Abstract:
A repeater is disclosed which is usable to permit a satellite phone, normally requiring a direct line of sight link to an orbiting satellite, to communicate with the satellite when the satellite phone is otherwise obstructed from communicating with the satellite. The repeater is usable in any situation in which the satellite phone is blocked from a direct line of site to the satellite, such as inside a building, aircraft, or natural formation (e.g., cave).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a repeater for a satellite communication device that permits communications between the communication device and the satellite without having a direct line of sight to the orbiting satellite. 
   2. Background of the Invention 
   Relatively recently, satellite phones have been introduced into the market. A satellite phone communicates directly with an orbiting satellite thereby permitting the user of the phone to make or receive a phone call from virtually anywhere on earth. A significant limitation is that there must be an unobstructed, direct line-of-sight between the satellite and the satellite phone. Thus, such phones are generally unusable inside buildings, houses, caves, airplanes or, in general, anywhere that the phone does not have direct line-of-sight to the satellite. A solution this problem would be highly desirable and would make satellite phone technology much more usable. 
   BRIEF SUMMARY OF THE INVENTION 
   The problems noted above are solved in large part by a repeater usable to permit a satellite phone, normally requiring a direct line-of-sight link to an orbiting satellite, to communicate with the satellite when the satellite phone is otherwise obstructed from communicating with the satellite. The repeater disclosed herein is usable in any situation in which the satellite phone is blocked from a direct line-of-site to the satellite, such as inside a building, aircraft, or natural formation (e.g., cave). 
   In accordance with one preferred embodiment, the satellite phone repeater comprises a first antenna (exterior) receptive to downlink signals transmitted by a satellite, a downlink low-noise amplifier that receives and amplifies signals from the first antenna to a second antenna (interior) that receives the amplified signals from the downlink amplifier and broadcasts the amplified signals to the satellite phone. The repeater also includes a third antenna (interior) receptive to signals transmitted by satellite phone, an uplink power amplifier that receives and amplifies signals from the third antenna, and a fourth antenna (exterior) that receives the amplified signals from the uplink power amplifier and broadcasts the amplified signals to be received by the satellite. 
   In accordance with another embodiment, the satellite phone repeater comprises a first antenna (exterior) receptive to downlink signals transmitted by a satellite and adapted to transmit uplink signals to the satellite. A second antenna (interior) is adapted to transmit signals to and receive signals from the satellite phone. This is accomplished by employing a diplexer that is positioned between the antenna and amplifiers. This embodiment also includes a downlink amplifier coupled between the first and second amplifiers. The downlink amplifier is adapted to amplify signals received from the satellite via the first antenna. Also included are an uplink amplifier coupled between the first and second amplifiers, a first diplexer disposed between the amplifiers and the first antenna, a second diplexer disposed between the amplifiers and the second antenna, and a control unit coupled to the first and second diplexers. The uplink amplifier is adapted to amplify signals received from the satellite phone via the second antenna. The control unit operates the first and second diplexers to permit two-way communications to occur between the satellite and the satellite phone via the first and second antennas. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
       FIG. 1  shows a system level diagram of a repeater providing a wireless interface between a satellite phone and an orbiting satellite especially when the phone does not have a direct line-of-sight to the satellite; 
       FIG. 2  shows a preferred embodiment of the downlink capability of the repeater; 
       FIG. 3  shows a preferred embodiment of the uplink capability of the repeater; 
       FIG. 4  shows an alternative embodiment of the repeater; and 
       FIG. 5  shows an alternative embodiment to that of  FIG. 3  which precludes the power amplifier from receiving any signals to amplify when no valid signal is present thereby minimizing crosstalk and interference. 
   

   NOTATION AND NOMENCLATURE 
   Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, different companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , in accordance with a preferred embodiment of the invention, a satellite  50  communicates with a satellite phone  52  located within a structure  54  that prevents effective communications between the phone  52  and the satellite  50 . The phone may be, for example, a 9520 Mobile Phone provided by Motorola. The structure  54  may be a building, a natural formation such as a cave, the exterior surface of an airplane, or in general any material or object that precludes an effective line-of-sight communication link between satellite  50  and phone  52 . In accordance with the preferred embodiment, a repeater  60  is provided which permits the satellite phone and satellite to communicate indirectly with each other. 
   The repeater  60  preferably enables two, two-way communication links—one link  62  to the satellite  50  and another link  64  to the satellite phone  52 . The repeater  60  functions to pass incoming transmissions from the satellite  50  to the phone  52 , as well as pass transmission from the phone to the satellite. As such, the repeater  60  provides a communication pipeline between the satellite and phone. The repeater preferably is located inside the structure  54 , but an antenna (not specifically shown in  FIG. 1 ) included as part of the repeater is positioned outside the structure  54  so that a direct line-of-sight to the satellite  50  can effectively be obtained with respect to the repeater. 
     FIGS. 2 and 3  show a preferred embodiment of the repeater  60 .  FIG. 2  shows an exemplary embodiment of the repeater usable to receive downlink (i.e., earth-bound) transmissions from the satellite and forward such transmissions on to the satellite phone  52 .  FIG. 3  shows an exemplary embodiment of the repeater  60  usable to receive satellite-bound (uplink) transmissions from the phone  52  and forward such transmissions on to the satellite  50 . 
