The high price of mobile data means it is difficult for South Africans who live in poor or rural areas to enjoy the benefits of a broadband Internet connection.
A South African startup named AfriCanopy plans to solve this problem by leveraging unused television white space (TVWS) spectrum to roll out high-speed, low-cost broadband to rural areas.
AfriCanopy recently gained approval for an eight-month trial project to implement the technology in the King Cetshwayo municipality in KwaZulu-Natal.
The company will provide 85,000 residents of the municipality and 50 schools in the area with low-cost Internet access, while creating 400 new jobs through its “Business-in-a-box” (BIAB) kits.
These kits include all the equipment required to provide services, airtime, and data on the TVWS broadband network.
MyBroadband spoke to AfriCanopy executive technical lead William Stucke about the technical details behind the project and its implications for low-cost mobile broadband in South Africa.
Stucke told MyBroadband that the service will use TVWS in the frequency range of 470 – 694MHz, courtesy of the CSIR’s Geo-Location Spectrum Database (GLSD).
“TV White Spaces are those portions of the terrestrial UHF TV broadcast band that are not used in a particular place for broadcasting TV,” he explained.
“In order to determine exactly which channels are available where, a GLSD has details of every TV transmitter in the country, including all its characteristics, such as location, transmitter power and frequencies, and antenna height, orientation and inclination.”
“A Master TVWS device is equipped with GPS and a back-channel to access the Internet,” he added.
“Once deployed and switched on, it uses these to tell the GLSD where it is, its ID, whose it is, what its characteristics are, and to request access to available TV channels.”
This database identifies channels that can be used without causing interference to any TV receivers in the vicinity. The Master TVWS device selects one of these and broadcasts a beacon signal on an allowed channel.
Slave TVWS devices listen for this signal and register with the Master device, which in turn registers all devices with the GLSD, and authorises their operation for a limited time.
“This is Dynamic Spectrum Assignment (DSA), and differs fundamentally from the traditional method, where spectrum is assigned manually, over a large area, for a long duration, and usually for exclusive use,” Stucke said.
“Instead, the TVWS devices must renew their ‘lease’ on the assigned spectrum – typically every day. In addition, if anything changes, or interference is reported, the TVWS devices must cease to use the offending channel immediately.”
“They can go through the requesting process for an alternative channel. They are secondary users of the spectrum and may not cause any interference to the primary users,” he noted.
Stucke explained that one of the main reasons this approach works is the disparity in transmitting power between TV broadcast transmitters and TVWS devices.
“Another reason is that broadcasting is a very inefficient usage of spectrum, as only every 4th channel may be used at each transmitter site, due to adjacent-channel interference on the antenna array,” he said.
Once broadcasters migrate from analogue TV transmission to digital, up to 75% of the spectrum will be unused at any one place, Stucke added.
Coverage and speed
The coverage of AfriCanopy’s initial trial network will comprise a central hub and four base stations arranged in a diamond pattern, each of which has four sector transceivers.
These base stations are 16km apart, and provide coverage up to 20km from the site itself, provided there is a line of sight to connected devices.
“As this part of rural KZN is pretty hilly, there are significant gaps in coverage in places,” Stucke noted.
“These are dealt with by making use of mesh Wi-Fi networks connected to each of the Primary BIAB points, thus extending the network behind hills and other obstructions.”
When it comes to the amount of bandwidth per user, this can vary depending on a number of factors, including the number of devices connected, and how many channels are available at any given time.
“Each base station TVWS transceiver can aggregate up to 20MHz, which gives it a total aggregate capacity (uplink + downlink) of up to 169Mbps with one CPE, or 157Mbps with 5 CPEs,” Stucke said.
He added that if only one user was connected to each CPE, they would get the maximum speed provided by the network, while if each served its maximum number of 850 connected users, this would be divided among all connected users.
Stucke said that if the company achieves its targets within the trial, it can always increase the network capacity.
The big difference between the TVWS network and traditional cellular networks is the price of data.
Stucke said the cost to carry a MB of data on AfriCanopy’s network is significantly lower than mobile network operators, and the company will sell data on a flat-rated basis so that users who are only buying 1MB at a time will pay less per MB than almost all options available from major mobile networks.
“The current model used by the mobile network operators favours the rich,” Stucke said. “If you can afford to buy 20+ GB at a time, you pay a moderately low price.”
“If you are only buying 10MB at a time, you pay much, much more.”
He added that AfriCanopy is hopeful to extend its trial duration following the initial eight-month period.
“The duration of phase 1 of the trial is eight months,” Stucke said. “This is extendable, on application, by a further six months. We intend to make use of this.”