Search

Recently, broadband optical access networks were being deployed worldwide to deliver large bandwidth to end users. Currently, the operators have been mainly deploying time-division multiplexing (TDM) passive optical networks (PON) in their networks. As bandwidth demand continues to increase, the industry further selected several next generation optical access (NGA) options to upgrade from current TDM-PON architectures. Besides increasing bandwidth requirement, current TDM-PONs suffers from limited reach and split-ratio. To further reduce the capital and operational expenditure requirements of current TDM-PON, NGA architectures must consolidate the number of central office sites. Long-reach optical access (LROA) architectures are promising solutions that employ optical amplifiers to increase optical budget to support longer reach and higher split-ratio in the distribution network. As more end users are supported over shared physical medium in LROA, access network security is of greater importance. The first part of this article reviews important LROA architectures and their enabling technologies. Moreover, few works in current literature address security weaknesses in LROA. The second part of this article reviews these security weaknesses as well as monitoring and control techniques employed in current TDM-PONs. In addition, a novel class of quasi-passive and reconfigurable devices is presented that addresses aforementioned security weaknesses and is suitable for LROA. [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]

The original 3-port waveguide circulator relies for its operation on a simple gyromagnetic post resonator with top and bottom electric walls and an open magnetic side wall with no variation of the fields along its axis. Its description is a seminal paper in the literature. The purpose of this study is to characterise its first circulation condition (frequency) using a finite-element package and to characterise its second (complex gyrator circuit) experimentally. This is done for one-third-height, half-height and full-height resonator posts. The shortest of these three resonators is compatible with the synthesis of a circulator with an equal ripple degree-2 frequency response with a return loss of 23 dB over a 20% bandwidth. This sort of junction is met in the design of the externally latched junction circulator. This study includes a characterisation of a composite post resonator geometry consisting of an undersized ferrite cylinder surrounded by a dielectric sleeve. [ABSTRACT FROM AUTHOR]

The concept of cognitive radio is to exploit efficiently the spectrum resources by allowing the coexistence of the primary and secondary users in the same bandwidth without interfering the performance of primary users. Three coexisting models (overlay, underlay and interleave) were presented in recent literature. In this study, the authors propose a hybrid cognitive network model with overlay and underlay models, whereby a primary link leases its fractions of transmission time to the secondary users for their cooperation (i.e. these nodes form as a virtual multiple input multiple output (VMIMO) group) under the outage constraints of the primary and secondary systems. A new cooperative protocol between primary and secondary users is presented. The authors attempt to achieve the maximum transmission capacity of the secondary users under the primary and secondary outage constraints, which depend on the secondary density in the cognitive network. This study gives the upper bound density of the secondary transmitters that are modelled as a homogeneous marked Poisson point process. The maximum density is achieved by computing an optimal set of system parameters such as power control factor of the secondary user and the dirty paper coding (DPC) parameter. Simulation results illustrate that the maximum secondary density obtained using VMIMO is superior to that obtained by direct primary transmission. [ABSTRACT FROM AUTHOR]

In a recent sequence of papers, a parallel-plate ridge gap waveguide has been introduced, that consists of a metal ridge in a metamaterial magnetic conductor surface, covered by a metallic plate at a small height above it. The gap waveguide is relatively simple to manufacture, especially at millimetre and sub-millimetre wave frequencies when compared with other solutions. The metamaterial surface is designed to provide a frequency band where parallel-plate modes are in cut-off, thereby allowing for a confined gap wave to propagate along the ridge. In a previous work, the authors have presented an approximate analytical solution for the confined quasi-TEM dominant mode of the ridge gap waveguide, when the surrounding metamaterial surface is in the form of a bed of nails. In this study, the authors investigation continues by providing an analytical expression of the modal dispersion equation of the first higher order ridge mode and of the characteristic impedance of the dominant mode. As in the previous paper, the field problem is divided in three regions, the central region above the ridge and the two surrounding side regions above the nails. Transverse mode-matching applied to a few modes representation in each region, results in a closed form expression of the dispersion equation of the first higher order mode. After summarising the formulation for the dominant quasi-TEM mode, the dispersion equation of the first higher order mode is derived, in order to give a criterion to maximise the unimodal bandwidth. Furthermore, three different closed form expressions of the dominant mode characteristic impedance are derived and compared with approximate expressions already used in literature. [ABSTRACT FROM AUTHOR]

