New Quantum-to-the-Home: Achieving Gbits/s Secure Key Rates via...

Research ArticleQuantum-to-the-Home Achieving Gbitss Secure Key Rates viaCommercial Off-the-Shelf Telecommunication Equipment

Rameez Asif12 and William J Buchanan12

1Centre for Distributed Computing Networks and Security School of Computing Edinburgh Napier UniversityEdinburgh EH10 5DT UK2The Cyber Academy Edinburgh Napier University Edinburgh EH10 5DT UK

Correspondence should be addressed to Rameez Asif rasifnapieracuk

Received 20 April 2017 Revised 31 May 2017 Accepted 27 June 2017 Published 6 August 2017

Academic Editor Vincente Martin

Copyright copy 2017 Rameez Asif and William J Buchanan This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

There is current significant interest in Fiber-to-the-Home (FTTH) networks that is end-to-end optical connectivity Currentlyit may be limited due to the presence of last-mile copper wire connections However in near future it is envisaged that FTTHconnectionswill exist and a key offeringwould be the possibility of optical encryption that can best be implemented usingQuantumKeyDistribution (QKD)However it is very important that theQKD infrastructure is compatible with the already existing networksfor a smooth transition and integration with the classical data traffic In this paper we report the feasibility of using off-the-shelftelecommunication components to enable high performance Continuous Variable-Quantum Key Distribution (CV-QKD) systemsthat can yield secure key rates in the range of 100Mbitss under practical operating conditions Multilevel phase modulated signals(119898-PSK) are evaluated in terms of secure key rates and transmission distances The traditional receiver is discussed aided bythe phase noise cancellation based digital signal processing module for detecting the complex quantum signals Furthermore wehave discussed the compatibility of multiplexers and demultiplexers for wavelength division multiplexed Quantum-to-the-Home(QTTH) network and the impact of splitting ratio is analyzedThe results are thoroughly compared with the commercially availablehigh-cost encryption modules

1 Introduction

Theoptical broadbandworld is taking shape and as it does soresearchers are carefully designing the networks and propos-ing the applications it will carry [1 2] Next-generation (NG)services such as cloud computing 3D high definition televi-sion (HDTV) machine-to-machine (M2M) communicationand Internet of things (IoT) require unprecedented opticalchannel bandwidths High-speed global traffic is increasingat a rate of 30ndash40 every year [3] For this very reason theM2MIoT applications will not only benefit from fiber-opticbroadband but also require it Both M2MIoT are using theInternet to transpose the physical world onto the networkedone Bandwidth-hungry applications are driving adoption offiber-based last-mile connections and raising the challenge ofmoving access network capacity to the next level 1ndash10Gbitssdata traffic to the home that is Fiber-to-the-Home (FTTH)

[4] The researchers believe that FTTH is the key to developa sustainable future as it is now widely acknowledged thatit is the only future-proof technology when it comes tobandwidth capacity speed reliability security and scalability

With more and more people using IoT devices and appli-cations data security is the area of endeavor concerned withsafeguarding the connected devices and networks in theIoT Encryption is the key element of data security in NGnetworks It provides physical layer of protection that shieldsconfidential information from exposure to the externalattacks The most secure and widely used methods to protectthe confidentiality and integrity of data transmission arebased on symmetric cryptography Much enhanced secu-rity is delivered with a mathematically unbreakable formof encryption called a one-time pad [5] whereby data isencrypted using a truly random keysequence of the samelength as the data being encrypted In both cases the main

HindawiSecurity and Communication NetworksVolume 2017 Article ID 7616847 10 pageshttpsdoiorg10115520177616847

2 Security and Communication Networks

Table 1 Overview of recent CV-QKD demonstrations

Sr Reference Protocol Receiver bandwidth Repetition rate Transmission distance Secure key rates

(1) J Lodewyck et al (2005) Gaussian 10MHz 1MHz 55 km Raw key rate up to1Mbitss

(2) Qi et al (2007) Gaussian 1MHz 100 kHz 5 km 30 kbitss(3) Y Shen et al (2010) Four-state 100MHz 10MHz 50 km 468 kbitss(4) W Xu-Yang et al (2013) Four-state NA 500 kHz 32 km 1 kbitss(5) Jouguet et al (2013) Gaussian NA 1MHz 805 km 07 kbitss(6) S Kleis et al (2015) Four-state 350MHz 40MHz 110 km 40 kbitss(7) R Kumar et al (2015) Gaussian + classical 10MHz 1MHz 75 km 049 kbitss(8) Huang et al (2016) Gaussian 5MHz 2MHz 100 km 500 bitss(9) S Kleis et al (2016) Four-state 350MHz 50MHz 100 km 40 kbitss(10) Qu et al (2016) Four-state 23GHz 20GHz Back-to-back ge12Mbitss

practical challenge is how to securely share the keys betweenthe concerned parties that is Alice and Bob Quantum KeyDistribution (QKD) addresses these challenges by usingquantum properties to exchange secret information that iscryptographic key which can then be used to encrypt mes-sages that are being communicated over an insecure channel

QKD is a method used to disseminate encryption keysbetween two distant nodes that is Alice and Bob Theunconditional security of QKD is based on the intrinsic lawsof quantum mechanics [6 7] Practically any eavesdropper(ie commonly known as Eve) attempting to acquire infor-mation between Alice and Bob will disturb the quantumstate of the encrypted data and thus can be detected bythe bona fide users according to the noncloning theorem[8] by monitoring the disturbance in terms of quantumbit-error ratio (QBER) or excess noise The quest for longdistance and high bit-rate quantum encrypted transmissionusing optical fibers [9] has led researchers to investigate arange of methods [10 11] Two standard techniques havebeen implemented for encrypted transmission over standardsingle mode fiber (SSMF) that is DV-QKD [12 13] and CV-QKD [14ndash16] DV-QKD protocols such as BB84 or coherentone-way (COW) [17] involve the generation and detectionof very weak optical signals ideally at single photon levelA range of successful technologies has been implementedvia DV-QKD protocol but typically these are quite differentfrom the technologies used in classical communications [18]CV-QKD protocols have therefore been of interest as theseprotocols can make use of conventional telecommunicationtechnologies Moreover the secure key is randomly encodedon the quadrature of the coherent state of a light pulse[19] Such an approach has potential advantages because ofits capability of attaining high secure key rate with modesttechnological resources

