K-means non-uniform-quantization digital-analog radio-over-fiber scheme for THz-band photonics-aided wireless fronthaul.

We propose a non-uniform-quantization digital-analog radio-over-fiber (NUQ-DA-RoF) scheme based on an advanced K-means NUQ algorithm and demonstrate it experimentally in a 2-m 300-GHz photonics-aided wireless fronthaul system. Results show that the NUQ-DA-RoF scheme achieves a SNR gain of ∼1.9 dB compared to the uniform-quantization DA-RoF (UQ-DA-RoF) at an equivalent Common Public Radio Interface equivalent data rate (CPRI-EDR). Remarkably, the NUQ-DA-RoF scheme exhibits an ∼1.6-dB power sensitivity enhancement over the UQ-DA-RoF at the 256-QAM SNR threshold. These findings highlight the advantages of the NUQ-DA-RoF scheme over UQ-DA-RoF in terms of power budget and SNR improvement, suggesting promising prospects for future radio access networks and wireless fronthaul.

SNR improved digital-delta-sigma-modulation radio-over-fiber scheme for D-band 4.6-km photonics-aided wireless fronthaul.

We propose a digital-delta-sigma-modulation radio-over-fiber (DDSM-RoF) scheme for wireless fronthaul and validate it experimentally in a D-band photonics-aided RoF transmission system. The 10-Gbaud DDSM-RoF signal with a common public radio interface equivalent data rate (CPRI-EDR) of 55.8 Gb/s is successfully transmitted in a 130-GHz 4.6-km wireless channel. The spectral efficiency (SE) is 5.58 bit/s/Hz and the capacity-distance product reaches 257 Gb/s·km. Up to 34.4-dB recovered signal-to-noise ratio (SNR) is observed to support the 1024-quadrature-amplitude-modulation (1024-QAM) transmission. Compared with the digital-analog-RoF (DA-RoF) scheme, the proposed DDSM-RoF achieves an SNR improvement of 5.9 dB.

Research on Penetration Loss of D-Band Millimeter Wave for Typical Materials.

The millimeter-wave frequency band provides abundant frequency resources for the development of beyond 5th generation mobile network (B5G) mobile communication, and its relative bandwidth of 1% can provide a gigabit-level communication bandwidth. In particular, the D-band (110-170 GHz) has received much attention, due to its large available bandwidth. However, certain bands in the D-band are easily blocked by obstacles and lack penetration. In this paper, D-band millimeter-wave penetration losses of typical materials, such as vegetation, planks, glass, and slate, are investigated theoretically and experimentally. The comparative analysis between our experimental results and theoretical predictions shows that D-band waves find it difficult to penetrate thick materials, making it difficult for 5G millimeter waves to cover indoors from outdoor macro stations. The future B5G mobile communication also requires significant measurement work on different frequencies and different scenarios.

Path Loss Measurement of Outdoor Wireless Channel in D-band.

D-band (110-170 GHz) has received much attention in recent years due to its larger bandwidth. However, analyzing the loss characteristics of the wireless channel is very complicated at the millimeter-wave (MMW) band. Research on D-band wireless channels has been focused on indoor short-distance transmissions, with few studies looking at outdoor long-distance wireless channels. In this paper, we provide the design of the D-band outdoor long-distance transmission system, propose the outdoor line-of-sight (LOS) propagation measurements, and study the outdoor D-band propagation loss characteristics with distances up to 800 m. The path loss model uses the Floating Intercept (FI) and the Close-In (CI) model is established based on the least square method. In the CI model, the path loss exponent is greater than 2 and increases with frequency, while in the FI model, the path loss exponent has no apparent frequency dependence. The results show that D-band path loss in long-distance outdoor scenarios is greater than that in free space, indicating that the propagation condition is worse than in free space. The results show that both models have similar performance. Under this basis, the model with the smallest number of parameters would be the optimal choice. In addition, these results prospectively provide a theoretical model for designing and optimizing high frequency mm-wave propagation measurements at a distance of 200 m and beyond.

Reflection Characteristics Measurements of Indoor Wireless Link in D-Band.

For the millimeter wave (mm-Wave) and terahertz (THz) indoor wireless communication system, the reflection channels need to be characterized and modeled. In this paper, the reflection measurements of the parallel polarized wave are carried out under multiple incident angles and five kinds of materials in the D-band (110-170 GHz). A modified reflection model with two parameters estimated by the minimum mean square error (MMSE) criterion is proposed. The results show that the measurements are in good agreement with the proposed model. Furthermore, a set of measured properties is demonstrated and it can be concluded that both the reflection coefficients and relative permittivity gradually decrease, whereas the surface roughness increases slightly with the increasing frequency, indicating a weak frequency dependence. Interestingly, the concrete board with high surface roughness, which means more power loss in a specular direction, has the lowest reflection loss at a certain frequency and incident angle. It implies that the reflection characteristics of indoor building materials are determined not only by surface roughness, but also by many other factors, such as relative permittivity, frequency, and incident angle. Our work suggests that the reflection measurements of indoor D-band wireless links have a prospective application for future indoor wireless communication systems.