Cen Ling

Experimental Multipath-Cluster Characteristics of 28-GHz Propagation Channel

In this paper, a channel measurement campaign is introduced, which utilizes direction-scan-sounding to capture the spatial characteristics of 28-GHz wave propagation channels with 500-MHz sounding bandwidth in office environments. Both line-of-sight and non-line-of-sight scenarios were considered. Measurements were performed by fixing a transmit pyramidal horn antenna, and rotating another one in the receiver site at 10° steps in azimuth. The antenna outputs are viewed as array signals, and a space-alternating generalized expectation-maximization (SAGE) algorithm is applied to estimate delay and angular parameters of multipath components. Benefiting from high resolution achieved by using the SAGE and deembedding of antenna radiation pattern and system responses, more multipath clusters with less spreads in delay and azimuth are found per channel compared with existing works on 28-GHz propagation. The statistics of channel parameters extracted here constitute a preliminary stochastic multipath-cluster spatial channel model.

Empirical Stochastic Modeling of Multipath Polarizations in Indoor Propagation Scenarios

In this contribution, a stochastic modeling approach is proposed for characterizing the polarization status of multipath components (MPCs) in propagation channels. The 2×2 polarization matrix of each MPC is represented by the geometrical parameters of two ellipses, i.e., the ovality, tilt angle, and size of each ellipse, as well as the rotating direction of electric field intensity along the ellipse. The statistics of these parameters including correlation behaviors among them extracted from measurement data constitute the stochastic polarization model for the propagation scenario of interest. Analytical expressions are presented for the transformation from the ellipse parameters to the 2×2 polarization matrix, and vice versa. Comparing with conventional polarization models addressing merely the cross-polarization ratios, the new model provides a more complete description for the per-path polarizations in terms of the power imbalance, tilting, and polarization spread. Furthermore, based on multiple-input multiple-output channel measurement data collected with 100-MHz bandwidth and at the center frequency of 5.25 GHz, stochastic polarization models of the proposed structure are extracted for five indoor scenarios. These models are complementary to the existing geometry-based stochastic channel models for generating realistic polarization matrices for MPCs.

Attitude Estimation for In-Service Base Station Antenna Using Downlink Channel Fading Statistics

A maximum-likelihood-estimation method is proposed for extracting the attitude of a sectoring base station (BS) antenna by using the received signal strengths observed by multiple user equipments (UEs) in this contribution. This method calculates the likelihood function of the antenna attitude derived by taking into account the multiscale fading statistics, that is, path loss, shadowing, and multipath fading. Depending on whether a calibration result of these fading statistics is available or not, the proposed method can be utilized in either calibration-based estimation (CBE) or calibration-free estimation (CFE) approaches. The performance of both methods is evaluated by Monte-Carlo simulations and real experiments. The results obtained demonstrate that the estimation accuracy of both CBE and CFE approaches increases when the percentage of UEs in the line-of-sight (LoS) condition among all available UEs increases and, moreover, the total number of UEs has no significant impact on the estimation accuracy. Furthermore, the CFE exhibits more robust performance than the CBE particularly in the case where the calibration results involve uncertainties.

Optimal power allocation and relay selection in spectrum sharing cooperative networks

Cooperative communication with spectrum sharing has been proved as an efficient way to reduce energy consumption. In this work, we address the problem of the best relay selection and optimal power allocation. In this system model, secondary user (SU) acts as relay to assist in the transmission of primary user (PU) with the reward to transmit its own information. On one hand, the SU is selected using the metric of the energy efficiency by considering the outage capacity and energy consumption in a decoding and forward (DF) relaying. On the other hand, the optimal power allocation is obtained from solving a convex optimization problem aiming at minimizing network energy consumption with guaranteed quality of service (QoS). It is observed that cooperative communication performs better than non-cooperation transmission in saving network consumption. It is also noted that more candidates of the SUs lead to lower power consumption of the network and better energy efficiency.

A preliminary study on anisotropic characteristics of propagation channels for Tx-Rx polarizations

In this contribution, both theoretical studies and measurement results are reported for investigating the anisotropic property of propagation channels with respect to (w.r.t.) the (linear) polarizations of the transmitter (Tx) and receiver (Rx) antennas. Under the assumption that the channel impulse response (CIR) is polarization isotropic, analytical expressions are derived for the K-factor and delay spread as functions of Tx-Rx polarizations, and furthermore, our deduction also shows that the rank of the signal subspace spanned by a multi-polarized narrowband channel is upper-bounded. Based on the measurements conducted in indoor scenarios, empirical CIRs measured with 12 Tx- and 2 Rx-polarization directions are applied to investigating the channel polarization anisotropy. It can be observed that the measured channels exhibit properties inconsistent with the theoretical results deduced under the polarization-isotropy assumption, implying that the realistic indoor propagation channels can be anisotropic w.r.t. the Tx-Rx polarizations.

Experimental Characterization and Multipath Cluster Modeling for 13–17 GHz Indoor Propagation Channels

The traffic explosion of mobile communications increasingly requires effective and realistic fifth-generation (5G) channel models. Recently, we have conducted measurement campaigns in lecture hall and laboratory scenarios using steerable beam antennas for characterizing 13–17 GHz channels. The Space-Alternating Generalized Expectation–maximization (SAGE) algorithm was applied to estimate the multipath components (MPCs) in delay and angle of arrival domains. These estimated MPCs were further grouped into clusters via the threshold-based approach. It is noticeable that the observed channel characteristics obtained using the SAGE algorithm are less antenna-specific than those using the raw received signals. The scatterer locations identified from the MPCs show excellent agreement with the physical objects in the environment. Moreover, we found that the configurations of antenna-half-power-beamwidth and rotation step size exert great influence on the channel characteristics. These results provide important references for the existing 5G channel sounding and data processing, which naturally leads to fidelity of future channel models.

Comparison of characteristics of 13–17 GHz propagation channels in indoor environments with different measurement configurations

In this contribution, a channel measurement campaign was carried out which employed directional scanning approach to capture the temporal and spatial characteristics of higher-frequency-band (HFB) wave propagation channel ranging from 13 to 17 GHz in lecture hall environments. The omni-directional antenna was equipped in the transmitter (Tx), and a horn antenna of certain half-power-beamwidth (HPBW) installed in the receiver (Rx) side was rotated during the channel measurements. The Space-Alternating Generalized Expectation-maximization (SAGE) algorithm was utilized to extract the multipath components (MPCs) based on the received signals. Furthermore, a threshold-based clustering approach was adopted to group the MPCs in delay, and angular domains. Moreover, composite and cluster-level channel behaviors and statistics were investigated based on the outputs of the SAGE algorithm and compared among the results for measurements conducted with various configurations. It is noted that the ratio of the antenna HPBW to the rotation step size, denoted as γ exerts significant effects on the antenna angular resolution, and thus influences the estimation performance. Additionally, it is observed that with the growth of γ, delay spread, AoA spread, cluster delay spread, cluster EoA spread and cluster path-loss exponent versus transmission distance have a tendency to decline.