During the last few years there has been growing interestin exploring CV-QKD as listed in Table 1 The key featureof this method is the use of a classical coherent receiver thatcan be used for dedicated photon-counting [20] After trans-mission the quadratures of the received signals are measuredusing a shot-noise limited balanced coherent receiver usingeither the homodyne or heterodyne method The lack of anadvanced reconciliation technique at low SNR values limits

the transmission distance of CV-QKD systems to 60 kmwhich is lower than that forDV-QKDsystems [21]The securekey rate of CV-QKD is limited by the bandwidth of thebalanced homodyne detector (BHD) and the performance ofreconciliation schemes which is degraded by the excess noiseobserved at high data rates [22]

In this article we present the initial results based onnumerical analysis to characterize and evaluate the distri-bution of secure data to the subscribers by implementingthe Quantum-to-the-Home (QTTH) concept We have sys-tematically evaluated the performance of using (a) phaseencoded data that is 119898-PSK (where 119898 = 2 4 8 16 ) togenerate quantum keys and (b) limits of using a high-speedBHD in terms of electronic and shot noise for commerciallyavailable coherent receiver to detect the CV-QKD signalsFurthermore the transceivers noise equivalent power (NEP)contributions from analogue-to-digital converter (ADC)and transimpedance amplifier (TIA) are modeled accordingto the commercial off-the-shelf (COTS) equipment Bothsingle-channel and especially wavelength division multi-plexed (WDM) transmissions are investigated We have alsoimplemented (a) local local oscillator (LLO) concept to avoidpossible eavesdropping on the reference signal and (b) aphase noise cancellation (PNC) module for offline digitalsignal processing of the received signals Moreover we havedepicted the trade-off between the secure key rates achievedand the split ratio of the access network considering thehybrid classical-quantum traffic These detailed results willhelp the people from academics and industry to implementthe QTTH concept in real-time networks Furthermore thedesigned system is energy efficient and cost effective

2 Characterization of Alice and Bob forCoherent Transmission

The schematic of the proposed simplified QTTH networkwith 119898-PSK based quantum transmitter (Alice) and LLObased coherent receiver (Bob) is depicted in Figure 1 AtAlice a narrow line-width laser is used at the wavelengthof 1550 nm having a line width of le5 kHz allowing it tomaintain low phase noise characteristics A pseudo-randombinary sequence (PRBS) of length 231 minus 1 is encoded for

Security and Communication Networks 3

Array waveguidegrating

Laser source

m-PSK transmitter(IQ modulator)

Polarizationcontroller

Spectrum analyzer

SMF-28 ber Polarizationcontroller

Signal analyzer

Classical coherentreceiver

FPGADAC(m-PSK symbol mapping)

Tunable optical attenuator

WDM-QKDsignals

Digital signal

processing

Local local oscillator (LLO)Alice Bob

Quantum channel

Figure 1 Schematic of the119898-PSK based quantum transmitter (Alice) and quantum receiver (Bob) for QTTH applications

+

Dow

ncon

vers

ion

DC cancellation Signal analyzer


+

Dow

ncon

vers

ion

DC cancellation

Incoming signal fromquantum channel

Local local oscillator (LLO)

Phase noise cancellation module

(In-phase)2

(Quadrature)2

Figure 2 Schematic of the digital signal processing (phase noise cancellation) module for quantum receiver (Bob)

single-channel transmission and delay decorrelated copiesare generated for the WDM transmission Furthermore weperform pulse shaping at the transmitter according to theNyquist criterion to generate intersymbol interference (ISI)free signals Resultant 1 Gbaud 4-PSK (four-state phase-shift keying) signal is generated after the radio-frequency(RF) signals are modulated via an electrooptical 119868119876 mod-ulator where RF frequency is kept at 2GHz The completemathematical model of CV-QKD protocol is explained inldquoAppendix Ardquo The modulation variance is modeled withthe help of a variable optical attenuator (VOA) just beforethe quantum channel We used the standard single modefiber (SMF-28) parameters to emulate the quantum channeland losses that is attenuation (120572) = 02 dBkm disper-sion (120573) = 165 psnmsdotkm and nonlinear coefficient (120574) =12 kmminus1sdotWminus1 As the QKD transmission occurs at a very lowpower level the impact of optical Kerr effects is consid-ered negligible The polarization mode dispersion (PMD)is considered as le02 psradickm that enables more realisticsimulations that is comparative to the real-world installedfiber networks

For implementing the coherent receiver COTS equip-ment has been modeled The receiver module (Bob) consistsof a 90∘ optical hybrid and a high optical power handlingbalanced photodiodes with 20GHz bandwidth The respon-sivity gain of TIA and noise equivalent power (NEP) of thereceiver at 1550 nm are 08 AW 4KsdotVW and 22 pWradicHzrespectively For our analysis we have kept the high powernarrow line-width local oscillator at the receiver that isintegral part of Bob in order to avoid any eavesdropping onthe reference signal That is why it is termed as local localoscillator (LLO)TheLLOphoton level is considered as 1times108

photons per pulse A classical phase noise cancellation (PNC)based digital signal processing (DSP) is implemented tomini-mize the excess noise as shown in Figure 2ThePNC stage hastwo square operators for in-phase and quadrature operatorsone addition operator and a digital DC cancellation blockassisted by a downconverter The detailed implementationof the PNC module is explained in ldquoAppendix Brdquo [23] Thecoherent receiver requires a specific signal-to-noise ratio(SNR) to detect the119898-PSK signal

As first step we quantified the coherent receiver to detectthe 119898-PSK signals as we know that specific modulation for-mats require a particular optical signal-to-noise ratio (OSNR)in order to be detected at bit-error rate (BER) thresholdAfter modulating the 4-PSK and 8-PSK signals back-to-backsignals are detected at the coherent receiver and normalizedsignal-to-noise ratio (1198641198871198730 the energy per bit to noisepower spectral density ratio) is plotted against BER Theresults are plotted in Figure 3(a) The BER threshold is setto be 38 times 10minus3 (119876-factor of ≃86 dB) corresponding to a7 overhead that is hard-decision forward error correction(HD-FEC) while soft-decision FEC (SD-FEC) level of BER21times10minus2 (119876-factor of ≃66 dB) can also be used correspond-ing to 20 overheard From the results we can depict thatminimum of 10 dB and 6 dB 1198641198871198730 values is required for the8-PSK and 4-PSK signals at HD-FEC while this limit canfurther be reduced to smaller values but at the cost of 20overheard in data rates that is SD-FECWe also investigatedthe ADC requirements to detect the 119898-PSK signals Theresults are plotted in Figure 3(b) The ADC resolution (bits)is investigated with respect to the SNR penalty for 1 and4Gbaud119898-PSK signals From the results it is clear that 6ndash8-bit ADC can be used to detect the 119898-PSK signals at differentbaud rates while keeping the SNR penalty le1 dB It is worth


