Data Communication in the License-Free Band


Ever since mankind first harnessed radio waves a century ago, the spectrum of radio frequencies from 3 Hz to 3 GHz has been exploited for a variety of applications. Interestingly, waves between 20 Hz to 20 KHz are audible to humans, with the best sensitivity in the range 1 KHz to 4 KHz.

The radio frequency (RF) spectrum is classified into different bands based on frequency values. Each band has its own communication range, which is dictated by the laws of physics. In general, the lower the frequency value, the higher the communication range. As such, radio bands are chosen for long, medium, and short-range communication based on the application. For example, space, defense, medical, broadcasting service and personal gadgets.

Radio communication was first used in defense application and extrapolated later into the space, public broadcasting, manufacturing and medical domains. For the past few decades, RF communications have been catering to mobile networks, hotspots, and personal area networks, and more recently are being used in body networks for managing wearable devices.

Unlike co-axial cable and fiber optics, which are dedicated, physical wires, RF spectrum is a shared medium and is accessible to everyone. Every country has its own governmental regulatory body that allocates spectrum to the military, telecommunication sector and for personal area networks. Being a scarce resource, some range of spectrum is licensed for specific applications, such as mobile networks that generate revenue. Frequencies in the industrial, scientific and medical (ISM) radio band can be used without a license or a fee.

While free, the ISM band does have guidelines for usage, such as transmitting power. The duration of continuous usage, measured in milliseconds, is also a controlled parameter. Also, occupancy within the ISM band has to be relinquished after usage for others to use. Frequency bands of 2.4 GHz, 5 GHz and 60 GHz are popular and license-free bands globally. Technologies like WLAN, Bluetooth, ZigBee, microelectromechanical systems (MEMS), and devices like baby monitor and cordless phone all use the 2.4 GHz frequency band.

The RF spectrum available for communications enables all types of information to be exchanged between individuals and gadgets, from a small sensor embedded in the body, to a satellite. Wireless communication connects everyone and everything, everywhere.

Two decades ago, the IEEE published the wireless local area network (WLAN) specification 802.11, which has maximum data communication throughput of 11 mb/s in the 2.4 GHz band. With continuous improvement in the radio technology in 2.4 GHz and 5 GHz, throughput is now measured in Gb/s, which is the industry standard for communications. The WLAN 802.11ax standard, which will hit the market in a few years, which could deliver throughput on the order of 10 Gb/s and more.

The 60 GHz license-free RF band is used for short-range, high-speed data transfer. IEEE 802.11ad specification provides the framework for this solution. Presentations and video conferences can be shared with overhead projectors using 802.11ad and it will replace HDMI and VGA cables in the near future. The data transfer speed in this band is 7 Gb/s and is likely to increase with the emergence of the IEEE 802.11ay standard. Combining the available frequency of operation within the band and increasing the bandwidth for communication will result in a four-fold increase in throughput in the near future.

So far, the discussion goes with throughput for a collision domain, where each user shares the RF medium in the vicinity. In a crowded environment, users often suffer from lack of access to the medium. Beam-forming techniques can control RF signals and improve the user experience by focusing the signal in a specific direction or location to achieve greater spatial diversity. Multiple users can then share the RF medium without interference. It saves power and unwanted disturbance to the neighbors, who can use the RF medium simultaneously to boost the user experience. With these features, the 802.11ay standard is expected to increase the data throughput to 176 Gb/s.

As the data throughput increases in the 2.4 GHz and 5 GHz bands and as reliability improves, it paves the way for seamless integration with other contemporary technologies such as LTE.

Frontier technologies continue to endeavor to make a breakthrough in the current limitation and make progress through all possible means. The new technique which is at the research level and primitive in its development is expected to grow further from the current stage and make big leeway other than with the RF medium. Other technology, Li-Fi uses visible light spectrum, which uses LEDs as the transmitter and photo light detector as the receiver, and is expected to produce a data throughput of 226Gb/s, in the near future.

About the Author


Sunder Kumaresan
Senior Engineering Project Manager

Sunder is a Senior Project Manager at Aricent having over 20 years of experience in Wireless Domain, Protocol Stack Development and Embedded Programming. He was involved in Zigbee Golden Unit Stack Development and has published papers on Ultrasound, Embedded System and Instrumentation. He is passionate about technological advancement and travelling.


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