Abstract:
In the radiocommunications system according to the invention, all stations (N 1  to N 7 ) transmit radio signals with respective identifications (I 1  to I 7 ) assigned to them. Each station (N 3 ) has a memory which holds a first list (LA 3 ) with those identifications (I 2 ; I 4 ) which this station (N 3 ) receives directly from the at least one neighboring station (N 2 ; N 4 ), and a second list (LB 3 ) with those identifications (I 3 , I 1 ; I 3 , I 5 ) which the at least one neighboring station (N 2 ; N 4 ) receives directly from its neighboring stations (N 3 , N 1 ; N 3 , N 5 ) and routes to said station (N 3 ). 
     The stations therefore need not each contain a scanning receiver in order to avoid simultaneous use of the same frequencies used by neighboring stations for transmission purposes. 
     The stations are therefore simple in construction. The radiocommunications system can also be a single-frequency system.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to a decentralized radiocommunications system as set forth in the preamble of claim  1  and to a radio station therefor. 
     2. Discussion of Related Art 
     DE 39 08 940 A1 discloses a decentralized radiocommunications systems with a number of radio stations. Each of the radio stations has at least one neighboring radio station with which it is in direct radio communication. The prior-art radiocommunications system makes available several pairs of channels for duplex transmission between the radio stations. To ensure reliable radiocommunication, prior to the establishment of a radio link, each radio station checks all channels to determine whether they are free, and creates a so-called channel occupancy list. Then, a radio link is established to a neighboring radio station on a free channel. If the neighboring radio station is not a destination station but is to serve as a relay station, it will evaluate its channel occupancy list to establish a radio link to a further radio station. This makes it possible to establish so-called radio chains. In the radiocommunications system described in DE 39 08 940 A1, however, each radio station must check all channels prior to the establishment of a radio link, i.e., each station must include a scanning receiver. In addition, a radio chain can be established in the prior-art radiocommunications system only if a free pair of channels is found for each of the radio links, i.e., if several radio frequencies are available. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a radiocommunications system having radio stations of simple construction. The establishment of radio links is to be independent of whether the radiocommunications system is a multifrequency system or a single-frequency system. 
     In accord with a first aspect of the invention, a decentralized radiocommunications system comprising a number of radio stations (N 1  to N 7 ), each radio station (N 3 ) having at least one neighboring radio station (N 2 ; N 4 ) with which it is in direct radio communication, characterized in that all radio stations (N 1  to N 7 ) transmit radio signals with respective identifications (I 1  to I 7 ) assigned to them, and that each radio station (N 3 ) includes a memory which holds a first list (LA 3 ) with identifications (I 2 , I 4 ) which said radio station (N 3 ) receives directly from the at least one neighboring radio station (N 2 ; N 4 ), and a second list (LB 3 ) with identifications (I 3 , I 1 ; I 3 , I 5 ) which the at least one neighboring radio station (N 2 ; N 4 ) receives directly from radio stations (N 3 , N 1 ; N 3 , N 5 ) neighboring said at least one neighboring radio station and routes to said radio station (N 3 ). 
     According to a second aspect of the invention, a decentralized radiocommunications system as claimed in claim  1 , characterized in that the second list (LB 3 ) also contains identifications (I 2 , I 4 , I 5 , I 6 , I 7 ) which other radio stations (N 1 , N 5 , N 6 , N 7 ) receive and route via the at least one neighboring radio station (N 2 ; N 4 ) to said radio station (N 3 ). 
     According to the invention, each radio station transmits radio signals with an identification assigned to it and includes a memory which holds a first list with those identifications which said radio station receives directly from the at least one neighboring radio station, and a second list with those identifications which the at least one neighboring radio station receives directly from its neighboring radio stations and routes to said radio station. 
     In this manner, current lists are stored in each radio station which indicate to which neighboring radio stations a direct radio link can be established and to which other radio stations an indirect radio link can be established. Since identifications are registered and stored, no channel-scanning receivers are necessary. The radiocommunications system can also be a single-frequency system. 
     These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows schematically a radiocommunications system with a number of radio stations; 
     FIG. 2 shows schematically the contents of the stored lists for a radio station; and 
     FIG. 3 shows schematically the structure of data packets which are transmitted by the radio station. 
     FIG. 4 shows a radio station according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 schematically shows a radiocommunications system with seven radio stations N 1  to N 7 . The radio stations are mobile stations which can move freely in an area. Accordingly, the radio propagation conditions change continuously in the radiocommunications system, so that not all of the radio stations can communicate with one another directly at any time. FIG. 1 illustrates a receiving situation in which the radio stations N 1  to N 7  can communicate with one another as follows: 
     A direct radio link in the transmit and receive directions (duplex link) exists between the radio stations N 1  and N 2 , N 2  and N 3 , N 3  and N 4 , N 4  and N 5 , and N 6  and N 7 . In addition, one-way radio links exist between N 5  and N 6 , with only N 6  capable of receiving from N 5 , and between N 5  and N 7 , with only N 5  capable of receiving from N 7 . The reasons why not each of the stations is in direct radio communication with any other station are essentially as follows: firstly, shadow loss caused by fixed or moving obstructions (shown hatched in FIG.  1 ); secondly, the changing nature of the wave path; thirdly, faults occurring in the transmitter or receiver section, so that only one-way radio communication is possible. 
