| 摘要 |
<p>According to the invention, a pilot signal (4) is transmitted from a base station on each available carrier. This is done for each available carrier and in every time slot of the carrier irrespective of whether or not a useful signal is transmitted in the time slot. The pilot signal contains a limited quantity of information concerning the base station, such as information about the radio interface. The information is time slot synchronized so that the same information is transmitted in every time slot. The pilot signal level varies, and in time slots which are in traffic use it is suitably lower than the level of the useful signal (1) proper, but in idle time slots it has a very low static level. It has the same band width Df as the normal useful signal. However, it is coded in a different way than the useful signal and in such a way that although it almost drowns in noise, it can still be extracted from the noise. The mobile gets information from the pilot signal on the state of channels (time slots) in the uplink direction. When deciding to perform channel exchange, it chooses any free channel it likes and transmits an access burst to the base station on this channel. If the base station accepts the channel, it will transmit back an access grant burst on the same channel, whereafter the base station and the mobile will immediately transfer the traffic to this channel.</p> |