In this paper, the relation between small-scale fade depth and channel bandwidth in an indoor environment is investigated. The fade depth, a measure of the signal power variability over a local region in space, is evaluated for narrowband, wideband and ultrawide-band channels. The experimental analysis is based on frequency-domain measurements in the 3.1–10.6 GHz microwave band. Physical insight into the fading process is provided, and the effect of increasing bandwidth and temporal resolution is discussed. A dual-slope empirical model is developed, which accurately describes the relationship between fade depth and channel bandwidth. It is demonstrated that the fade depth, considered at the three standard deviation values, converges to about 4 dB at 1 GHz bandwidth, and a further increase in bandwidth yields only a marginal improvement in fade mitigation. [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]

A compact planar microstrip ultra-wideband (UWB) bandpass filter (BPF) is presented in this paper. The proposed UWB filter is realised by cascading a high pass filter (HPF) and a low pass filter (LPF). The designed five-pole HPF consists of inter-digital capacitors and short-circuited stubs and has a sharp falling edge at the cutoff frequency. Additional slots are adopted to improve the return loss performance in the pass band. The LPF is realised mainly based on a non-uniform defected ground structure array in the ground. Combining these two structures, a new UWB bandpass filter is fabricated and measured. The measured results show that the proposed BPF has a wide bandwidth from 3.0–10.8 GHz, associated the 40 dB shape factor as low as 1.2. A group delay variation of less than 0.15 ns in the pass band from 3.0–10.8 GHz is obtained. It also achieves a wide stopband with 20 dB attenuation up to 20.0 GHz. [ABSTRACT FROM AUTHOR]

A semi-circle-fed microstrip patch antenna is presented in this paper. The proposed antenna is found to have a much broader impedance bandwidth when compared with the conventional L-slot antenna. The proposed antenna is able to achieve an impedance bandwidth of 63.7% for Voltage standing wave ratio (VSWR)<2, centred at ≃6 GHz. To the author's knowledge, this reported bandwidth is by far the largest achievable through the probe proximity coupled technique. A comparison between rectangular-shaped patch antenna and stub patch antenna using the same excitation mechanism is given. [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 circularly polarised (CP), radio-frequency identification (RFID) reader antenna with high return loss (RL) is presented. The antenna consists of a dual-polarised microstrip patch with high isolation and a Wilkinson power divider with a 90° phase shift between its two outputs. A novel analytical approach is developed for improving the RL of the dual-feed CP antenna and verified experimentally by fabricating and measuring a prototype antenna. The experimental results show that the RL of the prototype antenna is more than 30 dB over the frequency range of 866-936 MHz, which fully covers the bandwidth of North America (902-928 MHz) as well as South Korea (917-923.5 MHz) for a passive ultra-high-frequency RFID system. The peak antenna gain is above 8.1 dBic and the axial ratio is below 0.7 dB over the frequency range of 902-928 MHz. [ABSTRACT FROM AUTHOR]

The authors propose a new approach for network lifetime maximisation in visual wireless sensor networks (VWSN). The existence of redundant multiple sensing for some parts of the field results in additional computational complexity and requires more bandwidth and battery power in the nodes, hence reducing the network lifetime. In a VWSN, efficient node collaboration for data sensing and gathering is a key factor to determine network lifetime. The proposed approach provides a jointly optimised traffic routing and camera selection strategy to enhance the lifetime of the whole network. In this approach, different nodes can collaborate with each other to prevent unnecessary multiple sensing of different areas in the network, and at the same time collaborate in the routing of the generated traffics to the network sink. [ABSTRACT FROM AUTHOR]

In this study, previous theories on the minimum radiation-Q against antenna size are examined, basic assumptions are reviewed and an alternate formulation is presented. The radiation-Q limit varies with the amount of an estimated non-radiating energy, which is directly related to the energy velocity. The classic approximate Q formula of Chu is found to be equivalent to using the group velocity for the energy velocity. Other previous approaches implicitly assumed that the radiated-energy travels in the radial direction at the speed of light from the antenna sphere to the far-field region, which is not true. Based on this observation of the incorrect energy velocity, a time-domain approach is used to derive the fundamental limit on radiation-Q against electrical size of an antenna. A new form of radiation-Q is presented that provides a bound lower than all the previous results. The new limit, which is just below the Chu limit, holds for any antenna size, not just electrically-small antennas. The new radiation-Q limit provides antenna designers with a simple guide to estimate the minimum required antenna size for a given bandwidth and efficiency, thereby avoiding the search for an impractical antenna. [ABSTRACT FROM AUTHOR]

