A mobility management strategy for GPRS

In general packet radio service (GPRS), a mobile station (MS) is tracked at the cell level during packet transmission, and is tracked at the routing-area (RA) level when no packet is delivered. A READY timer (RT) mechanism was proposed in 3GPP 23.060 to determine when to switch from cell tracking to RA tracking. In this mechanism, a threshold interval T is defined. If no packet is delivered within T, the MS is tracked at the RA level. When a packet arrives, the MS is tracked at the cell level again. However, the RT mechanism has a major fallacy in that the RTs in both the MS and the serving GPRS support node may lose synchronization. This paper considers another mechanism called READY counter (RC) to resolve this problem. In this approach, a threshold K is used. Like the RT approach, the MS is tracked at the cell level during packet transmission. If no packets are delivered after the MS has made K cell crossings, the MS is tracked at the RA level. We also devise an adaptive algorithm called dynamic RC (DRC). This algorithm dynamically adjusts the K value to reduce the location update and paging costs. We propose analytic and simulation models to investigate RC, RT, and DRC. Our study indicates that RC may outperform RT. We also show that DRC nicely captures the traffic-mobility patterns and always adjusts the K threshold close to the optimal values.     

An automated field repair tracking system [telecommunicationproducts]

The purpose of repair tracking (RT) is to provide ongoing feedback of product reliability performance in the customer environment. The authors present an RT technique and provide an overview of its automated software implementation, which has been used to track several transmission system products. The RT implementation, referred to as the repair equipment analysis program (REAP), tracks the field performance of electronic equipment at system, subsystem, circuit pack, and component levels. The features of REAP include monthly reliability performance reports, alarms when degradation in performance is detected, model sensitivity analysis, problem areas isolation for initiating corrective actions, and specific customer performance studies. The approach encompasses the entire population during the product life using existing sales and repair data as main inputs. Further, it does not require customer involvement or product serialization     

Resource Allocation in OFDMA Wireless Communications Systems Supporting Multimedia Services

We design a resource allocation algorithm for downlink of orthogonal frequency division multiple access (OFDMA) systems supporting real-time (RT) and best-effort (BE) services simultaneously over a time-varying wireless channel. The proposed algorithm aims at maximizing system throughput while satisfying quality of service (QoS) requirements of the RT and BE services. We take two kinds of QoS requirements into account. One is the required average transmission rate for both RT and BE services. The other is the tolerable average absolute deviation of transmission rate (AADTR) just for the RT services, which is used to control the fluctuation in transmission rates and to limit the RT packet delay to a moderate level. We formulate the optimization problem representing the resource allocation under consideration and solve it by using the dual optimization technique and the projection stochastic subgradient method. Simulation results show that the proposed algorithm well meets the QoS requirements with the high throughput and outperforms the modified largest weighted delay first (M-LWDF) algorithm that supports similar QoS requirements.     

Characterization of a new cobalt precursor for focused beam deposition of magnetic nanostructures

The electrical and magnetic properties of nanowires deposited from cobalt tricarbonyl nitrosyl (Co(CO)₃NO) precursor by focused electron beam- and focused ion beam-induced deposition (FEBID and FIBID) have been investigated. As-deposited nanowires have similar Co content, around 50-55 at.%, but different electrical behaviour: FEBID nanowire is highly resistive (6.3 mΩ cm at RT) and non-metallic at low T, while the FIBID one has much lower resistivity (189 μΩ cm at RT) and it is metallic. The magnetic properties, tested with magnetoresistance measurements, reveal a non-magnetic behaviour for both nanowires. After 400 °C annealing in vacuum FEBID wire is much less resistive (62 μΩ cm at RT) and recovers the metallic behaviour at low T, and both FEBID and FIBID wires display ferromagnetic behaviour. Structural analysis by low energy-scanning transmission electron microscopy (LE-STEM) suggests that coarsening and interconnection of the Co nanograins are responsible for the improvement in electrical and magnetic properties.     

Cross-sectional TEM of Pd/InP and Au/lnP interfaces formed at substrate temperatures near 300 and 77K

Depositing Pd or Au on InP at cryogenic substrate temperatures has previously been found to significantly increase the barrier height of the resulting Schottky diode. In this work, cross-sectional transmission electron microscopy was used to determine the structural differences between metal/semiconductor (MS) interfaces formed at 300K (RT) and at 77K (LT). In the Pd/lnP case, RT samples exhibited a thick amorphous interaction layer at the MS interface, while LT samples only had a thin phosphorous-rich interfacial layer. However, in the Au/InP case, no amorphous interlayers were observed in any of the samples. Instead, a small amount of Au was found to extend into the InP lattice in the RT case which was not present in LT samples. The thermal stability of the barrier height was studied as well. LT Au/lnP samples were found to exhibit a distinct barrier height shift when annealed at 200°C which was linked to a grain coarsening in the polycrystalline Au layer at this temperature. X-ray diffraction was used to verify changes in the polycrystalline metal's average grain size. We conclude that a significant reduction in the interaction between the deposited metal and InP was responsible for the greatly enhanced barrier height observed in LT interfaces.     

