High-speed data streams can be sent without an accompanying clock signal, where the receiver generates a clock from an approximate frequency reference, and then phase-aligns to the transitions in the data stream with a phase-locked loop (PLL). This process is commonly known as clock and data recovery (CDR). CDR circuits operating at tens of gigabits per second pose difficult challenges with respect to speed, jitter, signal distribution, and power consumption. Half-rate 40-Gb/s CDR circuits have been implemented in bipolar technology but require large voltage supplies and draw high amounts of power. On the other hand, the recent integration of 10-Gb/s receivers in CMOS technology encourages further research on CMOS solutions for higher speeds, especially if it enables low-voltage, low-power realization.     (more...)

University of California researchers have developed an optimized mixture of graphene and multilayer graphene that utilizes high-yield liquid phase exfoliation techniques to significantly increase the thermal conductivity of thermal interface materials.  While current thermal interface materials have thermal conductivity values in the range of ~1 to 5 W/mK at room temperature, University of California researchers have achieved thermal conductivity values at or above 25 W/mK at room temperature with only small graphene loading fractions at 5% by volume.  The graphene and few layer graphene are utilized as filler materials with various base (or matrix) materials to form the thermal interface materials.   (more...)

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The increasing sophistication of wireless communication technologies, in particular power conscious portable devices, has made efficient, wide bandwidth, linear power amplifiers (PAs) that handle high peak-to-average signal power ratios critically important. Generally, PAs are the major consuming blocks in any transmitter chain and they alone account for about 70-80% of total power consumption in transmitter chips. Further, wireless communication technologies are increasingly using non-constant envelope modulation schemes for accommodating high data rates in low bandwidths. Designing a PA which can maintain close to peak efficiency over the wide dynamic range of such modulation schemes and also achieve power control is imperative to conserve battery power. (more...)

A novel method and apparatus to improve the overall quality of a reconstructed video signal at a given transmission rate, or to maintain the current signal quality at reduced transmission rates.  (more...)

Thousands of severely disabled patients are unable to communicate due to paralysis, locked-in syndrome, Lou Gehrig’s disease, or other neurological disease. Restoring communication in these patients have proven a major challenge. Prosthetic devices that are operated by electrical signals measured by sensors implanted in the brain are being developed in an effort to address this problem.  Investigators at University of California at Berkeley have responded to this challenge by developing an algorithm to decode speech, including arbitrary words and sentences, using brain recordings from the human cortex.  a computational model is trained that determines how recorded electrical signals at specific brain sites represent different speech features, for example acoustic frequencies.  The trained model then takes as input novel brain recordings and outputs a set of predicted speech features.  Once these steps are accomplished, speech sounds are either directly synthesized or words are identified from the predicted speech features using statistical techniques.  The brain signal decoding algorithm can decode speech solely from brain signals and may permit communication via thought alone.    (more...)

There are problems with discrimination speech from background noise in applications such as cell phones, hearing aids, telecommunications, automatic speech recognition, which limit the use of these important technologies. In response to this challenge, investigators at University of California at Berkeley have developed a speech filtering algorithm that improves intelligibility of speech in noisy backgrounds.  This speech filtering algorithm is applied as a first stage of processing, before transmission, analysis, or listening.  The speech filtering algorithm can be located in its entirety on a dedicated DSP or FPGA.   These systems allow the complexity needed for the computations of the gain stage, but still function fast enough for real-time denoising. The investigators have implemented the speech filtering algorithm using a computer to process signals offline (post-hoc). The inspiration for our model comes from our research on the statistics of animal vocalizations (including human speech) and on the responses of auditory neurons to these sounds. They have shown that neurons in avian primary and secondary auditory areas are tuned to represent the statistical structure of vocalizations. These areas are analogous to cortical auditory areas in humans.  The preferred embodiment uses many relatively narrow bands in the analysis filter-as low as 50 Hz bandwidth and spacing. Another embodiment uses fewer, wider bands in the analysis filter, perhaps several thousand Hz in width.The most significant advantage of X is its ability to exploit important, basic statistical information about all human speech in a simple fashion. Some of these properties are included implicitly in advanced ASR systems. Separating these simple, physically-driven features from more complicated verbal and syntactic rules brings this power to bear in simpler, lower-power systems like cell phones. Additional complexity is also the primary drawback of this system: it requires more computational power, and because it uses a longer history, it could introduce delays that are unacceptable for low- like hearing aids and cochlear implants. (more...)

