Quasonix RDMS, Инструкция по установке и эксплуатации

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3
rd
Generation Rack-
Mount RDMS™
111 Quasonix, Inc.
periodically change to extend the length over which phase trajectory of different data sequences can rejoin. This
increases the minimum distance, thereby improving the Eb/No performance.
Since the MHCPM waveform is heavily filtered, there is no traditional “eye” opening that can be viewed with an
oscilloscope. Therefore, a synthetic two point constellation display is produced from the output of the trellis detector
that is required to demodulate and recover the data. The trellis detector effectively computes the correlation between
the received signal and all possible phase trajectories that could have been generated by the transmitter. For each
data symbol, the one with the largest correlation is declared to be the winner, and two data bits are produced. The
“
constellation
”
display is created by multiplying the correlation value (real and imaginary) by the sign of the
individual data bit (+1 for 1, -
1 for 0). This produces a “BPSK”
-like constellation with two ideal dots at 0 degrees (x
= 1, y=0), or 180 degrees (x = -1, y=0). It behaves like a BPSK constellation in the sense that dots farther apart on
the x axis indicate a better signal, the dot spread relates to SNR, and dots that tilt to the left or right show phase
rotation.
Figure 187: MHCPM Constellation Figure 188: MHCPM Spectrum Display
STC Constellation
In the Space-Time Coding (STC) mode of operation, the data stream is encoded into two separate signals that each
contain a complete copy of the source data. These two signals are transmitted simultaneously on the same RF
frequency (usually over two separate antennas) to produce a radiated over-the-air signal that eliminates antenna self-
interference and improves message detectability with a similar bandwidth requirement as a conventional SOQPSK
system. The trade-off for these substantial benefits is an increase in receiver processing complexity. Unlike
traditional telemetry waveforms that are easy to process by looking at either the frequency or phase representation,
STC consists of the sum of two unsynchronized phase modulated signals with seemingly unrelated data that must be
recombined to recover the original source data.
While the spectrum display is virtually the same as the SOQPSK spectrum when the RDMS is running in STC
mode, the receiver display looks quite different than the usual SOQPSK constellation, as shown in Figure 189. The
individual parts of the display are labeled in Figure 190.
Since no traditional constellation exists for this mode, the RDMS displays the relative strength of each signal, the
difference in time of arrival between them, and the received strength of the embedded pilot sequences. In a typical
application, one of the signals is transmitted out the top antenna of a vehicle while the other signal is transmitted
from the bottom. In this setup, the height of the green line above the blue graduated horizontal bar represents the