Abstract: A device for composing or editing a string of characters representing information, such as a text message, comprises a character string display for displaying a character string being composed or edited and a character selection display for displaying a set of characters for use in composing or editing the character string. The character selection display can be activated to display the character set in a display area in which at least some of the individual characters of the set are arranged relative to a designated location in the display area, such as the center of the display area, at distances according to decreasing frequency of use, e.g. a number of characters that are most likely to be frequently used are arranged in close proximity to the designated location. A cursor is displayed in the character selection display area and keys are provided for moving the cursor from one character to another in the character selection display for indicating a desired character to be selected.

Abstract: A method for registering and controlling registration data for new and roaming pagers in a paging system. Messages for the pagers pass through an input messaging switch to the pager's home messaging switch, from which the messages are sent to an output messaging switch to be transmitted to the pagers. When a pager roams into and area, it sends out a registration message that is received by an output messaging switch. The output messaging switch then contacts the home messaging switch for the pager. The pagers are programmed with a home identifier, which they transmit as part of their registration message. The home identifier can be converted to the address of the pager's home node in home messaging switch. In this way, an output messaging switch knows which home messaging switch to contact when it receives a registration message from the pager. The home identifier in a pager can be reprogrammed through an over-the-air procedure.

Abstract: A method for validating a message packet communicated from a source node to a destination node in a computer network is disclosed. The source node and destination node have access to a clock mechanism synchronized with a common time frame. The method comprises generating a first security key using a time reference obtained from the clock mechanism and a password known by the source node and destination node, communicating the first security key with a message packet from the source node to the destination node, and when the first security key and message packet are received by the destination node, generating a second security key using the password and the time reference and comparing the second security key with the first security key. The message packet is discarded if the second security key does not correspond with the first security key.

Abstract: A method of modifying reverse channel messages in a two-way paging system (101) to authenticate reverse channel messages is disclosed. The intended frequency of the reverse channel message is converted into a unique binary integer. The binary integer is used to modify a checksum (207) in the reverse channel message so that the checksum is now dependent upon not only the message (205) contents but also the intended frequency of the reverse channel message. When received by a paging receiver (109) of the paging system, an identical calculation takes place and if the modified checksum transmitted with the reverse channel corresponds with the calculated checksum, the message is authenticated. Otherwise, the reverse channel message is rejected.

Abstract: A modulator that modulates and encodes data using data symbols, interspersed with pilot symbols, for transmission to another modem, and a demodulator that decodes data symbols of a signal received from another modem. In the demodulator, a received signal is sampled at four times the symbol rate. The sampled signal is converted to quadrature signals and low-pass filtered to produce a complex baseband signal. Data symbols in the complex baseband signal are sampled in synchronization with the start of each symbol based on the pilot symbols that are interspersed in the signal. By processing the pilot symbols, full modem synchronization is maintained down to a very low signal-to-noise ratio, through noise bursts, or even when the data symbols representing data are replaced by predefined sequences of data symbols that convey the dots and dashes of Morse code identifying the station transmitting the modulated signal.

Abstract: A method of validating communications between a transmitting component and a receiving component of a paging system is disclosed. The transmitting component prepares an application protocol data unit (APDU) for transmission by selecting predetermined portions of the APDU for hashing. A hash code is output by the hash method and included in the APDU. The receiving component retrieves the same predetermined portions of the APDU for hashing. The receiving component then compares the hash code in the APDU with the hash code the receiving component calculated. If there is a match, then the APDU is accepted as authentic. If there is not a match, then the APDU is rejected.

Abstract: An hierarchical addressing mechanism for use in a paging system is disclosed. The paging system assigns a compressed organization identifier to each of the organization identifiers for the organizations that are sharing the resources of the paging system. Each of the pagers within the paging system are provided with an associative table that associates the compressed organization identifiers with organization identifiers. In operation, the paging system forms a page by appending an address word to a message. The address word includes the compressed organization identifier determined from the associative table and the pager identifier for the called pager. In this manner, a more efficient method of addressing pagers is disclosed.

Abstract: A clock synchronization system for synchronizing a number of paging stations (24) with a system controller (23). Each paging station has a clock that includes a counter (52) that indicates the current local time and which is sequentially incremented by a counter advance signal applied thereto. A voltage controlled oscillator (58) generates the clocking signal that controls the advancement of the counter. A CPU (50) in the system controller monitors the time indicated by the counter and compares it to timing information received from a system clock. The timing information includes a time mark and a time mark send time. The system clock transmits to each paging system the time mark. At a future time, the system clock transmits the time mark send time which is the precise time at which the time mark was transmitted. The paging stations each measure the time interval between the time at which the time mark arrived and the time at which the time mark was transmitted by the system clock period.

Abstract: A modulator that modulates and encodes data using data symbols, interspersed with pilot symbols, for transmission to another modem, and a demodulator that decodes data symbols of a signal received from another modem. In the demodulator, a received signal is sampled at four times the symbol rate. The sampled signal is converted to quadrature signals and low-pass filtered to produce a complex baseband signal. Data symbols in the complex baseband signal are sampled in synchronization with the start of each symbol based on the pilot symbols that are interspersed in the signal. By processing the pilot symbols, full modem synchronization is maintained down to a very low signal-to-noise ratio, through noise bursts, or even when the data symbols representing data are replaced by predefined sequences of data symbols that convey the dots and dashes of Morse code identifying the station transmitting the modulated signal.

Abstract: A clock synchronization system for synchronizing a number of paging stations (24) with a system controller (23). Each paging station has a clock that includes a counter (52) that indicates the current local time and which is sequentially incremented by a counter advance signal applied thereto. A voltage controlled oscillator (58) generates the clocking signal that controls the advancement of the counter. A CPU (50) in the system controller monitors the time indicated by the counter and compares it to timing information received from a system clock. The timing information includes a time mark and a time mark send time. The system clock transmits to each paging system the time mark. At a future time, the system clock transmits the time mark send time which is the precise time at which the time mark was transmitted. The paging stations each measure the time interval between the time at which the time mark arrived and the time at which the time mark was transmitted by the system clock period.

Abstract: A simulcast system for broadcasting the same signal for a number of spaced-apart broadcast sites is disclosed. The system (20) of this invention includes a hub (28) adapted to receive the signal to be simulcast and a number of stations (30) that actually broadcast the signal. The hub places the digital signal packets referred to as PDBs (36). As pan of the signal packetization process, the hub evaluates the rate at which the signals should be broadcast and assigns a start time at which the signals should be broadcast; this information is attached to the PDBs. After a PDB is created it is forwarded to the stations over a link channel. Each station includes a station controller (32) and a station transmitter (34). The station controller, upon receiving a PDB, forwards the signal therein to the transmitter at the start time indicated and at the appropriate broadcast rate.