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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 28 — Dec. 31, 2012
  • pp: 29665–29672
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Spectrally efficient localized carrier distribution scheme for multiple-user DFT-S OFDM RoF- PON wireless access systems

Li Tao, Jianjun Yu, Qi Yang, Ming Luo, Zhixue He, Yufeng Shao, Junwen Zhang, and Nan Chi  »View Author Affiliations


Optics Express, Vol. 20, Issue 28, pp. 29665-29672 (2012)
http://dx.doi.org/10.1364/OE.20.029665


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Abstract

We propose a modified localized carrier distribution scheme based on multi-tone generation to generate 60 GHz mm-wave for different wireless users and it improves the carrier utilization efficiency by 33.3%. The principle of multiple-user discrete Fourier transform spread optical orthogonal frequency-division multiplexing (DFT-S OFDM) Radio-over-fiber (RoF) system is presented. This multiple-user system is applicable to passive optical network (PON). Then we demonstrate a 8x4.65 Gb/s multiple-user DFT-S OFDM RoF-PON wireless access system over 40 km fiber link and 60 GHz wireless link using two localized carrier distribution scheme with different spectral efficiency. Compared to conventional OFDM, 2.3 dB reduction of receiver power using DFT-S OFDM modulation scheme and the calculated BER performance for 8 wireless users clearly demonstrates the feasibility of this spectrally efficient multiple-user RoF-PON scheme.

© 2012 OSA

1. Introduction

2. Principle

The generation and recovery schematic diagram of DFT-S OFDM is introduced in [9

9. L. Tao, J. Yu, Y. Fang, J. Zhang, Y. Shao, and N. Chi, “Analysis of noise spread in optical DFT-S OFDM systems,” J. Lightwave Technol. 30(20), 3219–3225 (2012). [CrossRef]

11

11. Y. Tang, W. Shieh, and B. S. Krongold, “DFT-Spread OFDM for fiber nonlinearity mitigation,” IEEE Photon. Technol. Lett. 22(16), 1250–1252 (2010). [CrossRef]

]. It introduces one more Discrete Fourier Transform (DFT) than conventional OFDM scheme. At first, the MxN payload is divided into M sets, and N points DFT is employed for each set. Thus the OFDM baseband consists of MxN carriers, and then the baseband signal would be mapped from frequency domain into time domain through MxN points IDFT (Inverse Discrete Fourier Transform), which is similar to the conventional OFDM scheme. Because of the subband-basis process before the IDFT in the transmitter, the possibility of high peak is reduced.

Figure 2
Fig. 2 Schematic diagram of the multiple-user DFT-S OFDM RoF-PON wireless access system, ECL: external cavity laser, PM: phase modulator, EA: electronic amplifier, TOF: tunable optical filter.
shows the architecture of the proposed modified multiple-user DFT-S OFDM RoF-PON system. A multi-tone generator is employed to generate frequency-lock multi-tone. Then the optical signal carriers are separated from the generated multi-tone and demultiplexed for different base stations (BSs). Then the different channels are modulated by wireless data for delivery to BSs after multiplexing signal carriers and beat carriers. After transmission over fiber link, these channels are demultiplexed and the specified signal and beat carrier are picked up by the tunable optical filter (TOF) for each BS (only 3 BSs are shown in Fig. 2). It should be noted that the employed interleaver and TOF are replaced by the waveshaper (WSS) in our experiment for convenience. For the practical application, a fixed demultiplexer and filter could be designed to reduce the cost. These BSs are located in different place, thus the access coverage is increasing. At the BS, one signal carrier and one beat carrier with 60 GHz frequency spacing are beating at the PD, and then the DFT-S OFDM signal is conveyed by 60 GHz mm-wave and delivered through the antenna. In order to minimize the influence of fiber dispersion and nonlinearity distortion, a 4QAM DFT-S OFDM signal is employed for its efficient PAPR reduction [10

10. Q. Yang, Z. He, Z. Yang, S. Yu, X. Yi, and W. Shieh, “Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing,” Opt. Express 20(3), 2379–2385 (2012). [CrossRef] [PubMed]

,11

11. Y. Tang, W. Shieh, and B. S. Krongold, “DFT-Spread OFDM for fiber nonlinearity mitigation,” IEEE Photon. Technol. Lett. 22(16), 1250–1252 (2010). [CrossRef]

]. Note that the architecture of the multiple-user DFT-S OFDM RoF-PON system is the same for different localized carrier distribution scheme.

