. This results
in few additional correlations for fine timing synchronization. Therefore
overall processing burdens of both algorithms are almost same.
Secondly, I also think that coarse frequency offset cannot be
obtained only with the symmetric pattern. The coarse frequency offset can
be acquired efficiently from phase rotation between CP and tail of
symbol in symmetric pattern. When the coarse freq. offset is computed after
the coarse time synchronization, the performance under the symmetric pattern is
better than that under the repetitive pattern.
In
addition, I wonder if common preamble is useful in handover. Since preamble
indices of neighbor cells are known to SS through the messages related
to handover, acquisition of synchronization with neighbor cells can be
achieved as fast as the common preamble does. The common preamble right
before the cell-specific preamble in this case seems to
be overhead. The common preamble every second frame makes the time required
for scanning longer. Since the main objective of scanning is measurement of
CINR of neighbor cells, SS has to find the cell-specific preamble. Therefore, SS
wastes a frame including common preamble without obtaining
CINR.
This
is my short comment on common preamble and the repetitive pattern.
Best
Regards,
Bin-Chul
Ihm
Sent: Thursday, August 12, 2004 9:54 AMSubject: [STDS-802-16] Fwd: Re: [STDS-802-16] [PREAMBLE] - Technical discussion on preamble structure and sequence designHi, Bin-Chul:
I think it is a good comment. The real valued sequences in frequency domain yield conjugate symmetric patterns in time domain.
But, the time synchronization using the symmetric structure has some problems. In addition, the frequency offset estimation cannot be done using the symmetric structure only.
Firstly, the computational complexity required in the algorithm using symmetric pattern is much higher than the algorithm using repetitive pattern.
The algorithm using the symmetric structure has to newly calculate the correlation value by correlating all the time samples at every sample timing. In the algorithm using the repetitive pattern, on the other hand, the correlation value can be obtained by only adding the newest one sample value and discarding the oldest one sample value at every sample timing.
Since the timing hypotheses should be collected at every sample timing for a frame duration at least, the synchronization using repetitive pattern can much lower the computational complexity than the symmetric based algorithm.
Secondly, the coarse frequency offset estimation cannot be achieved from the symmetric structure only. Instead, you can easily obtain the frequency offset estimation by using the repetitive pattern, where you only need to compare the phase rotations between a pair of samples.
Regards,
Jiho Jang
Jiho Jang (Ph. D) NTP Development Team (System Lab. 2)
Telecommunication System Division
Telecommunication Network
SAMSUNG ELECTRONICS CO.,LTD
T. 82-31-279-3355
M. 016-9233-8541
------- Original Message -------
Sender : bcihm<bcihm@LGE.COM>
Date : 2004-08-12 09:26
Title : Re: [STDS-802-16] [PREAMBLE] - Technical discussion on preamble structure and sequence design
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 -----Sent: Thursday, August 12, 2004 5:29 AMSubject: [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