     In the receiving situation shown in FIG. 1, station N 2 , for example, cannot enter into direct radio communication with station N 5  but must establish a radio link via the other stations N 3  and N 4 , which act as relay stations. For a radio transmission between station N 4  and station N 7 , the situation as shown in FIG. 1 is as follows: Radio signals to be sent from N 4  to N 7  must be routed via stations N 5  and N 6 . Radio signals to be sent in the opposite direction, from station N 7  to station N 4  must only be routed via station N 5 . 
     As FIG. 1 shows by way of example, the situation may be very complex. The radio signals must be routed via one or more radio stations in order to finally arrive at the destination station. To ensure that radio communication and this routing can be carried out in a reliable manner, the radiocommunications systems according to the invention and the stations for this system have the following features, which will be described in reference to the situation for station N 3 . 
     Station N 3 , like each of the other stations, transmits radio signals with an identification assigned to it. Furthermore, station N 3 , like each of the other stations, has a memory in which a first list and a second list (FIG. 2) are stored. 
     As shown in FIG. 4, the stations may each include a signal processor including a microprocessor (CPU) with which to store and retrieve identifications to and from said lists. Each radio station will also have at least one antenna (ANT) for communicating with other stations. The antenna is connected to the signal processor via a connection C 1 , which is in turn connected to an Input/Output part of the signal processor and to a data, address and control bus (D, A, C). The memory may include both volatile (RAM) and nonvolatile (ROM) memory as known in the art. For example, the RAM of FIG. 4 may be used to store the lists of FIG.  2 . The radio station may also include an operator interface such as a keyboard and display or the like, which may be connected to the signal processor as shown through a connection C 2 . The operator interface and/or antenna can also be inside the radio station. 
     Like station N 3 , each of the other stations transmits radio signals with an identification assigned to it and with identifications from a first list and a second list. Also, each of the other stations includes a memory which holds a first list with those identifications which this station receives directly from the at least one neighboring station, and a second list with those identifications which all other stations receive directly from their respective neighboring stations. With each data packet, an identification from the first list and an identification from the second list is routed onward. With the identification which is assigned to the sending station, a first list is updated in the receiving station. With the identifications taken by the sending station from its first list and its second list, a second list is updated in the receiving station. The lists are created automatically upon turn-on and are shown completely in FIG. 2 for the receiving situation of FIG.  1 . 
     For station N 3 , this means: 
     The first list LA 3  stored in the memory contains first identifications which station N 3  receives directly from its neighboring stations N 2  and N 4 , namely the identifications I 2  and I 4 , respectively. These first identifications I 2  and I 4  are entered in a first column S of the first list LA 3 . Accordingly, the first column S contains those identifications which were transmitted by neighboring stations. A second column R of the first list LA 3  contains the identifications of those stations which received the identifications I 2  and I 4  from stations N 2  and N 4 , respectively. In this case, the second column R contains the identification for station N 3 , of course. The first list LA 3  thus indicates that station N 3  is receiving radio signals directly from the neighboring stations N 2  and N 4 . 
     The second list LB 3  contains the identifications which are received by the neighboring stations N 2  and N 4 . It also has a first column S, which contains the identifications of the sending stations, and a second column R, which contains the identifications of the receiving stations. In the example shown in FIG. 2, in the first row of list LB 3 , the identification I 3  has been entered in column S, and the identification I 4  in column R. This row thus indicates that station N 4  (R=I 4 ) has received a radio signal directly from station N 3  (S=I 3 ). In another row of list LB 3 , the identifications S=IS and R=I 4  are given. Accordingly, station N 4  has received a radio signal directly from station N 5 . In another row, S=I 3  and R=I 2 . 
     Accordingly, station N 2  receives radio signals directly from station N 3 . In a further row of the second list LB 3 , S=I 1  and R=I 2 . Accordingly, station N 2  receives radio signals directly from station N 1 . The second list LB 3  thus contains the identifications I 1 , I 3  and I 3 , I 5  received by all neighboring stations N 2  and N 4 , respectively. 
