How do we bring broadband to mobile phone? CK Mah muses
on the technologies that could make this a reality
mobile phones first became commercially available during the
early 80's, an explosion of mobile phone sales soon followed.
Today, mobile phones are estimated to be a US$40 billion industry,
with one in three people carrying a mobile phone.
Imagine the impact to our lives if mobile phones were introduced
much earlier. In fact, AT&T had developed a basic mobile
phone device back in the late 1940's, which used a small network
of low-powered transmitters.
But it took the regulators about 40 years before the first
mobile phones were approved for commercial use. Next in line
is the "great wireless revolution" that is suppose
to bring broadband Internet to the mobile device. But clear
voice and high data rates have been a challenge so far.
In addition, there is also the problem of global service delivery
due to the maze of incompatible transmission standards. Travellers
cannot get a global mobile dial tone today. In the US alone,
there are three major competing standardsTDMA, CDMA,
and GSMof which only GSM is compatible with the leading
standard in Europe and Asia.
However, mobile difficulties go beyond conflicting standards.
As emerging standards like 3G start to introduce broadband
multimedia interaction, it also means that the phones and
base stations need to be upgraded. These advances carry a
heavy price tag.
And these large investments could turn sour because there
is no clear killer application or service yet that would support
such an infrastructure. Telcos are hoping that new services
will be as successful as Japan's i-mode, which has gained
the support of millions of Japanese in allowing them to do
things like send text messages, buy stocks and check sport
scores. However, just last year, several European operators
spent heavily to offer WAP services, only to discover their
lack of customer support due largely to the low bandwidth.
Software Defined Radio
on the image for larger view)
a cognitive mobile phone dynamically negotiates the use
of unused frequencies
possible solution to avoid costly upgrades as demand changes
is a technology known as Software Defined Radio (SDR). The
"radio" here refers to equipment that communicates
through radio frequencies similar to that of mobile phones.
The main advantage of this approach is that it shifts the
workload off the wireless units from the dedicated components
to software that can be reprogrammed to work on different
standards and applications.
This concept is entirely different from the current mobile
phones and base stations, where virtually all signal processing
is carried out by dedicated electronic circuitry.
The move towards adaptable wireless networks that use programmable
software is one of the most important trends in the telecommunication
technology. Besides saving on upgrade investments, SDRs may
even be able to address technical issues.
As demand for wireless communication increases, so does the
demand for frequency channels. Software programmable wireless
networks could ease that bandwidth shortage since they could
seek out and use temporarily unoccupied channels.
In fact mobile phones are already moving in this direction.
Where mobile phones have previously relied on numerous hardware
components, in recent times, programmable chips have been
addedalthough their function is set immutably during
the manufacturing process.
Currently, dedicated chips still do most of the processing
work in mobile phones and base stations. These chips are designed
with simplicity in mind in order to help reduce manufacturing
cost. However, given the conflicting standards and uneven
advent of 3G networks, manufacturers are starting to see dedicated
components as a cost liability.
They are cheaper, but their life expectancy will be short.
This has resulted in raising the appeal level of general purposes
software that are programmable.
An Inside Look
If mobile phones and their base stations were actually computer-based
appliances, new software could download easily. But wireless
communication is fundamentally different, as mobile phones
must push the signals across the airwaves at precisely the
right power level in the correct transmission format.
They must also be tuned to receive incoming powerful signals
from one or more channels. Antennas catch irregular analogue
signals travelling through space on "carrier" frequencies.
Incoming signals must then be converted to an intermediate
frequency through the combination with another radio wave
produced inside the receiver.
Then the carrier wave gets subtracted to put the signal in
baseband, which is a power level and speed that ordinary digital
processors can handle. While the signal is in baseband, it
is translated into a stream of binary ones and zeroes, which
are in turn decoded, decrypted and formatted into voice or
data. Decoding and coding operations in baseband is one area
that will benefit from programmable software.
Next, manufacturers would like programmable software to handle
the intermediate frequency and radio frequency parts of the
job. This is a more difficult technological challenge as silicon
(which is the most common and least expensive chip material)
does not handle radio wave signals well.
The rise in computing complexity is accelerated by the push
to send signals that match 3G broadband wireless networks
speed which move data at megabits per second. These demands
mean that chips will require lots more power, which can be
easily attained for base stations but not for mobile phones.
To date, manufacturers are putting programmable chips mainly
into base stations that relay signals from mobile phones to
the network. Unlike mobile phones, base stations have no space
or power constraints. In fact, the more advanced base stations
can even shift among multiple channels and assume different
standards based on the type of communication transmission.
The Mobile Future
Wireless devices that can morph into different models on the
fly would be a boon to their users, but at the same time,
they create policy-management issues.
How should regulators license mobile phones and base stations
that can readily be changed after they are in use? How free
should third parties be to load new software into your phone?
How will it be possible to distinguish legitimate upgrade
of the network from rogues trying to subvert it?
In addition, there is a lack of spectrum for 3G services to
sniff out and utilise unused bandwidth in the spectrum. This
would require a cognitive radio (refer to Figure 1), which
scans its spectral environment, it would also feature built-in
memory, maps and positioning capabilities.
Further, for such mobile phones to re-orient to a new channel
for temporary use, they would have to get permission to "rent"
that spectrum for some period of time from the official licensee.
Practical implementation of this concept would also require
a payment system that employs the correct signal protocols.
Using such systems, intelligent mobile phones would be able
to scan the spectrum to find an unused channel. The range
of spectrum that are most commercially desirable can be referred
to as an endless wave of ocean itself. You can no more lease
electromagnetic waves than you can lease ocean waves.
Making that ocean available to billions of people could be
one impact of flexible software based wireless networks. But
before we reach this nirvana of spectrum abundance, we are
likely to see this "soft" technology promising to
extend the life cycle of base stations as well as your mobile
CK Mah writes for Network Computing-Asian
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