Abstract:
A communication system and method for vehicles, particularly trains, are described with the vehicle having antenna sets. Each antenna set includes a plurality of antennas mounted onto a convex-shaped vehicle roof in which an axis of one antenna set is approximately perpendicular to an axis of another antenna set and in which the antenna sets are mounted below roof level of the convex-shaped vehicle roof. A switching device is operable to switch between a first antenna configuration and a second antenna configuration based on a difference in measured signal power received at the antenna sets. The first antenna configuration is associated with a first stationary communication system of the plurality of stationary communication systems and a second antenna configuration is associated with a second stationary communication system of the plurality of stationary communication systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE 
       [0001]    This patent application claims the benefit from and priority to European Patent Application No. EP15165768, filed on Apr. 29, 2015. The above-identified application is hereby incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure generally relates to the field of communications and, in particular, to a system and a method that establishes wireless communication between a moving vehicle following a predefined path or track and base stations located along such a track. 
       BACKGROUND 
       [0003]    The widespread use of mobile communication devices for wireless data communication has made it a great challenge for manufacturers and operators of telecommunications networks to provide wireless data communication with sufficient bandwidth and broadband capacity. In particular, communication related issues can arise in transportation related use scenarios. For example, on a train where typically a large number of users attempt to simultaneously use broadband data communication services through the same limited number of base stations in range of the train, it can be very difficult to provide sufficient data communication capacity for a passing train. Moreover, the tremendous increase of the speed of trains has accentuated this problem since data communication resources need to be provided very quickly, with great bandwidth and broadband capacity, and for very short periods of time. 
         [0004]    Considering that modern high-speed trains or cars can travel at approximately 200 km/h or more, a customer&#39;s connection can be transferred to a new mobile network cell every 20 seconds, for example. Such rapid cell changes with many mobile communication users in a train pose a major technical challenge and call for different communication systems to cover an entire track. In such circumstances, it is desirable to provide a fast and reliable switching system and method. 
       BRIEF SUMMARY 
       [0005]    A system and/or method is provided for improved antenna switching in mobile communications for vehicles, substantially as shown in and/or described in connection with at least one of the figures, and as set forth more completely in the claims. 
         [0006]    These and other advantages, aspects, and novel features of the present disclosure, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and the attached drawings as listed below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1A  shows a train in the vicinity of a first stationary communication system according to an embodiment of the present disclosure. 
           [0008]      FIG. 1B  shows a schematic cross-section of the train in  FIG. 1A  according to an embodiment of the present disclosure. 
           [0009]      FIG. 2A  shows a train in the vicinity of a second stationary communication system according to an embodiment of the present disclosure. 
           [0010]      FIG. 2B  shows a schematic cross-section of the train in  FIG. 2A  according to an embodiment of the present disclosure. 
           [0011]      FIG. 3  illustrates a switching and control scheme for a vehicle-based antenna system according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1A  is a diagram illustrating schematically a top view of a moving train moving in the vicinity of a transceiver station. Referring to  FIG. 1A , there is shown a train  10  comprising a locomotive  15  and a number of coaches, of which coaches C 1  and C 2  are illustrated. The train  10  is on railroad tracks  19 . There is further shown a transceiver station  11  comprising a transceiver  11 B communicatively coupled to an antenna system  11 A. The antenna system  11 A can generate an illustrative radiation pattern, referred to as an RF antenna corridor  17 . A coach C 1 , C 2  can comprise an interior antenna  13 , a signal repeater  12 , a set of antennas A 1 , and a set of antennas A 2 . The set of antenna A 1  can comprise a plurality of antennas, of which two, A 11  and A 12 , are illustrated as black dots. The set of antennas A 2  similarly comprises a plurality of antennas, of which two, A 21  and A 22 , are illustrated as black dots. The antennas A 11  and A 12  are separated by a distance d 1 . Similarly, the antennas A 21  and A 22  are separated by the distance d 1 . The sets of antennas A 1  and A 2  are separated by a distance d 2 , as illustrated by the distance d 2  between antennas A 12  and A 22 . Generally, the antennas of one set are mounted on opposite sides of the vehicle with respect to those of the other set. In  FIG. 1A , the antennas A 11  and A 12  of the set A 1  are mounted on the right side (in direction of travel) while the antennas A 21  and A 22  of the set A 2  are mounted on the left side. The signal repeater  12  is communicatively coupled to the interior antenna  13  and to the sets of antennas A 1  and A 2 . 
