Indoor Radio Channel Research Articles

IN-BUILDING RADIO PROPAGATION AT 900 MHZ IN MULTI STORIED BUILDING

The proliferation of PCS has necessitated the complete characterization of radio channels existing inside buildings. The indoor radio channel differs from the conventional mobile radio channel in two aspects. First of all the distances taken in account are a lot small, and then the inconsistency of the environment is much larger for a smaller range of distance between transmitter and receiver. Indoor use of wireless systems poses one of the major design challenges, as indoor radio (RF) propagation is essentially a complex phenomenon. In this paper we will try to emphasis on this odd subject and will try to compute and place boundaries for use of wireless systems within buildings at 900 MHz. There are many good system design tools which have been developed solely for ground mobile cellular systems. However, no proper design tools have been developed for both ground mobile communication and in-building communications operated within one cellular system. As cellular systems are operated today, in-building communication is provided by transmitting radio signals from cell sites so that they penetrate the building walls to reach portable handsets inside buildings. In-building communication is harder to perform on the reverse link (portable-to-base link) than the forward link. Du to this it is difficult to mathematically put the model for all telecommunication systems in a single equation so many models coexist for different types of radio links for different situations. In this paper statically modelled is been explored. . The model rely on computing the median path loss for a link under a certain probability that the considered conditions will occur The modelling is done using simple measurements made especially for an intended communication system or spectrum allocation. This paper present radio signal propagation measurement and modelling at 900MHz, within a Hotel building in the city of Udaipur (India).

An Empirical Study of the Achievable Rates of Several Indoor Network-MIMO Techniques

This paper presents an empirical study of the achievable data rates of network multiple-input multiple-output (MIMO) techniques including zero-forcing (ZF), zero-forcing dirty paper coding (ZF-DPC) and dirty paper coding (DPC) using actual 4-by-4 indoor wireless channel measurements at 3.5 GHz. Their performances are contrasted with those of conventional techniques, in which either the base stations are not coordinated (NC), or their interference is avoided using frequency division (FD) multiplexing. The measurements were taken in aisle-to-office and large unobstructed hall scenarios. The study of these results reveals that, at high signal-to-noise ratios (SNRs), DPC and ZF-DPC can yield more than a three-fold increase in attainable data rates when compared to NC and FD. The gains obtained using ZF are smaller, but still significant. At low SNRs the system is noise-(rather than interference-) limited, and only DPC exhibits gains. The evaluations in this paper also show that collaborative systems such as DPC can benefit from interference-prone environments to yield increased transmission capacity. With regard to the propagation channel, the classical log-normal plus Rayleigh/Ricean fading model, with parameters fitted to the scenario type, was found to be good at predicting the statistics of the achievable data rates of all the strategies considered.

Angular and Shadowing Characteristics of Dense Multipath Components in Indoor Radio Channels

The dense multipath components (DMC) represent the part of the radio channel that cannot be characterized by using the specular components (SC). In this paper, the propagation characteristics of the DMC are analyzed in indoor environments based on extensive channel measurements. The results show that the contribution of the DMC to the total received power can vary as much as between 10% and 95%, being generally higher in non-line-of-sight than in line-of-sight scenarios. However, it was found that the DMC have a well distinguishable structure in the angular domain in all the investigated scenarios and, furthermore, the propagation mechanisms of the SC and DMC have large similarities. In addition, the effect of shadowing objects on the SC and DMC has been investigated.

A Generalization of Shift-Window Approach for UWB ISI Reduction

Mitigating inter-symbol interference (ISI) in impulse radio is one of the challenges in achieving the high data rate potential of Ultra Wideband (UWB). Available techniques such as the use of Multiband OFDM and equalizer provide a good solution but they require complex implementation. This letter investigates and expands a newly proposed ISI reduction technique proposed in named approach. The shift window approach was not designed to combat ISI under a severe indoor wireless channel. An enhancement based on the generalization of the shift window approach is introduced for ISI reduction for wireless personal area network (WPAN). The newly proposed approach is shown to perform better under severe ISI.

A Wideband Frequency-Domain Channel-Sounding System and Delay-Spread Measurements at the License-Free 57- to 64-GHz Band

A channel-sounding impulse-response identification system using the swept-frequency method is presented for the 57- to 64-GHz band. The swept-frequency channel sounder offers high time and frequency resolution of 1 ns and 625 kHz, respectively. The high dynamic range (70 dB) and the constant power output enable the nonlinearities of the channel-sounding system to be overcome within the coverage range, which is on the order of a picocell. This paper also reports the measurements and the analysis of wideband propagation data for various indoor radio channels at the 57- to 64-GHz band. The propagation characteristics are assessed for six different propagation environments. The results of the measurements for four environments are compared when horn antennas are employed at both terminal stations, and also when a horn and an omnidirectional antenna are used at the Tx and Rx terminals, respectively. Examining the statistical distributions of the multipath dispersion, the 90th percentile is about the same for both antenna configurations. For all environments under investigation, it was observed that the static delay spread values at the 90th percentile were below 62 ns.