Optimal resource allocation in multiservice CDMA networks

This paper addresses the problem of dynamic resource allocation in a multiservice direct-sequence code-division multiple-access (DS-CDMA) wireless network supporting real-time (RT) and nonreal-time (NRT) communication services. For RT users, a simple transmission power allocation strategy is assumed that maximizes the amount of capacity available to NRT users without violating quality of service requirements of RT users. For NRT users, a joint transmission power and spreading gain (transmission rate) allocation strategy, obtained via the solution of a constrained optimization problem, is provided. The solution maximizes the aggregate NRT throughput, subject to peak transmission power constraints and the capacity constraint imposed by RT users. The optimization problem is solved in a closed form, and the resulting resource allocation strategy is simple to implement as a hybrid CDMA/time-division multiple-access strategy. Numerical results are presented showing that the optimal resource allocation strategy can offer substantial performance gains over other conventional resource allocation strategies for DS-CDMA networks.     

基于矩阵判决的SCI/RT直接传输模式新方法

对SCI/RT(scalable coherent interface for real time)TRAIN协议直接传输模式的分析表明,标准直接传输模式具有延迟小的特点,但其对环路带宽的利用率不高。为增加直接传输模式可用环路带宽,提高环路利用率,提出了基于矩阵判决的直接传输新方法。基于OPNET软件建立协议模型,通过不同场景和节点数环路的仿真对比,表明该方法较标准直接传输模式具有更好环路利用率;根据不同的数据包发送模式,直接传输模式可用带宽至少提高约25%;且算法在不同规模和配置的环路中均可使用。     

Novel Radio Link Buffer Management Schemes for End-User Multi-class Traffic in High Speed Packet Access Networks

The requirement to provide multimedia services with QoS support in mobile networks has led to standardization and deployment of high speed data access technologies such as the High Speed Downlink Packet Access (HSDPA) system. HSDPA improves downlink packet data and multimedia services support in WCDMA-based cellular networks. As is the trend in emerging wireless access technologies, HSDPA supports end-user multi-class sessions comprising parallel flows with diverse Quality of Service (QoS) requirements, such as real-time (RT) voice or video streaming concurrent with non real-time (NRT) data service being transmitted to the same user, with differentiated queuing at the radio link interface. Hence, in this paper we present and evaluate novel radio link buffer management schemes for QoS control of multimedia traffic comprising concurrent RT and NRT flows in the same HSDPA end-user session. The new buffer management schemes—Enhanced Time Space Priority (E-TSP) and Dynamic Time Space Priority (D-TSP)—are designed to improve radio link and network resource utilization as well as optimize end-to-end QoS performance of both RT and NRT flows in the end-user session. Both schemes are based on a Time-Space Priority (TSP) queuing system, which provides joint delay and loss differentiation between the flows by queuing (partially) loss tolerant RT flow packets for higher transmission priority but with restricted access to the buffer space, whilst allowing unlimited access to the buffer space for delay-tolerant NRT flow but with queuing for lower transmission priority. Experiments by means of extensive system-level HSDPA simulations demonstrates that with the proposed TSP-based radio link buffer management schemes, significant end-to-end QoS performance gains accrue to end-user traffic with simultaneous RT and NRT flows, in addition to improved resource utilization in the radio access network.     

TEM investigation of Ti and Ti/Al bilayer as alternative diffusion barriers for Cu metallization for SAW device applications

The thermal stability of Ti and Ti/Al thin barrier layers for Cu metallizations of surface acoustic wave (SAW) devices has been investigated by resistance measurements and analytical transmission electron microscopy (TEM) using energy dispersive analysis (EDX), energy filtered analysis (EFTEM) within a temperature range between RT and 300 °C. Due to the strong increase of the sheet resistance of the sample containing the Ti/Al-barrier, structural changes in the Al layer lead to a failure at 300 °C, whereas the other sample containing Ti only as a barrier layer did not show any obvious structural changes.     

Effect of deposition temperature on electric conduction and microstructure of Au films

Electric conduction was studied on thin gold films deposited at room (RT = 300 K) and liquid nitrogen temperature (LT = 77 K). Microstructure properties, and surface morphology of metal films were investigated by transmission electron spectroscopy (TEM) and atomic force microscope (AFM). The film thickness was chosen less than several hundred angstroms. Electrical measurement found that the LT film showed several orders lower resistance compared to the film obtained at room temperature at very low (about 100 Å) thickness. TEM study found that the LT films showed much smaller density of grain boundaries than that of the RT samples. In AFM observation, for film thickness of 100 Å, LT film showed smoother and continuous surface while the RT film consisted of discrete islands. When the thickness increased to be 200 Å, the LT film showed much larger-sized grains compared to that of the RT film. It is possible that for LT deposition, two-dimensional larger-sized grains were first formed at low temperature deposition which later extended to be three-dimensional.     

