Leakage Cancellation in Wide Bandwidth Distributed Antenna Systems
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Solution Overview
Problem
Modern wireless telephone systems with Distributed Antenna Systems (DAS) face performance issues due to transmission leakage signals, which occur when the transmitting antenna's signal is not sufficiently isolated from the receiving antenna, affecting the performance of remote units.
Innovation Solution
A distributed antenna system with a cancellation circuit that includes a delay circuit, vector modulator, and bandpass filters to generate and adjust a cancellation signal, which is added to the received signal to cancel out transmission leakage, using a pilot signal generation circuit to optimize the cancellation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the transmitting and receiving antennas are physically separated to isolate them, then transmission leakage is reduced, but the device complexity and space requirements increase
Solution Approach 1:
The patent extracts the harmful transmission leakage signal from the received signal by generating a separate cancellation signal that replicates the leakage characteristics. This cancellation signal is then subtracted from the received signal to remove the harmful interference, effectively separating the desired signal from the interference without requiring physical antenna separation.
Solution Approach 2:
The patent introduces a cancellation signal as an intermediary element that mediates between the transmitting and receiving antennas. This cancellation signal acts as a virtual shield, compensating for the lack of physical isolation by providing an equal and opposite signal to counteract the leakage, thereby reducing the need for complex physical isolation structures.
2Productivity
If wide bandwidth is used to improve communication capacity, then data transmission rate increases, but transmission leakage cancellation becomes more difficult
Solution Approach 1:
The patent segments the wide bandwidth into multiple narrower frequency bands, each handled by a dedicated cancellation circuit with its own bandpass filter. This segmentation allows each cancellation circuit to operate effectively within a limited frequency range, making the overall system manageable despite the wide total bandwidth requirement for high data transmission rates.
Solution Approach 2:
The patent applies cancellation action selectively to specific frequency bands rather than attempting to cancel leakage across the entire wide bandwidth simultaneously. By focusing cancellation efforts on particular frequency segments where leakage is most problematic, the system achieves effective leakage reduction without requiring excessively complex circuitry that would be needed for full-bandwidth cancellation.
3Device complexity
If physical separation between antennas is reduced to simplify device structure, then device complexity decreases, but transmission leakage increases
Solution Approach 1:
The patent converts the harmful transmission leakage signal into a beneficial cancellation signal by capturing a portion of the transmitted signal and processing it to create an identical replica with opposite phase. This approach transforms the leakage from a detrimental interference into a useful reference signal that enables active cancellation, allowing reduced physical separation while maintaining performance.
Solution Approach 2:
The patent applies preliminary anti-action by generating the cancellation signal in advance and applying it to the received signal before further processing. This preemptive cancellation approach counteracts the leakage effect before it can degrade the received signal quality, enabling closer antenna placement without sacrificing communication performance.
4Reliability
If cancellation bandwidth is increased to cover wider frequency range, then leakage cancellation effectiveness improves, but device complexity and processing requirements increase
Solution Approach 1:
The patent divides the wide frequency range into multiple narrower cancellation bandwidth segments, each handled by a separate cancellation circuit with appropriate bandpass filters. This segmentation maintains cancellation effectiveness across the wide overall bandwidth by ensuring each individual circuit operates within its optimized frequency range, avoiding the complexity of a single wideband cancellation circuit.
Solution Approach 2:
The patent applies different cancellation characteristics to different frequency bands, with each cancellation circuit tailored to its specific frequency range. This local optimization ensures that each cancellation circuit is precisely matched to the leakage characteristics of its assigned band, maximizing cancellation effectiveness while minimizing the complexity of individual circuits compared to a monolithic wideband solution.
Data Source
AI summary
A system and methods for cancelling transmission leakage signals in a wide bandwidth Distributed Antenna System (“DAS”) having remote units is disclosed. An internal cancellation circuit within the remote unit is employed to reduce the transmitted leakage signals by generating a cancellation signal. This cancellation signal is added to the received signal to cancel the transmission leakage signal in the receiving signal path. A pilot signal generation circuit is employed to optimize the cancellation circuit operating parameters. The frequency of the pilot signal is swept over a range to determine the pilot frequency having the highest electromagnetic coupling. The amplitude and phase of the cancellation signal is then optimized to minimize the level of transmission leakage in the receiving transmission path.