Abstract:
A wireless communications system is arranged to provide data communications services, including error recovery, between at least one wireless end-user device and at least one one base station. The wireless end user device(s) receives(s) from the base station(s) unsolicited messages indicative of the status of data packets received by the base station(s). The wireless end-user device(s) transmit acknowledgement and request for retransmission messages only upon request, or when all the packets within a block of such packets have been received.
Abstract:
Currently, with optical time division multiplexing, a switching node is operated at the peak transmission rate. For example, if the data transmission rate is 10 Gbps, the line cards in the switching circuit are also required to operate at this rate despite the fact that the switching node does not actually need to access the data at this rate. Thus, the electronics, which includes the line cards at the switching node, is expensive and less reliable than a low-speed design. In this invention the requirement of operating the switching node electronics at the high speed link bit rate is eliminated by encoding the packet header field at a lower rate than the information in the data field. As a result, the line cards need only operate at the lower header rate. This is possible because the switching node does not need to process the data portion of the packet, but only the header information. The high-speed data portion of the packet is not optically to electrically converted at the switching node, but it passes almost transparently through the switching node. The invention also discloses overlapping several logical networks on the same physical network.
Abstract:
The advantages of both a color display and a high-resolution monochrome display are realized in a single display system by eliminating color filters from the display screen of the display system and illuminating the display screen with either colored light or white light to provide color or high-resolution monochrome capability, respectively. Simultaneous color and high-resolution monochrome capability is realized by illuminating predetermined portions of the display screen with only colored light while illuminating different portions of the display screen with only white light.
Abstract:
In a system for communicating primary and secondary data from a transmitter to a receiver, each of a first plurality of primary data word values is communicated by transmitting an individual channel symbol associated with that value, while at least one other primary data word value is communicated by transmitting a selected one of at least two other channel symbols associated with that one other value. The selected symbol is a function of the value of an individual secondary data word. In the receiver, both the primary and secondary data word values are recovered from the channel symbols thus transmitted.
Abstract:
Apparatus and a technique for equalizing non-linear distortion in a received modulated data signal by (1) forming tentative decisions as to the values of data symbols represented by the signal preferably using a receiver including a conventional linear equalizer, (2) constructing a replica of the non-linear distortion in response to the tentative decisions, and (3) forming a final decision as to the data symbol values in response to signals including the replica. If desired, the final decisions can also be stored and fed back to the processor which forms the replica, so that the replica is a joint function of past final decisions and future tentative decisions regarding the data symbols represented by the signal samples. The present invention provides increased accuracy by using tentative decisions rather than input samples to form the non-linear distortion replica.
Abstract:
Weighted sums of samples of an interference-corrupted data signal are generated to form phase-compensated, symbol-spaced samples. The interference-corrupted signal is at the same time subjected to conventional adaptive equalization and is otherwise processed so as to form tentative decisions as to the transmitted data. Cancellation signals representing the interference components of the phase-compensated samples are generated by forming respective weighted sums of the tentative decisions and each cancellation signal is combined with a respective phase-compensated sample to provide cancelled samples from which final data decisions are made. The weighting coefficients used to form the phase-compensated samples and the cancellation signals are adaptively updated in response to error signals derived from the difference between each cancelled sample and the corresponding final decision.
Abstract:
In a multipoint data communication system using quadrature-amplitude modulation, a master modem (20) and a plurality of tributary modems (11a, 11b . . . 11n) are interconnected via respective transmission channels (13a, 13b . . . 13n, 16). Adaptive equalizer circuitry (55, 56) in the master modem equalizes the channel from a particular tributary by multiplying samples of signals received from the tributary by an ensemble of tap coefficients associated with the tributary. The tap coefficient ensembles for each tributary are stored in a memory (91) from which they are retrieved at the start of transmission from that tributary. Timing-acquisition circuitry (29) within the master modem adjusts the phase of the latter's sampling circuitry (23, 27) at the start of transmission from a given tributary so that the received signals are sampled at the correct time points. In particular, a timing acquisition signal having spectral components only within the non-rolloff region of the equalized baseband-equivalent transfer function is transmitted by the tributary. The master samples and equalizes the received timing acquisition signal to form a succession of timing acquisiton equalizer outputs. The time by which the operation of the sampling circuitry is to be advanced or retarded is determined as a trigonometric function of two successive ones of the timing acquisition equalizer outputs. The timing acquisition signal is illustratively a double-dotting pattern having a four-symbol-interval period. That period is integrally related to the carrier frequency. This allows the samples needed in order to begin forming the timing acquisition equalizer outputs to be generated by replicating the samples taken over only four symbol intervals.
Abstract:
A system for performing non-invasive networked medical procedures including a number of in vivo medical devices, a communication path between at least two of the devices, an ex vivo control unit to control the behavior of the devices, and a wireless communication path between the control unit and at least one of the devices. An associated method for performing non-invasive networked medical procedures is also provided. Further included is a simulation method that utilizes accurate electromagnetic field simulations, using a software based test bench, to determine the maximum allowable transmitted power levels from in vivo devices to achieve a required bit error rates (BER) at an in vivo or ex vivo node (receiver) while maintaining the specific absorption rate (SAR) under a required threshold.
Abstract:
Security mechanisms are disclosed that protect the integrity of the candidate access node discovery procedures in a mobile communication network. In accordance with an aspect of the invention, an access node stores information on candidate access nodes in the mobile communication network and updates the information only after verifying information provided by a mobile terminal after a handoff from one access node to another access node. In accordance with another aspect of the invention, the information on candidate access nodes in the mobile communication network are associated with a particular mobile terminal and stored at the mobile terminal in a candidate access node list.
Abstract:
A system and method for optimizing usage of a communications transmission medium. The transmission medium may be sliced into time and frequency domains so as to create time-frequency slices for assignment to users having varying access rates and user-application requirements. Through scheduling of the various speed users within the frequency and time domains, the system and method can efficiently allocate and make use of the available spectrum, thereby accommodating higher rate users requiring greater bandwidths and time slot assignments while still preserving cost-efficient access for lower speed users. Depending on the signal modulation scheme, the time-frequency slices may be allocated on non-contiguous frequency bands. The system and method is also applicable to code-division multiple access (CDMA) techniques by slicing the available code space along time-code domains, frequency-code domains or, in three dimensions, along time-frequency-code domains. Users may be efficiently scheduled based on code space requirements so as to optimize user of the communication medium.