WO2006016129A1 - Method and apparatus for data communication within a physical link layer of a communications system - Google Patents

Method and apparatus for data communication within a physical link layer of a communications system Download PDF

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Publication number
WO2006016129A1
WO2006016129A1 PCT/GB2005/003086 GB2005003086W WO2006016129A1 WO 2006016129 A1 WO2006016129 A1 WO 2006016129A1 GB 2005003086 W GB2005003086 W GB 2005003086W WO 2006016129 A1 WO2006016129 A1 WO 2006016129A1
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Prior art keywords
signal
data
phase
transmitter
data signal
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PCT/GB2005/003086
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French (fr)
Inventor
David Srodzinski
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Elonics Limited
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Publication of WO2006016129A1 publication Critical patent/WO2006016129A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/12—Arrangements providing for calling or supervisory signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J9/00—Multiplex systems in which each channel is represented by a different type of modulation of the carrier

Definitions

  • the present invention relates to the field of communications systems. More particularly, this invention relates to a method and apparatus that permits direct communication of information between elements within the physical link layer of a communication system.
  • the OSI model 1 is .a seven layer reference model recommended by the International Standards Organisation (ISO) to provide a logical structure for network operations protocol.
  • a Physical Link Layer 2 is defined as the lowest layer and above this lies a Datalink Layer 3.
  • the Datalink layer 3 has several functions within the communication system, one of which is to perform the task of encoding a data signal into a form suitable for transmission and thereafter to decode the transmitted signal, as appropriate.
  • the Physical Link Layer 2 is often conveniently subdivided into a Physical Coding Sub-layer (PCS) 4, a Physical Media Attachment (PMA) layer 5 and a Physical Media Device (PMD) layer 6.
  • the PCS 4 encodes the data stream into a form suitable for transmission across the physical media.
  • the PMA 5 provides an attachment layer between PCS 4 and the PMD 6.
  • the PMD 6 is responsible for the physical transmission of the signal .
  • FIG 2 presents a schematic representation of a communication system 7, as is known to those skilled in the art e.g. a Sonet, an Ethernet or a Fibre Channel systems.
  • the communication system 7 is shown in a simplified form so as to comprise a transmitter 8 that performs the tasks of the PMD layer 6 and optionally also the PMA layer 5.
  • the transmitter 8 acts to convert the encoded electrical input signal "datain" 9, produced within the higher Datalink layer 3 and PCS layer 4, into a data signal 10 suitable for transmission through a propagation medium 11.
  • the data signal 10 comprise an optical signal for transmission through an optical fibre.
  • a receiver 12 At the output of the propagation medium 11 is located a receiver 12.
  • the receiver 12 is employed to detect the signals in a PMD layer 6 and PMA layer 5 device and convert them into an electrical output signal "dataout" 13 for packet de-coding within the PCS layer 4 and Datalink layer 3 of the communication system 7.
  • Figure 3 shows a typical time-domain data signal 10 transmitted within the propagation medium of Figure 2.
  • the y-axis 14 represents the amplitude of the data signal but could equally represent electrical voltage, power, or optical power in milli-watts (mW) .
  • the x-axis 15 represents time in units of nano-seconds (ns) .
  • the data is said to be logically high 16 when it is above a slice level 17 and likewise the data is said to be at a logical low 18 when it is below the slice level 17.
  • a low to high level data transition is termed a rising edge 19 and the high to low transition a falling edge 20.
  • Each logical bit of information lasts a duration known as the bit or symbol period 21, denoted "Ts".
  • Such data signals 10 are known to contain an amount of edge jitter, which is the equivalent of a pulse phase modulation noise, shown by the divergence of the edges dTl 22 and dT2 23.
  • Jitter can be random (data pattern independent) or deterministic (data pattern dependant) and low frequency (drift) or higher frequency.
  • the jitter is exaggerated in order to illustrate the phase modulation effect. In standard systems the jitter is kept very small from edge to edge so as to minimise errors when detecting the data. It should be noted that the data signal 10 presented is for illustrative purposes only and more or less complex distortion can occur.
  • PLL Phase Locked Loops
  • CDR clock data recovery
  • the bandwidth of the PLL's of such schemes is chosen sufficiently small in order to capture all the energy in the data but to reject noise and low frequency jitter components such as drift.
  • phase modulation effects are generally deemed to be detrimental to the accurate transmission of the data signals 10. Therefore, in order to compensate for these effects the PLLs are integrated within the physical link layer 2 so as to detect and thereafter compensate for the above described effects.
  • a significant disadvantage of the described communication system is that there is no facility, post data signal encoding, for inserting or extracting information at the Physical Link Layer 2, within the PMA layer 5 or the PCS layer 4.
  • the electrical input signals "datain" 9 have been encoded as data signals 10 within the standard Datalink layer 3 or the PCS layer 4 there is no means within the prior art systems for altering the data signals 10.
  • the prior art systems therefore do not provide a means for increasing the information transmitted by the system at the level of the Physical Link Layer 2.
  • a method of communicating information within the physical link layer of a communication system that comprises the steps of: 1) Employing a physical link layer transmitter to modulate the phase of a data signal to be transmitted within the communication system so as to incorporate an auxiliary data signal with the data signal; and 2) Employing a physical link layer receiver to extract the auxiliary data following transmission of the data signal within a transmission medium of the physical link layer.
  • auxiliary data is extracted without corruption of the data signal.
  • phase of the data signal is modulated at a frequency lower than a transmission frequency of the data signal.
  • the step of modulating the phase of the data signal comprises latching the data signal with a phase modulated clock signal.
  • the step of extracting the auxiliary data comprises the steps of: 1) Resolving the data signal into frequency components; 2) Extracting the frequency component of the data signal corresponding to the auxiliary data.
  • the auxiliary data signal comprises a coded data scheme.
  • the coded data scheme comprises one or more start of multiplexing characters that provide a means for activating the de-multiplexer within the receiver.
  • the coded data scheme may further comprise one or more control characters that provide a means for carrying out one or more of the functions contained within a group of functions comprising port identification, handshaking and data identification.
  • a transmitter for transmitting a data signal within a physical link layer of a communication system wherein the transmitter comprises a data insertion multiplexer that provides a means for phase modulating the data signal to be transmitted within the communication system so as to incorporate an auxiliary data signal with the data signal.
  • the data insertion multiplexer comprises a latch, to which the data signal provides an input, and a phase modulated signal generator that provides a clock signal for the latch.
  • phase modulated signal generator comprises an analogue phase modulator that provides a means for producing the phase modulated signal from a reference clock input signal.
  • phase modulated signal generator further comprises an analogue phase splitter that provides a means for splitting the reference clock signal into two or more synchronous input signals to be controllably combined by the analogue phase modulator so as to produce the phase modulated signal.
  • analogue phase splitter that provides a means for splitting the reference clock signal into two or more synchronous input signals to be controllably combined by the analogue phase modulator so as to produce the phase modulated signal.
  • phase modulated signal generator further comprises an encoder that provides a means for controllably selecting the proportional amounts of the two or more synchronous input signals to be combined within the analogue phase modulator.
  • phase modulated signal generator further comprises a data filter located between the encoder and the analogue phase modulator that functions as a low pass filter so limiting the rate of change of phase introduced to the phase modulated signal.
  • the phase modulated signal generator comprises a digitally controllable phase adjuster that provides a means for producing the phase modulated signal from a reference clock input signal.
  • an encoder generates a phase step word signal that is employed as a control signal for the digitally controllable phase adjuster.
  • the phase modulated signal generator comprises a phase locked loop that provides a means for producing the phase modulated signal from a reference clock input signal.
  • an encoder generates an encoded signal that is combined in a summation network with an output of a phase detector of the phase locked.
  • phase locked loop further comprises a low band pass filter that provides a means for removing the effects of noise from the phase modulated signal.
  • phase locked loop further comprises a voltage controlled oscillator that is driven by an output from the summation network so as to produce the phase modulated output.
  • phase modulated output is further employed as a feedback signal for the phase detector.
  • a receiver for receiving a data signal transmitted within the physical link layer of a communications system wherein the receiver comprises a data extraction de-multiplexer that provides a means for detecting and extracting a phase modulated auxiliary data signal incorporated within the transmitted data signal.
