Patent Abstract:
A stabilized ultra-high bandwidth capacity transceiver system that combines an E-band (71-76 GHz, 81-86 GHz) millimeter wave RF transceiver with an eye-safe adaptive optics Free Space Optical (FSO) transceiver as a combined apparatus for simultaneous point-to-point commercial communications. The apparatus has a high degree of assured carrier availability under stressing environmental conditions. The apparatus establishes and maintains pointing and stabilization of mmW RF and FSO optical beams between adjacent line of sight apparatuses. The apparatus can rapidly acquire and reacquire the FSO optical carrier link in the event the optical carrier link is impaired due to adverse weather.

Full Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This application relates to both radio frequency as well as free space optical data communication, particularly E-band millimeter wave Radio Frequency data communication. 
         [0003]    2. Description of the Related Arts 
         [0004]    In 2003, the FCC-licensed for use 13 GHz of spectrum in the 70 GHz and 80 GHz bands, also known as the E-band millimeter wave Radio Frequency (RF) spectrum. Ten bands in this spectrum were made commercially available for a broad range of fixed wireless applications operating at gigabit data transfer rates. Applications include point-to-point local wireless networks and broadband internet access. Communication of data through E-band signals potentially serves as a cheap alternative to more costly fiber solutions, particularly in urban areas due to the cost of laying fiber. E-band RF data transfer is a particularly cost effective solution for filling the gap for short-haul wireless connectivity in the so-called “last mile” between network service providers and customers. E-band RF data transfer can also offer data rates that overlap with lower the end of rates available with fiber-based solutions. 
         [0005]    Because of its location in the radio frequency spectrum (71-76 and 81-86 GHz), E-band data transmission is not very susceptible to interference due to fog, airborne particulates such as dust and atmospheric turbulence. E-band data transmission, however, is susceptible to degraded performance due to rain. Rain interferes with radio wave transmission in the E-band, such that during a rain storm, data transmission would necessitate repeated data retransmission at best or interrupted service at worst. 
         [0006]    Radio waves in the E-band have a narrow, pencil beam-like characteristic, and as a result antennas producing E-band signals can be placed in close proximity to one another without concern for adjacent channel interference. However, due to the narrow pencil-like characteristic of the E-band RF beam, an E-band transmitter must be precisely pointed at its receiver in order to ensure data transmission. Twist and sway movements due to wind and other weather can more easily disrupt data transmission in the E-band versus data transmissions that occurs at lower frequencies. 
       SUMMARY OF THE INVENTION 
       [0007]    To provide an integrated apparatus for free space data transmission, embodiments of the invention combine millimeter wave (mmW) Radio Frequency (RF) data transmission with Free Space Optical (FSO) data transmission on a common stabilized assembly. The apparatus may be used as part of a larger commercial communications network. The apparatus ensures high level of carrier availability, even under stressing environmental conditions. The apparatus further ensures that at least a mmW RF control link remains operational in the unlikely event that both rain and fog occur together. 
         [0008]    Components of the apparatus include a mmW transceiver and a FSO transceiver. The transceivers are mounted on a stabilized mounting platform connected to a gimbal assembly inside a sheltered enclosure. The sheltered enclosure is mounted on a stationary platform, for example at a cell site or a network point of presence, and is positioned at a height above the ground in order to line up with an adjacent cell site that is located a distance away, but still within line-of-sight. In one embodiment, the sheltered enclosure also includes stationary equipment for supporting the stabilized mounting platform. The stationary equipment includes electronics for electrical power conditioning and distribution, as well as a drive controller for the gimbal assembly, and the bulk of the signal processing electronics. Electronics on the stabilized platform are minimized to reduce its power consumption and weight. 
         [0009]    The gimbal assembly ensures that both the mmW RF antenna and the FSO transceivers are accurately pointed at an adjacent cell site containing the complement apparatus. Due to narrowness of both the mmW RF and FSO carrier beams, a high degree of stabilization is necessary for the moving platform. The gimbal assembly can correct for environmental effects that would otherwise disrupt communication by either of the transceivers (e.g., cell site vibration and sway). Coarse closed loop operation of the gimbal assembly is initially provided by the mmW RF transceiver, after which fine acquisition is performed by the FSO transceiver. The FSO transceiver includes fast steering mirror assembly that sends directional corrections to the gimbal assembly for pointing and stabilization of the transceivers. 
