Abstract: A personal computer's microprocessor is time-shared to provide the functions formerly provided by a microprocessor dedicated to a modem. This technique is transparent to software applications programs which interact with a modem. The personal computer utilizes an operating system, such as the Microsoft Windows operating system, in which a portion of the operating system, known as the communications driver, provides the interface between the operating system and the personal computer's serial and parallel communication ports. All communications between the communications driver and the rest of the operating system are examined. Those communications destined for a particular port associated with a modem not having a dedicated microprocessor are redirected while other communications destined for other ports are passed to the Microsoft Windows communications driver.

Abstract: The disclosed facility type determination technique ascertains whether or not a facility connection is solely digital. In the disclosed embodiments, this information is used to establish the rate at which data is coupled through the facility connection. More specifically, a predetermined test signal including a pseudorandom sequence of digital signals is transmitted through the facility or combination of facilities connecting a data source to a data destination after the connection between the source and destination is established. The received test signal is examined at the destination and the examination results are used to determine the rate at which data is subsequently transmitted between the data source and data destination. Advantageously, this technique does not restrict network facility management and can be employed in a variety of data communication applications.

Abstract: Symbols which are representative of customer data are transmitted in bursts. In the idle mode, i.e., the time intervals between bursts, symbol sequences which are a priori known to the receiver are transmitted. Such idle mode symbols maintain adaptive apparatus, such as NEXT cancellers and equalizers, in their properly converged state. To reduce crosstalk and spectral emissions, the idle mode symbols are selected to be the innermost symbols in the signal constellation encompassing the ensemble of all symbols.

Abstract: Timing control resolution between two communications devices is provided by assigning each device to one of a plurality of priorities and by transmitting an identification of this priority to the other communications device. The determination of which device is the master and which device is the slave is then resolved by comparing the received and transmitted identifications from the contending devices to a predetermined ranking of identification signals. When such identifications signals are the same, each device randomly selects an identification signal from a group of such signals. Preferably this group includes all of the identification signals except that transmitted in the immediately prior contention round. The received and transmitted identifications signals from the contending devices are then compared to the predetermined ranking of identification signals.

Abstract: A synchronization scheme for bidirectional data applications where the customer supplies data for transmission at a rate which is customer controlled. In accordance with the present invention, in each transmission direction, the customer data is converted into data symbols in a predetermined constellation. In response to these data symbols, additional symbols are added. In the disclosed embodiment, the additional symbols added are symbols lying outside of the constellation and are not used to represent customer data. The additional symbols added raise the symbol rate in each transmission direction to one higher than that provided by the symbols representative of the customer data alone. This higher symbol rate in each transmission direction is preferably the same, or the higher symbol rate in one direction is related to the higher symbol rate in the other direction by a rational number. At each receiver, the additional symbols are removed and customer data is recovered from its representative data symbols.

Abstract: To reduce near-end crosstalk (NEXT) in systems possessing excess bandwidth, a signal is transmitted from a first to a second location. At the second location, the received signal is examined and a characteristic of this signal is determined while the delay provided in the transmit signal path at this location is varied. Based on this examination, a particular amount of delay is introduced into the transmit signal path which reduces NEXT. This process is repeated for each direction of transmission. In the disclosed embodiment, the characteristic of the received signal which is determined is the mean square error and the amount of delay selected is that corresponding to the minimum mean square error.

Abstract: A modem, capable of simultaneously coupling voice and data signals, connects local digital terminal equipment (DTE) and a local telephone to a communications link. To prevent the local DTE from responding to a communications containing only voice signals, the local DTE is notified of an incoming communication only after detection of calling tone signals on the communications link. Such signals indicate a remote DTE desires to establish a data communications path with the local DTE. This operation advantageously prevents the modem from transmitting an annoying answer tone to a calling party.

Abstract: Loss of synchronization, due to a digital data signal having the same signal value for an extended number of bit or symbol periods, is overcome through the use of a coding scheme which assures transitions after each such period despite the absence of transitions in the signal to be encoded. Broadly, within the encoder, a digital input signal having m signal levels is transformed into a coded digital output signal having n possible signal values, where m<n. The transformation alters the current digital input signal value as a function of the previous coded digital output signal value and the current digital input signal value performed in a number system whose modulus is n. In a disclosed embodiment, a binary input signal is coded into an output signal having three signal levels.

Abstract: The present invention overcomes the prior art limitations by dividing a coverage area into very small regions or cells. The inventive system can be built as an adjunct to a wired telecommunication system such as a PBX. Advantageously, because of the relatively small size of each cell, transceivers in the inventive system can use very low transmission power, compared with a pico-cellular communications system, to communicate with a fixed transceiver. In addition, because of the relatively short distance between the mobile handset and the fixed transceiver, the communication paths between any two transceivers are reduced and, therefore, the multipath distortion which can affect the received signals is substantially reduced.A concomitant problem normally associated with relatively small cells is the need for a switching system which can accommodate the large amount of switching or handovers required to accommodate the various mobile units as they move from one cell to another.

Abstract: A technique for use in communications systems utilizing busy and idle modes. In the busy mode, symbols representative of data are transmitted to system end users. In the idle mode, during which no data is communicated to end users, idle mode symbols are transmitted. Such idle mode symbols are not used to represent data and are only transmitted during the idle mode. Advantageously, such idle mode symbols maintain adaptive apparatus, such as AGC circuits, NEXT cancellers and equalizers, in their properly converged state. In the disclosed embodiment, the idle mode symbols are the innermost symbols in a signal constellation and transition from the idle to busy mode is represented by the transmission of a predetermined number of outermost symbols in the signal constellation. Use of such symbols for idle-to-busy mode transitions advantageously provides ready detection of such transitions. In addition, use of the innermost symbols for the idle mode reduces spectral emission and crosstalk.

