Bringing broadband access to rural and remote areas
The Canadian experience
By Gérald Chouinard
Programmes to improve access
According to ITU’s World Telecommunication/ICT Development Report 2006,
Canada is sixth in the world for broadband access penetration. However, because
of the country’s huge size and often sparse population, special measures need to
be taken to try reaching all Canadian citizens. One third of communities (where
5 per cent of the Canadian population lives) still have no access to broadband services.
And even when a community is reached, not every resident has access to broadband.
This is especially true in rural areas, where the population density, beyond a
central town or village, may be too low to make broadband access cost-effective
using current technologies.
The Canadian government has taken steps to improve broadband access with programmes
offering communities subsidies for capital investment and satellite transmission
capacity, provided that they have developed plans for sustainable broadband access
services. In parallel with this, the Communications Research Centre Canada (CRC),
an agency of Industry Canada, launched the Rural and Remote Broadband Access (RRBA)
programme in April 2002. CRC conducts research, and develops and tests innovative
and cost-effective broadband access technologies and systems that should allow the
private sector to develop viable business models for the provision of broadband
services to Canada’s under-served areas.
The RRBA programme covers critical issues such as spectrum availability and interference,
reach, and deployment flexibility and equipment standardization. It involves participation
in international standards activities, with the aim of reducing the cost of broadband
access equipment, as well as offering Canadian expertise and technologies to countries
that face similar challenges.
What is the best delivery system?
Satellite communications can play a major role in reaching remote communities.
Because of their large and even coverage, satellites can provide broadband access
in various geographical settings, including rural, suburban and even urban. The
only drawbacks may be the impact of the inherent 0.5 second signal propagation delay
on some broadband applications and the centralized servers, and the cost of the
terminals. However, CRC has worked to minimize these problems.
Figure 1 —
Suitable broadband access technologies as a function of population
CRC assessed the various broadband access technologies, based on population density,
and looked at their merits in relation to their perceived complexity and cost (see
Figure 1). Special attention was given to the range between 1.5 person/km2
(below which only satellite technologies make sense) and 60 person/km2
(above which wired technologies, such as ADSL and cable, become cost-effective).
Serving this range of population density begs for the development of new wireless
broadband access technologies that will extend the reach to allow cost-effective
coverage of rural areas. Figure 1 gives an indication of the size of this potential
market in Canada, based on the 2000 census.
— Factors to be considered in the choice of the best frequency for wireless
broadband access systems to serve sparsely populated rural areas
The most important factors to be considered when trying to extend the range of
wireless technologies are depicted in Figure 2 as a function of the carrier frequency.
Again, the impact of these various factors is illustrated in terms of their relative
complexity and cost. The low UHF range, from 300 MHz to 1 GHz, comes out to be the
best frequency range for broadband access systems in rural areas. The use of radio
frequencies in this range can extend the reach of wireless broadband access systems,
allowing for a larger subscriber base in sparsely populated areas and making broadband
access economically sustainable. As a result of these findings, special attention
has been given to this range of frequencies in the RRBA programme.
|Offset-fed 30/20 GHz reflect-array
Satellite broadband access technologies
CRC’s work on satellite broadband access concentrated on trying to reduce the
cost and complexity of terminals operating with the new Canadian Anik-F2 satellite
in the 20/30 GHz bands. The use of such high frequencies permits a reduction in
terminal size and can provide an attractive solution for broadband access to remote
communities, and even to individual households.
A 45-cm circularly-polarized reflect-array antenna was developed, with an offset
feed with different focal points at 20 GHz and 30 GHz to avoid the need for a complex
waveguide orthomode transducer. This design meets the gain mask recommended by ITU’s
Radiocommunication Sector (ITU–R) with respect to discriminating among geostationary
satellites if the size of the antenna is greater than 70 cm.
Direct transceiver architecture is used for the terminals, so as to simplify
the hardware needed. Work was done on the miniaturization of a 30 GHz vector modulator
with a coupler, amplifiers, and an envelope detector in a single package, in order
to improve overall performance and reduce the cost of direct transceiver terminals.
CRC developed compensation techniques for receiver gain/phase balance, as well as
for power amplifier linearization. A frequency synthesizer was developed, and
meets the stringent requirements needed for systems operating with DVB-RCS (digital
video broadcasting — return channel satellite) open standard. DVB-RCS was selected
in order to use the Anik-F2 satellite capacity credit (in the 20/30 GHz band) for
CRC completed a study on innovative transport, network and link protocols for
the transmission of internet protocol (IP)-based broadband services over satellite
circuits. The satellite transmission capacity is maximized through the concerted
use of a link performance enhancer replacing the usual transmission control protocol
(TCP) to reduce the link latency and dynamic satellite bandwidth allocation, while
meeting specified levels of quality-of-service (QoS). It was found that the service
latency could be cut by more than 70 per cent and the end-user traffic throughput
could be increased by a factor of five. These improvements can be added through
either an upgrade to current open-standard DVB-RCS terminals, or through a more
optimized upgrade to future DVB-RCS terminals.
||Antennas used for the Wi-Fi experiment at 700 MHz
||MILTON subscriber terminal
Wireless broadband access using frequencies below 1 GHz
Investigations of the use of frequencies below 1 GHz for future broadband access
systems were carried out, with the aim of enhancing the coverage range at low cost.
