doi:10.1155/2007/78907 Research Article An Overview of Multigigabit Wireless through Millimeter Wave Technology: Potentials and Technical Challenges
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paper_title: Potential of UWB Technology for the Next Generation Wireless Communications

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This paper discusses the potential deployment of ultra-wideband (UWB) radio technology for next generation wireless communications. Firstly, the state-of-art in UWB technology is reviewed. Then, the current status of worldwide regulatory efforts and industrial standardization activities is discussed. Various technical challenges that remain to be solved prior to the successful deployment of UWB systems as well as the possible technical approaches are also reported. Specifically, we envisioned the potential of location awareness capabilities to provide new applications and usage models for future mobile terminals. An overview of the existing ranging and localization techniques is presented and some technical aspects as well as design trade-offs in terms of device complexity and ranging accuracy are highlighted. Finally, since UWB systems operate as overlay systems, issues of coexistence and interference with existing narrowband systems are presented.
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paper_title: In-Building Wideband Partition Loss Measurements at 2.5 GHz and 60 GHz

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This paper contains measured data and empirical models for 2.5&60 GHz in-building propagation path loss and multipath delay spread. Path loss measurements were recorded using a broadband sliding correlator channel sounder which recorded over 39,000 Power Delay Profiles (PDPs) in 22 separate locations in a modern office building. Transmitters and receivers were separated by distances ranging from 3.5 to 27.4 meters, and were separated by a variety of obstructions, in order to create realistic environments for future single-cell-per-room wireless networks. Path loss data is coupled with site-specific information to provide insight into channel characteristics. These measurements and models may aid in the development of future in-building wireless networks in the unlicensed 2.4 GHz and 60 GHz bands.
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paper_title: Influence of the human activity on wide-band characteristics of the 60 GHz indoor radio channel

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This paper presents propagation measurements in the presence of human activity for a 60 GHz channel. Series of 40-min-long measurements of the channel impulse response have been recorded with a sampling period of 1.6 ms, for a total duration of about 20 h. During measurements, the human activity (between zero and 15 persons) was observed with a video camera. The obstruction phenomenon due to the human bodies is characterized in duration and amplitude from the propagation characteristics (attenuation, coherence bandwidth) by means of an appropriate method. The results highlight and quantify the problems due to the human activity for high data rate communication systems. When the direct path is shadowed by a person, the attenuation generally increases by more than 20 dB, for a median duration of about 100 ms for an activity of one to five persons and 300 ms for 11-15 persons. Globally, the channel is "unavailable" for about 1% or 2% of the time in the presence of one to five persons. This channel characterization makes it possible to modelize the temporal variations of the 60 GHz channels. The results also give orientations for the design of high data rate communications systems and networks architectures at 60 GHz.
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paper_title: Digital Communication over Fading Channels

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noncoherent communication systems, as well as a large variety of fading channel models typical of communication links often found in the real world, including single- and multichannel reception with a large variety of types. The book gives many numerical illustrations expressed in large collections of system performance curves, allowing the researchers or system designers to perform trade-off studies of the average bit error rate and symbol error rate. This book is a very good reference book for researchers and communication engineers and may also be a source for supplementary material of a graduate course on communication or signal processing. Nowadays, many new books attach a CD-ROM for more supplementary material. With the many numerical examples in this book, it appears that an attached CD-ROM would be ideal for this book. It would be even better to present the computer program in order to be interactive so that the readers can plug in their arbitrary parameters for the performance evaluation. —H. Hsu
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paper_title: Antenna Theory: Analysis and Design

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The most-up-to-date resource available on antenna theory and design. Expanded coverage of design procedures and equations makes meeting ABET design requirements easy and prepares readers for authentic situations in industry. New coverage of microstrip antennas exposes readers to information vital to a wide variety of practical applications.Computer programs at end of each chapter and the accompanying disk assist in problem solving, design projects and data plotting.-- Includes updated material on moment methods, radar cross section, mutual impedances, aperture and horn antennas, and antenna measurements.-- Outstanding 3-dimensional illustrations help readers visualize the entire antenna radiation pattern.
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paper_title: In-Building Wideband Partition Loss Measurements at 2.5 GHz and 60 GHz

paper_content:

