|Taha H. Dahawi||Faculty of Engineering, Multimedia University, Persiaran Multimedia, 63100 Cyberjaya, Selangor, Malaysia|
|Zulfadzli Yusoff||Faculty of Engineering, Multimedia University, Persiaran Multimedia, 63100 Cyberjaya, Selangor, Malaysia|
|Redhwan Q. Shaddad||Faculty of Engineering, Taiz University, Taiz, Yemen|
|Mohd Shahril Salleh||TM R&D, Lingkaran Teknokrat Timur, Cyberjaya 63000, Malaysia|
|John M. Senior||Optical Networks Group, University of Hertfordshire, Hatfield AL10 9AB, UK|
Future passive optical networks will require simultaneous provision of wired and wireless services to provide high-capacity and high-speed information access network to overcome the capacity demand. In this paper, a converged fiber-wireless (FiWi) network architecture including an orthogonal frequency division multiplexing passive optical network (OFDM-PON) and a radio over fiber (RoF) system is proposed. Two multiple-input multiple-output radio over fiber channels are inserted into the left and right side of OFDM-PON spectrum, using a single-sideband frequency translation (SSB-FT) technique. The significant merit of the proposed architecture is its high spectral efficiency as the two multiple-input multiple-output radio over fiber channels and OFDM-PON transmit at the same frequency, which reduces the complexity of transceiver design by applying a novel method for the implementation of local oscillators in both transmitter and receiver. A proof-of-concept downstream link over 20 km standard-PON was conducted by simulation to demonstrate the performance of the proposed converged fiber-wireless network architecture and the link performance was assessed using error vector magnitude and bit error rate.
FiWi Network; OFDM-PON; RoF; SSB-FT
Mobile data traffic is increasing exponentially due to the rapid advancement in smartphone technology. The estimation of the total video communication traffic over mobile and fixed systems by 2020 will be around 2,600 times the traffic in 2010 (Osseiran, 2014; Suryanegara, 2016; Tornatore et al., 2017). Therefore, the next generation mobile network would require high-capacity and high-speed information access networks to overcome the capacity demand (Mitchell, 2014; Kani et al., 2017; Suryanegara & Asvial, 2018).
The parallel demand for both capacity and mobility requires researchers to come up with solutions that fuse the two aspects based on optical access network (Jarrar et al., 2015). The integration of such wireless system with optical access network is called a fiber-wireless (FiWi) network (Liu & Effenberger, 2017; Tzanakaki et al., 2017).
Radio over fiber (RoF) is one of the technologies that could be used in FiWi network to integrate the wireless system with optical network (Jia et al., 2007; Lim et al., 2018). It allocates and controls multiple wireless services at the central station to deliver the wireless signals as analogue signals to the base stations (BSs) through the optical fiber infrastructure. Thus, it greatly reduces the BS complexity and cost (Latunde, 2016). In addition, to reduce the capital expenditure (CAPEX) of RoF installation, RoF system should be integrated with the currently deployed optical network access using passive optical network (PON) which has ready fiber infrastructure in the form of fiber to the home (FTTH) and to the curb (FTTC) (Mitchell, 2014; Gutiérrez et al., 2016).
Passive optical networks are widely deployed today within optical access networks, which provide users with high-capacity and high-speed data at affordable cost (Da Silva et al., 2017). PONs based on orthogonal frequency division multiplexing (OFDM-PON) utilize the privileges of OFDM transmission, such as chromatic dispersion tolerance, long haul transmission, smooth convergence with current wireless system as well as high-capacity delivery (Cano et al., 2015; Senior et al., 2012). These advantages makes OFDM-PON one of the candidates for future access network implementation. The network topology for OFDM-PON comprises one optical line terminal (OLT) located at the central station and several optical network units (ONUs) at the customer side. In the optical distribution network (ODN), a passive optical power splitter is used to connect all the ONUs to the OLT. Figure 1 represents the topology of the standard OFDM-PON, showing that in the downstream (DS) scenario, signals are generated and optically modulated in the OLT and then transmitted through 20 km of a standard single mode fiber (SSMF). The signals are split to the ONUs via a splitter and then demodulated in ONUs at customer side. However, for the upstream (US) scenario, signals are transmitted from the ONUs to the OLT either using the same wavelength as that of the DS or a different wavelength. The ONU could be a house, a business office, or a base station for the wireless end, which could be utilized through the RoF technology.
Figure 1 OFDM-PON architecture
RoF in PONs has drawn considerable interest in recent research due to its simplicity and low cost deployment (Zhu et al., 2013; Wagner et al., 2016;). The advantage of these architectures is their capacity for scalability. However, some of the active components such as wavelength division multiplexer and demultiplexer are required to be used in the ODN section and a narrow optical filter is needed at the ONU resulting in expensive network architecture. Moreover, the coexistence of multi-RoF and time and wavelength division multiplexing passive optic network (TWDM-PON) has been recently reported in (Oliveira et al., 2017), where RoF and TWDM-PON are two separate systems each with different wavelengths, causing the TWDM-PON to have impact on the RoF system due to the nonlinear effects of cross-phase modulation.