A process for manufacturing a novel type of Vertical Cavity Surface Emitting Laser with low optical loss. (more...)

A novel Wavelength-Division Multiplexer device to interleave multiple signals into a multiplexed, multi-channel optical laser signal. (more...)

A novel VCSEL scheme in which an electrically-pumped short wavelength VCSEL is optically coupled to a long wavelength VCSEL for optically pumping the long wavelength VCSEL. (more...)

A novel method for creating a VCSEL structure that confines current diameter to less than that of the transverse optical mode, while maintaining a high degree of planarity in its layers. (more...)

A novel method for making a metal layer semiconductor laser with large bandwidth and the capability for high power output. (more...)

A long wavelength VCSEL that is optically pumped by a shorter wavelength VCSEL and is particularly useful for fiber-optic communication systems. (more...)

A method of fabricating diode lasers whose performance is essentially unchanged over designed temperature and bias ranges. (more...)

A wavelength-division-multiplexed array of long wavelength vertical cavity lasers, pumped by a short-wavelength optical pump. (more...)

On-chip capacitively transduced vibrating polysilicon micromechanical resonators have achieved quality factor Q's over 160,000 at 61 MHz and larger than 14,000 at about 1.5 GHz -- making them suitable for on-chip frequency selecting and setting elements for filters and oscillators in wireless communication applications. However, there are applications -- such as software-defined cognitive radio, that require even higher Q's at RF to enable low-loss selection of single channels (instead of bands) to reduce power consumption down to levels conducive to battery-powered handheld devices. To address those higher Q RF applications, researchers at UC Berkeley have invented design improvements to MEMS resonators that reduce energy loss and in turn increase resonator Q. In reducing energy loss to the substrate while supporting all-polysilicon UHF MEMS disk resonators, the Berkeley design improvements enable quality factors as high as 56,061 at 329 MHz and 93,231 at 178 MHz -- that are values in the same range as previous disk resonators using multiple materials with more complex fabrication processes. Measurements confirm Q improvements of 2.6X for contour modes at 154 MHz, and 2.9X for wine glass modes around 112 MHz over values achieved by all-polysilicon resonators with identical dimensions. The results not only demonstrate an effective Q-enhancement method with minimal increase in fabrication complexity, but also provide insights into energy loss mechanisms that have been largely responsible for limiting Q's attainable by all-polysilicon capacitively transduced MEMS resonators. (more...)

As powered electrical and mechanical devices have continued to be miniaturized, it has become increasingly important to limit the temperature rises of vulnerable components such as integrated circuits, small mechanical elements and light sources. The conventional passive heat transfer method most commonly used is to simply put a set of fins in the heat transfer path from the source of heat (e.g., a packaged device) to a region where a gaseous or liquid coolant contacts the fins, becomes heated, and then is allowed to contact or mix with a large volume of gas or liquid that is cooler. These finned heat transfer approaches have limits, and therefore researchers at UC Berkeley have developed a means of augmenting this conventional passive heat transfer with supplementary actively powered mechanisms. This novel approach increases the rate of contact and mixing -- and thereby, the rate of heat removal. The approach is appropriately sized (i.e., miniature), energy efficient, quiet, inexpensive, and has a long lifetime.  (more...)

Wind-generated ocean waves deliver energy to coastal ecosystems and fundamentally structure the physical environment and associated biological communities. Wave energy can determine the structure and function of nearshore ecosystems by modifying the relative strengths of disturbance, recruitment and species interactions. While measuring wave exposure at the appropriate spatial scales is fundamental to understanding marine ecosystems, this remains a challenge because instruments are expensive, difficult to use, or don’t measure at appropriated temporal scales. These instruments, such as the Acoustic Doppler Velocimeters (ADVs) and the Acoustic Doppler Current Profilers (ADCPs) are expensive and logistically difficult to deploy, requiring a support of vessels with hydraulic hoists for deploying heavy instrument packages.   These factors restrict the number of units that can be deployed concurrently, limiting the spatial coverage and resolution of measurements. Additionally, being a deterrent to research due to the acquisition cost of the instrument. As an alternate solution, UCSC has developed an inexpensive, accurate and precise instrument for measuring wave energy, known as the Underwater Relative Swell Kinetics Instrument (URSKI). (more...)

