Cellular Systems Cellular Concepts The cellular concept was a ...

EE5401 Cellular Mobile Communications
EE5401 Cellular Mobile Communications
A hard handover does “break before make”, ie. The
old channel connection is broken before the new
allocated channel connection is setup. This obviously
can cause call dropping.
In soft handover, we do “make before break”, ie. The
new channel connection is established before the old
channel connection is released. This is realized in
CDMA where also BS diversity is used to improve
boundary condition.
A
Hard:
B
Interference and System Capacity
In a given coverage area, there are several cells that
use the same set of frequencies. These cells are called
co-channel cells. The interference between signals
from these cells is called co-channel interference.
If all cells are approximately of the same size and the
path loss exponent is the same throughout the coverage
area, the transmit power of each BS is almost equal.
We can show that worse case signal to co-channel
interference is independent of the transmitted power.
It becomes a function of the cell radius R, and the
distance to the nearest co-channel cell D’.
A
Soft:
B
(a) Received power at a distance d from the
transmitting antenna is approximated by
−n
⎛ d ⎞
Pr
( d)
= P0
⎜
d
⎟ or
⎝ 0 ⎠
⎛ d ⎞
P r ( d)
( dBm ) = P0 ( dBm ) −10nlog
⎜
⎟
⎝ d0
⎠
(b) Useful signal at the cell boundary is the
weakest, given by P r (R). Interference signal from
the co-channel cell is given to be P r (D′)
.
Institute for Infocomm Research 53 National University of Singapore
Institute for Infocomm Research 54 National University of Singapore