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![Principles of Coherent Communication
Coherent communication technologies mainly include coherent modulation and coherent detection.
Coherent modulation uses the signals that are propagated to change the frequencies, phases, and
amplitudes of optical carriers. (Intensity modulation only changes the strength of light.)
Modulation detection mixes the laser light generated by a local oscillator (LO) with the incoming
signal light using an optical hybrid to produce an IF signal that maintains the constant frequency,
phase, and amplitude relationships with the signal light.
Formula for calculating optical signal electrical field strength:
)]
(
cos[
)
(
)
( t
t
t
A
t
E
where A is the amplitude, ω is the center frequency, and Φ is the phase. Therefore, the modulation
techniques can be: amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift
keying (PSK). Fig 3
The quick oscillations represent the
frequency or phase changes in the
optical carrier.
The figure on the right shows the ASK,
FSK, and PSK modulation techniques.
Page 35](https://image.slidesharecdn.com/opticaltxlec12ppt-250928203804-15ed2e33/85/optical-tx-lec-12-PPT-Presentations-design-pptx-35-320.jpg)
![Principles of Coherent Communication
An optical signal is modulated by its amplitude, frequency or phase with the modulated frequency
(assuming that the modulated frequency is ωs) over an optical carrier. When the optical signal is sent to
the optical receiver, it is mixed with the optical signal produced by the LO ωL. Then the photodetector
detects the mixed signal and produces an electrical signal that satisfies the ωIF = ωs-ωL formula.
According to the propagation theory for plane harmonic waves, the complex electric field distribution for
the received optical signal Es(t) and LO optical EL(t) can be calculated using the following formulas:
)]
(
exp[
)
( L
t
L
j
L
E
t
L
E
)]
(
exp[
)
( s
t
s
j
s
E
t
s
E
where,
Es: amplitude in the electric field of the received optical signal
EL: amplitude in the electric field of the LO optical signal
Φs: modulated phase of the received optical signal
ΦL: modulated phase of the LO optical signal
When Es(t) and EL(t) are parallel to each other and evenly fall onto the surface of the photodetector,
the intensity I of the overall incident light is proportional to [Es(t) + EL(t)]. That is, the following
formula is satisfied:
)
cos(
2
)
( L
S
IF
L
S
L
S t
P
P
R
P
P
R
I
In the formula, R is the response of the photodetector, PS and PL are the power of the
received optical signal and power of the LO optical signal, respectively.
(Formula 1)
(Formula 2)
(Formula 3)
Page 36](https://image.slidesharecdn.com/opticaltxlec12ppt-250928203804-15ed2e33/85/optical-tx-lec-12-PPT-Presentations-design-pptx-36-320.jpg)
optical tx lec 12 PPT Presentations design.pptx
- 1. Session agenda • CDC-F •Coherent VS non coherent system • Power commissioning procedure • PM parameters description
- 2. 2 ALCATEL-LUCENT — PROPRIETARYAND CONFIDENTIAL — RESTRICTED — SOLELY FOR AUTHORIZED PERSONS HAVING A NEED TO KNOW. COPYRIGHT © 2015 ALCATEL-LUCENT. ALL RIGHTS RESERVED. Agenda 1. Terminology 2. Flexibility levels of ROADM nodes and classification 3. Global trends for ROADMs 4. Enabling technologies 5. CDC-F and new ROADM node architectures 6. Trends for the future 7. Conclusions
- 3. Many terminology variantsexist in the industry ! ROADM naming simply means that ‘something ’ is remotely reconfigurable: It does not precise ‘what’. At minimum, transit connections shall be reconfigurable It primarily opposes to Fixed OADMs which are fully static. ‘ROADM’ family includes all below variants: Colored = Fixed-Color (FC, as opposed to Any-Color AC), aka ‘CL’ Fixed-Dir = directional (‘FD’ or just ‘D’, as opposed to Any-Dir AD), aka ‘DL’ Any-Color (AC) = colorless or Tunable OADM, aka ‘CLS’ or ‘TOADM’ Any-Dir (AD) = directionless ROADM, also known as ‘DLS’ CDC-F : Colorless Directionless Contentionless Flex-grid 1- Terminology: Here is how to get ideas clear
- 4. • MANDATORY FORROADM NODES, this is the basic: • transit connections can be remotely reconfigured • OPTIONAL FEATURES FOR ROADM NODES: 1. Color of terminated channels: Any-Color (AC) or colorless, as opposed to FC/colored 2. Direction of terminated channels: Any-Dir (AD), or directionless as opposed to FD/directional • existence of anydirectional A/D block or so called local OTS 3. Optimized for coherent only (extension « -C » in arch. naming): no fixed WDM filters 4. Capability to extract any color from any line port whatever the color of other A/D ports: THIS is contentionless From these options, we define a number of possible ROADM architectures defined in next slides 2- Functionality: flexibility options for ROADM nodes