Recently it has been shown that so-called gap waveguides can be generated in the gap between parallel metal plates. The gap waveguides are formed by metal ridges or strips along which local waves propagate, and parallel plate modes are prohibited from propagating by providing one of the surfaces with a texture that generates an artificial magnetic conductor (AMC) or an electromagnetic bandgap (EBG) surface on both sides of the ridges or strips. The bandwidth of the gap waveguide is determined by the cut-off bandwidth of a parallel-plate waveguide where one surface has such a texture (and no ridges or strips). This paper studies the bandwidths (or stop bands) of such parallel-plate cut-offs when the AMC or EBG is realised by a metal pin surface, corrugations or a mushroom surface. It is shown that cut-off bandwidths of up to 4:1 are potentially available, and thereby similar bandwidths should be achievable also for gap waveguides. [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]

The symbolic dynamics method of communication using chaotic systems has previously been shown to offer performance better than conventional binary phase shift keying (BPSK), while also providing similar spectrum efficiency. This is achieved by exploiting diversity in the waveform, through a mechanism similar to partial response signalling. In order to achieve this performance, a correlation method for detection has been proposed, but complexity was high and only performance in additive white Gaussian noise (AWGN) channels has been considered. It is demonstrated that the complexity can be reduced from requiring 1024 correlations per symbol down to only 32, while degrading performance only by 0.6 dB. The ability to further reduce the occupied bandwidth is investigated. Spectrum occupancy equivalent to a root-raised cosine-filtered BPSK signal is demonstrated, and performance is maintained when the reference waveforms are similarly filtered to maintain the signal match. Finally, a novel equalisation technique that incorporates a decision feedback structure into the correlation detector is proposed. Performance in multipath channels is investigated and shown to be effective. [ABSTRACT FROM AUTHOR]

A 0.9 V fully differential switched-opamp-based sixth-order switched-capacitor bandpass filter, which has frequency response centred at 1.118 kHz with a Q of 0.235 and power saving by a proposed low-power biquad structure, is designed for electroneurography acquisition systems. It is implemented in a 0.18 µm CMOS technology with a normal threshold voltage of 0.48 V. The measured peak signal-to-noise ratio is 52 dB at 1 kHz sinusoid wave with input amplitude of 1 Vpp. In addition, the measured power-supply rejection ratio and common-mode rejection ratio are >40 dB in the desired bandwidth and have peak values of 70 and 67 dB, respectively. A dynamic range of 50 dB for total harmonic distortion of 3% is obtained while dissipating 262 µW and occupying a chip area of 0.35 mm2. [ABSTRACT FROM AUTHOR]

The fundamental medium access control mechanism in IEEE 802.11 wireless LANs (WLANs)–distributed coordination function (DCF) only supports the best-effort service and does not support quality-of-service (QoS) differentiation. Enhanced distributed channel access (EDCA) in IEEE 802.11e supports delay differentiation. A new approach, EDCA+, is proposed to enhance QoS over WLANs. It simultaneously achieves bandwidth, delay and jitter differentiation by distinguishing the minimum contention window, the maximum backoff stage or persistent factor and packet-loss rate differentiation by distinguishing the retry limit. Analytical models are proposed to analyse the performance of EDCA+ in terms of throughput, bandwidth, delay, jitter and packet-loss rate. Extensive simulations are also carried out to evaluate the accuracy of the proposed performance models and to compare the performance of DCF, EDCA and EDCA+. The simulation results show that EDCA+ performs better than DCF and EDCA in ensuring integrated QoS, and that the proposed analytical models are valid. [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]

As the issue width and the number of function units of superscalar processors continue to increase, the fetch unit must support a large fetch bandwidth in order to fully utilise the datapath resources. This trend makes power issue worse in the fetch unit since the traditional instruction fetch mechanism is not optimised for power consumption. This paper explores the problem of extra power consumption in traditional instruction caches because of dynamic control flows. Capturing the dynamic paths/characteristics of code during the course of execution, trace caches provide a potential framework for power optimisation in the fetch unit. Our study shows that conventional trace caches (CTC) may increase power consumption in the fetch unit because of the simultaneous access to both the trace cache and the instruction cache, and sequential trace caches (STC) have the advantage of lower power consumption at the cost of a significant performance loss. In order to address this problem, we perform a detailed study of trace distribution and access locality. Based on this study, we first propose a new model, the selective trace cache (SLTC). SLTC uses both compiler and hardware support to selectively control trace cache lookup and update. Experimental evaluation shows that our selective trace cache achieves up to 42.2% power reduction over CTC and an additional reduction of up to 21.8% over STC, on the average, while only trading a performance loss of no more than 1.8% compared to CTC. Further, we propose a dynamic direction prediction based trace cache (DPTC), which eliminates the need for compilation and instruction set architecture (ISA) modification involved in SLTC. Powered by a fetch direction predictor, DPTC achieves competitive power efficiency. On the average, DPTC reduces the power consumption by up to 40.5% and 17.6% in the fetch unit compared to CTC and STC, respectively, by trading a performance loss of less than 2.4% to CTC. [ABSTRACT FROM AUTHOR]

