1.25 GBPS AND 2.5 GBPS DATA RATE TRANSMISSION OF 2D-CAP MODULATION FOR ACCESS NETWORK

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1 1.25 GBPS AND 2.5 GBPS DAA RAE RANSMISSION OF 2D-CAP MODULAION FOR ACCESS NEWORK M. B. Jaaar, M. B. Othman, N. M. Ridzuan, and M. F. L. Abdullah Optical Fiber and Communication Network, Research Group, Communication Engineering Department, Faculty o Electrical & Electronic Engineering, Universiti un Hussein Onn Malaysia, Batu Pahat, Johor, Malaysia nana91marliana@gmail.com ABSRAC We have investigated the carrierless amplitude phase (CAP) modulation ormat at dierent data streams or access network and simulated by using VPI sotware. he CAP signals with 1.25 Gbps and 2.5 Gbps are successully transmitted over 2 km o single-mode iber (SMF) with 155 nm SM-VCSELs. he 3.79 b/s/hz and 7.58 b/s/hz o spectral eiciency are reported or 2D-CAP o 1.25 Gb/s and 2.5 Gb/s. he receiver sensitivity at FEC limit or B2B o both 1.25 Gbps and 2.5 Gbps is dbm and dbm, with the dierence o 2.1 db have been observed. Ater 2 km o transmission, a 2.5 db dierence was detected at the orward error correction (FEC) limit with receiver sensitivity o dbm and dbm respectively. he result shows that the CAP modulation ormat has easibility and potential to deliver high data rate by employing simple baseband electronic design. Keywords: carrierless amplitude phase, data rate. INRODUCION In the today s reality, higher data speed surpassing one gigabit per second must be oered in uture wireless system to support current bandwidthhungry applications, like High-Deinition (HD) video and high speed internet. o achieve much aster wireless communication, it will be compulsory to develop higher carrier requencies in the uture. his is due to the congestion that aected by the large number o end-users sharing the similar requency spectra and the limited requency spectra at low requencies (A. Ng oma et al. 29). In addition, the increasing number o users will impose limitation to the data communication. Carrierless amplitude phase (CAP) modulation can be described as a multidimensional and multilevel modulation scheme,that employed orthogonal waveorms, one or each dimension. With the absence o carrier at the both transmitter and receiver, it makes CAP dierent with quadrature amplitude phase (QAM) while achieving the same perormance and spectral eiciency (SE) (M. I. Olmedo et al. 213). he origin o making the CAP become more increased interest is its well-known SE, which makes it very competitive with OFDM. Recently, due to its potentially high SE, CAP has gained increasing attention or optical communication (J. D. Ingham et al. 211), (M. Wieckowski et al. 211). CAP can be generated at high speed with the use o readily available low-cost transversal ilter and becoming a simpler scheme than orthogonal requency division multiplexing (OFDM) (J. D. Ingham et al. 211). Diering to OFDM, CAP is a single-carrier scheme that can lead to higher bit rates, and it is not as highly eected by the primary issue o OFDM, which is high peak to average power ratio (PAPR) (J. L. Wei et al. 212a). Additionally, by comparing the power dissipation, CAP system is signiicantly lower than in an OFDM system (J. L. Wei et al. 212b). Due to the lexibility o the CAP system, a sotware-controlled change in the tap coeicients o an electronic ilters can be used to achieved the generation o passband channels, without the necessity or upconversion using a mixer and local oscillator (J. D. Ingham et al. 211). It apparently shows that CAP modulation gives an outstanding development in producing eicient and compact optoelectronic devices that makes the optical communication system networks much simpler and has lower power signal processing with high data rate at a low cost. In this paper, we have programmed the CAP modulation ormat at dierent data streams and simulated by using VPI sotware or optical transmission. he CAP signals with 1.25 Gbps and 2.5 Gbps have been transmitted over 2 km o singlemode iber (SMF) with 155 nm SM-VCSELs. MOIVAION Carrierless amplitude phase (CAP) modulation, or originally called carrierless amplitude modulation /phase modulation (AM/PM) has been proposed by the Bell Labs as a viable modulation technique or high-speed communication links over copper wires in mid 1975s (D. D. Falconer, 1975). CAP modulation can be considered as