CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/915,309 filed Aug. 10, 2004, now U.S. Pat. No. 7,218,240, issued on May 15, 2007. 


   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   This invention was developed in the course of work under U.S. government contract MDA972-02-9-0005. The U.S. government may possess certain rights in the invention. 


   FIELD 
   This invention relates generally to communications systems and methods and, more particularly, to telecommunication systems used to improve situational awareness of users in human-in-the-loop systems. 
   BACKGROUND 
   A wide variety of situations exist in which improved situational awareness may be of critical importance. For instance, air traffic controllers need to be aware of where their aircraft are, where other controllers&#39; aircraft are as the aircraft enter air space controlled by the first controller, and to where those aircraft might be traveling. If the controllers knowledge can be improved, then it might be possible to safely allow more aircraft to traverse a given volume of airspace at any given time. Likewise, emergency workers responding to natural disasters, as well as members of the armed services, need to be aware of the actions their teammates and other parties may be undertaking. Failure to quickly and correctly comprehend and assess the situation (i.e. having insufficient situational awareness), particularly failure to know the positions of cooperating parties, may produce less than optimal team performance. 
   Situational awareness is also of increasing importance because many organizations are increasing the use of unmanned aerial vehicles (UAV) to reduce costs and personnel risks while also improving the organization&#39;s effectiveness. Scenarios in which several UAVs cooperate to accomplish a mission (e.g. a search) give rise to the possibility that the operator of one UAV may not accurately know the position of another UAV. Thus, the operator may partially duplicate a search already conducted by the operator of the other UAV or be unable to respond to requests for assistance from the other UAV operator. For example, if a UAV operator is pursuing two suspects and the pair of fugitives split up to escape, the operator of another UAV (who is unfortunately not aware of the pursuing UAV&#39;s current whereabouts) might be unable to acquire one of the two suspects rapidly enough to prevent one of the fugitives from evading the pair of pursuing UAVs that are cooperating such that first UAV maintains the pursuit of one suspect while the second UAV acquires, and pursues, the other suspect. 
   Thus, a need exists to provide a simple, intuitive way to improve the situational awareness of operators, particularly when more than one human-in-the-loop system cooperates with another to accomplish a common goal. 
   SUMMARY 
   It is in view of the above problems that the present invention was developed. The invention includes methods and systems used in communications systems to improve the situational awareness of the users of the communication system. 
   In a preferred embodiment, the present invention provides a computerized audio system that distinguishes between incoming audio signals and adjusts each signal to cause the recipient to perceive the signals as coming from a particular direction, distance, and elevation. To distinguish the incoming signals from each other the system may use a digital address of the sender (e.g. an I.P. address) or may use the phone line through which the audio signal comes (e.g. for a multi-line conference call). Of course, the present invention is not limited by these exemplary embodiments. For instance even a TDMA (Time Division Multiple Access) network could be used in conjunction with the present invention. Once the audio signals are distinguished from each other, the system then associates a relative position with each of the audio signals from which the recipient will perceive the audible signal (to be produced from the audio signal) as coming. The perceived positions associated with the signals may be distributed and arbitrarily associated with the signals to provide optimum audible separation of the sources. These arbitrary assignments are well suited for situations wherein the actual position of the signal&#39;s origin (i.e. the sound source) is unavailable or not of consequence. Where the position of the origin is known, or important to the recipient, the associated position may indicate the true direction to the source and may even be adjusted to give an indication of the distance to the source. For example, the bearing of the perceived position and that of the source may be approximately equal with the perceived distance being proportional to the true distance. In still other preferred embodiments, the perceived position may be chosen based on the location of a device associated with the source so that the perceived relative position does not match the position of the source itself. Rather, the perceived relative position matches that of the device. An example of the latter situation includes the source being an operator of a UAV and the perceived position being chosen so as to indicate the position of the UAV. Building on this concept, the location of a device controlled by the recipient of the audio signal may also be used to assign the perceived relative position of the sound. In other words, if the recipient is operating another UAV, the perceived position may be chosen to convey to the recipient the relative position of the source&#39;s UAV with respect to the recipient&#39;s UAV. 
