An OFDM-PON receiving end MAC layer data frame recovery method

Abstract

The application discloses a kind of OFDM-PON receiving end MAC layer data frame recovery method, ONU end receives the downlink data broadcasted by OLT, demodulates the bit data stream belonging to oneself from parallel subcarriers according to pre-allocated time slot, subcarrier and modulation format, carries out data splicing to the bit data stream demodulated in OFDM symbol subcarrier, is transmitted with fixed data bit width, carries out shift splicing operation to data by bit shift and mask operation, ensure that the data of last clock beat except entire frame data, all data is complete and effective, finally, correct data frame is recovered from the data after shift splicing by the length of frame header, complete the reception of data.The application realizes the data recovery of OFDM-PON receiving end MAC layer using hardware system, can realize the bit alignment of data and has universality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of passive optical network, and particularly relates to a MAC layer data frame recovery method for OFDM-PON receiving end. BACKGROUND

[0002] Internet traffic has been growing exponentially, and passive optical network (PON) has become the main solution for next-generation fiber access due to its huge transmission capacity. Orthogonal frequency division multiplexing passive optical network (OFDM-PON) has attracted widespread attention in the next-generation optical access network due to its high spectral efficiency and strong dispersion resistance. In the OFDM-PON system, the data frame is first divided into multiple sub-streams before transmission for transmission on different subcarriers. Since each OFDM symbol may only contain a fragment of the data frame, the receiving end faces a challenge: it needs to splice the data streams demodulated from multiple symbols to reconstruct the complete data frame. In particular, in the OFDM-PON system, each subcarrier may use different modulation formats according to the transmission conditions, which requires the processing of the data frame to be in bits, increasing the complexity and accuracy of data recovery at the receiving end.

[0003] Various bandwidth access network systems need to process and analyze the received data frame, and how to recover the complete data frame is a key step, so various frame recovery methods are needed. The application "Frame alignment device of broadband access network system" with application number CN105208467A proposes a frame alignment device of a bandwidth access network system, which realizes frame alignment in a PON system by using data bit adjustment and data bit alignment modules. However, in the scenario applicable to this method, the number of transmission bits of each parallel signal after serial-parallel conversion is the same. Weng Tianheng et al. proposed a data alignment and shift splicing method in "Design of FPGA-based DDR4 multi-channel controller [J]. Electronic Measurement Technology, 2022, 45(12)", and derived the corresponding formula, but this method is based on byte alignment and only splices data within a single burst, and is not suitable for bit alignment scenarios in OFDM-PON. SUMMARY

[0004] In view of the deficiencies of the prior art, the technical problem actually solved by the present application is the lack of universality and poor flexibility in existing data frame processing methods. The present application provides a MAC layer data frame recovery method for OFDM-PON receiving end, which uses a hardware system to realize frame recovery of OFDM-PON system, and can realize bit alignment of data and has universality.

[0005] To achieve the above-mentioned purpose, the present application provides a MAC layer data frame recovery method for OFDM-PON receiving end, comprising the following steps:

[0006] The ONU receives the downstream data broadcasted by the OLT, demodulates the bit data stream belonging to itself from the parallel subcarriers according to the pre-allocated time slot, subcarrier and modulation format;

[0007] The bit data stream demodulated from the OFDM symbol subcarrier is spliced for transmission with fixed data bit width;

[0008] The data is spliced by bit shifting and mask operation, ensuring that all data except the data of the last clock beat is complete and valid;

[0009] The correct data frame is recovered from the spliced data by the length of the frame header, and the data reception is completed.

[0010] Further, the bit data stream belonging to itself is demodulated from the parallel subcarriers, and the size of the bit data stream obtained by the ONU when demodulating the OFDM symbol is variable, depending on the number of allocated subcarriers and the efficiency of the modulation format.

[0011] Further, the size of the bit data stream obtained by the ONU when demodulating the OFDM symbol is variable, so the length of the data demodulated from each subcarrier after splicing is not fixed, and when transmitting with fixed data bit width in FPGA, the data transmitted in the last clock beat may not be all valid, and the missing data is filled with 0.

[0012] Further, the bit shifting and mask operation includes the following steps:

[0013] S1: The length L of each clock beat valid data is accumulated to obtain the length accumulation P, and the offset bit number M=P%S, S is the bus bit width, unit is bit, and % represents the remainder operation.

