Integration of IR-UWB Services into Single-and Multi-Channel Optical Coherent OFDM Network

Distribution of wireless communication signals over implemented optical networks is a challenged task since the presence of wireless services may affect the performance of the existing wired ones. This paper addresses the possibility of integrating impulse radio-ultrawideband (IR-UWB) wireless services into implemented coherent optical orthogonal frequency division multiplexing (CO-OFDM) network. Simulation results are presented for the transmission of a 625Mb/s UWB signal with either 50Gb/s single-channel or three-channel OFDM system. Both Gaussian monocycle and 5 th -order derivative Gaussian pulses are used to implement the UWB system with two modulation formats, namely ON-OFF keying (OOK) and biphase modulation (BPM). The simulation results reveal that the performance of the CO-OFDM channels is not affected in the presence of UWB signals.


1-INTRODUCTION
Impulse radio-ultrawideband (IR-UWB) signals are considered the most promising schemes for next generation short-rang broadband wireless communication and sensor networks [1,2]. The Federal Communication Commission (FCC) limits the power spectral density (PSD) of a UWB signal to -41 dBm/MHz over the spectral range 3.1-10.6 GHz. The low emitted PSD causes the wireless transmission distances to be limited within a few meters [3]. In this context, UWB-over-fiber (UWBoF) attracts increasing interest as a promising technology for extending the coverage of UWB services [4][5].
Further, several proposals have been reported in the literature to integrate UWB services into wavelength division multiplexing-passive optical network (WDM-PON) to provide high order data-rate and flexible wired and wireless services with a favorable cost [6][7][8].
The quest for higher spectral efficiency over long-haul fiber transmission has been studied intensively due to the exponential growth of global communications traffic [9]. Advanced signal processing and high-order modulation formats are the key technology to increase the spectral efficiency in these advanced optical communication systems [10,11].
Recently, optical orthogonal frequency division multiplexing (O-OFDM) has opened up to high-order modulation formats and sophisticated modulation schemes for long-haul optical communication systems [12,13]. In fact, coherent optical (CO) OFDM is considered as promising candidate for future long-haul high capacity transmission systems [14,15]. This is mainly due to its high spectral efficiency and advantages in overcoming transmission impairments such as chromatic dispersion and polarization-mode dispersion [16].
The aim of this paper is to present a feasibility study for integrating IR-UWB wireless services with implemented CO-OFDM network. Simulation results are reported for transmitting 625 Mb/s Gaussian monocycle and 5 th -order derivative Gaussian UWB signals with either single or three-channel CO-OFDM signals (50 Gb/s per channel). The target is to trace the interfering effect between the wireless and wired services. The simulation results are obtained using commercial software package, Optisystem (version 13.0).

2-CO-OFDM FIBER TRANSMISSION LINK
The transmission link of the single-channel CO-OFDM system is illustrated in Fig. 1. The system is simulated using 50 Gb/s QPSK signaling. Other parameter values used in the simulation are listed in Table 1.  , respectively. The simulation results reveal that CO-OFDM system under investigation can offer a received a BER less than 10 -9 when the length of the transmission link is less than 1344 km.

3-Multiplexing IR-UWB Signal with a Single-Channel CO-OFDM System
The starting point is to simulate the transmission of UWB signal with single-channel CO-OFDM. The system under investigation is illustrated schematically in Fig. 4 where the factor 0.5 introduced to take into account the effect of overlapping introduced by OFDM technique.
The transmission performance of the two-channel WDM system is simulated when the OFDM signal is multiplexed with each one of the four UWB signals. The results reveal that the presence of OFDM signal affects slightly the transmission performance of the UWB signals. In contrast, the transmission of UWB signal over the link will not affect the transmission performance of the CO-OFDM system. D e c e m b e r 0 5 , 2 0 1 4  Table 2 lists the BER for the four UWB signals after transmission over a single span with the CO-OFDM signal. The corresponding received eye diagrams of the IR-UWB signals are shown in Fig. 6. Results related to BERs corresponding to the transmission of UWB signals alone over the fiber are also given in the table. These results are used to calculate Figure of Degradation (FoD) (2) where BERW corresponds to the BER of the UWB signal when OFDM signal is present.
Note that BERn = 1 (i.e., FoD = 0) indicates that the WDM system introduces no power penalty compared with the singlechannel system. Further, BERn >1 (i.e., FoD > 0) indicates that the performance of the received channel in WDM system is degraded compared with the single-channel system. The results in Table 2 highlight the following fact: the performance of the UWB system is slightly degraded in the presence of CO-OFDM transmission and the degradation is more pronounced for monocycle BPM signaling. The FoD for this case is 1.6 compared with 0.06 -0.08 for other UWB formats. It is worth to mention here that the BER of the OFDM system is not affected by the presence of any type of IR-UWB signals and equals to 6.2 ×10 -19 after transmission over one fiber span.

4-Transmission of IR-UWB Signals with Three-Channel CO-OFDM System
The simulation performance in section 2-1 is repeated here The spectrum of the multiplexed signal corresponding to the transmission of the monocycle OOK signal with the threechannel optical OFDM is depicted in Fig. 7. Fig. 7: Spectrum of the multiplexed signal generated by combining the monocycle OOK signal with three-channel CO-OFDM system. Table 3 illustrates the effect of the presence of the OFDM signals on the performance of the transmitted UWB signals.
Note that the performance degradation of the transmitted UWB signal increases in the presence of three optical OFDM signals compared to the case with one OFDM signal and this effect is more pronounce for the monocycle OOK signaling. D e c e m b e r 0 5 , 2 0 1 4 It is worth to mention here that the presence of the UWB signal will not affect the performance of the three OFDM channels as shown in Fig. 8. The BER of each OFDM channel is 6.2 ×10 -19 after one span transmission in the presence or absence of UWB signals.

5-CONCLUSIONS
A feasibility study for integrating IR-UWB wireless services into implemented CO-OFDM network has been investigated. Simulation results have been reported for transmitting 625 Mb/s Gaussian monocycle and 5 th -order derivative Gaussian UWB signals with either single or three-channel CO-OFDM signals (50 Gb/s per channel). The simulation results reveal that the performance of the UWB signals is slightly degraded in the presence of OFDM signals and this effect is more pronounced as the number of OFDM channels increases. In contrast, the performance of the CO-OFDM channels is not affected by the presence of the wireless services.