Patent Publication Number: US-8971938-B2

Title: Non-interfering multipath communication system

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/449,455 filed May 30, 2003, and U.S. patent application Ser. No. 12/072,446, filed Jan. 26, 2008, each of which is incorporated herein by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     This invention relates to a non-interfering multipath communication system. 
     BACKGROUND OF THE DISCLOSURE 
     Monitoring and control systems such as used to supervise processing plants and manufacturing processes and machines have become a critical part of operations. A report of an unsafe or hazardous condition can shut down an entire facility operation resulting in huge costs and delays. Wired systems often use redundant conductor paths from the field station sensor/actuators to the base station to avoid incorrect signals or total loss of signals due to accident or failure. Wireless systems have become much more appealing due to their lower installation cost and ease of installation and redeployment. One problem with wireless and even wired systems is that if anything interferes with the delivery of the signal from the sensor/actuator transducer at a field station faulty reports or even worse no reports can precipitate a variety of unnecessary effort before the true situation can be determined. Redundancy is always a solution but often it adds to the complexity and power required as well as to the cost. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     It is therefore an object of this invention to provide improved non-interfering multipath communication system. 
     It is a further object of this invention to provide such an improved non-interfering multipath communication system which is simpler and more power efficient. 
     It is a further object of this invention to provide such an improved non-interfering multipath communication system which is more reliable, faster and more robust. 
     If it is a further object of this invention to provide such an improved non-interfering multipath communication system which continues communications between a field station and base station even when some paths are blocked. 
     If it is a further object of this invention to provide such an improved non-interfering multipath communication system which provides redundancy at little cost compared to wired systems. 
     If it is a further object of this invention to provide such an improved non-interfering multipath communication system which simplifies the identification of the point of failure. 
     The invention results from the realization that a truly effective non-interfering multipath communication system can be achieved by establishing base transmit and receive periods for a plurality of spaced apart transceiver devices of a base station, communicating between at least one field station and the base station through the transceiver devices and allocating at least a transmit period of the base station amongst the transceiver devices to maintain non-interfering multipath communication between the at least one field station and the base station even when some paths are blocked. 
     This invention features a non-interfering multipath communication system including a base station having base transmit and receive periods and including a plurality of spaced apart transceiver devices. There is at least one field station for communicating with the base station through the transceiver devices during the periods. The base station includes a controller device for allocating the periods amongst the transceiver devices to maintain non-interfering multipath communication between the at least one field station and the base station. 
     In a preferred embodiment the base station may include a base clock circuit for defining the base transmit and receive periods, and the field station may include a field clock circuit for defining field transmit and receive periods and at least one of the clock circuits may generate a sync clock pulse to synchronize the clock circuits with each other. The field station and the transceiver devices may communicate by conductors or via electromagnetic radiation, such as rf. The field stations may include at least one of a sensor transducer and an actuator transducer. The controller device may include means for allocating the periods to the transceiver devices randomly or in a predetermined order. 
     The invention also features a non-interfering multipath communication method including establishing base transmit and receive periods for a plurality of spaced apart transceiver devices of a base station and communicating between at least one field station and the base station through the transceiver devices. A period of the base station is allocated amongst the transceiver devices to maintain non-interfering multipath communication between the at least one field station and the base station. 
     In a preferred embodiment there are established field transmit and receive periods for the field station and a sync pulse is generated to synchronize the clock circuits with each other. The transmit periods may be allocated to the transceiver devices randomly or in a predetermined order. There may be established field transmit and receive periods for the field station and there may generated a sync clock pulse to synchronize the clock circuits with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram of a non-interfering multipath communication system including a base station with a number of remote spaced apart transceiver devices including a base station and a plurality of field stations; 
         FIG. 2  is a more detailed schematic block diagram of the base station of  FIG. 1 ; 
         FIG. 3  is a more detailed schematic block diagram of the field station of  FIG. 1 ; 
         FIG. 4  is an illustration of the sequence of signals between base station transceiver devices and a field station; 
         FIGS. 5 and 6  are a flowchart showing the method of operation of a field station according to this invention; and 
         FIGS. 7 and 8  are a flowchart showing the method of operation of the base station transceiver device according to this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. 
