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Solving the Issue
Now came the time to build the prototype In-net GoalCam system. Once the scope of work was defined from an engineering standpoint, VidOvation and their engineering team designed the first wireless, battery-powered, 720p59.94 HD SDI In-net GoalCam for goal verification and replay.
VidOvation was given a quick lead time of 12 days to provide the first prototype In-net GoalCam system for a New Islander’s charitable exhibition game in early June of 2011. Fortunately the time in planning, designing, and understanding the technology features and customer pain points paid off and the initial trials and testing went very well. After a second round of successful tests at the NHL R&D Camp in August of 2011, the National Hockey League saw how the In-net GoalCam would improve hockey officiating and replay so they moved forward with the project.
The initial prototype design of the GoalCam assumed that the receiver would be directly over each goal. After visiting a few hockey venues, it was quickly determined that the structure of each venue is unique. In many instances the In-net GoalCam receiver could not be mounted directly overhead. Changes were incorporated into the design to facilitate the movement and aiming of the camera/transmitter RF horn antenna.
Design Objective
The objective was to provide the NHL with a 60 GHz wireless in-net goal camera system. The goal mounted transmitter system was in a ruggedized and water resistant enclosure with an integrated 720p59.94 camera. The RF receiver unit was to be mounted above the goal in the ceiling of each NHL venue. The transmission distance was to be between 50 and 150 feet. Most NHL hockey venues are approximately 100 feet high. The system was to output uncompressed 1.485 Gbps HD-SDI video. One system was required per goal in all 30 venues for a total of 60 systems. The purpose of the camera system is to capture and record live video of the goal line for instant replay to support officials in reviewing disputed calls during every game (See figure 6 above). The GoalCam video is transported via an MPLS network to Toronto, Canada for replay and officiating by Hockey Operations.
60 GHz RF Technology
VidOvation utilized 60 GHz wireless RF technology with uncompressed 1.485 Gbps HD-SDI transport. The 60 GHz RF technology is fully uncompressed with no bit or resolution manipulation with un-coded broadcast quality video. This technology gives the officials a clear crisp image to review disputed calls.
Camera/Transmitter Unit
The goal side of the system has a combined RF transmitter and camera in a ruggedized housing. The housing is mounted on a quick release positive registration bracket mounted inside the top rear of each goal.
The camera/transmitter housing is fabricated from an extruded aluminum tube with Lexan polycarbonate shock resistant domes on each end. The camera lens is protected by the lower (front) dome, while the RF antenna is protected by the upper (rear) dome. (See Figure 7 above)
The camera/transmitter enclosure will withstand shock and impact from a 105 mph hockey puck and has been designed in a 6 inch maximum diameter cylindrical housing with no sharp corners or edges to protect player safety.
A shatterproof transparent Lexan polycarbonate dome is provided with a hydrophobic coating to prevent water/ice buildup and condensation. In the second generation GoalCam, VidOvation added a small fan to eliminate fogging condensation on the lower camera dome.
The camera/transmitter housing includes the 60 GHz RF transmitter with a custom 20 degree wide angle horn antenna. It also includes internal lithium-ion batteries that will support up to 5 hours of operation per charge.
The system incorporates a broadcast quality 720p 59.94 HD-SDI camera. The camera also includes a variable focal length, wide angle, 2.8 to 8mm lens.
A custom mounting bracket assembly to attach camera/transmitter unit to the top of the rear center goal post was designed for each camera system. The bracket includes a quick release for camera/transmitter unit removal and recharge.
The transmitter has a 20 degree beam with an RF cone coverage area of about 35 feet at an elevation of 100 feet. During a hockey game the goal is permitted to tip up on its mounting pins creating a few degrees of movement that the camera system must be able to handle without manual adjustment. With a 35 foot target area from the transmitter to the receiver above, the GoalCam link remains operational during any goal movement. The transmitting RF antenna horn can move plus or minus in the X and Y axis approximately 25 degrees. This gives the NHL flexibility if there is no ideal position to mount the GoalCam receiver directly over the goal.
Receiver Unit
The receiver unit is mounted overhead in the stadium rafters or catwalk at a mounting location giving a direct line of sight to the camera transmitter in the goal below (See figure 8 below). The receiver is typically able to be mounted on the catwalk above each goal. In a few cases there is no clear line of site from an overhead catwalk so a rigging crew is required to mount the receiver on steel beams in the top of the stadium.
There can be no obstructions, beams or wires between the line of sight of the GoalCam transmitter and receiver. Reflected signal can also cause multipath issues. All that is required is a clear line of sight for the cone shaped RF transmission.
The receiver unit has 2 reclocked BNC HD-SDI outputs with an external AC power supply with 12 VDC 4 pin XLR connector. The receiver is provided in a ruggedized weather resistant enclosure for long term reliable operation.
Each receiver connects to the fiber-optic HD SDI infrastructure at each hockey venue. Uncompressed video from the two In-net GoalCams and the two over-head GoalCams is distributed to the truck bay for the mobile production trucks to use in the televised game when the cameras capture an interesting play. The four GoalCam video signals are also encoded to MPEG-4 H.264 and tramsitted to Toronto via an MPLS network for access by league officials during a game.
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