среда, 13 июля 2011 г.

OFDM. COFDM: Rohde&Schwarz GN2130 digital voice modem

Rohde&Schwarz GN2130 digital voice modem
OFDM, Ch - 48, Sh - 56.25, Br - 44.4(4), QAM-16/PSK-4, k = 17/64

Author: SergUA6 
Band Width ~ 2700 Hz
Low Range ~ 360 Hz
Baud Rate 44.4(4) Hz
n-Ary (PSK/MPSK) Mixed QAM-16/PSK-4
Count of Carriers 48
Step between carriers 56.25 Hz
ACF Typical ~ 45 ms
RX mode  SSB




Sonorgams:

pic.1  General view


Diagrams:

pic.2 General quantity of the channels



pic.3 The constellation in the channel




R&S GN2130 - is the The voice modem, optionaly delivered to HF transceiver XK200 of R&S corporation. It is used for a speech transmission after conversions into a digital form, closing of the data by means of internal cryptoprocessor is possible. In this example, 48 channel OFDM signal is orginized, with standard enough parametres. 


Modulation in the channels is mixed QAM-16/PSK-4.  Features: it is necessary to mark presence of the auxiliary/pilot-symbols , in every second symbol through every one channel for synchronisation and customisation/fine tuning of the adaptive corrector the special signals are transmitted. Also there is a presence of the preamble with duration about 600 msec. Maximum common technical speed for QAM-16 is ~ 8533 bps.