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The article discusses various reports published within the issue, including "Analysis, Simulation and Measurements in Large-scale Packet Networks," "Adaptive Wavelet Based Multifractal Model Applied to the Effective Bandwidth Estimation of Network Traffic Flows," and "A Precedence-Enabled Per Hop Behavior: Impact on TCP and UDP Flows."

The article introduces various articles on computer network technologies, published in the special section of the periodical. The first paper deals with power fading using optimised chirped fibre Bragg grating. In the second paper, authors have theoretically derived the frequency response of the photodetector. Another paper in the section discusses the challenges to the antenna and microwave communities in terms of special requirements for antenna design, fabrication and integration.

Different approaches for the characterisation of relevant parameters of the low-voltage mains network, used for high-speed data transmission (BPL, broadband over power line) are described. Part 1 of the paper depicts the disturbance scenario of these BPL devices and the motivation will be given for the development of a new measurement procedure in CISPR for the estimation of the high-frequency characteristics of AC mains network. The improvements of the measurement method is not restricted to BPL applications, but can also be applied to other wire-based telecommunication systems. Part 2 of the paper shows the definitions and comparisons of different symmetry factors. The transfer of the results on the compliance test for BPL devices will be shown. [ABSTRACT FROM AUTHOR]

The paper proposes a new approximate calculation method of occupancy distribution and blocking probability in the full-availability group (FAG) with multi-rate traffic streams and bandwidth reservation. The algorithm involves calculation of system state probabilities by a convolution operation. In the paper, an effective method of calculating state probabilities in a reservation space of the system is derived. The analytical results of blocking probabilities in the FAG with bandwidth reservation, obtained on the basis of the proposed analytical method, are compared with the data obtained on the basis of other known analytical methods and with the simulation results. The accuracy of the proposed method is evaluated for different multi-rate Bernoulli (Erlang), Poisson (Engset), Pascal traffic streams. The method proposed is characterised by lower complexity than the convolution algorithm for the FAG with bandwidth reservation devised earlier. [ABSTRACT FROM AUTHOR]

To avoid poor efficiency of the power amplifiers, the opportunistic cophasing communication system randomises only the phase of beamforming vector elements, instead of randomising both amplitude and phase. The opportunistic cophasing system with multi-beam transmission is focused. The cophasing matrix with a rotation matrix is first constructed. Then, the upper and lower bounds of asymptotic system throughput are analytically derived, based on the theory of order statistics. Finally, simulation results demonstrate the effectiveness of the proposed method in terms of system throughput. [ABSTRACT FROM AUTHOR]

This paper is concerned with block acknowledgement (ACK) mechanisms in wireless regenerative relay networks. In an N-relay network, a total of (2N + 1) block ACK packets is required to acknowledge the data transmission between source and destination nodes via the N-relay nodes. In this paper, the authors propose a block ACK scheme based on network coding (NC) to significantly reduce the ACK overheads by Nblock ACK packets. In addition, this achieves a reduction of N(N-1) computational operators. Particularly, we derive the error probability of the determination of the packets to be retransmitted at the source and relays, which shows that the NC-based scheme also improves the reliability of block ACK transmissions. Furthermore, asymptotic signal-to-noise (SNR) scenarios for forward links are considered and a general expression of error probability in multi-relay networks is derived for each SNR scenario. Finally, simulation results are presented to verify the analytical findings and demonstrate a lower number of data retransmissions for a higher system throughput. [ABSTRACT FROM AUTHOR]

A Network Coordinate (NC) system is an efficient mechanism to predict Internet distance with scalable measurements. In this paper, we focus on the node churn problem – the continuous process of nodes arrival and departure – in distributed applications. Studies on Vivaldi, a representative distributed NC system, show that under node churn the prediction accuracy of the NC system will be seriously impaired. In this paper, we focus on how to handle the impact of node churn in Vivaldi. Firstly, we propose a simple solution by directly increasing the measurement frequency. Our experiments have demonstrated that this approach can reduce the harm of node churn. However, it increases the communication overhead as the measurement frequency grows. To avoid such expensive solution, we propose the design and implementation of Myth, a decentralised and fast convergence NC system. It introduces the merit of Landmark-based NC system to shorten convergence time in Vivaldi with slight extra overhead. Our experimental results show that Myth outperforms Vivaldi a lot under node churn, without compromising the performance under stable environment. Moreover, we have found that the use of Myth is a cost-effective way to achieve higher prediction accuracy; it will not only improve the prediction accuracy but also save the communication overhead. [ABSTRACT FROM AUTHOR]

