PROBABILISTICALLY SHAPED ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING

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First Claim
1. A method of optical communication, implemented at a transmitter in an optical communication network, comprising:
 mapping input data to complex symbols using a probabilistic shaped quadrature amplitude modulation (PSQAM) scheme;
converting the complex symbols from serial data to parallel data to obtain parallel complex symbols;
generating an OFDM signal from the parallel complex symbols;
adding a cyclic prefix to the OFDM signal;
converting the OFDM signal with the cyclic prefix from parallel data to serial data to obtain a serial OFDM signal;
generating a realvalue OFDM signal from the serial OFDM signal; and
transmitting the realvalue OFDM signal.
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Abstract
An optical signal transmission can use probabilistically shaped technique to improve performance and increase the transmission capacity. For instance, a 30Gbit/s/λ, probabilistically shaped (PS) 1024QAM DFTS OFDM was experimentally demonstrated over 40km SSMF in an intensity modulationdirect detection system. The Achievable Information Rate (AIR) 9.5344bits/QAM symbol of PS1024QAM modulation is first achieved in the experiment and shows feasibility for OFDM.
3 Citations
Using multilevel pulse amplitude modulation with probabilistic shaping  
Patent #
US 10,461,972 B2
Filed 10/30/2017

Current Assignee
ZTE Corporation

Sponsoring Entity
ZTE Corporation

Multicode probabilistic signal shaping using frequencydivision multiplexing  
Patent #
US 10,523,400 B2
Filed 11/20/2017

Current Assignee
Nokia Technologies Oy

Sponsoring Entity
Nokia Technologies Oy

Fiber input power selection for probabilistically shaped signals in optical networks  
Patent #
US 10,700,807 B1
Filed 07/01/2019