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The present invention relates to linking devices and displaying their information over a network and, more particularly, a method in which many different devices can upload multiple file types (code, text, audio files, etc.) that can be organized in a manner to be utilized over a network, such as the internet. (more...)

A novel photography method that provides, along with the actual picture taken, several alternative versions of the image. This method produces photo variations such as panoramas, collages, alternative views, composites based on moving subjects, and views using varying capture parameters such as focal length and exposure time. (more...)

UC San Diego inventors have designed a system that takes an arbitrary speaker array and provides focused sound projection that is: Spatialized—present a localized beam of high quality audio. Localized—present no sound for most of the listening area, except a localized area. Binaural—present a sound as being located external to the listener. Performance improves with the number of speakers in the array. The invention has been implemented successfully on a speaker array driven by specialized software. (more...)

A broadband absorptive multiplier as used in CMOS technologies is presented here and relates to microwave multipliers or mixers in general and in particular to absorptive switch networks for use in integrated wireless systems with very high bandwidth. (more...)

A novel design and fabrication methods of three-dimensional, wafer-scale, batch-fabricated angle/angular rate micro-shell resonator gyroscope with on-chip actuation and detection. (more...)

Vehicular Ad-Hoc networks (VANETs) play a critical role in enabling important active safety applications such as cooperative collision warning. These active safety applications rely on continuous broadcast of self-information by all vehicles, which allows each vehicle to track all its neighboring cars in real-time. The most pressing challenge in such safety-driven communication is to maintain acceptable tracking accuracy while avoiding congestion in the shared channel.   Investigators at University of California at Berkeley have developed a transmission control algorithm that adapts communication rate and power based on the dynamics of vehicular network and safety-driven tracking process. The innovative transmission rate and range control  solution uses a closed-loop control concept and accounts for wireless channel unreliability.  Simulation results confirm that if packet generation rate and associated transmission power forsafety messages are adjusted in an on-demand and adaptive fashion, robust tracking is possible  under various traffic conditions.  Verifying the robustness of the algorithm, the investigators observed its tracking performance in various traffic scenarios. Simulation results confirm that the innovative design is robust and can considerably reduce the tracking error compared to that of the de-facto solution (beaconing with 100-millisecond interval). (more...)

Rogue waves are abnormally large, steep waves that appear unexpectedly in the open ocean. These waves are rare, and occur much more commonly than predicted by conventional wave models. Although the formation of these extreme waves is not fully understood, it is widely believed that nonlinearity plays a central role. In the past, the study of rogue waves has focused on hydrodynamic studies and experiments. However, there are other physical systems that possess similar nonlinear characteristics and may also support rogue waves. UCLA researchers have discovered that rogue waves can arise in optics, and can be harnessed for applications. (more...)

Multimedia information systems have emerged as an essential component of many application domains ranging from library information systems to entertainment technology. This invention consists of a data layout and associated scheduling algorithm that support the continuous display of multimedia objects and eliminate the frequent disruptions and delays that are termed hiccups. This method accommodates objects with different delivery rates (MPEG-1, MPEG-2, uncompressed, etc.) and also handles multiple requests for the same or different objects. A wide range of bandwidths of objects can be handled easily (from sub-disk bandwidth to objects requiring the bandwidth of a number of disks). This method, which is entitled staggered stripping, will provide effective support for multiple users accessing the different objects in the database . It consists of allocating continuous media objects to a parallel collection of rotating storage devices such that: (a) the fetch of an object can be accomplished at a predefined rate (bytes/sec) that matches the desired delivery rate for the object, (b) at each instant only a subset of the storage device is used for a particular request for an object, (c) the exact subset of storage devices being used for a particular request changes over time in such a way that the request presents a balanced load across all of the storage devices, and (d) the allocation and scheduling scheme can accommodate a wide range of required object delivery rates without incurring collisions between requests. In staggered stripping, the exact method of stripping is a function of the object bandwidth requirement. Finally, this method of allocation enables a very efficient and simple scheduling algorithm. (more...)