         [0010]    In the unlikely event that both the RF and FSO carrier links are lost due to the simultaneous presence of both heavy rain and fog, the apparatus is capable of rapid reacquisition of a communications link. The apparatus uses a low data rate backchannel on the mmW RF carrier, which spreads a baseband carrier signal using a spread spectrum code, allowing for a much greater receiver sensitivity. This way, the mmW RF link is able to provide the gimbal assembly with at least the minimal amount of connectivity necessary to provide coarse control correction, even under inclement weather. This assists the FSO transceiver in reacquiring an optical link. 
         [0011]    According to another embodiment, the FSO link may be configured to have a significantly higher data rate than the RF link. In this case, the apparatus is also capable of prioritizing the transmission of data. In one embodiment, when higher levels of throughput are available on the FSO link, higher priority data is transmitted by both transceivers, and lower priority data is transmitted only by the FSO transceiver. In another embodiment, if the RF and FSO links have similar data rates, then high priority data may be sent on both links, and low priority data may be split between the remaining RF and FSO data capacity. 
         [0012]    In the event the transmission path is affected by rain, data transmission is minimally affected as the FSO transceiver is not significantly affected by rain. Conversely, if the transmission path is affected by fog or other particulate, data is also minimally affected as the mmW RF transceiver is not significantly affected by these weather conditions. 
         [0013]    Other features and objectives of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings, which by way of illustration, show preferred embodiments of the present invention and the principles thereof. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention or purview of the appended claims. 
         [0014]    In one embodiment, the data transmitted by the transceivers incorporates data protection and loss mitigation techniques. In one embodiment, data to be transmitted may be preprocessed to incorporate forward error correction to improve robustness against packet loss. In one embodiment, packet retransmission can be used to recover data lost to momentary connection outages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The teachings of the embodiments of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings. 
           [0016]      FIG. 1  is a system diagram of an integrated commercial communications network using two integrated communications apparatuses to communicate through free space. 
           [0017]      FIG. 2  is a side view of an integrated communications apparatus including an E-band mmW RF and a FSO transceiver, both mounted onto a gimbal-controlled platform, according to one embodiment. 
           [0018]      FIG. 3  is a diagram illustrating the components of the transceiver related to signal acquisition and reacquisition, according to one embodiment. 
           [0019]      FIG. 4  is a flowchart illustrating the process for communications link acquisition and reacquisition by the integrated communications apparatus, according to one embodiment. 
           [0020]      FIG. 5  is a block diagram of the electronics of the integrated communications apparatus, according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     General Overview and Benefits 
       [0021]    An integrated communication apparatus may be used as part of a commercial communications network to facilitate the exchange of fully duplexed data with another similar device. The apparatus is configured to maintain high carrier availability, or uptime, even in adverse weather conditions. The apparatus includes two transceivers, a millimeter wave (mmW) Radio Frequency (RF) transceiver, and a Free Space Optical (FSO) transceiver. In one embodiment, the mmW RF transceiver operates in the E-band RF range, or 13 GHz of spectrum in the 70 GHz and 80 GHz radio frequency bands. In one embodiment, the mmW RF transceiver is capable of operating outside the E-band RF range. The mmW RF transceiver may be used to transmit data and/or establish a link with an adjacent apparatus. In another embodiment, the E-band RF electronics support both a high data rate waveform, and an additional low data rate waveform with at least 20 dB of improved sensitivity. The low data rate waveform is intended primarily to provide a very robust command and control backchannel, and to assist in initial link acquisition or link re-acquisition. 
         [0022]    Benefits of the disclosed apparatus include enhancement of existing systems for commercial communications by augmenting presently available mmW RF systems which are subject to interruption from weather effects. The combination of mmW RF and FSO transceivers is complimentary, whereby the FSO supports connectivity during rain, which interrupts mmW RF transmission, and conversely the mmW RF supports connectivity during conditions where fog, snow, airborne particulate matter, and atmospheric turbulence interrupt the FSO. 
