The future of radio transmission? - Orbital Angular Momentum (OAM)

14th August 2013 – Written by Allan Law

One of the biggest limitations with radio transmission is congestion and capacity. Anyone using an access point in the 2.4Ghz frequency will attest to this. In large city areas, where we have tightly packed homes with wireless technology in pretty much every building creates an environment which is brimming with radio signals coming from everywhere. Regulatory bodies like OFCOM are having to police the airwaves and set rules in place so we do not over saturate the airspace, which would cause conflicts with connectivity.

We are recycling frequency spaces for new types of wireless technology that are emerging, simply because everything has been used already, for example 800Mhz is being used for 4G LTE in the UK, which is the same for some Freeview Digital TV broadcast frequencies in certain parts of the UK. Limitations in throughput speed means that high capacity wireless point to point links are reserved for specialist technologies using super high frequencies or lasers to achieve 1Gbps + speeds, which can be very costly.

A group of Swedish & Italian scientists have come up with a solution. A method has been found to be able to transmit multiple channels simultaneously on the same frequency, with the potential to pack an infinite number of steams into a single signal.

Currently, we use a method called Spin Angular momentum (SAM) which we alter to hold data onto. Now a method called Orbital Angular Momentum (OAM) is combined with SAM, which can enable multiple streams to be packed into a single signal. The signal phase sent in this method is formed into a Spiral shape, not unlike a Fusilli Pasta (pictured on the left), which is being called Radio Vorticity. This sounds like MIMO, but is a different technique, and it is thought that OAM can be combined with MIMO to multiply the number of streams as well.

The Swedish/Italian team demonstrated this in 2012, when they successful sent 2 streams over a single signal, over a distance of 442 meters. To create the orbital vortex wave shape a parabolic antenna was cut and a twist added to it slightly. 2 radios fed the antenna, and sent the 2 streams at the same time over one frequency. At the receiving end were 2 Yagi antennas receiving each stream.

In theory more twisted states can be added to allow more streams to be sent over the same frequency, and by adding multiplexing techniques the number of channels can potentially go up to 55 or more using the same frequency band. The possibility of super high capacity transmission is now possible, and applicable to all spectrums of frequencies, including light.

Another test was demonstrated in 2012 by NASA’s Jet propulsion Laboratory and key universities around the world where they used OAM and polarization multiplexing techniques to transmit an optical beam to transmit 2.56 Terabits per second of data!

Although this technology is in the experimental stages, it does show that a significant step has been discovered, and could potentially open up a new level of wireless transmission which has not been possible before.

Sources Radio Vorticity

Article categories: Outdoor Wireless


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