Security hacker another crime such as destroying information contained in that system". These subgroups may also be defined by the legal status of their activities. A white hat hacker breaks security for non-malicious reasons, either to test their own security system, perform penetration tests, or vulnerability assessments for a client - or while working for a security company which makes security software. The term is generally synonymous with ethical hacker, and the EC-Council, among others, have developed certifications, courseware, classes, and online training covering the diverse arena of ethical hacking. A "black hat" hacker is a hacker who "violates computer security for
Cyclic prefix formula_17. Cyclic prefix In telecommunications, the term cyclic prefix refers to the prefixing of a symbol, with a repetition of the end. The receiver is typically configured to discard the cyclic prefix samples, but the cyclic prefix serves two purposes: For the cyclic prefix to serve its objectives, it must have a length at least equal to the length of the multipath channel. The concept of a cyclic prefix is traditionally associated with OFDM systems, however the cyclic prefix is now also used in single carrier systems to improve the robustness to multipath propagation. A cyclic prefix is often used