WO2019076340A1

WO2019076340A1 - Frame headers for multi-level modulated signals in passive optical networks

Info

Publication number: WO2019076340A1
Application number: PCT/CN2018/110843
Authority: WO
Inventors: Junwen ZHANG; Jun Shan Wey; Weiliang Zhang; Dan GENG
Original assignee: Zte Corporation
Priority date: 2017-10-18
Filing date: 2018-10-18
Publication date: 2019-04-25

Abstract

An optical communication method includes optical data communications using different modulation schemes in different frames communicated from one optical device to another. The modulation scheme used for a frame may be indicated by information included in a header to the frame. A transmitting optical device may add the modulation information to the header and the receiving optical device may determine which demodulation to use based on the information included in the header associated with a frame. Different frames may be modulated according to different modulation schemes.

Description

FRAME HEADERS FOR MULTI-LEVEL MODULATED SIGNALS IN PASSIVE OPTICAL NETWORKS

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document claims the benefit of priority under 35 U.S.C. §119 (a) and the Paris Convention of International Patent Application No. PCT/CN2017/106721, filed on October 18, 2017. The entire content of the before-mentioned patent application is incorporated by reference as part of the disclosure of this document.

TECHNICAL FIELD

This patent document relates to digital communication, and, in one aspect, optical communication systems that use multi-level modulated signals.

BACKGROUND

There is an ever-growing demand for data communication in application areas such as wireless communication, fiber optic communication and so on. The demand on core and access networks are all growing higher because not only are user devices such as smartphones and computers using more and more bandwidth due to multimedia applications, but also the total number of devices for which data is carried over the whole network is increasing. For profitability and to meet increasing demand, equipment manufacturers and network operators are continually looking for ways in which operational and capital expenditure can be reduced.

SUMMARY

The present document discloses techniques for transmission and reception of optical data formatted as optical frames or data frames. In some embodiments, an optical line terminal (OLT) may transmit data frames that include frame headers and payload data for reception by an optical network unit (ONU) . The data frame headers may indicate a modulation scheme used for modulating the payload data. A transmitting optical device may add the modulation information to the header and the receiving optical device may determine which demodulation to use based on the information included in the header associated with a received data frame.

In one example aspect, a method of digital data transmission by an optical device is disclosed. The method may include generating, by the optical device, at least a first optical frame and a second optical frame, and/or transmitting a first header for the first optical frame. The first header may include a first indication of a first modulation applied to the first optical frame. The method may further include transmitting a second header for the second optical frame. The second header may include a second indication of a second modulation applied to the second optical frame. The second modulation may be a different modulation from the first modulation.

In another example aspect, a method of digital data reception by an optical device is disclosed. The method may include receiving, by the optical device, a first optical frame, wherein the first optical frame includes a first header and a first payload. The method may further include determining, from the first header, a first modulation applied to the first payload, demodulating the first optical frame according to the first modulation, and/or receiving a second optical frame. The second optical frame may include a second header and a second payload. The method may further include determining, from the second header, a second modulation applied to the second payload, and/or demodulating the second optical frame according to the second modulation different from the first modulation.

In another example aspect, an apparatus for optical digital communications is disclosed. The apparatus may include a receiver to receive digital data from a data source. The apparatus may further include a formatter to format the received digital data into a frame. The frame may include a frame header and payload data corresponding to the received digital data. The formatter may generate the frame header to include an indication of a modulation format for the payload data. The apparatus may further include a modulator to modulate a signal according to the received digital data and the modulation format. The apparatus may further include a transmitter to transmit the modulated signal.

In another example aspect, another apparatus for optical digital communications is disclosed. The apparatus may include a receiver to receive a modulated signal from a transmitter, wherein the modulated signal includes a frame header and a payload. The apparatus may further include a demodulator to demodulate the frame header, wherein the frame header includes an indication of a modulation format used to modulate the payload. The apparatus may include a payload demodulator to demodulate the payload according to the modulation format determined from the frame header. The apparatus may further include a formatter to format the demodulated payload for output to a data sink.

These, and other, aspects are disclosed in the present document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of an optical network, in accordance with some example embodiments.

FIG. 2 depicts an example of a data frame structure, in accordance with some example embodiments.

FIG. 3 depicts another example of a data frame structure, in accordance with some example embodiments.

FIG. 4 depicts another example of a data frame structure, in accordance with some example embodiments.

FIG. 5 depicts another example of a data frame structure, in accordance with some example embodiments.

FIG. 6 depicts an example of a process, in accordance with some example embodiments.

FIG. 7 depicts another example of a process, in accordance with some example embodiments.

FIG. 8 depicts an example of adding a delimiter field to an optical networking standard, in accordance with some example embodiments.

FIG. 9 depicts another example of adding a delimiter field to an optical networking standard, in accordance with some example embodiments.

FIG. 10 depicts another example of adding a delimiter field to an optical networking standard, in accordance with some example embodiments.

FIG. 11 depicts another example of adding a delimiter field to an optical networking standard, in accordance with some example embodiments.

FIG. 12 depicts an example of an apparatus, in accordance with some example embodiments.

DETAILED DESCRIPTION

Cloud networking, 5G mobile fronthaul, and high bandwidth video applications are driving the demand for increased capacity in access networks including optical networks. Capacity can be increased by moving to higher order modulations such as multi-level modulations which may provide increased spectral efficiency (SE) . There is a need for passive optical networks (PONs) with spectrally efficient, multi-level modulation formats to support increased data capacity. Conventional data transmission systems do not provide efficient transmission and reception of signals with varying modulation formats. Additionally, some transmission and reception processes benefit from low-latency link communications while other transmission and reception communications benefit from high reliability and accuracy.

In some example embodiments disclosed in the present document, a frame of data includes a frame header and payload data. The frame header includes an indication of the modulation scheme used for modulating the payload data. The techniques disclosed herein may be implemented by optical transmitters that operate in PONs. Examples of PONs used to describe the embodiments include PONs that use multi-level modulations such as pulse-amplitude modulation (PAM) for payload data.

