Wireless Distance Research Articles

Photonics millimeter wave bidirectional full-duplex communication based on polarization multiplexing.

We have proposed and experimentally implemented a photonics-aided large-capacity long-distance mm-wave bidirectional full-duplex communication system at the W-band based on polarization multiplexing. The same radio frequency (RF) carrier source is shared by both the uplink and the downlink, and a pair of orthomode transducers (OMTs) are used to separate the dual orthogonally polarized channels. To achieve the maximum spectrum efficiency and throughput, 10-Gbaud probabilistically shaped 256-level quadrature-amplitude-modulation (PS-256QAM) signals with 7.07 bit/symbol/Hz are transmitted in Ch. H and Ch. V. The system can support the bidirectional transmission with 103-Gbps data rate over 4600-m RF wireless distance. To the best of our knowledge, based on a photonics-aided bidirectional full-duplex system, this is the first time to realize a record-breaking bit rate-distance product at the W-band, i.e., 103 Gbps × 4.6 km = 473.8 Gbps•km.

Demonstration of 4096QAM THz MIMO wireless delivery employing one-bit delta-sigma modulation.

We experimentally demonstrate 2-Gbaud 4096-ary quadrature amplitude modulation (4096QAM) signal transmission over 2-m wireless distance at 370 GHz in a photonics-aided terahertz (THz)-wave communication system. By using one-bit quantized delta-sigma modulation (DSM) and photonics-aided technology, we successfully achieve the transmission of high-order QAM signals over THz multiple-input multiple-output (MIMO) links. After 2 m of free space transmission, its bit error rate (BER) is below the 20% soft-decision forward error correction (20% SD-FEC) threshold of 2.4 × 10-2. To the best of our knowledge, this is the first time to apply DSM technology in a THz MIMO link transmission.

Photonics-Aided Terahertz-Wave Wireless Communication Employing Advanced Post-Equalizer

In this letter, a novel MIMO linear and Volterra nonlinear equalizer (MIMOL-VNLE) is proposed for signal recovery in the photonics-aided terahertz wave (THz-wave) wireless communication system, which is proven to compensate for linear impairments, nonlinear impairments, and I/Q mixing effects simultaneously. Adopting the proposed algorithm, we experimentally demonstrated the single-channel transmission of 20-Gbaud 16-ary quadrature amplitude modulation (16QAM) THz-wave signal at 440-GHz over 1-m wireless distance.

A Spectrum-Efficient MoF Architecture for Joint Sensing and Communication in B5G Based on Polarization Interleaving and Polarization-Insensitive Filtering

The intelligentization of future society puts forward an urgent demand for high-precision sensing and ultra-high-speed wireless communications in the upcoming beyond fifth-generation (B5G) era. We propose and experimentally demonstrate a novel spectrum-efficient MMW-over-fiber (MoF) architecture for joint sensing and communication in B5G optical-wireless converged networks. The proposed MoF architecture is based on polarization interleaving and polarization-insensitive filtering. In the proposed architecture, the sensing and communication sidebands are generated simultaneously through asymmetrical single-sideband (ASSB) modulation, whereas the two local oscillator (LO) sidebands up-converting the sensing and communication signals to MMW band are obtained by carrier-suppressed double-sideband (CS-DSB) modulation. By interleaving the two sets of sidebands for sensing and communication in two orthogonal polarizations, the demand for higher bandwidth devices and the occupied spectral grid can thus be effectively reduced. The ASSB modulation eliminates the chromatic-dispersion- (CD) induced power fading for long-reach services. The polarization-insensitive filtering removes the need for complicated polarization tracking, resulting in a simple structure at the remote units (RUs) and polarization-free digital signal processing (DSP) at the user ends (UEs). Moreover, the two sets of sidebands originate from a shared laser, so frequency offset estimation (FOE) can be avoided to further reduce the complexity and power consumption of the DSP, thereby facilitating a user-friendly terminal. The experimental results show that a ±15-mm ranging accuracy at B5G MMW band for single-target detection is achieved, and a 30-cm ranging resolution for dual-target detection is also realized. Furthermore, a 23-Gbit/s error-free transmission rate at 28GHz over 5.41-km single-mode fiber (SMF) and 2-m wireless distance is successfully demonstrated without frequency offset compensation.

