Method and apparatus for vswr estimation using cross-correlation and real sampling without the need for time alignment

Abstract

Methods, apparatus, and computer program products using spectrum analysis or cross correlation techniques to discriminate against interference. These approaches are straight forward if both the forward and reflected signals contain complex or quadrature (I and Q) samples. But, if only single axis samples are available as is often the case to reduce the sampling rate, the resulting samples could represent the I component, the Q component or, more likely, some combination of the two. This generally requires some type of time alignment procedure to ensure proper phase. Assuming that the transmitted signal exists in complex form, this signal can be mathematically rotated in phase and then single axis sampled for comparison against the single axis reflected signal. If the rotation is done over equally spaced intervals that spans one complete cycle, the average of the absolute value all such return loss ratios will approach the actual return loss ratio and the interference will be suppressed. The resultant can be compared to a threshold value and trigger an alarm.