WO1991008616A1 - Multiplexeur/demultiplexeur de frequence pour signaux a representation numerique - Google Patents

Multiplexeur/demultiplexeur de frequence pour signaux a representation numerique Download PDF

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Publication number
WO1991008616A1
WO1991008616A1 PCT/NO1990/000175 NO9000175W WO9108616A1 WO 1991008616 A1 WO1991008616 A1 WO 1991008616A1 NO 9000175 W NO9000175 W NO 9000175W WO 9108616 A1 WO9108616 A1 WO 9108616A1
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WO
WIPO (PCT)
Prior art keywords
frequency
samples
procedure
signal
signals
Prior art date
Application number
PCT/NO1990/000175
Other languages
English (en)
Inventor
Petter M. Bakken
Original Assignee
Frobe Radio As
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Frobe Radio As filed Critical Frobe Radio As
Publication of WO1991008616A1 publication Critical patent/WO1991008616A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/02—Channels characterised by the type of signal
    • H04L5/06—Channels characterised by the type of signal the signals being represented by different frequencies
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H17/02—Frequency selective networks
    • H03H17/0248—Filters characterised by a particular frequency response or filtering method
    • H03H17/0264—Filter sets with mutual related characteristics
    • H03H17/0266—Filter banks

Definitions

  • This invention relates to a method for splitting a signal which is respresented by a sequence of sample values, a representation referred to as a digital representation of the signal, into two subsignals depending on frequency.
  • the invention concerns therefore a specific form of signal processing, frequency demultiplexing. This operation is based on filtering and has a frequent application in communications equipment and other equipments using signal processing.
  • a related type of signal processing is the combination of two signals into one, and at the same time maintain isolation between the two original signals by giving them a different frequency in the combined signal. This latter type of processing is referred to as frequency multiplexing and it will be shown in the description that the invention after simple and well known modifications can be applied to frequency multiplexing as well as to frequency demultiplexing.
  • the procedure in [1] represents the state of the technology for simple demultiplexing, i.e. a low number of MR. It is possible to demonstrate how the methods given in [1] can be modified to obtain multiplexing with the same efficiency in terms of MR.
  • the invention is related with the procedure described in [1] in the the sense that the result of the signal processing will, by a suitable equipment design, be identical to the application of the procedure in [1] .
  • the invention results in a more efficient procedure because the MR rate for the identical demultiplexing (or multiplexing) is reduced by a factor 2 related to the method described in [1] . This effect is obtained by applying the characteristic properties as given in the patent claims.
  • the invention together with additional particular features and advantage shall be explained more closely in the following description with reference to the drawings, in which:
  • Fig. 1 schematically and in principle shows how the invented demultiplexer can be applied not only to split a signal into two subsignals, but also into 8 output subsignals by combining 7 demultiplexing cells where each cell can be designed according to the invention
  • Fig. 2 which shows how undesired aliasing signals (a) are added into the desired signals for a critical sampling frequency (b) and for twice the critical sampling frequency (c),
  • Fig. 3 which shows an example on the state of the technology (from [2] ) and which results in efficient implementation when the signals are represented by real sample values.
  • Fig. 4 which shows one filter cell design according to the invention and useful for demultiplexing. Each output sample value is calculated as a weighted sum over 7 input sample values.
  • Fig. 5 which shows a filter cell designed according to the invention and suited for multiplexing. Each output sample value is calculated as a weighted sum over 7 input sample values.
  • each sample value of a signal can be represented with one or alternatively two numbers.
  • these are referred to as the inphase value (a) and the quadrature value (b) .
  • the phase of the signal is given as Arctg (b/a) and its amplitude is a 2 + b 2 . It is equivalent and for most purposes simpler to consider the number
  • sample value described by one single real number It is also possible to use sample value described by one single real number. In this case 2B samples per seconds are required to describe the signal referred to above. This type of sampling is referred to as real sampling.
  • Multiplexing is the opposite, or dual, process of demultiplexing and may be derived in a trivial way from demultiplexing.
  • the invention will first be described applied to demultiplexing, the situation where a portion of the frequency band is applied for several signals with frequency distance B and a bandwidth less than B, and these signals are to be separated from each other by means of calculations based on the digital representation of the signals. This situation occurs frequently in equipment for telecommunications and other similar purposes.