Example PONs may support multi-level modulation for payload data in some frames and non-return to zero/on-off keying (NRZ/OOK) modulation for payload data in other frames. Payload data of multi-level modulation or NRZ/OOK may coexist with frame headers modulated using NRZ/OOK. For example, some frames of data may be generated using NRZ/OOK, and other frames of data may be generated using multi-level modulation. Data frames may include frame headers. The frame header includes information indicating the modulation used in the associated payload data. From the frame header, a receiver determines the modulation used in the payload data for applying the correct demodulation scheme to the modulated payload data. This patent document discloses frame headers as well as indicator bit patterns used to indicate the modulation of frame payload data.

As further described throughout the present document, the optical communication used in various embodiments may use modulations that carry more than one bit per symbol. Increasing the number of bits per symbol may increase the data throughput of the optical network at each node using a multi-bit per symbol modulation. As a baseline, on-off keying (OOK) may produce one bit per symbol. An example of a multi-bit per symbol modulation includes pulse amplitude modulation such as PAM4 which has four levels (PAM4) and thus carries two bits per symbol. Higher order modulations may be used as well such as PAM8 (3 bits per symbol) , PAM16, (four bits per symbol) , PAM64 (eight bits per symbol) , and so on. Other types of modulation may be used for multi-bit per symbol modulation as well such as pulse position modulation, phase shift keying (e.g., BPSK, QPSK, 8PSK, etc. ) , or any other digital modulation. The disclosed techniques using frame headers and indicator bits can be implemented in optical transceivers that include an optical transmission/reception circuit operating using different modulations in different frames.

In some implementations, channel equalization may reduce the effects of imperfections (e.g., optical distortions) caused by the communications channel. Channel equalization may mitigate intersymbol interference, which may be caused by non-linear optical and/or electrical drive components. Equalization may cause data latency due to training of the equalizer and/or processing by the equalizer. Training an equalizer may include training symbols that are a known series of symbols for the equalizer to determine the effects of the channel and other imperfections. From the transmitted training sequence passed through the imperfect channel and components, the equalizer determines how to undo the imperfections caused and accordingly how to correct later sent data. In some example embodiments, equalization is performed using digital signal processing.

In a PON system, some processes such as the registration of optical network units (ONUs) , may benefit from low-latency link communications. Other communications such as control/management may benefit from high reliability and accuracy. In some example implementations, registration and/or control/management information may use NRZ-OOK to reduce latency and/or increase reliability. In some example implementations, a frame header is modulated using a predetermined modulation such as NRZ/OOK or other modulation. The receiver can demodulate the frame header and determine from the header which demodulation to use on the modulated payload data.

PONs may send/receive mixed modulation formats such as NRZ/OOK, duobinary, PAM-N, QAM, and so on, and/or mixed data rates using the same OLT and/or ONU. For example, an ONU or OLT may receive data frames with different modulations. The ONU or OLT may demodulate these data frames with different modulations according to the modulation information from the corresponding frame headers. A frame may have a frame header modulated using a different modulation than the corresponding payload data. For example, a frame header may be modulated according to NRZ/OOK and the payload may be modulated according to a multi-level modulation. In some example implementations, different ONUs and OLTs may have different modulation/demodulation capability. For example, one ONU or OLT may be capable of modulating and demodulating PAM4, while another ONU or OLT may be only capable of modulating and demodulating NRZ/OOK. In at least one implementation, higher throughput ONUs providing higher level modulation formats may coexist with ONUs that operate using lower order modulation formats such as NRZ/OOK. In PONs capable of operating using higher order modulations, some processes such as ONU registration may still be performed using lower order modulation such as NRZ/OOK.

The same ONU may be able to detect different modulation formats in the downstream signals, and the OLT may be able to detect different modulation formats in the upstream signals. In some example embodiments, frame structures are disclosed that are compatible with existing frame structures defined by standards organizations, such as the Institute for Electrical and Electronic Engineers (IEEE) and the International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T) .

Frame headers are disclosed to distinguish the modulation format in each frame. Some example embodiments use existing frame structures and include different delimiter codes in the synchronization preamble of frames to indicate the different modulation formats. Other example embodiments keep a basic frame structure but modify a frame header by adding an indicator pattern to indicate the different modulation formats. Other example embodiments, keep the basic frame structure while adding some forward error correction (FEC) protected bits after frame header to indicate the different modulation formats. In at least one embodiment, the modulation format comprises an N-level pulse amplitude modulation scheme, where N is an integer.

The PON can use time-division-multiplexing or wavelength-division-multiplexing depending on the splitter type. An OLT communicates with ONUs by transmitting downstream signals to the ONUs, and the OLT receives upstream signals from the ONUs. ONUs may transmit data during the assigned time slot (grant) managed by dynamic bandwidth allocation (DBA) of OLT. The different signal frames of downstream signals may contain different modulation formats, and the different signal frames of upstream signals may contain different modulation formats. An ONU may detect and demodulate different modulation formats in the downstream signals, and the OLT may detect and demodulate different modulation formats in the upstream signals.

FIG. 1 depicts an optical network, in accordance with some example embodiments. Optical network 100 includes optical line terminal (OLT) 110 connected to wavelength or power splitter/combiner 116 (referred to herein as a splitter 116) via fiber 112. Optical network units (ONUs) 130A-130C are connected to splitter 116 via fibers 132A-132C. Although FIG. 1 depicts splitter 116 multiplexing fiber 112 to three fibers 132A-132C, splitter 116 may multiplex fiber 112 to any other number of fibers such as eight, or 16, or 256, and so on. FIG. 1 depicts a system in which one or more of the ONUs 130A-130C and/or OLT 110 may operate using a frame header that includes information indicating the modulation format used on the payload data as described in FIGs. 2-11.

