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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 10 — May. 20, 2013
  • pp: 12282–12301
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An energy-efficient and elastic optical multiple access system based on coherent interleaved frequency division multiple access

Yuki Yoshida, Akihiro Maruta, Kenji Ishii, Yuji Akiyama, Tsuyoshi Yoshida, Naoki Suzuki, Kazuumi Koguchi, Junichi Nakagawa, Takashi Mizuochi, and Ken-ichi Kitayama  »View Author Affiliations


Optics Express, Vol. 21, Issue 10, pp. 12282-12301 (2013)
http://dx.doi.org/10.1364/OE.21.012282


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Abstract

This paper proposes a novel bandwidth-elastic and energy-efficient passive optical network (PON) based on the coherent interleaved frequency division multiple access (IFDMA) scheme. We experimentally demonstrate the coherent IFDMA-PON uplink transmission up-to 30 Gbps over a 30 km standard single-mode fiber with 2 × optical network units (ONUs). A low-complexity digital carrier synchronization technique enables multiple access of the ONUs on the basis of 78.1 MHz narrow band orthogonal subcarriers without any guard-bands.

© 2013 OSA

1. Introduction

Fig. 1 Elastic bandwidth provisioning on-demand in OFDMA-based PONs.

In this paper, as one of the coherent OFDMA-PONs, we propose a digital coherent interleaved FDMA-PON (IFDMA-PON) for future elastic and power-efficient PONs. First, we introduce a novel digitally supported PON architecture for the coherent OFDMA-PON. One major challenge in coherent OFDMA-PONs is the carrier synchronization of free-running lasers at the ONUs. In optical coherent multipoint-to-point communications, the carrier frequency offset (CFO) between multiple lasers at ONUs will introduce a collision between users’ subcarriers, which will be observed as a multi-user interference (MUI) at the OLT. To overcome the MUI problem, we employ cooperative DSPs for the CFO precompensation at each ONU and the MUI cancellation at the OLT. The advanced DSPs enable coherent multiple access based on narrow band orthogonal subcarriers, whose spectrum spacing is typically less than 100MHz. Then, we discuss the advantage of the IFDMA scheme in the coherent OFDMA-based PONs. Among the OFDMA schemes, IFDMA is known for having the lowest peak-to-average power ratio (PAPR) of the modulated signal and for its simplicity in the subcarrier generation process without using the discrete Fourier transform (DFT) [16

16. U. Sorger, I. De Broeck, and M. Schnell, “IFDMA – A new spread spectrum multiple access scheme,” in Proc. of IEEE International Conference on Communications , 1013–1017, (1998).

, 17

17. H. Myung, J. Lim, and D. Goodman, “Single carrier FDMA for uplink wireless transmission,” IEEE Vehicular Tech. Mag. 1 (3), 30–38 (2006) [CrossRef] .

]. In the proposed architecture, these characteristics are fully exploited to improve both optical and electrical power efficiencies at mass ONUs. The power consumption of DSP circuits is one concern in DSP-enabled PONs [18

18. OASE Deliverable D4.1: “Survey of next-generation optical access system concepts”, (Oct.2010). (available online:www.ict-oase.eupublicfilesOASE_WP4_D4_1_29th_October_2010_v1_0.pdf)

, 19

19. J. Baliga, R. Ayre, K. Hinton, W. V. Sorin, and R. S. Tucker, “Energy consumption in optical IP networks,” J. Lightwave Technol. 27 (13), 2391–2403 (2009) [CrossRef] .

], and the digital subcarrier generation realized using DFT, which is commonly implemented by a fast Fourier transform (FFT) circuit with multi-gigabit per second throughput, is a notable example of such a power hungry DSP in OFDMA-PONs. By removing FFT circuits from mass ONUs, the IFDMA-PON can improve the electrical power efficiency of OFDMA based PONs. In fact, the subcarrier generation without DFT in IFDMA achieved a 93% reduction of the power consumption compared with that in raw OFDMA [20

20. K. Ishii, Y Akiyama, T. Yoshida, N. Suzuki, T. Ichikawa, K. Koguchi, J. Nakagaw, T. Mizuochi, Y. Yoshida, A. Maruta, and K. Kitayama, “Low-power consumption DSP circuit design for IFDMA-based PON systems,” in Proc. of Opto-Electronics and Communications Conference , 770–771, (2011).

