Abstract:
Broadband networks for cellular operation are relatively short range and are deployed with infrastructure to serve the needs of a relatively high density of users. Land Mobile Radio (LMR) networks are relatively long range and deployed with infrastructure to serve a relatively low density of users. Methods are described which enable mobile devices to use an LMR network to coordinate operation of a broadband network to achieve higher data rates or use other aspects of the broadband network.

Description:
[0001]    This application claims priority to New Zealand patent application number NZ 615898, filed Sep. 24, 2013, which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to data rates in mobile radio systems and particularly but not only to systems which combine two or more wireless protocols such as P25 and LTE. 
       BACKGROUND TO THE INVENTION 
       [0003]    Long range communications are a key requirement for mission critical systems such as public safety and utility operations. Such systems are commonly private networks and are characterised by a need for operation over very wide geographic areas while offering service to a relatively low density of users. Land Mobile Radio (LMR) systems such as P25 have been a typical choice for such solutions because of its ability to offer economically acceptable coverage. This has typically been used for mission critical voice communication. DMR and Tetra are similarly used in some countries. 
         [0004]    Increasingly public safety users require more information. Maps, electronic forms and video are all examples of applications that are now aiding public safety and critical infrastructure such as electrical distribution in their operations. New technology such as LTE (Long Term Evolution), part of the 3GPP standards represent a communications path that can support such applications. There is however a challenge. LTE is not typically designed for economic long range operation in the same way as LMR. LTE represents a broadband technology which means the power of a transmission is spread over a relatively wide frequency allocation. LMR is a narrow band technology and as such its transmission is concentrated in a relatively narrow allocation of spectrum. In concentrating power in a relatively narrow allocation of spectrum, LMR is able to offer superior range. 
         [0005]    Cellular technology such as LTE provides an effective means of communicating relatively high rate data. This is typically accomplished using a relatively high density of cellular base sites to serve a relatively large population density of users. Commercial consumers are an example. LMR technology provides an effective means of communicating at a relatively low data rate. This is typically accomplished using a relatively low density of LMR base sites to serve a relatively low population density of users. Emergency services are an example. 
         [0006]    There exists a problem when relatively high data rates need to be communicated to a relatively low user population density. In this scenario, the economics of deploying broadband cellular technology can become questionable and LMR technology is unable to offer the required relatively high data rates required. There exists therefore a gap in the suitability of LTE or LMR in serving the need for high data rate over a wide area. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to provide for improved long range communications requiring relatively high data rates, by combining LMR and LTE. 
         [0008]    In one aspect the invention resides in a method of communicating with a mobile radio device, including: providing a first network of base stations which use a first bearer having a relatively low data rate, providing a second network of base stations which use a second bearer having a relatively high data rate, receiving location data from the mobile device at a base station using the first bearer, providing a directional beam toward the location of the mobile device at a base station using the second bearer, and transmitting data to or receiving data from the mobile device using the directional beam and the second bearer. 
         [0009]    In a further aspect the invention resides in a system for communicating with a mobile radio device, including: a first network of base stations which use a first bearer having a relatively low data rate, a second network of base stations which use a second bearer having a relatively high data rate, and a controller having a memory containing software instructions which cause the controller to: receive location data from the mobile device at a base station using the first bearer, provide a directional beam toward the mobile device at a base station using the second bearer, and transmit data to or receive data from the mobile device using the directional beam and the second bearer. 
         [0010]    Generally, the first network of base stations provides omnidirectional relatively long range RF communication and the second network of base stations provides directional relatively short range RF communication. The first bearer is LMR, DMR, TETRA or other relatively narrowband RF bearer, and the second bearer is LTE or other relatively broadband RF bearer. The method may further include receiving data at the mobile device relating to the directional beam, and moving the mobile device into the directional beam. 
         [0011]    In a further aspect the invention resides in a method of communicating with a mobile radio system, including: providing a mobile device having capability for using either of a first bearer with a relatively low data rate or a second bearer with a relatively high data rate, receiving data from a first base station using the first bearer, relating to location of a second base station which uses the second bearer, providing a directional beam from the mobile device toward the location of the second base station which uses the second bearer, and transmitting data from or receiving data at the mobile device using the directional beam and the second bearer. 
