[STDS-802-16] [PREAMBLE] Technical discussions of preamble sequence design.
Hi all,
I'd like to start a technical debate of preamble sequence designs since we
don't have one yet.
Let me start with defending my CAZAC preamble design.
First of all, I'd like to point out advantages of the proposal. For
technical details please refer
to the contribution document.
1. Adopt a single sequence (CAZAC) allowing a mechanizm for fast cell
searching.
2. Fully explore the frequency-time duality of CAZAC sequences (Chu,
Frank-Zadoff).
a. Sequence matched filtering can be done solely in frequency domain.
It yields comparable results in time domain.
b. Inherit timing and frequency offset ambiguity, CAZAC sequence
detection is not impaired
by unknown symbol timing offset and frequency offset. In other
words, detection of
CAZAC sequence is not affected by non-ideal capturing of time
waveform for FFT and unknown frequency offset.
Timing offset in time domain is translated into CAZAC cylic shift
in frequency domain. Detection
of CAZAC is not impaired.
c. Matched filtering (in frequency domain) of CAZAC sequence yields
accurate CIR (channel impulse response).
It produces channel quality info, time of arrival (for MSS
precision adjustment of timing in UL and during HO),
Precision windowing of FFT waveform capturing to minimze OFDM ISI,
etc.
d. WIth proper cell planning that neighering BSs maintian large CAZAC
code-phase spacing (so that multi-path responses
do not overlap), a single scan of the preamble symbol yields CIRs
(channel quality too) and timing (arrival time) of all cells
and segments (sectors). It provides a mechanizm to allow for fast
HO and fast wake-up during sleep (critical to reduce
MSS standby time).
3. Inherit CAZAC characteristics that PAPR is very low ( worst-case 2..6dB
in 1024-FFT, 2.7dB in 512-FFT, and 4dB in 128-FFT).
This is critical to achieve coherence detection where preamble can be
power-boosted.
Questions that may be raised.
1. How frequency offset can be corrected at powerup?
Answers:
a. Frequency offset greater than four carrier subspacings can be
detected/corrected by energy detection of guard band detections
and missing edge subcarriers (critical for MSS to relax the spec
high-precision TCXO).
b. Finer coarse frequency offset to be better than +-0.5 subcarrier in
PUSC can be achieved interpolating CIR results
(from CAZAC matched filtering in frequency domain) of adjacent
frequency segments.
c. +-4 carrier subspacings frequency correction can be done by
hypothesis testings of detected FCH symbols (similarity tests
of the four repetition codes). This is probably the only test
capable of determing false alarms in all preamble sequences.
d. Fine frequency and phase cancellation can only be done via pilot
channel tracking.
2. Since Chu and Frank-Zadoff sequence has time-frequency offset ambiguity,
how to tell them apart?
Answers:
Since initial frequency offset can be cancelled in (1), timing offset
can be immediately identified. Once MSS is in tracking mode,
frequency offset uncertainly is ruled out and timing offset is uniquely
determined.
3. Is there a lack of large code-phase spacing in PUSC deployment (Jeff
from Moto raised it).
Answers:
As soon as we establish that IDcell need not be tied to preamble
sequence, optimal cell planning to maximize CAZAC code-phase
spacing of neighering BS can resolve the concern over overlapping
multi-path responses. Coarse symbol timing of preamble
symbol can be done via CP and power-burst energy detection. CAZAC
code-phase identification is done using the quantization
effect of CAZAC code-phases.
I maintain that there is no need to create preamble sequences for different
segments. Also IDcell needs to be redefined and that
PUSC permutation should stay the same for all cells and zones.
I welcome all comments. Thanks in advance.
Jason Hou
ZTE San Diego,
(760) 419-2689.