Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Utility Patent
1996-10-16
2001-01-02
Vo, Nguyen (Department: 2745)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S009000, C455S518000
Utility Patent
active
06169880
ABSTRACT:
BACKGROUND
The present invention relates generally to radio communication systems employing repeaters, and in a particular to a radio communication system and method for sharing repeater processing load between a plurality of radio repeaters.
It is generally desirable to provide “balanced” mobile radio coverage within a radio communication system. A system is “balanced” when each mobile radio that receives messages from a given base site may, in turn, successfully transmit messages to the base site. This goal may be achieved to some extent by appropriately adjusting the location and output power of the base site equipment, as well as the output power of the mobile radios.
However, in many applications it is necessary to communicate between a base site and one or more hand-held portable radios. For instance, foot patrolmen typically carry small portable radios to communicate with a central base site. Also, squad car officers typically carry similar portable radios when leaving their vehicles to investigate an accident, complaint or disturbance. Because of size constraints, these smaller mobile radio units often do not have sufficient power to reach a central base site, thereby preventing balanced coverage.
System designers have addressed this problem through the use of repeaters. In operation, the low power portable radios transmit their messages to a repeater station, where the messages are forwarded to the base site, typically at a higher power level. The repeater station may be mobile. For instance, as illustrated in
FIG. 1
, messages transmitted by a police officer's
18
portable radio
20
might be transmitted to a repeater (not shown) housed in the officer's squad car
10
, and then forwarded to the base site
4
. Typically, vehicular repeaters employ a first frequency (f
2
) when communicating with the portable radios, and a second separate frequency (f
1
) when communicating with the base site equipment.
However, it is not uncommon to have plural squad cars (e.g. squad cars
10
,
12
,
14
, and
16
) report to the same scene at the same time. Each squad car may have its own repeater. As such, there arises the problem of choosing which repeater will relay messages from the portable radios to the base site. Interference will result if more than one repeater station attempts to relay the messages at the same time, because the repeaters typically relay messages from the portable radios to the base site using the same frequencies (f
1
and f
2
).
Traditionally, conventional systems have attempted to mitigate this problem by assigning the role of “priority” repeater to one of the repeaters. All messages transmitted from the portable radios are routed through the priority repeater to the central base site. One way of accomplishing this objective is by using random sampling to select one repeater from a group of repeaters. More specifically, each repeater in the vicinity of a portable radio receives messages transmitted by the portable radio. After receiving a message, each repeater generates an enable signal after a random time delay, and transmits the enable signal to other repeaters in the vicinity. The transmitted enable signal instructs the other repeaters to refrain from relaying the message to the base site. Thus, the first repeater to transmit its enable signal (as determined by the random time delay) will assume the role of “priority” repeater.
However, using random time intervals to choose the priority repeater imposes risks. There is a possibility that two repeaters may generate their enable pulses at the same time, and therefore simultaneously attempt to assume the priority role. Interference will then result. Furthermore, using random time intervals delays communication from the portable radios to the base site.
U.S. Pat. No. 4,056,780 to Faulkner presents one solution to the above noted problems. This system assigns a delay state to each on-scene repeater. The delay state depends on when the repeater came on-scene. That is, a first squad car to arrive at the scene of an accident, complaint or disturbance, is assigned a delay state of 0. Having the lowest delay state, this repeater assumes the role of repeating all portable radio messages to the base site. A second repeater to enter the region will transmit a tone indicating its presence, and assume a delay state of 0. Upon receiving the tone, the first repeater will increment its delay state to 1. Thereafter, when a message is received from a portable radio, each repeater starts a countdown timer. The initial value of the countdown timer is selected on the basis of its delay state. For example, the initial value may correspond to the delay state multiplied by some interval of time (such as 400 ms). Thus, the second repeater having a delay state of 0 will count down first, upon which it will relay the message from the portable radio to the base site. The first repeater will detect the transmission of the second repeater, and in response thereto, refrain from transmitting the message itself. However, if the second repeater leaves the area, the first repeater is allowed to count down to zero and relay the message. In this event, the first repeater will also decrement its delay state to once again assume the 0 state (e.g. thereby assuming the priority role once again).
The above technique decisively arbitrates between repeaters in a given geographic location, but has the negative consequence of depleting the battery supply of the priority repeater. For instance, suppose that three squad cars (equipped with repeaters) report to a scene of an accident. Further assume that all three repeaters remain on-scene for an extended period of time. According to the above described arbitration technique, the last-to-arrive repeater is assigned the role of priority repeater. This last-to-arrive repeater will remain the priority repeater for the entire length of the investigation. Operating one repeater for such an extended period of time may deplete its battery supply. Since repeaters are typically powered by the vehicle battery, the officer may return to his vehicle to find its battery depleted and the vehicle thereby rendered inoperative.
U.S. Pat. No. 5,056,152 to Truby attempts to solve this problem by discriminating between primary and secondary repeater units. Primary repeater units are housed within squad cars which typically have large enough batteries to power the repeater for extended periods of time. Secondary repeater units are housed within motorcycles (or like vehicles), which typically employ smaller batteries with shorter longevity. The technique taught by Truby assigns the role of priority repeater to a secondary repeater only if no primary repeaters are available. More specifically, the role of priority repeater is allocated to one of the on-scene primary repeaters according to the technique disclosed in the above-described U.S. Pat. No. 4,056,780. If no primary repeater is available, the first secondary unit to respond to the request assumes the role of priority repeater. That is, each secondary unit includes a count-down timer. When a request is entered for the services of a secondary repeater, each secondary repeater commences counting down. Each secondary repeater's count-down is governed by the software system of the repeater. The repeaters are not synchronized. Thus, the patentee asserts that it would be statistically unlikely that two specialized radios would count down to zero at the same time. The secondary repeater which does count down to zero first is assigned the role of relaying messages to the base site.
While it may be uncommon that two or more repeaters could simultaneously relay a message to the base site, the importance of message integrity in many applications demands assurances that this event will not happen. Furthermore, this technique may still deplete the battery of a primary repeater.
Accordingly, it is an exemplary objective of the present invention to ensure that two repeaters do not simultaneously assume the role of priority repeater. It is another exemplary objectiv
La Fratta Laurence A.
Priest Mark D.
Burns Doane Swecker & Mathis L.L.P.
Ericsson Inc.
Vo Nguyen
LandOfFree
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