Showing papers by "Chong Han published in 2017"

Three-Dimensional End-to-End Modeling and Analysis for Graphene-Enabled Terahertz Band Communications

Abstract: Terahertz (0.1–10 THz) band communication is envisioned as a key technology to satisfy the increasing demand for ultra-high-speed wireless links. In this paper, a 3-D end-to-end model in the THz band is developed that includes the graphene-based reflectarray antenna response and the 3-D multipath propagation phenomena. In particular, the architecture of a graphene-based reflectarray antenna is investigated, and the 3-D radiation pattern is modeled. Moreover, a 3-D THz channel model based on ray tracing techniques is developed as a superposition of the line-of-sight (LoS), reflected, and scattered paths. By using the developed end-to-end model, an in-depth analysis on the 3-D channel characteristics is carried out. Specifically, the gain at the main beam of the graphene-based reflectarray antenna is 18 dB, and the 3-dB beamwidths in the elevation and the azimuth planes are $7^\circ$ and $10^\circ$ , respectively. The use of the reflectarray leads to a decrease of the delay spread from 1.23 to 0.099 ns, which suggests that the resulting coherence bandwidth reaches 2 GHz. Moreover, the root mean square (rms) angular spread in the elevation plane is less than $0.12^\circ$ , which is one tenth of that without beamforming. Furthermore, the wideband channel capacity at THz frequencies is characterized, which can be enhanced with a larger transmit power, a lower operating frequency, a larger bandwidth, and a higher beamforming gain. Finally, the beamforming gain enabled by the reflectarray antenna is compromised at the cost of the strict beam alignment, and the deviation needs to be smaller than $11^\circ$ . The provided analysis and the channel physical parameters lay out the foundation and are particularly useful for realizing reliable and efficient ultra-high-speed wireless communications in the THz band.

Interference and Coverage Analysis for Terahertz Band Communication in Nanonetworks

Abstract: Interference is a critical factor affecting the per- formance of nanonetworks in the terahertz (THz) band. In this paper, on the basis of THz channel model, the interferences from surrounding omnidirectional nanosensors (NSs) and beamform- ing Base Stations (BSs) are derived in closed forms by using stochastic geometry methods respectively. Furthermore, the cor- responding Signal-to-Interference- plus-Noise-Ratio (SINR) and the coverage probabilities are investigated based on the proposed interference model. Simulation results, observed from the spectral windows at 1.0 THz, 4.5 THz and 9.1 THz, demonstrate that high density of BSs, beamforming antenna with small beam- width and low density of NSs are recommended to mitigate the interference and improve the coverage performance. Moreover, low frequency in THz band with low absorption coefficient is advocated to guarantee the correct reception with enough high received signal strength.

Timing Acquisition and Error Analysis for Pulse-Based Terahertz Band Wireless Systems

Abstract: Terahertz (THz) band communication is envisioned as a key technology to satisfy the increasing demand for ultrabroadband wireless systems, thanks to its ultrabroad bandwidth. Tailored for the unique properties of pulse-based communications in the THz band, two timing acquisition algorithms are proposed and analyzed thoroughly in this paper. First, a low-sampling-rate (LSR) synchronization algorithm is proposed, by extending the theory of sampling signals with finite rate of innovation in the communication context and exploiting the properties of the annihilating filter. The simulation results show that the timing accuracy at an order of ten picoseconds is achievable. In particular, the LSR algorithm has high performance with uniform sampling at $1/20$ of the Nyquist rate when the signal-to-noise ratio (SNR) is high (i.e., greater than 18 dB). Complementary to this, a maximum likelihood (ML) approach for timing acquisition is developed, which searches for the timing offsets by adopting a two-step acquisition procedure based on the ML criterion. The simulation results show that the ML-based algorithm is well suitable in the low SNR case with a half-reduced search space. For further evaluation, the error performance and the resulting bit-error-rate sensitivity to the timing errors in the LSR and the ML algorithms are both analytically and numerically studied. This paper provides very different and promising angles to efficiently and reliably solve the timing acquisition problem for pulse-based THz band wireless systems.

A Three-Dimensional Time-Varying Channel Model for 5G Indoor Dual-Mobility Channels

Abstract: This paper presents a time-varying channel model in three- dimensional environments for the 5G wireless system. Using the continuous-time Markov chain, the proposed model captures the statistical movement of the transceiver, the transition between line-of-sight and non-line-of-sight propagation scenarios, and the dynamic variation of propagation parameters. Moreover, a novel frequency- dependent factor that describes the dynamic path behavior is described in this model. According to the simulation results based on ray-tracing techniques and field measurements from the literature, the proposed time- varying channel model is validated at 5.2, 10, and 60 GHz. Furthermore, under realistic 5G device-to-device communication scenario, the simulation results and time- varying channel characteristics are highlighted, including the number of paths, path gain, delay spread, delay variation, Rician K-factor, and coherence bandwidth.

MRA-MAC: A Multi-Radio Assisted Medium Access Control in Terahertz Communication Networks

Abstract: Terahertz (THz) communication is envisioned as one of the key technologies to satisfy the increasing demand for higher-speed wireless communication networks. Thanks to the very small wavelengths at THz frequencies, the very large antenna array can be equipped to enable beamforming, which can effectively overcome the very high path loss and improve the communication distance. However, directional transmissions, as well as the peculiarities of the THz channel and physical layer, increase the difficulties of medium access control (MAC) design. In this paper, a multi-radio assisted (MRA-MAC) protocol in the distributed THz network is proposed and analyzed. The key idea is to enable 2.4/5 GHz omni-directional radio for control signaling and THz beamforming for data transmissions. A flowchart of the protocol and detailed operations are presented. Based on the models of THz pulse waveform and the THz channel with beamforming, the delay, the outage probability, and the network throughput are analytically investigated, supported by extensive simulation and numerical evaluations.

A memory-assisted MAC protocol with angular-division-multiplexing in terahertz networks

Abstract: Terahertz band communication is envisioned as a key technology to satisfy the increasing demand for ultra-highspeed wireless links. In this paper, a memory-assisted medium access control (MAC) protocol with angular-division-multiplexing (ADM) is proposed for the service discovery and communications in the THz network. In particular, the efficiency balance is achieved by equipping the nodes with (i) the omni-directional antennas at the service discovery phase, and (ii) directional antennas for message transmissions. Moreover, the memory is leveraged in the ADM scheme to assist the access point (AP) to skip the unregistered angular slots to improve the network performance. Based on the proposed MAC protocol, the analytical models of the interference, SINR, outage probability, throughput and the delay in the THz network are derived respectively. According to the simulation and numerical analysis, the results show that our proposed MAC protocol can effectively improve the throughput by over 15% and substantially reduce the delay, in comparison with the ADM scheme without the memory guidance.