OLT 110 may be located at a central location such as a central office of a network service provider. OLT 110 may include a plurality of optical transmitters and a plurality of optical receivers. The different optical transmitters and receivers may operate at different wavelengths, or multiple transmitters and receivers may operate at the same wavelength.

OLT 110 may include multiple transmitters. For example, OLT 110 may include optical transmitters to communicate with each ONU 130A-130C. Each transmitter may operate using a different wavelength. The different wavelengths may be carried by fiber 112 and demultiplexed by splitter 116 to multiple fibers such as fibers 132A-132C. In some example embodiments, one transmitter may generate a signal at a particular wavelength or may generate multiple wavelengths. In some implementations, a WDM may be included in OLT 110 to combine signals at different wavelengths onto fiber 112 which may be demultiplexed by wavelength by splitter 116. In another example, 256 OLT transmit signals may be demultiplexed by 116 from fiber 112 to 256 fibers connected to 256 ONUs. A wavelength division multiplexer may be the same device as a wavelength division demultiplexer. In another example, the optical transmitters may operate using one wavelength and the optical signals from the OLT 110 may be split by an optical power splitter 116. For example, 256 OLT transmit signals may be carried by fiber 112 and the power from fiber 112 may be split into 256 portions, one for each ONU. In another example, OLT may transmit signals for ONUs 130A-130C that may be carried from OLT 110 by fiber 112 and the power from fiber 112 may be split at 116 into portions and provided via fibers 132A-132C for each of ONUs 130A-130C.

OLT 110 may further include multiple receivers. For example, OLT 110 may include optical receivers to communicate with each ONU 130A-130C. Each receiver may operate using a different wavelength. The different wavelengths may be carried by multiple fibers such as fibers 132A-132C and multiplexed by splitter/combiner 116 onto fiber 112. In another example, 256 OLT receive signals carried by 256 fibers from 256 ONUs may be multiplexed by 116 onto fiber 112. At OLT 110, each optical signal (wavelength) may be coupled to a different optical detector or multiple wavelengths may be coupled to one detector. In another example, the optical receivers may operate using one wavelength, and the optical signals from the multiple ONUs to the OLT 110 may be combined by an optical power combiner/splitter 116. For example, 256 OLT receive signals from 256 ONUs may be carried by 256 fibers to combiner 116 and combined onto fiber 112 to OLT 110. In another example, OLT receive signals from ONUs 130A-130C may be carried from ONUs 130A-130C by fibers 132A-132C to power combiner 116, and the combined signal provided to OLT 110 via fiber 112.

Signals passed from the OLT to an ONU may be referred to as a downstream signal, and signals passed from an ONU to the OLT may be referred to as an upstream signal. Power splitters may support time division multiple access (TDMA) where multiple links use the same fiber and signal transmissions are separated by time. Wavelength Division Multiplexers (WDMs) support wavelength division multiple access (WDMA) where multiple links may use the same fiber and signals are separated by wavelength. Fiber 112 may pass signals from a plurality of transmitters and/or receivers in OLT 110. Splitter 116 may break-out the various wavelengths into separate fibers 132A-132C connected to each optical network unit such as 130A-130C. Although FIG. 1 depicts one OLT, one splitter 116, and three ONUs 130A-130C, optical network 100 may include more than on OLT, more than one splitter, and any number of connected ONUs.

Depending on the locations of the optical network units, optical network 100 may include fibers of substantial length. As an illustrative example, OLT 110 may be located at a central office. Fiber 112 may be 3 km long and connect OLT 110 to splitter 116. Splitter 116 may break-out the signals at various wavelengths into separate signals carried by separate fibers. For example, fiber 132A may connect splitter 116 to optical network unit 130A located 10 km from splitter 116 and carry signals to be received at optical network unit 130A at a first wavelength, and carry signals transmitted from optical network unit 130A on a second wavelength. Fiber 132B may connect splitter 116 to optical network unit 130B located 8 km from splitter 116 and carry signals to be received at optical network unit 130B at a third wavelength, and carry signals transmitted from optical network unit 130B on a fourth wavelength. Fiber 132C may connect splitter 116 to optical network unit 130C located 20 km from splitter 116 and carry signals to be received at optical network unit 130C at a fifth wavelength, and carry signals transmitted from optical network unit 130C on a sixth wavelength. Additional optical network units may be connected via additional fibers to splitter 116. The foregoing example indicated example distances and three optical network units, any other distances and/or number of optical network units may be used as well.

Each ONU may be connected to one or more fibers. For example, ONU 130A may be connected to fiber 132A. An optical network unit (ONU) may include an optical transmitter and an optical receiver. The optical transmitter may include an optical source that may be modulated to include data. In some example implementations, the optical source may be coupled to a semiconductor optical amplifier (SOA) . The power output from the optical source may be adjusted via a bias voltage and the SOA may further adjust the optical power via gain in the SOA coupled to a fiber.

In some example implementations, channel equalization may be used to reduce the effects of imperfections (e.g., optical distortions) caused by the communications channel and other effects. Equalization is used to “undo” the effects of the channel and imperfect components. Equalization may be performed on the transmissions received from ONUs 130A-130C. The same equalizer may be used for more than one of the transmissions from ONUs 130A-130C, or a different equalizer may be used for the signal from each of the ONUs 130A-130C. For example, transmissions from ONU 130A may pass through a first equalizer at OLT 110 to correct the distortions in transmissions from ONU 130A due to the components in OLT 110, fiber 112, splitter 116, fiber 132A, and the transmitter at ONU 130A. OLT 110 may include another equalizer for transmissions from ONU 130B. The receiver at each ONU may include equalizers to “undo” the distortions and other imperfections between each corresponding ONU and the OLT.

In some implementations, a linear equalizer may be used to process an incoming signal with a linear filter. In some implementations, a minimum mean squared error (MMSE) equalizer may be used to minimize the mean squared error when estimating the received signal. In some implementations, a zero-forcing equalizer may be used to approximate the inverse of the channel with a linear filter. In some implementations, a decision feedback equalizer may be used that adds a filtered version of previous symbol estimates to a linear equalizer. In some implementations, an adaptive equalizer may be used. Any of the forgoing types of equalizers, or any other equalizer, may be used for any of the downstream and upstream equalizers.