  • the data extraction de-multiplexer comprises a frequency resolving apparatus, which provides a means for resolving the data signal into frequency components, and a signal extractor . that provides a means for extracting the frequency component of the data signal corresponding to the auxiliary data.
  • the frequency resolving apparatus comprises a clocked phase detector.
  • the signal extractor comprises a low bandpass frequency filter.
  • the signal extractor further comprises a decoder.
  • the clock signal for the clocked phase detector is produced by passing an output from the low bandpass filter through a voltage controlled oscillator.
  • a communication system comprising one or more transmitters, one or more transmission media and one or more receivers wherein at least one of the one or more transmitters comprise a transmitter in accordance with the second aspect of the present invention. Most preferably at least one of the one or more receivers comprise a receiver in accordance with the third aspect of the present invention.
  • FIGURE 1 shows a schematic representation of a prior art Open Systems Interconnection (OSI) model
  • FIGURE 2 shows a schematic representation of typical physical link layer of a prior art communications system
  • FIGURE 3 shows a typical data signal transmitted within the communications system of Figure 2;
  • FIGURE 4 shows a schematic representation of a communications system at the physical link layer that employs the method and apparatus for inserting an additional data signal field in accordance with aspects of the present invention
  • FIGURE 5 shows a schematic representation of a data multiplexer employed by the communications system of Figure 4;
  • FIGURE 6 shows a schematic representation of an analogue phase splitter employed by the data multiplexer of Figure 5;
  • FIGURE 7 shows a schematic representation of a data filter employed by the data multiplexer of - Figure 5.
  • FIGURE 8 shows a schematic representation of an analogue phase modulator employed by the data multiplexer of Figure 5;
  • FIGURE 9 shows a schematic representation of a data demultiplexer employed by the communications system of Figure 4.
  • FIGURE 10 shows a frequency spectrum of a phase error signal "PEl" of the demultiplexer of Figure 9;
  • FIGURE 11 presents a coding scheme employed by an additional input data "Aux Datin" signaltransmitted within the communications system of Figure 4;
  • FIGURE 12 shows a schematic representation of an alternative embodiment of a data multiplexer employed by the communications system of Figure 4; and FIGURE 13 shows a schematic representation of a further alternative embodiment of a data multiplexer employed by the communications system of Figure 4.
  • a communications system 24 at the physical link layer that employs a method of inserting an additional field in accordance with an aspect of the present invention is presented in Figure 4.
  • the physical link layer of the communications system 24 can be seen to comprise common elements with the prior art system shown in Figure 2, and described above, therefore for clarity purposes the same reference numerals are employed throughout, as appropriate.
  • the communications system 24 can be seen to comprise a transmitter 8, a propagation medium 11 and a receiver 12.
  • the precise form of the data signals 10 generated by the transmitter 8 are again controlled by an electrical input signal "datain” 9 produced within the Datalink layer 3 before reaching the physical link layer of the communication system 24.
  • the receiver 12 again is employed to convert the detected data signals 10 into an electrical output signal "dataout” 13 for use within the datalink layer 3 of the communication system 24.
  • the transmitter 8 is partitioned into a data encoder 25, a data insertion multiplexer element (MUX) 26 and a physical output stage 27.
  • the signal transmitted via the propagation medium 11 is received at the receiver 12, which has been partitioned into an physical input stage 28, a data extraction de-multiplexer element (DEMUX) 29 and a data decoder 30.
  • An additional input data "Aux Datain” 31 field can be inserted within the normal input signal "datain” 9 by the MUX 26, as described below.
  • the additional input data "Aux Datin” 31 can then be extracted by the DEMUX 29, so as to provide a "Aux DataOut” 32 signal in addition to the normal output signal "Dataout” 13, as also described below.
  • the MUX 26 comprises a clock source 33, an analogue phase splitter 34, an analogue phase modulator 35, a latch 36, an encoded data filter 37 and an encoder 38.
  • the signals shown suggest single "wires", however in practical implementations the signals can also be differential with both positive and negative signals employed.
  • phase modulated clock “PMClock” 39 is employed to latch out the data signal 10.
  • the phase modulated clock “PMClock” 39 is itself low frequency phase modulated with the "Aux Datain” signal 31 that contains the additional low bandwidth data that is to be multiplexed onto the normally transmitted data, "Datain” 9.
  • the phase modulated clock “PMClock” 39 is generated within the apparatus as follows.
  • the Clock Source 33 outputs a "Clock" signal 40 that is the same, or a multiple frequency, of the data-rate of "Datain” 9.
  • the analogue phase splitter 34 then splits the Clock signal 40 into two synchronous phases, "ClockPl” 41 and "ClockP2" 42.
  • the two phases "ClockPl” 41 and “ClockP2” 42 may be conveniently spaced at 0.2 UI apart or approximately 2Ops by the action of the Analogue Phase Splitter 34. This spacing determines the maximum phase modulation possible and is typically a programmable or tuneable parameter.
  • the Analogue Phase Modulator 35 is employed to generate the phase modulated clock "PMClock” 39 signal.
  • This signal is a clock that is phase modulated by the action of the Analogue Phase Modulator 35.
  • the Analogue Phase Modulator's 35 modulation is controlled by two selection signals "SeIPl” 43 and “SelP2" 44 that act so as to select proportional amounts or mixes between the "ClockPl” 41 and “ClockP2" 42 clock phases, thus achieving the required phase modulation of the data signal 10.
  • the additional input data enters the MUX 26 unit via the "Aux Datain” signal 31. It is highly beneficial for the receiver 12 if the data rate of the "Aux Datain” signal 31 is frequency locked and synchronous to the "Clock" signal 40. To achieve this the "Aux Datain” 31 signalling rate is clocked from the "Clock” signal 40 divided down. For example a division ratio of 16384 implemented in a 14 bit counter (not shown) would provide an appropriate Fd/16384 signal.
  • the function of the Encoder 38 is to provide a "DC" balance and randomisation to the "Aux Datain” signal 31 through the employment of a suitable encoding scheme e.g. a 8bl0b coding scheme.
  • the Encoder 38 acts to scramble the "Aux Datain” signal 31 by employing a suitable psuedo-random binary sequence (PRBS) .
  • PRBS psuedo-random binary sequence
  • the encoded data signal "Enc Datain” 45 is then filtered within the Encoded Data Filter 37 that functions to provide the required low pass filtering so as to limit the maximum rate of change of the phase introduced to the data signal 10.
  • the Encoded Data Filter 37 thus prevents the spectrum of the "Aux Datain” signal 31 from encroaching into the spectral bandwidth of the normally transmitted data signal 10.
  • FIG. 6 shows further detail of the analogue phase splitter 34 employed by the MUX 26.
  • the Analogue Phase Splitter 34 splits the "Clock” signal 40 into two synchronous phases, “ClockPl” 41 and “ClockP2” 42 through the employment of emitter-coupled logic in a bipolar technology.
  • the "Clock” signal 40 is split through the employment of differential emitter coupled logic (ECL) signals w Clock_p" 46 and "Clock_n” 47.
  • ECL emitter coupled logic
  • the “ClockPl” 41 and “ClockP2” 42 signals are implemented in the differential ECL output signals "ClockPl_j ? " 48, "ClockPl_n” 49, “ClockP2_n” 50 and “ClockP2_p” 51 signals.
  • the delay between the "ClockPl" 41 and the “ClockP2" 42 phases can be adjusted using a variety of techniques so as to give the desired phase modulation maximum, for example adjusting a tuneable capacitor “Ctune” 52 or a tuneable current "Itaill” or “Itail2" 53.
  • Analogue Phase Splitter 34 can be implemented in a similar manner in another technology such as CMOS technology by employing source-coupled logic equivalents.
  • FIG. 7 a schematic representation of the encoded data filter 37 employed by the MUX 26 is presented.
  • the "Enc Datain” signal 45 input is converted to first and second differential ECL signals, 54 and 55 respectively, by a CMOS to ECL Converter 56 block.
  • the first and second differential ECL signals, 54 and 55 are then filtered by the actions of the resistors ⁇ Rfiltl” 57, “Rfilt2" 58, and capacitor “Cfilt” 59 that the combined effect is to function as low pass filter network.
  • the filtered signals "SeIPl” 43 and “SelP2" 44 signals are thus derived.