         [0023]    Integrating a mmW RF transceiver with a FSO transceiver provides an alternative solution to ground-based fiber optic communication systems. Fiber systems are expensive to deploy, as there is significant cost associated with the trenching and laying fiber in urban areas. The integrated communication apparatus provides a lower cost alternative to building a fiber optic network. 
         [0024]    As the apparatus incorporates two different transceivers, the apparatus is able to transmit data over more than one connection. This allows data of different priorities to be transmitted in the most efficient manner possible based on the weather conditions affecting the transceivers. The apparatus also resistant to malicious attempts to defeat or interrupt data delivery through jamming, interception or hacking, as data is capable of being transmitted over both RF and FSO transmission mediums. 
       System Structure 
       [0025]      FIG. 1  is a system diagram of an integrated commercial communications network using two integrated communications apparatuses to communicate through free space. An integrated communications apparatus  100   a  located at a first cell site is configured to communicate with another integrated communications apparatus  100   b  at a second cell site located remotely from the first cell site. The two apparatuses  100  do not have to be identical, so long as both devices are capable of transmitting and receiving both mmW RF  101  and FSO  102  transmissions at the relevant frequencies. The integrated communication apparatus  100  may be a stand-alone cell site, or attached to a cell site that performs other communications or network operations. The transceivers of the apparatus  100   a  are directed at another similar device  100   b  positioned a distance away within line of sight. 
         [0026]    The distance between apparatuses may depend upon historical weather data for the area being serviced. For example, if the service area frequently experiences rain or fog, the distance between sites may be smaller than if these weather conditions are less frequent or severe. Often, an apparatus will be positioned at a prescribed height above ground to prevent interruption of line of sight due to building or landscape features. The apparatus may be land-based, maritime-based (i.e., mounted on a seaborne vessel), or airborne. 
         [0027]      FIG. 2  is a side view of an integrated communications apparatus including an E-band mmW RF and a FSO transceiver, both mounted onto a gimbal-controlled platform, according to one embodiment. The apparatus  100  includes an environmental enclosure  203 . Inside the environmental enclosure  203 , a mmW RF transceiver  204  and a FSO transceiver  205  are coupled to a gimbal assembly  206 . In one embodiment, the gimbal assembly  206  is located external to the environmental enclosure  203 . 
         [0028]    In one embodiment, environmental enclosure  203  includes one or more apertures for transmitting signals. Each aperture is transparent to the transmissions at least one of the transceivers. In one embodiment, each aperture is constructed using a different material transparent to the transmissions of its associated transceiver. In one embodiment, the environmental enclosure  203  has a single common aperture, made of a material having qualities that allow propagation of both E-band mmW RF  101  and FSO  102  transmissions. In the example embodiment shown in  FIG. 2 , the apparatus  100  has only a single aperture  211 . In this embodiment, the housing of the environmental enclosure  203  is substantially transparent to mmW RF transmissions  101 . The aperture  211  for the FSO transceiver includes an optical window to FSO transmissions  102 . 
         [0029]    The environmental enclosure  203  provides protection against environmental deterioration or destruction for all internal electrical and mechanical components of the apparatus. In one embodiment, the environmental enclosure  203  may also provide for internal environment control of properties such as temperature, humidly, condensation, and moisture. The environmental enclosure  203  may also employ a heater, wiper, or other mechanism  212  to preclude or limit precipitation or ice formation on the aperture  211 . 
         [0030]    Both the mmW transceiver  204  and the FSO transceiver  205  are mounted on a moving platform  209 . In one embodiment, the FSO transceiver  205  is mounted to an optical bench, and the optical bench is mounted on the movable platform  209 . In one embodiment, the optical bench and moving platform  209  are identical. The moving platform  209  is connected to the environmental enclosure  203  through gimbal assembly  206 . Gimbal assembly  206  allows the transceivers to rotate within a range of motion on two axes dimensions, in order to assist the transceivers in forming communications links with other similar devices. Through their common mounting on the moving platform  209 , the motion of both is controlled by the gimbal assembly  206 . The transceivers share a near-common boresight. 
