The present document is the technical report for the Study Item on measurement gap enhancement in LTE.
The current measurement gap configuration and the corresponding RRC signalling were first introduced in Rel.8 back
in 2008. Since then, some fundamental evolutions in LTE have been realized. These include numerous new
technologies (e.g. carrier aggregation, FeICIC, CoMP, dual-connectivity, etc.), new network topologies (e.g.
Heterogeneous Network with small cells) and increased number of deployed bands and frequencies.
The main challenges of the existing measurement gap and the motivations for the further enhancement can be
summarized in the following four aspects:
Network impact and UE scheduling opportunity
Up to 15% of DL/UL resources are restricted from reception and transmission due to the existing
measurement gap configuration
Multiple Rx chains equipped in CA capable UE can potentially provide extra degrees of freedom to do the
measurement more efficiently, but they are not fully utilized at the moment.
Challenges with multiple Rx chains and single chip RF-IC implementation
UE can only be configured with single measurement gap pattern even equipped with multiple Rx chains
This significantly limits network and UE's flexibility to balance the measurement delay, power consumption
and spectrum efficiency, which can benefit from multiple RF chains.
Harmonic interference and/or synthesizer operations due to one Rx chain can result in the interruption on the
other Rx chains
The scenarios where involving synthesizer operating include, but not limited to, radio turned on/off, inter-frequency measurement, SCell activation/deactivation and/or SCell measurements.
The existing measurement gap pattern is inefficient to handle the Inter-RF chain interference issue. This
unnecessarily imposes significant implementation restriction.
UE power consumption and mobility
The potential benefit has been recognized to save UE power consumption by differentiating the measurement
requirements for the different frequency layers, e.g. coverage, offloading, etc. However, it is not easy to be
realized based on the existing measurement gap configuration.
The mobility performance can be considerably improved with measurement gap enhancement by reducing
the measurement delay of coverage layers.
With the ever-increasing number of deployed bands and frequencies, the existing inter-frequency/inter-RAT
measurement mechanism faces even more challenges to meet the performance requirements.
Limitations of the existing measurement gap pattern are identified in various technical areas
No enhancement has been made even though the importance of measurement gap enhancement has been well
The measurement gap related discussions are diverse and spread over quite a few topics.
It is desirable to address different measurement gap related issue in a single SI and the eventual enhancement
and design should be versatile enough to serve different purposes.
All in all, the effectiveness of new technologies and new network topologies evolved since Rel.8 not only greatly relies
on the measurement accuracy and reporting delay, but also on the measurement efficiency and the associated power
consumption at UE. All these issues motivate some effort to further investigate the measurement gap enhancement. It is
desirable to design an all-weathered and future-proofed inter-frequency/inter-RAT measurement solution by jointly
considering all aspects, including but not limited to delay, power consumption, flexibility and network performance.