Application: USE YOUR BROWSER "BACK" BUTTON TO RETURN © 1999 DR. ERNEST SIMO - SPACE2000 
Example: Changing the values of T_ADD, T_COMP, T_DROP, and T_TDROP generally have the following effects: - Increasing T_ADD and T_COMP makes it more difficult for a pilot to qualify for promotion to the active set. Hence, movement into the active set is slowed down. Decreasing these parameters generally has the opposite effect. - Decreasing T_ADD but increasing T_COMP makes it easier for a pilot to get into the candidate set, but harder for it to be promoted to the active set, particularly for relatively large values of T_COMP. - Decreasing T_DROP and increasing T_TDROP generally tend to retain pilots in the active set and, hence, movement out of the active set is slowed down. Increasing T_DROP and decreasing/shortening T_TDROP tend to more rapidly discharge pilots from the active set. - To take advantage of the increased performance typically achieved when a mobile is in two-way handoff, with one pilot in the active set, the handoff algorithm may well be set to facilitate the movement of a second pilot into the active set and to retain a pilot in the active set. Hence, at this time, T_ADD and T_COMP might be relatively low and T_DROP might be relatively low and T_TDROP relatively long to keep two pilots in the active. - To avoid possible problems with handoff dynamics when three pilots are in the active set (assuming the mobile has three RAKE-receiver fingers available), once two pilots are in the active set, the new handoff parameters conveyed with the HDM might well be set to allow only a very strong third pilot into the active set. At this time, T-ADD might set high perhaps to a value of - 6 dB or so. - If there are three pilots in the active set, the handoff parameters should typically be set so it is very easy to promote a strong pilot to the active set. This, however, requires that it is easy to demote at least one pilot from the active set. If replacement of a weak pilot in an active set containing three pilots with a strong new pilot is too time consuming regardless of the manner in which the handoff parameters are set, then direct intervention by using the HDM may be needed. Alternately, recognition of the likelihood of this problem could be used to speed-up the response of the computer-generated HDM. - In general, making it difficult to have three (but easy to have two) pilots in the active set, unless one is very strong relative to the others, seems to be a reasonable way to set the handoff parameters. Typical values for T_ADD are expected to be in the - 9 to -12 dB range, although, special cases may cause different values. The minimum T_ADD is expected to be about -17 dB. T_COMP is typically set to provide a ratio of between 1 and 2, or zero and 3 dB. Hence, T_COMP is between zero and 6. The System Parameter Message and the HDM both allow 4 bits for T_COMP. It is not unusual for T_COMP to equal zero. T_DROP is often set to be about the same as T_ADD. It may be a little lower, and T_TDROP a little longer, to retain pilots in the active set. T_TDROP is expected to be only a few (4 to 9) seconds, but Table 6.6.6.2.3-1 in IS-95 allows much longer values. Lower speed mobiles may use a longer T_TDROP since deep nulls may last longer. USE YOUR BROWSER "BACK" BUTTON TO RETURN © 1999 DR. ERNEST SIMO - SPACE2000 |
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