         [0031]    The environmental enclosure  203  also contains a stationary platform circuit board  207  and a moving platform circuit board  208  which together transmit, receive, and process data. The stationary platform circuit board  207  is located off of the moving platform  209 , and thus does not move with gimbal  206  motion. The stationary platform circuit board  207  exchanges power and data with external electronics separate from the apparatus  100  through cables and/or fibers  213  that pass through a port  210  in the environmental enclosure  203 . 
         [0032]    The moving platform circuit board  208  is located on the moving platform. The moving platform circuit board  208  includes those electronics that are only able to function in close proximity to the transceivers, or are best able to function in close proximity to the transceivers. Generally, it is preferable to minimize the mass and heat loading of the gimbal assembly  206 . Thus, electronics not required to be on the moving platform circuit board  208  are instead located on the stationary platform circuit board  207 . Removing unnecessary electronics from the moving platform circuit board  208  has the added benefit of minimizing the thermal loading of the moving platform  209 . In one embodiment, no electronics require close proximity to the transceivers, thus the moving platform circuit board  208  is omitted and all electronics for the apparatus are located on the stationary platform circuit board  207 . 
         [0033]    Data received at the transceivers is communicated to the moving platform circuit board  208 , which may perform some data processing before sending the data to the stationary platform circuit board  207  for possible further processing. The stationary platform circuit board  207  sends the data to external electronics through cables  213 . 
       Transceiver Structure and Signal Acquisition/Reacquisition 
       [0034]    The transceivers  204  and  205  of the apparatus  100  work in conjunction with the gimbal assembly  206  to establish communications links for data transmission.  FIG. 3  is a diagram illustrating the components of the transceivers related to signal acquisition and reacquisition, according to one embodiment. The mmW RF transceiver  204  includes a mmW RF antenna  314  for transmitting and receiving mmW RF transmissions. In one embodiment, the mmW RF antenna  314  is 0.3 meters in diameter, and has a field angle of approximately 0.9 degrees. The mmW RF antenna  314  is also used in coarse steering correction for the gimbal assembly  206 . 
         [0035]    The FSO transceiver  205  includes a FSO telescope  319 . The FSO telescope consists of an FSO boresight. The FSO telescope  319  consists of a laser  315  for transmitting FSO transmissions. In one embodiment, the laser  315  consists of a fully duplexed eye-safe 1550 nm central wavelength laser carrier. The FSO transceiver  205  additionally includes adaptive optics  316 . In one embodiment, the adaptive optics  316  include a wavefront sensor  317 . The adaptive optics  316  can consist of a low order system providing wavefront tip-tilt correction only, or a high order system providing higher order wavefront aberration correction (e.g., focus and higher). 
         [0036]    The adaptive optics  316  provides improved wavefront phase coherency for FSO transmissions, despite the presence of atmospheric turbulence. The adaptive optics  316  does this by providing for correction of both an inbound and/or outbound optical wavefront to improve the wavefront&#39;s optical point spread function, thereby maximizing the FSO transceiver carrier throughput. The adaptive optics  316  also measure the arriving optical wavefront and use the resulting measurements as data to determine how to best orient the movable platform  209  towards the adjacent apparatus. The adaptive optics  316  include fast steering assembly  318 . The fast steering assembly  318  includes a fast steering mirror (FSM)  321  and a FSM control  320 . In one embodiment, the FSM control  320  consists of a motor drive coupled to the movable platform  209 . 
         [0037]    The control system between the FSO transceiver  205  and the gimbal assembly  206  results in the transmission and reception of nearly collimated optical beams for establishing links and communicating data. As a result, the apparatus  100  is able to communicate FSO data over significantly larger distances than comparable FSO devices that must use divergent optical beams. In one embodiment, the FSO optical beam spreads over an angular range of less than one-tenth of a degree in any given direction. In one embodiment, the FSO has a link uptime of at least 99.9999% at a distance of four miles. 
