Dimming Consideration for OFDM-Based Visible Light Communications

In the field of indoor wireless networks, visible light communications would be contributing a vital role in the future. This paper investigates the performances of data transmissions using visible light based on unipolar orthogonal frequency division multiplexing (OFDM) and discusses possible approach for light dimming. Asymmetrically clipped optical OFDM (ACO-OFDM) is considered as a unipolar modulation scheme for intensity modulation with direct detection (IM/DD) on which visible light communications is based. This modulation can incorporate light dimming while not corrupting the communication link since, compared to the traditional DC biased optical OFDM (DCO-OFDM), ACOOFDM noise clipping component does not fall on data carrying subcarrier. To create more dimming levels pulse width modulation (PWM) is proposed to be used in conjunction with ACO-OFDM.Keywords: Orthogonal frequency division multiplexing (OFDM), light emitting diode (LED), signal clipping, visible light communication.Cite as:Sunil Deka, Poompat Saengudomlert, Sunandan Baruah "Dimming Consideration for OFDMBased Visible Light Communications", ADBU J.Engg.Tech., 2(1)(2015) 0021101(5pp

Architectural study of high-speed networks with optical bypassing

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (p. 155-158).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.We study the routing and wavelength assignment (RWA) problem in wavelength division multiplexing (WDM) networks with no wavelength conversion. In a high-speed core network, the traffic can be separated into two components. The first is the aggregated traffic from a large number of small-rate users. Each individual session is not necessarily static but the combined traffic streams between each pair of access nodes are approximately static. We support this traffic by static provisioning of routes and wavelengths. In particular, we develop several off-line RWA algorithms which use the minimum number of wavelengths to provide I dedicated wavelength paths between each pair of access nodes for basic all-to-all connectivity. The topologies we consider are arbitrary tree, bidirectional ring, two-dimensional torus, and binary hypercube topologies. We observe that wavelength converters do not decrease the wavelength requirement to support this uniform all-to-all traffic. The second traffic component contains traffic sessions from a small number of large-rate users and cannot be well approximated as static due to insufficient aggregation. To support this traffic component, we perform dynamic provisioning of routes and wavelengths. Adopting a nonblocking formulation, we assume that the basic traffic unit is a wavelength, and the traffic matrix changes from time to time but always belongs to a given traffic set.(cont.) More specifically, let N be the number of access nodes, and k denote an integer vector [k, k2, ..., kN]. We define the set of k-allowable traffic matrices to be such that, in each traffic matrix, node i, </= 1 </= N, can transmit at most ki wavelengths and receive at most ki wavelengths. We develop several on-line RWA algorithms which can support all the k-allowable traffic matrices in a rearrangeably nonblocking fashion while using close to the minimum number of wavelengths and incurring few rearrangements of existing lightpaths, if any, for each new session request. The topologies we consider are the same as for static provisioning. We observe that the number of lightpath rearrangements per new session request is proportional to the maximum number of lightpaths supported on a single wavelength. In addition, we observe that the number of lightpath rearrangements depends on the topological properties, e.g. network size, but not on the traffic volume represented by k as we increase k by some integer factor. Finally, we begin exploring an RWA problem in which traffic is switched in bands of wavelengths rather than individual wavelengths. We present some preliminary results based on the star topology.by Poompat Saengudomlert.Ph.D

Analysis and detection of jamming attacks in an all-optical network

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (p. 123-124).by Poompat Saengudomlert.M.S

Evolution Toward 5G Mobile Networks - A Survey on Enabling Technologies

In this paper, an extensive review has been carried out on the trends of existing as well as proposed potential enabling technologies that are expected to shape the fifth generation (5G) mobile wireless networks. Based on the classification of the trends, we develop a 5G network architectural evolution framework that comprises three evolutionary directions, namely, (1) radio access network node and performance enabler, (2) network control programming platform, and (3) backhaul network platform and synchronization. In (1), we discuss node classification including low power nodes in emerging machine-type communications, and network capacity enablers, e.g., millimeter wave communications and massive multiple-input multiple-output. In (2), both logically distributed cell/device-centric platforms, and logically centralized conventional/wireless software defined networking control programming approaches are discussed. In (3), backhaul networks and network synchronization are discussed. A comparative analysis for each direction as well as future evolutionary directions and challenges toward 5G networks are discussed. This survey will be helpful for further research exploitations and network operators for a smooth evolution of their existing networks toward 5G networks

Performance analysis of WPM‐based transmission with equalization‐aware bit loading

Wavelet packet modulation (WPM) is a multicarrier modulation (MCM) technique that has emerged as a potential alternative to the widely used orthogonal frequency‐division multiplexing (OFDM) method. Because WPM has overlapped symbols, equalization cannot rely on the use of the cyclic prefix (CP), which is used in OFDM. This study applies linear minimum mean‐square error (MMSE) equalization in the time domain instead of in the frequency domain to achieve low computational complexity. With a modest equalizer filter length, the imperfection of MMSE equalization results in subcarrier attenuation and noise amplification, which are considered in the development of a bit‐loading algorithm. Analytical expressions for the bit error rate (BER) performance are derived and validated using simulation results. A performance evaluation is carried out in different test scenarios as per Recommendation ITU‐R M.1225. Numerical results show that WPM with equalization‐aware bit loading outperforms OFDM with bit loading. Because previous comparisons between WPM and OFDM did not include bit loading, the results obtained provide additional evidence of the benefits of WPM over OFDM