The nbn – formerly the National Broadband Network – was established with a mandate to provide broadband to all Australians.
A key challenge in realising this goal is addressing the widening gap in the digital connectivity between the bush and urban areas. The initial estimates suggest approximately 1 million premises would be outside fixed line coverage by 2021. Satellite and fixed wireless technologies are bridging this gap.
As such, nbn has ordered two purpose-built satellites based on Space Systems Loral’s 1300 Series Satellite Platform. The satellites are named Sky Muster, which was chosen by competition.
The company also plans to explore a third satellite post-2021. The first of these two satellites, Sky Muster NBN-1A, is due to be launched within two months. But nbn is still waiting for a launch date for its second satellite, Sky Muster NBN-1B. These satellites will be placed in geosynchronous Earth orbits (GEO) located 36,000km above the equator.
The Sky Muster satellites are a relatively new generation of satellites and have the capability to establish dedicated coverage with spot beams of hundreds of kilometres in radius.
Spot beams work in a similar fashion to mobile network “cells” and will be used to cover both mainland Australia and many of its islands and external territories. The satellites will establish 101 spot beams to complete the coverage where fixed-line and fixed wireless options are not possible nor economical.
Sky Muster uses the frequency band known as the Ka-Band (sometimes referred to as 30/20GHz), with signals from Earth to the satellite being transmitted at 27GHz to 31GHz, and the signals back from the satellite to the Earth at frequencies between 17.7GHz to 22GHz.
Each spot beam will be assigned a pair of upstream and downstream frequencies with dedicated spot beam coverage. This allows the re-use of those frequencies for other spot beams, increasing the potential capacity of these satellites.
nbn has already built 10 gateway stations, which will provide access to the terrestrial network, and the data from the terrestrial network will be in turn transmitted up to the satellites. Satellites will operate in a “bent pipe” mode, meaning uplink signals from the gateways will be directed back to subscribers on the downlink frequencies.
Ups and downs
nbn plans to offer maximum download speeds of 25Mbps and upload speeds of 5Mbps with these satellites. If these rates can be realised, it is a remarkable improvement over current satellite offerings – Telstra’s satellite service offers 6Mbps down and 1Mbps up – and a significant improvement compared to dial-up services used by many rural subscribers today which peak at 54Kbps.
At these speeds, downloads will be fast. As with any wireless technology option, realistically achievable speeds will depend on a variety of factors: number of signed up premises per spot beam; signal degradation due to atmospheric conditions (the Ka band is more susceptible to rain attenuation, for example, in comparison to nbn’s current interim satellite service operating in the C-Band); and network capacity of the backbone network linking the ground based gateway stations.
While a number of technologies have been developed to improve rain-induced degradation, it is not clear whether nbn’s technical requirements of the satellite manufacturer included these. As more and more customers start to use satellite broadband, congestion might cause further degradation in the speeds experienced by subscribers. With lower uplink speeds below 5Mbps, subscribers might experience issues when accessing interactive services.
With satellite broadband, speed is not the only issue. Satellite systems can suffer from major delays between sending information to the satellite and routing it back to Earth. This is a natural limitation of a device positioned 36,000km away from the Earth’s surface.
The time taken for the radio wave signals to make the trip at theoretical speeds of 300,000km/s is around 240 milliseconds, or nearly a quarter of a second. This is extended to about half a second once network protocols are factored in. Adding the further delays in the terrestrial and submarine cable networks, the overall delay can exceed one second.
Delays, also latency, above one quarter of a second are easily noticeable by humans: we often experience this in TV reports via satellite phone. Excessive latencies would be a major issue for applications such as teledentistry or for any collaboration or intervention where real-time interaction is required.
Highs and lows
There are tweaks that internet service providers can do to minimise excess delay. However, the fundamental propagation delay associated with geosynchronous satellites cannot be minimised. This is why new global satellite players, such as OneWeb and SpaceX, plan to launch a constellation of satellites positioned in low Earth orbits (LEO) instead.
These will boost the speed towards 50Mbps as well as reduce latency to levels below human perception. Proponents are banking on future applications, where communications will be dominated by machines talking to other machines, or sensors talking to decision making systems.
Such applications – often described as the Internet of Things or the Internet of Everything – could be more delay sensitive and thus might demand such connectivity at higher bandwidth and with lower latency.
Despite the ongoing delays to the launch of the first satellite, rural and remote Australia anxiously waits to see the new and improved broadband service offerings.
This is the only way for close to half a million households across regional Australia to access genuine broadband (excepting latency issues), thus benefiting a range of industry sectors operating in these regions.