This invention is a wide-band, high-gain millimeter wave amplifier for imaging and communication applications. The developed prototype has set a record for wideband and high-gain operation. It utilizes a novel topology based on a hybridization of traveling wave on-chip propagation for high-bandwidth that is cascaded for high-gain. To our knowledge, this is the first time that a traveling wave cascaded topology has been demonstrated. Fundamentally, we believe this circuit can outperform any design based on traditional circuit topologies. (more...)

The present invention relates to a hearing device and, more particularly, to a device that can mechanically drive the ossicular chain while being located  in the ear canal. (more...)

Two novel alternative methods for modulating semiconductor lasers that enable much higher frequency modulation. (more...)

Without a distributed amplifier, most broadband amplifier bandwidths can be achieved around 1/10 to 1/3 of their fT only. Therefore, a high bandwidth amplifier requires high fT (at least 3-10 times of the amplifier bandwidth) transistors in order to achieve high bandwidth. Unfortunately, the current device technology is limited and in very high fT transistors, yield is still low. This leads to high cost and low yield.Even if high gain-bandwidth product could be achieved by a distributed amplifier, the major disadvantages of the distributed amplifier are large area, and high dc power consumption. Transistors were operated with high current density for high fT in order to achieve high bandwidth amplification. However, the transistors would become highly stressed resulting in reliability problems and short lifetimes. 50 ohm terminations are currently employed at the input and output of broadband amplifiers in order to obtain desirable input and output broadband impedance matches (low S11 and S22). However, the disadvantage is 3-dB losses at theirs inputs and outputs. (more...)

With the exception of light-based sensors, that change their light interaction properties, all sensors require some power in order to operate and provide a signal to a remote source. Light-based systems are readily blocked by typical obstructions such as buildings, trees, and vegetation. Some wireless systems require the use of on-board circuitry that temporarily charges up a battery or capacitor in the presence of an externally applied RF radiation, then use this electrical energy to re-transmit signal. This method is bulky, expensive, and can only transmit data at short distances. The need for a powered sensor/transmitter severely limits the deployment of such sensors in large scale such as over large geographic regions or as part of the civil infrastructure. (more...)

A new trend in wireless communications is to use multiple transmit and receive antennas such as those found in MIMO wireless systems, to attain higher data rate, better signal quality, and superior system flexibility. Transmit beamforming has been widely adopted for wireless systems with multiple transmit antennas. For a block fading channel, the Grassmannian beamformer has been shown to provide the best performance for given amount of feedback. However, the original Grassmannian beamformer does not take the time domain correlation of the channel fading into consideration. (more...)

Many space-time transmission schemes have been proposed recently to exploit the high channel capacity of MIMO communication systems. However, algorithms for a large antenna array (LAA) remain an open research problem. The standard channel estimation and space-time modulation schemes are not practical for LAAs due to high implementation complexity. (more...)

Ultra-Wide Band (UWB) wireless broadcasts are capable of carrying huge amounts of data up to 250 feet with extremely little transmit power and high immunity to interference and multipath fading. The spread spectrum characteristics of UWB wireless systems, and the ability of UWB wireless receivers to highly resolve the signal in multi-path fading channels make them a desirable wireless system of choice in a variety of high-rate, short- to medium-range communications. The ability of UWB systems to locate objects to within one inch is highly attractive to applications in the military, law enforcement and rescue agency realms. This UWB system approach is also pertinent to using active sensor networks and collision-avoidance. The circuit techniques that are used in a UWB transceiver are quite different from those used in current narrow bandwidth RF technology thus an incentive to design novel circuit topologies that achieve a gain-for-delay-tradeoff without affecting bandwidth and operating at substantially higher frequencies than conventional circuits. (more...)