a bandpass pulse amplitude modulation (PAM) in digital communication system (E. A. Lee et al. 1994), in which the carrier requency is near baseband. However, compare to pulse amplitude modulation (PAM), CAP has zero direct current (dc) power, where make it well suited to ac coupled channels. On the other hand, CAP has similarities to QAM modulation in its ability to support multiple levels in more than one dimension. However, CAP modulation viewed dier to QAM in the absence o carrier, whereas CAP uses ilters with orthogonal waveorms to separate the dierent data streams. his makes CAP transceiver simpler compared to QAM while achieving the same 566

2 perormance and spectral eiciency. he quality that have shown by CAP make it very popular or digital subscriber lines (DSLs) during mid and end o 199s (A. F. Shalash et al & G. H. Im et al. 1995) and were aimed or private consumers ADSL (J. J. Werner, 1992 & 1993). As high speed electronics became more aordable and demands o bandwidth raised, there were strong eorts to put into exploiting the available bandwidth o deployed copper cables (J. Gao, 22). However, CAP was proven to be very sensitive to non-lat spectral channels and required very complex equalizers (J. Gao et al. 1999), sacriicing the simplicity o CAP. Since then, CAP was pushed aside in avour o DM modulation and was compared by (A. F. Shalash et al. 1996) or line equalization. he interesting eature o CAP is the possibility to extend its signal basis to higher dimension, which were discussed by (I. hng et al. 1999) and (A. F. Shalash et al. 1999) or DSLs application. Unortunately, (X. ang et al. 23) was called or a question based on the unclear result that have been achieved by (I. hng et al. 1999) in terms o spectral eiciency (SE). Not only that, published work on high dimensional CAP up to year 27 (. Collins et al., 28), just ocused on simulation results rather than realistic practical experiments. hus, (M. B. Othman et al. 212) was successully proved it by demonstrating the multi-dimensional CAP modulation, while (G. Stepniak, 214) had compared the eiciency o N-Dimensional CAP modulation. In recent times, the idea or using CAP modulation has been rereshed in the ield o optical networks (R. Rodes et al. 211a) due to the possibility o generating the required orthogonal pulses by means o transversal ilters and the potential high spectrum eiciency. he (M. Wieckowski et al. 211) was demonstrated 2D-CAP 8-level per dimension (L/D) over 5 m long polymer optical iber (POF) by using resonance cavity light emitting diode (RC-LED) with a spectral eiciency 4.6 bit/s/hz. In the same year, (J. D. Ingham et al. 211) was investigated 4 Gbps 2D-CAP 4-L/D with analogue transversal ilter over standard single-mode iber (SSMF) and compared with the NRZ modulation in terms o dispersion and power budget. Additionally, in 211, (R. Rodes et al. 211a & 211b) were introduced WDM system using directly modulated vertical cavity surace emitting lasers (DM- VCSELs) with 2D-CAP 4-L/D over 26 km o SSMF with a 4 bit/s/hz o spectral eiciency. It was ollowed by (A. Caballero et al. 211) which has proposed the use o 2D- CAP 2-L/D with the transmission o 8 Gbps over 1 km o MMF by using VCSEL as a light source. PRINCIPLE OF CAP MODULAION Basically, the use o dierent signals as signature waveorms is a basic idea o the CAP system in order to modulate dierent data streams. he signature waveorms are generated by orthogonal shaping ilters at the transmitter. While at the receiver, the matched iltering is used to reconstruct the individual data streams. he match ilter used in the receiver has an impulse response which is the time domain inversion o the impulse response o the transmitter ilter. Data Input ransmitter Data Output Receiver Constellation Mapping Constellation Demapping CAP Filter 1 Upsampling + Downsampling CAP Filter 2 CAP Inversion Filter 1 CAP Inversion Filter 2 x1 x2 Digital to Analog Analog to Digital Figure-1. Block diagram o 2D-CAP transmitter and receiver. A block diagram o 2D-CAP transmitter and receiver can be seen in Figure-1. According to the given constellation, data in the transmitter has to be mapped (encoded) by converting a number o raw data bits into a number o multi-level symbols. In order to achieve the desired waveorm, these symbols are up-sampled and shaped by the CAP ilters, at which orcing required