- 1. > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER
(DOUBLE-CLICK HERE TO EDIT) < 1 AbstractFor the first time, time
packing technique is exploited for Tb/s super-channel field trial
transmission over long-haul distances. The transmission is
successfully performed on an installed Australian link between
Sydney and Melbourne composed by 995 km of uncompensated SMF with
real coexistent traffic. 40 and 100 Gbit/s co-propagating channels
are transmitted together with the super-channel in a 50 GHz ITU-T
grid without additional penalty. The super-channel encompass eight
sub-channels with low-level modulation format, i.e. DP- QPSK,
guaranteeing better OSNR robustness and reduced complexity with
respect to higher order formats. At the receiver side coherent
detection is exploited together with concatenated multiple state
BCJR detectors and LDPC decoder. A record (spectral efficiency x
distance) product of 9353 bit/s/Hzkm is achieved for a field trial
demonstration in a loop back configuration. Moreover, a 1 Tb/s
DP-DQPSK super-channel is successfully transmitted between Sydney
and Melbourne within four WSS slots (200 GHz). A maximum SE of 5.6
bit/s/Hz is achieved with an OSNR=15.8 dB. The system reliability
is proven through long term measurement. Index TermsOptical fiber
communication, Coherent communications, Optical fiber networks,
Differential phase shift keying, Adaptive coding. I. INTRODUCTION
ARRIERS around the world are seeing unparalleled growth in demand
driven by video and take-up of smart devices. In order to fulfill
market demand, optical transport networks need to improve in term
of flexibility, power consumption, and capacity. Being able to
support increasing spectral efficiency (SE) on installed fiber is
critical in allowing Carriers to leverage their existing
investments. Several techniques have been proposed to increase the
SE such as This work was supported in part by COTONE FIRB 2010
RBFR1040HM project and ARNO PAR FAS 2007-2013 project. L. Pot, G.
Meloni and T. Foggi are with the CNIT Photonic Networks National
Lab, via Moruzzi 1, 56124 Pisa, Italy (e-mail: [email protected]).
G. Berrettini, F. Fresi and M. Secondini are with Scuola Superiore
SantAnna, TECIP, via Moruzzi 1, 56124 Pisa, Italy. L. Giorgi and F.
Cavaliere are with Ericsson Research, via Moruzzi 1 56124 Pisa,
Italy. S. Hackett, A. Petronio, P. Nibbs and R. Forgan are with
Ericsson Australia, 818 Bourke Street, Docklands, Melbourne,
Australia. A. Leong, R. Masciulli and C. Pfander are with Telstra
Corporation Limited, 35 Collins Street, Melbourne, Australia.
Nyquist wavelength division multiplexing (WDM) [1], orthogonal
frequency division multiplexing (OFDM) [2], and
time-frequency-packing (TFP) [3]. Both Nyquist-WDM and OFDM
solutions, whose performance and complexity are basically
equivalent on the fiber-optic channel [4], employ orthogonal
signaling. In both cases, the orthogonality condition set a lower
limit to time- and frequency-spacing (the Nyquist criterion), such
that the achievable spectral efficiency is limited by the number of
levels of the underlying modulation format. In fact, higher
spectral efficiency requires higher-level modulation, e.g.,
16-quadrature amplitude modulation (QAM), with higher complexity
and lower resilience to signal-to-noise ratio (SNR) degradation and
nonlinear effects. As a theoretical upper bound in term of SE, the
Nyquist-WDM approach allows a channel spacing equal to the
baud-rate, avoiding both cross-talk due to inter carrier
interference (ICI) and inter-symbol interference (ISI). This
technique consists in transmitting channels having a rectangular
spectrum with a bandwidth equal to the baud-rate. Thus, channels at
different wavelengths do not overlap (ICI is avoided) and ISI does
not occur at the optimum sampling instant due to the sinc shaped