To overcome the problems mentioned above, this paper proposes a FiWi coexistence network between RoF and OFDM-PON, wherein both systems transmit with a single wavelength. In addition, expensive optical components such as tuneable optical filters at the ONUs and a WDM demultiplexer at the ODN are eliminated. At the earlier development stage of OFDM-PON led by the ACCORDANCE project (Kanonakis et al., 2012), RoF had been integrated with OFDM-PON through coexistence of multiple WiMAX and LTE channels over the PON and was successfully transmitted through a single channel. However, each channel required a local oscillator (LO) and bandpass filter (BPF) at the transmitter and receiver part of the PON system. This leads to a complex system, especially if multiple-input multiple-output (MIMO) system is considered. Therefore, a different technique is required to eliminate some LOs for the existing network to be efficiently used.
In this research, the coexistence of the two MIMO-RoF channels and OFDM-PON has been designed such that both systems transmit with a single optical channel and same carrier frequency utilizing the single-sideband frequency translation (SSB-FT) technique. The use of this technique was reported in (Liu & Seeds, 2010) for MIMO-RoF systems in order to reduce the number of LOs for three MIMO channels from three LOs to only one. However, the authors considered only wireless services and did not utilize the PON fiber infrastructure for the RoF system. In Elmagzoub et al. (2016), the authors reported a network architecture that could transmit two MIMO-RoF and wired signal over a standard PON system using polarization multiplexing. However, this method is only applicable for wavelength division multiplexing passive optical network (WDM-PON) and also requires two dual-drive Mach-Zehnder Modulator (DD-MZM) and polarization controllers for modulating the two MIMO signals and another MZM for the baseband wired signal, which make the system complex and costly. Thus, the contribution of this paper is to utilize SSB-FT in our proposed converged FiWi architecture including two MIMO-RoF and wired OFDM-PON to provide a cost-efficient transceiver design by reducing the number of LOs implementation that are required to allocate each MIMO and wired signal in the aggregated OFDM spectrum so that they do not overlap in the frequency domain. As a result, they could be modulating with only one MZM optical modulator and transmitting over a single optical channel without the need for a WDM demultiplexer at the ODN part of the PON system.
This paper is organized as follows: In Section 2, the description of the proposed method is presented; Section 3 illustrates the simulated modeling of the proposed network. Section 4 discusses the results and performance. Finally, concluding remarks are made in Section 5.
A FiWi network including an OFDM-PON and two MIMO-RoF systems using the SSB-FT technique has been demonstrated. The main advantage of the proposed architecture is to reduce the complexity of transceiver design of both the OFDM-PON and RoF systems by applying a novel method for the implementation of LOs in both the transmitter and receiver compared to previously reported network architectures that require a LO for each of the ONUs/BSs. In addition, only one LO was employed for both the two MIMO-RoF systems and OFDM-PON. Furthermore, both the RoF systems and OFDM-PON utilized the same carrier frequency to achieve a high spectrally efficient FiWi system. The network performance was evaluated based on EVM and BER measurements. The simulated results show that the OFDM-PON and the two MIMO-RoF system has achieved the EVM target with clear constellation points. In addition, the proposed FiWi converged system was compared with non-converged system that included only the two MIMO-RoF channels. The BER performance shows that a power penalty of 4.8 dB due to the interference from wired-OFDM to the two MIMO-RoF channels in a converged system and insertion loss of PON splitting ratio. The simulation results verify that our scheme could be a promising candidate for converged wired and wireless networks.
This work was funded by TM R&D Research Grant under Grant No RDTC/160914.
|R2-EECE-3265-20191017010357.jpg||Figure 1 OFDM-PON architecture|
|R2-EECE-3265-20191017010458.jpg||Figure 2 Implementation of SSB-FT technique over the proposed architecture|
|R2-EECE-3265-20191017010557.jpg||Figure 3 Simulated setup of converged OFDM-PON and RoF system|
|R2-EECE-3265-20191017010633.jpg||Figure 4 a-g The spectral of different optical and electrical signals at assigned points in Figure 3|
|R2-EECE-3265-20191017011634.jpg||Figure 5 EVM versus received optical power for wired and MIMO-RoF signals with B-T-B/20 km fiber transmission.|
|R2-EECE-3265-20191017011724.jpg||Figure 6 Constellation diagram at -9 dBm received optical power after 20 km transmission|
|R2-EECE-3265-20191017075011.jpg||Figure 7 BER versus received optical power for MIMO1 and MIMO2 with converged and non-converged system over 20 km fiber transmission|
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