Abstract: A cellular communication system (10) requests from subscriber units (30) to volunteer for handoff when a call resource shortage is about to occur. The subscriber units (30) may volunteer to handoff to another cell (24) depending on whether any adjacent or neighbor cell (24) provides adequate signal strength for servicing the on-going call. If there is another adjacent or neighbor cell (24) which provides adequate signal strength, the subscriber unit (30) can volunteer for handoff to the other cell. The cellular communication system (10) may accept the volunteer handoff request, whereby the subscriber unit (30) volunteering for handoff is handed-off to the other cell (24). However, the cellular communication system (10) may deny the handoff request. If the handoff request is denied, the subscriber unit (30) may have to drop the call or try to locate another cell to handoff its call before a predetermined amount of time expires.

Abstract: A communication system (100) includes satellites (102,104) and a mobile exchange unit (MXU) (120) for exchanging communication information with users. A satellite (102) generates synchronous timing frames requiring users operating through an MXU (120) to anticipate timing and frequency requirements to participate in communications. An MXU (120) must advance transmissions to a satellite (102) to insure transmissions arrive at satellite (102) within the proper synchronous receive window. Such advanced transmissions by MXU (120) interfere with reception of a ring alert/page transmission (130) which contains the location of broadcast channels (86) designating an incoming call or page data transmissions. The MXU (120) alternatively extracts a broadcast channel location from a candidate hand-off list being transmitted by a satellite (102) to in-use transceivers (310). The MXU 120 then distributes the location of the broadcast channel to those transceivers (310) presently not in-use.

Abstract: A system (28) provides communication services to mobile units (24). Mobile units (24) perform a unit-based location process (46, 48) to determine their locations. The system (28) performs a system-based location process (64, 66) to independently determine mobile unit locations. The system-based process may determine location less precisely than the unit-based process. A location selection process (104) evaluates the unit-determined location in view of a system-determined location error region to decide whether the unit-determined location is reliable. If the unit-determined location is reliable, it is used (120) to qualify communication services to be provided to the mobile unit (24). If the unit-determined location is unreliable, the system-based process is repeated (116) to improve the system-determined location precision, and the resulting system-determined location is used (118) to qualify communication services to be provided to the mobile unit (24).

Abstract: A plurality of subscriber units (16) operate in a communication system (10) having dynamic nodes such as satellites (12). A communication management center (14) controls interface parameters and protocol employed by subscriber units (16). A system and method is employed to dynamically alter interface protocol used by subscriber units (16). Communication management center (14) calculates a balance between a first portion of subscriber units (16) assigned to perform attach-detach registration and a second portion of subscriber units (16) assigned to abstain from performing attach-detach registration when associating and disassociation from communication system (10). As available communication bandwidth varies according to present of future communication patterns, subscriber units (16) may be dynamically reassigned perform or abstain from performing attach-detach registration.

Abstract: A subscriber unit (26) communicates with a satellite communication system (10) that projects cells. The satellites (12) and cells move relative to the earth. During every other TDMA frame, a subscriber unit (26) measures the signal strength of all candidate hand-off beams. The signal strength of the current beam is compared to the signal strength of the candidate hand-off beams. When the signal strength of the current beam is not the strongest, a counter is incremented (108). A hand-off is requested to the beam with the greatest signal level when the counter exceeds a predetermined threshold. Accordingly, only after the current antenna beam has not been the strongest beam for a certain period of time, is a hand-off requested. A different counter threshold is used for candidate hand-off beams from other satellites (12).

Abstract: In a communication system (10) which includes a communication unit (56) (CU), a Mobile-Switch Interface (50) (MSI), and a Mobile services Switching Center (40) (MSC), a method for location registration and call continuation involves the MSI (50) determining (174) whether the CU (56) intends to utilize a system service after the CU (56) completes a location updating process without releasing a channel between the CU (56) and the MSC (40). When the CU (56) does intend to utilize the system service directly after the location updating process, the MSI (50) allows the CU (56) to utilize the system service regardless of whether the MSC (40) indicated that the CU (56) cannot utilize the system service without first releasing the channel.

