This question appears in Mumbai University > Satellite Communication and Network subject

Marks: 10 M

Year: May 2013, Dec 2013

TDMA synchronisation

The synchronisation is achieved by introducing a transmit frame delay DN to mark the transmit frame timing of station. Thus, if station N transmits a burst at it transmit frame timing, this burst will arrive at the satellite at the same time as the reference burst.

On the basis of the techniques for determining DN, there may be two kinds of synchronisation process. They are open loop synchronisation and closed loop synchronisation. In one of them DN is determined by the earth station directly from monitoring its own transmission and the method is called closed loop control.

Closed loop synchronisation

In closed loop synchronisation method, the station observes the position of its own burst relative to the reference burst by measuring time interval between the reference burst unique word and the traffic burst unique word, computes the error and determines the new value for the delay DN. Thus in EN(i) is observed error then the contracted delay is $DN(i+1)$.

Open loop synchronisation

In the open loop synchronisation such that of cooperative synchronisation a control station listen to the burst ad sends the timing information back to each transmitting stations. The main thing in the instruction is the time delay DN. The control station transmits DN values to all the network members once every 32 multiframes. When entering the network, the station uses the DN supplied to it and in case it transmits abruptly, the error will b monitored by the control station, which will then send code for don’t transmit (DNTX) for no more transmission from the particular station.