I. INTRODUCTION
Mobile communications have been developed during the
last decade, reaching unexpected figures of active users
and making a reality services which nobody would ever
imagine before. Social networks, real-time navigation systems
along video-streaming services such You-tube or live music
comprise a huge list of on-line services whose use requires
high data throughput rates. In contrast with old tendency, now
the information flows in both sides, demanding vast amounts
of data traffic not only into the downlink, but also into the
uplink to share multimedia content on Internet.