Coherent Optical DFT-Spread OFDM

We consider application of the discrete Fourier transform-spread orthogonal frequency-division multiplexing (DFT-spread OFDM) technique to high-speed fiber optic communications. The DFT-spread OFDM is a form of single-carrier technique that possesses almost all advantages of the multicarrier OFDM technique (such as high spectral efficiency, flexible bandwidth allocation, low sampling rate and low-complexity equalization). In particular, we consider the optical DFT-spread OFDM system with polarization division multiplexing (PDM) that employs a tone-by-tone linear minimum mean square error (MMSE) equalizer. We show that such a system offers a much lower peak-to-average power ratio (PAPR) performance as well as better bit error rate (BER) performance compared with the optical OFDM system that employs amplitude clipping.Comment: This idea was originally submitted at Nov. 28th, 2009. After many times of rejection and resubmission, it was finally accepted by the journal of Advances in Optical Technologie

Suppression of Mutual Interference in OFDM Based Overlay Systems

A promising appraoch for overcoming spectrum scarcity are overlay systems that share a frequency band with already existing licensed systems by using the spectral gaps left by the licensed systems. Due to its spectral efficiency and flexibility orthogonal frequency-division multiplexing (OFDM) is an appropriate modulation technique for overlay systems. To enable a successful co-existence, techniques for suppressing mutual interferences between the overlay and the licensed system are proposed

Fifty Years of Noise Modeling and Mitigation in Power-Line Communications.

Building on the ubiquity of electric power infrastructure, power line communications (PLC) has been successfully used in diverse application scenarios, including the smart grid and in-home broadband communications systems as well as industrial and home automation. However, the power line channel exhibits deleterious properties, one of which is its hostile noise environment. This article aims for providing a review of noise modeling and mitigation techniques in PLC. Specifically, a comprehensive review of representative noise models developed over the past fifty years is presented, including both the empirical models based on measurement campaigns and simplified mathematical models. Following this, we provide an extensive survey of the suite of noise mitigation schemes, categorizing them into mitigation at the transmitter as well as parametric and non-parametric techniques employed at the receiver. Furthermore, since the accuracy of channel estimation in PLC is affected by noise, we review the literature of joint noise mitigation and channel estimation solutions. Finally, a number of directions are outlined for future research on both noise modeling and mitigation in PLC

An Optical Design Configuration for Wireless Data Transmission

The concept of 2D barcodes is of great relevance for use in wireless data transmission between handheld electronic devices. In a typical setup, any file on a cell phone for example can be transferred to a second cell phone through a series of images on the LCD which are then captured and decoded through the camera of the second cell phone. In this research, a new approach for data modulation in 2D barcodes is introduced, and its performance is evaluated in comparison to other standard methods of barcode modulation. In the proposed method, Orthogonal Frequency Division Multiplexing (OFDM) modulation is used together with Differential Phase Shift Keying (DPSK) over adjacent frequency domain elements to modulate intensity of individual pixels. It is shown that the bit error rate performance of the proposed system is superior to the current state of the art in various scenarios. A specific aim of this study is to establish a system that is proven tolerant to camera motion, picture blur and light leakage within neighboring pixels of an LCD. Furthermore, intensity modulation requires the input signal used to modulate a light source to be positive, which requires the addition of a dc bias. In the meantime, the high crest factor of OFDM requires a lower modulation index to limit clipping distortion. These two factors result in poor power efficiency in radio over fiber applications in which signal bandwidth is generally much less than the carrier frequency. In this study, it is shown that clipping a bipolar radio frequency signal at zero level, when it has a carrier frequency sufficiently higher than its bandwidth, results in negligible distortion in the pass band and most of the distortion power is concentrated in the baseband. Consequently, with less power provided to the optical carrier, higher power efficiencies and better receiver sensitivity will result. Finally, a more efficient optical integrated system is introduced to implement the proposed intensity modulation method which is optimized for radio over fiber applications

Successive Interference Cancellation in Clipped and Product Combining aided FFH Multi-User Systems

Abstract—In this contribution, we propose two successive interference cancellation (SIC) schemes for a fast frequency hopping (FFH) multiple access (MA) system using M-ary frequency shift keying (MFSK) and invoking multi-user detection (MUD). One of the proposed schemes invokes clipped combining, while the other scheme employs both product combining and clipped combining. The SIC schemes are adapted from a scheme proposed by U.-C. Fiebig in 1996. The basic principle of the SIC schemes is that detection is carried out in multiple stages and during each stage, only the most reliable symbols are detected. In subsequent stages, the interference contributed by the already detected symbols may be removed. The performance of the proposed schemes is evaluated and compared to that of Fiebig’s scheme, when the FFH-MFSK system operates in a Nakagamim fading MA channel. The simulation results demonstrate that the proposed schemes attain a better bit error rate performance than Fiebig’s scheme

Feasibility of Using Bandwidth Efficient Modulation to Upgrade the CMS Tracker Readout Optical Links

Plans to upgrade the LHC after approximately 10 years of operation are currently being considered at CERN. A tenfold increase in luminosity delivered to the experiments is envisaged in the so-called Super LHC (SLHC). This will undoubtedly give rise to significantly larger data volumes from the detectors, requiring faster data readout. The possibility of upgrading the CMS Tracker analog readout optical links using a bandwidth efficient digital modulation scheme for deployment in the SLHC has been extensively explored at CERN. Previous theoretical and experimental studies determined the achievable data rate using a system based on Quadrature Amplitude Modulation (QAM) to be ~3-4Gbit/s (assuming no error correction is used and for an error rate of ~10-9). In this note we attempt to quantify the feasibility of such an upgrade in terms of hardware implementation complexity, applicability to the high energy physics (HEP) environment, technological feasibility and R&D effort required.Comment: CERN CMS Note. 16 pages, 10 figure