- 5. A/D Fixed Any-Color colored colorless 1.Color ? 2. Direction ? Fixed Any-Dir Fixed Any-Dir FD-FC AD-FC FD-AC AD-AC A/D options: 3. Coherent Optimized ? No No No No Coh. Coh. CWR8x with SFD WR8x ROADM WR2 ROADM iROADM (just anounced) Config D’/D’’ (WR8x ROADM) TOADM (CWR8x ) AC-D-C (future) D/D’/D’’ (WR8x ROADM) ‘CDC’ or ‘CDC-F’ (F for flexgrid) Examples: 1830 existing and future architectures: Contentionless Contentioned AD-AC-C (future) 2- Classification of ROADMs according flexibility options
- 6. 3- Global trendsROADM Source: Infonetics Research 40G 100G Deployment Strategies: Global Service Provider Survey • We see more and more importance to keep the traffic in the lowest layer. 100G transmission reach is increasing from 1000km to >3000km in commercial deployment . There is no need for extra regeneration. • The flexibility of optical layer is increasing. Photonic ASON/GMPLS and Transport SDN are key technologies. To support this evolution, new kind of photonic node architectures appear, supporting CDC functionalities. trend
- 7. WSS FUNCTIONS • Any color(s)on any WSS port • DROP WSS: distributes the content of an input λ to output ports • ADD WSS: combines the content of input λs to one output port • No Add and Drop ports only at the same time • Per channel power management in addition (equalization) Ports used for dropped channels (e.g. colorless) Common Express ports WSS 1xN Drop WSS WSS Nx1 Ports used for added channels Common Express ports Add WSS DROP ADD WSS No mixed Add/Drop inside a WSS Express IN Add ports WSS 1x4 Express OUT 4- Enabling technologies: What is a Wavelength-Selective Switches (WSS) ?
- 8. mixer mixer ADC DSP Local oscillator (laser) •The Local Oscillator is a laser at the same nominal frequency as the transmitted signal and has the same function as local oscillators in wireless transmissions • Mixer is an interferometric structure used to extract PHASE and AMPLITUDE of EACH optical polarization • ADC (Analog to Digital Converter) is used to digitize the incoming electrical signal, and hand it to the DSP unit which performs demodulation tasks Incoming optical signal Coherent Receiver Output digital stream 4- Enabling technologies: Coherent Receiver
- 9. WDM DEMUX OOK RX (On/OffKeying) COHERENT RX 10G 100G The wavelength is selected directly in the coherent RX by tuning its local laser Coherent demultiplexing allows: • Cost optimization: no need for fixed color demux colorless • No constraint of frequency grid Flex Grid capable NON COHERENT COHERENT POWER SPLIT N lambdas 1 lambda N lambdas N lambdas l selection l selection 4- Enabling technology: Coherent Demultiplexing (OT)
- 10. WSS … l1 ln WSS Coupler WSS-based Tunable Demux TunableROADM: (= colorless, = any-color) • A transponder physically cabled to a given port can be tuned to whatever color • T&ROADM benefit: allows activation or routing of a service without any intervention at intermediate and end-sites (even in case of recoloring) Remotely “Reconfigurable” device (pass-thru can be remotely enabled or blocked) “Directional add/drop ports” (each port adds/drops from/to a fixed direction) “Colorless ports” (each port can be associated to whatever wavelength) From/to other directions Metro: Since 1830PSS R1.0 Core: Since 1830PSS R3.6 Colorless 5 – ROADM architectures: “Colorless” ports, Tunable ROADM
- 11. WSS … l1 ln WSS WSS-based Tunable Demux From/toother directions WSS-based Tunable Mux • T&ROADM with Directionless ports A transponder cabled to a given port can be tuned to whatever color, and can transmit/receive to/from whatever direction Enables remote rerouting of dynamic traffic with minimum deployed resources (existing transponders can be used to transmit/regenerate/recolor whatever wavelength in whatever direction) Enables Photonic Restoration: when a path fails, the same transponder can transmit through an alternative route “Colorless Directionless add/drop ports” • Each port can be associated to: • whatever wavelength • whatever direction Since 1830PSS R3.6 Colorless Directionless 5 – ROADM architectures: T&ROADM with “Directionless” ports