[0014] S2: According to the offset bit number M of the previous clock beat, the high bit data of M bits is wrapped around to the low bit, and the low bit data of (S-M) bits is wrapped around to the high bit.

[0015] S3: According to the length L of the current clock beat data, an effective data mask is generated, which has L bits of valid data, and the effective data mask is

[0016] data_length_mask={S-L{1′b0},L{1′b1}}

[0017] S4: According to the offset bit number M of the previous clock beat and the effective data mask of the current clock beat, a reorganized data mask is generated, which is

[0018] data_length_update_mask = {data_length_mask [S-M-1:0], M {1'b0}}

[0019] S5: generating a wrap-around data mask according to the offset bit number M of the previous clock tick and the valid data mask of the current clock tick, the wrap-around data mask being

[0020] data-length_wrap_mask = {S-M {1'b0}, data_length_mask [S-1:S-M]}

[0021] S6: shifting and recombining the data according to the wrap-around data of S2, the recombined data mask of S4 and the wrap-around data mask of S5, so as to ensure that all the data except the data of the last clock tick are all valid.

[0022] Further, the current data is subjected to a wrap-around operation according to the offset bit number M of the previous clock tick, and is subjected to a byte shift first and then a bit shift.

[0023] Further, the correct data frame is solved from the continuous data through the length indication of the frame header, and after all the data are subjected to the shifting and splicing, all the data except the data of the last clock tick are all valid, and the frame header has a fixed length indication unit indicating the payload length of the data frame in byte.

[0024] Technical effects

[0025] 1. The effective length and the offset bit number are used to obtain the recombined data mask and the wrap-around data mask, and the data splicing is completed through the mask indication, so that the flexibility is achieved.

[0026] 2. When the bit shift operation is performed, the byte shift is performed first and then the bit shift is performed instead of directly performing the bit shift, so that the consumption of the lookup table (LUT) resource is reduced, and the timing of the FPGA implementation is optimized.

[0027] 3. The multiple pieces of data with arbitrary bit length can be subjected to the shifting and splicing and the initial data can be recovered through the bit-by-bit mask operation and the length indication unit of the frame header, so that the universality is achieved.

[0028] The concept, specific structure and technical effects of the present application will be further described below with reference to the accompanying drawings, so that the purpose, features and effects of the present application can be fully understood. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a flowchart of an OFDM-PON receiving end MAC layer data frame recovery method of a preferred embodiment of the present application.

[0030] Figure 2 This is a flowchart of bit shifting and masking operations in a preferred embodiment of an OFDM-PON receiver MAC layer data frame recovery method;

[0031] Figure 3 This is a simulation result diagram after OFDM symbol demodulation data is spliced ​​together;

[0032] Figure 4 This is a simulation result diagram of the wraparound data and the effective data mask;

[0033] Figure 5 This is a simulation result diagram of reconstructed data mask and wrapped data mask;

[0034] Figure 6 This is a simulation result diagram of the shifted data;

[0035] Figure 7 The diagram shows the simulation results of byte shift and bit shift. Detailed Implementation

[0036] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0037] In the following description, specific details, such as particular internal procedures and techniques, are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will appreciate that the invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of the invention with unnecessary detail.

[0038] like Figure 1 The diagram shown is a flowchart of OFDM-PON receiver MAC layer data frame recovery provided by the present invention. This method is applied in the field of passive optical network technology and includes the following steps:

[0039] S101: The ONU receives downlink data broadcast by the OLT and demodulates its own bit data stream from the parallel subcarriers according to the pre-allocated time slots, subcarriers and modulation formats.

[0040] S102: Concatenate the bit data streams demodulated from the OFDM symbol subcarriers and transmit them with a fixed data bit width;

[0041] S103: The data is subjected to a shift splicing operation through bit shifting and mask operation, ensuring that all data except the data of the last clock tick is complete and valid;

[0042] S104: The correct data frame is recovered from the spliced data through the length indication of the frame header, completing the reception of the data.

[0043] As shown in Figure 2 , the bit shifting and mask operation specifically includes the following steps:

[0044] S201: The length L of each clock tick valid data is accumulated to obtain a length accumulation P, and the offset bit number M=P%S, S is the bus bit width, unit is bit, and % represents the remainder operation.

[0045] S202: According to the offset bit number M of the previous clock tick, the current data is subjected to a wraparound operation, the high bit data of M bits is wrapped around to the low bit, and the low bit data of (S-M) bits is wrapped around to the high bit.

