Cellular Access Point Proximity Detection for Underlay Handover
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Solution Overview
Problem
The integration of a large number of pico-cells underlaying a 3G network poses challenges in efficient handover and cell selection between macro-cells and underlay cells, particularly when using different frequencies, leading to increased interference and reduced mobility support.
Innovation Solution
A cellular communication system with an access point that performs proximity detection using non-UMTS wireless transmissions, temporarily transmits a pilot signal on the macro-cell frequency to facilitate switching of user equipment from the macro-cell to the underlay cell, allowing handovers based on same frequency measurements and minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If different frequencies are used for macro-cell and underlay cell to reduce interference, then interlayer interference is minimized, but handover/cell selection becomes more complex and same frequency measurements cannot be used
Solution Approach 1:
The patent introduces a frequency translation mechanism as an intermediary that converts underlay cell signals from the second frequency to the first frequency (macro-cell frequency) before transmission to mobile stations. This allows mobile stations to perform same-frequency measurements on underlay cells without actual frequency conversion at the receiver, thus maintaining simple handover algorithms while enabling different frequencies for interference reduction at the transmitter side
2Reliability
If soft handover is used to provide efficient handover with reduced interference, then handover performance is improved, but time synchronization requirements cannot be met by residential access points
Solution Approach 1:
The patent extracts the soft handover functionality from the traditional CDMA soft handover mechanism and implements it through a simplified approach using frequency translation and measurement reports. Instead of requiring time-synchronized signal recombination at the mobile station, the system uses macro-cell frequency measurements of translated underlay signals to trigger handovers, eliminating the need for precise time synchronization at residential access points while maintaining reliable handover performance
3Productivity
If underlay cells are deployed to increase capacity in densely populated areas, then system capacity is improved, but handover management between layers becomes more complex
Solution Approach 1:
The patent makes the frequency translation mechanism universal by implementing it at the underlay cell transmitter side for all underlay cells regardless of their specific location or configuration. This allows a single handover management algorithm to handle all underlay cells uniformly by translating their frequencies to the macro-cell frequency for measurement purposes, thus enabling capacity enhancement without proportionally increasing handover management complexity
Data Source
AI summary
A cellular communication system comprises an access point (101) which supports an underlay cell of a first cell on an underlay frequency using another frequency. A proximity detector (113) detects user equipment (109) in response to a wireless transmission therefrom, which uses a different transmission technology from a transmission of the cellular communication system. In response to the proximity detection, the access point (101) temporarily transmits a pilot signal on the first cell frequency. The user equipment (109) is then switched to the access point (109) and the underlay frequency in response to a detection indication from the user equipment (109) indicating that the pilot signal has been detected. Following the switch the access point (101) terminates the transmission of the pilot signal.