The equalizer may be implemented in a digital signal processor as executable code or in a field-programmable gate array (FPGA) , application-specific integrated circuit (ASIC) or other hardware. Equalization may require training of the equalizer. Training may include a series of symbols sent by a transmitter that are known in advance by the receiver. The equalizer may be trained based on the known symbols that are transmitted and the symbols that are received which may be distorted/imperfect due to the channel and component imperfections. Training may include determining filter weights, time delays, and/or coefficients, or other parameters. Equalizer training takes time to perform. The equalizer may be periodically trained due to component aging or component changes or the replacement of components. For example, an equalizer may be trained once per day, or at any other interval.

Instead of, or in addition to, equalization at a receiver, pre-distortion may be used at the transmitter. For example, the training process may determine distortions and/or non-linearities that may be compensated for by pre-distorting the transmitted signal such that the result of the pre-distortion followed by the distortion/imperfections in the channel/components is a signal without distortion or with reduced distortion. Pre-distortion at the transmitter may be combined with equalization at the receiver.

Higher order modulations may rely on a lower distortion channel and/or more linear components more heavily than a lower order modulation. For example, four-level pulse amplitude modulation (PAM4) may rely on a lower distortion/nonlinearity channel and components than on-off keying (OOK) .

For some types of messages where low latency and higher robustness is preferred, a lower order modulation such as OOK may be used. For example, the registration or discovery of ONUs, frame header, and communications performed before training is completed, may use lower order modulation such as NRZ-OOK. Registration of one or more ONUs with the OLT may be performed before payload data is sent. Registration of an ONU with an OLT is referred to as auto-discovery in some Institute for Electrical and Electronic Engineers (IEEE) Ethernet Passive Optical Network (E-PON) standards. Asused herein, registration and auto-discovery are synonymous.

In some example embodiments, after ONU registration, the OLT may switch to a higher throughput mode with a higher order modulation such as a multi-level modulation format for payload data. In some example embodiments, use of the higher order modulation may include two steps. For example, the OLT may send a downstream training frame including multi-level modulated signals to the a registered ONU. A newly registered ONU may also send an upstream training frame to the OLT. After training the equalizers at the ONU and/or OLT, the system may switch to a higher throughput mode using multi-level modulation format for payload data.

A transmitter may include a receiver to receive digital data from a data source. For example, the receiver may receive data packets via a wired interface such as Ethernet. The transmitter may include a formatter to format the received digital data into a frame for optical transmission. The frame may include a frame header and payload data corresponding to the received digital data. The formatter may generate the frame header to include an indication of a modulation format for the payload data. The transmitter may further include a modulator to modulate a signal according to the data and the modulation format. The apparatus may further include a transmitter to transmit the modulated signal.

A receiver may receive a modulated signal from a transmitter. The modulated signal may include a frame header and a payload. The receiver may include a demodulator to demodulate the frame header, wherein the frame header includes an indication of a modulation format used to modulate the payload. The receiver may include a payload demodulator to demodulate the payload according to the modulation format determined from the frame header. The receiver may include a formatter to format the demodulated payload for output to a data sink. For example, the formatter may arrange demodulated bits into packets for transmission via an interface such as Ethernet to a data sink.

FIG. 2 depicts an example of a data frame structure 200, in accordance with some example embodiments. Frame 210 includes frame header 220 and frame payload data 230. Frame 210 may be preceded by earlier frames and followed by subsequent frames. The precedent frames, the subsequent frames, and frame 210 may include payload data modulated using different modulations. Each frame may have a frame header that includes information about the modulation used on the payload data associated with the header. The frame header may be modulated according to a predetermined modulation to enable determination of the modulation format as well as for other purposes.

Frame 210 is a frame structure including frame header 220 followed by the frame payload data 230. Frame header 220 may be used for frame synchronization and may include a sync pattern 222 and/or a delimiter pattern 226.

The sync pattern 222 may provide for receiver clock recovery and receiver power level settling. The sync pattern may or may not be included in every frame in the downstream direction. For example, the sync pattern may be sent periodically but may not be needed every frame because synchronization may be maintained over multiple frames with one sync pattern.

The delimiter pattern 226 may provide a frame codeword or payload data synchronization. As noted above, different frames may include payload data that has been modulated according to different modulation formats. The frame header may include an indication of the modulation used to generate signals received as payload data Note: Different terminology may be used in different standards, such as IEEE or ITU-T. The foregoing terminology may be in accordance with that used in IEEE 10G-EPON standards.

FIG. 3 depicts another example of a data frame structure 300, in accordance with some example embodiments. Frame 310 includes frame header 320 and frame payload data 330. Frame 310 may be preceded by earlier frames and followed by subsequent frames including frame 350. Frame 350 includes additional frame header 360 and additional frame payload data 380. Each frame may have a frame header that includes information about the modulation used on the payload data associated with the header. For example, frame header 320 includes sync pattern 322 and/or a delimiter 326 and frame header 360 includes additional sync pattern 372 and/or additional delimiter 376. Delimiter 326 and delimiter 376 may include information or a code indicating the modulation used in frame payload data 330. Delimiter 326 and delimiter 376 may be included in a frame structure in an existing IEEE, ITU-T, or other standard. In some example standards, not all of the possible permutations of a field such as delimiter fields 326, 376 may be defined in the standard. Unused field permutations may be used to indicate payload modulation formats. For example, when N permutations (possible bit patterns) are unused by a standard, each of the N unused permutations may be used to indicate one modulation formats for payload data. For example, N unused permutations of delimiter 326 can be used to indicate one of N different modulations used on frame payload data 330.