time pulse. However, the concept of Nyquist-WDM would require the
use of a very specic optical spectral shaping, i.e., specic optical
lters, as discussed in [5]. Typically, fourth-order super-Gaussian
optical lters are used rather than ideal rectangular ones and small
guard bands must be considered, thus reducing the theoretical
achievable SE. Alternatively, Nyquist-WDM can also be obtained by
electrically shaping the modulator driving signals through analogue
filters or digital signal processing (DSP) by means of high speed
digital-to-analog converters (DACs) at the transmitter side. In the
former case, a quasi- rectangular shape is obtained by accepting a
bandwidth increase between 20-25%, that reduces the SE. In the
latter, the complexity and cost of the transmitter is increased due
to the requirements in terms of electrical bandwidth and sampling
rate for the DAC. All the above mentioned techniques cannot provide
an ideal rectangular shape due to technology limitations [6]. TFP
represents a different approach with respect to traditional
communications. TFP is a specific and practical implementation of
the faster-than-Nyquist (FTN) signaling technique [7], which allows
to overcome the Nyquist limit, High Spectral Efficiency Field Trial
Using Time-Packed Terabit/s DP-DQPSK Super- Channel Within Fixed
ITU-T Grid L. Pot, Member, IEEE, G. Meloni, G. Berrettini, F.
Fresi, T. Foggi, M. Secondini, L. Giorgi, F. Cavaliere, S. Hackett,
A. Petronio, P. Nibbs, R. Forgan, A. Leong, R. Masciulli, C.
Pfander, C
2. > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER
(DOUBLE-CLICK HERE TO EDIT) < 2 giving up the orthogonality
condition both in the time and frequency domains at the expense of
unlimited complexity receiver. In the TFP system, the receiver
complexity is fixed and a small performance degradation is
accepted. By TFP higher SE can be achieved with low-level
modulations [3][8][9], e.g., dual polarization quadrature phase
shift keying DP-QPSK), offering better performance in terms of
bandwidth requirement, energy efficiency, cost, and reliability.
Moreover, TFP assures the lowest requirements in term of electrical
bandwidth both at the transmitter and receiver, together with the
maximum degree of flexibility, and a full compatibility with
existing wavelengths extends current installed infrastructure
beyond 100 Gb/s, with minimal need for infrastructure renewal. In
order to increase link capacity and satisfy communication needs in
terms of data rate, distance, and flexibility, orthogonal
techniques have been used in experimental demonstrations in
combination with optical space, time, polarization, and wavelength
division multiplexing (SDM, OTDM, PDM, WDM). In particular, the
highest symbol rate of 160 Gbaud exploiting OTDM and the largest
single channel bit rate of 768 Gbit/s using dual polarization
(DP)-64QAM have been demonstrated in [10] and [11], respectively.
In terms of system capacity, a record value of 105 Tbit/s has been
demonstrated in [12] using multi-core fiber. On the other hand,
long propagation distances are also addressed. In [13] the authors
experimentally demonstrated transmission of a 4 Tbit/s
super-channel over a 12000 km link with time-domain hybrid
QPSK-8QAM modulation format. Moreover, the highest spectral
efficiency of 32 bit/s/Hz has been obtained through PDM-16QAM
coherent transmission over 12 spatial and polarization modes of a
few-mode fiber [14]. Among field trial demonstrations, in [15] they
demonstrated 21.7 Tbit/s using a DP-8QAM/QPSK modulation format
over 1503km with a maximum SE of 5.26 b/s/Hz while in [16] they
demonstrated DP-8QAM and DP-16QAM transmission over real installed
links of 1822 km and 634 km, respectively, with very high total
capacity and a SEdistance (d) product of about 9000 [bit/s/Hzkm].