- 12. 5 – ROADMarchitctures: low contention WR8-88 WR8-88 WR8-88 WR8-88 WR8-88 WR8-88 … x8 CWR8-88 CWR8-88 • Multiple A/D blocks can strongly mitigate contention • If # A/D blocks = # DEGREES NO CONTENTION WR8-88 WR8-88 … x8 CWR8-88 CWR8-88 Since 1830PSS R3.6 Colorless Directionless MESH CONNECTIONS: all to all (drawing simplified) … … … … West Line North Line East Line South Line Directionless A/D blocks Directionless A/D blocks Colorless directionless A/D ports N N N N N N Nx1 WSS inside on Tx 1xN WSS inside on Rx 1xN WSS inside on Rx
- 13. NETWORK BLOCKING No availablee2e path in the network using a single λ Principal cause of contention in scarsely meshed networks Cannot be solved by changing A/D block structure CONTENTION INTRA-NODE BLOCKING E2E path in the network using a single λ is available, contention arises in the A/D block Can be either managed or solved by changing A/D block structure 5 – ROADM architectures: Contention types in the photonic layer, not only intra-node
- 14. A B C D A/D contention: Directionless ROADMnode D cannot receive service 2 coming from B on any-dir port 2 Directionless ROADMs Any-Dir Drop port 1: service 1 lk lk A/D contention: Any-Dir Drop port 2 CANNOT terminate service 2 coming from B Service 2 Service 1 5 – ROADM architectures: What a directionless ROADM cannot do
- 15. Directionless (Any Direction)Colorless (Any Color) Transponders Line WSS: N:1 Wavelength Selective Switch Add/drop WSS: Each color available only once North Line South Line West Line East Line DEGREE 4 NODE EXAMPLE Limited WDM spectral efficiency Point of add/drop color contention: Only one drop per color 5 – ROADM architectures: Color contention in traditional directionless colorless ROADM nodes
- 16. CONTENTION IN ADD/DROP • Inthe same WSS device, the same color can only be multiplexed ONCE from a single input port toward the single output port • Intra-node contention only happens in Anydir A/D block (i.e. Directionless ROADMs), not an issue for directional ROADMs To Line WSS N E S W λ1 to S λ1 to W N:1 WSS device λ1 to N λ1 to E N ports 1 port WR8-88 WR8-88 Color Contentions in A/D Single output port = Color Contentions 5 – ROADM architectures: Contention in A/D blocks in colorless directionless ROADM nodes
- 17. K:H DEVICES • Supportmultiplexing toward H different output ports the same optical color from K different input ports • Do not support multiplexing more than one WDM color toward the same output port • Do not support broadcasting the same WDM color toward muliple ports at the same time λ1 to N λ1 to E N E S W λ2 to S λ2 to W K:H device K ports H ports Multiple output ports = Contentionless K:H is key for colorless directionless CONTENTIONLESS (CDC) nodes 5 – ROADM architectures: K:H Multicast Switch devices solve contention
- 18. Line WSS: N:1Wavelength Selective Switch Add/drop MCS: K:H Multicast Switch (K=inputs; H=outputs), each color available “H” times Add/Drop: resources not constrained to a specific direction Transponder: no color constrains to specific ports of the A/D Mux Directionless (Any Direction), Colorless (Any Color) Transponders North Line South Line West Line East Line DEGREE 4 NODE EXAMPLE Optimized WDM spectral efficiency Add/drop color contention solved up to “H” output ports times 5 – ROADM architectures: Colorless Directionless Contentionless node
- 19. No contentionby design Hardware ready to support Flexible Grid Supports up to 192 A/D channels per node in 1830PSS R8.0, pure coherent only, 8 line degrees FIBER SHUFFLE (MSH8-FSM) WR20-TFM WR20-TFM WR20-TFM WR20-TFM MCS8-16 … AMP ARRAY (AAR8A) MCS8-16 AMP ARRAY (AAR8A) Switched-gain amplifiers K:H devices inside A/D allows Multiple times lk Multiple l incl. lk Multiple l incl. lk 5 – ROADM architectures: Colorless Directionless Contentionless (‘CDC’ or ‘CDC-F’) High level architecture 1830PSS R8.0 20x1 WSS inside on Tx/Rx
- 20. 20:1 WSS 8 ports:Line 12 ports: a/d 16:8 (K:H) MCS 4 Bidir Amp WSS WSS WSS WSS WSS Fiber Shuffle Amps 8x16 8x16 8x16 16 Line interfaces 16 Line interfaces (130SCUPC, 130SNX10, 260SCX2) 1 to 16 1 to 16 1 to 8 1 to 8 1 to 8 Amps Amps Amps Amps Amps 1 to 12 blocks 1 to 12 1 to 24 1 to 8 Amps Amps 1 to 12 1 to 12 1 to 12 1 to 12 Colorless add/drop: Up to 192 step 1 (expandable) Optimized for Coherent signals only Ready for Flexible Grid applications (including A/D of Superchannels) Resolving up to H=8 color contention per wavelength A/D block group Line 1 Line 2 Line 3 Line 4 Line 8 WR20-TFM MSH8-FSM AAR8A MCS8-16 New building blocks in 1830PSS Multiple lk Multiple l incl. lk Multiple l incl. lk 5 – ROADM architectures: CDC detailed functional building blocks view