An effective design of a reconfigurable patch antenna, with a wide operational bandwidth for wireless communication and radar systems, is presented in this paper. The reconfigurable patch possesses an E-shaped structure and its operation frequency can be changed by integrated switches. The operational frequency of the antenna can cover an octave frequency range by utilising only two switch states. In state 1, the antenna operates from 9.2 GHz to 15.0 GHz and, in state 2, from 7.5 GHz to 10.7 GHz. Relative bandwidths of 48% and 35% are obtained in the two states, respectively. [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]

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]

Multi-hop relaying cellular network (MCN) is a recently proposed architecture to preserve the advantages of traditional single-hop cellular networks and ad hoc relaying networks. In MCNs, efficient bandwidth management plays an important role in determining network performance. In this study, a new cognitive radio bandwidth-sharing scheme is proposed based on the reversed Stackelberg game model. In the proposed scheme, base station (BS) and relay stations (RSs) are hierarchically interconnected and interacting with one another to effectively share the wireless bandwidth. By using a trust model, the BS appropriately reacts to selfish RSs to maximise network performance. This approach can promote cooperation with respect to adaptive bandwidth allocation. With a simulation study, it is demonstrated that the proposed scheme can approximate an optimised solution under widely diverse traffic load intensities. [ABSTRACT FROM AUTHOR]

Placement of mushroom electromagnetic bandgap (EBG) structures at the inset feedline of patch antenna operating at 4.8 GHz is analysed in this study. Proposed design for (i) single patch and (ii) two-element patch array exhibits significant improvement in return loss, bandwidth and mutual coupling loss. Parametric analysis confirms that the optimal position of EBG structures is at a distance of 1.5 mm on both sides of the feedline. It is established that the return loss increases by 8 dB and bandwidth increases by 3.2% for single patch with EBG structures at the feedline. A 6% reduction in antenna size is realised when compared with conventional placing of EBG. Likewise in double patch, placing the EBG structures on either side of the corporate feedline improves the return loss by 2.5 dB and a 12% reduction in size is achieved when compared with customary positioning of EBG. Bandwidth improves by 4.82%. The superior reduction of mutual coupling of double patch with inset edge feed having EBG structures at feedline, in addition to single-column mushroom EBG structures placed between the patches is demonstrated. The mutual coupling loss increases by 3.5 dB and a size reduction of 20% is accomplished. In antenna arrays, EBG structures at the feedline considerably reduce side lobe level and back lobe level and improve directivity, because of optimal radiation patterns. Simulations are validated experimentally. [ABSTRACT FROM AUTHOR]

Placing smaller cells in a heterogeneous network can be beneficial in terms of energy because better capacities can be obtained for a given energy constraint. These type of deployments not only highlight the need for appropriate metrics to evaluate how well energy is being spent, but also raise important issues that need to be taken into account when analysing the overall use of energy. In this study, handoff strategies, bandwidth allocation and path loss calculations in different scenarios, illustrate how energy can be consumed in a more efficient way when cell size is decreased. As a result, users can experience higher capacities while spending less energy, depending whether they handoff or not, increasing the overall performance of the network. [ABSTRACT FROM AUTHOR]

In multi-hop ad hoc networks, sources may pump more traffic into the networks than that can be supported, resulting in high end-to-end delay and packet-loss rate. Controlling the offered load at the sources can eliminate this problem. To conduct traffic control, the throughput of the network is necessary. In addition, the authors propose a concept of bandwidth mapping to analyse how much traffic in application can be injected to make the network supporting the maximum throughput. A multi-dimensional Markov model is built to analyse the performance of IEEE 802.11 DCF in unsaturated condition, in which M/G/1/K queuing model is used to analyse the service condition of the packet queue inside the node. The effects of carrier sensing property, hidden-node problem and signal capture property are considered together to analyse the contention experienced by the nodes in the network. Furthermore, the bandwidth mapping situation of voice and video traffic is analysed in string topology of a multi-hop ad hoc network. This analysis can provide a theoretical guide for the traffic admission control. [ABSTRACT FROM AUTHOR]

