Showing papers on "Telecommunications link published in 1992"

In transit detection of computer virus with safeguard

Abstract: Data is tested in transit between a source medium and a destination medium, such as between two computer communicating over a telecommunications link or network. Each character of the incoming data stream is tested using a finite state machine which is capable of testing against multiple search strings representing the signatures of multiple known computer viruses. When a virus is detected the incoming data is prevented from remaining on the destination storage medium. Both hardware and software implementations are envisioned.

Wireless telephone/satellite roaming system

Abstract: A wireless telephone system capable of servicing a roaming wireless telephone user includes a satellite communications system consisting of one or more orbiting satellites, each carrying a database of users, destination codes and call codes, within a satellite service area, a satellite control center, and a plurality of terrestrial communications links. The system operates by effecting communication between a terrestrial wireless telephone end user transceiver apparatus and a terrestrial communications link via a single relay through a single satellite or a succession of satellites wherein the relay station may be in motion relative to the end user transceiver apparatus and the terrestrial communications link, wherein the orbiting relay station effects the ultimate decision on linking based on stored on-board information and on-board processing, and wherein the end user transceiver apparatus, the orbiting satellite and the terrestrial communications link are operative in cooperation with the on-board database to effect hand-off from a first orbiting satellite to a second orbiting satellite. The satellite system is a single satellite or preferably a constellation of satellites orbiting near the earth, all of which are capable receiving requests for calls and participating in the call routing and call setup on an autonomous basis. The satellites are capable of decoding the calls, switching, handing off of calls to other satellites, and updating databases of users based on information provided by network control.

SIR-based power control in a CDMA system

Abstract: Power control in the use of direct-sequence code-division multiple-access (CDMA) techniques is addressed. Previous performance analyses of CDMA wireless mobile and personal communications have assumed the ability of power control to equalize the absolute signal powers of users received at each base station. A more practical, although analytically more complicated, uplink power controls technique that uses measurements of the received signal-to-interference ratio. (SIR) instead is studied. A combination of discrete-event link simulation and analysis of the obtained SIR statistics is used to explore the behavior of a CDMA system using SIR-based power control and to obtain performance estimates for such a system under various operating assumptions. The overall results indicate that power control based on SIR has the potential for somewhat higher system performance than power control based on absolute signal strength. >

In-store advertising system

Abstract: An in-store advertising system for displaying advertisements involves preparing graphical art from the actual products or from flat art, for each advertised product. Each frame is stored in computer memory as a digital graphics file. As desired, pricing and advertising copies are added as overlays to the digital art of each frame. Control data is defined for each frame indicating its destination location(s) and the run time for each destination location. The digital graphic files containing a digital frame and the respective control data for each frame are then loaded into an uplink control computer. The control data is analyzed by the uplink computer to compute an adlist which lists the digital frames and their respective destination locations. The uplink control computer is interfaced to a satellite addressable network control system (ANCS) to unmute the desired satellite receiver(s) at the remote location(s), based upon a predefined transmission script. The uplink computer then transmits the respective graphic files, control data and adlist via a satellite transmitter to a commercial broadcasting satellite. The remote receivers display the graphic data based on the code data.

Analysis of a multiple-cell direct-sequence CDMA cellular mobile radio system

Abstract: The performance of a multiple-cell direct-sequence code division multiple-access cellular radio system is evaluated. Approximate expressions are obtained for the area-averaged bit error probability and the area-averaged outage probability for both the uplink and downlink channels. The analysis accounts for the effects of path loss, multipath fading, multiple-access interference, and background noise. Two types of differentially coherent receivers are considered: a multipath rejection receiver and a RAKE receiver with predetection selective combining. Macroscopic base station diversity techniques and uplink and downlink power control are also topics of discussion. >

