Chirp Spread Spectrum Transmitter Permutation Modulation Data Rate
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Solution Overview
Problem
Conventional chirp spread spectrum (CSS) systems, such as LoRa, suffer from low data throughput due to their limitations in transmitting only one chirp per symbol duration, which restricts communication range and data rate, and require additional hardware for varying bandwidth settings, increasing costs and complexity.
Innovation Solution
The proposed CSS scheme transmits a sum of multiple chirps per symbol duration, using permutation modulation to increase data rate by selecting combinations of K chirps out of M, where M>K>=1, allowing for a higher number of unique sums and thus more information bits to be carried, while employing a low-complexity DFT-based receiver to detect the transmitted chirps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple chirps are transmitted per symbol duration using permutation modulation, then data rate is increased, but system complexity increases
Solution Approach 1:
The information signal is segmented into multiple chirp selections within each symbol duration. Instead of transmitting a single chirp, the system transmits K chirps selected from M available chirps, where each chirp carries a portion of the information. This segmentation allows the data rate to be increased by factor K while distributing the modulation complexity across multiple simpler chirp transmissions rather than requiring a single complex modulation scheme.
2Device complexity
If conventional CSS systems transmit only one chirp per symbol duration, then system complexity is reduced, but data throughput is limited
Solution Approach 1:
Multiple chirps are merged or combined within a single symbol duration to transmit more information. The system selects K chirps from M available chirps and transmits them together as one composite symbol. This merging approach allows the system to achieve higher data throughput equivalent to transmitting K separate symbols, while maintaining the simplicity of individual chirp transmission and enabling straightforward integration with existing CSS infrastructure.
3Adaptability or versatility
If different bandwidth settings are provided in LoRa modems, then communication flexibility is improved, but hardware cost increases
Solution Approach 1:
The system achieves different effective bandwidths and data rates by changing the parameter K (number of chirps selected from M) rather than requiring hardware changes for different bandwidth settings. By varying K, the system can simulate different bandwidth configurations and achieve the same flexibility as having multiple fixed bandwidth settings, but without the need for additional hardware components or complex reconfigurable circuits.
Data Source
AI summary
A transmitter stores mappings of distinct values of an information signal to corresponding ones of distinct combinations of K chirps taken from M chirps that are different from each other, such that each of the distinct values is mapped to a corresponding one of the distinct combinations of K chirps. The transmitter receives a distinct value among the distinct values of the information signal. The transmitter selects, based on the mappings, a distinct combination of K chirps among the distinct combinations of K chirps that is mapped to the distinct value. The transmitter sums the K chirps of the distinct combination of K chirps to produce a symbol that represents the distinct value. The transmitter modulates the symbol to produce a modulated symbol, and transmits the modulated symbol. A receiver receives a modulated symbol that conveys a distinct value, and recovers the distinct value using stored mappings.