Compact branch-line couplers (BLCs) are developed using π-equivalent shunt-stub-based artificial transmission lines (SSB ATLs). A conventional quarter-wave microstrip can be equivalent to a π-equivalent SSB ATL which is realised by a series high-impedance microstrip with two bilateral low-impedance shunt stubs. The SSB ATLs are then applied to implement a BLC. The low-impedance shunt stubs of the adjacent SSB ATLs are merged and replaced by the shunt branch-type structures. The folding technique is used to optimally miniaturise the coupler circuit size. Distributed-capacitor structures are employed to improve the operating bandwidth. At the design frequency 0.9 GHz, the developed 3- and 6-dB BLCs using shunt branch-type structures occupy about 8 and 8.2% of the circuit sizes of the conventional structures, respectively. In addition, the circuit size of the 3-dB BLC using shunt distributed-capacitor structures reduces to a 13.9% of the conventional one. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) technology is an emerging technique for dynamic spectrum access, which attempts to share licensed spectrum with licensed users opportunistically and dynamically to provide high bandwidth and efficient spectrum utilisation. In this study, the authors address the problem of finding combined precoder and power of CRs for dynamic spectrum sharing in interference networks. First, the authors present the precoder and power optimisation problem in spectrum underlay by considering both power and interference constraints where CR users coexist and transmit simultaneously with primary users. Then the authors particularise the problem of precoder and power adaptation to spectrum overlay where CRs operate only in idle frequency bands obtained from spectrum sensing. In the proposed approach, bandwidth use is expressed in terms of a finite set of discrete resources whose use is optimised by the CR transmitters in terms of achievable rate corresponding to individual link under operating constraints that restrict the operation of unlicensed secondary CR transmitters to protect licensed primary user transmissions. The authors formulate the optimal resource allocation for CR links as a constrained optimisation problem and solve using the Lagrange method. The authors illustrate the proposed algorithm with the help of numerical results obtained from simulations. [ABSTRACT FROM AUTHOR]

Transmission-line cloaking is a simple yet wideband technique for cloaking a mesh-like object. A novel transmission-line cloak design operating at microwave frequencies is presented with special emphasis in the design placed on ease of manufacture and practicality. The operation of the cloak is verified by studying the antenna blockage caused by the cloaked and uncloaked objects. It is shown both numerically and experimentally that the designed transmission-line cloak is capable of hiding a mesh-like metal object placed inside it from the incident wave in a variety of different scenarios and within a fairly wide frequency bandwidth. Also, the agreement between simulations and measurements is shown to be very good. [ABSTRACT FROM AUTHOR]

In the long-term evolution (LTE) time division duplex (TDD) systems, base stations (BSs) use uplink sounding reference signals (SRSs) to estimate downlink channel state information (CSI) for downlink beamforming transmissions. In the current SRS pattern scheme, because SRSs of up to eight users are multiplexed on the same time-frequency resources, there exist mutual interferences among these SRSs over fading channels. Thus, the current scheme impacts the estimation accuracy of CSI and degrades the beamforming performance. Based on the characteristics of TDD systems, the authors propose a SRS pattern scheme, in which each user sends SRSs only on the allocated bandwidth instead of on full bandwidth as in the current LTE TDD systems, to eliminate the interferences among SRSs. Simulations show that the proposed scheme outperforms the current scheme in the estimation accuracy for various frequency-selective and time-selective fading channels. In addition, compared with the current SRS pattern scheme, the proposed SRS pattern scheme is robust to frequency-selective channels, and does not be impacted by the timing offset, and provides the flexibility for the choice of channel estimator at the BS side. [ABSTRACT FROM AUTHOR]

An increasing number of Internet applications and services render network management more troublesome for bandwidth misuse and security concern. As a result, network traffic identification plays an increasingly important role in network management. Deep packet inspection (DPI) is one of the effective approaches. Conventional network devices lookup the header of a packet, but DPI means the network device is required to match a pattern in the payload of a packet. This study proposes a DPI system and WMT (Wu-Manber with trie) algorithm to classify popular network services; The Net-DPIS is developed based on Netfilter framework in Linux kernel. The authors show how to rearrange the rule policies to increase the performance of Net-DPIS. In the results, the authors show that WMT algorithm is faster than WM algorithm; Net-DPIS has higher average accuracy and performance than L7-filter. [ABSTRACT FROM AUTHOR]

