Thiago R. Raddo

Throughput Performance Evaluation of Multiservice Multirate OCDMA in Flexible Networks

In this paper, new analytical formalisms to evaluate the packet throughput of multiservice multirate slotted ALOHA optical code-division multiple-access (OCDMA) networks are proposed. The proposed formalisms can be successfully applied to 1-D and 2-D OCDMA networks with any number of user classes in the system. The bit error rate (BER) and packet correct probability expressions are derived, considering the multiple-access interference as binomially distributed. Packet throughput expressions, on the other hand, are derived considering Poisson, binomial, and Markov chain approaches for the composite packet arrivals distributions, with the latter defined as benchmark. A throughput performance evaluation is carried out for two distinct user code sequences separately, namely, 1-D and 2-D multiweight multilength optical orthogonal code (MWML-OOC). Numerical results show that the Poisson approach underestimates the throughput performance in unacceptable levels and incorrectly predicts the number of successfully received packets for most offered load values even in favorable conditions, such as for the 2-D MWML-OOC OCDMA network with a considerably large number of simultaneous users. On the other hand, the binomial approach proved to be more straightforward, computationally more efficient, and just as accurate as the Markov chain approach.

Performance comparison of hybrid 1-D WDM/OCDMA and 2-D OCDMA towards future access network migration scenario

In this paper, we provide a performance comparison and analysis between a hybrid 1-D WDM/OCDMA system and a 2-D WHTS OCDMA system. In the hybrid system, OOC is employed as users code sequence of the OCDMA dimension. The simulation results show that the hybrid system presents better performance than the 2-D WHTS OCDMA system, and show also that under a standard BER scenario, i.e., BER = 10-9, the hybrid system can support at least 75% more simultaneous users than the 2-D OCDMA system for the analyzed case study. The analysis suggests that the hybrid 1-D WDM/OCDMA system is a qualified migration scenario since it can provide a smooth migration path from current networks towards OCDMA networks.

Highly efficient FFH-OCDMA packet network with coherent advanced modulation formats

In this paper we present, for the first time, the modelling and performance analysis of packet OCDMA networks based on coherent advanced modulation formats, namely binary and quadrature phase shift keying (BPSK and QPSK). We investigate how each of these advanced modulation formats perform under fast frequency hopping (FFH) encoding. For all cases, we have accounted for the simultaneous effect of multiple-access interference (MAI) and beat noise (BN) that impair the overall physical and link layer performance. Results indicate that networks based on BPSK and QPSK modulations possess increased packet delivery efficiency regardless of the traffic activity when compared with legacy on-off keying (OOK) based networks. The efficiency gain is maximized for intermediate traffic activity, accounting for improvements in the order of 80%.

Performance evaluation of a multirate, multiclass OCDM/WDM optical packet switch

In this paper, we propose a novel optical code division multiplexing/wavelength division multiplexing (OCDM/WDM) optical packet switch architecture capable of supporting multirate and multi-quality of service (QoS) transmission. The main idea is to use multi-weight multi-length optical orthogonal code (MWML-OOC) as signature sequence to provide diversified data rates and services. The architecture of the proposed multiservice OCDM/WDM switch is also presented. Furthermore, in order to analyze the packet loss probability (PLP) of the switch, we derive a bit error rate (BER) expression of the MWML-OOC-based OCDM system. Finally, we show that using high codeword weight and low offered traffic lead to a better PLP.

Hybrid optical CDMA-FSO communications network under spatially correlated gamma-gamma scintillation

In this paper, we propose a new hybrid network solution based on asynchronous optical code-division multiple-access (OCDMA) and free-space optical (FSO) technologies for last-mile access networks, where fiber deployment is impractical. The architecture of the proposed hybrid OCDMA-FSO network is thoroughly described. The users access the network in a fully asynchronous manner by means of assigned fast frequency hopping (FFH)-based codes. In the FSO receiver, an equal gain-combining technique is employed along with intensity modulation and direct detection. New analytical formalisms for evaluating the average bit error rate (ABER) performance are also proposed. These formalisms, based on the spatially correlated gamma-gamma statistical model, are derived considering three distinct scenarios, namely, uncorrelated, totally correlated, and partially correlated channels. Numerical results show that users can successfully achieve error-free ABER levels for the three scenarios considered as long as forward error correction (FEC) algorithms are employed. Therefore, OCDMA-FSO networks can be a prospective alternative to deliver high-speed communication services to access networks with deficient fiber infrastructure.

