A Search for Good Pseudo-random Number Generators : Survey and Empirical Studies

In today's world, several applications demand numbers which appear random but are generated by a background algorithm; that is, pseudo-random numbers. Since late $19^{th}$ century, researchers have been working on pseudo-random number generators (PRNGs). Several PRNGs continue to develop, each one demanding to be better than the previous ones. In this scenario, this paper targets to verify the claim of so-called good generators and rank the existing generators based on strong empirical tests in same platforms. To do this, the genre of PRNGs developed so far has been explored and classified into three groups -- linear congruential generator based, linear feedback shift register based and cellular automata based. From each group, well-known generators have been chosen for empirical testing. Two types of empirical testing has been done on each PRNG -- blind statistical tests with Diehard battery of tests, TestU01 library and NIST statistical test-suite and graphical tests (lattice test and space-time diagram test). Finally, the selected $29$ PRNGs are divided into $24$ groups and are ranked according to their overall performance in all empirical tests

Delay-Doppler Channel Estimation with Almost Linear Complexity

A fundamental task in wireless communication is Channel Estimation: Compute the channel parameters a signal undergoes while traveling from a transmitter to a receiver. In the case of delay-Doppler channel, a widely used method is the Matched Filter algorithm. It uses a pseudo-random sequence of length N, and, in case of non-trivial relative velocity between transmitter and receiver, its computational complexity is O(N^{2}log(N)). In this paper we introduce a novel approach of designing sequences that allow faster channel estimation. Using group representation techniques we construct sequences, which enable us to introduce a new algorithm, called the flag method, that significantly improves the matched filter algorithm. The flag method finds the channel parameters in O(mNlog(N)) operations, for channel of sparsity m. We discuss applications of the flag method to GPS, radar system, and mobile communication as well.Comment: 11 page

Graphical User Interface and Microprocessor Control Enhancement of a Pseudorandom Code Generator

Modern digital communication techniques often require the generation of pseudorandom numbers or sequences. The ability to quickly and easily produce various codes such as maximal length codes, Gold codes, Jet Propulsion Laboratory ranging codes, syncopated codes, and non-linear codes in a laboratory environment is essential. This thesis addresses the issue of providing automated computer control to previously built, manually controlled hardware incorporating the Stanford Telecom STEL-1032 Pseudo-Random Number (PRN) Coder. By incorporating a microcontroller into existing hardware, the STEL-1032 can now be conveniently controlled from a MATLAB Graphical User Interface (GUI). The user can quickly create, save, and recall various setups for the STEL-1032 in an easy to use GUI environment. In addition to having complete control of the STEL-1032\u27s internal actions, the microcontroller adds an extra measure of control possibilities by using various signals as possible interrupt sources. The microcontroller can sample the STEL-1032\u27s various outputs at a rate up to 320 kHz and the data can be imported directly into MATLAB for further analysis

Development and application of spread-spectrum ultrasonic evaluation technique

A new approach to ultrasonic NDE called spread-spectrum ultrasonic evaluation (SSUE) is investigated. It regards the ultrasonic nondestructive evaluation as an acoustic-impulse-response estimation and characterization problem. This problem has been compared with the analogous problems of radio-detection-and-ranging from communications field and the seismic exploration problem of geophysics. Out of the various options for the impulse response estimation, the continuous pseudorandom signal correlation method has been shown to be the optimum for peak-power limited systems such as the ultrasonic NDE systems. The problem of self-noise and its consequences in pseudorandom correlation systems is investigated, followed by the development of various optimum and sub-optimum approaches to self-noise elimination. After verifying the theoretical results through computer simulations, a lab-grade SSUE instrument was developed and analyzed. Also, a new, efficient method for the implementation of DSP-based correlator is developed. The application of SSUE technique to various practical NDE situations like, flaw detection, velocity/thickness measurements, attenuation measurement, global integrity assessment, etc., was investigated through various laboratory experiments. It is concluded that the SSUE technique holds great promise for all ultrasonic NDE applications where high signal attenuation results into the loss of signal-to-noise ratios beyond workable limits;SSUE employs a non-traditional approach to ultrasonic NDE that makes it more robust and powerful. One significant feature of the SSUE technique is that it overcomes the maximum average power limitation of the existing techniques. Conventional pulsed ultrasonic NDE systems are peak power limited by the transducer breakdown voltage and the average power is limited by the narrow pulse duration which is important to maintain good resolution. In certain NDE applications there are factors other than the transducer peak power limitation, which limit the amplitude of the transmitted signal. In case of medical ultrasound devices, for example, the peak power limit arises from the risk of causing tissue damage. For such kind of applications, SSUE has a direct solution to increasing the average power while maintaining the resolution. Ultrasonic NDE instrument in a field or industrial environment is subject to all kinds of acoustic and electromagnetic interferences. This results into a degradation of instrument sensitivity and reliability. SSUE technique, by virtue of its robust operating principal, is capable of interference rejection to a much larger extent

Multiple range imaging camera operation with minimal performance impact

Time-of-flight range imaging cameras operate by illuminating a scene with amplitude modulated light and measuring the phase shift of the modulation envelope between the emitted and reflected light. Object distance can then be calculated from this phase measurement. This approach does not work in multiple camera environments as the measured phase is corrupted by the illumination from other cameras. To minimize inaccuracies in multiple camera environments, replacing the traditional cyclic modulation with pseudo-noise amplitude modulation has been previously demonstrated. However, this technique effectively reduced the modulation frequency, therefore decreasing the distance measurement precision (which has a proportional relationship with the modulation frequency). A new modulation scheme using maximum length pseudo-random sequences binary phase encoded onto the existing cyclic amplitude modulation, is presented. The effective modulation frequency therefore remains unchanged, providing range measurements with high precision. The effectiveness of the new modulation scheme was verified using a custom time-of-flight camera based on the PMD19-K2 range imaging sensor. The new pseudo-noise modulation has no significant performance decrease in a single camera environment. In a two camera environment, the precision is only reduced by the increased photon shot noise from the second illumination source