Typical bit rates
Transmission rates can vary dramatically based on location, time of day and number of people in a certain area. In good 4G areas, transmission rates may be as high as 10Mb/s to 12Mb/s, compared to an average of 1Mb/s to 3Mb/s in some 3G areas. Of course, it’s impossible to predict available bandwidth at a govem to,e. Therefore, another job of the bonding solution is to characterize each link every few milliseconds in terms of bandwidth, delay and loss rate. Then, it creates a Gaussian normal distribution graph for each parameter, assigns a real-time weight based on the graphs, and feeds this weight to the scheduling/queuing process. This allows for the best real-time decision regarding which link the next incoming packet should use. Typical bonding techniques use the following methods to overcome fluctuations:
- Adaptive bit rate: By changing the encoding rate on the fly, the bonding unit can maintain transmission even as bandwidth swings.
- Signal boost: The bonding unit may use special antennas that increase range compared to consumer air cards, as well as overcome multi-path fading in environments where signals bounce around different obstacles (walls, beams, etc.).
- Forward error correction (FEC): The unit will send redundant data along with the main feed, so that if some of the original packets are lost, the decoder can still recover the information. The Reed-Solomon FEC algorithm takes a predefined block of packets (FEC group) and calculates several augmented FEC packets. If, for example, the FEC group is composed of 20 packets, and we add four FEC overhead packets, any lost packet, up to four, can be recovered.
- Latency control: The higher the latency is, the more likely all data packets will arrive in time. Users can select a low latency (as low as sub-second end-to-end), which carries a greater risk of occasional packet loss. Or, a higher latency (anywhere from 2 to 60 seconds, or even store-and-forward) can be chosen, which provides more time to recover lost data.
End-to-end latency has a great effect on bonded link quality. If a user selects a low end-to-end delay, say one second, then considering encoding and decoding time, and SW processing time (approximately 500ms), the remaining time for a packet left to arrive from the transmitter to the receiver may be as low as 500ms.
- It’s up to users to decide which parameters to use, based on the content transmitted. On-the-move coverage, where changes are fast and individual link properties vary, a higher end-to-end delay profile will enable better recovery from changes without data loss. But, in areas with good cellular coverage, when the camera is static, a lower delay profile can work fine.
- Changing resolutions: As resolution increases, the bit rate also needs to increase. By lowering the output resolution, one can get by with lower bandwidth in congested locations. The bandwidth control engine detects any state where the outgoing bandwidth is lower than the encoding bandwidth. It will then decide whether to let the encoder use a higher Quantization Parameter (which lowers the encoder bandwidth), or perform a video scaling (feeding the encoder with a lower-resolution image) in order to lower the encoding bandwidth.
A good bonding engine will receive from the user general preferences (low delay, best quality, etc.). Based on these, it will automatically adjust bonding parameters. This means the engine will decide on a packet-by-packet basis how much FEC overhead to use, the optimal encoding rate, what resolution to use at any given time, what frame rate to use, what packets to drop under extreme low BW cases, what packet lost recovery mechanism to use (retransmit, FEC, error concealment, bad frame skip), and how to promptly compensate the overall system knobs upon any network behavior changes that affects the uplink capabilities.
Some of the most frequent recent uses for sports coverage include:
- Live ENG: Channels have utilized cellular bonding to transmit live from road games, press conferences and events like the NFL’s Super Bowl, NBA All-Star Weekend, the Olympics and the World Cup. A reporter or photographer can set up a live on-air shot from a single camera and send footage back while covering a team or a competition. All of this is done without trucks or hardwired connections.
- Upload edited packages: Reporters can upload edited packages from the road without relying on slow hotel Internet connections or individual mifi cards.
- Live behind-the-scenes camera: Broadcasters or franchises can set up exclusive behind-the-scenes web shows while walking around locker rooms, stadium suites, etc. Similarly, rather than only clipping sound bites, many stations’ and franchise’s websites stream coach and player press conferences for the benefit of devoted fans.
- Live varsity games and specialty sports: Thanks to the lower cost of cellular transmission, broadcasters, schools, new media publishers and specialty sports groups can transmit full games and competitions to the web that traditionally would not be shown on-air. Many times, these productions vary from one camera to a fully switched production fed to the bonded unit.
- In motion, in the field: Freed from line-of-sight restrictions, cables or trucks, broadcasters are using bonded backpacks to transmit races from onboard moving cars, boats and helicopters without requiring RF solutions.
Traditional uplink solutions provide guaranteed bandwidth. Yet, these can be costly and require line-of-sight, cabling or fixed locations. Cellular bonded uplink can vary in transmission rates, but it opens a variety of sports live coverage opportunities from new locations and on new platforms by understanding needed parameters. Networks, stations, new media publishers, leagues and teams can optimize the use of cellular bonding and create a breadth of new content offerings that were once too expensive or complex to produce.
—Ken Zamkow is director of sales and marketing, LiveU. Meir Schrieber is vice president, research and development, LiveU.