GPS Receiver Fast Time Fix Using Stored Data Bits
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Solution Overview
Problem
Conventional GPS receivers require significant time to determine the GPS clock time, which prolongs the time to first fix and increases power consumption or hardware cost when attempting to achieve ten millisecond or better time accuracy.
Innovation Solution
A GPS receiver that stores expected data bits and uses a coarse time estimate to identify a search range, comparing chunks of received data bits to determine the GPS clock time without waiting for Zcounts, thereby reducing latency and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the GPS receiver monitors GPS data bits to determine clock time using conventional methods (waiting for TLM and Zcount), then the GPS clock time can be determined accurately, but the time to first fix is significantly prolonged due to the need to wait for complete subframes
Solution Approach 1:
The patent performs preliminary actions by maintaining a time base in the GPS receiver that approximates GPS clock time with 10 millisecond or better accuracy before actual GPS time determination is needed. This preliminary time base allows the receiver to predict when TLM words should occur and to identify them quickly upon reception, eliminating the need to monitor for extended periods. The preliminary time base is maintained using a stable internal clock or by receiving time from other sources such as WWV radio signals or CDMA cellphone signals.
Solution Approach 2:
The patent uses partial monitoring of GPS data bits by only needing to detect the TLM word at the beginning of a subframe rather than waiting for complete subframes and multiple TLM words. By using the preliminary time base to predict TLM occurrence and performing only partial verification (checking for the presence of TLM rather than processing entire subframes), the receiver achieves time determination with significantly reduced monitoring time while maintaining sufficient accuracy for hot start operation.
2Loss of time
If the GPS receiver uses a stable internal clock or external time signals to achieve ten millisecond or better time accuracy, then the time to first fix is reduced, but hardware cost and power consumption increase
Solution Approach 1:
The patent employs periodic action by cycling between standby mode and operation mode. During standby mode, the receiver maintains a preliminary time base with minimal power consumption. When operation is needed, the receiver activates, uses the preliminary time base to quickly acquire GPS signals and determine accurate GPS clock time, then returns to standby mode. This periodic operation allows the receiver to maintain time-keeping capabilities only when necessary, significantly reducing overall power consumption while still achieving fast time to first fix when activated.
3Measurement precision
If the GPS receiver monitors GPS messages for extended periods to verify TLM words and determine clock time, then time accuracy is improved, but power consumption increases significantly
Solution Approach 1:
The patent performs preliminary time base maintenance using low-power mechanisms (stable internal clock or periodic external time signals) before GPS acquisition. This preliminary time base eliminates the need for extended monitoring of GPS data bits, as the receiver can predict TLM occurrence and quickly verify it upon signal acquisition. The preliminary action of maintaining approximate time reduces the active monitoring period from potentially seconds or minutes to just the time needed for signal acquisition and TLM verification, dramatically reducing power consumption while maintaining sufficient time accuracy for hot start operation.
Data Source
AI summary
A GPS receiver having a fast method for determining GPS clock time. The GPS receiver includes a signal processor for receiving GPS signals from GPS satellites and detecting current GPS data bits carried by the respective GPS signals, a chapter memory for storing a block of expected GPS data bits for the respective GPS satellites, and a GPS time detector for detecting a successful match when a chunk of the expected data bits within a selected search range within the block matches a chunk of the current data bits, and using the successful match for determining the GPS clock time. In an anytime embodiment the GPS receiver enters an operation mode at any time in order to minimize user request latency. In a focused embodiment the GPS receiver enters the operation mode at a prescribed time-of-entry in order to minimize power consumption for cycles of standby and operation modes.