Why the T18z May Handoff Less Than the 6190

When I first started testing the T18z, I certainly did not expect the phone to handoff any more or less than the 6190. After all, the network still has the final say on handoffs, although it does use information provided by the phone to assist it. That information comes in the form of signal readings for the neighboring channels. For the network to handoff less often, the Ericsson phone would have to be reporting something different than the 6190.

Now before we continue with my theory about this, I should point out that my understanding of the GSM spec is rather hazy in this area. If you understand the material I'm talking about better than I do, then please send e-mail to put me straight on this matter.

My theory begins with some information that I routinely see in the 6190 Field Test Mode screens. A number of screens give the signal quality in terms of values calls C1 and C2. Although the 6190 reports both of these values, it always shows both of them as identical values. In addition to which, those values are a direct reflection of the RSSI. You can convert from RSSI (given in dBm) to the C1 value by subtracting from 101.

The C2 value is supposed to represent a more complex representation of the signal quality. I would assume therefore that it also takes into consideration the level of the background noise present on the channel. If the T18z properly supports the C2 value, then it may very well be reporting more accurate information about the neighboring cells then does the 6190. That means the T18z might be reporting the neighbors as having poorer signals than their RSSI alone would tend to indicate.

If this theory is correct, then it gives the T18z a distinct advantage over the 6190 in situations where thrashing is likely to occur. I therefore decided to test the T18z and the 6190 in exactly that sort of situation. After countless tests I cannot escape the conclusion that the T18z is indeed handing off less often than the 6190. This means that you get less thrashing and less interference during a call in questionable areas.

Now one might expect that other new models, especially the Motorola L Series, also support C2. However, during tests of the Motorola L-2000 I found no appreciable difference in the handoff rate over the 6190. Although this does not disprove my theory, it does put it in question. Unfortunately, I have no way of finding out whether the Motorola L Series phones properly support C2 or not. If I can find out how to put the T18z or the Motorola into Field Test Mode, then I might be able to prove (or disprove) my theory once and for all.