Global Positioning System Reference
In-Depth Information
Conventionally, a major spectral problem for a mobile operator is frequency
reuse. This is the problem that signal strength does not fall in level enough with
distance once past the edge of cells. Before the channel can be reused, it must be
low enough in level to prevent cochannel interference so patterns of reuse are
planned so that sometimes several cells are needed in between (using other
channels) before the original one can be reused. With atmospheric absorption,
the reuse distance is very much less so channels can be reused several times
within an area of a square kilometer. This leads to a massive increase in the
information that can be communicated.
The main reason for holding up the adoption of this paradigm is the devices,
which are currently exotic and expensive. As semiconductor science advances it is
likely that new cheap devices may emerge, perhaps using nanotechnology.
From a Whereness perspective the prospect of a high density of very
wideband transmitters is ideal. In the built environment, these hotspots may be
built into the fabric of the buildings together with new LED lighting. Truly
massive bandwidths for mobile communications would result with potential also
for sensing and positioning.
9.1.2
Chaos and Convergence
The future of wireless looks chaotic as more new standards emerge and
commercial rivalries continue as wireless Internet access and cellular radio
standards overlap in capability. For example, GSM operators are deploying
domestic GPRS picocells to compete with open-WiFi. All these issues are beyond
the scope of this topic but the recent “Mobility and Convergence” issue of the
BT
Technology Journal
gives a good overview of digital radio preceded by
Hodgkinson's useful introduction to digital wireless [2].
New spectrum will be available (at a price) for new approaches such as
WiMax and similar higher powered and longer range wireless LAN technology.
All of these activities will add further opportunities to use wireless signals for
positioning and for Whereness applications to exploit the increased wireless
coverage. The need for convergence will increase because users do not generally
want to deal with the technicalities of manual network selection and will just want
services to configure automatically, regardless of which sort of mobile wireless
access network is used and who is providing any applications. Considerable work
is still needed to make device and service simplicity, via automation, a reality.
Portable equipment will become increasingly multibanded with their core
wireless components being affected by the recent software defined radio
movement. Most digital radios use similar processing blocks to perform functions
that include filtering signals, modulation and demodulation, generating signals,
and controlling smart antennae.
Traditionally, each of these intensive digital processing tasks was performed
in dedicated silicon subsystems or application specific integrated circuit (ASIC).
With software defined radio, however, common digital signal processors (DSPs)