  • the required filtering can be achieved by charging or discharging a current source through the capacitor "Cfilt" element 59.
  • FIG. 8 provides further detail of the analogue phase modulator 35 employed by the MUX 26.
  • the analogue phase modulator 35 is implemented using emitter-coupled logic in a bipolar technology.
  • the "ClockPl” 41 and “ClockP2" 42 input signals are implemented in the differential ECL signals “ClockPl_p” 60, “ClockPl_n” 61, w ClockP2_n” 62 and “ClockP2_jp” 63 signals.
  • the function of the phase selection input signals “SeIPl” 43 and “SelP2” 44 is to select proportions of the clock input signals to be mixed to form the output.
  • Output phase modulated Clock signals "PMClock_j?” 64 and "PMClock_n” 65 are thus differential ECL implementations of the "PMClock” 39 signal.
  • the analogue phase modulator 35 (not shown) can be implemented in a similar manner within another technology such as CMOS technology using source-coupled logic equivalents.
  • de-multimlexpers typically employ PPLs, the bandwidth of which are chosen sufficiently small in order to capture all the energy in the transmitted data but to reject noise and low frequency component drift.
  • the transmitter of the present system employs a pulse phase modulation multiplexing scheme designed to appear as a very low frequency modulation of the data carrier. As such the "Aux Datain" 31 would be naturally filtered within the known standard CDR receivers.
  • a schematic representation of the data DEMUX 29 employed within the receiver 12 of the communications system 24 is presented in Figure 9.
  • the data DEMUX 29 employs a modified CDR PLL based architecture.
  • an input data signal to the DEMUX 29, "Datain” 66 passes through a Phase Detector 67 where the detected phase is compared against a recovered "Clock” signal 68.
  • a resultant phase error signal “PEl” 69 is then filtered in a Loop Filter 70 so as to produce a filtered phase error signal "PE2" 71.
  • the filtered phase error signal "PE2" 71 is then employed to drive a Voltage Controlled Oscillator (VCO) 72 towards phase/frequency lock.
  • VCO Voltage Controlled Oscillator
  • the normally transmitted electrical output signal "Dataout” 13 is recovered through a Data Sample block 73, which can include additional filters and equalisation.
  • a Decoder block 74 is employed to monitor the filtered phase error signal "PE2" 71. Because the additional input data "Aux Datin” 31 is synchronous to the recovered "Clock” 68 signal, this clock can be used as a master reference, and a slave clock can then be used to conveniently clock the Decoder block 74 from a divided down version. For the MUX example given above a 14 bit or 16384 count counter running off the "Clock" signal 68 is employed for this purpose to clock the Decoder block 74.
  • the Decoder block 74 thus de-encodes the encoded, scrambled data to extract the additional input data "Aux Datin” 31 encoded onto the normally transmitted electrical output signal “Dataout” 13 so as to produce the additional output data "Aux Datout” 32.
  • Figure 10 shows a frequency spectrum of the phase error signal W PE1" 69 within the DEMUX 29 employed by the PLL based CDR receiver 12 of the communications system 24.
  • the x-axis 75 represents frequency on a logarithmic scale in Hertz (Hz) while the y-axis 76 represents power on a linear scale in decibels (dB) .
  • Fs 0.5/Ts.
  • the useful energy in the spectrum of the normally transmitted signal phase error extends for a finite bandwidth, here shown from a lower bound frequency FsI 79 to an upper bound frequency Fsu 80.
  • FsI Fs/100
  • Fsu 5xFs.
  • the lower frequency FsI is bounded and advantage is taken of this within the design of the receiver 12.
  • the Loop Filter 70 exhibits a low pass characteristic as represented by 81 and a notational bandwidth indicated by . FpIl 82 while the spectrum of the additional data "Aux Datain” 31 is represented at 83. Of particular note is the fact that the upper bound of the spectrum 83 is always less the bandwidth 82 of the Loop Filter 70. Hence, the "Aux Datain” 31 is essentially transparent to the Clock Data Recovery (CDR) circuit such that it does not impair or interference with the normally transmitted signal spectrum 77. Thus, the additional data "Aux Datain” 31 can be simply inserted, extracted and stripped from the transmitted signal using extended PLL methods and apparatus as described. This ability vastly simplifies the receiver designs with little additional overhead required.
  • CDR Clock Data Recovery
  • Figure 3 can be considered as a time domain representation of the frequency spectrum of Figure 10.
  • the additional data "Aux Datain” 31 appears as a low frequency modulation on the rising and falling edges, 19 and 20 respectively, of the data signal 10. As discussed above, this low frequency modulation effect is generally deemed to be detrimental within the systems described in the prior art and hence is actively avoided.
  • FIG 11 presents one possible coding scheme, 84 employed by the additional input data "Aux Datin" 31.
  • the coding scheme can be seen to comprise three sub fields, namely: • a series of unique Start Of Mux (SOM) characters 85 that act as a pre-amble for the receiver; • control characters CNTi to CNT n 86 that are used for port identification, handshaking, data identification; and other control functions; and • the data characters themselves DATl to DATn 87.
  • SOM Start Of Mux
  • control character field CNT 86 or the data field DAT 87 or elsewhere in the additional input data ⁇ Aux Datin" 31, there may also be included a unique physical port address so as to identifying a particular physical device on the link.
  • This information can be employed, for example, in links where a device acts as a physical layer repeater. Each device is then pre- assigned or dynamically assigned a unique identifier, as appropriate.
  • FIG. 12 An alternative embodiment of the data insertion multiplexer element (MUX) 88 employed by the communications system 24 is presented in Figure 12. This particular embodiment of the MUX 88 is suitable for implementation within lower speed communications systems 24.
  • the phase of the "PMClock" signal 39 is controlled using a Phase Stepper circuit 89.
  • the Phase Stepper circuit 89 is a digitally controllable phase adjuster element such as a Delay Locked Loop (DLL) or a Phase Interpolator. Control of the Phase Stepper circuit 89 is achieved via a "Phase Step Word" signal 90 that acts to add or remove phase offsets from the "Clock" signal 40.
  • DLL Delay Locked Loop
  • Phase Interpolator Phase Interpolator
  • the Encoder 30 acts to suitably condition the additional data input signal "Aux Datain” 31 and provides “DC” balance using a suitable coding scheme.
  • the Encoder 30 can provide the required low pass filtering that limits the maximum rate of change of the phase step so as to prevent the spectrum of the "Aux Datain” signal 31 from encroaching into the spectral bandwidth of the normally transmitted data signal 10.
  • the encoder 30 also provides a means for controlling the maximum allowable phase deviation.
  • a further alternative embodiment of the data insertion multiplexer element (MUX) 91 employed by the communications system 24 is presented in Figure 13.
  • the MUX 91 is particularly suited for employment within an integrated PLL communication system 24.
  • phase modulated clock "PMClock” 39 is generated within a modified PLL 92 as is now described.
  • a reference input clock, "Clock” 93, to a Phase Detector 94, is derived from a clock source 95 that is in the form of a separate PLL or a Clock Data Recovery (CDR) circuit located within the system.
  • CDR Clock Data Recovery
  • phase detector 94 produces a phase error signal "PEl” 98 onto which the additional input data "Aux Datain” 31 is added within a summation network 99.
  • a combined Phase Error signal "PE2" 100 is then filtered by a suitably low bandwidth Loop Filter 101 that produces a filtered phase error signal "PE3" 102.
  • the bandwidth of the Loop Filter 101 is specifically chosen so as to reject system noise but pass the phase data information, nominally set at Fd/1000.
  • the Encoder 38 provides a "DC" balanced signal using a suitable coding scheme between the input data "Datain” 9 and the "Aux Datin” 31.
  • the Encoder 38 suitably limits the maximum rate of change of the phase step so as to prevent the data spectrum of the "Aux Datin” 31 encroaching into the normally transmitted data bandwidth of the "Datain” 9.
  • the Encoder 38 also provides a control for the maximum allowable phase deviation of the "Aux Datin” 31 signal.
  • the filtered phase error signal "PE3" 102 is employed to control the oscillation frequency and phase of the voltage controlled oscillator (VCO) 72.
  • VCO voltage controlled oscillator
  • the "PMClock" 39 signal is employed as the clock signal for the Phase Detector 67. This embodiment is employed when the "Clock” 93 is only a sub-multiple of the desired latching "PMClock” 39 signal.
