Receiving apparatus in an optical quantum communication system

Abstract

The invention relates to a receiving apparatus (RX) in a quantum optical communication system (1).

Description

[0001] Our reference number: UDE 47749 P DEWO

[0002] Applicant number: NN

[0003] -1-

[0004] Receiving device in an optical quantum communication system

[0005] background

[0006] Increasing digitalization places enormous demands on data transmission. On the one hand, the amount of data to be transmitted is increasing, but on the other hand, it is also evident that an ever-greater proportion of data must be available in a timely manner.

[0007] Therefore, it is foreseeable that high-performance data transmission systems will become increasingly important in the future.

[0008] At the same time, it must also be noted that wired (electrical or optical) data transmission requires costly infrastructure, so it can be assumed that such infrastructure will either only be available in more urban areas or subsidized in less urban areas.

[0009] Wireless transmission systems offer a solution to this problem. However, existing solutions—such as mobile communications—only allow limited data rates. On the other hand, optical microwave links are being established for higher data rates.

[0010] Examples of such technologies are described in the section "Multiantenna techniques" by co-inventor Peter Jung in the book "Advanced mobile communications - Volume 1: Inner physical layer transceiver", pp. 176-518. - ISBN 978-3-11-123909-5, DOI: 10.1515 / 9783111239675. However, no implementations are shown.

[0011] From the article “Diversity with practical channel estimation” by WM Gifford, MZ Win, and M. Chiani, published in IEEE Transactions on Wireless Communications, vol. 4, 2005, no. 4, p. 1935- Our reference: UDE 47749 P DEWO

[0012] Applicant number: NN

[0013] -2- 1947. ISSN 1558-2248, https: / / doi.org / 10.1109 / TWC.2005.852127, describe common radio systems for the case of additive white Gaussian noise (AWGN). The cases discussed there involve a continuous normal distribution.

[0014] • However, the situation is different in optical quantum communication, because this does not have a continuous distribution, but is based on a discrete distribution, in particular a Laguerre distribution or its generalization, or

[0015] • a Bose-Einstein distribution or its generalization, i.e., the negative binomial distribution, or

[0016] • approximately a Poisson distribution or its generalization.

[0017] In the future, the economic importance of wireless optical transmission systems is expected to increase in order to achieve extremely high data rates well beyond 100 Gbit / s.

[0018] Wireless optical transmission systems represent a further development of radio-based transmission systems. It can be assumed that these will be laser-based, meaning that laser diodes will be modulated to transmit data.

[0019] Conventional (classical) optical transmission systems cannot handle this due to the necessary light power on the transmitter side.

[0020] Instead, quantum communication must be used to manage with extremely low light power and thus only a few quanta (photons). Current solutions are based on one-way transmission.

[0021] Recent research, based on the work of the two inventors Peter Jung and Guido Horst Bruck, such as the article "Wireless quantum optical communications with uncorrelated scattering multipath reception," published in ELECTRONICS LETTERS, September 2024, vol. 60, no. 17, also addresses uncorrelated scattering and multipath propagation in optical quantum communication. While the technological background is explored, a solution regarding the Our reference: UDE 47749 P DEWO

[0022] Applicant number: NN

[0023] -3- However, the subject matter of the present invention, as set forth below, is not given. Thus, neither the reception with several, total K d , diversity branches nor the procedure for implementing the subject matter according to the invention.

[0024] However, wireless optical transmission is also affected by multipath propagation. This results in a significant reduction in transmission quality, potentially leading to system failure.

[0025] Object of the invention

[0026] Against this background, it is an object of the invention to provide an improved arrangement that makes it possible to circumvent the previous problems and thus also to enable secure data transmission in multipath propagation.

[0027] The problem is solved by receiving devices according to the invention. Further advantageous embodiments are in particular the subject of the dependent claims, the description and the figures.

[0028] The invention is explained in more detail below with reference to the figures. These show:

[0029] Fig. 1 shows a schematic representation of a transmission system,

[0030] Fig. 2 shows a schematic representation of a receiving device in an optical quantum communication system according to embodiments of the invention, in particular in the case where no diversity reception is present.

