Nokia (Portugal)

The energy consumption problem in the mobile industry has become crucial. For the sustainable growth of the mobile industry, energy efficiency (EE) of wireless systems has to be significantly improved. Plenty of efforts have been invested in achieving green wireless communications. This article provides an overview of network energy saving studies currently conducted in the 3GPP LTE standard body. The aim is to gain a better understanding of energy consumption and identify key EE research problems in wireless access networks. Classifying network energy saving technologies into the time, frequency, and spatial domains, the main solutions in each domain are described briefly. As presently the attention is mainly focused on solutions involving a single radio base station, we believe network solutions involving multiple networks/systems will be the most promising technologies toward green wireless access networks.

The complexities of common equalizer schemes are analytically analyzed in this paper in terms of complex multiplications per bit. Based on this approach we compare the complexity of mode-division multiplexed digital signal processing algorithms with different numbers of multiplexed modes in terms of modal dispersion and distance. It is found that training symbol based equalizers have significantly lower complexity compared to blind approaches for long-haul transmission. Among the training symbol based schemes, OFDM requires the lowest complexity for crosstalk compensation in a mode-division multiplexed receiver. The main challenge for training symbol based schemes is the additional overhead required to compensate modal crosstalk, which increases the data rate. In order to achieve 2000 km transmission, the effective modal dispersion must therefore be below 6 ps/km when the OFDM specific overhead is limited to 10%. It is concluded that for few mode transmission systems the reduction of modal delay is crucial to enable long-haul performance.

In this letter, a nonlinear semi-analytical model (NSAM) for simulation of few-mode fiber transmission is proposed. The NSAM considers the mode mixing arising from the Kerr effect and waveguide imperfections. An analytical explanation of the model is presented, as well as simulation results for the transmission over a two mode fiber (TMF) of 112 Gb/s using coherently detected polarization multiplexed quadrature phase-shift-keying modulation. The simulations show that by transmitting over only one of the two modes on TMFs, long-haul transmission can be realized without increase of receiver complexity. For a 6000-km transmission link, a small modal dispersion penalty is observed in the linear domain, while a significant increase of the nonlinear threshold is observed due to the large core of TMF.

We propose a noniterative digital backward propagation technique, based on an inverse modified Volterra series transfer function to postcompensate transmission linear and nonlinear impairments in the presence of optical noise. Using a single-channel 40-Gb/s nonreturn-to-zero quadrature phase-shift-keying optical signal propagated over 20 × 80 km of standard single-mode fiber, and performing digital postcompensation around the Nyquist rate, our compensation algorithm is able to surpass the maximum accuracy obtained with a symmetric split-step Fourier method, enabling us to increase the nonlinear tolerance by approximately 2 dB.

A highly linear optical transmitter for radio-over-fiber subcarrier-multiplexed systems is presented. An integrated dual Mach-Zehnder modulator (MZM) is utilized to combine an optical carrier suppressed signal with an optical carrier. The proposed transmitter enables more than 10-dB improvement in the carrier-to-interference ratio compared to a quadrature biased MZM, and similar results to low biased MZM considering similar insertion loss. Negligible radio-frequency power dependence with temperature-induced bias drift is reported, while the low biased MZM is penalized by more than 12 dB for a 15% bias drift. The proposed transmitter reduces the minimum error vector magnitude from 4.2% to 3.5%, when compared to quadrature biased MZM, for a 54-Mb/s orthogonal frequency-division-multiplexed signal.

A sensing head configuration and the necessary interrogation parameters to simultaneously measure strain and temperature using a single fiber Bragg grating (FBG) are presented and demonstrated. By writing the FBG in a linearly etched fiber, we were able to use the information encoded in the peak wavelength and in the spectral width of the FBG. The spectral width of the grating depends uniquely on the applied strain and is temperature independent. An uncertainty of ±15.26 ¿¿ and ±1.92°C was achieved in the experimental verification.

