Traditional Radio Frequency Communication Research Articles

High-speed data transmission based on mode-locked optical frequency comb

<sec>With the rapid development of emerging technologies such as multimedia services, live broadcasting, video conferencing, and high-definition television, traditional radio frequency communication is unable to meet people 's growing demand for communication capacity and transmission rate. In recent years, optical communication has received extensive attention from the industrial and scientific communities due to its advantages of large bandwidth, high speed, low power consumption, light weight, and strong anti-interference ability. As an emerging light source, the optical frequency comb (OFC) has a wide spectral range, multi-wavelength, high stability, and good phase coherence, providing a new idea for studying microwave signals with simple system structure, strong tunability and high frequency stability. At the same time, the multi-optical mode characteristics of OFC are compatible with the current communication system based on wavelength division multiplexing technology. Hundreds of laser arrays in a traditional communication system can be replaced by only one laser, which greatly reduces the power consumption of the system.</sec><sec>Combining the above advantages, in this paper, a large-scale parallel high-speed optical communication system based on mode-locked OFC is proposed. The linewidth of the OFC locked to the rubidium atomic clock can reach 1 Hz, which is sufficient to support the transmission of high-order modulation signals. The electro-optic modulators are used to adjust the amplitude and phase of each optical mode of the mode-locked OFC and self-coherently map to the RF domain. The high-speed high-order modulation signal with coded information is obtained by frequency screening through a narrow-band filter. The communication capability of the microwave photonic modulation signal in the 16 quadrature amplitude modulation (QAM) format is verified by simulation. The 16QAM communication with the rate of 2, 6, and 14 Gbit/s is realized by using the photonic microwave signal on the 100 m space optical link, and the bit error rate (BER) is less than 10<sup>–6</sup>. The proposed large-scale parallel optical communication system based on mode-locked OFC can achieve high-speed information transmission with a compact system structure, which is suitable for inter-satellite communication, emergency communication, military communication and other fields.</sec>

A Comprehensive Survey on MIMO Visible Light Communication: Current Research, Machine Learning and Future Trends

Visible light communication (VLC) has contributed new unused spectrum in addition to the traditional radio frequency communication and can play a significant role in wireless communication. The adaptation of VLC technology enhances wireless connectivity both in indoor and outdoor environments. Multiple-input multiple-output (MIMO) communication has been an efficient technique for increasing wireless communications system capacity and performance. With the advantages of MIMO techniques, VLC can achieve an additional degree of freedom. In this paper, we systematically perform a survey of the existing work based on MIMO VLC. We categorize the types of different MIMO techniques, and a brief description is given. Different problem-solving approaches are given in the subsequent sections. In addition, machine learning approaches are also discussed in sufficient detail. Finally, we identify the future study direction for MIMO-based communication in VLC.

Model and channel characteristics of near field inter-body coupling communication

Near field inter-body coupling communication (NF-IBCC) is a short-distance wireless communication centered on the human body. It uses the electric field within close proximity of the human body to establish a channel, when electrodes as a radiation source keep in contact with the human body. NF-IBCC can achieve much higher data security and lower power consumption than traditional radio frequency communications, which is a potential communication technology applied to the internet of body (IoB). However, its channel model is not totally clear so far. In this letter, we propose a channel model. Then, the accuracy of the proposed model is verified. Finally, the effect of distances, postures, angles, and heights on the channel characteristics is analyzed and discussed. Our work lays a theoretical foundation for the system design of NF-IBCC and will promote its application to IoB.

Optimizing Networked Flying Platform Deployment and Access Point Association in FSO-Based Fronthaul Networks

Applying interconnected networked flying platforms (NFPs) as fronthauling is a promising solution to flexibly reconfigure the fronthaul network upon requests. Meanwhile, free space optical (FSO) communications has been demonstrated to achieve a higher data rate, longer transmission range, and less interference between two endpoints as compared to traditional radio frequency communications. This letter applies FSO communications in NFP relay networks, which can significantly enhance the network throughput. We investigate and formulate the joint NFP deployment and access point (AP) association problem in the context of an FSO-based NFP relay network, and design an efficient algorithm to solve it. Simulation results demonstrate the performance of the proposed algorithm.

