Typically, Frequency Division Duplex (FDD) bands are defined as the symmetric paired spectrum for DL and UL respectively; therefore, it can accommodate a fixed ratio of the maximum downlink and uplink traffic correspondingly. Such spectrum allocation in each region is quite static, generally will not change within tens of years before refarming or re-allocation. In practice, the ratio between uplink and downlink traffic changes over the time, then the static allocation of the frequency resources between downlink and uplink transmission in LTE is not efficient to support dynamic asymmetric cell traffic. According to some statistics of mobile network traffic [3, 4], some measured traffic ratio between DL and UL would be around than 4:1 and with the increased portion of video data for mobile traffic (2/3 by 2018), the ratio between DL and UL would be increased further. This implies that uplink resource can be fairly underutilized for the paired spectrum usage of FDD. Considering UL/DL traffic asymmetry and the limited available spectrum, mechanisms to utilize the underutilized uplink resources should be considered. It is however noted that, in some cases, UL traffic can be heavier than DL traffic depending on traffic situations (e.g., cloud computing). It can be also noted that asymmetry in DL/UL traffic intensity may not be directly translated to asymmetric resource utilization due to different data rate/spectral efficiency between DL and UL.

The objectives of this study are: Identify and document potential regional/band-specific regulatory possibilities/constraints for the use cases of utilizing UL spectrum for transmission from the network to UEs, including aspects such as Tx power levels, modulation schemes, type of transmitting nodes, etc.