Background Art One type of conventional video surveillance system consists of cameras that are deployed at remote locations that are desired to be monitored by security personnel. The images from the different cameras are displayed on one or more video monitors at a security console. This type of surveillance system has been effective for improving security in a monitored facility because the system provides images to the console in real-time, and the operator of the system can take immediate remedial action. In order to maintain the system operating at a relatively low cost, the remote locations have to be fixed (i. e., non-mobile remote locations).

The problem of violence between students while on school buses (70,000 school buses in North America) is an escalating one. Numerous reports on television show fights that take place in school buses. Because of this problem, many school districts in North America use video surveillance on school buses.

Problems of violence and other illegal activities are common on other forms of public transportation as well.

In another type of conventional video surveillance system used in school buses, video cameras and recorders are placed in a remote and mobile location.

School municipalities use this system to monitor violence on buses and prosecute offenders. The operator of the surveillance system (i. e., the school officials) places a video camera recorder in a sturdy tamper-proof box in the interior of the school bus,

so that the camera can record images of the interior of the bus. If a violent event takes place on the bus, the bus driver would notify school officials, who remove the videotape from the recorder. The school official uses the videotape to identify the perpetrator of the violence and take disciplinary action. In this type of system, however, real-time information is not provided to the operator of the system.

Instead, the images are recorded and then reviewed by the operator. The operator only learns about the violent events long after the event took place, when the damage has already been done. In addition to this disadvantage, without real-time information available there is no knowledge of the geographical location of the vehicle. Thus, the advantage of this second conventional system over the first conventional system is that it facilitates video surveillance from remote, mobile locations. The disadvantage of using this system consists in that the video image provided is not a real-time image, and therefore, the operator of the system cannot take immediate remedial action.

There are techniques that could be used for transmitting video or data signals from a mobile vehicle to a central location, but they all have intrinsic costs or problems. One such technique is direct broadcast. In direct broadcast a video camera is attached to a radio transmitter that directly transmits the image captured by the camera to a CMO. The transmission scheme of this technique has a limited range and runs into problems related to the transmission of a radio signal through obstacles such as tall buildings. Radio transmitters that can go longer distances are physically large and expensive.

An alternative to the use of direct broadcast radio transmitters is to use a third party communication service, such as a cellular telephone company. The cellular network would be used to transmit data from a camera at a remote mobile location to a CMO. Specifically, the Cellular Digital Packet Data (CDPD) standard for data communications (as opposed to simply voice communications) in a cellular system could be used. The main disadvantage of using a third party communication service is that the vehicle would need to establish and maintain an expensive link to a central cell tower (the user is charged on a per-minute basis) for using the CDPD

cellular telephone service. This method tends to be expensive and requires the presence of cell towers in the vicinity of the operator's transportation service.

Therefore, there is a need for a video surveillance system that facilitates the transmission of real-time information, including sound, image, and geographical location data, to a CMO from a remote and mobile location, wherein such information transfer is cost effective.

Disclosure of Invention Accordingly, it is an object of the present invention to meet the foregoing needs by providing systems and methods that perform real-time video monitoring of a remote and mobile environment in a cost-efficient manner.

Specifically, a system for meeting the foregoing needs is disclosed. The system includes at least one input monitoring unit that monitors an environment and produces a video and an audio signal corresponding to the environment; a CMO that displays image and sound information corresponding to the video and audio signals; and a self-organized mobile wireless communications network. The at least one input monitoring unit is remote from the CMO and transmits the video and audio signals to the CMO over the wireless communication network.

Both the foregoing general description and the following detailed description provide examples and explanations only. They do not restrict the claimed invention.

Brief Description of Drawings Figure 1 is a block diagram of the preferred embodiment of the video surveillance system of the present invention; and Figure 2 is a block diagram of the Video Monitoring Hardware in Figure 1.

Figure 3 is a diagram illustrating a communications network in accordance with the present invention; Figure 4 is a flow chart illustrating of the overall method of operation of each of the stations in the network of Fig. 3; Figure 5 is a flow chart illustrating an affiliation procedure employed in the

method of Figure 3; Figure 6 is a flow chart illustrating an affiliation check procedure employed in the method of Figure 4; Figure 7 is a flow chart illustrating a resignation check employed in the method of Figure 3; Figure 8 is a further resignation check procedure also employed in the method of Figure 3; and Figure 9 is a still further resignation check procedure employed in the over all method of Figure 3.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Best Mode for Carrying out the Invention Reference will now be made to preferred embodiments of this invention, examples of which are shown in the accompanying drawings and will be obvious from the description of the invention. In the drawings, the same reference numbers represent the same or similar elements in the different drawings whenever possible.

