Radio-over-fiber transport for the support of wireless broadband services [Invited]

TLDR: In this paper, a review of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed.

Abstract: Some of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from personal area networks (such as ZigBee and ultrawideband) through wireless local area networks to wireless metropolitan area networks (WiMAX) and third-generation mobile communications systems. The performance of the radio-over-fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified, and complete network demonstrations are implemented.

Figures

Fig. 3 shows the bit-error rate (BER) calculated from the measured Q factor according to

Table 1. MMF specificationsa

Fig. 17. EVM measurements for downlink UMTS radio over fiber transmission in the system of Fig. 16, as a function of central unit VCSEL RF drive power. Note: all other systems are present. [13].

Fig. 6. Original base-band monocycle and after up-conversion at 8.5 GHz , Ibias=3 mA.

Fig. 7. Experimental setup for performance analysis of MB-OFDM UWB-on-fiber.

Fig. 10. Measured EVM after up-conversion to fRF+2fLO=5.1 GHz as a function of the power ratio PRF/PLO between the RF signal and the local oscillator

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Additional Information
http://hdl.handle.net/10251/134320
Gomes, N.; Morant, M.; Alphones, A.; Cabon, B.; Mitchell, J.; Lethien, C.; Csörnyei, M....
(2009). Radio-over-fiber transport for the support of wireless broadband services. Journal of
Optical Networking. 8(2):156-178. https://doi.org/10.1364/JON.8.000156
https://doi.org/10.1364/JON.8.000156
The Optical Society

1
Radio over Fiber Transport for the Support of Wireless
Broadband Services
Nathan J. Gomes,
1
Maria Morant Pérez
2
, Arokiaswami Alphones
3
, Béatrice Cabon
4
, John
E. Mitchell
5
, Christophe Lethien
6
, Mark Csörnyei
7
, Andreas Stöhr
8
and Stavros Iezekiel
9,*
1
Department of Electronics, University of Kent, Canterbury, CT2 7NT, United Kingdom
2
Valencia Nanophotonics Technology Center - Universidad Politécnica de Valencia, Camino
de Vera, s/n, 46022 – Valencia, Spain
3
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore
639798
4
IMEP-LAHC,MINATEC-INPG 3 parvis Louis Néel, BP 257, 38016 Grenoble Cédex, France
5
Department of Electronic and Electrical Engineering, University College London, Gower St,
London, WC1E 6BT, United Kingdom
6
Institut d'Electronique, de Microélectronique et de Nanotechnologie
IEMN, UMR 8520,
Université des Sciences et Technologies de Lille, Avenue Poincaré, BP 60069, 59652 Villeneuve
d'Ascq - France and Research Federation IRCICA, FR 3024, Parc Scientifique de La Haute
Borne, 50 avenue Haley, 59652 Villeneuve d’Ascq, France
7
Department of Broadband Infocommunications and Electromagnetic Theory
Budapest University of Technology and Economics
Goldmann Gy. tér 3., Budapest, 1111, Hungary
8
Universität Duisburg-Essen, Optoelektronik, Lotharstr. 55, 47057 Duisburg, Germany

2
9
Department of Electrical and Computer Engineering, University of Cyprus, 75 Kallipoleos
Avenue, PO Box 20537, Nicosia 1678, Cyprus
*
Corresponding author: iezekiel@ucy.ac.cy
Some of the work carried out within the EU Network of Excellence ISIS on radio over
fiber systems for the support of current and emerging wireless networks is reviewed.
Direct laser modulation and externally modulated links have been investigated, and
demonstrations of single-mode fiber and multimode fiber systems are presented. The
wireless networks studied range from PANs (such as ZigBee and UWB) through wireless
LANs to wireless MANs (WiMAX) and third generation mobile communications systems.
The performance of the radio over fiber transmission is referenced to the specifications of
the relevant standard, protocol operation is verified and complete network demonstrations
have been implemented. © 2007 Optical Society of America
OCIS codes: (060.0060) Fiber optics and optical communications, (060.5625) Radio frequency
photonics.
1. Introduction
Radio over fiber (RoF) has become of increasing interest for the transport of wireless signals [1].
Radio over fiber can provide a number of advantages for wireless signal distribution, such as
improved coverage through the use of low power distributed antennas, transparency and
flexibility, trunking efficiency gains and lower cost of deployment [2]. Within the European
Network of Excellence “ISIS” (“Infrastructures for broadband access in wireless /photonics and
integration of strengths in Europe”) [3], partners have investigated radio over fiber transport of

