The use of large-size antenna arrays to implement pencil-beam forming techniques is becoming a key asset to cope with the very high throughput density requirements and high path-loss of future millimeter-wave (mm-wave) gigabit-wireless applications. Suboptimal beamforming (BF) strategies based on search over discrete set of beams (steering vectors) are proposed and implemented in present standards and applications. The potential of fully adaptive advanced BF strategies that will become possible in the future, thanks to the availability of accurate localization and powerful distributed computing, is evaluated in this paper through system simulation. After validation and calibration against mm-wave directional indoor channel measurements, a 3-D ray tracing model is used as a propagation-prediction engine to evaluate performance in a number of simple, reference cases. Ray tracing itself, however, is proposed and evaluated as a real-time prediction tool to assist future BF techniques.INDEX TERMS MIMO, beamforming, ray tracing, millimeter-wave propagation, channel measurements. 1314 2169-3536 2014 IEEE. Translations and content mining are permitted for academic research only.Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. VOLUME 2, 2014 ROBERT MÜLLER received the M.S. degree in electronic engineering from His areas of interest include high-frequency components design in Rogers and LTCC technology. Furthermore, he is also working on high-frequency front-end design, antenna design, ultrawideband system design, and special antenna array design for channel sounding applications. His research is focusing on channel sounding measurements system and analysis for further communication system in the field of V2V and cellular networks.CHRISTIAN SCHNEIDER received the Diploma degree in electrical engineering from the Ilmenau University of Technology, Ilmenau, Germany, in 2001, where he is currently pursuing the Dr.Ing. degree with the Institute for Information Technology. His research interests include space-time signal processing, turbo techniques, adaptive techniques, multidimensional channel sounding, channel characterization and analysis, and channel modeling for single and multiuser cases in cellular and vehicular networks. He was a recipient of the Best Paper Award at the European Wireless Conference in 2013.

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Abstract-The World Radiocommunications Conference WRC15 identified a number of frequency bands between 24-86 GHz as candidate frequencies for future cellular networks. In this paper an extensive review of propagation characteristics and challenges related to the use of millimetre wave in future wireless systems is presented. Reference to existing path loss models including atmospheric and material attenuation in recommendations of the International Telecommunication Union is given and the need for new multidimensional models and measurements is identified. A description of state of the art mm wave channel sounders for single and multiple antenna measurements is followed by a discussion of the most recent deterministic, semi-deterministic and stochastic propagation and channel models. Finally, standardization issues are outlined with recommendations for future research.

Vehicle-to-vehicle (V2V) channels exhibit unique properties due to the highly dynamic environment and low elevation of the antennas at both ends of the link. Of particular importance for the behavior of V2V channels, and consequent reliability of the communication link, is the severity and dynamics of blockage of both the line-of-sight and other multipath components (MPCs). The characteristics of blockage become more important as the carrier frequency increases, and the ability of the signal to penetrate through objects diminishes. To characterize the effects of vehicle blockage, we performed V2V channel measurements in four different frequency bands (6.75, 30, 60, and 73 GHz) in urban and highway scenarios. We analyzed the impact of the blocker size and position on the received power and fast fading parameters, as well as the frequency dependence of these parameters under blockage. Our results show that there is a strong influence of the size of the blocking vehicle on the blockage loss and the angular/delay spread. The position of the blocker relative to the transmitter and receiver also plays an important role. On the other hand, the frequency dependence is quite limited, with the blockage loss increasing slightly and the number of scattered MPCs reducing slightly as frequency increases. The main conclusion of this paper is that V2V communication will be possible in high (millimeter-wave) frequencies, even in the case of blockage by other vehicles. INDEX TERMS V2V, channel modeling, mmWave, cmWave, multi-band measurements, blockage.

Directional, dual-link, quad-polarized 60 GHz channel measurements have been carried out in a small-office environment. Purpose of the measurements is to study the directional properties of the channel in view of future multi-gigabit system adopting beam-forming or macro-diversity solutions. The impact of polarization on the characteristics of the channel is also addressed in the study.

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Frequency bands above 6 GHz are being considered for future 5G wireless systems because of the larger bandwidth availability and of the smaller wavelength, which can ease the implementation of high-throughput massive MIMO schemes. However, great challenges are around the corner at each implementation level, including the achievement of a thorough multi-dimensional characterization of the mm-wave radio channel, which represents the base for the realization of reliable and high-performance radio interfaces and system architectures. The main properties of the indoor radio channel at 70 GHz, including angular and temporal dispersion as well as an assessment of the major interaction mechanisms, are investigated in this study by means of UWB directional measurements and ray tracing simulations in a reference, small-indoor office environment.