]. In addition, the lower PAPR of the IFDMA signal enables a 6 dB higher optical power efficiency than other OFDMA signals in the electro-optic (E/O) conversion using Mach–Zehnder IQ modulators.

The remaining of this paper is organized as follows; Section 2 presents the CFO- induced MUI problem in the coherent OFDMA-PON and proposes the digital coherent PON architecture. In Section 3, we discuss the advantage of IFDMA among the OFDMA-based PONs and show how it can be a green solution. The experimental results are shown in Section 4. Section 5 summarizes and concludes this paper.

2. Digital coherent OFDMA-PON architecture

Fig. 2 MUI due to the CFO in coherent OFDMA-based PONs where Sk(i) and S(i) (f) denote the information-bearing symbol modulated on the kth subcarrier of the ith ONU and its spectrum in the analog domain, respectively. Meanwhile, Rk and R(f) are the demodulated symbol and the received spectrum, respectively.

To overcome the MUI problem, we propose a simple digitally enabled coherent OFDMA-PON architecture, as in Fig. 3. The key features in the architecture are the digital CFO precompensation at each ONU based on the channel state information (CSI) feedback and the OLT side DSP for the MUI cancellation. As an a analogy to the digital CFO compensation in the digital coherent receiver, the CFO precompensation is performed by multiplying the complex sinusoidal in the digital domain before E/O IQ modulation. Note that the CFO precompensation does not tune the laser wavelength but the allocation of the signal spectrum. The digital spectrum shifting is somewhat simple, but reasonable, because it enables sub-megahertz order precise frequency synchronization of the ONUs, which is not easily achieved by tuning the laser wavelength. The CFO parameter for the precompensation is estimated at the OLT, and each ONU accesses the CSI through the feedback path. The CSI feedback procedure is essentially the same as the granting and reporting procedure in current TDMA-PON standards [21

21. C. Lam, Passive Optical Networks (Academic Press, 2007).

], and hence it might not lose the feasibility of the proposed precompensation technique significantly. For instance, in current E-PON, the MPCPDU (multipoint control protocol data unit) consists of 64 byte [21

21. C. Lam, Passive Optical Networks (Academic Press, 2007).

] and the periodicity of the granting and reporting is order of tens of milliseconds typically [22

22. ITU-T Recommendation Y.1541, (2011).

], while the 8 byte CFO information feedback per ONU is required once a few tens of seconds in our demonstration will be shown in Sec. 4.

Fig. 3 Digital coherent OFDMA-PON architecture.

The MUI cancellation methods are free from the feedback delay and can significantly simplify the task for the carrier synchronization of the ONUs. However, most of the cancellation methods can be adopted for the CFO in less than half of the subcarrier spacing. Typically, the half subcarrier spacing is less than 50MHz (39 MHz in our demonstration) in current coherent OFDM systems. Meanwhile several hundred of megahertz in the initial CFO can easily be observed even with current narrow linewidth lasers. Therefore, the cooperative operation of the pre and post CFO compensation is important for realizing the coherent OFDMA-based PONs, i.e., keep the CFO between ONUs below a half of the subcarrier spacing via the CFO precompensation at each ONU and remove the MUI due to the residual CFO at the OLT via the MUI cancellation.

Note that a larger number of subcarriers within a given electrical bandwidth provide a finer granularity and less overhead due to the cyclic prefix (CP) but a tighter acceptable CFO range. Meanwhile, finer synchronization will be achieved at the expense of the system overhead due to faster CSI feedback and the increment of computational complexity of the MUI cancellation algorithm. Therefore, a deliberate choice is required for system designers for a number of subcarriers, the CSI feedback speed and periodicity, and the MUI cancellation algorithm, for a given set of lasers at ONUs.

