CN1169627A - Cable communication system and method - Google Patents

Abstract

A cabled yarn communication system architecture (10) includes several service nodes (12, 14, 16) which have several subscriber units (26). Several fibre optic communication connections (20, 22, 24) are coupled to the service nodes. Block step-down transformers (36, 38, 40) one for each service node, are coupled to the fibre optic communication connections. A matrix switch (42) is connected to the block step-down transformers and several base band processors (44) are connected to an output of the matrix switch. Preferably, each block step down transformer is able to transform any channel from several system channels.

Description

Cable communication system and method

The present invention relates generally to the communications field and relate more specifically to cable communication system and method.

The employing single-carrier modulated is used for single transceiver architecture that descending/upward signal is handled at the headend equipment place with typical two-way HFC (Hybrid Fiber Coax) system that carries out data/telephone service.Every single transceiver can provide the list " channel " of bidirectional transfer of information.This channel is a full duplex, adopts the symmetric part of bandwidth in descending (50-750MHz) and up (5-42MHz) path.The modulation of being adopted is quaternary PSK (or its modification) typically, and quaternary PSK (QPSK) provides acceptable performance and efficient when having the thermal noise of high level and entering noise (ingress noise) in uplink.This channel is further by being divided into bearer channel again at descending employing TDM (time division multiplexing) and at up employing TDMA (time division multiple access connection).

The channel transceiver letter machine that cable control unit (CCU) master control (host) at headend equipment place is a large amount of can be assigned to any uplink and downlink frequency centering to these channel transceiver letter machines on request.Typically, relaying transceiver from shared combination (common pool) is so that be quantitatively much more than available bearer channel user's service.When the request service, distribute a channel (time slot and relevant frequency), and this channel is got back in the combination after finishing service.

The uplink receiver of single transceiver provides single-channel gain, selection and carrier wave demodulation, this single channel can be tuned on the arbitrary evenly spaced channel in the upstream band.Be to keep quality of connection, exist high level enter noise the time carry out link conversion (transfer).CCU manages transceiver resources and the routing function of user data and PSTN (public telephone switching network) contact is managed.

By cable access unit (CAU), subscriber equipment and cable network interface, cable access unit (CAU) receive and demodulation descending carrier and user data sent to the CCU that is positioned at the headend equipment place.In the TDM/TDMA system, many CAU can be appended to single carrier wave or single frequency to last.Like this, single CCU transceiver can be supported many CAU.

Fig. 1 represents the up or return path of the part of typical HFC system.By optical fiber link, three service nodes are connected with headend equipment.The coaxial cable of CAU and system partly is connected.The whole RF radio frequencies of the output of the fibre optic receiver at headend equipment place compound (addition) also are connected with the CCU receiver of single group.Utilize the RF separator that public upward signal is fed to each CPX receiver in this group.

Because any receiver can be assigned to any up channel on arbitrary node in three nodes, this layout provides very high receiver junction efficiency.But, because the separator loss has increased the noise of receiver.And the thermal noise of all three nodes is compound with entering noise, and is provided on each transceiver, thereby reduces getable carrier-to-noise ratio (CNR).Because uplink spectrum is overlapping between service node, the total frequency spectrum efficient of the impossible restriction system of channel reuse.

A kind of alternative layout of expression among Fig. 2, three nodes are isolated mutually and are adopted a plurality of CPX to receive units so that service to be provided among the figure.The separator that the receiver input is presented in utilization is routed to a CPX reception unit to the output of the fibre optic receiver of each node.Solved the compound problem of enter relevant/thermal noise like this, thereby but because available receiver combination has been divided into the junction efficiency that has reduced receiver on the service node with Fig. 1.Please note if each node demand more than one receiver, still needs separator, thereby increases the noisiness of each receiver.

Other RF separation/composite layouts is possible, still, usually need be at receiver junction efficiency, noisiness, enter/trade off between the compound and complexity/cost of thermal noise.

Fig. 1 represents the cable communication system of prior art.

