  Ever since the inception of mobile telephony, the downlink and uplink of
cellular networks have been coupled, i.e. mobile terminals have been
constrained to associate with the same base station (BS) in both the downlink
and uplink directions. New trends in network densification and mobile data
usage increase the drawbacks of this constraint, and suggest that it should be
revisited. In this paper we identify and explain five key arguments in favor of
Downlink/Uplink Decoupling (DUDe) based on a blend of theoretical,
experimental, and logical arguments. We then overview the changes needed in
current (LTE-A) mobile systems to enable this decoupling, and then look ahead
to fifth generation (5G) cellular standards. We believe the introduced paradigm
will lead to significant gains in network throughput, outage and power
consumption at a much lower cost compared to other solutions providing
comparable or lower gains.