BER

10minus2

10minus4

10minus6

10minus8

EbN0 (dB)0 2 4 6 8 10 12 14 16 18

SD-FEC

HD-FEC

4-PSK8-PSK

(a)

0

1

2

3

4

5

6

SNR

pena

lty

BER

of10minus3

(dB)

1 Gbaud 4-PSK4 Gbaud 4-PSK


ADC resolution (bits)2 4 6 8 10 12

(b)

Figure 3 Performance comparison of classical data transmissions (a) averaged SNR with respect to 119898-PSK signals at different FEC levelsand (b) SNR penalty with respect to ADC resolution for different baud rates for119898-PSK signals

Table 2 Summary of the ADC minimum requirements to processthe119898-PSK signals

Sr Modulation ADC bandwidth ADC samplingrate (1198791199042)

(1) 4-PSK (4Gbaud) 4GHz 8GSs(2) 8-PSK (4Gbaud) 4GHz 8GSs(3) 8-PSK (266Gbaud) 266GHz 533GSs

mentioning here that high resolution ADCs can give youbetter performance but on the other hand they have highelectronic noise that is not beneficial for high secure keyrates in terms of QTTH We have also summarized the ADCrequirements [24] in terms of ADC bandwidth and ADCsampling rate (1198791199042) as listed in Table 2

3 Results and Discussions

31 Point-to-Point QKD Network Since the noise equivalentpower (NEP) determines electronic noise of the detectionsystem it is essential to select a TIA and ADC with lowerNEP in order to achieve a low electronic noise to shot noiseratio (ESR) In addition as the NEP of the TIA is amplifiedby the TIA itself it dominates the total electronic noiseHowever the ESR negligibly changes as the bandwidth ofthe detector is increased This is because both electronic andshot-noise variances linearly increase with bandwidth so it isbeneficial to use the receivers having 1ndash20GHz bandwidthSince 20GHz receivers are easily commercially availablewe have modeled them for our analysis Furthermore thequantum link comprises the standard SMF and VOA tomodel the channel loss Meanwhile the variance of theexcess noise is mainly due to the bias fluctuation of the119868119876 modulator and timing jitter of the Bob that is receivermodules It is estimated that the excess noise can be limited tobe as small as 001 [25] below the zero key rate threshold Afteroptimizing the transmission model (a) the corresponding

power is asympminus70 dBm [26] (b) the detector efficiency is 60and (c) reconciliation efficiency is 95

Based on the above-mentioned values we extended ourstudies to calculate the secure key rates (SKR) at differenttransmission distances that is transmittance valuesWe havekept the input power constant for every iteration Further-more SKR for both the 4-PSK and 8-PSKmodulation formatsunder collective attack [22] are depicted in Figure 4(a) Themaximum of 100Mbitss SKR can be achieved with this con-figuration by employing COTS modules for transmittance(119879) = 1 for 4-PSK modulation while SKR are asymp25Mbitssand 1Mbits at 119879 = 08 and 06 respectively From the graphit can also be concluded that the maximum transmissionrange for CV-QKD based network is 60 km Hence it isrecommended that this QKD protocol can efficiently be usedfor access network that is QTTH We have also investigatedthe performance of 8-PSK modulation and the results areplotted in Figure 4(a) We have seen degradation in thetransmission performance as compared to 4-PSKmodulationand this is due to the PNC algorithm that is implementedto process the received quantum signal This concept ofgenerating seamless quantum keys can further be enhancedfor wavelength division multiplexed (WDM) networks thatwill help to generate high aggregate SKR via multiplexingthe neighboring quantum channels In this paper we havemultiplexed 12 WDM quantum channels to generate theaggregate SKR with the channel spacing of 25 and 50GHzThe WDM-QKD results based on 4-PSK modulation areshown in Figure 4(b)

The results depict that the classical multiplexing tech-niques can efficiently be used to multiplex quantum signalswithout any degradation in the SKR We have multiplexedthe signals by using 25 and 50GHz channel spacing whileaggregate secure key rate can reach up to 12 Gbitss for a 12-channel WDM quantum system at 119879 = 1 The importanceof these results is due to the fact that next-generationPON services are already aiming at Gbitss data rates soQKD can match the data rates The 50GHz channel spaced


0 10 20 30 40 50 60 70 80Transmission distance ldquoLrdquo (km)

4-PSK8-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101

(a)


1-Ch 4-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101

WDM 4-PSK (50 GHz)WDM 4-PSK (25 GHz)

(b)

Figure 4 CalculatedQKD secure key rates as a function of transmission distance for (a) 4-PSK and 8-PSKmodulation and (b) single-channel(1-Ch) 4-PSK modulation and 12-channel WDM 4-PSK modulation with 25 and 50GHz channel spacing Simulations are performed byassuming 60 detector efficiency and 95 reconciliation efficiency

0 40 80 120 160 200 240Transmission distance ldquoLrdquo (km)

CV-QKD (4-PSK)DV-QKD (T12 protocol)

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

Figure 5 Performance comparison of CV-QKD versus DV-QKDfor access and metro networks

system shows negligible performance degradation as com-pared to single-channel transmission case whereas the25GHz channel spaced system depicts loss in SKR due tothe fact of intersymbol interference between the neighboringchannels This degradation can be easily compensated withthe help of efficient raised-cosine filters for pulse shapingat the transmitter From the results we can also infer thatthe quantum signals are compatible with traditional passiveoptical add-drop multiplexers (OADMs) but the insertionloss from adddrop modules can impact the SKR

A comparison of distance dependent secure key gen-eration rates between CV-QKD using 20GHz BHD andstate-of-the-art DV-QKD systems based on T12 protocol[27 28] is shown in Figure 5 The transmission distance ofCV-QKD systems limited by the lack of advanced recon-ciliation techniques at lower SNR is far lower than that

for DV-QKD demonstrations However comparison of DV-QKD and CV-QKD shows that CV-QKD has the potential tooffer higher speed secure key transmission within an accessnetwork area (100m to 50 km) Especially within 0ndash20 kmrange that is typical FTTH network the SKR generated byusing the traditional telecommunication components are 10 sof magnitude higher than those of DV systems

