Indoor Wireless Communication Research Articles

BRDF Models for the Impulse Response Estimation in Indoor Optical Wireless Channels

Indoor wireless optical communications (IWOCs) are highly conditioned by the communication channel, which depends on factors, such as the endpoints’ positions and the reflective surfaces inside the room. Reflections have an important impact on the channel properties, since both channel gain and multipath interference are directly affected by reflections. Therefore, the selection of the reflection model used in the channel characterization is a critical decision in order to achieve realistic and accurate channel estimation. Simulation software, for the IWOC channel impulse response estimation, usually simplifies reflections surfaces using basic models, such as the ideal diffuse reflector (Lambertian model) or Phong’s reflection scheme. However, these models do not provide accurate results when are used with some surfaces, like those with a high-level of specular reflection components. In this letter, the integration of new reflection models into the impulse response estimation of the IWOC channels is proposed. These models are based on bidirectional reflectance distribution function theories, such as Blinn’s or Lafortune’s models, which are frequently used in 3D image rendering.

On the Coverage of Multiple-Input Multiple-Output Visible Light Communications [Invited

Visible light communication (VLC) using multiple-input multiple-output (MIMO) has great potential for future high-data-rate indoor wireless communications. Owing to the dual function of white light-emitting diodes (LEDs), i.e., illumination and communication functions, both the illumination and communication coverages need to be evaluated when implementing an indoor MIMO-VLC system. In this paper, we present a comprehensive investigation of both the illumination and communication coverages of an indoor MIMO-VLC system. Two techniques are applied in the MIMO-VLC system for communication coverage improvement, including a non-Hermitian symmetry orthogonal frequency division multiplexing (NHS-OFDM) modulation scheme and an imaging angle diversity receiver. A general indoor imaging MIMO-VLC system using NHS-OFDM is described and the analytical bit error rate expression of the system is derived. The impact of LED pairing on the communication coverage of an indoor imaging MIMO-VLC system based on NHS-OFDM is also analyzed.

Indoor Airborne Ultrasonic Wireless Communication Using OFDM Methods.

Concerns still exist over the safety of prolonged exposure to radio frequency (RF) wireless transmissions and there are also potential data security issues due to remote signal interception techniques such as Bluesniping. Airborne ultrasound may be used as an alternative to RF for indoor wireless communication systems for securely transmitting data over short ranges, as signals are difficult to intercept from outside the room. Two types of air-coupled capacitive ultrasonic transducer were used in the implementation of an indoor airborne wireless communication system. One was a commercially available SensComp series 600 ultrasonic transducer with a nominal frequency of 50 kHz, and the other was a prototype transducer with a high- k dielectric layer operating at higher frequencies from 200 to 400 kHz. Binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), and quadrature amplitude modulation (QAM)-based orthogonal frequency division multiplexing modulation methods were successfully implemented using multiple orthogonal subchannels. The modulated ultrasonic signal packets were synchronized using a wireless link, and a least-squares channel estimation algorithm was used to compensate the phase and amplitude distortion introduced by the air channel. By sending and receiving the ultrasonic signals using the SensComp transducers, the achieved maximum system data rate was up to 180 kb/s using 16-QAM with ultrasonic channels from 55 to 99 kHz, over a line-of-sight transmission distance of 6 m with no detectable errors. The transmission range could be extended to 9 and 11 m using QPSK and BPSK modulation schemes, respectively. The achieved data rates for the QPSK and BPSK schemes were 90 and 45 kb/s using the same bandwidth. For the high- k ultrasonic transducers, a maximum data rate up to 800 kb/s with no measurable errors was achieved up to a range of 0.7 m. The attainable transmission ranges were increased to 1.1 and 1.2 m with data rates of 400 and 200 kb/s using QPSK and BPSK, respectively.

A multi-mode wideband omnidirectional monopolar patch antenna for indoor wireless communication systems

A wideband omnidirectional monopolar patch antenna merged multi-mode with a simple structure is proposed in this article. The antenna consists of a circular patch and a concentric annular ring, which is coupled-fed by a T-shape monopole at its center. A wideband performance is achieved by converging multi-mode: TM02 mode of the circular patch, TM02 mode of the annular ring and monopole mode of the T-shape monopole. The measured results show that the proposed antenna has an impedance bandwidth of 55.3% from 4.45GHz to 7.85GHz. All of the three resonant modes lead to conical radiation patterns in the elevation plane and omnidirectional radiation patterns in the azimuth plane, and the measured peak gain varies from 6.1 to 10 dBi within the operating band, which verifies it can be a good choice for indoor wireless communication systems.

