CN1135777C - Digital system for subscriber lines allowing high bit rates - Google Patents

Abstract

A connection between subscriber lines allowing high bit rates in elecommunications networks includes a subscriber line (5) connected to a line unit (1), and subscriber units (9) connected through the twisted-pair (7). Thd information is exchanged in two-direction in the cable by using the frequency multiplexing and the orthogonal carrier. Every lines and subscriber units include modulation units (19,37) for identifying anti-Fourier transform to the insymbols and demodulator units (29,43) for carrying out the discrete Fourier transform to the sample value of the transmission signal flow in cable (7). The transmission switch units (19,29) use the different carriers with the carriers used in switch units (37,43) on the opposite direction. It allows at least on a direcion the required computation amount is reduced by using the swithing specific characteristics when selecting the carriers. Only carrier with even label is used in the switch unit (37) on the direction come from the subscriber (3), and the output signal sent to the cable (7) will be composed of a sequence to be repeated, with a length that is only half of the length when all carriers are used, making it is only needed to compute and repete the sequence having a half length. In the switch unit (43) receiving such a signal repeating twice, the received symbols are divided into two equal segments, then they are added mutually together to carry out the compressed switching operation. In the opposite direction, the swith using all of the carriers can always be calculated. Furthermore, the lowest frequency can be allocated to the direction pointing to subscribers, which is because: in the opposite direction, the low-band transmission is particularly sensitive to the noise and interference, which should be avoided to use.

Description

Allow the digital system of the subscriber's line of high bit rate

The invention technical field

The present invention relates to allow with bit rate, the particularly digital system of the subscriber's line of bit rate communication very.

Background of invention

At present in telecommunications network, exist the demand that high bit rate communication is extended to the line user end, and provide high-speed digital communication to the apartment, the demand of private home and dwelling house etc.The cost that extends to the cable system in this corresponding geographical position should be too not high, and will use the general twisted-pair power cable in the existing communication as far as possible.

The suggesting method of realizing this high-speed communication is described in the disclosed International Patent Application WO 97/06619 of Telia AB and Mikeal Isaksson.This method also has concise and to the point description in the people's such as Mikael Isaksson of Telia Research AB document " slot--a kind of duplexing scheme proposals (Zipper-a Duplex SchemeProposal for VDSL Based on DMT) that is used for based on the VDSL of DMT " (ANSI T1E1.4/97-137, working group of the T1E1.4 technical point committee).Be applicable to the having earlier in the system of VDSL (very bit rate digital subscriber line), duplex or two-way communication are finished by using DMT (Discrete Multitone modulation), and wherein signal is sent on two identical lines two-wayly.In this method, all be modulated onto on the mutually different carrier wave of a plurality of frequencies in information on each direction, be to come selecting modulation mode and carrier wave on the whole according to a kind of use quadrature carrier and the method that is called as OFDM (OFDM).In communication, carrier frequency is separated by this way: some of them are used to the direction that down direction is a directed towards user, some other then be used to up direction promptly from the user to the switch direction.So just obtained real duplex communication, wherein information all is two-way transmission at any time.This method can be referred to as OFDD (orthogonal frequency duplex).In a preferred embodiment, be used on the direction, and remaining other also is the transmitting signal that whenever is used in alternately on the opposite direction certainly every one carrier frequency.Like this, even carriers can be used to down direction, and odd carriers can be used to up direction.

The shortcoming of this suggesting method is that each end of communication channel all must calculate FFT (fast fourier transform) and IFFT (anti-fast fourier transform) simultaneously, but is just avoiding this calculating in TDD (time division duplex) scheme of competition mutually with it.This just requires the processor at communication channel two ends will be operated on the very high clock frequency.

The use of quadrature carrier and the correlating transforms method in the digital television broadcasting field have description in the IEEE in March nineteen ninety-five Transanctions on Broadcasting the 41st volume the 1st phase the 1st to 6 page people's such as William Y.Zou article " COFDM: general introduction ( COFDM:Anoverview ) ".19857IEEETransactions on Communications337665675Leonard J.Cimini“ ( Analysis and simulation of a digital mobilechannel using orthogonal frequency division multiplexing ) ”EP-A1 0 616 445。

Use the system of OFDM to be described in european patent application 0 668 678, wherein the channel of even numbers can be used to send and receive and can not increase the complexity of processing significantly.This system and corresponding method are not considered to simplify necessary calculating, and are to use available processor to go to transmit more information on the contrary.This system does not use " slot " carrier frequency scheme that is put forward in people's such as International Patent Application WO of being quoted just now 97/06619 and Mikael Isaksson document.