   In a second preferred embodiment, the system provides sound cues to an operator in a scenario that includes spaced mobile platforms with a changing frame of reference, such as two remotely piloted vehicles operating in a shared airspace or a remotely piloted vehicle on a landing approach to a carrier. The cued operator receives an audible signal that includes cues for the relative position of the other platforms with respect to the position of the operator&#39;s vehicle. That is, in the case of two platforms, the signal is modulated to appear to the operator as though it were being transmitted to the operator from the location of the other platform, allowing the operator to know intuitively from the sound the relative spatial relationship between the operator&#39;s vehicle and the other platform. Since this system is synthetic there does not have to be actual communication between the two platforms. The present invention provides the operator of one platform cues so that the operator will know where the other platform(s) are. These cues could arise from active communication or by sensing the position of the other platforms. 
   In a third preferred embodiment, a system of mobile platforms is provided. The system includes a first and a second mobile platform with a relative position there between. Additionally, the system includes a communications subsystem and two controllers for the users to control the mobile platforms. The communications subsystem allows the first user to send an audio signal to the second user. Further, the communication subsystem modifies the signal so that the second user perceives an audible signal from the direction of the relative position of the second mobile platform with respect to the first mobile platform. In a preferred embodiment, the mobile platforms are unmanned aerial vehicles. 
   In a fourth preferred embodiment, a method of communicating at least one audio signal from a source to a recipient is provided. The method includes associating a relative position with the source and modifying the audio signal to convey the relative position. The modified signal is presented to the recipient so that the recipient perceives an audible signal conveying the relative position associated with the source. Where more than one source is present, the association of various relative positions with each source can be arbitrary and may also occur in real time. Further, the relative positions may be chosen from positions on a circle disposed about the recipient. In addition to modifying the signal(s) to reflect a relative position, the signal may be modified to reflect a relative movement. In yet other preferred embodiments, the associated relative position may be based on a spatial relative position or on a logical address associated with the signal. In yet other embodiments, the signal may be generated by speaking. 
   Another preferred embodiment provides a communication system. The system of the present embodiment includes a signal modifier and a position associater. The position associater associates a relative position with an audio signal. The signal modifier modifies the audio signal to convey the associated relative position and outputs the modified audio signal. Thus, the recipient perceives an audible signal conveying the associated relative position. In other preferred embodiments, the system includes an audio subsystem that accepts the modified audio signal and reproduces the audible signal (as modified) for the recipient. The signal modifier may also retrieve an acoustic model from a memory and use the model in modifying the audio signal. The system may also include a link to a telephony system from which the system accepts the audio signal and a caller identification signal. In these latter embodiments, the position associater may use the caller identification signal in associating the relative position with the voice signal. 
   Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 


   
     BRIEF DESCRIPTION OF DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  illustrates a system constructed in accordance with the principles of the present invention; 
       FIG. 2  illustrates a telecommunications system constructed in accordance with another preferred embodiment of the present invention; 
       FIG. 3  further illustrates the system of  FIG. 1 ; 
       FIG. 4  illustrates another system constructed in accordance with the principles of the present invention; 
       FIG. 5  further illustrates the system of  FIG. 4 ; and 
       FIG. 6  illustrates a method in accordance with the principles of the present invention. 
   


   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  illustrates a telecommunication system constructed in accordance with the principles of the present invention. 
   The present invention takes advantage of the ability of humans to use sound cues to judge the azimuth, elevation, and distance of a sound source. These audio cues can be simulated in electronic systems that feed headphones, loudspeakers, or other sound producing devices. The listener thus perceives the produced sound as coming from a particular position, even though the speakers are at different positions than the perceived position of the produced sound. To convey a particular azimuth, these systems typically create delays between the reception of a sound by one ear and the reception of the same sound by the other ear. In addition to the interaural delay, the system may create a slight difference in intensity, or volume, as received by one ear over the other to further enhance the “stereo” effect. 
