WiMAX supports very robust data throughput. The technology at
theoretical maximums could support approximately 75 Mbps per channel (in a 20
MHz channel using 64QAM ? code rate). Real world performance will be
considerably lower—perhaps maxing out around 45 Mbps/channel in some fixed
broadband applications. Remember however, that service across this channel
would be shared by multiple customers. Actual transmission capabilities on
a per customer basis could vary widely depending on the carrier’s chosen
customer base, which is actually an inherent strength because it can be defined
by QOS in a deliberate fashion to offer different bandwidth capabilities to
customers with different needs (and different budgets). Mobile WiMAX
capabilities on a per customer basis will be lower in practical terms, but much
better than competing 3G technologies. WiMAX is often cited to possess a
spectral efficiency of 5 bps/Hz, which is very good in comparison to other
broadband wireless technologies, especially 3G.
In practical terms, Sprint has stated that it intends to deliver service at 2
Mbps to 4 Mbps to its customers with Mobile WiMAX.
The modulation scheme, whether quaternary phase shift keying (QPSK), quadrature
amplitude modulation (16QAM, 64 QAM etc.) and their attendant code rate
variations deliver varying bandwidth capabilities by channel size. Like
most things wireless, the devil as they say is in the details. The good
news is that pretty much all of the news is good in this regard relative to
other broadband wireless and wireline competitors of WiMAX excepting LTE, which
is still at least two years away from reaching the field. The OFDMA®
technology actually supports multiple modulation schemes depending upon the
users range from the cell with users at closer range receiving signal across
more sub-channels at, for example, 64 QAM whereas a user at greater range would
receive signal across fewer sub-channels (with higher gain or power per channel)
using a lower bandwidth QPSK technique for example.
Many things affect transfer rate beyond simple radio capability—one major
element being distance from the base station. The physics of radio cannot
be avoided. Longer ranges result in lower bandwidth delivered. Also,
the spectrum channel size (1.e. 20 MHz or other) that regulation defines
as appropriate for different frequency bands will dictate bandwidth capabilities
at least to some extent. Also, remember that the RF and physical
environment play a strong role in throughput results. Essentially, the
real world blunts theoretical performance.
The physics of frequency range plays a powerful role in bandwidth capability.
The higher the frequency, the greater the bandwidth delivery potential and the
shorter range potential. Lower frequencies enjoy much greater range
capability, but trade that off with much lower bandwidth potential.
Fortunately, even with disclaimers centered on real world impediments, WiMAX
throughput is excellent. Perhaps no litmus test is as good as the results
that carriers report and several carriers have shared that they are consistently
achieving as much as 5 Mbps download speeds. Also, Clearwire has stated
that it believes it can deliver upwards of 10-15 Mbps once it has access to the
full Sprint panoply of spectrum in addition to its own and once it has shifted
to mobile WiMAX.
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