CDMA Base Station Antenna Systems with Offset Pilot Channels
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Solution Overview
Problem
CDMA cellular systems face challenges in increasing capacity without requiring complex calibration and additional hardware, as existing methods for using multiple narrow beams and common pilot channels can lead to signal cancellation and dropped calls due to coherent pilot channel signals.
Innovation Solution
An antenna system with multiple fixed beams connected to a beam-forming matrix, where transceivers provide slightly offset transmit frequencies or time-dependent phase offsets to reduce signal cancellation, allowing for increased capacity without complex calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple narrow beams with common pilot channel are used to increase capacity, then system capacity increases significantly, but signal cancellation occurs due to coherent pilot channel signals from multiple beams
Solution Approach 1:
The patent applies asymmetry by introducing frequency offsets to the pilot channels transmitted on different beams. Instead of using identical coherent pilot channels on all beams, each beam transmits pilot channels at slightly different frequencies, breaking the symmetry and preventing signal cancellation while maintaining the benefits of multiple narrow beams for increased capacity.
Solution Approach 2:
The patent changes the frequency parameter of the pilot channels transmitted on different beams. By offsetting the frequencies of pilot channels on various beams relative to each other, the system prevents coherent signal cancellation while maintaining reliable pilot channel reception, thus resolving the contradiction between capacity improvement and call continuity.
2Reliability
If separate wide beam antenna is used for overhead channels to avoid signal cancellation, then call reliability is maintained, but hardware complexity and calibration requirements increase
Solution Approach 1:
The patent makes the antenna array universal by enabling it to perform both functions: transmitting traffic channels on multiple narrow beams and broadcasting common overhead channels, all through the same antenna elements. The beam-forming matrix enables flexible signal routing, allowing the system to achieve reliable overhead channel transmission without requiring separate dedicated antennas for different functions.
Solution Approach 2:
The patent introduces dynamic frequency offset adjustment capability, allowing the system to adaptively manage pilot channel frequencies on different beams. This dynamic parameter adjustment enables the system to maintain optimal performance under varying conditions without requiring complex static hardware configurations or extensive calibration procedures.
3Productivity
If adaptive antenna array techniques are used to transmit overhead channels over the whole sector, then capacity is increased and call reliability is maintained, but calibration complexity and algorithm requirements increase significantly
Solution Approach 1:
The patent segments the overhead channel transmission by allocating different frequency-offset pilot channels to different beams, rather than attempting to coordinate complex adaptive beamforming across all antennas. This segmentation simplifies the system architecture by avoiding the need for complex calibration equipment and algorithms, while still achieving the benefits of multiple narrow beams for capacity improvement.
4Power
If fixed narrow beams transmit pilot channels coherently to maximize signal strength, then beam efficiency is improved, but signal cancellation occurs in areas where vector sum of pilot signals is null
Solution Approach 1:
The patent breaks the coherent symmetry of pilot channel transmission by introducing frequency offsets on different beams. This asymmetry prevents the vector sum cancellation effect that occurs with coherent signals, ensuring that mobile stations receive adequate pilot signal strength throughout the sector without experiencing nulls that would cause dropped calls.
Data Source
AI summary
Antenna systems are used for transmitting common overhead channels (pilot, sync, and paging channels) over a whole sector while transmitting and receiving unique traffic channels on individual beams in the sector. Each beam in the sector is transmitted at a frequency offset from other beams in the sector. The offset frequency is chosen such that the effect of cancellation of the pilot channel caused by the summing of signals from multiple beams is minimized. Alternative, each beam in the sector can have a time dependent phase offset relative to each other to minimize the effect of cancellation of the pilot channel caused by the summing of signals from multiple beams. System capacity is substantially increased since the number of traffic carrying beams per sector is increased without using more pilot channel PN offsets. Beams are fixed and the same antennas are used for the overhead channels as the traffic channels, obviating the need for complex algorithms and calibration procedures.