         [0038]    As both transceivers  204  and  205  share a common moving platform  209 , both transceivers generally move together in response to gimbal  206  motion. However, in one embodiment the FSO transceiver  205  is independently steerable from the mmW RF transceiver  204  using the FSM  408 . The wavefront sensor  317  measures the intensity conjugates of the arriving optical beam, and provides fine control data to the FSM control  320 . The FSM control  320  uses the control data to move and/or rotate the FSM  321  in order to precisely position the FSO optical boresight independent of the motion of the movable platform  209 . The FSO optical boresight is positioned to maximize the irradiance received at wavefront sensor  317  from an arriving optical beam. 
         [0039]    Gimbal assembly  206  provides stabilization for the transceivers, and controls coarse and fine motion for the movable platform  209  containing the transceivers. The gimbal assembly  206  is coupled to the transceivers and uses received transmissions from remote cell sites to orient the movable platform  209  towards a remote apparatus in order to establish FSO and mmW communications links. The gimbal assembly  206  also responds to external weather influences that would affect the position and orientation of the movable platform  209 . The gimbal assembly  206  includes an Inertial Measurement Unit (IMU)  313  which provides a local frame of reference for the position, velocity, and angular rotation of the gimbal assembly  206 . The IMU  313  includes accelerometers and gyroscopes. Thus, the IMU is capable of detecting motion of the movable platform  209  due to external weather forces that cause apparatus motion, such as twist and sway. 
         [0040]      FIG. 4  is a flowchart illustrating the process for communications link acquisition and reacquisition by the integrated communications apparatus  100 , according to one embodiment. Initially, apparatus at two cell sites are mechanically aligned  430  to point towards one another. In one embodiment, the mechanical alignment need only be performed once, upon initial installation of the apparatus. 
         [0041]    The apparatus acquires an initial communications link with another remote apparatus by transmitting  431  a mmW RF signal on a mmW monitoring channel. For the mmW RF transceiver  204 , “channels” represent specific time and radio frequency ranges that are recognized by the electronics of the apparatus  100  to perform specific purposes, such as data transfer or link acquisition/reacquisition. The monitoring channel may be a portion of the RF data channel, or alternatively the enhanced sensitivity back channel may also be used for this function. 
         [0042]    While the mmW RF transceiver  204  transmits  431  a signal on the mmW monitoring channel, the gimbal assembly  206  sweeps  432  over a search area using a coordinated scanning technique. The coordinated scanning technique minimizes the search area scanned to find the remote apparatus. The goal of the transmission  431  is to detect the presence of another remote apparatus, through the reception of mmW RF transmissions from the remote apparatus. 
         [0043]    The search area being scanned or swept by the gimbal assembly  206  converges based upon the distribution of mmW RF data being received from various volumes of scanned space. High amounts of received RF and FSO signal in a particular area are indicative of a apparatus in that area. The operation of the mmW RF transceiver  204  in conjunction with the gimbal assembly  206  to obtain an initial communications link may be referred to as “coarse correction” or “coarse control.” 
         [0044]    Concurrently with transmission  431  over the mmW monitoring channel, the FSO transceiver  205  may also transmit  433  a FSO signal. Typically, as the coordinated scanning technique focuses in on a remote apparatus, the FSO transceiver  205  will begin to receive incoming FSO transmissions from the remote apparatus at the wavefront sensor  317 . A scanning technique is applied to the FSM control  320  to scan  434  the FSM  320  over a search area in order to more precisely located the remote apparatus. In one embodiment, a centroid algorithm is applied to the FSM control  320  to help the FSM mirror  321  better locate the remote apparatus. The FSM control  320  communicates with the gimbal assembly  206  to more precisely orient the movable platform  209  to maximize communication link strength. The operation of the FSO transceiver  205  in conjunction with the gimbal assembly  206  and the FSM control  320  to obtain a stronger communications link may be referred to as “fine correction or “fine control.” 
         [0045]    In the event that both transceivers lose connection with the remote apparatus, the mmW RF transceiver  204  transmits  435  a signal over a mmW backchannel to reacquire the communications link. The mmW backchannel is a low bandwidth mmW RF channel used to maintain coarse control of the gimbal assembly  206  when the FSO transceiver  205  cannot connect with its remote counterpart. The transmitted  435  mmW backchannel consists of a baseband signal using a spreading code, which spreads baseband signal over a low and wide frequency range, where the frequency range is low and wide relative to the frequency range of the mmW RF data channel. A baseband signal has a low frequency noise-like structure. By sequentially spreading the baseband signal structure over a wide band of low frequencies, a high degree of mitigation is achieved against natural fade-producing sources associated with atmospheric interference. This is due, in part, to the fact that atmospheric interference at the operating frequencies of the mmW RF transceiver looks like noise. In one embodiment, the baseband signal transmission includes data. In this embodiment, a received mmW RF baseband signal from an adjacent apparatus is processed by the apparatus  100  in order to recover transmitted data. 