Dual-link capacity analysis of measured time-variant indoor radio channels

There has been extensive research about single link multiple-input multiple-output (MIMO) channels, both simulated and measured, but only a few studies have targeted multilink analysis with measured channel data. Hence, in this presented report, the authors analyse the influence of spatial separation of user terminals and the human shadowing effect on the MIMO capacity and on the signal-to-interference ratio in indoor radio channels.

Error Performance of Prerake Diversity Combining-Based UWB Spatial Multiplexing MIMO Systems over Indoor Wireless Channels

In this letter, we consider a novel ultra-wideband (UWB) spatial multiplexing (SM) multiple input multiple output (MIMO) structure, which consists of prerake diversity combiners in the transmitter and a zero forcing (ZF) detector in the receiver. For a UWB SM MIMO system with N transmit antennas, M receive antennas, and L resolvable multipath components, it is shown that the proposed prerake combining-based MIMO detection scheme has the diversity order of (LN - M + 1) and its BER performance is analytically presented in a log-normal fading channel and also compared with that of a rake combining-based ZF scheme.

Digital Transmission Over Millimeter-Wave Radio Channels: A Review [Wireless Corner

The propagation characteristics expected to occur in a typical - thus, multipath-reflective - indoor environment are treated analytically. It is shown that the mm-wave indoor radio channel can be considered as a discrete multipath channel that might be highly frequency selective for the high symbol rates of interest (2 Gb/s). Digital transmission over mm-wave channels is discussed, including some performance-improvement methods, and the suitability of some figures-of-merit that are commonly used to quantify transmission performance.

Statistical Characterization of 60-GHz Indoor Radio Channels

An extensive review of the statistical characterization of 60-GHz indoor radio channels is provided from a large number of published measurement and modeling results. First, the most prominent driver applications for 60 GHz are considered in order to identify those environment types that need to be characterized most urgently. Large-scale fading is addressed yielding path-loss parameter values for a generic 60-GHz indoor channel model as well as for the office environment in particular. In addition, the small-scale channel behavior is reviewed including the modeling of time-of-arrival and angle-of-arrival details and statistical parameters related to delay spread, angular spread and Doppler spread. Finally, some research directions for future channel characterization are given.

터널 환경에서의 전파전파 특성 모델링 연구

국내 환경의 경우, 산악 지형이 많은 지형적 특성상 수많은 터널이 존재한다. 터널은 무선 채널 환경 중 대표적인 음영지역으로서 실외 및 실내 환경의 무선 채널과는 다른 특성을 갖기 때문에 터널 환경에서의 안정된 서비스 품질을 확보하기 위해서는 전파 채널의 특성 연구가 필요하다. 특히 위성을 이용한 이동 서비스를 위해서는 터널에 의한 음영지역에서의 정상적인 위성 신호 수신이 필요하며, 이를 위해 Gap-Filler라고 하는 지상 중계기를 운영하게 되는데 이를 이용하기 위해서는 터널 환경에서의 전파전파 특성 분석을 바탕으로 한 Gap Filling 방법 연구가 필수적이다. 따라서 본 논문에서는 음영 지역에서의 정상적인 위성 신호 수신을 위하여 터널 환경에서의 ISM 대역의 전파전파 특성을 분석하고, 이를 바탕으로 효율적인 Gap Filling 방법에 대한 연구를 수행하였다. In the domestic environments, there are many tunnels since most of terrains have mountains. To ensure the quality of wireless network service in NLOS environment like tunnels which differ from indoor or outdoor wireless channels, researches on wave-propagation characteristics. through such channel are necessary. Especially, in such environment the ground repeater called Gap-Fillers are usually used for satellite mobile services. To make sure that mobile service using satellites in tunnels is available, the research about Gap Filling method is essential. This research is focus on the characterising the wave-propagation through tunnels, to find the appropriate frequency, HPBW of the Gap-Filler antennas, the number of Gap-Fillers, etc. In this paper, we present the effective Gap Filling method in tunnels for ISM band, based on analysis of ray tracing and measurement results.

Adaptive code-division multiple-access system for communications over indoor wireless optical channels based on random optical codes

The authors have designed an adaptive optical codes-based system for communications over the indoor wireless optical channel when large numbers of users access to the channel simultaneously. This system uses a code-division multiple access (CDMA) scheme based on the named random optical codes (ROC). The authors present the characteristics of this kind of optical codes and several results about its performance over noisy indoor wireless optical channels. Finally, the authors describe a CDMA system which adapts its performance to the number of users which are accessing simultaneously to the channel. The proposed system is able to maintain a target bit error rate adapting its data throughput independently of the number of simultaneous users in the optical environment, whenever certain conditions are accomplished.