There are two fundamental bandwidth-request mechanisms specified in the IEEE 802.16 standard: contention-based random access and contention-free polling. For example, non-real-time polling and best-effort services mainly rely on the contention-based mechanism to submit bandwidth requests to the base station (BS). However, the performance degrades considerably when the number of requests is high and they collide with each other. To avoid collision, the standard supports a truncated binary exponential backoff resolution. Nevertheless this resolution is inefficient in dispersing the requests when the network traffic is overloaded. In order to improve the efficiency of the random-access mechanism in the standard, the authors propose a new mechanism that aids mobile stations (MSs) in sending bandwidth requests more efficiently and also avoiding peak traffic. By using the mechanism, MSs send bandwidth requests under low loads, thus avoiding collisions. [ABSTRACT FROM AUTHOR]

Mobile communication industries are increasingly contributing to the worldwide energy consumption and CO2 emission. This study addresses a number of key radio resource management (RRM) strategies across PHY and MAC layers for reducing base station energy consumption, as measured by a 'Joules per bit' metric. These strategies including power efficient link adaptation, exploitation of multi-user diversity and trading bandwidth for energy efficiency. By collectively taking advantage of those RRM strategies, a multi-user adaptive power and resource allocation algorithm is proposed to ease the power requirements of a base station, while maintaining the same levels of service to the user. The scheduling algorithm is applied to an LTE downlink simulator and its performance is evaluated for various traffic load conditions. The results show that the proposed algorithm achieves a significant energy saving (up to 86%) over a conventional non-energy aware resource allocation scheme. Furthermore, the energy efficiency performance of various multiple antenna techniques is evaluated along with the impact of control signalling overhead. These multiple antenna schemes are then incorporated into the proposed scheduling algorithm and the additional achievable energy savings are quantified. [ABSTRACT FROM AUTHOR]

The great potential of free space optics (FSO) communication motivates to use it for future requirement of high bandwidth links. However, the widespread use of this technology has been hampered by the reduced availability because of weather effects. To overcome these shortcomings a back-up link can be used so that the combined hybrid network may achieve carrier class availability. A hybrid, FSO/wireless LAN (WLAN) self-synchronising architecture is presented, which provides transparent connectivity without protocol overhead. The switching from one link to another needs efficient algorithms to achieve the optimal bandwidth utilisation while maintaining availability. Generally, the received signal strength is considered as a parameter for switching between the links. In this study, link selection has been analysed for a variety of algorithms, including filtering and hysteresis, using measured data of fog events. The combination of time and power hysteresis is found to be the optimum solution. [ABSTRACT FROM AUTHOR]

In radar target detection, the adaptive normalised matched filter (ANMF) detector is often used to detect moving targets in sea and land clutter environment. Its performance depends on estimation of clutter covariance matrix. The sample covariance matrix (SCM) estimator has been thoroughly analysed for independent and identically distributed Gaussian clutter vectors. Many radar systems on service use range-oversampling receivers. Referred to the range-oversampling model in the weather and oceanic radars, the spatial correlation model of range-oversampled clutter vectors is established, the error of the SCM estimator is analysed, and the range-oversampling gain, relevant to the oversampling factor and the receiver's bandwidth, is derived. The experiments using raw radar clutter data are made to verify the range-oversampling gain, showing that the range oversampling improves the performance of the ANMF detector. [ABSTRACT FROM AUTHOR]

A hybrid coupler design composed of multiple circular sectors is presented. It is designed to cover wireless local-area network bands at 2.4, 5.25 and 5.8 GHz, ultra-wideband at 3.1-4.8 GHz, digital multimedia broadcasting at 2.6 GHz and WiMax at 3.5 GHz. The coupler achieves an amplitude imbalance of 1 dB and a phase error of 5° at the outputs within the design frequency range. The developed coupler was compared with other existing designs in literature. It demonstrated advantages in terms of wide operating bandwidth as well as small physical size. [ABSTRACT FROM AUTHOR]

Three ultra-wideband (UWB) microstrip band-pass filters (BPFs) are proposed using tunable electromagnetic band gap (EBG)-embedded multiple-mode resonator (MMR) and fork resonator. In the first case, a compact dual-band BPF is implemented using a cascade of a multimodal fork resonator with tunable EBG. The fork resonator forms the basic structure yielding multiple band-pass realisations and the EBG selects the desired bands. This yields a compact dual-band BPF with sharp cut-off characteristics, wide bandwidth and low insertion loss. In the second case, a lower UWB filter is proposed by tuning an EBG-embedded MMR with parallel coupled microstrip line. Open circuited coupling stubs are introduced within the EBG structure to suppress higher order pass bands. In the third case, an upper UWB BPF is proposed in a similar manner as the lower UWB filter. However, the EBG-embedded MMR structure and the coupling technique are different. It is shown that the measured results are well matched to the predicted ones in terms of insertion/return losses over the plotted frequency range of 0.1-20.0 GHz. All simulations were performed with advanced design system (ADS) momentum (2.5D method of moments). [ABSTRACT FROM AUTHOR]

