If you've ever wondered why MetroPCS's 4G LTE network is so slow compared to its larger rivals, well the FCC revealed exactly why this week. In the document approving the merger between MetroPCS and T-Mobile USA, the FCC says that "MetroPCS has been forced to deploy its LTE network over a mere 1.4 x 1.4MHz or 3.0 x 3.0MHz of spectrum." Hence MetroPCS is seeing LTE speeds of less than 5 Mbit/s -- sometimes much less -- in the tens of towns and cities it has deployed 4G in. By comparison, AT&T Inc. and Verizon Wireless have 2x10MHz pipes to play with for LTE. As we've seen recently, that can result in averages nudging 19 to 15 Mbit/s in the top markets, with AT&T being ranked best for data speed. The FCC says that T-Mobile -- like Sprint Nextel Inc. -- would have had to deploy LTE in 2x5MHz channels in some areas with the additional MetroPCS spectrum, leaving it at a speed disadvantage. Now the carrier will be able to cover just under half the U.S. population in nearly 250 cellular market areas with LTE. In contrast, AT&T expects to cover nearly all the U.S. population -- 300 million -- with LTE by the end of 2014, even though it did not succeed in acquiring T-Mobile for its spectrum. Post-transaction, T-Mobile will continue to be the smallest service provider of the four national wireless operators, with around 42 million subscribers, as compared to 115 million for Verizon Wireless, 106 million for AT&T, and 56 million for Sprint Nextel. — Dan Jones, Site Editor, Light Reading Mobile