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The drive for data
In the developed markets, interest was growing fast in third-generation
(3G)
cellular. 3G’s promised suite of data-based mobile services—always-on
Internet
connectivity, e-mail, video telephony, and streaming video—proved
increasingly
attractive in an industry with flagging
ARPU and slowing subscription rates.
To bring 3G to life, new wireless
technologies were needed that supported packet-switched (rather than
circuit-switched) high-speed data—many had been under development
for some years.
In 1999, the International Telecommuni-cations Union sanctioned just
five technical standards for 3G cellular. Two would
ultimately dominate, and both were code division multiple access (CDMA)-based:
wideband CDMA (W-CDMA) as the
migration path for Europe and Asia’s global system for mobile communications
(GSM) networks, and CDMA2000 (and its variants 1x and 3x) for North America’s
and
Asia’s CDMA systems.
W-CDMA would be deployed in a new spectrum band in Europe and parts of
Asia—the 2.1 GHz band—so it demanded new networks with new
BTS sites. This would be a challenge, as fresh sites were already rare.
Clearly, multiband (GSM 900 MHz, GSM 1800 MHz, W-CDMA 2100 MHz) and broadband
antenna solutions would be
essential. CDMA2000, on the other hand, offered an upgrade path for existing
2G CDMA networks that did not require new spectrum, and was a essentially
a BTS software and
channel card upgrade. Both technologies required entirely new handsets,
with new
chip sets, and a suite of
new services.
For GSM operators, the prospective
move from time division multiple access (TDMA)-based GSM to a CDMA-based
technology presented immediate network management challenges—challenges
already impacting heavily on the mature 2G CDMA networks of North America
and parts of Asia. Where TDMA planning strategies
are based on minimizing co-channel
interference by reusing a select number
of channels over a group of cells,
CDMA-based systems use the full
frequency band in each cell. Moreover,
CDMA cells are said to ‘breathe’—the size of the cells
varies with the number of callers within the cell, the transferred data
rate and so on.
The resulting co-channel interference that can occur in the CDMA-based
network
increases the noise floor, and progressively depletes the capacity of
the network. It
presents a notoriously tougher network planning challenge when compared
with GSM, particularly in addressing
the soft handover/capacity tradeoff of
CDMA-based networks.
There was a clear need for a ‘built for
3G and maturing 2G’ cellular antenna
solutions—an antenna that would provide the flexibility demanded
by the CDMA technologies, specifically the precision
control of the cell footprint size, shape,
direction and power. To compensate for CDMA-style cell breathing and
often
less-than-optimal site locations, variable electrical tilt (to provide
continuous
adjustment of cell footprint size) was
also a must.
In response to this need, RFS developed an entirely new suite of high-performance
cellular antennas—the Optimizer family. The 3G-ready antenna suite
provides upper side lobe suppression better than 20 dB across the entire
tilt and frequency range, significantly increased gain and null
fill as standard. Variable electrical tilt
functionality is extended across a wide
0 to 10 degrees, to provide the network planning flexibility and precision
footprint control. The accompanying tilt technology, RFS’s Optimizer
RT, permits antenna tilt from the tower base or the network
management centre (NMC), and tilts
all lobes—front, rear and side—equally, thus minimizing interference.
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