GPS Receiver Burst Interference Immunity via Dynamic AGC
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Solution Overview
Problem
GPS receivers in close proximity to radio frequency transmitters, such as cellular phones, face signal overload issues due to interference, leading to reduced sensitivity and operability, with existing solutions like filtering or high linearity LNAs increasing power consumption and system complexity.
Innovation Solution
A method and system that utilize an automatic gain control (AGC) component to detect signal overload conditions, allowing for the substitution of a locally generated bit pattern in the radio receiver's back-end to minimize noise accumulation, thereby maintaining signal-to-noise ratio during overloads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter is used to block interfering signals from the co-located transmitter, then the GPS receiver is protected from overload, but the sensitivity of the GPS receiver is permanently reduced and power consumption increases
Solution Approach 1:
The invention implements dynamic gain control in the LNA based on detection of transmitter burst patterns. The LNA gain is adjusted in real-time: reduced during expected burst periods to prevent overload, and restored to high sensitivity when bursts are not present. This dynamic adaptation resolves the contradiction by making the protection mechanism active only when needed, rather than permanently attenuating the signal or consuming excess power.
Solution Approach 2:
The system uses preliminary detection of transmitter burst patterns to anticipate interfering signals before they overload the receiver. By detecting the characteristic timing patterns of transmitter bursts in advance, the system can pre-adjust the LNA gain or activate filtering only during the expected burst windows, preventing overload without continuously degrading GPS signal sensitivity or consuming additional power.
2Reliability
If a high linearity LNA is used to amplify GPS signals despite interfering transmissions, then signal reception is maintained, but power consumption increases which is not acceptable in portable devices
Solution Approach 1:
The LNA operates with dynamically adjusted gain based on the detected presence of transmitter bursts. During burst periods, the gain is reduced to prevent overload; during normal periods, the gain is maximized for optimal GPS signal reception. This eliminates the need for a continuously high-linearity (high-power) LNA configuration, reducing average power consumption while maintaining reception capability when needed.
3Reliability
If additional filtering is added after the LNA to reject interfering signals, then overload of the mixer is prevented, but the size, power consumption and cost of the filter increase
Solution Approach 1:
The invention uses dynamically controllable filtering or gain reduction that activates only during detected transmitter burst periods. This temporal selectivity means the filtering mechanism is not continuously engaged, reducing its impact on GPS signal sensitivity and allowing for a less complex, lower-power, and smaller filter design compared to continuous filtering approaches.
Solution Approach 2:
By preliminarily detecting transmitter burst patterns, the system activates filtering or gain reduction only during the specific time windows when interfering signals are expected. This prevents mixer overload without requiring a continuously active complex filtering system, thereby reducing overall device complexity, power consumption, and cost.
4Reliability
If all received signals are filtered before down conversion, then interference from co-located transmitters is blocked, but the sensitivity of the GPS receiver is permanently reduced irrespective of whether the transmitter is transmitting
Solution Approach 1:
The filtering or gain control is dynamically adjusted based on real-time detection of transmitter activity. During burst periods, protection is activated; during normal periods, the full sensitivity is restored. This temporal differentiation resolves the contradiction by making protection conditional rather than permanent, ensuring GPS signal sensitivity is not continuously degraded.
Solution Approach 2:
The system preliminarily detects transmitter burst patterns and activates filtering or gain reduction only during the anticipated interference windows. This ensures that GPS signals are protected from overload only when necessary, while maintaining full sensitivity during periods when no interference is present, thus resolving the contradiction between protection and sensitivity.
Data Source
AI summary
GPS signals are typically weak and thus easily interfered with by other radio transmissions in the same or adjacent frequency bands. Interference can be especially problematic when the GPS receiver is co-located with a communications device that includes a radio transmitter, such as a cellular telephone. The transmitted signal from the co-located communication device can overload (or saturate) the GPS receiver front-end designed to receive weak GPS signals. In such a situation no useful information can be extracted from the received GPS signals originating from the GPS satellites. Described herein is a novel apparatus and method that can be used to minimize the effect of co-located interference on a GPS receiver.