The emergence of new Internet paradigms has changed the common properties of network data, increasing the bandwidth consumption and balancing traffic in both directions. These facts raise important challenges, making it necessary to devise effective solutions for managing network traffic. Since traditional methods are rather ineffective and easily bypassed, particular attention has been paid to the development of new approaches for traffic classification. This article surveys the studies on peer-to-peer traffic detection and classification, making an extended review of the literature. Furthermore, it provides a comprehensive analysis of the concepts and strategies for network monitoring.

Service providers emphasize the need for faster, cheaper and more reliable deployment of broadband networks, therefore making the hardware manufacturers pursue innovative solutions driving down component complexity, installation time, required skill level and, ultimately, the overall deployment cost for an access network structure. The current dramatic increase in the fiber-to-the-home (FTTH) deployment pace along with the general desire to eventually migrate completely to these systems, puts the passive optical network (PON) deployment issues in the spotlight of current academic and system vendor research. Numerous publications explore new technology developments leading to the reduction in the overall costs required to deploy FTTH networks today, especially in terms of the PON structure, installation time, and required craftsman skill level.

The coordination methodologies of CAMBADA, a robotic soccer team designed to participate in the RoboCup middle-size league (MSL), are presented. The approach, which relies on information sharing and integration within the team, is based on formations, flexible positionings and dynamic role and positioning assignment. Role/positioning assignment follows a new priority-based algorithm that maintains a competitive formation, covering the most important roles/positionings when malfunctions lead to a reduction of the team size. Coordinated procedures for passing and setplays have also been implemented. With this design, CAMBADA reached the 1st place in the RoboCup'2008 world championship. Competition results and performance measures computed from logs and videos of real competition games are presented and discussed.

This letter proposes the use of a refractive index profile with a graded core and a cladding trench for the design of few-mode fibers, aiming an arbitrary differential mode delay (DMD) flattened over the C+L band. By optimizing the core grading exponent and the dimensioning of the trench, a deviation lower than 0.01 ps/km from a target DMD is observed over the investigated wavelength range. Additionally, it is found that the dimensioning of the trench is almost independent of the target DMD, thereby enabling the use of a simple design rule that guarantees a maximum DMD deviation of 1.8 ps/km for a DMD target between -200 and 200 ps/km.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We present, for the first time, extensive simulation and experimental characterizations of single SOA-MZI-based multiwavelength conversion (MWC) of NRZ data at 10 Gb/s and RZ data at 40 Gb/s under various parametric conditions deploying ITU standard 100- and 200-GHz channel spacing. We analyze, in particular, the physical performance impairments caused by high-order four-wave mixing interference. Our simulation results indicate the promising performance of the MWC up to eight channels with 200-GHz channel spacing. We further experimentally demonstrate four-channel 10-Gb/s error-free MWC with signal regeneration possibilities and 40-Gb/s MWC with moderate penalties, based on commercially available integrated SOA-MZIs. We obtained clear, open converted eye diagrams and achieved negligible difference in channel performance among all MWC channels at both bit rates. Our results proved the excellent performance of a simple scheme for various future network and system applications, such as all-optical wavelength multicast and grid networking. </para>

This letter proposes a new power equalization scheme based on cascaded semiconductor optical amplifiers, for 10-Gb/s ethernet passive optical networks with uneven topology. For networks with a large number of subscribers, the proposed equalization scheme enables a 16-dB reduction of the receiver dynamic range.

A concerted fight against botnets is needed in order to avoid them from becoming a serious threat to global security in the forthcoming years. Zombie detection is currently performed at the host and/or network levels, but these options have important drawbacks: antivirus, firewalls and anti-spyware are not effective against this threat because they are not able to detect hosts that are compromised via new or target specific malicious software and were not designed to protect the network from external attacks or vulnerabilities that are already present inside the local area network. To overcome these limitations, we propose a new botnet detection approach based on the identification of traffic patterns: since each network application, whether it is licit or illicit, has a characteristic traffic pattern that can uniquely identify it, the detection framework will rely on an Artificial Neural Network to identify the licit and illicit patterns. After the identification phase, the system will generate alarms to the system administrator, that can trigger the most appropriate security actions, like blocking the corresponding IP addresses, putting them under a deeper surveillance or acting over some suspicious network segment. A general detection framework was developed in order to incorporate the detection methodology itself, as well as the data collection and storage modules and all the necessary management functions. Some performance tests were already carried out on the proposed system and the results obtained show that the system is stable and fast and the detection approach is efficient, since it provides high detection rates with low computational overhead.

