In this paper, an infrared wireless communication system based on Multiple Pulse Position Modulation (MPPM) employing angle-diversity detection is studied via simulation. The system can also be easily adapted for Visible Light Communications. MPPM is proposed as a modulation method to improve bandwidth efficiency in PPM. The system designed allows for comparing the performance based on the computation of the bit error rate (BER) as a function of the SNR for different MPPM and PPM modulation schemes employing angle-diversity detection. In this paper, two of the three ways to achieve angle-diversity detection are studied: conventional and sectored receivers. The results show a significant enhancement when angle-diversity receivers are employed, with the sectored receiver offering the highest performance. Furthermore, the results show that PPM offers a good performance for lower bit rates, though the BER increases rapidly when the bit rate is increased, even when angle-diversity receivers are used. MPPM proves to be more bandwidth efficient than PPM, since it allows to use a wider pulse for transmission of the same number of information bits per symbol.
In this paper, an infrared wireless communications system based on THSS techniques employing angle-diversity
detection is studied via simulation. Although the system is designed to operate at infrared wavelengths, it can also be
used for Visible Light Communications (VLC). Time-Hopping codification is based on splitting the symbol period into
several short slots. In order to specify which slots are used to transmit and which are not, the use of maximum length
sequences is considered. The remaining time slots can be used by other users so as to provide the system with multiple
access capabilities. In this paper, a 2-PPM modulation scheme is selected because it yields good results in infrared
systems as well as in VLC. Furthermore, the THSS system allows for selecting the number of pulses per symbol to be
transmitted and makes use of an optimum maximum-likelihood receiver for AWGN channels with the ability to choose
between hard or soft decision decoding. The system designed allows for comparing the performance based on the
computation of the bit error rate (BER) as a function of the pulse energy to noise power spectral density ratio, for
different configurations in single-user and multi-user environments. The results show a significant enhancement when
angle-diversity receivers are used as compared to employing receivers using a single-element detector with a wide field
of view (FOV). In this paper, two angle-diversity structures are compared: conventional and sectored receivers. Although
the sectored receiver exhibits better BER than the conventional receiver, its implementation is more complex.
This paper presents a study of the design of a conventional receiver structure that offers improved performance with
respect to the main IR channel parameters, such as path loss and rms delay spread. To this end, we use a recently
proposed model for the effective signal-collection area of a conventional angle-diversity receiver that is nearer to real
behaviour than the ideal model. The inclusion of this model in the Monte Carlo ray-tracing algorithm allows us to study
those optical links that are characterized by the use of these receivers and investigate the structure of the conventional
receiver that yields improve performance with respect to the IR channel parameters. Based on the obtained results, we
propose the use of a conventional receiver composed of seven branches o photodiodes. One oriented towards the ceiling,
and six looking at an elevation of 56° with a separation of 60° in azimuth. For each element, a CPC with a FOV=50° must
be used. Furthermore, the proposed structure is evaluated in a representative link budget using L-PPM modulation
schemes.
In this paper, an adaptive Orthogonal Frequency Division Multiplexing (OFDM) system is proposed for multiuser
communications over indoor wireless optical channels. The designed system uses multi-user least-squares
(LS) detection techniques applied to SDMA-OFDM schemes, in conjunction with angle diversity reception. The
system, which does not present an excessive complexity, supports high bit rates for multiple users, beyond
one hundred megabits per second. It also mitigates the channel fluctuations induced when either the space
distribution or the number of emitters and receivers varies. The performance of the new proposed scheme
is compared with an adaptive single-user system described in previous works. The obtained results show a
significant improvement with respect to previous adaptive single-user one, since the new scheme allows adaptively
managing the system throughput on a multi-user environment.
The indoor optical channel simulation can significantly benefit the design of high performance infrared (IR) systems, but requires algorithms and models that accurately fit the channel characteristics. One of the limitations of the IR links is the intersymbol interference caused by multipath dispersion. For fixed emitter and receiver locations, multipath dispersion is completely characterized by the channel impulse response. Therefore, to have an algorithm and a propagation model that allow us to determine the impulse response for different IR links is necessary. The use of angle-diversity receivers makes possible the reduction of the impact of ambient light noise, path loss and multipath distortion, in part by exploiting the fact that they are often received from different directions than the desired signal. Basically, there are three ways to get angle-diversity detection: using conventional, imaging or sectored receivers. In contrast to previous works, we present a model for sectored receivers, that is, a set of photodiodes placed in hemispheric form, upon which a Monte Carlo based ray-tracing algorithm allows us to obtain the impulse response and to study those optical links that are characterized by the use of sectored receivers. Using the obtained results, it is possible to establish those parameters of the sectored receiver structure that better performances present with respect to the IR channel features: the path loss and the rms delay spread.
KEYWORDS: Reflection, Solar concentrators, Receivers, Optical filters, Systems modeling, Monte Carlo methods, Compound parabolic concentrators, Reflectors, Signal detection, Infrared detectors
Recently there has been growing interest in using infrared (IR) light for broadband indoor wireless communications. There are two major limitations for establishing a wideband infrared communications link. The first and most important limit is the power requirements of such a link. The second important impairment is the intersymbol interference caused by multipath dispersion. The use of angle-diversity receiver allows to achieve high optical gain and a wide field of view simultaneously, it can reduce the impact of ambient light noise, path loss and multipath distortion, in part by exploiting the fact that they are often received from different directions than the desired signal. The advantages achieved depend on how signal received in the different elements are detect and processed. For this reason, we have developed a fast simulation tool that allows to study the influence of the IR channel and to propose new techniques and receiver structures for those systems. The indoor optical channel simulation can significantly benefit the design of high performance IR systems, but requires models that fit correctly the channel characteristics. In contrast to previous works, we define new models for the emitter, lenses, receiver, nonimaging concentrators and reflectors upon which a Monte Carlo ray-tracing algorithm allows to study different links. The inclusion of these models benefit the design of IR links since the are nearer to real behavior than the ideals models. The use of this simulation tool allowed us to analyze the behavior of several links and suggest a configuration of a receiver using angle diversity.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.