On the Secrecy Rate of Spatial Modulation Based Indoor Visible Light Communications
Pith reviewed 2026-05-25 17:39 UTC · model grok-4.3
The pith
The paper derives lower and upper bounds on secrecy rate for spatial modulation in indoor VLC systems under optical intensity constraints and identifies a greedy transmitter selection scheme as optimal.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
For spatial modulation indoor VLC with a passive eavesdropper, lower and upper bounds on the secrecy rate are derived under non-negativity plus average optical intensity constraints and under the additional peak optical intensity constraint. The bounds are shown to be tight by numerical evaluation, with only small gaps remaining at high SNR. A greedy selection scheme for choosing the active transmitter is proposed and demonstrated to outperform both uniform selection and channel-adaptive selection.
What carries the argument
Spatial modulation with active-transmitter selection (uniform, channel-adaptive, or greedy) applied to the indoor VLC channel model under non-negativity and optical-intensity constraints.
If this is right
- At high SNR the secrecy-rate bounds exhibit only small gaps, allowing the lower bound to serve as a reliable performance predictor.
- The greedy selection scheme consistently achieves the highest secrecy rate of the three transmitter-selection methods examined.
- The derived bounds apply separately to the average-power-only constraint set and to the joint average-plus-peak constraint set.
- Asymptotic high-SNR expressions for the bounds can be used to predict secrecy-rate scaling without repeated numerical integration.
Where Pith is reading between the lines
- The same bounding technique could be applied to other single-active-transmitter schemes such as index modulation in VLC.
- If an active eavesdropper were present, the current bounds would no longer guarantee security and a different analysis would be required.
- The performance ordering among selection schemes may change when the number of transmitters or the room geometry is altered.
Load-bearing premise
The eavesdropper is passive and its channel state is known or can be bounded, while the indoor VLC propagation follows the standard line-of-sight plus diffuse model used to compute mutual information.
What would settle it
In a controlled indoor VLC testbed, measure the empirical secrecy rate with a real passive eavesdropper whose channel differs from the modeled LOS-plus-diffuse statistics and check whether the measured value lies inside the derived lower and upper bounds.
Figures
read the original abstract
In this paper, we investigate the physical-layer security for a spatial modulation (SM) based indoor visible light communication (VLC) system, which includes multiple transmitters, a legitimate receiver, and a passive eavesdropper (Eve). At the transmitters, the SM scheme is employed, i.e., only one transmitter is active at each time instant. To choose the active transmitter, a uniform selection (US) scheme is utilized. Two scenarios are considered: one is with non-negativity and average optical intensity constraints, the other is with non-negativity, average optical intensity and peak optical intensity constraints. Then, lower and upper bounds on the secrecy rate are derived for these two scenarios. Besides, the asymptotic behaviors for the derived secrecy rate bounds at high signal-to-noise ratio (SNR) are analyzed. To further improve the secrecy performance, a channel adaptive selection (CAS) scheme and a greedy selection (GS) scheme are proposed to select the active transmitter. Numerical results show that the lower and upper bounds of the secrecy rate are tight. At high SNR, small asymptotic performance gaps exist between the derived lower and upper bounds. Moreover, the proposed GS scheme has the best performance, followed by the CAS scheme and the US scheme.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper derives lower and upper bounds on the secrecy rate of spatial modulation (SM) VLC systems with multiple transmitters under two optical intensity constraint sets (non-negativity + average; non-negativity + average + peak), analyzes high-SNR asymptotics, and proposes channel-adaptive selection (CAS) and greedy selection (GS) schemes that outperform uniform selection (US). Numerical results are presented to show that the bounds are tight and that GS yields the highest secrecy rate.
Significance. If the bounds are valid, the work supplies concrete analytical tools and selection heuristics for physical-layer secrecy in intensity-constrained SM-VLC, a setting of practical interest for indoor secure communications. The reported numerical tightness of the bounds and the consistent performance ordering among US/CAS/GS constitute verifiable strengths.
major comments (1)
- [System model / Secrecy rate bounds] System model and secrecy-rate derivation sections: the lower/upper bounds and the optimality claims for CAS/GS are obtained by direct substitution of Eve’s LOS+diffuse channel coefficients into the mutual-information expressions. For a passive Eve these coefficients are not known a priori at the transmitter; the manuscript does not state the precise assumption (worst-case Eve, statistical knowledge, or perfect CSI) under which the derived expressions remain valid secrecy-rate guarantees. This assumption is load-bearing for both the analytic bounds and the numerical superiority of GS.
minor comments (2)
- [Abstract] Abstract: the statement that “small asymptotic performance gaps exist” is not quantified; a sentence giving the observed gap values (or a reference to the relevant figure) would improve clarity.
