Multi-Channel FM Transmission Using I/Q Frequency Offsets
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Solution Overview
Problem
Conventional FM communication systems face interference issues between personal low-power FM transmitters and regular FM broadcast radio, limiting the coexistence of multiple channels on FM bands.
Innovation Solution
A method and system for transmitting multiple channels on FM bands by generating radio frequency signals with distinct frequencies using weighted sums of in-phase and quadrature baseband signals, allowing for simultaneous or alternating transmission on the same frequency, and employing intermediate and radio frequency modulation to minimize image frequency rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If personal low-power FM transmitters operate on FM bands, then portable audio transmission is enabled, but interference with regular FM broadcast radio occurs
Solution Approach 1:
The patent segments the FM band into multiple narrowband channels (e.g., 12 channels spaced 100 kHz apart within a 1 MHz range). Each channel operates independently with its own carrier frequency, allowing personal transmitters to share the FM spectrum without causing harmful interference to broadcast radio by occupying only specific frequency slots.
Solution Approach 2:
The patent changes the frequency parameter by using frequency modulation to shift the carrier frequency dynamically. The system modulates the carrier frequency based on audio input, enabling multiple channels to coexist on the FM band by varying the frequency parameter across different channels while maintaining compliance with spectral masks to avoid broadcast interference.
2Quantity of substance
If multiple channels are transmitted on the same frequency, then channel capacity increases, but signal interference and reception quality deteriorate
Solution Approach 1:
The patent transitions from single-frequency transmission to multi-dimensional frequency-space transmission. By allocating channels across different frequency offsets (e.g., ±50 kHz, ±100 kHz from the center frequency) and using quadrature modulation (I/Q channels), the system accommodates multiple channels in the frequency dimension while maintaining orthogonal signal structures that minimize mutual interference.
Solution Approach 2:
The patent introduces an intermediary frequency synthesis stage that generates precisely spaced carrier frequencies for each channel. This intermediary process ensures that channels are separated by sufficient frequency spacing (e.g., 100 kHz) to prevent overlap, while still allowing dense channel packing. The frequency synthesis acts as a mediator between the desire for multiple channels and the need to maintain signal integrity.
3Adaptability or versatility
If frequency modulation is used for multiple channels, then channel diversity increases, but image frequency interference increases
Solution Approach 1:
The patent extracts and removes image frequency components through selective filtering. The system design anticipates image frequency generation from frequency modulation and employs bandpass filters tuned to each channel's center frequency to extract the desired signal while rejecting image frequencies. This extraction approach allows multiple FM channels to operate simultaneously by eliminating the harmful image components.
Solution Approach 2:
The patent applies preliminary frequency planning and spectral masking before transmission. The channel frequencies are pre-calculated to avoid image frequency conflicts with broadcast bands, and spectral masks are applied to limit out-of-band emissions. This preliminary action prevents image frequency interference from propagating into adjacent channels or broadcast frequencies, enabling channel diversity without harmful side effects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables seamless switching between multiple channels based on RDS/RBDS information, improving coexistence and reception quality for portable devices, and allowing for broadcasting different content streams to different listeners.
Implementation Method 1
The plurality of radio frequency transmission signals may be frequency modulated signals
Implementation Method 2
Suitable combinations of the one or more baseband signals may be modulated in a radio frequency transmission chain that may comprise intermediate frequency modulation and radio frequency modulation
Data Source
AI summary
Aspects of a method and system for transmitting multiple channels on FM bands may include generating from one or more baseband signals, a plurality of radio frequency transmission signals each at a different radio frequency, wherein the one or more baseband signals comprise an in-phase signal component and/or a quadrature signal component. Suitable combinations of the one or more baseband signals may be modulated in a radio frequency transmission chain that may comprise intermediate frequency modulation and radio frequency modulation. The suitable combinations of the one or more baseband signals may be weighted sums. The plurality of radio frequency signals may each carry distinct information. One of the plurality of radio frequency signals may be centered at a frequency f1+f2 and another one of said plurality of radio frequency signals may be centered at a frequency f1−f2, where f1 and f2 are frequencies.