Brief summary of the invention

One object of the present invention be to provide a kind of at for example true duplex line uniline or communication channel on transmit the method for information two-wayly, allow simultaneously can reach minimum at the necessary operand of circuit or communication channel two ends.

Another object of the present invention is suitably to select carrier frequency on circuit or communication channel when information is sent out, so that OFDD can be effectively utilized.

A further object of the invention just is selected at the carrier wave of the information that sends on the circuit, so that when using OFDD, noise and Recombinant Interferon access and reduce.

Like this, if select carrier wave with suitable manner on the uplink and downlink direction, some characteristic of DFT (discrete Fourier transform (DFT)) and IDFT (anti-discrete Fourier transform (DFT)) just can be utilized to reduce desired amount of calculation.Therefore as can be seen, if the DMT transmitter only uses the carrier wave of even-numbered, then the signal of time domain output can comprise and has only half repetitive sequence of original series length.This point can be utilized in the following way: calculate the sequence of half length, then it is carried out repetition.In an identical manner, be the carrier wave of 4 multiple if the DMT transmitter only uses label, then a sequence will be repeated four times, and the length of DFT and IDFT has only 1/4th of original series, and the signal of output also must be repeated four times, or the like.

Like this, can design communication network according to the mode of in the people's such as Mikael Isaksson of International Patent Application WO of being quoted 97/06619 and Telia Research AB document, being advised generally.This network generally will comprise two at least each other can two-way ground exchange message node.Each node comprises first converting means, and it is designed to the digital information that sends to the another one node from the frequency domain transform to the time domain, and first converting means uses the time domain orthogonal carrier wave in this conversion, generates the information after the conversion then.Each node also comprises the transfer device that links to each other with first converting means, and this transfer device can be to the information after the another one node transmits conversion.And a receiving system that is used to receive from another nodal information is all arranged in each node, and each node also comprises second converting means that links to each other with receiving system.The information that second converting means is designed to receiving system is received transforms from the time domain to frequency domain.First converting means and second converting means are designed to and can come information converting according to discrete Fourier transform (DFT) or anti-discrete Fourier transform (DFT).The carrier wave that uses in the carrier frequency of using in first converting means in node and another node is inequality, and first converting means is only determined Fourier transform or inverse-Fourier transform to portion of carriers, then when carrying out the conversion of needed or suitable number of times, in fact it repeat the transformed value that obtained.In addition or at this supplemental instruction, the carrier wave that is used for communicating by letter in one direction can comprise all frequencies in the low-frequency range.

Second converting means in another node is by the received signal section of being divided into, thereby determine to carry out respectively anti-discrete Fourier transform (DFT) or discrete Fourier transform (DFT), then must be to two mutual additions of continuous segment of major general, and come the computational transformation value according to the result of addition at last.

Useful is, the carrier wave that first converting means in node and second converting means in the another one node only use even-numbered.

First converting means in the node can comprise encoder apparatus, and it is designed to the information of wanting conversion is encoded into and is suitable for according to the discrete Fourier transform (DFT) of use portion of carriers or the symbol that anti-discrete Fourier transform (DFT) is carried out conversion.The carrier wave that is comprised in this part has so preferred label, is the label of a plurality of powers of 2 of 2,4 or 8 etc. time.

Purpose that the present invention adds and advantage will provide in description subsequently, and wherein some can be seen in description significantly, perhaps can obtain in an application of the invention knowing from experience.Objects and advantages of the present invention can realize by this method, process, means and the combination of specifically noting in appended claims.

The accompanying drawing summary

With reference to the accompanying drawings and consider the detailed description of the unrestriced embodiment provide subsequently, can understand the special innovation characteristic of the present invention that proposes in appended claims better, and intactly understand institutional framework of the present invention and content and from invention resulting above-mentioned and other some characteristics, wherein:

Fig. 1 is the block diagram that is used for the network portion that communicates with the user,

Fig. 2 is a block diagram of describing the efficient converter unit work that is used to modulate the information that will be sent out,

Fig. 3 a and 3b are the sketches of describing the add operation be used to the short sequence recovering to be sent out,

Fig. 4 describes to be used for the work principle figure that demodulation has received the efficient converter unit of information,

Fig. 5 a and 5b are the schematic diagrams of describing the carrier frequency be used to distribute asymmetric communication.

