Edward Mutafungwa

Multiclass optical orthogonal codes for multiservice optical CDMA networks

Optical code division multiple access (CDMA)-based networks are an interesting alternative to support various traffic types of multimedia applications with highly variable performance targets. Generally, multilength codes are designed to support multirate services, while the multiweight codes are designed to support differentiated quality of service (QoS) for multimedia applications. However, existing optical orthogonal codes (OOCs) are limited to single class or multiclass with restricted weight and length properties. Therefore, there exists a lack of flexibility in the existing OOCs to support arbitrary rate and QoS. This paper presents a proposal of generation procedure and performance analysis of joint multiweight multilength strict OOCs. The approach used in this paper is to apply a methodology strongly relying on developed analytical theory that is supported by computer optimization, because it has turned out that it is mathematically intractable to construct unconstraint joint multilength multiweight OOCs using pure algebraic techniques. The generated code set fulfills the conditions of strictly OOCs, namely, the maximum nonzero shift autocorrelation and the maximum cross correlation constraints of one. The mark position difference (MPD) approach is used to generate in a flexible way the multiclass code set. The MPD results in the simple evaluation of multiclass code set cardinality. Furthermore, the multiple-access interference (MAI) in a multiclass OOC system is evaluated by modeling the interference per class as a Poisson distribution to simplify performance evaluation with acceptable accuracy.

Performance Evaluation of Next Generation Free-Space Optical Communication System

Free-space optical communication systems can provide high-speed, improved capacity, cost effective and easy to deploy wireless networks. Experimental investigation on the next generation free-space optical (FSO) communication system utilizing seamless connection of free-space and optical fiber links is presented. A compact antenna which utilizes a miniature fine positioning mirror (FPM) for high-speed beam control and steering is described. The effect of atmospheric turbulence on the beam angle-of-arrival (AOA) fluctuations is shown. The FPM is able to mitigate the power fluctuations at the fiber coupling port caused by this beam angle-of-arrival fluctuations. Experimental results of the FSO system capable of offering stable performance in terms of measured bit-error-rate (BER) showing error free transmission at 2.5 Gbps over extended period of time and improved fiber received power are presented. Also presented are performance results showing stable operation when increasing the FSO communication system data rate from 2.5 Gbps to 10 Gbps as well as WDM experiments.

Interference mitigation by practical transmit beamforming methods in closed femtocells

We present an analysis of a femtocellular communications network and the impact of cochannel interference on link performance. Furthermore, we propose a method whereby user terminals can maintain a controlonly connection to an adjacent femtocell for interference mitigation purposes. Specifically, we provide an emphasis on suboptimal but practical methods that rely on transmit beamforming. Our numerical results demonstrate that even simple multiantenna methods can be effectively used to suppress co-channel interference provided that control channel connection between interfering femto-base station and user terminal is allowed.

An improved wavelength-selective all-fiber cross-connect node

A flexible and transparent optical network, can be realised by deploying fully-optical cross-connect nodes (OXNs). We propose some modifications on previously reported all-fiber OXN. These modification aim to enhance the optical spectral efficiency, modularity and spectral response of the OXN. Simulations of the OXN and its modified version indicate a significant increase in the cascadability achieved by the modified OXN.

Dominant interferer mitigation in closed femtocell deployment

In this paper, we analyze the interference distribution and gain of beamforming in closed access femtocells in downlink of a two-tier HSDPA cellular network. We show through simulations that indoor femtocell deployment leads to a dominant interferer scenario. According to results even simple null steering method based on the scarce codebook of HSDPA transmit diversity mode 1 can be beneficially applied. Performance evaluations are carried out through HSDPA compliant system simulations.

Comparative analysis of the traffic performance of fiber-impairment limited WDM and hybrid OCDM/WDM networks

Optical code-division multiplexing (OCDM) is a technique that is currently generating considerable research interest. This paper analyzes and compares the traffic performance of wavelength-division multiplexing (WDM) and hybrid OCDM/WDM-based optical networks. The analysis considers the influence of the limitations of fiber-induced signal impairments on traffic performance and comparisons are performed for an example network utilizing different standardized fiber types. Furthermore, comparisons of traffic performance are also made between different lightpath schemes used in WDM and OCDM/WDM networks. The analysis results show that the OCDM/WDM lightpath schemes significantly outperform the WDM lightpath schemes for given blocking probability criteria. Moreover, the analysis indicates that fiber nonlinearity (which limits the minimum channel spacing) affects the traffic performance more severely compared to fiber dispersion (limits code cardinality).

Multi-access-interference mitigation using power control in optical-CDMA star networks

This paper investigates optical power control to enhance capacity of optical CDMA star coupled networks. We consider a network in which the nodes encode their optical signal by prime codes, and the resulting error rate performance is inspected with and without power control. Network impairments, such as fiber attenuation, star coupler loss, thermal noise and shot noise, are taken into account while inspecting the number of supported users. We use a well known centralized power control algorithm to adjust the laser power levels. In short range optical networks, as for instance local area networks (LANs) and metropolitan area networks (MANs), the thermal and shot noise levels can be very small compared to the signal level, thus, noise-free or multiple access interference (MAI) limited case is of interest. In our analysis, the star network is partitioned into access part and broadcasting part. We proof that in the MAI noise dominated scenario, the broadcasting part of the network is irrelevant with respect of the optimum power control problem. In this case, the users can apply a lookup table containing information about the access part of the network to set their optimum transmission power levels. We note that whenever a node is switched on or off, the other active nodes should update their power levels in order to maintain or upgrade their respective error rate limits.

Grid and Pervasive Computing Workshops

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Exploiting femtocellular networks for emergency telemedicine applications in indoor environments

24.95 ▶ springer.com/mycopy M. Rautiainen, University of Oulu, Oulu, Finland; T. Korhonen, Aalto University, Helsinki, Finland; E. Mutafungwa, Aalto University, Helsinki, Finland; E. Ovaska, VTT Technical Research Centre of Finland, Oulu, Finland; A. Katasonov, VTT Technical Research Centre of Finland, Oulu, Finland; A. Evesti, VTT Technical Research Centre of Finland, Oulu, Finland; H. Ailisto, VTT Technical Research Centre of Finland, Oulu, Finland; A. Quigley, University of St. Andrews, St. Andrews, United Kingdom; J. Häkkilä, Nokia Research Center, Oulu, Finland; N. Milic-Frayling, Microsoft Research, Cambridge, United Kingdom; J. Riekki, University of Oulu, Oulu, Finland (Eds.) Grid and Pervasive Computing Workshops

Experimental demonstration of next-generation FSO communication system

This paper presents a proposal for a solution for rapid provisioning of mobile broadband data connectivity for emergency telemedicine applications in indoor environments. The proposed solution relies on the exploitation of existing femtocellular network resources available at emergency sites in indoor environments. Extensive simulations are carried out to compare the performance of our new proposed complementary femtocellular approach to the conventional macrocellular mobile networking approach in a UMTS/WCDMA network operating environment. The simulation results indicate at least an order of magnitude reduction in service outage rates when femtocells are utilized, in the comparison to the macrocellular case for multiple dwelling unit buildings located on the cell edge.