Study on 3GPP Rural Macrocell Path Loss Models for Millimeter Wave Wireless Communications

Little research has been done to reliably model millimeter wave (mmWave) path loss in rural macrocell settings, yet, models have been hastily adopted without substantial empirical evidence. This paper studies past rural macrocell (RMa) path loss models and exposes concerns with the current 3rd Generation Partnership Project (3GPP) TR 38.900 (Release 14) RMa path loss models adopted from the International Telecommunications Union - Radiocommunications (ITU-R) Sector. This paper shows how the 3GPP RMa large-scale path loss models were derived for frequencies below 6 GHz, yet they are being asserted for use up to 30 GHz, even though there has not been sufficient work or published data to support their validity at frequencies above 6 GHz or in the mmWave bands. We present the background of the 3GPP RMa path loss models and their use of odd correction factors not suitable for rural scenarios, and show that the multi-frequency close-in free space reference distance (CI) path loss model is more accurate and reliable than current 3GPP and ITU-R RMa models. Using field data and simulations, we introduce a new close-in free space reference distance with height dependent path loss exponent model (CIH), that predicts rural macrocell path loss using an effective path loss exponent that is a function of base station antenna height. This work shows the CI and CIH models can be used from 500 MHz to 100 GHz for rural mmWave coverage and interference analysis, without any discontinuity at 6 GHz as exists in today's 3GPP and ITU-R RMa models.Comment: To be published in 2017 IEEE International Conference on Communications (ICC), Paris, France, May 201

Modeling and characterization of urban radio channels for mobile communications

Results of this thesis contribute in modeling and characterization of radio channels for future mobile communications. The results are presented mainly in three parts: a) modeling of propagation mechanisms, b) methodology of developing a propagation model, c) characterization of urban radio channel. One of the main propagation physical phenomena that have an important role in diverting signals to non line of sight scenarios is the diffraction process. This thesis proposes diffraction coefficients that have better agreement with finite difference time domain solution and rigorous diffraction theory than the coefficient commonly used in propagation predictions for mobile communications. The importance of diffuse scattering has also been investigated and showed that this physical process may have a key role in urban propagation, with a particular impact on the delay spread and angular spread of the signal at the receiver. This thesis proposes wideband propagation models for main and perpendicular streets of urban street grids. The propagation models are ray-based and are given in explicit mathematical expressions. Each ray is characterized in terms of its amplitude, delay, and angle of arrival, angle of departure for vertical and horizontal polarizations. Each of these characteristics is given in a closed mathematical form. Having wideband propagation model in explicit expression makes its implementation easy and computation fast. Secondary source modeling approach for perpendicular streets has also been introduced in this thesis. The last part of the thesis deals with characterization of urban radio channels for extracting parameters that help in successful design of mobile communication systems. Knowledge of channel characteristics enables reaching optimum trade off between system performance and complexity. This thesis analyzes measurement results at 2 GHz to extract channel parameters in terms of Rake finger characteristics in order to get information that helps to optimize Rake receiver design for enhanced-IMT2000 systems. Finger life distance has also been investigated for both micro- and small cell scenarios. This part of the thesis also presents orthogonality factor of radio channel for W-CDMA downlink at different bandwidths. Characterization of dispersion metrics in delay and angular domains for microcellular channels is also presented at different base station antenna heights. A measure of (dis-) similarity between multipath components in terms of separation distance in delay and angular domains is introduced by the concept of distance function, which is a step toward in development of algorithm extraction and analysis multipath clustering. In summary, the significant contributions of the thesis are in three parts. 1) Development of new diffraction coefficients and corrections of limitations of existing one for accurate propagation predictions for mobile communications. 2) Development of wideband propagation models for urban street grid. The novelty of the model is the development in explicit mathematical expressions. The developed models can be used to study propagation problem in microcellular urban street grids. 3) Presenting channel parameters that will help in the design of future mobile communication systems (enhanced-IMT2000), like number of active fingers, finger life distance, and orthogonality factors for different bandwidths. In addition, a technique based on multipath separation distance is proposed as a step toward in development of algorithms for extraction and analysis of multipath clusters.reviewe

Multipath propagation model for line-of-sight street microcells in urban area

This paper proposes a multipath propagation model for line-of-sight (LOS) street microcells with building roof base sites (BS) in urban areas, Multipath propagation characteristics are of great importance in evaluating the performance of digital systems and designing wireless links. Typical delay profiles are measured to clarify their statistical characteristics in LOS street microcells. The channel sounder used is a sliding correlator with 30-Mb/s PN code and a center frequency of 2.6 GHz. The measurements clarify the features of delay profile and mean RMS delay spread. The proposed delay profile model explains one plausible mechanism of multipath propagation. The delay profiles calculated using the model agreed well with the measured profiles. Furthermore, the factors influencing the RMSs delay spread are investigated, and the regression equation of medium RMS delay spread on a sidewalk is established. The proposed model can evaluate the transmission characteristics of wireless digital communication systems in multipath propagation environment

Study the Carrier Frequency Offset (CFO) for Wireless OFDM

Due to high proficiency with high bandwidth efficiency, orthogonal frequency division multiplexing (OFDM) has been selected for broadband wireless communication systems. Since OFDM can provide large data rates with sufficient robustness to radio channel impairments, and due to its robustness against the multipath delay spread, OFDM has always been a designated technique for broadband wireless communication mobile systems. Nevertheless, OFDM suffers from Carrier Frequency Offset (CFO). CFO has been recognized as a major disadvantage of OFDM. CFO can lead to the frequency mismatch in transmitter and receiver oscillator. Lack of the synchronization of the local oscillator signal (L.OSC), for down conversion in the receiver with the carrier signal contained in the received signal, can cause the performance of OFDM to degrade. In other words, the orthogonality of the OFDM relies on the condition that the transmitter and receiver operate with exactly the same frequency reference. If this is not the case, the perfect orthogonality of the subcarrier will be lost, which can result in CFO. In this research, the source of creating CFO and the major CFO estimation algorithms have been reviewed and discussed in literature. We then proposed some algorithms and techniques for estimating and compensating for the effect of CFO. We showed that our proposed methods have a better performance with low complexity