Optics & Laser Technology 47 (2013) 347–354

Contents lists available at SciVerse ScienceDirect

Optics & Laser Technology

0030-39

http://d

n Corr

Infocom

Tel.: þ6

E-m

journal homepage: www.elsevier.com/locate/optlastec

A novel optical single-sideband frequency translation technique fortransmission of wireless MIMO signals over fiber-wireless system

Redhwan Q. Shaddad a,b,n, Abu Bakar Mohammad a, Abdulaziz M. Al-Hetar a,b, Samir A. Al-Gailani a,c

a Lightwave Communications Research Group (LCRG), Infocomm Research Alliance, Universiti Teknologi Malaysia, 81310 Johor, Malaysiab Communication and Computer Engineering Department, Faculty of Engineering and Information Technology, Taiz University, Yemenc Industrial Technical Institute, Mua’lla, Aden, Yemen

a r t i c l e i n f o

Article history:

Received 3 August 2012

Received in revised form

12 September 2012

Accepted 19 September 2012

Keywords:

Fiber wireless access network

Radio over fiber

Optical single-sideband frequency

translation

92/$ - see front matter & 2012 Elsevier Ltd. A

x.doi.org/10.1016/j.optlastec.2012.09.028

esponding author at: Lightwave Communicat

m Research Alliance, Universiti Teknologi Ma

0 172559558; fax: þ60 75536155.

ail address: rqs2006@gmail.com (R.Q. Shadda

a b s t r a c t

The fiber-wireless (FiWi) access network is a powerful hybrid architecture of optical backhaul and

wireless front-end to support high data rates and throughput with minimal time delay. By using radio

over fiber (ROF) technique, the optical fiber is well adapted to propagate multiple wireless services

having different carrier frequencies. However, multiple wireless signals which have the same carrier

frequency cannot propagate over a single optical fiber on the same wavelength, such as multi-input

multi-output (MIMO) signals. A novel optical single-sideband frequency translation technique is

designed and simulated to solve this problem. 240 Mb/s 802.11n MIMO signals are proposed to

transport over FiWi system using the proposed approach at 2.4 GHz and 5.0 GHz carrier frequencies.

The crosstalk between MIMO signals with the same carrier frequency is excluded, since each MIMO

signal is carried on a specific optical wavelength. Error vector magnitude (EVM) values of �29.83 dB

(for 2.4 GHz) and �28.41 dB (for 5.0 GHz) have been achieved for bit error rate (BER) 10�5 in the

proposed FiWi system.

& 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Next generation access networks are projected to support highdata rate, broadband multiple services, scalable bandwidth, andflexible communications for manifold end-users. There are manyemerging optical and wireless access technologies proposed forthese requirements [1–3]. The optical fiber access networksprovide high-bandwidth digital services and long-distance com-munication, but less ubiquitous. The wireless access networksprovide flexible and ubiquitous communication with a lowdeployment cost. However, its deployment scalability is limitedby the spectrum and range limitations [4–6]. The FiWi accessnetwork is a powerful hybrid architecture of optical backhaul andwireless front-end. This hybrid FiWi access network supportshigh data rates and throughput with minimal time delay [7]. TheFiWi networks are achieved by integrating optical access tech-nologies (such as, passive optical networks (PONs)) and wirelessaccess technologies (such as, cellular systems, worldwide inter-operability for microwave access (WiMAX), and wireless fidelity(WiFi)) using ROF techniques [7–10].

ll rights reserved.

ions Research Group (LCRG),

laysia, 81310 Johor, Malaysia.

d).

For broadband access services, there is strong competitionamong several access technologies. Among the various emergingoptical and wireless access technologies, the orthogonal fre-quency division multiplexing (OFDM) based technology is themost promising technology because it provides high transmissioncapacity, efficient bandwidth access, high flexibility on dynamicbandwidth allocation, and robust dispersion tolerance in bothoptical and wireless links [1,11]. Since the bandwidth demand ofthe wireless end user (WEU) increases dramatically in the wire-less front-end, the optical backhaul is used to provide broadbandinterconnections between the central office (CO) and all theaccess points (APs). In this integrated network, complexity ofthe AP structure is reduced by moving the routing, bandwidthallocation, and processing functionalities to the CO. The FiWisystem can offer essential benefits to future service providers [7].

