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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.

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.

In this contribution, a high-resolution parameter estimation algorithm is derived based on the Space-Alternating Generalized Expectation-maximization (SAGE) principle for extracting multipath parameters from the output of sliding correlator (SC). The SC allows calculating channel impulse responses with a sampling rate less than that required by Nyquist criterion, and hence is widely used in real-time wideband (e.g., >500 MHz) channel sounding for the fifth generation wireless communication scenarios. However, since the sounding signal needs to be sent repetitively, the SC-based solution is unacceptable for time-variant channel measurements. The algorithm proposed here estimates multipath parameters by using a parametric model of both low- and high-frequency components of the SC’s output. The latter was considered as distortions and discarded in the conventional SC-based channel sounding. The new algorithm allows estimating path parameters with less repetitions of transmitting the sounding signal and still exhibits higher estimation accuracy than the conventional method. Simulations are conducted and illustrate the root mean square estimation errors and the resolution capability of the proposed algorithm with respect to the bandwidth and the length of the SC’s output. These studies pave the way for measuring time-variant wideband propagation channels using SC-based solutions.

Cooperative communication with spectrum sharing has been proved to be an efficient way to reduce energy consumption. In this work, an optimal power allocation algorithm is proposed for mobile cooperative beamforming networks, where several secondary users (SUs) collaboratively act as relay nodes to assist the transmission of a primary user (PU) in reward of transmitting their own information. The optimal power allocation scheme is obtained by solving a convex optimization problem aiming at minimizing network energy consumption with guaranteed quality of service (QoS) for both PU and SUs. Simulation results show that with the consideration of overheads, circuit power, and energy costs for message sharing, a cooperative beamforming network augmented with our proposed power allocation algorithm performs better in scenarios of more SUs in terms of higher energy efficiency and less power consumption per unit throughput. Additionally, the proposed scheme outperforms the conventional best-relay selection approach in the aspects of power consumption per unit throughput, energy efficiency, and network power consumption. Furthermore, simulations also demonstrate that the derived cooperative beamforming algorithm exhibits superior performance in energy saving than conventional methods in high-speed scenarios.

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.

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.

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.

In this contribution, a maximum-likelihood-based approach is proposed for estimating the attitudes of sectoring base station (BS) antennas based on the power of the received signals observed by multiple user equipments (UEs) in a cellular network. The proposed method calculates the likelihood of the antenna attitude by taking into account both the large-scale fading statistics, i.e. path loss, shadowing, and the small-scale fading attributed to multi-path propagation. The performance of the method is evaluated by simulations in both urban and rural scenarios, where a random-propagation-graph method is applied to generating realistic channel impulse responses by using directional antenna patterns. Results show that by using the proposed method, accurate estimates of the antenna attitude can be obtained when the observations from more UEs are available and the line-of-sight (LoS) condition dominates the channels between the BS and the UEs.