32 QTTH Network Most of the efforts on the QKD systemdesign and experimental demonstrations are limited to labenvironments and point-to-point transmissions while actualFTTH networks have in-line optical devices including butnot limited to routers switches passive splitters add-dropmultiplexers and erbium doped fiber amplifiers (EDFA)as envisioned in Figure 6(a) This restricts the deploymentof QKD networks along with the classical data channelsHowever in this paper we have investigated the compatibilityof optical network components and their impact on thesecure key rates We have emulated the scenario of a typicalquantum access network as shown in Figure 6(b)

The optical line terminal (OLT) consists of a QKD trans-mitter that is in this paper a 119898-PSK modulated transmitteris modeled The optical distribution comprises (a) standardsingle mode fiber of 5 km length and (b) passive opticalsplitter with different split ratios The commercially availablesplitters have insertion loss that is listed in Table 3 Thevariable splitting ratio is vital for the secure key rates as it willcontribute to the attenuation and excess noise of the systemTo test the simulation model under realistic conditions wehave also added 015 dB splicing loss for every connectionwith the passive optical splitter The results are depicted inFigure 7 where we have plotted the SKR with respect tothe splitting ratio of the system It can be deduced fromthe graph that for a 1 times 2 splitting ratio the SKR dropsdown to asymp10Mbitss per user while the SKR of 1Mbitsscan be achieved with the splitting ratio of 1 times 4 Moreover


Metropolitancore network

Access network

FTTH

FTTH

FTTH

Amplicationregeneration stage

Classical data(a)

Quantum data

QKDOLT

QKDONU

QKDONU

QKDONU

(b)

QKD OLT

QKDONU

QKDONU

QKDONU

Classical OLT

MU

X

Classical dataQuantum dataHybrid trac

DEM

UX

ClassicalONU

ClassicalONU

ClassicalONU

(c)

Figure 6 (a) Deployment of FTTH network with classical optical components (b) downstream and upstream quantum access network and(c) hybrid classical-quantum traffic in access networks

the classical telecommunication components can be usedto design a seamless QTTH network and for short rangetransmission as well as for data center applications it canperform better as compared to the much expensive DV-QKDsystems [10]

33 Hybrid Classical-Quantum Traffic in Access NetworksFor the commercial compatibility of quantum signals withthe existing optical networks the wavelength and optimumpower assignment to the signals are very much importantDifferent wavelength assignment [29ndash31] techniques havebeen investigated to avoid possible intersymbol interference

Table 3 Summary of the average attenuation (dB) associated withthe standard passive optical splitters

Sr Split ratio Average loss (dB)(1) 1 times 2 3 dB(2) 1 times 4 75 dB(3) 1 times 8 11 dB(4) 1 times 16 142 dB(5) 1 times 32 178 dB(6) 1 times 64 211 dB(7) 1 times 128 238 dB


0 2 4 6 8 10 12 14 16Passive split ratio

QTTH network

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

Figure 7 Performance comparison of QTTH network with diversepassive split ratios as a function of achieved secure key rates

between the classical and quantum signals The best possiblesolution is to place the classical channels at 200GHz channelspacing [31] in order to avoid any interference with theweakly powered quantum signals Most importantly we haveimplemented the concept of LLO hence local oscillator signalis not generated from transmitter by using 90 10 coupler[18] So apparently with LLO and 200GHz channel spacingthere is no cross-talk among the hybrid classical-quantumsignals in the quantum channel This is very much ideal forcommercially available telecommunication components inthe C-band (1530 to 1565 nm) Furthermore with 200GHzchannel spacing the classical channels can be encoded upto 400Gbits line rate with advanced modulation formatsthat is dual-polarization 119898-QAM (119898 = 16 32 64 )But most importantly high data rate classical channelsneed sophisticated high bandwidth receivers that inherentlyhave high electronics noise Due to this reason they arenot suitable for quantum multiplexed signals as shownin Figure 6(c) As we are investigating a 20GHz coherentreceiver we have kept the data rate at 25 Gbitspolarizationof quadrature phase-shift keying (119876PSK) signals for classicaldata The power of the classical data channels is optimizedbelow minus15 dBm The quantum channel loss in this analysiscorresponds to the 20 km of the optical fiber The resultsfor quantum signals at diverse wavelengths are depicted inFigure 8Thewavelength windows that are not occupied withthe quantum channels are used for classical data transmissionof 119876PSK signals These signals are efficiently detected belowthe HD-FEC level while the SKR of the quantum signals areasymp10MbitssWe can conclude from the results the compatibil-ity of quantum signals with the classical telecommunicationcomponents Furthermore L-band (1565ndash1625 nm extendedDWDM band) can also be used to generate the hybridclassical-quantum signals as broadband lasers are readilyavailable commercially

4 Conclusion

To summarize we have theoretically established a QTTHtransmission model to estimate the potential of using the

153000 154000 155000 156000Wavelength assignment (nm)

Quantum signals

109

108

107

106

105

104

103

101

102Se

cure

key

rate

s ldquoSK

Rrdquo (b

itss

)

Figure 8 Optimum system performance and wavelength assign-ment for hybrid classical-quantum traffic in an access network

commercially available modules to generate the quantumkeys From the results we can depict that CV-QKD protocolis beneficial for short range transmission distances and it isconcluded that 100Mbitss SKR can be achieved for 119879 = 1while for FTTH networks 25Mbitss SKR can be achievedfor 119879 = 08 that is equivalent 10 km of the optical fibertransmission These key rates are much higher than thecommercially available encrypters based onDVprotocolTheCV-QKD protocol is compatible with network componentslike multiplexers and demultiplexers Due to this benefit wecan multiplex several quantum signals together to transferaggregate high SKR in the range of 1 Gbitss Moreover thesplitting ratio associated with the commercially availableoptical passive splitters influences the SKR and dramaticallydecreases beyond 1 times 8 splitting ratio These results providea solid base to enhance the existing telecommunicationinfrastructure andmodules to deliver end-to-end optical dataencryption to the subscribers