In this paper, we successfully demonstrate time-packed (TP)
transmission over an uncompensated installed link between Sydney
and Melbourne operated by Telstra including 100 GHz spaced 40 and
100 Gbit/s real co-propagating traffic. Resorting to information
theoretic principles and advanced signal processing techniques, we
optimized sub-channel bandwidths and inter-channel spacing, thus
maximizing the SE, achieving a SEd record for field trial
demonstration of 9353 [bit/s/Hzkm] with an optical SNR (OSNR) of
14.8 dB. Moreover, 1 Tb/s DP-DQPSK super-channel was successfully
transmitted through single mode fibers (SMFs) within 200 GHz of
spectral occupancy, with an OSNR=15.6 dB. A maximum SE of 5.6
bit/s/Hz was demonstrated with an OSNR of 15.8 dB. In order to
verify the system robustness performances were measured including
artificial PMD addition and long term measurements confirmed the
system reliability. The paper is organized as follows. Section II
describes TFP principle of operation giving an example of a
possible practical transceiver implementation. In section III the
details of the implemented system and the installed link are
described. Section IV collects field trial detailed results
including single way transmission, long-term measurements, and
loopback transmission. II. TIME-FREQUENCY PACKING The concept TFP
is here described through a graphical representation of the signal
both in the time and the frequency domains. A. Time Packing A
binary signal is obtained through a sequence of pulses with given
shape, amplitude 1 or 0, and time duration T=1/R where R is the
signaling rate. The spectral content of the signal is entirely
confined within the bandwidth B providing a spectral efficiency SE=
R/B [b/s/Hz]. By keeping the same bandwidth it is possible to
increase the rate R>R (T=1/R R/B. Similarly, SE can be increased
by keeping fixed R and filtering the signal with a bandwidth B
2R/Bt (see Fig. 2). Even in the case spectral overlap, FTN theory
[7] gives a way for eliminating the impact of ICI through a proper
code and using an unlimited complexity receiver. As for the T t
s(t) T t s(t) ISI 1 1 10 1 1 10 3. > REPLACE THIS LINE WITH YOUR
PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 3 time
packing case, also in the frequency space if a small amount of ICI
can be tolerated, TFP provides a practical code for a fixed
receiver complexity. In this case, differently from time packing, a
multiple-carrier system must be employed that allows to increase
coding efficiency due to correlation among adjacent channels. Fig.
2. Frequency packing principle The two techniques can be combined
in the TFP with a consequential increase of the SE. SE enhancement
will be a compromise between the code rate and the acceptable
performance degradation caused by ISI, ICI, and transmission
impairments. Moreover due to the possibility of code rate
adaptation without any change in the transmitter and receiver
hardware, TFP provides large flexibility to the system. In the
following we will consider TP due to single-user receiver
constraint. A simple example of practical TP transceiver for a 40
Gbaud system is shown in Fig. 3. In order to generate a DP-DQPSK
exploiting TP each polarization includes two data streams at 34.6
Gbit/s. A typical 4% FEC and a 9/10 binary encoder are used giving
a gross transmission rate of 40 Gbit/s per quadrature and 80 Gbit/s
per polarization. The transmitter assembles a total gross capacity
of 160 Gbit/s for a net information rate of 138.4 Gbit/s within an
optical bandwidth of 20 GHz, giving a SE=6.92. TP is simply
obtained through 10 GHz low-pass filtering. Among different filter
shapes, best performance in terms of SE given a fixed receiver
complexity, are obtained by minimizing ISI. Moreover, all the
electronics and optoelectronic circuits following the low-pass
filter (LPF) have a bandwidth requirement of 10 GHz, including the
MZ drivers, the IQ modulator, the coherent receiver, and the ADC.
At the receiver side, a standard coherent detection is used. The
four analogue signal coming out from the 10 GHz photodetectors
included in the receiver are digitized through an 8-bit 10 GHz ADC.