3. IFDMA: Energy-efficient OFDMA without DFT

3.1. Electrical power efficiency in digital subcarrier generation

One known drawback of the raw OFDMA scheme is the high PAPR of the modulated signal. Due to constructive and destructive interference between hundreds or thousands of subcarriers, the time-domain waveform of the OFDMA signal becomes like a Gaussian noise, and a peak power of 10 dB larger than the average power, is observed in some cases. Single carrier FDMA (SC-FDMA) is a technique that is used to reduce the PAPR of the raw OFDMA and has been widely employed in current mobile uplinks, such as in 3GPP-LTE [3

3. 3GPP TS 36.300, 3rd Generation Partnership Project Technical Specification Group Radio Access Network, “Evolved universal terrestrial radio access (E-UTRA) and evolved universal terrestrial radio access network (E-UTRAN); Overall description; Stage 2 (Release 8).”

]. IFDMA is a special class of SC-FDMA where a comb-shaped subcarrier allocation is employed. The Fig. 4(a) shows a basic schematic of subcarrier generation in SC-FDMA in the digital domain. In the raw OFDMA, orthogonal subcarriers are efficiently generated using an inverse FFT (IFFT) circuit. In SC-FDMA, information-bearing symbols are precoded by the smaller size FFT before mapping on the frequency bins of the IFFT. The FFT precoding is known to reduce the PAPR if a localized or interleaved subcarrier set is employed as the basis of FDMA. A notable feature of IFDMA is the simplified circuit for the subcarrier generation [16

16. U. Sorger, I. De Broeck, and M. Schnell, “IFDMA – A new spread spectrum multiple access scheme,” in Proc. of IEEE International Conference on Communications , 1013–1017, (1998).

]. The SC-FDMA subcarrier generation process in Fig. 4(a), i.e., FFT, interleaved subcarrier mapping, and IFFT, is mathematically equivalent to the blockwise repetition and the user dependent phase rotation operation shown in Fig. 4(b). Thus, it is possible to generate subcarriers without any FFT circuits, and the computational complexity is reduced to O(KM) from O(KM log(KM)) + O(M log(M)) when K ONUs are exist and KM-point IFFT is used to assign M subcarriers per ONU uniformly. The feature is attractive in high-speed optical access systems in terms of power consumption.

Fig. 4 Schematics of the digital subcarrier generation in (a) SC-FDMA and (b) IFDMA; S/P: Serial-to-Parallel conversion, P/S: Parallel-to-Serial conversion, (I) FFT: (Inverse) Fast Fourier Transform, CP Inst.: Cyclic Prefix Insertion.

In current PONs, 65% of the overall PON power is consumed in mass ONUs [19

19. J. Baliga, R. Ayre, K. Hinton, W. V. Sorin, and R. S. Tucker, “Energy consumption in optical IP networks,” J. Lightwave Technol. 27 (13), 2391–2403 (2009) [CrossRef] .

]. Moreover, in the future digitally enhanced PON ONUs, high-throughput DSP subsystems can be the major energy consumer [18

18. OASE Deliverable D4.1: “Survey of next-generation optical access system concepts”, (Oct.2010). (available online:www.ict-oase.eupublicfilesOASE_WP4_D4_1_29th_October_2010_v1_0.pdf)

]. For instance, in the 10 Gbps ONU in the Hybrid WDM/O-OFDM-PON, whose ONU configuration is almost the same as the ONU in the coherent OFDMA-PON, nearly 70 % of the power is consumed at the DSP circuit for the OFDM modulation/demodulation. An IFFT circuit with throughput of several gigasample per second is a notable example of such a power hungry DSP subsystem at the ONU. By removing the high-speed IFFT from the mass ONUs, the IFDMA-PON can decrease the total power consumption of OFDMA based PON systems.

In [20

20. K. Ishii, Y Akiyama, T. Yoshida, N. Suzuki, T. Ichikawa, K. Koguchi, J. Nakagaw, T. Mizuochi, Y. Yoshida, A. Maruta, and K. Kitayama, “Low-power consumption DSP circuit design for IFDMA-based PON systems,” in Proc. of Opto-Electronics and Communications Conference , 770–771, (2011).

