On Friday, Sprint released three new LTE devices capable of accessing Sprint’s new LTE networks: its ESMR LTE network, and its 2.5GHz LTE network. Combined with its existing PCS LTE network, this will finally bring Sprint LTE performance up to levels that subscribers at other operators enjoy.

Two weeks ago, SoftBank closed its deal with Sprint, and Sprint closed its deal with Clearwire. The result is a new Sprint Corporation that has over 200MHz of spectrum in most parts of the country, most of it usable for LTE TDD on 2.5GHz (LTE Band 41). Immediately after closing, Sprint modified the terms of its user agreement to let Sprint WiMAX users upgrade early to LTE right away (by giving them a free LTE phone without forcing a contract renewal) or leave without a termination fee. The result is that Sprint can immediately cut back or shut down Clearwire’s WiMAX for new LTE TDD service and finally offer service on par with its competitors.

Robert Herron of S4GRU’s speed test of Sprint LTE TDD in Denver, CO

With the release of the new "tri-band" LTE data devices that support LTE FDD on ESMR/PCS and LTE TDD on 2.5GHz (a Netgear hotspot and data stick, and a MiFi) and "tri-band" smartphones coming in the next few months, Sprint has silently activated LTE TDD in eight metropolitan markets, according to S4GRU. These markets are:
• Chicago, IL
• Denver, CO
• Los Angeles, CA
• Miami, FL
• New York City, NY
• San Francisco, CA
• Seattle, WA
• Tampa, FL

Sprint’s LTE TDD network is being deployed with a temporal division ratio of 3:2 for downlink-to-uplink operations, according to an FCC filing by Clearwire. This means that downlink operations are permitted 1.5 times longer than uplink operations, allowing for a slight boost in downlink performance over an FDD scheme of the same carrier channel size, while cutting uplink performance to compensate. This trade-off is considered acceptable because it would not have been noticed anyway, as the transmit power restrictions for devices prevent fully utilizing uplink channel space to the maximum capacity in FDD schemes.

Sprint’s "tri-band" LTE devices support LTE TDD (Time Division Duplex) with carrier channel sizes up to 20MHz. Given the temporal/time division ratio, this means that LTE TDD devices will be able to get download speeds close to 95Mbps (as opposed to the 72Mbps for a comparable 20MHz LTE deployment split into 2x10MHz for FDD). This is because the effective amount of spectrum being allocated to downlink is around 12MHz, while the effective amount of uplink spectrum is 6MHz (if the temporal ratio was translated to frequency division).

The days of pokey mobile broadband performance will finally be over as Sprint rolls out LTE TDD across its urban footprint. Average speeds are around 30Mbps (with expectations to rise over time as Sprint widens to 40MHz and 80MHz channels through carrier aggregation), definitely on par with competitors.

Sprint also has another unusual benefit to its LTE TDD network deployment. In areas where Sprint’s LTE TDD network has usable channels in the middle of the 2.5GHz band, it can also use a little-known feature called "multiple frequency band indicator" to allow LTE TDD devices that use LTE band 38 (an alternate subset 2.5GHz TDD band class designed to permit both LTE FDD and LTE TDD operations on 2.5GHz) onto its network. LTE band 38 is used in Latin America, Europe, Asia, and soon Canada. The device ecosystem is expected to be quite large, and Sprint will have the unique opportunity to offer roaming to users of those devices.

For now, Sprint has earned its name by sprinting ahead with LTE TDD.