[0031] Fig. 3 is a schematic representation of a receiving device in an optical quantum communication system according to embodiments of the invention, particularly in the case of diversity reception. Our reference: UDE 47749 P DEWO

[0032] Applicant number: NN

[0033] -4- Fig. 4 shows a schematic representation of a receiving device in an optical quantum communication system according to embodiments of the invention, in particular in the case where diversity reception is present, and

[0034] Fig. 5 shows a detail of a receiving device in an optical quantum communication system according to embodiments of the invention.

[0035] The invention will now be described in more detail with reference to the figures. It should be noted that different aspects are described, each of which can be used individually or in combination. That is, each aspect can be used with different embodiments of the invention, unless explicitly presented as a pure alternative.

[0036] Furthermore, for the sake of simplicity, reference will generally be made to only one entity at a time. Unless explicitly stated otherwise, the invention may also include several of the entities concerned. Therefore, the use of the words "a", "an", and "one" should only be understood as an indication that at least one entity is used in a simple embodiment.

[0037] Unless explicitly stated otherwise, the following descriptions of procedures stipulate that the individual steps of a procedure can be arranged and / or combined in any order. Furthermore, unless expressly indicated otherwise, the procedures can be combined with one another.

[0038] Information with numerical values ​​should generally not be understood as exact values, but also include a tolerance of + / - 1% to + / - 10%.

[0039] References to standards or specifications are to be understood as references to standards or specifications.

[0040] Specifications that are valid / were valid at the time of filing and / or – insofar as priority is claimed – at the time of the priority application are to be understood as such. However, this does not constitute a general [reference / reference]. Our reference: UDE 47749 P DEWO

[0041] Applicant number: NN

[0042] -5- Exclusion of applicability to subsequent or replacing standards or specifications is to be understood.

[0043] The optimal data detectors proposed according to the invention overcome the dilemma and allow secure quantum-supported data transmission.

[0044] Unlike the prior art, the invention in all embodiments is based on a Laguerre-based transition metric with finitely countable and discrete-value input variables.

[0045] The following terms will be used below:

[0046] OK d (single value, number of diversity branches);

[0047] O

[0048]

[0049] (K d Values, average number of photons of thermal background noise at the receiver input);

[0050] OK d ■ 2 w v different values, average number of signal photons at

[0051]

[0052] Receiver input during a transition from state S to state s i+1 of the multi-way channel);

[0053] o N

[0054]

[0055] ^^ e {0,1 ••• ÄZ max} (K d ■ ((V max + 1) different values, number of photons counted at the receiver input);

[0056] o D (single value, number of modes at the receiver input);

[0057] or] (single value, efficiency of the photon counter at the receiver input); o N d (single value, dark count of the photon counter at the receiver input); can be, for example, in a look-up table - together then K d ■ 2 W P x K d ■ (

[0058]

[0059] N max + 2) Values ​​- are stored

[0060] In embodiments of the invention, aspects such as diversity reception and multimode reception are explicitly included. Our reference: UDE 47749 P DEWO

[0061] Applicant number: NN

[0062] -6- Without limiting the generality of the invention, other graph-based suboptimal data detection methods, such as the M-algorithm, stack algorithm, generalized stack algorithm, etc., may also be considered.

[0063] Before the invention is explained in more detail below, graph-based optimal data detectors will first be briefly explained.

[0064] This study considers optimal data detection in a wireless optical quantum communication system for the case of (uncorrelated) multipath propagation, which causes intersymbol interference (ISI) in the receiver (RX). Examples of such graph-based optimal data detectors include...

[0065] • the optimal sequencing detectors, e.g., using the Viterbi algorithm (VA) or the soft-output Viterbi algorithm (SOVA), and

[0066] • the optimal symbol detectors, e.g., using the Bahl-Cocke-Jelinek-Raviv algorithm; abbreviated.

[0067] BCJR algorithm.

[0068] In multipath propagation over an (uncorrelated) scattering multipath channel, which causes intersymbol interference at the receiver RX, the average number of signal photons depends on the state of the time-discrete combined transmission channel, which is modeled as a finite state machine and is therefore perfectly suited for consideration in optimal data detectors using ML (Maximum Likelihood) and MAP (Maximum a posteriori) data detectors, thereby reducing the adverse effects of intersymbol interference on bit and block error probabilities.