This paper contains measured data and empirical models for 2.5&60 GHz in-building propagation path loss and multipath delay spread. Path loss measurements were recorded using a broadband sliding correlator channel sounder which recorded over 39,000 Power Delay Profiles (PDPs) in 22 separate locations in a modern office building. Transmitters and receivers were separated by distances ranging from 3.5 to 27.4 meters, and were separated by a variety of obstructions, in order to create realistic environments for future single-cell-per-room wireless networks. Path loss data is coupled with site-specific information to provide insight into channel characteristics. These measurements and models may aid in the development of future in-building wireless networks in the unlicensed 2.4 GHz and 60 GHz bands.
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paper_title: Statistical characterization of the UWB propagation channel in indoor residential environment

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This paper presents a statistical characterization of an ultra wideband (UWB) indoor propagation channel based on measurements conducted in various types of high-rise apartments in several cities of Korea. Measurements were carried out in the frequency band of 3–10 GHz. Various communication links were considered including both line-of-sight (LOS) and non-LOS (NLOS) scenarios, which covered within-the-room and room-to-room propagations. The measurement procedure allows us to characterize both the large-scale and the small-scale statistics of the channel. The aim here is to study in more detail the statistical characteristics of the UWB propagation channel and to provide insight for future statistical channel modeling work. Channel characteristics examined include the distance and frequency dependency of path loss, shadowing fading statistics, and multipath temporal-domain parameter statistics such as the mean excess delay, RMS delay spread, and the number of dominant paths. Copyright © 2005 John Wiley & Sons, Ltd.
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paper_title: Millimeter-wave propagation at street level in an urban environment

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Measurements on point-to-point transmission at street level were performed in downtown Denver, CO, with RF probes that operated at 9.6, 28.8, and 57.6 GHz. All probes were mounted on self-contained vehicles, permitting a variety of path scenarios. Information on performance of these channels for propagation in an urban environment on both line-of-sight and non-line-of-sight paths is presented. For non-line-of-sight (non-LOS) paths obstructed by buildings of several common materials, results that showed signal attenuations in excess of 100 dB. When the LOS followed a path directly through clear glass walls, the attenuation was small at all probe frequencies. However, when the glass wall had a metalized coating to reduce ultraviolet and infrared radiation, the attenuation increased by 25 to 50 dB for each metallized layer. In most cases no signals could be detected through steel reinforced concrete or brick buildings. >
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paper_title: Molisch, “The ultra-wide bandwidth indoor channel: from statistical model to simulations

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We establish a statistical model for the ultra-wide bandwidth (UWB) indoor channel based on an extensive measurement campaign in a typical modern office building with 2-ns delay resolution. The approach is based on the investigation of the statistical properties of the multipath profiles measured in different rooms over a finely spaced measurement grid. The analysis leads to the formulation of a stochastic tapped-delay-line (STDL) model of the UWB indoor channel. The averaged power delay profile can be well-modeled by a single exponential decay with a statistically distributed decay constant. The small-scale statistics of path energy gains follow Gamma distributions whose parameters m are truncated Gaussian variables with mean values and standard deviations decreasing with delay. The total received energy experiences a lognormal shadowing around the mean energy given by the path-loss power law. We also find that the correlation between multipath components is negligible. Finally, we propose an implementation of the STDL model and give a comparison between the experimental data and the simulation results.
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paper_title: Investigating the effects of antenna directivity on wireless indoor communication at 60 GHz

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This paper investigates the nature of the indoor radio channel at 60 GHz, with regard to its use for future high bit-rate broadband wireless networks. It is proposed that, for operation in the millimetre-wave indoor channel, directional antennas can be used to mitigate multipath effects, thus reducing the need for complex equalisation or multi-carrier techniques. An image based, ray-tracing prediction model is used to study the channel characteristics and to analyse the variation in received power, RMS delay spread and k-factor within a typical operating environment. The performances of different antenna combinations are investigated and narrowbeam, suitably aligned antennas are shown to reduce received delay spread for both LOS and non-LOS locations. The effects of non-optimal antenna alignment are observed, and system outage is determined for certain system design criteria. The results suggest that it will feasible to combat multipath effects using switched-beam directional antennas.
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paper_title: On the robustness of ultra-wide bandwidth signals in dense multipath environments

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The results of an ultra-wide bandwidth (UWB) signal propagation experiment, using bandwidth in excess of 1 GHz, performed in a typical modern office building are presented. The robustness of the UWB signal in multipath is quantified through cumulative distribution functions of the signal quality in various locations of the building. The results show that an UWB signal does not suffer multipath fading.
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paper_title: Reflection and transmission behaviour of building materials at 60 GHz

