User's Manual

3 Detailed Description
APCD-LM043-4.0 29
The channel bandwidth also determines the minimum adjacent channel spacing for colocated
CCUs.
Channels
There are 101 channels in the band, set in 0.2 MHz increments:
Table 6 LMS4000 900MHz Radio Network Channelization
Modulation
The CCU-EUM radio channel is based on DSSS (Direct-Sequence Spread Spectrum) signals,
modulated with CCK and Barker-coded BPSK and QPSK, similar to that defined in IEEE
802.11 for the 2.4 GHz ISM band.
DSSS offers the following advantages:
• Reduced power spectral density: Spreading over a wider bandwidth reduces the
spectral density (power per Hz of bandwidth) of the transmitted signal, allowing
simultaneous operation of many spread-spectrum systems in the same frequency
band and geographic area. The reduced spectral density also allows you to meet the
regulatory emissions requirements in the ISM frequency bands.
• Transmission security: It is technologically more difficult to recover (or jam, in the
case of military communications systems) spread-spectrum signals than it is to
recover conventional narrowband signals.
Channel Center Frequency
Lowest channel 905.0 MHz
... 905.2 MHz
... 905.4 MHz
... ...
... 924.8 MHz
Highest channel 925.0 MHz