         [0013]    The train  10  is powered by the locomotive  15  which is mechanically coupled to the coaches C 1 , C 2  as illustrated and moves the train  10  towards (as shown) or away from the transceiver station  11  along the railroad track  19 . 
         [0014]    The transceiver station  11  can be operable to transmit and/or receive radio frequency signal in accordance with one or more RF technologies, for example, mobile communication standards such as GSM, UMTS, WCDMA, 4G, LTE, HSDPA, HSUPA, 5G, and WiMAX 802.16. The transceiver station  11  can also be referred to as a base station or Node B in accordance with various embodiments of the present disclosure. The transceiver station  11  comprises a transceiver  11 B, which comprises suitable logic, circuitry, and/or code to generate and process radio and/or baseband signals in accordance with mobile communication standards. The signals received and/or generated at the transceiver  11 B, respectively, are then transmitted/received through the antenna system  11 A. The antenna system  11 A can comprise one or more antennas in general, but can typically comprise a plurality of antennas to allow various protocols of multiple-input multiple-output (MIMO) communication such as 2×2 communication with a mobile transceiver system such as those installed in the train coaches C 1 , C 2 , for example. For example, antenna system  11 A can be configured to receive and transmit a cross-polarized signal, i.e., receive and transmit two signals concurrently that are polarized differently, for example, horizontally and vertically. The antenna system  11 A can also be suitably configured to support other MIMO schemes in accordance with various embodiments of the present disclosure. The antenna system  11 A can be configured such that it receives and transmits favorably along the railroad tracks  19 . Such a favorable reception/transmission area is illustrated by the exemplary RF antenna corridor  17 . 
         [0015]    The coaches C 1 , C 2  can be adapted to any purpose including, but not limited to, the carriage of persons and/or goods. The interior antenna  13  can comprise suitable logic, circuitry, and/or code to receive and transmit radio frequency signals to mobile transceivers typically located inside the carriage (not shown), for example, inside the carriages C 1 , C 2 , in which interior antennas  13  are located. The mobile transceivers receiving from or transmitting to the interior antennas  13  can be mobile handsets or computers operated by train passengers, or can be machine-operated mobile communication transceiver such as those used for machine-to-machine communications, for example. The interior antenna  13  is typically placed in the interior of a carriage and can comprise any type of RF antenna type suitable for its operating frequencies. This can include printed antennas, leaky feeders, or any other antenna technology adapted to a mobile communications technology. 
         [0016]    The signal repeater  12  can comprise suitable logic, circuitry, and/or code to process radio signals received from the interior antenna  13  or the sets of antennas A 1 , A 2 . Moreover, the signal repeater  12  can be operable to control, configure, and adapt the configuration of the sets of antennas A 1  and A 2 . Similarly, the signal repeater  12  is operable to process radio signals for transmission over the interior antenna  13  or the sets of antennas A 1 , A 2 . Typically, in a downlink scenario, a signal repeater  12  can receive radio signals transmitted from the transceiver station  11  via one or more of the antenna sets A 1 , A 2 . The signals can then be processed for retransmission over the interior antenna  13 . The reprocessing can comprise, but is not limited to, amplifying, decoding, and/or re-encoding of the radio signal and can be at radio frequency, intermediate frequencies, or baseband frequencies in accordance with various embodiments of the present disclosure. Similarly, in an uplink scenario, the signal repeater  12  can receive radio signals on the interior antenna  13  and process these suitably for transmission via the sets of antennas A 1 , A 2  to a receiver, for example, transceiver station  11 . 