], we have experimentally investigated the power consumption of the FPGA (field-programmable gate array) -based 10 Gbaud OFDMA transmitter circuits. The Fig. 5(a) depicts the IFDMA transmitter by employing the static random access memory (SRAM)-based FPGA circuit, and a comparison of the power consumption of the IFDMA circuit and a conventional OFDMA circuit is shown in Fig. 5(b). In the experiment, the ALTERA Stratix IV FPGA is used. The sampling rate and operation accuracy are 30 Gsample/s and 8 bit, respectively, and the toggle rate is 12.5 %. As in Fig. 5(b), the high-throughput IFFT circuit in the 10 Gbaud OFDMA nearly consumes 100W. Meanwhile, the proposed IFDMA circuit that employs the SRAM-based circuit demonstrated up to 93% reduction in power consumption.

Fig. 5 Configuration of the SRAM-based FPGA circuit for IFDMA subcarrier generation and the power consumption of the conventional OFDMA and the proposed circuits versus the number of subcarriers.(courtesy of [20])

3.2. E/O conversion efficiency

Fig. 6 (a) An image of the O/E conversion via the single MZM and (b) the projection of the linear E/O IQ conversion region by using a DP-MZM with the ideal electrical pre-distortion on the complex baseband plane.
Fig. 7 Examples of the trajectories of (a) OFDMA w/ localized allocation and (b) IFDMA baseband signals where the ideal rectangular pulse shaping is employed.

The expected OPE for IFDMA is up to 50% (−3 dB). In PONs where the system power budget is defined by the power of the laser source and the sensitivity of the receiver, the loss of the laser power during the E/O conversion directly affects the reach of the system. The 6 dB improvement of the OPE implies that the IFDMA-PON can extend the reach by 20 km (in the case where the fiber loss = 0.3 dB/km) compared with the PON that is based on the raw OFDMA.

In addition, the IFDMA scheme also has an advantage in its nonlinear tolerance over the other OFDMA-PONs. In [32

32. Y. Yoshida, A. Maruta, and K. Kitayama, “On the peak-to-average power ratio distribution along fiber in the optical OFDM transmissions,” in Proc. of Euro. Conf. Optical Commun., paper We.10.P1.69, (2011).

], we reported the PAPR enhancement phenomenon in the optical OFDM transmission. The high-PAPR OFDM signal is known to be susceptible to the fiber nonlinearity even if the average launched power is a few. Moreover, after tens of kilo meters propagation over SSMF, the PAPR of the optical OFDM signal is suddenly increased by more than 1 dB due to the optical Kerr effect. This increases the severity of nonlinear penalty in OFDMA-PONs relative to that in the conventional PONs. The low-PAPR IFDMA scheme is also expected to improve the nonlinear tolerance of OFDMA-PONs.

4. Experimental results

Fig. 8 Experimental setup for a 2 × ONU up-to a 30 Gbps coherent IFDMA-PON uplink.

The Fig. 9 shows the transmitted IFDMA frame designs for ONU1 and ONU2. Each frame consists of a 109 ns preamble and a 576 ns data payload. The data payload contains 40 IFDMA symbols, and the orthogonality between the users’ payloads is achieved via the OFDMA sense. Besides, in order to acquire the ONU-by-ONU CSI including the CFO parameter, the users’ preambles should also be decomposable at the OLT. Here, to ease the task for the offline CSI estimation, the orthogonality is realized by just assigning a different time slot for each preamble, namely TDMA, as shown in Fig. 9. This will lead a huge overhead when a large number of ONUs are co-exist. However, the overhead can be avoided in practical situations by employing orthogonal sequences, such as the Zadoff–Chu sequence, as preambles and/or CSI-tracking techniques with short periodic pilots.

Fig. 9 Transmitted frame designs for ONU1 and ONU2.