Digital signal processing includes resampling, used for having two
samples/symbol, automatic frequency control (AFC) that compensate
for frequency mismatch between the incoming signal and the local
oscillator (LO) and a taps two dimensional fractionally-spaced
feed- forward equalizer (2D-FFE) that compensate for linear
propagation impairments. The equalizer output feeds four parallel
4-state Bahl, Cocke, Jelinek, Raviv (BCJR) detectors [18], working
on the four signal quadratures, followed by four low density parity
check (LDPC) decoders. The BCJR and LDPC blocks iteratively
exchange information (for a maximum of 20 iterations) to achieve
MAP detection according to the turbo-equalization principle [19].
The 2D-FFE equalizer is adaptively controlled to converge to the
matched filter output of the Ungerboeck observation model [20] and
the estimated channel coefficients (the five central ones) are used
to determine path metrics for the BCJR detectors. III. SYSTEM
DESCRIPTION A. Link TP has been implemented and its effectiveness
validated in a field trial experiment. Different transmission
measures have been Bt=2B f S(f) Bt REPLACE THIS LINE WITH YOUR
PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 4
performed over an installed fiber link, provided by Telstra,
connecting the two largest Australian cities Sydney and Melbourne,
as shown in Fig. 4, through the intermediate node sited in
Canberra. The 995 km link is divided into 15 uncompensated SMF
spans, whose lengths are indicated in Fig. YY. Shorter spans are
padded as indicated in the figure to match the minimal nominal gain
value of the subsequent amplifier. Each amplifier could be
configured in order to guarantee a power ranging between -3 dBm and
+1 dBm for each 50 GHz slot with a limitation for the total output
power of 22 dBm (i.e., 128 slots @ +1 dBm ). A reconfigurable
add/drop multiplexer (ROADM) site, based on a 50 GHz wavelength
selective switch (WSS) is present after 294 km (5 spans) in
Canberra. The transmission characteristic of the WSS into the link
can have a big impact over the system optimization criteria and the
overall performance, especially when a super-channel is
transmitted. In fact, in a gridless scenario, multiple carriers
used for super-channel transmission can be equally spaced allowing
SE maximization. When one or more WSS are used in the link multiple
carriers must fit the grid and the real transmission bandwidth. For
that reason, WSS has been properly characterized, as shown in Fig.
5, in the spectral region where the super-channel is allocated. In
our experiments two carriers have been used for each slot for a
total number of eight sub-carriers within 4 slots that corresponds
to 200 GHz. Fig. 5. Canberra WSS characterization with particular
highlighting the filter asymmetry. Additionally, for each slot, the
filter shape exhibits some asymmetries that affects system
optimization in term of wavelength allocation. In particular, the
low frequency edge is much smoother with respect to the high
frequency edge, as shown in the picture inset. As shown in the link
figure, the signal arriving in Melbourne could be either received
or looped back through an almost identical link, passing another
WSS in Canberra and received in Sydney for a total link length of
about 1995 Km. All the data signals are generated in Sydney where
3x40 Gbit/s and a 100 Gbit/s commercial cards are multiplexed
together using a 100 GHz multiplexer having 50 GHz filters on the
International Telecommunication Union Telecommunication
Standardization Bureau (ITU-T) grid. A 3 dB coupler has been used
in order to add the Tbit/s super- channel. A coherent receiver was
also used in Sydney both for back-to-back system characterization
and loop back measures. Melbourne site hosted 40, 100 Gbit/s, and
coherent receivers. B. Super-channel transmitter Fig. 6. TP
transmitter A total aggregate bit rate of 1.12 Tb/s is obtained by
means of eight optical carriers [3], each modulated by a 140Gbit/s
narrow filtered DP-QPSK signal, corresponding to 35 Gbaud.