  • the VCO 72 is implemented in another oscillating or phase distorting device that has a controllable frequency/phase such as a current, a charge controlled oscillator or an interpolation circuit.
  • a further alternative embodiment of the MUX 91 employs a Loop Filter that is split into two distinct sections.
  • One filter section comprises an analogue filter constructed by using a passive resistor and capacitor components with a charge pump adding or subtracting current.
  • the function of this first filter section is to process the phase error signal "PEl" 98 with a filter bandwidth « Fd/1000.
  • a second filter is then employed to process the "Aux Datin" 31 signal with bandwidth > Fd/10000 and ⁇ Fd/1000.
  • This filtered signal is then input directly to the VCO 72 using a digitally controlled loop filter to add and subtract charge to the loop.
  • the summation network 99 is located after the two section Loop Filter.
  • the input "Clock” 93 is replaced with the received input data "Datain” 9 or a derivative of the phase error signal "PEl” 98 transformed into a Clock-Data Recovery Loop.
  • the frequency of the "PMClock” 39 used to latch the data is directly frequency locked to the received data and phase modulated inside the PLL/CDR function.
  • the described method may also be readily incorporated within a number of transmission media including, but not limited to, over air, optical fibre, printed circuit board or cable.
  • different types of transmission signal formats may be employed including, but not limited to serial, parallel, analogue, digital, modulated, un-modulated, return to zero coding, non return to zero coding, encoded data, non encoded data, multi-level, binary, continuous or discontinuous, framed, burst or packet based or any combination of these.
  • transmission techniques may also be employed including, but not limited to, electrical, electro-magnetic, magnetic or optical means.
  • the described method relates to a communication system where only one transmitter and one receiver is used with one media channel.
  • transmission can be made from more than one transmitter sharing one or more media channels to one or more receivers.
  • the transmitter and the receiver are described as being two separate elements or components of the system.
  • the transmitter and the receiver can be joined or part joined within the same combined element or component of the system, as relevant to multi-channel bi- directional applications.
  • the transmitter and/or the receiver can comprise a different combination of separate elements in a combination with less or additional elements so as could be viewed to act as a transmitter and or receiver, respectfully.
  • FIG. 1 Further alternative embodiments to the communication system include the system comprising: • additional filters, transducers, amplifiers, sensors or other elements or components between the transmitter and receiver; • separate sections of media, separated by filters, transducers, sensors, transponders, transceivers, transmitters, receivers or other elements so as the break the media into one or more sections of not necessarily the same type of media; and
  • the CNT data can contain a unique physical port address identifying that physical device on the link layer. This can be used, for example, in links where a device is employed as a physical layer repeater. Each device can then be pre- assigned or dynamically assigned the unique identifier as appropriate.
  • link status flags can also be included within the control character field CNT 86, or elsewhere within the additional input data "Aux Datain" 31. These flags are then employed to arrange a handshaking protocol for establishing link-up status between all sets of transmitters and receivers before any data is transferred. The flags can also be employed to provide acknowledgement of successful data transfer in conjunction with a suitable error detection scheme in the data, such as cyclical redundancy checking (CRC) .
  • CRC cyclical redundancy checking
  • the above method provides a means for improving the efficiency of a communications systems by exploiting existing relevant standards to transmit a quantity of additional data by encoding it as an additional low frequency phase modulation on an existing data information signal.
  • additional data can be used for any purpose as desired, but in the described embodiment the additional data is required specifically for the physical link.
  • the information can include transmitter and receiver physical parametrics and such information is then employed in addition to any existing data provision within any known standard.
  • the additional information is conveniently multiplexed within the physical link layer whilst being transparent to the normally transmitted data signals. Employing this method puts no extra bandwidth requirement on the communications system.
  • a significant benefit of multiplexing this data at the physical link layer itself is that it allows data to be added, extracted and stripped within the physical layer device at the point where the information is both available and required. This is architecturally efficient and leads to a performance, cost and size superior solution when compared to other conceivable alternatives.

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Abstract

A method and apparatus that permits direct communication of information between elements within a physical link layer of a communication system is described. This is achieved by exploiting existing relevant standards to transmit a quantity of additional data by encoding it as an additional low frequency phase modulation on an existing data information signal transmitted within the communications system. Importantly the additional information is effectively transparent to the normally transmitted data signals and so these signals are not corrupted by the presence of the additional data while no extra bandwidth requirement is placed on the communications system. The described method and apparatus is architecturally efficient and leads to a solution that exhibits an improved performance, cost and size.

Description

Method and Apparatus for Data Communication Within a Physical Link Layer of a Communication System
The present invention relates to the field of communications systems. More particularly, this invention relates to a method and apparatus that permits direct communication of information between elements within the physical link layer of a communication system.
Background Art
A schematic representation of an Open Systems Interconnection (OSI) model 1 is presented in Figure 1. The OSI model 1 is .a seven layer reference model recommended by the International Standards Organisation (ISO) to provide a logical structure for network operations protocol. Within the OSI model 1 a Physical Link Layer 2 is defined as the lowest layer and above this lies a Datalink Layer 3. The Datalink layer 3 has several functions within the communication system, one of which is to perform the task of encoding a data signal into a form suitable for transmission and thereafter to decode the transmitted signal, as appropriate. The Physical Link Layer 2 is often conveniently subdivided into a Physical Coding Sub-layer (PCS) 4, a Physical Media Attachment (PMA) layer 5 and a Physical Media Device (PMD) layer 6. The PCS 4, encodes the data stream into a form suitable for transmission across the physical media. The PMA 5 provides an attachment layer between PCS 4 and the PMD 6. The PMD 6 is responsible for the physical transmission of the signal .
Figure 2 presents a schematic representation of a communication system 7, as is known to those skilled in the art e.g. a Sonet, an Ethernet or a Fibre Channel systems. The communication system 7 is shown in a simplified form so as to comprise a transmitter 8 that performs the tasks of the PMD layer 6 and optionally also the PMA layer 5. The transmitter 8 acts to convert the encoded electrical input signal "datain" 9, produced within the higher Datalink layer 3 and PCS layer 4, into a data signal 10 suitable for transmission through a propagation medium 11. In this example the data signal 10 comprise an optical signal for transmission through an optical fibre.
At the output of the propagation medium 11 is located a receiver 12. The receiver 12 is employed to detect the signals in a PMD layer 6 and PMA layer 5 device and convert them into an electrical output signal "dataout" 13 for packet de-coding within the PCS layer 4 and Datalink layer 3 of the communication system 7.
Figure 3 shows a typical time-domain data signal 10 transmitted within the propagation medium of Figure 2. The y-axis 14 represents the amplitude of the data signal but could equally represent electrical voltage, power, or optical power in milli-watts (mW) . The x-axis 15 represents time in units of nano-seconds (ns) . The data is said to be logically high 16 when it is above a slice level 17 and likewise the data is said to be at a logical low 18 when it is below the slice level 17. A low to high level data transition is termed a rising edge 19 and the high to low transition a falling edge 20. Each logical bit of information lasts a duration known as the bit or symbol period 21, denoted "Ts".
Such data signals 10 are known to contain an amount of edge jitter, which is the equivalent of a pulse phase modulation noise, shown by the divergence of the edges dTl 22 and dT2 23. Jitter can be random (data pattern independent) or deterministic (data pattern dependant) and low frequency (drift) or higher frequency. In Figure 3 the jitter is exaggerated in order to illustrate the phase modulation effect. In standard systems the jitter is kept very small from edge to edge so as to minimise errors when detecting the data. It should be noted that the data signal 10 presented is for illustrative purposes only and more or less complex distortion can occur.
It is known to those skilled in the art for high performance data receivers to employ Phase Locked Loops (PLL) so as to recover the clock from a transmitted data signal. This clock is then used to sample the received data in order to determine the logic state sent, in a scheme commonly referred to as clock data recovery (CDR) . The bandwidth of the PLL's of such schemes is chosen sufficiently small in order to capture all the energy in the data but to reject noise and low frequency jitter components such as drift. Thus within the prior art systems phase modulation effects are generally deemed to be detrimental to the accurate transmission of the data signals 10. Therefore, in order to compensate for these effects the PLLs are integrated within the physical link layer 2 so as to detect and thereafter compensate for the above described effects.