Systems and methods consistent with the present invention enable the wireless transmission of real-time audio and video, and geographical location information from distinct remote locations to a system operator's premises (i. e., CMO). For purposes of the following description, the systems and methods consistent with the present invention are only described with respect to video monitoring systems that are remotely deployed in mobile vehicles. The description should also be understood to apply to situations in which the monitoring systems are placed in fixed remote locations.

Figure 1 shows a system 100 used to transmit real-time information from a video monitoring system in a mobile vehicle in a manner consistent with the present invention. The term"vehicle"as used in this invention refers to a school bus, a taxi, or any other kind of public transportation vehicle. The essential components of system 100 include at least one mobile vehicle 102 carrying video monitoring

hardware 101, and a CMO 108 having RF communication means 124 and a personal computer 112. An Internet web site 116, and at least one computer 118 at a remote location 122 can optionally be added to system 100, in order to allow a customer to access some of the images obtained by the CMO 108, but without incurring the high operational costs of running such an Office. Antennas are shown for Global Positioning System (GPS) signal transmission and reception 104 and for conventional RF communications (106 and 110).

The GPS antenna 104, connected to the Video Monitoring Hardware 101, receives a signal from a GPS satellite indicating the position of the vehicle. A conventional RF antenna 106 is also connected to the Video Monitoring Hardware 101, and is used to establish wireless communication links with other mobile vehicles 102 and with the CMO 108.

The Video Monitoring Hardware 101 includes a Personal Computer 202 (see Figure 2) that serves as a node of a wireless network of computers that are interconnected via the aforementioned wireless communications links. The computer 202 runs networking software that implements a technique for Self- Organizing a Mobile Wireless Station Network". For clarity, this technique is briefly described here, but it is described in detail at the end of the specification. In essence, the technique allows cellular telephone-like radio frequency (RF) communication of digital data, but the data hops from one node to the other, and therefore, this method does not require cell-towers (base stations).

The networking software moves data from a source (e. g., any of the vehicles) to a destination (the CMO) over a wide area by keeping track of all nodes in the near vicinity and routing data to the intended destination via the best nearby node. The best nearby node may be chosen on the basis of the quality of the RF connection, the available data bandwidth, data speed, or any other factor that would help increase the efficiency of the network. Consequently, a group of vehicles can use relatively short-range low-power RF transceivers to communicate over a large area.

The CMO 108 is the recipient of all of the real-time images and location information received from the several monitoring systems 101 deployed in the

mobile vehicles 102. The CMO 108 includes an antenna 110 for receiving the real- time information signal from the vehicles 102 over the air, and RF communication means 124 that downconverts, demodulates, and detects the received signal. The Personal Computer 112 displays the several images received from the vehicles 102, and downloads those images into an Internet web site 116. The Internet web site 116 is memory space reserved in the computer server of an Internet service provider, and contains information pertinent to the person or corporation contracting for that memory space. The web site can be accessed by persons through a computer that is connected to the Internet. Some web sites require a special password for accessing the information contained therewith, wherein the persons acquiring access to the web site obtain a password to enter the web site. In the present invention, the person acquiring the right to access the information on the web site is a customer (e. g., a taxi company), which uses the computer 118 located in the customer premises 122 to access the Internet web site 116.

Figure 2 depicts a block diagram of the Video Monitoring Hardware 101 of Figure 1. It includes a video camera 208, a GPS transceiver 206, and a small personal computer 202 with a PCMCIA RF transceiver 204. The video camera 208 captures real-time images and sound from inside the vehicle 102. The camera is physically connected to the computer 202 and passes the sound and image information to the computer via that connection. The GPS transceiver 206 decodes the GPS signal received by the antenna 104 from a GPS satellite (not shown) and sends the decoded signal to the computer 202.

The computers 202 in the wireless network are programmed to collect video images and audio from the cameras, and location coordinates from the GPS transceiver 206. The computer 202 forwards that information along a dynamically determined path to the CMO 108 which collects video images and GPS information from every node. The computer 202 includes a PCMCIA RF transceiver 204 that forwards the acquired real-time information to other PCMCIA RF transceivers 204 in the system.