[0069] ML and MAP data detectors, i.e., optimal data detectors, are "forward / backward algorithms." They are based either on the principle of optimal control (Bellman, 1950s), leading to the Viterbi algorithm (VA) or the soft-output Viterbi algorithm (SOVA), or on optimal symbol detection. ML and MAP data detection are used in virtually all mobile phones that support 2G / GSM cellular networks. Our reference: UDE 47749 P DEWO

[0070] Applicant number: NN

[0071] -7-

[0072] It is widely known among communications engineers, especially mobile communications engineers, that failing to take into account intersymbol interference caused by multipath propagation leads in the vast majority of cases to enormous performance losses and system failures.

[0073] Optimal data detectors have become part of textbooks on digital and mobile communications over the last four decades; see, for example, section 3.9, pp. 347-479, in Jung, P.: Advanced mobile communications - Volume 1: Inner physical layer transceiver.

[0074] Berlin: De Gruyter, 2024

[0075] among many others. The discussion of data detectors is based on the modeling of transmission by a finite state machine. The revelation explicitly includes this knowledge.

[0076] The aforementioned optimal data detectors exhibit the following characteristics:

[0077] • the calculation of the transition metric, which is based on the statistics of the channel (likelihood function) and, in the case of MAP schemes, also of the source (a priori probabilities of the data symbols),

[0078] • the forward recursion, which uses the calculated values ​​of the transition metric, • the backward recursion, which can use the calculated transition metric values ​​in the case of optimal symbol detection (BCJR), or does not use the calculated transition metric values ​​in the case of sequence detectors (VA, SOVA), and, • optionally, the soft output generation stage, which calculates the true or approximate log-likelihood ratios (LLRs).

[0079] Starting from the optimality requirements

[0080] • for optimal tracking detectors, which are achieved through b

[0081] o equal to arg maxP J v}|{£>}j are given (ML case), respectively.

[0082] o equal to arg maxP ^{£>}|{ v] are given (MAP case), and

[0083] • for optimal symbol detectors, identified by our mark: UDE 47749 P DEWO

[0084] Applicant number: NN

[0085] -8- o equal to arg max P (ML case) are given, or.

[0086]

[0087] o equal to arg max P {{b_i}|{N̂}} are given (MAP case)

[0088] It follows that the proposed optimal data detectors required for the discussed application differ from the data detectors used, for example, in 2G / GSM mobile communications in the calculation of the transition metric, while the known forward and backward recursions as well as the soft-output generation stage can be reused.

[0089] Mobile phone optimal detectors are based on the likelihood function derived from the Gaussian distribution, which yields the transition metric in the versions by Forney or Ungerboeck.

[0090] However, if one assumes that a single-mode laser is in a coherent (Glauber) state and the background radiation is in a thermal state, then the Laguerre distribution emerges as the correct likelihood function for the case of one-way propagation, i.e., without intersymbol interference (ISI). This result can be found "classically" and using quantum mechanics, i.e., in quantum communication. However, all these results fail to account for multipath propagation and thus also for intersymbol interference, which must be contained.

[0091] Unlike in the prior art, the invention now modifies the aforementioned likelihood function based on the Laguerre distribution by explicitly including the hypothetical average number of signal photons that predominate at the receiver due to multipath reception, referred to as

[0092]

[0093] & Furthermore, the Forney / Ungerboeck transition metrics are replaced by the corresponding transition metrics based on the Laguerre distribution q. ML sj, s i+1 ) (ML case) or q^ MAP s;,s i+1 ) (MAP case). Since the calculation of the transition metrics of mobile phone receivers differs significantly from the case discussed in the invention, the corresponding calculation of the transition metrics is described below.

[0094] The invention makes it possible to modify known radio front ends of transmitters and receivers of conventional radio communication systems (2G, 3G, 4G, 5G,...) using lasers and photon counters. Our reference: UDE 47749 P DEWO

[0095] Applicant number: NN

[0096] -9-replace, as well as modify 2G-based optimal data detectors by incorporating the novel Laguerre-based transition metric.

