CN110048983A - A kind of synchronous method of IM/DD-OFDM passive optical network receiver - Google Patents
A kind of synchronous method of IM/DD-OFDM passive optical network receiver Download PDFInfo
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- CN110048983A CN110048983A CN201910297821.9A CN201910297821A CN110048983A CN 110048983 A CN110048983 A CN 110048983A CN 201910297821 A CN201910297821 A CN 201910297821A CN 110048983 A CN110048983 A CN 110048983A
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- ofdm
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0062—Network aspects
- H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
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- Computer Networks & Wireless Communication (AREA)
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- Synchronisation In Digital Transmission Systems (AREA)
Abstract
The invention discloses a kind of synchronous method of IM/DD-OFDM passive optical network receiver comprising the steps of: step 1: passive optical network receiver receives OFDM frame structure；Step 2: OFDM frame structure received to step 1 carries out related operation；Step 3: normalized is done to step 2 calculated result, obtains ratio relative value.The invention avoids correlation peaks to be influenced by distance factor, reduces algorithm occupied resource in Real-time hardware system while not losing and receiving data amplitude information.
Description
Technical field
The present invention relates to a kind of synchronous method, especially a kind of side of synchronization of IM/DD-OFDM passive optical network receiver
Method.
Background technique
In order to cope with other high bandwidth emerging services such as HD video, cloud computing, orthogonal frequency division multiplexing (OFDM) technology quilt
It is introduced into passive optical network (PON).OFDM PON has the advantages such as spectral efficient, the flexible, resisting chromatic dispersion of subcarrier distribution.Its
The OFDM PON that middle intensity modulated directly detects (IM/DD) structure is highly suitable for inexpensive PON application.Therefore OFDM PON at
For the access net solution of next-generation most prospect.
In the communication system based on OFDM technology, timing synchronization (STS) has the bit error rate (BER) performance of system
Very big influence.Intersymbol interference (ISI) can be caused if generating symbol time offset (STO).For this problem, mainstream at present
Scheme be first to send the synchronous training sequence of specific structure before sending OFDM frame, receiving end carries out related calculation to detect amplitude peak
Value, including auto-correlation computation and computing cross-correlation.
Auto-correlation computation utilizes the repetitive structure of OFDM frame start position training sequence, and receiving end is identical by two length
Window to receive data carry out delay auto-correlation.Only when two windows are aligned with training sequence position, have biggish
Thus correlation peak can index out frame start position.And cross-correlation is not required to the training sequence with repetitive structure, passes through a window
Mouth does computing cross-correlation and can find correlation peak to reception data and local sequence.
In above-mentioned two classes relevant way, due to only transmitting real number signal, auto-correlation in IM/DD-OFDM PON system
Operation will lead to noise superposition, it is difficult to generate sharp correlation peak.And computing cross-correlation can solve this problem, but its phase
It closes peak value and depends critically upon reception power, this brings difficulty to the frame start position judgement of receiver.
Summary of the invention
Technical problem to be solved by the invention is to provide a kind of sides of synchronization of IM/DD-OFDM passive optical network receiver
Method, avoid correlation peak is influenced by distance factor.
In order to solve the above technical problems, the technical scheme adopted by the invention is that:
A kind of synchronous method of IM/DD-OFDM passive optical network receiver, it is characterised in that comprise the steps of:
Step 1: passive optical network receiver receives OFDM frame structure；
Step 2: OFDM frame structure received to step 1 carries out related operation；
Step 3: normalized is done to step 2 calculated result, obtains ratio relative value.
Further, OFDM frame structure includes cyclic prefix CP, synchronous training sequence and orthogonal frequency in the step 1
Multiplexed symbols OFDM Symbol.
Further, the synchronous training sequence includes the bipolarity nonreturn to zero code and connect zero that amplitude is a, and even zero setting exists
For making the cross-correlation peak value amplitude of receiving end decay rapidly behind bipolarity nonreturn to zero code.
Further, the step 2 is specially
OFDM frame structure received to step 1 carries out related operation:
Wherein, s (k) is the sequence as bipolarity nonreturn to zero code part in receiving end storage, and r (k) indicates to receive
Data, N are sliding window size, and d and k respectively represent position number in current time and correlation window.
Further, when corresponding position local sequence is 1, cumulative item, which takes, receives data itself；When local sequence be 0, then
Cumulative item is the opposite number for receiving data.
Further, the step 3 is specially
Normalized is done to the calculated result of step 2, obtains ratio relative value:
Wherein, N and m is successively the size and location serial number of average window, and d represents current time.
Further, the N takes 2 integral number power.
Compared with prior art, the present invention having the following advantages that and effect:
1, the present invention passes through normalized calculating, is influenced so as to avoid correlation peak by distance factor, it may be assumed that PON system
Difference caused by different distance user receives the timing synchronization system that power has no effect on this project exploitation in system；
2, synchronous method of the invention has done simplification to traditional related operation, by taking opposite number to replace local sequence and connect
Data multiplication is received, it is occupied in Real-time hardware system algorithm can be reduced while not losing and receiving data amplitude information
Resource.