- [Introduction / System model] Notation: the distinction between the two constraint scenarios is introduced only in the abstract and introduction; a single compact table summarizing the constraint sets and the corresponding bound expressions would aid readability.
Simulated Author's Rebuttal
We thank the referee for the constructive comment on the system model and the need to clarify assumptions regarding the eavesdropper's channel state information. We address this point below and will revise the manuscript to make the assumptions explicit.
read point-by-point responses
-
Referee: [System model / Secrecy rate bounds] System model and secrecy-rate derivation sections: the lower/upper bounds and the optimality claims for CAS/GS are obtained by direct substitution of Eve’s LOS+diffuse channel coefficients into the mutual-information expressions. For a passive Eve these coefficients are not known a priori at the transmitter; the manuscript does not state the precise assumption (worst-case Eve, statistical knowledge, or perfect CSI) under which the derived expressions remain valid secrecy-rate guarantees. This assumption is load-bearing for both the analytic bounds and the numerical superiority of GS.
Authors: We agree that the CSI assumption for Eve must be stated explicitly, as it is currently implicit. The secrecy-rate bounds are derived under the assumption of perfect knowledge of both the legitimate receiver's and Eve's channel coefficients at the transmitter. This corresponds to a worst-case Eve scenario for the purpose of computing the secrecy rate (i.e., the transmitter designs the scheme knowing Eve's LOS+diffuse coefficients). The CAS and GS schemes are likewise defined under this perfect-CSI assumption, as they select the active transmitter based on both channels. We will add a clear statement in the system model (Section II) and secrecy-rate derivation (Section III) specifying that the analysis assumes perfect CSI of Eve. Note that if only statistical CSI of Eve were available, the secrecy rate would instead be defined via ergodic or outage formulations, which is outside the scope of the current derivations but could be explored in future work. revision: yes
Circularity Check
No significant circularity; bounds derived from standard mutual-information expressions
full rationale
The paper derives lower/upper secrecy-rate bounds and asymptotic high-SNR gaps directly from the standard secrecy-capacity formula (mutual information difference) under non-negativity, average-intensity, and (in one case) peak-intensity constraints for the SM transmitter selection schemes. These expressions are evaluated using the LOS+diffuse channel model for both Bob and Eve; the CAS/GS selection rules are explicit functions of the same channel coefficients. No step reduces a claimed prediction to a fitted parameter by construction, no uniqueness theorem is imported from prior self-work, and no ansatz is smuggled via citation. The derivation chain is therefore self-contained against external information-theoretic benchmarks and receives score 0.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Standard definitions of secrecy rate as difference of mutual informations
- domain assumption Indoor VLC channel model with line-of-sight and diffuse components
Reference graph
Works this paper leans on
-
[1]
J. G. Andrews, S. Buzzi, W. Choi, S. V . Hanly, A. Lozano, A. C. K. Soong, and J. C. Zhang, “What will 5G be?” IEEE J. Sel. Areas Commun. , vol. 32, no. 6, pp. 1065-1082, Jun. 2014
work page 2014
-
[2]
N. Ishikawa, S. Sugiura, and L. Hanzo, “50 years of permutation, spatial and index modulation: From classic RF to visible light communications and data storage,” IEEE Commun. Surv. Tur ., vol. 20, no. 3, pp. 1905-1938, Mar. 2018
work page 1905
-
[3]
Spatial modulation for generalized MIMO: Challenges, opportunities, and implementation,
M. D. Renzo, H. Hass, A. Ghrayeb, S. Sugiura, and L. Hanzo, “Spatial modulation for generalized MIMO: Challenges, opportunities, and implementation,” Proc. IEEE, vol. 102, no. 1, pp. 56-103, Jan. 2014
work page 2014
-
[4]
Space modulation on wireless fading channels,
A. Chau and S.-H. Yu, “Space modulation on wireless fading channels,” in IEEE V eh. Technol. Conf., Atlantic City, USA, vol. 3, pp. 1668-1671, Oct. 2001