- 21. 2 slotwide Dual 1x20 WSS pack Multi-fiber connectors for connection to Fiber Shuffle 1x20 WSS WTD 2% Line Side (to ingress/egress amps) Duplex LC connection Add/drop (multi-fiber Connectors) 1x20 WSS WTD 5% INV •Signal In/Out ADD1 ADD2 DROP1 DROP2 Simplicity and minimum installation effort CDC building blocks in 1830PSS: TWIN 1x20 WSS ‘WR20-TFM’
- 22. To Fiber Shuffle To MCS card Drop OA Add OA 310 10 3 RS-232 Comms Alarms & Controls Analog controls Power Supplies Disable WSS facing MPO (8 of 12 fibers used) MCS facing MPO OA1 OA2 OA3 OA4 OA5 OA6 OA7 OA8 Due to high insertion losses inherent in the CDC-F architecture the AAR-8A (Amplifier ARray – 8 Amps) is required to amplify up to 16 channels between the Fiber Shuffle and the Multicast Switch. Each AAR-8A provides loss compensation for up to 4-degrees. The AAR-8A connects the MSH8- FSM and the MCS8-16, and provides the correct amount of gain for the channels. Two MPO connectors are supported on the faceplate. AAR8A is 1-slot full height card Separation of the gain block from the multi-cast switch Allows growth from 4-D to 8-D simply by adding another gain block Enables CDC-F architecture with minimal fibering via fiber ribbon plugs CDC building blocks in 1830PSS: ADD/DROP AMPLIFIERS – AAR8A
- 23. To Amps (D1-4) To Amps (D5-8) 16x OT The MCS8-16(MultiCast Switch supporting up to 8-degrees, with 16 client ports) is a 1-slot wide full height card. The 16-client ports are LC-based, while the connections to the Amp Array (AAR-8A) are MPO-based. The card is capable of providing multicasting function for up to 8-optical degrees. Separation of the gain block from the multi-cast switch Allows A/D capacity growth in simple and modular manner Enables CDC-F architecture with minimal fibering via fiber ribbon plugs CDC building blocks in 1830PSS: MULTICAST SWITCH – MCS8-16
- 24. • Provides thefiber shuffle between degrees, to/from the MCS add/drop blocks, and to the expansion layer of the CDC-F ROADM. • Passive, rack mounted 3-RU pizza box style card that handles all of the WSS interconnections including the mesh connections, pre-configured for degree 8 support. • Two ribbon connectors for each dual WSS card (with up to eight WSS cards supported to service eight degrees); each with up to 20 fibers. 3RU To/From WR20-TFM To/From AAR-8A for Degrees 1-4 To/From AAR-8A for Degrees 5-8 Future expansion CDC building blocks in 1830PSS: MSH8-FSM- Meshed Fiber Shuffle
- 25. T X P MESH CONNECTIONS WR8-88 WR8-88 WR8-88 WR8-88 T X P WR8-88 CWR8-88 ITLB SFD44BSFD44B WR8-88 CWR8-88 ITLB SFD44B SFD44B WR8-88 WR8-88 WR8-88 WR8-88 T X P WR8-88 WR8-88 … x8 CWR8-88 CWR8-88 WR8-88 WR8-88 … x8 CWR8-88 CWR8-88 T X P MESH CONNECTIONS MESH CONNECTIONS WR20-TF WR20-TF WR20-TF WR20-TF AMPARRAY … x28 MULTICAST SWITCH MULTICAST SWITCH AMPARRAY • Colored/Directionless A/D blocks allow to change the direction of a service, but not the color, thus limiting re-routing options • Colorless/Directionless A/D blocks allow to change both the color and the direction of a service, but are still prone to contention in case the desired color is already in use in the A/D block • Colorless/Directionless/Contentionless A/D blocks allow to change both the color and the direction of a service without constraints on the desired color TX P TX P TX P TX P Anydir but fixed color Any-Dir, Any-Color Any-Dir, Any-Color, no A/D contention 5 – Directionless ROADM architectures: Compliance with GMPLS & readiness to SDN Conf D’ Conf D CDC
- 26. Provisioning Disaster Recovery Management of Spares OpticalSpectrum Defragmentation • Capacity growth without complex planning (OPEX saving); • Transpdrs assigned without manual operation (no ports re-cabling, OPEX saving) • Transpdrs can be redeployed according changing service demands (OPEX and CAPEX savings) from SDN Ctrlr • Transpdrs can be flexibly reassigned by NMS or GMPLS-CP without on site intervention (OPEX savings) • Spare transpdrs can be shared among all ROADM directions (CAPEX saving) • Spare transpdrs can be supervised and monitored for health (OPEX saving) • Optical Spectrum can be defragmented to maximize the available network capacity (OPEX and CAPEX savings) 5 – ROADM architectures: CDC-F ROADM KEY BENEFITS
