Grigorios A. Kalivas

Millimeter-wave channel measurements with space diversity for indoor wireless communications

Indoor wireless communication systems experience deep multipath fading due to the presence of people, antenna movement, and other environmental factors. The objective of this paper is to present results concerning envelope fading and large-scale attenuation properties of the signal based on narrowband measurements carried out at 21.6 and 37.2 GHz with and without antenna diversity. By using various transmitter-receiver arrangements in measurements which were taken over one floor of a university building, envelope statistics of received signal are produced with and without antenna diversity. It is shown that the statistical distributions follow the Rayleigh curve and hence a diversity gain close to 10 dB can be obtained for an availability of 99%. Power law exponents and wall loss factors are also calculated to assist in the design of future indoor radio systems in the millimeter frequency range. >

Millimeter-wave channel measurements for indoor wireless communications

Propagation losses for the indoor radio channel at 21.6 GHz and 37.2 GHz are examined. The propagation measurements carried out are used to quantitatively present, through enveloped distribution, the effects of spatial fading, which is due to multipath propagation, and temporal fading, which is due to people moving in the building. Attenuation is given in the form of the exponent of the distance-power law.<<ETX>>

Indoor radio path loss comparison between the 1.7 GHz and 37 GHz bands

Third generation indoor wireless systems providing broadband communications will make use of higher frequency millimeter wave bands. In the planning of these networks it would be useful to estimate coverage based on the many studies of indoor propagation at L-band coupled with knowledge of the building structure. This paper presents results of a comparison between path loss at 1.75 GHz and 37.2 GHz from 100 locations throughout four buildings. The authors analyze the large scale path loss in line of sight and obstructed paths, compare this with building layout and construction and then estimate transmission loss through walls. Results indicate that at 1.75 GHz the non line of sight signals decayed with distance to the exponent N=2.7 while for 37.2 GHz on average N=3.5. The propagation loss through walls at 37.2 GHz showed a much higher dependence on construction type than at 1.7 GHz.

Channel characterization for indoor wireless communications at 21.6 GHz and 37.2 GHz

This paper presents results of narrowband and wideband measurements of the indoor wireless channel at 21.6 GHz and 37.2 GHz. Narrowband measurements with antenna diversity were carried out using a modified Spectrum Analyzer operating as a two channel receiver. With this arrangement, two different environments were considered and in each between 10 and 20 measurements were taken. Average cumulative distribution functions are computed and distance-power law exponents are estimated. Wideband characterization involved a Vector Network Analyzer which collects frequency-domain measurements of the channel transfer function H(f) at 21.5 GHz. The duration of each of these measurements was 100 msec during which there was no motion or movement of people in the environment. This ensures that the channel remains static. The impulse response of the channel is then calculated using Inverse Fourier Transformation. From the above measurements, average and worst case statistics can be derived and used to evaluate radio coverage for various systems configurations. Such configurations include line-of-sight and obstructed measurements within environments such as rooms and hallways. Values for the delay spread are also calculated which will permit evaluation of maximum transmitted symbol rates for intersymbol interference-free indoor radio communication.

A New Slotline-Microstrip Frequency Halver

A novel frequency-halving structure employs a matched pair of varactors in a configuration composed of both slotline and microstrip transmission-line sections. A planar 4th-order Marchand balun simultaneously provides both output matching and a balance-to-unbalance transition.

Carrier frequency offset estimation and correction for Hiperlan/2 WLANs

The performance of carrier frequency offset (CFO) estimators is examined when applied to Hiperlan2 modems. The performance of various estimator procedures is evaluated by means of simulation. A new estimation scheme is proposed for Hiperlan2 that takes advantage of the structure of the physical frames. Its major advantage is that the estimator operating range is extended to fulfil a worst-case scenario of CFO for Hiperlan2. A CFO correction architecture is also proposed which consists of 2 parts; a coarse CFO estimator that feeds a numerically controlled oscillator (NCO) to remove a part of CFO, and a fine CFO estimator-corrector that uses linear phase extrapolation to correct the phase shift caused by the remaining CFO.

Space-diversity issues in the context of a B-ISDN-oriented indoor radio environment

A first assessment of the applicability and the tradeoffs involved in a switched (antenna) diversity approach is presented here as seen in the context of a future indoor wireless network operating in the mm-wavelength radio spectrum targeted to provide radio access to asynchronous transfer mode local area networks (ATM LANs) and broadband integrated services digital networks (B-ISDN). Measurements conducted at 21.6 GHz are used to examine the gain variation of switched-diversity alternatives in terms of cumulative distribution functions. The performance of a two-branch post-detection code diversity combining scheme under Rayleigh fading conditions is also included for purposes of comparison. The results of our work here confirm the hypothesis that the choice of the employed antenna diversity technique in combination with the selected micro-cellular architecture have significant effects on both the throughput and the measured performance of future radio links.

An all-digital feed-forward CFO cancellation scheme for HIPERLAN/2 in multipath environment

A multicarrier transmission system is sensitive to carrier frequency offset (CFO) that produces severe inter-carrier interference (ICI). In this work a novel architecture for CFO cancellation is proposed for HIPERLAN/2 type modems. The proposed architecture consists of two parts: a coarse and a fine CFO cancellation subsystem. In the coarse subsystem an extended range correlation type time domain CFO estimation scheme is employed. Then a complex numerically controlled oscillator (CNCO) is used to reduce the main part of the CFO effects. In the fine CFO correction subsystem, a frequency-domain pilot-based estimator is proposed. The proposed scheme measures the phase drift of HIPERLAN/2 pilots in frequency domain and produces an estimation of the relative phase drift of each sample in the time-domain. The result is used to correct the remaining effects of the CFO. The proposed novel architecture is an all-digital feed-forward scheme that means no feedback to the analog front-end of the receiver is required. This fact reduces the implementation complexity.

The design of a radio link for indoor wireless communications at 29 GHz

This paper outlines the design of an experimental indoor broadband radio system at 29 GHz. Based on this design, the availability of this system is presented for various cell sizes and transmitted power values. The system has a maximum information bit rate of 155 Mb/sec and a maximum receiver noise figure of 8 dB. Channel measurements and modeling which were performed during an earlier stage of the project provided some of the parameters for the design of the system. These include distance-power law exponents and received fading envelope statistics. The design of the link is based on a quadrature up/down converter configuration. Both the transmitting and receiving parts have one front-end RF stage at 29 GHz and one IF stage at 2.5 GHz. Several different scenarios with different antenna types and orientations are considered taking into account experimentally determined channel characteristics such as received signal power distributions and large scale attenuation losses. The link design and the calculated availability figures demonstrate that reliable indoor portable radio systems can accommodate microcells of radius up to 50 m.<<ETX>>

Characterization of the frequency stability of frequency-hopping sources

A method that applies time-domain stability measures, hitherto used only in the context of fixed-frequency sources, to the characterization of frequency-hopped sources is introduced. This method has been successfully applied to the testing of a novel practical frequency-hopping synthesizer. It is shown that despite the fact that hopping sources exhibit an orders-of-magnitude larger amount of short term noise than stable free-running frequency sources, some of the techniques used to estimate the noise of stable sources are also applicable to hopping voltage-controlled oscillator systems.<<ETX>>