Characterizing indoor wireless channels via ray tracing combined with stochastic modeling

We investigate the reliability of radio channel simulators in predicting channel responses throughout a well-specified environment. Indoor environments for which the geometric layout and material properties of surfaces are known lend themselves to such site-specific simulation. We assess the performance of this approach by comparing its predictions with measurements in a specific static environment. The good agreement on path loss, Ricean K-factor and RMS delay spread, over the set of paths measured and simulated, suggests that a well-designed radio simulator can be used reliably to predict system behavior. Typically, wireless channel models obtained through this or similar techniques do not capture the temporal variability in the channel response due to people movement in the environment. We treat the time-varying part of the channel response using stochastic processes. Using channel sounding experiments for several typical office scenarios, we show that autoregressive processes can be used to model the time-varying tap gains for several different motion scenarios.

3D-Wave Propagation Analysis of Indoor Wireless Channels Utilizing Hybrid Methods

A full 3D hybrid method for analyzing electromagnetic wave propagation in buildings with realistic wall types and structures is presented. This hybrid method combines full-wave techniques which are used for the analysis of one unit cell of inhomogeneous periodic walls with a ray-tracing-like field calculation for the interaction between the walls. Consequently, the method can overcome the inadequacy of traditional ray-tracing in the presence of inhomogeneous periodic wall structures like cinderblock, rebar structure, etc. but is still computationally tractable. Because of this, both indoor wireless channel characterizations and signal fading statistics are shown to be more accurate with this method. Numerical results of the hybrid method are presented for two simple scenarios and validated with theory and measurement. Furthermore, numerical results for a realistic indoor scene are given and compared to a scene where the periodic walls are replaced with effective homogeneous walls. For both setups, the propagation channel is characterized, fast fading signal statistics are extracted and the inadequacies of the homogeneous wall implementation are pointed out.

Investigation of the Effect of Building Dielectric Parameters on Indoor Radio Channel Characteristics

The unlicensed industrial, scientific, and medical (ISM) band at 2.4 GHz has gained increased attention recently due to high data rate communication systems developed to operate in this band. In this paper the investigation of the indoor electromagnetic propagation and indoor radio channel characteristics have been performed at this band. Electromagnetic waves propagate by means of reflection, refraction, and diffraction. Reflection mechanisms are dependent on the nature of the surface, dielectric properties, polarization, incidence angle, and material thickness. The effect of the incidence angle and material thickness on the reflection coefficients for both horizontal and vertical polarization has been studied. Two-dimensional ray-tracing simulation has been performed to show the influence of building electromagnetic properties on indoor radio channel parameters, signal level, RMS delay spread, and coherence bandwidth. Results show the influence of the permittivity is more important than the influence of the order of reflection considered for the ray- tracing model. It is shown that, compared with power level, RMS delay spread is more sensitive to the building dielectric parameters. Maximum RMS delay spread is dependent on the dielectric parameters of the surrounded walls. Keywords: Radio propagation, Dielectric parameters, Indoor Channel Parameters

Turbo Code with Modified LLR and Performance Analysis for Bluetooth Packets in Indoor Environments

Most of the restrictions in indoor environments do not exist for outdoor sites. The main limitations for indoors are the attenuation of walls and the multipath fading effects. The signal propagation is limited by the standard free space path loss in outdoor environments or free space. The loss in free space is usually equal to the range squared whereas the loss exponent for indoors is more like the 4th power. This study investigates the performance of turbo codes with modified Maximum-A-Posteriori (MAP) decoding algorithm for Bluetooth data packets in indoor environments over the frequency selective Rayleigh fading channels; which are also called as indoor wireless communication channels. In order to reduce the computational complexity of turbo decoders, MAP algorithm is modified in this study. Bit error rate (BER) versus energy of bit-to-noise ratio (E b /N o ) of modified MAP algorithms for Bluetooth data packets at 2.4 GHz industrial-scientific-medical (ISM) band are evaluated by means of computer simulations. Thus, modified logarithmic likelihood ratio (LLR) method can significantly reduce the computational complexity of the MAP algorithm. Furthermore, the performances of different types of forward error correction (FEC) coding for Bluetooth data packets are compared in the study.

