Showing papers by "Qualcomm published in 1989"

Method and system for providing a soft handoff in communications in a cdma cellular telephone system

Abstract: In a cellular telephone system a system for directing communications between a mobile user and cell-sites as a mobile user changes cell-site service areas. The mobile user includes an apparatus for, while in communication with another system user via one cell-site, determining a transition of the mobile user from the cell-site service area to the service area of another cell-site. The system includes circuitry responsive to the indication for coupling communications between the mobile user and the other system user via the new cell-site while the mobile user also remains in communication with the system user via the first cell-site. The system further includes apparatus responsive to the coupling of the communications between the mobile user and the other system user via the new cell-site for terminating the communications between the mobile user and another system user via cell-site with communications continuing between the mobile user and the system user via the new cell-site.

A pragmatic approach to trellis-coded modulation

Abstract: Since the early 1970s, for power-limited applications, the convolutional code constraint length K=7 and rate 1/2, optimum in the sense of maximum free distance and minimum number of bit errors caused by remerging paths at the free distance, has become the de facto standard for coded digital communication. This was reinforced when punctured versions of this code became the standard for rate 3/4 and 7/8 codes for moderately bandlimited channels. Methods are described for using the same K=7, rate 1/2 convolutional code with signal phase constellations of 8-PSK and 160PSK and quadrature amplitude constellations of 16-QASK, 64-QASK, and 256-QASK to achieve, respectively, 2 and 3, and 2, 4, and 6 b/s/Hz bandwidth efficiencies while providing power efficiency that in most cases is virtually equivalent to that of the best Ungerboeck codes for constraint length 7 or 64 states. This pragmatic approach to all coding applications permits the use of a single basic coder and decoder to achieve respectable coding (power) gains for bandwidth efficiencies from 1 b/s/Hz to 6 b/s/Hz. >

Direct digital synthesizer driven phase lock loop frequency synthesizer

Abstract: A frequency synthesizer which uses a direct digital synthesizer (DDS) to drive a phase lock loop The DDS generates a highly accurate periodic signal of a frequency selected from a plurality of reference frequencies A phase lock loop receives the DDS generated reference signal and a divide-by-N signal for generating an output signal at a frequency determined by the divide-by-N signal The frequency resolution of the phase lock loop is N times the reference signal In a second embodiment, the DDS is incorporated within the feedback path of the phase lock loop An input reference frequency signal is provided to the phase lock loop with the DDS clock signal provided as a function of the phase lock loop output frequency The DDS receives an input frequency control signal which determines the DDS step size The synthesizer output frequency is a function of the input reference , the number of bits in the digital word of the frequency control signal and the DDS step size as determined by the frequency control signal Optional dividers may be provided in the feedback path which may further affect the synthesizer output frequency

Finding the best set of K paths through a trellis with application to multitarget tracking

Abstract: A solution is presented to the problem of finding the best set of K completely unmerged paths through a trellis with M/sub /i>or=K states at depth i in the trellis, i=0, 1, 2, . . ., N. Here, 'best set' means that the sum of the metrics of all K paths in the set is minimized, and 'completely unmerged' means that no two paths pass through a common state. The solution involves using the Viterbi algorithm on an expanded trellis. This result is then used to separate the tracks of K targets optimally in a simplified model of a multitarget radar system. The model includes measurement errors and false alarms, but it does not include the effects of missing detections or merged measurements. >

Dual satellite navigation system

Abstract: A method and system for determining the position of an object using a fixed station and a plurality of earth orbit satellites whose positions are known. Separate periodic signals are transmitted from the fixed station via first and second satellites to the object whose postion is to be determined. The phase offset in periodic characteristics of the periodic signals as received from the first and second satellites is measured at the object. The phase offset corresponds to a relative time difference in propagation of the signals traveling two different paths to the object. The object transmits via the first satellite a return signal indicative of the measured relative time difference. This return signal is activated some time in the future according to the object local time, which is slaved to receipt of the periodic signal sent through the first satellite. This future time is the start of the particular time period as decided by the fixed station's schedule. At the fixed station, an instantaneous round trip delay, determined by the time offset of the current transmission clock time relative to the receive clock time of reception of the return signal, along with the measured relative time difference sent back on the return signal, is used to calculate the distances between the first and second satellites to the object. From these distances the position of the object is calculated.

Collision resolution algorithms in multistation packet-radio networks

Abstract: The performance of a multistation packet-radio network in which the nodes of the network employ some collision resolution algorithm (CRA) for accessing a shared radio channel is analyzed. The two CRAs considered here are the binary-tree CRA (BTCRA) and the clipped binary-tree CRA (CBTCRA). The exact analysis of a multistation network with these access schemes is intractable. Therefore, the authors present an approximate method that captures the interactions among the nodes of different stations. The mean idea is to view the interference among the nodes of different stations as independent random noises and compute the probabilities of these noises, taking into account the interactions between the nodes. Numerical results of the approximate analysis are presented and compared with the results of simulations. >

Channel access protocols for half duplex satellite terminals

Abstract: The author shows why carrier-sense multiple access (CSMA) is unusable with the combination of half duplex terminals and the success/failure channel. Distributed round-robin and distributed reservation protocols are given as examples of two classes of usable protocols. The author shows how to convert the success/failure channel to a something/nothing channel-(a channel in which accesses can be distinguished from no accesses)-so that group-testing techniques can be used to make reservations efficiently. The round-robin protocols are relatively simple but are generally not satisfactory for large terminal populations. The more complex reservation protocols using group testing perform satisfactorily over a wide range of conditions. Even with this sophisticated protocol, half duplex networks are not as efficient as full duplex networks. For full duplex terminals, ALOHA can be used to obtain relatively short reservation cycles that are almost independent of the number of terminals. >

Why is CDMA the solution for mobile satellite communication

Abstract: It is demonstrated that spread spectrum Code Division Multiple Access (CDMA) systems provide an economically superior solution to satellite mobile communications by increasing the system maximum capacity with respect to single channel per carrier Frequency Division Multiple Access (FDMA) systems Following the comparative analysis of CDMA and FDMA systems, the design of a model that was developed to test the feasibility of the approach and the performance of a spread spectrum system in a mobile environment Results of extensive computer simulations as well as laboratory and field tests results are presented