Orthogonal frequency division multiplexing ofdm is attracting increasing attention in optical communication systems, thanks to its inherent benefits such as high spectral efficiency and resistance to frequencyselective channels. Abstractwe present a novel optical orthogonal frequency division multiplexing oofdm scheme, suitable for inten sitymodulated directdetection systems. Since the signals generated in ofdm systems are complexvalued, they cannot be directly used in direct detection optical systems. Such systems also have the important advantage of very narrow channel spacing in optical frequencydivision multiplexing ofdm systems. Enhanced unipolar orthogonal frequency division multiplexing euofdm is a novel unipolar multicarrier modulation scheme used in intensity modulation and direct detection systems for optical. Whereas in coherent detection, the principle of optical mixing is utilized with local oscillator and. In directdetection oofdm it is detrimental to transmit a strong carrier, as this leaves less.
The real valued ofdm signal is generated by using a complex conjugate extension for the input to ifft 5. Improved directdetection optical ofdm system it is clear from fig. Directdetection ofdm received optical spectrum left, its components middle and the results right of photodetection in the electrical domain. In direct detection system, there is no need of carrier generator at the receiver avoiding the circuit complexity. In section 2, the principle of a direct detection optical ofdm system with data clipping.
The architecture of ddoofdm system is similar to figure 1. The efficiency of precoding is investigated on a recently discussed approach for optical ofdm, capable of direct detection based on compatible singlesideband modulation compssb 8,9. Ofdm systems for optical communication with intensity modulation. A conventional asymmetrically clipping optical acoofdm is applied to. Recent research efforts have focused on optical ofdm techniques that optimize spectral and energy ef. Ofdm systems for optical communication with intensity.
For singlechannel ddoofdm systems, high papr gives rise to fiber. However, coherent optical ofdm coofdm is the next generation technology for the optical communications, since it integrates the advantages of both coherent systems and ofdm systems. Experimental demonstration of costeffective intensity. A clustering algorithm to resist multipath effect for ofdmvlc system jie ma, jing he, zhihua zhou, yaoqiang xiao proc. Performance analysis of optical ofdm transmission systems. Block diagram of optical ofdm using direct detection. A performance analysis was conducted to compare the performance of direct detection and coherent detection schemes in terms of their ber, dispersion tolerance and q factor. A detailed analysis of clipping distortion introduced by digital clipping and normalization is provided. Comparison of orthogonal frequencydivision multiplexing and onoff keying in. Compared with the coherent optical ofdm coofdm 1, the lowerpriced and lesscomplex directdetection optical ofdm ddoofdm 2. Furthermore, the side information generated in pts is transmitted by pilot sequences which increase the utilization of subcarriers.
Spectral efficiency and receiver sensitivity in direct. Pdf performance of asymmetrically clipped optical ofdm. This approach applies the signal to the amplitude of the transmitted ssbsignal 10. Simulation of digital optical receiver of intensity. Impact of machzehnder nonlinearity on the receiver. Experimental validation of a constantenvelope ofdm system. Asymmetrically clipped absolute value optical ofdm for. Also a performance comparison is done to show the signi. The power consumption and cost of optical ofdm are still the major obstacles to its. Passive optical network pon has become a preferable access technique for cloud computing due to its elastic bandwidth capacity and transmission stability. Du, low sample rate transmitter for directdetection optical ofdm, optical fiber telecommunications ofc 2009, san diego, paper owm4. The system uses a traditional dualdrive mzm transmitter and a directdetection receiver. Singlesideband ssb directdetection optical orthogonal frequency division multiplexing ofdm transmission is experimentally demonstrated in a system with 125 km.
The advantages and methods for optical single sideband ossb and channel estimation are analyzed completely. The software allows for the isolated simulation of each block, as well as the complete simulation of the whole system. An optical ofdm transmitter encodes transmitted symbols. The electrical parameters of the generated ofdm and ceofdm signals see inset 1 and 2 of fig. One way to realize vlc is intensity modulation direct detection imdd. Several key technologies in ddoofdm system have been discussed. There are two basic ways to implement ofdm in optical systems 14. A comprehensive theoretical model of direct detection dd optical orthogonal frequency division multiplexing oofdm system is described in general. The application of ofdm in optical fiber communication systems. The signaltointerferenceplusnoise ratio of the noised singlesideband optical orthogonal frequencydivision multiplexing ssboofdm signal in a directdetection ofdm system is first deduced. Directdetection optical ofdm transmission system with pre. Performance investigation of ofdmbased softwaredefined. Twofold peaktoaverage power ratio reduction technique in. Peng, directdetection optical ofdm, in optical fiber communication conference, osa technical digest online optical society of america, 2014, paper th3k.
Direct detection systems are immune to clipping noise and has a simple receiver architecture whereas coherent detection systems have complex transceiver design but superior. In imdd, orthogonal frequency division multiplexing ofdm, originally employed in radio frequency communication, is considered as a strong candidate solution to. Performance analysis of direct detection and coherent detectiosystem for optical ofdm using qam and dpsk. Intensity modulation and direct detection imdd is a costeffective optical communication strategy which finds wide applications in fiber. Performance evaluation and simulation of ofdm in optical. Optical ofdm has recently attracted lots of interest because of its simple equalizer for compensating the linear impairments throughout the link1,2. Recently, coherent optical orthogonal frequency division multiplexing coofdm has been considered for the next generation 400gbs long haul data transmission.