   Distance may also be simulated simply by varying the intensity of the sound. In the alternative, these systems can apply a model of sound propagation in a particular acoustic environment (e.g. a snowy field or a conference room) to the audio signal to cause the recipient to perceive the desired position of the sound. For instance, the model can add echoes with appropriate delays to indicate sound reflecting off of various surfaces in the simulated environment. The model may also “color” (e.g. adjust the timbre of the sound) the sound to indicate the atmosphere, and other objects, attenuating the sound as it propagates through the environment. As to the perceived elevation of a sound source 7  these systems may also color the audio signal to approximately match the coloring done by the human ear when a sound comes from a particular elevation. Thus, the system is capable of producing quadraphonic, surround sound, or three-dimensional affects to convey the relative position and orientation of one platform  16  with respect to the other platform  18 . 
   Turning now to  FIG. 1 , the exemplary system  10  includes a voice message recipient  12  and a voice source  14  along with a pair of platforms  16  and  18  controlled by the recipient  12  and source  14 , respectively. The system  10  includes means to appraise the recipient  12  of the position of the platform  18  relative to the platform  16 . Further, the knowledge of the relative location of the platform  18  may be imparted to the recipient  12  in real time and in an intuitive manner as is herein described. It will also be understood that the recipient may act as an audio source and visa versa. As shown, the platforms  16  and  18  may be unmanned aerial vehicles (UAVs), although the platforms could be any type of platform capable of having a position, or movement, independent of the recipient  12  and source  14 . Exemplary mobile platforms include aircraft, spacecraft, unmanned aerial vehicles (whether remotely piloted or autonomous), submersible vehicles, cranes, tools (e.g. assembly or machining robots), trucks, cars, etc. In general, though, mobile platforms include any vehicle capable of movement or being moved. Thus, the system also includes communication links  20  and  22  between the operators  12  and  14  and the exemplary UAVs  16  and  18  as shown in  FIG. 1 . An additional communication link  24  is shown between the vehicle of recipient  12  and the vehicle of source  14 . While the communication link  24  usually carries audio signals, other signals (e.g. video signals from the UAVs  16  and  18  and digital data) are within the scope of the present invention. Also shown are the fields of view  26  and  28  of the UAVs  16  and  18 . While the recipient  12 , the source  14 , and the UAVs  16  and  18  might be within the field of view of one another, or even co-located, frequently these components will be separated by some distance and will likely be shielded from the view of each other. Nonetheless, the operators of the UAVs  16  and  18  frequently desire to know where the UAV operated by the other operator is positioned. 
   With continuing reference to  FIG. 1 , the UAV  16  has a heading  30  which is also shown having been translated to the recipient  12  as  30 . From the UAV  16 , relative position  32  point toward the UAV  18  and the source  14 . Also, relative positions  36  and  38  point from the recipient  12  to the UAV  18  and to the source  14 . Generally, the recipient  12  knows the position of the UAV  16  and the position of the source  14 , although this is not always the case. Frequently the recipient  12  is ignorant of the position of the UAV  18  since it is controlled by the source  14 . 
   In operation, the recipient  12  controls the UAV  16  via the data link  20  and receives information from the UAV  16  via the link  20 . In particular, the recipient  12  views the field of view  26  and adjusts the operation of the UAV  16  according to the information thereby derived. Similarly, the source  14  controls the UAV  18 . When the source  14  desires assistance from the UAV  16 , the source  14  communicates its desire for assistance over the link  24 . In turn, the recipient  12  of the request steers the UAV  16  to the vicinity of the UAV  18 , thereby adding the capabilities of the UAV  16  to those of the UAV  18 . Of course, this optimal scenario presupposes that the recipient  12  knows the relative position of the UAV  18  with respect to the UAV  16 . If this is not the case, the recipient  12  may steer the UAV  16  in such a manner as to not render the requested assistance (i.e. the recipient  12  turns the UAV  16  the wrong way). 
   With reference now to  FIG. 2 , a block diagram of the system  10  is shown. In particular,  FIG. 2  includes a relative position and orientation subsystem  50 . The subsystem  50  includes a relative position comparator  54 , a signal modifier  56 , and a sound reproducer  57 . The UAVs  16  and  18  in  FIG. 2  also include navigation subsystems  58  and  60 . The navigation subsystems  58  and  60  may be any type of navigation subsystem capable of ascertaining the position and orientation of the UAVs  16  and  18 . To that end,  FIG. 2  shows GPS (Global Positioning System) based navigation subsystems  58  and  60  communicating with a GPS satellite  62 . 