Throughput performance analysis of multirate, multiclass S-ALOHA OFFH-CDMA packet networks

In this paper, we propose a new throughput expression for multirate, multiclass slotted-ALOHA optical fast frequency hopping code-division multiple-access (OFFH-CDMA) packet networks considering a Poisson distribution for packet composite arrivals. We analyze the packet throughput performance of a three-class OFFH-CDMA network, where multirate transmissions are achieved via manipulation of the users code parameters. It is shown that users transmitting at low rates interfere considerably in the performance of high rate users. Finally, we perform a validation procedure to demonstrate that the proposed multirate throughput expression converges towards the single rate expression (considered as the network limiting case).

Comparison between Mamdani and Sugeno fuzzy inference systems for the mitigation of environmental temperature variations in OCDMA-PONs

This paper presents a comparative study between the Mamdani and Sugeno fuzzy inference systems (FIS) for intelligent traffic transmission over optical code-division multiple-access (OCDMA) network architectures. This FIS is capable of mitigating environmental temperature variation effects in the transmission link which are known to play an important role in the overall performance of the network. The paper outlines the basic difference between both Mamdani and Sugeno type FIS for this approach. The results highlight the performance of the two systems and the computational advantages of using Sugeno- type over Mamdani-type.

Multirate FFH-OCDMA networks based on coherent advanced modulation formats

In this paper, we propose and evaluate the performance of a new scheme for multirate optical code-division multiple-access (OCDMA) networks based on coherent advanced modulation formats, namely binary and quadrature phase shift keying (BPSK and QPSK). The proposed scheme employs BPSK and QPSK modulation formats for low and high rate transmission users, respectively. In addition, we develop a general formalism that allows performance evaluation of legacy networks based on on-off keying (OOK) modulation format. We investigate how the coherent demodulation of encoded fast frequency hopping (FFH) signals under multiple access-interference (MAI) can improve the network performance. It is shown for the first time that simultaneous users of different transmission rates can surprisingly achieve BER levels in the error-free region.

Throughput evaluation of multirate, multiservice 2-D OCDMA packet networks

In this paper, we carry out a performance comparison and analysis between two two-class multirate OCDMA packet networks in terms of bit error rate (BER) and throughput. We employ multiple-pulses-per-row (MPR) codes as signature sequence of an incoherent network to achieve multirate and multiservice transmissions. We derive BER and packet success probability expressions, considering multiple-access interference (MAI) as the main noise source, in order to evaluate the network throughput. Finally, simulation results show that low rate users have larger linear region than high rate class.

BER performance improvement in FFH-OCDMA networks with BPSK modulation format

In this paper, the performance of optical fast frequency hopping code-division multiple-access (FFH-OCDMA) network based on binary phase shift keying (BPSK) modulation format under both ideal and non-ideal encoding scheme scenarios is addressed for the first time. The results show that the BPSK modulation format increases significantly the signal-to-interference ratio (SIR) and, consequently, the overall network performance. Even though the signal waveforms under non-ideal scenario suffer higher degradation, the BPSK modulation format is still robust to maintain transmissions with error-free even when the network capacity in terms of simultaneous users is under full operation. In addition, it is shown that on-off keying (OOK) - based networks are not good candidates for future FFH-OCDMA implementations in this MAI limited scenario. On the other hand, our results pave the way for BPSK-based networks, which are seen as potential candidates for next generation passive optical networks (NG-PONs).