Mi-Fi: The new extension to the ubiquitous Wi-Fi

In an era where radio spectrum is rationed out to the operators by the government, more stringent is the case in emerging countries such as India, innovative uses of the available spectrum is the order of the day. One such technology is the use of ubiquitous Wi-Fi access points at home or office which in turn is connected to the Digital Subscriber Line (DSL) landline connection. Popularly known as “Wi-Fi off load”, this is a method by which the data traffic is diverted from the carrier’s macro cellular network to a localized Wi-Fi network, installed typically in homes, enterprises or public locations, thus relieving the licensed spectrum used.  Such Wi-Fi hot spots can be deployed by the owner of the venues as “Private hot spots” (e.g. homes, office premises, Cafes and Restaurants such as Starbuck, Costa Coffee, hotels); or by the Internet Service Providers (ISPs) as “public hotspots” typically in areas such as Airports and Malls; or mobile operators either by themselves or in partnership with ISPs as “carrier Wi-Fi hotspots” (see details in the article written by me and Chakravarthy Buchi in Voice & Data at: http://www.voicendata.com/voice-data/news/170992/is-wi-fi-offloading-really-good ).

An extension of the above is “Mi-Fi” (referring to My Wi-Fi, the brand coined and used by Novatel Wireless in the U.K. who first introduced it in the U.S. in 2009) where wireless long haul is provided typically through 4G-LTE network connection instead of the DSL landline. Thus the Mi-Fi routers are portable and flexible and can connect multiple Wi-Fi enabled devices such as Smartphones, Tablets and Laptops.

Following are the use cases for Mi-Fi deployment:

1. Stationary usage where the users connect to the Mi-Fi router at hme, office, hotels or even public places for accessing the data networks including the Internet. The LTE backhaul provides the needed bandwidth and the licensed frequency spectrum of the LTE network is used for aggregated traffic hence providing the required trunking gain and efficiencies.
2. Usage in mobile public transport such as buses, trains where the Mi-Fi router provides the occupants with local Wi-Fi access, connecting them through the wireless backhaul to the Internet. Of course, the handovers across the cells (i.e. eNodeBs) need to take place while the vehicle moves across locations.
3. Mobile handovers where a nomadic user moves from the macro cellular network to the Mi-Fi zone where the communication is seamlessly transferred to the local Wi-Fi connectivity provided through the router. This use case is very important in countries such as India where the licensed spectrum allocated to the macro cellular operator is often limited. As soon as the handover takes place the licensed spectrum in the macro network is relieved as in the case of the typical “Wi-Fi offload” scenario.

The international standards agencies such as 3GPP have incorporated most of the above features in the recent standards for the device makers to develop compatible devices.

However, there are a couple of issues still remain:

1. How do we seamlessly handover voice calls in Circuit Switched mode on the macro cellular network to the local packet switched based Wi-Fi zone?
2. How do we incorporate untrusted Wi-Fi networks operated by independent Internet Service Providers (ISPs) in to Mi-Fi zones?

There seems to be interest especially from the 3G and Broadband Wireless operators in India in a large scale deployment of Mi-Fi devices and services..

Co-authored by: Sreejith Krishnan, Satish Bhat and Dr. V. Sridhar