Tim Corneel Wilhelmus Schenk

Coherent Optical 25.8-Gb/s OFDM Transmission Over 4160-km SSMF

We discuss coherent optical orthogonal frequency division multiplexing (CO-OFDM) as a suitable modulation technique for long-haul transmission systems. Several design and implementation aspects of a CO-OFDM system are reviewed, but we especially focus on phase noise compensation. As conventional CO-OFDM transmission systems are very sensitive to laser phase noise a novel method to compensate for phase noise is introduced. With the help of this phase noise compensation method we show continuously detectable OFDM transmission at 25.8 Gb/s data rate (20 Gb/s after coding) over 4160-km SSMF without dispersion compensation.

121.9-Gb/s PDM-OFDM Transmission With 2-b/s/Hz Spectral Efficiency Over 1000 km of SSMF

We discuss optical multi-band orthogonal frequency division multiplexing (OFDM) and show that by using multiple parallel OFDM bands, the required bandwidth of the digital-to-analogue/ analogue-to-digital converters and the required cyclic prefix can significantly be reduced. With the help of four OFDM bands and polarization division multiplexing (PDM) we report continuously detectable transmission of 10 times121.9-Gb/s (112.6-Gb/s without OFDM overhead) at 50-GHz channel spacing over 1,000-km standard single mode fiber (SSMF) without any inline dispersion compensation. In this experiment 8 QAM subcarrier modulation is used which confines the spectrum of the 121.9 Gb/s PDM-OFDM signal within a 22.8 GHz optical bandwidth. Moreover, we propose a digital signal processing method to reduce the matching requirements for the wideband transmitter IQ mixer structures required for PDM-OFDM.

Long-haul transmission of16×52.5 Gbits/s polarization-division- multiplexed OFDM enabled by MIMO processing (Invited)

Focus Issue on Orthogonal-Frequency-Division Multiplexed Communications Systems and Networks We discuss the realization and performance of polarization-division-multiplexed orthogonal frequency division multiplexing (PDM-OFDM) for long-haul transmission systems. Polarization demultiplexing of the PDM signal at the receiver is realized by employing a multiple-input multiple-output (MIMO) detector. Using a recirculating loop a long-haul transmission experiment is reported of 52.5 Gbits/s PDM-OFDM (40 Gbits/s after coding) over 4160 km of standard single-mode fiber (SSMF). In this transmission experiment, 16 wavelength-division-multiplexed (WDM) channels are transmitted at 50 GHz channel spacing, and we show that MIMO processing in the receiver enables both polarization demultiplexing and a large PMD tolerance.

Human-centric connectivity enabled by body-coupled communications

With the growing number of mobile devices surrounding a persons body, there is an increasing need to connect this electronic equipment efficiently into a wireless body-area network. In this article we review the body-coupled communications technology, which we show to be a viable basis for future BANs. In BCC, the human body is used as a signal propagation medium, which provides a key benefit - the communication is centered around the user and limited to his or her close proximity, that is, this technology provides human-centric connectivity. This enables unique applications that are illustrated in this work. Moreover, we outline the fundamental properties of the BCC technology and provide different trade-offs and challenges for modulation and protocol design. This article also discusses the outlook for BCC and suggests a number of important research topics.

Experimental characterization of the body-coupled communications channel

Body-coupled communications (BCC), in which the human body is used as a communications channel, has been shown to be a promising solution for wireless body-area networks (WBANs). For successful deployment of these BCC-based WBANs, it is necessary to develop a clear understanding of the channel behavior. Therefore, this paper presents the key characteristics of the capacitively-coupled on-body channel used for BCC. This is based on an experimental study, which was carried out with a specifically designed measurement system. The goal of the study was to reveal the influence of electrode design, electrode position and body motion on the propagation loss and to characterize the experienced interference. It is concluded that the maximum propagation loss for the whole body channel is below 80 dB. Moreover, the frequency dispersion and the influence of body movement on channel attenuation are shown to be much smaller than for radio frequency (RF) WBAN channels. From the results we conclude that BCC can result in a simpler, more robust, and lower-power WBAN than what is achievable with traditional RF solutions.

Uniform Illumination Rendering Using an Array of LEDs: A Signal Processing Perspective

An array of a large number of LEDs will be widely used in future indoor illumination systems. In this paper, we investigate the problem of rendering uniform illumination by a regular LED array on the ceiling of a room. We first present two general results on the scaling property of the basic illumination pattern, i.e., the light pattern of a single LED, and the setting of LED illumination levels, respectively. Thereafter, we propose to use the relative mean squared error as the cost function to measure the uniformity of the realized illumination pattern, and provide an analysis for this cost function. Based on the analysis, the design of a basic illumination pattern is discussed. The performances of a few basic illumination patterns are compared, and an approach for optimizing the basic illumination pattern through a weighted combination of these basic patterns is also proposed. A weighted combination of Gaussian and raised-cosine functions is found to yield the best results. Finally, three basic regular grid shapes for an LED array are compared. The results show that 13% and 39% of LEDs can be saved for the same degree of uniformity, using the hexagonal instead of the rectangular and triangular grid, respectively.

An analytical model for the illuminance distribution of a power LED

Light-emitting diodes (LEDs) will play a major role in future indoor illumination systems. In general, the generalized Lambertian pattern is widely used as the radiation pattern of a single LED. In this letter, we show that the illuminance distribution due to this Lambertian pattern, when projected onto a horizontal surface such as a floor, can be well approximated by a Gaussian function.

Optical OFDM - A Candidate for Future Long-Haul Optical Transmission Systems

We review coherent-optical orthogonal frequency division multiplexing (OFDM) for long-haul optical transmission systems. Two important aspects of such systems are reviewed: RF-aided phase noise compensation and polarization division multiplexing enabled by MIMO processing.

Enhanced Illumination Sensing Using Multiple Harmonics for LED Lighting Systems

This paper considers frequency division multiplexing (FDM) based illumination sensing in light emitting diode (LED) lighting systems. The purpose of illumination sensing is to identify the illumination contributions of spatially distributed LEDs at a sensor location, within a limited response time. In the FDM scheme, LEDs render periodical illumination pulse trains at different frequencies with prescribed duty cycles. The problem of interest is to estimate the amplitudes of the individual illumination pulse trains. In our previous work, an estimation approach was proposed using the fundamental frequency component of the sensor signal. The number of LEDs that can be supported by this estimation approach is limited to around 100 LEDs at a response time of 0.1 s. For future LED lighting systems, however, it is desirable to support many more LEDs. To this end, in this paper, we seek to exploit multiple harmonics in the sensor signal. We first derive upper limits on the number of LEDs that can be supported in the presence of frequency offsets and noise. Thereafter, we propose a low complexity successive estimation approach that effectively exploits the multiple harmonics. It is shown that the number of the LEDs can be increased by a factor of at least five, compared to the estimation approach using only the fundamental frequency component, at the same estimation error.

Receiver-Based Compensation of Transmitter-Incurred Nonlinear Distortion in Multiple-Antenna OFDM Systems

To enable an efficient implementation of multiple-antenna OFDM systems, this paper proposes an approach to reduce the influence of transmitter-induced nonlinearities in such systems. The approach comprises a preamble design, an estimation method and a digital compensation algorithm. Correction for the nonlinearities of the different transmitter branches is applied in the receiver, which requires no extra hardware. A numerical performance evaluation shows that the proposed approach can successfully be applied with minimal performance degradation compared to non-impaired systems.