Adaptive decimation (AD) is a technique that aims at compressing images with a very small amount of computations and memory requirement. For images that contain moderate amounts of textural content, the method exhibits satisfactory performance and in general provides good visual quality and acceptable coding fidelity at low bit-rate of around 0.2 bpp. Although the complexity of the method is relatively light when compared with the existing compression methods, it still involves a considerable amount of computations that would require the use of medium-speed processors to achieve real-time operation. In the paper, a novel image encoder based on the principles of AD is reported. The scheme is near-computation-free as it involves on average a single fixed point multiplication plus a few other summing and logical operations for every four pixels. Experimental results reveal that, despite the substantial reduction in complexity, the performance of proposed method is similar to, if not better than, the existing AD encoding algorithms. [ABSTRACT FROM AUTHOR]

Powerful rate-compatible codes are essential for achieving high throughput in hybrid automatic repeat request (ARQ) systems for networks utilising packet data transmission. The paper focuses on the construction of efficient rate-compatible low-density parity-check (RC-LDPC) codes over a wide range of rates. Two LDPC code families are considered; namely, regular LDPC codes which are known for good performance and low error floor, and semi-random LDPC codes which offer performance similar to regular LDPC codes with the additional property of linear-time encoding. An algorithm for the design of punctured regular RC-LDPC codes that have low error floor is presented. Furthermore, systematic algorithms for the construction of semi-random RC-LDPC codes are proposed based on puncturing and extending. The performance of a type-II hybrid ARQ system employing the proposed RC-LDPC codes is investigated. Compared with existing hybrid ARQ systems based on regular LDPC codes, the proposed ARQ system based on semi-random LDPC codes offers the advantages of linear-time encoding and higher throughput. [ABSTRACT FROM AUTHOR]

Previous work has shown that TCP (transmission control protocol) Vegas outperforms the more widely deployed TCP Reno in both wired and wireless networks. It was also shown that when both TCP variants coexist on the same wired links, Reno dominates because of its more aggressive behaviour. This paper examines for the first time the compatibility between Reno and Vegas in wireless IEEE 802.11 ad hoc networks. It is shown that Vegas generally dominates in the heterogeneous Reno/Vegas network scenario; a startling result that is inconsistent with what is seen in wired networks. It is shown that the wireless ad hoc network environment does not reward the aggressive behaviour of Reno. On the other hand, Vegas, with its more accurate yet more conservative mechanisms, is able to capture most of the bandwidth. This is found to be true when using the on-demand routing protocols of dynamic source routing (DSR) or ad hoc on-demand distance vector (AODV): the failure of a node to reach a next-hop node because of media access control (MAC)-sublayer repeated collisions is reported to the routing protocol, which then declares a route error that impacts Reno in a more serious way than Vegas. When the table-driven routing protocol destination-sequenced distance vector (DSDV) is used, Reno and Vegas share the network bandwidth in a fairer manner. Generally, fairness in this environment can be improved by reducing the TCP maximum window size. [ABSTRACT FROM AUTHOR]

Structures such as square or circular microstrip patch antennas may support two orthogonal resonant modes. The paper presents a new method of utilising the dual-mode property to increase the bandwidth of microstrip antennas. The input impedance of such a dual-mode antenna may be represented as a second-order ladder network of coupled resonators, where each resonator is coupled to a load resistor. A theoretical method for evaluating the coupling values in the network is presented, enabling the bandwidth of a dual-mode antenna to be maximised. A theoretical bandwidth improvement of up to 3:1 is achieved when compared to a single-mode antenna. This is confirmed with an experimental dual-mode circular microstrip patch antenna. [ABSTRACT FROM AUTHOR]

The transconductance and the transresistance modes might act as the bridge transferring from voltage mode to current mode and vice versa, respectively. This paper presents a new mixed-mode (including voltage, current, transconductance, and transresistance modes) high-order universal filter structure using n+1 differential difference current conveyors (DDCCs), n grounded capacitors and n+2 grounded resistors, which are the minimum components necessary for realising an nth-order mixed-mode universal filtering response (low-pass, high-pass, band-pass, band-reject, and all-pass) from the same topology. Moreover, the proposed circuit simultaneously achieves nearly all of the main advantages. H-Spice simulation results confirm the theory. [ABSTRACT FROM AUTHOR]

The arrayed waveguide grating (AWG) multiplexer is a key component in wavelength division multiplexing fibre-optic communication systems. In this paper, an integrated optical 64×64 AWG with 0.4 nm (50 GHz) channel spacing at 1.55 µm based on silicon-on-insulator substrate is designed and analysed. An optimal value of waveguide separation at the junction between the arrayed waveguides region and the free propagation region is obtained. To get a better uniformity for 64 channel output while insertion loss and crosstalk are taken into account, an improved design is described using a tapered waveguide structure at each end of the AWG. [ABSTRACT FROM AUTHOR]

