Abstract:
Method and apparatus for generating random numbers are disclosed. In one aspect, a method for generating random numbers for use in a wireless communication device provides for generating random numbers, gathering a sample of the generated random numbers, and computing at least one metric, such as mean value, standard deviation, and/or entropy. The method further provides for comparing the metric with a corresponding reference value and adjusting the metric based on a result of said comparison so that the generated random numbers achieve a desired distribution. In another aspect, an apparatus for generating random numbers includes an analog noise generator and hardware components for generating random numbers and feedback values to adjust the random numbers. The apparatus further includes a processor capable of executing instructions to carry out control algorithms for adjusting the random numbers.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   The described embodiments were made with government support under United States government contract MDA904-01-G-0620/J.O. 0002 awarded by the National Security Agency (NSA), Maryland Procurement Office. The government may have certain rights in these described embodiments. 

   FIELD 
   The present invention relates to random number generators. More specifically, the present invention relates to methods and apparatus for stable, consistent, self-calibrating random number generators for high-volume production of wireless communication devices. 
   BACKGROUND 
   In wireless communications terminals or devices, there is a need for random-number generators, e.g., for cryptographic applications. However, variations in the operating conditions (such as changes in temperature, voltage and current) and variations in component characteristics (due to inconsistencies in component manufacturing, aging, shelf life and operational life) cause existing random-number generators to vary in the performance of generating random numbers. Consequently, similar devices manufactured to perform uniformly fluctuate in their performance because the constituent random-number generators vary in their characteristics and; thus, produce different random-number distributions. 
   There is a need, therefore, for random-number generators that perform uniformly in spite of variations in component characteristics, operating conditions, and environment. There is also a need for similarly manufactured devices to operate similarly and show uniform and consistent performance. 
   SUMMARY 
   The disclosed embodiments provide novel and improved methods and apparatus for generating random numbers. In one aspect, a method for generating random numbers for use in a wireless communication device provides for generating random numbers and gathering a sample of the generated random numbers. The method further provides for computing at least one metric, such as mean value, standard deviation, and/or entropy, based on the gathered sample, and comparing the metric with a corresponding reference value. The method further provides for adjusting the metric based on a result of the comparison so that the generated random numbers achieve a desired distribution. 
   In another aspect, an apparatus for generating random numbers includes an analog noise generator and hardware components for generating random numbers and feedback values to adjust the random numbers and their distribution. The apparatus further includes a processor capable of executing instructions to carry out control algorithms for adjusting the random numbers and their distribution. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become more apparent from the detailed description of the embodiments in connection with the drawings set forth below: 
       FIG. 1  illustrates a block diagram of a random-number generator; 
       FIG. 2  illustrates a flow chart for generating random numbers; 
       FIG. 3  illustrates noise voltage waveforms for similarly manufactured devices; 
       FIG. 4  illustrates random-number distributions for similarly manufactured devices without adjustment; and 
       FIG. 5  illustrates similar random-number distributions for similarly manufactured devices with automatic adjustment. 
   

   DETAILED DESCRIPTION 
   Before several embodiments are explained in detail, it is to be understood that the scope of the invention should not be limited to the details of the construction and the arrangement of the components set forth in the following description or illustrated in the drawings. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     FIG. 1  illustrates a block diagram of an automatic self-adjusting random-number generator  100 , according to one embodiment. Random-number generator  100  generally includes analog noise generator hardware  102 , control processor hardware  104 , and control processor software module  106 . Analog noise generator hardware  102  provides a random analog voltage that is normally distributed with a mean value X and a standard deviation S. Analog noise generator hardware  102  may also include a noise diode  108  and an amplifier  110  for signal conditioning, according to one embodiment. The noise diode may be used in its reverse breakdown region, biased to operate on the “knee” of this part of the operating characteristic. When the diode is operated in this region, the AC voltage at its terminals is a Gaussian distribution with flat spectral density over its bandwidth. 
   The control processor hardware  104  includes an ADC (analog to digital converter)  112 , a CPU (central processing unit) or computer, and DACs (digital to analog converters)  114  and  116 . The ADC  112  quantizes the normally distributed analog noise voltage based on the voltage reference (V-Ref) value and generates random numbers. The CPU in conjunction with the control software module computes at least one metric, based on a sample of the quantized noise voltage, e.g., random numbers, adjusts the reference voltage (V-Ref) input to the ADC  112 , and the DC offset input of the amplifier  110 , in order to “fit” the distribution of the random numbers into the full range “window” of the ADC&#39;s capability. The DC offset represents the mean X of the random numbers, and the reference voltage (V-Ref) represents the standard deviation of the random numbers. The ADC reference voltage corresponds to the full-scale quantization capability of the ADC, i.e., it sets the maximum voltage into the ADC that can be digitized without over scaling the converter. Thus, adjusting the reference voltage is directly proportional to the peak-to-peak voltage conversion of the ADC. 
