In recent researches Coding techniques are used in OTDR approach improve Signal-to-Noise Ratio (SNR). For example, the use of simplex coding (S-coding) in conjunction with OTDR can be effectively used to enhance the Signal-to-Noise Ratio (SNR) of the backscattered detected light without sacrificing the spatial resolution; In particular, simplex codes have been demonstrated to be the most efficient among other suitable coding techniques, allowing for a good improvement in SNR even at short code lengths. Coding techniques based on Simplex or Golay codes exploit a set of different sequences (i.e. codes) of short (about 10 ns) NRZ laser pulses to increase the launched energy without impairing the spatial resolution using longer pulse width. However, the required high repetition rate of the laser pulses, hundreds of MHz for meter-scale spatial resolution, is not achievable by high peak power lasers, such as rare-earth doped fibre or passive Q-switched ones, which feature a maximum repetition rate of few hundred kHz. New coding technique, cyclic simplex coding (a subclass of simplex coding), tailored to high-power pulsed lasers has been proposed. The basic idea is to periodically sense the probing fibre with a multi-pulse pattern, the repetition period of which is equal to the fibre round-trip time. This way, the pattern results as a code spread along the whole fibre, with a bit time inversely proportional to the code length. The pulse width can be kept in the order of 10 ns to guarantee a meter-scale spatial resolution and the peak power can be set close to the nonlinear effect threshold.