четверг, 21 января 2010 г.

New update! Improved bit stream.

Please watch small video-clip about new update.

In all previous versions, the bit stream received as a result of demodulation of PSK signals in SA, was represented as relative corners, that caused some problems with the subsequent processing of the received data.

From version and above, universal PSK demodulator in SA, produces a bit stream in conditional codes of absolute corners. Such approach in the first, removes set of artificial problems with the subsequent data conversion, because to receive bites from absolute codes of corners does not represent special complexity, and in the second, it is a standard format for the majority of similar solutions.

We have divided/separated operation of the viewer, and operation of the demodulator, although they are still closely connected, but can work in different dimensions n-Ary. It allows to select an optimal mode of demodulation, that is certainly positively influences on the quality of a bit stream.

Two new units are added:

1) Vectors dem - at active state shows working positions of the demodulator, in the form of the vector diagram.
2) Dem output as - the list of modes accessible to the demodulator, it is possible to select any, depending on a signal and the task.

The bit stream is output by the demodulator in the form of codes of positions of absolute corners, which are occupied with a constellation point, at the time moment, which is corresponding to clock synchronization. The zero vector is displayed by light-blue colour, and encoded as 0, other positions are encoded by increasing and numbered counter-clockwise from a zero vector.

The list of operating modes of the demodulator includes:
1) standard mode
2) modes for demodulation of relative sorts, such as PI/4 DQPSK and similar.

For these sorts of signals, mapping of constellation with reduced arity in a mode of the first difference, and besides, turn of the constellation on an appropriate corner is characteristic. All this is well-known, but it was an absolute barrier for the qualitative demodulation in former versions.

In the list of modes of demodulation, for such signals these modes are flagged by s character (s means- special/shifted).

Please, pay attention that dimension of a viewer n-Ary 8 does not correspond to dimension of demodulation 4, and besides, special shift is necessary. In usual universal demodulators, it calls very serious problems with the quality of a bit stream for such signals.

One more example of receiving of a direct bit stream for the signal Orbcomm: it is possible thanks to the fact, that modulation used, in this case, is SDPSK, and it is equivalent to PI/2 DBPSK( or other names, PSK-2 with phase rotation, PSK-4 without transitions on 180 etc). And as it is binary sort of modulation, there is possibility to receive bits directly from the demodulator.

It is known that such sort of manipulation concerns to half-modes, and the signal can be demodulated by the frequency detector ( as a compulsory measure of course). Let's compare quality of the received bit stream with the coherent demodulator in SA and the bit stream, received in the frequency detector. Naturally, in this case, the stream from SA demodulator is more preferable, because all possibilities of coherent processings are realised.