A common form of asynchronous communication mechanism (ACM) provides a one-way data transfer connection between two concurrent processes in which the writer uses a control algorithm to release data within the mechanism and the reader uses a control algorithm to acquire data within the mechanism, without recourse to arbitration or exclusion which could impede the progress of either the writer or the reader. When execution of the control algorithms is distinct, the reader acquires the latest data item released by the writer. When execution of the control algorithms overlaps, the reader acquires either a data item which is being or has been released during the overlapped acquisition, or the data item which is the latest released prior to the start of acquisition. The particular data item acquired is determined by the interleaving of critical events in each algorithm. The paper formally analyses a pair of algorithms to determine the way in which the data item acquired depends on the precise ordering of interleaved algorithm events. New insights into the notion of data freshness in ACMs are gained, and the essential similarity between several well known pairs of control algorithms is exposed. The formal analysis of ACM algorithms complements the previously derived formal specifications for such ACMs. [ABSTRACT FROM AUTHOR]

Spectrally efficient (2bit/s/Hz) 1 Tbit/s DWDM transmission of 111 Gbit/s no-guard-interval PDM CO-OFDM signals with 50 GHz spacing over DSF is demonstrated. The record transmission distance of 2100 km was achieved for a 100 Gbit/s-data-rate CO-OFDM system. [ABSTRACT FROM AUTHOR]

Considering the need for an optimised routing strategy as the most effective network dynamic for the lifetime and overall performance of a relay-based unstructured network, commonly used in wireless sensor systems, usually has been overlooked in order to be properly adopted for its practical real-time working environment has been studied in this paper. Following an investigation for using the quality-of-service management routing strategy, the authors propose a velocity-based routing protocol with a reliability and energy-efficiency routing scheme to enhance the network real-time routing performance, energy efficiency and transmission reliability upon adopting our new routing method. Our proposed method makes use of some intelligent functions (on the fly) including (i) selection of eligible relay node using two-hop neighbourhood information, (ii) estimated delivery velocity and (iii) energy aware-based energy-cost using the newly defined performance index. Some extensive simulation results are gathered and compared with our experimental results obtained for conventional routing schemes. The numerical results validate our claims of superiority of the new routing method for flexibility upon diversified requirements in different application scenarios. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose two cognitive relaying schemes based on overlay and underlay, which exploit the cooperation opportunities inherent in primary retransmission to improve secondary throughput. If a primary signal is not decoded by the primary receiver (PR), a secondary user (SU) can be selected to relay it invisibly along with the primary retransmission. For overlay cognitive relaying, SUs intend to reduce primary retransmission time by relaying primary message, so that more access opportunities are available. While in underlay cognitive relaying, SU allocates part of its power to help primary user (PU) and the remaining power is used to transmit secondary message simultaneously. By controlling the phase of the relay signal, signals retransmitted from primary transmitter (PT) and SU can constructively combine at the PR. In both relaying schemes, we consider the best-relay selection as well. We define some novel metrics to evaluate the performance of PU and SU. For PU, we study the improvements in outage performance and average transmitting time per packet, while for SU, we consider the cooperation gain and cooperation efficiency, respectively. Theoretical analysis and numerical results verify the validity of both schemes, and a comparison is made between them. [ABSTRACT FROM AUTHOR]

The increasing applications of networking have caused limitation of dynamic bandwidth allocation (DBA) in next generation access networks such as Ethernet passive optical network (EPON). In this paper, Arishtat, a novel EPON-based DBA method has been proposed that shows advantages over currently available methods. In Arishtat, which is based on the auction theory, optical line terminal runs an auction-based process to effectively register optical network units bandwidth requests and allocates the highest bidders based on the amount of available bandwidth. Simulation results indicate significant improvements comparing to Fair sharing using dual-service-level agreements, and 'limited service' interleaved polling with adaptive cycle time methods regarding quality of service parameters such as packet loss, throughput, line utilisation and the execution time of running method. [ABSTRACT FROM AUTHOR]

