Performance Evaluation of Sub-carrier Multiplexed SAC-OCDMA System Using Optimal Modulation Index

Zero Cross-Correlation (ZCC) code stands out amongst the most helpful codes in Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA) system because of its features like zero cross-correlation and high auto-correlation. However, for long-range communication, as the number of user’s increases, the performance of the system is degraded. In this paper, we made an effort to enhance the performance of SAC-OCDMA system using Dense Wavelength Division Multiplexing (DWDM). SAC-OCDMA is an inseparable part of the global optical communication systems. It provides high speed, high bit-rate, security and high bandwidth for advanced services in different networks. Therefore, the hybrid DWDM and SAC-OCDMA system makes it believable to create other codes like multi diagonal (MD) and random diagonal (RD). Our results show that the number of users increases ten times by using a combination of 20-channel DWDM and SAC-OCDMA ZCC code system at a bit-rate of 10 Gbps for 60 Kms.

This paper proposes an integration of optical Code Division Multiple Access (OCDMA) with new catenated Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme. This effective combination based on Zero Cross Correlation (ZCC) code can enhanced the system capacity and increased spectral efficiency by fully utilizing the available electrical bandwidth. We investigate the performance of the proposed system for various number of user, number of weight and effective power. The performance assessment is carried out by means of the signal to noise ratio (SNR) and bit error rate (BER) for up to five catenated OFDM bands transmitted simultaneously through optical link at 622 Mbps. More specifically, mathematical expressions for SNR and BER performance are derived. The corresponding numerical results are presented and compared with traditional OCDMA-ZCC system to verified the feasibility of the proposed system. The results show that with OCDMA/catenated-OFDM based on ZCC code provides 86% more number of permissible user for SNR of 15 dB. In addition, this integration provides higher receiver sensitivity; an approximately –22.5 dBm for 20 number of user with 8 number of weight. It is also found that, to accommodate more user, the system requires higher effective power at the receiver.

In this paper, the performance of a binary phase shift keyed random\ntime-hopping impulse radio system with pulse-based polarity randomization is\nanalyzed. Transmission over frequency-selective channels is considered and the\neffects of inter-frame interference and multiple access interference on the\nperformance of a generic Rake receiver are investigated for both synchronous\nand asynchronous systems. Closed form (approximate) expressions for the\nprobability of error that are valid for various Rake combining schemes are\nderived. The asynchronous system is modelled as a chip-synchronous system with\nuniformly distributed timing jitter for the transmitted pulses of interfering\nusers. This model allows the analytical technique developed for the synchronous\ncase to be extended to the asynchronous case. An approximate closed-form\nexpression for the probability of bit error, expressed in terms of the\nautocorrelation function of the transmitted pulse, is derived for the\nasynchronous case. Then, transmission over an additive white Gaussian noise\nchannel is studied as a special case, and the effects of multiple-access\ninterference is investigated for both synchronous and asynchronous systems. The\nanalysis shows that the chip-synchronous assumption can result in\nover-estimating the error probability, and the degree of over-estimation mainly\ndepends on the autocorrelation function of the ultra-wideband pulse and the\nsignal-to-interference-plus-noise-ratio of the system. Simulations studies\nsupport the approximate analysis.\n

A hybrid spectrally amplitude coded (SAC) optical code division multiple access (CDMA) with subcarrier multiplexing (SCM) scheme is a potential candidate for future broadband access solutions in the communication network. In this work, the performance of hybrid technique is investigated. Theoretical derivations are developed based on the zero cross correlation (ZCC) code. The performances are evaluated taking into account the relevant noises such as thermal noise, shot noise and inter modulation noise. Design parameters such as number of optical channels, number of subcarriers, and input power are varied to see their effect on the system performances. Simulation analysis using Optisys simulator is also done and compared to the numerical theoretical results. We measured the performance based on the merits of received power, input power and bit error rates of the received signals. Results revealed that power penalty due to increased number of channels in the hybrid system is lower compared to the conventional OCDMA system, and hence improving the system performance in term of power efficiency. This exhibits the ability of the hybrid system to be one powerful technique as a candidate for future access network. Key words: Spectral amplitude coding-optical code division multiple access (SAC-OCDMA), subcarrier multiplexing (SCM), zero cross correlation (ZCC), broadband access network.

