Showing papers by "Qualcomm published in 1994"

Mobile station assisted soft handoff in a CDMA cellular communications system

Abstract: In a code division multiple access (CDMA) spread spectrum cellular communication system in which a mobile station user communicates with another system user via at least one base station, wherein each base station transmits a common pilot signal of a different code phase with respect to other base stations in said system, a method for directing communications between said mobile station user and said base stations. The mobile station monitors the signal strength of pilots and reports the measured signal strength to a system controller via the base station through which it is communicating. Command messages from the system controller to a new base station and the mobiles station establishes communication through the new base station in addition to the communication through the current base station. When the mobile station detects the falling below a predetermined level of the signal strength of a pilot corresponding to at least one of the base stations through which the mobile station is communicating, the mobile station reports the measured signal strength indicative of the corresponding base station to the system controller via the base stations through which it is communicating. Command messages from the system controller to the identified base station and the mobiles station terminates communication through the corresponding base station while communications through the other base station or base stations continue.

Soft handoff extends CDMA cell coverage and increases reverse link capacity

Abstract: The effect of handoff techniques on cell coverage and reverse link capacity is investigated for a spread spectrum CDMA system. It is shown that soft handoff increases both parameters significantly relative to conventional hard handoff. >

A motion planner for nonholonomic mobile robots

Abstract: This paper considers the problem of motion planning for a car-like robot (i.e., a mobile robot with a nonholonomic constraint whose turning radius is lower-bounded). We present a fast and exact planner for our mobile robot model, based upon recursive subdivision of a collision-free path generated by a lower-level geometric planner that ignores the motion constraints. The resultant trajectory is optimized to give a path that is of near-minimal length in its homotopy class. Our claims of high speed are supported by experimental results for implementations that assume a robot moving amid polygonal obstacles. The completeness and the complexity of the algorithm are proven using an appropriate metric in the configuration space R/sup 2//spl times/S/sup 1/ of the robot. This metric is defined by using the length of the shortest paths in the absence of obstacles as the distance between two configurations. We prove that the new induced topology and the classical one are the same. Although we concentrate upon the car-like robot, the generalization of these techniques leads to new theoretical issues involving sub-Riemannian geometry and to practical results for nonholonomic motion planning. >

Other-cell interference in cellular power-controlled CDMA

Abstract: An improved series of bounds is presented for the other-cell interference in cellular power-controlled CDMA. The bounds are based on allowing control by one of a limited set of base stations. In particular, it is shown that the choice of cellular base station with least interference among the set of N/sub c/>1 nearest base stations yields much lower total mean interference from the mobile subscribers than the choice of only the single nearest base station. >

Dual distributed antenna system

Abstract: A distributed antenna system (30, 35) is utilized in a communication system for providing multipath signals which facilitate signal diversity for enhanced system performance. Each node (200) of the antenna system (30, 35) comprises more than one antenna (196). Each antenna (196) at a common node (200) provides a path having a different delay to the base station (100).

Distributed voice recognition system

Abstract: A distributed voice recognition system includes a digital signal processor (DSP)(104), a nonvolatile storage medium (108), and a microprocessor (106). The DSP (104) is configured to extract parameters from digitized input speech samples and provide the extracted parameters to the microprocessor (106). The nonvolatile storage medium contains a database of speech templates. The microprocessor is configured to read the contents of the nonvolatile storage medium (108), compare the parameters with the contents, and select a speech template based upon the comparison. The nonvolatile storage medium may be a flash memory. The DSP (104) may be a vocoder. If the DSP (104) is a vocoder, the parameters may be diagnostic data generated by the vocoder. The distributed voice recognition system may reside on an application specific integrated circuit (ASIC).

Mobile users: to update or not to update?

Abstract: Tracking strategies for mobile users in wireless networks are studied. In order to save the cost of using the wireless links mobile users should not update their location whenever they cross boundaries of adjacent cells. The paper focuses on three natural strategies in which the mobile users make the decisions when and where to update: the time-based strategy, the number of movements-based strategy, and the distance-based strategy. The authors consider both memoryless movement patterns and movements with Markovian memory along a topology of cells arranged as a ring. They analyze the performance of each one of the three strategies under such movements, and show the performance differences between the strategies. >

Method and apparatus for determining the transmission data rate in a multi-user communication system

Abstract: A method and apparatus are described for controlling the data rates for communications to and from a base station and a plurality of remote users. The usage of the communications resource whether the forward link resource (from base station to remote users) or reverse link resource (from remote users to base station) is measured. The measured usage value is compared against at least one predetermined threshold value and the data rates of communications or a subset of communications on said communications resource is modified in accordance with said comparisons.

