A novel RF sensing circuit using injection locking and frequency demodulation for cognitive radio applications

Abstract

Abstract-A novel RF sensing circuit for a cognitive radio to sense spectral environment is proposed using injection locking and frequency demodulation techniques. The research starts with deriving a generalized locking equation for oscillators as a theoretical basis, and then develops the sensing principle and circuit architecture to a practical and useful level. To accurately evaluate the sensing performance, a discrete time approach is investigated to compute the sensed output signal. In the experiments, a prototype circuit is designed in the 2.4-GHz industrial-scientific-medical band to cover a sensing frequency range from 2.4 to 2.484 GHz. The spectrum scanning over the 84-MHz bandwidth is accomplished in less than 1 ms. The experimental results agree quite well with the theoretical predictions, showing that the proposed RF sensing circuit can fast and reliably detect frequency and power for analog and digital modulation signals.

Cognitive Polar Receiver Using Two Injection-Locked Oscillator Stages

“…Injection locking and pulling phenomena in oscillators have been extensively studied [8]- [15]. The classic analysis developed by Adler [8] considers that a weak sinusoidal signal interferes with an oscillator.…”

“…Although the derived generalized locking (4) gives the phase dynamics of an oscillator under injection, gaining an analytical solution while considering a modulated injection signal is a rather complex task. Therefore, in this paper, performance of the proposed polar receiver is evaluated by using a discrete-time domain approach proposed in [15]. By starting with a numerical method known as the Euler method [17], the derivative can be replaced by the finite-difference approximation (9) where (10) Therefore, (4) is rewritten as (11) where (12) A situation in which is sufficiently small makes it sensible to make an approximation that is equal to .…”

“…By starting with a numerical method known as the Euler method [17], the derivative can be replaced by the finite-difference approximation (9) where (10) Therefore, (4) is rewritten as (11) where (12) A situation in which is sufficiently small makes it sensible to make an approximation that is equal to . Replacing by in the right-hand side of (11) and rearranging lead to (13) (14) (15) This approach is advantageous in that can be calculated recursively by (13) instead of solving differential equation (4); in addition, it is compatible with an arbitrary modulated injection signal. However, under some circumstances, approximating a derivative by the Euler method may not be sufficiently accurate.…”

“…In the beginning of the tuning period from frequency to , the ILO experiences the injection-pulling condition since is too far from in the frequency to be locked. The instantaneous frequency of an oscillator under the injection-pulling condition is frequency modulated with , which has an average beat frequency given as [13], [15] …”

A Novel Vital-Sign Sensor Based on a Self-Injection-Locked Oscillator

“…These movements cause a Doppler shift that is proportional to the velocity of movement in the reflected signal. Therefore, the received signal's instantaneous frequency is a delay version of the VCO output instantaneous frequency plus the reflected Doppler shift, that is (22) where is the speed of light and is the round-trip propagation delay given by . Comparing (22) and (5) with substitutions of (6) and (7) yields the instantaneous phase modulation, due to the Doppler effect, given by (23)…”