Polyphase Digital Bit Generator for Low-Rate Multiband RF Transmission
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Solution Overview
Problem
Current multi-band RF transceivers face challenges in designing efficient and flexible systems for contiguous and non-contiguous CA transmission due to issues like out-of-band noise, reduced Signal-to-Noise Ratio, and stringent sampling rate requirements, which hinder the development of compact, agile, and reconfigurable radio transceivers capable of supporting multiple standards and bands.
Innovation Solution
A high-speed digital bit generator system that employs digital polyphase interpolation filters, oscillator banks, mixer banks, and parallel digital combiners to achieve two-dimensional parallelization of signals, reducing the sampling rate requirements and enabling efficient multi-band transmission by filtering out-of-band noise and using delta-sigma or PWM pulse encoding for noise shaping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If digital upconversion is performed after pulse encoding, then the system can use lower sampling rates, but out-of-band noise distributed over the entire spectrum degrades system performance
Solution Approach 1:
The patent inverts the conventional processing order by performing pulse encoding before digital upconversion, rather than after. This inversion allows the signal to be encoded at a lower sampling rate first, then upconverted to the target frequency. The key insight is that pulse encoding creates a constant envelope signal that can be efficiently upconverted without generating excessive out-of-band noise, resolving the contradiction between low sampling rate and system performance.
Solution Approach 2:
The patent applies preliminary pulse encoding to the baseband signal before upconversion. By encoding the signal into a pulsed representation with constant envelope beforehand, the system prepares the signal in a form that is optimized for subsequent upconversion and amplification. This preliminary action enables efficient processing at lower sampling rates while maintaining signal quality.
2Reliability
If digital upconversion is performed before pulse encoding, then sampling rates must be at least twice the carrier frequency, but this imposes challenging requirements on the Pulse Encoder and analog front-end
Solution Approach 1:
The patent inverts the conventional processing sequence by performing pulse encoding before digital upconversion. Instead of upconverting the baseband signal first and then encoding, the system encodes the baseband signal into a pulsed constant envelope representation first, then performs digital upconversion. This inversion dramatically reduces the sampling rate requirements and simplifies the hardware requirements for both the pulse encoder and analog front-end.
3Adaptability or versatility
If integer multiples of modulators sampling frequencies are used for multiband transmission, then multiple bands can be supported, but the inherent decrease in Signal-to-Noise Ratio reduces performance
Solution Approach 1:
The patent segments the multi-band transmission problem by applying independent pulse encoding to each frequency band's baseband signal before upconversion. Rather than processing all bands together through a single modulator, the system encodes each band separately using the inverted approach (pulse encoding before upconversion), then combines the upconverted signals. This segmentation preserves the Signal-to-Noise Ratio for each band while still achieving multi-band transmission capability.
Data Source
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AI summary
A radio frequency (RF) transmitter includes a set of input ports to receive baseband samples of a signal to be transmitted on a set of disjoint frequency bands, a set of filter banks, there is one filter bank for each input port, each filter bank includes a plurality of digital polyphase interpolation filters to sample a shifted phase of the corresponding sequence of baseband samples and to interpolate the sampled phases to produce a plurality of sequences of interpolated baseband phased samples with the shifted phase, and a set of oscillators banks, each oscillator bank includes a plurality of polyphase Digital Direct Synthesizer (DDS) corresponding to the plurality of digital polyphase interpolation filters to generate a plurality of sequences of samples of digital waveform.