Pathloss Study for 61 GHZ Wave D2D Communications in Indoor Environment

The present paper deals with device-to-device (D2D) communication for millimeter wave and its performance in indoor wireless communication application. The 61 GHz Industrial Scientific and Medical band is considered for verification of link visibility and path loss behaviour. Line-of-sight (LOS) blockage is the major problem in indoor wireless communication as the signal gets attenuated when the LOS path comes across any obstacle. To overcome this problem, directional antennas are used through which the direction of propagation can be diverted. While selecting such non-line-of-sight (NLOS) path, the transmission path must offer relatively lesser attenuation. The output of this work would be useful for identification of NLOS paths by using beam switching mechanism for D2D communication.

System theory of the integrating sphere as a model for the wireless optical indoor communication channel

The integrating sphere is the base for a physical model of the wireless optical indoor communication channel. The author has found that the approximate expression for the channel transfer function for the integrating sphere used in that model can be replaced by an exact expression. A comparison shows that the approximation is valid for a wide range of interest, however there are some differences for high frequency values. For the impulse response (obtained by the inverse Fourier transform), the author observes significant deviations in the time region where first order reflections contribute significantly to the curve shape.

Acoustic analogs for the characterization room electromagnetics

In indoor wireless communication the radio channel is comprised of the direct and diffuse multipath components. As in the acoustics case these diffuse components are the result of non-specular and random scattering. This state-of-affairs is particularly problematic for short-range millimeter wavelength radio system. The Eyring model has recently been shown to be effective in modeling the electromagnetic power decay profile in rooms. In this work temporal decay rates of the energy in coupled spaces is considered. The role which inter-room transmission and energy absorption play on the power decay profile will be examined. Special session: Acoustics Network Protocol, Underwater Acoustic Communications. Pacs Number: 43.60.Dh, 43.38.Si

A Cooperative Wireless Sensor Network for Indoor Industrial Monitoring

Industrial wireless sensor networks are getting popular for indoor monitoring of heavy machinery and large factories to make a reliable decision on the state of machines in a certain area of interest. However, the indoor wireless communication channel is not always reliable, and observations of some sensors cannot be reported successfully to the base station. In order to deal with this problem, we propose a cooperative WSN scheme by introducing a novel cooperation mechanism and a medium access control protocol. The proposed scheme effectively increases the probability of correct decision about the state of the machine, reduces the probability of false alarms at a given signal level, and reduces the overall energy consumption as compared to noncooperative schemes. We also present a closed-form expression for the symbol-error rate analysis of the proposed scheme, which shows that our proposed scheme achieves full diversity order offered by the cooperation scheme.

Experimental evaluation in wireless communications

This editorial sums up relevant topics on the assessment of wireless communication systems covered by the especial issue entitled “Experimental Evaluation in Wireless Communications.” The topics include practical aspects on the implementation of distributed asynchronous non-linear kernel methods over wireless sensor networks; localization methods based on the exploitation of radio-frequency identification (RFID) wireless sensors and cellular networks or on sparsity approximations; channel sounding and assessment of broadband orthogonal frequency-division multiplexing (OFDM)-based wireless systems in high-speed vehicular communications; coexistence analysis of femtocell-based and outdoor-to-indoor systems; techniques for peak-to-average power ratio (PAPR) reduction; new solutions for baseband and radio frequency (RF) hardware impairments in full-duplex wireless systems; and, finally, suitability of interference alignment for broadband indoor wireless communications.

Indoor Use of Gray and White Spaces: Another Look at Wireless Indoor Communication

Television (TV) white space (WS) constitutes a key technology to support the increasing worldwide growth of spectrum demand with several regulation standards that are already available for long- and medium-range communications. At the same time, estimations based on WS spectrum databases (SDBs) indicate that the availability of TVWS is often very limited in dense urban areas where spectrum resources are more needed. Therefore, the benefits provided by the utilization of TVWS have yet to be fully assessed. In this article, we rethink the utilization of TVWS in indoor communication environments through novel three-dimensional (3-D) spectrum-sharing mechanisms. Based on measurements that demonstrate the differences in terms of spectrum opportunities at different floors of the same building, we propose an underlay spectrum-sharing architecture to enable a per-building finegrained reuse of TV frequencies while protecting the operations of TV receivers in a neighborhood. We evaluate the effectiveness of the proposed spectrum-sharing architecture over several urban environments in Italy by taking into account many real characteristics of the scenarios. Our results demonstrate that through our architecture, more spectrum resources than what are reported in the SDB can be available for indoor scenarios, even in highly congested urban areas, paving the way to novel TVWS applications.

