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384 INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.11, NO.5, SEPT 2016

IEEE 802.15.3C Transmission over Multimode Fiber Links: Performance Comparison of RF and IF over Fiber Architectures Moussa El Yahyaoui , Ali El Moussati *, Kamal Ghoumid , Basil Al-Mahdawi , Catherine Lepers Signals, Systems and Information Processing team, National School of Applied Sciences, Oujda, Morocco Nanomedecine Lab, Universite de Franche-Comté, 16 route de Gray, 25030 Besançon, France Mine-Telecom, SAMOVAR UMR 5157 CNRS, Télécom SudParis, Evry, France E-mail: [email protected] Abstract-In this paper we investigated two solutions for distributing 802.15.3c signal over Multi-Mode Fiber (MMF) to solve the problem of limited coverage at 60 GHz. The first solution consists of the transmission of the signal at 60 GHz directly over fiber (RFoF) and the second solution consists of the transmission of the signal at intermediate frequency 5 GHz over fiber (IFoF). The millimeter wave is generated using the Optical Carrier Suppression (OSC) technique, and the optical link is based on MMF without optical amplifiers in order to obtain a low cost architecture. The systems are evaluated and analyzed by Bit Error Rate (BER) and Error Vector Magnitude (EVM) performance. The comparison between the two solutions is based on the fiber length, the complexity and cost of the implementation. Index Terms- 60 GHz, BER, EVM, IEEE 802.15.3c, Multi-Mode Fiber, Radio over Fiber.

I. INTRODUCTION The wired technologies such as xDSL and Fiber to The Home connections provide high broadband access network, which now allow the delivery of multi-gigabit wireless services. Current wireless network systems have limited bandwidth capacity, i.e. WIFI 802.11a provides up to 54 Mb/s and 802.11n provides up to 400 Mb/s [1]. However, new indoor wireless applications, such as the wireless multimedia applications (IPTV, Wireless-HD, in-room gaming) and kiosk applications, need higher data throughput. Current data rates, like uncompressed video streaming signals, require several GHz of bandwidth for the transmission

[2]. To support these high data bandwidths new radio standards such as IEEE 802.11ad and IEEE 802.15.3c, which can provide up to 7 Gb/s throughput, use unlicensed 7 GHz band at 60 GHz [2-3]. The 60 GHz frequency band has limited coverage distance (around 10 m) due to high free-space losses (loss over 1 m at 60 GHz is 68dB) and the waves cannot penetrate the walls. Hence, there is a need for a waveguide to carry these waves. The best candidate is optical fiber due to the low loss offered. Wireless network based on Radio over Fiber technology combining both, high bandwidth capacity of optical communication and flexibility of wireless access, can help in extending 60 GHz radio coverage in indoor environments. In this work we investigate the use of radio over fiber solution to significantly increase the covered spaces such as large rooms or even whole buildings. Millimeter RoF technology is becoming the promising solution for the broadband access networks, because it can increase the bandwidth capacity, coverage area and mobility and it decrease the cost of base station [4]. In such system, each base station consists of simple and compact optoelectronic repeater connected by fiber link to the central station. The architecture of the RoF home network is presented In Fig 1, which consists of a Home Communication Controller (HCC) and Radio Access Points (RAPs). RAPs are linked to a central management networks HCC unit through optical fiber. The optical fiber transports the radio signals transparently. The signal generation and

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processing are centralized in the HCC, and the antennas are dumb and simple.

II. ARCHITECTURES OF TRANSPORT TECHNOLOGIES IN RADIO OVER FIBER

Wireless Personal Area Network WPAN IEEE 802.15.3c has been proposed for the future high data rate, which operates in the 60 GHz millimeter-wave band. IEEE 802.15.3c supports uncompressed video streaming at 1.78 or 3.56 GB/s, and higher bandwidth downloading in Kiosks [3]. Recently, numerous studies of RoF using millimeter wave have been published [4- . In the paper [6] the authors considered the RoF system with Single Mode Fiber (SMF) to reach 40 km at 40 GHz. In this paper the RoF system is based on MMF. The use of MMF is justified by the cost-effectiveness and many buildings have legacy optical fiber infrastructure networks based on MMF. Moreover we used Optical Carrier Suppression (OCS) technique to overcome the limitation of modal-bandwidth of MMF. A simulation of 802.15.3c PHY RoF system, using the co-simulation technique between OptiSystem and Simulink, has been realized.