A significant disadvantage of the described communication system is that there is no facility, post data signal encoding, for inserting or extracting information at the Physical Link Layer 2, within the PMA layer 5 or the PCS layer 4. Thus, once the electrical input signals "datain" 9 have been encoded as data signals 10 within the standard Datalink layer 3 or the PCS layer 4 there is no means within the prior art systems for altering the data signals 10. The prior art systems therefore do not provide a means for increasing the information transmitted by the system at the level of the Physical Link Layer 2.
It is an object of an aspect of the present invention to provide a method and apparatus that permits direct communication of information between elements within the physical link layer of a communication system.
According to a first aspect of the present invention there is provided a method of communicating information within the physical link layer of a communication system that comprises the steps of: 1) Employing a physical link layer transmitter to modulate the phase of a data signal to be transmitted within the communication system so as to incorporate an auxiliary data signal with the data signal; and 2) Employing a physical link layer receiver to extract the auxiliary data following transmission of the data signal within a transmission medium of the physical link layer.
Most preferably the auxiliary data is extracted without corruption of the data signal.
Most preferably the phase of the data signal is modulated at a frequency lower than a transmission frequency of the data signal.
Preferably the step of modulating the phase of the data signal comprises latching the data signal with a phase modulated clock signal.
Preferably the step of extracting the auxiliary data comprises the steps of: 1) Resolving the data signal into frequency components; 2) Extracting the frequency component of the data signal corresponding to the auxiliary data.
Optionally the auxiliary data signal comprises a coded data scheme. Typically, the coded data scheme comprises one or more start of multiplexing characters that provide a means for activating the de-multiplexer within the receiver. The coded data scheme may further comprise one or more control characters that provide a means for carrying out one or more of the functions contained within a group of functions comprising port identification, handshaking and data identification. According to a second aspect of the present invention there is provided a transmitter for transmitting a data signal within a physical link layer of a communication system wherein the transmitter comprises a data insertion multiplexer that provides a means for phase modulating the data signal to be transmitted within the communication system so as to incorporate an auxiliary data signal with the data signal.
Preferably the data insertion multiplexer comprises a latch, to which the data signal provides an input, and a phase modulated signal generator that provides a clock signal for the latch.
Preferably the phase modulated signal generator comprises an analogue phase modulator that provides a means for producing the phase modulated signal from a reference clock input signal.
Preferably the phase modulated signal generator further comprises an analogue phase splitter that provides a means for splitting the reference clock signal into two or more synchronous input signals to be controllably combined by the analogue phase modulator so as to produce the phase modulated signal.
Preferably the phase modulated signal generator further comprises an encoder that provides a means for controllably selecting the proportional amounts of the two or more synchronous input signals to be combined within the analogue phase modulator.
Preferably the phase modulated signal generator further comprises a data filter located between the encoder and the analogue phase modulator that functions as a low pass filter so limiting the rate of change of phase introduced to the phase modulated signal.
Optionally the phase modulated signal generator comprises a digitally controllable phase adjuster that provides a means for producing the phase modulated signal from a reference clock input signal. In this embodiment an encoder generates a phase step word signal that is employed as a control signal for the digitally controllable phase adjuster.
Alternatively the phase modulated signal generator comprises a phase locked loop that provides a means for producing the phase modulated signal from a reference clock input signal. In this embodiment an encoder generates an encoded signal that is combined in a summation network with an output of a phase detector of the phase locked.
Preferably the phase locked loop further comprises a low band pass filter that provides a means for removing the effects of noise from the phase modulated signal.
Preferably the phase locked loop further comprises a voltage controlled oscillator that is driven by an output from the summation network so as to produce the phase modulated output.
Preferably the phase modulated output is further employed as a feedback signal for the phase detector.
According to a third aspect of the present invention there is provided a receiver for receiving a data signal transmitted within the physical link layer of a communications system wherein the receiver comprises a data extraction de-multiplexer that provides a means for detecting and extracting a phase modulated auxiliary data signal incorporated within the transmitted data signal.
Preferably the data extraction de-multiplexer comprises a frequency resolving apparatus, which provides a means for resolving the data signal into frequency components, and a signal extractor . that provides a means for extracting the frequency component of the data signal corresponding to the auxiliary data.
Preferably the frequency resolving apparatus comprises a clocked phase detector.
Preferably the signal extractor comprises a low bandpass frequency filter.
Preferably the signal extractor further comprises a decoder.
Preferably the clock signal for the clocked phase detector is produced by passing an output from the low bandpass filter through a voltage controlled oscillator.
According to a fourth aspect of the present invention there is provided a communication system comprising one or more transmitters, one or more transmission media and one or more receivers wherein at least one of the one or more transmitters comprise a transmitter in accordance with the second aspect of the present invention. Most preferably at least one of the one or more receivers comprise a receiver in accordance with the third aspect of the present invention.
Brief Description of Drawings
In the following detailed description of the preferred embodiments or mode, reference is made to the accompanying drawings, which form part hereof, and in which are shown, by way of illustration, specific embodiments in which aspects of the invention may be practised. It is to be understood that other embodiments may be utilised and structural changes may be made without departing from the scope of the present invention.
FIGURE 1 shows a schematic representation of a prior art Open Systems Interconnection (OSI) model;
FIGURE 2 shows a schematic representation of typical physical link layer of a prior art communications system;
FIGURE 3 shows a typical data signal transmitted within the communications system of Figure 2;
FIGURE 4 shows a schematic representation of a communications system at the physical link layer that employs the method and apparatus for inserting an additional data signal field in accordance with aspects of the present invention; FIGURE 5 shows a schematic representation of a data multiplexer employed by the communications system of Figure 4;
FIGURE 6 shows a schematic representation of an analogue phase splitter employed by the data multiplexer of Figure 5;
FIGURE 7 shows a schematic representation of a data filter employed by the data multiplexer of -Figure 5; and
FIGURE 8 shows a schematic representation of an analogue phase modulator employed by the data multiplexer of Figure 5;
FIGURE 9 shows a schematic representation of a data demultiplexer employed by the communications system of Figure 4;
FIGURE 10 shows a frequency spectrum of a phase error signal "PEl" of the demultiplexer of Figure 9;
FIGURE 11 presents a coding scheme employed by an additional input data "Aux Datin" signaltransmitted within the communications system of Figure 4;
FIGURE 12 shows a schematic representation of an alternative embodiment of a data multiplexer employed by the communications system of Figure 4; and FIGURE 13 shows a schematic representation of a further alternative embodiment of a data multiplexer employed by the communications system of Figure 4.
Detailed Description
A communications system 24 at the physical link layer that employs a method of inserting an additional field in accordance with an aspect of the present invention, is presented in Figure 4. The physical link layer of the communications system 24 can be seen to comprise common elements with the prior art system shown in Figure 2, and described above, therefore for clarity purposes the same reference numerals are employed throughout, as appropriate.
In particular, the communications system 24 can be seen to comprise a transmitter 8, a propagation medium 11 and a receiver 12. The precise form of the data signals 10 generated by the transmitter 8 are again controlled by an electrical input signal "datain" 9 produced within the Datalink layer 3 before reaching the physical link layer of the communication system 24. The receiver 12 again is employed to convert the detected data signals 10 into an electrical output signal "dataout" 13 for use within the datalink layer 3 of the communication system 24.
The transmitter 8 is partitioned into a data encoder 25, a data insertion multiplexer element (MUX) 26 and a physical output stage 27. The signal transmitted via the propagation medium 11 is received at the receiver 12, which has been partitioned into an physical input stage 28, a data extraction de-multiplexer element (DEMUX) 29 and a data decoder 30. An additional input data "Aux Datain" 31 field can be inserted within the normal input signal "datain" 9 by the MUX 26, as described below. The additional input data "Aux Datin" 31 can then be extracted by the DEMUX 29, so as to provide a "Aux DataOut" 32 signal in addition to the normal output signal "Dataout" 13, as also described below.
Turning now to Figure 5 a schematic representation of a MUX 26 employed by the communications system 24 is presented. The MUX 26 comprises a clock source 33, an analogue phase splitter 34, an analogue phase modulator 35, a latch 36, an encoded data filter 37 and an encoder 38. Note that throughout the Figures the signals shown suggest single "wires", however in practical implementations the signals can also be differential with both positive and negative signals employed.