3×3 MIMO 60-GHz OFDM-RoF System With Long-Distance Wireless Transmission Enabled by MIMO Volterra Filtering

A 3×3 60-GHz multiple-input multiple-output (MIMO) radio-over-fiber system with an MIMO Volterra filter was demonstrated. The main objective of the proposed scheme is to compensate for the nonlinear distortion caused by radio frequency (RF) power amplifiers (PAs) before the signals reaches the transmitter antennas—particularly when the PAs operate with a high input power to achieve a high output RF power for long-distance wireless transmission. When the required wireless transmission distance is only 7 m, the 3×3 MIMO system with careful control of the PA input power can achieve a data rate of 126 Gbps. However, the data rate decreases rapidly over a longer wireless distance because of the larger loss. By eliminating nonlinear distortion and interchannel interference simultaneously, MIMO Volterra filtering can significantly increase the achievable data rate of a long-distance system. When the required data rate is 90 Gbps (or 100 Gbps), the maximum wireless transmission distance is 118 m (or 70 m) with the aid of MIMO Volterra filtering, but it is only 74 m (or 40 m) without MIMO Volterra filtering.

Transmission of 1024-QAM OFDM at 28 GHz Radio Frequency Using 5G Millimeter Wave Phased Array Antenna

We experimentally demonstrate the transmission of multiorder quadrature amplitude modulation (QAM) millimeter wave (MMW) orthogonal frequency division (OFDM) signal at 28 GHz radio frequency (RF). To overcome these unfavorable channel properties such as high path loss, propagation loss, rain fading, etc., 5G MMW phased array antenna has been used. Meanwhile, probabilistic shaping (PS) technology is applied to extend transmission distance, and Volterra nonlinearity compensation (VNC) technology is used to alleviate the system nonlinearity. Using 5G MMW phased array antennas and technologies of PS and VNC, 6.72 Gbit/s 1024-QAM OFDM signal at 28 GHz can be transmitted over 55-m wireless distance in our experiment, satisfying the normalized general mutual information (NGMI) threshold of 0.83 with 25% soft-decision forward-error-correction (SD-FEC) overhead. To the best of our knowledge, this is the first time to demonstrate the transmission of multiorder QAM OFDM signal at 28 GHz RF using 5G MMW phased array antenna.

104 Meters Photonics-Aided Terahertz Wireless Transmission Without Terahertz Amplifier

In this letter, we experimentally demonstrate a long-distance, large-capacity and photonics-aided wireless terahertz (THz) transmission system without THz amplifier. Using dielectric lenses and advanced digital signal processing (DSP), we have achieved 124 Gbit/s signal transmission over 54 meters wireless distance and 44 Gbit/s signal transmission over 104 meters wireless distance. For all we know, this is the longest wireless distance that can be achieved by using dielectric lenses without any THz amplifiers.

OFDM-PS-256QAM signal delivery at 47.45 Gb/s over 4.6-kilometers wireless distance at the W band

Photonics technology is a promising way to generate high-frequency millimeter waves, which is also a key technology to realize the convergence of fiber-optic and wireless communication. To meet the actual application requirements, kilometer-level wireless distance, large-capacity, and high-spectral-efficiency systems are urgent requirements. Based on the photonics-aided system at the W band, we achieve a net rate of 47.45-Gb/s signal delivery over a 10-km single-mode fiber-28 (SMF-28) and 4.6-km wireless free-space link. The spectral efficiency of the system is 4.97 bit/s/Hz. To the best of our knowledge, this is the first demonstration at more than a 4-km wireless distance level at the W band based on a photonics-aided system, and we achieve a record product of the single-channel transmission rate and wireless distance, i.e., 47.45 Gb/s × 4.6 km = 218.27 Gb/s km. The experimental results provide a good reference value for improving the transmission distance and data rate of the radio-over-fiber (ROF) system, and will play an important role in the future beyond the 5G era.

Wireless transmission of a 200-m PS-64QAM THz-wave signal using a likelihood-based selection radius-directed equalizer.

