Multiplex communications – Wide area network – Packet switching
Patent
1991-04-24
1993-07-06
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370123, 370 50, H04J 400
Patent
active
052260380
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for converting and a method for processing electronic multiplex signals, and an apparatus for processing such signals. Thus, on the one hand the invention relates to filtering of electronic signals combined with conversion from frequency-division multiplexing (FDM) of the signals to time-division multiplexing (TDM) of the signals, whereby many filter functions must be performed in parallel in order to separate the signals from each other. On the other hand, the invention is concerned with filtering of signals combined with conversion from time-division multiplexing of the signals into frequency-division multiplexing of the signals, whereby many filter functions must be performed in parallel in order to avoid frequency overlap of the signals in an undesired manner. In this connection the invention can be considered to relate to a combined electronic filter bank.
The invention also comprises a combination of conversion from FDM to TDM and subsequent conversion from TDM back to FDM, both taking place in one or more units having intermediate analogue and/or digital signal processing. This makes possible bandpass filtering of the signals with great flexibility in the choice of center frequency and bandwidth for implementing filter functions, and with a low processing requirement, power consumption and space requirement compared to other, known solutions based on present-day technology.
Conversion between FDM and TDM formats is today known by filtering and sampling, respectively, modulation of sample sequences, for each individual signal, and combination of sample sequences or signals to TDM or FDM formats. This results in large circuit arrangements with a high volume and power consumption. Moreover, so-called transmultiplexer techniques are known [1, 2] (See list of references at the end of this description). These are to a large extent based on digital processing for carrying out the filter functions and require a relatively high processing capacity.
Further, techniques are known based on the analogue-chirp-Z Fourier transform [3, 4], in which a Fourier transform of an analogue signal sequence is performed either by the steps of multiplication (M), convolution (C) and finally multiplication (M) with so-called chirp signals (FM sweep signals), i.e. an MCM transform; or by the steps of convolution, multiplication and convolution with such signals, i.e. a CMC transform.
From the patent literature reference can be made to European patent publication No. 214,649 which relates to conversion from FDM to TDM by complete Fourier transform, and therefore is encompassed within the field of known techniques mentioned above. Of greater interest is U.S. Pat. No. 4,578,790 which describes a system having in principle a structure somewhat related to that to which the present invention is directed. That U.S. patent, however, is specialized in the direction of single sideband multiplexing and purely digital filtering processes. It utilizes the digital technique in order to obtain simplification and does not at all discuss analogue processing in order to perform the individual functions in the transform.
The invention may be regarded to be most closely related to the above mentioned CMC transform, but is distinguished therefrom in that for the FDM-to-TDM case the first convolution (filtering) is omitted while at the same time the response of the filter employed for the last convolution is somewhat modified, but without substantially changing the complexity of the filter. In the TDM-to-FDM case the last filter is omitted and the first filter is modified.
More directed statements of the invention as of well as the novel and specific features thereof are found in the claims, of which claims 1 and 2 are respectively related to each of the two cases just mentioned.
The change in the frequency response of the corresponding chirp filters from the MCM circuits to the circuits proposed here, can in both cases be described as follows, in which it is assumed that a filtering of the signals is desired whic
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patent: 4237551 (1980-12-01), Narasimha
patent: 4578790 (1986-03-01), Molo et al.
patent: 4754449 (1988-06-01), Crookshanks
patent: 4901310 (1990-02-01), Ichiyoshi
patent: 5038344 (1991-08-01), Kawamura
Frobe Radio A/S
Jung Min
Olms Douglas W.
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