Demodulation element assignment in a system capable of receiving multiple signals

Abstract: In a receiver having a plurality of demodulation elements (204A, 204B, 204C), a method of assigning the plurality of demodulation element to a set of available signals. A first method emphasizes diversity of transmitting devices so that power control is optimal. A second method emphasizes the maximum signal strength available to produce aggregate maximum signal strength. Both methods control the number of reassignments so that excessive data is not lost during the reassignment process. The apparatus comprises the plurality of demodulation elements (204A, 204B, 204C), at least one searcher element (202), and a controller (200).

Multirate serial viterbi decoder for code division multiple access system applications

Abstract: A Viterbi decoder (20) for recovering the original bit data stream that was convolutionally encoded as a code symbol stream in a Code Division Multiple Access (CDMA) mobile communication system (22). The decoder (20) simultaneously decodes at the several data rates associated with certain multirate vocoders. The decoder (20) can decode at an unknown data rate in either continuous or framed packed modes. It accomplishes this by simultaneously decoding at multiple rates and by creating one or more data quality metrics for each decoded data packet. Special input and output buffering is provided to isolate the decoder (50) from system timing constraints. The input buffer (48) includes selection and accumulation logic to organize code symbol data into the packet order for repeat mode or random burst mode at lower frame data rates. Decoded data packets for each of several predetermined data transfer rates are held in an output buffer (54) for about half of the decoding cycle, thereby permitting the system microprocessor to examine and select the appropriate decoded data packet. The decoder (50) also can be reconfigured to operate at any one of several predetermined convolutional encoding algorithms. The Viterbi decoder (20), implemented as a single monolithic integrated circuit, can be used in any and all of many different multiuser telecommunications channels.

Method and system for the dynamic modification of control parameters in a transmitter power control system

Abstract: In a communication system in which direct sequence spread spectrum modulation techniques are used, interference is generated in communications by remote stations since the communications share the same frequency spectrum. In order to increase system capacity the power level of the remote station transmitters are controlled by the local station. A setpoint in generated at the local station by a power control processor (118) and compared by a comparator (120) with the remote station signal strength measured at the local station by a power averager (114). The result of this comparison is used to generate power level adjustment commands by a command generator (122) which are transmitted to the remote station. The remote station is responsive to the power level adjustment commands for increasing or decreasing remote station transmitter power. In a spread spectrum communication system in which data is encoded at variable data rates, the local station determines via a rate determination processor (116) the rate at which received data was encoded by the transmitting remote station. The data is decoded by decoder (112) at each possible rate with error metrics generated that are representative of the quality of the data decoded at each rate. A rate decision algorithm is used by processor (116) to evaluate the error metrics and make a decision on the rate at which the data was transmitted. A pattern match of rate decisions is used by processor (118) to modify a setpoint so as to closely control the transmitting power of the remote station as a function of the quality of the received data.

Fast forward link power control in a code division multiple access system

Abstract: The power control process of the present invention enables a mobile radiotelephone to continuously update the base station on the power output required. The base station sends a frame to the mobile at a particular rate. If the mobile received and decoded the frame correctly, it sets a power control bit in the next frame to be transmitted to the base station. Based on the error rate of the received power control bits, the base station determines whether to increase or decrease the transmit power.

Method and apparatus for performing handoff between sectors of a common base station

Abstract: A method and apparatus providing softer handoff of a mobile unit (90) between sectors (50, 70 and 80) of a common base station (60). A sectorized base station (60) comprises a set of demodulation elements (240A-204N). Each demodulation element (240A-204N) may be assigned to a signal from one of a plurality of sectors. The output of the demodulators (240A-204N) are combined before the decoding process independent of the sector from which the data originated. This configuration provides improved output data reliability, more stable power control, and more efficient use of resources at the base station.