Switch for serial or parallel communication networks

Abstract: A communication switch apparatus and a method for use in a geographically extensive serial, parallel or hybrid communication network linking a multi-processor or parallel processing system has a very low software processing overhead in order to accommodate random burst of high density data. Associated with each processor is a communication switch. A data source and a data destination, a sensor suite or robot for example, may also be associated with a switch. The configuration of the switches in the network are coordinated through a master processor node and depends on the operational phase of the multi-processor network: data acquisition, data processing, and data exchange. The master processor node passes information on the state to be assumed by each switch to the processor node associated with the switch. The processor node then operates a series of multi-state switches internal to each communication switch. The communication switch does not parse and interpret communication protocol and message routing information. During a data acquisition phase, the communication switch couples sensors producing data to the processor node associated with the switch, to a downlink destination on the communications network, or to both. It also may couple an uplink data source to its processor node. During the data exchange phase, the switch couples its processor node or an uplink data source to a downlink destination (which may include a processor node or a robot), or couples an uplink source to its processor node and its processor node to a downlink destination.

Fully meshed cdma network for personal communications terminals.

Abstract: A network of personal communications terminals (10), also called pico terminals, communicating in CDMA mode includes a reference station for transmitting a pilot tone that is pre-corrected at the reference and is used at the remaining stations for frequency control, transmit power control, and antenna acquisition and tracking. All pico terminals (10) are in the same uplink beam (12) and downlink beam (14). Each pico terminal (10) is given a unique PN code for receiving signals intended for receipt by that terminal. Voice activation is used for sharing the satellite transponder power and bandwidth in a fully Demand-Assignment-Multiple-Accessing (DAMA) manner. Uplink power control is used to mitigate the CDMA near-far problem.

Performance limitations of TDD wireless personal communications with asynchronous radio ports

Abstract: A wireless personal communications system, based on a TDMA architecture, using asynchronous ports (radio base stations) and the TDD (time division duplexing) method is evaluated using computer simulations. It is shown that, without port synchronisation TDD methods cannot achieve the uplink quality obtainable by the FDD (frequency division duplexing) method.

Performance issues and algorithms for dynamic channel assignment

Abstract: Performance issues and algorithms for dynamic channel assignment (DCA) in a time division multiple access (TDMA) portable radio system are considered. With DCA, a radio port can use any carrier frequency in any available time-slot to set up a radio link with a portable. The portable selects a radio port prior to channel assignment for initial access or link transfer. Port and portable together determine the proper combination of time-slot and carrier frequency. Once established, a radio link remains unchanged until a call is completed or a link transfer occurs. Some limitations of DCA, such as difficulty in providing beacon signals, blind slots, frequency switching speed requirements, assignment delay and failures, and synchronization requirements, diminish its perceived advantages. Since uplink and downlink radio channels experience different interferences, asymmetric performance can occur. An algorithm that improves the balance of two-way performance is proposed. However, performance trade-offs inherent in DCA limitations still need to be addressed. >

Simultaneous cancellation of cross interference and ISI in CDMA mobile radio communications

Abstract: In this paper, data estimation in the uplink of a synchronous mobile radio system applying CDMA is considered. In mobile radio systems applying CDMA, multipath propagation leads on the one hand to ISI and on the other hand, together with time-variance, to cross interference between the signals of different users, regardless whether the user codes are chosen orthogonal or not. A linear unbiased data estimation algorithm is presented which cancels both ISI and cross interference perfectly by jointly detecting the different user signals, thus leading to unbiased estimates of the transmitted data symbols. This algorithm is less complex than MLSE performed e.g. by the Viterbi algorithm and furthermore, the complexity does not depend on the kind of the applied linear modulation scheme, which opens a simple way to offer services with different data rates in one system. By theoretical analysis and simulation, the performance of the unbiased data estimation algorithm is examined under the assumption that the radio channel impulse responses are known at the receiver. The price to be paid for the interference cancellation is SNR-degradations, which are calculated for typical mobile radio situations in urban areas. The resulting average uncoded bit error probabilities lead to the conclusion that systems applying the unbiased data estimation algorithm are well-suited for mobile radio applications. >