Detailed description of the invention
Fig. 1 is a kind of OFDM frame structure signal of the synchronous method of IM/DD-OFDM passive optical network receiver of the invention
Figure.
Fig. 2 is the Optical Fiber Transmission structural schematic diagram of the OFDM-PON of the embodiment of the present invention.
Fig. 3 is the correlation peak schematic diagram under the different fiber distances of the embodiment of the present invention.
Fig. 4 is that the correlation peak of the embodiment of the present invention increases curve synoptic diagram with fiber lengths.
Specific embodiment
Below by embodiment, the present invention is described in further detail, following embodiment be explanation of the invention and
The invention is not limited to following embodiments.
As shown in Figure 1, a kind of synchronous method of IM/DD-OFDM passive optical network receiver of the invention, includes following step
It is rapid:
Step 1: passive optical network receiver receives OFDM frame structure；OFDM frame structure includes cyclic prefix CP, synchronous instruction
Practice sequence and OFDM symbol OFDM Symbol.Behind synchronizing sequence, add OFDM symbol (OFDM Symbol)
Information.Total length is consistent with an OFDM data symbol lengths.Synchronous training sequence includes the bipolarity nonreturn to zero code that amplitude is a
With company zero, even zero is arranged in behind bipolarity nonreturn to zero code for making the cross-correlation peak value amplitude of receiving end decay rapidly.
Step 2: the received OFDM frame structure of step 1 carries out related operation:
Wherein, s (k) is the sequence as bipolarity nonreturn to zero code part in receiving end storage, and r (k) indicates to receive
Data, N are sliding window size, and d and k respectively represent position number in current time and correlation window.When corresponding position sheet
Ground sequence is 1, and cumulative item, which takes, receives data itself；When local sequence is 0, then the item that adds up is the opposite number for receiving data.Above formula
In simplification has been done to related operation, by taking opposite number to replace local sequence and receiving data multiplication.Reception number can not lost
According to reduction algorithm occupied resource in Real-time hardware system while amplitude information.
Step 3: normalized is done to step 2 calculated result, obtains ratio relative value:
Wherein, N and m is successively the size and location serial number of average window, and d represents current time.Due to computing cross-correlation
No image of Buddha auto-correlation computation is like that by correlated results divided by data power is received, therefore directly by rear N number of absolute correlated results
Mean value acquires ratio relative value as denominator.Wherein N takes 2 integral number power, can be replaced additionally with shifting function within hardware
Division arithmetic reduces resources occupation rate.When ratio relative value is greater than decision threshold, then current data is frame head synchronous training sequence
First sampled point, the CP before removing training sequence and each OFDM symbol can find OFDM symbol initial position, complete
It is synchronous.
Below by specific embodiment, the present invention will be further described:
Fig. 2 shows the Optical Fiber Transmission structure and corresponding Digital Signal Processing (DSP) operation of OFDM-PON.Hair
Sending end adds frame preamble training sequence, and scaled symbol position cross-correlation STS proposed in this paper is completed in receiving end.Wherein, OFDM-
Transmitter:OFDM transmitter；Offline: off-line data handles part；PRBS: pseudo-random binary sequence；QAM
Mapping: quadrature amplitude modulation mapping；Hermitian Symmetry: hermitian is symmetrical；IFFT: inverse fast fourier transform,
Add head: increase synchronous head；Add CP: increase cyclic prefix；AWG: Arbitrary Waveform Generator；ECL: outside cavity gas laser；MZM:
Mach zhender tune device system；VOA: adjustable optical attenuator；SSMF: standard single-mode fiber；OFDM-Receiver:OFDM is received
Machine；PD: photodetector；Oscilloscope: real-time oscilloscope；Symbol Time Synchronization: Symbol Timing
It is synchronous；Remove CP: cyclic prefix is removed；FFT: Fast Fourier Transform (FFT), Channel Estimation: channel estimation,
QAM demapping: quadrature amplitude modulation demapping.
Power into standard single-mode fiber (SSMF) by adjustable optical attenuator (VOA) fixed attenuation is 0dBm, after making
Continuous experiment condition is consistent.Used here as tri- kinds of length of 7km 24km30km SMF simulated range optical line terminal (OLT) no
Same optical network unit (ONU).
If Fig. 3 is signal after 0km, 7km, 24km and 30km optical fiber, the reception signal correlation peak result of measurement.Its
In the obtained peak value of the first behavior tradition computing cross-correlation, the second row is that scaled symbol position computing cross-correlation obtains peak value.
It can be seen that in Fig. 3, propose method using this project, calculated peak amplitude is not caused by because of transmission range difference
Receive the inconsistent influence of power.Receiver can accomplish the STS transparent to transmission range.