Sub-channels bandwidth and spacing have been optimized according to
the TP technique [3][9] to maximize the achievable spectral
efficiency with the desired detector complexity. In particular,
each quadrature data (Fig. 6) is narrow filtered by an electrical
6-cavities low-pass filter with a cut-off frequency of 10 GHz (much
lower than the Nyquist limit). Moreover, unequal channel spacing
(20/30 GHz) is adopted to account for the guard bands between
adjacent 50 GHz WDM slots, unrequired by TP but imposed by the
mid-link WSS. For that reason, a net wasted bandwidth of about 30
GHz must be considered that translates in a SE reduction of about
15%. The system can exploit different LDPC codes to trade-off net
SE and error correction capability [18]. In particular, irregular
LDPC codes [21] with rate 9/10, 8/9, 5/6, 4/5, 3/4 and 2/3, can be
configured, keeping constant the line rate, depending on
accumulated OSNR and propagation penalties, to realize an adaptive
optical interface capable to finely adjust the transmitted capacity
to the propagation conditions. A code word length of 64800 bit,
proposed for the future 2nd generation satellite digital video
broadcasting (DVB-S2) standard [22], is used. An error floor below
10-6 is expected, which can be reduced below 10-15 by properly
concatenating outer hard-decision codes, with small additional
overhead ( REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER
(DOUBLE-CLICK HERE TO EDIT) < 5 3 bottom. The photodetected
signals at the output of four balanced photodiodes (two for each
polarization) are sampled and digitized by four 8-bit, 50
Gsample/s, 20 GHz bandwidth analog-to-digital converters (ADC) and
then digitally processed. In the experiment, in fact, a real time
oscilloscope is used to sample and store data. Off-line digital
processing is performed considering blocks of 8105 samples at a
time. Accumulated dispersion (~17000ps/nm/km) is compensated by a
frequency domain equalizer, while a 33 taps two dimensional
fractionally-spaced feed-forward equalizer (2D-FFE) accounts for
other linear impairments (e.g., polarization rotation, residual
dispersion, polarization mode dispersion (PMD)). IV. FIELD TRIAL
RESULTS In Fig. 7 the optical spectrum of the super-channel
generated at the transmitter side in Sydney is depicted. The eight
DP-QPSK channels were unevenly spaced (20/30 GHz) considering the
asymmetric channels spacing required for the transmission of the
super-channel through the WSS in Canberra. In particular four
couple of channels were centered in the four 50 GHz spaced WSS
ports corresponding to the central frequencies of 192.75 THz, 192.8
THz, 192.85 THz and 192.9 THz respectively. A. Back to back
measurements In Fig. 8 back to back measurements performed for each
channel are reported, considering a baud rate of 35 GBd. References
BER measures were performed by averaging over 10 blocks of samples,
each containing 8 randomly-selected code words per quadrature per
polarization, for a total of (10 8 64800 2 2 ) information bits
(when a code rate is used). BER values below 10-6 could not be
reliably measured, such that the LDPC error floor (expected below
10-6 ) was not observed in the experimental setup. Fig. 7. Optical
spectrum of the generated super-channel Fig. 8. Back to back
measurements B. System optimization and transmission performance In
order to investigate the contribution of intra-super- channel
non-linear effects on the propagation the super- channel was
transmitted through the link between Sydney and Melbourne (995 km)
and the achieved SE was measured as a function of the channel power
(Fig. 9). The measure was performed considering the information
carried out by the channel 4 (one central channel), over an
occupied bandwidth of 200/8 GHz. Fig. 9. Spectral efficiency as
function of the channels power Fig. 9 indicates an optimal channel
power of about -1dBm that minimizes the contribution of nonlinear
fiber propagation including SPM and XPM. In the same operating
conditions the power penalties have been measured over all the
sub-channels after 995 km transmission with respect to the back to
back as shown in Fig. 10. A maximum penalty of 1.3dB is obtained.
