Abstract

Driven by continuously growing mobile traffic, line rate of digital mobile fronthaul (MFH) network keeps surging. 4-level pulse amplitude modulation (PAM4) is a promising format to provide such high data capacity, due to its bandwidth and cost efficiency. In this paper, we propose an improved method to reduce mobile signal distortion caused by bit error of optical transmission. The concept comes from the characteristic that high order sample bit error induces far severer performance degradation to radio signal than low order one. In the solution, high order sample bits and low order sample bits are interleaved, so that they are respectively mapped to first bit (1stb) and second bit (2ndb) of PAM4 symbol. On the other hand, amplitude levels of PAM4 are set unequal to broaden the “middle eye”, levering accuracy of 1stb. Hence, the total fidelity of mobile signal is enhanced. The feasibility is confirmed both theoretically and experimentally. The investigation is based on two typical digital systems, i.e., 16-bit uniform quantizing and 8-bit nonuniform quantizing. Experimental results indicate that, EVM of LTE-A like radio signal decreases by up to 13dB in uniform quantizing system, and by up to 5dB in nonuniform quantizing system, compared with conventional equally-spaced PAM4.

© 2017 Optical Society of America

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References

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    [Crossref]
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2016 (4)

2015 (2)

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

X. Gao, O. Edfors, F. Tufvesson, and E. G. Larsson, “Massive MIMO in real propagation environments: Do all antennas contribute equally?” IEEE Trans. Wirel. Commun. 63(11), 3917–3928 (2015).
[Crossref]

2014 (2)

L. Tao, Y. Wang, Y. Gao, and N. Chi, “High order CAP system using DML for short reach optical communications,” IEEE Photon. Technol. Lett. 26(13), 1348–1351 (2014).
[Crossref]

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

2011 (1)

S. Parkvall, A. Furuskar, and E. Dahlman, “Evolution of LTE toward IMT-Advanced,” IEEE Commun. Mag. 49(2), 84–91 (2011).
[Crossref]

2010 (1)

Agata, A.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Bae, S. H.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Che, D.

Cheng, N.

Chi, N.

L. Tao, Y. Wang, Y. Gao, and N. Chi, “High order CAP system using DML for short reach optical communications,” IEEE Photon. Technol. Lett. 26(13), 1348–1351 (2014).
[Crossref]

Chung, Y. C.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Dahlman, E.

S. Parkvall, A. Furuskar, and E. Dahlman, “Evolution of LTE toward IMT-Advanced,” IEEE Commun. Mag. 49(2), 84–91 (2011).
[Crossref]

Edfors, O.

X. Gao, O. Edfors, F. Tufvesson, and E. G. Larsson, “Massive MIMO in real propagation environments: Do all antennas contribute equally?” IEEE Trans. Wirel. Commun. 63(11), 3917–3928 (2015).
[Crossref]

Effenberger, F.

Furuskar, A.

S. Parkvall, A. Furuskar, and E. Dahlman, “Evolution of LTE toward IMT-Advanced,” IEEE Commun. Mag. 49(2), 84–91 (2011).
[Crossref]

Gao, X.

X. Gao, O. Edfors, F. Tufvesson, and E. G. Larsson, “Massive MIMO in real propagation environments: Do all antennas contribute equally?” IEEE Trans. Wirel. Commun. 63(11), 3917–3928 (2015).
[Crossref]

Gao, Y.

L. Tao, Y. Wang, Y. Gao, and N. Chi, “High order CAP system using DML for short reach optical communications,” IEEE Photon. Technol. Lett. 26(13), 1348–1351 (2014).
[Crossref]

Gomes, N. J.

Han, S.

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

He, X.

J. Zhang, Z. Xiao, Y. Tian, and X. He, “Hybrid particle swarm optimizer with advance and retreat strategy and clonal mechanism for global numerical optimization,” in IEEE Congress on Evolutionary Computation (IEEE, 2008), pp. 2060–2066.

Hong, U. H.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Hu, W.

I, C.-L.

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

Ji, H.

Kim, H.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Larsson, E. G.

X. Gao, O. Edfors, F. Tufvesson, and E. G. Larsson, “Massive MIMO in real propagation environments: Do all antennas contribute equally?” IEEE Trans. Wirel. Commun. 63(11), 3917–3928 (2015).
[Crossref]

Li, G.

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

Li, Z.

Liu, X.

Nkansah, A.

Pan, Z.

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

Parkvall, S.

S. Parkvall, A. Furuskar, and E. Dahlman, “Evolution of LTE toward IMT-Advanced,” IEEE Commun. Mag. 49(2), 84–91 (2011).
[Crossref]

Rowell, C.