         [0046]    During reacquisition of the link by the FSO transceiver, the mmW RF transceiver  204  transmits  435  a signal on the mmW backchannel, the gimbal assembly  206  sweeps  436  over a search area. The apparatus  100  reduces the search area scanned using feedback provided by reception of RF transmissions from the remote apparatus over the mmW backchannel. The feedback functions to maintain coarse pointing control of gimbal assembly  206  while the FSO transceiver attempts to reacquire the optical link. Fine feedback is provided to the gimbal assembly  206  by data received at the FSO transceiver  205 , 
         [0047]    In one embodiment, the apparatus also monitors the health of both mmW and FSO data links in real time over the mmW backchannel. In one embodiment, health monitoring also includes information regarding the real time status of the gimbal assembly  206 . This information may be externally communicated to a user interested in monitoring the health of the communications network links. In one embodiment, the data signal sent over the backchannel from a first apparatus to a second apparatus provides control information for the intensity with which the second apparatus should transmit optical signals via the FSO transceiver from the second apparatus to the first apparatus. In this embodiment, the control information is based on the intensity of optical signals received at the FSO transceiver of the first apparatus. 
       Apparatus Electronics 
       [0048]      FIG. 5  is a block diagram of the electronics of the integrated communications apparatus, according to one embodiment. Data is communicated within the apparatus  100  between the transceivers  204  and  205 , through the electronics, and out to an external interface in either an electronic format, such as gigabit Ethernet format, or in an optical format. In one embodiment, the electronics of the apparatus  100  include a stationary platform circuit board  207  and a moving platform circuit board  208 . 
         [0049]    The stationary platform circuit board  207  may communicate between the moving platform circuit board  208  and with an external electronics interface associated with a user. External power  309  is received at the stationary platform circuit board  207  and is conditioned  317  and distributed  318  for use by the moving platform circuit board  208  or other components of the apparatus  100 . In one embodiment, the stationary platform circuit board  207  also contains drive electronics (DACs)  319  for gimbal assembly  206 , as well as drive electronics  319  for the fast steering mirror control  320  of the FSO transceiver  205 . 
         [0050]    In one embodiment, the stationary platform circuit board  207  includes a Data Path FPGA  310  that comprises logic for processing of transceiver data  312  and an optical power control  313 . The Data Path Field Programmable Gate Array (FPGA)  310  may include or be attached to a microprocessor unit (MPU)  311 . FPGA  310  interfaces to moving platform circuit board  208  with stationary platform circuit board  207  through link serial interconnects  308   a  and  308   b . Interconnects  308  allow the stationary platform circuit board  207  to control operational functionality of transceivers  204  and  205 . In one embodiment, the link serial interconnects  308  include interconnect  308   c  which provides coaxial functionality and incorporates E-band baseband and intermediate frequency (IF) electronics  304 . E-baseband and IF electronics  304  ports RF data between moving platform and stationary circuit boards  207  and  208  in quadrature. 
         [0051]    The stationary platform circuit board  207  may also include a variable optical attenuator (VOA)  315  to control the amplitude of the data received over optical fiber output  314   a  from the FSO transceiver  205 . The stationary platform circuit board  207  also includes an Erbium Doped Fiber Amplifier (EDFA)  316  to control the amplitude of the data to be transmitted by the FSO transceiver  205 . The EDFA may be followed by a VOA to allow rapid high accuracy control of the transmit power level. Data received (Rx) and transmitted (Tx) by the transceivers is transported to and from the moving platform circuit board  208  to the stationary platform circuit board  207  through connection  314 . Connection  314  may be an electrical cable or optical fiber depending upon the embodiment. In one embodiment, the connection  314   a  with the FSO transceiver  205  comprises an optical fiber, whereas the connection  314   b  with the mmW RF transceiver  204  comprises a cable. 
