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Many manufacturers have recently come to market with video transmission systems that combine multiple data links established using 4G LTE cellphone radio modems. To get the high data rates required for professional video, multiple channels are “bonded” together. At the signal source, the video is parceled out into packets that are distributed across multiple cellular modems. These packets are then fed into one or more commercial mobile phone networks and subsequently delivered via IP connections to the receiving device which is typically located at the broadcaster’s facility. At the receiver, the multiple packet streams are gathered and realigned to put them back in the proper order since the delay through each channel may be different.
For routine usage these systems are very reliable and easy to operate. As long as adequate mobile phone network coverage is available, the signals are cleanly delivered with reasonably low amounts of delay. Problems can arise in two circumstances: on the edges of cellular coverage areas, and in locations where large gatherings of other users are present. As traffic loads increase, most mobile phone systems are designed to allocate smaller amounts of bandwidth to each user, which includes cellular data modems. When this happens, the encoder at the camera site must either drop the connection or reduce the bit rate by using lower frame rates, reduced image resolution, or lower quality factors. In some extremely overloaded instances, the mobile phone infrastructure may refuse to permit new connections to be made or potentially even drop existing connections.
Some bonded cellular systems provide a range extender function. This may consist of special antennas designed to reach cell towers that are further away from crowded areas or a deployable device that connects remotely to the camera backpack system to perform the same function. Most devices also provide a mechanism to locally record video in the event of a complete loss of cellular connections; this content can then be transmitted once a cellular connection is re-established.