Secure transmission in a W-band RoF system based on delta-sigma modulation.

In this Letter, a delta-sigma modulation (DSM) encryption technique in a W-band RoF system is proposed. By performing DSM with different over-sample ratios (OSRs) on the OFDM signal based on the controlled keys generated by the chaotic system at the transmitter and performing constellation masking to disturb the transmitting signal for encryption, a high-order QAM-OFDM-DSM encrypted signal is achieved. In order to further improve the security of the system, bit bidirectional diffusion scrambling is used to resist chosen-plaintext attacks. After experimental verification, under the same transmission power, the encrypted DSM signal can achieve better security than single OSR of DSM signals through a 50-km standard single-mode fiber (SSMF) and a 3-m wireless channel, with the gain of sensitivity increased by ∼1 dBm. From the reliability of the system, the encrypted signal of the proposed scheme can be recovered, which meets a hard decision-forward error correction (HD-FEC) threshold of 3.8 × 10-3.

Secure RoF system based on key nested polar code and feedback neural network.

With the development of 6 G network, the issue of information security is becoming more and more significant. In this paper, a secure RoF system based on key nested polar code and feedback neural network (FNN) is proposed. For the nested polar code, the original key is randomly selected from the constructed codebook and the index of key is encoded by inner polar code which is placed at the location with better channel quality bit of the frozen bit of outer polar code, for the other part of outer polar code, information bits are encrypted by chaotic sequence generated by 4-D cellular neural network. The polar coded sequence is mapped to the 16-QAM symbol for orthogonal frequency division multiplexing (OFDM) and then the OFDM signal is modulated to the optical pulse, which is delivered to users through 50 km standard single-mode fiber and 5 m wireless channel. In the receiver, successive cancellation list (SCL) decoder is used for decoding outer polar code and FNN is used for decoding inner polar code to reduce the latency. The experimental results show that, compared with the existing scheme, when the bit err rate is 10-3, the received optical power (ROP) gain of the proposed scheme with SCL2 decoder and SCL4 decoder is ∼1.2 dB and ∼1.6 dB, respectively. And compared with the traditional OFDM signal with polar code, when the bit err rate is 10-3, the ROP gain of the proposed scheme with SCL4 decoder is ∼1 dB. What's more, the randomness of the chaotic key sequence, the ability to resist brute-force attacks and the ability to resist chosen-plaintext attacks are elaborated. Therefore, the proposed scheme can greatly improve the security of the system while ensuring the correct transmission of information.

GS-16QAM OFDM with ANN scheme combined with LFM signal for joint communication and radar sensing system.

In this Letter, an integrated waveform geometrically shaped (GS) 16 quadrature amplitude modulation (QAM) based orthogonal frequency division multiplexing (OFDM) communication signal combined with a linear frequency modulation (LFM) radar signal is proposed and experimentally demonstrated in a W-band communication and radar detection system. The proposed method can generate communication and radar signals simultaneously. The inherent error propagation and the interference of the radar signal limit the transmission performance of the joint communication and radar sensing system. Thus, an artificial neural network (ANN) scheme is proposed for the GS-16QAM OFDM signal. After 0.8-m wireless transmission, the experimental results show that the receiver sensitivity and normalized general mutual information (NGMI) of the GS-16QAM OFDM are improved compared with that of the OFDM with uniform 16QAM at the forward error correction (FEC) threshold of 3.8 × 10-3. In addition, multi-target radar detection in centimeter level radar ranging is realized.

Coordinated-security based on probabilistic shaping and encryption in MMW-RoF system.

A coordinated-security probabilistic shaping (PS) physical layer encryption scheme is proposed for a W-band millimeter-wave radio-over-fiber (MMW-RoF) system. This scheme mainly includes substituting encryption, coordinated encrypted PS, and unequal length grouping scrambling, which can realize the coordination between PS and chaotic encryption. The key space of the proposed scheme is 10103, which can effectively prevent against brute force cracking and chosen-plaintext attacks. The encrypted orthogonal frequency division multiplexing (OFDM) signal is successfully transmitted over 50-km standard single-mode fiber (SSMF) and a 5-m wireless channel. The results show that the proposed scheme achieves 0.8-dB received optical power gain at a bit error rate (BER) of 10-3 compared with a traditional OFDM signal. The superiority of the proposed scheme in security performance and BER performance has been verified.

One-time pad scheme based on polar code and OFDM for MMW-RoF system at W-band.

The physical layer security of millimeter-wave radio-over-fiber (MMW-RoF) system at W-band is a promising topic. This paper experimentally demonstrates a one-time pad scheme based on polar code and orthogonal frequency division multiplexing (OFDM) for MMW-RoF system. In the proposed scheme, the initial key is obtained by looking-up table mapping randomly, and chaotic sequence is generated by using 4-D cellular neural network (CNN). The key for next frame is placed in the partial frozen bits of polar code, which can realize the one-time pad mechanism. The encrypted OFDM signal carried by 100GHz millimeter-wave is successfully transmitted over 50 km standard single-mode fiber (SSMF) and 5 m wireless channel in this experiment. The experimental results show that, compared with the traditional OFDM signal, the proposed scheme in SCL8 decoder can achieve ∼4.1 dB gain at the BER of 10-3, which can effectively use the frozen bits of polar code to transmit more information and improve the security and reliability of the whole system.

Security enhancement of a W-band millimeter-wave signal based on 3D Hilbert scrambling and diffusion.