Fig. 1 shows architecture of a FiWi access network. The opticalbackhaul is a tree network connecting the CO and wireless front-end. The optical backhaul comprises of an optical line terminal(OLT) at the CO, a standard single mode fiber (SSMF), a remotenode (RN), and multiple APs. The wireless front-end consists ofwidespread APs to penetrate numerous WEUs. In this study, thewireless front-end is established using WiFi technology based onthe IEEE 802.11n wireless local area network (WLAN). The802.11n WLAN enhances the system capacity on a time-varyingmultipath fading channel by using a MIMO OFDM technique [12].Two basic concepts are employed in 802.11n to increase the

Fig. 1. FiWi access network architecture.

R.Q. Shaddad et al. / Optics & Laser Technology 47 (2013) 347–354348

physical layer (PHY) data rates: MIMO and 40 MHz bandwidthchannels. There are four spatial streams and four antennasinstead of a single spatial stream and one antenna, which increasethe data rate. These streams are multiplexed at the transmitterand demultiplexed at the receiver by using a spatial divisionmultiplexing (SDM) technique. The 802.11n WLAN has manyinteresting characteristics such as high coverage, great through-put, high reliability and operates in both 2.4 GHz and 5.0 GHzradio frequency (RF) bands [13].

The transport of the wireless signal in the FiWi system issubject to several impairments, including dispersion effects in thefiber link and multipath fading in the wireless link [7]. Thespectral efficient OFDM transmission provides an effective solu-tion to eliminate intersymbol interference (ISI) caused by dis-persive channels [11]. It is a known fact that multiple wirelesssignals having the same carrier frequency, such as MIMO signalsspecified in the 802.11n standard, cannot propagate over a singleoptical fiber on the same wavelength. A traditional solution usingwavelength division multiplexing is expensive for this particularapplication, since the system then requires several optical sourcesand photodetectors [14].

In this paper, a new architecture of the FiWi system isproposed and designed based on an optical backhaul whichtransports wireless MIMO OFDM signals over fiber. A noveloptical single-sideband frequency translation technique isdesigned and simulated to transport MIMO signals specified inthe 802.11n standard over a single optical fiber to provide240 Mb/s data rate at the WEU. The performance of the proposedFiWi system is analyzed in terms of BER, EVM, and signal-to-noiseratio (SNR). MATLAB, OptiSystem 11.0 and Advanced DesignSystem (ADS) 2008 software tools are used to simulate theproposed FiWi system, where the 802.11n signals are modulatedat the carrier frequencies of 2.4 GHz and 5.0 GHz.

This paper is organized as follows: in Section 2, the literaturereview for transport of wireless MIMO signals over optical fiber isintroduced, the principles of the proposed novel method areelaborated in Section 3, the FiWi system design and simulationconsiderations are covered in Section 4, Section 5 is dedicated todescribe the result analysis and discussion, and finally, Section 6concludes the paper and suggests future work.

2. Transport of wireless MIMO signals over fiber

For wireless broadband transmission, the MIMO radio systemhas been developed [13] and implemented using multiple trans-mit/receive antennas. MIMO system is distinguished by improvingtransmission range/reliability, and delivering higher data transmis-sion rates over the single-input single-output (SISO) system. One ofthe main problems of wireless link is a channel fading, especially inthe multipath channels. The merge of the throughput improve-ment and path diversity proposed by MIMO technique [15] withthe OFDM immunity to dispersive fading of channel is consideredas a favorable combination for the broadband wireless accessnetwork [16,17].

