Characterisation of real GPRS traffic with analytical tools

With GPRS and UMTS networks lunched, wireless multimedia services are commercially becoming the most attractive applications next to voice. Because of the nature of bursty, packet-switched schemes and multiple data rates, the traditional Erlang approach and Poisson models for characterising voice-centric services traffic are not suitable for studying wireless multimedia services traffic. Therefore, research on the characterisation of wireless multimedia services traffic is very challenging. The typical reference for the study of wireless multimedia services traffic is wired Internet services traffic. However, because of the differences in network protocol, bandwidth, and QoS requirements between wired and wireless services, their traffic characterisations may not be similar. Wired network Internet traffic shows self-similarity, long-range dependence and its file sizes exhibit heavy-tailedness. This paper reports the use of existing tools to analyse real GPRS traffic data to establish whether wireless multimedia services traffic have similar properties as wired Internet services traffic

User behaviour modelling for resource management in a hybrid UMTS/DVB-T network

Third generation mobile networks such as UMTS are designed to enhance the deployment of multimedia services providing high data rates and new flexible communication capabilities. However, these systems are interference limited and as such their performance is lowered in the case of a large number of users generating heavy traffic. A solution to this problem is to interconnect the UMTS network to a Digital Video Broadcasting-Terrestrial (DVB-T) network, so that the lack of capacity of UMTS during busy periods can be offset by the high bit rate available on the broadcast network. In order to justify this choice a prediction of the number of subscribers requesting the new multimedia applications designed for this scenario is needed. This paper focuses on the user behaviour modelling for multimedia services in a hybrid UMTS/DVB-T platform. The aim of the paper is to provide operators with a forecast of the demand for new multimedia services showing how they can be subject to a very high number of subscriptions, which UMTS would hardly be able to handle

Seamless soft handover in DVB-H networks

DVB-H (Digital Video Broadcasting for Handhelds) is a standard specified by the DVB Organization specifically for the broadcast of TV-like content and data to handheld devices, such as mobile phones, which have unique requirements in terms of power consumption, screen-size and mobility. Seamless handover in such a unidirectional network is especially challenging. In this paper we describe the handover issues of DVB-H networks and propose a novel seamless soft handover mechanism based on measuring CDF (Cumulative Distribution Function) of the signal to noise ratio (SNR) in the DVB-H terminal receiver front-end . Details of the algorithm is given and simulation is done to prove the benefits of such soft handover scheme

Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems

Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion

Performance analysis of time slicing in DVB-H

TV is the biggest media and the last one missing from mobile phones. Digital Video Broadcasting for Handhelds (DVB-H) is the latest development from the DVB Project targeting handheld, battery powered devices such as mobile telephones, PDAs(Personal Digital Assistants), etc. Time Division Multiplexing (TDM) is the technology that is usually used in computer and telecommunication systems. Time slicing is one of the characteristics that makes it possible to broadcast high resolution TV programes and fast IP data services to battery powered handheld terminals. This paper discusses the characteristics and advantages of Time slicing algorithm in DVB-H and presents the performance analysis of time slicing in DVB-H through both theoretical analysis and software simulation

Incorporating Digital Repeaters into the Soft Handover Standard in Digital Video Broadcasting Handheld

Digital Video Broadcasting for Handhelds (DVB-H) is a standard for broadcasting IP data services to portable devices. Handover in unidirectional broadcast networks is a novel issue introduced by this technology. This paper proposes and analyses the Repeater Aided Soft Handover (RA_handover) algorithm for a DVB-H receiver with MIMO antennas and presents the benefits of implementing RA_handover compared with a handover process without repeaters. For network planning and optimisation purposes simulation models are developed to analyse the RA_handover approach. It is shown that RA_handover could greatly improve the quality of service and consume much less front-end battery power than a handover method without repeaters. In addition, the cost introduced by the algorithm is briefly estimated. In conclusion, curves are given that show the relationship between quality of service and consumed battery power, which provide further support for including RA_handover in the DVB-H soft handover standard. The paper provides valuable outcomes for service providers and standard policy makers

Impurity scattering and Friedel oscillations in mono-layer black phosphorus

We study the effect of impurity scattering effect in black phosphorurene (BP) in this work. For single impurity, we calculate impurity induced local density of states (LDOS) in momentum space numerically based on tight-binding Hamiltonian. In real space, we calculate LDOS and Friedel oscillation analytically. LDOS shows strong anisotropy in BP. Many impurities in BP are investigated using $T$-matrix approximation when the density is low. Midgap states appear in band gap with peaks in DOS. The peaks of midgap states are dependent on impurity potential. For finite positive potential, the impurity tends to bind negative charge carriers and vise versa. The infinite impurity potential problem is related to chiral symmetry in BP

Management of Digital Video Broadcasting Services in Open Delivery Platforms

The future of Digital Video Broadcasting (DVB) is moving towards solutions offering an efficient way of carrying interactive IP multimedia services over digital terrestrial broadcasting networks to handheld terminals. One of the most promising technologies is Digital Video Broadcasting-Handheld (DVB-H), at present under standardisation. Services deployed via this type of DVB technologies should enjoy reliability comparable to TV services and high quality standards. However, the market at present does not provide effective and economical solutions for the deployment of such services over multi-domain IP networks, due to their high level of unreliability. This paper focuses on service management, service level agreement (SLA) and network performance requirements of DVB-H services. Experimental results are presented concerning QoS sensitivity to network performance of DVB-H services delivered over a multi-domain IP network. Moreover, a solution for efficient and cost effective service management via QoS monitoring and control and network SLA design is proposed. The solution gives DVB-H operators the possibility of fully managing service QoS without being tied to third party operators

Theoretical studies of 63Cu Knight shifts of the normal state of YBa2Cu3O7

The 63Cu Knight shifts and g factors for the normal state of YBa2Cu3O7 in tetragonal phase are theoretically studied in a uniform way from the high (fourth-) order perturbation formulas of these parameters for a 3d9 ion under tetragonally elongated octahedra. The calculations are quantitatively correlated with the local structure of the Cu2+(2) site in YBa2Cu3O7. The theoretical results show good agreement with the observed values, and the improvements are achieved by adopting fewer adjustable parameters as compared to the previous works. It is found that the significant anisotropy of the Knight shifts is mainly attributed to the anisotropy of the g factors due to the orbital interactions.Comment: 5 page