Appendix

A Mathematical Model for CV-QKD Signals

Alice generates random 119898-PSK symbols that can be opti-mized from pseudo-random binary sequence (PRBS) at thetransmitter that is 119868(119905) 119876(119905) isin minus1 +1 These randomsymbols are upconverted to radio-frequency (RF) domainwith corresponding in-phase and quadrature signals [25] thatare denoted by 119878119868(119905) and 119878119876(119905) Mathematically these twocomponents can be expressed as in

119878119868 (119905) = 119868 (119905) cos (1205961119905) minus 119876 (119905) sin (1205961119905) 119878119876 (119905) = 119868 (119905) sin (1205961119905) + 119876 (119905) cos (1205961119905)

(A1)

where1205961 is the RF angular frequencyThe output is then usedas the input of 119868119876 modulator Mach-Zehnder modulator


(MZM) The resultant optical field can be expressed as in(A2) and further simplified as in (A3)

119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)

where 119860 refers to the modulation index and 119875119904 120596 and1205931(119905) represent the power angular frequency of the carrierand phase noise For evaluating the modulation variance 119881119860of the optical signal expressed as shot-noise units (SNUs)the parameter 119860 and variable optical attenuator (VOA) aremodeled To further simply the mathematical model thequantum channel loss is expressed as the attenuation of theoptical fiber Moreover channel introduced noise variance isexpressed as in

120594line = 1119879 + 120598 minus 1 (A4)

where 119879 is the transmittance (relation between transmissionlength and attenuation ie 119879 = 1 for back-to-back and119879 = 02 for 80 km fiber transmission) and 120598 is theexcess noise Practically possible excess noise contributionsexpressed as SNUs [18 32] may come from the imperfectmodulation laser phase noise laser linewidth local oscillatorfluctuations and coherent detector imbalance [33]

In this paper we have used the concept of a local localoscillator (LLO) It is a very vital configuration to keep thelaser at the receiver that is Bobrsquos side in order to preventany eavesdropping attempt on the quantum channel to getthe reference information of the incoming signalThe electricfield of the LLO can be expressed as in

119864LLO (119905) = radic119875LLO119890119895[120596LLO119905+1205932(119905)] (A5)

where 119875LLO 120596LLO and 1205932(119905) represent the power angularfrequency and phase noise of the LLO respectively Thestructure of the Bob comprises a 90∘ optical hybrid andtwo balanced photodetectors The coherent receiver has anoverall efficiency of 120578 and electrical noise of119881el Practically119881elcomprises electrical noise from transimpedance amplifiers(TIA) as well as contribution from the analogue-to-digitalconverters (ADCs)The receiver added noise variance can beexpressed as in

120594det = (2 + 2119881el minus 120578)120578 (A6)

Furthermore the total noise variance of the systemincluding Alice and Bob can be expressed as in

120594system = 120594line + 120594det119879 (A7)

B Digital Signal Processing (DSP) Module

Conventionally in order to detect the weakly poweredincoming quantum signals a high power local oscillator isrequired It is very important to select the local oscillatorwith narrow line width so that the laser fluctuations cannotcontribute to the system excess noise Furthermore it willhelp the coherent receiver to have a low complex digital signalprocessing (DSP) module that is phase noise cancellation(PNC) algorithm As a prerequisite for PNC module thephotocurrents of the in-phase and quadrature signals afterthe balanced photodetectors have to be measured accuratelyMathematically they can be expressed as in

119894119868 (119905)

prop radic2 cos [(120596 minus 120596LO) 119905 + 1205931 (119905) minus 1205932 (119905) + 1205874 ]

minus 119860119868 (119905) cos [(120596 + 1205961 minus 120596LO) 119905 + 1205931 (119905) minus 1205932 (119905)]+ 119860119868 (119876) cos [(120596 + 1205961 minus 120596LO) 119905 + 1205931 (119905) minus 1205932 (119905)]+ 119899119868

119894119876 (119905)

prop radic2 sin [(120596 minus 120596LO) 119905 + 1205931 (119905) minus 1205932 (119905) + 1205874 ]


(B1)

where 119899119868 and 119899119876 define the in-phase and quadrature com-ponents of the additive phase noise that needs to be com-pensated We have implemented the phase noise cancellation(PNC) algorithm [25] By combining the squares of the in-phase and quadrature component of photocurrents as in(B1) that is 1198942119868(119905) + 1198942119876(119905) and cancelling the DC componentthe final result can be expressed as in

119894119878 (119905) prop 2radic2119860119868 (119905) cos(1205961119905 minus 1205874 ) + 2radic2119860119876 (119905)

sdot cos(1205961119905 minus 1205874 ) + 2radic2 119899119868

sdot cos [(120596 minus 120596LO) 119905 + 1205931 (119905) minus 1205932 (119905) + 1205874 ] 119899119876

sdot sin [(120596 minus 120596LO) 119905 + 1205931 (119905) minus 1205932 (119905) + 1205874 ]

(B2)

The final step in the DSP module is to downconvert theRF signalThe resultant in-phase and quadrature componentscan be expressed as in

119903119868 = LPF [119894119878 (119905) cos(1205961119905 minus 1205874 )] = minusradic2119860119868 + 1198991015840119868

119903119876 = LPF [119894119878 (119905) sin(1205961119905 minus 1205874 )] = minusradic2119860119876 + 1198991015840119876

(B3)


where 1198991015840119868 and 1198991015840119876 are the equivalent additive noise that is addedduring the transmission and detection processes prior toDSPmodule By considering (B3) it is concluded that the original119898-PSK signals can be detected without any frequency andphase distortions

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

The authors would like to acknowledge the project researchsupport from Edinburgh Napier University UK for ProjectSTRENGTH (Scalable Tuneable Resilient and EncryptedNext Generation Transmission Hub)

References

[1] R Asif ldquoAdvanced and flexible multi-carrier receiver archi-tecture for high-count multi-core fiber based space divisionmultiplexed applicationsrdquo Scientific Reports vol 6 Article ID27465 2016

[2] Y Ding V Kamchevska K Dalgaard et al ldquoReconfigurableSDM switching using novel silicon photonic integrated circuitrdquoScientific Reports vol 6 Article ID 39058 2016

[3] C LamH Liu B Koley X Zhao V Kamalov andVGill ldquoFiberoptic communication technologies whatrsquos needed for datacen-ter network operationsrdquo IEEE Communications Magazine vol48 no 7 pp 32ndash39 2010

[4] C F Lam ldquoFiber to the home getting beyond 10 Gbsrdquo Opticsand Photonics News vol 27 no 3 pp 22ndash29 2016