Method and apparatus for handoff between different cellular communications systems

Abstract: A method and system for performing an intersystem handoff of communication with a mobile station between base stations of first and second cellular systems is disclosed herein. At the mobile station, a quantifiable parameter of a signal transmitted by a second base station of the second system is measured. When the measured value of the quantifiable parameter passes through a first predetermined level, the mobile station communicates a signal quality message via a first base station of the first system to a first mobile switching control station. A channel request message is then communicated from the first mobile switching control station to a second mobile switching control station within the second system. At the second base station, a quantifiable parameter of the signal received from the mobile station is also measured. The second base station establishes communication with the mobile station when the measured value of the quantifiable parameter passes through a predetermined level. Alternately, the signal strength of a first pilot signal transmitted by the first base station is measured at the mobile station. A handoff request message is then sent to the second base station when the measured signal strength of the first pilot signal becomes less than a second predetermined level, thereby mobile station communication to be established. The provision of a voice link between the mobile switching control stations allows for the forwarding of an existing connection between the first and second cellular systems, and enables the performance of soft intersystem handoffs.

System and method for orthogonal spread spectrum sequence generation in variable data rate systems

Abstract: A method and system for allocating a set of orthogonal PN code sequences of variable length among user channels operative at different data rates in a spread spectrum communication system is disclosed herein. PN code sequences are constructed that provide orthogonality between users so that mutual interference will be reduced, thereby allowing higher capacity and better link performance. In an exemplary embodiment, signals are communicated between a cell-site and mobile units using direct sequence spread spectrum communication signals. Information signals communicated on the cell-to-mobile link channels are encoded, interleaved, and modulated with orthogonal covering of each information symbol. Orthogonal Walsh function codes of varying length are employed to modulate the information signals. Code assignments are made on the basis of channel data rates in a manner which results in improved utilization of the available frequency spectrum. A substantially similar modulation scheme may be employed on the mobile-to-cell link.

Method and apparatus for the transmission of variable rate digital data

Abstract: A communication system for transmitting variable rate data is disclosed wherein redundancy is added to the variable rate data to provide repetition symbols. The repetition symbol data is transmitted with symbol energy scaled in accordance to the rate of the variable rate data when the variable rate data is greater than or equal to a nominal data rate. When the variable rate data is less than the nominal data rate, the symbol data is transmitted at nominal symbol energy and redundancy is removed by transmission gating of a proportion of the transmission symbol data determined in accordance with the rate of the variable rate data. Furthermore, a receiver for receiving the variable rate data is disclosed which uses the redundancy in the transmitted data symbol stream to make a corrected estimate of the transmitted symbol data.

Method and apparatus for determining data rate of transmitted variable rate data in a communications receiver

Abstract: A system for determining the rate at which data has been encoded in the receiver of a variable-rate communications system The data is received in frames having a fixed number of symbols Multiple copies of symbols fill the frame when data is encoded at less than the full rate At an encoding rate of one fourth the full rate, for example, each symbol in the frame is repeated four times The incoming symbols are provided to multiple paths for decoding Each path decodes the symbols at one of the possible rates Error metrics, which describe the quality of the decoded symbols, are extracted and provided to a processor The error metrics may include Cyclic Redundancy Check (CRC) results, Yamamoto Quality Metrics, and Symbol Error Rates The processor analyzes the error metrics and determines the most probable rate at which the incoming symbols were encoded

Data burst randomizer

Abstract: A method and system, for use in a communication system in which data is transmitted in data frames of a predetermined time duration, for the positioning of the data within the data frames for transmission. A computation circuit computes according to the deterministic code a pseudorandom position for the data within each data frame. A positioning circuit positions the data within each data frame in the computed position.

Microcell engineering in CDMA cellular networks

Abstract: The demand for cellular radio services is growing rapidly, and in heavily populated areas the need arises to shrink the cell sizes and "scale" the clustering pattern. The extension of the service into the PCN domain, mostly in-buildings and in pedestrian areas, further enhances this trend. The vision of the "third generation" cellular systems incorporates micro- and picocells for pedestrian use, with macrocells for roaming mobiles. Connectivity between all these cells, while maximizing total system capacity, is the main challenge facing the "third generation architects." The CDMA cellular system, which shares the same frequency channel across the system (reuse pattern of one) and applies soft handoff between the cells, has already shown, both by analysis and by tests, to have full connectivity between the microcells and the overlaying macrocells without capacity degradation. The parameters involved in the engineering of a heterogeneous CDMA network are discussed in the paper. Factors that determine the size of the cell, the soft handoff zone, and the capacity of the cell clusters are analyzed, and engineering techniques for overlay-underlay cell clustering are outlined. >

