CDMA Pseudo-Noise Offsets: Locating Cell Sites

The following information relates to Telus Mobility in BC. The orientation of offsets is different for ClearNET, and may be different for other providers. Thanks to Steve Romaine's Cellular Information Site, for his Field Debug information clued me in to the basics of how this all relates.

One of the most interesting things to look at in the Call Status Mode Display is the Pseudo-Noise offset. (AAA & FFF) You can use this information to tell what cell sites your phone is currently using, and any soft-handoff candidates that the phone may be combining information from for error correction & redundancy.

One of the nifty ways about PN offsets are that there are three per cell site, which means, you can use it as a rough guide as to which direction your tower is as well. The lowest usually, directed towards the south-east, the next towards the east, and the highest north-east. The numbers are always increments of 160. The diagram to the right shows an illustration of the layout of the tower at the Open Learning Agency near Sanderson Way & Willingdon in Burnaby. (Tower Config 5 on the chart)

Telus uses increments of four for each of their 'tower configurations, and I have made a table of the offsets that you can expect. If you think you've found a tower, circle around it, and you should see the corresponding numbers on the chart, 160 apart.

Cfg SE W NE Cfg SE W NE Cfg SE W NE Cfg SE W NE
1 4 164 324 11 44 204 364 21 84 244 404 31 124 284 444
2 8 168 328 12 48 208 368 22 88 248 408 32 128 288 448
3 12 172 332 13 52 212 372 23 92 252 412 33 132 292 452
4 16 176 336 14 56 216 376 24 96 256 416 34 136 296 456
5 20 180 340 15 60 220 380 25 100 260 420 35 140 300 460
6 24 184 344 16 64 224 384 26 104 264 424 36 144 304 464
7 28 188 348 17 68 228 388 27 108 268 428 37 148 308 468
8 32 192 352 18 72 232 392 28 112 272 432 38 152 312 472
9 36 196 356 19 76 236 396 29 116 276 436 39 156 316 476
10 40 200 360 20 80 240 400 30 120 280 440 40 160 320 480

I recently scouted out a few towers in the area of my home, to see how far my phone was actually picking up signals. From my house, my phone will show PN offsets from about 10 different towers. I will possibly do up some kind of map to illustrate my results.

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Ryan Goolevitch - ryang@trideja.com
Last Modified August 21, 2001