3. Experimental setup and results

Figure 3
Fig. 3 Experimental setup of the DFT-S OFDM multiple-user RoF-PON system, ECL: external cavity laser, PM: phase modulator, EA: electronic amplifier, IM: intensity modulator, AWG: arbitrary waveform generator, WSS: waveshaper.
indicates the experimental setup of multiple-user RoF-PON system. For the multi-tone generator, a lightwave at 1550.2 nm from external cavity laser (ECL) with a linewidth less than 100 kHz is employed as a signal source. The phase modulator (PM, Vπ = 2.9V) is driven by 15 GHz RF signal. The first waveshaper (WSS1, Finisar WS-AA-4000S) is employed to separate the signal carriers and beat carriers. The transmitted DFT-S OFDM wireless data is generated off-line by MATLAB program and mapped to 4-QAM constellation. The DFT-S OFDM baseband signal is constructed with 256 subcarriers. It’s divided into 4 sub-bands, 4 subcarriers of each sub-band are used for phase estimation. A discrete multi-tone (DMT) technique [12

12. J. Lee, F. Breyer, S. Randel, J. Zeng, F. Huijskens, H. P. van den Boom, A. M. Koonen, and N. Hanik, “24-Gb/s transmission over 730 m of multimode fiber by direct modulation of an 850-nm VCSEL using discrete multi-tone modulation,” Opt. Fiber Conf. (OFC 2007), Anaheim, USA, PDP 6, Mar. 2011.

] is utilized and the resulting output after IDFT is of real value. This leads to a much simpler cost-effective transmitter structure. For the conventional OFDM modulation scheme, the number of subcarriers in the baseband signal is also 256 and 16 subcarriers are chosen for phase estimation. An arbitrary waveform generator is used to produce RF signals at 5 GSample/s, and subsequently driving intensity modulator (IM) between the minimum and maximum transmission. The fiber launch power is set to 2.3 dBm.

After 40 km fiber link, the second waveshaper (WSS2) is used as a multi-band pass filter and the specified signal carrier and beat carrier are filtered and beating at the PD to generate 60 GHz mm-wave for one wireless user, the optical spectrum is shown in Fig. 4(d) and Fig. 5(d) respectively. Then the 60 GHz mm-wave is amplified by a power amplifier (PA) with bandwidth of about 7 GHz centered at 60 GHz and broadcasted through a double-ridge guide rectangular horn antenna with a gain of 15 dBi, frequency range of 50-75 GHz. At the end user terminal, the broadcasted wireless signal is received by another 60 GHz horn antenna with 15 dBi gain at frequency range of 50-75 GHz. The broadcast distance between two antennas is 4 cm. The distance is not very long, but we would improve it in the future work. The received signal is amplified before mixing with 60 GHz RF clock using a V-band balanced mixer for direct signal down-converted, then amplified with an electronic amplifier again after a lowpass filter (LPF) [2

2. J. Yu, G. K. Chang, Z. Jia, A. Chowdhury, M. F. Huang, H. C. Chien, Y. T. Hsueh, W. Jian, C. Liu, and Z. Dong, “Cost-effective optical millimeter technologies and field demonstrations for very high throughput wireless-over-fiber access systems,” J. Lightwave Technol. 28(16), 2376–2397 (2010). [CrossRef]

]. The down-converted 4QAM DFT-S OFDM signal is then sampled by a high-speed oscilloscope at a sampling rate of 50 GSa/s and processed off-line with a MATLAB program. Each signal carrier and its corresponding beat carrier could be chosen for different wireless users, so the bit rate for single user is 4.65 Gb/s, taking into account the pilot cost.