OSNR profiles are also reported, for completeness, in the same
picture, for all sub-channel power settings ranging from -3dBm to
+1dBm. Taking the optimized sub-channel power as -1dBm the received
OSNR ranges between 15 and 16dB along the channels with 0.1nm
resolution bandwidth, a value which is compatible with the majority
of deployed DWDM links. Fig. 10. Channels power penalties and OSNR
for different channel powers In order to understand the
potentiality of the TP technique, the maximum achievable SE for
each channel was measured. In particular, both the baud rate and
the code rate were tuned with the target of maximizing the
transmitted information. One 100 Gb/s and three 40 Gb/s DP-QPSK
channels are transmitted together with the eight carriers
super-channel. The initial frequency gap between the super-channel
and the co- propagating ones is 800 GHz and will be reduced to 100
GHz in order to investigate fiber non-linear cross-talk effects.
Fig. 11 shows the input and optical spectra for the considered
configurations: a) transmitted super-channel without 40 and 192.7
192.75 192.8 192.85 192.9 192.95 [10dB/div] Frequency [THz] 1.E-08
1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 13 14 15 16
Penalty[dB] OSNR [dB] ch1 ch2 ch3 ch4 ch5 ch6 ch7 ch8 4.00 4.50
5.00 5.50 -4 -3 -2 -1 0 1 2 SE[bit/s/Hz] P/Ch [dBm] 10 12 14 16 18
20 0 2 4 6 8 10 192.7 192.75 192.8 192.85 192.9 192.95 Penalty[dB]
Frequency [THz] P/Ch=-3dBm P/Ch=-1dBm P/Ch=-0.5dBm P/Ch=0dBm
P/Ch=0.5dBm P/Ch=1dBm OSNR[dB] 6. > REPLACE THIS LINE WITH YOUR
PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 6
100Gb/s channels, b) transmitted super-channel with 40 and 100Gb/s
channels 800GHz spaced, c) transmitted super- channel with 40 and
100Gb/s channels 100GHz spaced. The achieved SE for each channel is
reported in Fig. 12. Fig. 11. a) transmitted time-frequency-packed
DP-QPSK super-channel without 40 and 100Gb/s channels, b) with 40
and 100Gb/s channels 800GHz spaced, c) with 40 and 100Gb/s channels
100GHz spaced Fig. 12. Maximum channels SE Odd channels perform
slightly worse due to the asymmetric filtering response of the WSS
highlighted in the Fig. 5. The three cases of Fig. 12 show no
appreciable performance difference, giving evidence of negligible
interference between the super channel and neighboring 40 and
100Gb/s channels. Similarly, no penalty was measured on the 40 and
100Gb/s channel due to the super-channel presence. In order to
verify the receiver capability to compensate linear impairments, a
PMD emulator was added just before the coherent receiver,
introducing an additional deferential group delay up to 200 ps. SE
values remain unchanged introducing 170 ps, and dropped of 5% with
200 ps. Results are reported in Fig. 4. These values have been
obtained by using a code rate of 5/6 for all subchannels, and the
performance have been measured over channel 4. Fig. 13. SE as a
function of the additional PMD In order to validate the system
stability, long term BER measurements have been performed. In
particular, for a more accurate statistic about the system
functioning, a new (but with the same rate) code word has been
randomly generated every 15 minutes, and the BER has been computed.