  • the invention is applicable to splitting a signal in two parts depending on frequency. This type of operation is established in current technology. By repeating the splitting in a structure referred to as a tree-structure, it is possible to devide the signal into any number of channels.
  • the tree-structure lends itselves in particular to the case where the number channels is a power of two.
  • a tree-structure for eight channels is shown in fig. 1.
  • the tree-structure consists of 7 cells and by including into all cells devices to give all output signals zero center frequency it is obvious that all cells can be made identical if so preferable. Due to this property it is possible to concentrate the remaining of the description on how each cell is realized in state of the art technology and according to the invention.
  • the useful bandwidth is at the most 2B and for complex sampling the lowest sampling frequency which can be used without deteriorating the signal is 2B.
  • This sampling rate is referred to critical sampling.
  • Critical sampling is often applied, however, its disadvantage is that it is often too difficult to limit the total frequency spectrum at the input to 2B.
  • undesired signal outside the 2B bandwidth will be added to the desired signal by a well known mechanism for sampled signals. By increasing the sample frequency to, for example 4B, it is possible as shown in fig. 2 to accept undesired signal outside the band 2B without these interfering with the desired signals.
  • the signal processing which shall be carried out in the cell is well known both in principles and in applications.
  • the signal will be band limited to B in a filter (1) for the upper frequency divided channel.
  • the lower bandwidth now permit every second sample value to be removed after which the signal is transposed in frequency to be centered on zero frequency.
  • the same procedure is applied to the lower frequency divided channel in a filter (2) .
  • the two filters can be made identical except for their center frequencies.
  • the filter coefficients are referred to as the filter coefficients. Because the filters have a center frequency different from zero the coefficients must be complex valued. In spite of this, the two filters can be derived from a socalled prototype filter with real coefficients. The prototype filter is centered at zero frequency and has a correct filtering characteristics for the purpose except for the center frequency. The important quality of the design is to use a simplest possible filter and still realize the required degree of filtering. For filters which are to be designed as ASICs, simplicity is primarily to use a lowest possible number of MR of the type shown in eq. 1 between data and coefficients. A well known and frequently used technique is that if the requirements to the frequency response of the filter prototypes are as follows:
  • H(f) l 0 ⁇ f ⁇ B/2 (pass-band)
  • H(f) 0 3B/2 ⁇ f ⁇ 2B (stop-band)
  • a filter with this property is referred to as a half-band filter.
  • the pass-band and the stop-band can increase or decrease by the same amount without affecting the half-band property of the filter.
  • the fact that the upper (in frequency) and the lower (in frequency) filter has a common prototype is used for simplification. This property makes it possible to apply the same multiplications for both filters.
  • This technique is referred to as polyphase technique for two channels or as quadrature mirror filters for two channels.
  • each coefficient must be multiplied with the complex number
  • the complexity is reduced to 2n MR.
  • the complexity can be reduced from 2n MR to n MR by applying the symmetry that exists in the prototype filter even if this symmetry is not present in the filters (U:) and (L:).
  • the invention will lead to reduction of the MR rate by a factor of two which is a significant simplification of signal processing equipment for multiplexing/demultiplexing in relation to the state of the art. Filters of other types exploit in current technology the symmetry of the filter coefficient to reduce the number of multiplication by adding suitable data prior to multiplication by the procedure shown in Fig. 3.
  • each input sample is instead multiplied with the coefficience value h(0), h(l), h(3), etc. (dependent on the length of the filter).
  • multiplexing of the channels can be considered as a trivial modification of the demultiplexing.
  • the methods for such modification are described in [3].
  • This invention therefore is applicable to both demultiplexing and multiplexing.
  • a trivial modification of the procedure for demultiplexing according to the invention transforms to a procedure for multiplexing.
  • Multiplexing according to the invention will require n MR to calculate each output sample when the output sample is a weighted sum of 4n-l input samples. In this weighting a number, 2n-2, of the weighting factors are zero.
  • the invention leads to the same efficiency improvement related to current state of the art for demultiplexing and multiplexing.
  • Fig. 5 is derived in a trivial way from Fig. 4.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Mathematical Physics (AREA)
  • Stereophonic System (AREA)
  • Measurement And Recording Of Electrical Phenomena And Electrical Characteristics Of The Living Body (AREA)
  • Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)

