Motorola PTP 500 User's Guide download pdf (Page 63)

PTP 300 and PTP 500 Series User Guide Wireless operation

phn-1115_006v000

Sep 2010

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OFDM and channel bandwidth

The PTP 300 and PTP 500 Series transmit using Orthogonal Frequency Division

Multiplexing (OFDM). This wideband signal consists of many equally spaced sub-

carriers. Although each sub carrier is modulated at a low rate using conventional

modulation schemes, the resultant data rate from all the sub-carriers is high. OFDM

works exceptionally well over a Non-Line-of-Sight (NLoS) channel.

The channel bandwidth of the OFDM signal is configurable to one of three values:

5 MHz, 10 MHz and 15 MHz. Higher bandwidths provide greater link capacity at the

expense of using more spectrum. Systems configured for a narrower channel

bandwidth provide better receiver sensitivity and can also be an appropriate choice in

deployments where the amount of free spectrum is limited.

Each channel is offset in center frequency from its neighboring channel by 5 MHz.

NOTE

The Channel Bandwidth must be configured to the same value at both ends

of the link.

Spectrum management

The spectrum management feature of the PTP 300 and PTP 500 Series monitors the

available wireless spectrum and directs both ends of the wireless link to operate on a

channel with a minimum level of co-channel and adjacent channel interference.

Spectrum management measurements

The system performs two mean signal measurements per TDD cycle, per channel. This

mean measurement represents the mean received signal power for the

40 microseconds measurement period.

The Spectrum Management algorithm collects measurements equally from all

channels. This process is called the Channel Availability Check (hereafter referred to

by the acronym CAC). The CAC uses a round-robin channel selection process to collect

an equal amount of measurements from each channel. The CAC measurement process

is not altered by the channel barring process. Measurements are still collected for all

channels irrespective of the number of barred channels.

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Motorola PTP 500 User's Guide Page 63