The use of a feedback link in wireless orthogonal frequency division multiplexing (OFDM) systems is analysed. Although open-loop scenarios have been rigorously investigated in the literature, closed-loop scenarios, in which there is a feedback link from a strong to a weak user, have not been thoroughly studied. The study mainly focus on the recently proposed dynamic pilot symbol arrangement strategy. It was shown in a recent paper that for coherent OFDM transmission, this strategy is capable of delivering substantial gains in the performance. Pilot symbols are used to sample channel behaviour so that data symbols can be decoded correctly. However, these pilots do not need to be arranged so as to estimate the channel in the best possible way. In this work, the authors propose a pilot symbol arrangement strategy that minimises the bit error rate, we analyse the solution in detail and propose a low complexity search that maintains most of the quality of an exhaustive search. This low complexity search makes the pilot symbol method viable for medium to large-scale OFDM systems. The authors also analyse the use of a Wiener filter for channel estimation combined with the dynamic pilot symbol strategy and show that it delivers good gains in comparison to a simple maximum likelihood channel estimate. [ABSTRACT FROM AUTHOR]

Current interconnection architectures based on electronics are approaching their physical limitations especially in terms of interconnection wiring and power density. To overcome these issues, the flexibility and the scalability of optical technologies can be exploited. This paper considers a modular optical interconnection architecture that consists of multiple cards, supporting a fixed number of ports and interconnected through a passive optical backplane. A two-step scheduling framework (TSS) is proposed, which exploits the modularity of the architecture and the existing scheduling algorithms, while satisfying the peculiar scheduling constraints of the architecture. In TSS, an intra-card step decides the wavelength switching configuration and then an inter-card step decides the space switching configuration. Each step can be run in parallel, on the cards and on the wavelengths, respectively. TSS is compared against a single-step scheduler suitable for non-modular architectures, under different traffic patterns and architecture configurations. TSS performs better in terms of lower packet delay, higher throughput and lower computational complexity. Finally, the possibility of increasing the packet transfer rate (transfer speedup) can be included in TSS without additional complexity and is especially beneficial for the bursty and skewed traffic patterns, typically experienced in real scenarios. [ABSTRACT FROM AUTHOR]

Conventional cooperative diversity techniques consider a three-node setup, which involves a pair of source–destination nodes and a signal relay node. It is noted that the existing cooperation schemes are performed in a session-based manner in which the role of each node being a source or relay remains unchanged during each session. The radio resource allocation and the associated performance analysis are not jointly performed. As a result, resource utilisation is less efficient. In this paper, an energy-efficient quality-of-service (QoS)-aware cooperative transmission strategy based on joint resource allocation is proposed. Two source nodes with distinct destinations and QoS requirements are simultaneously considered in resource allocation to optimise the energy efficiency. The QoS outage probability is derived analytically and the attainable energy efficiency is investigated for the proposed scheme. Numerical results show that significant performance gain can be achieved for both node pairs with the proposed cooperation scheme. [ABSTRACT FROM AUTHOR]

Time variations of a doubly selective wireless channel and insufficient cyclic prefix (CP) length of an orthogonal frequency division multiplexing (OFDM) transmission system cause intercarrier interference (ICI) and interblock interference (IBI) as significant limitations. This paper investigates the problem of joint ICI and IBI mitigation in single-input multiple-output OFDM (SIMO-OFDM) systems. It is assumed, unlike most existing literature, that the channel delay spread is larger than the CP, and also the channel varies on each OFDM block. First, doubly selective channel is modelled using basis expansion model (BEM) and a closed-form expression for signal-to-interference-plus-noise ratio (SINR) is derived. Then, a time-domain equaliser is developed, which maximises the SINR for all subcarriers. Moreover, a frequency-domain equalisation approach is proposed which is based on the MSE minimisation per tone. A low-complexity implementation of the per-tone equaliser is also derived. An important feature of the proposed equalisers is that no bandwidth expansion or redundancy insertion is required except for the CP. Finally, complexity comparison and simulation results over Rayleigh fading channel are provided to illustrate the effectiveness of the proposed approaches. Since both equalisers are designed in the frequency domain, they provide significant interference cancellation. [ABSTRACT FROM AUTHOR]

Signal transmission with the help of relay(s) in wireless networks can achieve spatial diversity without the need of having multiple attennas at the source and/or destination. Among various signal processing techniques proposed for the relays, the adaptive decode-and-forward (DF) relaying strategy, recently proposed by Wang et al. and generally referred to as smart relaying, has been shown to achieve the maximal spatial diversity even when imperfect detection is committed at the relays. The work by Wang et al., however, only considers Rayleigh fading channels. This paper extends the diversity analysis of the smart relaying technique to the important Nakagami and Hoyt generalised fading channels. Performance analysis proves that, at high signal-to-noise ratio, the maximal diversity order achieved by the smart relaying system under the Nakagami channel is mSD+min{mSR, mRD}, where mSR, mRD and mSD are the fading figures of the source–relay (S–R), relay–destination (R–D) and source–destination (S–D) links. Under the Hoyt fading channel, the diversity order is 2. The obtained results on the diversity order are shown to be insensitive to the quality of the R–D feedback channel. [ABSTRACT FROM AUTHOR]