[0097] Figure 1 shows a general transmission system (for the case without diversity reception). It assumes that data to be transmitted is handed off to a transmitter. The transmitter can then perform processing, such as channel coding, interleaving, etc., before the data is transmitted as a binary data vector to a photon emitter, such as a laser. The photon emitter, e.g., the laser, emits a number of signal photons, for example, Poisson-distributed. The signal photons then travel through the transmission medium. The transmission path represents a linear (uncorrelated) scattering multipath channel.

[0098] Additionally, photons from the thermal background noise (corresponding to a Bose-Einstein distribution) also act on a photon counter, for example a photoconductor, at the receiver. The photon counter delivers a discrete number of photons. This number of photons is then supplied to a receiving device RX according to the invention.

[0099] Figure 2 shows a receiving device RX according to the invention in an optical quantum communication system 1, specifically for the case where no diversity reception is present, i.e. for Kd=1.

[0100] This receiving device RX according to the invention comprises a channel estimation unit CHE, which operates on a photon number vector N to characterize the channel by true or estimated channel parameters, further comprising downstream of the channel estimation unit CHE a calculation unit LLC, which provides likelihood increments based on true or estimated likelihood values ​​without prior information, wherein these likelihood increments are evaluated in a transition metric calculation unit TMC in addition to the photon number vector N to generate transition metric increments q (ML) (5 b s i+1 ) to determine. Our reference: UDE 47749 P DEWO

[0101] Applicant number: NN

[0102] -10- The computing unit LLC, as shown in Figure 5, can include a processing unit CPU, for example a suitable microprocessor, microcontroller, DSP, FPGA, ASIC or a combination thereof, and a look-up table LT.

[0103] In the single-mode case, the following applies:

[0104] - CXJ) A - f Li RT, I - - |

[0105]

[0106] (1 + N a ) Ni - +} 1 + / VJ N a (l + N a ')J or in the multimode case applies

[0107] (N / a) Ni ex ( Zd = l bild') ^(£>-1) ( _ ^d=l N

[0108]

[0109] (1 + N a ~) N i +D ( 1 + N a J Ni \ N^l + Na)

[0110] where in figures 2...4 N dThe mean number of "dark counts" and q denote the efficiency. Obviously, the formula for the single-mode case can be obtained from the formula for the multimode case given above by setting the variable d = l. That is, the multimode case is characterized by d > l.

[0111] This also applies to:

[0112] N a -► r]N a + N d and N

[0113]

[0114] ^ [Sb bi] -> bii + N d

[0115] It should be noted that the number of received signal photons varies over time, particularly due to turbulence during transmission. The rate of this change depends significantly on the speed of movement of the transmitter and receiver, as well as on spatial disturbances along the transmission path. With slow movements, the temporal fluctuation during the transmission of short data bursts is negligible. Otherwise, the aforementioned turbulence leads to temporal fluctuations in the received light intensity / (t). Then, the original, temporally stable value becomes...

[0116]

[0117] b j TO / (t)^ [s . ö .].

[0118] Diversity reception is characterized by the fact that insights regarding a source can be gained using multiple reception units. Instead of individual evaluations, an overall analysis of the insights from the individual reception units is performed. Our reference: UDE 47749 P DEWO

[0119] Applicant number: NN

[0120] -11-More insights can be gained from joint consideration than from individual consideration.

[0121] In the case of diversity reception with K d Diversity branches apply to the logarithmic versions of the transition metric increments.

[0122] K d ( j — i In| f-li + i Af a J z fcrf — 1 (1 + jC l + < d) P kd \ < d \l + < d) )Jj

[0123]

[0124] d) J

[0125] The above size is

[0126] • N- a the at kd -th detector received number of photons,

[0127] •

[0128]

[0129] [sb ■] ' e am ^d' ten Detector present average signal photon number for the transition from s £ after s £+1 and

[0130] • N a a the at k d -th detector mean number of noise photons.

