Zhimeng Zhong

Channel modeling based on random propagation graphs for high speed railway scenarios

In this paper, a channel modeling method based on random-propagation-graph is elaborated, validated, and applied to characterizing time-variant channels observed in typical environments for high-speed railway wireless communications. The advantage of the proposed method is that the frequency-tempo-spatial channel coefficients, as well as the multi-dimensional channel impulse responses in delay, Doppler frequency, direction of arrival (i.e. azimuth and elevation of arrival) and direction of departure are calculated analytically for specific environments. The validation of the proposed method is performed by comparing the statistics of two large-scale parameters obtained with those described in the well-established standards. Finally, stochastic geometry-based models in the same format as the well-known spatial channel model enhanced (SCME) are generated by using the proposed method for the high-speed scenarios in the rural, urban, and suburban environments.

Channel Measurement and Packet-Level Modeling for V2I Spatial Multiplexing Uplinks Using Massive MIMO

Massive multiple-input multiple-output (MIMO) is a key technology in fifth-generation (5G) networks. By using a large number of antenna elements placed in a 2-D array, an evolved Node B (eNB) can form multiple vertical beams in the elevation domain and adaptively track moving vehicles. Thus, the throughput and spatial multiplexing efficiency in vehicle-to-infrastructure (V2I) access can be significantly increased. However, multipath spatial propagation in wireless channels results in the angular spread of the power arrival profile, which causes intersector interference in massive-MIMO beamforming and becomes a limiting factor for the system capacity. In this paper, we investigate the channel propagation characteristics and the intervehicle interference in the elevation-domain spatial multiplexing for V2I mobile access and develop a packet-level channel model that can be used for system design and network protocol simulations. First, a measurement campaign for the urban macrocell street uplink channels was performed using a 3-D MIMO channel sounder, and the elevation power spectra (EPSs) on the eNB side were measured. Then, the intersector interference in the vertical beamforming is evaluated based on the antenna array pattern and channel EPS. Finally, a packet-level channel model in the form of a finite-state Markov chain (FSMC) is proposed for the V2I elevation multiplexing uplinks. The model describes the received signal-to-interference ratio (SIR) variation when a vehicle is moving toward an eNB. The steady-state distribution of the FSMC is analytically derived and verified by simulations. Based on the stochastic process of the SIR, the concepts of “large/small-scale multiplexing fading” are proposed. The field measurement results in this work have revealed the spatial power arrival profiles of the V2I street channels that are critical for the MIMO system design, and the proposed packet-level channel model provides an enabling tool for the analysis and simulation of the V2I elevation multiplexing links in the 5G networks.

System-Level Channel Modeling Based on Active Measurements from a Public 3G/UMTS Network

In this contribution, two measurement campaigns are reported which were conducted in urban areas of Shanghai for characterizing the radio channels in an operating Universal Mobile Telecommunications System (UMTS). The signals on the common pilot channels transmitted by multiple NodeBs (NBs) are used to calculate the channel impulse responses (CIRs). A Space-Alternating Generalized Expectation-maximization (SAGE) algorithm is applied to extracting the delays, Doppler frequencies and complex attenuations of multiple specular path components from the CIRs. Based on the delay spreads calculated, the channels are categorized into three types, i.e. the single-path, two-path and multi-path. Based on the measurements at more than 1400 locations for 74 NBs, the statistics of system-level channel characteristics, such as the percentage of channels per NB belonging to different categories and the length of the distance within which the same channel category is observed are extracted.

The correlation properties of subchannel fading for non-continuous carrier aggregation based on indoor ultra-wideband measurement

The new multichannel/multicarrier technologies have drawn great attention recently to support high data rate in mobile multiple-access environments, such as the carrier aggregation (CA) as a part of 4G LTE-Advanced enhancement. On the way to the development of multicarrier technologies, there is a considerable need to understand and utilize the correlation properties of distinct subchannels, which, however, has not been reported in the literature. Based on the extensive indoor ultra-wideband (UWB) channel measurement, this paper develops a new approach to analyze the correlation of the large and small-scale fading of arbitrarily separated subchannels. The approach avoids the high complexity and cost of the conventionally probing the multiple subchannels simultaneously using channel sounders which would be too complicated to implement. We first propose a modified CLEAN algorithm to reliably extract channel impulse responses (CIRs) from the measured pulse response waveforms with substantially varying noise floor. Then the cross-correlation of the fading of two distinct subchannels, the autocorrelation of the fading of a single subchannel and the correlation of the multipath profile over a small area are analyzed. The study has revealed how significantly the channel response would change when the receiver travels from room to room or just over a distance of dozen of wavelength, and how two separated subchannels are correlated. In our view, the acquired new insights on subchannel correlations could provide guidelines for efficient designs and performance predictions of multicarrier communication systems.

A study on spatial-temporal dynamics properties of indoor wireless channels

The short-range, wideband wireless networking in office or residential buildings has been an emerging technology to support high quality multimedia services. Understanding the spatial-temporal dynamic properties of indoor wireless channels is essential to design the adaptive transmission protocols for optimizing the system performance. In this paper, we extend the propagation graph in [1] to study the channel dynamics of two scenarios. First, human Body Shadowing Effect (BSE) is very common in the indoor environments and can dramatically decrease the received signal energy when the significant propagation paths are blocked. We build an analytical model to estimate the power attenuation by the BSE. Second, we consider the movement of the mobile terminal and calculate the Doppler frequency shift and spectrum spread using the propagation graph. The paper provides new analytical methodologies to study the channel dynamics. Compared to the traditional ray tracing, the proposed method has much lower computational complexity and thus can be used for fast on-line estimation of the channel variation.