   The UAVs  16  and  18  send their absolute positions and the absolute orientation of UAV  16  to the relative position comparator  54  which then generates a vector defining the relative position of the UAV  18  with respect to the position and orientation of UAV  16 . Of course, the system can be designed to generate relative position vectors for essentially any number of platforms without departing from the scope of the present invention. The relative position of UAV  18  is forwarded to the audio signal modifier  56  that also accepts the audio signal from the source  14 . The modifier  56  then modifies the audio signal to convey the relative position of the UAV  18  (with respect to the UAV  16 ) to the recipient  12 . The manner of modifying an audio signal to convey a relative position involves adjusting one, or more, parameters that affect the manner in which a listener perceives the audible signal. While the relative position vector may be determined in any coordinate system (e.g. in terms of Cartesian x, y, and z coordinates relative to the UAV  16 ), the cue, or modification to the sound, will convey the relative position to the operator of UAV  16 . 
   For instance, intensity of the audible signal may be adjusted so that, as the intensity increases, the user perceives the sound source  14  as being closer. Reverb and echo may also be used to enhance the impression of distance to the perceived position of the sound. Stereo audio systems also adjust various parameters (e.g. interaural time, intensity, and phase differences) to create the impression that a sound source  14  is located at a particular position in a two dimensional area surrounding the recipient. A non-exhaustive list of other measures of the audio signal&#39;s timbre that may be modified to reflect the relative position or velocity of the UAV  18  include; thickening, thinning, muffling, self-animation, brilliance, vibrato, tremolo, the presence or absence of odd (and even) harmonics, pitch (e.g. the Doppler Effect), dynamics (crescendo, steady, or decrescendo), register, beat, rhythm, and envelope including attack and delay. 
   For the present invention, these terms will be defined as follows. “Thickening” means shifting the pitch of a signal so that the signal is heard at one, or more, frequencies in addition to the original pitch. Thickening may be used to create the illusion of a source moving closer to the recipient. 
   “Thinning” means passing the signal through a low, high, band, or notch filter to attenuate certain frequencies of the signal. Thinning may be used to create the illusion that the source is moving away from the recipient. “Self animation” refers to frequency-dependent phase distortion to accentuate frequency variations present in the original signal. The term “brilliance” refers to the amount of high frequency energy present in the spectrum of the audio signal. “Vibrato” and “tremolo” refer to the depth and speed of frequency (vibrato) and amplitude (tremolo) modulation present in the signal. The distribution of harmonics within the signal also affects the way that a listener hears the signal. If there are only a few odd harmonics present, the listener will hear a “pure” sound rather than the thin, reed-like sound caused by the elimination of even harmonics. For more information on timbre parameters, the reader is referred to the source of these definitions: Brewster, S., Providing a Model For the Use of Sound in User Interfaces [online], June 1991, [retrieved on Apr. 25, 2004]. Retrieved from the Internet :&lt;URL: http://www.cs.york.ac.uk/ftpdir/reports/YCS-91-169.pdf&gt;. 
   The audio signal modifier  56  shown by  FIG. 2  may adjust appropriate combinations of these parameters to cause the recipient  12  to perceive the audible signal (which will be reproduced from the audio signal) as coming from the relative position of the UAV  18 . By “audio signal” it is meant that the signal is an electrical signal, or waveform, which represents a sound, or sounds. Audio signals may, of course be created from audible signals, and vice versa, by suitable conversion via, for instance, a microphone. By “audible signal” it is meant a signal capable of being heard (e.g. a sound or sounds). Additionally, the modification of the audio signal may be such that the variation of the pre-selected parameter(s) is proportional to the distance between the UAV  16  and  18 . Thus, when the source  14  speaks, or otherwise generates a sound for representation in the audio signal, the recipient  12  will hear the corresponding, reproduced, audible signal as if the recipient  12  were co-located with the UAV  16  and as if the source  14  was co-located with the UAV  18 . In other words, from the perspective of the recipient  12 , the sound appears to come from the relative position  32  as translated to reference  32 ′ at the recipient&#39;s  12  location. If the recipient  12  is trained to associate the perceived position  32 ′ with the relative position  32  of the UAV  18 , the system  10  appraises the recipient  12  of the relative position of the UAV  18  in real-time and in an intuitive manner. 