Uplink null intrusion rejection for satellite communications systems

Abstract: A satellite communications system includes a feed array and reflector receiving antenna coupled to a dual-mode network, for generating two channels, with independent signals representing two beams, one for each channel. Each output channel of the dual-mode network contains redundant information relating to a plurality of information channels. In the absence of an interfering signal or intrusion, the combined signals are amplified and block frequency-converted, then de-multiplexed into separate channels, which are each applied through selection switches to a transmitter multiplexer for retransmission. An alternate signal is tapped from each of the two received signal channels, phase controlled, and combined, to produce a combined signal representing a receive antenna beam with a null controllable in position in response to phase. The combined signal is demultiplexed into separate information channels. In the presence of an intrusion in one of the channels, the selection switch for that channel is set to an alternate position, in which the alternate signal is selected for transmission. Since the alternate signal includes a null in the receive beam, the position of the null may be set to the location of the intrusion signal to suppress the signal.

The Autonomous Data Optical Relay Experiment: first two way laser communication between an aircraft and submarine

Abstract: The Autonomous Data Optical Relay Experiment (ADORE) was held at the Sea Test Range of the Pacific Missile Test Center off the coast of Southern California near San Nicolas Island during May 22-24 and May 28, 1991. The optical communication system operated with a green downlink based on a diode-pumped frequency-doubled Nd:YAG transmitter communicating with a quartz birefringent filter receiver and a blue uplink using an alexandrite laser wavelength shifted to the 455-nm doublet of cesium vapor sending information to a cesium filter receiver. Major achievements of the test included: first duplex laser communication with a submerged submarine; uplink initiated duplex laser communication from a submarine; demonstration of technologies which offer substantially higher performance at lower cost and risk compared with earlier efforts; extending the range and utility of laser communication by error correction coding and pulse summing; and establishing and experimental baseline for developing and investigating covert laser communication with submarine. >

Improved gsm interference band selection and reduced power handover

Abstract: A method is offered of achieving a desired C/I ratio within a cellular system, at reduced transmitter power levels, by measuring a signal loss on a downlink between a base site transmitter (31) and mobile receiver (20) and calculating an uplink signal magnitude at a base site receiver A communication channel is then selected from a number of communication channels based upon comparison of the uplink signal magnitude with pre-measured interference levels of each channel of the number of channels to produce a desired C/I ratio

Capacity evaluation of cellular CDMA

Abstract: The paper is concerned with the capacity of a cellular code division multiple access (CDMA) system in Rayleigh fading with log-normal shadowing. The capacity in terms of the number of users per cell per Hz is shown to be very sensitive to assumed values of various parameters. CDMA capacity is shown to be possibly greater than the proposed TDMA capacity under certain assumptions and vice versa under others. An asymmetry between the uplink and downlink capacities in CDMA is shown based on the finding that the uplink intracell interference power is only half of that in the downlink. >

Rain compensation algorithm for ACTS mobile terminal

Abstract: The initial advanced communication technology satellite (ACTS) mobile terminal (AMT) demonstrations will involve two-way communications between the high-bit-rate link evaluation terminal (HBR-LET), which is a fixed terminal (FT), and a van-housed mobile terminal (MT). The HBR-LET has the capability of adjusting its transmitted uplink power over an approximately 10 dB range to compensate for forward uplink rain attenuation. However, because of size and weight limitations, the MET cannot use power control as a rain compensation technique. Consequently, the AMT rain compensation algorithm (RCA) is based on a formula for varying the transmitted data rate in either direction to maintain link performance within acceptable limits. The objective of the AMT RCA is to ensure reliable operation in both the forward and return directions despite the possibility of uplink or downlink fading due to rain events in the vicinity of the FT or MT. In particular, the RCA must maintain at least a 3 dB link margin at the highest possible transmission rate (AMT can operate at 9.6, 4.8, or 2.4 kb/s) permitted by the prevailing channel conditions. The 3 dB minimum link margin is a system design safety factor to accommodate conceivable implementation losses. >

