Specifications

Location Handover
Handover
D-6 68P81095E55-E August 08, 2000
Fading
Fading is the reduction of radio link quality based on distance for the source
(antenna). This may involve multiple sources, bounced signals, and normal
dissipation over distance. The types are:
•Small Scale
• Medium Scale
• Large Scale
Small Scale Small Scale fading and interference relates to the distribution of the radio link by
other signals carrying similar information. The units of measure used in small scale
are in orders of magnitude of the wavelength in the signal envelope. The arrival of a
multipath signal that is exactly ½ a wavelength out of sync cancel the reception of
that signal data bit. This typically involves bounced signals or multipath interference
(Rayleigh distribution). This is diagrammed in Figure D-2
Figure D-2 Multipath Interference
Typically an signal must be 2dB stronger than normal analog RF.
For a non-moving mobile this requires 10dB difference (9db for enhanced systems)
at 10% Bit Error Ratio (BER) (Error bits/total bits.)
With a moving mobile the difference is to 19db (18db enhanced) at 4% BER.
The difference in the arrival time of received packets determine the MSs ability to
use the packet. The packets are synchronized with the GPS timing reference and
requires the packets arrive within a 10-12 microseconds (10-12 µs) time window.
Other packets are rejected. There is a maximum round trip delay of 0.75
microseconds (one-way about 69.75 miles) if other parameters can be maintained
Medium Scale Medium scale fading relates to cross-frequency rejection. Signals of other
frequencies (noise) may have arrival times the increase or cancel the amplitude of the
signal. The unit of measure of this type is generally on the order of tens of
wavelengths. This type of interference is typically 8 dB (nominal for GSM). The
average power typically follows lognormal distribution.
Large Scale Large scale fading relates to general energy dissipation of distance. The units of
measure or in the order of miles. The median average power typically varies in
Power-law fashion with path length (the further away the less powerful the signal).
Minor changes in arrival time
create multipath (Rayleigh)
interference
Radio waves "bounce" (reflect)
off structures and are picked up
by the mobile
Software selects best host cell.
Packet timing determines best signal
path (rejects out of sync packets)
T. N. French