Performance of Single and Multichannel Coherent Reception under Rician Fading

In the present work, simple closed-form series solutions for the average error rate of several coherent modulation schemes such as, binary phase shift keying (BPSK), binary frequency shift keying (BFSK), differential binary phase shift keying (DBPSK), quadrature phase shift keying (QPSK), offset-QPSK, minimum shift keying (MSK), and square M-ary quadrature amplitude modulation (M-QAM), operating over frequency non-selective slow Rician fading channel and corrupted by additive white Gaussian noise (AWGN) are derived. Further, to improve the link quality, receiver antenna space diversity is considered, where multiple independent and identically distributed (i.i.d.) as well as uncorrelated signal replicas are combined before successive demodulation. The proposed linear predetection combiner follows optimum maximal ratio combining (MRC) algorithm. Starting from a novel unified expression of conditional error probability the error rates are analysed using probability density function (pdf) based approach. The derived end expressions, consisting of rapidly converging infinite series summations of Gauss hypergeometric function, are accurate, free from any numerical integration and general enough, as it encompasses as special situations, some cases of non-diversity, non-fading AWGN and Rayleigh fading. Symbol or, bit error probabilities (SEP/BEP) are graphically displayed against signal to noise ratio (SNR) per bit per channel for all the digital modulation schemes stated above with different values of diversity order L and varying values of the channel specular-to-scatter ratio or, the Rician parameter K, as found from the measured statistics of mobile and indoor wireless channels. In addition, to examine the dependence of error rate performance of M-QAM on the constellation size M, numerical results are plotted for various values of M. Selected simulation results are also provided to verify the analytical deductions. The series solutions presented in current text realize a trade-off between precision and complexity and offers valuable insight into the performance evaluation over a fading channel in a unified manner.

Estimation of CFO and Channels in Phase-Shift Orthogonal Pilot-Aided OFDM Systems with Transmitter Diversity

We present a CFO estimation algorithm and an associated channel estimation method for broadband OFDM systems with transmitter diversity. The CFO estimation algorithm explores the TD structure of the transmitted symbols carrying pilots and data, relying solely on the data component present on the symbols to estimate the CFO, thus avoiding additional overhead like training symbols or null subcarriers. An intermediate output of the CFO algorithm provides an easy-to-get initial CIR estimate that will be improved with the utilization of a TD LMMSE filter. The feasibility of the investigated methods is substantiated by system simulation using indoor and outdoor broadband wireless channel models. Simulation results show that the joint algorithms provide a near optimal system's performance.

Human body shadowing variability in short-range indoor radio links at 3–11 GHz band

Measurement results for human body shadowing and local environmental effects in short-range indoor radio channels are presented. A narrowband measurement system, comprising a signal generator, two identical triangular monopoles and a spectrum analyser, was used in the measurements. When the radio link was periodically blocked by a human body with various objects in and around the link, fading depths of up to 15 dB and even more were observed at spot frequencies of 3–11 GHz band. Standard deviation and its range for human body blockage are estimated for different radio link scenarios simulating real environments. The distribution of human body shadowing was analysed and compared with known distribution functions.

IEEE 802.15.4 표준에 적용을 위한 음성부호화 기술

Due to the various constraints such as feasible size of data payload and low transmission power, no technical specifications on the voice communication are included in the Zigbee standard. In this paper, a voice coding technique for application to the IEEE 802.15.4 standard, which is the basis of Zigbee communication, is presented. Here, both high compression and good waveform recovery are essential. To meet those requirements, a multi-stage discrete wavelet transform (DWT) block and a binary coding block consisting of two different pulse-code modulations are exploited. Theoretical analysis and simulation results in an indoor wireless channel show that the voice coder with 2-stage DWT is most appropriate from the viewpoint of compression and waveform recovery. When the line-of-sight component is dominant, the voice coding scheme has good recovery capability even in the moderate signal-to-noise power ratios. Hence, it is considered that the presented scheme will be a technical reference for the future recommendation of voice communication exploiting Zigbee.

An OFDM Symbol Design for Reduced Complexity MMSE Channel Estimation

In this paper we revisit the minimum mean square error (MMSE) pilot-aided channel estimation for broadband orthogonal frequency division multiplexing (OFDM) systems. The careful design of OFDM symbol leads to the proposal of a simplified time-domain (TD) MMSE estimator. By exploring the Fourier properties of the symbol, the investigated method eliminates the need to use direct or inverse discrete Fourier transforms (DFT/IDFT) before the channel estimation, by using the TD received symbol samples as the input to the MMSE filter. Moreover, performing the estimation in TD (where the channel impulse response (CIR) energy is mainly limit to a small set of samples), makes way to a simple, nonetheless efficient estimation of the filter parameters. The performance of the channel estimation scheme, using the estimated parameters, presents a tolerable degradation when compared with the ideal situation (a-priori knowledge of the channel correlation and noise variance), while exhibiting a reduced computational load. The feasibility of the investigated method is substantiated by system simulation using indoor and outdoor wireless channel models.