     There is shown in  FIG. 1  a non-interfering multipath communication system,  10 , according to this invention, including the base station,  12 , having a controller,  14 , and plurality of remote transceiver devices,  16   a ,  16   b ,  16   c ,  16   d ,  16   n , which communicate with a plurality of field stations,  18   a ,  18   b ,  18   c ,  18   n , the communication between transceiver devices,  16   a - 16   n  and field stations  18   a - 18   n  may be rf as indicated by the antennas  17   a - n  and  19   a - n , respectively, in  FIG. 1  or it may be by solid conductors such as coaxial cable not shown for clarity. 
     Controller  14 , includes CPU  20 ,  FIG. 2 , and memory  22 , which includes stored program data. Also included in controller  14  is clock circuit  24  which operates in conjunction with the similar clock circuit in each of the field stations to synchronize the operation of the system. An external interface  26  is provided to enable the CPU  20  of controller  14 , to transmit to and receive information from the world outside of system  10 . Each field station as indicated by field station  18   a ,  FIG. 3 , also includes a CPU  30  and a memory  32  which includes stored program data and a clock circuit  34 . A transceiver  36  with antenna  19   a  is provided to broadcast the information from CPU  30  and to receive information from the base station for CPU  30 . Field station  18   a  also includes a transducer  38  which may include an actuator: for example, for operating a valve, switch, or a sensor for monitoring temperature, pressure, weight, ambient light, or any other parameter. 
     In operation CPU  20  in controller  14  provides a succession of acknowledge sync signals from transceiver device  16   a - 16   n  which is delivered to the one or more field stations  18 - 18   n . As shown in  FIG. 4 , the base station sends out an acknowledge sync signal at time slot  50  to the first field station  18   a , at time slot  52  to the second field station  18   b , and so on. For this example the acknowledge sync signal explanation of base station operation is just with respect to two field stations in order to simplify the description. After the acknowledge sync signal has been sent out from remote transceiver device A at times  50  and  52  to field stations  18   a  and  18   b  there is provided two corresponding time slots  54  and  56  during which field station  18   a  and  18   b  respectively, can respond with their status. Following this an acknowledgement sync signal will be sent out from remote transceiver device B,  16   b  to field station  18   a  in slot  58  and to field station  18   b  in slot  60 . Following this the base station provides two time slots,  62  and  64  for field stations,  18   a  and  18   b  to respond with their status. Following this controller  14  enables remote transceiver device C,  16   c  to send an acknowledged synchronized signal in time slot  66  to field station  18   a , and in time slot  68  to field station  18   b . Following this, two time slots,  70  and  72 , are provided for field station  18   a  and  18   b , respectively, to respond with their status. Assuming there are only three remote transceiver devices A, B, and C,  16   a ,  16   b , and  16   c , the base station would then return to slots  50  and  52  where it would cause remote transceiver device A,  16   a , again to send out acknowledge sync signals to field station  18   a  and  18   b , respectively. Although the description is limited to just three transceiver devices A, B, C, namely,  16   a ,  16   b , and  16   c , and two field stations, field station  1  and field station  2 ,  18   a , and  18   b , this is not a necessary limitation of the invention, as any number of remote transceiver devices and field stations may be employed. In addition, although the acknowledge sync signals are sent out in order A, B, and C, this is not a limitation of the invention, as any order, including random order may be imposed by CPU  20  on the issuance of the acknowledge synchronize signals and the time slots for replies. 
     During the aforementioned operation of the base station, each field station as exemplified by the following description of field station  1 ,  18   a , is going through one or more of the following operations. Assuming for purposes of discussion that we are discussing field station  1 ,  18   a , it might be in a standby condition where it is monitoring the condition of the sensor for example. If during that monitoring period the field station determines that the synchronism of its clock  34  with the clock of the base station  24  is slipping, it will turn on and seek to find an acknowledge sync signal. Since it turns on at point  80 , well after the acknowledge sync signal has been sent at  50  and  52 , it awaits the next acknowledge sync signal at  58 ,  60 , at which time it once again synchronizes its clock,  82 , with the base station and returns to the monitoring state  84 . 
     Alternatively, while the field station is in a monitoring condition,  86 , it may be triggered by either a sensor event or a so-called “watch dog” event. A watch dog event occurs simply because the timer has been set to force the field station to communicate after a certain period of time, even if it has nothing to say, just to ensure that it is still operative. Thus, either a sensor event or a watch dog event triggers the field station at  88 . Assuming at this point that it has synchronism between its clock circuit and that of the base station, it waits until its slot  62  becomes available, and transmits and then waits  92 . Then turns its receiver on at  94  and receives an acknowledgement  96  that its transmission  90  has been properly received. It then returns to the monitor state  98 . 