This study investigates the superposition-based cooperative transmission system. In this system, a key point is for the relay node to detect data transmitted from the source node. This issued was less considered in the existing literature as the channel is usually assumed to be flat fading and a priori known. In practice, however, the channel is not only a priori unknown but subject to frequency selective fading. Channel estimation is thus necessary. Of particular interest is the channel estimation at the relay node which imposes extra requirement for the system resources. The authors propose a novel turbo least-square channel estimator by exploring the superposition structure of the transmission data. The proposed channel estimator not only requires no pilot symbols but also has significantly better performance than the classic approach. The soft-in-soft-out minimum mean square error (MMSE) equaliser is also re-derived to match the superimposed data structure. Finally computer simulation results are shown to verify the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a novel technique for adaptive modulation over limited diversity fading channels with channel state information at the transmitter. Limited diversity channels such as those encountered in indoor orthogonal frequency division multiplexing systems are characterised by the fact that achievable diversity orders are limited by the channel and not by code-free distances. The authors first propose a novel analysis technique for the performance of coded modulation on limited diversity block fading channels with different modulation sets on each block. The authors then propose adaptive modulation techniques for maximising the throughput at a fixed bit error probability and also for minimising the bit error probability at a fixed rate. Lastly, the authors show simulation results that support the arguments presented in the paper. [ABSTRACT FROM AUTHOR]

Multiple-input, multiple-output (MIMO) radars enhance performance by transmitting and receiving coded waveforms from multiple locations. This paper describes MIMO techniques that can be used to improve radar performance, especially in airborne Ground Moving Target Indicator (GMTI) applications. The authors begin by showing how MIMO techniques can lower airborne radar clutter to noise ratios (CNRs). This results in smaller losses when observing stationary or low-velocity targets. Next, the authors consider the implementation of MIMO radar modes using electronically scanned arrays (ESAs). Specifically, the authors show how MIMO techniques, applied to subarray-based ESAs, can cause high grating lobes and/or reduced search rates. To address this problem, the authors describe new space–time waveform coding techniques that can be used to improve performance. Two space–time waveform encoding approaches are proposed: (i) an overlapped virtual transmit subarray approach, and (ii) a beamspace MIMO approach. A third approach, involving conventional MIMO waveforms and irregular subarrays, is also briefly considered. [ABSTRACT FROM AUTHOR]

The wide spectrum of ultra wideband (UWB) communications makes it inevitable to consider strategies for avoiding and mitigating interference from narrowband wireless systems such as GPS, UMTS, and WLAN, or other UWB wireless technologies. In this paper, we provide a performance analysis of multiband orthogonal frequency division multiplexing (MB-OFDM) UWB in the presence of binary phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions under Nakagami-m fading. In the bit-error rate (BER) analysis, several UWB interferers are considered to affect the MB-OFDM signal. A Gaussian approximation is considered for the UWB interferers and used in the analysis of the BER performance of the MB-OFDM UWB system. The Nakagami-m distribution is applied to characterise the amplitude of the fading channels for both the reference signal and the interference signals. Furthermore, a waveforming technique is considered for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios. [ABSTRACT FROM AUTHOR]

In this paper, a key pre-distribution model with the concept of key pool generation in distributed sensor networks (DSNs) is proposed. In this scheme, additional information is inserted into each group during key pool generation. The nodes in the DSNs can use this extra information to increase system performance. A concrete example is given to clarify this concept and prove that the added information in the scheme can greatly improve connectivity between nodes even if node deployment is sparse or non-uniform. In addition, high connectivity decreases the energy consumption of wireless communication between sensor nodes and extends the life of these nodes. [ABSTRACT FROM AUTHOR]

The most widely used topology in the design of the cellular stripline circulator is that comprising a planar gyromagnetic resonator, biased above the uniform mode resonance, symmetrically coupled by quarter-wave transformers between ferrite substrates. Its operation is still, however, largely semi-empirical. The purpose is to reconcile, in the case of a side-coupled triangular resonator, its network, magnetic and physical parameters. The magnetic variables of the substrate are uniquely established by the weakly magnetised model of the gyrator circuit and its effective permeability. The procedure outlined here is applicable to the construction of devices below 2 GHz with specifications of up to 25% bandwidth at 1.20 voltage standing wave ratio (VSWR) points (23 dB isolation). This sort of circuit is met in the design of ultra high frequency (UHF) circulators for use in cellular products. [ABSTRACT FROM AUTHOR]

