Performance of Iteratively Decoded Parallel Concatenated Error Control Codes in Phase Noise Corrupted BPSK Systems

We consider multilength variable-weight time-and-frequency-hopping (TFH) codes for optical code-division multiple-access (CDMA) networks. To design a TFH code that can support differentiated requirements on transmission rates (TRs) and bit error rates (BERs), we propose a general construction method for two-dimensional optical CDMA code sequences with arbitrary code lengths and variable code weights. The cross-correlation peak and the autocorrelation sidelobe of the proposed code are made to be at most '1' and '0', respectively, for any pair of different-length and different-weight code sequences. We show that the ratio between signal-to-interference ratios (SIRs) of the codes with different weight and length can effectively be approximated by the ratio of the code weights, regardless of the code lengths for the proposed codes. Therefore, independent adjustment of code length and weight can differentiate TR and BER for multiple service classes, and it simplifies code design for the service differentiation. We also demonstrate BER performances under various conditions and corroborate that the proposed codes accomplish accurate and fine-tuned differentiation of TR and BER compared to the fixed-weight or fixed-length codes.

This study introduces an accurate design and optimisation of a passive optical code division multiple access (OCDMA) network encoder using the coupled cavity waveguide (CCW) as an optical delay line. Such CCW has the capability of providing more time delay with minimum encoder size. The proposed design and analysis are based on the two-dimensional (2D) photonic crystal (PhC) structure. Additionally, two different 2D-PhC structures are studied, in which a silicon material with an effective refractive index of 3.487 is used. The first structure is a silicon bar in air background, whereas the second one is air holes in a silicon substrate. Furthermore, the behaviour of the proposed 2D-PhC structures is studied over the wavelength, ranging from 1300 to 1600 nm. Since the structure geometry is simple with a clear operating principle, it is sufficient to use in the photonic integrated circuits. Moreover, the performance analysis of such design is investigated in terms of the bit error rate (BER) calculations. Finally, the results showed that a 21% BER performance enhancement was achieved using the optimised silicon bars in air background encoder model and this model can be utilised for the multimedia applications in the OCDMA networks.

To combat with multiple-users interference and malicious eavesdropping, this talk presents a double signatures scrambling scheme over wavelength/time for a cryptographic optical code-division multiple-access (OCDMA) network data transmissions. Optical switches and fiber delay lines are placed with arrayed-waveguide grating (AWG) coder/decoders (codecs) to realize wavelength-spreading and time-hopping. On the transmitter side, user data bits are sliced into spectral chips, coded into pseudo-noise (PN) signature codes, and conducted with different PN-code units of time-delay. In the receiver side, complementary delay lines first reverse the summed spectral chips back into the same time basis, then optical switches follow the associated signatures to turn on-off spectral chips into balanced detector for the final data decoding. By changing signature codes frequently, the eavesdroppers cannot catch on the changing code speed and have little chance to detect the channel waveform to solve the code. With such wavelength/time scrambling scheme, data transmission reliability in OCDMA network can be greatly enhanced.

In optical code-division multiple access (OCDMA) networks using a well-known prime code, the code weight w is always fixed to the maximum number of users M (i.e. the code size). When M becomes very large the resulting cost and optical power losses of OCDMA encoder/decoder can be very high. To overcome this difficulty, an efficient design is presented for OCDMA networks, which is based on the modified prime (MPR) codes. The use of MPR codes can maintain the fixed w for a given bit error rate and any M. While MPR codes still preserve the same cross-correlation constraint as prime codes.

Multiple Access Interference (MAI) is the major reason for the system degradation in the Optical Code Division Multiple Access (OCDMA). MAI increases with the number of simultaneous users, resulting in deterioration in the performance and limits the maximum number of simultaneous users. Optical Hard Limiter (OHL) is known to improve the performance of the conventional OCDMA system. However, in the present of other sources of noise, the improvement is not considerable. Moreover, the need for dynamic threshold value in the conventional OCDMA receiver to recover the data is very demanding requirement particularly in the high speed LANs. To overcome these limitations, some studies have been conducted on the Optical Parallel Interference Cancellation (OPIC) through this paper. OHL is placed in front of the receiver side to mitigate the effect of MAI. The study focuses on the lowest threshold value i.e. Th=1. The results are compared to the conventional OCDMA and it shows that, OHL is effective to reduce the power of MAI and a better performance can be obtained by selecting the smallest threshold value.

Internet, multimedia, tele-medicine and distant learning were the few high speed services offered to the end-user by a broadband access network. Optical fibres are used in the Fiber To The Home (FTTH) architecture to replace the metallic cables partially or completely to the end-user. The performance of the FTTH architecture was improved by implementing various coding schemes and modulation formats. In this paper, FTTH architecture with the Fiber Bragg Grating (FBG) based OCDMA (Optical Code Division Multiple Access) network was proposed. The reliability of the communication between appropriate transmitter and receiver is analysed. OCDMA offers high reliability communication in the FTTH architecture.