   In a preferred embodiment, the subsystem  50  is implemented with a modern DSP (digital signal processing) chip set for modifying the signal to include the audible cues. A high-performance DSP set allows the user to program the subsystem  50  to perform many sophisticated modifications to the signals, such as modifying each signal to match the acoustics of a particular conference room in the Pentagon with the window open. Basic modifications (e.g. phase shift, volume modification, or spectral coloring), though, can be performed by even a relatively modest 80286 CPU (available from the Intel Corp, of Santa Clara, Calif.). One of the reasons the present invention does not require sophisticated DSP hardware is that audio information is conveyed at relatively low frequencies (i.e. less than about 20,000 Hz). Thus, the present invention may be implemented with many types of technology. However, in the current embodiment, the DSP chip is coupled to a digital-to-analog stereo output (e.g. a Sound Blaster that is available from Creative Technologies Ltd. of Singapore). 
     FIGS. 2 and 3  show yet another preferred embodiment that includes an additional UAV  70  (controlled by a source  76  over a link  74 ). The presence of the additional source  76  complicates the recipient&#39;s task, in that the sources  14  and  76  might produce an audio signal at the same time. Because the recipient may not be able to a priori determine which source  14  or  76  to attend to first, the recipient  12  will generally prefer to be able to listen to both sources  14  and  76  at the same time. 
   The system  10  enhances the recipient&#39;s  12  ability to listen to both sources by providing the audible separation desired by the recipient  12 . More particularly, the audio signal modifier  56  may be configured to modify the individual audio signals from the sources  14  and  76  to convey the relative positions  32  and  78  of the respective UAVs  18  and  70 . When the audible signals are reproduced by the sound subsystem  57 , the recipient  12  perceives the audible signal (associated with the source  14 ) coming from relative position  32 ′ and the other audio signal (associated with source  70 ) coming from relative position  78 . Thus, the system  10  separates the audible signals as if the recipient  12  and the sources  14  and  76  were listening to each other at the positions of the respective UAVs  16 ,  18 , and  70 . The audible separation provided by the present invention, therefore, enhances the ability of the recipient  12  to follow the potentially simultaneous conversations of the sources  14  and  76 . 
   In still another preferred embodiment, the relative position  36  between the recipient  12  and the UAV  18  may be used to modify the audio signal from the source  14 . Thus, the source  14  would appear to speak from the position of the UAV  18 . In yet another preferred embodiment, the relative position  38  between the recipient  12  and the source  14  may be used to modify the audio signal. In still another preferred embodiment, the relative positions  32 ′ is not limited by two dimensions (e.g. east/west and north/south). Rather, the relative position  32 ′ could be along any direction in three-dimensional space as, for example, when one of the sources  14  is onboard a mobile platform such as an aircraft or spacecraft. 
   While many of the embodiments discussed above may be used with mobile platforms, the invention is not limited thereby. For instance, situational awareness for a teleconference participant includes knowing who is speaking and distinguishing each of the speaking participants from each other even though they may be speaking simultaneously. While humans are able to distinguish several simultaneous conversations when speaking in person with one another, the teleconference environment deprives the participant of the visual cues that would otherwise facilitate distinguishing one source from another. Thus, embodiments of the present invention may also be employed with many different communication systems as will be further discussed. 
   Now with reference to  FIG. 4 , another preferred embodiment of the present invention is illustrated. A system  100  includes a plurality of audio signal sources  114 , a communication link  122 , a position associater  155 , an audio signal modifier  156 , a sound subsystem  157 , and a recipient  112 . One of the differences between the system  10  of  FIG. 2  and the system  100  of  FIG. 4  is that the system  100  generates relative positions for the sources  114  rather than receiving position data from the sources  114 . Additionally, the communications link  122  facilitates communications among the multiple sources  114  and the recipient  112  (e.g., the link can provide teleconferencing capabilities to combinations of the sources and the recipient). In a preferred embodiment, the communications link  122  associates an identifier with each source  114  and provides the identifier to the subsystem  150 . One such identifier is the caller identification numbers of the sources  114 A,  114 B, and  114 C. Thus, the telephone number associated with each source  114  may be supplied to the subsystem  150  separately from the audio signals from the sources  114 . Another useful identifier (when the link  122  includes a teleconferencing system) is the line number on which each of the sources  114  calls into the teleconference. Of course, the link  122  will know, or be programmed to retrieve, the telephone number of the recipient  112 . 