   Referring now to  FIG. 2 , the repeater  60  includes an amplifier  72  and antennas  70  and  74 . The antenna  70  receives earth-bound (downlink) signals from satellite  50  and provides those signals to amplifier  72 . Antenna  70  is located near the downlink receiver  60  in a configuration which gives the antenna a direct line-of-sight to the satellite. For example, the downlink receiver  60  will be housed in an enclosure. The antenna  70  will be mounted on an outer surface of the enclosure. Alternatively, the antenna  70  may be mounted apart from the receiver and connected to the receiver&#39;s electronics via a suitable low-loss RF coaxial cable in accordance with known techniques. The antenna  70  may be any suitable antenna such as the S67-1575-109 exterior aircraft antenna manufactured by Sensor Systems. This particular antenna has a frequency response of 1616-1626.5 MHz and a return loss of −9.5 dB. 
   The downlink transmissions received by antenna  70  are provided to amplifier  72  which filters and amplifies the downlink signal. The amplifier  72  is any suitable low-noise amplifier usable as described herein. One suitable embodiment of amplifier  72  is the Iridium low noise amplifier (LNA) which has a frequency response of 1600-1650 MHz, a gain of +76 dB, a P1dB of +10 dBm, an input voltage of +15.0 VDC and a maximum current rating of 190 mA. 
   From the amplifier  72 , the filtered and amplified signals are provided to the satellite phone  52  via antenna  74 . Antenna  74  need not have a direct line-of-sight to the satellite  50 . Rather, antenna  74  need only be able to transmit signals to the satellite phone  52  which generally is in relatively close proximity to the downlink receiver  60 . The antenna  74  may be any suitable antenna and, in fact, may the same type of antenna as antenna  70 . As such, antenna  74  may also be the S67-1575-109 exterior aircraft antenna manufactured by Sensor Systems having a frequency response of 1616-1626.5 MHz and a return loss of −9.5 dB. 
   Referring now to  FIG. 3 , an embodiment of the repeater  60  is shown permitting uplink transmissions to occur from satellite phone  52  to satellite  50  without the phone having a direct line-of-sight to the satellite. In this embodiment, the uplink transmitter  60  has an antenna  80  which is coupled to the repeater similar to how antenna  70  coupled to the downlink receiver in FIG.  2 . Antenna  80  is used to transmit signals received from the phone through the uplink transmitter to the satellite  50 . The uplink transmitter  60  also couples to an antenna  82  which receives signals from phone  52  and provides those signals to the uplink transmitter&#39;s electronics comprising, in accordance with the preferred embodiment, two preamp stages  86  and  88  and an power amplifier  84 . Antennas  80  and  82  may the same types of antennas as are used to implement antennas  70  and  74  in FIG.  2 . The two preamp stages  86  and  88  may the same, or different. In one embodiment, the preamp stages comprise Iridium XMIT Preamps which have a frequency response of 1600-1650 MHz, a return loss of 2.0:1, a gain of +56 dB, a P1dB of +10 dBm, an input voltage of +15 VDC, and a maximum current of 150 mA. The power amplifier  84  preferably comprises an Iridium XMIT Power Amplifier which has a frequency response of 1600-1650 MHz, a return loss of 2.0:1, a gain of +36 dB, a P 1  dB of +38 dBm, an input voltage of +15 VDC, and a maximum current of 3500 mA. Although the embodiment shown in  FIG. 3  includes three amplifier/preamp stages, in other embodiments, the preamp stages could be combined together into a single preamp stage. Further, all three stages could be combined together into a single stage. 
   An alternative embodiment of repeater  60  is shown in FIG.  4 . In this embodiment, only one pair of antennas  90  and  92  is used for both downlink and uplink transmissions between satellite and satellite phone. As shown, antenna  90  is used for the communication link to the satellite and antenna  92  is used for the communication link to the phone. Both antennas may be implemented using the same type of antennas described previously. 
   In the embodiment of  FIG. 4 , receiver  60  preferably includes a pair of electronically controlled diplexers  98  and  99 , a control unit  100  and a pair of amplifiers  94  and  96 . Other components may be included as desired. Amplifier  94  is used to amplify downlink signals from the satellite before transmitting such signals to the satellite phone. Amplifier  96  amplifies the uplink signals from the satellite phone before transmitting the signals to the satellite. 
   Under control of control unit  100 , diplexers  98  and  99  selectively couple the RF energy from either the uplink amplifier  96  or the downlink amplifier  94  between antennas  90  and  92 . The diplexers work in concert based on the control signal  102  from the control unit  100  either to switch uplink amplifier  96  into the closed transmission path between antennas  90  and  92  (as shown in  FIG. 4 ) or to switch downlink amplifier  94  into the closed transmission path. The control unit  100  thus causes RF energy to be transmitted from antenna  90  to antenna  92  for a brief period of time followed by transmitting the RF energy from antenna  92  to antenna  90  for a brief period of time. This process is repeated numerous times per second in a way that is generally unnoticeable to a user of the satellite phone. In accordance with known diplexing techniques, the control unit  100  extracts control pulses from the satellite signal to determine when to switch between amplifiers  94  and  96 . 