Fig. 2 represents the cable communication system of prior art.

Fig. 3 is a calcspar, and expression is according to the cable communication system of a kind of preferred forms of the present invention.

Fig. 4 is a calcspar, and expression is used for the fibre optic receiver according to cable communication system of the present invention of Fig. 3.

Fig. 5 is a calcspar, and expression is used for a plurality of grouping low-converters (block down converter) of Fig. 3 according to a kind of preferred forms of the present invention.

Fig. 6 is the calcspar of multiphase filter and discrete Fourier transform processor.

Fig. 7 is the bank of filters curve.

Fig. 8 represents filter/low-converter processing.

Fig. 9 is a calcspar, the multiphase filter according to a kind of preferred forms of the present invention shown in the presentation graphs 6.

Figure 10 is a calcspar, expression character matrix electric wire connecting junction and a plurality of baseband processor.

Fig. 3 represents the calcspar of a kind of cable communication system architecture (HFC system) 10, and this system can provide the junction efficiency that does not have thermal noise of the prior art and enter noise problem.By a plurality of optic communication links 20,22 and 24, a plurality of service nodes (a plurality of node) 12,14 are connected with the headend equipment 18 of cable communication system 10 with 16, and wherein each link of a plurality of optic communication links comprises a fibre optic transmitter 30, an optical cable 34 and a fibre optic receiver 32.Each node in a plurality of service nodes 12,14 and 16 and a plurality of subscriber unit (CAU-optical cable addressed location) 26 is coupled (coupled).By a coaxial cable 28, a plurality of subscriber units 26 are connected with separately a fibre optic transmitter 30.For the purpose of preferred forms, HFC system 10 bears up (from user to the headend equipment) traffic.Usually, second fibre optic transmitter, second receiver and the second cable (not shown) are born descending traffic.The present invention relates to how to handle uplink information, so this specification will only be discussed uplink information stream.

The headend equipment 18 of cable communication system 18 has a plurality of grouping low- converters 36,38 and 40, and is corresponding one by one with each service node 12,14,16 respectively.A plurality of grouping low- converters 36,38 and 40 have the ability that simultaneously all a plurality of system channels (a plurality of channel) is down-converted to base band.Here employed channel is a particular carrier wave frequency, and a channel is divided into some time slots usually.A general communication session only needs single time slot, and is referred to as communication channel.If for example there are 60 channels, each grouping low- converter 36,38 and 40 can be each channel (carrier frequency) down-conversion (moving) in 60 channels to base band.Constitute a plurality of baseband channels like this.Be not that whole baseband channels all will have actual communication session.The a plurality of baseband channels (being a plurality of baseband signals or a baseband signal) that have an actual communication session are transferred to a plurality of Base-Band Processing by a matrix switch (character matrix electric wire connecting junction) 42 and want on the baseband processor in 44.Controller 46 is given each subscriber unit 26 traffic channel assignment.Controller 46 determines that channel of a plurality of baseband channels has useful signal, and by signal-arm this information is sent to matrix switch 42.

As can be seen, figure is that the output of fibre optic receiver 32 does not have addition when adopting the system of Fig. 3, thus enter and thermal noise not compound.In addition, because grouping low- converter 36,38 and 40 can must make that no longer a channel that is used on a service node 12,14 and 16 is not used in another service node to the arbitrary channel down-conversion in a plurality of system channels.In case when downconverting the signal on the base band, signal is that electricity is isolated each other, can handle by any baseband processor 44.

Fig. 4 is the calcspar of fibre optic transmitter 30.Radio frequency (RF) receiver 50 is coupled with the coaxial cable 28 that is connected with a plurality of subscriber units 26 of Fig. 3.The output 52 of RF receiver 50 and an optical sender 54 are coupled.Output 56 coupled into optical fibres 34 of optical sender 54.The RF receiver receive from the signal of coaxial cable 28 for being transmitted as form along coaxial line.Fibre optic transmitter 30 becomes this conversion of signals along the form of optical fiber cable transmission, and optical sender 54 sends signal along optical fiber 34 then.