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Mobile radio communications at very high data rates require wide bandwidths which are only available at very high frequency bands. In order to model millimetre wave radio scenarios profound knowledge of the reflection and transmission properties of building materials is required. For a variety of typical smooth and rough building materials reflection scattering, bistatic reflection and transmission measurements have been carried out at 50 GHz. This document introduces briefly the basic physical principles of reflection and transmission as well as the used measuring technique. The measurement results are presented graphically and in tabular form. Additionally, the comparison of measured and calculated profiles is given, using a heuristic approach for permittivity estimation.
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paper_title: Polarization dependence of multipath propagation and high-speed transmission characteristics of indoor millimeter-wave channel at 60 GHz

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Measurements of polarization dependence of multipath-propagation characteristics were conducted at 60 GHz in a room within a modern office building. Delay profiles were measured using a swept frequency method with a high time-delay resolution of 2 ns. Directions of arrival of the multipath components reflected from walls were analyzed by rotating a narrow-beam receiving antenna with an angular resolution of 5 degrees. Results of this experiment showed that multipath delayed waves due to wall reflection can be effectively suppressed by employing circular polarization instead of linear polarization. Based on this experimental result, a computer simulation was made to clarify the polarization dependence of the high-speed transmission characteristics of an indoor communications system operating at 60 GHz. >
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paper_title: A generic statistical-based UWB channel model for high-rise apartments

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A generic statistical-based ultrawide-band (UWB) indoor channel model which incorporates the clustering of multipath components (MPCs) is proposed. The model is derived using measurement data collected in the frequency band of 3-10 GHz in various types of high-rise apartment under different propagation scenarios. The measurement procedure allows the characterization of both the large-scale and the small-scale statistics of the channel. The main objective is to study multipath propagation behavior, particularly the phenomenon of clustered MPCs. The description of clustering observed in the channel uses two classes of parameters which characterize the clustering and the MPCs respectively. All parameters are described by a set of empirical probability density functions derived from the measured data such as the distribution of clusters and MPCs, cluster and MPC arrival statistics and small-scale amplitude fading statistics. A new distribution, namely, a mixture of two Poisson processes, is proposed to model the ray arrival times. This new distribution fits the empirical data better than the single Poisson process proposed in the conventional Saleh-Valenzuela (S-V) model. Analysis results show that the small-scale amplitude fading statistics are best modeled by the Weibull distribution. The Weibull b-shape parameter is lognormally distributed and is found to be invariant across the excess delay. Additionally, the temporal correlation between adjacent path amplitudes is investigated. The amplitude temporal correlation coefficients are found to be relatively small, and thus, can be assumed to be negligible in reality. The proposed model can provide a realistic simulation platform for UWB communication systems.
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paper_title: A novel wideband dynamic directional indoor channel model based on a Markov process

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A novel stochastic wideband dynamic spatio-temporal indoor channel model which incorporates both the spatial and temporal domain properties as well as the dynamic evolution of paths when the mobile moves is proposed based on the concept of a Markov process. The derived model is based on dynamic measurement data collected at a carrier frequency of 5.2 GHz in typical indoor environments. Multipath components are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization algorithm prior to identification of path "birth" and "death" using a new data analysis method. Analysis shows that multiple births and deaths are possible at any instant of time. Furthermore, correlation exists between the number of births and deaths. Thus, an M-step 4-state Markov channel model (MCM) is proposed in order to account for these two effects. The spatio-temporal variations of paths within their lifespans are taken into consideration by the spatio-temporal vector which was found to be well modeled by a Gaussian probability density function while the power variation can be modeled by a simple low-pass filter. In addition, the methodology used to extract the MCM parameters from the measurement data is also presented. Due to the distinction in the birth-death statistics, the model is generalized through segmentation of the measurement runs and can be completely parameterized by several sets of Markov parameters associated with the type of environment and scenario under consideration. The implementation of the model is also detailed and, finally, the model is evaluated by comparing key statistics of the simulation results with the measurement results.
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paper_title: Effects of antenna directivity and polarization on indoor multipath propagation characteristics at 60 GHz