- 27. Coherent system features Asmobile networks evolve towards LTE, smart terminals are widely used, and new services such as FBB users' IPTV, VoD, and cloud computing continue to emerge, the transmission capacity of conventional networks cannot meet requirement. To address the requirements, Huawei introduces transmission systems using the coherent technology. Huawei coherent transmission systems use advanced technologies such as ePDM- QPSK, ePDM-BPSK, and coherent detection to meet the high-speed transmission requirements on OSNR, CD tolerance, PMD tolerance, and nonlinear effects. Huawei provides large-capacity coherent solutions, offering ultra-large bandwidths (100G and 40G). A system using a coherent board (such as LSC, LTX, TN15LSXL, TN55NS3, and TN54NS4) is a coherent transmission system. 100G/40G ePDM-BPSK systems are coherent systems. They use DSP chips for coherent detection, delivering superior performance in mitigating dispersion. Therefore, no DCM is required in these systems for dispersion compensation. For 40G DQPSK systems and other non-coherent systems, DCMs are required for dispersion compensation. The DCU board can also be used on the line.
- 28. Coherent system features 1-simply the coherent system in receive uses a local oscillator to generate a laser light that has the same frequency as the received signal , Then the receiver processes the light waves with a synchronous circuit to ensure that the phase of the local laser light is the same as the phase of the received signal. In this manner, the receiver recovers the amplitude, phase, and polarization of the received signal. A coherent system offers better OSNR performance than a non-coherent system. This remarkably extends the 40G/100G transmission distance. 2- in Coherent system u dont care for dispersion, noise, and nonlinear effects because the coherent receiver uses DSP digital signal processing to eliminate interference factors such as dispersion, noise, and nonlinear effects
- 32. Coherent system keytechnologies
- 33. Coherent Tx &Rx system
- 35. Principles of CoherentCommunication Coherent communication technologies mainly include coherent modulation and coherent detection. Coherent modulation uses the signals that are propagated to change the frequencies, phases, and amplitudes of optical carriers. (Intensity modulation only changes the strength of light.) Modulation detection mixes the laser light generated by a local oscillator (LO) with the incoming signal light using an optical hybrid to produce an IF signal that maintains the constant frequency, phase, and amplitude relationships with the signal light. Formula for calculating optical signal electrical field strength: )] ( cos[ ) ( ) ( t t t A t E where A is the amplitude, ω is the center frequency, and Φ is the phase. Therefore, the modulation techniques can be: amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). Fig 3 The quick oscillations represent the frequency or phase changes in the optical carrier. The figure on the right shows the ASK, FSK, and PSK modulation techniques. Page 35
- 36. Principles of CoherentCommunication An optical signal is modulated by its amplitude, frequency or phase with the modulated frequency (assuming that the modulated frequency is ωs) over an optical carrier. When the optical signal is sent to the optical receiver, it is mixed with the optical signal produced by the LO ωL. Then the photodetector detects the mixed signal and produces an electrical signal that satisfies the ωIF = ωs-ωL formula. According to the propagation theory for plane harmonic waves, the complex electric field distribution for the received optical signal Es(t) and LO optical EL(t) can be calculated using the following formulas: )] ( exp[ ) ( L t L j L E t L E )] ( exp[ ) ( s t s j s E t s E where, Es: amplitude in the electric field of the received optical signal EL: amplitude in the electric field of the LO optical signal Φs: modulated phase of the received optical signal ΦL: modulated phase of the LO optical signal When Es(t) and EL(t) are parallel to each other and evenly fall onto the surface of the photodetector, the intensity I of the overall incident light is proportional to [Es(t) + EL(t)]. That is, the following formula is satisfied: ) cos( 2 ) ( L S IF L S L S t P P R P P R I In the formula, R is the response of the photodetector, PS and PL are the power of the received optical signal and power of the LO optical signal, respectively. (Formula 1) (Formula 2) (Formula 3) Page 36