Current Assignee
Fujitsu Limited

Sponsoring Entity
Fujitsu Limited

No References
22 Claims
 1. A method of optical communication, implemented at a transmitter in an optical communication network, comprising:
mapping input data to complex symbols using a probabilistic shaped quadrature amplitude modulation (PSQAM) scheme; converting the complex symbols from serial data to parallel data to obtain parallel complex symbols; generating an OFDM signal from the parallel complex symbols; adding a cyclic prefix to the OFDM signal; converting the OFDM signal with the cyclic prefix from parallel data to serial data to obtain a serial OFDM signal; generating a realvalue OFDM signal from the serial OFDM signal; and transmitting the realvalue OFDM signal.  View Dependent Claims (2, 3, 4, 5, 6)
 7. A method of optical communication, implemented at a receiver in an optical communication network, comprising:
receiving and converting a realvalue OFDM signal to a complexvalue OFDM signal; removing cyclic prefix from the complexvalue OFDM signal; converting, after removing the cyclic prefix, the complexvalue OFDM signal from serial data to parallel data to obtain a parallel OFDM signal; generating, from the parallel OFDM signal, complex symbols based on a probabilistic shaped quadrature amplitude modulation (PSQAM) scheme; and demapping the complex symbols using a probabilistic shaped quadrature amplitude demodulation scheme to obtain an output signal.  View Dependent Claims (8, 9, 10, 11)
 12. A wireless communication device comprising a processor and a memory, wherein the memory stores instructions that, when executed, cause the processor to:
map input data to complex symbols using a probabilistic shaped quadrature amplitude modulation (PSQAM) scheme; convert the complex symbols from serial data to parallel data to obtain parallel complex symbols; generate an OFDM signal from the parallel complex symbols; add a cyclic prefix to the OFDM signal; convert the OFDM signal with the cyclic prefix from parallel data to serial data to obtain a serial OFDM signal; generate a realvalue OFDM signal from the serial OFDM signal; and transmit the realvalue OFDM signal.  View Dependent Claims (13, 14, 15, 16, 17)
 18. A wireless communication device comprising a processor and a memory, wherein the memory stores instructions that, when executed, cause the processor to:
receive and converting a realvalue OFDM signal to a complexvalue OFDM signal; remove cyclic prefix from the complexvalue OFDM signal; convert, after removing the cyclic prefix, the complexvalue OFDM signal from serial data to parallel data to obtain a parallel OFDM signal; generate, from the parallel OFDM signal, complex symbols based on a probabilistic shaped quadrature amplitude modulation (PSQAM) scheme; and demap the complex symbols using a probabilistic shaped quadrature amplitude demodulation scheme to obtain an output signal.  View Dependent Claims (19, 20, 21, 22)
1 Specification
This patent document claims the benefit of U.S. Provisional Patent Application No. 62/470,112, filed on Mar. 10, 2017. The entire content of the beforementioned patent application is incorporated by reference as part of the disclosure of this document.
The widespread adoption of multimedia services, broadband internet, and cloud services, among others, has driven the demand of high transmission capacity of optical systems such as shortreach links, access, and metro networks.
The present document discloses, among other things, an exemplary 30Gbit/s/λ, probabilistic shaping (PS)1024Quadrature Amplitude Modulation (QAM) Discrete Fourier Transform Spread (DFTS) Orthogonal Frequency Division Multiplexing (OFDM) that can be transmitted and received over 40km standard single mode fiber (SSMF) in an intensity modulation direct detection (IMDD) system. In an exemplary embodiment, the PS1024QAM format successfully achieved an Achievable Information Rate (AIR) of 9.5344bits/QAM symbol without chromatic dispersion (CD) compensation, nonlinearity equalization and preequalization.
In an exemplary embodiment, a method of optical communication, implemented at a transmitter in an optical communication network, comprises mapping input data to complex symbols using a probabilistic shaped quadrature amplitude modulation (PSQAM) scheme, converting the complex symbols from serial data to parallel data to obtain parallel complex symbols, generating an OFDM signal from the parallel complex symbols, adding a cyclic prefix to the OFDM signal, converting the OFDM signal with the cyclic prefix from parallel data to serial data to obtain a serial OFDM signal, generating a realvalue OFDM signal from the serial OFDM signal, and transmitting the realvalue OFDM signal.
In some embodiments, the PSQAM scheme is based on a predetermined pulseamplitude modulation (PAM) level distribution. In some embodiments, the PSQAM scheme comprises a PS1024QAM scheme.
In some embodiments, the generating of the OFDM signal from the parallel complex symbols includes performing an Npoint Inverse Fast Fourier Transform (IFFT) on the parallel complex symbols, wherein N is an integer.
In some embodiments, the OFDM signal is a Discrete Fourier TransformSpread (DFTS) OFDM signal, and wherein the generating of the OFDM signal from the parallel complex symbols includes performing an Lpoint Fast Fourier Transform (FFT) on the parallel complex symbols to obtain an Lpoint DFTS signal, and performing an Npoint Inverse Fast Fourier Transform (IFFT) on the Lpoint DFTS signal to obtain the DFTS OFDM signal, wherein N is equals to a number of subcarriers of the DFTS OFDM signal and wherein N and L are integers.
In some embodiments, the realvalue OFDM signal is generated by performing subcarrier modulation on the serial OFDM signal.
In another exemplary embodiment, a method of optical communication, implemented at a receiver in an optical communication network, comprises receiving and converting a realvalue OFDM signal to a complexvalue OFDM signal, removing cyclic prefix from the complexvalue OFDM signal, converting, after removing the cyclic prefix, the complexvalue OFDM signal from serial data to parallel data to obtain a parallel OFDM signal, generating, from the parallel OFDM signal, complex symbols based on a probabilistic shaped quadrature amplitude modulation (PSQAM) scheme, and demapping the complex symbols using a probabilistic shaped quadrature amplitude demodulation scheme to obtain an output signal.