By using ROF techniques, the optical fiber is well adapted topass multiple wireless signals having different carrier frequencies.However, multiple wireless signals which have the same carrierfrequency cannot propagate over an optical fiber, such as MIMOsignals feeding multiple antennas in FiWi system. This problemstarts once multiple MIMO signals are combined and modulatedonto a single optical carrier. Individual MIMO signals could not beseparated and recovered thereafter with regular electrical filter-ing. The solution for this problem was proposed using WDM andsub-carriers multiplexing (SCM) [14,18] techniques. These tech-niques are not cost-effective, since multiple optical sources andphotodetectors are required.

Transmission of three wireless MIMO signals all with 2.44 GHzcarrier frequency over an optical fiber is proposed and demon-strated using an electrical single-sideband frequency-translationtechnique [19]. The proposed approach decreased the maximumcrosstalk level between the different MIMO channels as comparedto transport the same signals by SCM technique.

In this paper, we propose and demonstrate transport of twowireless MIMO signals with the same carrier frequency over afiber in the FiWi system using an optical single-sideband fre-quency translation technique. The novel approach does not needlow-frequency local oscillators (LOs) at the OLT and the AP ascompared to [19]. One optical source is enough to transportseveral MIMO signals over the optical fiber by using the opticalsingle-sideband frequency translation technique. The FiWi systembased on the new approach can also support the wavelengthreuse technique, so one optical source is enough to generate theoptical carrier which is reused at the AP, and many wavelengthswhich convey number of MIMO signals over the SSMF [20].

3. Principles of optical single-sideband frequency translationfor transport of wireless MIMO signals over fiber

The block diagram of the proposed approach is shown inFig. 2(a). This technique uses the optical double sideband (ODSB)technique to generate three wavelengths for each laser diode (LD):the two single-sideband wavelengths (such as ld11, ld12 as shown inFig. 2(a)), and same optical carrier frequency (such as l1). The twosingle-sideband wavelengths ld11, ld12 are used to modulate twoMIMO signals separately. The wavelength l1 is reused to generateuplink wavelength at the AP, using the optical carrier suppressionand separation (OCSS) modulation scheme [8,21].

A dual-arm modulator (DAM) is used to generate the threewavelengths from the LD. Fig. 2(b) shows the wavelength of theLD as the inset (i), and the three generated wavelengths from theDAM as the inset (ii). Two optical interleavers (ILS) are used afterthe DAM to separate the three generated wavelengths into twochannel groups: one continuous wave (CW) wavelength l1, andother single-sidebands with the two downlink wavelengths ld11,

ld12 (as shown in Fig. 2(b) inset (iii)) which are used to modulatethe MIMO signals at the external intensity optical modulators

R.Q. Shaddad et al. / Optics & Laser Technology 47 (2013) 347–354 349

(IMs). The channel spacing between each downlink wavelengthand the CW wavelength is fo, so the channel spacing of thegenerated downlink wavelength pair is determined by twice thefrequency of the sinusoidal clock 2� fo, as illustrated in Fig. 2(b) inset(iii). The type of the used ILs is 1:2 WDM interleaver, since each ILseparates even channels from odd channels across a WDM combonto two different output ports. The amplitude spectrum at eitherof the two output ports has a pass-band and a stop-band periodicallywith a free-spectral range (FSR) [22]. In this design, the WDM ILsare implemented by using 2:2 AWG routers in WDM demultiplexingmode. Because the number of channels per output port is small,the worst-case frequency offset has small value, which can beneglected [22].