A key component of an efficient multipath routing is the optimal traffic allocation strategy that deals with how the traffic should be distributed among the multiple paths. In this study, two intelligent traffic distribution policies that minimise the experienced delay by the end user are proposed. For such delay minimisation, the authors investigate and compare average delay minimisation and maximum delay minimisation (MDM) over all the paths. It will be shown that MDM is a more efficient strategy for end-to-end delay minimisation. Based on this fact, an intelligent algorithm that can minimise the maximum delay of all paths is proposed using an adaptive traffic sharing scheme. [ABSTRACT FROM AUTHOR]

Benzocyclobutene (BCB) polymer is proposed in this study as an innovative and versatile substrate material for millimetre-wave reflectarrays. The excellent material features in terms of low loss, low dielectric constant and strong dielectric stability against frequency and temperature are highlighted. The design, realisation and test of a 60 GHz reflectarray with 21×21 variable-sized patches giving a focused boresight beam pattern are fully described. The BCB thickness is chosen on the basis of a parametric analysis performed on the unit cell to optimise the performances in terms of dielectric losses and radiation bandwidth. The in-house fabrication process able to assemble multi-layered BCB substrates is described in detail. Experimental results on the radiation pattern and the boresight gain are used to validate both the synthesis and the manufacturing process. [ABSTRACT FROM AUTHOR]

The authors present a novel design of a wide bandwidth polyphase up-sampling filter bank formed by cascading external shaping filters, arbitrary interpolators and two stages of polyphase channelisation. The channeliser synthesises 160 channels with 6-MHz frequency centres and thus spans a two-sided baseband bandwidth of 960 MHz. The two stages of channelisation first form super channels from ten sets of 16-channels each in 32-path polyphase channelisers operating at an output sample rate of 192 MHz. These ten super channels are, in turn, channelised by a 16-path polyphase channeliser operating at an output sample rate of 1536 MHz. The two-stage approach permits the ten sets of first stage super channel channelisers to operate at an easy to implement medium sample rate. The complex baseband signal is further up-sampled 1-to-2 and translated to a digital intermediate frequency and pre-compensated for the sin(x)/x distortion of the output digital-to-analogue converter. [ABSTRACT FROM AUTHOR]

With the emergence of various broadband services, a lot of bandwidth fragments will be generated during the operation of services being mapped into optical channels, which will waste too many bandwidth resources and decrease the transmission performance of optical networks. Traffic grooming strategy in dynamic optical networks can optimise the utilisation of bandwidth resources and reduce the blocking probability. However, in the distributed control plane of automated switched optical networks, all the traffic grooming strategies are implemented in each control node, and resource collision will still occur because the same link resource may be used by two path computation requests or traffic engineering information flooded by open shortest path first-traffic engineering protocol may be not synchronous at each control node or signalling delay time is too long. To reduce the collision of resource, a unified control plane is designed based on path computation element (PCE) for Internet protocol over wavelength division multiplexing networks, and a novel PCE-based traffic grooming strategy is proposed in the framework of unified control plane. Based on this strategy, four PCE-based traffic grooming algorithms are proposed and compared with the distributed traffic grooming strategy without PCE on a simulation platform implemented using disperse event simulation tool OMNET++. [ABSTRACT FROM AUTHOR]

This paper discusses about fibre to the home. Introducing fibre to the home (FTTH) systems using a Gigabit passive optical network (GPON) architecture. This has eroded ZON's market share, forcing it to invest in its FTTC network and DOCSIS 3.0 cable modems to keep up with current demands. ZON is now considering investing in FTTH to maintain its competitiveness. [ABSTRACT FROM AUTHOR]

User selection for access network is considered to be one of the distinct features of heterogeneous wireless systems, in which users with multi-network interface terminals can freely select access network for better quality of service with lower expense. On the other hand, service providers (SPs) will have to face more intense competition for attracting more subscribers and increasing their profits, which can be achieved through either non-cooperative or cooperative strategies. In this study, the authors propose a unified quantification model for evaluating the access service of heterogeneous systems. The relation between competitive SPs and users is described by different game models, based on general assumptions and practical application scenarios. A novel network selection scheme for maximising user performance-cost ratio (PCR) is proposed. Numerical results demonstrate that all SPs can achieve Nash equilibrium price under non-cooperative game framework and coalition price for cooperative game case to maximise their absolute profits, and the maximal PCR criterion for user network selection scheme is analysed under different scenarios. [ABSTRACT FROM AUTHOR]