In recent years, multiple-input multiple-output (MIMO) systems have proven to enhance data rate and provide robust signal reception under a variety of environmental settings. However, its employment of multiple antennas in turn require multiple branches of RF front ends resulting in increased power consumption and increased component costs. Additionally, with the advent of multi-band, multi-standard, and multi-mode radios in conjunction with MIMO techniques, the number of required RF front ends can greatly multiply. These factors provide the motivation to develop circuit techniques to maximize the reuse of components for different bands. (more...)

With advances of radio communication technology, various radio communication services available using wireless terminals such as mobile phones, personal digital assistants, personal computers, and notebook computers are under development. For example, Global System for Mobile communication (GSM), Personal Communication Services (PCS), World Interoperability for Microwave Access (WiMAX), Wireless Local Area Network (WLAN), Wireless Broadband Internet (WiBro), and Bluetooth. The GSM uses 890~960 MHz band, the PCS uses 1.8 GHz band, and the WiMAX uses 3.6~3.8 GHz band. The WLAN uses 2.4 GHz band which is Industrial, Scientific & Medical (ISM) band in IEEE 802.11b, and 5 GHz band which is Unlicensed National Information Infrastructure (UNII) in IEEE 802.11a. The Wibro uses 2.3 GHz band and the Bluetooth uses 2.4 GHz.To overcome this problem, a reconfigurable antenna system would be advantageous not only to receive various wireless communication services on the single antenna, but also to use the services at the same time. (more...)

Radio antennas must maintain their paraboloid shape and directional positioning in order to work properly. However wind can load the antenna dish and cause it to lose its shape and position. To address this situation, researchers at UC Berkeley have developed a support system that strengthens antenna dishes and provides several structural enhancements. The support system consists of reinforcements that enable firm radial and torsional support as well as an optimal amount of axial flexibility and support. This design allows for a large open area so that azimuth and elevation-bearing systems can be positioned near to the reflector vertex. This positioning enables lower loads and less structural requirements for the pedestal and drives. (more...)

The performance of radio antennas can be degraded from interference caused by thermal radiation as well as signals traveling along the ground and reflected by the ground. To minimize these sources of interference, researchers at UC Berkeley have developed design enhancements for radio antennas. These refinements minimize thermal background noise as well as low radio frequency interference, and they don?t intercept radiation along the symmetry axis of the antenna, or any rays that reach the feed (detector). (more...)

The image processing of synthetic aperture radar (SAR) can be used to capture extremely high-resolution images. Corner turners are the signal-processing devices used to perform these data-intensive operations. Current corner turners require huge amounts of memory and consequently are expensive. An alternative corner turner based on custom, programmable chips has been proposed, but it is also expensive. To address this issue, researchers at UC Berkeley have developed a novel design for a corner turner that doesn?t rely on memory to perform the voluminous transpose operations. In comparison to the alternative approaches, this highly efficient Berkeley corner turn is less expensive. (more...)

Log-periodic antennas provide the frequency independent performance that is necessary for applications in which large portions of the electromagnetic spectrum are scanned. However, the high frequency limit of these antennas is restricted because their amplifiers must be located far from the feed vertex so that they don?t interfere with radiation patterns ? and this in turn requires a long transmission line that results in unacceptable performance degradation. To address these issues, researchers at UC Berkeley have developed a non-planar log-periodic antenna that improves performance through several design refinements that include the ability to place an amplifier within the antenna. Small microwave telescopes that incorporate these design improvements can achieve unprecedented A/T over multi-octave bandwidths. In comparison to previous log-periodic antennas, this Berkeley design improves the gain, polarization purity, and transmission line losses. The antenna is capable of concurrent transmission or reception of two orthogonal polarization modes, and it includes elements that decrease the amount of cross-polarization coupling that occurs between the arms of the antenna. Moreover, this design also allows for the attachment of cryogenic electronics to enhance signal sensitivity and the performance of low noise amplifiers. (more...)