The paper presents information security breaches affecting the US military computer networks. [ABSTRACT FROM AUTHOR]

The performance of multi-homed transport protocols tolerant of network failure is studied. It evaluates the performance of different retransmission policies combined with path failure detection thresholds, infinite or finite receive buffers for various path bandwidths, delays and loss rate conditions through stream control transmission protocol simulation. The results show that retransmission policies perform differently with different path failure detection threshold configurations. It identifies that retransmission of all data on an alternate path with the path failure detection threshold set to zero performs the best in symmetric path conditions but its performance degrades acutely in asymmetric path conditions even when the alternate path delay is shorter than the primary path delay. It illustrates that retransmission of all data on the same path with the path failure detection threshold set to one or zero gives the most stable performance in all path configurations. [ABSTRACT FROM AUTHOR]

The incremental redundancy mechanism defined for enhanced general packet radio service (EGPRS) (also known as type-II hybrid ARQ) is considered here. The optimum packet combining strategy is identified and is then used to assess the performance of transmission control protocol/internet protocol in the transmission of bulk data over an EGPRS system. The influence of other key system operating parameters is also assessed and a set of optimal operating parameters is derived and discussed. [ABSTRACT FROM AUTHOR]

Reconfigurable optical add/drop multiplexers (ROADMs) will play a key role in next-generation dynamically provisioned wavelength networks. Existing ROADM subsystems, manufactured with different designs and technologies, are suffering from either high insertion losses, especially for the passing-through (express)-channels, or high manufacturing costs that are preventing their rapid deployment in networks. An architecture for an ROADM subsystem that integrates the best features of the latest available ROADM designs is proposed. The proposed ROADM subsystem, denoted as a Hybrid-ROADM, exhibits a lower insertion loss (∼7 dB for express-channels) than existing ROADMs while offering simplification and cost benefit. A metro network testbed has been configured to demonstrate and compare the performance of the proposed Hybrid-ROADM module against currently available ROADM subsystems. The obtained results indicate that our Hybrid-ROADM shows better performance in metro networks than the latest available ROADM subsystems and will reduce the overall network operating costs. [ABSTRACT FROM AUTHOR]

Flexible macroblock ordering (FMO) is a new error resilience feature in the H.264 (MPEG-4 part 10) video coding standard. The paper exploits FMO to offer a new classification algorithm for prioritised video transmission. Instead of using the default mapping structures of FMO, an optimisation algorithm in which the more important macroblocks (MBs) are categorised in a separate slice group (SG), which corresponds to high-priority packets for transmission, is proposed. The importance of each MB is determined based on its eventual influence on picture quality. This is assessed by considering the fact that the successful transmission of an MB not only enhances the quality of the associated pixels, but also improves the quality of its adjacent lost MBs by improving the efficiency of error concealment. It is assumed that the network can offer a prioritised service for successful transmission of the high-priority SG. Based on this, a vulnerability factor for each MB is determined, and a certain proportion of high-vulnerability MBs at each frame to limit the impact of temporal error propagation is intra-updated. It is shown, where the proposed mapping algorithm outperforms the default mappings of the H.264 codec, that this prioritised transmission will improve the subjective and objective video quality in situations with a high probability of transmission errors. [ABSTRACT FROM AUTHOR]

This paper studies the possible improvement in RF link properties that can stem from electrically cascading several laser sources and combining the light from each source into a single information-carrying light beam. The effect of carrier recycling is first studied within a discrete architecture consisting of n individual laser diodes macroscopically connected in series. An RF link gain improvement proportional to n2, and a link noise figure improvement proportional to n is found. The model is validated by experimental data. The architecture nonetheless carries some drawbacks, including the need for a zero-loss optical combining device to benefit from the RF link gain improvement, and some bandwidth shortcomings. The effect of carrier recycling within an integrated laser device, a so-called bipolar cascade laser, is then studied. In order to push back the limitations of the discrete architecture, the device consists of n active regions integrated into a single laser cavity. A rate equation model is applied to this promising structure and it is found that, in good agreement with previously published results, the external efficiency is expected to increase by a factor of n, leading to a possible RF link gain improvement by a factor of n2. However, because the laser noise is dominated by the photon corpuscular noise, a weak influence of electrically cascading active junctions into a single laser cavity on the laser intensity noise, and thus on the link noise figure, is expected. [ABSTRACT FROM AUTHOR]

