Millimeter-wave (mmW) frequencies between 30 and 300 GHz are a new frontier for cellular communication that offers the promise of orders of magnitude greater bandwidths combined with further gains via beamforming and spatial multiplexing from multielement antenna arrays. This paper surveys measurements and capacity studies to assess this technology with a focus on small cell deployments in urban environments. The conclusions are extremely encouraging; measurements in New York City at 28 and 73 GHz demonstrate that, even in an urban canyon environment, significant non-line-of-sight (NLOS) outdoor, street-level coverage is possible up to approximately 200 m from a potential low-power microcell or picocell base station. In addition, based on statistical channel models from these measurements, it is shown that mmW systems can offer more than an order of magnitude increase in capacity over current state-of-the-art 4G cellular networks at current cell densities. Cellular systems, however, will need to be significantly redesigned to fully achieve these gains. Specifically, the requirement of highly directional and adaptive transmissions, directional isolation between links, and significant possibilities of outage have strong implications on multiple access, channel structure, synchronization, and receiver design. To address these challenges, the paper discusses how various technologies including adaptive beamforming, multihop relaying, heterogeneous network architectures, and carrier aggregation can be leveraged in the mmW context.

Millimeter-Wave Cellular Wireless Networks: Potentials and Challenges

Communication at millimeter wave (mmWave) frequencies is defining a new era of wireless communication. The mmWave band offers higher bandwidth communication channels versus those presently used in commercial wireless systems. The applications of mmWave are immense: wireless local and personal area networks in the unlicensed band, 5G cellular systems, not to mention vehicular area networks, ad hoc networks, and wearables. Signal processing is critical for enabling the next generation of mmWave communication. Due to the use of large antenna arrays at the transmitter and receiver, combined with radio frequency and mixed signal power constraints, new multiple-input multiple-output (MIMO) communication signal processing techniques are needed. Because of the wide bandwidths, low complexity transceiver algorithms become important. There are opportunities to exploit techniques like compressed sensing for channel estimation and beamforming. This article provides an overview of signal processing challenges in mmWave wireless systems, with an emphasis on those faced by using MIMO communication at higher carrier frequencies.

An Overview of Signal Processing Techniques for Millimeter Wave MIMO Systems

With the severe spectrum shortage in conventional cellular bands, millimeter wave (mmW) frequencies between 30 and 300 GHz have been attracting growing attention as a possible candidate for next-generation micro- and picocellular wireless networks. The mmW bands offer orders of magnitude greater spectrum than current cellular allocations and enable very high-dimensional antenna arrays for further gains via beamforming and spatial multiplexing. This paper uses recent real-world measurements at 28 and 73 GHz in New York, NY, USA, to derive detailed spatial statistical models of the channels and uses these models to provide a realistic assessment of mmW micro- and picocellular networks in a dense urban deployment. Statistical models are derived for key channel parameters, including the path loss, number of spatial clusters, angular dispersion, and outage. It is found that, even in highly non-line-of-sight environments, strong signals can be detected 100-200 m from potential cell sites, potentially with multiple clusters to support spatial multiplexing. Moreover, a system simulation based on the models predicts that mmW systems can offer an order of magnitude increase in capacity over current state-of-the-art 4G cellular networks with no increase in cell density from current urban deployments.

http://apps.fcc.gov/ecfs/document/view;NEWECFSSESSION=ThTmVg1SGvsFqgxGKYfckQC26BmBGYLH2jpL5z0dMms1j21m5YTC!-1110365353!-349327291?id=60001013324

Millimeter Wave Channel Modeling and Cellular Capacity Evaluation

Polarimetric radar measurements were conducted for bare soil surfaces under a variety of roughness and moisture conditions at L-, C-, and X-band frequencies at incidence angles ranging from 10 degrees to 70 degrees . Using a laser profiler and dielectric probes, a complete and accurate set of ground truth data was collected for each surface condition, from which accurate measurements were made of the rms height, correlation length, and dielectric constant. Based on knowledge of the scattering behavior in limiting cases and the experimental observations, an empirical model was developed for sigma degrees /sub hh/, sigma degrees /sub vv/, and sigma degrees /sub hv/ in terms of ks (where k=2 pi / lambda is the wave number and s is the rms height) and the relative dielectric constant of the soil surface. The model, which was found to yield very good agreement with the backscattering measurements of the present study as well as with measurements reported in other investigations, was used to develop an inversion technique for predicting the rms height of the surface and its moisture content from multipolarized radar observations. >