         [0017]    The set of antennas A 1 , A 2  can comprise suitable logic, circuitry, and/or code to receive and transmit radio signals in accordance with a radio communications protocol suitable for reception from and transmission to a transceiver station  11 . This can, as described above for transceiver station  11 , typically comprise one or more mobile communications protocols/standards. The set of antennas A 1 , A 2  can be operable to utilize multiple antenna protocols, for example, MIMO, using the exemplary plurality of antennas A 11 , A 12  and A 21 , A 22 , respectively. The antennas A 11 , A 12 , A 21 , A 22  can comprise suitable logic, circuitry, and/or code to receive and transmit radio frequency signals at their respective operating radio frequency. 
         [0018]    In many instances, the transceiver antenna system  11 A can be located approximately along the railroad track  19 , typically at a height greater than that of the train  10 . Choosing a height of the antenna system  11 A greater than the train can improve an effective transmission and reception range of the transceiver station  11  and, furthermore, often result in a line-of-sight (LOS) signal reception/transmission between the sets of antennas A 1 , A 2  and the transceiver antenna system  11 A. 
         [0019]      FIG. 1B  shows an exemplary schematic cross-section of the train in  FIG. 1A . Referring to  FIG. 1B , there is shown a coach C 1  of a train  10  on a railway track  19  and an illustrative transceiver antenna system  11 A. The cross-section of the coach C 1  further shows an antenna A 11  and an antenna A 21 . The antenna A 11  is, for example, part of the antenna set A 1  as shown in  FIG. 1A . The antenna A 21  is, for example, part of the antenna set A 2  as shown in  FIG. 1A . There is further shown a train roof  101 , which is typically made of an electrically conducting material, e.g., metal. There is also shown an angle y between some axis of antennas A 11  and antenna A 21 , due primarily to the location and orientation of the antennas A 11  and A 21  on the roof  101 . The orientations of the antennas of a set can also be regarded as the orientation of the set itself. The reference numbers used in  FIG. 1B  correspond to the respective elements shown and described for  FIG. 1A . As illustrated, a transceiver antenna system  11 A of the stationary communication system can be located at a height greater than height of the train  10 . 
         [0020]    The train roof  101  can typically be curved (or arched) or otherwise be of a convex shape as seen in the exemplary cross-section of  FIG. 1B . For example, the roof  101  can be convex, but approach a curved roof  101  as illustrated through a plurality of straight segments. The angle y can advantageously be chosen to be close to 90 degrees and can, in practice, be approximately 75-100 degrees. In this exemplary configuration with an angle y of approximately 90 degrees, the antennas A 11  and A 21  can be operable to receive and transmit RF fields that can be cross-polarized. For example, antenna A 11  can receive primarily a vertically polarized signal component of a transmitted cross-polarized RF signal from the transceiver antenna system  11 A, and antenna A 21  can receive primarily a horizontally polarized signal component of a transmitted cross-polarized RF signal from the transceiver antenna system  11 A. The conductive roof can act as ground plate of the antennas. Such an arrangement can similarly be used to transmit a cross-polarized signal via antennas A 11  and A 21 . 
         [0021]    As mentioned above, in a scenario as illustrated in  FIG. 1A  and  FIG. 1B , a strong LOS signal path can often exist between the transceiver antenna system  11 A and the sets of antennas A 1  and A 2 . The antennas A 11  and A 12  can receive a substantially same signal slightly phase-shifted (e.g., delayed) due to the separation d 1  of the antennas A 11  and A 12 . The phase shift between the signals received at A 11  and A 12  can depend on the separation distance d 1  between A 11  and A 12 , as well as the geometric position of the set of antennas A 1  with regard to the transceiver antenna system  11 A. The received signals at A 11  and A 12  can be coherently combined to constructively add both received signals. In some cases, a delay line, possibly adaptive, can be used to compensate the phase-shift incurred between the received signals at antennas A 11  and A 12 . In other cases, it can suffice to simply connect the antennas A 11  and A 12  and, in particular, when the delays between the received signals can be relatively small. Similarly, the received signals at antennas A 21  and A 22  can be combined. 