Interframe video encoding and decoding system

Abstract: A video compression system and method for compressing video data for transmission or storage by reducing the temporal redundancy in the video data is described. A frame of video data is divided into a variable number of blocks of pixel data of varying size, and each block of data is compared to a window of pixel data in a reference frame of pixel data, typically the previous frame. A best matched block of pixel data is selected from the window of pixel data in the reference frame, and a displacement vector is assigned to describe the selected block location in the reference frame relative to the current block of pixel data. The number and size of the blocks of pixel data are permitted to vary, in order to adapt to motion discontinuities in the sequential frames of pixel data. This is to allow prediction blocks of pixel data in the current frame to be smaller in areas of high activity, while maintaining high levels of compression, achieved by using larger prediction blocks, in areas of the frame with low levels of activity. A frame of predicted pixel data is assembled from variable size blocks of prediction data and subtracted from the current frame of pixel data. Only the residual difference, the displacement vectors and an indication of the block sizes used in the prediction are needed for transmission or storage.

Pilot carrier dot product circuit

Abstract: An method and apparatus for computing a scalar projection of a vector onto another vector. The apparatus comprises a multiplying circuit and a summing circuit. The multiplying circuit is for multiplying a value representative of a first component of a first vector with a value representative of a first component of a second vector to provide a first intermediate value, and for multiplying a value representative of a second component of a first vector with a value representative of a second component of a second vector to provide a second intermediate value. The summing circuit sums the first and second intermediate values to provide a resultant value representative of the scalar projection of the first vector onto the second vector. The apparatus may further comprise a storing circuit and a selection circuit. The storing circuit is for storing the values representative of the first and second components of the first vector, and the values representative of the first and second components of the second vector. The selection circuit provides an ordered supply of these values to the multiplying circuit.

Method and apparatus for reducing the average downlink transmitted power from base stations during soft handoff

Abstract: A plurality of methods for achieving the soft or softer handoff process such that the performance of a system is improved. A first method is based on delaying the softer handoff process. A second method is based on reducing the power of transmissions from the sector having the weakest signal strength. A third method is based on eliminating transmissions from the sector having the weakest signal strength. A fourth method adds a new base station or sector only when the mobile unit is in need of additional power to operate properly. In all four methods, reverse link demodulation in each sector may continue with or without the transmission of the forward link. In all four methods the operation could be based on the signal strength of the reverse link signal or the forward link. It is also possible to combine two or more of these methods to create a hybrid method.

Method and apparatus for controlling power in a variable rate communication system

Abstract: A method and apparatus for controlling transmission power in a variable rate communication system is disclosed. The method disclosed provides for a closed loop power control method. A first remote station controls the transmission power of a second remote station by transmitting a rate dependent power control signal to the second remote communication station. Since only the second communication knows its transmission rate a priori, it must determine its course of action in accordance with both the received power control signal and the knowledge of its transmission rate. In the present invention, the power control system reduces the amount of overhead required by restricting the possible rate transition of the variable rate communication system. The power control system further increases its efficiency by allocating the power control bits top various rate hypotheses in accordance with the probability of the rate hypothesis and the perceptual impact of power control for frames of data transmitted at the hypothetical rate.

Method of invoking and cancelling voice or data service from a mobile unit

Abstract: A method of invoking and cancelling voice and data service between a mobile unit and a base station. Using a standard telephone system, the connection for a voice service and a data service is the same. With the introduction of the digital wireless link, the voice connection and the data connection are different. Therefore new dialing commands which indicate the intent of the connection are created. These commands can also be used to designate the intent of the call from a mobile unit capable of data and voice service but not capable of simultaneous voice and data service. They can also be used to invoke simultaneous voice and data services.

