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Will Sprint go with TD-LTE in the United States? They own most of the 2.5-2.6 GHz band in the United States and don’t have to conform to any artificial FCC ghetto for unpaired frequencies. TD-LTE is better suited for asymmetrical data use and it’s a world standard, supported by China, India and satellite provider Lightsquared, according to China Daily.

Chipsets that support both WiMAX and TD/FD-LTE are becoming available from multiple vendors. There are lots of TD-LTE chipset options:

Sprint doesn’t have 700 MHz FD-LTE spectrum like Verizon and AT&T, so conforming to them just for easier roaming is not an option, anyway. In addition, TD-LTE equipment will be available in volume as China and India ramp up in the next few years.

Perhaps Sprint’s “delay” in announcing an LTE commitment may be tied to getting all the TD-LTE ducks in a row. TD-LTE also makes sense for carriers like MetroPCS and Cricket Wireless who have limited LTE spectrum. Voice over LTE is expected to eliminate the need to fallback to older CDMA networks for voice, further enhancing its viability.

Here are some advantages / disadvantages of Time Division Duplex and Frequency Division Duplex in LTE networks.

Parameter LTE-TDD LTE-FDD
Paired spectrum Does not require paired spectrum as both transmit and receive occur on the same channel Requires paired spectrum with sufficient frequency separation to allow simultaneous transmission and reception
Hardware cost Lower cost as no diplexer is needed to isolate the transmitter and receiver. As cost of the UEs is of major importance because of the vast numbers that are produced, this is a key aspect. Diplexer is needed and cost is higher.
Channel reciprocity Channel propagation is the same in both directions which enables transmit and receive to use on set of parameters Channel characteristics different in both directions as a result of the use of different frequencies
UL / DL asymmetry It is possible to dynamically change the UL and DL capacity ratio to match demand UL / DL capacity determined by frequency allocation set out by the regulatory authorities. It is therefore not possible to make dynamic changes to match capacity. Regulatory changes would normally be required and capacity is normally allocated so that it is the same in either direction.
Guard period / guard band Guard period required to ensure uplink and downlink transmissions do not clash. Large guard period will limit capacity. Larger guard period normally required if distances are increased to accommodate larger propagation times. Guard band required to provide sufficient isolation between uplink and downlink. Large guard band does not impact capacity.
Discontinuous transmission Discontinuous transmission is required to allow both uplink and downlink transmissions. This can degrade the performance of the RF power amplifier in the transmitter. Continuous transmission is required.
Cross slot interference Base stations need to be synchronised with respect to the uplink and downlink transmission times. If neighbouring base stations use different uplink and downlink assignments and share the same channel, then interference may occur between cells. Not applicable

Samsung, HTC and Nokia/Microsoft would be good partners to have on board for any Sprint LTE announcement. Apple, too, of course. Wang Jianzhou, China Mobile’s chairman, said repeatedly that China Mobile is in talks with Apple to launch the iPhone on its TD-LTE network.

Realistically, any TD-LTE phone support probably wouldn’t happen until 2012 at the earliest. TD-LTE commercial availability is reportedly about a year behind FD-LTE.

China Mobile Research Institute and SkyCross this week demoed the world’s first compact, tunable MIMO antenna that covers 12 frequency bands ranging from 700 MHz to 2.7 GHz for TD & FDD-LTE, TD-SCDMA, and GSM. Some handsets need as many as ten antennas. Skycross iMAT technology permits a single radiating element to behave like multiple antennas.

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