Abstract: A method for correcting random errors, and detecting and replacing fading errors in radio frequency (RF) digital transmissions, such as voice transmission. In a Dynamic Bit Allocation Sub-Band Coder (DBASBC), bits corresponding to sub-band energy levels are protected before transmission. In the received signal, errors in the protected bits are corrected at the bit level using a correction algorithm. Where this correction algorithm fails, the failure is detected and an estimated energy value is synthetically regenerated for the corrupted energy value.

Abstract: A dispatching console system (20) for handling communications transmissions includes a main processor (50) and a co-processor (52). The main processor (50) receives external console control commands which specify a desired settable (i.e., connect/disconnect) relationship between audio devices in communication with the console and issues main processor commands to the co-processor (52). The co-processor (52) controls a switching circuit (72) in an audio tower (24). The switching circuit (72) is a matrix of cross-point switches (220) which connects and disconnects selected communication devices. In addition to the main processor commands, desired settable relationships between audio devices can also be mandated by device activation input signals which are applied through the audio tower (24) to the co-processor (52).

Abstract: A radiotelephone having a hinged flip cover that protects a keypad when closed and assists the operation of the microphone when open. The key pad and display are located on the same side of the radiotelephone and a microphone and speaker are on the other side. The flip cover is hinged to a bottom edge of the radiotelephone. The hinge pivots through an angle of greater than 180 degrees. Accordingly, the hinge folds over at least a portion of the keypad when closed and unfolds to the opposite side of the radiotelephone to form an angle of less than 180 degrees with that opposite side. A microphone and antenna may be located within the flip cover.

Abstract: A Code Division Multiple Access (CDMA) communication system which contains a calling channel which is used to inform silent mobiles that they are being called. In the system, the calling channel is chosen to be the strongest overlapping signal so that it reaches mobiles which are located on the cells extreme boundaries. The interference other signals experience because they overlap with the calling channel may be avoided by having the mobiles first demodulate the calling channel signal and then subtract it out before demodulating their own signal.

Abstract: A centralized telephone interconnect system for an RF multisite system. Multiple publicly trunked radio sites are networked together through a multisite switch. The centralized telephone interconnect system couples a series of land telephone lines to the multisite switch so that a mobile radio user anywhere in the multisite system is accessible to telephone communications. The telephone interconnect system supports individual calls, group calls and dispatcher console calls. The system includes a centralized interconnect controller that supervises the operation of the interconnect system and a telephone line switching network that connects telephone lines to the multisite switch. A centralized telephone interface module within the multisite switch connects to the centralized interconnect controller and switching network.

Abstract: In a trunked radio frequency communications system, a dynamic regrouping scheme includes an effective user interface, automatic support of multi-site systems, the capability to program individual radio transceivers with multiple new groups dynamically, a fast rate of reconfiguration, instantaneous switch over to prevent radios from residing in immature groups, and a satisfactory mode of operation should the site controller (or site controllers in non-fault tolerant systems) fail. Some of the dynamic regrouping features includes unlimited prestored plans and source and destination groups per plan, regrouping at the plan or destination group level, an advanced user interface, automatic support of multiple sites, fast regrouping at the rate of over 30 radios per second while reducing loading on the system control channel, and fast activation/deactivation. Each plan can be immediately activated or deactivated and users are effectively regrouped together.

Abstract: A distributed switching network (switch) routes audio and control signals throughout the switch from various audio sources to one or more audio destinations. Audio sources such as mobile/portable radio units (via RF repeater transmitters), dispatch consoles, and landline telephone subscribers (via the central telephone switching network) are preassigned and routed onto an audio channel (i.e. a time slot) on a time division multiplexed (TDM) audio bus through a corresponding node. Each microprocessor controlled node is connected to plural control message buses provided for transferring control messages between nodes. A first supervisory node is physically connected at one end of the message buses and an end node is connected at the other end. If the end node fails to respond to a polling message from the supervisory node within a predetermined time period, the supervisory node assumes that the current messaging bus is faulty and initiates a bus switching operation to an alternate messaging bus.

Abstract: A distributed switching network (switch) routes audio and control signals throughout the switch from various audio sources to one or more audio destinations. Audio sources such as mobile/portable radio units (via RF repeater transmitters), dispatch consoles, and landline telephone subscribers (via the central telephone switching network) are preassigned and routed onto an audio channel (i.e. a time slot) on a time division multiplexed (TDM) audio bus through a corresponding interface module. These interface modules broadcast digitized audio and data signals to all other interface modules over their preassigned TDM bus slot. Audio routing is performed to the audio destinations through corresponding interface modules that selectively "listen" to active TDM network channels. A digital voice interface module is provided in the switch to permit audio sources/destinations otherwise lacking certain digital processing capabilities (e.g. encryption/decryption) to participate in such digitally based calls.

