How do we bring broadband to mobile phone? CK Mah muses on the technologies that could make this a reality

When 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 standards—TDMA, CDMA, and GSM—of 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

One 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 added—although 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 phones.

CK Mah writes for Network Computing-Asian Edition. You can send your feedback to editor@networkmagazineindia.com