An energy-saving method for the receiver of a real-time IMDD OFDM-PON system

Abstract

The present invention provides an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system, which is an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system based on multiple clock domains at the physical layer. By utilizing the Hermitian symmetry characteristic of the receiving end of the real-time IMDD OFDM-PON system and the feature that the channel estimation module only needs to operate briefly, the clock working time or clock working frequency of different modules is controlled, providing an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system based on multiple clock domains at the physical layer, and providing a specific implementation scheme, which simply and effectively reduces the power consumption of the receiving end of the real-time IMDD OFDM-PON system and has strong compatibility.

Description

Technical Field

[0001] The present invention relates to the field of communication systems, and in particular to an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system. Background Art

[0002] The rapidly growing communication industry, ICT, accounts for 8% of the global power consumption, and 70% of which is consumed in the access network. Therefore, the development of energy-saving access networks has become a research hotspot. Passive optical network (PON), with its low power consumption and high transmission speed, is considered to be an important and promising research direction. In the past 20 years, intensity modulation direct detection orthogonal frequency division multiplexing passive optical network (IMDD OFDM-PON) has been widely studied and applied due to its robustness to dispersion, high spectral efficiency, and low cost. However, due to the characteristics of OFDM itself, the real-time IMDD OFDM-PON system consumes more energy than the traditional real-time TDMA-PON system. Therefore, the research on energy-saving solutions for the real-time IMDD OFDM-PON system has become an important research direction.

[0003] The existing physical layer energy-saving solutions for the receiving end of the real-time IMDD OFDM-PON system are divided into two main directions. One direction is to reduce the sampling accuracy of the ADC and the size and bit width of the FFT, but this solution often comes at the cost of system flexibility or performance. The other direction is to utilize the broadcast characteristic of the downstream real-time IMDD OFDM-PON system to reduce power consumption by reducing the repeated demodulation of frames, but this solution can only reduce the power consumption of the ONU and cannot reduce the power consumption of the OLT. At the same time, regardless of which direction, there is a lack of energy-saving research on further utilizing the physical layer characteristics of the real-time IMDD OFDM itself. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to utilize the physical layer characteristics of the real-time IMDD OFDM-PON itself for energy-saving design of the receiving end of the real-time IMDD OFDM-PON system. The present invention provides an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system, which is an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system based on a multi-clock domain of the physical layer. By utilizing the Hermitian symmetry characteristic of the receiving end of the real-time IMDD OFDM-PON system and the feature that the channel estimation module only needs to run briefly, the clock working time or clock working frequency of different modules is controlled, providing an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system based on a multi-clock domain of the physical layer, and providing a specific implementation scheme; it simply and effectively reduces the power consumption of the receiving end of the real-time IMDD OFDM-PON system and has strong compatibility.

[0005] To achieve the above object, the present invention provides an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system, including the following steps:

[0006] S1, After the real-time IMDD OFDM-PON data is sampled by the ADC, it reaches the full-speed clock domain;

[0007] S2, The data will gradually flow through the frame synchronization module, CP removal module, and FFT module in the full-speed clock domain to complete data frame synchronization, remove redundant CP, and OFDM demodulation functions respectively, obtaining the training sequence TS and OFDM symbols;

[0008] S3, The training sequence TS is sent to the channel estimation module in the controlled clock domain to complete channel estimation and output channel parameters to the channel equalization module in the half-speed clock domain;

[0009] S4, Extract the valid part of the OFDM symbol and send it to the half-speed clock domain, gradually flowing through the channel equalization module and demodulation module. In the channel equalization module, the OFDM symbol is channel-equalized using channel information, and the equalization result is delivered to the demodulation module to obtain demodulated data;

[0010] S5, Output the demodulated data to the MAC layer to complete data reception of the IMDD OFDM-PON system.

[0011] Further, the receiving end of the real-time IMDD OFDM-PON system includes three clock domains: a full-speed clock domain, a controlled clock domain, and a half-speed clock domain.

[0012] Further, the full-speed clock domain is a clock domain that matches the ADC sampling rate and system parallelism. The controlled clock domain is a clock domain generated by the full-speed clock passing through a gating module. The half-speed clock domain is a clock domain generated by dividing the full-speed clock by two.

[0013] Further, the control signal is responsible for the switch of the gating module. When one beat before the FFT module outputs the training sequence TS, the control signal is pulled high and pulled low after a fixed delay D. At this time, the gating module is opened, and the controlled clock is equal to the full-speed clock. At this time, the channel estimation module works normally and outputs channel information.

[0014] Further, the fixed delay D is determined by the running time required by the channel estimation module. Generally, D accounts for less than 5% of the duration of one IMDD OFDM-PON frame.

