вторник, 15 февраля 2011 г.

OFDM, COFDM: CIS-128

CIS-128
Br~21, Sh~23.5, Ch-128 in use, total 129 - 1 as gap/off/skiped
OFDM, COFDM


Author: SergUA6
Band Width ~3000-3100 Hz
Low Range 470-500 Hz
Baud Rate ~21 Hz
n-Ary (PSK/MPSK) Mixed mode QAM-16 and PSK
Count of Carriers 129 - 1
Step between carriers ~23.5 Hz
ACF ~476-477 ms
RX mode SSB


Sonograms:

pic.1 General view

pic.2 Clock frequency of manipulation (classical method of recieveing)




Diagrams:
pic.3 The signal's detalization in OFDM module

pic.4 Detalization of the signal if OFDM module


pic.5 Detalization of the signal if OFDM module


Pictures:

pic.6 ACF of the signal

pic.7 CCF of two adjacent fragments with duration 250 ms


CIS-128 - is an interesting enough signal, though quality of the record is not so high. Nevertheless, rather easily it is possible to receive all main parameters in module OFDM. It is shown on the pictures.

It is very interesting that there is divergence ACF with a real state of affairs. ACF shows that there is a periodicity in 10 symbols in the signal. The detailed analysis in module OFDM allows to find out that every fifth symbol is specia l(synchro), and it is logical to expect, that ACF will be with the same period, but it is not so. This moment is easily specified with usage of CCF function. As it is shown on rice 7.

It is well visible that every fifth symbol special (synchro), but special (synchro) symbols different, and alternate through one. It also shows ACF as in this case the repetition period is really equal to 10 symbols.

CCF allows to receive more fine and exact structure, where it is displayed both the general period of special (synchro) symbols, which is equal 5 symbols (steps), and the period of separately even and odd symbols, which is equal already to 10 steps.

One more feature of this record which is well visible in dynamics - is the intensive use of modulation QAM-16 in the first half of the signal, and episodical/rare in the second part of the signal.