Efficiency-fairness tradeoff in telecommunications networks

Introducing the concept of /spl alpha/-fairness, which allows for a bounded fairness compromise, so that no source is allocated less than a fraction /spl alpha/ of its fair share, this letter studies tradeoffs between efficiency (utilization, throughput or revenue) and fairness in a general telecommunications network with relation to any fairness criterion. We formulate a linear program that finds the optimal bandwidth allocation by maximizing efficiency subject to /spl alpha/-fairness constraints. This leads to what we call an efficiency-fairness curve, which shows the benefit in efficiency as a function of the extent to which fairness is compromised.     

Strictly nonblocking directional-coupler-based switching networksunder crosstalk constraint

Directional-coupler (DC)-based switching systems can switch signals at the rate of several terabits per second. Such switches can also transmit signals with multiple wavelengths simultaneously. Despite these advantages, DCs suffer from an intrinsic crosstalk problem that must be overcome in building a robust switching system. In this paper, the principles of constructing strictly nonblocking DC-based photonic switching systems under various crosstalk constraints are explored. We demonstrate how crosstalk adds a new dimension to the theory of switching systems. We find the sufficient nonblocking condition for photonic networks under crosstalk constraints and demonstrate that some well-known nonblocking networks can tolerate a stricter crosstalk constraint while retaining their hardware complexity. The theory developed in the paper can guide us in making the design tradeoff between the level of crosstalk and the amount of hardware     

The latency/bandwidth tradeoff in gigabit networks

It is argued that delays through gigabit networks are dominated by propagation delay, so communications techniques and protocols for megabit networks would be inefficient or ineffective for gigabit networks. The latency-bandwidth tradeoff for gigabit networks is discussed, and an example of it is presented. It is concluded that gigabit networks have forced network designers to deal with propagation delays due to the finite speed of light     

Throughput-range tradeoff of wireless mesh backhaul networks

Wireless backhaul communication is expected to play a significant role in providing the necessary backhaul resources for future high-rate wireless networks. Mesh networking, in which information is routed from source to destination over multiple wireless links, has potential advantages over traditional single-hop networking, especially for backhaul communication. We develop a linear programming framework for determining optimum routing and scheduling of flows that maximizes throughput in a wireless mesh network and accounts for the effect of interference and variable-rate transmission. We then apply this framework to examine the throughput and range capabilities for providing wireless backhaul to a hexagonal grid of base stations, for both single-hop and multihop transmissions for various network scenarios. We then discuss the application of mesh networking for load balancing of wired backhaul traffic under unequal access traffic conditions. Numerical results show a significant benefit for mesh networking under unbalanced loading.     

Amplifier induced crosstalk in multichannel optical networks

The effect of crosstalk introduced due to gain saturation in an optical amplifier when it is used for amplifying multiple channels in a wavelength division multiplexed (WDM) network employing ON-OFF keying with direct detection is studied. The system power penalty is quantified as a function of the amplifier input power, the number of channels, and the extinction ratio     

Statistical analysis of crosstalk accumulation in WDM networks

Accumulation of inband crosstalk in all-optical networks is studied. By applying statistical methods, we have investigated how inband crosstalk accumulation influences the performance of optical networks of different configurations. Our study shows that there exists a delicate dependence between network topology and robustness with respect to accumulation of inband crosstalk. A method is proposed to design optical networks with optical paths satisfying a certain level of inband crosstalk performance     

Modeling of in-band crosstalk in WDM optical networks

In this paper, we analyze three different simulation models which allow the impact of in-band crosstalk on the transmission performances of wavelength division multiplexing (WDM) optical networks to be evaluated: an accurate simulation (AS), a Gaussian correlated noise (GCN) model, and a Gaussian white noise (GWN) model. In the AS, an interfering channel is generated at each node and added to the signal after an optical filtering. The final result must be averaged with respect to the message transmitted on the interfering channels and to the phases of the optical carriers. In the GCN the crosstalk term is modeled as a Gaussian correlated noise, whose spectrum coincides with that of the interfering channel. This model can be further simplified if the noise is also assumed uncorrelated (GWN approximation). The results obtained by these simulation models are also compared with those produced by an analytical model allowing to evaluate the in-band crosstalk penalty     

