Optical wireless broadband (OWB) is quick to install, requires no Independent Communications Authority of South Africa (ICASA) licence and it can provide up to 10 Gbps bandwidth over a distance of up to 2,5 km. Also referred to as free space optics, OWB is developed from the ground up and manufactured in South Africa – the best kept secret!
Optical wireless broadband is based on infrared laser technology operating in the unregulated 850 nm band which is used for this service worldwide. Ironic that it could not be deployed in South Africa until some five years ago, as before then it was illegal to communicate across a public road, which was the domain of Telkom. With the communication across a public road restriction out of the way the market opened up for OWB deployment in South Africa.
This technology is an attractive alternative solution to be used in conjunction with extremely high frequency (EHF) equipment to provide high-speed short-haul links. There is less attenuation due to rain than with EHF systems. However, OWB doesn’t work well in foggy conditions.
According to Wietz Joubert, co-founder and MD of Redline Technologies, the company that developed the system in South Africa, it is basically a high capacity short haul telecoms device. The company developed the system totally in-house from the ground up and is said to be the only company in the southern hemisphere to supply both the local, African and European markets. It is also setting its sights on the American market.
The requirement for high capacity short haul links will be driven by the deployment of LTE with multiple base stations or small cells in close proximity to be interconnected. Because the equipment is mainly mounted on buildings there is no need for wayleaves which are still the biggest bugbear in the mobile communications and optic fibre industries.
Redline’s current system will provide reliable communication over a 2 km line of sight distance providing 1 Gbps in both directions. – with no bandwidth scaling or reduction in bandwidth, i.e. a full duplex link.
The product was developed over the past four years incorporating some of the latest technologies. The product has four lasers integrated into the transmit head which allows a range of up to 2,5 km but also provides for redundancy. Operations are on the conservative side and coverage is specified as between 1,5 to 2 km.
Use is made of a single receiver. The four transmit lasers are fully synchronised, transmitting the same information at the same time. The transmit lasers and the receiver can operate in close proximity of each other with no interference and are built into the same enclosure. It is possible to operate hundreds of systems in a metro without any interference.
The beam divergence is about 2 mrad which is very narrow. It translates to approximately 0,120 . A question often asked is: “with such a narrow beam width how stable is the system?” Is it affected by, for instance, building sway?
Redline’ss latest version includes autonomous alignment. This means that once the two units receive a signal they lock onto each other and then follow the position of the strongest signal. This is achieved by two small motors which control the x and y axis and then it tracks accurately with a resolution of 0,10.
Each laser only has an output of 10 mW and is totally eye safe even if one looked directly into the laser. To put this into perspective, the output of a laser pointer is up to 500 mW.
Atmospherics can influence the coverage with fog being the main problem. However the systems would not usually be installed in areas where low-lying fog occurs. According to the company, 1,5 km long OWB links have held in very heavy storms. A 2,5 Gb unit is currently being worked on and by late 2015 it is hoped to have a 10 Gb unit fully developed. The higher bandwidth has been made possible with new laser developments. The detector side is less of a constraint for higher bandwidth as similar ones have been developed for the optic fibre industry.
One of the main advantages of free space optics is that can be installed fast. In some countries it is used for quick deployment of services while fibre routes are being planned, wayleaves obtained and the fibre route built. When the fibre comes into service the free space optics equipment can be redeployed elsewhere.