   $ Using the identifications associated with the sources  114  to distinguish one source from another, the position associater  155  associates a relative position to each of the audio signals from the sources  114 . In one embodiment, the relative position is assigned based on a combination of the area codes and prefixes of the sources  114  and the recipient  112 . Thus, for teleconferences, the recipient  112  hears the sources  114  as they are distributed about the recipient  112  in the context of the communication system to which the link  122  links and the geographic area that it serves (i.e. nationally or internationally). For local calls, the recipient  112  hears the sources  114  as they are distributed about the recipient  112  in the context of a local telephone exchange (e.g. about the city or locale). In another preferred alternative, the position associater  155  arbitrarily associates a relative position with each of the sources  114 . For example, the position associater  155  may appear to place the sources  114  on a circle so that the recipient  114  perceives the sources spaced apart evenly along an imaginary circle around him. The associater  155  forwards the assigned relative positions to the voice modifier  156 . Then, using the associated relative positions, the signal modifier  156  modifies the audio signals to convey those relative positions to the recipient  112 . Thus, the system  100  may operate to maximize the audible separation of the sources  114  for the recipient  112 . In yet another preferred embodiment, each recipient  112  can adjust the relative position associated with each of the sources  114  to best meet his needs, e.g. placing a male and a female voice close together because they can be easily distinguished by vocal quality while placing similar voices far apart to improve awareness of which source is speaking. 
   In the alternative, the signal modifier  156  may retrieve an acoustic model from a memory  153  for use in modifying the audio signals. Regardless of whether the modifier uses a model  153  to modify the audio signal, or adjusts particular parameters (as previously discussed), the modifier sends the modified audio signal to the sound system  157 . The sound system  157  then reproduces the audible signals in accordance with the modification so that the recipient  112  perceives the audible signals as coming from the associated relative positions  132 . 
     FIG. 5A  illustrates the separation perceived by the recipient  112  in Washington, D.C. (produced by the system  100  of  FIG. 4 ) of a first source  114 A in St. Louis, Mo., from a second source  114 B in Chicago, Ill., and from a third source  114 C in Los Angeles, Calif. The recipient  112  perceives the audible signal of source  114 A as if it is coming from the direction  132 A, while the audible signals from sources  114 B and  114 C are perceived as if coming from the directions of Chicago and Los Angeles, respectively. The directions  132  can be looked up, or calculated, using the area code found in the caller identification signals from the sources  114 . Thus, the recipient  112  intuitively associates the sources  114  with their relative positions  132  and is therefore better able to distinguish the sources  114  from each other. 
     FIG. 5B  schematically represents the separation of sources  114  in a system where the actual positions of the sources  114  and the recipient  112  (and mobile platforms under their control) are not of particular importance to the recipient  112 . In situations such as these, neither the absolute positions nor the relative positions need be reflected in the perceived positions, although audible separation of the sources  114  is still desired. One such situation is a teleconference in which all of the participating sites can be considered as both sources and recipients. From the perspective of a particular site  112 , the other participating sites are sources  114  that the recipient  112  desires to have audibly separated. The system  100  assigns arbitrary relative positions, or directions  132 , to each of the sources. To treat each source  114  equally, the system also assigns the positions such that each source  114  will be perceived to be on a circle disposed about the recipient  112 . In this manner, the sources  114  will appear to be equidistant. Further, while the directions  132  are shown as being evenly disturbed about the circle, no such restriction is implied for the present invention. In particular, the directions could be grouped on one side, or the other, of the circle. The perceived positions could even be coincident. Such groupings may be useful in simulating a speaker (or source) addressing a group (of recipients) via a teleconference. Also, while the apparent positions of the sources  114  are shown being equidistance from the recipient  112 , the perceived relative positions could be at different distances from the recipient  112 . Thus, the relative positions  132  may provide any desired degree of separation between the sources  114  when they are associated arbitrarily (i.e. without regard to actual or relative positions) or at the discretion of recipient  112 . 
