Abstract:
In one aspect the present invention provides a mechanism to carry analog video, digital video and other types of data over a single cable simultaneously between the camera modem and the monitor modem. The analog video has low latency and can be used as real time monitoring, while the digital video is usually compressed high definition video and carried in IP packets. In the camera modem, the analog video is digitized and decoded into digital video, which is further compressed by a near-zero latency video encoder. All types of data, including the compressed analog video and digital video, are multiplexed together to form a single digital stream and transmitted over the cable. In the monitor modem at the other end of the cable, the near-zero latency video stream originated from analog video is de-multiplexed from the single digital downstream, decompressed and finally the corresponding analog video is reconstructed.

Description:
[0001]    This application refers to the prior provisional application under U.S. application Ser. No. 61/669,881 filed on Jul. 10, 2012. 
     
    
     SUMMARY OF THE INVENTION 
       [0002]    In one aspect the present invention provides a mechanism to carry analog video, digital video and other types of data over a single cable simultaneously between the camera side modem and the monitor side modem. The analog video has low latency and can be used as real time monitoring, while the digital video is usually compressed high definition video and carried in IP packets. In the camera modem, the analog video is digitized and decoded into digital video, which is further compressed by a near-zero latency video encoder. All types of data, including the compressed analog video and digital video, are multiplexed together to form a single digital stream and transmitted over the cable. In the monitor modem at the other end of the cable, the near-zero latency video stream originated from analog video is de-multiplexed from the single digital downstream, decompressed and finally the corresponding analog video is reconstructed by the analog encoder. 
         [0003]    In another aspect the present invention uses one monitor modem with a single transceiver inside to exchange data with multiple camera modems through multiple cables by time-division multiple access (TDMA) or orthogonal frequency-division multiple access (OFDMA). In TDMA embodiment, different cameras are assigned with different time slots to carry their two-way communication traffic; in OFDMA embodiment, different cameras are assigned with different frequency bins or a combination of time slots and frequency bins to carry their two-way communication traffic. Link discovery, synchronization and negotiation are designed to support plug-n-play. That is, when a camera is connected, its link can be automatically established without disruption of other links; similarly; when a camera is disconnected, its link can be terminated without disruption of other established links. 
         [0004]    In another aspect the present invention provides a repeater mode, a mechanism to extend the cable run without degrading analog video quality. The repeater mode also enables multiple cameras to share a single long-reach cable. In one embodiment of the present invention, a pair of monitor modem and camera modem can be connected back-to-back to form such a repeater. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is an embodiment of the present invention. 
           [0006]      FIG. 2  illustrates the camera modem. 
           [0007]      FIG. 3  illustrates the analog video processor. 
           [0008]      FIG. 4  illustrates the monitor modem. 
           [0009]      FIG. 5  illustrates the analog video de-processor. 
           [0010]      FIG. 6  illustrates the cascade connection of the monitor modems. 
           [0011]      FIG. 7  illustrates an embodiment of IP engine. 
           [0012]      FIG. 8  illustrates another embodiment of IP engine. 
           [0013]      FIG. 9  illustrates the repeater structure. 
           [0014]      FIG. 10  illustrates an embodiment of the repeater connections. 
           [0015]      FIG. 11  illustrates another embodiment of the repeater connections. 
           [0016]      FIG. 12  illustrates the slot assignment and probing slot. 
       
    
    
     BACKGROUND OF THE INVENTION 
       [0017]    1. Field of Invention 
         [0018]    The present invention relates to security surveillance systems. 
         [0019]    2. Background 
         [0020]    In security surveillance systems, the analog cameras provide video in analog formats such as CVBS (color, video, blanking, and sync). The analog video has the advantage of near-zeros latency, which is critical for some surveillance environments, such as banks and casinos. However, the transmission distance is limited because the analog video quality degrades as cable length increases. On the other hand, high definition (HD) internet protocol (IP) cameras provide the convenience of remote monitoring because IP packets are used to transmit videos. Ethernet repeaters and switches can be used to extend Ethernet link without degrading the video quality and the video can be viewed over LAN or even the internet. At the same time, HD IP cameras can provide higher video quality than analog cameras. But IP cameras put some challenges on the security surveillance transmission systems. Firstly, IP packets are usually transmitted over Ethernet cables, which are not compatible with existing coaxial cables or twisted pair cables. Secondly, IP streaming video may require a return channel for acknowledgement packets, which does not exist in traditional surveillance systems. Thirdly, the HD videos usually have high latency, resulting from IP transmission delay and video compression and decompression. Thus it is not suitable for real time security surveillance. 
         [0021]    The present invention provides a mechanism to transmit both the analog video and digital IP video simultaneously over the existing infrastructure, such as the coaxial cable or twisted pair cable. This enables the surveillance system to combine the advantages of near-zero latency of analog video and high quality of digital HD video. Furthermore, the present invention provides a mechanism to use repeaters to extend the cable without degrading the analog video quality. 
         [0022]    In security surveillance systems, the monitor side usually needs to monitor many security cameras at the same time. It is convenient and cost effective to use only one modem to receive videos from multiple cameras. The present invention presents a mechanism to use a single monitor side modem to communicate with multiple camera modems. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  is an embodiment of the present invention, which contains n camera modems  101 ,  103 ,  105  and one monitor modem  109  which are connected by n cables  106 ,  107 ,  108  respectively. Video/data information can be exchanged between the cameras  100 ,  102 ,  104  and the monitor side unit  120 . The monitor side unit  120  can be a DVR (digital video recorder), a personal computer, or other monitoring devices. The camera can provide multiple outputs, such as HD IP video, analog CVBS video and/or downstream audio. The monitor side unit can also provide multiple outputs, such as IP packets, RS  485 , upstream audio, and/or PTZ (pan, tilt, zoom) control signal. The present invention uses a single monitor side modem to communicate with multiple cameras. The two-way traffic between each camera modem and the monitor modem may contain multiple streams, including, but not limited to, analog video, digital video, audio, RS485 and PTZ control. 
         [0024]    In  FIG. 1 , n is a small integer number, such as 1, 2, 3 or 4. The number of camera modems connected to the monitor modem may change over time. The monitor modem is able to detect the existence of a camera modem automatically. When a camera modem is connected, the monitor modem can find it automatically and establish the two-way communication link without disruption of other established links. Similarly, a camera modem can be disconnected and its link can be terminated without disruption of other established links. 
         [0025]    The details of the camera modem  101 ,  103  or  105  are shown in  FIG. 2 . The camera provides two signals to the camera modem. One is the analog video  200 . The other is downstream digital IP video/data  210 . The digital data can be audio, RS 485 or other types of data depending on camera implementations. Another input signal of the camera modem is the digital data/clock signal  220  used for repeater function. The repeater retransmits the received signal and thus extends the signal to a longer distance. 
         [0026]    In  FIG. 2 , the analog video signal  200  is processed by an analog video processor  201  to convert analog video signal  200  into digital data stream  202 . The analog video processor  201  is shown in  FIG. 3 , where the analog video signal  200  is firstly converted into digital signal by the analog video decoder  250  and then the resulting digital video signal  252  is processed by the compression block  251 . The analog video decoder  250  digitalizes the analog video by means of deriving the corresponding digital video, or simply digitalizes the analog waveform. The compression block  251  reduces the data size while keeps the feature of near-zero latency of the analog video. In another embodiment of the present invention, the analog camera can provide signal  252  or signal  202  directly. The compression block  251  adopts near-zero latency compression methods such as DPCM (Differential pulse-code modulation), or Motion JPEG. The three input signals  202 ,  210 ,  220  are then multiplexed into one digital downstream  207  by the downstream multiplexer  203  and sent to the cable by the modulator  204 . The multiplexer  203  needs to tag each input signal with a different identity number, or group it according to a pre-defined rule known to both the transmitter and the receiver such that the receiver is able to recover each individual signal. The modulator  204  converts the digital data  207  into a modulated signal suitable for transmission over the cable. Different modulation schemes can be used, such as QAM (Quadrature amplitude modulation) modulated single carrier signal or DMT (discrete multi-tone modulation). In the modulator, appropriate coding is also necessary to improve transmission reliability over frequency selective and noisy channel commonly seen over the cable. 
         [0027]    At the same time, in  FIG. 2 , the camera modem receives upstream signal  206  from the cable and the demodulator block  231  decodes the received signal  206  and generates upstream digital data  230 . On another embodiment of the present invention, the downstream and/or upstream digital data may not be in the format of IP packet and are called service data. The service data can also be exchanged between the cameras and the DVR. Signal  230  can be sent out directly as upstream repeater output, or it can be de-multiplexed into upstream IP data  241  and upstream service data  242 . 
         [0028]    The monitor modem  109  is shown in  FIG. 4 . The downstream signal  300  received from the cable is demodulated by the demodulator  310  and generates signal  311  which recovers the digital downstream data  207  transmitted by the corresponding camera modem. The output of the demodulator  311  can be sent out directly as the downstream repeater output, or it can be de-multiplexed into two types of streams of data by downstream demultiplexer  330 . One type of stream  332  goes into the analog video de-processor  340  to recover the analog video. The reconstructed analog video  341  recovers the analog video from camera  100 ,  342  recovers the one from  102 , and  344  recovers the one from  104 . The other stream  331  is downstream digital IP video/service data. The analog video de-processor  340  is shown in  FIG. 5 , where a decompression block  345  is followed by an analog video encoder  346 . The decompression block  345  recovers digital video signal  252  from the compressed digital video data. The analog video encoder  346  reconstructs the analog video signal  200 , which can be directly viewed or recorded by the existing analog security surveillance equipments. The compression and decompression processes in  FIG. 2  and  FIG. 4  incur near-zero delay and thus reserve the real time feature of analog video link. In another embodiment of the present invention, digital video signal recovered by the decompression block can be sent out directly with a digital format, such as BT. 656 format. In the upstream direction, the upstream IP data  351 , upstream service data  352 , and/or upstream repeater input  353  are multiplexed into one signal digital stream  321  by the multiplexer  350 . The upstream data  321  is modulated by the modulator  320  and sent to the cable. 
         [0029]    In the monitor modem as shown in  FIG. 4 , there are two interfaces called uplink interface and downlink interfaces respectively. At the uplink interface, the modem receives upstream data  362  from the DVR and sends downstream data  361  to the DVR. At the downlink interface, the modem receives downstream data  364  from another monitor modem and sends upstream data  363  to another monitor modem. These two interfaces are used for direct connection with a DVR or cascade connection with another monitor modem. In the cascade mode, two or more monitor modems are connected together by the uplink interface and downlink interface. A cascade connection is exemplified in  FIG. 6 , where m monitor modems  1200 ,  1210 , . . . ,  1240  are cascaded together and the first modem  1200  is connected to the DVR controller  1250  by the interface  1201 . The cascade connection is useful for security surveillance application, where a single DVR controller  1250  can control multiple monitor modems and thus multiple cameras without LAN switch. 
         [0030]    In  FIG. 4 , there is an IP engine  360 , which connects the IP uplink interface signals  361  and  362 , the IP downlink interface signals  363  and  364  and the internal IP interface signals  331  and  351 . The IP engine  350  decides how to forward the packets from one interface to other interfaces depending on the forwarding policy. Conventionally the IP engine is a multiple port open systems interconnection (OSI) model layer 2 switch. One aspect of the invention significantly simplifies the switch design by removing the switching database and the associated MAC address learning, aging and lookup for forwarding. One embodiment of the IP engine is detailed in  FIG. 7 , where the IP combiner  900  is an apparatus that merges two input streams into one output stream by forwarding both input streams to the same output port with appropriate buffering and scheduling. In  FIG. 7 , the IP combiner  900  merges both downstream digit IP input  360  and IP downlink downstream  364  into IP uplink downstream  361 , while IP uplink upstream  362  is simply duplicated to upstream IP data  351  and IP downlink upstream  363 . As can be seen in  FIG. 7 , the upstream IP packets originated from DVR simply go to all cameras. In this embodiment, the IP engine does not need to recognize the MAC address or the IP address, and packet forwarding is implemented in layer 1. This embodiment supports IP traffic between a monitor side host and a camera while the inter-camera IP traffic is prohibited. This can be a desired security feature for some applications that require all installed IP cameras to be electronically isolated from each other. 
         [0031]    Another embodiment of such IP engine implemented in layer 2 is detailed in  FIG. 8 . Similar to the previous embodiment shown in  FIG. 7 , the downstream digital IP  360  and IP downlink downstream  364  are both forwarded by IP combiner  1000  to produce IP uplink downstream  361 . However downstream  360  is filtered by IP filter  1010  and a filtered downstream digital IP  1011  is produced. A typical IP filter passes some incoming IP packets while discards all the others. Similarly, IP uplink downstream  361  is filtered by IP filter  1030  and the filtered IP uplink downstream  1031  is generated. Stream  1031  and IP uplink upstream  362  are merged by IP combiner  1040  to generate upstream IP data  351 . The filtered downstream digital IP  1011  is also merged with IP uplink upstream  362  to form IP downlink upstream  363 . One embodiment of the present invention uses an IP filter that only passes broadcast traffic and IP multicast traffic while discards all unicast traffic. The IP filtering is simply based on destination address type, not on an address itself. The destination address can be the destination MAC address or IP address of the packet. If the destination address is a broadcast address or a multicast address, the packet is passed through the IP filter, otherwise not passed. This allows the broadcast traffic and multicast traffic from one camera to reach other cameras connected to the same monitor modem, those connected to cascaded monitor modems as shown in  FIG. 6  and further all others connected by IP networks. Without building a complicated and costly full-blown switch, the present invention allows limited communication between cameras. The inter-camera broadcast and multicast can be used to support inter-camera cooperation, where cameras can, for example, exchange instant information within a network or a group without knowing each other&#39;s IP address, and form an intelligent camera network that can watch, track and record a certain object of interest. Another embodiment of the said IP filter is an all-pass filter which simply passes all incoming traffic to the output. For the all-pass filter, its input is directly wired to its output. This supports all broadcast, multicast and unicast traffic among all cameras and DVR. 
         [0032]    The present invention provides a mechanism to connect a camera modem and a monitor modem together to function as a repeater as shown in  FIG. 9 . In the downstream direction, the monitor modem  410  sends the downstream repeater output signal  411  directly to the input port of the downstream repeater input signal  220  at the camera modem  420 ; in the upstream direction the camera modem  420  sends the upstream repeater output signal  412  to the input port of the upstream repeater input signal  353  at the monitor modem  410 . The signals connecting the two modems are both digital signals and repeaters can be used as many times as necessary to extend the cable. Since the analog video remains in the digital format intact, the analog video quality does not degrade over repeaters or extended cables. In addition to cable interfaces  415  and  416 , the repeater can provide an optional camera interface as shown in  FIG. 9 , including analog video input  421 , downstream digital IP video/service data  422 , upstream IP data  423  and upstream service data  424 . This allows a camera to be directly connected to the repeater. The repeater without optional camera interface is used to connect multiple cameras in a star topology, as detailed in  FIG. 10  while the repeater with optional camera interface is used to connect multiple cameras in a daisy-chain topology, as detailed in  FIG. 11 . 
         [0033]    An example of the repeater connection without using the camera interface to form a star topology is shown in  FIG. 10 , where the central node is repeater 1 labeled as  520  and leaf nodes are cameras 1, 2, . . . , n labeled as  500 ,  502 , . . . ,  504  respectively. In this exemplary security camera network, m repeaters  520 ,  530  are connected by cables  521 . The number m can be any integer number greater than or equal to 0. If m is equal to zero, that is, no repeater is used, then  FIG. 10  becomes the same as  FIG. 1 . if one or more repeaters are used, multiple cameras are connected by the repeater  520 . The transmission distance can be extended by using repeaters and the cables  521 ,  531  between repeater  520  and monitor modem  540  are shared by multiple cameras including  500 ,  502 , . . . ,  504 . The last repeater  530  is connected with the monitor modem  540 , which is connected to the monitor device  550  such as a DVR. 
         [0034]      FIG. 11  shows another example of using repeater connection to form a daisy-chain topology where multiple cameras are connected with the multiple repeaters through the optional camera interface. Each repeater is directly connected with a new camera through its optional camera interface. At repeater 1 labeled as  1120 , the traffic between DVR  1150  and camera 1 labeled as  1100  is relayed. At the same time, camera 2 labeled as  1160  is directly connected to repeater 1 through its camera interface. Other cameras such as  1170  are connected to other repeaters such as  1130  in a similar fashion. Depending on the factors such as the location of cameras and DVR, a star topology, a daisy-chain topology or a hybrid combination of both can be chosen to minimize the total installation cost of a specific security camera network. 
         [0035]    The present invention provides a method for one monitor modem with single transceiver inside to exchange data with multiple camera modems by a multiple access scheme. Each camera modem can communicate independently with the monitor modem. If there are n cameras, n communication links are established by using a single monitor modem. In one embodiment, the n communication links use time-division multiple access to share the same monitor modem. The communication time is divided into multiple time slots as shown in  FIG. 12 . Time slot i is assigned for communication link between camera modem i and the monitor modem. To avoid multiple camera modems sending at the same slot and causing collision, negotiation and synchronization are necessary. 
         [0036]    In an established communication link, half duplex or full duplex can be used to communicate in both directions. For example, half duplex can be used in  FIG. 12  in order to reduce the complexity of analog design. In slot i, the modem does not transmit and receives at the same time. Thus communications in both directions can share the same frequency bandwidth on the same cable. If frequency division multiple access (FDMA) based full duplex is used, signals in two directions occupy different frequency band. Filters are usually needed to separate signals in two directions to prevent interference from each other. OFDMA can also be used to support full duplex. Typically different frequency bins are assigned to downstream and upstream respectively. All of these schemes can be implemented within the scope of the present invention. 
         [0037]    In  FIG. 12 , a probing slot  600  can be inserted between two groups of multiple time slots. In the probing slot, a training sequence can be sent to different cables with unknown status. By checking the response corresponding to the training sequence, it can be found out if a new camera is connected into the system or a camera just leaves the systems. If a new camera modem is found, slots can be assigned to the new camera modem and the communication link between the new camera modem and the monitor modem can be established. If a camera modem leaves the system, its assigned slots can be released and assigned to other connected camera modems. During this process, other communication links shall not be disrupted. In the probing slot, signals can also be sent to the connected cameras and the probing signals can be used as training to improve synchronization or equalization. The present invention does not limit how the slots are assigned. Some camera modems can occupy more slots than other cameras. Based on the required data rate, camera modems can negotiate with the monitor modems to request or release slots dynamically. For example, when two repeaters are connected back to back, all the slots can be occupied by a single modem pair.