Based on a photonics-aided scheme, we achieve an experimental demonstration of a, to the best of our knowledge, record-breaking 200-m terahertz (THz)-wave wireless delivery at 335 GHz with the aid of a pair of high-gain polytetrafluoroethylene (PTFE) lenses. By using a 10-GBaud probabilistically shaped 64-ary quadrature amplitude modulation (PS-64QAM) signal and advanced digital signal processing (DSP) including a likelihood-based selection radius-directed equalizer (LBS-RDE), the single-carrier net bit rate of the wireless delivery reaches 44 Gbit/s. High-speed THz-wave communication with up to 200-m wireless distance is successfully realized based on a photonics-aided scheme for the first time.

124.8-Gbit/s PS-256QAM Signal Wireless Delivery Over 104 m in a Photonics-Aided Terahertz-Wave System

We experimentally demonstrate 16-GBaud probabilistic shaped 256-ary quadrature amplitude modulationsignal transmission over 104-m wireless distance at 339 GHz in a photonics-aided terahertz (THz)-wave communication system. Thanks to the pair of poly tetra fluoroethylene lenses and PS technique, we successfully achieve a record single line rate of 124.8 Gbit/s and net spectral efficiency of 6.2 bit/s/Hz. To the best of our current knowledge, it is the first time to achieve >100 m and >100 Gbit/s single-carrier 256QAM THz-wave signal wireless delivery.

THz-over-fiber transmission with a net rate of 5.12 Tbps in an 80 channel WDM system.

An experimental demonstration of the ultra-large-capacity terahertz (THz)-wave signal transmission over a 20-km wired and 54-m wireless distance in an 80-channel wavelength division multiplexing (WDM) system is successfully realized for the first time, to the best of our knowledge. Based on optical asymmetric single-sideband (ASSB) modulation and advanced digital signal processing (DSP) algorithms, we achieve a record line rate of 6.4 Tbit/s (net rate of 5.12 Tbit/s) in a THz-over-fiber communication system. This experimental demonstration can provide an effective solution for ultra-large-capacity THz-over-fiber communication in future 6G networks.

High-Speed Terahertz Band Radio-Over-Fiber System Using Hybrid Time-Frequency Domain Equalization

The radio-over-fiber (RoF) orthogonal frequency division multiplexing (OFDM) system at Terahertz (THz) band has been a promising solution to meet the demand for high capacity and flexibility. The signals transmitted in the RoF system will suffer severe impairments caused by the wireless multi-path effect, optical fiber transmission, and photoelectric device response. The time-frequency domain equalization (TFDE) based on the two-dimension convolution (Conv2D) neural network (NN) is proposed to resist the linear and nonlinear impairments of the RoF-OFDM system. Furthermore, complex convolution is applied to compensate for the complex channel response. Compared with several baseline models, the detailed performance improvement and model size discussion of the complex-valued Conv2D NN TFDE are investigated. With the aid of the complex-valued Conv2D NN TFDE, the 16 Gbaud 16-ary quadrature amplitude modulation (16QAM) signals are delivered over 54.6 m wireless distance and 20 km standard single mode fiber. The line rate of this RoF system achieves 53.5 Gbit/s.

Complex-Valued 2D-CNN Equalization for OFDM Signals in a Photonics-Aided MMW Communication System at the D-Band

Orthogonal frequency division multiplexing (OFDM) is a promising solution in photonics-aided millimeter-wave (MMW) communication systems, which combine the features of fiber and wireless links. In such a fiber-wireless system, the broadband OFDM signals could be affected by the multipath effect, chromatic dispersion, frequency synchronization error, and other complex impairments. Therefore, both inter-symbol interference (ISI) and inter-carrier interference (ICI) will cause performance degradation. In this experiment, a D-band photonics-aided MMW communication system is demonstrated. To compensate for the linear and nonlinear distortions during the fiber and wireless transmission, we proposed a novel time-frequency domain equalizer based on a two-dimensional convolutional neural network (2D-CNN) with a complex-valued structure. Moreover, a residual branch is adopted. We investigate the bit error rate (BER) performance of the OFDM signals transmission with different modulation formats. With the aid of complex-valued 2D-CNN based equalization, 40 Gbit/s 16QAM and 55 Gbit/s PS-64QAM signals can be successfully transmitted over 200 m wireless distance at the D-band while satisfying the HD-FEC (3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> ) and SD-FEC (2.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> ) threshold, respectively. Moreover, the complex-valued structure can bring significant sensitivity improvements compared to the real-valued 2D-CNN equalization.