In order to further verify the correctness of STS algorithm, it is bent with the increased variation of fiber lengths that Fig. 4 depicts correlation peak
Line, as shown in the figure.Optical fiber transmission from 0km to 30km, has only decayed 1.98% set forth herein the peak amplitude of algorithm, and demodulate
Planisphere is correct, it was demonstrated that DSP operation in rear end is completed under the premise of accurately finding each OFDM symbol initial position.Its
In, Length of optical fiber: fiber lengths；Peak amplitude: correlation peak.Pr(dBm): different optical fiber
Apart from corresponding received optical power, corresponding points are inserted into the signal constellation (in digital modulation) figure under the fiber distance.
PON is widely used in the occasion that user network access and Industry Control, video monitoring etc. need multicast communication.It is based on
The PON system of OFDM technology can cope with the high bandwidth transmission of current Various Complex business, the demand of flexible dispatching resource.Symbol
Timing Synchronization technology is that first step DSP is operated in OFDM PON physical layer receiver, only accurately finds and receives data frame starting
Position is possible to correctly restore initial data.IM/DD-OFDM PON structure is simple, has lower cost, is suitble to extensive portion
Administration.The PS-CC STS algorithm that the present invention designs solves in IM/DD-OFDM PON system since euclidean distance between node pair is inconsistent, connects
Receive the problem of power difference is larger, and the data frame start position that may cause is judged by accident.
The normalized calculated result of the present invention avoids correlation peak by different due to receiving power caused by distance difference
The influence of cause.It was proved that the algorithm can accurately find OFDM symbol after the transmission of different distance optical fiber in signal
Initial position.Since its structure is simple, complexity is lower, is suitable for the real-time OFDM based on field programmable gate array (FPGA)
PON system.
Above content is only illustrations made for the present invention described in this specification.Technology belonging to the present invention
The technical staff in field can do various modifications or supplement or is substituted in a similar manner to described specific embodiment, only
It should belong to guarantor of the invention without departing from the content or beyond the scope defined by this claim of description of the invention
Protect range.
Claims (7)
1. a kind of synchronous method of IM/DD-OFDM passive optical network receiver, it is characterised in that comprise the steps of:
Step 1: passive optical network receiver receives OFDM frame structure；
Step 2: OFDM frame structure received to step 1 carries out related operation；
Step 3: normalized is done to step 2 calculated result, obtains ratio relative value.
2. a kind of synchronous method of IM/DD-OFDM passive optical network receiver described in accordance with the claim 1, it is characterised in that:
OFDM frame structure includes cyclic prefix CP, synchronous training sequence and OFDM symbol OFDM in the step 1
Symbol。
3. a kind of synchronous method of IM/DD-OFDM passive optical network receiver according to claim 2, it is characterised in that:
The synchronous training sequence includes the bipolarity nonreturn to zero code that amplitude is a and connects zero, and even zero is arranged after bipolarity nonreturn to zero code
Face is for making the cross-correlation peak value amplitude of receiving end decay rapidly.
4. a kind of synchronous method of IM/DD-OFDM passive optical network receiver described in accordance with the claim 1, it is characterised in that:
The step 2 is specially
OFDM frame structure received to step 1 carries out related operation:
Wherein, s (k) is the sequence as bipolarity nonreturn to zero code part in receiving end storage, and r (k) indicates to receive data,
N is sliding window size, and d and k respectively represent position number in current time and correlation window.
5. a kind of synchronous method of IM/DD-OFDM passive optical network receiver according to claim 4, it is characterised in that:
When corresponding position local sequence is 1, cumulative item, which takes, receives data itself；When local sequence is 0, then the item that adds up is to receive data
Opposite number.
6. a kind of synchronous method of IM/DD-OFDM passive optical network receiver described in accordance with the claim 1, it is characterised in that:
The step 3 is specially
Normalized is done to the calculated result of step 2, obtains ratio relative value:
Wherein, N and m is successively the size and location serial number of average window, and d represents current time.
7. a kind of synchronous method of IM/DD-OFDM passive optical network receiver according to claim 4, it is characterised in that:
The N takes 2 integral number power.
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| EP3913875A1 (en) * | 2020-05-22 | 2021-11-24 | Nokia Solutions and Networks Oy | Joint synchronization and equalizer initialization for downstream pon |
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Effective date of registration: 20211215 Address after: 226400 Zhongtian Industrial Park, Hekou Town, Rudong County, Nantong City, Jiangsu Province Patentee after: ZHONGTIAN BROADBAND TECHNOLOGY Co.,Ltd. Patentee after: Zhongtian Communication Technology Co., Ltd Address before: 226400 Zhongtian Industrial Park, Hekou Town, Rudong County, Nantong City, Jiangsu Province Patentee before: ZHONGTIAN BROADBAND TECHNOLOGY Co.,Ltd. |
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