[0131] In the case of multimode mode, the following applies accordingly:

[0132] ' <d ' C i a) 'y D i\i ic,ii ( y D i\i ic,ii / V fkdJ ln - D ln{l + / V ( kdJ ], J. (Dl)

[0133]

[0134] FC d =i.1 + 1 + 1 N a^ l 1 W^ a) (1 + W^ a) )

[0135] The above size is

[0136]

[0137] ] d ' e am ^d' tenDetector present average signal photon number in all modes for the transition from s £ after s £+1 .

[0138] For a very large mode number D » 1 and a small mean noise photon number N a « 1 follows approximately

[0139] (oo \ ~D

[0140]

[0141] n=0 / Our reference: UDE 47749 P DEWO

[0142] Applicant number: NN

[0143] -12-

[0144] / )v (fed) \^ kd) 1 + N^) 1 j ( yD iw^d)

[0145] Äd=l / V M,|s t , / ) t |,di 1 . I / n. ^ v Dd=1 NV ^ (kds) i' b d' d \ | N ^

[0146] N (kd) (1 + Na d ^ W (fc d )[ I ^(fcd) )

[0147]

[0148] The approximate transition metric increments (corresponding to a Poisson distribution) are now as follows.

[0149] • in the single-mode case with one diversity branch

[0150] N

[0151]

[0152] i InpV^ [ s . b .] + N a ] - ln{ / V ( -!} -(A / ^ [ s . b .] + / V ff )

[0153] • in the multimode case with one diversity branch

[0154] (D (D

[0155] + DN a N^[ s . b .i d + DN a

[0156]

[0157] d=ld = l

[0158] • in the single-mode case with / diversity branches

[0159] K d

[0160] y Dvf fcd) ln f Äffi. ö .] + N„ d) ] - In fwf fcd) 11 - (N^. b.} + Ä^ d) )l

[0161]

[0162] kd 1

[0163] and

[0164] • in the multimode case with / f d Diversity branches

[0165] K d r DA / D y / t wf l fed) In J jy / < N^. b.] d + DN a (kd) ( | - In bvf I fed) 11 J - | IT / t N^ H r \ s u. b üi. ] J> d U' + DN" u d)

[0166]

[0167] kd=l ^d=l J \d=l

[0168] Using Stirling's approximation formula

[0169] ln{n!} « n ln{n} — n

[0170] - this allows for a fast and precise approximation for larger n (e.g., n=751 leads to a deviation of less than 1‰) - one also obtains

[0171] In the single-mode case with one diversity branch. Our reference: UDE 47749 P DEWO

[0172] Applicant number: NN

[0173] -13-

[0174]

[0175] + N a ] - ln{W ;} + Ni - (N^ SM + N a )

[0176] • in the multimode case with one diversity branch

[0177] ( DA / D ^ iln Niü*i, b il d + - Ni ln{JV t} + N,- - I [ s . &.] d + DN a j

[0178]

[0179] \d=l ) \d=l ) • in the single-mode case with / diversity branches

[0180] K d [< d) In {jvX ;] + N^} ~ N^ In [N^] + N^ - (N^ iibi] + N^)]

[0181]

[0182] ^d~ 1 and

[0183] • in the multimode case with / < d Diversity branches

[0184] Kd / D x / D y 7V t Cfcd) In y N^. b.] d + DNa*) - N} W In fwf fed) ] + N^ - YN^. b.] d + DN^ fc

[0185]

[0186] d =l vd = l / \d=l

[0187] If, instead of lasers, light sources that emit thermal states are used, as is the case to a good approximation with light-emitting diodes (LEDs), then the following results are obtained with the logarithmic binomial coefficient.

[0188] (- / £) _ 1 + N. U ((D - 1 + 011 In N

[0189]

[0190] l\ iy / i / ) = ln bl ivVj,! m \L) — 11 J 1 JH

[0191] the logarithmic variants of the transition metric increments according to a Bose-Einstein distribution as follows

[0192] • in the single-mode case with one diversity branch

[0193]

[0194] N + N a ] ~ (Ni + 1) ln{l + + N a ]

[0195] • in the multimode case with one diversity branch

[0196] ( D f ( DN n^iici + AO — (Ni + ß) In j 1 + N^ s.ib ^ d + N a

[0197]

[0198] d=l ' V d=l in the single-mode case with / diversity branches Our reference: UDE 47749 P DEWO

[0199] Applicant number: NN

[0200] -14- K d y [< d) ln ö .] + N„ d) ] - (N^ kd) + 1) In f 1 + N^.

