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Adaptive Quantizer

IP.com Disclosure Number: IPCOM000092443D
Original Publication Date: 1966-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 34K

Publishing Venue

IBM

Related People

Muehldorf, EI: AUTHOR

Abstract

This adaptive digital receiver automatically adjusts the receiver code word length to the minimum necessary to maintain a preselected output signal-to-noise ratio thus optimizing the total system performance.

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Adaptive Quantizer

This adaptive digital receiver automatically adjusts the receiver code word length to the minimum necessary to maintain a preselected output signal-to-noise ratio thus optimizing the total system performance.

A signal from the front end, not shown, of a communication receiver is applied to input 1 of heterodyning circuitry 2 which shifts the input signal frequency down to an intermediary level. The intermediary level signal is amplified in intermediary frequency amplifier 3 and then is sampled by sampler 4. The sampled signal is quantized and coded in quantizer-coder 5. The number of quantum levels and the corresponding number of bits in the digital code is controlled by computer 6. The data from quantizer-coder 5 is fed into computer
6. Here it is reconstructed according to digital algorithmic methods such as filtering, analyzing, or other digital processing techniques. The fully processed signal is then fed out of computer 6 at terminal 7 to a display device, not shown, or other utilization device.

In this communication system, there are two types of noise. First, the signal at output terminal 8 of amplifier 3 is contaminated by a certain amount of thermal noise stemming from both the equipment and the transmission medium background. Second, the process of quantizing introduces additional quantization noise. The latter decreases with an increasing number of quantum levels, or stated in an equivalent manner, decreases with an increasing code word length. The performance quality of the overall system is measured in terms of these noise components and specifically by the signal-to-noise ratio, average powers of the output signal at terminal 7. Since both noise components, thermal and quantization, are not correlated, it is assumed that the total output average noise power is the sum of the thermal and the quantization noise components. Under this assumption, one criterion for optimal operation of the system is to have both noise components equal. Other criterion can be chosen such as where the relative contributions of the noise components differ or where other factors such as the total received signal power are included in the criterion.

Increasing the code word length of the signal into computer 6 has the desirable effect of increasing the output signal quality by decreasing the quantization noise and increasing the signal-to-noise ratio. It also has the deleterious effect of slowing down the computer handling time. A tradeoff exists between the coding, code word length, and the total system...