In Fig. 14 are reported all the measurements taken over 12 hours,
and it is shown that only in two cases the BER has been measured
with higher value than 10-6 . Being the code words randomly
generated the two cases indicates that few codes must be avoided in
a practical implementation. In the figure is also reported the
number of iterations between the decoder and the BCJR, required for
the BER computation. Fig. 14. Required iterations for BER
computation and BER measurements The estimated frequency offset
between the considered received channel and the local oscillator,
evaluated by the AFC algorithm, is also reported in Fig. 15 for
each measurement of Fig. 14. Fig. 15. Frequency offset estimated by
the AFC algorithm at the receiver C. Three equally spaced channels
experiment In order to verify the TFP technique potentiality in
terms of spectral efficiency enhancement for the transmission of a
DP- DQPSK signal, three evenly spaced 140 Gb/s channels was
transmitted through the Telstra network. In particular, the
channels were 25 GHz spaced and the central channel frequency was
matching with the network WSSs. The signals were transmitted
firstly from Sydney to Melbourne (995 km- single way) and then in a
loop back configuration Sydney-Melbourne-Sydney (1990 km). For both
the cases, the channels were filtered by the WSS at Canberra. As
schematically depicted in Fig. 16, the signals were equally spaced,
and the central channel suffered the crosstalk from the adjacent
channels, due to the shape characteristics of the electrical filter
employed at the transmitter (Fig. 6). The WSS at Canberra, filtered
out large part of the adjacent channel but the crosstalk impairment
was unchanged for the second part of 192.5 192.7 192.9 193.1 193.3
193.5 193.7 193.9 194.1 OpticalPower [10dB/div] Frequency [THz]
without adiacent channels with 800Ghz spaced channels with 100GHz
spaced channels 3 3.5 4 4.5 5 5.5 6 192.70 192.75 192.80 192.85
192.90 192.95 SE[bit/s/Hz] Frequency [THz] with 800GHz spaced
channels with 100GHz spaced channels without adjacent channels 4
4.5 5 5.5 0 50 100 150 200 250 SE[bit/s/Hz] PMD [ps] 1.E-06 1.E-05
1.E-04 1.E-03 1.E-02 1 3 5 7 9 11 0 1 2 3 4 5 6 7 8 9 10 11 12 13
BER Numberofiterations Time [hrs] -500 -400 -300 -200 -100 0 5 10
15 Estimatedfreq.offset [MHz] Time [hrs] 7. > REPLACE THIS LINE
WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT)
< 7 the link (Canberra-Melbourne). The same happened for the
loop back configuration (Fig. 16). In Table I, the achieved
spectral efficiency is reported together with the employed code
rate and the OSNR of the received channel for the single way and
the loop back transmission. In the loop back configuration a SE of
5.6 bit/s/Hz was achieved corresponding to a record SEd product of
9353 bit/s/Hzkm. Being the adjacent channel strongly distorted from
the Canberra WSS, all the measurement was performed on the central
channel. Fig. 16. Schematic of filtering effect for evenly spaced
channels V. CONCLUSIONS Spectral efficiency enhancement of a
Telstra installed long haul uncompensated link has been proven by
exploiting time packing technique. A 1Tb/s DP-QPSK super-channel
has been successfully transmitted through an Australian link
between Sydney and Melbourne (995 km), within 200 GHz in a fixed
ITU-T grid scenario. The compatibility with deployed 50 GHz grid
optical filters has been ensured, without network upgrading
requirements. Time packing was used to maximize the achievable SE
with constrained modulation and detection complexity, while LDPC
rate was adapted to the available OSNR and propagation conditions
to approach the achievable SE of 5 bit/s/Hz (including a reduction
of 15% due to the wasted guard bands in a fixed grid scenario).
System performance has been evaluated considering real co-
propagating traffic (40 and 100Gb/s channels) without additional
penalty. 1990 km transmission in loop back configuration has been
performed with a SEd product record for field trial demonstration
of 9353 bit/s/Hzkm with an OSNR of 14.8 dB. The system performance
has been evaluated considering artificial additional PMD verifying
the receiver capability to compensate linear impairments. Long term
measurements have been also performed. The obtained results
demonstrate the possibility for operators to seamlessly migrate
toward beyond 100Gb/s networks with minimal need of infrastructure
renewal. VI. ACKNOWLEDGMENT The word data is plural, not singular.
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Nov. 2007. Sydney Canberra (WSS) Melbourne TABLE I ACHIEVED SE FOR
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SE [bit/s/Hz] Baud rate [GBd] Employed code rate OSNR @ RX [dB]
Single way 5.6 35 4/5 15.8 Loop back 4.67 35 2/3 14.8 8. >
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