As mentioned above, the information and pictures from all of the mobile vehicles 102 could optionally be presented on an Internet web site 116. Customers can monitor the location and video information of the mobile vehicles of their interest from their computer 118 at a remote location 122.

A typical operation of the video surveillance system would start by having the camera 208 in the vehicle 102 capture the sound and image of two students involved in a fight. The computer 202 receives these video and audio signals, as well as information provided by the GPS transceiver 206 about the geographical location of the vehicle 102.

The computer 202 runs a first program to digitize the image received, runs a second program to monitor the GPS signal received, and runs a third program, namely a multihop networking program, to implement the method disclosed in the aforementioned patent. The computer 202 sends the real-time information to the PCMCIA RF transceivers 204. The transceiver 204 transmits the information to either a PCMCIA transceiver 204 in another vehicle 102, or if this vehicle in particular is the closest vehicle to the CMO 108, to the RF communication means 124 of the CMO 108.

If nodes in the system, located at point A and point B (e. g., a mobile vehicle and the CMO), are within radio range of each other, they will transmit directly and not impact any other nodes when using the technique for self-organizing a mobile wireless station network. If nodes at point A and point B are out of direct radio range, the network software finds a route for the data to go from point A to point B via other nodes of the system. This route is determined by collecting information from all the other nodes in the system, particularly, information about the nodes connectivity.

Nodes at both point A and point B can be stationary or mobile. The networking software is always monitoring its neighbors and updating its links, so as nodes move geographically, the links may change, but the message will still get to point B.

The foregoing discussion shows only the general operational principles of the self-organized mobile wireless communications network used in the present invention. The manner in which the transceivers 204 acquire information about the vicinity of other transceivers 204, and specific details about the networking aspects of the invention are explained in the aforementioned patent.

When the real-time information arrives at the CMO computer 112, the sound, image and geographical location information are displayed on the screen of the computer 112. A security officer in the CMO 108 oversees the operation of the video surveillance system. When a problem arises in one of the school buses, the security officer calls the police to report the incidents, and provides the police with information about the school bus location.

As an alternative to having the security officer monitor all of the incoming images from different school buses, the images can be automatically downloaded to an Internet web site. When this approach is used, the company that is responsible for downloading the real-time information to the web site and for running the video surveillance system is still referred to as an operator. The persons that buy access into the operator's web site are the customers.

The different images in the Internet web site 116 correspond to particular sub-groups of school buses and can be accessed by customers. The images are accessed by using a personal computer 118 with an Internet connection and with an Internet web browser (e. g., Netscape Navigator).

One advantage of the operator-customer scheme over the single operator scheme is that the location of the customer (customer premises 122) does not depend on the location of the buses because the images are transmitted to the customer computer 118 through the Internet. By contrast, the location of the operator (CMO 108) depends, on the location of the buses that carry the video surveillance system.

That is, because the PCMCIA transceivers 204 have a limited coverage range, for example, 2 miles, the operator location 108 is limited to the location of the school district. In the situation in which the video monitoring system is used for other

purposes (not in school buses), the operator 108 must be located within a certain range of at least one of the PCMCIA transceivers 204.

Another advantage of the operator-customer scheme is that it allows customers at remote locations 122 to enjoy the benefits of the present invention, without incurring in costs of running a CMO. This is particularly important when a customer has an interest in monitoring only a subgroup of the vehicles that are part of the system 100.

The system of the present invention works well in an environment where there are a number of nodes in a geographical area, where the nodes can use each other as data relays to the destination. A problem that might arise is that of"dead" spots. As mentioned before, the PCMCIA transceivers 204 have limited coverage.

For the system to function, all of the RF transceivers, including the PCMCIA transceivers 204 as well as the RF communication means 124 of the operator, must be within a certain distance of each other. If one of the transceiver units 204 is isolated from the rest of the RF transceiver network (e. g., more than 2 miles apart from other transceivers 204 currently operating in the network), that transceiver unit will be unable to successfully transmit real-time information to the CMO 108.

The solution to the dead spots problem is to have transceiver relay units placed in boxes attached, for example, to telephone poles located in the dead spots.

The decision of placing relay units in telephone poles is left to the system designer for that particular school district, since factors such as the bus routes and the city layout differ for each system.

In conclusion, the present invention provides a new way of communicating images or messages between two points. Data is sent between two points, A and B, either directly from point A and point B, or can be transmitted from point A to point B, indirectly via a number of intermediate peer transceivers running the same networking software.