For the offline processing, the cyclic prefix is removed after signal synchronization and digital bandpass filter. 256x2 points DFT is used to convert the signal in time domain into frequency domain. Then the baseband signal is separated, and 4 sub-band signals are processed individually. The processing of channel and phase noise estimation are the same as conventional OFDM for each sub-band, then a 64-point IDFT is used to recover the signal. For the conventional OFDM scheme, the offline process is similar to DFT-S OFDM, but there is no baseband separation and extra IDFT process. The captured and processed DFT-S OFDM block includes over 160 symbols. So the total bits for bit error counting are approximate to 105.

4. Conclusion

Acknowledgments

This work was partially supported by the NHTRDP (973) of China (Grant No. 2010CB328300), and NNSF of China (No. 61107064, No. 61177071, No. 600837004), Doctoral Fund of Ministry of Education, Pujiang Fund and Shuguang fund.

References and links

1.

Z. Jia, J. Yu, and G. K. Chang, “A full-duplex radio-over-fiber system based on optical carrier suppression and reuse,” IEEE Photon. Technol. Lett. 18(16), 1726–1728 (2006). [CrossRef]

2.

J. Yu, G. K. Chang, Z. Jia, A. Chowdhury, M. F. Huang, H. C. Chien, Y. T. Hsueh, W. Jian, C. Liu, and Z. Dong, “Cost-effective optical millimeter technologies and field demonstrations for very high throughput wireless-over-fiber access systems,” J. Lightwave Technol. 28(16), 2376–2397 (2010). [CrossRef]

3.

L. Chen, J. Yu, S. Wen, J. Lu, Z. Dong, M. Huang, and G. K. Chang, “A novel scheme for seamless integration of RoF with centralized lightwave OFDM-WDM-PON system,” J. Lightwave Technol. 27(14), 2786–2791 (2009). [CrossRef]

4.

Z. Cao, J. Yu, H. Zhou, W. Wang, M. Xia, J. Wang, Q. Tang, and L. Chen, “WDM-RoF-PON architecture for flexible wireless and wire-Line layout,” J. Opt. Commun. Netw. 2(2), 117–121 (2010). [CrossRef]

5.

T. Nakasyotani, H. Toda, T. Kuri, and K. Kitayama, “Wavelength-division-multiplexed millimeter-waveband radio-on-fiber system using a supercontinuum light source,” J. Lightwave Technol. 24(1), 404–410 (2006). [CrossRef]

6.

H. Toda, T. Yamashita, T. Kuri, and K. Kitayama, “Demultiplexing using an arrayed-waveguide grating for frequency-interleaved DWDM millimeter-wave radio-on-fiber systems,” J. Lightwave Technol. 21(8), 1735–1741 (2003). [CrossRef]

7.

J. Yu, Z. Jia, T. Wang, and G. K. Chang, “A novel radio-over-fiber vonfiguration using optical phase modulator to generate an optical mm-wave and centralized lightwave for uplink connection,” IEEE Photon. Technol. Lett. 19(3), 140–142 (2007). [CrossRef]

8.

J. Yu, G. K. Chang, A. M. J. Koonen, and G. Ellinas, “Radio-overoptical fiber networks: introduction to the feature issue,” J. Opt. Netw. 8(5), 488–490 (2009). [CrossRef]

9.

L. Tao, J. Yu, Y. Fang, J. Zhang, Y. Shao, and N. Chi, “Analysis of noise spread in optical DFT-S OFDM systems,” J. Lightwave Technol. 30(20), 3219–3225 (2012). [CrossRef]

10.

Q. Yang, Z. He, Z. Yang, S. Yu, X. Yi, and W. Shieh, “Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing,” Opt. Express 20(3), 2379–2385 (2012). [CrossRef] [PubMed]

11.

Y. Tang, W. Shieh, and B. S. Krongold, “DFT-Spread OFDM for fiber nonlinearity mitigation,” IEEE Photon. Technol. Lett. 22(16), 1250–1252 (2010). [CrossRef]

12.

J. Lee, F. Breyer, S. Randel, J. Zeng, F. Huijskens, H. P. van den Boom, A. M. Koonen, and N. Hanik, “24-Gb/s transmission over 730 m of multimode fiber by direct modulation of an 850-nm VCSEL using discrete multi-tone modulation,” Opt. Fiber Conf. (OFC 2007), Anaheim, USA, PDP 6, Mar. 2011.