Downstream power backoff in CO/RT-deployed xDSL networks

To gradually expand their networks, operators deploy new xDSL technologies from remote terminals (RT's) closer to the customer. However, since xDSL lines deployed from an RT can share a binder with lines deployed from the central office (CO), a near-far problem is introduced and crosstalk may cause a severe performance degradation for the CO-deployed lines. RT lines have to be careful about how to allocate transmit power to the transmission frequencies, such that the impact on the CO lines is acceptable. Noise Impact (NI) methods have been proposed based on a target noise shape generated by the disturbers (RT lines). In this paper new methods based on the actual impact on the bit rate of the victims (CO lines) are proposed. These Bit Impact (BI) methods closely approximate the optimal power allocation.     

Effect of 100 MeV O7+ ion beam irradiation on radio frequency reactive magnetron sputtered ZnO thin films

Zinc oxide (ZnO) thin films were deposited on sapphire substrates at room temperature by radio frequency (RF) magnetron sputtering. These films were irradiated with 100 MeV O⁷⁺ ions of the fluencies 5×10¹³ ions/cm² at room temperature (RT) and at liquid nitrogen temperature (LNT). Profilometer studies showed that the roughness of pristine and LNT irradiated ZnO thin films were higher than that of the RT irradiated ZnO thin film. The glancing angle X-ray diffraction analysis reveals a reduced intensity and increased full width at half maximum (FWHM) of the (002) diffraction peak in the case of LNT irradiated film indicating disorder. However, the intensity and FWHM of the (002) diffraction peak in the case of RT irradiated ZnO thin films are comparable to those of the pristine film. UV–visible transmission spectra show that the percentage of transmission and band gap energy are different for RT and LNT irradiated films. While the pristine ZnO thin film exhibits two emissions—a broad emission at 403 nm and a sharp emission at 472 nm in its photoluminescence spectrum; the emission at 472 nm was absent for the irradiated films. The atomic concentrations of zinc and oxygen during the irradiation process were obtained using auger electron spectroscopy.     

Combined Connection Admission Control and Packet Transmission Scheduling for Mobile Internet Services

Mobile Internet access is expected to be the most popular communication service in the near future. In this paper, we investigate radio resource management for mobile Internet multimedia systems that use the orthogonal frequency division multiple access and adopt the adaptive modulation and coding technique. It is assumed that real-time (RT) service such as streaming video and best-effort (BE) services such as file transfer protocol and hypertext transfer protocol coexist in the systems. We suggest two levels of radio resource management schemes: the connection admission control (CAC) scheme at the first level and the packet transmission scheduler at the second level. The proposed scheduler does not assign higher priority to RT packets over BE packets unconditionally. Instead, only the RT packets that are close to the deadline are given higher priority. Therefore, the performance of BE services is improved at the cost of RT services. To control the performance degradation in RT services within an acceptable level, the CAC algorithm functions as a congestion controller. The combined effects of the proposed CAC and packet scheduling by using the cross-layer simulation that covers from the physical layer to the Internet application layer are evaluated. The numerical results show that the proposed schemes greatly improve the performance of BE services while maintaining the quality of video service at an acceptable level.     

A new statistical model for site-specific indoor radio propagationprediction based on geometric optics and geometric probability

The ray-tracing (RT) algorithm has been used for accurately predicting the site-specific radio propagation characteristics, in spite of its computational intensity. Statistical models, on the other hand, offers computational simplicity but low accuracy. In this paper, a new model is proposed for predicting the indoor radio propagation to achieve computational simplicity over the RT method and better accuracy than the statistical models. The new model is based on the statistical derivation of the ray-tracing operation, whose results are a number of paths between the transmitter and receiver, each path comprises a number of rays. The pattern and length of the rays in these paths are related to statistical parameters of the site-specific features of indoor environment, such as the floor plan geometry. A key equation is derived to relate the average path power to the site-specific parameters, which are: 1) mean free distance; 2) transmission coefficient; and 3) reflection coefficient. The equation of the average path power is then used to predict the received power in a typical indoor environment. To evaluate the accuracy of the new model in predicting the received power in a typical indoor environment, a comparison with RT results and with measurement data shows an error bound of less than 5 dB     

Modeling of the threshold operation of 1.3-/spl mu/m GaAs-based oxide-confined (InGa)As-GaAs quantum-dot vertical-cavity surface-emitting lasers