   The embodiment shown in  FIG. 4  advantageously requires only two antennas, instead of four antennas as shown in  FIGS. 2 and 3 . The use of a control unit  100  and diplexers  98  and  99  enable the receiver  60  of  FIG. 4  to have a reduced the number of antennas. 
   As one of ordinary skill in the art would know, the various antennas used in the embodiments described above may need to be positioned in a way that reduces the potential for one antenna to pick up the transmission from another antenna. In  FIG. 4 , for example, it is possible for transmissions from antenna  92  to the satellite phone to also be received by antenna  90  and reamplified and provided again to antenna  92 . Thus, the antennas  90 ,  92  preferably are separated so as to increase RF isolation between the antennas  90  and  92 . This practice reduces the potential for such “cross talk.” This can be accomplished in accordance with known techniques and principles by positioning the antennas sufficiently far apart which, of course, will depend on the specific parameters of each application, as would be well known. In addition, two types of isolation may be employed when possible. The first, horizontal isolation, is a practice in which the antennas are horizontally separated or distanced as far apart as possible. For example, in an aircraft scenario, antenna  90  may be positioned on the front end of the aircraft and antenna  92  may be positioned at the rear end of the aircraft. The distance between the antennas  90  and  92  is the horizontal isolation. The second, vertical isolation, is another practice in which the antennas are vertically separated or distanced as far apart as possible. For example, in a fixed or stationary environment, the uplink antenna  90  may be positioned on a communications tower several feet above the downlink antenna  92 . The uplink antenna  90  must be placed above the downlink antenna  92  because the uplink antenna  90  may be radiating, for example, 5 watts to the satellite. This energy must refrain from entering the downlink antenna  92  and subsequent amplification path. 
   It should be understood that isolation is not limited to any one method. A combination of horizontal and vertical isolation will be employed when possible. Isolation maximization will reduce or eliminate the uplink signal from interfering with the downlink signal, and vice versa. Poor isolation will result in locking up or confusing the satellite phone, as would be understood by those of ordinary skill in the art. Consequently, without proper isolation, communication between the phone and satellite will be inconsistent or impossible. 
   The embodiments described above advantageously permits a user of a satellite phone to use the phone even though the orbiting satellite is obstructed thereby precluding direct communications between phone and satellite. A repeater has been shown and described which functions as a communication link between the satellite and the phone, thereby freeing the phone to be used in a location otherwise obstructed from the satellite. 
   In accordance with a further effort to improve isolation and help minimize crosstalk/interference, the input signal to the power amplifier  84  in  FIG. 3  preferably is only provided to the power amplifier when a valid uplink signal is present.  FIG. 5  shows the architecture of  FIG. 3  to which this feature has been added. As shown in  FIG. 5 , a coupler/detector  110 , RF delay  112  and RF switch  114  have been added. The coupler/detector  110  couples between the output of the preamp  88  and the RF switch  114 . The RF switch is disposed between the preamp  86  and the power amp  84 . The RF delay preferably is included between preamp stages  86  and  88 . 
   The coupler/detector  110  preferably samples the RF signal from the preamp stage  88  and compares the sampled signal to a predetermined threshold to determine if a valid signal (e.g., voice conversation) is present. With no valid signal being present, the RF switch  114  normally is in an open state preventing a signal from being provided to the power amp  84 , thereby preventing the power amp  84  from amplifying interference or crosstalk signals. If the coupler/detector  110  determines that a valid signal is present, the coupler/detector asserts its output signal which comprises a control signal to the RF switch  114  and which causes the RF switch to close. The closing of the RF switch permits the valid RF signal to be provided to the power amp  84  for further amplification and transmission to the antenna  80 . Then, when a valid signal ceases (e.g., the user of the satellite phone ceases talking), the coupler/detector  110  causes the RF switch  114  to open thereby preventing the power amp from amplifying any signals. 
   As one of ordinary skill in the art will appreciate, there is time delay for the coupler/detector  110  to detect the presence of a valid signal, assert the output control signal, and the RF switch  114  to close. To prevent the valid signal from arriving at the RF switch  114  before the RF switch has a chance to close, a time delay element (i.e., RF delay  112 ) is included in the signal path. Thus, RF delay  112  accounts for the delay in the signal path that is introduced by the action of the controller/detector  110  and RF switch  114 . The RF delay  112  can be any suitable time delay and of course correlates to the time delay created by the action of the coupler/detector  110  and RF switch  114 . A suitable value for the RF delay  112  is a delay which results in the RF switch  114  closing approximately 2 nanoseconds before the arrival of the RF signal from preamp  86 . Further, the coupler/detector  110  preferably causes the RF switch  114  to open approximately 2 nanoseconds after the valid RF signal ceases. Thus, the RF switch preferably is closed fast enough for the RF signal to pass through and be amplified in its entirety via power amp  84 . 
   The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.