     The second list LB 3  further contains information on the other stations N 1 , N 5 , N 6 , and N 7 . In one row of the list it is indicated that station N 1  receives radio signals directly from station N 2  (S=I 2  and R=I 1 ). For station N 5  it is indicated that this station receives directly from N 4  or N 7  (S=I 4  and R=I 5 ; S=I 7  and R=I 5 ). A further row indicates that N 6  receives directly from N 5  or N 7  (S=IS and R=I 6 ; S=I 7  and R=I 6 ), and that N 7  receives directly from N 6  only (S=I 6  and R=I 7 ). 
     By storing the lists LA 3  and LB 3  shown in FIG. 2, station N 3  has connection data which indicate to which neighboring stations N 2  and N 4  a direct radio link can be established and to which non neighboring stations N 1 , N 5 , N 6 , and N 7  an indirect radio link can be established. The other stations of the radiocommunications system have corresponding lists, so that radio signals can be quickly and easily routed within the radiocommunications system. 
     The following describes in more detail with the aid of FIG. 3 how the stored lists are created. The method is identical in each station, so that it can be applied to a decentralized wireless LAN (local area network). 
     The radiocommunications system described is a digital system in which data packets are transmitted. FIG. 3 a  schematically shows the structure of such a data packet DAT. Each packet begins with two data fields H, hereinafter also referred to as “headers”. If no packets with data have to be transmitted, empty packets with the headers are transmitted at sufficient time intervals so that the two lists (see FIG. 2, LA 3  and LB 3 ) can be continuously updated. The first data field contains information from the first list, and the second data field contains information from the second list. FIG. 3 b  shows three data packets which are transmitted by station N 3  one after the other, namely the packets DAT, DAT′, and DAT″. Each of the packets has a first data field HA 3 , HA 3 ′, HA 32 ″ and a second data field HB 3 , HB 3 ′, and HB 3 ″. Each first data field contains information from the first list (see FIG. 2, LA 3 ), and each second data field contains information from the second list (see FIG. 2, LB 3 ). 
     With each transfer of the information from the lists into the headers, the information from the respective next rows of the lists is transferred, so that the transfers occur periodically. Each data field is subdivided into four subfields, namely a first subfield S, a second subfield R, a third subfield CT, and a fourth subfield CL. The subfields CT and CL are also contained in the lists LA 3 , LB 3  of FIG. 2; they are not shown there for the sake of clarity. The first subfield S contains the identification of a sending station, and the second subfield R contains the identification of a station which receives the transmitted identification. These subfields S and R have entries which correspond to the entiries in columns S and R of the lists of FIG.  2 . The third subfield CT contains a time stamp, and the fourth subfield CL contains a count. The entries in the subfields will now be explained in more detail with the aid of the example of FIG. 3 b:    
     Let us assume that station N 3  received the identification I 2  from neighboring station N 2 . The identification I 2  was stored in column S of the first list LA 3 . This information S=I 2  and R=I 3  now is to be sent to other stations. 
     In addition, station N 3  had earlier received, via neighboring station N 4 , a radio signal which contained the identifications S=I 6  and R=I 7 . These identifications were entered in subfields of the data field (header) of the radio signal. Accordingly, station N 7  (R=I 7 ) can be received directly by station N 6  (S=I 6 ). This information S=I 6  and R=I 7  was stored in the second list LB 3  of station N 3  and now is to routed to other stations. 
     Before sending the data packet DAT, station N 3 , by accessing the first list LA 3 , forms the first data field HA 3  with the following entries: S=I 2 , R=I 3 , CT= 21 , and CL= 10 . During the creation or replacement of the entry in the first list, the count CL was set at a maximum value (for example 10). 
     During the access to the first list, the count CL is decremented by one for the next access. When the counter has reached a lower limit, the entry in the first list is deleted. 
     Thus, the first data field HA 3  provides the following information: Station N 3  can receive directly from station N 2  (S=I 2  and R=I 3 ). The information has the time stamp CT=21 and the count CL=10. The time stamp CT corresponds to the current system time and indicates at what time the data field HA 3  was created. Consequently, the time stamp CT indicates how old the data field is, and the count CL indicates how often the data field has already been routed onward. 
     Both the time stamp and the count are criteria of the dwell time of a data field in the radiocommunications system. Based on these criteria, an “obsolete” data field can be removed before or after the radio transmission when the count has reached a lower limit. Or it can be replaced after the radio transmission by a “more recent” data field if the time stamp is more up to date. 
     In addition to the first data field, station N 3 , by accessing the second list LB 3 , forms the second data field HB 3  with the following entries: S=I 6 , R=I 7 , CT=3, and CL=7. For the next access, the count CL in the second list is decremented by 1. When the count has reached a lower limit, the entry in the second list is deleted. The data field HB 3  contains the following information: Station N 7  has received a radio signal directly from station N 6 . The data field HB 3  was created by station N 7  at the time CT=3. This system time is retained when the information is routed onward. The information that station N 7  receives directly from station N 6  (S=I 6  and R=I 7 ) has already been routed onward within the radiocommunications network three times ( 3 =10−CL=10−7). By sending this data packet DAT with the associated data fields HA 3  and HB 3 , the abovementioned information is communicated to the stations adjacent to station N 3 , i.e., to stations N 2  and N 4 . 