4.1. Impact of the digital CFO precompensation

First, we verify the proposed digital CFO precompensation technique. The Fig. 10 shows the complementary cumulative distribution function (CCDF) of the estimated CFO between the ONUs and examples of the received (partial) spectrum at the OLT. In Fig. 10(a), we observe the collision of users’ subcarriers due to the CFO; the comb-shaped spectrum of ONU2 (blue) almost overlaps with the spectrum of ONU1 (red) where the estimated CFO is 43 MHz, while the subcarrier spacing is 78.1 MHz. Note that the spectrums are observed one after the other for visualization here. Statistically, from the CCDF (the red dotted line), the CFO larger than 160 MHz is observed 90% of the time without the precompensation, while the half subcarrier spacing in this experiment is 39 MHz. Therefore there is a need for some CFO compensation or reduction techniques at the ONU side.

Fig. 10 CCDF of the CFO between ONU1 and ONU2 (left) and examples of the received signal spectrums (a) without the CFO precompensation and (b) with the precompensation.

Note that the CFO is estimated based on the preamble of each transmitted data frame. Hence the CFO here is the accumulated version of the fluctuation of the laser’s wavelength during the IFDMA frame duration. Essentially, there are two requirements for the lasers used for coherent OFDMA transmission; 1) the laser are stable as they are said to be quasi-synchronous during a given transmitted frame [33

33. S. Barbarossa, M. Pompili, and G. B. Giannakis, “Channel-independent synchronization of orthogonal frequency-division multiple access systems,” IEEE J. Select. Areas Commun. 20 (2), 474–486 (2002) [CrossRef] .

], and 2) the CFOs are less than a half of the subcarrier spacing to avoid the significant performance degradation due to the collisions between user’s subcarriers. The CCDF here directly denotes the outage probability of these two requirements.

The Fig. 10(b) shows the received spectrum with the proposed digital CFO precompensation technique, where the initial CFO is the same as in Fig. 10(a). In Fig. 10(b), the two comb-shaped spectrums are properly shifted to inter-mesh, and hence, the orthogonality between the subcarriers is restored. From the CCDF (the blue line), we observe a significant reduction of the CFO via the proposed precompensation method, e.g., the probability of observing a CFO larger than ±5 MHz is around 4%, which is sufficiently small for the coherent OFDMA transmission with 78.1 MHz subcarrier spacing. One concern is the periodicity and/or the latency required for the CSI feedback for the CFO precompensation, and further investigations using real-time front ends are necessary to clarify the requirements for the CSI feedback performance. In the experiment, the AWG and the DSA are operated in store-and-forward manner. Moreover the CFO is estimated in offline manner. Therefore the latency of the CSI feedback path results in second order and much longer than the typical round trip time in PONs. Even so, the CSI feedback of once every a few tens of seconds is sufficient to maintain the carrier synchronization owing to the narrow linewidth of the ECLs.

4.2. Back-to-back sensitivity

Next, we evaluate the sensitivity of the OLT in a back-to-back configuration, i.e., SSFM1 = SSFM2 = 0 km. The Fig. 11 depicts the received optical power versus the BER performances of each ONU, where 64 subcarriers out of 128 subcarriers are equally assigned to both ONUs, and the QPSK format is employed. The resulting transmission rate is 10 Gbps for each user and 20 Gbps in total without the FEC and CP overhead. Both ONUs achieve error-free transmission with 7% FEC (BER = 3.8 × 10−3[34

34. ITU-T Recommendation G.975.1 2004, Appendix I.9.

]) for a received power larger than −35.5 dBm. Moreover, we observe almost Gaussian-like distributions in the received constellations for both ONUs without any imaging component between them. This means that the MUI due to the CFO between the two free-running ECLs is successfully compensated via the ONU side precompensation and the OLT side MUI cancellation.

Fig. 11 BER performance of each ONU versus the received optical power in a back-to-back 10 Gbps × 2 ONUs QPSK-IFDMA uplink.