CRC developed prototypes of a duplex frequency converter between the 2.4 GHz band
and 700 MHz. These prototypes were successfully used in a field trial with simple
UHF antennas where Wi-Fi connectivity was established at 5 Mbit/s over a range of
5 km in a non line-of-sight point-to-point setup at 700 MHz. It was observed that
the range of 802.11b/g WLAN operating at 700 MHz can double in non line-of-sight
conditions and quadruple in line-of-sight, as compared to 2.4.GHz.
|24-petal MILTON Hub antenna
The MILTON system
CRC also completed the development of its 5 GHz multimedia wireless access system
called MILTON (microwave-light organized network ). As a last-mile solution that
can interface with optical fibre and Gigabit Ethernet networks, this technology
is well suited to cover dense portions of rural communities where the bulk of the
population is within a 1.8-km radius (10 km2 area). The
system can reuse frequency up to six times by means of a 24-petal hub antenna.
Currently, the system provides up to 22 Mbit/s forward and 3.4 Mbit/s return
capacity per subscriber and can serve up to about 700 homes. It includes low-cost
subscriber terminals using double dielectric-layer patch antenna technology (20x20cm,
17 dBi gain) and a 24-petal rosette hub antenna. Cognitive radio functions that
make cells highly adaptive in the presence of interference were added to the hub
and user terminals.
The MILTON system has been deployed for field trials in a suburb of Ottawa. One
hub and six terminals have been in operation since September 2004. In December 2004,
the Government of India made the MILTON technology a prime area of investigation
for its Centre of Development of Telematics (C-DOT), and acquired the technology
for field tests in Bangalore.
Broadband access through digital television broadcasting
Because of their wider coverage capabilities, broadcast transmission technologies
can be effective in bringing broadband access to rural areas. For example, digital
television (DTV) can carry about 20 Mbit/s of broadband capacity in a 6 MHz television
channel over a coverage area of up to 70 km radius. CRC reviewed the three current DTV technology standards used across the world, and found them to be well suited
for carrying broadband applications in the forward direction. CRC verified the extent
of coverage in the field and confirmed that it can be improved and shaped using
The concept of using DTV-ATSC in the forward direction and DVB-RCT for the return
link was studied to provide two-way, high-speed data services for broadband access.
DTV-ATSC is the digital television standard developed by the Advanced Television
System Committee in the United States. The Digital Video Broadcasting Project in
Europe has adopted the DVB-RCT (return channel terrestrial) standard.
An experimental DTV transmitter station is being upgraded in the Ottawa area
to allow a full-scale demonstration of this bi-directional service. Researchers
have demonstrated the feasibility of encapsulating IP data over the DTV transport
stream, using a high-capacity data server that integrates multimedia applications
and a prototype of a low-cost IP receiver. A bridge from the DTV IP receiver to
Wi-Fi is also being developed.
In Canada as elsewhere, the transition from conventional analogue television
to DTV offers the opportunity to use television bands more efficiently and free
spectrum for other applications, such as broadband access. Distributed transmission
networks using synchronized transmitters operating on a single channel could be
implemented to carry the same television programming over large areas. Network planning
studies were conducted, based on the TV Ontario network, to test the applicability
of the distributed transmission concept on a large scale. TV Ontario uses different
channels to broadcast the same programme across the province and consists of high
and medium power transmitters and a large number of low-power frequency-translators
distributed over the territory. It was found that common channels could be used
in moderately congested areas by employing groups of low-power translators in a
single-frequency network mode.
Using these technologies around the world
The use of the 20/30 GHz bands for satellite broadband access allows for small
and potentially low-cost terminals that should make it easier to deliver services
to any remote location where there is satellite coverage. The use of such high frequency
bands will, however, limit the applicability of the technology to areas of the world
with little precipitation because the signal tends to be heavily attenuated by rain.
The MILTON system has potential in populated areas where no wired infrastructure
With respect to the use of the low UHF range for wireless broadband access, this
should have a global appeal — especially in developing countries where the UHF
spectrum is not heavily used. In the transition from analogue to digital television
broadcasting, broadcasters could take advantage of the data transmission capability
of the new DTV systems to provide data services such as broadband access, as long
as means are found to provide for the return channel.
Gérald Chouinard, Manager of the Rural and Remote Broadband Access
programme, Communications Research
With the development of new
standards, such as the IEEE 802.22 wireless regional area network (WRAN) standard, low cost broadband access technology could become available and usable in television
bands worldwide. The technology will include cognitive radio features that will
allow sensing the presence of television broadcast signals in the area and avoid
potential interference by automatically selecting an unused television channel for
its operation. This could have a huge impact on efforts to create broadband access
in large developing countries. Although best suited for sparsely populated rural
areas, it could also be a cost-effective solution in more populated areas where
some television spectrum remains unused.