An empirical model and an inversion technique for radar scattering from bare soil surfaces

With the explosive growth of mobile data demand, the fifth generation (5G) mobile network would exploit the enormous amount of spectrum in the millimeter wave (mmWave) bands to greatly increase communication capacity. There are fundamental differences between mmWave communications and existing other communication systems, in terms of high propagation loss, directivity, and sensitivity to blockage. These characteristics of mmWave communications pose several challenges to fully exploit the potential of mmWave communications, including integrated circuits and system design, interference management, spatial reuse, anti-blockage, and dynamics control. To address these challenges, we carry out a survey of existing solutions and standards, and propose design guidelines in architectures and protocols for mmWave communications. We also discuss the potential applications of mmWave communications in the 5G network, including the small cell access, the cellular access, and the wireless backhaul. Finally, we discuss relevant open research issues including the new physical layer technology, software-defined network architecture, measurements of network state information, efficient control mechanisms, and heterogeneous networking, which should be further investigated to facilitate the deployment of mmWave communication systems in the future 5G networks.

A survey of millimeter wave communications (mmWave) for 5G: opportunities and challenges

Measurements of multipath-propagation characteristics were conducted at 60 GHz in a room within in a modern office building. Delay profiles were measured by a swept frequency method with a high time-delay resolution of 2 ns. Direction-of-arrivals of the multipath components reflected from walls analyzed by rotating a narrow-beam receiving antenna with an angular resolution of 5 degrees. As a result of this experiment, it was found that multipath delayed waves due to wall reflections can be effectively suppressed by employing circular polarization instead of linear polarization. Based on this experimental result, a computer simulation was made to make clear the polarization dependence of the high-speed transmission characteristics of a indoor communications system operating at 60 GHz. >

Multipath measurement at 60 GHz for indoor wireless communication systems

Experiments designed to measure the backscattering coefficient of soil surfaces were performed indoors using a 60-GHz scatterometer. The roughness of the soil surface was measured with a laser profile meter to determine the roughness dependence of the scattering coefficient. The incidence angle dependence of the measured backscattering coefficient shows distinctive features according to the roughness of the soil surface. These results are compared with estimates from a small-perturbation theory. >

Measurement of soil backscattering with a 60-GHz scatterometer

The Tropical Rainfall Measuring Mission (TRMM) radar measures rain echo from space. The signal-to-noise ratio (SNR) and the number of independent samples (N) used for averaging are the two major factors which determine the accuracy of the rain echo power measurement. The rain radar does not directly measure the rain echo power, instead, it measures the total received power, which is the sum of the rain echo power and the receiver noise power. The rain echo power is derived by taking the difference between the total received power and the receiver noise power. Experimentally obtained total received power and receiver noice power values always have some errors. Thus, the rain echo power is sometimes estimated as a negative value when the SNR is small

Error analysis of rain echo power of spaceborne radar measurements

In 1992, the Communications Research Laboratory (CRL) commenced a research and development project for millimeter-wave indoor communications systems in the 60-GHz band. The objective of this project is to develop, as an alternative to hard-wired networks, high-speed indoor wireless communications systems that have transmission rates as high as 160 Mbps compatible with ATM (asynchronous transfer mode networks) for high-speed data and video transmission. As a first step in this project, millimeter-wave indoor propagation studies are currently in progress. In this article, the current CRL research activities on indoor propagation and the characterization of indoor construction materials at 60 GHz relevant to the development of high-speed millimeter-wave indoor communications systems are overviewed, mainly from an experimental viewpoint, by introducing the experimental facilities at CRL.

Propagation studies at 60 GHz for millimeter-wave indoor communications systems

The development activity and the evaluation results of indoor WLAN demonstrators at 60 GHz band was reported. Three model systems that have each different way of modulation, multiple access, and planar patch antenna with MMIC amplifiers were proposed. The evaluation of data transmission and conformity for the wired application such as ATM or 100BASE-TX was examined by these demonstrators in a typical office-like room.

Toshio Ihara

Papers

Multipath measurement at 60 GHz for indoor wireless communication systems

Measurement of soil backscattering with a 60-GHz scatterometer

Error analysis of rain echo power of spaceborne radar measurements

Propagation studies at 60 GHz for millimeter-wave indoor communications systems

Development and evaluation on the millimeter-wave indoor wireless LAN demonstrators