Airtel 4G LTE services were launched in India amid much fanfare last month. With this, India became one of the few countries with 4G services available as of now. Shortly after this, the new Apple iPad with LTE was also released in the country on 27 April, 2012. However to the disappointment of many, the iPad won’t be compatible with the 4G services provided by Airtel and will only work on the 3G network. Nokia isn’t even releasing the 4G variant of the Lumia 900 in India. So one can not help but wonder why don’t these devices work on 4G when LTE services are available?
LTE( Long Term Evolution) is a standard for wireless communications of high speed data for mobile communications. Although marketed as a 4G wireless service it isn’t truly 4G. It promises to deliver peak theoretical speeds of 300Mbps(downlink) and 75.4Mbps(uplink).
Coming to the problem at hand, LTE comes in two variants. The first one being Time-division Duplexing( TDD-LTE) and the other being Frequency-division Duplexing( FDD-LTE). TDD is the application of time-division multiplexing to separate outward and return signals. It emulates full duplex communication over a half duplex communication link. FDD on the other hand means that the transmitter and receiver operate at different carrier frequencies.
Both the variants are incompatible with each other, that is devices designed for one cannot be used on the other. In US (and Japan) carriers have deployed FDD-LTE. As such the products released in the US are FDD-LTE compatible. However, in India (and China, Australia and UK as well) TDD technology is being adopted instead. As such these devices(which are made for the US market) will be incompatible on the 4G network here. You can still buy the SIM version of the iPad, or get a Lumia 900 from the US (costs really cheap at 450$) as they will still support the 3G networks available in the country.