Analysis of digital-analog hybrid transmission scheme for video surveillance system

    As surveillance gradually develops from analog standard definition to digital high definition, hybrid digital-analog transmission (simultaneous digital-analog transmission) has emerged as an analog plus IP transmission solution. Its characteristics are that analog video signals and IP signals are transmitted on the cable at the same time, and the transmission distance exceeds that of traditional coaxial transmission CVBS or IP transmission of high-definition video signals.

   Demand Analysis

    Surveys show that by 2016, 500 million cameras will be installed worldwide. By observing the development trends of analog cameras and IP cameras, it can be predicted that video surveillance solutions based on IP transmission will become more and more common.

    As surveillance gradually develops from analog standard definition to digital high definition, hybrid digital-analog transmission (simultaneous digital-analog transmission) has emerged as an analog plus IP transmission solution. Its characteristics are that analog video signals and IP signals are transmitted on the cable at the same time, and the transmission distance exceeds that of traditional coaxial transmission CVBS or IP transmission of high-definition video signals.

    From the perspective of the communication protocol framework of the network system, whether the network cable or coaxial cable is used as the medium, it is located in the physical layer of the transmission. While solving the transmission problem, it will not affect any upper-layer applications or software. This type of transmission method that combines the advantages of analog and digital will significantly improve the convenience of users.

   Application Cases

    Take Intersil, one of the main monitoring chip suppliers in the current market, for example. Its SLOC series chipset solution realizes CVBS+IP hybrid transmission. In this solution, a dedicated transmission chip modulates the CVBS analog video signal and the IP network video signal onto a coaxial cable. At the receiving end, a dedicated demodulation chip separates and restores the two signals. In this process, no software modification is required for other front-end and back-end devices, and the overall signal transmission distance is extended to 300-500m.

    In terms of manufacturer applications, many manufacturers provide SLOC solutions (in the form of dedicated transmission equipment) through external accessories (plus sending boxes and receiving boxes); some manufacturers also use an embedded approach and design SLOC solutions directly into new cameras and NVRs (such as SONY).

    Problems and solutions

    After understanding the needs, what kind of specific solution does the end user want to see? There are several factors involved.

    1. The solution is stable, easy to use and easy to implement

    Support common signal types, meet various common transmission rates and transmission distances;

    Easy to test/use, no configuration required, plug and play, convenient for engineering personnel;

    The hardware solution is simple, and basic functions are completed by a single chip.

    2. Reuse existing coaxial cable infrastructure

    The original system often uses various types of coaxial cables for transmission, so the hybrid transmission solution must support various coaxial cables of different standards (materials) and meet the practical transmission distance of 200 meters or more without repeaters. For equipment/system suppliers, designing products to cover most application scenarios and withstand the test of actual applications will be a must.

    3. Analog and digital signals can be used independently

    In actual use, due to various reasons, interface damage, network instability and other factors may occur. The system needs to independently transmit a certain signal (without interfering with each other) while supporting mixed transmission of analog and digital signals.

    4. Diverse product forms and abundant market choices

    As practical products become more and more popular, in addition to independent dedicated transmission equipment, new cameras and DVR/NVRs also need to start supporting mixed transmission (reception) modes (interfaces), which gives distributors and integrators more choices, and end users can benefit more from customized solutions;

    Standard unification and system compatibility: This requires that equipment suppliers can use a common signal standard, and the standard is uniformly released by a third-party authoritative organization. In this way, equipment from different manufacturers can be interconnected, making the market for such products more mature.

    In a monitoring system upgrade project for a certain building, the property owner needed to upgrade the original monitoring system from a traditional analog monitoring system to a network monitoring system. Such a solution, in the absence of a hybrid signal transmission solution, usually requires additional rewiring in addition to upgrading network cameras and NVRs, and requires more complex system installation and debugging and other actual expenses. However, under the goal of budget reduction and waste reduction, the hybrid transmission solution that does not require rewiring not only greatly saves expenses and reduces the waste and pollution caused by rewiring, but also meets the user's requirements for shortening the upgrade time, and finally successfully completes the project.

    In terms of equipment selection, the contractor originally did not have a solution for mixed signal transmission. When the user added the requirement of "not changing the original wiring" in the bidding requirements, they were very lucky to find a manufacturer that could provide this type of dedicated transmission equipment. It happened that the equipment could support both network and analog inputs, and could also be connected to the original coaxial wiring.

    As end users become more and more cost-conscious in project spending, there will be more and more upgrade projects that require reducing duplicate construction. We hope that the gradual maturity of digital-analog hybrid solutions will bring more convenience to more users.

   future

    Here, the author is limited by the breadth and depth of his vision and briefly shares some of the development directions and possibilities of hybrid transmission that he personally believes in:

    Bidirectional control: Although IP currently supports bidirectional communication, there are still some occasions that require independent coaxial visual control.

    PoC/E: The ability to use network cables for power supply is already a mature application of standard IP cameras, but in hybrid transmission solutions, there is still a need to promote the maturity of this function.

    Mixing more signals: Currently, HD-SDI and some other video signals also exist in the surveillance market. In the process of its popularization, will some manufacturers mix HD-SDI/CVBS or other signals with network signals, or mix two or all of them together?

    Cost control: More effectively converting performance advantages into high cost-effectiveness remains an effective way to promote end-user acceptance of new solutions.