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

Shieh, W.

Shim, H. K.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Suzuki, M.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Tanaka, K.

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

Tao, L.

L. Tao, Y. Wang, Y. Gao, and N. Chi, “High order CAP system using DML for short reach optical communications,” IEEE Photon. Technol. Lett. 26(13), 1348–1351 (2014).
[Crossref]

Tian, Y.

J. Zhang, Z. Xiao, Y. Tian, and X. He, “Hybrid particle swarm optimizer with advance and retreat strategy and clonal mechanism for global numerical optimization,” in IEEE Congress on Evolutionary Computation (IEEE, 2008), pp. 2060–2066.

Tufvesson, F.

X. Gao, O. Edfors, F. Tufvesson, and E. G. Larsson, “Massive MIMO in real propagation environments: Do all antennas contribute equally?” IEEE Trans. Wirel. Commun. 63(11), 3917–3928 (2015).
[Crossref]

Wake, D.

Wang, Y.

L. Tao, Y. Wang, Y. Gao, and N. Chi, “High order CAP system using DML for short reach optical communications,” IEEE Photon. Technol. Lett. 26(13), 1348–1351 (2014).
[Crossref]

Xiao, Z.

J. Zhang, Z. Xiao, Y. Tian, and X. He, “Hybrid particle swarm optimizer with advance and retreat strategy and clonal mechanism for global numerical optimization,” in IEEE Congress on Evolutionary Computation (IEEE, 2008), pp. 2060–2066.

Xu, Z.

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

Yi, L.

Yuan, F.

Zhang, J.

J. Zhang, Z. Xiao, Y. Tian, and X. He, “Hybrid particle swarm optimizer with advance and retreat strategy and clonal mechanism for global numerical optimization,” in IEEE Congress on Evolutionary Computation (IEEE, 2008), pp. 2060–2066.

Zhou, L.

IEEE Commun. Mag. (2)

C.-L. I, C. Rowell, S. Han, Z. Xu, G. Li, and Z. Pan, “Toward green and soft: A 5G perspective,” IEEE Commun. Mag. 52(2), 66–73 (2014).
[Crossref]

S. Parkvall, A. Furuskar, and E. Dahlman, “Evolution of LTE toward IMT-Advanced,” IEEE Commun. Mag. 49(2), 84–91 (2011).
[Crossref]

IEEE Photon. Technol. Lett. (1)

L. Tao, Y. Wang, Y. Gao, and N. Chi, “High order CAP system using DML for short reach optical communications,” IEEE Photon. Technol. Lett. 26(13), 1348–1351 (2014).
[Crossref]

IEEE Photonics Technol. Lett. (1)

S. H. Bae, H. K. Shim, U. H. Hong, H. Kim, A. Agata, K. Tanaka, M. Suzuki, and Y. C. Chung, “25-Gb/s TDM optical link using EMLs for mobile fronthaul network of LTE-A system,” IEEE Photonics Technol. Lett. 27(17), 1825–1828 (2015).
[Crossref]

IEEE Trans. Wirel. Commun. (1)

X. Gao, O. Edfors, F. Tufvesson, and E. G. Larsson, “Massive MIMO in real propagation environments: Do all antennas contribute equally?” IEEE Trans. Wirel. Commun. 63(11), 3917–3928 (2015).
[Crossref]

J. Lightwave Technol. (2)

J. Opt. Commun. Netw. (1)

Opt. Express (2)

Other (8)

J. Zhou, C. Yu, M. Gurusamy, and H. Kim, “25-Gb/s OOK and 4-PAM transmission over >35-km SSMF using directly modulated 1.5-μm VCSEL,” in Proc. Conf. Optical Fiber Commun. (2016), paper Th1J. 7.
[Crossref]

H. Xin, K. Zhang, H. He, and W. Hu, “EVM reduction in digital mobile fronthaul by sample bits interleaving and uneven PAM4” in Proc. Conf. Optical Fiber Commun. (2017), paper Tu3G. 5.

B. Guo, W. Cao, A. Tao, and D. Samardzija, “CPRI compression transport for LTE and LTE-A signal in C-RAN,” in in Proc. Int. ICST Conf. on Comm. and Networking in China. IEEE, 843–849 (2012).

J. Zhang, Z. Xiao, Y. Tian, and X. He, “Hybrid particle swarm optimizer with advance and retreat strategy and clonal mechanism for global numerical optimization,” in IEEE Congress on Evolutionary Computation (IEEE, 2008), pp. 2060–2066.