[5] R Horstmeyer B Judkewitz I M Vellekoop S Assawawor-rarit and C Yang ldquoPhysical key-protected one-time padrdquo Sci-entific Reports vol 3 Article ID 03543 2013

[6] N Gisin G Ribordy W Tittel and H Zbinden ldquoQuantumcryptographyrdquo Reviews ofModern Physics vol 74 no 1 pp 145ndash195 2002

[7] H-K Lo M Curty and K Tamaki ldquoSecure quantum key dis-tributionrdquo Nature Photonics vol 8 no 8 pp 595ndash604 2014

[8] W K Wootters and W H Zurek ldquoA single quantum cannot beclonedrdquo Nature vol 299 no 5886 pp 802-803 1982

[9] B Frohlich M Lucamarini J F Dynes et al ldquoLong-distancequantum key distribution secure against coherent attacksrdquoOptica vol 4 no 1 p 163 2017

[10] B Frohlich J F DynesM Lucamarini et al ldquoQuantum securedgigabit optical access networksrdquo Scientific Reports vol 5 ArticleID 18121 2015

[11] L C Comandar M Lucamarini B Frohlich et al ldquoQuantumkey distribution without detector vulnerabilities using opticallyseeded lasersrdquoNature Photonics vol 10 no 5 pp 312ndash315 2016

[12] X Ma B Qi Y Zhao and H-K Lo ldquoPractical decoy state forquantum key distributionrdquo Physical Review A - Atomic Molec-ular and Optical Physics vol 72 no 1 Article ID 012326 2005

[13] Y Zhao B Qi X Ma H-K Lo and L Qian ldquoExperimentalquantum key distribution with decoy statesrdquo Physical ReviewLetters vol 96 no 7 Article ID 070502 2006

[14] D B S Soh C Brif P J Coles et al ldquoSelf-referenced con-tinuous-variable quantum key distribution protocolrdquo PhysicalReview X vol 5 no 4 Article ID 041010 2015

[15] P Jouguet S Kunz-Jacques A Leverrier P Grangier andE Diamanti ldquoExperimental demonstration of long-distancecontinuous-variable quantum key distributionrdquoNature Photon-ics vol 7 no 5 pp 378ndash381 2013

[16] D Huang P Huang H Li T Wang Y Zhou and G ZengldquoField demonstration of a continuous-variable quantum keydistribution networkrdquo Optics Letters vol 41 no 15 pp 3511ndash3514 2016

[17] D Stucki C Barreiro S Fasel et al ldquoContinuous high speedcoherent one-way quantum key distributionrdquo Optics Expressvol 17 no 16 pp 13326ndash13334 2009

[18] B Qi L-L Huang L Qian and H-K Lo ldquoExperimentalstudy on the Gaussian-modulated coherent-state quantum keydistribution over standard telecommunication fibersrdquo PhysicalReview A - Atomic Molecular and Optical Physics vol 76 no 5Article ID 052323 2007

[19] I Derkach V C Usenko and R Filip ldquoPreventing side-channeleffects in continuous-variable quantum key distributionrdquo Phys-ical Review A - Atomic Molecular and Optical Physics vol 93no 3 Article ID 032309 2016

[20] Y Painchaud M Poulin MMorin andM Tetu ldquoPerformanceof balanced detection in a coherent receiverrdquoOptics Express vol17 no 5 pp 3659ndash3672 2009

[21] A Leverrier R Alleaume J Boutros G Zemor and PGrangier ldquoMultidimensional reconciliation for a continuous-variable quantum key distributionrdquo Physical Review A - AtomicMolecular and Optical Physics vol 77 no 4 Article ID 0423252008

[22] Y-M Chi B Qi W Zhu et al ldquoA balanced homodyne detectorfor high-rate Gaussian-modulated coherent-state quantum keydistributionrdquo New Journal of Physics vol 13 no 1 Article ID013003 2011

[23] R Asif and W J Buchanan ldquoSeamless cryptographic key gen-eration via off-the-shelf telecommunication components forend-to-end data encryptionrdquo in Proceeding of the 10th IEEEInternational Conference on Internet of Things (iThings) rsquo17Paper ID SITNndash2 June 2017

[24] C-Y Lin R Asif M Holtmannspoetter and B SchmaussldquoNonlinear mitigation using carrier phase estimation and dig-ital backward propagation in coherent QAM transmissionrdquoOptics Express vol 20 no 26 pp B405ndashB412 2012

[25] Z Qu I B Djordjevic and M A Neifeld ldquoRF-subcarrier-assisted four-state continuous-variable QKD based on coherentdetectionrdquo Optics Letters vol 41 no 23 pp 5507ndash5510 2016

[26] A Karlsson M Bourennane G Ribordy et al ldquoSingle-photoncounter for long-haul telecomrdquo IEEE Circuits and DevicesMagazine vol 15 no 6 pp 34ndash40 1999

[27] L C Comandar B Frohlich M Lucamarini et al ldquoRoom tem-perature single-photon detectors for high bit rate quantum keydistributionrdquo Applied Physics Letters vol 104 no 2 Article ID021101 2014

[28] B Korzh C C W Lim R Houlmann et al ldquoProvably secureand practical quantum key distribution over 307km of opticalfibrerdquo Nature Photonics vol 9 no 3 pp 163ndash168 2015

[29] R Asif F Ye and TMorioka ldquo120582-selection strategy in C+L band1-Pbits (448WDM19-core128 Gbitschannel) flex-grid spacedivision multiplexed transmissionrdquo in Proceedings of the Euro-pean Conference on Networks and Communications EuCNC2015 pp 321ndash324 fra July 2015


[30] M Razavi ldquoMultiple-access quantum key distribution net-worksrdquo IEEE Transactions on Communications vol 60 no 10pp 3071ndash3079 2012

[31] S Bahrani M Razavi and J A Salehi ldquoOptimal wavelengthallocation in hybrid quantum-classical networksrdquo in Pro-ceedings of the 24th European Signal Processing ConferenceEUSIPCO 2016 pp 483ndash487 hun September 2016

[32] S Fossier E Diamanti T Debuisschert A Villing R Tualle-Brouri and P Grangier ldquoField test of a continuous-variablequantum key distribution prototyperdquo New Journal of Physicsvol 11 no 4 Article ID 045023 2009