   In another preferred embodiment an end-of-message marker is added to each signal to provide the recipient yet another cue for identifying the source of the signal. The current embodiment is particularly useful where the signals have a clearly identifiable ending point (e.g. a stream of digital packets in a voice-over-IP stream that&#39;s activated by a push-to-talk button). Additionally a specific type of modification can be assigned to the different signals to help identify it or distinguish it. For example, one particular signal carrying a voice stream could be modified in tone (e.g. the speaker could be made to sound like Donald Duck), volume (e.g. the voice of a military officer with higher rank is amplified above the volume of subordinate&#39;s voice), or other characteristics. Further, one could add background noise for each of the apparent positions of the signals to aid the recipient. Adding the background noise can thus help the recipient remember and locate others who are online but not speaking. The background noise can also help characterize each speaker. More particularly, clanking tread could be added to the voice stream of a tank driver while the roar of jet engines could be added to a fighter pilot&#39;s voice stream as background noise. 
   With reference now to  FIG. 6 , a method in accordance with a preferred embodiment of the present invention is illustrated. The method  200  includes modeling an acoustic environment to determine how the environment alters audio signals propagating through it. For instance, surfaces in the environment will cause reverb-producing reflections, obstructions will cause echoes, and distance will cause attenuation of the original signal. Thus, as the environment is traversed the audio signal perceived will vary with position. Preferably, the acoustic environment will resemble the locale of interest to the recipient and the source (e.g. an area where the UAVs are to operate). A pre-selected audio signal is then created in the acoustic environment. A sensor, preferably located near the center of the environment, is then used to detect and record the audio signal as altered by the environment. The source of the pre-selected signal is then moved and recorded again with the sensor. The process repeats until the pre-selected signal is generated, and recorded, at a number of points sufficient to adequately characterize the environment. Using knowledge of the pre-selected signal, a model (or transfer function) of the environment may be extracted from the accumulation of recorded signals. The model therefore allows any subsequent audio signal to be modified to reflect how it would be perceived, if the source were located at a particular position in the environment, and as heard from the position of the sensor. Once the model, or transfer function, is determined, it is then stored in operation  204 . 
   At some time, audio signals are generated by at least one source in operation  206 . These audio signals are sent to the recipient via any of a wide variety of communications technologies such as electromagnetic links (e.g. RF, Laser, or fiber optic) or even via WANs, LANs, or other data distribution networks. Along with the audio signals, relative position signals may also be generated in operation  208 . In the alternative, the relative positions may be derived from absolute position signals. In yet another alternative, the relative positions may be generated in an arbitrary manner as herein discussed. Each audio signal may then have a relative position, and motion, assigned to it in operations  210  or  212 , respectively. When relative motions are assigned to an audible signal, the Doppler Effect, crescendos, decrescendos, and other dynamic cues are particularly well suited to convey the relative motion to the recipient. The audio signal may then be modified according to the relative position (and motion) associated with it. The audible signal may then be reproduced for the recipient who perceives the audible signals as if they were originating from their respective relative positions. 
   In view of the foregoing, it will be seen that the several advantages of the invention are achieved. Systems and methods have been described for providing increased situational awareness via separation of audible sources. The advantages of the present invention include increased capabilities for two, or more operators to cooperate in achieving a common objective. Further, the participants of conversations conducted in accordance with the principles of the present invention enjoy improved abilities to follow the various threads of conversations that occur within the overall exchange. Additionally, the participants waste less time and effort identifying the sources of comments made during the teleconference. 
   The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 
   As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
Communication systems and apparatus to allow a user to perceive the relative spatial location or present position of other elements of interest in a control space, such as the location of a speaker participating in a telephone conference or that of an aircraft carrier to a remotely piloted vehicle on final approach. The system inserts synthetic sound cues into the communication to the user that represent the relative position(s). In one embodiment, the user will perceive the communication as though it were communicated through free space to the user from the relative position of the represented source, so that, for example, the squad leader will perceive his wingman to be at his immediate left. Methods of conveying relative position sound cues are also provided.