# Interest of Beamsteering on the Received Optical Power in Indoor Optical Wireless Communications

Haitham Al Satai, Bastien Béchadergue, Luc Chassagne

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Haitham Al Satai, Bastien Béchadergue, Luc Chassagne. Interest of Beamsteering on the Received Optical Power in Indoor Optical Wireless Communications. Junior Conference on Wireless and Optical Communications - JWOC, Oct 2022, Palaiseau, France. hal-05327873

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# Interest of Beamsteering on the Received Optical Power in Indoor Optical Wireless Communications

Haitham AL Satai<fnref n="1" />,<fnref n="2" />, Bastien Béchadergue<fnref n="1" />, Luc Chassagne<fnref n="1" />

**Abstract**- As a complement to radio frequency, optical wireless communication (OWC) can be employed for illumination and communication in indoor environments. The crucial aspect of working with wireless communication systems is the link quality, i.e., the need for a high signal-to-noise ratio and thus received signal power. As a suggested solution, beamsteering is a promising technique to improve OWC's performance since being able to form beams and steer them increases systems' flexibility and usability. This paper compares the received optical power with and without an ideal beamsteering solution in order to evaluate the benefit such a solution can bring to an indoor OWC system.

**Index Terms** - Optical wireless communications (OWC), beamsteering, link budget, Internet of things (IoT).

## I. INTRODUCTION

As radio wireless communication is developing, the available radio spectrum is reaching its limit. Optical wireless communication (OWC), which refers to the wireless transmission of data over the optical band, is a complementary solution to radio frequency (RF) wireless communications and a promising component of 6G networks due to its many features, including license-free optical spectrum, security, high speed, broad bandwidth, and free electromagnetic interference [1]. Several OWC systems, mainly based on light emitting diodes (LED) and laser diodes, have been demonstrated for various use cases such as indoor networking – also called LiFi –, vehicular communication, or even underwater communications.

To improve the performance of any wireless communication system, it is usually necessary to increase the signal-to-noise ratio (SNR) at the receiver level, that is, in the OWC case, the received optical power so that a higher link power budget is available. In that regard, beamsteering is a promising solution, as it enables to form narrow and high intensity beams that are steered toward the receiver rather than broadcasting widely diffused signals. In this way, a total wireless throughput beyond 8.9 Tbps has been reported in [3]. However, the theoretical analysis that quantifies the benefits brought by such a solution in terms of received optical power gain has never been carried out so far.

In this paper, we investigate the interest in using a beamsteering technique to improve the collected optical power in an indoor environment with a single LED source and a single receiver. A MATLAB simulation is used to calculate the optical power distribution with/without beamsteering.

## II. SYSTEM ARCHITECTURE AND MODELING

The investigated setup consists in a single LED-based access point (AP) mounted on the ceiling of a 20 m × 20 m × 3 m room, as illustrated in Fig.1. On the other end of the link, a user equipment (UE) moves in an x-y plane 0.85 m above the floor. Two scenarios referred to as ‘with beamsteering’ and ‘without beamsteering’ are studied.

In the first scenario (‘with beamsteering’), the AP and UE are facing each other whatever the UE position, i.e. their normal vectors $\vec{n}_{AP}$ and $\vec{n}_{UE}$ are always collinear and of opposite direction. In such a case, the angle of irradiance $\phi$ between the AP’s normal and the direction of emission is null, as the angle of incidence $\psi$ between the UE’s normal and the direction of reception (i.e. $\phi = \psi = 0$). In the second case (‘without beamsteering’, represented in Fig. 1), the AP is pointing toward the floor whereas the UE is pointing toward the ceiling so that whatever the UE’s position, we have $\phi = \psi$.

<figure><img src="image_2.png" /><figcaption>Fig. 1: Indoor OWC scenario studied.</figcaption></figure>

In a typical OWC system, the optical power $P_r$ received by the UE can be computed as follows:

$$P_r = H_{LoS}(0) \times P_t, \quad (1)$$

where $P_t$ is the optical power transmitted by the AP and $H_{LoS}(0)$ is the channel gain coming from the line-of-sight (LoS) propagation path of length $d$ between the AP and UE. Note that a non-LoS path also exists but is here neglected as its contribution is negligible except at the edges of the room [4]. The LoS channel gain $H_{LoS}(0)$ is then commonly defined as [5]:

$$H_{LoS}(0) = \begin{cases} \frac{A_{PD}(m + 1)}{2\pi d^2} \cos^m(\phi) \cos(\psi) & \text{if } 0 \le \psi \le \Psi_c \text{ and } 0 \le \phi \le \pi/2, \\ 0 & \text{otherwise,} \end{cases} \quad (2)$$

where $A_{PD}$ is the sensitive area of the UE’s photodetector, $m$ is the LED order of Lambertian emission, which is related to its semi-angle at half-power $\Phi_{1/2}$ by $m = -\ln2/\ln(\cos(\Phi_{1/2}))$, and $\Psi_c$ is the field of vision (FoV) of the UE receiver.

<footnote n="1">¹Laboratoire d'Ingénierie des Systèmes de Versailles, UVSQ-University of Paris-Saclay, 10-12 avenue de l'Europe, 78140 Vélizy-Villacoublay</footnote>

<footnote n="2">²Corresponding author: haitham.al-satai@uvsq.fr</footnote>
### III. SIMULATION RESULTS AND DISCUSSIONS

According to the above analysis, we simulate a room of 20 × 20 × 3 m with an AP in the middle of the ceiling and a UE moving across an x-y plane 0.85 m above the floor. Detailed information about the parameters used during the simulations is provided in Table I.