Abstract: The present invention relates to correlation apparatus in which samples of a received signal are demultiplexed and coupled to a plurality of correlators in cyclic fashion so that successive samples are coupled to a different correlator in the plurality. Each correlator provides an output which is coupled to multiplexing apparatus. This apparatus is especially useful for determining signal dispersion characteristics and avoids the "null taps" associated with conventional correlation apparatus.

Abstract: A conferencing bridging technique for compressed information signals which monitors the signal energy transmitted by each conferee. When there is only one conferee speaking, the summing circuit in the bridge unit is bypassed along with the speech decoding/coding apparatus and the talking conferee's signal is broadcast to all conferees. If there is more than one conferee speaking at any given time, then only the speaking conferee's signals are routed to an associated speech decoder wherein those conferees' compressed signals are decompressed. These decompressed signals are then combined by the summing circuit and the sum is recompressed and broadcast to all conferees. Advantageously, the above-described technique eliminates the signal degradation associated with tandeming of signal decoding and coding operations and permits the sharing of a smaller number of signal decoders among a larger number of conferees.

Abstract: A signal dispersion cancellation structure receives incoming signal samples at an incoming rate, stores these samples in a first memory and then writes these samples at a submultiple of the incoming rate into a plurality of second memories. Each second memory is associated with a finite impulse response (FIR) filter and the second memory samples are coupled to the associated FIR filter at the incoming rate. Advantageously, apparatus is also provided which enables any sample in a second memory to be provided to the associated FIR filter and outputted therefrom at a time related to the position of any signal dispersion.

Abstract: Distortion and instability due to echoes in conference communications is reduced through the use of an echo estimating filter disposed in a conference bridging circuit. This circuit includes a signal combiner which receives information signals from each of the parties in the conference communications and provides an output signal which is a combination of the received information signals and an echo compensation signal. The echo estimating filter provides this echo compensation signal in response to the combiner output signal. Advantageously, the echo estimating filter can be fixed or adaptive. In the latter case, the adaptation can be in response to the received information signals or to training sequences.

Abstract: Timing recovery circuitry for recovering digital data generates a timing signal which is a function of the delay provided by an equalizer to one or more predetermined frequency components of its input signal. Advantageously, this approach is applicable to systems which utilize one or more baseband or passband equalizers. The disclosed embodiments of the present invention pertain to a dual-duplex system. In such a system, the digital data to be transmitted is divided into two different digital signals and each signal is coupled through an associated transmission channel. At the receiver, the received version of each transmitted signal is processed by an associated equalizer and the outputs therefrom are combined to recover the digital data. In the disclosed embodiments of the present invention, the necessary timing signal for such recovery is a function of the delay introduced by each equalizer to at least one predetermined frequency component of that equalizer's input signal.

Abstract: A signal despreader for use in a CDMA system processes samples of the received signal with filtered replicas of the code coefficient sequences associated with the system users. The symbols transmitted by each system user are recovered using a filtered replica of that user's associated code coefficient sequence. In the disclosed embodiment, the communications channel between each system user's transmitter and the base station is bandlimited. Accordingly, within each user's transmitter, filtering apparatus having a frequency characteristic is utilized to limit the frequency spectrum of each coded signal to a predetermined bandwidth equal to or less than that of the communications channel. Each filtered replica, pursuant to the present invention, reflects this frequency characteristic. In addition, the communications channel also has a frequency characteristic, and each filtered replica can reflect this characteristic as well.

Abstract: Despreading of the received signal in a CDMA system is provided using code coefficient sequences which are derived from those utilized by the system users to encode their respective symbols. Each derived code coefficient sequence is a function of the correlation between a different user's code coefficient sequence and the code coefficient sequences of all other users. Advantageously, this technique substantially reduces interference effects and is suitable for use in the despreader of differentially or nondifferentially coded CDMA systems.

Abstract: To recover the bits from various users in an asynchronous CDMA communications system, samples of the received signal are processed using blocks of code coefficients. Each code coefficient block includes the sequence of code coefficients for each user which formed the received signal samples. Each sequence has the same number of code coefficients and this number is equal to the product of a predetermined number of bit intervals and the number of code coefficients per bit interval. Processing of the received signal samples using this block formation completely eliminates interference including the so-called leading and lagging edge effects and can be implemented with blocks that include the code coefficients in one or more bit intervals.

Abstract: A synchronization scheme for a digital communications system wherein customer data is connected to a synchronous communications network utilizes auxiliary symbols to provide frame synchronization. Each such auxiliary symbol lies outside of a conventional symbol constellation and is only used to represent framing information. Variations of the customer data rate relative to an expected rate are compensated for by the use of stuff and delete bits in each frame. These bits can be either customer data bits or ancillary bits depending on the direction of this variation. Advantageously, the auxiliary symbols also provide a determination of whether the stuff and delete bits in any frame are customer data or ancillary bits.

Abstract: A communications switching system such as a PBX, central office switch and the like, responds to an incoming call to a called party by signaling a paging device as well as some other communications device having communications capability different from that of the paging device. In the disclosed embodiment, which pertains to a private branch exchange (PBX), this other communications device is one which provides two-way voice communications. Advantageously, the paging device may also be provided with the capability of signalling the communications system that the called party will shortly answer the call via a communications device possessing two-way voice communications. Upon receipt of this pager-transmitted signal, the communications system, if desired, can be provided with the ability to provide an announcement to the calling party of the called party's intent to answer the call.