   According to one embodiment, control processor software module  106  operates on a sample of random numbers produced by the ADC  112  and computes the mean X and the standard deviation S of the chosen sample for feeding back into the DACs  114  and  116 , respectively. The mean value X is used to control the location of the peak of the histogram of the random numbers generated by the ADC  112 , as shown by the waveform  118 . The standard deviation S is used to control the width of the histogram of the random numbers generated by the ADC  112 , as shown by the waveform  120 . 
   In typical random-number generator systems, where only a few are being built and the operating environment is quasi-static, the systems may be adjusted by changing their parts to achieve consistent random-number distribution across all systems. However, in a high-volume production, such as mobile phones, there is a need for automatic adjustment capability that provides for consistent random-number distribution across high-volume production and under varying operating conditions. 
     FIG. 2  illustrates a flow chart for adjusting random-number distributions, according to one embodiment. In step  202 , some initial values for the DC offset and reference voltage (V-Ref) are chosen, which may be the final values obtained when the random-number generator was last adjusted. In step  204 , a sample of the random numbers produced by the ADC  112  is selected. In step  206 , the mean value of the selected sample of random numbers is computed and compared to a reference mean value. The reference mean value may be chosen based on the ADC bit width of the random-number generator. For example, for an 8-bit ADC, the reference or desired mean value would be 127 to conform to a desired Gaussian random-number histogram  122 . The reference mean value of 127 corresponds to the midpoint of the 8-bit ADC range. Based on the comparison conducted in step  206 , the DC offset value input to the amplifier  110  is adjusted, in step  208  or  210 , as the case may be, through some linear, nonlinear, or adaptive control algorithm well known in the art. 
   Similarly, in step  212 , the standard deviation value of the selected sample of random numbers is computed and compared to a reference standard deviation value. The reference standard deviation value may be chosen based on the accuracy or ADC full scale value of the random-number generator. For example, for an 8-bit ADC  112 , the reference or desired standard deviation value would be about 42 to conform to the desired Gaussian random-number histogram  122 . The reference standard-deviation value of 42 corresponds to about one-sixth of the 8-bit ADC range, providing a random-number distribution of six sigma in the ADC. Based on the comparison conducted in step  212 , the input to the DAC  116  is adjusted, in step  214  or  216 , as the case may be, through some linear, nonlinear, or adaptive control algorithm well known in the art. 
     FIG. 3  illustrates three noise voltage waveforms generated by three similarly manufactured devices. These noise voltages waveforms correspond to the signals generated at the output of the respective amplifiers  110 . These waveforms generally have different mean and standard deviation values, because of the difference in the constituent component characteristics, operating conditions, and environment. 
     FIG. 4  illustrates three random-number distributions for the three similarly manufactured devices mentioned above in connection with  FIG. 3 , without automatic adjustment. These random-number distributions correspond to the random-numbers generated at the output of the respective ADCs  112 . They still have different mean and standard deviation values. 
     FIG. 5 , however, illustrates three uniform random-number distributions for the similarly manufactured devices mentioned above in connection with  FIG. 3 , with automatic adjustment mechanism. These random-number distributions correspond to the random numbers generated at the output of the respective ADCs  112 . They desirably have same, or very close, mean and standard deviation values, in spite of the difference in their constituent component characteristics, operating conditions, and environment. 
   Therefore, the control processor and software module disclosed herein adjust the random-number generator to produce similar random-number distributions across numerous similarly manufactured devices under varying operating conditions. For example, after the mean and sigma adjustment criteria have been met, the random-number generator is considered calibrated and ready to provide random numbers for the desired application with metrics that are consistent over initial production, environmental variations and life cycle of the product. 
   In another embodiment, additional metrics such as entropy, which indicates how much randomness exists in the generated random numbers, may also be computed and adjusted for adjusting the performance of the random-number generator. 
   Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and protocols. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
   Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. 
   The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e. g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
   The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a MS-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
   The description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments, e. g., in an instant messaging service or any general wireless data communication applications, without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.