User's Manual

142 Operation
Chapter 4 - Operation and Administration
The basic time element (symbol) used by a system operating in TDD mode is 68
microseconds for a bandwidth of 3.5 MHz and 50 microseconds for a bandwidth of
5 MHz. This symbol size is translated to a round trip delay of approximately 20
km for 3.5 MHz bandwidth and 15 km for 5 MHz bandwidth, or a cell radius of 10
km or 7.5 km, respectively.
The values range for the Maximum Cell Distance is from 10 to 50 km for a
bandwidth of 3.5 MHz, and 7 to 45 km for a bandwidth of 5 MHz (representing a
maximum delay of 6 symbols).
The default is 20 km.
4.8.5.3.2 Phy Parameters
The Phy menu enables viewing/updating the Bandwidth parameter:
4.8.5.3.2.1 Bandwidth
The frequency bandwidth used by the radio. A change in the Bandwidth
parameter will take effect only after resetting the AU.
The Admin Status of all Channels belonging to the same AU must be disabled to
enable a configuration change in the Bandwidth parameter.
The available options are:
1 - 1.75 MHz
2 - 3.5 MHz
3 - 5.0 MHz
4 - 7 MHz
NOTE
For Non-Line-Of-Sight (NLOS) links using refractions, the cell distance should be higher than the
line-of-sight distance. Typically a 10% margin is a good estimate for the increase in distance due to
the NLOS operation.
NOTE
An SU located at a distance larger than the Maximum Cell Radius will be rejected during the
network entry process.
NOTE
The actual value that the system will use is a multiple of the the one-way delay for a single basic
time element: N*10 km for a bandwidth of 3.5 MHz or N*7.5 km for a bandwidth of 5 MHz, where N
is a an integer from 1 to 6. The value configured for the Maximum Cell Radius will be up-rounded to
the nearest applicable value.