Adaptive pre-compensation of LEDs for improved decoding of N-CSK in visible light communication

We propose an adaptive pre-compensation with second order memory less polynomial to mitigate dynamic nonlinearity in LEDs. The scheme improves the performance of IEEE 802.15.7 standard N-level colour shift keying (N-CSK) modulation for indoor visible-light optical wireless communication system. LED linearization technique is implemented for 16-CSK system and its decoding performance is analyzed employing Voronoi cell segmentation of constellations. The decoding performance of 16-CSK is further improved by optimizing the distance between adjacent signal constellations in the transmitter. The performance of the scheme is simulated by Monte Carlo method and verified experimentally. The symbol error rate and error vector magnitude at the receiver shows significant improvement of decoding performance of 16-CSK through optimized modulation and pre-distortion compensation of LEDs.

Design of a Microstrip Bowtie Antenna for Indoor Radio-Communications

In this paper, a microstrip bowtie patch antenna (MBPA) for wireless indoor communications is carried out. Here, a microstrip transmission-line feed network was designed in order to match the MBPA. The proposed antenna uses a ground plane with the aim of narrowing down the back lobes in comparison with bowtie sheet antennas, which radiation pattern is omni-directional. The far-field pattern of the antenna was simulated using a finite-element numerical algorithm and obtained by interpolation employing near-field equipment. The experimental results are described in detail intending to agree well with the simulated predictions. The antenna was designed, measured and built and its far field performance was evaluated with a 2.11 GHz resonant frequency. The azimuth and elevation antenna patterns, antenna gain and, the matching frequency were the main parameters obtained to analyze the antenna behaviour. The antenna has a gain approximately equal to 8.77 dBi and its beam-widths are higher than 100° in E plane.

Analyzing Wireless Indoor Communications by Blockage Models

The performance of wireless cellular networks in indoor scenarios is in large parts characterized by the blockage objects such as walls. These objects can be included in the system model in several ways. We present in this paper different wall generation methods, ranging from approaches from random shape theory (in 1-D and 2-D) to semideterministic and heuristic approaches. To attain comparable results, we ensure that the average wall volume for each method is constant. This results in the same average attenuation for distinct paths, which is shown analytically as well as by simulations. We apply a regular transmitter grid, show the influence of the relative orientation between walls and transmitter–receiver path and also elaborate on the influence of interferers in different tiers around the desired transmitter. Based on the average attenuation, we introduce the necessary approximations to yield tractable expressions for average performance in terms of Signal-to-Interference Ratio (SIR). These approximations are necessary to reflect the fluctuations among the instantaneous SIR values for the individual realizations of the blockage scenario and also due to the spatial correlation of blockages influencing several transmitter-signals simultaneously. Our results show a good accordance among the analytical and simulation results. Furthermore, we find the random wall generation method in two dimensions as the worst case scenario and the regular wall generation method as the best case scenario under the constraint of constant average wall volume.

A Multiband Dual-Polarized Omnidirectional Antenna for Indoor Wireless Communication Systems

In this letter, a multiband dual-polarized omnidirectional antenna is studied. Two printed circular dipole arrays are employed for horizontal polarization (HP), while a simplified discone antenna is used for vertical polarization (VP). The two dipole arrays are fixed on the top and bottom of the VP element, respectively, and combined by a diplexer to make up the HP elements. The VP element is composed of three radiation patches with an external profile of a discone shape, which significantly lower the antenna's fabrication cost. To realize a compact structure, the HP element together with a circular patch works as the ground plane for the VP element. Simulated and measured results show that the frequency bands of 690 MHz–1.03 GHz and 1.69–3.21 GHz for HP and 770–980 MHz and 1.70–3.75 GHz for VP are achieved. Good port isolation, low cross-polarization level, and omnidirectional radiation patterns for both HP and VP in the azimuth plane are obtained over the whole working bands, which indicate that the proposed antenna can be widely used for indoor multiple-input–multiple-output (MIMO) communication systems.

Robust Transceivers Design for Multi-Stream Multi-User MIMO Visible Light Communication

Visible light communication (VLC) is an emerging technique that uses light-emitting diodes to combine communication and illumination. It is considered as a promising scheme for indoor wireless communication that can be deployed at reduced costs, while offering high data rate performance. This paper focuses on the design of precoding and receiving schemes for downlink multi-user multiple-input multiple-output VLC systems using angle diversity receivers. Two major concerns need to be considered while solving such a problem. The first one is related to the inter-user interference, basically inherent to our consideration of a multi-user system, while the second results from the users’ mobility, causing imperfect channel estimates. To address both concerns, we propose robust precoding and receiver that solve the max-min SINR problem. The performance of the proposed VLC design is studied under different working conditions, where a significant gain of the proposed robust transceivers over their non-robust counterparts has been observed.