[0201] k

[0202]

[0203] d = 1 and

[0204] • in the multimode case with / C d Diversity branches

[0205] + W (fca) ln<'VW ( / ? a) , + JV (fca) + W (fca)

[0206]

[0207] ■d=l

[0208] If one compares the above transition metrics for the same fashion trend and diversity, it is noticeable that the first part of the formula is identical in each case, whereas the last part of the formula differs.

[0209] The channel estimation unit CHE can estimate the channel based on the method of moments. L a In the figures, this denotes a priori information, e.g., a priori log-likelihood ratio (LLR) sequence, which can be provided, for example, by a channel decoder after an initial turbo equalization iteration.

[0210] Using the LLC unit of calculation, (all) transition probabilities based on transition metric increments can therefore be provided while neglecting prior information.

[0211] In general, the calculation can be performed as follows, whereby the single-mode case can subsequently be easily derived from the multi-mode case by setting the number of modes D to 1. In the calculation, it is assumed that N is the number of photons from the photon counter, while N a and

[0212]

[0213] & ] originate from the channel assessment unit CHE.

[0214]

[0215] ln{, V„| • N, - ln{l + N„} ■ N t + D) -

[0216] 1 y _ i J,(DI) ( 1 'V ier U + ■ 2_, N ^s i ,b i ],d + lnlL N . I - + ■ 2_, N ^s i ,b i ],d I d

[0217]

[0218] =l V \ d=l ' ) Our reference: UDE 47749 P DEWO

[0219] Applicant number: NN

[0220] -15- This allows the transition metric to be determined:

[0221] L a ,i = ln {pr{b'=O}}' mit Pr ^ 1 = + Pr ^ 1 = °) = 1 G Nt Pr ^i = 0} =

[0222] 1 - Pr{bj = 0}

[0223] e La - 1 <=> Pr{ö( = 1} = 1

[0224] Prfo = 0} 1 + e La - 1

[0225] <=> 1 = Pr{öj = 0} {1 + e Lai ] <=> Pr{öj = 1}

[0226] 1 Pr{b i = 0} = Pr{b; = 1} =

[0227] 1 + e La > 1 1 + e L, J - 1

[0228] <=> ln{Pr{£>j = 0}} = — ln{l + e La i ] <=> ln{Pr{bj = 1}} = — ln{l + e La <'} Which results in: q (ML) (s;, Sj +1 ) = f(N a , Nf) or q^ AP K Si ,s i+1 ) = IntfAbi = Q}} + f{N a , N^ Sl , bA , N>) =

[0229] ( - ln{l + e La '-} + f(N a , Ä^ [s. A] , M) for = 0

[0230]

[0231] (- ln{l + e~ La i} + f(N a , N^.^, for b t = 1

[0232] As already shown, in embodiments, a receiving device RX in an optical quantum communication system 1 can also have a channel estimation unit CHE, which operates on a photon number vector N to characterize the channel by true or estimated channel parameters, further comprising downstream of the channel estimation unit CHE a computation unit LLC, which provides guess increments based on true or estimated guess values, wherein these guess increments are provided in a transition metric computation unit TMC in addition to the photon number vector N and a priori information L a to be evaluated to determine the transition metric increments q(M>ip)(- s . s.+1 ) zu determine.

[0233] However, as shown in Figure 3, a receiving device RX for diversity reception can also readily provide a plurality of identical logical receiving devices per diversity reception branch. Our reference: UDE 47749 P DEWO

[0234] Applicant number: NN

[0235] -16-each a separate channel estimation unit CHEi... and a separate calculation unit LLCi... shall be provided, with the respective estimated probability increments being made available to a common transition metric calculation unit TMC.

[0236] That is, with the embodiment of Figure 3, a maximum ratio combining (MRC) can be provided.

[0237] Without loss of generality, a physical receiver of the same type can be provided for each of the identical logical receivers. Alternatively, it would also be possible to process sequentially counted photons according to a diversity receiver branch using a physical receiver. Obviously, there can also be hybrid forms; for example, with four (4) diversity receiver branches, two (2) physical receivers could each process two (2) diversity receiver branches.