Abstract

Procédé pour fractionner un signal de répartition en fréquence représenté par des valeurs échantillons complexes numériques en deux signaux distincts en fonction de la fréquence au moyen de deux filtres sélectifs en fréquence. Pour ce faire, on multiplie les échantillons d'une entrée sur deux avec des nombres réels. Les valeurs échantillons restantes et les produits obtenus sont ensuite soumis à des opérations simples, par exemple retard, changement de signe, permutations et addition, jusqu'à ce que l'on obtienne les valeurs souhaitées pour les échantillons de sortie. La présente invention décrit en outre un procédé correspondant pour la combinaison de deux signaux, qui peut découler du procédé de fractionnement décrit ci-dessus.
PCT/NO1990/000175 1989-11-29 1990-11-29 Multiplexeur/demultiplexeur de frequence pour signaux a representation numerique WO1991008616A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO894750 1989-11-29
NO894750A NO169266C (no) 1989-11-29 1989-11-29 Fremgangsmaate for aa splitte et signal representert ved punktproever i to signal anhengig av frekvensbaand, eller for aa kombinere signaler i to frekvensbaand til ett signal

Publications (1)

Publication Number Publication Date
WO1991008616A1 true WO1991008616A1 (fr) 1991-06-13

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ID=19892629

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PCT/NO1990/000175 WO1991008616A1 (fr) 1989-11-29 1990-11-29 Multiplexeur/demultiplexeur de frequence pour signaux a representation numerique

Country Status (3)

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AU (1) AU6888191A (fr)
NO (1) NO169266C (fr)
WO (1) WO1991008616A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0534255A2 (fr) * 1991-09-23 1993-03-31 Hughes Aircraft Company Emetteur/recepteur numérique à usage multiple par multplexage en temps
GB2344036A (en) * 1998-11-23 2000-05-24 Mitel Corp Single-sided subband filters; echo cancellation

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3621737C2 (fr) * 1986-06-28 1988-04-28 Ant Nachrichtentechnik Gmbh, 7150 Backnang, De

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3621737C2 (fr) * 1986-06-28 1988-04-28 Ant Nachrichtentechnik Gmbh, 7150 Backnang, De

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0534255A2 (fr) * 1991-09-23 1993-03-31 Hughes Aircraft Company Emetteur/recepteur numérique à usage multiple par multplexage en temps
EP0534255A3 (en) * 1991-09-23 1993-09-15 Hughes Aircraft Company Multiple use digital transmitter/transceiver with time multiplexing
GB2344036A (en) * 1998-11-23 2000-05-24 Mitel Corp Single-sided subband filters; echo cancellation
US6522747B1 (en) 1998-11-23 2003-02-18 Zarlink Semiconductor Inc. Single-sided subband filters
GB2344036B (en) * 1998-11-23 2004-01-21 Mitel Corp Single-sided subband filters

Also Published As

Publication number Publication date
NO169266C (no) 1992-05-27
NO169266B (no) 1992-02-17
AU6888191A (en) 1991-06-26
NO894750L (no) 1991-05-30
NO894750D0 (no) 1989-11-29

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