         [0022]    The distance d 2  between the sets of antennas A 1  and A 2  can typically exceed d 1  and can depend on the particular shape of the coach roof  101  and the specific antenna arrangement chosen. For this reason and the angular positioning of antennas (as illustrated by angle y), the received signals at the set of antennas A 1  and A 2  can be approximately uncorrelated and can be used in a variety of multiple antenna protocols, including MIMO. For example, by coherently combining the antennas signals within each set as described above, there will be two effective antennas, one each for the set of antennas A 1  and A 2 . If, for example, the transceiver antenna system  11 A employs two cross-polarized antennas, an effective 2×2 MIMO channel can be created between a coach (e.g., coach C 1 ) and the transceiver antenna system  11 A. 
         [0023]      FIG. 2A  shows an example of a train in the vicinity of a second stationary communication system. Referring to  FIG. 1B , there is shown a train  10 , railroad tracks  19 , and a transceiver station  11 . The transceiver station  11  can comprise a transceiver  11 B communicatively coupled to an antenna system  11 C. The antenna system  11 C can comprise a plurality of leaky feeder cables, sometimes also referred to as cable antennas, illustrated by the dot-dashed double line. The reference numbers in  FIG. 2A  can refer to substantially similar elements with the same numbers as described for  FIG. 1A . 
         [0024]    The leaky feeders in antenna system  11 C can be operable to transmit and/or receive radio frequency signal in accordance with one or more RF technologies, for example, mobile communication standards such as GSM, UMTS, WCDMA, 4G, LTE, HSDPA, HSUPA, 5G, and WiMAX 802.16. The leaky feeder cables of antenna system  11 C can run approximately parallel to the railroad track  19 . 
         [0025]      FIG. 2B  shows an exemplary schematic cross-section of the train in  FIG. 2A . Referring to  FIG. 2B , there is shown a train  10  and a transceiver antenna system  11 C. The transceiver antenna system  11 C can comprise a plurality of leaky feeder cables, of which two are illustrated as dots, mounted on a mount  18 . There is also shown a leaky feeder separation distance d 3 . The reference numbers in  FIG. 2B  can refer to substantially similar elements with the same numbers as described for  FIG. 1A ,  FIG. 1B , and  FIG. 2A . 
         [0026]    The mount  18  can be enabled to mount the leaky feeder cables of transceiver antenna system  11 C in a desirable position with respect to the railroad track  19 . For example, as illustrated in  FIG. 2B , the mount  18  can mount the plurality of leaky feeder cables at a certain height above the ground and/or relative to the coach C 1 , and substantially parallel to the railroad track  19 . Furthermore, the mount  18  can allow the single leaky feeder cables to be mounted at a desirable separation distance d 3  to each other. 
         [0027]    As illustrated in  FIG. 2B , when the transceiver station  11  is transmitting to the coach C 1  (or any other coach of train  10 ), the leaky feeder cables of antenna system  11 C can typically be mounted lower than the height of the train coach roof  101 , i.e., below roof level. In this scenario, there can often be line of sight from the antenna system  11 C to the set of antennas mounted on the side of the train that is physically closer to the antenna system  11 C. In the illustrated example in  FIG. 2B , this is the set of antennas A 2 . In such a scenario, the antennas A 21  and A 22  can receive most of the energy transmitted from the transceiver antenna system  11 C. On the other hand, the antennas on the side of the coach farther away from the leaky feeder cables will receive significantly weaker signals. In this example, the antennas A 11  and A 12  will receive less signal power than the antennas A 21  and A 22 . Because of the radiation characteristics of the leaky feeder cables of antenna system  11 C, the signals received at antennas A 21  and A 22  can be uncorrelated and hence allow a variety of MIMO schemes to be applied. A suitable MIMO scheme can, for example, be a 2×2 MIMO scheme as proposed in the LTE mobile communication standard. The above scenario is also applicable to the scenario in which the antenna systems A 1 , A 2  from the coach are transmitting to the transceiver system antennas  11 C, as well as to the case in which the leaky feeder cables are located on the other side of the railroad track  19 . 