[0015] Further, extract the valid part of the OFDM symbol. Specifically, utilize the Hermitian symmetry characteristic of the receiving end of the real-time IMDD OFDM-PON system to extract the first half of the points of the OFDM symbol, reducing the data volume of the system by half, enabling the subsequent equalization and demodulation modules to meet the system throughput requirements by operating at only half the frequency of the previous stage.

[0016] Further, the frame synchronization is specifically to use the synchronization header of 80 zeros and 2 ones for the unordered adc data to find the starting point of the OFDM frame and reorganize the data into a specified format. x_CP represents the CP part of an OFDM symbol or the training sequence TS, and the training sequence TS is an OFDM symbol with known transmitted information. x represents the data part of the OFDM symbol or the training sequence TS.

[0017] Further, the specific function of the CP removal module is to remove x_CP from the frame synchronization result to obtain x and input it into the FFT module.

[0018] Further, when the X output by the FFT is the training sequence TS, then input the training sequence TS into the channel estimation module, and obtain the channel parameters through the LS channel estimation algorithm and send them to the channel equalization module.

[0019] Further, the channel equalization module and the OFDM symbol input to the FFT module complete channel equalization together, remove the frequency offset and phase offset of the data, and provide a normalization factor to obtain the normalized constellation diagram and input it into the demodulation module.

[0020] Technical Effects

[0021] An energy-saving method for the receiving end of a real-time IMDD OFDM-PON system based on multiple clock domains in the physical layer of the present invention utilizes the Hermitian symmetry characteristic of the receiving end of the real-time IMDD OFDM-PON system and the characteristic that the channel estimation module does not need to operate for a long time, sets multiple working clock domains in the physical layer, reduces the working clock frequencies of channel equalization and demodulation and the clock working time of the channel estimation module, thereby achieving the purpose of energy saving at the receiving end of the real-time IMDD OFDM-PON system. In addition, this solution has high generality and can be well combined with other energy-saving solutions for use.

[0022] The following will further illustrate the concept, specific structure and technical effects generated by the present invention with reference to the drawings to fully understand the purpose, features and effects of the present invention. Brief Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the system structure of an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to a preferred embodiment of the present invention;

[0024] Figure 2 It is a schematic diagram of the frame structure of an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to a preferred embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of the data stream of an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to a preferred embodiment of the present invention. Detailed implementation manners

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] In the following description, specific details such as specific internal programs and technologies are put forward for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0028] The present invention provides an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system, which is characterized by including the following steps:

[0029] S1, after the real-time IMDD OFDM-PON data is sampled by the ADC, it reaches the full-speed clock domain with a 32-bit parallelism, as Figure 3 shown by the adc on the left;

[0030] S2, the data will gradually flow through the frame synchronization module, the CP removal module and the FFT module in the full-speed clock domain to complete the data frame synchronization, remove the redundant CP and the OFDM demodulation functions, and the training sequence TS and the OFDM symbol;

[0031] S3, the training sequence TS is sent to the channel estimation module in the controlled clock domain to complete the channel estimation and output the channel parameters to the channel equalization module in the half-speed clock domain;

[0032] S4. Extract the valid part of the OFDM symbol and send it to the half-speed clock domain. It gradually flows through the channel equalization module and the demodulation module. In the channel equalization module, the OFDM symbol is equalized using the channel information, and the equalization result is sent to the demodulation module to obtain the demodulated data. Among them, extracting the valid part of the OFDM symbol specifically means extracting the first half of the points of the OFDM symbol by using the Hermitian symmetry characteristic of the receiving end of the real-time IMDD OFDM-PON system, reducing the data volume of the system by half, so that the subsequent equalization and demodulation modules only need to run at half the frequency of the previous stage to meet the system throughput requirements.

[0033] S5. Output the demodulated data to the MAC layer to complete the data reception of the IMDD OFDM-PON system.

[0034] Among them, the receiving end of the real-time IMDD OFDM-PON system includes three clock domains: the full-speed clock domain, the controlled clock domain, and the half-speed clock domain. The full-speed clock domain is the clock domain that matches the ADC sampling rate and the system parallelism. The controlled clock domain is the clock domain generated by the full-speed clock passing through the gating module. The half-speed clock domain is the clock domain generated by dividing the full-speed clock by two.

[0035] The control signal is responsible for the switch of the gating module. When the previous beat of the training sequence TS is output by the FFT module, the control signal is pulled high and pulled low after a fixed delay D. At this time, the gating module is opened, and the controlled clock is equal to the full-speed clock. At this time, the channel estimation module works normally and outputs the channel information. The fixed delay D is determined by the running time required by the channel estimation module. Generally, D only accounts for less than 5% of the duration of an IMDD OFDM-PON frame.