[0046] S203: According to the length L of the current clock tick data, an effective data mask is generated, which has L bits of valid data, and the effective data mask is

[0047] data_length_mask={S-L{1′b0},L{1′b1}}

[0048] S204: According to the offset bit number M of the previous clock tick and the effective data mask of the current clock tick, a recombination data mask is generated, which is

[0049] data_length_update_mask={data_length_mask[S-M-1:0],M{1′b0}}

[0050] S205: According to the offset bit number M of the previous clock tick and the effective data mask of the current clock tick, a wraparound data mask is generated, which is

[0051] data_length_wrap_mask={S-M{1′b0},data_length_mask[S-1:S-M}}

[0052] S206: According to the wraparound data of S202, the recombination data mask of S204, and the wraparound data mask of S205, the data is subjected to a shift recombination, ensuring that all data except the data of the last clock tick is complete and valid.

[0053] Embodiment one:

[0054] The number of bits demodulated by the ONU receiving end from one OFDM symbol l represents the lowest serial number of the pre-allocated subcarrier, h represents the highest serial number of the pre-allocated subcarrier, C i represents the number of bits transmitted by the ith subcarrier within a single symbol, which is related to the modulation format of the subcarrier, for example, a subcarrier using 16QAM modulation can transmit 4 bits of data within one symbol. In the present example, 7 subcarriers are pre-allocated to use the 32QAM modulation format, and 1 subcarrier is pre-allocated to use the 16QAM modulation format, and the calculation gives C = 39. The transmission of data in the FPGA has a fixed bus width, which is generally 32 bits, 64 bits, 128 bits, or 256 bits, and in the present example, the bus width is 32 bits. Therefore, in the present example, the bits demodulated by the ONU within one OFDM symbol are spliced to fill one clock cycle of 32 bits of data, and the second clock cycle has only 7 bits of valid data, with the rest filled with 0. Figure 3 The splicing of the bit stream data demodulated by part of the OFDM symbols in a frame of data is shown, and there are 3 OFDM symbols of data, with (1, 1) indicating the first clock cycle of data spliced from the first OFDM symbol, with 32 bits of valid data, and similarly (1, 2) has 7 bits of valid data, stored in big-endian mode. The length L of the valid data for each clock cycle is accumulated to obtain the length accumulation P, and the offset number of bits M is calculated, giving (1, 1) L = 32, P = 32, M = 0; (1, 2) L = 7, P = 39, M = 7; (2, 1) L = 32, P = 71, M = 7; (2, 2) L = 7, P = 78, M = 14; (3, 1) L = 32, P = 110, M = 14; (3, 2) L = 7, P = 117, M = 21. Next, the data is wrapped around, and the corresponding mask is generated, taking (2, 1) as an example, the offset number of bits M of the previous clock cycle is 7, so the 7 bits of high-order data are wrapped around to the low-order, and the 25 bits of data are wrapped around to the high-order, and the valid data mask data_length_mask = 32{1'b1} is generated according to the current valid length L = 32. The original data of (2, 1) is 32'h100e0c0a, and the data after bit wrapping is 32'h07060508, as shown in Figure 4 Then, the reorganization data mask data_length_update_mask = {25{1'b1}, 7{1'b0}} and the wrap-around data mask data_length_wrap_mask = {25{1'b0}, 7{1'b1}} are generated according to the valid data mask, as shown in Figure 5As shown. According to the reconstructed data mask, the high 25 bits of the wrapped data are concatenated with the 7 bits of valid data from the previous clock cycle to form 32 bits of fully valid data. According to the wrapped data mask, the low 7 bits of the wrapped data are left to be concatenated with the data from the following clock cycle to form 32 bits of fully valid data. Similarly, the 14 bits of high-order data of (3,1) are wrapped back to low-order data, and the 18 bits of low-order data are wrapped back to high-order data. The resulting reconstructed data mask data_length_update_mask = {18{1′b1}, 14{1′b0}}, and the resulting wrapped data mask data_length_wrap_mask = {18{1′b0}, 14{1′b1}}. According to the reconstructed data mask, the high 18 bits of the wrapped data are concatenated with the 14 bits of valid data from the previous clock cycle to form 32 bits of fully valid data. According to the wrapped data mask, the low 14 bits of valid data are left to be concatenated with the data from the following clock cycle. Figure 6 As shown, the data streams demodulated from the three OFDM symbols are shifted and concatenated to form 32 bits of fully valid data for three clock cycles and 21 bits of valid data for one clock cycle. These data will continue to be shifted and concatenated with the data demodulated from the subsequent OFDM symbols. Finally, the correct data frame is recovered from the shifted and concatenated data by the byte length indication in the frame header, thus completing the data reception.

