Wireless technology is not new to musicians. Wireless mics and instrument transmitters have been around for many years. More live performers also choose to use wireless in-ear monitors onstage. But a new generation of hardware and software is emerging that will enable wireless control of sound systems, EQs, effects and other audio tools for live and studio use.
This leads to issues surrounding the two leading wireless computing protocols in use today – Wi-Fi and Bluetooth. While the two technologies serve different purposes (Wi-Fi is essentially wireless Ethernet, while Bluetooth is a wireless connection scheme for computers, cell phones, PDAs and other peripheral devices), both are likely to be operating side by side in an automated studio or at the main mix station. Because both Wi-Fi and Bluetooth share the crowded 2.4 GHz Industrial, Scientific, and Medical (ISM) band, you may wonder whether they will interfere with one another. The answer is yes, but…
Both technologies are inherently resistant to other wireless devices by virtue of their use of spread spectrum techniques. However, increasing interference is likely to result in a slowing of data transfer rates or lost data packets. Only in extreme conditions, such as setting a Bluetooth enabled cell phone down next to an operating microwave oven, is it likely that communications will cease altogether.
The Federal Communications Commission qualifies devices that radiate radio frequency interference as either intentional or unintentional radiators. There are plenty of both in the 2.4 GHz ISM band. Unintentional radiators of RF energy include almost all electrical devices! The FCC sets practical limits on how much energy can be unintentionally radiated. But while the electromagnetic interference from your PC will not disrupt your wireless device, a nearby microwave oven certainly can. So designers of hardware and applications have to build in ways to cope with inevitable interference. The solution to operating successfully near microwave ovens and such is to move them farther away or somehow provide further shielding. In a concert hall or convention center, you, the wireless user, should perform an RF site survey to identify sources of interference.
Neither Wi-Fi nor Bluetooth was originally designed with mechanisms in place to deal with the interference that each creates for the other. But the industry has aggressively pursued solutions.
Wi-Fi and Bluetooth both occupy a section of the 2.4 GHz ISM band that is 83 MHz wide.
Bluetooth hops between 79 different 1 MHz-wide channels in this band to avoid interference. Wi-Fi’s carrier remains centered on one channel that is 22 MHz wide. There is only room for three non-overlapping channels in this frequency band, so there can be no more than three different Wi-Fi networks operating in close proximity. When a Bluetooth radio and a Wi-Fi radio are operating in the same area, the single 22 MHz wide Wi-Fi channel occupies the same frequency space as 22 of the 79 Bluetooth channels. When a Bluetooth transmission lands on a frequency that’s occupied by a simultaneous Wi-Fi transmission, interference can occur.
Bluetooth’s channel-hopping scheme can result in be either degradation of data throughput, or with time-sensitive information such as voice, packets can be lost. Wi-Fi deals with interference like Ethernet does. If a transmission fails it assumes that a collision has occurred due to two stations trying to transmit simultaneously, and an Automatic Repeat Request (ARQ) is issued. Many Wi-Fi applications also utilize an optional automatic data rate modification feature that reduces the data rate to 5.5, 2, or even 1 Mbps, in an effort to lower the Bit Error Rate.
The Bluetooth SIG and the IEEE Wi-Fi working group have defined mechanisms and recommended practices to ensure the coexistence of Bluetooth and Wi-Fi networks. These range from allowing a Wi-Fi device and a Bluetooth device to alternate transmissions, and a mechanism that inserts a 1 MHz-wide null in the Wi-Fi bandwidth that coincides with the current Bluetooth center frequency. In addition, Bluetooth has incorporated a process called adaptive frequency hopping that avoids channels with the most interference.
Wi-Fi and Bluetooth can happily coexist, even when interference does occur. This means you will be able to run your soundboard via remote control and use your laptop with a wireless mouse and both should work fine. And the future of wireless data transmission in audio applications promises some amazing benefits for musicians.