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<p>Reconfigurable intelligent surfaces (RIS) offer a cost-effective solution for enhancing both spectral and energy efficiency in next-generation wireless networks by employing numerous low-cost passive elements that reflect incident signals with tunable phase shifts. These capabilities are particularly advantageous for long range (LoRa) systems in internet of things (IoT) applications, where reliable long-distance communication is essential. This paper investigates a RIS-assisted LoRa communication system operating under non-line-of-sight (NLoS) conditions, where a LoRa device transmits data to a gateway via a RIS. Under a narrowband assumption, the RIS is modeled by frequency-flat reflection coefficients across the signal bandwidth. To avoid practical hardware constraints, discrete phase shifts are considered at each RIS element. Two phase-optimization strategies are proposed: an exhaustive search method, suitable for small RIS arrays, and a genetic algorithm-based approach, scalable to large deployments. Both strategies aim to maximize the received signal power at the gateway. Bit error rate (BER) performance is evaluated at the output of a coherent receiver. Simulation results show that the proposed RIS-assisted LoRa system significantly improves BER compared with conventional LoRa over a Rayleigh fading channel, achieving <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(10^{-4}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>4</mn> </mrow> </msup> </math></EquationSource> </InlineEquation> BER. The gap with respect to the ideal additive white Gaussian noise (AWGN) channel is about 10 dB, and increasing the number of RIS elements further enhances performance via improved beamforming and higher SNR, highlighting the potential of RIS-assisted LoRa for reliable and energy-efficient low-power-wide-area-network (LPWAN) operation.</p>

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Optimization of discrete phase shifts in RIS-assisted LoRa communication systems

  • 期刊论文

  • 发表日期：

    2026年6月3日

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  • Ali Kotti,
  • Zouhair Ben Jemaa,
  • Safya Belghith

摘要

Reconfigurable intelligent surfaces (RIS) offer a cost-effective solution for enhancing both spectral and energy efficiency in next-generation wireless networks by employing numerous low-cost passive elements that reflect incident signals with tunable phase shifts. These capabilities are particularly advantageous for long range (LoRa) systems in internet of things (IoT) applications, where reliable long-distance communication is essential. This paper investigates a RIS-assisted LoRa communication system operating under non-line-of-sight (NLoS) conditions, where a LoRa device transmits data to a gateway via a RIS. Under a narrowband assumption, the RIS is modeled by frequency-flat reflection coefficients across the signal bandwidth. To avoid practical hardware constraints, discrete phase shifts are considered at each RIS element. Two phase-optimization strategies are proposed: an exhaustive search method, suitable for small RIS arrays, and a genetic algorithm-based approach, scalable to large deployments. Both strategies aim to maximize the received signal power at the gateway. Bit error rate (BER) performance is evaluated at the output of a coherent receiver. Simulation results show that the proposed RIS-assisted LoRa system significantly improves BER compared with conventional LoRa over a Rayleigh fading channel, achieving \(10^{-4}\) 10 - 4 BER. The gap with respect to the ideal additive white Gaussian noise (AWGN) channel is about 10 dB, and increasing the number of RIS elements further enhances performance via improved beamforming and higher SNR, highlighting the potential of RIS-assisted LoRa for reliable and energy-efficient low-power-wide-area-network (LPWAN) operation.