We experimentally demonstrate a bi-directional Terabit+ UDWDM coherent PON with Nyquist shaped 16QAM modulation, offering up to 10 Gb/s service capabilities per user/wavelength in a total spectrum of 12.8 nm over 40 km of SSMF.

Optical transport networks are at the turning point from providing semi-permanent connections to being engineered to efficiently support dynamic optical connection services. Vital to this transition is the availability of node architectures that improve the flexibility of add/drop port utilization, thereby enabling the transponder connected to a port to be reused to realize connections with different wavelength channels or using different input/output fiber links (directions). This paper assesses the network-wide blocking performance provided by node architectures with different degrees of freedom for port reuse. The performance assessment not only clearly highlights the relevance of maximizing the chances of transponder sharing in transport networks, but also shows that the network topology determines which of the degrees of freedom for port reuse is more relevant.

Optical transport networks are evolving towards the support of dynamic setup/tear-down of services, demanding efficient accommodation of heterogeneous bandwidth requirements while minimizing capital and operational expenditures. Integrated OTN/DWDM networks can attain this objective by optimizing the utilization of traffic grooming and optical bypass at transit nodes. Moreover, the multiplexing of mixed lower order optical channel data units into a higher order data unit in a single stage enables to avoid bandwidth fragmentation, improving the wavelength channel utilization in these networks. This paper evaluates the blocking performance of an integrated OTN/DWDM network for different node and input traffic setups.

The interest in the evolution of current PON systems toward high-data-rate systems capable of providing a future-proof platform for delivery of truly subscriber-oriented and personalized triple-play services resulted in the recent kickoff of the 10 Gb/s Ethernet PON system standardization effort in the IEEE . Ethernet PON has become a network of choice for low-cost subscriber-oriented digital service delivery, taking over the market previously dominated by DSL and cable modems. In this article we examine the current development process of 10 Gb/s EPON systems in more detail, standardized in the framework of the IEEE 802.3av task force, looking at the technical challenges, drivers, and possible evolution scenarios of the emerging high-data-rate access systems..

We present a multi-objective framework to jointly optimize cost and spectrum in a survivable flexible-grid network with multiple transponder profiles. Through the use of an evolutionary algorithm, the sharing of spectral and interface resources is explored to clearly show the cost/spectrum design trade-off according to different sharing policies.

In this letter, the performance of maximum-likelihood (ML) detection is evaluated and compared with the zero-forcing (ZF) and minimum mean square error (MMSE) equalizers for a 3 × 158-Gb/s mode-division multiplexed dual-polarization quadrature phase shift keying orthogonal frequency division multiplexing transmission impaired by mode-dependent loss. The receiver schemes are compared in terms of performance and complexity. The simulations show that the ML approach outperforms both ZF and MMSE equalization for strongly coupled modes. However, the complexity of the ML detection is significantly higher and increases faster with the number of modes used for transmission and the modulation format order.

The increasing number of applications offering their services over peer-to-peer (P2P) platforms is changing the properties of the traffic within computer networks. Their massive use raises a few imperative challenges for network administrators and Internet service providers, regarding the quality of service and security of their networks. It such scenario, it is important to develop mechanisms to control and efficiently manage the P2P traffic and prepare the networks to support it, for which it is necessary to study the effect of P2P applications in the traffic of computer networks and to develop methodologies to characterise its behaviour. In this paper, the characteristics of the traffic generated by P2P applications are analysed from the behavioural point of view, and entropy is used to measure the heterogeneity embedded in the packet sizes. The results obtained show evident difference between P2P and non-P2P traffic, being the proposed approach applicable to real-time and high-speed networks with encrypted P2P traffic, where the existing methodologies are useless.