Back in February I wrote about the new Dual Carrier HSDPA feature
in 3GPP Release 8 to push beyond the current 5 MHz single carrier limit
of HSDPA. In short, the feature allows bundling of two adjacent 5 MHz
carriers if supported by the mobile device for higher throughput or a
better scheduling gain due to the higher capacity of the resulting
channel. But do network operators today have adjacent 5 MHz channels to use the feature? I've had a look at the frequency band assignments for Germany, Austria and Switzerland and in all cases the network operators have at least 10 MHz of continuous spectrum in the 2.1 GHz band. Some even have 15 MHz, i.e. 3 adjacent 3G carriers.
In some countries, not all of the initial licensees have made it to the network operation phase so some bandwidth is lying dormant these days. In Germany, for example, Mobilkom and Hutch3G never made it out of the box. Their 10 MHz bands are currently unused and might at some point be offered for sale to the current four operators or new entrants. In the meantime, 3GPP is pushing forward in Release 9 to go beyond the dual carrier specification to enable the bundling of even more carriers. An interesting detail in this debate is that in Release 9 the bundled not all of the carriers will probably have to be adjacent anymore. This is quite important for T-Mobile in Germany, for example. They are a bit unfortunate when it comes to the third carrier as their frequency assignment is not adjacent to one of the assignments of the two parties that gave up.
And looking even further into the future, it might very well be that 3GPP will specify a multi-band/multi-carrier HSDPA operation in Release 9 as indicated here by 3G Americas. That would go far beyond the cooperative use of different frequency bands I discussed in a previous post. Quite a challenge for mobile device hardware designers as it's already a challenge to design a small device with half a dozen or more antennas. In the future, a future dimension is added to the equation by having to make sure that several antennas can be used for transmitting and receiving data simultaneously without interfering with each other.
And by the way: According to the 3G Americas paper above, similar things are happening with LTE-Advanced as well, the maximum 20 MHz channel bandwidth has become too narrow already in the hunt for ever higher speeds.