Detailed Description Of The Invention

Among Fig. 1 the described system of block diagram is the part of telecommunications network, and it has been described by the information that sends is used DMT (Discrete Multitone) modulation so that realize from transmission network 1 to the user 3 connection.Bit stream arrives line unit 5 or arrives transmission network 1 from line unit 5 from transmission network 1 respectively.A pair of copper twisted pair cable 7 extends to subscriber unit 9 from line unit 5, and this subscriber unit 9 can be connected with telephone set 11, computer 13, facsimile equipment 15 and other input and output electronic equipment of being used by user 3.The bit stream that arrives line unit 5 from transmission network 1 is encoded encoder 17 and forms suitable symbol, and these symbols are imported into the IFFT unit 19 that links to each other with the output of encoder 17.The output of IFFT unit 19 links to each other with D/A 21, and the output of this transducer is connected to twisted-pair feeder 7 by hybrid circuit 23.Twisted-pair feeder 7 is connected to hybrid circuit 25 in the same way in subscriber unit 9.The output signal of hybrid circuit 25 is sent to A/D converter 27, and the output of this transducer is connected to the FFT unit 29 that is used to carry out computing function, and this result of calculation is sent to the decoder 31 that links to each other with 29 outputs of FFT unit.The output of decoder 31 is connected to user interface 33, and therein, what will receive according to this unit for example is that the speech message or the bit stream of data-signal are handled that receive and decoded bit.Like this, user interface 33 will have the terminal that is used for connecting various subscriber equipment 11,13,15 etc.

Similarly, can be handled by user interface 33 from signal output, that be sent to subscriber unit 9 such as one of subscriber equipment 11,13,15 etc., resulting bit stream is encoded in encoder 35.The symbol that is encoded obtains handling then in IFFT unit 37, and the data after institute's conversion are converted into analog form in D/A 39.Signal by the output of D/A 39 is sent to hybrid circuit 25, by this circuit analog signal is sent on the twisted-pair feeder 7 again.The signal that is transmitted is received by corresponding hybrid circuit 23 in the line unit 5, and is converted into digital form in A/D converter 41.Handle this digital signal in FFT unit 43, resulting symbol is decoded in decoder 45, thereby produces bit stream so that deliver to transmission network from circuit.Encoder, decoder, D/A and A/D converter and hybrid circuit are respectively the interior known component units of field of signal transmissions that the communication system of employing quadrature carrier is connected with the two-wire user.Hybrid circuit 23,25 is from circuit or subscriber unit received signal, and this signal transmitted by twisted-pair feeder 7, thereby generate nonideality, deviation may minimum signal, this signal is by simultaneously or the output of the hybrid circuit of link to each other with the interior section of each corresponding circuit and subscriber unit (for example linking to each other with the A/D converter that is provided therein) automatically is provided.

DMT (Discrete Multitone) the modulation and demodulation process of using during user shown in Figure 1 connects generally comprises: at first, encoder 17,35 transforms to suitable parallel form to the incoming symbol that serial arrives; Modulate by 19,37 pairs of a plurality of carrier waves of conversion or IFFT unit then.Modulated carrier wave is addition mutually in the step in the end in the IFFT unit, and its resulting result is sent to D/A 21,23.When the sampled signal that receives is separated timing, handle accordingly.

Use direct discrete Fourier transform (DFT) (DFT) can implement the modulation and demodulation process effectively in anti-discrete Fourier transform (DFT) (IDFT) and the demodulation by in modulation, using.As IFFT unit 19,37 and the FFT unit 29,43 that provides among the figure, the numerical procedure of IDFT and DFT can be modified into the various forms of anti-fast fourier transform IFFT that are used to modulate and be used for the direct fast fourier transform FFT of demodulation.

The communication that folk prescription makes progress is discussed below.To incoming bit stream encode (in 17 or 35) can obtain symbolic vector { X ₀, X ₁..., X _2N-1, by the sequence { x of following formula by anti-discrete Fourier transform (DFT) (in 19 or 37) calculating time domain ₀, x ₁..., x _2N-1}: $x_n=\frac{1}{2N}\underset{m=0}{\overset{2N-1}{\mathrm{\Σ}}}{X}_m{W}_{2N}^{-\mathrm{mn}}.......\left(1\right)$ For n=0,1 ..., 2N-1, wherein $W_N=e^{-j\frac{2\mathrm{\π}}{N}}........\left(2\right)$

If we suppose only to occur in the primary signal even number composition, i.e. X _2k+1=0, k=0,1 ..., N-1, this just means the cataloged procedure that must be adjusted at the front of carrying out in the encoder 17,35, obtains following formula: $x_n=\frac{1}{2N}\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{X}_{2k}\·W_N^{-\mathrm{kn}}......\left(3\right)$

Yet, W _NWith N is the cycle, so x _nIt also is the cycle, that is: with the same intervals

x _n＝x _n+N (4)

Like this, time domain sequences { x ₀, x ₁..., x _2N-1Can be by repetitive sequence { x ₀, x ₁..., x _N-1And obtain, this sequence is to remove the anti-discrete Fourier transform (DFT) of this zero symbolic vector, that is, this time domain sequence is actually { x ₀, x ₁..., x _N-1, x ₀, x ₁..., x _N-1.

Under only comprising the situation of carrier wave that label is 4 multiple in the original symbol vector, just have corresponding 4 times in the time series and repeat, wherein first part is repeated in time domain sequences 4 times.For label is the carrier wave composition of 8,16 equimultiples, and corresponding situation is also set up, so conversion causes first's transformed value to do 8 times, 16 times repetition respectively.This has explanation in Fig. 2, wherein carry out once its length and reduced R IFFT operation doubly in device 201, thereby produce such sequential value, and this sequential value is repeated R time in receiving system 203, is used to be sent to the value that D/A goes so that produce.

Under the situation of having only odd carriers upwards to be used to transmit at folk prescription, i.e. X _2k=0, k=0,1 ..., N-1 then can be complicated more with the top corresponding calculated of sketching.Different is, signal must be repeated but simultaneously by negate.In this case, each sampling must be done extra complex multiplication in time domain.

Exist by only having the method that FFT that N orders calculates the FFT of 2N real input signal point, this can be referring to the 708th page to 714 pages of the works " Digital Signal Processing " of the J.G.Proakis of MacMillan publishing company publication in 1992 and D.G.Manolakis.The similar methods that is used for the IFFT of 2N the real output signal of putting also can obtain.Under the situation of having only the odd numbered carrier wave, because complicated more repetitive process can not directly be used the method that these are applicable to real input and output signal respectively.Therefore, in the most simple and practical scheme, at folk prescription upwards concerning transmission, the multiple that the carrier wave label should preferred 2,4,8 etc.For other frequency that is used for going up the signal transmission in the other direction, calculate the discrete Fourier transform (DFT) of using all carrier frequencies.

Corresponding with inverse-Fourier transform described above, because discrete Fourier transform (DFT) also has periodicity, so in receiver, also may reduce the amount of calculation of demodulation.As shown in Fig. 3 a and 3b, the symbol that receives is divided into the smaller portions of the equal length of respective numbers, and can add up these parts mutually.Calculate the FFT of the compression of label then with lesser amt.For example, for the carrier wave that contains even-numbered, each receiving symbol is divided into the part of two equal lengths, and these two parts are wanted mutual addition.And add operation causes all undesirable carrier waves to be eliminated, and and then can reduce noise and interference in the receiver, and for example when only using the carrier wave of even-numbered, in receiver, only calculate the FFT of half label number.

In Fig. 4, provide the ball bearing made using of carrying out additional calculation.Input sample stream is transmitted through summing junction 401, promptly from its input to output, can only hold the suitably memory 403 of divided shorter length to having again.The first of time domain sample value of input is transmitted through memory 403, and turns back to second input of summing junction 401 by the control of switch 405, and the next part addition of flowing at this and input sample.Repeat this process by desired number of times, switch 405 pushes on another position so that addition, level and smooth sample stream is input to the frequency domain value that FFT unit 407 goes to calculate the input value of having compressed quantity then.

In the communication of the symmetrical full duplex in communication channel, particularly in twisted-pair feeder 7, information can be with identical speed rates on both direction.As prior art was advised, the carrier wave of even-numbered can be used on the direction, and the carrier wave of odd numbered can be used on the rightabout.On the direction of using the even-numbered carrier wave, the needed amount of calculation of modulation and demodulation can be reduced to generally half of amount of calculation of all carrier waves being calculated discrete Fourier transform (DFT).On the direction of using the odd numbered carrier wave, preferably consider to use the conversion of calculating all carrier waves, so on the whole, to compare with should on both direction, all using the conversion of calculating all carrier waves, amount of calculation can be saved (1-(1+1/2)/2=) 1/4.In some cases and do not require the communication (for example send as film etc. video data to family) of symmetry, can for example distribute available carrier frequency like this in asymmetric mode, thereby in total number of carriers, in per 4 or per 8 carrier frequencies information that is used to send from user side is just arranged.So on from user's direction in converter unit 37 and 43 desired amount of calculation will be to use all carrier waves the desired amount of calculation of conversion 1/4 and 1/8, this saves amount of calculation 3/8 and 7/16 respectively.