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In millimeter-wave indoor communications systems, the radiation patterns and polarizations of the antennas at base stations and remote terminals have a significant influence on channel characteristics. The work reported in this paper investigated the effects of the radiation patterns of the antennas at remote terminals on multipath propagation characteristics. These effects were investigated by indoor propagation measurements at 60 GHz conducted in a modern office room and by ray-tracing simulations based on geometrical optics. Multipath channel characteristics are compared in terms of impulse responses and their root-mean-square (rms) delay spreads for an omnidirectional antenna and for three directive antennas with different beam widths. From the results of measurements and ray-tracing simulations, the use of a directive antenna at the remote terminal is demonstrated to be an effective method of reducing the effects of multipath propagation. Further reduction in the multipath effects is found to be achieved by the use of circular polarization instead of linear polarization with the directive antennas.
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paper_title: A Comprehensive Standardized Model for Ultrawideband Propagation Channels

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A comprehensive statistical model is described for ultrawideband (UWB) propagation channels that is valid for a frequency range from 3-10 GHz. It is based on measurements and simulations in the following environments: residential indoor, office indoor, builtup outdoor, industrial indoor, farm environments, and body area networks. The model is independent of the used antennas. It includes the frequency dependence of the path gain as well as several generalizations of the Saleh-Valenzuela model, like mixed Poisson times of arrival and delay-dependent cluster decay constants. A separate model is specified for the frequency range below 1 GHz. The model can thus be used for realistic performance assessment of UWB systems. It was accepted by the IEEE 802.15.4a Task Group as standard model for evaluation of UWB system proposals. This paper also presents a critical assessment of the applicability of the model and possible generalizations and improvements
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paper_title: Frequency Selectivity of 60-GHz LOS and NLOS Indoor Radio Channels

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This paper analyzes the frequency selectivity, which is caused by multipath effects, of indoor line-of-sight (LOS) and non-LOS (NLOS) channels based on channel measurements in the frequency band of 60 GHz. The coherence bandwidth is determined to characterize frequency selectivity figures of the channels employing the combination of omnidirectional, fan-beam and pencil-beam antennas at transmitter (TX) and receiver (RX) sides. The results quantitatively show how far directional configurations are more effective for combating multipath effect than the omnidirectional ones for LOS channels. The frequency selectivity of the fan-beam-to-fan-beam configuration is less sensitive to misaligned TX-RX beams than the fan-beam-to-pencil-beam one. In addition, when omnidirectional antennas are used at both TX and RX side, the frequency selectivity of a NLOS channel is less sensitive to the TX-RX height difference than that of a LOS channel. Moreover, coherence bandwidth is empirically related to root-mean-squared delay spread. Lastly, the results presented in this paper lead to some useful insights into antenna configurations and beamformer designs for a 60-GHz radio system.
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paper_title: A new statistical wideband spatio-temporal channel model for 5-GHz band WLAN systems

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In this paper, a new statistical wideband indoor channel model which incorporates both the clustering of multipath components (MPCs) and the correlation between the spatial and temporal domains is proposed. The model is derived based on measurement data collected at a carrier frequency of 5.2 GHz in three different indoor scenarios and is suitable for performance analysis of HIPERLAN/2 and IEEE 802.11a systems that employ smart antenna architectures. MPC parameters are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization (FD-SAGE) algorithm and clusters are identified in the spatio-temporal domain by a nonparametric density estimation procedure. The description of the clustering observed within the channel relies on two classes of parameters, namely, intercluster and intracluster parameters which characterize the cluster and MPC, respectively. All parameters are described by a set of empirical probability density functions (pdfs) derived from the measured data. The correlation properties are incorporated in two joint pdfs for cluster and MPC positions, respectively. The clustering effect also gives rise to two classes of channel power density spectra (PDS)-intercluster and intracluster PDS-which are shown to exhibit exponential and Laplacian functions in the delay and angular domains, respectively. Finally, the model validity is confirmed by comparison with two existing models reported in the literature.
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paper_title: On the energy capture of ultrawide bandwidth signals in dense multipath environments

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A quasi-analytical experimental analysis is described in this paper to quantify the tradeoff between energy capture and diversity level in a RAKE receiver using measured received waveforms obtained from ultrawide bandwidth signal propagation experiments.
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paper_title: Statistical Characteristics of 60 GHz Wideband Indoor Propagation Channel