[0238] In a further embodiment according to Figure 4, a receiving device RX for diversity reception is shown comprising a plurality of identical logical receiving devices per diversity reception branch, each provided with its own channel estimation unit CHEi..., wherein the following are added to the channel estimation units CHEi...A selection unit SEL is provided which selects a diversity receiving branch based on a previously defined selection rule and then provides the photon number vector corresponding to the selected diversity receiving branch, along with the true or estimated channel parameters determined in the associated channel estimation unit, to a common computation unit LLC, wherein the presumption increments provided by the common computation unit LLC are evaluated in a transition metric computation unit TMC in addition to the corresponding photon number vector to determine the transition metric increments q^. MZ 's i ,s i+1 ) to determine.

[0239] For example, the SEL selection device can select the channel that has the greatest value —

[0240]

[0241] ;1 [shown]. Our reference: UDE 47749 P DEWO

[0242] Applicant number: NN

[0243] -17- According to one embodiment, it may also be provided that the transition metric calculation unit TMC, in addition to the photon number vector N, also includes a priori information L a evaluates in order to (instead of q) (ML) (s b S( +1 )) the transition metric increments q(M>ip)(- s . s.+1 ) zu determine.

[0244] According to a further embodiment, the selection device SEL can also select one of the diversity reception branches based on the channel parameters determined by its own channel estimation units CHEi... In an alternative embodiment of the invention, the selection device SEL selects one of the diversity reception branches based on control information supplied from an external source.

[0245] Furthermore, it can be provided that the externally supplied control information originates from a higher communication layer of the quantum communication system 1. For example, a control message providing the control information can be transmitted using suitable protocols.

[0246] Furthermore, it may be provided in the design that the calculation unit LLC has a look-up table LT for determining the presumption increments.

[0247] In particular, in the embodiments of the invention, the probability increments can be both exact and approximate (logarithmic) probability values.

[0248] Furthermore, the a priori information L a exhibit a logarithmic a priori probability ratio sequence.

[0249] It should be noted at this point that all averages b and N aThese values ​​are purely real and non-negative. That is, they represent energies or powers; they do not serve as purely multiplicative weights. Our reference: UDE 47749 P DEWO

[0250] Applicant number: NN

[0251] -18- It should also be noted that a single-receiver case can be provided for. This is particularly important for multimode operation with D ≥ 1, and the transition metric increments disclosed for the first time in this document come into play.

[0252] f N a 1 2jd=l 2jd=l

[0253]

[0254] l J- "r ™ a J 1 + N a N a (l + N a ) Jj in the case of a laser in the transmitter or

[0255] (D f ( D Nn,[ Si ,bi],d + AO — GV; + D) In ​​j 1 + d + N a

[0256]

[0257] d=l ' V d=l in the case of a thermal light source or an LED in the transmitter or with a very large number of modes (D (D

[0258] + DN a N^SiJOild. + DNa

[0259]

[0260] d=ld = l

[0261] or

[0262] ( D 1 / D ml n N^[ S . &.] ;d + DAM — N[ ln{JV t} + - IN^ s.ib ^ d + DN a

[0263]

[0264] Vd=l ' \d=l is used.

[0265] A single-receiver setup is also possible using a selector combiner in both single-mode and multi-mode modes. This involves the use of at least two photon counters, which are switched during reception. Such switching can be initiated in various ways, for example, by signaling or by control from a higher-level protocol layer.

[0266] Finally, it should be noted that in the case of a single recipient as well as in the case of a recipient with multiple diversity branches, both

[0267]

[0268] or the channel coefficients s w as well as N a The timing may fluctuate because the quantum optical transmission channel can exhibit turbulence. Our reference: UDE 47749 P DEWO

[0269] Applicant number: NN

[0270] -19- The receiving device can be set up for single-mode reception as well as for multi-mode reception without further ado.

[0271] The receiving devices proposed according to the invention are unique because they can be precisely adapted to the specific optical transmission channel, in particular optical quantum communication.