Analysis of a new multiaccess/switching technique for multibeam satellites in a prioritized ISDN environment

Abstract: A performance analysis to compute the packet loss, call blocking, and packet delays of a typical user in an integrated voice-data-video satellite internetworking environment is discussed. The uplink technique used is a hybrid packet/circuit switched approach of the demand assignment type, while the downlink is a time-division-multiplexing (TDM) technique. Onboard the satellite, a baseband nonblocking switch is used to route the packets from input to output ports. Various amounts of input and output buffering as well as priority rules and blocking resolution algorithms are used. The authors conduct a performance analysis for the problems at hand and identify the best ranges for the different parameters involved. >

Simultaneous TDMA communication system

Abstract: A network of satellites delivers communications through bi-directional communication links between individual ones of the satellites. Each satellite terminates a plurality of links. All satellites are synchronized to recognize a constant duration frame structure. For each link in the network, satellites at both ends of the link simultaneously transmit data communications into their respective ends of the link using the same frequency band. Transmissions into all links supported by a satellite occur simultaneously. The transmissions continue for a duration that is responsive to the distance between the satellites. Transmissions cease for all links supported by a satellite when the communications from the opposing link nodes have nearly propagated the entire distances between the satellites. After ceasing transmissions, each satellite receives the communications previously transmitted from the opposing satellites into the links therebetween.

A study on diversity techniques in a 5.8 GHz microwave link for traffic management systems

Abstract: Future traffic management systems require a bidirectional communication between roadside beacons and vehicles. Several studies are concentrated on a short range microwave link for this application. Multipath fading effects, due to reflections on the road, vehicles or buildings, may interfere with the communication. In this paper, antenna and frequency diversity techniques are considered for a solution of the multipath fading problem. The results demonstrate that an efficient improvement of the link performance can be achieved. >

The effects of port synchronization on TDMA personal communications for two duplexing methods

Abstract: The effects of synchronous ports on the signal-to-interference ratio (SIR) in an interference-limited time-division multiple access (TDMA) personal communications system for both the time-division duplexing (TDD) and frequency-division duplexing (FDD) methods are evaluated using computer simulations. It is quantitatively shown that if the port transmissions are synchronized, both duplexing schemes perform equally well, but TDD requires port synchronization to achieve reasonable uplink quality. A system-wide port synchronization in a large service area where the ports are widely distributed may be difficult to implement economically and reliably. >

Hybrid signaling for the air interface for a wireless access communications system

Abstract: A hybrid signaling scheme is proposed for wireless access communications systems for fixed wireless access (FWA) and to support an interface to service providers who may wish to offer personal communications systems (PCS) applications to the end users This scheme is effectively made up of 5 physical signaling channels These channels comprise a dedicated time slot for alerting, an unprotected downlink bit per frame per time slot for power control, 9 out-of-band bits per frame per time slot for associated signaling, 14 downlink bits for synchronization and in-band signaling using the 64 bearer bits per frame In addition to the alerting function the dedicated time slot will also be used for emergency 911 alerting, blocked port notification, broadcast messages and service provider identification >

A multirate digital multicarrier demodulator: design, implementation, and performance evaluation

Abstract: Frequency-division multiple access (FDMA) and single channel per carrier (SCPC) in the uplink and time-division multiplexing (TDM) in the downlink are employed in the system described. To interface FDMA in the uplink and TDM in the downlink, multicarrier demodulation (MCD) is required onboard the satellite. The operation of the onboard MCD is the separation of each individual channel and subsequent demodulation. The results, which concern onboard frequency demultiplexing and demodulation for low-bit-rate carriers, are constrained by the requirement that new-generation payloads could serve the stations already active in the INTELSAT Business System. A digital hardware design that implements an MCD that can process three channels at 4.4 Mb/s or 12 channels at 1.1. Mb/s is described. The test results confirm the MCD feasibility, and further improvements are expected from a semicustom implementation. >