Radio over Fiber systems are generally classified into three main types of transport architecture: Radio Frequency (RF), intermediate frequency (IF) and baseband over fiber. A full duplex system can use different transport architectures on the uplink and the downlink as shown in Fig 2. In the RF-over-fiber architecture the wireless signal are transported directly over the fiber at radio carrier frequency without the need of frequency equipment (up converter or down converter) at RAP. The IF-over-fiber architecture consists in transporting the radio signal at an Intermediate Frequency (IF) over fiber, this architecture require the frequency conversion at RAP, which increase the complexity of implementation. The Baseband over fiber architecture consists in transposing the digital signal onto an optical carrier for transmission over fiber from the HCC station to the RAP; this solution is not practical for millimeter waves because of high cost and complexity implementation of RAP.

This paper is organized as follows; in the first paragraph, we present the architecture of Radio over Fiber system, and then we introduce the IEEE 802.15.3c standard. Finally, we provide numerical results of the simulation of the IEEE 802.15.3c PHY RoF system.

Fig.1.

RoF home network architecture Fig.2. Transport technologies of the radio over fiber

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The choice of architecture determines the required equipment to be used at the RAP and the complexity of the system. In Table 1, we present the advantages and drawbacks of each architecture. RoF systems based on baseband over fiber transport schemes requires very expensive equipment for each access point, for this reason we limited our study to architectures RFoF and IFoF. Table 1: Benefits and drawbacks of RF, IF and BB architectures Optical architecture RF Signal over fiber

IF Signal over fiber

Baseband Signal over fiber

Benefits

Drawbacks

Simple RAP implementation. Centralized control signal processing at HCC.

Sensitivity of chromatic dispersion that seriously limits the transmission distance of the fiber. Local oscillators and mixers at each radio access point. Limit the ability to upgrade or reconfigure the radio network. Very expensive equipment at each radio access point.

Chromatic dispersion lower than the transmission RFover-fiber. Integrating electronic components in low cost. Significantly reduce the effects of chromatic dispersion.

III. SIMULATION SETUP The simulation setup is developed in OptiSystemTMV7.0 and SIMULINK . The downlink path is considered from the HCC to the RAP. The RoF system design is composed of two major parts: The optical link architecture, and the transmitter and receiver of HSI interface. A. RF over fiber The Radio Frequency over Fiber RFoF architecture designed with OptiSystem software is shown in Fig 3. The in-phase (I) and quadrature (Q) components are firstly transposed to 5GHz by mixing with an oscillator split in two paths with a 90 degree phase shift. The continuous-wavelength (CW) optical source of 850 nm wavelength, that offer high bandwidth compared to 1300 nm in case of OM4 MMF fiber (Efective Modal Bandwidth at 850nm: 5000

MHz.km) [ ] , which is used to generate the optical carrier. The electrical IF signal controls a first Mach-Zehnder modulator MZM1 for obtaining a modulated optical carrier. OCS modulation is performed by leading the two arms of the second Mach-Zehnder modulator with an RF signal phase-shifted by π and polarizes the modulator to its minimum intensity Vπ . The optical signal is transported by OM4 MMF fiber to the receiver. At the receiver side, the photodetector (PD) converts the optical signal to an electrical signal. The received signal is then amplified, filtered and demodulated to recover I and Q signals.

Fig.3. RF over fiber architecture implemented in OptiSystem

B. IF over fiber The intermediate frequency over fiber (IFoF) architecture is shown in Fig 4. The in-phase (I) and quadrature (Q) components are transposed to IF by mixing them with an RF oscillator split in two paths with a 90 degree phase shift, and then transposed to optical form by an external modulator MZM. The modulated signal is transported by an OM4 MMF fiber to the receiver. At the reception the photodiode PD converts the optical signal into electrical signal. The received signal is amplified and demodulated to recover I and Q signals.