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This paper presents statistical properties of the space-time propagation channel at 60 GHz. An extensive measurement campaign is conducted for three different type of corridors in an office building. The 60 GHz channel sounder used is capable of measuring the complex-valued space time channel data accurately and the multipath components are resolved both in space and time domain with 1 GHz measurement bandwidth. Throughout the measurements the line-of-sight (LOS) path is ensured. The parameter estimation is performed using space-alternating generalized expectation (SAGE) algorithm. Parameters for the directional channel model such as root mean square (RMS) delay spread, Ricean K-factor and angular spread are calculated. Statistical models for the power delay spectrum (PDP) and the power azimuth spectrum (PAP) are given
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paper_title: A 60 GHz integrated antenna array for high-speed digital beamforming applications

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A 60 GHz integrated four-element planar antenna array is developed. Each antenna is integrated with a sub-harmonic I/Q mixer based on APDPs for the convenience of high-speed signal processing such as adaptive beamforming. An average conversion loss of four channels of less than 10.6 dB is achieved. Amplitude imbalance and phase deviation between I and Q outputs of each channel are less than 2.5 dB and 7/spl deg/, respectively. The array is used to construct a digital beamforming system along with an IF circuit block and DSP modules. Beam scanning results are successfully demonstrated.
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paper_title: Millimeter-wave circular polarized beam-steering antenna array for gigabit wireless communications

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This paper presents a 2/spl times/2 beam steering antenna with circular polarization at 61 GHz for high speed communications. It demonstrates approximately 14 dBi directivity and twenty degree half power beamwidth. The cross polarization is at least 14 dB. Design method, simulation, manufacture and characterization of the antenna are presented. The proposed small-scale array antenna is suitable for various high speed wireless applications.
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paper_title: Millimeter-wave CMOS design

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This paper describes the design and modeling of CMOS transistors, integrated passives, and circuit blocks at millimeter-wave (mm-wave) frequencies. The effects of parasitics on the high-frequency performance of 130-nm CMOS transistors are investigated, and a peak f/sub max/ of 135 GHz has been achieved with optimal device layout. The inductive quality factor (Q/sub L/) is proposed as a more representative metric for transmission lines, and for a standard CMOS back-end process, coplanar waveguide (CPW) lines are determined to possess a higher Q/sub L/ than microstrip lines. Techniques for accurate modeling of active and passive components at mm-wave frequencies are presented. The proposed methodology was used to design two wideband mm-wave CMOS amplifiers operating at 40 GHz and 60 GHz. The 40-GHz amplifier achieves a peak |S/sub 21/| = 19 dB, output P/sub 1dB/ = -0.9 dBm, IIP3 = -7.4 dBm, and consumes 24 mA from a 1.5-V supply. The 60-GHz amplifier achieves a peak |S/sub 21/| = 12 dB, output P/sub 1dB/ = +2.0 dBm, NF = 8.8 dB, and consumes 36 mA from a 1.5-V supply. The amplifiers were fabricated in a standard 130-nm 6-metal layer bulk-CMOS process, demonstrating that complex mm-wave circuits are possible in today's mainstream CMOS technologies.
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Title: An Overview of Multigigabit Wireless through Millimeter Wave Technology: Potentials and Technical Challenges
Section 1: INTRODUCTION
Description 1: This section introduces millimeter wave (mmWave) technology, emphasizing its history, applications, and the advantages of 60 GHz technology for multigigabit wireless indoor communication. It also outlines the structure of the paper.

Section 2: WORLDWIDE REGULATIONS AND STANDARDIZATION
Description 2: This section discusses the current worldwide regulation and standardization efforts for the 60 GHz band, including specifics for North America, Japan, Australia, Korea, and Europe, along with industrial standardization efforts.

Section 3: APPLICATION SCENARIOS
Description 3: This section explores application scenarios enabled by mmWave technology, particularly focusing on uncompressed high-definition video streaming. It outlines technical requirements for such applications.

Section 4: FEASIBILITY STUDY
Description 4: This section performs a feasibility study on the 60 GHz radio technology, analyzing Shannon capacity, power margins, and the role of antennas in achieving high data rates, considering both AWGN and multipath channels.

Section 5: TECHNICAL CHALLENGES
Description 5: This section addresses the technical challenges and open issues that need to be resolved for successful deployment of 60 GHz technology. It covers challenges related to channel propagation, antenna technology, RF solutions, and modulation schemes.

Section 6: CONCLUSION
Description 6: This section summarizes the key points discussed in the paper, emphasizing the potential of 60 GHz technology and the benefits it offers for multigigabit applications, while also pointing out the ongoing efforts and challenges that need further research.