[0036] In S2, the specific function of frame synchronization is to use the synchronization header of 80 0s and 2 1s for the unordered adc data to find the starting point of the OFDM frame and reorganize the data into the format in Figure 3 where x_CP represents the CP part of an OFDM symbol or the training sequence TS. The training sequence TS is an OFDM symbol with known transmitted information. x represents the data part of the OFDM symbol or the training sequence TS. The specific function of the CP removal module is to remove x_CP in the frame synchronization result to obtain x, as shown in Figure 3 Subsequently, x representing an OFDM symbol or the training sequence TS, taking 64 points as an example, is input to the FFT module. Due to the Hermitian symmetry characteristic, only 32 points in the output X are valid, as shown in Figure 3As shown. At this time, if the output X is the training sequence TS, it is input to the channel estimation module; if it is an OFDM symbol, it is input to the channel equalization module. The training sequence TS input to the channel estimation module obtains the channel parameters through the LS channel estimation algorithm and sends them to the channel equalization module. The channel equalization module and the OFDM symbol input to the FFT module complete the channel equalization together, remove the frequency offset and phase offset of the data, and provide a normalization factor to obtain the normalized constellation diagram and input it to the demodulation module. Finally, the bit stream is obtained and output to the MAC layer to complete the data reception of the IMDD OFDM-PON.

[0037] The following will take the real-time IMDD OFDM-PON receiver energy-saving system based on the multi-clock domain of the physical layer implemented on the ML605 FPGA board as an example for illustration. The system block diagram is as Figure 1 shown, and the frame structure is used as Figure 2 shown. The specific steps of the system are as follows:

[0038] The real-time IMDD OFDM-PON receiver energy-saving system in the embodiment of the present invention uses a 4G ADC to be responsible for sampling, inputs the sampling data with a 32-bit parallelism, and provides a 125MHz clock for the subsequent receiving module to use. The frame used by this system consists of a synchronization header for frame synchronization composed of 80 0s and 2 1s, 2 training sequences TS of 80 points (each consisting of 16 points of CP and 64 points of data), and 100 OFDM symbols of 80 points (each consisting of 16 points of CP and 64 points of data). This system needs to use Figure 3 the 32-bit parallelism 64-point FFT shown for OFDM demodulation, and can utilize the Hermitian symmetry characteristic of the IMDD OFDM-PON to change the effective data volume of 64 points to 32 points, reducing it by half.

[0039] The real-time IMDD OFDM-PON receiver energy-saving system in the embodiment of the present invention includes a frame synchronization module, a CP removal module, an FFT module, a channel estimation module, a channel equalization module, a demodulation module, and a MAC layer.

[0040] Among them, the frame synchronization module is responsible for using the synchronization header of the received IMDD OFDM-PON data frame to find the starting point of this frame. The CP removal module is responsible for extracting the 64-point data in each training sequence TS and OFDM symbol. The FFT module is responsible for performing OFDM demodulation processing. The channel estimation module is responsible for using the training sequence TS to perform LS channel estimation for each frame. The channel equalization module is responsible for using the channel information output by the channel estimation module to perform channel equalization on the OFDM demodulation result of the FFT module, removing the frequency offset and phase offset of the data, and providing a normalization factor. The demodulation module is responsible for demodulating the data after equalization by QAM modulation to convert the data into a binary bit stream. The MAC layer represents other modules that will use these data streams.

[0041] The specific steps of an energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to an embodiment of the present invention include:

[0042] S1. After the real-time IMDD OFDM-PON data is sampled by a 4G ADC, it reaches the full-speed clock domain with a 32-bit parallelism, provides a 125 MHz full-speed clock, and generates a controlled clock domain under the control of a 125 MHz gating clock module through a gating clock module, and generates a half-speed clock domain of 62.5 MHz through a frequency division by two module;

[0043] S2. A single-frame data will gradually flow through the frame synchronization module, the CP removal module, and the FFT module in the full-speed clock domain to complete data frame synchronization, remove redundant CP, and OFDM demodulation functions respectively. First, two training sequences TS and 100 OFDM symbols are obtained in chronological order. At the same time, the control signal of the gating module is pulled high for 8 beats and then pulled low one beat before the output of the training sequence TS, so that the controlled clock is equal to the full-speed clock when the two training sequences TS arrive and equal to 0 after the channel information is obtained;

[0044] S3. When the FFT module outputs two training sequences TS, the data is sent to the channel estimation module in the controlled clock domain, and the channel estimation is completed within 8 beats and the channel parameters are output to the channel equalization module in the half-speed clock domain;

[0045] S4. When the FFT module outputs 100 OFDM symbols, since this system is a 64-point system, the valid part of the OFDM symbol, that is, the first 32 points, is extracted and sent to the half-speed clock domain, and gradually flows through the channel equalization module and the demodulation module. In the channel equalization module, the OFDM symbol is channel-equalized using the channel parameters, and the equalization result is delivered to the demodulation module to obtain demodulated data;

[0046] S5. Output the demodulated data to the MAC layer to complete the data reception of the IMDD OFDM-PON system.