The normally transmitted serial data "Datain" 9 is clocked via the latch 36 so as to produce the data signal 10. A phase modulated clock "PMClock" 39 signal is employed to latch out the data signal 10. The phase modulated clock "PMClock" 39 is itself low frequency phase modulated with the "Aux Datain" signal 31 that contains the additional low bandwidth data that is to be multiplexed onto the normally transmitted data, "Datain" 9. The phase modulated clock "PMClock" 39 is generated within the apparatus as follows.
The Clock Source 33 outputs a "Clock" signal 40 that is the same, or a multiple frequency, of the data-rate of "Datain" 9. The analogue phase splitter 34 then splits the Clock signal 40 into two synchronous phases, "ClockPl" 41 and "ClockP2" 42. For example, in a lOGBps system application the two phases "ClockPl" 41 and "ClockP2" 42 may be conveniently spaced at 0.2 UI apart or approximately 2Ops by the action of the Analogue Phase Splitter 34. This spacing determines the maximum phase modulation possible and is typically a programmable or tuneable parameter.
The Analogue Phase Modulator 35 is employed to generate the phase modulated clock "PMClock" 39 signal. This signal is a clock that is phase modulated by the action of the Analogue Phase Modulator 35. The Analogue Phase Modulator's 35 modulation is controlled by two selection signals "SeIPl" 43 and "SelP2" 44 that act so as to select proportional amounts or mixes between the "ClockPl" 41 and "ClockP2" 42 clock phases, thus achieving the required phase modulation of the data signal 10.
The additional input data enters the MUX 26 unit via the "Aux Datain" signal 31. It is highly beneficial for the receiver 12 if the data rate of the "Aux Datain" signal 31 is frequency locked and synchronous to the "Clock" signal 40. To achieve this the "Aux Datain" 31 signalling rate is clocked from the "Clock" signal 40 divided down. For example a division ratio of 16384 implemented in a 14 bit counter (not shown) would provide an appropriate Fd/16384 signal.
The function of the Encoder 38 is to provide a "DC" balance and randomisation to the "Aux Datain" signal 31 through the employment of a suitable encoding scheme e.g. a 8bl0b coding scheme. Alternatively, the Encoder 38 acts to scramble the "Aux Datain" signal 31 by employing a suitable psuedo-random binary sequence (PRBS) . The encoded data signal "Enc Datain" 45 is then filtered within the Encoded Data Filter 37 that functions to provide the required low pass filtering so as to limit the maximum rate of change of the phase introduced to the data signal 10. The Encoded Data Filter 37 thus prevents the spectrum of the "Aux Datain" signal 31 from encroaching into the spectral bandwidth of the normally transmitted data signal 10.
Figure 6 shows further detail of the analogue phase splitter 34 employed by the MUX 26. The Analogue Phase Splitter 34 splits the "Clock" signal 40 into two synchronous phases, "ClockPl" 41 and "ClockP2" 42 through the employment of emitter-coupled logic in a bipolar technology. In particular the "Clock" signal 40 is split through the employment of differential emitter coupled logic (ECL) signals wClock_p" 46 and "Clock_n" 47. The "ClockPl" 41 and "ClockP2" 42 signals are implemented in the differential ECL output signals "ClockPl_j?" 48, "ClockPl_n" 49, "ClockP2_n" 50 and "ClockP2_p" 51 signals. The delay between the "ClockPl" 41 and the "ClockP2" 42 phases can be adjusted using a variety of techniques so as to give the desired phase modulation maximum, for example adjusting a tuneable capacitor "Ctune" 52 or a tuneable current "Itaill" or "Itail2" 53.
In an alternative embodiment the function of the Analogue Phase Splitter 34 can be implemented in a similar manner in another technology such as CMOS technology by employing source-coupled logic equivalents.
Turning now to Figure 7 a schematic representation of the encoded data filter 37 employed by the MUX 26 is presented. The "Enc Datain" signal 45 input is converted to first and second differential ECL signals, 54 and 55 respectively, by a CMOS to ECL Converter 56 block. The first and second differential ECL signals, 54 and 55, are then filtered by the actions of the resistors λλRfiltl" 57, "Rfilt2" 58, and capacitor "Cfilt" 59 that the combined effect is to function as low pass filter network. The filtered signals "SeIPl" 43 and "SelP2" 44 signals are thus derived.
In an alternative embodiment of the encoded data filter 37 (not shown) the required filtering can be achieved by charging or discharging a current source through the capacitor "Cfilt" element 59.
Figure 8 provides further detail of the analogue phase modulator 35 employed by the MUX 26. The analogue phase modulator 35 is implemented using emitter-coupled logic in a bipolar technology. The "ClockPl" 41 and "ClockP2" 42 input signals are implemented in the differential ECL signals "ClockPl_p" 60, "ClockPl_n" 61, wClockP2_n" 62 and "ClockP2_jp" 63 signals. The function of the phase selection input signals "SeIPl" 43 and "SelP2" 44 is to select proportions of the clock input signals to be mixed to form the output. Output phase modulated Clock signals "PMClock_j?" 64 and "PMClock_n" 65 are thus differential ECL implementations of the "PMClock" 39 signal.
In an alternative embodiment, the analogue phase modulator 35 (not shown) can be implemented in a similar manner within another technology such as CMOS technology using source-coupled logic equivalents. As discussed above prior art de-multimlexpers typically employ PPLs, the bandwidth of which are chosen sufficiently small in order to capture all the energy in the transmitted data but to reject noise and low frequency component drift. However, the transmitter of the present system employs a pulse phase modulation multiplexing scheme designed to appear as a very low frequency modulation of the data carrier. As such the "Aux Datain" 31 would be naturally filtered within the known standard CDR receivers.
A schematic representation of the data DEMUX 29 employed within the receiver 12 of the communications system 24 is presented in Figure 9. The data DEMUX 29 employs a modified CDR PLL based architecture. In particular, an input data signal to the DEMUX 29, "Datain" 66, passes through a Phase Detector 67 where the detected phase is compared against a recovered "Clock" signal 68. A resultant phase error signal "PEl" 69 is then filtered in a Loop Filter 70 so as to produce a filtered phase error signal "PE2" 71. The filtered phase error signal "PE2" 71 is then employed to drive a Voltage Controlled Oscillator (VCO) 72 towards phase/frequency lock.
The normally transmitted electrical output signal "Dataout" 13 is recovered through a Data Sample block 73, which can include additional filters and equalisation. A Decoder block 74 is employed to monitor the filtered phase error signal "PE2" 71. Because the additional input data "Aux Datin" 31 is synchronous to the recovered "Clock" 68 signal, this clock can be used as a master reference, and a slave clock can then be used to conveniently clock the Decoder block 74 from a divided down version. For the MUX example given above a 14 bit or 16384 count counter running off the "Clock" signal 68 is employed for this purpose to clock the Decoder block 74. The Decoder block 74 thus de-encodes the encoded, scrambled data to extract the additional input data "Aux Datin" 31 encoded onto the normally transmitted electrical output signal "Dataout" 13 so as to produce the additional output data "Aux Datout" 32.
To aid understanding of the present invention Figure 10 shows a frequency spectrum of the phase error signal WPE1" 69 within the DEMUX 29 employed by the PLL based CDR receiver 12 of the communications system 24. In particular, the x-axis 75 represents frequency on a logarithmic scale in Hertz (Hz) while the y-axis 76 represents power on a linear scale in decibels (dB) .
The normally transmitted data phase error component has a frequency spectrum 77 centred on the data-rate frequency 78, denoted Fs. Fs is given by the relationship Fs = 0.5/Ts. The useful energy in the spectrum of the normally transmitted signal phase error extends for a finite bandwidth, here shown from a lower bound frequency FsI 79 to an upper bound frequency Fsu 80. Typically, FsI = Fs/100 and Fsu = 5xFs. Of particular significance is the fact that the lower frequency FsI is bounded and advantage is taken of this within the design of the receiver 12.
