An acknowledgement paging system is described which fits within the existing infrastructure of a paging network and which provides low cost manufacture and low power operation while still enabling the acknowledgement paging over long distances. The acknowledgement paging system consists of a standard paging transmitter and a plurality of remote paging units which respond to a page using frequency-hopped spread-spectrum differential bi-phase shift keying communications. The plurality of pagers are assigned to groups with each group being assigned a separate starting location in a common, repeating pseudo-random noise code which determines the frequency hops. The grouping of pagers minimizes the collisions of acknowledgment transmissions between groups and the enables a large number of paging units to operate within a single geographic area. The pagers include a special double loop PLL synthesizer to produce an accurate narrow band frequency and to change or hop frequencies in a rapid fashion. The base receiving unit employs special algorithms for retrieving very low power acknowledgement paging messages in a noisy environment by using data redundancy, data interleaving, soft decoding and error correction codes to strip the bi-phase-modulated, frequency-hopped spread-spectrum digital data transmitted from the remote pocket pagers. A history of the frequency and phase drift is used during reception of the acknowledgement messages to predict the phase and frequency drift of the encoded digital information to further reduce decoding error. Signal to noise ratios are determined for each frequency hop and relatively noisy hops are discarded or minimized in a soft decoding process based redundancy of data bits.
This application is a divisional of 08/158,441, filed Nov. 24, 1993, now U.S. Pat. No. 5,430,759; which is a continuation-in-part of 07/961,776, filed Oct. 15, 1992, now U.S. Pat. No. 5,335,246; which is a continuation-in-part of 07/932,610, filed Aug. 20, 1992, abandoned.
A method of reducing computation in spread spectrum signals in which a spread spectrum signal sent by a transmitting station (SS1) includes a group and an individual identity code. A receiver (10, 12) stores the received signals based on their group codes and analyses the stored signals on a group by group basis. This greatly reduces this computation required when recovering individual messages from a number of simultaneously transmitted spread spectrum signals. Optionally the transmitting station may send the group and individual identity code signals simultaneously as quadrature signals.
A network comprises a plurality of GPS navigation receivers with two-way radio data communication for communicating the current computed positions of individual mobile units to other mobile units in the network and to stationary dispatch controllers connected in by the public switched telephone network. Ordinary telephone personal pager service is carried out transparently in the network for non-GPS equipped mobile units.
A method for communication between inside and outside of a transmission medium using the transmission medium as a communication line, includes the steps of: receiving an electric signal having information related to a transmission medium from a plurality of sensors inside the transmission medium; conducting the electric signal to the transmission medium; and sensing the electric signal flowing to the outside of the transmission medium. Because a modulating unit is not necessary, a power consumption is minimized. In addition, since an electric signal is directly conducted to a medium, it is not necessary to use an antenna, and thus, degradation of a reception rate according to a directional property of the antenna can be prevented. Moreover, since the electric signal is directly generated in the medium and the medium is directly used as an electric conductor, the overall size of a transmitter is reduced.
A radio transmission system including many radio transmitters using frequency hopping carriers to intermittently transmit very short messages indicative of status of stimuli associated with the transmitters. The transmitters transmit transmissions independently of a receiver receiving the transmissions and independent of each other. In operation, radio transmitters transmit messages at varying frequencies at time intervals that can be varied as well. The frequency and time intervals are varied according to patterns that can be determined individually for each transmitter. A receiver holds data indicative of the future transmission frequency and time for each transmitter and updates the data based on the time and the content of the received messages. In addition, a simple method is provided to generate a very large number of orthogonal frequency-time hopping sequences that are individual for each transmitter and based on the transmitter ID.
To enable positional information to be provided even if a signal intensity of a received GPS signal is low by compensating a phase inversion of a navigation message and performing a phase integration over a long period. A base station 20 continuously receives the GPS signal 11 and extracts therefrom information for supporting reception and positioning computation in a GPS receiver 30 and retains the information. The base station 20 transmits the support information to the GPS receiver 30 via a communication line 40 when the GPS receiver needs the information. The base station 20 supports reception time synchronization in the GPS receiver 30. The GPS receiver 30 receives the GPS signal 11, generates an intermediate frequency signal through down-conversion, and then stores an A/D conversion data in a memory unit. In the GPS receiver 30, the GPS signal data stored in the memory unit 33 is subjected to integration with phase of the GPS signals aligned based on the support information (satellite navigation message and phase inversion information) supplied from the base station 20, and then positioning computation is performed using the integral GPS data.
