predicted migration path for existing GSM carriers in the short-term is
a move to the 2.5G technologies (most commonly the packet-switched General
Packet Radio Service (GPRS)), then to a UMTS/EDGE mix for those with UMTS
licenses, and EDGE-only for those without. Intermediate scenarios may
see existing GSM carriers quickly deploy UMTS in the larger cities, EDGE
in smaller centres, and GPRS enhanced GSM in rural areas.
While the GSM-to-GPRS leap will incur minimal expense (in many cases requiring
only a simple base station software upgrade), both the GSM-to-UMTS and
GSM-to-EDGE migration will pose base station RF problems. Although EDGE
certainly allows reuse of existing GSM and DCS spectrum, the shift in
modulation techniques (from GSMs GMSK modulation to EDGEs
8PSK) will demand improvements in base station filtering. EDGEs
eight-phase modulation generates power peaks and requires tight control
of the modulation error vector magnitude over the signal processing,
explains Jean-Philip-pe Michel, RFSs Mobile Antenna Systems Product
Manager for Europe. To achieve this, operators will need base station
filters and combiners with peak power handling and better linearity. This
is an area RFS has already worked on with base station OEMs. But
this, he says, is minor when compared to the GSM-to-UMTS migrationthe
move from GSM to UMTS is not simply a shift in operating spectrum; it
is a complete change in RF technology. It will require entirely new infrastructure
to be implementedand at a pace weve not seen before!
This raises an interesting issue. How will new base station infrastructure
be deployed at record speeds in regions such as Europe where base station
site acquisition is all but impossible?
According to many in the industry, co-siting and even multiband antennas
and feeder cable sharing will become a 3G practical reality. Siemens
director of RF engineering, Helmut Heinz, believes the financial and timing
realities of realising virgin 3G sites will outweigh the disadvantages
of co-siting. The true cost of a new sitethe concrete, the
towers, mains, air conditioning and the site itselfis very much
comparable to the cost of the base station alone. Factoring this in with
the difficulty of acquiring new sites, Im sure operators will try
to use as many existing sites as possible, particularly in the first phase.
Environmental issues, he says, will force many operators to also consider
multi-band antenna deployment. In particularly congested urban sites,
multiplexed feeder cable solutions may also prove necessary where new
feeder cabling is difficult.
Others view 3G deployment from a more purist RF aspect, citing limited
flexibility in cell planning and intermodulation as long-term drawback
to co-location. Radio network planning manager with new Spanish UMTS-only
operator XFERA, Kari Junttila, supports this view. Junttila recently completed
five years with Finnish operator Sonera (formerly Telecom Finland), where
he was instrumental in guiding the operator through its first phase 3G
At Sonera we tried to avoid co-siting wherever possible, Junttila
says. In my opinion this is the greatest 3G deployment challengeto
keep the two radio systems separate. Nevertheless, he acknowledges
that co-siting and even antenna sharing will be a necessity in some cases.
We all know about the lack of antenna sites. From a global perspective,
co-siting is certainly not the best technical solution, but it is probably
the easiest solution.