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Fig 4. IF over fiber architecture implemented in OptiSystem.

C. 802.15.3c HSI PHY model Fig. 5 shows the block diagram of the HSI PHY mode modeled in Simulink according to the standardsof802.15.3c. The HSI PHY is designed for Non Line of Sight (NLOS) operation and uses Orthogonal Frequency-Division Multiplexing (OFDM) with a forward error correction based on Low-Density Parity-Check (LDPC) code. The data bits encoded by two LDPC encoders (use 1/2 and 3/4coding rate), and the output of LDPC encoder is multiplexed to form a single data stream. After the data multiplexer, the bits are interleaved by a bloc interleaver of length of 2688 bits. The interleaved bits are mapped into a serial complex data using the QPSK, 16QAM or 64QAM modulation format. Each group of 336 complex numbers is assigned to an OFDM symbol. The output data of the constellation mapper are then parallelized, and pilots and null tones are added up before the tone interleaver. The tone interleaver assures that neighboring symbols are not mapped into adjacent subcarriers. The interleaved tones are modulated by OFDM modulator that consists of 512-point IFFT. Finally, adding a cyclic prefix of 64 tones is added and then transmitting the symbols in the optical link.

Fig. 5. Block diagram of HSI PHY model implemented in MATLAB

As for the receiver, the received signal is removed from the cyclic prefix and then demodulated by OFDM that consist of 512-point FFT. Since the output of the de-mapper is sensitive to the amplitude of the input symbols, a block for channel estimation and gain correction has been implemented in SIMULINK [10]. The obtained bit stream is de-interleaved and demultiplexed into 2 bit streams to be decoded with the LDPC decoders. Tab.2 shows the parameters of HSI OFDM system. Table 2: HSI modulation and coding schemes parameters MCS index

Data rate(Mb/s)

Modulation scheme

LDPC codes rate

QPSK 16QAM 64QAM

IV. RESULTS AND DISCUSSION After running the simulation of the complete system, we obtained the following results:

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According to [8], the EVM threshold for successful transmission is 10% and 25% for 16QAM and QPSK modulation respectively. The insets of Fig. 7(a) shows the constellation diagrams at the receiver of RFoF. As can be seen from this figure, the QPSK signal could travel almost 3050 m with its EVM reaching 25% although a 16QAM signal could only travel up to 2450 m successfully. On the other side, Fig. 7(b) shows the constellation diagrams at the receiver of IFoF. As can be seen from this figure, the QPSK signal could travel almost 310 m with its EVM reaching 25% although a 16-QAM signal could only travel up to 230 m successfully.

Fig. 6. HSI OFDM electrical and optical spectrum: (a) electrical spectrum at 5 GHz, (b) optical spectrum at 5 GHz and (b) optical spectrum at 60 GHz.

Fig. 8 shows the received electrical power after photo detector for both architecture IFoF and RFoF using QPSK modulation. After 450 m and 3600m of respectively RFof and IFoF, the noise power become very important compared to signal power (Es/No≤ ), which explain the power constant, and it is difficult to recover the original information in this case.

HSI OFDM electrical spectrum at IF-frequency shown in Fig 6(a) is transposed to optical signal by external modulation using MZM1 as shown in Fig 6(a). The generation of 60 GHz signals by OCS technique shown in Fig 6 (b) is obtained by applying a 27 GHz to dual arm MZM2.

Fig. 7. Constellation diagram at receiver. (a) RFoF case. (b) IFoF Case.

Fig.8. Electrical received power: (a) IFoF case, (b) RFoF case.

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which has lower attenuation compared to 850 nm MMF, hence the distance achieved. Table : Comparison between previously published works with proposed systems Refs

RF/IF carrier (GHz)

system RFoF System

IFoF System

Fig.9. BER vs. MMF length for RFoF system.

