LTE UE Control Channel Design for Narrowband Measurement
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Solution Overview
Problem
Low-cost LTE user equipment (UEs) with bandwidth reduction face challenges in camping on LTE cells with larger bandwidth, inability to decode control channels, and limitations in intra-frequency measurement and channel quality reporting, leading to reduced cell coverage and inefficient scheduling.
Innovation Solution
Novel control and data channel designs, including allocation of resources in narrow subbands, configuration of control channel information, measurement gaps, and frequency hopping, enable UEs to camp on LTE cells, perform intra-frequency measurements, and assess channel quality across wider bandwidths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If bandwidth reduction is implemented to reduce UE cost, then device cost is reduced, but the UE cannot decode control channels spanning the whole bandwidth
Solution Approach 1:
The control channel resources are segmented into multiple search spaces (common and dedicated) with different aggregation levels. The common search space uses aggregation levels 4 and 8 for robust coverage, while the dedicated search space uses aggregation levels 1, 2, 4, and 8. This segmentation allows the UE to decode control information reliably even with limited bandwidth processing capability.
Solution Approach 2:
Different aggregation levels are assigned to different search spaces based on their specific requirements. The common search space, which carries critical system information, uses higher aggregation levels (4 and 8) for better reliability, while the dedicated search space can use lower aggregation levels (1, 2, 4, 8) for more efficient resource utilization. This local quality differentiation ensures reliable control channel decoding for bandwidth-reduced UEs.
2Productivity
If BR-UEs are scheduled at non-center PRB pairs to support more UEs, then scheduling flexibility is improved, but the UEs cannot perform intra-frequency measurements
Solution Approach 1:
Measurement gaps are configured periodically for BR-UEs, allowing them to temporarily suspend normal reception and perform intra-frequency measurements at specific intervals. This periodic action ensures that measurements are performed regularly without requiring continuous access to center PRB pairs, thus maintaining both scheduling flexibility and measurement capability.
3Device complexity
If the UE is limited to contiguous 6 PRB pairs for cost reduction, then device complexity is reduced, but the UE cannot assess channel quality across the whole bandwidth
Solution Approach 1:
The UE performs channel quality assessment on a partial basis by measuring CSI-RS resources within its limited 6 PRB pair bandwidth. While this doesn't cover the entire cell bandwidth, it provides sufficient channel quality information for the UE's scheduling and link adaptation needs. The serving eNodeB can use this partial measurement information along with other available data to make scheduling decisions.
Data Source
AI summary
Methods to support measurements for LTE user equipments are proposed. Due to reduced bandwidth design for cost reduction, resources for UEs are limited to contiguous six physical resource block (PRB) pairs (1.4 MHz). Six or less contiguous PRBs per narrow sub-band located in the whole channel bandwidth is allocated for transmission and reception for UEs. Novel control channel and data channel designs are proposed to make UEs be able to camp on LTE cells. Methods for intra-frequency measurement, for received signal time difference (RSTD) measurement, and for channel quality assessment for UEs are also provided. In one embodiment, UE is allocated with a measurement gap for intra-frequency measurements and RSTD measurements. In another embodiment, UE is configured with a frequency-hopping pattern and receives a PRB pair starting index per subframe for CSI measurement.