NTT DOCOMO is deploying new W-CDMA base stations equipped with newly developed remote radio equipment (RRE) units to provide both existing W-CDMA and forthcoming LTE service. 
RRE (also known as remote radio head) allows the relatively easy and efficient installation of LTE base stations to existing W-CDMA base stations. Compared to existing equipment, it also helps to lower operational costs thanks to its reduced weight, size and energy consumption. The RRE-equipped base station comprises a master unit for signal processing and maintenance functions and the RRE for modulating and demodulating both W-CDMA and LTE signals transmitted and received via antenna. The two are linked by optical fiber
NTT DOCOMO said the RRE-equipped base stations will account for about half of the initial LTE base stations when DOCOMO becomes one of world’s first operators to launch an LTE service in December 2010.
The deployment is a part of DOCOMO’s initial plan to layer a 2GHz LTE network over its existing 3G network to provide dual W-CDMA/LTE service, which will combine the benefits of LTE’s high transmission speeds with 3G’s wide-area coverage as the LTE network is expanded gradually.
http://www.nttdocomo.com/pr/2009/001465.html