         [0052]    The moving platform circuit board  208  communicates data received at the transceivers  204  and  205  to the stationary platform circuit board  207 , and may also communicate with an external interface. In one embodiment, the moving platform circuit board  208  consists of a FPGA  303 . The moving platform FPGA  303  also includes a bi-directional external interface through link  308   b . The moving platform  303  may include or be connected to a digital signal processor (DSP)  322 . The moving platform FPGA  303  communicates with a temperature sensors  320  and serial peripheral interface (SPI) flash sensors  321 , which output to an external interface. The moving platform FPGA  303  communicates with the FSO transceiver  205  through three sensors: an inertial stabilization sensor  325  capable of measuring the motion of the moving platform  209  to provide feedback to the gimbal assembly  206 , a FSM drive electronics  324  coupled to the FSM control  320  for controlling the direction of the FSO transceiver  205 , and a quadrature cell control electronics  323  for closed-loop optical beam stabilization. 
       Data Transmission 
       [0053]    Both transceivers  204  and  205  of the apparatus  100  are capable of transmitting data at more than one data carrier rate, and may transmit over more than one channel at the same time. In one embodiment, the mmW RF transceiver  204  transmits data over several channels simultaneously using a phase shift keying digital modulation scheme. In one embodiment, the FSO transceiver  205  may transmit over multiple channels simultaneously using dense wavelength division multiplexing (DWDM). 
         [0054]    The transceivers may employ forward error control correction (FEC) to an outbound data stream in order to reduce the need for retransmission of lost bits. The transceivers may also be configured to retransmit lost data in response to a retransmission signal received from the adjacent apparatus. 
         [0055]    The apparatus  100  is capable of transmitting data of different priorities at different times and over different transceivers depending upon link conditions. In one embodiment, data is broken out into high priority data and low priority data. 
         [0056]    In one embodiment, if both the FSO transceiver link and mmW RF transceiver link are active, both high and low priority data are transported by the FSO transceiver  205 . Concurrently, only high priority data is also transmitted by the mmW RF transceiver  204 . This redundancy reduces the need for retransmission of lost high priority data, thereby increasing the overall speed at which high priority data is transmitted. Low priority data, in contrast, is transmitted only by the FSO transceiver  205 . The FSO transceiver  205  transmits both high and low priority data because it generally has a higher transmission capacity than the mmW RF transceiver  204 . 
         [0057]    In the event of rain, data transmitted by the mmW RF transceiver  204  may not be received, however data transmitted by the FSO transceiver  205  will be received. The FSO transceiver  205  does not experience performance degradation due to rain because the radius of raindrops is significantly larger than the wavelength of the FSO optical carrier allowing for less cross-sectional scattering of the propagated laser beam radiation. In the event of fog or other particulate-based weather events, data transmitted by the FSO transceiver  205  may not be received, however data transmitted by the mmW RF transceiver  204  will be received. FSO transceiver  205  emissions are susceptible to interference due to clouds, dense fog, snow, airborne volcanic particulates. Their radii are sufficiently small so as to permit cross-sectional scattering of the propagated FSO optical beam resulting in a loss of power at the receiving FSO aperture. The FSO beam may also be scattered by very strong atmospheric turbulence under some circumstances. In contrast, mmW RF radiation near the E-band is larger in wavelength than these particulates, and thus is not affected by them. The E-Band wavelength is also much larger than any perturbation that can be introduced buy atmospheric turbulence, and is therefore not effected by turbulence. Thus, the apparatus  100  is able to transmit data over at least one connection under a range of different adverse weather conditions. In one embodiment, as high priority data is transmitted over both transceivers, high priority data will be received by a remote apparatus even under the above described weather conditions. 
         [0058]    In the event that the communications link has unused available transmission bandwidth, low priority data may be transmitted as high priority data in order to ensure maximum use of available transmission capacity and to minimize delays due to transmission time. 
       Additional Considerations 
       [0059]    Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed in detail above. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents.

Technology Classification (CPC): 7