     Station N 2 , for example, gets the information from the first data field HA 3  that station N 3  can receive radio signals from it direct (S=I 2  and R=I 3 ). Information from the first data field is checked in the receiver N 2  to see whether it was originally created by N 2  itself; if so, it will be discarded. Otherwise the information will be entered in the second list in station N 2  if not already contained therein and if the count CL has not already decreased below a lower limit; otherwise this information will be discarded. If the information is already contained in that second list, it will be updated if it bears a more recent time stamp. If it has already been entered with a more recent time stamp, it will be discarded. 
     From the second data field HB 3 , station N 2  gets the information that station N 7  can receive radio signals directly from station N 6  (S=I 6  and R=I 7 ). Based on the received data field HB 3 , station N 2  will also check its second list and, if necessary, renew it (analogously to data field HA 3 ). Finally, as a result of the fact that station N 2  has received an arbitrary packet from station N 3 , the first list of station N 2  is updated. An entry S=I 3  and R=I 2  is made in the first list if this entry is not already present. The count CL, which determines the dwell time of the information, is set to a maximum value (for example 10). If the information is already contained in the first list of station N 2 , the count CL will only be reset to the maximum value. 
     The same applies analogously for station N 4 : If station N 4  has received the data packet DAT with the data fields HA 3  and HB 3 , then N 4  will check its second list by means of the data fields HA 3  and HB 3  and, if necessary, supplement or renew it. Having received a data packet from station N 3 , station N 4  will supplement or renew its first list. 
     By exchanging data packets with the above-described data fields (headers) in the entire radiocommunications system, it is ensured that updated lists are always available in each station. 
     Besides the packet DAT, FIG. 3 b  shows two further packets DAT′ and DAT″, which are transmitted by station N 3  with the next packet or the next packet but one, i.e., one or two cycles later. The packet DAT′ contains a first data field HA 3 ′ with the information S=I 4 , R=I 3 , CT=22, and CL=10. Accordingly, this first data field HA 3 ′ provides the information that station N 3  can receive radio signals directly from station N 4 , and that this information was created at the system time CT=22 (one cycle later) and has not yet been routed onward (CL=10). The packet DAT′ further contains a second data field HB 3 ′ with the following information: S=I 4 , R=I 5 , CT=4, and CL=2. Accordingly, the second data field provides the following information: Station N 5  can receive radio signals directly from station N 4 . This information was created at the system time CT=4 and has already been routed onward eight times (8=10−CL). 
     The further packet DAT″ has a first data field HA 3 ″ with the following information: S=I 2 , R=I 3 , CT=23, and CL=9. This data field HA 3 ″ differs from data field HA 3  of the first data packet DAT only in that it has already been routed onward once (1=10−CL) and carries the most recent time stamp CT=23 in station N 3 . Accordingly, station N 3  transmits the same information again two cycles later, as it already did in conjunction with the packet DAT. By this repeated transmission it is ensured that the information is also received at those stations which did not receive it before. When the count CL has reached a lowest value, this means that station N 2  was no longer received by station N 3  and thus has failed or is in a shadow region. The information is then discarded from the first list and thus no longer broadcast in the wireless LAN. By this mechanism, the information can be deleted from the first lists throughout the wireless LAN. After a certain time, the neighboring stations will also discard this information from the respective second lists until it is known in the entire network that this path S=I 2 , R=I 3  can no longer be used. The packet DAT″ further contains a second data field HB 3 ″ with the following information: S=I 2 , R=I 1 , CT=7, and CL=5. Thus, by transmission of this data field, the other stations are informed that station N 2  can receive directly from station N 1 . This information has already been routed onward five times (5=10−CL=10−5). If this information is not renewed in the second list of station N 3  by reception via any other station in the wireless LAN, after a few further transmissions, it will be deleted from the second list of station N 3  as soon as the count CL, after being decremented on each transmission, has reached a lower limit. By this mechanism, the paths in the second lists can be deleted throughout the wireless LAN if communication is no longer possible. 
     In the radiocommunications system described above, all stations have the information necessary to route radio signals onward in arbitrary receiving situations. This information is continuously updated. The radiocommunications system is especially suited for use as a decentralized mobile radio system, such as a military radio system, for cordless office communication, or for wireless computer networking (wirelss LAN). The radiocommunications system need not necessarily make available several channel pairs but may also be a single-frequency system. In the above example, the information to be exchanged is transmitted together with the user data. It is also possible to transmit information separately from the user data, for example over a separate signaling channel. While the above embodiment is directed to a digital packet-radio system, it is to be understood that the invention is also applicable to analog radio transmission.