The OLT implements an 802.11n MIMO data processor. TheMIMO data processor generates two MIMO signals X1, X2 with thesame carrier frequency f1 as shown in Fig. 2(b) inset (iv) and (v),respectively. The two MIMO signals X1, X2 are biased to becompatible with the nature of the optical signals and then opticallymodulated by the two IMs on the two assigned wavelengths ld11,

ld12, respectively. In this method, each IM modulates the MIMOsignal X1, X2 by using optical single sideband with carrier (OSSBþC)modulation scheme as illustrated in Fig. 2(b) as the insets (vi) and(vii), respectively. The OSSBþC modulation method enhances opti-cal spectral efficiency for transporting modulated RF signals overoptical fiber, and overcomes the fiber chromatic dispersion problem[7,8]. The modulated optical signals with the downlink wavelengthpair (ld11, ld12) are amplified by an optical amplifier (such as erbiumdoped fiber amplifier (EDFA)) and then coupled with the optical CWsignals with wavelength l1) as shown in Fig. 2 inset (viii). Thecoupled optical signal propagates along an SSMF.

The AP receives the optical downstream, interleaves it into theCW optical signal with the wavelength (l1), and the two modu-lated optical signals with the wavelengths (ld11, ld12) as shown inFig. 2(b) in the insets (ix–xi). There is a small additive noise whichis produced by the optical segment. The AP then converts the twomodulated optical signals directly to the suitable electrical signalsby using an optical receiver for each signal. The electrical signalsare then band-pass filtered according to the allocated RF fre-quency f1 by using BPFs to get the MIMO OFDM signals (X01, X02).The wireless MIMO signals then propagate to the WEU using 2�2MIMO technique.

Fig. 2. Transport of wireless MIMO signals over optical fiber using the optical single-si

(b) power spectra of the signals according to the indicated insets in the structure.

4. FiWi system design

FiWi system design comprises of an OLT at the CO connected to awireless AP through an SSMF in the downstream direction as shownin Fig. 2(a). The AP then transmits the wireless MIMO signalsthrough the wireless channels to the MIMO end-user. In this paper,the FiWi system is designed to transport wireless 802.11n MIMOsignals over fiber using a novel optical single-sideband frequencytranslation technique. In the CO, the WiFi 802.11n data processorgenerates two MIMO signals. The OFDM technique is implementedwith a 64-Quadrature amplitude modulation (QAM). The 802.11nprocessor is designed to provide a 240 Mb/s data rate with a channelbandwidth of 40 MHz. The two MIMO signals (X1, X2) are modulatedon RF carrier frequency f1 which is selected from the 2.4 GHz or5.0 GHz RF frequency bands.

The LD generates an optical signal with a wavelength l1¼

1552.500 nm (193.100 GHz). The DAM, with a clock frequencyfo¼25 GHz, is used to produce the two downlink wavelengths {ld11¼

1552.725 nm (193.075 GHz), and ld12¼1552.323 nm (193.125 GHz)}as shown in Fig. 3. The two downlink wavelengths ld11 and ld12

are used to modulate the two MIMO signals X1, X2 separately atIMs. Furthermore, a CW optical signal with optical carrier l1¼

1552.500 nm (193.100 GHz) is created at the CO. This signal is reusedat the AP to produce uplink wavelengths. Fig. 3 shows the inputoptical power spectra of the down/uplink channels to the SSMF as theinset (i). The wireless MIMO-OFDM signals (X1 and X2) with the RFcarrier frequency of 5.0 GHz are upconverted over upper single-sideband of the optical carrier wavelengths ld11 and ld12 usingOSSBþC modulation scheme as shown in Fig. 3 in the insets (ii)and (iii), respectively. The frequency separation between each down-link wavelength and its optical single-sideband is 50 GHz as shown inFig. 3. The three optical signals with wavelengths (ld11, ld12 and l1)are coupled and then propagated along a 20 km SSMF with attenua-tion of 0.2 dB/km and dispersion coefficient of 17 ps/nm/km. In thisdesign, the launched optical power into the fiber has a suitable value(3.701 dBm) to avoid signal impairment by fiber nonlinearity [23].

The AP receives the optical downstream, interleaves it to themodulated optical signals, and then converts it directly toelectrical signals by using PDs with power sensitivity of�30 dBm. The electrical signals are band-pass filtered accordingto the allocated RF frequency by using BPFs to get the MIMO

deband frequency translation (a) block diagram of the proposed FiWi system and

Fig. 2. Continued.

