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The Pilot Channels
By Dr. Ernest Simo
1.0 The Pilot Channels
The Pilot Channels are always on Walsh code channel zero. They serve as a demodulation reference for the mobile receivers, and for handoff level measurements, and thus must be present in every station. Pilot channels carry no information. They essentially consist of Short PN chips and facilitate rapid pilot searches by the mobiles.
The amplitude of the pilot and it's spatial distribution must be carefully controlled because their relative amplitudes affect handoff boundries between stations.
The Short PN code pair (PNl and PNQ) is generated by a modified linear feedback shift register. The resulting sequences have a length of 215 or 32,768 chips. At 1.2288 Mcps, this means a period of 26.667 ms.
All Base Stations and Sectors use the same short code, and thus have the same pilot waveform. They are distinguished from one another only by the phase (Short PN code Offset) of the pilot. The air interfaces stipulate that pilot phases be nominally assigned to stations in multiples of 64 chips, giving a total of 215-6=512 possible assignments. The 9-bit number that identifies the pilot phase assignment is called the Pilot Offset.
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By Dr. Ernest Simo
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