Method and apparatus for maintaining synchronization in a simulcast system

A simulcast system having a transmitter controller capable of synchronizing and maintaining synchronization of a plurality of base sites coupled to the transmitter controller, the plurality of base sites having transmitters capable of transmitting data as radio frequency transmission at substantially the same time, said transmitter controller comprising:

• generator for generating time marks at predetermined time periods;
• data divider, coupled to the generator, for dividing the data into predetermined packets to be interposed between at least a pair of time marks;
• transmitter, coupled to the data divider, for transmitting the data packets and time marks to the plurality of base sites;
• the base sites comprising:
• base site receivers for receiving the data packets and time marks;
• clocks, coupled to the base site receivers, for measuring the time between pairs of time marks;
• base sites controller, coupled to the clocks, for determining when there are variations in time between any pairs of time marks and the predetermined time periods;
• timer, coupled to the base sites controller, for adjusting a delay time at each of the plurality of base sites in response to a variation in time between time marks at the corresponding base site;
• and
• said timer for delaying retransmission of data from a receipt of a start command by a predetermined delay time determined for each of the plurality of base sites to enable a retransmission of data at substantially the same time by the plurality of base sites.

A method for maintaining synchronization of data transmissions in a simulcast system, the simulcast system having a transmitter controller capable of synchronizing and maintaining synchronization of a plurality of base sites coupled to the transmitter controller, the plurality of base sites having transmitters capable of transmitting data as radio frequency transmission at substantially the same time, said method comprising the steps of:

• (a) generating time marks at a predetermined time periods;
• (b) dividing the data into predetermined packets to be interposed between at least a pair of time marks;
• (c) transmitting the data packets and time marks to the plurality of base sites;
• (d) periodically transmitting the data packets including the time marks to the plurality of base sites for determining variations in time to the plurality of base sites;
• (e) receiving the data packets and time marks by the plurality of base sites;
• (f) measuring the time between each consecutive pair of time marks;
• (g) determining when there are variations in time between pairs of time marks and the predetermined time period;
• and
• (h) adjusting for the difference in propagation delay of the respective base sites responsive to step (g) to compensate for variations in the propagation delays to the plurality of base sites.