As an illustrative example, when delimiter 326 has 8 bits, and thus can represent 64 different states, where 48 values are used to represent flags, states, or other information in a standard, and 16 are not defined in the standard, then the 16 undefined values may be used to indicate 16 different modulations. In this example, the number N, as shown in Table 390 depicted in FIG. 3, may be 16 and the 16 values not used in the standard are codes 1-16, where each code indicates one of modulation formats 1-16. The frame header 320 may be modulated according to a predetermined modulation to enable reading of the header. A receiver matches the delimiter code to the corresponding modulation format, and then demodulates the payload data according to the matched modulation format.

FIG. 4 depicts another example of a data frame structure 400, in accordance with some example embodiments. Frame 410 includes frame header 420 and frame payload data 430. Frame 410 may be preceded by earlier frames and followed by subsequent frames. Frame header 420 includes sync pattern 422, delimiter 426, and indicator pattern 450. Frame header 420 is similar to frame

headers

320 and 220 except in frame header 420, the information indicating the modulation used for payload data 430 is included in indicator bits 450 rather than in delimiter 426. As an example, for indicator pattern 450 to indicate one of 16 different modulation formats, indicator pattern 450 would include at least 4 bits.

FIG. 5 depicts another example of a data frame structure 500, in accordance with some example embodiments. Frame 510 includes frame header 520, frame payload data 530, and indicator bits 540. Frame header 520 is similar to frame

headers

220, 320, and 420 except in frame header 520 the information indicating the modulation used for payload data 430 is included in indicator bits 540 rather than in the frame header. For indicator bits 540 to indicate one of 8 different modulation formats, indicator bits 540 would include at least 3 bits.

FIG. 6 depicts an example of a process 600, in accordance with some example embodiments. At 610, a frame is detected. The frame is then separated into a payload and a preamble. The preamble includes the frame header and indicator bits if indicator bits are present outside the frame header (see, for example, FIG. 5) . The frame is separated into the payload and the preamble because determination of the modulation used in the payload takes processing time that extends beyond the duration of the preamble. In order to not lose payload data during the delay, the payload data may be stored in data buffer 620. The preamble is processed to determine the modulation format at 630 and 640. After the modulation format is determined, the data buffer is read into a read buffer at 650 and demodulated at 660 according to the identified modulation format.

FIG. 7 depicts another example of a process 700, in accordance with some example embodiments. At 710, a frame is detected. The frame is then separated into a payload and a preamble. The preamble includes the frame header and indicator bits if indicator bits are present outside the frame header (see, for example, FIG. 5) . The frame is separated because determination of the modulation used in the payload takes processing time that extends beyond the duration of the preamble. In order to not losepayload data during the delay, the payload data may be processed by multiple demodulators at the same time. For example, the payload data may be processed by

demodulators

735, 740, and 745 as well as others (not shown) in parallel. Each demodulator operates according to one of the possible demodulation formats. For example, demodulator 735 may be PAM 4 demodulation, demodulator 740, may be PAM 8 demodulation, and demodulator 745 may be QAM 16 demodulation. While the demodulators are operating on the payload data, the modulation format is identified at 730 from information in the header or indicator bits as described above. Based on the identified modulation format, the correct demodulator output is chosen as one of the outputs from

demodulators

735, 740, or 745.

FIG. 8 depicts an example of adding an indication of payload modulation format to an existing optical networking standard, in accordance with some example embodiments. In the example of FIG. 8, the frame structure includes a guard times 810 (T_on) and 850 (T_off) sync pattern 820, burst delimiter 830, and payload 840. FIG. 8 depicts adding payload modulation format information to an IEEE 10 Gigabit per second Ethernet Passive Optical Network (10G-EPON) standard. IEEE 10G-EPON includes a frame header with a 400 nanosecond sync pattern and a 66-bit burst delimiter in an upstream direction (ONU to OLT) . In accordance with the foregoing description, modulation format information may be added to the 10G-EPON standard using any of at least three alternative schemes. In a first scheme, delimiter codes not used in the standard (as described above) may be used to indicate a modulation format while keeping the size of delimiter codes at 66 bits. A second scheme includes adding, between the burst delimiter and the payload, a bit pattern to indicate the modulation format used. Because bits are added, the total length of the frame header is increased. A third scheme includes adding FEC protected bits to indicate the payload modulation format after the burst delimiter. The FEC protected bits may be modulated using NRZ/OOK.

FIG. 9 depicts another example of adding a delimiter field to an optical networking standard, in accordance with some example embodiments. FIG. 9 depicts adding payload modulation format information to an ITU-T Gigabit Passive Optical Network (G-PON) upstream or ITU-T 10-Gigabuit Passive Optical Network (XG-PON) upstream frame. In the example of FIG. 9, the frame structure includes physical synchronization block upstream (PSBu) 920, and payload 930. PSBu 920 includes preamble 922 and delimiter 926. The PSBu includes preamble 922 for receiver settling and clock recovery, and a burst delimiter 926 for frame codeword synchronization that is 32-64 bits in length. In accordance with the foregoing description, modulation format information may be added to the ITU-T GPON or XG-PON standard using any of at least three alternative schemes. In a first scheme, delimiter codes not used in the standard may be used to indicate a modulation format while keeping the size of delimiter codes at 32-64 bits. A second scheme includes adding, between the burst delimiter and the payload, a bit pattern to indicate the modulation format used. Because bits are added, the total length of PSBu is increased. A third scheme includes adding FEC protected bits after PSBu to indicate the payload modulation format after the burst delimiter. The FEC protected bits may be modulated using NRZ/OOK.

FIG. 10 depicts another example of adding a delimiter field to an optical networking standard, in accordance with some example embodiments. FIG. 10 depicts adding payload modulation format information to an ITU-T G-PON downstream or ITU-T XG-PON downstream frame. In the example of FIG. 10, the frame structure includes physical synchronization block downstream (PSBd) 1020, and payload 1030. PSBd 1020 includes physical synchronization sequence (PSync) 1022 and pattern 1026. PSync is a 64-bit pattern and has the same or similar function as the above-described delimiter. In accordance with the foregoing description, modulation format information may be added to the ITU-T GPON or XG-PON standard using any of at least three alternative schemes. In a first scheme, Psync codes not used in the standard may be used to indicate a modulation format while keeping the size of delimiter codes at 64 bits. A second scheme includes adding between the PSync and the payload an bit pattern to indicate the modulation format used. Because bits are added, the total length of PSBd is increased. A third scheme includes adding some FEC protected bits after PSBd to indicate the payload modulation format after the burst delimiter. The FEC protected bits may be modulated using NRZ/OOK.

