RF Node Despreading for Fast Frequency-Agile Link Reacquisition
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Solution Overview
Problem
In resilient communications environments, such as mesh or ad-hoc networks, the delay in reacquiring direct sequence spread spectrum communications links due to varying frequencies and bandwidths leads to significant data loss, as conventional methods require long delays in changing center frequencies and interrupting existing communications.
Innovation Solution
A radio frequency communications system that includes a first RF node transmitting a sequence of pilot symbols spread with a complex spreading code sequence, and a second RF node receiving these symbols to perform despreading for N sample offset delays, cross-correlation to select a desired despreading sequence, and determine phase and timing offsets, allowing quick switching to a new frequency of operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional frequency hopping spread spectrum is used to protect RF communications from interference, then communication security and interference resistance are improved, but signal variations over time increase and reacquisition delay increases
Solution Approach 1:
The patent applies preliminary action by pre-synchronizing multiple RF nodes to the same GPS time reference before frequency changes occur. This pre-synchronization ensures that when frequency hopping occurs, all nodes can rapidly reacquire the signal without lengthy delays, as they already share a common time reference framework. The GPS-based time synchronization is established in advance to enable quick frequency transitions.
Solution Approach 2:
The patent introduces GPS time reference as an intermediary mechanism that mediates the frequency hopping process. By using GPS-derived time information as a common reference, the system enables RF nodes to independently determine when frequency changes occur and rapidly resynchronize without requiring lengthy handshaking or reacquisition protocols. The GPS time reference acts as a neutral mediator that coordinates frequency transitions across the network.
2Stability of the object's composition
If direct sequence spread spectrum is used because there are fewer signal variations over time, then signal stability is improved, but the ability to quickly reacquire connections after frequency changes deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the frequency parameter of the direct sequence spread spectrum signal based on GPS-derived time information. When a frequency change is detected or scheduled, the system modifies the carrier frequency while maintaining the direct sequence spreading structure. This allows the signal to retain its stability characteristics while enabling rapid frequency transitions for reacquisition.
3Reliability
If frequency changes are made to shift signals to advantageous parts of the communications band, then communication quality is improved, but data loss increases due to transmission interruptions
Solution Approach 1:
The patent applies continuity of useful action by using GPS-synchronized timing to coordinate frequency changes across all RF nodes simultaneously. This synchronization ensures that frequency transitions occur continuously and seamlessly without gaps in communication. Data transmission continues uninterrupted because all nodes switch frequencies at the same predetermined time instances, eliminating the break-before-make interruptions that cause data loss.
4Adaptability or versatility
If GPS-derived time information is used to synchronize frequency changes, then frequency agility coordination is improved, but system complexity increases
Solution Approach 1:
The patent applies universality by using the GPS receiver's time output for multiple purposes: it provides both the primary time reference for frequency synchronization and serves as a universal timing source for all RF nodes in the network. This multi-functional use of GPS time information simplifies the overall system architecture, as a single GPS-derived time source coordinates frequency changes, data transmission timing, and signal synchronization across the entire network without requiring separate timing mechanisms.
Data Source
AI summary
A radio frequency (RF) communications system may include a first RF node that transmits data, including a new frequency of operation, and a sequence of pilot symbols spread with a complex spreading code sequence. A second RF node may receive an incoming signal from the first RF node and perform despreading for N sample offset delays to generate N despreading sequences for the sequence of pilot symbols. The second RF node may perform a cross-correlation to select a desired despreading sequence from the N despreading sequences, determine a phase offset and timing offset, process the incoming signal based upon the desired despreading sequence, phase offset and timing offset, and switch to the new frequency of operation.