Multiplex communications – Generalized orthogonal or special mathematical techniques – Particular set of orthogonal functions
Reexamination Certificate
1999-05-10
2002-09-10
Ton, Dang (Department: 2661)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Particular set of orthogonal functions
C375S342000, C370S203000, C370S316000, C370S437000, C370S543000, C455S012100
Reexamination Certificate
active
06449244
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to implementations of orthogonal narrowband channels in a digital demodulator, and more particularly, relates to a methodology to adapt a multi-rate processing algorithm and channel spacing of an existing channelizer design for implementation of orthogonal narrowband channels of different input data rates and input channel group bandwidths.
2. Related Art
Generally, multi-channel wireless communication systems such as satellite communication systems may contain a certain number of transponders for communications over a broad geographical area. Each transponder may be a receiver-transmitter pair. The receiver of a satellite system may be a wideband receiver that may cover a wide range of communication frequencies within an available multi-channel bandwidth. The range of communication frequencies may depend on the number of channels the satellite communication systems can handle. Channelizers may be used to separate an input wideband signal of a specific spectrum received from an antenna into a plurality of narrower band channels for further processing. The wideband signal may carry different channels using different frequency bands, different time slots, different spread spectrum coding, or a combination of any two or more of these techniques. The channelizers may be considered as wideband channelizers and/or narrowband channelizers used to separate an input wideband signal into smaller sections of constituent channels. The term “wideband” may not be limited to any particular spectral range. Rather, wideband may imply a spectral coverage of at least the useful communication range over which the multi-channel wireless communications system may operate. Narrowband may, on the other hand, imply only a portion of the spectrum, for example, the width of an individual channel. Narrowband channels may be referred to as subchannels of a channel group. For example, a 15 MHz channel group may contain 50 narrowband channels each with a 300 kHz bandwidth. Many channelizers may operate on radio frequency (RF) or baseband, analog or digital signals.
Typically, multiple levels of channelization are required to access the data in the narrowband channels. However, the channelizers are typically designed for a specific channel group bandwidth and data rate set that depends on the arrangement of the prior levels of channelization. Several methodologies for typical channelizer designs are known. For example, theoretical basis for such a channelizer design is described in “
Multirate Digital Signal Processing
” by R. E. Crochiere and Rabiner, published in 1983 by Prentice Hall, Englewood Cliffs, N.J., which publication is incorporated herein by reference in its entirety. Theoretical basis for multichannel demodulator designs is provided in “
Narrowband Channel Group Multichannel and Multimode Demodulator
” by Russell R. Rhodes and Dean P. Kolba, published in August 1997 by MIT Lincoln Laboratory. Additional basis for orthogonal narrowband channel spacing of such demodulator designs is described in “
Orthogonal Spacing For Narrowband Channels In The Advanced EHF Waveform
” by Mark Maleski et al., published in September 1997 by Booz-Allen & Hamilton. However, many contemporary channelizer designs are afflicted with considerable design constraints. Examples of the design constraints may include the following: the input data rate must be the same as the input channel bandwidth; the discrete Fourier transform (DFT) size must be the same as the number of valid output channels; and the input bandwidth must be full with valid channels. Moreover, once a channelizer design is realized for a specific channel group bandwidth and data rate set, such a channelizer may not be reconfigured and/or adapted for operations with different input data rates and input channel group bandwidths. Consequently, contemporary methodology for typical channelizers is not flexible for use in multiple data rate applications. Accordingly, there is a need for a uniform and reliable methodology used to adapt a multi-rate processing algorithm and channel spacing of a channelizer design and to develop a channelizer architecture for implementation of orthogonal narrowband channels of different input data rates and input channel group bandwidths. Such a methodology must be flexible and maintain the ability to reconfigure channelization process to account for changes in channel layout and data rate.
SUMMARY OF THE INVENTION
In accordance with the present invention, an innovative channelizer design methodology is provided to design a single orthogonal channelizer for implementation of orthogonal narrowband channels of different input data rates. The channelizer design methodology includes obtaining information relating to an input sampling rate, an input channel group bandwidth, a number chips per hop which varies in accordance with a modulation mode, a hop time and a valid symbol time per hop of an input signal; calculating an output sampling rate of the input signal based on the number chips per hop and the valid symbol time per hop; calculating a number samples per chip based on the input sampling rate and the output sampling rate, and a number samples per hop based on the input sampling rate and the hop time, respectively; determining a discrete Fourier transform (DFT) size less than the number samples per chip; calculating a channel spacing of the input signal based on the input sampling rate and the discrete Fourier transform (DFT) size; determining a number of valid output channels of the input signal based on the input channel group bandwidth and the channel spacing; determining a number of data samples of the input signal and which data samples are to be blanked on either side of a chip boundary based on the number samples per hop and the number chips per hop; and determining a:circular shift value based on the sample number modulo the discrete Fourier transform (DFT) size, where the sample number is from zero to the number samples per hop minus one.
The number of data samples of an input signal to be blanked, the circular shift value, and the discrete Fourier transform (DFT) size are then used to construct a single orthogonal channelizer comprising a blanking filter and cyclic shift block which performs sample blanking operations in accordance with the number of data samples of said input signal to be blanked, and phase shift operations in accordance with the circular shift value, and a discrete Fourier transform (DFT) block which performs discrete Fourier transform (DFT) computations in accordance with the DFT size. The single orthogonal channelizer obtained using the innovative channelizer design methodology of the present invention is provided for efficiently servicing multiple input data rates with minimal additional hardware for reconfiguration while realizing design hardware savings. The configurable orthogonal channelizer may be implemented with an efficient hardware architecture using blanking filter, cyclic shift and discrete Fourier transform techniques to separate an input signal of different channel group bandwidths into a plurality of individual channels at different data rates. The orthogonal channelizer can be configurable to separate data samples of an input signal into a first plurality of individual channel(s) with a spacing of a bandwidth frequency of the input signal at a first data rate using sample blanking operations, cyclic shift operations and discrete Fourier transform (DFT) computations, when a selected mode of channelization corresponds to the first data rate. Similarly, the single orthogonal channelizer can also be configurable to separate data samples of the input signal into a second plurality of individual channel(s) with a spacing of twice a bandwidth frequency of the input signal at a second data rate using sample blanking operations, cyclic shift operations and selected discrete Fourier transform (DFT) computations, when a selected mode of channelization corresponds to the second data rate. Likewise, the single orthogon
Baron Henry
Ton Dang
TRW Inc.
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