The present invention discloses a video surveillance system that uses ad-hoc networking to move data from vehicle to vehicle until the data reaches a CMO. The alternative to ad-hoc networking is to use commercial wireless telephone

technology, like CDPD, to transmit video images from a mobile vehicle to a cell site, and from the cell site to the CMO. The use of commercial wireless telephone technology, however, is an expensive alternative.

The wireless network technology allows an operator (e. g., a school district) to inexpensively monitor vehicles in real time. The main advantage of real-time monitoring over video recording is that real-time monitoring allows the operator to act immediately, as opposed to after the fact. If a security officer is watching a real- time image of the interior of a vehicle, and sees a fight break out, the officer can call the police and give them the location of the bus. The police would then be able to stop the violence before the situation gets out of control.

Other benefits which an operator may take advantage of consist in providing a service in which customers are informed of the arrival time of a public transportation vehicle to their destination, since the real-time information that is available includes the geographical location of the vehicles 102. Riders of school buses, transit buses, and taxis always want to know when the vehicle will arrive at their destination. A customer (e. g., a taxi company) with access to an Internet web site can be friendlier to its patrons by having this information readily available. This would prove to be especially useful in inclement weather, when a person wants to spend as little time as possible standing in the rain.

In the case where the video surveillance system of this invention is used as part of a building security system, the disclosed ad-hoc networking technique offers additional benefits over conventional video surveillance systems. One type of conventional video surveillance system requires the installation of cables or fibers to relay the signal from the camera locations to a CMO. The present invention makes use of RF transceiver technology, which saves the cost of cable installation.

If direct broadcast technology is used to transmit the signal captured by the camera instead of cable technology, large radios would still be needed, which cost more than the small RF transceivers used in the present invention. Furthermore, the self-configuring nature of ad-hoc networking techniques save the cost and complexity of setting up traditional radio links.

Technique for Self-Oranizing a Mobile Wireless Station Network As noted previously the disclosed invention utilizes a technique for self- organizing a mobile wireless station network. A detailed description of the above technique will be described herein. The technique allows individual mobile radio stations to operate in a manner such that they will automatically organize or configure themselves into an efficient network. Each station is assumed to have both transmitting and receiving capabilities, i. e. to be operational as a transceiver.

The network may, for example, be operated as a packet switched digital data network for communicating messages from one station to another once configuration is established. As is understood by those skilled in the art, procedures exist for routing messages over a network, even when the configuration of the network may occasionally change. Likewise, there are procedures for measuring or rating the connectivity of a network in a particular configuration or in alternate configurations. The present invention does not directly concern these procedures though their availability is assumed in the following description.

The present technique employs a plurality of stations which are essentially similar particularly in that each station can transmit at either a relatively high power level or at a relatively low power level, suitable for relatively long or relatively short network links respectively. Likewise, each station can operate at least in two basic modes, one of the modes being as a message gateway for a cluster of other (non-gateway) stations, the other mode being a relatively local mode operating as a non-gateway station. The cluster gateway stations operate at relatively high power level to communicate with other cluster gateway stations and thereby form a network backbone typically providing longer distance network links.

Referring now to Fig. 3, the communications network illustrated there employs a plurality of similar mobile stations, some of which are operating as cluster gateways. The cluster gateway stations are indicated by squares and are

designated by reference characters 11-15, whereas the non-gateway stations are indicated by circles and, for the most part, are not identified by individual reference characters. Established channels or data communications links connecting various of the cluster gateways are designated by reference characters 21-26. Links connecting non-gateway stations to gateway stations are shown by similar lines but, for the most part, without identification by individual reference characters.

While Fig. 3 illustrates a particular interconnection of the various stations shown, it should be understood that this configuration of connections is not pre- determined and that other patterns of connections might easily arise in accordance with the present invention. Further, the pattern of connections can change during operation, both to accommodate the introduction of new stations and to allow for the withdrawal or movement of one of the attached stations. The mode of operation of each station is controlled by an embedded microprocessor as is becoming increasingly conventional and the technique of operation described herein is intended to be implemented automatically by the programming of the microprocessors in accordance with the teaching herein.

In the overall method, shown in Fig. 4, of operating each station so as to effect the automatic organization of stations, certain of the procedures incorporated in the technique are described initially only in general functional terms and are then described in greater detail with respect to others of the drawings.