Fig. 5 represent to divide into groups calcspar of low-converter and matrix switch (42).A plurality of grouping low- converters 36,38 and 40 have the input filter 60 that the output with fibre optic receiver 32 is coupled.Filtered signal (multichannel) is through A/D converter (A/D) 62 digitlizations.The output of A/D converter 62 is a plurality of digitized node signals 64.A plurality of digitlization node signals 64 are by multiphase filter 66 filtering, to form a plurality of filtering signals 68.Through discrete Fourier transform (DFT) processor (digital down converter) 70, a plurality of filtered signals are by Digital Down Convert.The output of DFT processor 70 is a plurality of baseband channels 72.Those baseband channels 72 that have actual communications session are the baseband signals on a plurality of ports that are transferred to a plurality of Base-Band Processing ports 74 by character matrix electric wire connecting junction 42.

Fig. 6 is the calcspar of multiphase filter 66 and DFT processor 70.Multiphase filter defines the different digital filter of a kind of input and output sample rate.Adopt multiphase filter can reduce digital filter and the required processing speed of DFT processor.Digitlization node signal 64 is by a delay network 78, and this network for example has 128 taps as shown in Figure 6.Each tap is divided by 1/128th the factor by minute calculation device 80 calculates.Divide the output of calculation device 80 to be coupled in a plurality of filter sections 82 one.The output of a plurality of filter sections 82 is handled by DFT processor 70.The output of DFT processor 70 is a plurality of baseband channels 72.128 baseband channels of expression among Fig. 6, but be not that the actual channel (a plurality of system channel) that uses in the cable communication system 10 is all being represented in all output.Therefore, be not that all output 72 all is connected with matrix switch 42.By adopting the combination of multiphase filter 66 and DFT processor 70, only need the single filter structure that the baseband filtering group shown in Fig. 7 just can be provided and to the down-conversion of a plurality of system channels.The available following math equation of the combination of multiphase filter and DFT processor is represented in digital z transform domain: $X_k\left(z\right)=\underset{n=0}{\overset{M-1}{\mathrm{\Σ}}}{}^{-\mathrm{kn}}\left(z^{-n}{E}_n\left(z^M\right)X\left(z\right)\right)$ Wherein Xk (z) is a delivery channel of DFT processor, and M is the input channel sum, and W is DFT entry of a matrix element and W=e ^{-j2 π/M}, En (z ^M) be the response of a certain multiphase filter element.In this preferred forms, as shown in Figure 6 M be 128 and also multiphase filter constitute by 128 filter sections 82.This combination is equal to a plurality of filtering shown in Fig. 8/down-conversion element (element), and the array output of each multiphase filtering element provides the baseband filtering response among Fig. 8, and closes function or e by compound ^{J ω}x ⁿProduct (ω wherein _k=2 π k/M) provide the down-conversion of signal.

The calcspar of a kind of specific implementation of expression multiphase filter structure in Fig. 9.Delay network 78 (z ^M) and divide the function of calculating device 80 to postpone input 102 by rectification and realize.The output that rectification postpones input 102 is connected with 128 filter sections 82, and each filter section provides response E _n(z ^M), the combination of each filter response and the Ho of the channel baseband response shown in Fig. 7 is provided.Please note that Fig. 7 only represents preceding 64 system channels.The aliasing that remaining 64 channel is input samples amasss and is useless.

Figure 10 is the calcspar of character matrix electric wire connecting junction 42 and relevant input and output.Matrix switch 42 is each service node 12,14 and the 16 a plurality of baseband channels (a plurality of input) 72 that receive from DFT processor 70.Each output sampling of a plurality of baseband channel output samplings is input to RAM (random access memory) 110 for storage through the parallel input 111 of high-speed segmenting.Matrix switch 42 also receives the signal-arm that comes self-controller 46.This signal-arm is stored in pointer memory ₁₁₂And point to the section of expression actual communications session among the RAM 110.The section of representing actual communications session through along and be sent in a plurality of baseband processor 44 one to going here and there a plurality of outputs of transducer 113.Scan and send to digital spectrum analysis device 116 through 114 pairs of all sections of memory scanning device.Digital spectrum analysis device (frequency spectrum analyser) 116 is handled these information so that determine in the cable communication system 10 the noise that enters on all channels simultaneously.Controller 46 utilizes this information and selects available optimum channel in the link conversion.As shown, baseband processor 44 is made up of a square root raised cosine filter 118 and a digital signal processor 120, and digital signal processor provides symbol timing recovery, symbol detection and TDMA to go functions such as framing.

As above summarize, preferred forms of the present invention has been avoided the compound problem that enters noise in the conventional H FC bilateral system by the cancellation service node to the addition of the input of headend equipment.The present invention is by sending upward signal to junction efficiency that the character matrix electric wire connecting junction keeps receiver through the grouping low-converter.Then the character matrix electric wire connecting junction is routed to available baseband processor to upward signal, thereby low enter noise, high efficiency receiver relay system are provided.

Like this, to providing junction efficiency to increase to enter and the cable communication system of thermal noise is illustrated at the receiver place.Although the present invention illustrates that together with its concrete execution mode many according to the above description changes, modification and modification are tangible for those skilled in the art.Therefore, intention comprises all changes, modification and distortion in the appended claims book.

Claims (10)

1. cable communication system comprises:

A plurality of service nodes, each node in a plurality of service nodes has a plurality of subscriber units;

A plurality of optic communication links, each link of a plurality of optic communication links is connected with a node in a plurality of service nodes;

A plurality of grouping low-converters respectively are used for a node of a plurality of service nodes, and a plurality of grouping low-converters and a plurality of optic communication links are coupled;

A matrix switch that is connected with a plurality of grouping low-converters; And

A baseband processor that output is coupled of a plurality of and this matrix switch.

2. the cable communication system of claim 1, each grouping low-converter of wherein a plurality of grouping low-converters any channel in can a plurality of system channels of down-conversion.

3. the cable communication system of claim 2, each grouping low-converter of wherein a plurality of grouping low-converters is all a plurality of system channels of down-conversion simultaneously.

4. the cable communication system of claim 1, each in wherein a plurality of grouping low-converters comprises:

An analog to digital converter;

A multiphase filter that receives digitized signal from this analog to digital converter; And

The Fourier transform generator that an output of one and multiphase filter is coupled.

5. the cable communication system of claim 1, each unit in wherein a plurality of subscriber units can send on each channel of a plurality of system channels.

6. one kind the method for a plurality of channel demodulations in the cable communication system, and repeatedly, the method comprising the steps of on each node of a plurality of service nodes of these channels in this cable communication system:

(a) receive a plurality of channels for each node of a plurality of service nodes;

(b) for a plurality of channels of each node down-conversion of a plurality of service nodes to form a plurality of baseband channels;

(c) determine to be included in a plurality of baseband signals on a plurality of baseband channels; And

(d) a plurality of baseband signals are transferred on the baseband processor.

7. the method for claim 6, wherein step (b) and then comprise step:

(b1) be a plurality of channels of each node digitlization of a plurality of service nodes, to form a plurality of digitlization node signals;

(b2) each signal to a plurality of digitlization node signals carries out filtering, to form a plurality of filtering signals; And

(b3) a plurality of filtering signals are carried out Digital Down Convert to form a plurality of baseband signals.

8. the method for claim 7, wherein step (b2) comprises the step of a plurality of digitlization node signals being carried out multiphase filtering.

9. the method for claim 7, wherein step (b3) comprises a plurality of filtering signals is carried out the step that Fourier handles.

10. the method for claim 6, wherein step (c) and then comprise step:

(c1) reception pointer signal, this signal indicate that channel is a baseband signal in a plurality of baseband channels.

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