Method and apparatus for digital correlation

A computer-readable storage medium having stored therein a computer program for correlating first and second digital signals wherein both signals contain a series of numerical data values, the computer program, when executed, performs the steps comprising of:

• (a) sequentially calculating products of corresponding numerical data values of the first and second digital signals and providing a cumulative sum thereof;
• (b) upon deviation of the cumulative sum from between upper and lower thresholds levels, increasing or decreasing the cumulative sum by a predetermined amount so as to return the cumulative sum to between said threshold levels;
• and
• (c) providing a correlation parameter as a function of the number of occurrences of deviation of the cumulative sum from between upper and lower thresholds.

An apparatus for correlating a first signal and a second signal, both the first and second signals contain a series of numerical data values, comprising:

• a processor arranged to execute code to perform steps comprising of:
• (a) sequentially calculating products of corresponding numerical data values of the first and second signals and providing a cumulative sum thereof;
• (b) upon deviation of the cumulative sum from between upper and lower thresholds levels, increasing or decreasing the cumulative sum by a predetermined amount so as to return the cumulative sum to between said threshold levels;
• and
• (c) providing a correlation parameter as a function of the number of occurrences of deviation of the cumulative sum from between upper and lower thresholds.

A GPS receiver comprising receiver means for receiving a subject signal containing a target pseudorandom noise code;

• and processing means for generating early and late replica code signals corresponding to the target code, correlating the subject signal with the early and late replica code signals and returning respective early and late correlation values, and calculating a code phase discriminator for determining whether the target code has been acquired;
• wherein the correlation between the subject signal and the early and late replica code signals is performed by steps:
• (a) sequentially calculating products of corresponding numerical data values of the subject signal and early and late signals and providing a cumulative sum thereof;
• (b) upon deviation of the cumulative sum from between upper and lower thresholds levels, increasing or decreasing the cumulative sum by a predetermined amount so as to return the cumulative sum to between said threshold levels;
• and
• (c) providing the early and late correlation values as a function of the number of occurrences of deviation of the cumulative sum from between upper and lower thresholds.