Refarming 900 MHz
Momentum is growing, fueled by rapidly rising demands for mobile broadband services, for exploiting existing 2G frequencies below 1 GHz (for example 900 MHz in Europe and Africa and 850 MHz in the Americas) for the deployment of broadband (or so-called 3G) technologies.
These motivations are to reduce the costs and expand the capacity of mobile broadband networks beyond what can be achieved with broadband networks deployed in the core 3G bands (i.e. 2.1 GHz and AWS (1.7 GHz) depending on the region and country). The 3G systems deployed by the majority of 2G operators (i.e. the GSM or 3GPP community) are based on the WCDMA (wideband code division multiple access) air interface.
The introduction of 3G systems into 2G bands, which involves their partial occupation of existing GSM 850/900 MHz frequencies, raises both technical and regulatory issues. In the technical or engineering context it poses risks of a degradation of the quality and an increase in the number of dropped voice calls of GSM subscribers if no reasonable allocation of frequencies is made between the 3G and 2G networks.
Reciprocally a potentially adverse effect of the existing GSM network on the new 3G network must be mitigated. In addition the commercial success of these initiatives depends on the availability of economically priced multi-frequency 3G devices that cover the 850/900 bands as well as frequencies above 1GHz.
In the regulatory and competitive context, the issue is one of policies that affect how increasingly precious spectrum below 1 GHz, which includes current 850/900 MHz allocations as well as future or in a very few countries recently allocated new digital dividend spectrum, should be made available to (or even redistributed among) competing mobile operators.
Frequencies below 1 GHz can offer significant advantages over higher frequency bands, including:
- Lower network costs (capex and opex) in network deployments in coverage limited (notably rural) areas thanks to their longer propagation ranges (substantially fewer base stations are required), and
- Superior in-building penetration to provide better service indoors (and reduce the need for solutions such as femtocells), which is where much, or even the majority of “mobile” communications traffic is actually delivered and initiated.
The cost savings of using 900 MHz compared to 2100 MHz for providing 3G services can be considerable, amounting to a reduction of between 40-60% in terms of numbers of base stations in some areas. This reduction translates to comparable savings in the capex and opex required to install and run a radio access network. It also enables savings in backhaul links since fewer stations have to be connected and greater concentrations of traffic can be achieved (more users per base station). In addition 900 MHz can be used to help meet needs for capacity expansion.
The challenges encountered when refarming 900MHz spectrum include:
- Managing and minimizing interference between the GSM and 3G (WCDMA) networks
- Protecting existing investments through sharing of feeders and antennas
- Maintaining overall GSM capacity and quality, despite, as is typical, using 5MHz of spectrum allocations in 900MHz for a single WCDMA carrier
- Unifying operation and maintenance of the two networks to minimize opex.
As of end-2009 some ten 3G 900MHz networks had been put into commercial use. More significantly several dozen more (perhaps 60+) are being planned or will be deployed during 2010.
The numbers of terminal devices that support 3G 900MHz are also growing rapidly as the addressable market size grows large enough to attract vendors’ attention, with more countries in Europe, the Middle East, Africa, Asia, and Oceania, as well as in the Americas in the closely related 850 MHz frequencies, recognizing the value of deploying mobile broadband networks in this originally 2G-only band.
Longer term it is envisaged that next generation wireless technologies, notably LTE, will also be deployed in frequency bands originally used for 2G networks.
Refarming 900 MHz spectrum << online discussion
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