Method and device for estimating RF interference in Wi-Fi communication by measuring time delays in RF transmission
A device and method measures transmission efficiency of wireless RF energy packets for each 802.11 channel and relates these measurements to the presence of RF interference. The invention is implemented using a single computing device with an installed wireless network adapter that implements the CSMA/CA transmission protocol.
When installing a wireless network or troubleshooting one that performs poorly it is important to select a channel that is not subject to RF interference from other devices. With wireless systems it is difficult to predict the propagation of radio waves and to detect the presence of interfering signals without the use of test equipment. Typically an RF spectrum analyzer is the preferred tool for detecting and identifying sources of interference and for providing information that allows optimal configuration of a Wi-Fi network. There are also commercial devices designed to measure RF interference.
In general, their short-comings fall under two categories—either they do not employ an 802.11 device for measuring the effect of RF interference or they require multiple devices—e.g. an access point (AP) and wireless stations (STAB) —that are specially programmed to implement a custom protocol.
The primary object of the invention is to present a single device for use with a general purpose computer that can measure efficiency of transmission of energy packets in the various available RF channels for the ultimate purpose of selecting one or more channels for use by an AP.
Method for configuring wireless links for a live entertainment event
A method of assigning channels (each having a center frequency from a frequency set) to a set of sound sources for a live entertainment event performance, said sound sources having a hierarchy of importance to entertainment event success. First, the frequencies are ranked in terms of susceptibility to interference from intermodulation products created by the frequency set. Then, high importance sound sources are assigned the most reliable channels—that is, those having a center frequency that has a relatively low susceptibility to interference from intermodulation products.
When coordinating RF transmitters it is important to take into account the phenomenon of intermodulation (IM) distortion. Intermodulation distortion is caused by non-linear amplifiers and signal processing used in most audio hardware. Intermodulation distortion between two or more frequencies will form additional frequency signals (intermodulation products). These new signals occur at the sum and difference frequencies of the original signals and at multiples of those sum and difference signals. If intermodulation products fall within the bandwidth of a receiver, intermodulation interference may occur.
Those configuring wireless equipment for a live entertainment event, typically referred to as “RF coordinators,” are faced with many challenges. Typically, for a concert or a sporting event, multiple systems independently operating in parallel communicate by means of wireless signals. These systems may collectively use dozens of wireless channels, each typically having a width on the order of 25 KHz.
In a live concert, there are wireless channels assigned to lead singers, various accompanying instruments, backup singers, in-ear monitors worn by musicians, and two-way radio communications between people coordinating the performance. In addition, if there is news coverage of the event the news reporters will have wireless communication devices, also competing for clean spectrum space.
Sporting events also have a pall mall assortment of sound sources that must be transmitted wirelessly to receivers. Coaches and assistant coaches are connected by wireless units. News crews are equipped with wireless communication devices.
Moreover, clean spectrum space is not necessarily easy to find, as the 470 MHZ to 700 MHZ spectrum typically used for live events is, for the most part, shared with UHF TV stations. Because of this, even the same concert, with the same set of performers and instruments, cannot have the same wireless channel assignments from one city to the next on a multi-city tour.
Avoiding interference caused by intermodulation products is a critical issue in this environment. There are software tools available to assist an RF coordinator in assigning channels to their wireless equipment. The current state of the art is for the software tool to perform an intermodulation analysis and compute a frequency set. The resultant frequency set includes a list of frequencies that are guaranteed to be “intermodulation-compatible”—that is, the intermodulation products computed from the frequencies in the frequency set are guaranteed to be a specified distance removed from each frequency in the set. Sometimes, when intermodulation analysis is performed using strict criteria for frequency survival then the resultant frequency set is too small to accommodate all the audio gear that requires channel assignments. In this case the intermodulation analysis can be repeated using less stringent frequency survival criteria, and this results in a frequency set that contains more members but which is also less reliable than one computed using stricter criteria. Typically, all frequencies in a frequency set are treated as being equally reliable and the RF coordinator typically assigns them, in no particular order, to their wireless equipment. To be more exact, an RF coordinator assigns channels to their wireless equipment, where a channel is a frequency band (typically 25 KHz wide) whose center frequency is a member of the frequency set.