User Guide

PMP 450 Planning Guide
Adaptive modulation
PMP 450 units can transport data over the wireless link using a number of different modulation modes. The
radio automatically selects QPSK (Quadrature Phase Shift Keying) - SISO, QPSK-MIMO, 16-QAM
(Quadrature Amplitude Modulation) - MIMO, 64-QAM - MIMO, or 256-QAM - MIMO based on the RF
environment to provide 1x, 2x, 4x, 6x and 8x operation.
MIMO
Multiple-Input Multiple-Output (MIMO) techniques provide protection against fading and increase the
probability that the receiver will decode a usable signal. When the effects of MIMO are combined with those of
OFDM techniques and a high link budget, there is a high probability of a robust connection over a non-line-of-
sight path.
The sub-feature that comprises the MIMO technique utilized in the PMP 450 product is:
• Matrix B: This technique provides for the ability to double the throughput of a radio transmission under
proper RF conditions. Different data streams are transmitted simultaneously on two different antennas.
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.
Encryption
The Cambium PMP 450 Series supports optional encryption for data transmitted over the wireless link. The
PMP 450 Series supports the following forms of encryption for security of the wireless link:
• DES (Data Encryption Standard): An over-the-air link encryption option that uses secret 56-bit keys and 8
parity bits. DES performs a series of bit permutations, substitutions, and recombination operations on
blocks of data. DES encryption does not affect the performance or throughput of the system.
• AES (Advanced Encryption Standard): An over-the-air link encryption option that uses the Rijndael
algorithm and 128-bit keys to establish a higher level of security than DES. AES products are certified as
compliant with the Federal Information Processing Standards (FIPS 197) in the U.S.A.
Further reading on wireless operation
For information on planning wireless operation, see the following:
• Regulatory planning on page 1-57 describes the regulatory restrictions that affect radio spectrum usage,
such as frequency range.
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pmp-0047 (March 2014)