FIG. 11 depicts another example of adding a delimiter field to an optical networking standard, in accordance with some example embodiments. FIG. 11 depicts adding payload modulation format information to an ITU-T G-PON downstream or ITU-T XG-PON downstream frame. In the example of FIG. 11, the frame structure may be referred to as a superframe that includes physical synchronization block downstream (PSBd) 1120, and payload 1130. The payload may include payload for multiple ONUs. To avoid multiple modulation formats in a superframe payload 1130, two schemes may be used. In a first scheme, the OLT may allocate the downstream data to a superframe from multiple ONUs based on the modulation format. Data with the same modulation format will be packaged in the same superframe payload 1130. Selecting frames and packaging into superframes will take some time thereby causing a delay. In a second scheme, the super-frame is divided to several sub-frames, and each sub-frame includes a separate modulation identification header such as a PSync pattern, indicator pattern, or FEC protected bits for modulation format identification as described above. The subframes may be packaged into a superframe.

FIG. 12 depicts an apparatus, in accordance with some example embodiments. The description of FIG. 7 also refers to FIGs. 1-11. Operations and management of the disclosed optical network unit such as ONUs 130A-130C and OLT 110 may include an apparatus such as 1200. In an optical network unit, apparatus 1200 may perform one or more of the processes described with respect to FIGs. 1-11. Apparatus 1200 may also perform other status and control functions and include interfaces to other devices. FIG. 12 at 1200 is a block diagram of a computing system, consistent with various embodiments such as the OLT and/or ONU described above.

The computing system 1200 may include one or more central processing units ( “processors” ) 1205, memory 1210, input/output devices 1225 (e.g., keyboard and pointing devices, display devices) , storage devices 1220 (e.g., disk drives) , and network adapters 1230 (e.g., network interfaces) that are connected to an interconnect 1215. Apparatus 1200 may further include optical devices 1240 including one or more of lasers, detectors, semiconductor amplifiers, and other optical and optoelectronic components. Optical devices 1240 may connect to an optical line terminal, optical network unit via one or more fibers 1245. The interconnect 1215 is illustrated as an abstraction that represents any one or more separate physical buses, point to point connections, or both connected by appropriate bridges, adapters, or controllers. The interconnect 1215, therefore, may include, for example, a system bus, a Peripheral Component Interconnect (PCI) bus or PCI-Express bus, a HyperTransport or industry standard architecture (ISA) bus, a small computer system interface (SCSI) bus, a universal serial bus (USB) , IIC (I2C) bus, or an IEEE standard 1394 bus, also called “Firewire. ”

The memory 1210 and storage devices 1220 are computer-readable storage media that may store instructions that implement at least portions of the described technology. In addition, the data structures and message structures may be stored or transmitted via a data transmission medium, such as a signal on a communications link. Various communications links may be used, such as the Internet, a local area network, a wide area network, or a point-to-point dial-up connection. Thus, computer-readable media can include computer-readable storage media (e.g., "non-transitory" media) and computer-readable transmission media.

The instructions stored in memory 1210 can be implemented as software and/or firmware to program the processor (s) 1205 to carry out actions described above. In some embodiments, such software or firmware may be initially provided to the processing system 1200 by downloading it from a remote system through the computing system 1200 (e.g., via network adapter 1230 or optical devices 1240) .

The various embodiments and techniques disclosed in the present document may be described using a clause-based format as follows.

1. A method of data transmission by an optical device, including: generating, by the optical device, at least a first optical frame and a second optical frame; transmitting, by the optical device, a first header for the first optical frame, wherein the first header includes a first indication of a first modulation applied to the first optical frame; and transmitting, by the optical device, a second header for the second optical frame, wherein the second header includes a second indication of a second modulation applied to the second optical frame, wherein the second modulation is a different modulation from the first modulation.

2. A method of data reception by an optical device, the method comprising: receiving, by the optical device, a first optical frame, wherein the first optical frame includes a first header and a first payload; determining, from the first header, a first modulation applied to the first payload; demodulating the first optical frame according to the first modulation; receiving, by the optical device a second optical frame, wherein the second optical frame includes a second header and a second payload; determining, from the second header, a second modulation applied to the second payload; and demodulating the second optical frame according to the second modulation different from the first modulation.

3. The method of any of clauses 1-2, wherein the first modulation comprises an N-level pulse amplitude modulation scheme, where N is an integer.

4. The method of any of clauses 1-3, wherein the second modulation comprises an on-off keying modulation scheme.

5. The method of any of clauses 1-4, wherein the optical device is an optical line terminal.

6. The method of any of clauses 1-4, wherein the optical device is an optical network unit.

7. The method of any of clauses 1-6, wherein the first optical frame and the second optical frame operate in accordance with a standard.

8. The method of clause 7, wherein the standard is an ITU-T Gigabit Passive Optical Network (G-PON) upstream or an ITU-T 10-Gigabuit Passive Optical Network (XG-PON) upstream frame.

9. The method of clause 7, wherein the standard is an IEEE E-PON.

10. The method of clause 7, wherein the first indication and the second indication are included in bit patterns in a delimiter field that are not defined in the standard.

11. The method of clause 7, wherein the first indication and the second indication are included in bit patterns in indicator bits that are not defined in the standard, wherein the indicator bits are forward error correction encoded.