         [0028]    The transceiver antenna system  11 C, specifically, the leaky feeder cables, can be installed on either side of the railroad track  19 . From the above-described reception characteristics, it can be advantageous to communicatively couple the antennas A 11  and A 21  and A 12  and A 22 , respectively. In this case, two effective antennas can be formed, a first one from the coupled antennas A 11  and A 21 , and a second one from the coupled antennas A 12  and A 22 . These two effective antennas based on the physical antennas A 11 , A 12 , A 21  and A 22  can be used to receive and/or transmit from leaky feeder cables of the transceiver antenna system  11 C installed on either side of the railroad track  19 . In other words, such a configuration can be operated without regard to the side of the track  19  on which the leaky feeders are located. 
         [0029]      FIG. 3  illustrates a switching and control scheme for a vehicle-based antenna system in accordance with an embodiment of the present disclosure. Referring to  FIG. 3 , there is shown a switching device  20  which can be integrated within the signal repeater  12  as shown in  FIG. 1A ,  FIG. 1B ,  FIG. 2A , and/or  FIG. 2B , an antenna configuration MODE  1 , and an antenna configuration MODE  2 . The switching device  20  can comprise a comparator  21  and the switch  22 . The antenna configuration MODE  1  can comprise antennas A 11 , A 12 , A 21  and A 22 , whereby antennas A 11  and A 12 , and antennas A 21  and A 22  can be communicatively coupled, respectively, with each pair of coupled antennas forming a single effective antenna. The antenna configuration MODE  2  can comprise antennas A 11 , A 12 , A 21  and A 22 , whereby antennas A 11  and A 21 , and antennas A 12  and A 22  can be communicatively coupled, respectively, with each pair of coupled antennas forming a single effective antenna. There is also shown a signal power of the set of antennas A 1  and A 2 , denoted by P 1  and P 2 , respectively. The reference numbers in  FIG. 3  can refer to substantially similar elements with the same numbers as described in  FIG. 1A ,  FIG. 1B ,  FIG. 2A , and  FIG. 2B . 
         [0030]    The switching device  20  or the signal repeater  12  can, in addition to the functionality already described above, comprise suitable logic, circuitry, and/or code to compare a plurality of signal powers and control a plurality of possible antenna configuration modes, for example, MODE  1  and MODE  2 . The comparator  21  can comprise suitable logic, circuitry, and/or code to compare the signal power of a plurality of input signals and to operate the switch  22 . The switch  22  can comprise suitable logic, circuitry, and/or code to be operable to switch between a plurality of configurations and/or signal paths between one or more inputs and one or more outputs. 
         [0031]    Along a railroad track  19 , both scenarios of a transceiver station  11  with a transceiver station antenna system  11 B, as described in  FIG. 1A  and  FIG. 1B , or with a transceiver station antenna system  11 C, as described in  FIG. 2A  and  FIG. 2B  can be employed on different segments of the railroad track  19 . The selection of an antenna system can depend on, among other factors, terrain, cost, ease of installation, and/or required throughput. Accordingly, it can be desirable to adapt the vehicle-based configuration to be operable with both transceiver station antenna systems  11 B and  11 C. 
         [0032]    As described with respect to  FIG. 1A  and  FIG. 1B , in a scenario using a transceiver antenna system  11 B, it can be advantageous to communicatively couple the antenna pairs A 11 , A 12  and A 21 , A 22 , respectively, to form two effective antennas. In some cases, the antenna pairs can, as described above, be communicatively coupled such that a phase-delay between the coupled antennas can be approximately compensated to form a single effective antenna. This is referred to as antenna configuration MODE  1 . Similarly, in a scenario using a transceiver antenna system  11 C, it can be advantageous to communicatively couple the antenna pairs A 11 , A 21  and A 12 , A 22 , respectively. This is referred to as antenna configuration MODE  2 . 