A physical layer enhancement scheme of the W-band millimeter-wave signal based on chaotic grouping and segmentation encryption, 3D Hilbert scrambling, and diffusion is proposed in this paper. Chaotic grouping and segmentation bit-level encryption can enhance the randomness of data and enlarge the key space. 3D Hilbert scrambling and chaotic diffusion are performed in symbol and subcarrier domains. The correlation of data can be effectively reduced after encryption. The analyses show that the key space of the proposed scheme can reach ∼10152. The encrypted W-band millimeter-wave signal can be successfully transmitted in the orthogonal frequency division multiplexing (OFDM) radio-over-fiber (RoF) system of 50-km standard single-mode fiber (SSMF) and 3-m wireless channel, and the experimental results demonstrate that the proposed scheme can enhance the security of the system without negatively affecting transmission performance.

Underwater optical wireless communication performance enhancement using 4D 8PAM trellis-coded modulation OFDM with DFT precoding.

A 4D 8-pulse amplitude modulation trellis-coded modulation-based orthogonal frequency division multiplexing (4D 8PAM TCM-OFDM) scheme combined with discrete Fourier transform (DFT) precoding is proposed and experimentally demonstrated in an underwater optical wireless communications system. It can resist power fading caused by the attenuation, scattering, and reflection in the water channel. The experimental results show that, after transmission over the water-air channel and at the bit error rate of 3.8×10-3, the improvement in the receiver sensitivity is 0.88 dB using the 4D 8PAM TCM-OFDM scheme, compared to the conventional 64QAM-OFDM scheme. In addition, the proposed 4D 8PAM TCM-OFDM scheme combined with DFT precoding can compensate for unbalanced impairments, and it can obtain 1.28 dB receiver sensitivity improvement, compared to the conventional 64QAM-OFDM scheme with DFT precoding.

Probabilistic shaping based constellation encryption for physical layer security in OFDM RoF system.

The physical layer security of radio-over-fiber (RoF) system is a very important problem for future communication. In this paper, a novel probabilistic shaping (PS) based constellation encryption scheme is proposed in which two bit-level encryption operations are firstly performed according to chaotic sequences and hash values. The chaotic sequences are generated by hyperchaotic system and hash values are obtained by SHA-512. Then PS is applied to enhance transmission performance. After PS-16-quadrature amplitude modulation (QAM), constellation encryption is implemented aiming at maintaining overall shaping distribution unchanged and improving security. An encrypted PS-16-QAM orthogonal frequency division multiplexing (OFDM) signal is successfully transmitted over 50 km standard single-mode fiber (SSMF) and 5 m wireless channel in our experiment. The results demonstrate that the key space of 10121 is achieved to defend malicious attacks. Moreover, the proposed PS-based encryption scheme can obtain approximately 2.4 dB gain at a BER of 10-3 compared with traditional OFDM signal. Thus, the proposed scheme has a good application prospect in the future OFDM-RoF system due to the dominant BER and security performance.

Secure transmission of W-band millimeter-wave based on CNN and dynamic resource allocation.

A secure transmission scheme of a W-band millimeter-wave radio-over-fiber (RoF) system based on cellular neural network (CNN) and dynamic resource allocation is proposed, in which 7-D CNN chaotic system is composed to heighten the anti-deciphering ability of a secure system, and the spectrum resources are optimized by dynamic allocation. The analyses show that the key space of our scheme can reach approximately 10112. The encrypted W-band millimeter-wave signal is successfully transmitted in the filter-OFDM RoF system of 50-km SSMF and 5 m wireless channel, and the experimental results illustrate that our proposed scheme can enhance the bit error ratio performance by approximately 0.3 dB compared with the traditional one.

Enabling user mobility for optical camera communication using mobile phone.

We propose and experimentally demonstrate an optical camera communication (OCC) supporting user mobility. A mobile test platform is designed to emulate user mobility. In the mobile scenario, dynamic column matrix selection algorithm is proposed to select an appropriate column matrix with high extinction-ratio (ER) while avoiding the blooming effect. The mobile phone is placed on the moving track to receive the visible light at a vertical distance of 60 cm. By varying the moving speed at 20, 40, 60, 80, and 100 cm/s and lateral distance at 50 and 70 cm respectively, the system performance using the proposed algorithm is investigated. The experimental results show that with the increase of lateral distance (far from the light source) and user moving speed, the system performance gets degraded. Moreover, it demonstrates that the mobile system can achieve a throughput of 4.08 kbps under a low illuminance of 275 lx.

Discriminative Style Learning for Cross-Domain Image Captioning.

The cross-domain image captioning, which is trained on a source domain and generalized to other domains, usually faces the large domain shift problem. Although prior work has attempted to leverage both paired source and unpaired target data to minimize this shift, the performance is still unsatisfactory. One main reason lies in the large discrepancy in language expression between two domains, where diverse language styles are adopted to describe an image from different views, resulting in different semantic descriptions for an image. To tackle this problem, this paper proposes a Style-based Cross-domain Image Captioner (SCIC) which incorporates the discriminative style information into the encoder-decoder framework, and interprets an image as a special sentence according to external style instructions. Technically, we design a novel "Instruction-based LSTM", which adds the instruct gate to collect a style instruction, and then outputs a specified format according to that instruction. Two objectives are designed to train I-LSTM: 1) generating correct image descriptions and 2) generating correct styles, thus the model is expected to accurately capture the semantic meanings of an image by the special caption as well as understand the syntactic structure of the caption. We use MS-COCO as the source domain, and Oxford-102, CUB-200, Flickr30k as the target domains. Experimental results demonstrate that our model consistently outperforms the previous methods, and the style information incorporating with I-LSTM significantly improves the performance, with 5% CIDEr improvements at least on all datasets.