- 37. Principles of CoherentCommunication In general, the LO optical power PL is far higher than PS. Therefore, formula 3 can be simplified as follows: ) cos( 2 L S IF L S L t P P R RP I (Formula 3.1) As shown in the preceding formula, the first expression is a DC constant, and the second expression is the signal current produced after the coherent detection is performed and it includes the signal information transmitted by the transmitter: ) cos( 2 ) ( L S IF L S out t P P R t i (Formula 3.2) Fig 4 Structure of the coherent optical communication system Page 37
- 38. 40G Coherent ePDM-BPSK •40 Bit/s over every wavelength • DGD up to 90 ps at 1 dB penalty in extreme cases (for example, cases in which very old fibers are used) • CD tolerance up to ±60,000 ps/nm at 1 dB penalty • Superior performance in withstanding nonlinear fiber effects, enabling submarine transmission over a distance of 6500 km • Hitless upgrade from existing 10G/40G systems • Capacity up to 80 x 40G and distance >2000 km, achieving the same performance as the 10G ULH technology • Note: The product indicators and specifications covered in this slide are subject to the product documentation. This note applies to the whole document. 21.5 Gbit/s Data Laser Pre- coder Pre- coder 21.5Gb/s Data PBS x y PBC x y PBS Laser 90o Hybrid 90o Hybrid PBS x y ADC DSP Tx Rx Coherent receiver ePDM-BPSK transmitter 0 1 PBS: polarization beam splitter PBC: polarization beam combiner 10G 40G 100G Page 38
- 39. FAQ-1: What IsPDM Modulation? 1. Light is a transverse wave that consists of photons moving in directions perpendicular to the propagation direction. t Signal propagation direction Photon oscillation direction 2. A PBS splits the light into two optical signals in the x and y directions that are perpendicular to each other. • The optical signals in other oscillation directions are filtered out. • The x and y directions are two polarization directions of light. Polarization division multiplexing Theoretically, a light wave can be split into N polarization directions to achieve ultra-high-speed communication, but signals in the N polarization directions are hard to modulate and demodulate. Page 39
- 40. Signal Input I Q Signal Output Phase θ 00 0 1 1 1 1 0 π/4 3π/4 5π/4 7π/4 28Gb/s Data Pre- coder Pre- coder 28Gb/s Data Σ FAQ-2: What Is QPSK Modulation? π/2 Optical signal on the x-pol Sinωt Cosωt I Q + - s(t) =I*Cosωt-Q*Sinωt=√2 Cos(ωt+θ) I Q 00 01 11 10 Schematic representation of the mapping relationship (constellation) The distribution of the signal vector is called a constellation diagram. Because a constellation diagram can fully and clearly depict the mapping relationship of digital modulation, many documents only use a constellation diagram to illustrate digital modulation. Therefore, digital modulation is also called constellation modulation. Code stream I Q QPSK θ Quadrature Phase Shift Keying Four phases with equal spacing, such as π/4, 3π/4, 5π/4, and 7π, are used to carry signals. Page 40
- 41. FAQ-6: What TechnologiesAre Crucial for Coherent Communication? 40G/100G key technologies DSP High speed DSP Advanced modulation (ePDM-QPSK/BPSK) Coherent receiver High performance FEC High speed ADC The high performance FEC algorithm increases the OSNR margin and can provide error correction to ensure 4E-3 BER. The DSP technique reduces CD and PMD effects. High-speed ADC is the core technology and can be provided by only a few vendors at the present time. The advanced modulation format reduces the baud rate for transmission. A coherent receiver can theoretically increase the OSNR by 3 dB. Known as HFEC on the NMS Page 41
- 42. ePDM-QPSK Transmitter CoherentReceiver Schematic Diagram of ePDM-QPSK Modulation The PDM technique reduces the baud rate by 1/4, increases the OSNR margin, and reduces the bandwidth requirements of photonic devices. The coherent receiver uses the LO laser that has the same frequency as the received signal for interference. Through interference between the LO laser signal with the received signal, the receiver restores the phase and polarization state information from the received signal. In addition, the receiver uses the DSP technique to compensate for the CD and PMD. In applications of 100 Gbit/s over single wavelengths, the frequency spacing can be 50 GHz or 100 GHz, improving the spectral efficiency. Dispersion is no longer a factor limiting system transmission because there is no DCM insertion, reducing the requirements on optical amplifiers and system configurations and increasing the OSNR margin. There is no need to use DCMs and existing 10G/40G systems can be losslessly upgraded to 100G systems. Page 42