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.5625) Fiber optics and optical communications : Radio frequency photonics

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: November 5, 2012
Revised Manuscript: November 21, 2012
Manuscript Accepted: December 4, 2012
Published: December 20, 2012

Citation
Li Tao, Jianjun Yu, Qi Yang, Ming Luo, Zhixue He, Yufeng Shao, Junwen Zhang, and Nan Chi, "Spectrally efficient localized carrier distribution scheme for multiple-user DFT-S OFDM RoF- PON wireless access systems," Opt. Express 20, 29665-29672 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-28-29665


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References

  1. Z. Jia, J. Yu, and G. K. Chang, “A full-duplex radio-over-fiber system based on optical carrier suppression and reuse,” IEEE Photon. Technol. Lett.18(16), 1726–1728 (2006). [CrossRef]
  2. J. Yu, G. K. Chang, Z. Jia, A. Chowdhury, M. F. Huang, H. C. Chien, Y. T. Hsueh, W. Jian, C. Liu, and Z. Dong, “Cost-effective optical millimeter technologies and field demonstrations for very high throughput wireless-over-fiber access systems,” J. Lightwave Technol.28(16), 2376–2397 (2010). [CrossRef]
  3. L. Chen, J. Yu, S. Wen, J. Lu, Z. Dong, M. Huang, and G. K. Chang, “A novel scheme for seamless integration of RoF with centralized lightwave OFDM-WDM-PON system,” J. Lightwave Technol.27(14), 2786–2791 (2009). [CrossRef]
  4. Z. Cao, J. Yu, H. Zhou, W. Wang, M. Xia, J. Wang, Q. Tang, and L. Chen, “WDM-RoF-PON architecture for flexible wireless and wire-Line layout,” J. Opt. Commun. Netw.2(2), 117–121 (2010). [CrossRef]
  5. T. Nakasyotani, H. Toda, T. Kuri, and K. Kitayama, “Wavelength-division-multiplexed millimeter-waveband radio-on-fiber system using a supercontinuum light source,” J. Lightwave Technol.24(1), 404–410 (2006). [CrossRef]
  6. H. Toda, T. Yamashita, T. Kuri, and K. Kitayama, “Demultiplexing using an arrayed-waveguide grating for frequency-interleaved DWDM millimeter-wave radio-on-fiber systems,” J. Lightwave Technol.21(8), 1735–1741 (2003). [CrossRef]
  7. J. Yu, Z. Jia, T. Wang, and G. K. Chang, “A novel radio-over-fiber vonfiguration using optical phase modulator to generate an optical mm-wave and centralized lightwave for uplink connection,” IEEE Photon. Technol. Lett.19(3), 140–142 (2007). [CrossRef]
  8. J. Yu, G. K. Chang, A. M. J. Koonen, and G. Ellinas, “Radio-overoptical fiber networks: introduction to the feature issue,” J. Opt. Netw.8(5), 488–490 (2009). [CrossRef]
  9. L. Tao, J. Yu, Y. Fang, J. Zhang, Y. Shao, and N. Chi, “Analysis of noise spread in optical DFT-S OFDM systems,” J. Lightwave Technol.30(20), 3219–3225 (2012). [CrossRef]
  10. Q. Yang, Z. He, Z. Yang, S. Yu, X. Yi, and W. Shieh, “Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing,” Opt. Express20(3), 2379–2385 (2012). [CrossRef] [PubMed]
  11. Y. Tang, W. Shieh, and B. S. Krongold, “DFT-Spread OFDM for fiber nonlinearity mitigation,” IEEE Photon. Technol. Lett.22(16), 1250–1252 (2010). [CrossRef]
  12. J. Lee, F. Breyer, S. Randel, J. Zeng, F. Huijskens, H. P. van den Boom, A. M. Koonen, and N. Hanik, “24-Gb/s transmission over 730 m of multimode fiber by direct modulation of an 850-nm VCSEL using discrete multi-tone modulation,” Opt. Fiber Conf. (OFC 2007), Anaheim, USA, PDP 6, Mar. 2011.

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