transmission properties on the signals. hose properties include the limited bandwidth, zero cross channel intererence (CCI), and zero inter-symbol intererence (ISI), allowing or the perect reconstruction (PR) at the receiver side. For the 2-dimensional o the CAP modulation (2D-CAP), shaping ilters use the properties o a wellknown square-root raised cosine (SRRC) ilter with zero- ISI, merged with the orthogonal properties o sine and cosine waveorms that has zero-cci. Beore components can be iltered, symbols have to be up-sampled in order to meet the sampling rate criterion. he sampling rate has to be at least two times higher than the highest requency component o the generated signal. he usual up-sampling actors are 3 or 4, depending on the roll-o actor o the raised cosine (RC) ilter used to design shaping ilters. It has to be chosen properly in order to avoid any aliasing eects. he most important part o the CAP system is a proper shaping ilters. As mentioned beore, basic CAP modulation ormat which is 2D-CAP employs a product o a SRRC with sine and cosine waveorms in order to achieve the PR in the receiver. SRRC ilters are widely used or matched iltering. A combined response o two SRRC ilters, which is transmitting and receiving ilter, is the one o a RC ilter. he raised cosine waveorm can be expressed as in equation (1) and the SRRC waveorm can be expressed as in equation (2), where is a symbol period and α is the roll-o actor inluencing the amount o the excess bandwidth. h RC t t t sin c cos t Laser PD MMF (1) 567

3 h SRRC t cos 4 1 t 1 t sin 4t 1 4t he roll-o actor or baseband systems can be expressed as in equation (3), where W is a bandwidth used by the signal and 1/2 is a minimum bandwidth required or the baseband signal with the symbol rate o. or the passband modulations, this ormula is dierent, where 1/2 is changed into 1/ in order to allocate requency space or positive as well as negative sideband o the signal. 1 W 2 (3) 1 2 RC and SRRC are baseband ilters, at which suitable or shaping baseband signals such as PAM. With little alteration, those ilters can be relocated into the passband and that is exactly what is done in the CAP systems. Continuous-time impulse responses o the CAP ilters can be expressed as in equation (4) and (5), where c is a requency suitable or the passband ilters. Filter 1 is represents as the in-phase ilter and ilter 2 is represents as the quadrature ilter. h t cos 2 t c t sin 2 t 2 (2) (4) 1 SRRC h (5) 2 SRRC c A pair o waveorms 1 and 2 constitute a Hilbert pair. Hilbert pair represents the two signals o the same magnitude response and a phase response shited by 9 o. Figure-2 presents the both impulse and the requency response o the typical CAP ilters with an up-sampling actor o 4. he resultant o two orthogonal signals are added and converted rom digital to analog orm. he combined requency spectrum o 2D-CAP and added pulse shape in time domain are shown in Figure-3. At the receiver side, the signals are converted back to digital orm. he matched ilter are created by reversing the order o coeicients in the ilter to recover the original sequence o symbols. he symbols are then down-sampled and de-mapped (decoded), so that the original data can be recovered. Amplitude a.u ime (ns) Magnitude (db) Frequency (MHz) Figure-2. Impulse response and requency response o 2D-CAP ilter (M. B. Othman et al. 212). Amplitude a.u ime (ns) 192 Magnitude (db) Frequency (MHz) Figure-3. 2D-CAP added pulse response and combined requency spectrum (M. B. Othman et al. 212). Multilevel/ Dimension Mapping Upsampling Multidimensional Filter Inversion o Multidimensional Filter Downsampling Multilevel/ Dimension Demapping BER calculation VPI \ MALAB MALAB / VPI ransmitter PD Laser Receiver VOA Figure-4. Simulation setup o 2D-CAP modulation. SIMULAION SEUP he waveorms o the CAP modulation ormat has been programmed with the sampling rate o 5 GSa/s and 1 GSa/s. Figure-4 illustrated a simple network coniguration o the CAP transmitter and receiver. he oline generated test signal is based on the pseudo random binary sequence (PRBS) with the length o in order to construct the CAP signal. According to the QAM constellation, data in the transmitter is mapped by converting a 1.25 Gbps and 2.5 Gbps o data bits into a number o multi-level symbols. hese symbols are up-sampled to 4 samples per symbol and use the CAP ilters to shape it in order to achieve square-root raised cosine (SRRC) waveorms. hese waveorms are multiplied by sine or cosine waveorms to achieve orthogonality between them and move rom baseband to passband. All o this step will be perormed in MALAB and integrated with VPI sotware or the optical network design. he 155 nm single-mode vertical-cavity surace emitting laser (SM-VCSEL) are directly modulated with the CAP signal. he signal is then propagated through 2 km o singlemode ibre (SMF). For bit error rate (BER) measurements, a variable optical attenuator (VOA) is used ransmission medium 568