G. John, Proakis and Masoud Salehi, Digital communications, (McGraw-Hill, 1995), Chap. 4.

M. Zhu, X. Liu, N. Chand, F. Effenberger, and G. K. Chang, “High-capacity mobile fronthaul supporting LTE advanced carrier aggregation and 8× 8 MIMO,” in Proceedings of Optical Fiber Communication Conference (OFC, 2015), M2J–3.
[Crossref]

J. Wang, Z. Yu, K. Ying, J. Zhang, F. Lu, M. Xu, and G.-K. Chang, “10-Gbaud OOK / PAM4 digital mobile fronthaul based on one-bit / two-bit delta-sigma modulation supporting carrier aggregation of 32 LTE-A signals with up to 256 and 1024QAM,” in Proceedings of ECOC 2016, paper W1H.2.

CPRI specification V6.1 (2014–7-1). (2014). [Online]. Available: http://www.cpri.info/spec.html

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Figures (9)

Fig. 1
Fig. 1 Proposed digital mobile fronthaul system based on unequally-spaced PAM4. ADC: analog to digital converter, SSMF: standard single mode fiber, DAC: digital to analog converter, 1stb: first bit of PAM4 symbol, 2ndb: second bit of PAM4 symbol, γ: ratio of different constellation distances. Uniform quantizing system: n = 16, nonuniform quantizing system: n = 8.
Fig. 2
Fig. 2 Radio signal at different phases.
Fig. 3
Fig. 3 Bit error ratio of 1stb and 2ndb with different γ.
Fig. 4
Fig. 4 EVM of radio signal with different γ. (a) Uniform quantizing system; (b) Nonuniform quantizing system . When γ = 1, equally-spaced PAM4 is taken, which is also the conventional method. 13dB and 5dB EVM reduction can be observed in uniform quantizing system and nonuniform quantizing system.
Fig. 5
Fig. 5 Optimal γ value verus different peak SNR
Fig. 6
Fig. 6 Experiment setup. PPG: pulse pattern generator, EML: electro absorption modulator laser, SSMF: standard single mode fiber, VOA: variable optical attenuator, DSO: digital storage oscilloscope
Fig. 7
Fig. 7 EVM performance versus ROP when uniform quantizing is taken: (a) BtB, (b) 20km. (c) optimal γ value versus ROP. The table shows constellations of γ = 1 and optimal γ @-20dBm and −16dBm.
Fig. 8
Fig. 8 EVM performance versus ROP when nonuniform quantizing is taken: (a) BtB, (b) 20km. (c) optimal γ value versus ROP.
Fig. 9
Fig. 9 Amplitude distribution of unequally-spaced PAM4 signal.

Tables (3)

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Table 1 Uniform Quantizing

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Table 2 Nonuniform Quantizing

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Table 3 EVM Improvement Results

Equations (15)

Equations on this page are rendered with MathJax. Learn more.

Δ i (mT)= ε i (x(mT))
E[ Δ i 2 ]=E[ ε i 2 (x)]= P ei ε i 2 (x)p(x)dx
N= i=1 n E[ Δ i 2 ]
P Fe = 1 4 erfc( w 1 2 σ )
P Se = 1 2 erfc( w 2 2 σ )
E[ Δ 16 2 ]= P e16 (2x) 2 p(x)dx
E[ Δ i 2 ]= P ei ( 2 i16 x max ) 2 p(x)dx= P ei ( 2 i16 x max ) 2
N= i=1 n E[ Δ i 2 ] = P Fe i=9 16 E[ Δ i 2 ] + P Se i=1 8 E[ Δ i 2 ]
E[ Δ 8 2 ]= P e8 (2x) 2 p(x)dx
E[ Δ i 2 ]=E[ ε i 2 (x)]= P ei ( f 1 (f(x/ x max )± 2 i8 )× x max x) 2 p(x)dx
N= i=1 n E[ Δ i 2 ] = P Fe i=5 8 E[ Δ i 2 ] + P Se i=1 4 E[ Δ i 2 ]
P Fe = P e ( S 2 | S 3 )×P( S 3 )+ P e ( S 3 | S 2 )×P( S 2 )
P Se = P e ( S 1 | S 2 )×P( S 2 )+ P e ( S 2 | S 1 )×P( S 1 )+ P e ( S 3 | S 4 )×P( S 4 )+ P e ( S 4 | S 3 )×P( S 3 )
P Fe = 1 4 erfc( w 1 2 σ )
P Se = 1 2 erfc( w 2 2 σ )

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