The ability to use both TDD and FDD spectrum in LTE networks is a great opportunity to increase capacity and to tap into more affordable spectrum bands, but it is also a challenge that has started to spur innovation among mobile operators, writes Monica Paolini. Japanese carrier Softbank's new 4G network is one of the earliest examples of a TDD deployment integrated within a wide FDD 3G network. What makes the Softbank network different from other LTE networks is not intrinsically due to the fact that it uses TDD. Rather, it is Softbank assets and requirements that pushed the operator in a new direction. To deploy the network, Softbank bought Willcom's 2.5 GHz spectrum, but it also inherited its 1.9 GHz Personal Handy-phone System (PHS) network infrastructure--a very dense collection of urban sites that serves as the initial footprint for the 4G deployment, with sites, backhaul and antennas shared between the two networks. Commentary