System architecture for an advanced Canadian communications satellite demonstration mission

Abstract: This paper describes an advanced communications satellite system that provides single hop interconnectivity and interworking for both an advanced private business network (APBN) and a personal communications network (PCN) in the Ku and Ka bands respectively. The discussion of the system architecture highlights the following key system features: . on board processing including self-routing fast packet switching and some aspects of network control . APBN MF-TDMA uplink with a hybrid access protocol that combines random and reservation ALOHA access . system (symbol) synchronous operation It will be shown that a satellite system design that comprises the above features can dynamically establish links and efficiently allocate the satellite resource amongst the user terminal population for a mix of voice and data traffic. An overall network perspective is given that examines the interface of such an advanced satcom system to the terrestrial network in the context of the OSI model.

Multiplexing on the downlink of a TDMA-based radio system

Abstract: The author addresses signal multiplexing on the downlink of a TDMA-based radio system This issue was addressed through the comparison of two candidate techniques, TDM and TDMA The multiplexing method is important to call setup and link transfer times, co-channel interference, and implementation complexity The effects differ from an outdoor, local exchange application, to an indoor private application The study shows that the outdoor, local exchange application is best served by a TDM downlink, while certain indoor business applications may best be served by a TDMA downlink >

Bit error measurements on a 5.8 GHz mobile radio channel for short range traffic management systems

Abstract: To investigate the performance of a planned short range traffic management system with data rates more than 1 Mbit/s in case of multipath effects, an experimental system has been built. Bit error properties are investigated by recording transmitted pn-sequences in real time and off-line analysis using correlation techniques. Measurement results regarding the dependence of bit errors and clock errors on the covered distance are presented for the downlink. The results show that a sufficient range of about 25 m is achievable for synchronous data transfer. >

Terminal for use in a data communications network

Abstract: Methods and apparatus are set forth which enable a data communications network (1) to perform decentralised uplink network control functions (decentralised away from the centralised general communications controller (GCC) level of the network hierarchy); (2) to minimise, or in some cases eliminate, the overhead expended in making power lever (signal strength) determinations and assessments at both the GCC and base station levels of the network hierarchy (for the purpose of managing uplink communications); and (3) to allow individual subscriber radios (terminals) to dynamically determine the most desirable base station to communicate with when exchanging information a host computer via a shared RF communication channel (the link between a terminal and the base station). Additionally, an illustrative radio frequency data communication network, built in accordance with the teachings of the invention as a modified version of an existing network, is described where the modified network incorporates the aforementioned methods and apparatus.

A variant of the CSMA protocol suitable for a mobile radio LAN

Abstract: A variant of the carrier sense multiple access (CSMA) protocol known as idle-signal casting multiple access (ICMA), which is suitable for use in a mobile radio LAN where the effect of multipath signal fading on the performance of the protocol is not insignificant, is described and analyzed. The analysis differs from previous work in that the model incorporates specifically the effects of signal fading on channel access and packet transmission. Numerical results, which are validated by simulation results, are obtained using a realistic example to permit a quantitative study of the performance of the protocol. >

Low Earth-orbit store-and-forward satellites in the amateur radio service

Abstract: The authors review the current state of the art in amateur radio store-and forward satellite communications. Several operating satellite systems are described along with the procedures, equipment, and software required to access them. For PACSAT-1 empirical data have been used to estimate a downlink bit error probability of 6.0E-5. A further description of downlink performance is given through the examination of data-link layer frame retry rates encountered during file downloading operations. Typical examples of characteristics of downlink signal fading are given for PACSAT-1. A breakdown of downlink usage by data type is given for PACSAT-1. To show how the PACSAT-1 and UoSAT-5 satellites are utilized on a day-to-day basis, graphical summaries of two weeks of PACSAT-1 and three weeks of UoSAT-5 operation are included. >