3
various wireless signal types, ranging from those proposed for personal area networks (PANs),
through wireless local area networks (LANs), and particularly the ubiquitous WiFi networks, to
metropolitan and wide area networks (MANs, and WANs). Of course, while novel radio over
fiber techniques may have been used, or experiments may have been testing the boundaries for
the use of low-cost components, where transmission of standard wireless signals has been
demonstrated, performance is always measured using metrics for the wireless signals specified in
the standards documents. Usually, such performance is specified in terms of error vector
magnitude (EVM) in the multilevel signal constellation points, but signal-to-noise ratio (SNR)
and bit-error ratio (BER) are also physical layer performance metrics. However, the standards
also specify higher layer protocol operation, and in this paper, studies of such effects in radio
over fiber systems are also presented. The paper is structured as follows: in Sections 2 to 4,
experiments on the physical layer performance of wireless PANs, LANs and MANs/WANs,
respectively, are presented. In Section 5, the performance limitations of a high-quality radio
over fiber link using an external modulator are theoretically exposed. In Section 6, the higher
layer protocol effects that have been observed for wireless LAN transport over fiber are
discussed, while in Section 7 the demonstration of a wireless sensor network using radio over
fiber is presented. Section 8 describes the demonstration of 60 GHz RoF systems transmitting
broadband data up to 12.5 Gb/s for potential applications in home area networks (HANs).
Medium-range outdoor transmission at several Gb/s has also been achieved. Finally, the work is
summarized in Section 9.

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2. Radio over fiber link experiments: PANs
There is currently great interest in ultra-wideband (UWB) communications for future
personal area networks (PANs). The growing interest in UWB is due to its excellent
coexistence with other licensed and unlicensed wireless services, its low radiated power,
the tolerance to multi-path fading and the low probability of interception due to its wide
spectrum and low energy.
UWB wireless transmission technology targets short-range high bit-rate communications,
potentially exceeding 1 Gbit/s. In this section several experiments using UWB technology
are reported. In the first case, the use of the impulse-radio (IR) radio technique is used in a
scenario which could be seen as a viable solution for the distribution of high-definition
audio/video content in fiber-to-the-home (FTTH) networks. A high-bandwidth external
optical modulator and standard single-mode fiber (SSMF) are used for IR-UWB
transmission over up to 60km of fiber. In the second experiment, a single-mode vertical
cavity surface emitting laser (VCSEL) is used for IR-UWB transmission in conjunction
with frequency upconversion. Although only upconversion up to low frequencies is
demonstrated, the principle could be applied to upconversion to millimeter wave
frequencies where radio spectrum of interest for such applications exists (such as the 62
GHz to 66 GHz band). The third experiment examines the transmission of multiband
orthogonal frequency division multiplexed (MB-OFDM) UWB signals for indoor fiber
installations that are typically based on multi-mode fibers (MMF), VCSELs operating at
850 nm, and low-cost receivers.

Frequently asked questions

Q1. What have the authors contributed in "Radio over fiber transport for the support of wireless broadband services" ?

In this paper, the authors investigated the performance of a high-quality radio over fiber link using an external modulator and the dependence of EVM on both the VCSEL bias current and the RF/LO power ratio. 

Q2. What are the future works mentioned in the paper "Radio over fiber transport for the support of wireless broadband services" ?

The intended future application in this scenario would be home area networks, but outdoor experiments have also shown the ability for error-free ( i. e. BER < 10-9 ) transmission up to 40 m. 

Q3. How many MAC check measurements are required during deployment?

