Expanding PDCCH Control Region Symbols for LTE Handover
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Solution Overview
Problem
The existing handover process in LTE networks is negatively affected by interference from shifted Cell Specific Reference Signals (CRS) between cells, leading to reduced handover performance and increased loss of service, especially for voice services.
Innovation Solution
Increasing the number of Orthogonal Frequency Division Multiplexing (OFDM) symbols in the control region of a downlink OFDM-subframe during handover, specifically when a Signaling Radio Bearer is scheduled, to enhance the robustness of the Physical Downlink Control Channel (PDCCH) and minimize interference from neighboring cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of OFDM symbols in the control region is increased during handover, then the robustness of the PDCCH is improved and handover performance is enhanced, but the data region size is reduced and spectral efficiency is compromised
Solution Approach 1:
The network node dynamically adjusts the number of OFDM symbols in the control region based on whether a UE is in handover. During handover, the control region is expanded to provide robust PDCCH transmission, while during normal operation, the control region is minimized to maximize data transmission. This dynamic adaptation resolves the contradiction by making the system flexible rather than static.
Solution Approach 2:
The control region size is periodically adjusted according to the handover status of UEs. When handover is detected, the control region is temporarily expanded; when handover is complete, the control region returns to its minimum size. This periodic adjustment ensures that the system maintains high reliability during critical handover periods while preserving high spectral efficiency during normal operation.
2Productivity
If the control region size is minimized to maximize data region, then spectral efficiency is improved, but the PDCCH becomes more susceptible to interference from shifted CRS in neighboring cells
Solution Approach 1:
The system dynamically changes the control region size based on interference conditions. During handover when interference from shifted CRS is most problematic, the control region is expanded to provide protection. During normal operation when interference is less critical, the control region is minimized to maintain high spectral efficiency.
Solution Approach 2:
The network node changes the parameter of control region size (number of OFDM symbols) based on the operational state. By adjusting this parameter dynamically, the system can optimize the balance between spectral efficiency and interference resistance depending on whether handover is occurring.
3Reliability
If voice services are prioritized during handover, then connection quality is improved, but data transmission during handover is reduced
Solution Approach 1:
The system periodically adjusts resource allocation based on service priority. During handover events, resources are temporarily reallocated to prioritize voice services over data transmission. After handover completes, the allocation returns to normal, maximizing data transmission. This periodic reallocation resolves the contradiction by making temporary sacrifices in data rate to ensure voice service reliability during critical moments.
Solution Approach 2:
The resource allocation is dynamically adjusted based on the type of service and operational state. During handover, the system dynamically shifts resources to support voice services with higher priority, accepting reduced data transmission. This dynamic resource management allows the system to adapt to changing requirements and maintain connection quality when needed.
Data Source
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AI summary
A method performed by a network node 110, for handling handover of a user equipment (UE) 120, wherein the network node 110 serves a first cell 130 comprising one or more UEs 120. When the network node 110 has detected that a Signaling Radio Bearer (SRB) is determined to be scheduled for a UE 120 in handover from the first cell 130 to a second cell 131, the network node 110 increases the number of OFDM-symbols included in a control region of a downlink OFDM-subframe sent in the first cell 130 in a Transmission Time Interval (TTI) related to the handover. By increasing the number of OFDM-symbols of the control region only during the handover, the physical downlink control channel (PDCCH) is spread in time into symbols not polluted by CRS symbols from neighboring cells. Thereby the number of unsuccessful handovers and lost service is effectively reduced.