Fig.10. BER vs MMF length for IFoF system.

Fig. 9 and Fig. 10 show BER performances of three MCS (as shown in Tab. 2) versus MMF fiber length for RFoF and IFoF architectures. As we can see in these graphs, we have reached up to 350 m MMF fiber with BER less than 10-6 in the case of RFoF. For the IFoF architecture, we have reached up to 3300 m with BER less than 10-6 in the case of IFoF. As we can see, this architecture achieves higher distance compared to RFoF. Table shows the features and performances of some works compared to proposed system. As we can notice that the researchers considered RF carriers lower than 60 GHz used in our work. Moreover, ref [1 ] used the 1330 nm MMF,

] ] Proposed system ] ] Proposed system

Optical modulation OFM DSB

MMF length (m)

BER -

OCS

-

DSB DSB

-

DSB

-

-

As a conclusion, the advantage of RFoF is that it can potentially reduce the complexity of the 60 GHz radio access points (RAPs), but has limited distance (up to 360 m in our case). While for the IFoF it can reach long distance (up to 3400 m in our case), but the RAP hardware now requires LOs and mixers for the frequency conversion processes, which may limit the ability to upgrade or reconfigure the radio network with the provision of additional radio channels or the implementation of required changes in RF frequency. IF radio signal transport allow transmission over low cost multimode fiber and several commercial RoF products are based on the distribution of radio signals over MMF since many buildings have legacy optical fiber infrastructure networks based on multimode fibers. The best performances of IFoF can be explained by low dispersion at the IF frequency compared to RF frequency.

V. CONCLUSION We have presented and evaluated RFoF and IFoF links with HSI physical layer mode. This work has been done by co-simulation technique. We have calculated the BER performance of the system for various modulation schemes QPSK, 16QAM and 64QAM. The results show that the MMF fiber link distances can achieve 350 m and m for respectively RFoF and IFoF using QPSK modulation at BER=10- . The IFoF is

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suitable for long distances of (500 m – m) where the architecture is less expensive and more complicated. Otherwise the RFoF is suitable for distances below 1km where the architecture has a medium cost and simplified and flexible radio access point. REFERENCES IEEE Std 802.11n: “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 5: Enhancements for Higher Throughput”, pp. 1- , Oct. . IEEE Std P802.11ad: “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment : Enhancements for Very High Throughput in the GHz Band”, pp. 1-667, June . IEEE std 802.15.3c: “IEEE Standard for Information technology-- Local and metropolitan area networks-- Specific requirements-- Part 15.3: Amendment 2: Millimeter-wave-based Alternative Physical Layer Extension”, pp. 1- , Oct. . R.V. Prasad, B. Quang, K. Chandra et al., “Analysing IEEE 802.15.3c protocol in Fi-Wi hybrid networks”, IEEE Consumer Communications and Networking Conference (CCNC), Las Vegas, NV, pp. 749, Jan. . M. Liso Nicolas, M. Jacob, and T. Kurner, “Physical layer simulation results for IEEE 802.15.3c with different channel models”,Advances in Radio Science, vol. 9, pp. 173-177, Aug. 2011. J.W. Zhang et al., “Experimental demonstration of Gb/s CAP 64QAM radio-over-fiber system over 40 GHz mm-wave fiber-wireless transmission”, Optics Express, vol. 21, pp. 26888, Nov. . M. Elyahyaoui, A. El Moussati, K. Ghoumid, S. Mekaoui and T. Gharbi, “Performance evaluation of coherent optical OFDM communications using LDPC codes”, International Journal of Microwave and Optical Technology, vol. 11, pp. - , Jan. . R. Schmogrow, B. Nebendahl, M. Winter et al., “Error Vector Magnitude as a Performance Measure for Advanced Modulation Formats”, IEEE Photonics Technology Letters, vol. 24, pp. - , Jan. . 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., vol. 18, pp. 1726– , Aug. . D. Pepe and D. Zito, System-level simulations investigating the system-on-chip implementation of 60 GHz transceivers for wireless uncompressed

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