User's Manual

Table Of Contents
5 Radio Link Planning and Regulations
78
Interference can be minimized by increasing the radio channel separation between units
which are in close proximity, for example for units on the same mast. This may not always be
possible if the mast is hosting a large number of links and if spectrum is limited. Also, the
achieved reduction may not always be sufficient. Another way to reduce interference is to
reduce the transmit power of an interfering radio. Again, this may not always be possible if the
link causing the interference does not itself have sufficient radio gain margin to allow the
power of its radios to be reduced.
5.12.2 TDD Synchronization
T
DD synchronization overcomes these issues by aligning the radio frame of all links in the
network such that all Master units transmit at the same time and receive at the same time.
This eliminates interference between units on the same mast if the units on the mast are
configured as Master units. This illustrated in Figure 28 where the frames of the two links are
aligned in time.
Figure 35 TDD Synchronization And Co location Example
Due to propagation delay, a mechanism exists where an interfering signal from a remote
Master unit arrives at a victim Master delayed in time. This would occur when Master units
are installed on different masts. Similarly, an interfering signal from a remote Slave unit will
arrive at a victim Slave unit delayed in time. Correct configuration of TDD synchronization
ensures that the delayed signals do not overlap with the receive portion of the victim frame. In
order to eliminate the interference from delayed signals, the configuration and the resulting
TDD frame structure will actually depend upon characteristics of the overall network such as
the longest link and the maximum distance between interfering Master units and interfering
Slave units. The installation wizard requests that these parameters are entered when TDD
synchronization is enabled. This is covered in detail in Section 14 “TDD Synchronization
Config
uration and Installation Guide”.