[33] D Huang D Lin C Wang et al ldquoContinuous-variable quan-tum key distribution with 1 Mbps secure key raterdquo OpticsExpress vol 23 no 13 Article ID 017511 pp 17511ndash17519 2015

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of


International Journal of

RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal of

Volume 201

Submit your manuscripts athttpswwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Table 1 Overview of recent CV-QKD demonstrations

Sr Reference Protocol Receiver bandwidth Repetition rate Transmission distance Secure key rates

(1) J Lodewyck et al (2005) Gaussian 10MHz 1MHz 55 km Raw key rate up to1Mbitss

(2) Qi et al (2007) Gaussian 1MHz 100 kHz 5 km 30 kbitss(3) Y Shen et al (2010) Four-state 100MHz 10MHz 50 km 468 kbitss(4) W Xu-Yang et al (2013) Four-state NA 500 kHz 32 km 1 kbitss(5) Jouguet et al (2013) Gaussian NA 1MHz 805 km 07 kbitss(6) S Kleis et al (2015) Four-state 350MHz 40MHz 110 km 40 kbitss(7) R Kumar et al (2015) Gaussian + classical 10MHz 1MHz 75 km 049 kbitss(8) Huang et al (2016) Gaussian 5MHz 2MHz 100 km 500 bitss(9) S Kleis et al (2016) Four-state 350MHz 50MHz 100 km 40 kbitss(10) Qu et al (2016) Four-state 23GHz 20GHz Back-to-back ge12Mbitss

practical challenge is how to securely share the keys betweenthe concerned parties that is Alice and Bob Quantum KeyDistribution (QKD) addresses these challenges by usingquantum properties to exchange secret information that iscryptographic key which can then be used to encrypt mes-sages that are being communicated over an insecure channel

QKD is a method used to disseminate encryption keysbetween two distant nodes that is Alice and Bob Theunconditional security of QKD is based on the intrinsic lawsof quantum mechanics [6 7] Practically any eavesdropper(ie commonly known as Eve) attempting to acquire infor-mation between Alice and Bob will disturb the quantumstate of the encrypted data and thus can be detected bythe bona fide users according to the noncloning theorem[8] by monitoring the disturbance in terms of quantumbit-error ratio (QBER) or excess noise The quest for longdistance and high bit-rate quantum encrypted transmissionusing optical fibers [9] has led researchers to investigate arange of methods [10 11] Two standard techniques havebeen implemented for encrypted transmission over standardsingle mode fiber (SSMF) that is DV-QKD [12 13] and CV-QKD [14ndash16] DV-QKD protocols such as BB84 or coherentone-way (COW) [17] involve the generation and detectionof very weak optical signals ideally at single photon levelA range of successful technologies has been implementedvia DV-QKD protocol but typically these are quite differentfrom the technologies used in classical communications [18]CV-QKD protocols have therefore been of interest as theseprotocols can make use of conventional telecommunicationtechnologies Moreover the secure key is randomly encodedon the quadrature of the coherent state of a light pulse[19] Such an approach has potential advantages because ofits capability of attaining high secure key rate with modesttechnological resources

During the last few years there has been growing interestin exploring CV-QKD as listed in Table 1 The key featureof this method is the use of a classical coherent receiver thatcan be used for dedicated photon-counting [20] After trans-mission the quadratures of the received signals are measuredusing a shot-noise limited balanced coherent receiver usingeither the homodyne or heterodyne method The lack of anadvanced reconciliation technique at low SNR values limits

the transmission distance of CV-QKD systems to 60 kmwhich is lower than that forDV-QKDsystems [21]The securekey rate of CV-QKD is limited by the bandwidth of thebalanced homodyne detector (BHD) and the performance ofreconciliation schemes which is degraded by the excess noiseobserved at high data rates [22]

In this article we present the initial results based onnumerical analysis to characterize and evaluate the distri-bution of secure data to the subscribers by implementingthe Quantum-to-the-Home (QTTH) concept We have sys-tematically evaluated the performance of using (a) phaseencoded data that is 119898-PSK (where 119898 = 2 4 8 16 ) togenerate quantum keys and (b) limits of using a high-speedBHD in terms of electronic and shot noise for commerciallyavailable coherent receiver to detect the CV-QKD signalsFurthermore the transceivers noise equivalent power (NEP)contributions from analogue-to-digital converter (ADC)and transimpedance amplifier (TIA) are modeled accordingto the commercial off-the-shelf (COTS) equipment Bothsingle-channel and especially wavelength division multi-plexed (WDM) transmissions are investigated We have alsoimplemented (a) local local oscillator (LLO) concept to avoidpossible eavesdropping on the reference signal and (b) aphase noise cancellation (PNC) module for offline digitalsignal processing of the received signals Moreover we havedepicted the trade-off between the secure key rates achievedand the split ratio of the access network considering thehybrid classical-quantum traffic These detailed results willhelp the people from academics and industry to implementthe QTTH concept in real-time networks Furthermore thedesigned system is energy efficient and cost effective

2 Characterization of Alice and Bob forCoherent Transmission

The schematic of the proposed simplified QTTH networkwith 119898-PSK based quantum transmitter (Alice) and LLObased coherent receiver (Bob) is depicted in Figure 1 AtAlice a narrow line-width laser is used at the wavelengthof 1550 nm having a line width of le5 kHz allowing it tomaintain low phase noise characteristics A pseudo-randombinary sequence (PRBS) of length 231 minus 1 is encoded for



Laser source



Spectrum analyzer


Signal analyzer




WDM-QKDsignals

Digital signal

processing


Quantum channel


+

Dow

ncon

vers

ion



+

Dow

ncon

vers

ion

DC cancellation




(In-phase)2

(Quadrature)2







BER

10minus2

10minus4

10minus6

10minus8

EbN0 (dB)0 2 4 6 8 10 12 14 16 18

SD-FEC

HD-FEC

4-PSK8-PSK

(a)

0

1

2

3

4

5

6

SNR

pena

lty

BER

of10minus3

(dB)




(b)













4-PSK8-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101

(a)


1-Ch 4-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101


(b)




109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)









Access network

FTTH

FTTH

FTTH


Classical data(a)

Quantum data

QKDOLT

QKDONU

QKDONU

QKDONU

(b)

QKD OLT

QKDONU

QKDONU

QKDONU

Classical OLT

MU

X


DEM

UX

ClassicalONU

ClassicalONU

ClassicalONU

(c)








QTTH network

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)