Investigation on performance of special-shaped 8-quadrature amplitude modulation constellations applied in visible light communication

Light-emitting diode (LED)-based visible light communication (VLC) has become a potential candidate for next-generation ultra-high-speed indoor wireless communication. In this paper, four special-shaped 8-quadrature amplitude modulation (QAM) constellations are investigated in a single-carrier VLC system. It is numerically verified and experimentally demonstrated that circular (7,1) shows obvious superiority in the performance of the dynamic range of signal voltage peak-to-peak (vpp) value and bit error rate (BER). Next best is rectangular, followed by triangular; circular (4,4) has the worst performance. A data rate of 1.515 Gbit/s is successfully achieved by circular (7,1) employing a red chip LED over 0.5 m indoor free space transmission below a BER threshold of 3.8×10−3. Compared with circular (4,4), the traditional 8-QAM constellation, circular (7,1) provides a wider dynamic range of signal vpp, a higher data rate, and a longer transmission distance. To the best of our knowledge, this is the first investigation into the performance differences of special-shaped 8-QAM constellations in a high-speed, single-carrier VLC system, and the results comprehensively demonstrate that circular (7,1) is the optimal option.

Broadband circular patch antenna with monopolar radiation pattern for indoor wireless communication

A circular patch antenna with wide impedance bandwidth and monopolar radiation pattern for indoor wireless communication is proposed and analyzed in this paper. The antenna is a combination of circular patch and four capacitive feeds. By incorporating a cross-connected shorted conducting strip over the circular patch, the proposed antenna provides an enhanced impedance width of 65.4%, ranging from 1.46 to 2.88 GHz. Four capacitive feeds improve the design flexibility and make the ripple of horizontal radiation pattern less than 3 dB. A prototype of the proposed structure has been fabricated and measured. Both the simulated and measured results show that the proposed design has a stable monopolar radiation pattern over a wideband frequency range and a peak gain of 5.0 dBi, which can be widely applied for indoor wireless communication such as GSM1800, CDMA2000, WCDMA, and TD-LTE systems.

Broadband omnidirectional distributed antenna for indoor wireless communication systems

A broadband omnidirectional distributed antenna is studied theoretically and experimentally. By loading three shorted coupling patches over the top of the radiation patches and a circular sleeve on the ground plane, the bandwidth of the antenna which is excited by a truncated cone feeding structure is significantly enhanced. Results show that an impedance bandwidth of 152% ranging from 0.97 to 7.09 GHz is achieved. Omnidirectional radiation patterns in the horizontal plane, low cross polarisation level, and stable antenna gain ranging from 2.1 to 7.3 dBi are realised over the operating band, which suggests the distributed antenna can be widely used in indoor wireless communication systems.

Integration of variable-rate OWC with OFDM-PON for hybrid optical access based on adaptive envelope modulation

In this paper, we investigate an integrated optical wireless communication (OWC) and orthogonal frequency division multiplexing based passive optical network (OFDM-PON) system for hybrid wired and wireless optical access, based on an adaptive envelope modulation technique. Both the outdoor and indoor wireless communications are considered in the integrated system. The data for wired access is carried by a conventional OFDM signal, while the data for wireless access is carried by an M-ary pulse amplitude modulation (M-PAM) signal which is modulated onto the envelope of a phase-modulated OFDM signal. By adaptively modulating the wireless M-PAM signal onto the envelope of the wired phase-modulated constant envelope OFDM (CE-OFDM) signal, hybrid wired and wireless optical access can be seamlessly integrated and variable-rate optical wireless transmission can also be achieved. Analytical bit-error-rate (BER) expressions are derived for both the CE-OFDM signal with M-PAM overlay and the overlaid unipolar M-PAM signal, which are verified by Monte Carlo simulations. The BER performances of wired access, indoor OWC wireless access and outdoor OWC wireless access are evaluated. Moreover, variable-rate indoor and outdoor optical wireless access based on the adaptive envelope modulation technique is also discussed.

Effect of optimal Lambertian order for cellular indoor optical wireless communication and positioning systems

We propose and analyze an optimized Lambertian order (OLO) of light-emitting diode for both indoor cellular optical wireless communication and positioning systems. We carry out analysis for the system consisting of a Lambertian source and a tilted optical receiver, and develop an expression for OLO for four-, six-, and nine-cell configurations. We investigate the channel characteristics including the optical path loss, impulse response, transmission bandwidth, and positioning accuracy for the proposed systems with and without OLO, showing that there is a significant improvement in the transmission bandwidth as well as the positioning accuracy when employing OLO. For example, for a four-cell configuration with the optimum Lambertian order, 99% of cumulative distribution function of the estimation errors is within the Cramer–Rao bound (CRB) accuracy of 6.7 to 26.7 cm, compared to the CRB accuracy of 12.8 to 29.7 cm for the Lambertian order of m=1.