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This paper explores the potential benefits of combining the use of injection-locking techniques with GPS signals as a common clock source when applied to a low-cost Software Defined Radio (SDR) to improve the accuracy of coherent multiple receivers. Coherent systems impose severe requirements on the frequency stability of the signal source at the receiver. In this work, injection-locked oscillators are used as local clock receivers, which inherently synchronizes the SDR analog digital converter (ADCs) sampling times and keeps the local oscillator locked on to the GPS stimulus periodic signal. This paper illustrates the hardware modifications needed for to the injection locking oscillators of eight RTL-SDR radios and the theory behind it, and experimentally measures the degree of coherency in the frequency, phase and time synchronization to verify the proposed method. The coherency demonstrated in the results prove the feasibility of using beamforming, multiple input multiple output (MIMO) and RF transmitter geo-localization.
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This content will become publicly available on September 1, 2026
On the Feasibility of Distributed Phase Synchronization for Coherent Signal Superposition
In this study, we analyze the feasibility of distributed phase synchronization for coherent signal superposition, a fundamental enabler for paradigms like coherent over-the-air computation (OAC), distributed beamforming, and interference alignment, under mobility and hardware impairments. With the focus on coherent OAC, we introduce phase-coded pilots (PCPs), a strategy where the radios communicate with each other to eliminate the round-trip phase change in the uplink (UL) and downlink (DL) to align the phase of the received symbol at a desired angle. In this study, considering a carrier frequency offset (CFO)-resilient multi-user procedure, we derive the statistics of the phase deviations to assess how fast the phase coherency degrades. Our results show that residual CFO is a major factor determining the duration of phase coherency, in addition to the non-negligible effects of mobility and the number of nodes in the network. We also provide a proof-of-concept demonstration for coherent signal superposition by using off-the-shelf radios to demonstrate the feasibility of PCPs in practice
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- Award ID(s):
- 2438837
- PAR ID:
- 10653504
- Publisher / Repository:
- IEEE
- Date Published:
- Page Range / eLocation ID:
- 1 to 6
- Subject(s) / Keyword(s):
- Distributed phase synchronization, phase offset, residual carrier-frequency offset, over-the-air computation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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