In Fig. 12, we increase the bit rate by employing the 8PSK format. The resulting transmission rate is 15 Gbps for each ONU and 30 Gbps in total (24.6 Gbps with CP and 7% FEC overheads). From the figure, for a received power larger than −27.5 dBm, both ONUs achieve a 7% FEC error-free operation. In comparison with the QPSK case, we observe a 7 dB penalty in the OLT sensitivity, while the theoretical penalty is around 5 dB at the BER of 1.0 × 10−3[35

35. J. G. Proakis and M. Salehi, Digital Communications, 5th ed., (McGraw-Hill International Editions, 2008).

]. A part of the additional 2 dB penalty may be from the IQ imbalance at the DP-MZMs. As seen in the constellations in Fig. 12, the received signal has some skew between the IQ components, which is mainly due to the unstable bias voltages at the DP-MZMs. This type of IQ skew is called a transmitter IQ imbalance and is known to induce unexpected MUI at the receiver side in OFDMA systems [36

36. Y. Yoshida, K. Hayashi, H. Sakai, and W. Bocquet, “Analysis and compensation of transmitter IQ imbalances in OFDMA and SC-FDMA systems,” IEEE Trans. Signal Process. 57 (8), 3119–3129 (2009) [CrossRef] .

].

Fig. 12 BER performance of each ONU versus the received optical power in a back-to-back 15 Gbps × 2 ONUs 8PSK-IFDMA uplink.

4.3. Feasibility on the 10G-PON scenario

Fig. 13 BER performance of each ONU versus the received optical power in a 15G bps × 2 ONUs 8PSK-IFDMA uplink over a 20km SSFM.

4.4. Demonstration of the bandwidth-elastic multiple access

Finally, we demonstrate the elastic bandwidth allocation in the coherent IFDMA-PON. In the demonstration, SSFM1 and SSFM2 set to 20 km and 10 km, respectively. Due to the difference in the access spans, ONU2 suffers from a 3 dB loss in the optical signal-to-noise power ratio (OSNR) when compared with ONU1. To mitigate the OSNR degradation without decreasing the bit rate of ONU2, we assign 96 subcarriers out of 128 with the QPSK format for ONU2. The remaining 32 subcarriers are allocated for ONU1 with the 8PSK format. The resulting transmission rates are 7.5 Gbps for ONU1 and 15 Gbps for ONU2, excluding the overheads. The Fig. 14 depicts the BER performances, received constellations, and subcarrier-by-subcarrier error vector magnitude (EVM) performances, where the optical power at the OLT input is −17.24 dBm. The BERs for ONU1 and ONU2 are 9.7 × 10−4 and 1.2 × 10−3, respectively, and a 7% FEC error-free operation is observed on both ONUs. To the best of our knowledge, this is the first demonstration of no guard-band and bandwidth-elastic optical multiple access based on the OFDMA scheme.

Fig. 14 Subcarrier-by-subcarrier EVM performance and resulting constellations in the no guard-band elastic IFDMA-PON uplink.

Meanwhile, we observe a severe distortion on the constellations in Fig. 14. In fact, the constellations are rather broadened compared with the EVM performances. This is mostly due to the imperfection in the synchronization of the sampling timing at the OLT.

5. Numerical results

Fig. 15 CFO distribution model: a) PDF and b) CCDF.

Fig. 16 Simulation setup

Table 1. Simulation parameters

table-icon
View This Table

Fig. 17 Average BER performance versus the number of ONUs.

The blue dashed and solid lines in Fig. 17 represent the average BER versus K with and without the MUI cancellation technique, respectively. Here we employ the Laplace distribution with λ = 6.2 × 106 for the CFO distribution. It is not easy to relate λ and the laser linewidth. The laser frequency stabilization technique is different for a required linewidth, and the CFO distribution after precompensation may be different as well. However, with a simple scaling, λ = 6.2 × 106 corresponds to the linewidth of around 40kHz. In this case, with the help of the MUI cancellation at the OLT, the FEC error-free operation can achieved for every ONU count.

6. Conclusion

Acknowledgment

This work has been financially supported by the R&D program, SCOPE, funded by the Ministry of Internal Affairs and Communications (MIC), Japan (FY.2011–2013).

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X. Chen, A. Li, D. Che, Q. Hu, Y. Wang, J. He, and W. Shieh, “High-speed fading-free direct detection for double-sideband OFDM signal via block-wise phase switching,” in Proc. of Opt. Fiber Commun. Conf., PDP5B.7, (2013).

29.

I. Dedic, “High-speed CMOS DSP and data converters,” in Proc. of Opt. Fiber Commun. Conf., paper OTuN1, (2011).

30.