4 and placed ater the ibre. At the receiver, the photodetector (PD) is used to detect the signals directly. Ater that, the signals are stored or demodulation. All the data that have been stored will be processed in MALAB sotware. o retrieve the original sequence o symbols, the time inversions o the transmission ilters are implemented. he symbols are down-sampled and de-mapped beore the data can be recovered. Since the 7% orward error correction (FEC) overhead is taken into account, the transmission quality can be assessed using receiver sensitivity at a BER o 2.8 x 1-3. he CAP signals with 1.25 Gbps and 2.5 Gbps are successully transmitted over 2 km o SMF with 155 nm SM-VCSELs b/s/hz and 7.58 b/s/hz o spectral eiciency are reported or 2D-CAP o 1.25 Gbps and 2.5 Gbps respectively. he result shows that the easibility and potential o CAP modulation ormat to deliver high data rate by employing simple baseband electronic design. In order to increase the spectral eiciency with the higher data rate, CAP signal requires excess bandwidth due to the higher up-sampling actor. All o these actors need to be considered in system design. However, CAP modulation ormat has higher possibility to increase the number o level as well as number o dimension with the absence o carrier. ACKNOWLEDGEMENS his work was ully supported by Fundamental Research Grant Scheme (Vot No.: 1416) and Universiti un Hussein Onn Malaysia (UHM). REFERENCES [1] F. Shalash and K. K. Parhi (1996). Comparison o discrete multitone and carrierless AM/PM techniques or line equalization. IEEE International Symposium on Circuits and Systems, pp Figure-5. BER against received optical power (ROP) o D-CAP or 1.25 Gbps and 2.5 Gbps. RESUL Data rate o 1.25 Gbps with 5 GSa/s sampling rate has been compared with 2.5 Gbps or sampling rate up to 1 GSa/s, as shown in Figure-5. he bit error rate (BER) against received optical power (ROP) was measured in order to compare the sensitivity. he solid symbols describe the optical back-to-back (B2B), while the hollow symbols describe the 2 km o SMF transmission. he receiver sensitivity at FEC limit or B2B o both 1.25 Gbps and 2.5 Gbps is dbm and dbm, with the dierence o 2.1 db have been observed. Ater 2 km o transmission, a 2.5 db dierence was detected at the FEC limit with receiver sensitivity o dbm and dbm respectively. All o the signals are successully demodulated below FEC limit ater transmission. his can be clearly seen in Figure-5, where the constellation diagram with a BER is approximately 1 x 1-3 ater 2 km o SMF transmission. CONCLUSIONS In this paper, we have programmed the CAP modulation ormat at dierent data streams and have been simulated by using VPI sotware or optical transmission. [2] F. Shalash and K. Parhi (1999). Multidimensional Carrierless AM/PM Systems or Digital Subscriber Loops. IEEE rans. On Comm., vol. 47, no. 11, pp [3] Anthony Ng oma and Mike Sauer (29). Radioover-Fiber Systems or Multi-Gbps Wireless Communication. Proc. o SPIE-OSA-IEEE Asia Communications and Photonic, SPIE vol I-1. [4] Antonio Caballero, ien hang Pham, J. B. Jensen and Idelonso aur Monroy (211). Carrierless N- Dimensional Modulation Format or Multiple Service Dierentiation in Optical In-home Networks. Proc. IPC, pp. 3-31, paper um4. [5] D. D. Falcooner (1975). Carrierless AM/PM. in Bell Laboratories echnical Memorandum. [6] E. A. Lee and D. G. Messerschmitt (1994). Digital Communication. Kluwer Academic Publishers, Norwell, Mass. [7] G. H. Im, D. Harman, G. Huang, A. Mandzik, M. H. Nguyen, and J. J. Werner (1995) Mbps 16- CAP AM LAN Standard. J. Sel. Areas Comm., vol. 13, no. 4, pp [8] Grzegorz Stepniak (214). Comparison o Eiciency o N-Dimensional CAP Modulations. Journal o 569

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