Intensity modulation and direct detection imdd systems with vertical cavity. Osa theoretical and experimental investigation of direct. Pdf performance analysis of direct detection and coherent. High data rate coherent optical ofdm system for longhaul. Optical ofdm received a great attention after proposing it as a modulation technique for the longhaul transmission in both direct and coherent detection. In rf wireless systems, ofdm has become the modulation of choice to combat temporal dispersion. Intensity modulation and direct detection imdd is a costeffective optical communication strategy which finds wide applications in fiber communication, freespace optical communication, and indoor visible light communication. In this method an optical carrier is transmitted whose relative. Performance analysis of a dual polarization coofdm system.
Directdetection optical ofdm oluyemi omomukuyo and j. Instead of direct detection of the pure optical ofdm signal, an optical carrier must be delivered either by the transmitter using direct detection ofdm or by a local oscillator in the receiver using coherent optical ofdm via a heterodyne or intradyne approach. Optical orthogonal frequency division systems with direct. In direct detection ofdm, a photodiode is used while in the latter the principle of optical mixing is utilized. Enabling high capacity directdetection optical ofdm. Pmd tolerant directdetection polarization division. Dsp for directdetection ofdm system digital signal. Theoretical and experimental investigation of direct. Before sending through the optical wireless channel, the optical modulated signal is filtered by optical filter and amplified by optical amplifier. Intensity modulation and direct detection imdd systems with verticalcavity. Note that the conclusion of the optimal modulator null bias point for the rto upconversion is fundamentally independent of the detailed waveform of v iq. Although the major difference between rf and ow based ofdm lies in the front end of transmitter and receiver, but due to the unipolar nature of optical intensity in imdd system. Ssmi cancellation in directdetection optical ofdm with.
Performance analysis of direct detection and coherent. Research on transmission of directly detected highorder qamofdm signals. Ofdm based direct detection optical communication system ofdm based optical communication systems are categorized into direct detection and coherent detection systems. Self coherent optical ofdm, an interesting alternative to. In this paper, we propose a novel scheme of orthogonal frequency division multiplexing ofdm for intensity modulation direct detection imdd optical systems. A data clipping and normalization technique is employed to improve the performance of the overall direct detection optical orthogonal frequency division multiplexing dcoofdm system. Direct detection system an overview sciencedirect topics. Ofdm has not been used in practical optical communication systems because the bipolar waveform cannot be used in intensitymodulated direct detection imdd systems. It is shown that even for differential group delay dgd of 4bw bw is the ofdm signal bandwidth, the degradation due. Due to the advantages of simple and costeffective configuration, the ddoofdm system tends to be applied in access network for short reach. This paper investigates the architecture of single channel and four channel direct detection and coherent detection optical ofdm systems. In this paper a theoretical study is conducted regarding the effect of oofdm in radio over fiber networks rof.
Novel power efficient optical ofdm based on hartley. Orthogonal frequency division multiplexing ofdm has recently been introduced in optical. The paper presents a performance analysis of a coherent optical ofdm system in terms of its ber. This paper presents a systemic theoretical and experimental investigation of compatiblessb modulation in longdistance optical ofdm transmission. On the other hand, directdetection dd significantly reduces the system complexity. Least square estimation is used to estimate the pilot signals phase to recover the side information. For the 12 gbits colorless implementation, the awg generates the ofdm signal and its hilbert transform. The normalization operation amplifies the clipped data signal to the maximum input amplitude of a digital.
Lowcomplexity directdetection optical ofdm systems for high data. Precoding based peaktoaverage power ratio reduction for. Intensity modulation and direct detection imdd is a costeffective optical. For long haul transmission systems coherent detection is beneficial compared to direct detection as it provides higher sensitivity. Pdf ofdm systems for optical communication with intensity. By using this novel scheme of an ofdm optical system, not only odd subcarriers but also even subcarriers can be modulated to transmit a clipping optical signal. From the many architectures being proposed for oofdm, the use of direct detection is particularly interesting for the downlink of passive optical networks as costefficient optical network units onus are required. In this article, we have demonstrated an optical orthogonal frequency division multiplexing ofdm intensity modulation and direct detection imdd system with different modulation techniques such as quadrature amplitude modulation qam and phase. For direct detection dd oofdm system, an optical launch power of 12, 15, and 0 dbm is required for transmitting 20 gbps bpsk, 50 gbps qpsk, and 100 gbps 16qam over 31, 28, and 15 km, respectively. Research on ssmi cancellation in directdetection optical ofdm with novel halfcycled ofdm. It has many variants which reflect the different requirements.
Theoretical and experimental investigation of compatible. The system was simulated at 50gbps for a transmission distance of km over standard single mode fiber. For instance, for direct detection optical ofdm, it is still optimal to bias the modulator at the null point to minimize rto upconversion nonlinearity. We show by simulation the impact variations in both the bias point of a machzehnder modulator and the amplitude of the driving signal has on the receiver sensitivity of a directdetection optical ofdm system with 4qam modulation. In this paper a theoretical study is conducted regarding the effect of oofdm in radio over fiber. We also proposed and experi mentally demonstrated a novel dd. Theoretical and experimental investigation of direct detection. Asymmetrically clipped absolute value optical ofdm for intensitymodulated directdetection systems abstract. The resulting signal has to be biased for driving an external optical mzm in order to achieve sufficient carrier power for direct detection. Key technologies for optical ofdm in optical longhaul. A direct detection optical ofdm aims for simpler transmitter or receiver than coofdmfor lower costs. Performance analysis of direct detection and coherent detection system for optical ofdm using qam and dpsk veneetha nair1, joseph george k.