Method and apparatus for providing a communication link quality indication

Abstract: A link quality improvement system for a cellular communication system in which portable units are used to facilitate communication of information signals between system users, via at least one cell-site, using code division multiple access spread spectrum communication signals. The system enables users to improve the quality of reverse communication links from the portable units to the cell-site by providing to each system user a link quality signal indicative of power received at the cell-site relative to an optimum level of received power. At a cell-site communicating with a portable unit associated with a particular system user, the portable unit transmitted power is measured as received at the cell-site. A command signal is generated at the cell-site and transmitted to the portable unit for adjusting portable unit transmitter power. The command signals are also accumulated in order to enable generation of a link quality signal in response thereto. In a preferred implementation the link quality signal is an audible interference signal inducing the system user to adjust orientation of the portable communication unit so as to improve signal quality on the reverse link.

Method and apparatus for detecting fault conditions in a vehicle data recording device to detect tampering or unauthorized access

Abstract: A system and method for detecting fault conditions within a vehicle recording device are disclosed herein. The fault detection technique may be implemented in a vehicle in which are incorporated one or more vehicle sensors for monitoring one or more operational parameters of the vehicle. A recording device disposed within the vehicle is used to collect vehicle operation data produced by the one or more vehicle sensors. The fault detection technique of the invention contemplates storing a current time value at regular intervals during periods in which the recording device is provided with a source of main power. Time differences are determined between consecutive ones of the stored time values, and the time differences compared to a predetermined maximum value. A power loss fault condition is registered when at least one of the time differences exceeds the predetermined maximum value. In a preferred implementation an indication of the existence of the power loss fault condition is transmitted to a central control station. Fault detection may also be effected within a vehicle recording device by repeatedly storing a cumulative value of an operational parameter registered by a sensor unit incorporated within the vehicle. The last stored cumulative value is compared to a cumulative value currently registered the sensor unit, and difference value is determined therebetween. A fault condition is indicated when the difference value exceeds a predetermined maximum value. Again, an indication of the existence of the fault condition may then be transmitted to a central control station.

Method and apparatus for testing a digital communication channel

Abstract: A system and method for testing signal transmission quality within a digital communication system is disclosed herein The system may be incorporated within a digital cellular communication system in which information is exchanged over spread spectrum communication channels, among a plurality of mobile users, via at least one cell-site The system contemplates testing a digital communication channel by transmitting a test sequence of digital data over the communication channel The test sequence of digital data transmitted over the communication channel is received at a receiving station, within which is also generated a replica of the test sequence of digital data The accuracy of transmission over the communication channel is then determined by comparing the replica of the test sequence of digital data to the test sequence of data received over the communication channel The system allows the test sequence of digital data to be transmitted at one of a set of known data rates, with the receive station being disposed to identify the data rate associated with each test sequence of digital data In a preferred implementation transmission of the test sequence involves generating a first plurality of data packets, which collectively comprise the test sequence of digital data Each data packet is assigned one of a multiplicity of data rates in accordance with a first pseudorandom process, and is then transmitted at the data rate assigned thereto

Soft Handoff Extends CDMA Cell Coverage and Increase Reverse Link Capacity

Abstract: We present a simple model for analyzing the soft handoff, and hard handoff performance as well as quantitative performance improvement measures for the capacity of the reverse links. The results will be based on a propagation model that represents the μth power of the distance (average path loss) and the log-normal component representing the shadowing losses.

Method and apparatus for reducing the average transmit power of a base station

Abstract: A plurality of methods for achieving the soft or softer handoff process such that the performance of a system is improved. A first method is based on delaying the softer handoff process. A second method is based on reducing the power of transmissions from the sector having the weakest signal strength. A third method is based on eliminating transmissions from the sector having the weakest signal strength. A fourth method adds a new base station or sector only when the mobile unit is in need of additional power to operate properly. In all four methods, reverse link demodulation in each sector may continue with or without the transmission of the forward link. In all four methods the operation could be based on the signal strength of the reverse link signal or the forward link. It is also possible to combine two or more of these methods to create a hybrid method.

Multiple frequency communication device

Abstract: The dual band code division multiple access radio of the present invention operates on multiple frequencies simultaneously on either transmit or receive The transmit path operates by splitting the transmit intermediate frequency (IF) path (103) and mixing the IF to two different transmit frequencies using two frequency synthesizers (140 and 145) The receive path (104) has two RF channels (116 and 117) that are mixed with the frequencies generated by the synthesizers (140 and 145) and summed into one IF strip Thus the radio of the present invention can perform a soft hand-off between frequencies while communicating with both base stations simultaneously Additional mixing paths and synthesizers can be added if it is desired to communicate with more than two base stations simultaneously