4 Conclusion



Quantum signals

109

108

107

106

105

104

103

101

102Se

cure

key

rate

s ldquoSK

Rrdquo (b

itss

)



Appendix




(A1)




119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)


120594line = 1119879 + 120598 minus 1 (A4)





120594det = (2 + 2119881el minus 120578)120578 (A6)


120594system = 120594line + 120594det119879 (A7)



119894119868 (119905)



119894119876 (119905)



(B1)






(B2)




(B3)





Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











Laser source



Spectrum analyzer


Signal analyzer




WDM-QKDsignals

Digital signal

processing


Quantum channel


+

Dow

ncon

vers

ion



+

Dow

ncon

vers

ion

DC cancellation




(In-phase)2

(Quadrature)2







BER

10minus2

10minus4

10minus6

10minus8

EbN0 (dB)0 2 4 6 8 10 12 14 16 18

SD-FEC

HD-FEC

4-PSK8-PSK

(a)

0

1

2

3

4

5

6

SNR

pena

lty

BER

of10minus3

(dB)




(b)













4-PSK8-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101

(a)


1-Ch 4-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101


(b)




109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)









Access network

FTTH

FTTH

FTTH


Classical data(a)

Quantum data

QKDOLT

QKDONU

QKDONU

QKDONU

(b)

QKD OLT

QKDONU

QKDONU

QKDONU

Classical OLT

MU

X


DEM

UX

ClassicalONU

ClassicalONU

ClassicalONU

(c)








QTTH network

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)



4 Conclusion



Quantum signals

109

108

107

106

105

104

103

101

102Se

cure

key

rate

s ldquoSK

Rrdquo (b

itss

)



Appendix




(A1)




119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)


120594line = 1119879 + 120598 minus 1 (A4)





120594det = (2 + 2119881el minus 120578)120578 (A6)


120594system = 120594line + 120594det119879 (A7)



119894119868 (119905)



119894119876 (119905)



(B1)






(B2)




(B3)





Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










BER

10minus2

10minus4

10minus6

10minus8

EbN0 (dB)0 2 4 6 8 10 12 14 16 18

SD-FEC

HD-FEC

4-PSK8-PSK

(a)

0

1

2

3

4

5

6

SNR

pena

lty

BER

of10minus3

(dB)




(b)













4-PSK8-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101

(a)


1-Ch 4-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101


(b)




109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)









Access network

FTTH

FTTH

FTTH


Classical data(a)

Quantum data

QKDOLT

QKDONU

QKDONU

QKDONU

(b)

QKD OLT

QKDONU

QKDONU

QKDONU

Classical OLT

MU

X


DEM

UX

ClassicalONU

ClassicalONU

ClassicalONU

(c)








QTTH network

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)



4 Conclusion



Quantum signals

109

108

107

106

105

104

103

101

102Se

cure

key

rate

s ldquoSK

Rrdquo (b

itss

)



Appendix




(A1)




119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)


120594line = 1119879 + 120598 minus 1 (A4)





120594det = (2 + 2119881el minus 120578)120578 (A6)


120594system = 120594line + 120594det119879 (A7)



119894119868 (119905)



119894119876 (119905)



(B1)






(B2)




(B3)





Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











4-PSK8-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101

(a)


1-Ch 4-PSK

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)

109

108

107

106

105

104

103

102

101


(b)




109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)









Access network

FTTH

FTTH

FTTH


Classical data(a)

Quantum data

QKDOLT

QKDONU

QKDONU

QKDONU

(b)

QKD OLT

QKDONU

QKDONU

QKDONU

Classical OLT

MU

X


DEM

UX

ClassicalONU

ClassicalONU

ClassicalONU

(c)








QTTH network

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)



4 Conclusion



Quantum signals

109

108

107

106

105

104

103

101

102Se

cure

key

rate

s ldquoSK

Rrdquo (b

itss

)



Appendix




(A1)




119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)


120594line = 1119879 + 120598 minus 1 (A4)





120594det = (2 + 2119881el minus 120578)120578 (A6)


120594system = 120594line + 120594det119879 (A7)



119894119868 (119905)



119894119876 (119905)



(B1)






(B2)




(B3)





Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











Access network

FTTH

FTTH

FTTH


Classical data(a)

Quantum data

QKDOLT

QKDONU

QKDONU

QKDONU

(b)

QKD OLT

QKDONU

QKDONU

QKDONU

Classical OLT

MU

X


DEM

UX

ClassicalONU

ClassicalONU

ClassicalONU

(c)








QTTH network

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)



4 Conclusion



Quantum signals

109

108

107

106

105

104

103

101

102Se

cure

key

rate

s ldquoSK

Rrdquo (b

itss

)



Appendix




(A1)




119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)


120594line = 1119879 + 120598 minus 1 (A4)





120594det = (2 + 2119881el minus 120578)120578 (A6)


120594system = 120594line + 120594det119879 (A7)



119894119868 (119905)



119894119876 (119905)



(B1)






(B2)




(B3)





Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











QTTH network

109

108

107

106

105

104

103

102

101

Secu

re k

ey ra

tes ldquo

SKRrdquo

(bits

s)



4 Conclusion



Quantum signals

109

108

107

106

105

104

103

101

102Se

cure

key

rate

s ldquoSK

Rrdquo (b

itss

)



Appendix




(A1)




119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)


120594line = 1119879 + 120598 minus 1 (A4)





120594det = (2 + 2119881el minus 120578)120578 (A6)


120594system = 120594line + 120594det119879 (A7)



119894119868 (119905)



119894119876 (119905)



(B1)






(B2)




(B3)





Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











119864 (119905) = cos [119860119878119868 (119905) + 1205872 ] + 119895 cos [119860119878119876 (119905) + 120587

2 ]

sdot radic119875119904119890119895[120596119905+1205931(119905)](A2)

119864 (119905) ≃ radic2119875119904119890119895[120596119905+1198951205874] minus 119860 sdot [119868 (119905) + 119895119876 (119905)]

sdot radic2119875119904119890119895[(120596+1205961)119905+1205931(119905)](A3)


120594line = 1119879 + 120598 minus 1 (A4)





120594det = (2 + 2119881el minus 120578)120578 (A6)


120594system = 120594line + 120594det119879 (A7)



119894119868 (119905)



119894119876 (119905)



(B1)






(B2)




(B3)





Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













Acknowledgments


References



































RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation














RoboticsJournal of





Journal of



RotatingMachinery



Journal of

Volume 201


VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









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