work page 2001
-
[5]
Spatial modulation - A new low complexity spectral efficiency enhancing technique,
R. Y . Mesleh, H. Haas, C. W. Ahn, and S. Yun, “Spatial modulation - A new low complexity spectral efficiency enhancing technique,” in Int. Conf. Commun. Netw. China , Beijing, China, pp. 1-5, Oct. 2006
work page 2006
-
[6]
R. Y . Mesleh, H. Haas, S. Sinanovic, C. Ahn, and S. Yun, “Spatial modulation,” IEEE Trans. V eh. Technol., vol. 57, no. 4, pp. 2228-2241, Jul. 2008
work page 2008
-
[7]
Spatial modulation: Optimal detection and performance analysis,
J. Jeganathan, A. Ghrayeb, and L. Szczecinski, “Spatial modulation: Optimal detection and performance analysis,” IEEE Commun. Lett. , vol. 12, no. 8, pp. 545-547, Aug. 2008
work page 2008
-
[8]
Detection algorithm for spatial modulation system under unconstrained channel,
M. X. Guo, C. Jia, and Y . H. Shen, “Detection algorithm for spatial modulation system under unconstrained channel,” in IEEE Int. Conf. Commun. Technol. , Nanjing, China, pp. 458-461, Nov. 2010
work page 2010
-
[9]
Generalised sphere decoding for spatial modulation,
A. Younis, S. Sinanovic, M. Di Renzo, R. Y . Mesleh, and H. Haas, “Generalised sphere decoding for spatial modulation,” IEEE Trans. Commun. , vol. 61, no. 7, pp. 2805-2815, Jul. 2013
work page 2013
-
[10]
A new low-complexity near-ML detection algorithm for spatial modulation,
Q. Tang, Y . Xiao, P. Yang, Q. Yu, and S. Li, “A new low-complexity near-ML detection algorithm for spatial modulation,” IEEE Wirel. Commun. Lett. , vol. 2, no. 1, pp. 90-93, Feb. 2013
work page 2013
-
[11]
Information-guided channel-hopping for high data rate wireless communication,
Y . Yang and B. Jiao, “Information-guided channel-hopping for high data rate wireless communication,” IEEE Commun. Lett., vol. 12, no. 4, pp. 225-227, Apr. 2008
work page 2008
-
[12]
Bit error probability of SM-MIMO over generalized fading channels,
M. D. Renzo and H. Haas, “Bit error probability of SM-MIMO over generalized fading channels,” IEEE Trans. V eh. Technol., vol. 61, no. 3, pp. 1124-1144, Mar. 2012
work page 2012
-
[13]
On the performance of full-duplex two-way relay channels with spatial modulation,
J. Zhang, Q. Li, K. J. Kim, Y . Wang, X. Ge, and J. Zhang, “On the performance of full-duplex two-way relay channels with spatial modulation,” IEEE Trans. Commun. , vol. 64, no. 12, pp. 4966-4982, Dec. 2016
work page 2016
-
[14]
Design guidelines for spatial modulation,
P. Yang, M. D. Renzo, Y . Xiao, S. Li, and L. Hanzo, “Design guidelines for spatial modulation,” IEEE Commun. Surv. Tutor ., vol. 17, no. 1, pp. 6-25, First quarter 2015
work page 2015
-
[15]
R. Mesleh, H. Elgala, and H. Haas, “Optical spatial modulation,” IEEE/OSA J. Opt. Commun. Netw. , vol. 3, no. 3, pp. 234-244, Mar. 2011
work page 2011
-
[16]
Spatial modulation applied to optical wireless communications in indoor LOS environments,
T. Fath, H. Haas, M. Di Renzo, and R. Mesleh, “Spatial modulation applied to optical wireless communications in indoor LOS environments,” in IEEE Global Telecommun. Conf. , Kathmandu, Nepal, pp. 1-5, Dec. 2011
work page 2011
-
[17]
T. Fath and H. Haas, “Performance comparison of MIMO techniques for optical wireless communications in indoor environments,” IEEE Trans. Commun. , vol. 61, no. 2, pp. 733-742, Feb. 2013
work page 2013
-
[18]
N. Ishikawa and S. Sugiura, “Maximizing constrained capacity of power-imbalanced optical wireless MIMO communica- tions using spatial modulation,” IEEE/OSA J. Lightwave Technol. , vol. 33, no. 2, pp. 519-527, Jan. 2015. 30
work page 2015
-
[19]
On the performance of spatial modulation-based optical wireless communications,
J.-Y . Wang, Z. Yang, Y . Wang, and M. Chen, “On the performance of spatial modulation-based optical wireless communications,” IEEE Photon. Technol. Lett. , vol. 28, no. 19, pp. 2094-2097, Oct. 2016
work page 2094
-
[20]
Adaptive spatial modulation based visible light communications: SER analysis and optimization,
J.-Y . Wang, J. Zhu, S. Lin, and J. Wang, “Adaptive spatial modulation based visible light communications: SER analysis and optimization,” IEEE Photon. J. , vol. 10, no. 3, pp. 1-14, Jun. 2018
work page 2018
-
[21]
Channel-adapted spatial modulation for massive MIMO visible light communications,