<table><caption>Table I: Simulation Parameters.</caption><thead><tr><td>Parameter</td><td>Value</td></tr></thead><tbody><tr><td>Room dimension</td><td>20 × 20 × 3 m</td></tr><tr><td>Semi-angle at half-power (Φ<sub>1/2</sub>)</td><td>10°, 30°, 60°</td></tr><tr><td>Optical power radiated (P<sub>t</sub>)</td><td>1 W</td></tr><tr><td>Height of the UE</td><td>0.85 m</td></tr><tr><td>Sensitive area of the photodetector (A<sub>PD</sub>)</td><td>10<sup>-4</sup>m<sup>2</sup></td></tr><tr><td>FoV of a receiver (Ψ<sub>c</sub>)</td><td>60°</td></tr></tbody></table>

Simulation is conducted in MATLAB to calculate the received optical power distribution across the reception plane, with and without beamsteering and for different semi-angles at half-power (10°, 30°, and 60°). The resulting distributions when Φ₁/₂ = 60° are shown on Fig. 2, with on top the distribution ‘with beamsteering’ and at the bottom the one ‘without beamsteering’.

<figure><img src="image_3.png" /><figcaption>Fig. 2 Received power when Φ₁/₂ = 10° with beamsteering (top) and without beamsteering (bottom).</figcaption></figure>

We can see that whether beamsteering is used or not, the received optical power is the largest at the center of the reception plane. This is because the absolute distance *d* between the AP and the UE increases as the UE moves from the center, so that *H*<sub>LOS</sub>(0) and thus *P*<sub>r</sub> decrease to reach their lowest values where *d* is maximum, i.e. at the corners of the room.

We also notice that although identical at the center of the room, *P*<sub>r</sub> is larger with beamsteering than without beamsteering at any other point, especially at the corners where it reaches -33.9 dBm in the first case and -50.4 dBm in the second case. Assuming data can be retrieved as long as *P*<sub>r</sub> > -25 dBm [5], our results show that using beamsteering with a Φ₁/₂ = 60° LED source allows maintaining connectivity over a circular coverage area of radius 5 m, versus 2.5 m without beamsteering.

Table II lists the maximum gain provided at the corner of the room by beamsteering when LED sources of various directivity (i.e. of various Φ₁/₂) are used, along with the radius

of the circular coverage area obtained with and without beamsteering. It can be seen that the more directive the source, the greater the optical power gain and coverage, thus showing that beamsteering is all the more interesting with narrow beams. However, there is no need of very directive sources to cover the whole room as a semi-angle at half-power of 10°, corresponding to common LED spots, is enough for this.

<table><caption>Table II: The value of Difference in received power distribution for three semi-angles at half-power</caption><thead><tr><td>Semi-angle at half-power</td><td>Optical gain (dB)</td><td>Coverage radius with/without beamsteering (m)</td></tr></thead><tbody><tr><td>Φ<sub>1/2</sub> = 10°</td><td>380.9 dB</td><td>10 / 0.5</td></tr><tr><td>Φ<sub>1/2</sub> = 30°</td><td>47.9 dB</td><td>7.5 / 2</td></tr><tr><td>Φ<sub>1/2</sub> = 60°</td><td>16.47 dB</td><td>5 / 2.5</td></tr></tbody></table>

### IV. CONCLUSION

In this paper, we investigate whether beamsteering techniques can optimize the optical power at the receiver level in an indoor OWC system. The system's performance in terms of power gain and coverage with/without beamsteering is assessed based on MATLAB simulations. It is found that beamsteering significantly improves the optical power distribution as well as the coverage of the system compared to when it is not used. This work is nevertheless based on the use of a theoretical threshold of optical power to maintain the link, which could be improved in the future by using a finer model of the receiver including a noise model to estimate the SNR and the bit error rate distributions in various setups (different modulation schemes, perfect beamsteering versus misaligned configurations etc.).

### ACKNOWLEDGMENT

This work was supported by the French National Research Agency (ANR) through the project SAFELIFI under grant ANR-21-CE25-0001-0.

### REFERENCES

[1] N. Chi, Y. Zhou, Y. Wei, and F. Hu, “Visible light communication in 6G: Advances, challenges, and prospects”, *IEEE Vehicular Technology Magazine*, vol. 15, no. 4, pp. 93-102, 2020.

[2] C. Shen, C. Ma, D. Li, J. Hu, G. Li, P. Zou, J. Zhang, Z. Li, and N. Chi, “High-speed visible laser light communication: Devices, systems and applications”, *Broadband Access Communication Technologies XV*, vol. 11711, pp. 18-27, 2021.

[3] T. Koonen, F. Gomez-Agis, F. Huijskens, K. A. Mekonnen, Z. Cao, and E. Tangdiongga, “High-capacity optical wireless communication using two-dimensional IR beam steering”, *Journal of Lightwave Technology*, vol. 36, no. 19, pp. 4486-4493, 2018.

[4] L. An, H. Shen, J. Wang, Y. Zeng, and R. Ran, “Energy efficiency optimization for MIMO visible light communication systems”, *IEEE Wireless Communications Letters*, vol. 9, no. 4, pp. 452-456, 2019.

[5] Z. Ghassemlooy, W. Popoola, S. Rajbhandari, *Optical Wireless Communications: System and Channel Modelling with MATLAB®, CRC Press*, 2019.