Cambium Networks PMP 450 Series, Installation Manual

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Chapter 1: Product description 37
TDD frame paramet ers
The TDD burst duration varies depending on the following:
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Channel Bandwidth
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Cyclic Prefix
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Frame Period
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Frame configuration - Downlink Data
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Link operation – Dynamic Rate Adaptation
O FDM and Channel Bandw idt h
The PMP/PTP 450 Platform Family transmits 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 the sub-carriers is high.
OFDM works exceptionally over a Non-Line-of-Sight (NLoS) channel.
The channel bandwidth of the OFDM signal is configurable to one of the following values: 5, 7, 10, 15, 20, 30,
and 40 MHz. Higher bandwidths provide greater link capacity at the expense of using more bandwidth.
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.
Note
The channel bandwidth must be configured to the same value at both ends of the
link. Not all channel bandwidths are available in all regulatory bands.
Cyclic Prefix
OFDM technology uses a cyclic prefix, where a portion of the end of a symbol (slot) is repeated at the
beginning of the symbol (slot) to allow multi-pathing to settle before receiving the desired data. A 1/16
cyclic prefix means that for every 16 bits of throughput data transmitted, an additional bit is used. For your
convenience, the 450 Platform Family ODUs have been locked to a 1/16 CP.