Multipath DoA Estimation by Rotational Invariance on Array Channel Impulse Response

To characterize multipath spatial propagations in three-dimensional space is critical in wireless channel measurements and modeling. Due to the large number of paths and the correlation among multipath signals, the direction-of-arrival (DoA) estimation for propagation paths is a challenging issue. In this letter, we propose a new multipath DoA estimation scheme, named Multipath DoA Estimation by Rotational Invariance on Array Impulse Response (MERIA), which utilizes the rotational invariance of array channel impulse response matrix and estimates the DoAs of arriving paths individually and sequentially. Simulations and field measurement experiments have demonstrated that MERIA can estimate incident angles of a large number of paths and suppress multipath interference effectively. Therefore, by using MERIA in field channel measurements, the requirements on the antenna array size and the hardware complexity of channel sounders can be reduced significantly.

Empirical modeling of cross-correlation for spatial-polarimetric channels in indoor scenarios

In this paper, propagation channel measurement data obtained by using the wide-band multiple-input-multiple-output (MIMO) channel sounder - PROPsound - is applied to analyzing the cross-correlation behavior of spatial-polarimetric (SP) channels in indoor environments. Four antennas are selected from the transmitter (Tx) array and from the receiver (Rx) array to form a 2×2 spatial MIMO channel, with each spatial element consisting of co-located ±45°-polarized antennas. The characteristics of the resultant 16 × 16 narrow-band SP Channel Correlation Matrix (CCM) are studied for five indoor environments of different types. Results show that the Kronecker model proposed in the 3rd Generation Partnership Project (3GPP) TS36.101, which describes the SP CCM as the Kronecker product of the separate Tx and Rx spatial CCMs, and the 4×4 polarimetric CCM, is inapplicable in indoor scenarios. As an alternative, we propose to consider the cross-correlation coefficient of SP channels as a random variable, and apply its empirical statistics for stochastic modeling. Results also show that the empirical distribution of the off-diagonal elements of SP CCM is distinctive with respect to the types of environments.

Dual-polarized channel characterization based on measurements in in-service UMTS networks

In this contribution, the measurements conducted in an in-service Universal Mobile Telecommunication System (UMTS) network in the Minghang campus of Shanghai Jiaotong University, China, are reported. The outdoor measurement data collected in 205 locations in the coverage of a NodeB (NB) is applied to investigate the narrowband characteristics of ±45°-polarized 2×2 channels. The results show that under the empirical configurations, the cross-correlation of differently polarized channels at the user equipment (UE) side is stronger than at the NB side; the distributions of largest and second largest eigenvalues of the 4 × 4 polarized channel covariance matrix are well-fitted by lognormal distributions, and for the other eigenvalues Beta distributions are more appropriate. Furthermore, the statistics of the decay constant of the eigenvalues with respect to the eigenvalue indices is presented. Finally, the dependence of the capacity of a polarized channel on the condition number of the polarization correlation matrix, and inter-dependence between the condition number and the channel cross-polarization discrimination (XPD) are investigated.

MIMO Channel Measurement and Characterization for 26GHz Wave in Outdoor Scenarios

In this paper, by using a multiple-input multiple-output (MIMO) antenna array, a channel measurement campaign in outdoor environments is introduced. The measurement campaign captures the spatial characteristics of centimeter wave (cm-wave) propagation at the center frequency of 26 GHz . By using the parametric approach of the Space-Alternating Generalized Expectation-maximization (SAGE) algorithm, the channel characteristics in the delay and spatial domains are extracted, and compared with the channel model below 6 GHz. Our analysis shows that the channel dispersions in the delay and directional domains are smaller at the 26 GHz. Furthermore, single-user (SU)-MIMO and multi-user (MU)-MIMO channel matrix properties are investigated, and show that the MU-MIMO channel has good orthogonal property. It implies that MU-MIMO will be one promising MIMO technique in cm-wave band.

Measurement and Analytical Study of the Correlation Properties of Subchannel Fading for Noncontiguous Carrier Aggregation

The new multichannel/multicarrier technologies can potentially support much higher data rates in mobile multiple-access environments, such as carrier aggregation (CA) defined in the fourth-generation Long-Term Evolution Advanced enhancement. The correlation properties of noncontiguous subchannels are critical for the performance of CA, including cell coverage, frequency diversity, and channel state estimation. This paper has studied the correlation of the large-scale fading (LSF) and small-scale fading (SSF) of arbitrarily separated subchannels by realistic channel measurement and analytical modeling. We first obtain the subchannel correlation from the ultrawideband (UWB) channel measurement. This new approach avoids probing multiple subchannels simultaneously with channel sounders, which would be prohibitively complicated. The cross correlation of two distinct subchannels and the autocorrelation of a single subchannel are evaluated. Second, a new propagation model for the Nakagami-m fading in a multipath environment is proposed. The frequency-domain level crossing rate (FD-LCR) is defined and derived based on the propagation model. Then, a Markov chain for the frequency fading of the wideband channel is established, which can generate the correlated gain/power of subchannels in a wide bandwidth. Therefore, this model can be used as a fast simulator of CA over correlated subchannels. Finally, the cross correlation coefficients (CCCs) between two Nakagami-m fading subchannels obtained from the measurement and the proposed Markov model are compared with the analytical results in the literature. This paper provides important insights into the fading correlation of the multicarrier channels and can be applied to the design and simulation of indoor/outdoor multicarrier communications.