In order to avoid failures in operation caused by the timeout uncertainty in a large scale metropolitan environment, multiple MAC level check measurements are required during deployment to ensure reliable network functioning by keeping off the uncertainty region. 

Q4. How much reduction in throughput is achieved when using the basic access method in a TCP?

When using the basic access method in a TCP downlink the reduction in throughput increases from 10%, when no fiber is used, to 15% for 13.1km of fiber. 

Q5. What is the maximum power required for the receiver to perform?

A receiver power level of -21 to -19 dBm is required for achieving the target BER performance from the system with the use of FEC. 

Q6. How many EVMs are required for the whole path?

The EVM (rms) required for IEEE 802.11g transmission must be less than 5.6% for the whole path (i.e. including both optical and wireless paths). 

Q7. What is the effect of the increased fiber length on the throughput of the system?

As the fiber length is increased, the throughput of the system steadily decreases due to the increased waiting time between packet transfers caused by the fiber propagation. 

Q8. What is the frequency up-conversion needed in future WiMax systems?

frequency up-conversion is necessary in future WiMax systems (for example) since they can exploit the 2 GHz to 66 GHz band. 

Q9. What is the effect of channel errors on the MAC protocol?

Channel errors, which cause lost frames as specified by Frame Error Rates (FER) shown in Figs. 24 and 25, also affect the performance of the MAC protocol since they increase the number of retransmissions at the MAC level. 

Q10. What is the effect of MAC level checks on the performance of a wireless network?

In particular, multiple MAC level checks are needed during network deployment in order to avoid timeout uncertainty due to clock jitter. 

Q11. How many dBi can be used to transmit data?

Calculations show that by using high-gain antennas (50 dBi), transmission up to approximately 1 km at a BER of 10-9 is possible for 12.5 Gb/s operation with a 99% link availability. 

Q12. What is the effect of streamlining the acknowledgment procedure?

This streamlining of the acknowledgment procedure has been shown to dramatically improve performance when used in radio over fiber systems [25], although care must be taken to guard against unduly high frame loss due to noise/errors and collisions when the numbers of acknowledgments are reduced. 

Q13. What are the physical layer performance metrics for wireless PANs?

such performance is specified in terms of error vector magnitude (EVM) in the multilevel signal constellation points, but signal-to-noise ratio (SNR) and bit-error ratio (BER) are also physical layer performance metrics. 

Q14. How many gb/s of IR-UWB transmission can be achieved?

Experiments have shown the feasibility of 1.25 Gb/s IR-UWB transmission (using external modulation), with a BER of 10-9 being achieved for lengths of standard single-mode fiber up to 50 km. 

Q15. What is the effect of the time-outs on the receiver?

These time-outs, set with the assumption of only a relatively short wireless channel, will expire and result in lost packets if exceeded by the time delay introduced by the addition of optical fiber. 

Q16. What is the way to achieve a BER of 10-3 to 10-4?

For the simulated RoF system model, the authors can see that an Input Power of -14 to -16 dBm would be ideal to achieve a BER of 10-3 to 10-4 for a fiber length of less than 1 km, without the use of FEC. 

Q17. What is the correlation coefficient between the emitted and received pulses?

The The authorbias =3 mA case was chosen after evaluating the Pearson product-moment correlation coefficient (MCV [6]) between the emitted and received pulse after up conversion, which led to a maximum correlation coefficient of ρ=0.94 and 0.76 forI bias =3 mA and 6 mA respectively. 

Q18. What is the maximum length of a ZigBee network?

The maximum fiber length that can be inserted into the sensor network is limited by the timeout parameters of the MAC layer acknowledgement signals [27]. 

Q19. What is the way to use the optical backbone in indoor networks?

Wireless indoor communication systems applying an optical backbone provide an economic and flexible approach for sensor area networks in buildings. 

Q20. What is the average carrier amplitude of an OFDM input signal?

With the input SNR being held constant, the average carrier amplitude Asig,Av of an OFDM input signal vsig(t) was swept through a range of levels.