Claims

Our reference number: UDE 47749 P DEWO Applicant number: NN -20- Claims 1. Receiving device (RX) in an optical quantum communication system (1), comprising a channel estimation unit (CHE) which operates on a photon number vector (N) to characterize the channel by true or estimated channel parameters, further comprising downstream of the channel estimation unit (CHE) a computation unit (LLC) which provides, without a priori information, guess increments based on true or estimated guess values, wherein these guess increments are evaluated in a transition metric computation unit (TMC) in addition to the photon number vector (N) to generate transition metric increments q (ML) (s i , s i+1 ) to determine.

2. Receiving device (RX) in an optical quantum communication system (1), comprising a channel estimation unit (CHE) which operates on a photon number vector (N) to characterize the channel by true or estimated channel parameters, further comprising downstream of the channel estimation unit (CHE) a computation unit (LLC) which provides guess increments based on true or estimated guess values, wherein these guess increments are provided in a transition metric computation unit (TMC) in addition to the photon number vector (N) and a priori information (L a ) evaluated to determine the transition metric increments q (MAP) (s i ,s i+1 ) to determine.

3. Receiving device (RX) in an optical quantum communication system (1) for diversity reception comprising a plurality of identical logical receiving devices per diversity reception branch, each provided with its own channel estimation unit (CHEi.) and its own computation unit (LLCi.), wherein the respective estimated probability increments are provided to a common transition metric computation unit (TMC).

4. Receiving device (RX) in an optical quantum communication system (1) for diversity reception according to claim 3, characterized in that for each of the identical logical receiving devices an identical physical receiving device is provided. Our reference number: UDE 47749 P DEWO Applicant number: NN -21- is provided.

5. Receiving device (RX) in an optical quantum communication system (1) for diversity reception comprising a plurality of identical logical receiving devices per diversity reception branch, each provided with its own channel estimation unit (CHEi.), wherein a selection device (SEL) is provided downstream of the channel estimation units (CHEi.) which selects a receiving channel based on a previously defined selection rule and then provides the photon number vector corresponding to the selected receiving channel, together with the true or estimated channel parameters determined in the associated channel estimation unit, to a common computing unit (LLC), wherein the presumption increments provided by the common computing unit (LLC) are evaluated in a transition metric computing unit (TMC) in addition to the corresponding photon number vector to determine the transition metric increments q(ML) (s i , s i+1 ) to determine.

6. Receiving device (RX) in an optical quantum communication system (1) for diversity reception according to claim 5, in which the transition metric calculation unit (TMC) receives, in addition to the photon number vector (N), an a priori information (L a ) evaluates to determine the transition metric increments q MAP st, s i+1 ) to determine.

7. Receiving device (RX) in an optical quantum communication system (1) for diversity reception according to claim 5 or claim 6, characterized in that the selection device (SEL) selects one of the diversity reception branches based on the channel parameters determined by its own channel estimation units (CHEi.).

8. Receiving device (RX) in an optical quantum communication system (1) for diversity reception according to claim 5 or claim 6, characterized in that the selection device (SEL) selects one of the diversity reception branches based on control information supplied from outside.

9. Receiving device (RX) in an optical quantum communication system (1) for diversity reception according to claim 8, characterized in that the externally supplied control information is processed by a higher communication layer of the Our reference number: UDE 47749 P DEWO Applicant number: NN -22- quantum communication system (1) originates.

10. Receiving device (RX) in an optical quantum communication system (1) according to one of the preceding claims, characterized in that the computation unit (LLC) has a look-up table (LT) for determining the probability increments.

11. Receiving device (RX) in an optical quantum communication system (1) according to one of the preceding claims, characterized in that the probability increments are exact or approximate logarithmic probability values.

12. Receiving device (RX) in an optical quantum communication system (1) according to one of the preceding claims, characterized in that the a priori information (L a ) exhibits a logarithmic a priori probability ratio sequence.

13. Receiving device (RX) in an optical quantum communication system (1) according to one of the preceding claims, characterized in that the receiving device is configured for single-mode reception.

14. Receiving device (RX) in an optical quantum communication system (1) according to one of the preceding claims, characterized in that the receiving device is configured for multimode reception.

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