With reference to Fig. 4, each station is initially activated as initially indicated by the POWER on step 31. A delay of random duration, within preselected bounds, is provided as indicated at step 33. As indicated, this random delay is also introduced in several other of the program flow paths which merge at juncture 32 and is influential in implementing the general and fair allocation of roles to the various stations. After the delay, the station executes an affiliation procedure 35 during which it attempts to affiliate with an existing cluster gateway station. This affiliation procedure is described in greater detail hereinafter with

reference to Figure 5.

If the affiliation procedure is successful, as tested at block 37, the station commences operation as a cluster member as indicated at block 39 with operation being at the lower power level.

As is understood by those skilled in the art, packet switched network procedures typically include acknowledgement messages which confirm that a message transmitted has been received by the intended station and thus, each station is able to determine, on an ongoing basis, if it continues to be able to communicate through the network. This testing is indicated at reference character 41 and, so long as the station continues to be able to communicate, it remains as an existing cluster member. However, if at some point the station determines that it is no longer able to communicate, the program flow returns to the juncture indicated by reference character 32 and, after the random delay re-executes the affiliation procedure 35. During the affiliation procedure, the station may affiliate with a different cluster gateway, assuming that it is within range of any such station. In addition, each cluster member periodically executes an affiliation check procedure as indicated at block 43.

The affiliation check procedure is described in greater detail hereinafter with reference to Figure 6. So long as the affiliation check is satisfactory, the station again remains as a cluster member with its pre-existing affiliation. If a check is failed, the program flow again returns to the juncture point 32 and, after the random delay, re-executes the affiliation procedure 35.

If, on any attempt to execute the affiliation procedure 35, the attempt fails, the station enters operation as a cluster gateway as indicated by reference character 45. As indicated previously, a station operating as cluster gateway transmits at the higher power level. One of the additional functions performed by each station operating as a cluster gateway is to periodically broadcast so called beacon messages which establish the stations presence and its availability to operate as a gateway for a cluster of member stations. Further, each cluster gateway station will periodically transmit messages, at least to the other gateway

stations, which identify at least the members which leave affiliated with that gateway. Thus, the gateway stations can maintain a data structure indicating the present constituency of the network and the configuration of the network backbone. When it is stated herein that a station is operating at the higher power level, what is meant is that the station is operating at the higher power level in transmitting messages over the links which are established between gateway stations. It should not be inferred that the station will necessarily operate at the higher power level when communicating with affiliated member stations when that level of power would not be needed.

Periodically, each gateway station tests its proximity conditions to other gateway stations, e. g., by signal strength measurements or using other data available through the exchanging of messages by the cluster gateway stations which make up the network background. If the test indicates that proximity conditions are exceeded, i. e., that the particular station's operation as a gateway is possibly redundant and/or unnecessary, the station executes a resignation procedure as indicated at reference character 49. This resignation procedure is described in greater detail with reference to Figure 7. If the conditions for resignation are met as tested by the procedure indicated by reference character 51, the operational procedure returns to the juncture point 32 and after the random delay, again attempts the affiliation 35 procedure during which the station may commence operation as a cluster member rather than a cluster gateway as previously.

If the conditions are not met, the station remains in operation as a cluster gateway station as indicated at reference character 45.

With reference to Figure 5, a station executing the affiliation procedure 35 collects beacons from all gateway stations within range and establishes a list of such beacons as indicated by reference character 55. Gateway stations with signal strengths below a pre-selected threshold are ignored as indicated at block 57. If no gateway stations an the list are left, as tested at block 59, the affiliation procedure is terminated as unsuccessful, equivalent to a NO result from the

procedure as indicated at block 37 in Figure 4.

The available gateway stations, i. e., those with sufficient signal strength, are ordered in a list progressing from the most preferred or most powerful to the least.

This is indicated at reference character 61. As will be understood, the beacon collection and ordering procedure can also be implemented as a continuous or background operation so as to maintain a"preferred list"of gateway stations since such a list is also utilized at other points in the overall procedure as described hereinafter.

As indicated at reference character 63, an affiliation request message is then sent to the gateway station which is most preferred, i. e., the one at the top of the ordered list as indicated at reference character 63. If, within a predetermined time interval, a response message is received from the addressed gateway station, the candidate affiliate member sends off a message confirming its affiliation to that gateway station, as indicated at block 67, and the procedure is terminated as being successful, i. e., a YES decision out of the test 37 of Figure 4.