In preferred unrestriced embodiment, always on the down direction, just calculate the conversion of using all carrier waves on the direction of directed towards user.This portion of carriers that has just further caused being used in (just on the direction from the user) on the up direction should not be used to transmission information on this direction, but is used to transmission in the opposite direction.This point can be carried out utilization in the selection of planning frequency of utilization.For example, if consider disturbing factor, should avoid low carrier frequency on up direction, these frequencies can be used to the down direction transmission by correspondingly being modified in the cataloged procedure that carries out in the encoder 17,35.

In Fig. 5 a, available frequencies is illustrated as the rectangle arranged side by side that is arranged to a row, and the call number or the label of the frequency of representative represented in the position of rectangle in a row.Using label is that the 4th in per four frequencies is used to up signaling under the situation of uplink communication of carrier wave of 4 multiple, as intersecting the rectangle of heavy line represents by indicating among the figure.As shown in Fig. 5 b, the low frequency carrier signal in them is transferred to the transmission that is used on the down direction, as intersecting the rectangle of fine line represents by indicating among the figure.

A kind of telecommunications network that allows to use computation requirement processor, that have simplification that for example function is not really powerful like this, has been described.Can realize this point by the characteristic of using symmetrical or asymmetrical mathematic(al) manipulation.

Though provide and described specific embodiment of the present invention at this, to one skilled in the art, many additional advantages, modifications and variations all will obtain at an easy rate.Therefore, the present invention is not limited to some specific detail, representational equipment and at this example that provides and describe on its relative broad range.Correspondingly, the various modifications of being made do not break away from appended claims and to the spirit or scope of defined total inventive concept in the equivalent.Therefore appended claims should contain all and fall into modifications and variations within the spirit scope of the present invention.

Claims (7)

1. telecommunications network, comprise at least two can mutual two-way ground exchange message node, each node comprises:

Be used for the digital information that sends to another node is carried out first converting means of conversion, described first converting means be set to quadrature carrier by using time domain digital information from the frequency domain transform to the time domain, thereby produce the information of conversion,

With the transfer device that first converting means links to each other, this transfer device is set to the information after another node transmits conversion, and

The receiving system that is used for the information that receives from another node,

Link to each other with receiving system and be used for the information that receives from receiving system is transformed from the time domain to second converting means of frequency domain,

This telecommunications network is characterised in that:

First converting means and second converting means are set to come information converting according to discrete Fourier transform (DFT) or anti-discrete Fourier transform (DFT),

In one of them node first converting means use with another node in the different orthogonal carrier frequencies of orthogonal carrier frequencies used,

First converting means in the first node is set to determine discrete Fourier transform (DFT) or anti-discrete Fourier transform (DFT) that the part quadrature carrier is carried out, thereby generates transformed value, repeated transformation value then.

2. the network in the claim 1, it is characterized in that different in second converting means and the first node in the Section Point, it is designed to by the reception information section of being divided into, so that determine to carry out respectively anti-discrete Fourier transform (DFT) or discrete Fourier transform (DFT), must be at least continuous two mutual additions of section, then according to the value of computational transformation as a result of addition.

3. claim 1 or 2 described networks is characterized in that the quadrature carrier that first converting means in the first node and second converting means in another node are designed to only use even-numbered.

4. claim 1 or 2 described networks, it is characterized in that first converting means in the first node comprises encoder apparatus, it is designed to the information of wanting conversion is encoded into and is suitable for according to the discrete Fourier transform (DFT) of a part of quadrature carrier of use or the symbol that anti-discrete Fourier transform (DFT) is carried out conversion.

5. claim 1 or 2 described networks is characterized in that, the label that is included in the quadrature carrier in the described part quadrature carrier is a plurality of powers of 2.

6. claim 1 or 2 described networks is characterized in that the quadrature carrier that is used for communicating by letter in one direction comprises all frequencies of low-frequency range.

7. telecommunications network, comprise at least two can mutual two-way ground exchange message node, each node comprises:

Be used for the digital information that sends to another node is carried out first converting means of conversion, described first converting means is set in conversion process, and use the quadrature carrier of time domain to come digital information from the frequency domain transform to the time domain, thereby produce the information of conversion,

With the transfer device that first converting means links to each other, this transfer device is set to the information after another node transmits conversion, and

The receiving system that is used for the information that receives from another node,

Second converting means that links to each other, is used for the information that receives from receiving system is transformed from the time domain to frequency domain with receiving system,

Telecommunications network is characterised in that:

First converting means and second converting means are set to and can come information converting according to discrete Fourier transform (DFT) or anti-discrete Fourier transform (DFT),

Wherein in a node first converting means be set to use with another node in the different orthogonal carrier frequencies of orthogonal carrier frequencies used,

The quadrature carrier that is used for communicating by letter in one direction comprises all frequencies of low-frequency range.

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