Hadamard Processing of Multi-Channel Pre-Digitized Data for Bandwidth Compression
Lee,David K.
General Dynamics C4 Systems
Bahr,Randy K.
General Dynamics C4 Systems
To effectively manage bandwidth in a digital communication system, it is desirable to use the minimum number of quantizing bits necessary to achieve desired system performance. For a system with parallel input signals, where the average power for each signal source is dynamic, it is especially difficult to efficiently allocate quantization bits.
We present a solution to this problem by utilizing “hadamard-matrix processing” (HMP) which consists of a decorrelator followed by the hadamard matrix operation. If the input signals are uncorrelated, the hadamard-matrix operation transforms the parallel signal sources to have the equivalent average power prior to quantization, thereby effectively minimizing the overall number of quantization bits required to achieve system performance. To insure that the signals are uncorrelated, we implement a decorrelator prior to the hadamard. Different decorrelator methods of varying complexity are examined. We show that the decorrelation methods when used with the Hadamard matrix can influence the immunization of “signal clipping” due to quantization in addition to realizing significant system capacity and/or power gains.
We demonstrate the performance of the HMP on the Mobile-User Objective System (MUOS) through simulation by comparing overall G/T degradation for different scenarios.
The results show a potential additional gain of 1.4 dB for 6-bit quantization relative to operating the Hadamard without the use of a decorrelator. Note that without the Hadamard, similar G/T degradation would require substantially more quantization bits. This amount of gain has a significant impact on system bandwidth and/or satellite power reduction.
David K. Lee received the B.S. and M.S. degrees in Electrical Engineering from Kansas State University, Manhattan, Kansas in 1994 and 1996, respectively. He is currently a doctoral candidate at the University of Southern California (USC) Viterbi School of Engineering, Los Angeles, CA where his research interests are in the areas of iterative detection and wireless communication. Since 1996, he has been with General Dynamics (formerly Motorola Space Systems) in Scottsdale, AZ where he currently works as a senior communication systems engineer.