Rural Communications

While broadband communication uptake is increasing rapidly, there is a significant fraction of remote and rural Australia for which terrestrial communications approaches (such as fibre and microwave links) will remain too expensive. Satellite systems can complement broadband terrestrial networks with flexibility and immediate coverage. Their advantages include wide area coverage and broadcast capability. However existing satellite solutions, which usually involve one satellite connection per user at costs of above $3/minute or $0.15/Mbit of data, are obviously not economically viable.

While the concept of supplying communications needs via a single satellite hub is not new, applying the combination of a number of leading edge transmission technologies to enable efficient resource utilization and sharing between many users provides a significant difference to the affordability of this approach. A factor of ten reduction in the satellite bandwidth cost is achievable today by the combined use of these technologies, e.g. Satellite-WiFi. A further reduction by another order of magnitude could be possible in the next couple of years by using higher order modulation techniques.

Key Research Challenges

Traffic Aggregation

Aggregation of traffic within each community to a single satellite access point. This requires interfacing with different existing communication standards, identification and establishing appropriate levels of priority for each user/application.

A rural community typically comprises:

  • A medical centre using, or having a desire to use telemedicine services such as image transfer and video conference and web browsing.
  • An educational centre or school with typical internet needs such as web browsing, file transfers and emails.
  • A community centre open to the public such as internet cafe
  • A set of individual users with typical internet and email needs

Traffic bandwidth shaping and management

It is important to consider that not only are a diverse range of applications required, but the times those services are required and the priorities they carry are all important considerations in dimensioning a solution. For instance, some interactive telehealth services require large transmission rates, are very sensitive to time delays and are not used very often. Another application such as file transfer normally requires a relatively high transmission bandwidth, but is typically not time sensitive. Web browsing, which is perhaps the most popular internet service, can tolerate some transmission delays and is also somewhat variable in its required transmission bandwidth. With the combination of factors to consider when sending information, including bit rate, transmission delay and priority, a significant improvement can be gained by appropriate transmission and bandwidth scheduling from a single satellite hub. Each data transmission will depend on its service type (i.e., medical centre, school centre, community centre, individual user) and its traffic class which is characterized by the time sensitivity factor (video conferencing, web browsing, email etc).

Optimum transmission techniques

Most of the current satellite communication systems employ rate 1/2 or 3/4 error control coding and QPSK or 8PSK modulation. Modern modulation and coding systems can give great improvements in spectral efficiency (i.e., the amount of transponder bandwidth required for a given bit rate) and the power efficiency (i.e., the transmit power or antenna size required to give the required bit error rate performance). New iterative techniques that can compensate the effects of nonlinear satellite channels make possible the use of high order QAM modulations that operate very close to saturation at high data rates. The iterative demapping/decoding techniques used for turbo-like codes allow efficient transmission of 3 to 6 information bits/symbol, compared to 1 to 2 information bits/symbol used in current systems.

Wireless last-mile distribution techniques

To realise the full benefits of this approach, an efficient distribution technique is required to connect end users to the satellite access point. In a typical rural community most subscribers are located within several kilometres of the satellite earth station, and few might be up to 10 km away. While several alternatives exist (such as ADSL, 3G wireless, LMDS) recent market research shows that modern wireless local area networks (WiFi) will provide an excellent solution for last-mile distribution.

More Information

Australian Rural Communications Researchers

Abolhasan, Mehran
Barbulescu, Sorin Adrian
Bhaskaran Pillai, Sibi Raj
Conder, Phillip
Dadej, Arkadiusz (Arek) J
Esselle, Karu P
Fitzpatrick, Paul
Jones, Haley M
Karmakar, Nemai
Khan, Jamil Yusuf
Kibria, M. Rubaiyat
Naguleswaran, Sanjeev
Ngo, Nghia Hieu
Rice, Mark
Sithamparanathan, Kandeepan

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