Due to several inherent advantages of VCSEL devices, such as their ability to form densely packed arrays, on-wafer testing, and low power consumption, VCSELs offer a lower cost alternative to traditional edge-emitting lasers and improved performance over light emitting diodes (LEDs). Until the development of the present invention, (Ga,In,Al)N VCSELs only existed as optically pumped structures. Such structures require the implementation of large and costly pumping lasers, which limits their practical and commercial utility. (more...)

In data networks employing optical time-division multiplexing (OTDM), each network node must carry out a number of key functions in order to efficiently process an optical signal that is modulated with both a data stream and timing signals. In particular, the processing of each channel within the signal requires simultaneous demultiplexing, packet add/drop, clock recovery and synchronization, and data stream regeneration. At present, incorporating all of these functions into an optical network node poses severe trade-offs between hardware complexity and cost on one hand and problems of channel ambiguity and cross-talk on the other. (more...)

In multi-user communication over linear, dispersive, and noisy channels, the received signal is composed of several transmitted signals corrupted by inter-symbol and inter-user interference and noise. Multi-user detection techniques for multi-input multi-output (MIMO) systems present significant advantages over single user detection techniques that treat inter-user interference as additive color noise and lump its effects with thermal noise. Such previous techniques have proven costly to implement for multi-user detection on severe-inter-symbol interference channels. In addition, current methods lack practical MIMO receivers with feedforward and feedback finite impulse response (FIR) filters whose coefficients can be computed in a single computation in real-time under various MIMO detection scenarios.  (more...)

Vertical-cavity surface-emitting lasers (VCSELs) at 1.55 micrometers are important in telecommunications networks. However, the absence of a substrate that is suitable for both technologically developed distributed Bragg reflectors (DBRs) and quantum well active regions has hindered the development of these devices. Several groups have attempted to overcome mirror limitations on InP substrates by examining AlGaAsSb-based DBRs. The high-index contrast of these DBRs leads to a lower penetration depth than that seen in traditional InGaAsP-based DBRs, which implies a lower optical loss in the structure. However, only optically-pumped VCSELs using such DBRs have been have been demonstrated.  DESCRIPTION: Scientists at the University of California have developed a single-growth, room temperature, electrically pumped 1.55 micrometer VCSEL. (more...)

Vertical-cavity surface-emitting lasers (VCSELs) are a new class of semiconductor lasers that are used in many optoelectronic applications. VCSELs have optical cavities that are perpendicular to substrate, as opposed to conventional edge-emitting lasers that emit light in a direction parallel to the semiconductor substrates. As a result, VCSELs emit optical radiation in a direction perpendicular to the substrate, which leads to various performance and application-adaptable improvements. Although both short and long wavelength VCSELs have provided solutions for many evolving optical applications, certain drawbacks exist, such as the need to electrically pump and conduct heat through the multilayer mirror stacks. In addition, the mirror stacks themselves have demonstrated limited thermal conductivity and excessive optical loss. Double-intracavity contacted VCSELs minimize or overcome these complications. (more...)

Vertical-cavity surface-emitting lasers (VCSELs) have demonstrated great promise as low-cost components in high-speed transceivers. Although they have been successful for shorter wavelength (850nm) systems, problems with excessive resistance and temperatures have limited the capabilities of these lasers in systems requiring wavelengths of 1.55 micrometers. (more...)

The vertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser diode for long wavelengths that is becoming a popular choice for high-performance components for optical fiber networks. The VCSEL emits a laser beam vertically from the top surface of a wafer and is quickly replacing the conventional edge-emitting semiconductor lasers. Several advantages VCSELS have over edge-emitters include: VCSELs can be tested at several stages throughout the production process unlike edge-emitters, the VCSEL structure can be integrated in two-dimensional array configurations, several thousand VCSELs can be produced on a single GaAs wafer, and the yield of VCSEL production is much more controllable all of which leads to higher performance at lower cost. Other current applications for VCSELs include analog broadband signal transmission, absorption spectroscopy, and any number of fiber optic communication devices. (more...)

