However, due to their implementation complexity,
they have been left as an option. In addition to these three, OFDMA specifies two more
optional FEC methods.
Modulation Both OFDM and OFDMA PHYs support four different types of modulations:
BPSK, QPSK, 16-QAM, and 64-QAM. Adaptive modulation both for uplink and
downlink are supported.
482 Chapter 15
Smart Antenna Technology
Advanced antenna technologies take advantage of spatial diversity that can be provided
by multiple antennas to improve the performance of an RF channel. Some of the
well-developed advanced antenna technologies are Smart Antenna Systems (SASs),
Space-Time Coding (STC), and Multiple-In-Multiple-Out (MIMO). WiMAX provides
support of technologies for frequencies below 11 GHz. Among these technologies, perhaps
the most interesting is the smart antenna technology.
Smart Antenna Systems, referred to as Adaptive Antenna Systems (AASs) in the
standard, allow for beam forming of the RF signal by using multiple antenna elements
spatially separated from each other. Beam forming by means of smart antennas creates
a narrower beam of signals bringing with it several benefits.
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