User's Manual

3 Detailed Description
30 APCD-LM043-4.0
• Interference suppression: The same mechanism that de-spreads the desired signal
in the receiver, spreads undesired signals, which then appear to the receiver as lower
levels of RF noise. This effect is illustrated in Figure 18.
Figure 18 Effect of Despreading
Data Rate
The raw channel bit rate is 2.75 Mbps. The maximum data rate presented to the MAC layer is
2.4 Mbps, which translates to a peak FTP rate of about 2 Mbps.
Colocated Channels
A maximum of four orthogonal (nonoverlapping) channels can be provisioned at a single CAP
but WaveRider recommends a maximum of three. To ensure adequate isolation between
channels, a minimum co-channel spacing of 6.6 MHz is recommended, as is the use of
channel filters and a properly engineered antenna system. A possible frequency set for a
three-channel CAP is
• 905.0 MHz
• 915.0 MHz
• 925.0 MHz
A separate CCU, channel filter, transmission line, lightning protector, and antenna are
required for each of the orthogonal channels.
Duplexing
The radio channel uses Time Division Duplexing (TDD), which means that the CCU or EUM is
in either receive or transmit mode, but does not transmit and receive at the same time.
Transmit Power
The maximum transmit power (HIGH power setting) of the CCU and EUM is +26 dBm,
measured at the unit’s RF connector. It does not include gains and losses from antennas,
transmission lines, and lightning arrestors, all of which affect the ERP (Effective Radiated
Power) from the CAP or customer’s premise. Refer to Appendix D on page 185 for a
discussion of related FCC and Industry Canada guidelines.
Before De-spreading
Interferer
Desired
Signal
After De-spreading
Desired Signal
Inteferer
Becomes