Statistical Evaluation and Synthetic Generation of Ultra-Wideband Distance Measurements for Indoor Positioning Systems

Wireless positioning systems are a key enabler for a variety of applications. In indoor environments, Global Navigation Satellite Systems are not available, hence technological alternatives are required. Ultra-Wide Band (UWB) radios provide high-precision distance measurements, however are still prone to ranging errors due to the environment. For localization system design and testing, this leads to cost-intense field trials in which localization methods are validated. As an alternative, publicly available UWB datasets exist, which however are also limited to only certain environmental conditions. In order to provide a more general evaluation basis, we present and discuss a procedure which allows the synthetic generation of UWB distance measurements with respect to theoretical error sources and parameterization based on a conducted measurement campaign. This contribution builds an understanding of commonly present errors for wireless distance measurements and their effects on ranging residual distributions in the distance domain. In addition, we discuss the influences of non-line-of-sight and multipath conditions. Based on this work, distance measurements with respect to the multipath richness of the propagation environment can be generated, helping to flexibly evaluate positioning methods for various emerging applications for telematics systems in the consumer, industrial, or transportation sector. These application fields are ranging from unmanned aerial vehicles, in-house parking systems, and intelligent freight wagons to connected aircraft cabins.

Real-time demonstration of 103.125-Gbps fiber-THz-fiber 2 × 2 MIMO transparent transmission at 360-430 GHz based on photonics.

In this Letter, we experimentally demonstrate the first real-time transparent fiber-THz-fiber 2 × 2 multiple-input multiple-output (MIMO) transmission system with a record line rate of 125.516 Gbps at 360-430 GHz based on photonic remote heterodyning, hybrid optoelectronic down-conversion, and commercial digital coherent modules. The 103.125-Gbps net data rate using dual-polarization quadrature phase-shift keying (DP-QPSK) modulation is successfully transmitted over two spans of 20-km standard single-mode fiber (SSMF) and 60-cm wireless distance under 15% soft-decision forward error correction (SD-FEC) for a pre-FEC bit error ratio (BER) threshold of 1.56 × 10-2 (post-FEC BER < 10-15). The optical signal to noise ratio (OSNR) margin and the stability of the transmission system are extensively investigated. To the best of our knowledge, this is the first time to realize >100-Gbps real-time transparent fiber-THz-fiber link transmission at beyond the 350-GHz band, making it a promising scheme to pave the way towards a practical seamless integration of a fiber-THz-fiber link to the future 6G mobile communication system.

Delivery of Polarization-Division-Multiplexing Wireless Millimeter-Wave Signal over 4.6-km at W-Band

We proposed and established a large-capacity, long-distance wireless millimeter-wave (mm-wave) signal delivery system at W-band based on photonics-aided mm-wave generation technology, polarization-division-multiplexing (PDM), and advanced devices. We demonstrated the wireless transmission of 10-Gbaud PDM-QPSK, PDM-16QAM, and PDM-PS-64QAM mm-wave signals in the W-band up to 4.6-km, respectively. The multiple-input multiple-output (MIMO) Volterra equalizer (VE) is employed during the Rx offline digital signal processing (DSP) to compensate for impairments and further improve the system transmission performance. Our demonstrated system can generate and deliver 10-Gbaud (110 Gb&#x002F;s) PDM-PS-64QAM (5.5 bits&#x002F;symbol&#x002F;polarization) mm-wave signal at 88.5-GHz over 4.6-km wireless distance with a bit-error-rate (BER) below the soft-decision forward error correction (SD-FEC) threshold of 2.4 &#x00D7; 10^&#x2212;2. Considering the SD-FEC threshold of 2.4&#x00D7;10^-2 with 20&#x0025; overhead, the maximum net rate of 91.6 Gb&#x002F;s in this system can be achieved. To the best of the authors&#x0027; knowledge, it&#x0027;s the first time to demonstrate single-carrier PDM-PS-64QAM (91.6 Gb&#x002F;s) wireless mm-wave signal delivery over 4.6 km at W-band.