R. Bouziane, P. Milder, R. Koutsoyannis, Y. Benlachtar, J. C. Hoe, M. Puschel, M. Glick, and R. I. Killey, “Design studies for ASIC implementations of 28 GS/s optical QPSK- and 16-QAM-OFDM transceivers,” Opt. Express 19 (21), 20857–20864 (2011) [CrossRef] [PubMed] .

31.

D. J. F. Barros and J. M. Kahn, “Optical modulator optimization for orthogonal frequency-division multiplexing,” J. Lightwave Technol. 27 (13), 2370–2378 (2009) [CrossRef] .

32.

Y. Yoshida, A. Maruta, and K. Kitayama, “On the peak-to-average power ratio distribution along fiber in the optical OFDM transmissions,” in Proc. of Euro. Conf. Optical Commun., paper We.10.P1.69, (2011).

33.

S. Barbarossa, M. Pompili, and G. B. Giannakis, “Channel-independent synchronization of orthogonal frequency-division multiple access systems,” IEEE J. Select. Areas Commun. 20 (2), 474–486 (2002) [CrossRef] .

34.

ITU-T Recommendation G.975.1 2004, Appendix I.9.

35.

J. G. Proakis and M. Salehi, Digital Communications, 5th ed., (McGraw-Hill International Editions, 2008).

36.

Y. Yoshida, K. Hayashi, H. Sakai, and W. Bocquet, “Analysis and compensation of transmitter IQ imbalances in OFDMA and SC-FDMA systems,” IEEE Trans. Signal Process. 57 (8), 3119–3129 (2009) [CrossRef] .

OCIS Codes
(060.1660) Fiber optics and optical communications : Coherent communications
(060.2330) Fiber optics and optical communications : Fiber optics communications

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: January 16, 2013
Revised Manuscript: April 30, 2013
Manuscript Accepted: May 2, 2013
Published: May 13, 2013

Citation
Yuki Yoshida, Akihiro Maruta, Kenji Ishii, Yuji Akiyama, Tsuyoshi Yoshida, Naoki Suzuki, Kazuumi Koguchi, Junichi Nakagawa, Takashi Mizuochi, and Ken-ichi Kitayama, "An energy-efficient and elastic optical multiple access system based on coherent interleaved frequency division multiple access," Opt. Express 21, 12282-12301 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-10-12282


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References

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  29. I. Dedic, “High-speed CMOS DSP and data converters,” in Proc. of Opt. Fiber Commun. Conf., paper OTuN1, (2011).
  30. R. Bouziane, P. Milder, R. Koutsoyannis, Y. Benlachtar, J. C. Hoe, M. Puschel, M. Glick, and R. I. Killey, “Design studies for ASIC implementations of 28 GS/s optical QPSK- and 16-QAM-OFDM transceivers,” Opt. Express19 (21), 20857–20864 (2011). [CrossRef] [PubMed]
  31. D. J. F. Barros and J. M. Kahn, “Optical modulator optimization for orthogonal frequency-division multiplexing,” J. Lightwave Technol.27 (13), 2370–2378 (2009). [CrossRef]
  32. Y. Yoshida, A. Maruta, and K. Kitayama, “On the peak-to-average power ratio distribution along fiber in the optical OFDM transmissions,” in Proc. of Euro. Conf. Optical Commun., paper We.10.P1.69, (2011).
  33. S. Barbarossa, M. Pompili, and G. B. Giannakis, “Channel-independent synchronization of orthogonal frequency-division multiple access systems,” IEEE J. Select. Areas Commun.20 (2), 474–486 (2002). [CrossRef]
  34. ITU-T Recommendation G.975.1 2004, Appendix I.9.
  35. J. G. Proakis and M. Salehi, Digital Communications, 5th ed., (McGraw-Hill International Editions, 2008).
  36. Y. Yoshida, K. Hayashi, H. Sakai, and W. Bocquet, “Analysis and compensation of transmitter IQ imbalances in OFDMA and SC-FDMA systems,” IEEE Trans. Signal Process.57 (8), 3119–3129 (2009). [CrossRef]

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