In situ method for power re-equalization of wavelength pulses inside of OCDMA codes

A simple in-situ method to equalize power among individual wavelengths pulses representing two-dimensional wavelength-hopping time-spreading OCDMA code originally generated by a fibre Bragg grating-based OCDMA encoder is presented. Experimental data obtained in a field-based multiuser OCDMA testbed shows that applying this method results in system performance enhancements which was demonstrated by observing improved bit error rate (BER) during the field trials

Novel power saving architecture for OCDMA code generation

Fiber Bragg grating (FBG) optical reflectors have become used for encoding and decoding optical code division multiple assess (OCDMA) data. We observed that only about 20% of the power that enters into an optical FBG en/decoder is reflected and the remaining 80% is not used in the en/decoding process. We present a novel architecture that will enable both cost and energy efficiency in the process of generating optical CDMA codes. The architecture achieves effective utilization of available optical power. We have been able to achieve power savings of up to 3dB for a 4-user OCDMA system

Terrorism, Security Challenge and Implications on Nigeria’s Good Neighbourliness

Nigeria lies between five francophone countries with geo strategic and security implications. In this wise, Nigeria’s good neighbuorliness becomes an important political framework of interest.  International terrorism since the wake of the 11th September attack on America has metacised into local terrorism perpetrated by the Boko Haram group in the case of Nigeria. Boko Haram terrorism has been internationalized with linkages with Isis and has spread its tentacles beyond the shores of Nigeria into neighbouring states of Chad, Niger, and Cameroon. Since Independence, Nigeria has wittingly dwelt within a choking Franco phony politics of survival.  She had maintained a policy of good neighbouliness that has cost her continued friendship with France and economic openness to assist the African neighbours a breeding air of survival.  In the wake of the new politics of international terrorism and with the spread of terrorist activities beyond the Nigerian borders into neighbouring States, this policy (good neighbourliness) becomes an agenda for analytical consideration. This is the relevance of this research paper which considers Nigeria’s security challenge as implicative on good neighbouliness. The paper argues that, the security of Nigeria and its neighbours are negatively implicated and that this political framework (good neighbourliness) needs to be reviewed to take care of new arising challenges. Keywords: Good Neighbourliness, Security Challenge, Terrorism, Nigeria

Workability, compressive strength and initial surface absorption of laterized concrete

This paper investigated the workability, compressive strength and initial surface absorption of plasticised laterized concrete at the water/cement ratios of 0.30, 0.50 and 0.70. Slump, compressive strength at 7, 14, 21 and 28 days and initial surface absorption after 10 minutes (ISA-10) at 28, 60 and 90 days were determined at the laterite contents of 0, 20, 40, 60, 80 and 100%. ISA-10 was also assessed at 28-day strengths of 20, 25 and 30 N/mm2. Results showed that superplasticiser dosage increased with increasing content of laterite and for economic dosage laterite content should be limited to 40%. At equal water/cement ratios, compressive strength reduced with increasing content of laterite and ISA-10 increased with increasing content of laterite. The results also showed a strong relationship between ISA-10 and compressive strength and that laterized concrete, when specified on the basis of strength, would have resistance to initial surface absorption comparable with that of the conventional concrete if laterite content is limited to 40%. Hence, for good workability, compressive strength and permeation resistance, laterite content of concrete should be limited to 40%

Enhancing data centre networking using energy aware optical interconnects

In a fast changing world where information technology drives economic prosperity, the number of data centres has grown significantly in the past few years. These data centres require large amount of energy in order to meet up with increasing demands. An overview of energy efficient optical interconnects as a means of reducing energy consumption without compromising speed and accuracy was presented. New methods by which energy efficiency can be achieved using OCDMA multiplexing techniques for future optical interconnections were discussed. We also presented some challenges that might inhibit effective implementation of the OCDMA multiplexing scheme

OCDMA receiver with built-in all-optical clock recovery

A receiver that incorporates an all-optical clock recovery approach for synchronisation suitable for use in incoherent OCDMA transmission is demonstrated. The developed solution was implemented and tested in a multiuser environment using the 2D-WHTS coding scheme on incoherent OCDMA transmission with 2.5 Gbit/s data rate. The receiver with built-in all-optical clock recovery was tested by taking the BER for the received data when synchronised with the all-optically recovered clock from the incoming OCDMA traffic and when an RF synthesiser was used to the generate the clock. Improvement of ∼7.5 dBm was observed with the all-optical clock recovery approach. The related eye diagrams and the wavelength spectrum were also recorded

Investigation of all-optical switching OCDMA testbed under the influence of chromatic dispersion and timing jitter

First part of this paper presents an all-optical switching OCDMA testbed investigation under the influence of the residual chromatic dispersion resulted from different locations of the receiving terminal. The investigation was carried out using incoherent 2D-WH/TS OCDMA codes based on picosecond pulses at OC-48 (2.5Gb/s) data rate. The testbed itself is based on a fully chromatic dispersion compensated (with sub-picosecond accuracy) 17 km bidirectional fiber link connecting University of Strathclyde and Glasgow University. We have found that a high performance penalty in the form of BER deterioration was incurred when even a relatively short length of optical fiber was added to a fully compensated transmission link in order to relocate the receiving terminal (we tested increments up to 275m of SMF-28). Second part of this paper reports on the testbed performance when an OCDMA receiver with built in all-optical clock recovery was implemented to mitigate the detrimental effects of the link timing jitter on the picosecond switching based all-optical time gate

Towards higher scalability of hybrid optical CDMA network

A novel approach for improving the number of simultaneous users in a hybrid OCDMAOTDMA network is proposed and analysed. OCDMA system is based on two-dimensional wavelength-hopping time-spreading codes with multi-wavelengths picosecond carriers. The scalability increase was achieved by adding a third dimension to separate OCDMA user groups within OTDMA time slots by assigning them into different wavelength bands. We have shown this will scale-up the system capacity proportionally to the number of assigned wavelength bands. A self-clocking all-optical time gate was then demonstrated as an effective means for suppressing the growing detrimental multi access interference noise resulted from this capacity increase

Effect of variations in environmental temperature on 2D-WH/TS OCDMA code performance

Extensive research has been carried out on the performance investigation of two-dimensional wavelength hopping/time spreading optical code division multiple access (OCDMA) codes, which are based on picosecond multiwavelength pulses under the influence of temperature variations resulting from changing environmental conditions. Equations have been derived to theoretically evaluate the extent to which such temperature changes will degrade the overall OCDMA system performance. To mitigate these negative effects on the OCDMA system, several steps have been introduced to improve the code robustness. System design improvements have then been investigated. We also found they would help to improve the spectral efficiency