         [0012]    In a still further aspect the invention resides in mobile device for communicating with a mobile radio system, including: a transceiver arrangement having capability for using either of a first bearer with a relatively low data rate or a second bearer with a relatively high data rate, and a controller having a memory containing software instructions which cause the mobile device to: receive data from a first base station using the first bearer, relating to location of a second base station which uses the second bearer, provide a directional beam from the mobile device toward the second base station which uses the second bearer, and transmit data or receive data at the mobile device using the directional beam and the second bearer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Preferred embodiments of the invention will be described with respect to the accompanying drawings, of which: 
           [0014]      FIGS. 1 , shows a typical LMR system with a typical broadband system in the same geographic area. 
           [0015]      FIG. 2  shows the broadband beam being extended to serve distant users. 
           [0016]      FIG. 3  shows a flow chart for the mobile device communicating location data. 
           [0017]      FIG. 4  shows a flow chart for the network side of an integrated LMR and broadband system. 
           [0018]      FIG. 5  shows an alternative system where multiple directional antennae are located at a base site. 
           [0019]      FIG. 6  shows switching apparatus for selecting between the antennae in  FIG. 5 . 
           [0020]      FIG. 7  shows a process for selecting which antenna to use. 
           [0021]      FIG. 8  shows one implementation of a mobile device. 
           [0022]      FIG. 9  illustrates a simple application for directing users to the nearest broadband connectivity. 
           [0023]      FIG. 10  shows the extended range effect of a directional antenna at the mobile device. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    Referring to the drawings it will be appreciated that the invention can be implemented in a range of different ways using a variety of different narrowband and broadband communication systems such as LMR and LTE. 
         [0025]      FIG. 1  illustrates a traditional LMR system overlaid with a traditional broadband or cellular system. Each system includes a network of base stations which transmit according to respective bearer protocols. LMR sites are commonly deployed with a relatively high powered base station through an omnidirectional antenna yielding wide area coverage. In this case the transmission is occurring on a frequency pair for uplink and downlink, referred to as bearer B 1 , operating at site  10 . Broadband sites are typically deployed as a triad of base stations serving three directional antennas creating sectors of connectivity. In this case the transmission is occurring on a different frequency pair, referred to as bearer B 2  operating at sites  11  and  12 . The LMR and cellular networks are typically separate but in this example are shown joined through an idealised control system  13 . 
         [0026]    Also shown in  FIG. 1  are mobile devices  15 ,  16 . Each device has a number of bearer technologies available through respective bearer units or transceivers, and antennae. In particular this includes but is not limited to a narrowband bearer such as LMR and a broadband bearer such as LTE. Further, each bearer unit within a mobile device is connected to a processing platform referred to as a hub which is also able to offer services to applications either on board or to external connected devices. Each hub typically contains a processor and memory containing software instructions and is also connected to a GPS receiver in order to determine location data. In this example, neither mobile device  15  or  16  is within coverage of the broadband sites  11  and  12  yet they are both within coverage of the LMR site  10 . Both mobile devices have data to be transferred which requires the relatively high data rate capability of broadband. 
         [0027]      FIG. 2  offers a visualisation of how broadband connectivity can be achieved in  FIG. 1 . In this case, both mobile devices  15 ,  16  are closest to the broadband site  11  and each device is close to an individual sector of the site. Location information is transmitted by the mobile devices over the LMR system and processed in the control system  13 . The broadband sectors of site  11  are directed towards the mobile devices thus enabling broadband communication. The antenna technology required to form and direct the sectors or beams of a broadband system is well known and need not be described in detail. It will be appreciated that forming a directional beam includes forming the beam use of an adaptive antenna, orienting the beam at a moveable antenna, or selecting the beam from a range of antennae. 
