Accession Number : AD0915349

Title :   Time Domain Analysis of an Automatic Gain Control Weighted Diversity Combining System.

Descriptive Note : Technical publication,

Corporate Author : NAVAL MISSILE CENTER POINT MUGU CA

Personal Author(s) : Hill, E. R.

Report Date : 14 DEC 1973

Pagination or Media Count : 61

Abstract : The time domain performance of an automatic gain control (AGC) weighted diversity combiner is studied for deterministic radio frequency (RF) input fading envelopes. The non-linear differential equation relating the AGC voltage to the RF input fading envelope is derived. For given fading signals this differential equation is evaluated (by computer) for the AGC voltages at discrete points in time. This information is used to compute the combiner output signal-to-noise ratio (SNR) at these times. It is shown that the AGC weighted combiner is optimum (maximal-ratio) only for fade rates where the AGC loop can track the fading RF input signals perfectly. It is found that (for certain fading signals) a critical fade rate exists (for a given AGC time constant) for which the AGC weighted combiner reaches a condition of worst performance. At higher fade rates the performance approaches that of an equal-gain combiner for RF signals of equal average value. It is shown that by using both the amplitude-modulated (AM) an AGC voltages for weighting, a maximal-ratio combiner can be built which is not limited by the tracking rate of the AGC loop. (Existing AGC weighted combiners can be modified by use of one external logarithmic amplifier per channel.) Also, it is shown that an optimum diversity selector can be implemented by use of both the AM and AGC voltages. (Author)

Descriptors :   (*AUTOMATIC GAIN CONTROL, FEEDBACK), (*INFORMATION THEORY, FADING(ELECTROMAGNETIC WAVES)), (*RADIO TELEMETRY, PERFORMANCE(ENGINEERING)), INTERMEDIATE FREQUENCIES, SIGNAL TO NOISE RATIO, NUMERICAL ANALYSIS, DIGITAL COMPUTERS, AMPLITUDE MODULATION, COMPUTER PROGRAMS, RESPONSE, TRANSIENTS.

Subject Categories : Electrical and Electronic Equipment
      Cybernetics
      Radio Communications

Distribution Statement : APPROVED FOR PUBLIC RELEASE