R.Q. Shaddad et al. / Optics & Laser Technology 47 (2013) 347–354350

OFDM signals (X01, X02) which are the same as the transmittedsignals (X1, X2) with small noise generated by the optical elementsand the optical link. The wireless MIMO signals (X01, X02) propa-gate through MIMO channel to the WEU using 2�2 MIMO OFDMtechnique. The AP supports data rate up to 240 Mb/s through100 m outdoor wireless link with high spectral efficiency of 6. Thegeneral specification of the optical backhaul and wireless front-end of the proposed FiWi system is summarized and shown inTable 1.

The SNR and the BER are estimated according to [24]. TheMIMO system has been considered over the fiber-wireless channel.The purpose of the MIMO channel estimation, in the receiver, is toidentify the optical channel and wireless channel between eachpair of transmit and receive antennas. For MIMO channel estima-tion, a high throughput long training field (HT-LTF) is provided inthe high throughput-mixed format (HT-MF) preamble of the IEEE802.11n. This technique is called training symbol-based channelestimation [12,17], since a long training symbol is transmitted for

Fig. 3. Optical power spectra of the allocated channels at the OLT.

Table 1The general specification of the proposed FiWi system.

Parameter Value

Optical Backhaul

Transmitted power of LD 5 dBm

Receiver sensitivity �30 dBm

Fiber length 20 km

Attenuation 0.2 dB/km

Dispersion coefficient 17 ps/nm/km

Optical modulation method OSSBþC

Wireless Front-end

Transmitted power of the AP 16 dBm

Carrier frequencies 2.4 GHz or 5.0 GHz band

Channel bandwidth 40 MHz

Data rate of the AP 240 Mb/s

Link range 100 m

Channel type Fading channel

Radio technology OFDM MIMO

Size of MIMO system 2�2 MIMO

Modulation 64-QAM

Coding scheme Convolutional code of rate 2/3

Bandwidth efficiency 6

R.Q. Shaddad et al. / Optics & Laser Technology 47 (2013) 347–354 351

each spatial stream indicated by the selected modulation andcoding scheme (MCS) [13]. In the simulation design, the frequencyselective behaviors caused by chromatic dispersion in the opticallink and channel fading in the wireless link are characterized in thetraining symbols at the IEEE 802.11n data processor in the OLT. The

training symbol-based channel estimation is followed by themaximum likelihood (ML) MIMO detection process which deter-mines the transmitted data symbols from the received signal[15,17]. In contrast, the training-based channel estimation hasthe relatively low computational complexity at the receiver anddraws more interests in the OFDM system [25].

5. Results and discussion

The group of the wavelengths (ld11, l1 and ld12) are received atthe AP and then demultiplexed. The AP downconverts the opticalsignals at the interleaved downlink wavelengths (ld11 and ld12) tothe corresponding MIMO OFDM signals and bandpass filter themaccording to the RF carrier frequency. The detected electricalsignal is filtered by using 8th order Butterworth BPFs, with a60 MHz bandwidth, and center frequencies 2.4 GHz or 5.0 GHz.The frequency responses of these BPFs are illustrated inFig. 4(a) and (b) for the center frequencies 2.4 GHz and 5.0 GHz,respectively. These filters have a frequency response as deter-mined by the following transfer function [26]

H fð Þ ¼ a:B2

� �n

Pn�1k ¼ 0 j f�f c

� �� B

2 :exp j p2 1þ 2kþ1n

� �� �� � ð1Þ

where H(f) is the transfer function of the BPF, f is the frequencyparameter, n is the order of the filter, a is the insertion loss (a has

Fig. 4. (a,b) The frequency response of the BPFs, and (c–f) the spectra of the transmitted wireless signals X01 and X02; at 2.4 GHz and 5.0 GHz frequencies.

R.Q. Shaddad et al. / Optics & Laser Technology 47 (2013) 347–354352

been setting to one in the simulation design), B is the 3 dB filterbandwidth, and fc is the filter center frequency.

