Showing papers on "Base station published in 1975"

Apparatus for establishing communication between a first radio transmitter and receiver and a second radio transmitter and receiver

Abstract: In a radio communication system having a command or base station and one or more controlled or mobile stations, the base station continuously transmits outbound function messages in binary bit form to the mobile stations. Each outbound function message comprises a sequence of binary bits forming a first synchronizing word, a first address word transmitted three times, a second inverted synchronizing word, a second address word transmitted three times, a third inverted synchronizing word, and a command word transmitted three times. All mobile stations receive the outbound messages and synchronize on them, but only that mobile station whose address is transmitted responds. Each mobile station is synchronized when it properly receives two consecutive synchronizing words in sequence, and remains in synchronization unless five consecutive synchronizing word errors occur. The response from the mobile station to the base station is an inbound message also in binary bit form. Each inbound message comprises a preamble followed by the first synchronizing word, the first address word transmitted three times, the second inverted synchronizing word, the second address word transmitted three times, the third inverted synchronizing word, and a response word transmitted three times. This inbound message or response has a bit rate that is 11/2 times the outbound message bit rate so that other mobiles can respond to their respective messages as they are transmitted by the base station. The base station anticipates each inbound message and uses the preamble and the first synchronizing word to synchronize itself with the inbound message. Thus, high speed binary function controls are reliably provided between a base station and one or more mobile stations in the environment of radio frequencies, particularly those in the land mobile service.

Mobile radio extension unit with punch through operation

Abstract: A mobile radio extension unit for converting a conventional mobile transceiver having a transmitter and a receiver to use as a repeater or transponder for establishing a bidirectional communications link between a transceiver of limited range and a base station or other mobile transceivers in the network. In a mobile communications system network having a plurality of extension units, associated mobile radios, and limited range transceivers, each extension unit includes means for automatically inhibiting multiple transmissions by units within range of one another and for providing punch through priority communications from a limited range transceiver to the base station or other mobile transceivers via one selected extension unit when the receiver associated therewith is repeating a communication to the transceiver.