Abstract: Two or more signal paths are provided for receiving a radio frequency signal. One or more signal paths include conventional bandpass filters for eliminating interference and noise signals. One or more remaining signal paths include reduced filtering devices for increasing the sensitivity of a radio frequency receiver to the desired signal. Each of the receiving paths is coupled to a respective radio frequency amplifier. Provided that each radio frequency amplifier has equivalent current-source output impedances, the output signals from each amplifier are added constructively if they are in-phase. If the output signals are out-of-phase, a phase inverter inverts the phase of one signal so that the signals may be added constructively. The combined signals of the two or more radio frequency amplifiers pass through various signal processing components associated with conventional superheterodyne receivers. A control unit produces gain variation signals for controlling the gain of each radio frequency amplifier.

Abstract: Individual information signals encoded with a common block error-correction code are assigned a unique scrambling mask, or signature sequence, taken from a set of scrambling masks having selected correlation properties. The set of scrambling masks is selected such that the correlation between the modulo-2 sum of two masks with any codeword in the block code is a constant magnitude, independent of the mask set and the individual masks being compared. In one embodiment, when any two masks are summed using modulo-2 arithmetic, the Walsh transformation of that sum results in a maximally flat Walsh spectrum. For cellular radio telephone systems using subtractive CDMA demodulation techniques, a two-tier ciphering system ensures security at the cellular system level by using a pseudorandomly generated code key to select one of the scrambling masks common to all of the mobile stations in a particular cell.

Abstract: In a radiotelephone system, the control channel of each cell can be configured to broadcast absolute information about its cell and relative information about other cells including the characteristic of the cell. Further, the location of other control channels may also be included among the information broadcast over a control channel of a particular cell. This information is then used to lock a mobile unit to a preferred cell.

Abstract: A self-adjusting quadrature modulator and modulation method improve the accuracy with which digital data is impressed on an RF carrier, which is particularly useful for systems having Viterbi, echo-integrating demodulators and for systems using subtractive CDMA techniques. The method and apparatus involve receiving one's own transmission with a suitable modulation assessment receiver and determining the modulation error relative to the theoretically perfect transmission expected by the receiver. The measured error is used to adjust the modulation to minimize the error. The modulation assessment receiver may use log-polar signal processing to measure phase and (log)amplitude instead of cartesian I and Q components, and then convert to cartesian form. In addition, correction factors determined by the modulation assessment receiver can be directly identified with certain transform components produced by the Fast Walsh Transform.

Abstract: A method and apparatus for digital radio communication employs separation of a frame of data to be transmitted into key bits, critical bits and unprotected bits. The key bits are processed to provide parity bits. The parity bits, and key bits are convolutionally encoded using a tail-biting scheme and merged with unprotected bits, and then transmitted. At the receiver, the decoder splits the received data into convolutionally encoded bits and unprotected bits, and trellis decodes the convolutionally encoded bits into a number of possible paths through a trellis using a generalized Viterbi algorithm. The tail-biting scheme reduces the number of bits that must be transmitted. Paths having errors in the key bits are rejected, and the path having the best metric without key bit errors is used in decoding the transmitted information. In the event that there is no such path, a previously selected path is substituted and decoded.

Abstract: A method and apparatus for demodulating data symbols transmitted through a fading communication channel. A plurality of first predetermined data symbols, a plurality of unknown data symbols, and a plurality of second predetermined data symbols are sequentially received. The received pluralities of data symbols are stored, and first and second sets of reference signals from the stored pluralities of first and second predetermined data symbols, respectively, are determined. The stored unknown data symbols based on the first set of reference signals are forward-demodulated, beginning with unknown symbols received nearer the first predetermined data symbols. The stored unknown data symbols based on the second set of reference signals are backward-demodulated, beginning with the unknown data symbols received nearer the second predetermined data symbols. Quality values indicative of demodulation qualities of the forward- and backward-demodulated data symbols are determined.

Abstract: An adaptive maximum likelihood demodulator for demodulating digital radio signals on a channel which contains impairments like inter-symbol interference, frequency errors or distortion, that vary with time. The demodulator does not employ channel models to generate signal predictions but rather directly updates the signal predictions for each state without going through the intermediate step of updating a channel model.

Abstract: A microcomputer within a duplex RF transceiver operates in an interrupt-driven manner to simultaneously encode and decode CTCSS signalling (with one microcomputer interrupt service routine being devoted to CTCSS encode, and another microcomputer interrupt service routine being devoted to CTCSS decode). Such encoding and decoding of CTCSS signalling is accomplished using minimal external control hardware (e.g., two flip flops and an inexpensive conventional multipurpose counter/timer chip). The resulting arrangement is inexpensive, reliable and requires only a few components in addition to the appropriately programmed microcomputer in order to provide simultaneous encoding and decoding of CTCSS signals in a full duplex RF transceiver context.

Abstract: The invention relates to a method and to an arrangement for demodulating a signal (f) preferably frequency modulated with digital information, and then particularly a frequency shift modulated signal, with a frequency counter detector (16) which directly produces a digital value representative of the instantaneous frequency of the frequency modulated signal. In order to obtain the lowest possible uncertainty in frequency detection at unchanged counter frequencies (f.sub.r), the frequency modulated signal is mixed down to a difference frequency (f.sub.3) which is insignificantly higher than the sampling frequency (f.sub.s) required to extract the modulation information from the instantaneous counter value (N.sub.2) The frequency counter detector begins a counting sequence during each of the periods of the difference frequency.