In Orthogonal frequency division multiple access (OFDMA) cellular system, the user at the different location of the cell requires different number of subcarriers to satisfy the user’s data rate requirement. In this paper, based on the Interference to Signal Ratio (ISR), we analyze the average number of downlink subcarriers required at inner and outer region for the two-hop OFDMA cellular system. Firstly we propose a two-hop OFDMA cellular system model. Then based on this model, we calculate the Cumulative Distribution Function of ISR at inner and outer region respectively, and obtain the theoretical analysis results for the average number of subcarriers required at two regions of the reference cell. Finally, with the help of the numerical calculation and Monte-Carlo simulations, we analyze the impact of the various parameters on the average number of subcarriers required of the two-hop cellular system. And the results are compared with the average number of subcarriers required of the one-hop cellular system.

The main purpose of this study is to present a comparison of different codes used for SAC-OCDMA systems. The main feature of compared codes is that they have a zero cross-correlation which eliminates both MAI and PIIN. Hence, a Direct Detection is used at a receiver, which reduces the complexity of receiver structure thereby reducing system cost. The comparison is based on some parameters: cardinality or number of users supported by each code, the effective received power from every user, the code length and BER. The results presented are based on the theoretical calculation of SAC- OCDMA systems using direct detection.

Orthogonal Frequency Division Multiplexing (OFDM) is an encoding method that are hugely utilized in wireless communication due to its high number of advantages such as tolerance for multipath delay spread, frequency selective fading channels immune and also power efficiency. The bad side of this method is it has high Peak Average Power Ratio (PAPR) that will generate nonlinear distortions and severe power penalty. In this research, Selective Mapping (SLM) method is proposed to solve the problem of high PAPR but from previous researches, it could be seen that in SLM, the search complexity increases as the number of phase sequence increase. To solve this issue, Firefly Algorithm (FA) is applied to optimize the function of SLM. The modulation method used is Quadrature Phase Shift Keying (QPSK). By the end of the process, CCDF and BER plots are computed. The performance of PAPR reduction in OFDM system are analyzed by different number of subcarriers, phase sequences, randomization parameters and iterations using CCDF graphs. The performance of OFDM channel through AWGN channel is studied with different number of subcarriers. By using SLM method only, the PAPR values manage to be reduced by 0.4–3 dB but with FA-SLM algorithm, the PAPR values can be reduced by 5–9.5 dB. With these results, it is concluded that the combination of SLM with FA can help to improve computational complexity in SLM and eventually reduce PAPR value in OFDM system.

We compare the spectral efficiency of unipolar and bipolar encoding for spectral-amplitude coding optical code-division multiple access (SAC-OCDMA) systems operating with incoherent sources considering the intensity noise as the primary noise source. For both encoding techniques, the spectral efficiency of four SAC codes such as Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC) is evaluated and compared as a function of the number of users and code length for a BER= 10−10. Analytical derived equations and results verified that ZCC code can support high number of users and leads to the best achievable spectral efficiency than other SAC codes considered. Furthermore, bipolar encoding improves the spectral efficiency as compared to unipolar technique, e.g., bipolar ZCC has 7.7 dB spectral efficiency advantage than unipolar ZCC.

In this contribution, we consider the performance of multiple-input multiple-output (MIMO) code division multiple access (CDMA) system for digital image transmission over correlated Rayleigh fading channel. MIMO system employs multiple antennas both at the transmitter and receiver. In our work, we consider turbo coded system to investigate the performance of MIMO-CDMA system. We realize turbo code using parallel concatenated convolutional encoder and second convolutional encoder is preceded by random interleaver. Further the output of two convolutional encoder are punctured to get rate of ½. At the receiver, we employ iterative decoding algorithm to reduce the effect of multiple access interference (MAI) and Inter-Symbol-Interference (ISI) and median filters to reduce the effect of salt and pepper noise.. In particular, we evaluate the performance of coded MIMO-CDMA system using Zero forcing (ZF) - multi-user detection (MUD) and minimum mean square error (MMSE)-MUD detection technique to mitigate the effects of multi-stream interference (MSI). It is shown through the simulation study that our considered coded MIMO-CDMA system with MMSE algorithm achieves better picture quality with less signal-to-noise ratio (SNR) as compared to ZF MUD.