Vehicle repeater prioritization system

Abstract: An improved repeater adds on to each mobile transceiver of a radio wave communication system for selectively controlling rebroadcasts to an associated portable station. Novel circuitry within each associated repeater eliminates rebroadcast interference among local units, while keeping retransmission delay at an optimized minimum. At turn on, detector circuitry senses if a nearby repeater is broadcasting. In response thereto, programmable delay circuitry is activated to a high incremental state. Where no repeater broadcast is sensed, a program signal is transmitted which increments all nearby repeaters to their next higher delay state. On reception of a signal to be rebroadcast, the repeater whose delay circuitry is in the lowest incremental state initiates rebroadcast, thereby inhibiting the remaining units. A special feature of the programmable delay circuitry is that each repeater is automatically assigned a unique incremental delay time whereby repeater prioritization is positively established. Rebroadcast delay time is kept to a minimum as the system assures that one repeater is at the lowest delay priority. BACKGROUND OF THE INVENTION The present invention relates generally to radio wave communication systems of the type employing a base station, a plurality of portable stations and a plurality of mobile repeating stations, and more particularly to improved means for, and a method of, assigning a rebroadcast priority to the repeaters in such systems in a mamnner to minimize undesireable interference. Mobile ratio wave communication systems normally comprise a base station and a plurality of mobile stations, each of which is typically located with an automotive vehicle. In many applications, such as police work, it is important for the user to maintain communication with the base station or other mobile transceivers upon leaving his mobile vehicle. To resolve this problem various repeater add-on systems have been proposed. Generally, such systems interconnect with the mobile transceiver whereby the audio signal from the transceiver is reprocessed through a second transmitter and broadcast on a second frequency to a portable transceiver. Likewise, signals from the portable transceiver are received in a second receiver and applied to the mobile transceiver where they are broadcast back out on the mobile-base station frequency. A problem with such repeater systems occurs when a plurality of mobile transceivers are in the same locale. In this situation each repeater will attempt to rebroadcast base station, mobile, or portable transmissions. Simultaneous broadcasts by nearby repeaters results in interference creating loss of intelligibility of the transmitted signals. One solution to the interference problem is to operate the various repeaters and their respective portable transceivers on different frequencies. However, this anticipates a complicated and cumbersome system. A second solution, known in the art, contemplates a random sampling technique. Accordingly, a random sampling generator is to be included in each repeater in the communications system. Once a signal to be retransmitted is received the first repeater whose random sampling generator creates an enable pulse following the received signal transmits a lockout to any other repeaters and proceeds to repeat the incoming information. This system has several undesirable drawbacks. First there is a considerable delay time introduced by the sampling function. This delay is in addition to the normal attack times of a transmiter or receiver. The increased delay time might be as long as the disable period of a random sampling generator. Further, there remains a significant probability of interference among transceiver units using the random sampling method. Finally, if the sampling generators are identical and enable pulses occur at similar times in two or more units there is the possibility that the pulses may tend to remain in synchronism and interference would occur on each transmission. The only means to break the interference would be waiting until the enable pulses drift out of synchronization or to shut off one of the offending repeaters. OBJECTS OF THE INVENTION It is an object of the present invention, therefore, to provide a repeating system which eliminates interference between nearby repeator units. It is a further object of the present invention to provide a repeating system as described above which initiates rebroadcasts with a minimum delay time. A further object of the present invention is to provide a repeating system as described above which is fully automatic in operation. Briefly, according to the invention, a radio wave communication system comprises a base station and mobile stations broadcasting signals at a first frequency, a portable station receiving signals broadcast at a second frequency, and a plurality of repeaters receiving signals broadcast at a first frequency and rebroadcasting said signals at the second frequency. Each repeater comprises delay circuitry delaying rebroadcasts for a programmed time period; a detector sensing for signals broadcast at the second frequency during the delay period and including means inhibiting repeater rebroadcast in response to a received detect signal; and means for programming the time delay. The programmed delay circuitry includes a clock, a counter, and comparator means instituting rebroadcast at a predetermined count. The counter outputs a high count in its first mode and an initial count in its second mode. Further, the counter is adapted to increment its count output in a first polarity responsive to received program signals, and in a second polarity in response to input clock pulses. On reception of a signal to be rebroadcast, the clock initiates and begins counting down the counter. The first repeater to be incremented to its lowest state is the first to satisfy the comparator whereby retransmission occurs locking out the remaining repeaters. Repeater programming occurs when a portable unit is removed from the repeater mobile transceiver. At this time the repeater senses whether or not a transmission is occurring on the second frequency, acting to transmit a program signal incrementing all nearby repeaters to the next higher counter state in the absence of a second signal, and otherwise incrementing its own counter to a higher state if a detected signal is present. Thus, generally, the last repeater to enter an area will be the one in the lowest incremental state, hence the one to repeat all transmissions. Should the repeater in the lowest counter state leave the area, a remaining repeater in the second highest priority will rebroadcast after its time delay, and reset its own counter to the lowest state whereby minimum time delay is established for subsequent transmissions.

Computer prediction of field strength in the planning of radio systems

Abstract: The application of a method of predicting the field strengths from mobile radio base station transmitters and in radio links is presented, and the extension of the method to facilitate frequency assignment is outlined. The topographic data for a country are stored in a computer and programs are provided which predict the signal levels produced by a specific transmitter at points spaced 0.5 km apart. A further program enables a plotter to be used to derive signal level contours which can be overlaid on a map. The field strength prediction method is proving valuable in the siting of VHF base stations, in the reduction of field testing required for mobile systems, and in the study of possible areas of cochannel interference. It has also been extended to effect path calculations for point-to-point radio links. An extension of the cochannel interference study in which channel assignments are made by a logical procedure so as to maintain co-channel interference below some chosen level while making the minimum demands on the spectrum is outlined. The method described has potential applications in national frequency planning.

Statistical analysis of communications: Range and reliability in the presence of interference

Abstract: In this paper, a statistical method is developed for analysis of interference in land mobile communication systems Reduction of communication range and degradation of system reliability are calculated This method can be used for cases in which a desired signal is transmitted by a base station (or mobile unit) and received by a mobile unit (or base station) and is interfered with by a signal transmitted either by a fixed station or a mobile unit The spatial probability distribution of mobile units is considered The method is applicable to any frequency band for which path loss statistics are known An example of this method is given which calculates reduction in communication range, area and degradation of communication reliability for different values of splatter protection and distributions of mobile units