In some embodiments, the generating of the complex symbols comprises performing an Npoint Fast Fourier Transform (FFT) on the parallel OFDM signal to obtain intermediate complex symbols, wherein N is equal to a number of subcarriers of the OFDM signal, performing postequalization on the intermediate complex symbols to obtain parallel equalized complex symbols, converting the parallel equalized complex symbols to serial complex symbols, performing decision directed least mean square (DDLMS) equalization on the serial complex symbols to obtain the complex symbols.
In some embodiments, the OFDM signal is a Discrete Fourier TransformSpread (DFTS) OFDM signal, and the generating of the complex symbols comprises performing an Npoint Fast Fourier Transform (FFT) on the parallel OFDM signal to obtain DFTS complex symbols, wherein N is equal to a number of subcarriers of the DFTS OFDM signal, performing postequalization on the DFTS complex symbols to obtain equalized DFTS complex symbols, performing an Lpoint Inverse Fourier Transform (IFFT) on the equalized DFTS complex symbols to obtain parallel equalized complex symbols, converting the parallel equalized complex symbols to serial complex symbols, and performing decision directed least mean square (DDLMS) equalization on the serial complex symbols to obtain the complex symbols.
In yet another example aspect, the abovediscussed methods may be implemented in a communication apparatus that includes a memory, a processor and a network interface. The processor may read instructions from the memory to implement the abovedescribed methods.
These and other aspects, and example implementations and variations are set forth in the drawings, the description and the claims.
In the description, section headings are used only for ease of understanding and do not limit the disclosed embodiments and technology to any particular section. In this patent document, the term “exemplary” is used to mean “an example of” and does not imply that the described technique is an “ideal” or “preferred” technique. The term technique may refer to an embodiment using software, hardware, or a combination thereof.
Nowadays, demand for ultrahigh data rate optical transmission is continuously growing. To meet the increasing demand on high data communication bandwidth, developers are continuously looking for new ways to carry a greater number of data bits over existing communication infrastructure. For instance, direct detection (DD) optical transmission is considered the more attractive and feasible solution due to the system construction cost, computation complexity and lower power consumption. Recently, probabilistic shaping (PS) has become a particularly promising technology in coherent optical system due to its higher spectral efficiency (SE), higher capacity and same computation complexity.
Compared with conventional quadrature amplitude modulation (QAM) schemes, PSQAM modulation could overcome the lack in granularity with Shannon capacity, while standard QAM formats offer a coarse granularity in SE and a penalty in signal noise ratio (SNR). However, PSQAM modulation is now investigated by theoretical analysis and simulation results in coherent optical system. The experimental results are rare and most of them focus on PS64QAM or PS256QAM format with single carrier modulation. Some other experimental results of single carrier PS1024QAM modulation in coherent receiver show that the achievable information rate is only 5.9bits/QAM symbol for PS dualpolarization (DP) 1024QAM. However, the information rate for a uniform DP1024QAM could be 20bits/QAM symbol (10bits/Sa×2=20bits/Sa) and the information rate for a uniform DP8QAM could be 6bits/QAM symbol. So considering the forward error correction (FEC) threshold, the single carrier PS1024QAM modulation of some other experimental results could only support uniform DP8QAM format. Besides, orthogonal frequencydivision multiplexing (OFDM) with optimized bitloading and powerloading per subcarrier is another way to improve performance. Nevertheless, it can bring large computation complexity in the transmitter and receiver sides while PSQAM modulation could save this additional cost. It is one interesting topic to investigate whether the system performance can be improved by using PS technology in OFDM system.
This patent document experimentally demonstrates an exemplary 30Gbit/s/λ probabilistically shaped 1024QAM DFTS OFDM over 40km SSMF in an IMDD system. The Achievable Information Rate (AIR) of 9.5344bits/QAM symbol is successfully achieved by PS1024QAM format. As further discussed below, the comparison between OFDM and Discrete Fourier Transformspread (DFTS) OFDM with and without PS shows the feasibility for further performance improvement in bandwidthconstrained system. To the best of our knowledge, this is the first time a PS modulation format is employed in OFDM modulation, e.g., in a PS1024QAM configuration, and the high AIR is achieved under the FEC threshold.
In optical communication, data is transmitted over optical carriers, e.g., glass or plastic optical fibers by modulating using a variety of different techniques. Some techniques implement data modulation in the electrical domain, e.g., by processing electronic signals. Alternatively, or in addition, data modulation can also be achieved in the optical domain.
Principle and Experiment Setup
One reason for introducing the exemplary probabilistic shaping is that most fiber communication systems can be powerconstrained. In addition to the characteristics of the modulation formats in the linear area, the nonlinear limitations affect the signal, especially highlevel signal. PS can facilitate sending of different level signals uses nonuniform probabilities. In some embodiments, PS can allow for the delivery of lowlevel signals with lower energy more often than the highlevel signals with higher energy. Some benefits of using PS techniques can include saving the average transmitted energy and keeping the same signal quality with less transmitted energy. PS is useful for any kind of modulation formats, such as 16QAM, 32QAM, 64QAM or higher order.
In
In some embodiments, an optional FFT operation 308 (shown with dashed lines) can be performed where an optional Lpoint FFT can be used to transform the parallel complex symbols to the Lpoint DFTS FFT signal, such as a 2048point DFTS FFT signal. In embodiments where a Lpoint DFTS FFT signal is obtained, a subsequent IFFT operation 310 can be performed where a Npoint IFFT 310 can be used to transform the Lpoint DFTS FFT signal to an OFDM signal with an Lpoint DFTS FFT. The N value for the IFFT can be the number of subcarriers of the OFDM signal. In some other embodiments, the IFFT operation 310 can be performed without first performing an FFT operation 308 so that an Npoint IFFT can be used to transform the parallel complex symbols to an OFDM signal without a DFTS FFT signal.