In this paper, a comparison between direct-current-biased optical orthogonal frequency-division multiple-access (DCO-OFDMA) and synchronous one-dimensional (1-D) optical code-division multiple-access (OCDMA) is performed for optical wireless communication (OWC). Line-of-sight (LOS) channel conditions are considered in an indoor downlink scenario. The bit-error ratio (BER) performance is investigated in an additive white Gaussian noise (AWGN) channel under the conditions of equal spectral and power efficiency. For DCO-OFDMA and 1-D OCDMA, the negative-level clipping effect and multiple-access interference (MAI) are considered, respectively. For the OCDMA scheme, the categories of optical orthogonal codes (OOCs) and unipolar Walsh-Hadamard codes (WHCs) are employed. The time-division multiple-access (TDMA) is also represented in the context of synchronous OCDMA by the use of identity matrices. In order to enhance the 1-D OCDMA spectral efficiency, unipolar M-ary pulse amplitude modulation (M-PAM) is employed. The BER performance versus the average electrical signal-to-noise ratio (SNR) per bit is illustrated both for the single and the multiple-user communication using Monte Carlo simulations.

For compact optical code-division multiple access (CDMA) networks, a novel cyclic optical encoder/decoder based on an arrayed waveguide grating (AWG) router is proposed. The proposed encoder/decoder treats multiple codewords of the two-dimensional Reed-Solomon code simultaneously using the cyclic property of the AWG router and the code, and multiple subscribers can share the encoder/decoder in networks. With the proposed encoder/decoder, optical CDMA networks become compact and cheap, since the number of encoders/decoders required in the network is reduced. The feasibility of the proposed encoder/decoder is demonstrated experimentally.

To provide Quality of Service (QoS) and data rate differentiation, we investigate in this paper a 2 dimensional optical code division multiple access (OCDMA) technique. A 2D multi-weight coding scheme with parallel mapping technique is developed. The system enhancement is assessed thanks to the use of Forward Error Correction (FEC) based on Low Density Parity Check (LDPC) codes. In order to have an efficient correction power, we develop an adaptation of the LDPC decoding algorithm to the specific multiple access interference distribution in a multimedia OCDMA network. The proposed network permits a high number of users to communicate with high data rates adapted to a multimedia transmission (voice, data and video) with corresponding QoS (10-3, 10-6, 10-9).

We compared the theoretical bit-error-rate (BER) and throughput performance limits of 2-D time-wavelength and coherent time-spreading optical code division multiple access (OCDMA) communication systems. The results show that the BER performance of the coherent time spreading OCDMA scheme is much superior to 2-D time wavelength scheme in the multiple access interference (MAI) noise limited case without considering beat noise, and the beat noise affects the system performance seriously and appears as a dominant source of noise for the two kinds of OCDMA systems. Nevertheless, the 2-D time wavelength scheme has better tolerance to beat noise than coherent time spreading OCDMA scheme, and the superiority is more apparent with the increasing of the code length N. While the coherent time spreading scheme has higher peak throughput, and it supports a higher throughput than the 2-D time wavelength scheme at higher offered loads.

This paper presents the study of a receiver device for the optical code division multiple access (OCDMA) called the optical parallel interference cancellation (Opt-PIC). The performance of OCDMA system is known to be easily influenced by the multiple access interference (MAI) caused by other simultaneous users. To overcome this problem, there is a strong demand for the design of new detection scheme that will be efficient enough to improve the performance of the OCDMA system, while minimizing the effects of the MAI. In this paper, some studies have been conducted on the Opt-PIC specifically for the lowest threshold value. Studies have been carried out not only using the conventional method but also using a hard limiter. The results are compared to the previous techniques used to mitigate the effect of MAI.

This paper proposes a novel incoherent transceiver structure for the optical modulation scheme deploying polarization shift keying (Pol-SK) in conjunction with optical code-division multiple-access (OCDMA). The system has been accurately analyzed taking into account the presence of optical amplifier spontaneous emission (ASE) noise, electronic receiver noise, photodiode shot-noise and also multiple access interference (MAI). The application of optical tapped-delay lines in the receiver as the CDMA-decoder has also been investigated. In terms of spreading code, a newly introduced prime code family named as double-padded modified prime code has been utilized. A comprehensive set of results in the literatures showed that the performance of the binary system is approximately 3 dB better than intensity modulations. Therefore, in our following proposed transceiver architecture we have also employed binary Pol-SK modulation. Our results indicate that the proposed architecture consumes less power while enhances the system capacity. Moreover, since the optical beam power is constant, the system has immunity against the self- and cross-phase modulations. Above all, the polarization-based scheme is more promising for very-long-haul high-speed transmissions over the OCDMA networks.

This paper describes a higher order statistics (HOS) based efficient receiver for the detection of complete and/or truncated direct-sequence spread spectrum (DS-SS) signals in the presence of noise and multiple access interference (MAI). Such signals are inefficiently detected by conventional matched filters or intercept receiver. The detection procedure of the HOS receiver is based on the characteristic patterns of the third order cumulants of maximal-length-sequences (m-sequences), which are used as spreading sequences to generate the DS-SS signals. These patterns have peaks, which remain almost discernible for truncated signal intercepts in the presence of MAI and noise, allowing the detection of individual users. The computer simulations prove the efficiency of the suggested receiver structure.

This paper investigates the use of a two-photon absorption photodetector for all-optical signal processing. Continuous, wavelength selective chromatic dispersion monitoring in a high-speed multi-wavelength system is discussed. The reduction of multiple access interference in an optical code division multiple access network using a TPA photodetector is also presented.

This work demonstrates the potential of electronic signal processing for applications in optical code division multiple access networks. The proposed designs are based in distributed topologies allowing operation at speeds close to the cut-off frequency of the transistors employed. We discuss structures capable of encoding and decoding time-domain and multi-wavelength optical CDMA signals. A scheme for mitigating of the impact of group velocity dispersion in multi-wavelength OCDMA systems is also analysed.