One of the critical factors for the success of outdoor/urban small cells is low cost wireless backhaul. Various technologies at different frequency bands are being actively proposed, with the lightly licenced 60GHz V-Band being a popular early choice. One way of assessing whether the industry is on-track to achieve that lower price point is to examine investments and progress being made today by RF silicon vendors.

Here, we can clearly see a couple of associated applications that should accelerate development of this specific technology generally, enabling lower costs in the longer term.

An advantage for 60GHz is that it has applications for the consumer market, potentially involving huge volumes. Wi-Gig, also known as 802.11ad, delivers unlicensed Wi-Fi service at these high frequencies, offers extremely fast data rates of 1Gbps or more over very short range (1 to 2 metres). Here in the UK at least, the unlicensed spectrum assigned for general public Wi-Fi use is adjacent to the lightly licenced band available for backhaul and wide area use.

Some of the benefits from investment aimed at consumer Wi-Gig should spill over to address small cell backhaul applications too.

Three main use cases

Very broadly speaking, the 60GHz band has a few distinct use cases:

• Cable replacement (wireless HDMI video), removing the need for all that ugly cabling between your TV and set-top box. Links would be very short range, perhaps only be a metre or less, and incorporated into consumer equipment.
• Wi-Gig (Faster Wi-Fi) for Laptop/tablet/smartphones: Providing Gigabit wireless connections in the same room, such as connecting to printers, downloading HD movies and/or syncing large files quickly
• High speed point-to-point outdoor radio links, for small cell backhaul and/or connecting networks between buildings up to 1km apart.

Mainstream RF chipset companies all actively investing

Pretty much all of the large companies in the RF chip industry are now investing in their own 60GHz chipsets. This will ultimately drive the cost of these radio links down. It is said there are perhaps 2-3 silicon products already available in the market today, with another 4-5 in development.

Dedicated 60GHz frequency designs required for each type of usage

Few if any of these 60GHz products will be directly suitable for more than one of the three use cases above. The standards for Wi-Gig and outdoor 60GHz point-to-point links are diverging, making it more difficult to meet both requirements in a single device. Multiple cable replacement standards compete with each other.

Outdoor chipsets have to meet more demanding performance levels, so it's hard to design a product that satisfies both indoor and outdoor markets. Some have tried (and failed), and realistically this probably isn't achievable within the short term.

At these higher frequencies, these chipsets are very frequency specific – it isn't feasible today to share the same chipset design for both 60GHz and 80GHz bands, so companies have to make an early target market investment decision.

A further complication is that even for indoor "Wi-Fi style" applications, there are different requirements. For example, the radio link used to connect between a laptop and printer would be more difficult to maintain than one connecting between audio-visual boxes serving a TV close in the same stack. Longer-range links even within the same room have to deal with physical objects in the path and reflections that might require some beam steering capability and the ability to cope with minor disruptions.

Cable replacement standard proliferates

The use case of wirelessly connecting two devices for streaming HD Video has many competing solutions today. Wireless HD, which also operates at 60GHz, uses a different radio scheme to Wi-Gig.

Several other options include Intel's Wi-Di, Wi-Fi Miracast, WHDI (Wireless Home Digital Interface), Apple's Airplay and Wireless USB.

My guess is that the integration of the Wi-Gig standard within the overall Wi-Fi will boost its adoption and mass market appeal because it satisfies the widest range of use cases.

Investment in outdoor 60GHz silicon

Some of these mass market targeted developments should benefit the design and availability of outdoor 60GHz chipsets. Evidence of that includes a couple of recent datapoints:

• Infineon's announcement late last year that production had started on their 60GHz transceivers targeted for small cell backhaul, with commercial availability before the end of 2013.
• BluWireless, based in Bristol, UK, winning a further £2 million round of funding and continue to develop core IP for chipset designers. 

While 60GHz point-to-point links can't address all the needs of outdoor small cell backhaul, the continued industry investment in this field indicates it's likely to make a significant contribution.

Part of a wider solution set

Other backhaul technologies are also getting substantial investment too of course. The 70/80GHz E-Band, which can achieve longer distances because it's not so affected by Oxygen absorption, is already being adopted for outdoor backhaul of existing networks. Dedicated chipsets and wireless products are already available.

There continues to be a lot of investment in many other solution too, from Non-Line-of-Sight technology at lower frequencies too (typically below 6GHz), use of microwave bands, and even free space optical. For a wider review of the range of backhaul technologies being considered, read our earlier roundup of the various small cell backhaul technologies and players.