TDMA Scheduling in Spatially Extended LiFi Networks

Optical Wireless Communication (OWC) has attracted significant attention from academia and industry as a promising solution to complement traditional radio frequency communication. In Light-Fidelity (LiFi) networks, to enable soft handover and provide robustness against blockage of the line-of-sight links, LiFi receivers are designed to see multiple LiFi transmitters within their field-of-view. To trade-off spatial multiplexing with harmful interference, a proper user scheduling technique is required. In this work, we first derive practical and exact expressions for determining which simultaneous transmissions will create harmful interference and should be scheduled in multiple time-slots. Afterwards, relying on this expression, we propose our semi-distributed Spatially Extended TDMA algorithm, which is based on a time division contention–free access scheme. In contrast to more complex algorithms in the state-of-the-art, our scheduling protocol can reduce the computation time while also achieving a superior minimal user throughput. For a scenario with 9 transmitters and up to 15 receivers, our protocol is at least a factor 120 faster and can improve the minimal user throughput up to 91%, making it suitable for practical roll-out as a promising solution for very dense LiFi networks.

Cooperative Hybrid VLC-RF Systems With Spatially Random Terminals

In this paper, a cooperative hybrid visible light communication (VLC)-radio frequency (RF) relay system, which includes a transmitter (S) with a cluster of light emitting diodes (LED) lamps, a relay (R), and a destination (D), is taken into consideration. Moreover, decode-forward (DF) and amplify-forward (AF) schemes are considered at R to aid the data transmissions between S and D. Specially, R is randomly located in the coverage of the LED lamps, D is randomly distributed out of the coverage of the LED lamps. Then, VLC is employed for S-R link, and a traditional RF communication technology is adopted over the R-D link. Considering Nakagami- $m$ fading over the R-D link, and the randomness of the locations of R and D, the statistical characteristics of the received signal-to-noise ratio at D under AF scheme, and the ones at R and D under the DF scheme are characterized, respectively. Subsequently, approximated analytical and asymptotic expressions for the outage probability of the considered system are derived, as well as the approximated expression for the average symbol error rate of M-ary quadrature amplitude modulation scheme under the DF scheme. Finally, simulation and numerical analysis are conducted to verify the correctness of our proposed models.

On the human body communications: wake-up receiver design and channel characterization

By modulating the electric field induced to a human body, it is possible to transfer data wirelessly using the body as a transmission medium. This method is referred to as human body communication (HBC), which has multiple advantages in comparison with the traditional radio frequency (RF) communication. First, it alleviates the traffic load from the radio channels, which are becoming more and more congested, as the number of connected wireless devices increases rapidly. Second, HBC can potentially provide higher security than traditional RF communication since the electric field stays in the vicinity of a human body, which makes eavesdropping more challenging. Third, the attenuation in the HBC frequency band is lower than in bands used by the other radio technologies for wireless body area networks. To improve energy efficiency in HBC, one approach is to utilize a wake-up receiver (WUR). The WUR is continuously listening for a pre-defined wake-up signal, which activates the other electric circuitry (e.g., sensing, processing, and communication). The use of WURs can significantly reduce the energy consumption and increase the lifetime of the sensing applications. In this work, we propose a superregenerative WUR solution which employs self-quenching and loose synchronization method and operating at sufficiently low (1.25 kbps) data rate in order to obtain high sensitivity while keeping the energy consumption low. This enables to achieve sensitivity of −97 dBm for 10−3 bit error rate while consuming only 40 μW. The details of the design and the performance evaluation results of the proposed solution are in the paper. Also, the paper reports the results of the practical measurements characterizing the impact of the electrode location on the path loss in an HBC channel. The presented results show that the proposed system can potentially enable communication between two any points on the body with low transmit power.