Dual band wireless outperforms fibre-optics

In answer to every communications officer, CTO and network administrator’s wish for ‘more’ - more bandwidth for additional capacity, faster speeds, greater security, smaller footprint and cost-efficacy - wireless data link technology is now eclipsing fibre as the go-to solution to meet these demands. No longer bound by the constraints of hard-wired fibre optic links, businesses can free up space previously used to route fragile fibreglass strands along with all the hardware necessary to convert electronic streams to light pulses and then back to electronic again.

With high capacity and high speeds, wireless data communication links can leap across chasms in space to connect line-of-sight buildings at distances of several kilometres using highly directional, pencil-thin beams that prevent interference and strengthen security.

For years, wireless communications have enjoyed modest success over that of fibre-optics and coaxial cable, thanks to their untethered ability to span distances without the need for digging trenches and laying fibre or copper wire. But wireless has been traditionally limited in its capacity to transport Gb quantities of data due to bandwidth limitations set by the FCC.

That all changed, however, with the opening of the 71-76 and 81-86GHz band, referred to as the ‘E-Band’ range of MMW frequencies. Relatively unknown in the commercial world, the MMW spectrum has been utilised for military communications for decades. Unlike frequencies found lower in the EM spectrum, the E-Band offers tremendous, uninterrupted bandwidth to enable wireless data transmission at speeds and capacities on par with the best fibre optic communication systems. Practical data rates in the E-Band band can meet and exceed 40Gb/s.

No longer limited by ground-bound fibre, which requires the underground trenching of streets and sidewalks to establish a physical connection across city blocks; businesses can now channel vast quantities of communication data between buildings and/or campuses.

At the same time, transmission speeds via wireless prove faster than cable because of less latency. Even high quality fibre optic cable experiences significant latency issues in some applications that require precise synchronisation. Expanding upon the improved functionality of wireless is the recent development of dual-capacity MMW wireless in a single polarisation that only requires one antenna.

Light licensed

This technology, pioneered by HXI, simultaneously carries two, independent, full duplex ‘GigE’ signals for a total throughput of 2.5Gb/s. Two dual capacity models, the HLS8454 and the HLS8654, are the latest in HXI’s Gigalink LightSpeed radio product line. The company’s earlier GigaLink Speed radios were among the first MMW radios in the 60 and 70GHz band to achieve FCC certification for unlicensed and light licensed commercial applications.

“This technology creates a value proposition by providing two high speed, high bandwidth lines for the price of one, since putting two communication links on a single antenna gives you twice the capacity with half the hardware,” says Wayne Pleasant, an independent RF consultant and former Chairman of the Wireless Communication Industry Association (WCIA) committee charged with helping the FCC establish guidelines.

“If you have multiple customers or users in a building you can sell, or dedicate, one radio link channel to one customer and the other channel to a different customer or user, without crossover,” continues Pleasant. Previous systems required the use of two antennas to attain full duplex capability. To compensate, some systems multiplex the outgoing and incoming signal on top of each other, but that process exacts a big penalty in terms of latency losing many nanoseconds which add up quickly. The use of a single antenna, with a single polarisation, eliminates the need for multiplexing. Latency is negligible at less than 2ns.

At the same time, using a single antenna adds to the already-increased security that MMW wireless affords. “Channelising two signals together on one frequency poses a greater security risk,” explains Pleasant. “But by using two independent frequencies that single polarisation technology allows, each line is kept totally separate from the other. It’s the highest security you can have for independent GigE transport.”

As if MMW radios and antennas weren’t already very small - measured in inches rather than feet - the use of a single polarisation antenna further reduces the footprint of the system. This addresses the concern over potential ‘visual pollution’ caused when mounting a large quantity of antennas to the side of a building. Given just a single out-the-door unit consisting of both the transmitter/receiver and a single antenna on each end, dual-capacity MMW wireless saves duplication costs. When compared to the expense of laying fibre across the ground, wireless becomes extremely cost effective.

Early adopters

Now that the E-Band spectrum has opened to the commercial world, many businesses are taking advantage of wireless communications instead of fibre. Wireless technology is finding wide acceptance among motion picture, TV, sports and electronic news gathering organisations for the placement of digital video cameras in remote locations up to 500m or more from the receiver, without wires or fibre cluttering the shot or needing a grip to manage the cables.

The industry has traditionally struggled for some time to identify connections that can keep up with the rapidly increasing bandwidth required for high definition filming. The escalating demand is being driven not only by higher resolution devices, but also with the upsurge in popularity of 3D/HD motion pictures and television monitors. Because 3D is shot essentially utilising two cameras filming slightly offset images that are synchronised to create the dimensional effect, two independent HD streams must be transmitted simultaneously. This immediately doubles the data transmission requirement and presents the challenge of doing so through a delivery system that has no latency issues.

Because recording digital 3D/HD over fibre optic cable poses significant latency issues that can affect the synchronisation of the two digital streams of data, complex and expensive multiplexers are required, which lead to racks of equipment on-site and results in a completely non-portable solution. Dual band wireless, on the other hand, facilitates 3D programming. The dual channel model can transport independent, uncompressed video signals from two HD cameras or alternately, 3D/HD, with both input signals transported in perfect synchronisation at 2.970GB/s (combined). This is all without the need for compression or forward error correction, avoiding the associated latency that could cause ghosting.

The advent of LTE networks created a new backhaul connectivity problem; the question became how to connect the growing number of smaller base stations to the core. This dilemma is exacerbated by concerns over frequency congestion and interference in dense cell deployments where four or more picocells would be mounted on light poles in a single parking lot or on a rooftop, for example.

The most obvious solution for high speed transmission of data-intensive content would be to establish a physical connection using fibre optic cabling. However, the cost and challenge of implementing fibre to each micro or picocell site is prohibitive, particularly in urban areas where streets and sidewalks cannot easily be trenched. But with typical link distances for picocell backhaul estimated to a few hundred metres between sites, and microcells less than 2km, this represents the ideal distances for implementing the highly directional characteristic of MMW systems. Narrow beam antennas allow systems in these bands to be engineered in close proximity to one another without causing interference. With dual-band, single polarisation antennas, the net result is higher use of the spectrum with less visual pollution.

The technological advancements made in dual-band MMW wireless radios promise to catapult it over land-bound fibre as the communications medium of choice for many other applications and industries in the coming years.