## 1 Introduction  
Ultrasonic guided wave testing is an important method of non-destructive testing (NDT) techniques because of its potential to evaluate the durability, the physical and mechanical properties of pipelines [1]. This method is widely used to test pipeline integrity over a long distance from any location [2]. Different types of guided waves can propagate in any bounded medium, such as the well-known Rayleigh (surface) waves or the Lamb waves on plates [3]. An array has many transducers used in a pulse-echo mode installed around the pipe circumference to excite signals in low frequencies of ultrasound at any inspection location. The purpose is to generate a single axisymmetric wave pattern. However, guided waves suffer from high attenuation when they propagate in attenuating material pipes and multiple modes due to the excitation, which reduces the power of echo signals and induces corruption caused by coherent noise [4]. Therefore, the excitation amplitude of input signals needs to be enhanced to acquire featured signal responses. For industrial purposes, many of these pipelines need to carry explosive and flammable material such as oil or natural gas. The common inspection systems are not suitable due to the high voltage (typical above 50 Volts) used by the pulsing circuitry. It may has high possibility of dangerous to cause high-voltage sparks, even a potential risk to create a fire or explosion [5]. The problem must be solved in a safe manner. Therefore, an inspection system operated by low-voltage ultrasound is required in these specific application environments. Another critical point of industrial interest is to develop an innovative technique for fault detection in pressurized pipes. It is the case of the Transient Test-Based Techniques (TTBTs). Even if in the last two decades they have been used mainly for water pipes, it can be used for any fluid. Transient Test-Based Techniques identify leaks and other possible faults (e.g., partial blockages, and pipe wall deteriorations) straightforwardly on the basis of the measured reflected pressure waves [6; 7]. It is worth noting that, with respect to other techniques, TTBTs are very attractive since the duration of the test is very short and they allow detecting also devious defects (e.g., partial blockages, illegal branches) which do not give rise to any exterior sign. Moreover, small, but sharp, amplitude pressure waves allow reliable fault detection [8]. Therefore, it is also necessary to use advanced signal processing methods for improving the transient signal performance, such as its the signal-to-noise ratio (SNR) or others. Generally, there are many techniques to improve the inspection system performance by increasing the SNR, such as wavelet transform, pulse compression and so on. In the case of poor SNR, it is tough for wavelet transform to filter the signal coefficients in every decomposition layer effectively, which may cause the denoising failure [9]. The pulse-compression technique is commonly used by radar, sonar and echography to enhance the echo SNR. This method depends on a combination of cross-correlation with a reference signal [10]. There are two modulation methods in pulse compression, including frequency modulation and phase modulation. Coded excitation is phase modulation on a pulse. [PERSON] first proposed the technique applied to medical ultrasound imaging systems in 1979 [11]. However, there are few studies within the literature on coded excitation in recent years due to the time-bandwidth limitation of this technique. [PERSON] considered using coded excitation to ultrasound system for improving the SNR [12]. Afterwards, the digital beamforming with signal compression was used in the ultrasound system. Later, [PERSON] and [PERSON] gave a general construction for an odd length binary Golay sequence pair of length 26 from a Barker sequence of length 13 and a related Barker sequence of length 11 [13]. However, their work focused on the theoretical research for coded excitation only. [PERSON] et al.