12. An apparatus for optical digital communications, the apparatus comprising: a receiver to receive digital data from a data source; a formatter to format the received digital data into a frame, wherein the frame includes a frame header and payload data corresponding to the received digital data, and wherein the formatter generates the frame header to include an indication of a modulation format for the payload data; a modulator to modulate a signal according to the digital data and the modulation format; and a transmitter to transmit the modulated signal.

13. The apparatus for optical digital communications as in clause 12, wherein the receiver receives additional digital data, and wherein the formatter formats the additional digital data into an additional frame, the additional frame including an additional frame header indicating an additional modulation format, wherein the additional modulation format is different from the modulation format.

14. The apparatus for optical digital communications as in any of clause 12-13, wherein the modulation format comprises an N level pulse amplitude modulation scheme, where N is an integer.

15. The apparatus for optical digital communications as in any of clauses 12-14, wherein the frame header is modulated according to an on-off keying modulation scheme.

16. The apparatus for optical digital communications as in any of clauses 12-15, wherein the frame operates in accordance with a standard.

17. The apparatus for optical digital communications as in clause 16, wherein the standard is an ITU-T Gigabit Passive Optical Network (G-PON) upstream or an ITU-T 10-Gigabuit Passive Optical Network (XG-PON) upstream frame.

18. The apparatus for optical digital communications as in clause 16, wherein the standard is an IEEE E-PON.

19. The apparatus for optical digital communications as in clause 16, wherein the indication is included in a bit pattern in a delimiter field that is not defined in the standard.

20. The apparatus for optical digital communications as in clause 16, wherein the indication is included a bit pattern in indicator bits that are not defined in the standard, wherein the indicator bits are forward error correction encoded.

21. An apparatus for optical digital communications, the apparatus comprising: a receiver to receive a modulated signal from a transmitter, wherein the modulated signal includes a frame header and a payload; a demodulator to demodulate the frame header, wherein the frame header includes an indication of a modulation format used to modulate the payload; a payload demodulator to demodulate the payload according to the modulation format determined from the frame header; and a formatter to format the demodulated payload for output to a data sink.

22. The apparatus for optical digital communications as in clause 21, wherein the receiver receives an additional modulated signal including an additional frame header and an additional payload, wherein the demodulator demodulates the additional frame header to determine an additional modulation format for the additional payload, and wherein the payload demodulator demodulates the additional payload according to the additional modulation format that is different from the modulation format.

23. The apparatus for optical digital communications as in any of clauses 21-22, wherein the modulation format comprises an N level pulse amplitude modulation scheme, where N is an integer.

24. The apparatus for optical digital communications as in any of clauses 21-23, wherein the frame header is modulated according to an on-off keying modulation scheme.

25. The apparatus for optical digital communications as in any of clauses 21-24, wherein the frame header operates in accordance with a standard.

26. The apparatus for optical digital communications as in clause 25, wherein the standard is an ITU-T Gigabit Passive Optical Network (G-PON) upstream or an ITU-T 10-Gigabuit Passive Optical Network (XG-PON) upstream frame.

27. The apparatus for optical digital communications as in clause 25, wherein the standard is an IEEE E-PON.

28. The apparatus for optical digital communications as in clause 25, wherein the indication is included in a bit pattern in a delimiter field that is not defined in the standard.

29. The apparatus for optical digital communications as in clause 25, wherein the indication is included a bit pattern in indicator bits that are not defined in the standard, wherein the indicator bits are forward error correction encoded.

30. A method of data reception by an optical device, the method comprising: receiving a modulated signal from a transmitter, wherein the modulated signal includes a frame header, a payload, and an indication of a modulation format used to modulate the payload; demodulating the payload according to the modulation format determined from the frame header; and formatting the demodulated payload for output to a data sink.

31. The method of clause 30, wherein the frame header further includes a delimiter, and wherein the modulation format is determined from unused field permutations in the delimiter.

32. The method of any of clauses 30, wherein the modulation format is determined from indicator bits contained in the frame header.

33. The method of any of clauses 30-32, further comprising: separating the frame header and the payload of the modulated signal; storing the payload into a data buffer; determining the modulation format from the frame header; and reading the payload stored in the data buffer after determining the modulation format.

34. An optical communication apparatus comprising an optical transceiver and a processor, wherein the processor is configured to implement a method recited in clauses 1-11 or 30-33.

A computer readable medium having code stored thereon, wherein the code, when executed by a processor, causes the processor to implement a method recited in any of clauses 30-33.

The above description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in some instances, well-known details are not described in order to avoid obscuring the description. Further, various modifications may be made without deviating from the scope of the embodiments. Accordingly, the embodiments are not limited except as by the appended claims.

Reference in this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not for other embodiments.

The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. Terms that are used to describe the disclosure are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the disclosure. For convenience, some terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term is the same, in the same context, whether or not it is highlighted. It will be appreciated that the same thing can be said in more than one way. One will recognize that “memory” is one form of a “storage” and that the terms may on occasion be used interchangeably.

Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for some terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any term discussed herein is illustrative only, and is not intended to further limit the scope and meaning of the disclosure or of any exemplified term. Likewise, the disclosure is not limited to various embodiments given in this specification.

Without intent to further limit the scope of the disclosure, examples of instruments, apparatus, methods and their related results according to the embodiments of the present disclosure are given below. Note that titles or subtitles may be used in the examples for convenience of a reader, which in no way should limit the scope of the disclosure. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In the case of conflict, the present document, including definitions will control.

The disclosed and other embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document) , in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code) . A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit) .

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

Specific language and examples should not be construed as limitations on the scope of an invention that is claimed or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

Only a few examples and implementations are disclosed. Variations, modifications, and enhancements to the described examples and implementations and other implementations can be made based on what is disclosed.