If the candidate member does not receive a response message from the addressed gateway station, that gateway deleted from the list as indicated at block 69. If no other possible gateway station exists on the list, as tested at block 71, the procedure is terminated as unsuccessful. If there is another possible gateway station which affiliation would be appropriate, the procedure returns to the block 63 so that an affiliation request can be sent off to that gateway station.

In the affiliation check procedure of Figure 2, each member station stores in an appropriate data structure, a number of"B"recent beacons from its own gateway, i. e., the gateway station with which it is affiliated. The data structure includes the signal strength of the various beacons. Periodically, as determined by a timer step 75, a test is performed, as indicated at reference character 77, to determine if a predetermined fraction of the beacons are of an amplitude which is above a threshold signal strength value. In other words, the member determines whether communications with the current gateway are reliable. If the fraction criteria is met, the affiliation check ends as being successful and, if not, it ends as

being unsuccessful, this being the test 4-ndicated by reference character 43 in Figure 4.

In the procedure of Figure 7, which further illustrates the resignation check procedure identified by reference character 49 in Figure 4, a station, presently acting as a gateway, broadcasts a resignation request message as indicated at block 81. Assuming they receive the request message, the linked cluster stations and affiliated member stations execute check procedures, as illustrated in Figure 8 and 9 respectively, and send response messages as appropriate. After predetermined length of time, determined as indicated at block 83, the acting station determines if it has received resignation confirmation messages from all neighboring gateway stations and all member stations affiliated with it. If all such other stations have sent such message and they have been received by the resigning gateway station, the procedure terminates as successful. If any neighboring gateway station or affiliated member station does not provide such a confirming message, the procedure terminates as unsuccessful and the station continues in its role as a gateway.

Each linked or neighboring gateway station receiving a resignation request from another gateway station, i. e., as broadcast at step 81 in Figure 7, executes the procedure illustrated in Figure 8. Using the data which the station has collected regarding the configuration of the network, the receiving gateway station checks to see if the requesting gateway station is an articulation point in the network backbone configuration. As is understood by those skilled in the art, the removal of a node at an articulation point would break the connectivity of the network backbone. if the requesting station is an articulation point, as tested block 89, the present gateway station does not, at block 91, send a confirmation message.

Accordingly, the requesting gateway station will be blocked from resigning.

If the requesting station is not an articulation point, the gateway station receiving the resignation request sends the appropriate confirmation message, as indicated at block 93, so that the requesting station can resign if all other affected station also confirm.

If a non-gateway or member station receives a resignation request from the gateway station with which it is affiliated, the member station checks, as indicated at block 95, to determine whether another gateway station is available for affiliation,. this check being made using the data in the list prepared at step 61 in the procedure of Figure 5 or from the preferred list if the beacon collection and ordering procedure is being performed as a background task. If another gateway station is available for affiliation, the appropriate confirmation message is sent, as indicated at block 97. On the other hand, if no alternate gateway station is available, no confirmation message is sent, as indicated at block 99, so that the proposed resignation is inhibited.

While the resignation check illustrated in Figure 8 inhibits resignation if backbone connectivity is broken, it should be understood that there are various ways of measuring connectivity in a network and a decision to inhibit resignation may be predicated on a reduction in connectivity level below a pre-selected level according to measurements made in accordance with these known schemes.

By way of illustrating the resignation process, it is useful to consider the gateway station 12 in the network configuration illustrated in Figure 3. Station 12 provides a communication path connecting stations 11 and 13 with station 14 but these paths are-redundant since direct paths exist between each station 11 and 13 and station 14. Likewise while gateway station 12 has a member station 30 affiliated with it this station could presumably also affiliate with existing gateway station 14. Accordingly, it can be seen that the resignation of the proposed gateway station 12 from its gateway status could be expected to be allowed in accordance with the procedures of the present invention. Further, when station 12 again attempts affiliation procedure it could be expected to be successful in affiliating as a member with gateway station 14.

While the present invention contemplates a network which includes a plurality of similar stations each of which can transmit at either a high power level or a low power level, it should be understood that such a network can also accommodate non-similar stations. For example, the network could accept

messages from single power handheld units which do not incorporate the capability of activity as a cluster gateway but which merely affiliate as members.

Likewise, while two power levels have been described together with a two level network architecture, it should be understood that the method of the invention is inherently recursive. Thus, a three or four level architecture can be straight forwardly implemented, using successively higher power levels to establish longer distance links which couple gateways for clusters of lower level gateways.

In view of the foregoing it may be seen that several objects of the present invention are achieved and other advantageous results have been attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it should be understood that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.