- 43. ePDM-BPSK Transmitter CoherentReceiver Schematic Diagram of ePDM-BPSK Modulation The PDM technique reduces the baud rate by 1/2, increases the OSNR margin, and reduces the bandwidth requirements of photonic devices. The coherent receiver uses the LO laser that has the same frequency as the received signal for interference. Through interference between the LO laser signal with the received signal, the receiver restores the phase and polarization state information from the received signal. In addition, the receiver uses the DSP technique to compensate for the CD and PMD. Compared with the 40G ePDM-QPSK format, the ePDM-BPSK format offers better performance in mitigating nonlinear effects. In applications of 40 Gbit/s over single wavelengths, the frequency spacing can be 50 GHz or 100 GHz, improving the spectral efficiency. Dispersion is no longer a factor limiting system transmission because there is no DCM insertion, reducing the requirements on optical amplifiers and system configurations and increasing the OSNR margin. There is no need to use DCMs and traditional 10G/40G systems can be losslessly upgraded to coherent 40G systems. Page 43
- 44. Advantages of CoherentCommunication Over Non-coherent Communication Application Coherent Communication Non-coherent Communication 1. DCM-free systems Offers high dispersion tolerance and no DCMs are required, eliminating the necessity of engineering surveys for fiber dispersion and thereby reducing the CAPEX and OPEX. Eliminates the system penalty introduced by DCMs. Offers a low dispersion tolerance. Engineering survey must be performed to learn the fiber dispersion. In addition, DCMs must be used on the line and TDCMs must be used for OTU boards to fine-tune dispersion. DCMs will introduce penalty to the systems. 2. ASON systems Makes ASON rerouting easier and quicker because of high dispersion tolerance. (DSP enables dispersion search to complete within 1000 milliseconds.) Makes ASON rerouting complex because of low dispersion tolerance. Routes selection during rerouting is affected by the dispersion compensation design and therefore rerouting is slow. (TDC adjustment is completed within seconds.) 3. High PMD fiber transmissions Allows for PMD as high as 25-30 ps@1 dB and therefore suitable for most fiber transmissions. Uses DQPSK modules that allow for PMD of 6 ps@1dB and therefore electrical regenerators must be used when high PMD fibers are used, for example, the Telmex project. 4. Low-latency applications Does not require DCMs. The transmission latency only results from fibers and FEC processing. Requires DCMs which introduce latency. For 1000 km transmission, DCMs introduce 1 ms latency. As electrical processing technologies become mature, coherent communication will be the trend of high-speed transmissions. Page 44
- 45. Appearance of 100GCoherent Boards TN12LSC 100G coherent boards Wavelength conversion boards: TN12LSC, TN11LTX Wavelength conversion and regeneration boards: TN11LTX in regeneration mode (no XFP module is configured on the client side of the board) Slot: The TN12LSC board occupies four slots and the first slot represents the board slot on the NMS. The TN11LTX board occupies four slots and the second slot represents the board slot on the NMS. For details, see the product documentation. TN11LTX STAT ACT PROG SRV OUT IN LSC TX RX LSC STAT ACT PROG SRV OUT IN LTX LTX TX2 RX2 TX4 RX4 TX6 RX6 TX8 RX8 TX10 RX10 RX1 TX1 RX3 TX3 RX5 TX5 RX7 TX7 RX9 TX9 Page 45
- 46. Appearance of 40GCoherent Boards 100G coherent line boards Line boards: TN55NS3 boards with PDM-BPSK modules Line boards: TN56NS3 boards with PDM-QPSK modules Slot: The TN55NS3 board occupies two slots and the second slot represents the board slot on the NMS. The TN56NS3 board occupies one slot. For details, see the product documentation. TN55NS3 TN15LSXL 40G coherent tributary/line boards Wavelength conversion boards: TN15LSXL Wavelength conversion and regeneration board: No independent regeneration board. The TN55NS3 line board working in regeneration mode (Relay Mode on the NMS) can be used for electrical regeneration. Slot: The TN15LSXL board occupies three slots and the second (middle) slot represents the board slot on the NMS. For details, see the product documentation. NS3 NS3 STAT ACT PROG SRV IN OUT NS3 NS3 STAT ACT PROG SRV IN OUT TN56NS3 Page 46
