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Technology Update : Issue no. 3/2009

3G and 2G co-location

WCDMA/HSPA and GSM co-location: the fast, efficient route to full mobile broadband coverage
Hans Beijner

Contrary to popular belief, full mobile broadband coverage does not require significant new investments in new radio sites. The co-location of WCDMA/HSPA with existing GSM sites provides a very effective way of achieving full coverage with an excellent business case.

Two decades of experience in mobile services has shown how good coverage is essential for user take-up and usage. GSM rollouts around the world have demonstrated time and again how the adoption of mobile voice services accelerated rapidly – in classic hockey-stick fashion – as soon as coverage reached a certain level.

Now, we are rapidly approaching the point where mobile broadband will enjoy similar exponential growth – provided operators do not slow the pace at which they roll out coverage.

Why coverage matters
People’s expectations of broadband coverage are continually increasing – they expect to have ever-faster access to internet-based services wherever they travel. These expectations are driven by the desire to always be online and by increased use of real-time data as well as machine-to-machine (M2M) applications.

The result – as people use a range of devices to access mobile voice, mobile media and internet-based services both in the home, at the office, and outside – is a rapid increase in mobile broadband traffic. This increase is being driven by the capabilities of notebooks, laptops and other devices that consume growing quantities of mobile bandwidth. Feature phones and smartphones are also on the rise, and although they consume less bandwidth than, say, laptops, their sheer quantity will have an impact on total traffic volume and further drive the need for full coverage.

In addition, there is growing demand for fixed broadband to be delivered over cellular networks, especially in regions that lack wireline infrastructure. It is often assumed that people who live in the towns and cities of developed markets lead the take-up of mobile broadband. And to some extent this is true. But this reality hides an important aspect of mobile broadband: its potential to offer significantly better wide-area broadband coverage than any competing technology in rural and remote areas. Many of the “town” people who subscribe to mobile broadband services mainly use their subscriptions while they are away from their homes – for instance, as they travel for business or pleasure. Therefore, although the subscriptions are taken out by city-dwellers, the real benefit is rural coverage.

Good coverage, and the mobility it enables, is thus one of the key differentiators that mobile operators can use in their marketing campaigns against both fixed and mobile competitors. It is also an important factor in the service awards accorded by magazines and consumer organizations. Therefore, it makes sense for operators to extend coverage at sites that will increase traffic and boost revenue across the entire network – even though, initially, some sites do not appear to have an obvious business case.

The case for reusing sites
The reality, today, is that in most markets there are fewer deployments of WCDMA/HSPA on 2100MHz than there are deployments of GSM on 900MHz (GSM900). Therefore, the coverage of mobile broadband delivered over WCDMA/HSPA is often less than that of GSM900 voice service.

In addition, there is a common misconception that more sites are needed to deliver full WCDMA/HSPA coverage than for GSM900 coverage, casting doubt on the business case for mobile broadband outside areas with heavy traffic.

Through co-location, however, WCDMA/HSPA coverage on 2100MHz can, in fact, be made equal to or better than that available from a GSM 900MHz network (Figure 1). Ericsson has shown

  • that it is technically feasible to deploy WCDMA/HSPA at existing GSM sites where there is no WCDMA coverage – providing contiguous coverage and 1Mbps throughput at the cell edge; and
  • a sound business case for operators who have good mobile broadband experience.

Figure 1. Co-location solution gives contiguous coverage with good throughput.


The receiver sensitivity of WCDMA is better than that of GSM. This is the primary reason that WCDMA has a 7dB link budget advantage over GSM at 900MHz. Even at 2100MHz and taking into account the difference in path loss due to higher frequency, WCDMA on 2100MHz has a 2dB link budget advantage over GSM900. The net result is that GSM900 and WCDMA2100 give roughly the same coverage.

Far from needing to deploy expensive new radio sites in new frequency bands (with all the additional cost and effort incurred by site acquisition, planning, implementation, and possibly the acquisition of new spectrum) operators can optimize their investment in a WCDMA/HSPA 2100MHz network with one-to-one site reuse. Co-locating WCDMA/HSPA 2100MHz base stations with GSM 900MHz base stations

  • cuts overall site-related capital expenditures (CAPEX) for rolling out new mobile broadband coverage; and
  • reduces long-term operational expenses (OPEX) for transmission, power, site rental, and operation and maintenance.

In summary, operators who want to provide the next level of mobile broadband service as quickly as possible – offering full coverage that meets the needs of home and enterprise users in cities and rural areas alike – have a compelling case for co-locating GSM and WCDMA/HSPA radio sites.

CONTRIBUTORS

Hans Beijner joined Ericsson in 1984 to work with radio base station design. Initially he served as a design engineer and later as a senior specialist. In 1996, he moved to Japan to serve as a product manager for a variety of radio products. After returning to Sweden, in 2004, he has worked as technical sales support manager and in product marketing. He is currently a marketing manager for product area radio. Hans holds a degree in electronic engineering from the University of Linkoping, Sweden.