The Loop Filter 70 exhibits a low pass characteristic as represented by 81 and a notational bandwidth indicated by . FpIl 82 while the spectrum of the additional data "Aux Datain" 31 is represented at 83. Of particular note is the fact that the upper bound of the spectrum 83 is always less the bandwidth 82 of the Loop Filter 70. Hence, the "Aux Datain" 31 is essentially transparent to the Clock Data Recovery (CDR) circuit such that it does not impair or interference with the normally transmitted signal spectrum 77. Thus, the additional data "Aux Datain" 31 can be simply inserted, extracted and stripped from the transmitted signal using extended PLL methods and apparatus as described. This ability vastly simplifies the receiver designs with little additional overhead required.
It will be appreciated by those skilled in the art that Figure 3 can be considered as a time domain representation of the frequency spectrum of Figure 10. In this representation the additional data "Aux Datain" 31 appears as a low frequency modulation on the rising and falling edges, 19 and 20 respectively, of the data signal 10. As discussed above, this low frequency modulation effect is generally deemed to be detrimental within the systems described in the prior art and hence is actively avoided.
Figure 11 presents one possible coding scheme, 84 employed by the additional input data "Aux Datin" 31. The coding scheme can be seen to comprise three sub fields, namely: • a series of unique Start Of Mux (SOM) characters 85 that act as a pre-amble for the receiver; • control characters CNTi to CNTn 86 that are used for port identification, handshaking, data identification; and other control functions; and • the data characters themselves DATl to DATn 87.
Within the control character field CNT 86, or the data field DAT 87 or elsewhere in the additional input data λΛAux Datin" 31, there may also be included a unique physical port address so as to identifying a particular physical device on the link. This information can be employed, for example, in links where a device acts as a physical layer repeater. Each device is then pre- assigned or dynamically assigned a unique identifier, as appropriate.
An alternative embodiment of the data insertion multiplexer element (MUX) 88 employed by the communications system 24 is presented in Figure 12. This particular embodiment of the MUX 88 is suitable for implementation within lower speed communications systems 24. In this scheme the phase of the "PMClock" signal 39 is controlled using a Phase Stepper circuit 89. The Phase Stepper circuit 89 is a digitally controllable phase adjuster element such as a Delay Locked Loop (DLL) or a Phase Interpolator. Control of the Phase Stepper circuit 89 is achieved via a "Phase Step Word" signal 90 that acts to add or remove phase offsets from the "Clock" signal 40. In this embodiment the Encoder 30 acts to suitably condition the additional data input signal "Aux Datain" 31 and provides "DC" balance using a suitable coding scheme. In addition, the Encoder 30 can provide the required low pass filtering that limits the maximum rate of change of the phase step so as to prevent the spectrum of the "Aux Datain" signal 31 from encroaching into the spectral bandwidth of the normally transmitted data signal 10. Furthermore, the encoder 30 also provides a means for controlling the maximum allowable phase deviation.
A further alternative embodiment of the data insertion multiplexer element (MUX) 91 employed by the communications system 24 is presented in Figure 13. The MUX 91 is particularly suited for employment within an integrated PLL communication system 24.
The function of the Latch 36 is as previously described above. However in this embodiment the phase modulated clock "PMClock" 39 is generated within a modified PLL 92 as is now described. A reference input clock, "Clock" 93, to a Phase Detector 94, is derived from a clock source 95 that is in the form of a separate PLL or a Clock Data Recovery (CDR) circuit located within the system. "Clock" 93 acts so as to guarantee that the "PMClock" 39 signal is frequency locked to the input data "Datain" 9. The phase of "Clock" 93 is compared against "ClockFB" 96 within the Phase Detector 94, "ClockFB" 96 being produced from a feed back from the Latch 36 to the Phase Detector 94 via a Divider 97.
As a result the phase detector 94 produces a phase error signal "PEl" 98 onto which the additional input data "Aux Datain" 31 is added within a summation network 99. A combined Phase Error signal "PE2" 100 is then filtered by a suitably low bandwidth Loop Filter 101 that produces a filtered phase error signal "PE3" 102. The bandwidth of the Loop Filter 101 is specifically chosen so as to reject system noise but pass the phase data information, nominally set at Fd/1000.
The Encoder 38 provides a "DC" balanced signal using a suitable coding scheme between the input data "Datain" 9 and the "Aux Datin" 31. In addition the Encoder 38 suitably limits the maximum rate of change of the phase step so as to prevent the data spectrum of the "Aux Datin" 31 encroaching into the normally transmitted data bandwidth of the "Datain" 9. Furthermore the Encoder 38 also provides a control for the maximum allowable phase deviation of the "Aux Datin" 31 signal.
The filtered phase error signal "PE3" 102 is employed to control the oscillation frequency and phase of the voltage controlled oscillator (VCO) 72. The output from the VCO 72 thus provides the "PMClock" 39 signal that is applied both to the Latch 36 and also as the feedback to the Divider 97.
In an alternative embodiment of the MUX 91 (not shown) the "PMClock" 39 signal is employed as the clock signal for the Phase Detector 67. This embodiment is employed when the "Clock" 93 is only a sub-multiple of the desired latching "PMClock" 39 signal.
In an alternative embodiment of the MUX 91 (not shown) the VCO 72 is implemented in another oscillating or phase distorting device that has a controllable frequency/phase such as a current, a charge controlled oscillator or an interpolation circuit.
A further alternative embodiment of the MUX 91 (not shown) employs a Loop Filter that is split into two distinct sections. One filter section comprises an analogue filter constructed by using a passive resistor and capacitor components with a charge pump adding or subtracting current. The function of this first filter section is to process the phase error signal "PEl" 98 with a filter bandwidth « Fd/1000. A second filter is then employed to process the "Aux Datin" 31 signal with bandwidth > Fd/10000 and < Fd/1000. This filtered signal is then input directly to the VCO 72 using a digitally controlled loop filter to add and subtract charge to the loop. In this embodiment the summation network 99 is located after the two section Loop Filter.
In a yet further alternative embodiment of the MUX 91 (not shown) the input "Clock" 93 is replaced with the received input data "Datain" 9 or a derivative of the phase error signal "PEl" 98 transformed into a Clock-Data Recovery Loop. In this embodiment the frequency of the "PMClock" 39 used to latch the data is directly frequency locked to the received data and phase modulated inside the PLL/CDR function.
Further alternative embodiments that will be apparent to those skilled in the art include extending the described system to comprise more than one channel, two-way channels or multi-channel systems with additional input data "Aux Dataln" 31 fields being exchanged between these channels.
The described method may also be readily incorporated within a number of transmission media including, but not limited to, over air, optical fibre, printed circuit board or cable. Similarly different types of transmission signal formats may be employed including, but not limited to serial, parallel, analogue, digital, modulated, un-modulated, return to zero coding, non return to zero coding, encoded data, non encoded data, multi-level, binary, continuous or discontinuous, framed, burst or packet based or any combination of these.
Different types of transmission techniques may also be employed including, but not limited to, electrical, electro-magnetic, magnetic or optical means. The described method relates to a communication system where only one transmitter and one receiver is used with one media channel. However, in alternative embodiments, transmission can be made from more than one transmitter sharing one or more media channels to one or more receivers. Furthermore the transmitter and the receiver are described as being two separate elements or components of the system. However, in alternative embodiments, the transmitter and the receiver can be joined or part joined within the same combined element or component of the system, as relevant to multi-channel bi- directional applications. In yet further alternative embodiments the transmitter and/or the receiver can comprise a different combination of separate elements in a combination with less or additional elements so as could be viewed to act as a transmitter and or receiver, respectfully.
Further alternative embodiments to the communication system include the system comprising: • additional filters, transducers, amplifiers, sensors or other elements or components between the transmitter and receiver; • separate sections of media, separated by filters, transducers, sensors, transponders, transceivers, transmitters, receivers or other elements so as the break the media into one or more sections of not necessarily the same type of media; and
Alternative coding schemes and data structures can also be readily incorporated within the additional input data "Aux Dataln" fields 31. In particular the CNT data can contain a unique physical port address identifying that physical device on the link layer. This can be used, for example, in links where a device is employed as a physical layer repeater. Each device can then be pre- assigned or dynamically assigned the unique identifier as appropriate.
In a further embodiment of the above method it may be desirable not to extract the additional output data "Aux DataOut" 32 fields at the DEMUX but instead to employ this element to pass on or alternatively add additional data. This would be the case, for example, where the device is employed as a physical link layer repeater. This would allow for physical link information to permeate through the system to the channel final receiver. In this way the final receiver can gather all the additional input data "Aux Dataln" 31 fields on the link whilst each repeater in the link can also receiving its necessary physical link data. Such features can be added by having a suitable pass/block flag set in the control character CNT of the additional data field.