Performance implications of component crosstalk in transparentlightwave networks

We find both theoretically and experimentally that crosstalk due to small component imperfections in transparent lightwave networks will tend to generate large performance degradations. The most severe degradations, which arise from interference between signal and crosstalk electric fields, are far larger than those predicted from simple power-addition without field interference. Systems corrupted by crosstalk from a single source of optical-field leakage appear to require component crosstalk levels ϵ⩽-20 dB, if conventional receivers are used. Since the degradations are believed to depend on N√ϵ, where N is the number of crosstalk generators, each producing a crosstalk power level of ϵ, the problem is expected to grow rapidly severe with network size     

Energy-efficient resource allocation for multi-RAT networks under time average QoS constraint

Wireless Networks - In this paper, we propose an energy-efficient resource allocation algorithm for multiple radio access technologies (multi-RAT) networks, where the user equipments (UEs) transmit...     

Coherent and incoherent crosstalk in WDM optical networks

The impact of coherent and incoherent crosstalk on an optical signal passing through optical cross-connect nodes (OXC's) in wavelength division multiplexing (WDM) optical networks is studied, and the analytical expressions are given. Such crosstalk will be generated when the optical propagation delay differences of optical paths in an OXC do not exceed the coherent time of the lasers. While causing fluctuation of signal power, coherent crosstalk may cause noise or not, depending on the relationship between the optical propagation delay differences and the time duration of one bit of the signal. Incoherent crosstalk may cause very high noise power, because it can be a coherent combination of crosstalk contributions. The statistical impact of all crosstalk contributions on signal is studied by simulation, and the concept of quantile is proposed to relax the crosstalk specification requirement for components. The crosstalk specification requirements are then obtained for components used in WDM optical networks with different scales     

Analysis of homodyne crosstalk in optical networks usingGram-Charlier series

Homodyne crosstalk with the same wavelength as the signal causes severe system performance degradation in optical networks by beating with the desired signal. Gaussian approximation is found to overestimate the system degradation. A correction to Gaussian approximation, Gram-Charlier series is used to analyze homodyne crosstalk. Both bit error rate (BER) and power penalty are calculated for multiple homodyne interferers     

Impairment constraint multicasting in translucent WDM networks: architecture, network design and multicasting routing

The popularity of broadband streaming applications requires communication networks to support high-performance multicasting at the optical layer. Suffering from transmission impairments in multi-hop all-optical (transparent) WDM multicasting networks, the signal may be degraded beyond the receivable margin at some multicast destinations. To guarantee the signal quality, we introduce a translucent WDM multicasting network to regenerate the degraded signals at some switching nodes with electronic 3R (reamplification, reshaping and retiming) functionality. The translucent network is built by employing three kinds of multicasting capable switching architectures: (1) all-optical multicasting capable cross connect (oMC-OXC), (2) electronic switch and (3) translucent multicasting capable cross connect (tMC-OXC). Among them both the electronic switch and tMC-OXC are capable of electronic 3R regeneration. Furthermore, we propose a multicast-capable nodes placement algorithm based on regeneration weight, and two multicasting routing algorithms called nearest hub first and nearest on tree hub first to provide signal-quality guaranteed routes for the multicasting requests. The numerical simulation on two typical mesh networks shows that it is sufficient to equip 30% of the nodes or less with signal-regeneration capability to guarantee the signal quality.     

On the performance/complexity tradeoff in block turbo decoder design

In this letter, tradeoffs between very large scale integration implementation complexity and performance of block turbo decoders are explored. We address low-complexity design strategies on choosing the scaling factor of the log extrinsic information and on reducing the number of hard-decision decodings during a Chase search.     