         [0028]      FIG. 3  is a flow diagram illustrating how a mobile device is configured to periodically communicate location data over the LMR network. A timer is set  30  and then counts down  31 . When the time period has expired  32  the current location information for the mobile is sent  33  to the network. The rate at which the position is reported is generally related to the expected speed of mobility of the terminal device. In one example the terminal device may report its location every  10  seconds. This represents a practical time scale to allow for a change in position that may require slight adjustment of the beam direction. 
         [0029]      FIG. 4  is a flow diagram showing operation of the control system in the combined LMR and LTE networks. From start, the system is listening  40  for reports coming over the 
         [0030]    LMR network offering location status for the mobile devices  15  or  16 . Upon reception of a location report  41  along with a flag indicating the need to communicate high rate data, the controller will calculate which sector is best aligned to serve the device and calculate  42  the angle and reachability of the device. If it is possible  43  to reach the device then a beam will be directed  44  to those coordinates for the duration of the session. A broadband connection is established  45  and data is transferred  46  until the session is complete  47 . 
         [0031]      FIG. 5  shows an alternative system in which site  51  is populated with multiple directional antennae which provide coverage over multiple sectors. Mobile device  15  is travelling from sector A into sector B. Location data is transmitted by the mobile device while travelling. At a suitable stage the communication between the mobile and site  51  changes from the antenna for sector A to the antenna for sector B so that broadband connectivity is maintained. Otherwise a message may be sent to the mobile to indicate that coverage could be lost depending on the extent of travel. 
         [0032]      FIG. 6  shows a switching system for multiple antennae at a cellular base site. In this case a single broadband base station  60 , referred to as eNodeB in LTE, is connected to one of six directional antennae A to F. An RF switch  61  is controlling which antenna is selected at any time on lines  1  to  6 . This switch is controlled by a processor  62  which receives mobile location data and operates a software algorithm to calculate which switch position will be selected. 
         [0033]      FIG. 7  is a flow diagram for calculating which antenna should be selected in  FIG. 6 . Initially, the system is waiting  70  for location data from a mobile device. Once suitable data has been received  71  an angle from the base station to the mobile unit is calculated  72 . Given this angle and knowing the antenna configuration, the optimal antenna for communicating with the mobile device is selected  73 . The switch  61  is then actuated  74  to connect the base station to the antenna. A broadband connection can then be established  75  with mobile device to enable transfer  76  of data at a relatively high rate. The session is eventually completed  77 . 
         [0034]      FIG. 8  shows a mobile device or terminal in the system of  FIG. 1 . The device has a transceiver for each bearer through which an RF connection is required, in this case a P25 radio  80  and an LTE radio  81 , each with a respective antenna system. The transceivers are operated by a control unit  82  which sends or receives data through serial connection  83 , Ethernet connection  84  or USB connection  85 , for example. In this example, the control unit is managing traffic flow from an external device  86  such as a laptop, via the Ethernet interface. Periodically, the control unit also monitors GPS location from an attached GPS unit  87 , and reports location data over LMR, using the P25 radio, as shown in  FIG. 3 . Location information can be carried by a number of package types including TSBK (Trunked Signalling Block) on a P25 control channel. In another form, the location information can be reported as P25 packet data on either traffic channels or conventional radio channels. 
         [0035]    Preferably the mobile device is reporting its own location data to the overall infrastructure using the LMR network of base stations. In another form, the infrastructure can conversely report the location of broadband sites, and the estimated coverage of those sites, to mobile devices via the LMR network. A periodic broadcast of site information over the LMR network can be made. A mobile receiving the location of broadband sites has two options. 
         [0036]      FIG. 9  illustrates how the user of a mobile device can be simply informed about the nearest available broadband connectivity. An arrow graphic indicates a direction and distance of travel for the user in order for broadband connectivity to be established. The indicated travel would bring the mobile device into one of the sectors of a nearby broadband site. 
         [0037]      FIG. 10  illustrates the effective range of broadband connectivity can be extended as a result of a directional antenna  100  in the mobile device. Alternatively or as well as the indication in  FIG. 9 , the control unit  82  can operate the directional antenna to be directed toward a nearby broadband site in order to establish connectivity.