Delivery of 40 Gbit/s W-band signal over 4600 m wireless distance employing advanced digital signal processing

We experimentally built a photonics-aided long-distance large-capacity millimeter-wave wireless transmission system and demonstrated a delivery of 40 Gbit/s W-band 16-ary quadrature amplitude modulation (QAM) signal over 4600 m wireless distance at 88.5 GHz. Advanced offline digital signal processing algorithms are proposed and employed for signal recovery, which makes the bit-error ratio under 2.4×10-2. To the best of our knowledge, this is the first field-trial demonstration of >4 km W-band 16QAM signal transmission, and the result achieves a record-breaking product of wireless transmission capacity and distance, i.e., 184 (Gbit/s)·km, for high-speed and long-distance W-band wireless communication.

A 5G/Sub-Terahertz Heterogeneous Communication Network

In this paper, a heterogeneous communication system capable of delivering 5G/sub-terahertz signal carriers over an arbitrary long fiber and separated transmission links is presented by employing direct detection, multiplexing techniques, and advanced digital signal processing. In this experiment, the 3.5 GHz and 28.5 GHz carrier frequencies, representing 5G links, deliver 4 Gb/s 16-QAM OFDM signals to separate user ends over a 1-meter wireless link distance. Later, the sub-terahertz wireless communications of 4 to 10 Gb/s QPSK and 8-QAM signals with varying carrier frequencies of 125-,175- and 225 GHz, over wireless distances (&#x003C; 80 cm) are presented and evaluated. The results indicate that by increasing optical power from 12dBm to 13dBm the bit error rate decreases 2 order of magnitudes. Eventually, with the assistance of artificial intelligence, a nonlinear equalizer (AI-NLE) prototype is introduced. The results indicate that the AI-NLE successfully decreases the number of errors in received data by one order of magnitude. The proposed heterogeneous system is compatible with radio-over-fiber technology, cost-effective, and easy to deploy, making it a promising candidate for indoor terahertz communication.

D-band signal generation and transmission without optical filter based on optical carrier suppression and single-sideband modulation.

We experimentally demonstrated a novel and simple scheme to generate D-band millimeter-wave (mm-wave) signal without optical filter based on optical carrier suppression (OCS) and single-sideband (SSB). One intensity modulator (IM) driven by radio frequency (RF) signal at 50 GHz is firstly employed to generate two tones with channel spacing of 2 x RF frequency based on OCS. Another subsequent in-phase/quadrature (I/Q) modulator driven by RF signal at 30 GHz is then applied to generate SSB signal by using independent sideband (ISB). No optical filter is needed so that the whole system can be simplified. After using a D-band photomixer for detection, we finally generated the vector mm-wave at 130 GHz. Based on the proposed system, 4-Gbaud/8-Gbaud quadrature phase shift keying (QPSK) information carried by the generated D-band mm-wave signals were transmitted over 22.5-km single model fiber (SMF) and 1-m wireless distance radio-over-fiber (ROF) link. Bit-error-ratio (BER) performances under hard/soft-decision forward-error-correction (FEC) threshold are shown respectively in cases of two different signals transmission rates.

A Wireless Fully-Passive Acquisition of Biopotentials.

Biopotential signals contain essential information for assessingthe functionality of organs and diagnosing diseases. We present a flexible sensor, capable of measuring biopotentials, in real time, in awireless and fully-passive manner. The flexible sensor collects and transmits biopotentials to an external reader without wire, battery, or harvesting/regulating element. The sensor is fabricated on a 90 μm-thick polyimide substrate with afootprint of 18×15×0.5mm3. The wireless fully-passive acquisition of biopotentials is enabled by the RF (Radio Frequency) microwave backscattering effect where the biopotentials are modulated by an array of varactors with incoming RF carrier that is backscattered to the external reader. The flexile sensor is verified and validated by emulated signal and electrocardiogram (ECG), electromyogram (EMG), and electrooculogram (EOG), respectively. A deep learning algorithm analyzes the signal quality of wirelessly acquired data, along with the data from commercially available wired sensor counterparts. Wired and wireless data shows <3% discrepancy in deep learning testing accuracy for ECG and EMG up to the wireless distance of 240mm. Wireless acquisition of EOG further demonstrates accurate tracking of horizontal eye movement with deep learning training and testing accuracy reaching up to 93.6% and 92.2%, respectively, indicating successful detection of biopotentials signal as low as 250 μVPP. These findings support that the real-time wireless fully-passive acquisition of on-body biopotentials is indeed feasible and may find various uses for future clinical research.