Abstract: A communication system includes base communication units (105, 155) facilitating a communication link with portable communication units (110) in motion relative to base communication units. The relative motion between base communication units (105, 155) and portable communication units (110) introduces Doppler frequencies into communication links (115, 165). When portable communication units (110) travel in a predictable direction (119), frequency offsets for Doppler compensation are generally predictable. However, when portable communication units (110) move erratically in relationship to a base communication unit (105, 155), frequency offsets for Doppler compensation are not easily calculated. Incorporation of velocity vector data into the frequency offset calculation for Doppler compensation provides reliable tracking and Doppler frequency compensation for erratic motion of portable communication units (110).

Abstract: A cellular communication network (10) includes base stations located in orbiting satellites (12) and any number of subscriber units (26). The satellites (12) monitor the quality of signals received from subscriber units (26) and provide link quality indicator (62) data which subscriber units (26) interpret as instructions to adjust their transmit power levels. Subscriber units (26) evaluate received signal strength and received signal quality to determine whether the signals received at the subscriber units (26) are being interfered with. Subscriber units (26) evaluate the link quality indicator (62) and the quality of signals received at the subscriber units (26) to determine whether the signals received at the satellites (12) are being interfered with. When interference is detected, the subscriber units (26) request a hand-off to another channel (30) within the same cell (28).

Abstract: A method and apparatus for making a call connection in a communication system (10) having multiple communication units (26) (CU), and at least one communication antenna (12) that moves with respect to the CUs (26). The method involves determining (154) whether a call attempt from a source CU (26) to a target CU (50) is successful. When the call attempt is not successful, a control facility (24) predicts (xxx) when one of the antenna (12) will move within an optimal call initiation area (124), within which there is an increased likelihood of establishing a communication link with the target CU (50). At the time when the antenna (12) will move within the optimal call initiation area (124), the system attempts to contact the target CU (50) and, if successful, informs the target CU (50) to wait while the system calls the source CU (26) and connects the call.

Abstract: A communication network (10) includes a number of satellites (12) traveling in low earth orbits (14). The satellites (12) broadcast data which identify particular cells (34) within which communication may take place and geographic locations for the cells (34). A radio unit (26) located near the earth's surface receives these broadcast data and calculates a satellite position relative to the radio unit (26). Based upon this position, the radio unit (26) predicts when target satellites (12) will reach their maximum elevation angles relative to the radio unit (26) and the future times at which these maximum elevation angles will be reached. These predictions are then presented to a user of the radio unit (26).

Abstract: A cellular telecommunication network (10) includes base stations located in satellites (12) orbiting the earth and includes any number of subscriber units (26). Each satellite (12) receives cell cluster lists (54) that are valid for cells (28) the satellite (12) projects toward the earth and for predetermined periods of time. Each cell cluster list (54) includes target cell entries (60) that identify cells (28) into which subscriber units (26) operating in a local cell (28) may request a hand-off. The entries (60) identify communication channels associated with the target cells. Upcoming communication channel changes are indicated as separate entries (60) for identical cells (28). Subscriber units (26) receive the list (54) and evaluate the communication channels for the local cell and the target cells in order to make a hand-off decision.

Abstract: A subscriber unit (30) operates in a synchronous communication system having dynamic nodes such as satellites (12). Satellites (12) employ a strict transmit and receive time window and all transmissions directed to satellites (12) must fall within the receive window to be recognized. In a dynamic communication system where low earth orbit satellites (12) continuously orbit, propagation timing between a satellite (12) and a subscriber unit (30) vary rapidly over a wide range. Subscriber unit (30) must approximate a transmit timing advance for use in inaugurating a transmission to satellite (12). Subscriber unit (30) utilizes a valid geolocation position when available but when a position is unavailable or stale, relies on configuration characteristics of the constellation for generating an initial approximation of propagation delay.