The filtered signal is amplified by using RF amplifier providing asuitable transmitted power level (16 dBm). At the AP, the trans-mitted MIMO OFDM signals X01 and X02 at the RF carrier frequency of2.4 GHz have spectra shown in Fig. 4(c) and (d), respectively. Inaddition, the spectra of the transmitted MIMO OFDM signals X01 andX02 at 5.0 GHz carrier frequency are shown in Fig. 4(e) and (f),respectively. There is no crosstalk between the MIMO OFDM signalswhich have the same frequency, because each signal is carried on anindependent wavelength with a large channel spacing. The band-widths of the MIMO OFDM signals X01 and X02 are 40 MHz allocatedon the same RF carrier frequency. These signals are transmitted onthe wireless channel to the MIMO WEU.

The BER was analyzed to evaluate the system performance.Fig. 5 shows BER versus SNR for the received signal at the receiverof the WEU. The additive white Gaussian noise (AWGN) channeland fading channel models were simulated in the wireless MIMOOFDM system, since 20 km SSMF with a dispersion coefficient of17 ps/nm/km is considered in the optical backhaul. The SNRrequired for a BER of 10�5 as specified for RF transmission canbe determined for the plots in Fig. 5(a) under AWGN channel for

2.4 GHz and 5.0 GHz carrier frequencies. The SNR values of 15 dBand 16.5 dB achieved BER of 10�5 at the carrier frequencies of2.4 GHz and 5.0 GHz, respectively. In addition, BER versus SNR,under fading channel for 2.4 GHz and 5.0 GHz carrier frequencies,is shown in Fig. 5(b). The SNR values of 28 dB and 30 dB achievedBER of 10�5 at the carrier frequencies of 2.4 GHz and 5.0 GHz,respectively. There is a small difference between the required SNRto achieve BER of 10�5 at the carrier frequencies of 2.4 GHz and5.0 GHz for the both wireless channel models.

The optical signal-to-noise ratio (OSNR) is estimated at theoptical receiver entrance point with 0.1 nm noise bandwidth. TheBER performance versus the OSNR is shown in Fig. 6. Whenthe AWGN wireless channel is taken into account, low OSNRvalues (17.26 dB and 19.24 dB) are required to achieve a mini-mum BER of 10�5 at the WEU for the frequencies 2.4 GHz and5.0 GHz, respectively, as shown in Fig. 6(a). To realize a good BERperformance considering the fading channel in wireless link, highOSNR values (32.61 dB and 34.11 dB) are required for the fre-quencies 2.4 GHz and 5.0 GHz, respectively, as shown in Fig. 6(b).The optical amplifier generates the most noise which is producedby the optical backhaul [27]. The created noise from the wirelesschannel and receiver front-end dominates the whole FiWi system

Fig. 5. BER versus SNR at the receiver of the WEU considering (a) the wireless

AWGN channel and (b) the wireless fading channel. Fig. 6. BER versus OSNR considering (a) the wireless AWGN channel and (b) the

wireless fading channel.

R.Q. Shaddad et al. / Optics & Laser Technology 47 (2013) 347–354 353

performance, especially when the wireless fading channel isconsidered [24].

Fig. 7(a) and (b) shows the simulated 240 Mb/s 64-QAMconstellation diagrams for the transmitted and received signalsfrom the data processor at the OLT to the wireless end-user at theRF carrier frequencies of 2.4 GHz and 5.0 GHz, respectively. Clearscatter-plots are achieved for the both RF frequencies, for a SNR of30 dB and BER close to 10�5, which is well detected andundistorted, indicating little degradation due to the transmissionover the FiWi link. The EVMs of �29.83 dB (for 2.4 GHz) and�28.41 dB (for 5.0 GHz) achieved the good performance of theproposed system. The EVMs are calculated considering thefollowing equation [28]:

EVM dBð Þ ¼ 10:log10

SMk ¼ 19Stx,k�Srx,k9

2

SMk ¼ 19Stx,k9

2

" #ð2Þ

where EVM is the value of the difference between a collection ofreceived symbols and transmitted or ideal symbols, Stx,k is thecorresponding transmitted symbol of the constellation associatedwith the kth symbol, Srx,k is the received symbol associated withStx,k, and M is the number of the symbols for the Inphase-

Quadrature constellation.