K. Xu, H. Yu, and Y .-J. Zhu, “Channel-adapted spatial modulation for massive MIMO visible light communications,” IEEE Photon. Technol. Lett. , vol. 28, no. 23, pp. 2693-2696, Dec. 2016
work page 2016
-
[22]
J.-Y . Wang, H. Ge, J.-X. Zhu, J.-B. Wang, J. Dai, and M. Lin, “Adaptive spatial modulation for visible light communications with an arbitrary number of transmitters,” IEEE Access , vol. 6, pp. 37108-37123, Jun. 2018
work page 2018
-
[23]
Power efficient generalized spatial modulation MIMO for indoor visible light communications,
C. R. Kumar and R. K. Jeyachitra, “Power efficient generalized spatial modulation MIMO for indoor visible light communications,” IEEE Photon. Techno. Lett. , vol. 29, no. 11, pp. 921-924, June 2017
work page 2017
-
[24]
Effect of synchronization error on optical spatial modulation,
H. G. Olanrewaju and W. O. Popoola, “Effect of synchronization error on optical spatial modulation,” IEEE Trans. Commun., vol. 65, no. 12, pp. 5362-5347, Dec. 2017
work page 2017
-
[25]
Iterative combinatorial symbol design for spatial modulation in MIMO VLC systems,
E. Curry and D. K. Borah, “Iterative combinatorial symbol design for spatial modulation in MIMO VLC systems,” IEEE Photon. Technol. Lett. , vol. 30, no. 5, pp. 483-486, Mar. 2018
work page 2018
-
[26]
Physical-layer security for MISO visible light communication channels,
A. Mostafa and L. Lampe, “Physical-layer security for MISO visible light communication channels,” IEEE J. Sel. Areas Commun., vol. 33, no. 9, pp. 1806-1818, Sep. 2015
work page 2015
-
[27]
On the secrecy capacity of MISO visible light communication channels,
M. A. Arfaoui, Z. Rezki, A. Ghrayeb, and M.-S. Alouini, “On the secrecy capacity of MISO visible light communication channels,” in IEEE Global Commun. Conf. , Washington, DC, USA, pp. 1-7, Dec. 2016
work page 2016
-
[28]
Discrete input signaling for MISO visible light communication channels,
M. A. Arfaoui, Z. Rezki, A. Ghrayeb, and M.-S. Alouini, “Discrete input signaling for MISO visible light communication channels,” in IEEE Wirel. Commun. Netw. Conf. , San Francisco, USA, pp. 1-6, Mar. 2017
work page 2017
-
[29]
Physical-layer security for indoor visible light communications: Secrecy capacity analysis,
J.-Y . Wang, C. Liu, J. Wang, Y . Wu, M. Lin and J. Cheng, “Physical-layer security for indoor visible light communications: Secrecy capacity analysis,” IEEE Trans. Commun. , Jul. 2018, DOI: 10.1109/TCOMM.2018.2859943
-
[30]
Secure hybrid VLC-RF systems with light energy harvesting,
G. Pan, J. Ye, and Z. Ding, “Secure hybrid VLC-RF systems with light energy harvesting,” IEEE Trans. Commun. , vol. 65, no. 10, pp. 4348-4359, Oct. 2017
work page 2017
-
[31]
On secure VLC systems with spatially random terminals,
G. Pan, J. Ye, and Z. Ding, “On secure VLC systems with spatially random terminals,” IEEE Commun. Lett. , vol. 21, no. 3, pp. 492-495, Mar. 2017
work page 2017
-
[32]
Fundamental analysis for visible-light communication system using LED lights,
T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron. , vol. 50, no. 1, pp. 100-107, Feb. 2004
work page 2004
-
[33]
Tight bounds on channel capacity for dimmable visible light communications,
J.-B. Wang, Q.-S. Hu, J. Wang, M. Chen, and J.-Y . Wang, “Tight bounds on channel capacity for dimmable visible light communications,” IEEE/OSA J. Lightwave Technol. , vol. 31, no. 23, pp. 3771-3779, Dec. 2013
work page 2013
-
[34]
Elements of Information Theory ,
T. M. Cover and J. A. Thomas, “ Elements of Information Theory ,” Hoboken, NJ, USA: Wiley, 2006
work page 2006
-
[35]
Information Theory: Coding Theorems for Discrete Memoryless Systems ,
I. Csiszar and J. Korner, “ Information Theory: Coding Theorems for Discrete Memoryless Systems ,” New York: Academic, 1981
work page 1981
-
[36]
On the capacity of free-space optical intensity channels,
A. Lapidoth, S. M. Moser, and M. A. Wigger, “On the capacity of free-space optical intensity channels,” IEEE Trans. Inf. Theory, vol. 55, no. 10, pp. 4449-4461, Oct. 2009
work page 2009
-
[37]
A. Chaaban, J.-M. Morvan, and M.-S. Alouini, “Free-space optical communications: Capacity bounds, approximations, and a new sphere-packing perspective,” IEEE Trans. Commun. , vol. 64, no. 3, pp. 1176-1191, Mar. 2016
work page 2016
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.