The pilot channel provides several critically important functions to the forward links in IS-95 systems. As its definition states, the pilot channel is only modulated by the PN spreading codes. This facilitates the process of generating a time synchronized replica at the receiver of the PN spreading sequences used at the transmitter to modulate the Synchronization, paging, and traffic channels transmitted from that base station. The power of the pilot is an indication to the mobile of its ability to successfully use the signals from the base station transmitting that pilot. The individual pilots are recognizable based on a specific offset of the short pilot PN sequences which have a period of exactly 215 chips. The pilot channel also provides the coherent reference signal needed to demodulate the coherent Binary Phase Shift Keying (BPSK) modulation used on the forward link. The pilot channel, when processed by the pilot searcher, also identifies the multipath-delay structure on which the mobile receiver bases its decisions of how best to use its RAKE-receiver fingers. To provide all these important functions reliably, the power level at which the pilot channel is transmitted is typically higher than the power used on any other channel. A pilot-power level of 2 Watts is not unusual. With a total forward-link power output of say 8 Watts, the pilot power is usually on the order of 25% of the total forward-link power.
发表于 2012-9-5 14:06:57