6. Conclusions and future work

The hybrid FiWi system is proposed and demonstrated basedon the transmission of wireless 802.11n MIMO signals over fiberby using an efficient novel optical single-sideband frequencytranslation technique. The proposed FiWi system supports thewavelength reuse technique, so one optical source is enough togenerate the optical carrier which is reused at the AP, and manywavelengths for carrying multiple wireless MIMO signals over thefiber. The crosstalk between different MIMO signals with thesame RF carrier frequency is excluded, since each MIMO signal iscarried on a specific optical wavelength. The physical layerperformance has been reported in terms of the BER, the EVM,and the SNR. The proposed FiWi system achieved transmission ofwireless 802.11n MIMO signals over 20 km SSMF and along100 m outdoor MIMO wireless channel. This was investigatedusing RF carrier frequencies of 2.4 GHz and 5.0 GHz to provide240 Mb/s data rate with a channel bandwidth of 40 MHz.

In future, this system can be redesigned by using higher datarate up to 600 Mb/s based on IEEE 802.11n. In addition, multiple2�2 MIMO signals with different frequencies on the samefrequency band of 2.4 GHz or 5.0 GHz could be multiplexed andthen transmitted over fiber using the proposed novel approach.

Fig.7. The constellation diagram of the transmitted and received signals from the

data processor at OLT to the WEU, considering (a) 2.4 GHz and (b) 5.0 GHz.

R.Q. Shaddad et al. / Optics & Laser Technology 47 (2013) 347–354354

Acknowledgments

We greatly appreciate Universiti Teknologi Malaysia andPhotonics Research Laboratory for providing the facilities whichenabled this work to be accomplished. We would also like tothank the Ministry of Science, Technology and Innovation(MOSTI), Malaysia for sponsoring this work under project votenumber 73720.

References

[1] Chow CW, Yeh C, Wang C, Wu C, Chi S, Lin C. Studies of OFDM signal forbroadband optical access networks. IEEE Journal on Selected Areas inCommunications 2010;28(6):800–7.

[2] Shaddad, R, Mohammad, AB, Idrus, S, Al-hetar, A, Al-geelani, N. Emergingoptical broadband access networks from TDM PON to OFDM PON, In:Proceedings of PIERS 2012, Kuala Lumpur, Malaysia, 2012. p. 102–6.

[3] Kuran M, Tugcu Tuna. A survey on emerging broadband wireless accesstechnologies. Computer Networks 2007;51(11):3013–46.

[4] Ghazisaidi V, Maier M, Assi C. Fiber-wireless (FiWi) access networks: asurvey. IEEE Communications Magazine 2009;47(2):160–7.

[5] Kazovsky L, Wong S, Ayhan T, Albeyoglu K, Ribeiro M, Shastri A. Hybridoptical-wireless access networks. Proceedings of the IEEE 2012;100(5):1197–225.

[6] Shaddad R, Mohammad A, Al-Hetar A. Performance evaluation for opticalbackhaul and wireless front-end in hybrid optical-wireless access network.Journal of Optoelectronics and Advanced Materials 2011;5(4):376–80.

[7] Lim C, Nirmalathas A, Bakaul M, Gamage P, Lee K, Yang Y, et al. Fiber-wirelessnetworks and subsystem technologies. Journal of Lightwave Technology2010;28(4):390–405.

[8] Jia Z, Yu J, Ellinas G, Chang G. Key enabling technologies for optical-wirelessnetworks: optical millimeter-wave generation, wavelength reuse, and archi-tecture. Journal of Lightwave Technology 2007;25(11):3452–71.