[0047] In a traditional IMDD OFDM-PON system, DSP modules including frame synchronization, CP removal, FFT, channel estimation, channel equalization, and demodulation are usually placed in a clock domain with the same frequency, and this clock domain is not shut down. However, due to the structure and Hermitian symmetry characteristics of the OFDM frame in the IMDD OFDM-PON system, the channel estimation module only needs to operate for a very short time, as Figure 2 shown, and the data volume is halved after passing through the FFT module, as Figure 3 shown. By using a gated clock to control the operating time of the channel estimation module and reducing the clock frequency of the channel equalization and demodulation modules to half of the operating frequency of the FFT module, the system power consumption can be effectively reduced.

[0048] The present invention designs a receiver system for a real-time IMDD OFDM-PON with multiple clock domains by utilizing the OFDM frame structure and Hermitian symmetry characteristics of the IMDD OFDM-PON system. By reducing the operating frequency and operating time of some DSP modules, the power consumption of the entire system is effectively reduced. And in this specific embodiment, the receiving end of a single real-time IMDD OFDM-PON system has an energy-saving efficiency of 15% compared with the traditional scheme, which proves the correctness of this method. This scheme is applicable to both the OLT and ONU, and the better the energy-saving effect of this scheme in a more complex real-time IMDD OFDM-PON system.

[0049] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. An energy-saving method for the receiving end of a real-time IMDD OFDM-PON system, characterized in that, It includes the following steps: S1. After the real-time IMDD OFDM-PON data is sampled by the ADC, it reaches the full-speed clock domain; S2. In the full-speed clock domain, the data will gradually flow through the frame synchronization module, the CP removal module, and the FFT module, respectively completing data frame synchronization, removing the redundant CP, and OFDM demodulation functions, to obtain the training sequence TS and OFDM symbols; S3. The training sequence TS is sent to the channel estimation module in the controlled clock domain, completes channel estimation and outputs the channel parameters to the channel equalization module in the half-speed clock domain; S4. The valid part of the OFDM symbol is extracted and sent to the half-speed clock domain, and gradually flows through the channel equalization module and the demodulation module. In the channel equalization module, the OFDM symbol is channel equalized by using the channel information, and the equalization result is delivered to the demodulation module to obtain the demodulated data; S5. Output the demodulated data to the MAC layer to complete the data reception of the IMDD OFDM-PON system; Among them, the receiving end of the real-time IMDD OFDM-PON system includes three clock domains: the full-speed clock domain, the controlled clock domain, and the half-speed clock domain.

2. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to claim 1, characterized in that, The full-speed clock domain is the clock domain that matches the ADC sampling rate and the system parallelism. The controlled clock domain is the clock domain generated by the full-speed clock passing through the gating module. The half-speed clock domain is the clock domain generated by dividing the full-speed clock by two.

3. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to claim 2, characterized in that, The control signal is responsible for the switch of the gating module. When one beat before the FFT module outputs the training sequence TS, the control signal is pulled high and pulled low after a fixed delay D. At this time, the gating module is opened, and the controlled clock is equal to the full-speed clock. At this time, the channel estimation module works normally and outputs the channel information.

4. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to claim 3, characterized in that, The fixed delay D is determined by the running time required by the channel estimation module, and D accounts for less than 5% of the duration of one IMDD OFDM-PON frame.

5. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to claim 1, characterized in that, Extracting the valid part of the OFDM symbol specifically means using the Hermitian symmetry characteristic of the receiving end of the real-time IMDD OFDM-PON system to extract the first half of the points of the OFDM symbol, reducing the data volume of the system by half, so that the subsequent equalization and demodulation modules only need to run at half the frequency of the previous stage to meet the system throughput requirements.

6. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to claim 1, characterized in that, The frame synchronization specifically means using the synchronization header of 80 0s and 2 1s to find the starting point of the OFDM frame for the disordered adc data, and reorganizing the data into a specified format. x_CP represents the CP part of an OFDM symbol or the training sequence TS. The training sequence TS is an OFDM symbol with known transmitted information. x represents the data part of the OFDM symbol or the training sequence TS.

7. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to claim 6, characterized in that, The specific function of the CP removal module is to remove x_CP in the frame synchronization result to obtain x and input it to the FFT module.

8. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system according to claim 7, characterized in that, When the X output by the FFT is the training sequence TS, the training sequence TS input to the channel estimation module uses the LS channel estimation algorithm to obtain the channel parameters and send them to the channel equalization module.

9. The energy-saving method for the receiving end of a real-time IMDD OFDM-PON system as claimed in claim 8, wherein, The channel equalization module completes channel equalization together with the OFDM symbol input to the FFT module, removes the frequency offset and phase offset of the data, and provides a normalization factor to obtain the normalized constellation diagram and input it to the demodulation module.

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