In the paper, the self-consistent optical-electrical-thermal-gain threshold model of the oxide-confined (OC) quantum-dot (QD) (InGa)As-GaAs vertical-cavity surface-emitting diode laser (VCSEL) is demonstrated. The model has been developed to enable better understanding of physics of an operation of GaAs-based OC QD VCSELs in a full complexity of many interactions in its volume between individual physical phenomena. In addition, the model has been applied to design and optimize the low-threshold long-wavelength 1.3-/spl mu/m GaAs-based OC QD VCSELs for the second-generation optical-fiber communication systems and to examine their anticipated room-temperature (RT) performance. An influence of many construction parameters on device RT lasing thresholds and mode selectivity has been investigated. Some essential design guidelines have been proposed to support efforts of technological centers in producing low-threshold single-mode RT devices.     

Room-temperature continuous-wave laser operation of electrically-pumped 1.55 /spl mu/m VECSEL

A report is presented on room-temperature (RT) continuous-wave (CW) laser emission at 1.55 /spl mu/m of an all InP-based electrically-pumped vertical external-cavity surface-emitting laser (EP-VECSEL). Threshold currents of 1.4 kA/cm/sup 2/ and output powers of up to 0.3 mW were measured under CW operation at RT. A maximum output power of 2.7 mW has been obtained in quasi-CW operation at a heatsink temperature of 10.5/spl deg/C. This first result demonstrates that EP-VECSELs are a potential candidate for the realisation of compact vertical-cavity emitting sources.     

Cooperative quadrature spatial modulation with Euclidean distance and capacity optimized antenna selection

In this study, new cooperative‐quadrature spatial modulation techniques based on Euclidean distance and capacity optimized antenna selection techniques (EDAS‐CQSM and COAS‐CQSM) are proposed for cooperative communication systems. The considered cooperative system consists of three terminals that are the source terminal (ST), relay terminal (RT), and destination terminal (DT). The decode‐and‐forward (DF) cooperative technique is considered to retransmit the signal at the RT. In order to improve the performance of the conventional QSM demodulator in the RT and DT, both antenna selection techniques have been used in both the ST and RT to reduce performance degradation due to error propagation of the DF scheme. Therefore, the overall performance of the considered CQSM system has been increased. Furthermore, computer simulations have shown that the proposed EDAS/COAS‐CQSM systems have better the performances than the cooperative spatial modulation (CSM), CQSM, EDAS‐CSM, COAS‐CSM, and traditional DF‐based cooperative system with the same bit rate.     

Resonant tunneling devices with multiple negative differential resistance and demonstration of a three-state memory cell for multiple-valued logic applications

A new resonant-tunneling (RT) functional device with two peaks in the current-voltage (I-V) characteristic has been demonstrated. Contrary to conventional RT devices, the peaks are obtained using a single resonance of the quantum well. The peak's separation is voltage tunable and the peak currents are nearly equal, which is important for a variety of device applications. Using a single device, a three-state memory cell has been implemented.     

Novel metal-semiconductor-metal photodetectors on bulk semi-insulating indium phosphide

Depositing Pd or An on InP at substrate temperatures near 77 K (LT) has previously been found to significantly reduce the interaction between the metal and semiconductor upon formation of the interface. In this letter, this technique was used to fabricate metal-semiconductor-metal photodetectors (MSMPDs) on semi-insulating (SI) InP substrates with superior characteristics compared to detectors formed using standard room temperature (RT) metal deposition. Detectors having a LT-Ps-SI-InP structure had a dark current of 80 nA at 5 V, which was a factor of 4 lower than the dark current of conventional MSMPDs. Additionally, LT-Pd-SI-InP MSMPDs exhibited excellent saturation characteristics and a responsivity of 0.75 A/W. Detectors with an indium-tin-oxide (ITO)-LT-Au (200 /spl Aring/)-SI-InP structure had a higher responsivity of 1.0 A/W, due to the relative transparency of this metallization. In contrast, MSMPDs with RT metallizations had poor saturation characteristics, consistent with the results of others. The difference in the illuminated characteristics of MSMPDs with RT and LT metallizations was due to a change in the internal photoconductive gain mechanism. In RT detectors, hole trapping at interface states near the cathode dominated the gain mechanism. In LT detectors, the difference in carrier transit-times dominated.     

Some Issues With Using Radiative Transfer Approach to Scattering From Layered Random Media With Rough Interfaces

The radiative transfer (RT) approach is widely used in applications involving scattering from layered random media with rough interfaces. Although it has been successful in several disciplines it is well known that this approach involves certain approximations. In this paper these assumptions and approximations are reexamined. To enable this a statistical wave approach is employed to this problem and the governing equations for the first and second moments of the wave functions are derived. A transition is hence made to arrive at a system of equations corresponding to that of the RT approach. It is hence found that more conditions are implicitly involved in the RT approach than generally believed to be sufficient.