[9] Ghazisaidi N, Maier M. Fiber-wireless (FiWi) access networks: challenges andopportunities. IEEE Network 2011;25(1):36–42.

[10] Shaddad R, Mohammad A, Al-Hetar A. Analysis of physical layer performance ofhybrid optical-wireless access network. Optics Communications 2011;284(20):4894–9.

[11] Pham DT, Hong MK, Joo JM, Han SK. Heterogeneous gigabit orthogonalfrequency division multiplexing/radio over fiber transmissions of wired andwireless signals using a reflective semiconductor optical amplifier and single-arm mach-zehnder modulator. Microwave and Optical Technology Letters2012;54(8):1954–8.

[12] Yang H. A road to future broadband wireless access: MIMO-OFDM-based airinterface. IEEE Communications Magazine 2005;43(1):53–60.

[13] Perahia E, Stacey R. Next generation wireless lans: throughput, robustness,and reliability in 802.11n. New York: Cambridge University Press; 2008.

[14] Zelst, System for transporting multiple radio frequency signals of a multipleinput, multiple output wireless communication system to/from a centralprocessing base station, U.S. Patent Application 2004, 20040017785A1:1-8.

[15] Paul T, Ogunfunmi T. Evolution, insights and challenges of the PHY layer forthe emerging ieee 802.11n amendment. IEEE Communications Surveys &Tutorials 2009;11(4):131–50.

[16] Zhang W, Xiang-Gen X, Letaief K. Space-time/frequency coding for MIMO-OFDM in next generation broadband wireless systems. IEEE Wireless Com-munications 2006;14(3):32–43.

[17] Cho. Y, Kim J, Yang WY, Kang C-G. MIMO-OFDM wireless communicationwith MATLAB. Wiley; 2010.

[18] Seto H, Shoki S, Ohshima. Optical subcarrier multiplexing transmission forbase station with adaptive array antenna. IEEE Transactions on MicrowaveTheory and Techniques 2001;49(10):2036–41.

[19] Liu C, Seeds A. Transmission of wireless MIMO-type signals over a singleoptical fiber without WDM. IEEE Transactions on Microwave Theory andTechniques 2010;58(11):3094–101.

[20] Shaddad R, Mohammad A, Al-Hetar A. Spectral efficient hybrid wirelessoptical broadband access network (WOBAN) based on transmission ofwireless MIMO OFDM signals over WDM PON. Optics Communications2012;285(20):4059–67.

[21] Akanbi O, Yu J, Chang G, New A. Scheme for bidirectional WDM-PON usingupstream and downstream channels generated by optical carrier suppressionand separation technique. IEEE Photonics Technology Letters 2006;18(2):340–2.

[22] Cao S, Chen J, Damask JN, Doerr CR, Guiziou L, Harvey G, et al. Interleavertechnology: comparisons and applications requirements. Journal of Light-wave Technology 2004;22(1):281–9.

[23] Xin X. The key technology in optical OFDM-PON. ZTE Communication2012;10(1):40–4.

[24] Fernando, X.N., Anpalagan, A., On the design of optical fiber based wirelessaccess systems, In: Proceedings of IEEE international conference on commu-nications 2004, Canada.

[25] Jansen SL, Morita I, Schenk TC, Tanaka H. Long-haul transmission of16�52.5 Gbits/s polarization-division multiplexed OFDM enabled by MIMOprocessing. Journal of Optical Networking 2008;7(2):173–82.

[26] Jeruchim M, Balaban P, Shanmugan K. Simulation of communication sys-tems: modeling, methodology, and techniques. New York: Kluwer AcademicPublishers; 2002.

[27] Shieh W, Djordjevic I. OFDM for optical communications. New York: Elsevier;2010.

[28] Moscoso-Martir M, Fernandez I, Monux A. Signal constellation distortion and berdegradation due to hardware impairments in six-port receivers with analog I/Qgeneration. Progress in Electromagnetics Research 2011;121:225–47.