Multicast communication generalizes the unicast (point-to-point) and broadcast (one-to-all) communication models in computer networks to multipoint dissemination of messages. A source only needs to send packets once to the network interface and from there they are transparently replicated on their transmission paths to the receivers. This method is indispensable for high-volume data transfer applications, such as distributed software updates, newscasts, on-demand video, and telecollaboration systems. However, when the multicasting concept is adapted and deployed with IP multicast protocols in the Internet, those systems cannot provide reliable or order-preserving delivery of packets to a multicast group. As a result, there is no guarantee that all of the packets sent from a source to a group of receiving hosts are disseminated without error or that the consistency and coherence of the data has been preserved. (more...)

Collaborative Multimedia Applications (CMA) allow users to share information and efforts in real-time and are becoming increasingly popular for group telecollaboration across wide-area networks. Although reliable multicasting has improved in recent years, many fundamental coordination problems limit the widespread sharing of virtual workspaces. The resulting consequences, such as flawed telepresence, mutual awareness coordination problems, speech initiation conflicts, and diminished interaction, can be remedied by an effective mediation protocol. (more...)

Current medium-access control (MAC) protocols for wireless networks are based on collision-avoidance handshakes between sender and receiver. Most of these systems are based upon a sender-initiated handshake, in which the sender uses a short control packet to ask the receiver for permission to transmit and then only transmits if the receiver sends a clear-to-send notification. However, under high-traffic conditions, an influx of control packets can adversely affect the network. (more...)

Present Internet applications are likely to operate over paths that either exhibit a high degree of asymmetry or appear asymmetric due to significant load on the reverse data path. Under such conditions, the transmission control protocol (TCP) method of counting messages that acknowledge correctly received data (ACKs) results in significant underutilization of the link with higher capacity due to loss of ACKs on the slow link. In addition, ACK loss leads to outbursts of data traffic on the forward path. As a result, networks need an improved congestion control algorithm that is resilient to ACK loss. (more...)

Business activities are increasingly being conducted via the Internet. These applications, such as financial services, securities exchanges, and emergency services will require reliable Internet connectivity. On-demand routing protocols provide this reliability by allowing for multiple links with separate gateway links to the Internet. However, current systems are subject to the counting-to-infinity problem, which can decrease network performance. For example, when a destination fails or becomes unreachable from a network component, a source trying to obtain a path to the destination finds that its flood-search for the destination fails. It is unable to determine the mode of failure and may continue to repeat a search for an unreachable destination, which causes congestion due to the repeated queries. As a result, current systems require external mechanisms to stop sources from sending unnecessary queries. However, difficulties in these systems arise in determining the length of hold-down times and how many times a source should persist in requesting a destination path. (more...)

Medium-access control (MAC) protocols based on collision avoidance have become increasingly important over the past few years due to their simple applicability to wireless local-access networks (LANs) and ad-hoc networks. In traditional collision-avoidance protocols, the transmitting node first sends a request-to-send (RTS) packet to the receiver, which, if it receives this RTS correctly, responds with a clear-to-send (CTS) signal. In this system, a sender can transmit a data packet only after successfully receiving a CTS. However, to prevent data packets from colliding with other packets at the intended receivers in networks with a single channel, the senders must sense the channel before sending the RTS. This carrier sensing or assignment of unique codes to nodes ensures that the intended receivers hear data packets without interference from hidden sources. However, this can limit the applicability of these systems because the senders and receivers must find each other's codes before communicating with one another. (more...)

Wafer fusion is a powerful technique for fabricating structures that cannot be realized by conventional epitaxial growth and processing. Wafer fusion provides an extra degree of freedom in the design and fabrication of 3-D photonic devices. Large switch arrays can be produced by displacing the input and output waveguides vertically in different planes. Compact high-extinction-ratio directional couplers are essential to the switching process. (more...)

VCSELs (vertical-cavity surface-emitting lasers) capable of emitting long wavelengths are of interest in optical communication systems. Unfortunately, for a given wavelength, materials ideal for the formation of the gain region of a VCSEL are not always ideally suited for formation of the mirror regions of the VCSEL. Currently, the mirror designs for these lasers tradeoff decreased performance in the gain region for increased mirror reflectivity. Also, conventional designs are subject to poor electrical and thermal conductivity of the mirror regions that can result in overheating, negatively impacting device performance characteristics. (more...)