In some embodiments, the OFDM signal with or without an Lpoint DFTS FFT can be upsampled by performing an upsampling operation 312 to allow for better interpolation of transmitted data. At the cyclic prefix operation 314, cyclic prefix (CP) is added to the OFDM signal to alleviate the intersymbol interference (ISI) incurred by chromatic dispersion (CD). At the second conversion operation 316, a parallel to serial (P/S) conversion is performed on OFDM signal with CP to obtain a serial OFDM signal with complex values. At the third conversion operation 318, a serial OFDM signal with complex values can be converted to a realvalue OFDM, and subsequently transmitted over an optical fiber, as described in this patent document. In some implementations, the realvalue OFDM signal can be generated by modulating the serial OFDM signal with the complex phase quantity of the serial OFDM signal. In some other implementation, realvalue OFDM signal can be generated by using subcarrier modulation.
At the conversion operation 352, the receiver side DSP receives the realvalue OFDM signal transmitted over an SSMF and converts the realvalue OFDM signal into a complex value OFDM signal. At the removing operation 354, the cyclic prefix is removed from the complex valued OFDM signal. In some embodiments, after the removing operation 354, a downsampling operation 356 can be performed on the complex value OFDM signal by removing the samples added to the sequence by the upsampling operation performed by the transmitter.
At the second conversion operation 348, the complex value OFDM signal can be converted from a serial to parallel to obtain a parallel complex value OFDM signal. Next, an FFT operation 360 is performed on the parallel complex value OFDM signal using an Npoint FFT (N may be an integer power of 2) to obtain raw complex symbols associated with a probabilistic shaped quadrature amplitude modulation (PSQAM).
At the postequalization operation 362, the raw complex symbols are equalized to provide nonlinear compensation to obtain equalized complex symbols. In some embodiments, postequalization operation 362 can be performed to simultaneously estimate the response of a nonlinear system and capture the memory effect of devices or fiber. In some embodiments, where the received signal is an DFTS OFDM signal, the output of the postequalization operation 362 is equalized DFTS complex symbols.
In some embodiments where the received OFDM signal is a DFTS OFDM signal, a IFFT operation 364 (shown with dashed lines) is optionally performed after the postequalization operation 362. At IFFT operation 364, an Lpoint IFFT can be used to transform the equalized DFTS complex symbols to obtain parallel equalized complex symbols associated with a probabilistic shaped quadrature amplitude modulation (PSQAM).
After the postequalization operation 362 (for received OFDM signal without DFTS FFT) or after the optional IFFT operation 364 (for received OFDM signal with DFTS FFT), the parallel equalized complex signal can be converted to a serial complex OFDM signal at the third conversion operation 366.
At a second equalization operation 368, a decision directed least means square equalization can be performed to compensate phase and also to realize intersymbolinterference equalization, which can be a linear procession.
At the demapping operation 370, the serial complex OFDM signal can be demapped by using a probabilistic shaping quadrature amplitude demodulation scheme to obtain output data 372.
Results and Discussion
The BER performance with different lasers is shown in
An exemplary 30Gbit/s/λ PS1024QAM DFTS OFDM over 40km SSMF is experimentally demonstrated in an IMDD system. Without CD compensation, nonlinearity equalization and preequalization, the AIR of 9.5344bits/QAM symbol is successfully achieved by PS1024QAM format. The comparisons of OFDM and DFTS OFDM with and without PS show the feasibility for further performance improvement in short distance optical transmission. To the best of our knowledge, this is the first time a PS1024QAM format is employed in OFDM modulation and the high AIR is achieved under the FEC threshold.
Any known algorithms to perform probabilistic shaping can be utilized. In some embodiments, probabilistic shaping can be accomplished by the methods described in Raphaeli, et al., Constellation Shaping for Pragmatic TurboCoded Modulation With High Spectral Efficiency, or Yankov et. al., Constellation Shaping for FiberOptic Channels With QAM and High Spectral Efficiency, or Buchali et al., Rate Adaptation and Reach Increase by Probabilistically Shaped 64QAM: An Experimental Demonstration, or Silva et al., Experimental Comparison of Gains in Achievable Information Rates from Probabilistic Shaping and Digital Backpropagation for DP256QAM/1024QAM WDM Systems.
It will be appreciated that the patent document discloses an optical signal transmission that can use probabilistically shaped technique to improve performance and increase the transmission capacity. For instance, a 30Gbit/s/λ probabilistically shaped (PS) 1024QAM DFTS OFDM was experimentally demonstrated over 40km SSMF in an IMDD system. The Achievable Information Rate (AIR) 9.5344bits/QAM symbol of PS1024QAM modulation is first achieved in the experiment and shows feasibility for OFDM.
The disclosed and other embodiments and the functional operations and modules 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 machinereadable storage device, a machinereadable storage substrate, a memory device, a composition of matter effecting a machinereadable 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 machinegenerated 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 standalone 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 nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVDROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.
While this document contains many specifics, these 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 subcombination. 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 subcombination or a variation of a subcombination. 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.