[0055] Example 2:

[0056] This example will illustrate the wraparound operation proposed in this invention, which involves shifting the current data based on the offset bit number M of the previous clock cycle, first performing byte shifting and then bit shifting. For example... Figure 7 As shown, the original data (3, 1) is 32'h34302c28. The offset bits of the previous clock cycle are M = 14. Therefore, the data is first shifted by bytes, wrapping the high byte of data back to the low byte and the low 3 bytes back to the high byte, resulting in the shifted data 32'h302c2834. Then, this data is shifted by bits, wrapping the high 6 bits back to the low byte and the low 26 bits back to the high byte, resulting in the shifted data 32'h0b0a0d0c. These two shift operations complete the bit shifting, reducing the consumption of lookup table (LUT) resources and optimizing the timing of the FPGA implementation.

[0057] The preferred embodiments of the present application have been described above in detail. It should be understood that modifications and variations to the present application can be affected by those skilled in the art without departing from the scope of the application. Accordingly, it is intended that all of the subject matter of the above description and the claims be interpreted to encompass all such modifications and changes.

Claims

1. A method for recovering data frames at the MAC layer of an OFDM-PON receiver, characterized in that... Includes the following steps: The ONU receives downlink data broadcast by the OLT and demodulates its own bit data stream from the parallel subcarriers according to the pre-allocated time slots, subcarriers and modulation formats. The bit data streams demodulated from the OFDM symbol subcarriers are concatenated and transmitted with a fixed data bit width; The data is shifted and concatenated by bit shifting and masking operations to ensure that all data in the entire frame is complete and valid except for the data in the last clock tick. The correct data frame is recovered from the shifted and spliced ​​data by using the length indication of the frame header, thus completing the data reception; The bit shifting and masking operation includes the following steps: S1: Length of valid data for each clock tick L The sum is accumulated to obtain the total length. P Offset bits S The bus width is expressed in bits, and it represents the modulo operation. S2: Based on the offset bits of the previous clock cycle M Perform a wraparound operation on the current data, M The most significant bit of data is wrapped around the least significant bit. S - M The low-order bits of data wrap around to the high-order bits; S3: Based on the length of the current clock tick data L Generate a valid data mask, with L Bit valid data, valid data mask is ， S4: Based on the offset bits of the previous clock cycle M The reconstructed data mask is generated by combining the valid data mask of the current clock tick with the reconstructed data mask. ， S5: Generate a wraparound data mask based on the offset bit number M of the previous clock cycle and the effective data mask of the current clock cycle. The wraparound data mask is: ， S6: Based on the wrap-around data of S2, the reassembled data mask of S4, and the wrap-around data mask of S5, the data is shifted and reassembled to ensure that all data in the entire frame except for the data of the last clock beat is valid. The offset bits based on the previous clock cycle M Perform a wraparound operation on the current data, first shifting the bytes, then shifting the bits.

2. The OFDM-PON receiver MAC layer data frame recovery method as described in claim 1, characterized in that, The process of demodulating its own bit data stream from parallel subcarriers When demodulating OFDM symbols, the size of the bit data stream obtained by the ONU is variable, depending on the number of subcarriers allocated and the efficiency of the modulation format.

3. The OFDM-PON receiver MAC layer data frame recovery method as described in claim 2, characterized in that, The size of the bit data stream obtained by the ONU when demodulating OFDM symbols is variable. Therefore, the length of the data after being spliced ​​together from the demodulated data of each subcarrier is not fixed. When transmitting data with a fixed data bit width in the FPGA, the data transmitted in the last clock cycle is not all valid, and the missing data is padded with 0.

4. The OFDM-PON receiver MAC layer data frame recovery method as described in claim 1, characterized in that, The correct data frame is extracted from continuous data by using the length indication of the frame header. After all data has been shifted and spliced, all data except the last clock tick is valid. The frame header has a fixed length indication unit, indicating the payload length of the data frame in bytes.

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