     Alternatively with the field station once again in a monitoring mode  100  waiting for a sensor event or a watch dog event, a trigger occurs at  102  after which the system waits for its slot to transmit at  104 , and then waits again at  106 . But now it receives nothing back at  108  because the path between this particular field station and the transceiver device, C,  16   c , is blocked. At this point the field station waits again  110 , then transmits once again in its own slot  112  and waits again  114 . Now it receives an acknowledge sync from transceiver device, B,  16   b , instead of C,  16   c  and since the message has been received at  118  the system goes back to the monitoring state at  120 . Thus, any time the path between a field station and a particular one of the operative transceiver devices,  16   a - 16   n  is blocked, the field station will simply recycle and attempt to retransmit until it finds a path to at least one of the transceiver devices,  16   a - 16   n , so it can communicate fully with the base station. Although the explanation of field station  1 ,  18   a  in  FIG. 4 , has been made with respect to it containing a sensor only, it may contain a sensor and an actuator or just an actuator. If the actuator is the active component, at the moment, then during those time slots such as  54 ,  56 ,  62 ,  64 ,  70 ,  72  when the station is sending back the sensor information, the converse would occur. That is, the base station, during those time slots would be sending information to cause the operation of the actuator. 
     The operation and method of this invention is shown with respect to field stations in  FIGS. 5 and 6  and with respect to the base station in  FIGS. 7 and 8 . Initially, the field station monitors the sensors, its watch dog clock and its own synchronous clock,  150 ,  FIG. 5 . If the field station synchronous clock has expired,  152 , the field station will wait until the base acknowledge sync signal is expected  154  and then turn on the field transceiver  156 . It then listens until the base acknowledge sync is received  158 , where upon it re-syncs the field station sync clock,  160  and then returns to the monitoring of the field station sensor, watch dog clock and sync clock in step  150 . If in step  152 , the field station sync clock is ok, the system goes directly to step  162 , where it queries whether the sensor has been triggered or the watch dog clock has expired. If it has, then the system waits till the field station slot is available,  164 , transmits its status  166 , waits until the acknowledge sync time occurs  168  and then receives the acknowledge sync  170 . If the sensor trigger has not occurred and the watch dog clock is not expired in step  162 , the system simply returns to monitoring the field station sensors, watch dog clock and sync clocks in step  150 . After the acknowledge sync has been received in step  170  the query is made as to whether the acknowledge sync was received in good form, in step  172 . If it was, the synchronous clock is resynchronized  174  and the system waits until the acknowledge sync status time occurs  176  and then it receives the acknowledge sync status in step  178 . If then the acknowledge status is bad in step  180 , or if the acknowledge receipt failed in step  172 , the system increments the count of failed messages,  182 . If in step  184  the failed message count equals the maximum, the sensor trigger is cleared  186  and the watch dog clock is reset  188 . If in step  180  the acknowledge status is ok, then the failed message count is cleared in step  190 . If in step  184  the failed message count is less than the maximum, the system returns to wait until the field station slot is available in step  164 . After the watch dog clock is set in step  188  the system once again returns to monitor the field station sensors, watch dog clock and sync clock in step  150 . 
     The method and operation of the base station begins with selecting the active base station remote transceiver via a random or pre-selected sequence method,  200   FIG. 7  and then sending an acknowledgement on the selected remote transceiver  202 . The base station then listens on all remote transceivers for incoming field station status,  204 . Each field station status is then parsed as received by each remote transceiver using error checking codes  206 . Then for each field station  208  there is selected all the field station statuses received by each remote transceiver for each field station  210 . If any particular field station status is error free, then an acknowledgement is marked ok, otherwise the acknowledgement is marked failed  212 . Then all of the statuses received for that particular field station are compared and if they are identical to the error free status, the path is indicated as ok, otherwise this path may be identified as one which is blocked or in which there is some sort interference that needs to be addressed  214 . The system then returns in step  216  to step  208  to perform this loop for the next field station, after first incrementing, in step  218 , the number of the field station. If in step  216  the maximum number of field stations has been reached the system returns to step  200  where the base station selects a remote transceiver according to some random or pre-selected sequence method. 
     Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. 
     Other embodiments will occur to those skilled in the art and are within the following claims: