Abstract:
A method and apparatus are disclosed for wirelessly communicating signals from trailer-mounted cameras to a towing vehicle, where the techniques overcome packet loss challenges caused by interferences, fading and poor signal strength. An advanced spectrum hopping algorithm monitors conditions on multiple channels in multiple frequency bands, detects congestion or collisions needing mitigation, and migrates transmissions as needed to other channels with greater free capacity. Network coding techniques are provided which transmit data packets via multiple paths, where the redundancy provides robustness against data packet losses. The multiple path network coding approach may include spectral diversity, where packets are transmitted on different bands, and spatial diversity, where packets are transmitted via different routes such as direct and repeater-based.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0001]    This invention relates generally to wireless cameras used with vehicles and, more particularly, to a method for improving the performance and reliability of wireless communications between cameras mounted on trailers and the towing vehicle, where the method uses channel hopping, spectrum hopping, network coding and path diversity techniques to achieve improved communications. 
       Discussion of the Related Art 
       [0002]    Modern digital cameras are used in many vehicle-related applications—providing images for a driver&#39;s viewing, and providing input for automated systems such as parking assist and lane keeping. It is desirable to extend the advantages of digital cameras to vehicle trailer applications, but this application has proved problematic to implement. 
         [0003]    It is, of course, possible to use hardwired connections to communicate signals from a trailer-mounted camera to the towing vehicle. However, the signal and power wires increase weight and cost, and represent a significant reliability disadvantage due to wire wear and the possibility of pinching or severing of the wires. In addition, hardwired trailer camera implementations must anticipate the number and location of cameras on the trailer—and both the vehicle and the trailer must be wired to accommodate the anticipated configuration of cameras. These disadvantages have prevented the widespread use of trailer-mounted cameras. 
         [0004]    It is far preferable to use wireless technology to communicate signals from trailer-mounted cameras to the towing vehicle. Unfortunately, wireless camera communications have suffered from poor performance and reliability issues, due to the challenges in wirelessly communicating the relatively high-bandwidth camera video signals from the trailer to the towing vehicle under highly dynamic driving environments. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with the teachings of the present invention, a method and apparatus are disclosed for wirelessly communicating signals from trailer-mounted cameras to a towing vehicle, where the techniques overcome packet loss challenges caused by interferences, multi-path fading, shadowing and poor signal strength. An advanced spectrum hopping algorithm monitors conditions on multiple channels in multiple frequency bands, detects congestion or collisions needing mitigation, and migrates transmissions as needed to other channels with greater free capacity. Network coding techniques are provided which transmit data packets via multiple paths, where the redundancy in both the data and the transmission path provides robustness against data packet losses. The multiple path network coding approach may include spectral diversity, where packets are transmitted on different bands, and spatial diversity, where packets are transmitted via different routes such as direct and repeater-based. 
         [0006]    Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an illustration of a group of wireless transmissions over multiple channels in multiple frequency bands, where collisions between the transmissions occur on some of the channels; 
           [0008]      FIG. 2  is a block diagram of a system for managing wireless communications between trailer-mounted cameras and a towing vehicle; 
           [0009]      FIG. 3  is an illustration of a group of wireless transmissions over multiple channels in multiple frequency bands, where collisions between the transmissions are eliminated by migrating some of the transmissions to different channels using the system of  FIG. 2 ; 
           [0010]      FIG. 4  is a flowchart diagram of a method for selecting wireless frequency bands and channels for multiple trailer-mounted cameras communicating with the host vehicle; 
           [0011]      FIGS. 5  A/B/C are conceptual diagrams illustrating how duplication and network coding techniques can be used to overcome packet loss and improve video frame recovery; and 
           [0012]      FIG. 6  is a flowchart diagram of a method for managing wireless communications between trailer-mounted cameras and a towing vehicle. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0013]    The following discussion of the embodiments of the invention directed to reliable wireless communications between trailer-mounted cameras and a towing vehicle is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the discussion below is directed to cameras on a trailer communicating with the towing vehicle, but the methods and system are equally applicable to any wireless camera image transmission application. 
         [0014]    Many modern vehicles include cameras which provide images of scenes in and around the vehicle, where the images can be viewed as video by the driver, or the images can be used in automated systems such as parking assistance and lane keeping assistance. Such cameras are typically installed as original equipment by vehicle manufacturers, who integrate the cameras and the interfaces with vehicle video displays and other vehicle systems. Furthermore, vehicle-based cameras can typically easily be hardwired for both power and data signals, as the cameras are included in the vehicle specification and comprehended in vehicle design from the beginning. 
         [0015]    Many applications can be envisioned where trailer-mounted cameras could be employed to the benefit of the driver of the towing vehicle. These applications include trailer docking, trailer backing assistance and/or automation, boat launching/landing, trailer cornering clearance, trailer tire monitoring, trailer interior cabin monitoring, and others. The aforementioned applications may display raw video feeds from multiple cameras, or provide composite synthesized images such as a bird&#39;s eye view, or a combination of both types of views. 
         [0016]    Unlike vehicle-mounted cameras, however, the number and placement of trailer-mounted cameras are not specified by vehicle manufacturers. For this and other reasons, it is highly desirable to use wireless communications between trailer-mounted cameras and the towing vehicle. Many challenges must be overcome, however, in order to ensure reliable, high quality video from multiple trailer-mounted cameras using wireless communications. These challenges include wireless traffic congestion on channels in the Industrial, Scientific and Medical (ISM) radio frequency bands of 2.4 GHz and 5 GHz, out-of-band interference from other neighboring bands, varying conditions due to mobility and blockage/fading effects, and range coverage issues for long trailers. 
         [0017]      FIG. 1  is an illustration of a group of wireless transmissions over multiple channels in multiple frequency bands, where collisions between the transmissions occur on some of the channels. A first wireless communications band  100  includes channels  110  and  120 , among others not shown. A second wireless communications band  200  includes channels  210  and  220 , among others. The bands  100  and  200  may represent the ISM frequency bands of 2.4 GHz and 5 GHz, which are commonly used for consumer wireless or “Wi-Fi” communications. The channels  110 ,  120 ,  210  and  220  can be any channels within the bands  100  and  200 , where the actual channels would have designations such as Channel  1 , Channel  11 , Channel  151  and Channel  181 . 
         [0018]    At a particular moment in time, wireless transmissions  10 ,  20 ,  30 ,  40  and  50  occur in the bands  100  and  200 . It can be seen in  FIG. 1  that the transmissions  10  and  20  both occur on the channel  110  at the same time, resulting in a collision as shown at  14 . It can also be seen that the transmissions  40  and  50  both occur on the channel  220  at the same time, resulting in a collision as shown at  44 . In the scenario shown in  FIG. 1 , the transmissions  10  and  50  (shown with dashed outlines) are transmissions or interference from an external source—that is, a source over which a channel management system on a host vehicle/trailer has no control. The external transmissions  10  and  50  may be from wireless equipment on passing vehicles using the channels  110 / 220 , may be side-band noise from another channel, or otherwise. In any case, the transmissions  10  and  50 , which cause the collisions  14  and  44 , cannot be controlled but must be compensated for because they are disruptive to the transmissions  20  and  40 . 
         [0019]      FIG. 2  is a block diagram of a system  300  for managing wireless communications between trailer-mounted cameras and a towing vehicle. The system  300  is designed to address the problem illustrated in  FIG. 1 , according to the discussion below. The system  300  includes components onboard a trailer  310  and other components onboard a towing vehicle  350  (only the rear portion shown). Trailer-mounted cameras  312 ,  314 ,  316  and  318  are mounted at various locations on the trailer  310 . The trailer-mounted cameras  312 - 318  as illustrated are simply representative of the number and locations of cameras which may be used. Of course, more or fewer cameras could be installed on the trailer  310 , and the camera locations, orientations, interior/exterior placement, etc. may all be configured as desired. 
         [0020]    Each of the trailer-mounted cameras  312 - 318  includes a transmitting module  320 . The transmitting module  320  is shown in  FIG. 2  as being associated with the camera  318 ; however, it is to be understood that each of the cameras  312 - 318  has the features shown in the transmitting module  320 . The camera  318  provides images to an encoder/decoder (codec)  322 . The codec  322  converts the video signal from the camera  318  between digital and analog formats, or between different digital formats, as would be understood by one skilled in the art. The codec  322  provides the video signal to a socket  330 , which provides the signal to a Wi-Fi tuner/driver  342 . The Wi-Fi tuner/driver  342  communicates with a baseband circuit  344 , which in turn communicates with a radio frequency (RF) front end  346 . The RF front end  346  is capable of communicating on both the frequency bands  100  and  200  . . . that is, on 2.4 GHz and/or 5 GHz. A transmitting channel manager  332  controls the band and channel on which the signal from the RF front end  346  is transmitted, as discussed below. 
         [0021]    Onboard the towing vehicle  350  is a receiving module  360 . The receiving module  360  includes an RF front end  362 , a baseband circuit  364  and a Wi-Fi tuner/driver  366 . The RF front end  362  (in the vehicle  350 ) receives RF signals from the RF front end  346  (on the trailer  310 ). The baseband circuit  364  converts and delivers the video signal to the Wi-Fi tuner/driver  366 . It is to be understood that the RF front end  362  will be able to switch between different channels fast enough such that from application point of view, it is able to operate on multiple channels simultaneously, as shown in  FIG. 1 , where some transmissions may be desirable signals from the trailer-mounted cameras  312 - 318 , and some transmissions may be undesirable noise from external interference sources. 
         [0022]    A scanner  370  and a socket  372  communicate with both the Wi-Fi tuner/driver  366  and a receiving channel manager  380 . The receiving channel manager  380  reassembles the video feeds from the trailer-mounted cameras  312 - 318 , on whatever channels they are being communicated, and passes them along to a codec  382 . The codec  382  converts the video signals as necessary for display on a display unit  390 . The display unit  390  may be a center console display, such as is typically used for navigation and audio/visual system display in vehicles. The display unit  390  may also be incorporated in a rear-view mirror, or elsewhere in the towing vehicle  350 . 
         [0023]    The receiving channel manager  380  performs another important function besides providing video feeds to the codec  382 . The channel manager  380  also scans across and monitors conditions on many communications channels—not only the channels currently being used by the transmitting module  320 , but other channels as well—and communicates with the transmitting channel manager  332  to dictate which bands and channels should be used for each of the trailer-mounted cameras  312 - 318 . The channel selection method used by the receiving channel manager  380 —intended to minimize contentions across all occupied channels—is discussed below in connection with  FIG. 4 . 
         [0024]    It is to be understood that the transmitting channel manager  332  and the receiving channel manager  380  are programmable computing devices including a processor and a memory module. It is to be further understood that the elements shown in the transmitting module  320  and the receiving module  360 —from the codecs through the RF front ends—may be combined or realized using different combinations of hardware and software. 
         [0025]    The image frame communications between the transmitting module  320  and the receiving module  360  may be compressed using any known technology. For example, the transmissions from the trailer-mounted cameras  312 - 318  may follow a sequence including i-frames, p-frames and b-frames—where the i-frames are complete image frames, the p-frames are predicted frames holding only the changes in the image from the previous frame, and the b-frames are bi-predictive frames holding only differences between the current frame and both the preceding and following frames. Such compression techniques are known in the art, and are independent from the channel management system and method discussed herein. 
         [0026]      FIG. 3  is an illustration of a group of wireless transmissions over multiple channels in multiple frequency bands, where collisions between the transmissions are eliminated by migrating some of the transmissions to different channels using the system  300  of  FIG. 2 .  FIG. 3  shows the same five transmissions ( 10 - 50 ) and the same bands/channels as were shown in  FIG. 1 . In  FIG. 3 , all collisions have been eliminated by moving some of the transmissions to different channels. As described previously, the transmissions  10  and  50  are external interference—and there is nothing that the channel manager  380  can do to move or eliminate them. However, the transmissions  20 / 30 / 40  are under the control of the channel managers  332 / 380  of the system  300 , and these transmissions can be moved to different channels to alleviate congestion and eliminate collisions. 
         [0027]    Comparing  FIG. 3  to  FIG. 1 , it can be seen that the transmissions  10  and  50  remain on the same channels, as they are from an external source and cannot be controlled. The transmissions  30  and  40  are moved from channels  120  and  220 , respectively, to channel  210 . Being relatively smaller, the transmissions  30  and  40  can both be handled on the channel  210  without contention. Moving the transmission  40  off of channel  220  eliminates the collision  44 . Additionally, the transmission  20  is moved from the channel  110  to the channel  120  vacated by the move of the transmission  30 . Moving the transmission  20  off of channel  110  eliminates the collision  14 . The migration of the transmissions  20 - 40  to different channels results in a balanced utilization of the channels  110 - 220 , with no contentions. Of course, in a real implementation, many more channels would be in play, and the migration of transmissions to different channels is an ongoing process, not a one-time event. This is discussed further below. 
         [0028]      FIG. 4  is a flowchart diagram  400  of a method for selecting wireless frequency bands and channels for the multiple trailer-mounted cameras  312 - 318  communicating with the towing vehicle  350  of  FIG. 2 . At box  402 , communications are established from one or more of the trailer-mounted cameras  312 - 318  through the transmitting module  320  to the receiving module  360  of the towing vehicle  350 . At box  404 , the receiving channel manager  380  evaluates channel conditions of occupied channels by analyzing received data packets. The received data packets can be used to determine the congestion conditions of occupied channels (channels used by the transmitting module  320 ) by evaluating packet delivery ratio (PDR), end-to-end latency, jitter, or received signal strength indicator (RSSI). 
         [0029]    At box  406 , the receiving channel manager  380  periodically evaluates channel conditions of non-occupied channels—that is, channels which are not currently being used for communications between the transmitting module  320  and the receiving module  360 . The monitoring of the non-occupied channels at the box  406  is a proactive step to identify clear channels which may be used if occupied channels experience congestion and/or collisions. At decision diamond  408 , it is determined by the receiving channel manager  380  whether the occupied channels are experiencing congestion or collisions which warrant switching some transmissions to a different channel. If no congestion on the occupied channels is being experienced, then the process continues at box  410  with no channel changed commanded by the receiving channel manager  380 , and the process returns to the box  404  to continue channel condition evaluation. 
         [0030]    If, at the decision diamond  408 , congestion is being experienced, then at box  412  the receiving channel manager  380  commands one or more of the trailer-mounted cameras  312 - 318  to switch to a different channel. The command is sent from the receiving channel manager  380  to the transmitting channel manager  332 , causing the transmitting module  320  to switch to a different channel for at least one device. The different channel may be on the same band (the band  100  or  200 ) as was previously being used, or may be on a different band. Furthermore, the receiving channel manager  380  may consider band limitations of certain of the trailer-mounted cameras  312 - 318 , and may make combination channel migrations in order to both alleviate congestion and respect device band limitations. An example of a combination channel migration was illustrated in  FIGS. 1 and 3 , where the transmission  30  was moved from channel  120  to channel  210 , the transmission  40  was moved from channel  220  to channel  210  and the transmission  20  was moved from channel  110  to channel  120 —and these three channel migrations were made in order to alleviate collision situations on two channels involving external interference. 
         [0031]    In monitoring channel conditions and migrating transmissions to different channels, the receiving channel manager  380  may give preference to orthogonal channels, or channels whose signal waveforms have a phase difference of 90 degrees. 
         [0032]    Even with the channel migration techniques discussed above, some contentions and collisions will still be inevitable. These contentions and collisions may cause data packet loss which results in reduced quality video display in the towing vehicle  350 . It is desirable to mitigate the effects of packet loss as much as possible in the system  300  of  FIG. 2 . Network coding can be used for this purpose. 
         [0033]      FIGS. 5  A/B/C are conceptual diagrams illustrating how network coding techniques can be used to overcome packet loss and improve video frame recovery.  FIG. 5A  is an illustration  500  showing a basic concept of added extra redundancy to preemptively counteract uncertainty in loss-prone communications channels. An image frame  502  designated A, and an image frame  504  designated B, are shown at origination  510  and are to be transmitted—for example, transmitted from the transmitting module  320  to the receiving module  360  of  FIG. 2 . At transmission  512 , the image frames  502  and  504  are duplicated—that is, each of them is transmitted twice. This duplication is a preemptive way of counteracting data packet loss at the cost of introducing extra overhead. At reception  514 , one copy of the image frame  502  and one copy of the image frame  504  have been at least partially lost in transmission, resulting in the two fully-recovered frames and the two frames with uncertainty. At delivery  516 , the intact frames from reception  514  are used to provide full recovery of the original image frames  502  and  504 . However, if both copies (original and duplicate) of A are lost or both copies (original and duplicate) of A are lost, the intact image could not be recovered. 
         [0034]    The above is just one example of redundancy for loss-mitigation. Other examples include transmitting one full resolution image as the main package, and another one downsized image (or a series of downsized images as an image pyramid) as a redundant package for mitigating data loss. This approach may be advantageous because from an imaging/viewing/image-processing point of view, a few pixels loss or image resolution down-sampling may still be acceptable, but drop-frame or bad-frame are not. 
         [0035]      FIG. 5B  is an illustration  520  showing how image frame duplication can be used with the system  300  of  FIG. 2  to provide a wireless camera communications system which combines the loss-mitigation benefits of duplication with the loss-prevention benefits of adaptive channel management. In this case, four image frames are shown; an image frame  522  designated A and an image frame  524  designated B are included in a packet  532 , while an image frame  526  designated C and an image frame  528  designated D are included in a packet  534 . The packets  532  and  534  are sent in a transmission  542 . In the technique of  FIG. 5B , each of the frames is duplicated and sent via a second transmission. This is shown on the right side of  FIG. 5B , where packets  536  and  538  contain duplicate copies of image frames A/B and C/D, respectively. The packets  536  and  538  are sent in a transmission  544 , which preferably follows a different path than the transmission  542 , a concept which is discussed further below. 
         [0036]    Using the technique depicted in  FIG. 5B , a data packet loss rate of 10% results in a frame error rate of only about 2%. These results demonstrate the loss-mitigation benefits of even a simple frame duplication approach applied to wireless image data transmission. When combined with the packet-loss-prevention benefits of adaptive channel management, a very high quality video stream is achieved. 
         [0037]    A more sophisticated and advanced approach is a network coding solution.  FIG. 5C  is an illustration  550  showing how advanced network coding can be used with the system  300  of  FIG. 2  to add even greater loss-mitigation benefits to the loss-prevention benefits of adaptive channel management. In  FIG. 5C , four image frames are again shown; A, B, C and D. However, instead of simply duplicating each of the image frames as was done in the simple duplication approach of  FIG. 5B , an advanced network coding technique is used. In the example shown, a (4,2) Reed-Solomon error correcting code approach is employed—where each image frame is split into two parts (such as the even and odd interlacing fields of a full frame) and each of the two parts is coded two different ways—resulting in four partial representations (sub-frames) of each of the frames A, B, C and D. For those skilled in this art, it should be understood that other advanced source coding and/or network coding mechanisms could be applied in this scenario; also other types of parameter configurations could be applied in this scenario as well. 
         [0038]    In the illustration  550  of  FIG. 5C , the image frame data will again be sent in two transmissions,  552  and  554 , which again preferably follow different paths from the transmitter to the receiver. The transmission  552  includes packets  560  and  570 , and each of the packets includes four image sub-frames. For example, the packet  560  includes a sub-frame  562  which is a first piece of the image A designated A 1 , a sub-frame  564  which is a first piece of the image B designated B 1 , a sub-frame  566  which is a first piece of the image C designated C 1 , and a sub-frame  568  which is a first piece of the image D designated D 1 . The packet  570  similarly includes four sub-frames  572 - 578 , which contain the second piece of the four frames A/B/C/D. The transmission  554  includes packets  580  and  590 , where the packet  580  includes four sub-frames  582 - 588  which contain the third piece of the four frames A/B/C/D, and the packet  590  includes four sub-frames  592 - 598  which contain the fourth piece of the four frames A/B/C/D. 
         [0039]    In the network coding approach, when the original N pieces of contents are coded into M pieces of coded content (N&lt;M), the original content could be recovered as long as (N+ε) piece of coded content could be recovered. In this particular case, as long as slightly more than 2 piece of these four frames are received correctly, the original content could be fully recovered even if other coded contents are lost due to channel fading or other adversary effects. 
         [0040]    Advanced network coding such as the (4,2) Reed-Solomon technique shown in  FIG. 5C  adds computational overhead to both the transmitting and receiving ends of the system, but also improves error correcting robustness considerably over the naïve duplication of  FIG. 5B . Using the advanced network coding approach of  FIG. 5C , a data packet loss rate of 10% results in a frame error rate of only about 0.4%—which is a five-fold improvement over the naïve duplication results. Depending on communications channel congestion, packet loss rates, available computational power and other factors, naïve duplication or advanced network coding may be chosen for a particular application. 
         [0041]    The duplication and network coding techniques of  FIGS. 5B and 5C  require computations on both the transmitting and receiving ends. These computations may occur in any suitable element within the transmitting module  320  and the receiving module  360 . For example, if the transmitting channel manager  332  is positioned in-line between the codec  322  and the socket  330 , the network coding may be performed in the channel managers  332 / 380 . 
         [0042]    In the duplication and network coding techniques of  FIGS. 5B and 5C  discussed above, the concept of sending two data transmissions (the two parts of a corresponding pair) via different paths is introduced as a means of providing robustness against packet loss. Two techniques for path differentiation are proposed—spectral diversity, and spatial diversity. 
         [0043]    Spectral diversity refers to sending the two data transmissions ( 542  and  544  in  FIG. 5B , or  552  and  554  in  FIG. 5C ) over different ISM bands. Leveraging the high-speed switching capability of the Wi-Fi chipset in the circuits  342 / 344 / 346  of the transmitting module  320 , the network-coded data packets can be transmitted over the 2.4 GHz and 5 GHz bands (bands  100  and  200 ) almost simultaneously. The 2.4 GHz and 5 GHz bands are highly uncorrelated—meaning that any errors or erasures experienced by data packets sent over the 2.4 GHz band are extremely unlikely to also be experienced by a companion data packet transmitted over the 5 GHz band. For example, in  FIG. 5C , if the sub-frame  572  (A 2 ) is lost in the transmission  552  sent over the 2.4 GHz band, it is extremely unlikely that the sub-frame  592  (A 4 ) will also be lost in the transmission  554  sent over the 5 GHz band. Thus, even with the loss of A 2 , enough data will be available on the receiving end to fully recover the A frame. This benefit of spectral diversity further improves the reliability of data transmissions using duplication or network coding. 
         [0044]    Spatial diversity refers to sending the two data transmissions ( 542  and  544  in  FIG. 5B , or  552  and  554  in  FIG. 5C ) over different physical routes from transmitter to receiver. Referring back to FIG.  2 —the first transmission ( 552 ) can be sent directly from the transmitting module  320  to the receiving module  360 , while the corresponding second transmission ( 554 ) can be sent from the transmitting module  320  to the receiving module  360  via a repeater  396 . The two signal paths, direct vs repeated, are highly uncorrelated—meaning that any errors or erasures experienced by data packets sent over the direct path are extremely unlikely to also be experienced by a companion data packet transmitted over the repeated path. The repeater  396  also provides range extension for any of the cameras  312 - 318  which may be near the edge of their wireless signal range from the receiving module  360 —such as for long trailers, or cameras mounted in obstructed locations in or on a trailer. The benefits of spatial diversity illustrated above further improve the reliability of data transmissions using duplication or network coding. 
         [0045]      FIG. 6  is a flowchart diagram of a method  600  for managing wireless communications between trailer-mounted cameras and a towing vehicle. The method  600  of  FIG. 6  incorporates all of the channel management, network coding and path differentiation techniques discussed above. At box  602 , communications are established from one or more of the trailer-mounted cameras  312 - 318  through the transmitting module  320  to the receiving module  360  of the towing vehicle  350 . 
         [0046]    At box  604 , the channels and bands used for transmission are evaluated and optimized by the receiving channel manager  380 . The actions taken at the box  604  were detailed earlier in the flowchart diagram  400  of  FIG. 4 —where the receiving channel manager  380  monitors both occupied and non-occupied channels, and instructs the transmitting channel manager  332  to change channels and/or bands as necessary to alleviate any communications congestion which is being experienced on occupied channels. 
         [0047]    At box  606 , image frames from the trailer-mounted cameras  312 - 318  are processed by the transmitting module  320  using duplication or network coding, where image frame redundancy is added to data packets to be transmitted, and the data packets are arranged in corresponding pairs of transmissions. Simple duplication or advanced network coding may be used, as discussed above. As discussed above, the network coding may be performed in the channel manager  332 , or in another component of the transmitting module  320 . At box  608 , each corresponding pair of transmissions is wirelessly transmitted from the transmitting module  320  to the receiving module  360 . Each corresponding pair of transmissions may be sent via two different paths from the transmitting module  320  to the receiving module  360 . That is, one half of each pair is sent via a first path, and the other half of each pair is sent via a second path, where the different paths may employ spectral diversity or spatial diversity. 
         [0048]    At box  610 , the corresponding pairs of transmissions are received by the receiving module  360 . At box  612 , the receiving module decodes the received transmissions, including converting the network-coded image frames contained in the data packets back to whole image frames. At box  614 , the image frames are displayed on a display unit connected to the receiving module  360 —such as the display  390  in the towing vehicle  350 . 
         [0049]    The method of  FIG. 6  and the apparatus of  FIG. 2  provide for simple, high-reliability wireless communication of images from cameras to a remote receiver/display—such as from trailer-mounted cameras to a towing vehicle. The combination of channel and spectrum hopping, network coding and path diversity result in a wireless image transmission solution which first minimizes data packet loss and then mitigates the adverse effects of any packets which are lost. Using these techniques, cameras can be added to a trailer with performance and reliability comparable to that of a hardwired connection, but the simplicity and flexibility of a wireless implementation. 
         [0050]    The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.