Editor's Notes
- #12 In the following slides we will review 4 approaches that can be very effective in mitigating intra-node contention. The first solution is to increase the number of anydir A/D blocks in the node when traffic grows. In the slide we show a 4 degree nodes with 3 anydir A/D blocks. 1830 supports up to 10 degrees where the degree is either a line degree or an anydir A/D block. For example a degree 7 can scale up to 3 anydir A/D blocks, a degree 6 up to 4 and so on. Note that in case line degree = A/D block number, the contention is solved. This approach allows for a very modular solution and can substantially reduce contention
- #13 First of all it’s important to distinguish between the two causes of contention in a network: 1- Network blocking: in this case a WDM demand cannot be routed in because an available e2e path is not available using a single lambda. This is the main cause of contention in lightly meshed networks (average degree ~3) and cannot be solved with any A/D block structure. The only way to deal with this contention cause is to either add additional fibers on a path or to increase the level of meshing in the network 2- Intra-node blocking: in this case a path is available in the network but the required color cannot be used in the existing A/D blocks. This problem can be solved using inherently contentionless A/D blocks that make sure the required color is always available, or can be mitigated using various means In the following slides we will clarify where contention arises in the node and the possible approaches that can be used to mitigate the contention.
- #40 1. Gray code: The QPSK coordinates are four symmetric points on a circle. Using four phases, the QPSK modulation scheme encodes 2-bit symbols. The QPSK coordinates are represented using gray codes as 00, 01, 11, 10 rather than using conventional binary bits (00, 01, 10, and 11). According to the preceding information, gray code is a binary numeral system where two successive values differ in only one bit. The use of gray codes is to minimize the BER. Let us use the phase corresponding to binary digits "11" as an example for illustration. When detecting errors, a conventional modulation system generally checks the 01 and 10 values only. Because there is only one bit error, most of the error processing schemes can restore the correct signal (for example, the conventional FEC can correct one bit error). If conventional bit codes 00, 01, 10, and 11 are used, the data receiver will regard the codes 11 as the adjacent codes 10 or 00. When the receiver regards the codes 11 as 00, the two bits are incorrect and the receive can hardly recover the source signal using an error correction technique. Therefore bit errors are generated. 2. I/Q modulation in the figure I/Q modulation is also called quadrature modulation because the I and Q signals are modulated onto carriers that are perpendicular to each other. One of the carriers used by the I/Q modulation is a cosine wave and the other is a sine wave. The cosine wave is perpendicular to the sine wave, which means they differ by π/2 phase (90 degrees). In the figure, the optical signal on the x-pol is split into two. Assuming that the signal is cosωt (independent of the initial phase), the lower signal is sinωt after the phase is shifted by π/2. The two signals are transmitted in directions perpendicular to each other. 3. Optical communication is a method of transmitting information by mainly using two properties of light: propagation speed and anti-interference capability. Take the laser signal operating at 192.1 THz as an example (the signal can be generated by a laser of which the center wavelength of the laser light is 192.1 THz). The signal transmits 192.1*1012 wavelengths every second. A 40G signal is 43 Gbit/s and that of a 100G signal is 100 Gbit/s, which means 43 or 100 x 109 bits are transmitted every second. Therefore, each signal bit occupies up to one thousand wavelengths of an optical signal. Generally, the waveform of a high-frequency signal is called "envelope".