The channel bandwidth
and the achievable throughput are listed in Table 15.2.
Multi-Carrier Modulation (OFDM and OFDMA) One of the significant limitations of the
original PHY development, which would have ruled out ubiquitous deployment of
WiMAX, was its LOS limitation. Subsequent to the development of the original PHY, a
new PHY standard was developed that was targeted for NLOS operation.
Due to the propagation characteristic of waveforms below 11 GHz, use of a singlecarrier
system gets severely affected by multipath, where the multipath duration could
be larger than the short symbol duration needed to transmit high-bandwidth data using
Channel Size
(MHz)
Symbol Rate
(MBd)
Bit rate (Mb/s)
QPSK
Bit rate (Mb/s)
16-QAM
Bit rate (Mb/s)
64-QAM
20 16 32 64 96
25 20 40 80 120
28 22.4 44.8 89.6 134.4
TABLE 15.2 Channel Bandwidth and Throughput (Source: IEEE 802.16-2004)
WiMAX 481
a single carrier. One of the techniques that has gained significant ground combating
the effects of multipath is Orthagonal Frequency Division Multiplexing (OFDM).
In this technique, the physical channel is split into large numbers of subchannels and
the data transmission is multiplexed among the multiple channels.
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