The performance of a binary phase shift keyed random time-hopping impulse radio system with pulse-based polarity randomization is analyzed. The effects of multiple access interference are investigated for both chip-synchronous and asynchronous systems. It is shown that the performance of a chip-synchronous system is the same as that for the symbol-synchronous case studied in E. Fisher and H. V. Poor (Oct. 2-4, 2002). The asynchronous system is modelled as a chip-synchronous system with uniformly distributed timing jitter on the transmitted pulses of interfering users. This extends the analytical technique developed for the chip-synchronous case to the asynchronous case. An approximate closed-form expression for the probability of error, expressed in terms of the autocorrelation function of the transmitted pulse, is derived for the asynchronous case. The analysis shows that the chip-synchronous assumption can result in over-estimating the error probability, and hence that the system design based on this approximation will he on the safe side. The degree of over-estimation mainly depends on the autocorrelation function of the UWB pulse and signal-to-interference-plus-noise-ratio (SIR) of the system. Simulations studies support this approximate analysis.

In this paper the Double Weight code (DW) family which is used as a proposed code in optical spectral code division multiple access system (OSCDMA) has been studied using the Modified Double Weight code (MDW) which has across correlation value equals to one. By eliminating the intersection columns of this code we can reduce the cross correlation value from one to zero. This code is named Zero Cross-correlation Code (ZCC) [1]. Therefore, the Multiple Access Interference (MAI) can be reduced. Also, a general equation is used to generate the basic matrix of the code with the cross correlation equal zero instead of that in the existing construction technique. In this paper, we also show the advantages of this equation. All of these studies concentrate on the basic matrix of modified double weight code with zero cross correlation value.

Various optical communication technologies use Optical-Code Division Multiple Access (Optical-CDMA) as a channel access technique, which allows transmission of different users simultaneously over the optical communication channel. Therefore, Optical-CDMA permits free undue interference transmission of several users. Whereas Wavelength-division multiple access (WDMA) is a technique that can be implemented on how the optical channel can be divided into subchannels. This paper proposes a Hybrid WDMA-Optical-CDMA over multi-mode fiber (MMF) transmission system for short haul-local area network. The WDMA system is carried out by using four Laguerre-Gaussian (LG) modes that operate over four main wavelengths (1551 nm, 1550 nm, 1549 nm and 1548 nm). Additionally, the Optical-CDMA system is carried out by using one dimension Zero Cross-Correlation (ZCC) code to overcome multiple access interference (MAI) between the four ZCC codes. The performance of our system is evaluated based on eye diagrams, Q-Factor and bit-error rates (BER) measurements.

This paper provides some design considerations of pilot structure for 1-antenna and 2-antenna IEEE802.16m. Space-Zone (SP-Zone) and Mobility-Zone (MB-Zone) concepts are introduced to use different numbers of subcarriers and symbols between pilots according to the radio environment and mobile speed to improve the system performance comparing with the conventional fixed number of subcarriers and symbols between pilots.

The use of smart or adaptive array antennas has attracted considerable interest in the mobile communications community. We investigate the combined use of an adaptive/smart array antenna and Rake receiver (space-time processing) to jointly mitigate the effect of multiple access interference (MAI) and multipath fading in a CDMA system, while taking angle spread into account. We provide simulation results concerning mean bit error rate (BER) performance of such a system for different numbers of antenna elements, numbers of users and angle spreads. The obtained results show that the investigated smart antenna system can effectively combat adverse MAI and fading effects and improve the CDMA system performance.

This paper studies the effects of multiple access interference (MAI) for ultra wideband (UWB) systems in AWGN and multipath fading channels. Time hopping (TH) and direct sequence (DS) based UWB spreading approaches are performed, utilizing binary pulse amplitude modulation (PAM) and pulse shape modulation (PSM). Both the possibilities of having synchronous and asynchronous users have been taken into account. In the fading channel case, different coherent and non-coherent detection methods have been considered. Simulated performance results are depicted for the above mentioned UWB systems when a variable number of equally powered users are operating in the channel. Results show that in both the AWGN and fading channel the DS system performance shows sensibly different results in the synchronous and asynchronous case. This is due to the continuous time transmission of the different users. This problem does not occur in systems using TH spreading since the different users are less overlapped in time, due to the spreading approach used. In the fading channel, TH systems show a general higher performance loss in all cases compared to DS, in contrast to what happens in the AWGN case. That is, the allocation of the TH codes creates a higher interfering effect due to MAI in the presence of multipath fading. In general, DS-based systems outperform the corresponding TH ones.