IEEE 802.11af Tutorial : White-Fi basics

White-Fi, based on the IEEE 802.11af standard, represents a significant advancement in wireless communication by utilizing TV white spaces (unused portions of the UHF and VHF spectrum) for data transmission. This technology extends the range of Wi-Fi beyond conventional frequency bands, enabling better coverage in rural and less densely populated areas where TV spectrum is underutilized. This 802.11af tutorial covers White-Fi basics, 802.11af features, physical layer and benefits of White-Fi technology.

Introduction

The frequency spectrum has been allocated for two types of services viz. licensed and unlicensed. Day by day use of wireless spectrum is becoming more and more due to advancement of wireless technologies and standards. IEEE 802.11af standard is developed for spectrum sharing. This standard helps unlicensed White space devices and other licensed services to share the spectrum. The standard also covers rules to fulfill international regulatory domains.

Unused frequency spectrum is referred as white space and devices designed to use this through spectrum sharing is referred as White Space Devices(WSDs). TV white space exists in the broadcast VHF/UHF television bands. As it operates below 1GHz this signal frequency will go through less material obstruction compare to other bands and hence it is ideal for non line of sight communication/coverage. Due to lower frequency, TVWS frequency band used in IEEE 802.11af will have less path loss compare to other 2.4 GHz and 5.7 GHz bands. This technology is also referred as White-Fi.

The technology White-Fi uses the unused frequencies in TV signal spectrum. Microsoft has pioneered the project to provide last mile connectivity in the countries which include India, Kenya, singapore, US and UK.

As we know 200-600 MHz frequency is used for TV channels to carry the data. In India, 93% of this spectrum is not utilised. White-Fi will make use of this vacant spectrum to provide the connectivity. The unused spectrum spaces are commonly referred as White space and hence the name White-Fi. Many technology companies are looking at using this unused portion to provide the last mile internet access to the users.

802.11af features

Following are the silent features of IEEE 802.11af White-Fi:
•   Operates in TV bands 470 to 790 MHz (Europe) and 54 to 698 MHz (USA)
•   Single Channel Bandwidth(W) supported are 6,7,8 MHz, Other possible supported combinations are 2W,W+W,4W,2W+2W.
•   Single spatial stream is mandatory in WSDs.
•   MIMO with 4x STBC and 4x Multiuser diversity

802.11af Physical Layer

IEEE 802.11af defines physical layer for WSD devices to use and operate in TVWS frequency bands. This physical layer replaces HT and VHT specifications developed previously for WLAN 802.11a OFDM and 802.11ac variants. As mentioned PHY supports channel bandwidth combinations as outlined above. It supports 144 OFDM subcarriers for 6 and 8 MHz bandwidth channels. It supports 168 subcarriers for 7 MHz bandwidth channels. In as single channel bandwidth subcarriers are arranged as follows:
•   Data Subcarriers: -58 to -2, 2 to 58
•   DC carrier: Index 0
•   Pilot carriers: Total 6 at indices -53,-25,-11,+11,+25,+53

Key benefits of White-Fi

Following are the advantages of White-Fi.
1. Longer Range: Due to the lower frequencies used, signals can travel further and penetrate obstacles better than traditional Wi-Fi operating at 2.4 GHz or 5 GHz.
2. Spectrum Efficiency: By leveraging dynamic spectrum access and cognitive radio technology, White-Fi enables efficient use of unused spectrum, reducing interference and optimizing bandwidth usage.
3. Affordable Connectivity: White-Fi has the potential to provide affordable internet access in underserved areas, bridging the digital divide and supporting applications like remote education, telemedicine, and smart agriculture.

Conclusion

However, challenges such as spectrum regulation, coexistence with licensed users, and infrastructure costs must be addressed to realize its full potential. Despite these hurdles, White-Fi's ability to provide broad, cost effective wireless coverage makes it an attractive solution for expanding internet access globally, particularly in rural and hard to reach regions.

11ac and 11af tutorial Links

WLAN RELATED LINKS

What is?