In a bi-directional or multi-directional communications system embodiment link status flags can also be included within the control character field CNT 86, or elsewhere within the additional input data "Aux Datain" 31. These flags are then employed to arrange a handshaking protocol for establishing link-up status between all sets of transmitters and receivers before any data is transferred. The flags can also be employed to provide acknowledgement of successful data transfer in conjunction with a suitable error detection scheme in the data, such as cyclical redundancy checking (CRC) .
The above method provides a means for improving the efficiency of a communications systems by exploiting existing relevant standards to transmit a quantity of additional data by encoding it as an additional low frequency phase modulation on an existing data information signal. Such additional data can be used for any purpose as desired, but in the described embodiment the additional data is required specifically for the physical link. The information can include transmitter and receiver physical parametrics and such information is then employed in addition to any existing data provision within any known standard.
The additional information is conveniently multiplexed within the physical link layer whilst being transparent to the normally transmitted data signals. Employing this method puts no extra bandwidth requirement on the communications system. A significant benefit of multiplexing this data at the physical link layer itself is that it allows data to be added, extracted and stripped within the physical layer device at the point where the information is both available and required. This is architecturally efficient and leads to a performance, cost and size superior solution when compared to other conceivable alternatives.
The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

Claims
1) A method of communicating information within the physical link layer of a communication system the method comprising the steps of: 1) Employing a physical link layer transmitter to modulate the phase of a data signal to be transmitted within the communication system so as to incorporate an auxiliary data signal with the data signal; and 2) Employing a physical link layer receiver to extract the auxiliary data following transmission of the data signal within a transmission medium of the physical link layer.
2) A method of communicating information as claimed in Claim 1 wherein the auxiliary data is extracted without corruption of the data signal.
3) A method of communicating information as claimed in Claim 1 or Claim 2 wherein the phase of the data signal is modulated at a frequency lower than a transmission frequency of the data signal.
4) A method of communicating information as claimed in any of the preceding claims wherein the step of modulating the phase of the data signal comprises latching the data signal with a phase modulated clock signal.
5) A method of communicating information as claimed in any of the preceding claims wherein the step of extracting the auxiliary data comprises the steps of : 1) Resolving the data signal into frequency components; 2) Extracting the frequency component of the data signal corresponding to the auxiliary data.
6) A method of communicating information as claimed in any of the preceding claims wherein the step of incorporate an auxiliary data signal further comprises incorporating a coded data scheme within the auxiliary data signal comprises .
7) A method of communicating information as claimed in Claim 6 wherein the coded data scheme comprises one or more start of multiplexing characters that provide a means for activating a de-multiplexer within the receiver.
8) A method of communicating information as claimed in Claim 6 or Claim 7 wherein the coded data scheme further comprise one or more control characters that provide a means for carrying out one or more of the functions contained within a group of functions comprising port identification, handshaking and data identification.
9) A transmitter for transmitting a data signal within a physical link layer of a communication system wherein the transmitter comprises a data insertion multiplexer that provides a means for phase modulating the data signal to be transmitted within the communication system so as to incorporate an auxiliary data signal with the data signal. 10 ) A transmitter as claimed in Claim 9 wherein the data insertion multiplexer comprises a latch, to which the data signal provides an input, and a phase modulated signal generator that provides a phase modulated signal for use as a clock signal for the latch.
11) A transmitter as claimed in Claim 10 wherein the phase modulated signal generator comprises an analogue phase modulator that provides a means for producing the phase modulated signal from a reference clock input signal.
12) A transmitter as claimed in Claim 11 wherein the phase modulated signal generator further comprises an analogue phase splitter that provides a means for splitting the reference clock signal into two or more synchronous input signals to be controllably combined by the analogue phase modulator so as to produce the phase modulated signal.
13) A transmitter as claimed in Claim 12 wherein the phase modulated signal generator further comprises an encoder that provides a means for controllably selecting the proportional amounts of the two or more synchronous input signals to be combined within the analogue phase modulator.
14) A transmitter as claimed in Claim 13 wherein the phase modulated signal generator further comprises a data filter located between the encoder and the analogue phase modulator that functions as a low pass filter so limiting the rate of change of phase introduced to the phase modulated signal . 1 15) A transmitter as claimed in Claim 10 wherein the
2 phase modulated signal generator comprises a
3 digitally controllable phase adjuster that provides
4 a means for producing the phase modulated signal
5 from a reference clock input signal. 6
7 16) A transmitter as claimed in Claim 10 wherein the
8 phase modulated signal generator comprises a phase
9 locked loop that provides a means for producing the 10 phase modulated signal from a reference clock input Ll signal.
12
13 17) A transmitter as claimed in Claim 16 wherein the
14 phase locked loop further comprises a low band pass
15 filter that provides a means for removing the
16 effects of noise from the phase modulated signal. 17
18 18) A transmitter as claimed in Claim 16 or Claim 17
19 wherein the phase locked loop further comprises a ZO voltage controlled oscillator that is driven by an Zl output from a summation network so as to produce the Z2 phase modulated output.
Z3 .
Z4 19) A transmitter as claimed in any of Claims 16 to
Z5 Claim 18 wherein the phase modulated output is
16 further employed as a feedback signal for the phase
Z7 locked loop.
Z8
Z9 20) A receiver for receiving a data signal transmitted
30 within the physical' link layer of a communications
31 system wherein the receiver comprises a data
32 • extraction de-multiplexer that provides a means for
33 detecting and extracting a phase modulated auxiliary data signal incorporated within the transmitted data signal .
21) A receiver as claimed in Claim 20 wherein the data extraction de-multiplexer comprises a frequency resolving apparatus, which provides a means for resolving the data signal into frequency components, and a signal extractor that provides a means for extracting the frequency component of the data ' signal corresponding to the auxiliary data.
22) A receiver as claimed in Claim 21 wherein the frequency resolving apparatus comprises a clocked phase detector.
23) A receiver as claimed in Claim 21 or Claim 22 wherein the signal extractor comprises a low bandpass frequency filter.
24) A receiver as claimed in any of Claims 21 to 23 wherein the signal extractor comprises a decoder.
25) A receiver as claimed in Claim 23 or Claim 24 wherein the clock signal for the clocked phase detector is produced by passing an output from the low bandpass filter through a voltage controlled. oscillator.
26) A communication system comprising one or more transmitters, one or more transmission media and one or more receivers wherein at least one of the one or more transmitters comprise a transmitter as claimed . in any of Claims 9 to Claim 19. 27) A communication system as claimed in Claim 26 wherein at least one of the one or more receivers comprise a receiver as claimed in any of Claims 20 to 25.
PCT/GB2005/003086 2004-08-07 2005-08-05 Method and apparatus for data communication within a physical link layer of a communications system WO2006016129A1 (en)

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GB0417615.2 2004-08-07

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4088831A (en) * 1975-07-03 1978-05-09 International Standard Electric Corporation Synchronization for PCM transmission systems
US6295272B1 (en) * 1998-04-20 2001-09-25 Gadzoox Networks, Inc. Subchannel modulation scheme for carrying management and control data outside the regular data channel
US20020114048A1 (en) * 2000-08-12 2002-08-22 Brown Matthew D. Apparatus and method for attaching a data sub-channel to a digital payload

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4088831A (en) * 1975-07-03 1978-05-09 International Standard Electric Corporation Synchronization for PCM transmission systems
US6295272B1 (en) * 1998-04-20 2001-09-25 Gadzoox Networks, Inc. Subchannel modulation scheme for carrying management and control data outside the regular data channel
US20020114048A1 (en) * 2000-08-12 2002-08-22 Brown Matthew D. Apparatus and method for attaching a data sub-channel to a digital payload

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
KAZUTAKA NOGAMI ET AL: "PHASE MODULATION I/O INTERFACE CIRCUIT", IEEE INTERNATIONAL SOLID STATE CIRCUITS CONFERENCE, IEEE SERVICE CENTER, NEW YORK, NY, US, vol. 37, 1 February 1994 (1994-02-01), pages 108 - 109,318, XP000507077, ISSN: 0193-6530 *

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