IOSR Journal of Electronics and Communication Engineering (IOSR-JECE) e-ISSN: 2278-2834,p- ISSN: 2278-8735.Volume 9, Issue 6, Ver. I (Nov - Dec. 2014), PP 01-04 www.iosrjournals.org www.iosrjournals.org 1 | Page Evaluation of the bit error rate and Q-factor in optical networks Tomáš Ivaniga 1 , Petr Ivaniga 2 1 (Department of Electronic and Multimedia Communications, Faculty of Electrical Engineering and informatics/ University of Technology Košice, Košice, Slovaki a) 2 (Department of Transportation Networks, Faculty of Management Science and Informatics/ University of Žilina, Žilina, Slovakia) Abstract: The article defines the relation between the error parameters in networks that are built on optical transmission paths in relation to the optical wireless links. Due to the large volume of the transmitted data caused by the association of many tributary signals, the high demands on the transmission error are expected. The aim of the article is to develop measurement methods, evaluation of individual error parameters and explain the relation between them. Keywords: Bit Error Ratio, Quality Factor. I. Introduction Development in backbone networks goes the way of fully optical network elements based on dense wavelength multiplexing of DWDM technology with a terabit capacity on a thousands of miles distance. The advantage of DWDM technology is the possibility of effective recovery and amplification of the signal, using a single erbium-doped fiber amplifier for all channels, which technologically enables the recovery and the gain for all channels simultaneously, and is convenient for the transmission in the core networks. Optical devices, permitting the transmission of such capacities, are complicated as they have to deal with a number of physical parameters such as a signal attenuation, noise, polarization dispersion, chromatic dispersion, non-linear interference and much more. This article aims to define the relation between the error parameters in optical networks in relation to the optical wireless links, which are using the atmosphere as a transmission medium for the propagation of optical beam. Optical fiber-free joints are sensitive to the state of the transmission environment and compared to the conventional optical link, the connection quality depends on the time of a day, air condition etc. II. Basic Definition Of The Bit Error Rate One of the main parameters describing the quality of the data link is a bit error rate BER (Bit Error Rate). With BER is possible to compare the quality of different systems for data transmission. Bit error rate is defined by the following equation, (1) where n c is the number of bits received in error and N B is the total number of bits received in the defined time interval. [1] For modern transmission networks is used the information transfer in larger blocks called packets. The packet consists of a certain number of bits that can be selected or prescribed by the type of network. The occurrence of incorrectly transmitted bit causes degradation of the entire packet. In terms of the error rate, the large amount of data are lost. This error is determined by the relationship (2). (2) – number of transmitted packets with the occurrence of at least one incorrectly transmitted bit – total number of transmitted packets For optical fiber-free connections is defined significant error parameter and it is the relative time interval p, which expresses the percentage of the link downtime t i to the total time of operation T c according to equation (3). This parameter is based on the possibility of a connection failure due to atmospheric turbulence and fluctuation of received power. For reliable determination of this parameter for a particular connection must be selected sufficiently long period T c . This is usually the period of one year.