Denial-of-service attacks represent a major threat to modern organisations who are increasingly dependent on the integrity of their computer networks. A new approach to combating such threats introduces active routers into the network architecture. These active routers offer the combined benefits of intrusion detection, firewall functionality and data encryption and work collaboratively to provide a distributed defence mechanism. The paper provides a detailed description of the design and operation of the algorithms used by the active routers and demonstrates how this approach is able to defeat a SYN and SMURF attack. Other approaches to network design, such as the introduction of a firewall and intrusion detection systems, can be used to protect networks, however, weaknesses remain. It is proposed that the adoption of an active router approach to protecting networks overcomes many of these weaknesses and therefore offers enhanced protection. [ABSTRACT FROM AUTHOR]

Ultra-wideband (UWB) links are inherently subject to interference from other narrowband communication links. The paper proposes a solution for suppressing these narrowband interference sources that is based on using an analogue filter bank (AFB) for pre-processing the received signal. The AFB outputs are subsequently processed by a combination of maximum ratio combining (MRC) and generalised matched filter (GMF) processing. This receiver architecture requires significantly less processing than the optimum GMF processing while achieving a comparable performance in the context of narrow band interference (NBI). Furthermore, because the AFB consists of low-order bandpass filters of modest selectivity, monolithic integration is practical. Hence, the AFB is potentially a low-cost manufacturable implementation of the UWB receiver. Analysis and simulated performance of the AFB architecture are presented in this paper. The metrics used are the overall theoretical capacity and signal-to-noise ratio of the receiver decision variable. These results are presented as a function of the overall receiver complexity for different compositions of narrow and wide bandwidth channel noise. It is also shown that AFB forms a signal space of dimension equal to the number of bandpass filters and that the processing can effectively cancel multiple tones up to this dimensionality. [ABSTRACT FROM AUTHOR]

This paper provides an overview of the emerging antenna features that are the technologies for inclusion in the initial release of Mobile WiMax, and examines the various application areas of these techniques as well as the advantages and limitations each are likely to possess. [ABSTRACT FROM AUTHOR]

Dicode pulse-position modulation (PPM) has been proposed as an alternative modulation format to conventional digital PPM, since it offers comparable receiver sensitivities while operating at significantly lower slot-clock rates. A recent numeric analysis considered the performance of dicode PPM, using slope detection, in a dispersive environment. In this paper, consideration is given to an alternative detection strategy, and new results are presented that show that intersymbol interference (ISI) can be eliminated through the use of central decision detection combined with raised cosine filtering. This leads to a more simplified receiver design and results in equivalent sensitivity performance at high fibre bandwidths and significantly improved performance at lower fibre bandwidths. Practical approximations to this approach are considered and design rules presented for determining the bandwidth of both the preamplifier and a simple 3rd order Butterworth equalisation filter. It is shown that setting the bandwidth of both the preamplifier and equaliser to 0.6 times the dicode slot rate gives sensitivities within 0.2 dB of ideal dicode PPM raised cosine filtering, and that such a receiver can operate over a wide range of fibre bandwidths, with minimal degradation in sensitivity. [ABSTRACT FROM AUTHOR]

For the cost-effective realisation of the next-generation wavelength-division-multiplexed passive optical network (WDM PON), the possibility is evaluated of using the 4-ary pulse-amplitude-modulated (PAM) signal for the high-speed (>10 Gbit/s) operation of the TO-can packaged reflective semiconductor optical amplifier (RSOA) having a 3 dB bandwidth of only about 2.2 GHz. The results show that, owing to the compact spectrum of the 4-ary PAM signal, the deleterious effects of this limited bandwidth as well as the sensitivity degradations caused by the chromatic dispersion can be significantly alleviated. As a result, an error-free transmission of 11 Gbit/s, 4-ary PAM signal over 20 km of singlemode fibre can be demonstrated. [ABSTRACT FROM AUTHOR]

A 20 Msymbol/s, 64 and 128 QAM coherent signal has been successfully transmitted over 525 km using heterodyne detection with a frequency-stabilised fibre laser and an offset-locking technique. Error-free transmission (7 bit/symbol) has been achieved. [ABSTRACT FROM AUTHOR]

Eighty-nine 42.7 Gbit/s, 100 GHz-spaced WDM channels in a 72 nm seamless band were transmitted over 40×100 km of fibre using carrier-suppressed return-to-zero differential-phase-shift-keyed modulation format with a balanced receiver, all-Raman amplification, a broadband dynamic gain equaliser and a zero-dispersion discrete Raman amplifier. [ABSTRACT FROM AUTHOR]