Claims

A method of data transmission by an optical device, comprising:

generating, by the optical device, at least a first optical frame and a second optical frame;

transmitting, by the optical device, a first header for the first optical frame, wherein the first header includes a first indication of a first modulation applied to the first optical frame; and

transmitting, by the optical device, a second header for the second optical frame, wherein the second header includes a second indication of a second modulation applied to the second optical frame, wherein the second modulation is a different modulation from the first modulation.
A method of data reception by an optical device, the method comprising:

receiving, by the optical device, a first optical frame, wherein the first optical frame includes a first header and a first payload;

determining, from the first header, a first modulation applied to the first payload;

demodulating the first optical frame according to the first modulation;

receiving, by the optical device a second optical frame, wherein the second optical frame includes a second header and a second payload;

determining, from the second header, a second modulation applied to the second payload; and

demodulating the second optical frame according to the second modulation different from the first modulation.
The method of any of claims 1-2, wherein the first modulation comprises an N-level pulse amplitude modulation scheme, where N is an integer.
The method of any of claims 1-3, wherein the second modulation comprises an on-off keying modulation scheme.
The method of any of claims 1-4, wherein the optical device is an optical line terminal.
The method of any of claims 1-4, wherein the optical device is an optical network unit.
The method of any of claims 1-6, wherein the first optical frame and the second optical frame operate in accordance with a standard.
The method of claim 7, wherein the standard is an ITU-T Gigabit Passive Optical Network (G-PON) upstream or an ITU-T 10-Gigabuit Passive Optical Network (XG-PON) upstream frame.
The method of claim 7, wherein the standard is an IEEE E-PON.
The method of claim 7, wherein the first indication and the second indication are included in bit patterns in a delimiter field that are not defined in the standard.
The method of claim 7, wherein the first indication and the second indication are included in bit patterns in indicator bits that are not defined in the standard, wherein the indicator bits are forward error correction encoded.
An apparatus for optical digital communications, the apparatus comprising:

a receiver to receive digital data from a data source;

a formatter to format the received digital data into a frame, wherein the frame includes a frame header and payload data corresponding to the received digital data, and wherein the formatter generates the frame header to include an indication of a modulation format for the payload data;

a modulator to modulate a signal accordi ng to the digital data and the modulation format; and

a transmitter to transmit the modulated signal.
The apparatus for optical digital communications as in claim 12, wherein the receiver receives additional digital data, and

wherein the formatter formats the additional digital data into an additional frame, the additional frame including an additional frame header indicating an additional modulation format, wherein the additional modulation format is different from the modulation format.
The apparatus for optical digital communications as in any of claim 12-13, wherein the modulation format comprises an N level pulse amplitude modulation scheme, where N is an integer.
The apparatus for optical digital communications as in any of claims 12-14, wherein the frame header is modulated according to an on-off keying modulation scheme.
The apparatus for optical digital communications as in any of claims 12-15, wherein the frame operates in accordance with a standard.
The apparatus for optical digital communications as in claim 16, wherein the standard is an ITU-T Gigabit Passive Optical Network (G-PON) upstream or an ITU-T 10-Gigabuit Passive Optical Network (XG-PON) upstream frame.
The apparatus for optical digital communications as in claim 16, wherein the standard is an IEEE E-PON.
The apparatus for optical digital communications as in claim 16, wherein the indication is included in a bit pattern in a delimiter field that is not defined in the standard.
The apparatus for optical digital communications as in claim 16, wherein the indication is included a bit pattern in indicator bits that are not defined in the standard, wherein the indicator bits are forward error correction encoded.
An apparatus for optical digital communications, the apparatus comprising:

a receiver to receive a modulated signal from a transmitter, wherein the modulated signal includes a frame header and a payload;

a demodulator to demodulate the frame header, wherein the frame header includes an indication of a modulation format used to modulate the payload;

a payload demodulator to demodulate the payload according to the modulation format determined from the frame header; and

a formatter to format the demodulated payload for output to a data sink.
The apparatus for optical digital communications as in claim 21, wherein the receiver receives an additional modulated signal including an additional frame header and an additional payload,

wherein the demodulator demodulates the additional frame header to determine an additional modulation format for the additional payload, and

wherein the payload demodulator demodulates the additional payload according to the additional modulation format that is different from the modulation format.
The apparatus for optical digital communications as in any of claims 21-22, wherein the modulation format comprises an N level pulse amplitude modulation scheme, where N is an integer.
The apparatus for optical digital communications as in any of claims 21-23, wherein the frame header is modulated according to an on-off keying modulation scheme.
The apparatus for optical digital communications as in any of claims 21-24, wherein the frame header operates in accordance with a standard.
The apparatus for optical digital communications as in claim 25, wherein the standard is an ITU-T Gigabit Passive Optical Network (G-PON) upstream or an ITU-T 10-Gigabuit Passive Optical Network (XG-PON) upstream frame.
The apparatus for optical digital communications as in claim 25, wherein the standard is an IEEE E-PON.
The apparatus for optical digital communications as in claim 25, wherein the indication is included in a bit pattern in a delimiter field that is not defined in the standard.
The apparatus for optical digital communications as in claim 25, wherein the indication is included a bit pattern in indicator bits that are not defined in the standard, wherein the indicator bits are forward error correction encoded.
A method of data reception by an optical device, the method comprising:

receiving a modulated signal from a transmitter, wherein the modulated signal includes a frame header, a payload, and an indication of a modulation format used to modulate the payload;

demodulating the payload according to the modulation format determined from the frame header; and

formatting the demodulated payload for output to a data sink.
The method of claim 30, wherein the frame header further includes a delimiter, and

wherein the modulation format is determined from unused field permutations in the delimiter.
The method of any of claims 30, wherein the modulation format is determined from indicator bits contained in the frame header.
The method of any of claims 30-32, further comprising:

separating the frame header and the payload of the modulated signal;

storing the payload into a data buffer;

determining the modulation format from the frame header; and

reading the payload stored in the data buffer after determining the modulation format.
An optical receiver comprising a processor configured to implement a method recited in any of claims 30 to 33.
A computer-readable medium having code stored thereon, wherein the code, when executed by a processor of an optical communication apparatus, causes the processor to control the optical communication apparatus to implement a method recited in one or more of claims 1-11 or 30-33.