         [0033]    When a transceiver antenna system  11 B is used for a particular segment of the railroad track  19 , the received signal power from the transceiver  11  of the set of antennas A 1  and the set of antennas A 2  is similar in antenna configuration MODE  1 . Hence, the antenna configuration MODE  1  can remain active and can be advantageous, as described for  FIG. 1A  and  FIG. 1B . On the other hand, in antenna configuration MODE  1 , when a transceiver antenna system  11 C is used for a particular segment of the railroad track  19 , the received signal power from the transceiver  11  by the set of antennas A 1  and the set of antennas A 2  is significantly different. In particular, as described for  FIG. 2A  and  FIG. 2B , the set of antennas on the side of the coach that is closer to the antenna system  11 C can receive significantly higher signal power than the other set of antennas. For example, as illustrated in  FIG. 2B , the set of antennas A 2  would receive significantly higher signal power than the set of antennas A 1  because the set of antennas A 2  is physically closer to the transceiver antenna system  11 C, whereas the set of antennas A 1  might be out of sight of the transceiver antenna system  11 B and electromagnetically shielded partially by the presence of the train roof  101 . Thus, in a scenario where a transceiver antenna  11 C is active, it can be advantageous to switch from antenna configuration MODE  1  to antenna configuration MODE  2 , as described above with reference to  FIG. 2A  and  FIG. 2B . The comparison of the respective signal powers can be performed in the comparator  21  and be a basis by which the switch  22  is operated. In accordance with various embodiments of the present disclosure, the comparison of the signal powers and the switching between antenna configuration modes can be integrated into the signal repeater  12 , or performed in another equipment, for example, a dedicated hardware switching device  21  not integrated into the signal repeater  12 . 
         [0034]    Thus, the signal powers of the sets of antenna A 1  (signal power P 1 ), and A 2  (signal power P 2 ) can be compared in antenna configuration MODE  1 . If the signal power P 1  is substantially similar to the signal power P 2 , the antenna configuration MODE  1  might be desirable and hence no antenna configuration change is necessary. On the other hand, if the signal power P 1  is substantially different from the signal power P 2 , the antenna configuration MODE  2  might be desirable and the vehicle-based antenna system can switch from antenna configuration MODE  1  to antenna configuration MODE  2 . In a typical train system, an exemplary threshold to change antenna configuration mode from MODE  1  to MODE  2  can be a power difference of approximately 6 dB. As will be known to a person skilled in the art, the threshold value is exemplary and can depend on a wide variety of factors in a particular communication system. Moreover, the threshold value can be adaptively changed in some scenarios. In the present example, if the difference in signal power P 1  to P 2  is less than or equal to 6 dB, the antenna configuration remains or changes back to MODE  1 . On the other hand, if the difference in signal power P 1  to P 2  exceeds 6 dB, the antenna configuration changes from MODE  1  to MODE  2  or remains in MODE  2  depending on the prior status. 
         [0035]    In accordance with various embodiments of the present disclosure, it is also possible in the above switching scheme to compare the signal power of one antenna each from the sets of antennas A 1  and A 2 , instead of the set powers as described above. For example, the power at antenna A 11 , P(A 11 ), and the power at antenna A 21 , P(A 21 ), can be used to determine a switching condition. Similarly, the pair P(A 11 ), P(A 22 ), the pair P(A 12 ), P(A 21 ), and the pair P(A 12 ), P(A 22 ) can be used to determine a switching condition, for example. It is also possible to further refine the comparison, for example, by taking into account which of the powers P 1  and P 2  are larger to determine the side of track on which the leaky feeder is located. In such a case, the switching can be adapted to establish the communication link only through antennas located on the respective side of the vehicle. 
         [0036]    The above-described compare and switch scheme can be applicable to a comparison of any measure related to signal power or amplitudes, mean amplitudes, etc. reasonably related to the signal power at the relevant antennas or sets of antennas. This includes, but is not limited to, averaged values, correlated values, and/or peak/trough analysis of such measures. 
         [0037]    Though described using a train  10  as an example, the systems and methods described above can be applied in any communication system using fast switching of in-vehicle equipment between two or more different stationary communications systems along the trajectory of the vehicle. The vehicle can be a coach of a train, the train itself, or a different type of vehicle such as guided bus, a car, etc. 
         [0038]    The distance d 1  between the two antennas of each set A 1 , A 2  can be the order of half the wavelength of the center frequency of the communication link or larger. The same applies to the distance d 3  between the signal cables of the leaky feeder  11 C antennas.