Wi-Fi technology is familiar to most modern computer users as a primary means for connecting computers and tablets to network infrastructure. Many consumers and businesses operate private Wi-Fi networks, and a number of providers offer Wi-Fi connections in public areas such as airports, stores and restaurants.
Advances in Wi-Fi technology have driven bit rates higher over the past fifteen years, making it feasible to use it for some video applications. However, before deploying these solutions, it’s prudent to analyze their benefits and drawbacks.
The 2.4 GHz Wi-Fi frequency band (ranging from 2.4 GHz to 2.47 GHz) is extremely crowded. Figure 1 shows the channels that are available – notice that only channels 1, 6 and 11 do not overlap when used at their full bandwidth of 20 MHz. The heavy traffic within this frequency band is due to the great popularity of wireless connections for all types of portable equipment including laptops, tablets, security cameras, and many other devices. Also, because this band is unlicensed, there are essentially no protections that prevent another user from turning on their device and causing harmful interference at any time in any location. These factors often combine to make the 2.4 GHz band of Wi-Fi less desirable for professional quality wireless video transmission.
The 5 GHz band is a significant improvement over the 2.4 GHz band, although it is subject to most of the same technical issues. Historically, most laptop and tablet devices have not included 5 GHz Wi-Fi radios, so in general, the level of interference is much lower than at 2.4 GHz. In addition, there are significantly more non-overlapping channel frequencies available (a total of 21) in two blocks from 5.15 to 5.35 GHz and 5.47 to 5.825 GHz These factors combine to make the 5 GHz band a much better choice for professional video applications that use unlicensed Wi-Fi connections.
The latest generation of Wi-Fi devices (including 802.11n and 802.11ac) support MIMO capabilities. This requires the transmitter and/or the receiver to use several antennas to create multiple signal pathways. The data transmitted over these channels can be added together to boost the overall transmission rate to 600 Mbps and beyond. To achieve these extreme bit rates over short distances, three antennas must be installed on both the transmitter and receiver, and the local RF environments must be relatively quiet.
As a rule, Wi-Fi systems use adaptive bitrate algorithms to ensure connectivity under rapidly varying RF channel conditions. While this is very desirable for forming reliable connections, it can cause havoc with video streams that won’t work below a minimum bit rate threshold. Accordingly, some wireless systems built for video transmission have the ability to disable this feature, but these run the risk of losing connectivity if the RF environment deteriorates too much.