Polyphase channelization system

Abstract

A polyphase channelizer converts an intermediate frequency wideband signal into a complex signal that is sampled by parallel analog-to-digital converters having a bank of samplers respectively clocked by staggered clocking signals for respective converters for feeding I and Q quadrature samples to a polyphase filter bank of finite impulse response filters driving a fast Fourier transform processor for providing channelized digital signal outputs. The parallel analog-to-digital converters can operate at lower speeds but are parallel connected for effectively operating at required higher speeds. The channelizer channelizes the wideband signal using a polyphase clock for enabling high speed sampling and converting through low speed parallel analog to digital converters.

Description

STATEMENT OF GOVERNMENT INTEREST[0001]The invention was made with Government support under contract No. F04701-00-C-0009 by the Department of the Air Force. The Government has certain rights in the invention.FIELD OF THE INVENTION[0002]The invention relates to the field of communication systems. More particularly, the present invention relates using parallel low speed analog to digital converters in combination with polyphase channelization for processing of wideband signals in communication systems.BACKGROUND OF THE INVENTION[0003]The present and future generations of satellites need to operate with small earth terminals as with mobile vehicle or hand held terminals. Such satellites need to be user oriented in that the user terminal needs to be relatively less complex and have small power, weight and low cost requirements. Such communications systems may be realized at the cost of increasing the complexity of the space borne equipment and central earth stations. An example of such ...

AI Technical Summary

Benefits of technology

[0035]Another object of the invention is to provide a polyphase channelization communication system using low speed analog digital converters connected in parallel to effectively provide high speed processing of wideband signals.

[0036]The present invention is directed to a communication system for wideband signal processing through parallel analog to digital converters (ADCs) in combination with polyphase channelization. The ADCs can be low speed ADCs operating in parallel to provide effective high speed analog to digital (A / D) conversion. The polyphase channelization enables the use of the low speed ADCs. The polyphase channelization is perfected by a polyphase channelizer includes a complex mixer for downconversion of the input wideband signal into baseband quadrature signals that are fed into the parallel A / D converters having a plurality of converter channelized outputs. The converter channelized outputs are fed into a bank of polyphase filters and a fast Fourier transform (FFT) processor that provides a plurality of channelized digital outputs. The wideband input signal is downconverted into a quadrature signal and converted into digital form for processing by the filter bank and FFT processor. The FFT processor combines polyphase filter outputs so as to produce digital output signals for the communication input channels at different carrier frequencies separated and downconverted to baseband. The digital output signals have a zero center frequency. When the wideband composite signal input is over a complex baseband or IF, individual channels have different center frequencies. Thus, the polyphase channelizer performs both functions of the frequency downconversion and separation. In the polyphase filtering, the task of filtering is divided into smaller tasks performed by individual filters. Thus, the filter length and hence computational task performed by individual polyphase filters is only 1 / N of the filter length in direct implementation of a single bandpass filter. In addition, the same polyphase filters are shared by all the channels to reduce the computational task by approximately by a factor of N. The polyphase channelizer offers channelized baseband digital processing of wideband signals using low speed ADCs for reduced power consumption.

Problems solved by technology

Such communications systems may be realized at the cost of increasing the complexity of the space borne equipment and central earth stations.

In broadband satellites having nominal bandwidths in GHz regimes, major limitations are inherent in analog to digital (AD) conversion of the received broadband signal.

This high-speed conversion rate imposes limitations on the ability of A / D converters operating at such high speeds as well as increasing power requirements and costs.

Such a hybrid analog and digital structure suffers from the disadvantages of the analog processing in terms of weight and power requirements of the analog filters and lacks the advantages of completely digital processing.

However, the application of FFT results in a circular convolution of the input signal segment and the filter impulse response instead of the desired linear convolution.

The communication of broadband signals require A / D converters operating at a very high rate imposing limitations in terms of availability and power requirements.

The A / D conversion is a major limitation in extending DSP applications to higher and higher bandwidth signals.

In a given state of A / D conversion technology, there are severe restrictions in terms of availability, the cost and power requirements versus the required sampling rate, and A / D conversion accuracy measured in terms of the number of bits per sample.

Thus for a wide band signal, in conventional implementation, the A / D converter may not be available, may not have the required number of bits, or may require excessive power, or may be exceedingly expensive.

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