40 × 40 Gbit/s ultra-long haul transmission over 2160 km of cabled and field-deployed dispersion-managed fibre (DME) with extremely low total dispersion ripple (±27 ps/nm over C-band) is demonstrated. No per channel dispersion compensation is required. A Q factor margin of 1.4 dB to standard 7% forward error correction limit is achieved. [ABSTRACT FROM AUTHOR]

The article offers news briefs in Asia. A 17-member telecommunications consortium is investing a total of US$560m to construct the first high-bandwidth fibre-optic submarine cable linking south east Asia with the U.S. The construction of the first Airbus A320 final assembly line outside Europe has started in Tianjin, China. Singapore’s investment arm, Temasek Holdings Ltd., has raised US$355.4 million from the sale of its 3.3 percent stake in Telekom Malaysia.

Kish proposed a scheme to exchange keys between two parties under the concealment of thermal noise. We show that the theoretical model in the scheme implicitly assumes thermal equilibrium throughout the communication channel. This assumption, however, is invalid in real communication systems. A slight temperature difference in the channel, as demonstrated in the paper, will lead to security failure. [ABSTRACT FROM AUTHOR]

In this study, a collection of agents performing a shared task making use of relative information communicated over an information network is considered. A two-step control design procedure for distributed control of such systems is proposed. The control law is guaranteed to provide a certain level of H2 performance at a network level. An analysis of the proposed control law in the presence of delays in the relative information is carried out to obtain a bound on the maximum delay possible. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a novel channel and queue aware algorithm for allocating power and subcarrier to users in orthogonal frequency division multiple access (OFDMA) networks. The proposed algorithm utilises a utility function to simultaneously balance and improve the efficiency and fairness of radio resource allocation. In contrast to the conventional approaches in the literature, in which it is assumed that the OFDMA system is able to support a continuous set of bit rates, here, in the system model the authors consider the fact that in practical OFDMA systems only a limited set of bit rates are supported. Furthermore, the authors do not consider the full buffer assumption and note that in practice a user scheduled for transmission might not always have data to transmit. By formulating the radio resource allocation the authors then show optimal bit loading results in a greedy algorithm that employs both bit removal and bit filling procedures. The solutions are developed in the framework of a matroid theory. The authors then analyse the average system throughput and investigate the performance of the proposed algorithm through simulations. Comparisons to similar approaches are also conducted which indicates significant performance improvement. [ABSTRACT FROM AUTHOR]

Power delivery for biomedical implants is a major consideration in their design for both measurement and stimulation. When performed by a wireless technique, transmission efficiency is critically important not only because of the costs associated with any losses but also because of the nature of those losses, for example, excessive heat can be uncomfortable for the individual involved. In this study, a method and means of wireless power transmission suitable for biomedical implants are both discussed and experimentally evaluated. The procedure initiated is comparable in size and simplicity to those methods already employed; however, some of Tesla's fundamental ideas have been incorporated in order to obtain a significant improvement in efficiency. This study contains a theoretical basis for the approach taken; however, the emphasis here is on practical experimental analysis. [ABSTRACT FROM AUTHOR]

This study addresses the mean square detectability problem for multi-output networked systems via single packet or multiple packets transmission, where a multiplicative white noise model the unreliability of output channels. For the single packet case, by adopting the bisection technique, the authors give the critical value (lower bound) of mean square capacity for ensuring mean square detectability. For the m-parallel multiple packets transmission strategy, a necessary and sufficient condition on overall mean square capacity for mean square detectability in terms of the Mahler measure or topological entropy of the plant is presented, under the assumption that the given network resource can be allocated among all the output channels. Applications in erasure-type channel and channel with stochastic sector-bounded uncertainty are provided to demonstrate the results. [ABSTRACT FROM AUTHOR]

To enhance the quality of transmissions, all digital communication systems use error-correcting codes. By introducing some redundancy in the informative binary data stream, they allow one to better withstand channel impairments. The design of new coding schemes leads to a perpetual evolution of the digital communication systems and, thus, cognitive radio receivers have to be designed. Such receivers will be able to blind estimate the transmitter parameters. In this study, an algebraic method dedicated to the blind identification of punctured convolutional encoders is presented. The blind identification of such encoders is of great interest, because convolutional encoders are embedded in most digital transmission systems where the puncturing principle is used to increase the code rate to reduce the loss of the information data rate because of the redundancy introduced by the encoder. After a brief recall of the principle of puncturing codes and the construction of the equivalent punctured code, a new method dedicated to the blind identification of both the mother code and the puncturing pattern is developed when the received bits are erroneous. Finally, case studies are presented to illustrate the performances of our blind identification method. [ABSTRACT FROM AUTHOR]