Local Oscillator Offset for Non-Contiguous Carrier Aggregation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Non-contiguous carrier aggregation in radio communication systems poses challenges for Direct Conversion Receivers due to high power signals between carrier clusters, leading to increased demands on dynamic range and image rejection, causing interference and degradation in signal quality.
Innovation Solution
A method and receiver architecture where the local oscillator is set to a frequency offset from the center of the band defined by the outer edges of the frequency regions occupied by the clusters, allowing for improved image rejection and reduced interference by minimizing the impact of high power signals on the receiver's dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Direct Conversion Receiver uses a local oscillator centered on the band to receive non-contiguous carrier aggregation signals, then the receiver structure is simple and economical, but high power signals in the frequency region between carrier clusters cause interference and exceed dynamic range requirements
Solution Approach 1:
The patent applies asymmetry by offsetting the local oscillator frequency from the center of the band. Instead of placing the LO at the center frequency, it is positioned at a specific offset frequency that places the image reject frequency in a guard band region where no desired signals are present. This asymmetric positioning allows the receiver to tolerate high power signals in the band center region without causing interference to desired signals, thereby resolving the contradiction between simple receiver structure and interference rejection capability
2Object-affected harmful factors
If the local oscillator is offset from the center frequency to improve image rejection, then interference from high power signals is reduced, but the receiver complexity increases
Solution Approach 1:
The patent changes the frequency parameter of the local oscillator from a centered position to an offset position. Specifically, the LO frequency is set to f_LO = f_center - Δf, where Δf is chosen so that the image reject frequency falls in a guard band. This parameter change improves image rejection performance while maintaining relatively simple receiver architecture, as it primarily involves adjusting the LO frequency rather than adding complex filtering or processing stages
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
This approach enhances the signal-to-noise ratio and reduces interference, enabling reliable reception of non-contiguous carrier aggregation signals by optimizing the local oscillator placement and using distinct bandpass filters for improved image rejection and dynamic range management.
Implementation Method 1
A direct conversion receiver (DCR) uses a local oscillator placed within the radio frequency bandwidth occupied by the signals to be received to directly convert the signals to baseband
Implementation Method 2
Signals on the high side of the local oscillator are mixed to the same baseband frequency band as signals on the low side of the local oscillator, and in order to separate out the high and low side signals, it is necessary to mix the signal with two components of the local oscillator in quadrature (i.e. 90 degrees out of phase with one another)
Implementation Method 3
The I and Q components are digitised separately, and may be processed digitally to reconstruct the separate high side and low side signals. The reconstructed high and low side signals may be filtered in the digital domain to separate carrier signals received within the receiver bandwidth of the DCR
Data Source
AI summary
A receiver uses a local oscillator to receive data transmitted via a combination of radio frequency signals using carrier aggregation. Each radio frequency signal occupies a respective radio frequency band and the radio frequency bands are arranged in two groups, a first group and a second group, separated in frequency by a first frequency region, each of the groups including one or more radio frequency bands and the first group occupying a wider frequency region than the second group. The radio frequency signals are processed using the local oscillator by setting the local oscillator, during the processing, to a frequency that is offset from the centre of a band defined by outer edges of the frequency regions occupied by the two groups.