A micromachined W-band through waveguide together with a passband filter embedded with a pair of H-plane bends is presented here. The novel design of the bend enabled direct and accurate connection between the micromachined circuit and standard waveguide flanges. The devices were fabricated using thick SU-8 photoresist technology. They were constructed with six gold- or silver-coated SU-8 layers, each of a thickness of 0.635 mm. These layers were then bonded on top of each other to form the waveguide and filter. A measured average insertion loss of 0.5 dB or 0.0278 dB/mm has been achieved by the 18 mm long through waveguide, and the return loss is better than 18.8 dB in the whole W-band. The asymmetrical capacitive irises coupled filter shows a -3 dB bandwidth of 8.61 GHz at a central frequency of 88.47 GHz. The passband insertion loss was measured to be between 0.97 and 1.1 dB and reflection loss is better than 15 dB. This performance demonstrates the potential of employing this micromachining and multi-layered technique to fabricate millimetre and submillimetre waveguide components. [ABSTRACT FROM AUTHOR]

In this study, the authors study a game-theoretic framework for the problem of multiuser rate allocation in multimedia communications. The authors consider the multimedia users to be autonomous, that is, they are selfish and behave strategically. The authors propose a rate allocation framework based on a pricing mechanism to prevent the selfish users from manipulating the network bandwidth by untruthfully representing their demands. The pricing mechanism is used for message exchange between the users and the network controller. The messages represent network-aware rate demands and corresponding prices. The authors show that a Nash equilibrium can be obtained, according to which the controller generates allocations that are efficient, budget balanced and satisfy voluntary participation. Simulation results demonstrate the validity of the proposed framework. [ABSTRACT FROM AUTHOR]

Conventional multibeam satellite communications systems ensure coverage of wide areas through multiple fixed beams where all users inside a beam share the same bandwidth. The authors consider a new and more flexible system where each user is assigned his own beam, and the users can be very geographically dispersed. This is achieved through the use of a large direct radiating array coupled with adaptive beamforming so as to reject interferences and to provide a maximal gain to the user of interest. New fast-converging adaptive beamforming algorithms are presented, which allow one to obtain good signal to interference and noise ratio with a number of snapshots much lower than the number of antennas in the array. These beamformers are evaluated on reference scenarios. [ABSTRACT FROM AUTHOR]

Bandwidth is an extremely valuable and scarce resource in wireless networks. Therefore efficient bandwidth management plays an important role in determining network performance. Adaptive bandwidth reservation and borrowing algorithms are proposed for multimedia cellular networks here. Based on the well known game-theoretic concept of bargaining, wireless bandwidth is controlled as efficiently as possible while ensuring quality-of-service (QoS) guarantees for higher-priority traffic services. Under dynamic network condition changes, control decisions in the proposed algorithms are made adaptively to strike a well-balanced network performance. This dynamic online approach can provide adaptability, feasibility and efficiency for real-world network operations. With a simulation study, the proposed scheme approximates an optimised solution under widely diverse traffic load intensities. [ABSTRACT FROM AUTHOR]

This study presents the design, control and implementation of a high bandwidth electromagnetic fast tool servo (FTS) that has the potential for use in diamond-turning of non-rotationally symmetric surfaces. The FTS is driven by a normal stress electromagnetic fast linear actuator and a custom current amplifier. It is controlled by a host-target real-time computer system. To achieve the high tracking and disturbance rejection performance required for the non-rotationally symmetric turning process, the controller is designed through a combined active disturbance rejection control and a feed-forward scheme. This combination exploits the unique disturbance estimation and compensation concept as well as the known reference acceleration signal. The controller design does not need an explicit mathematical model of the plant, and it employs an extended state observer to estimate the unmodelled plant dynamics, non-linear cutting force load, machine tool dynamics and other uncertainties. A digital first-order inertia filter is specially designed to reduce the effect of the position feedback signal noise. A prototype of the electromagnetic FTS with a travel of 50 µm is developed using the design approach. The experimental results are presented to illustrate the design procedures and demonstrate that the FTS achieves 10 kHz closed-loop bandwidth, 0.011 µm positioning error and 0.03 µm maximum tracking error. [ABSTRACT FROM AUTHOR]