非互易网络的无耗约束条件

该文论述了在非互易条件下,无源无耗网络的各种约束表征：例如,阻抗[Z]矩阵可以存在实部。它并不与能量定律相悖,即在这种情况下,阻抗矩阵中的电阻并不代表损耗,其负阻也不表示有源增益;传输[A]矩阵也反映出|det[A]|=1的似互易特性。文中给出了具体实例。     

Optimal energy-delay tradeoff for opportunistic spectrum access in cognitive radio networks

Cognitive radio (CR) has been considered as a promising technology to enhance spectrum efficiency via opportunistic transmission at link level. Basic CR features allow secondary users (SUs) to transmit only when the licensed channel is not occupied by primary users (PUs). However, waiting for an idle time slot may lead to large packet delays and high energy consumption. We further consider that the SU may decide, at any moment, to use another dedicated way of communication (4G) in order to transmit his packets. Thus, we consider an Opportunistic Spectrum Access (OSA) mechanism that takes into account packet delay and energy consumption. We formulate the OSA problem as a Partially Observable Markov Decision Process (POMDP) by explicitly considering the energy consumption as well as packets’ delay, which are often ignored in existing OSA solutions. Specifically, we consider a POMDP with an average reward criterion. We derive structural properties of the value function and we show the existence of optimal strategies in the class of the threshold strategies. For implementation purposes, we propose online learning mechanisms that estimate the PU activity and determine the appropriate threshold strategy on the fly. In particular, numerical illustrations validate our theoretical findings.     

Inter-channel crosstalk phenomena in optical time divisionmultiplexed switching networks

The nature of inter-channel crosstalk arising in OTDM switching networks formed from imperfectly isolated 2×2 crosspoints and optical delay lines is investigated and a novel classification is identified. It is shown that the mixing of crosstalk and signal waveforms which are either, a) mutually coherent or, b) incoherent and (optical) frequency matched to within the receiver bandwidth, may result in intensity noise and far greater performance degradation than for c) incoherent signals whose optical beat frequency exceeds the receiver bandwidth. Initial experimental studies indicate that crosspoint isolation <-15 dB is required if undilated networks containing more than four crosspoints are to be realised     

Extinction ratio induced crosstalk system penalty in WDM networks

The authors derive an analytical solution for crosstalk-induced penalty in wavelength routers with consideration of the extinction ratio. Both theoretical and experimental results suggest that the extinction ratio can induce a system penalty and should be kept to at least ~15 dB to maintain the penalty below 1 dB for a total crosstalk level of ~-23 dB     

芯片设计中串扰噪声的分析与改善

集成电路设计进入了超深亚微米领域,金属层增加,线宽减小,使电路的性能和密度都得到了很大的提高,但也引入了愈来愈严重的互连线效应,并最终引发了信号完整性问题.在这其中,串扰噪声是一个关键的问题.本文探讨了噪声产生机制并进行定量分析,结合作者实际设计阐述该问题的解决方法.     

Radiation and scattering tradeoff design for conformal arrays

A tradeoff between gain and radar cross section is presented for waveguide aperture antennas mounted on a circular cylinder. The radiation and scattering characteristics are investigated as a function of frequency, various array lattices and different impedance loads using a method of moments code combined with asymptotic techniques. First, single aperture elements in a cylinder are considered and then different arrays. It is shown that it is possible in some cases to maximize the radiation and minimize the scattering properties with a suitable choice of impedance loads. The importance of mutual coupling is investigated and it is found that under certain circumstances it is possible to draw conclusions from calculations where mutual coupling has been omitted. The radiation and scattering properties of cylindrical arrays have been compared to the corresponding quantities for planar arrays and the advantages/disadvantages of the two concepts are illustrated.     

Accurate design methodology to prevent crosstalk

Presented are the effects of a guard trace with the optimal number of grounded vias that gives maximum efficiency for preventing crosstalk in parallel double micro-strip lines in a high-speed printed circuit board layout. Compared to a guard trace with two terminal grounded vias, the near-end crosstalk is reduced from 95 to 30 mV and the far-end crosstalk is reduced from 121 to 56 mV