![]() ![]() The problem is that conventional Wi-Fi systems can only increase signal levels by adding more power or by bolting on high-gain directional antennas to their APs which increase gain in one direction, but limit coverage to a smaller area. ![]() To achieve a high SINR, Wi-Fi systems must either increase signal gain or decrease interference. ![]() A higher SINR translates into higher data rates and more spectrum capacity. Given the negative impact of RF interference on user throughput, SINR is a much better indicator of what kind of performance can be expected from a Wi-Fi system. SINR is the difference between the signal level and the level of interference. But as soon as interference comes along network managers have something else to worry about: the Signal-to-Interference plus Noise Ratio, also referred to as SINR. Typically a higher SNR results in fewer bit errors and higher throughput. SNR compares the difference between strength of the receive signal level and the noise floor. Wanted: stronger signals and less interferenceĪ common metric for predicting how Wi-Fi systems will perform is the Signal-to-Noise (SNR) Ratio. But what does the client see? Will moving to a cleaner channel really benefit the user's experience? In these scenarios, interference is determined from the vantage point of the AP. The channel changing approach also doesn't take into consideration what's best for the client. However Wi-Fi signals don't stop and travel beyond these architected limits. To minimize co-channel interference, network managers try to architect their networks - and the limited spectrum available to them - by spacing APs far enough apart so they can't hear or don't interfere with each other. ![]() Channel changing creates a domino effect as neighboring APs change channels to avoid co-channel interference.Ĭo-channel interference is created when devices interfere with each other by using the same channel or radio frequency to transmit and receive Wi-Fi signals. Even within the 5GHz band, only four non-overlapping 40MHz wide channels exist after eliminating Dynamic Frequency Selection (DFS), a mechanism to allow unlicensed devices to share spectrum with existing radar systems.Ĭhannel changing by an AP requires connected clients to disassociate and re-associate, causing disruption to voice and video applications. Within the 2.4GHz frequency, the most widely used Wi-Fi band, there are only three non-interfering channels. With limited channels to change to, this technique can cause more problems than it solves. While changing channels is a useful technique to deal with continuous interference on a given frequency, interference tends to be highly variable and intermittent. Adding more APs creates - you guessed it - more interference.įinally, most WLAN vendors would have you believe that the best approach to dealing with Wi-Fi interference is "channel changing." This is where a different or "cleaner" channel is automatically selected for the AP when RF interference increases. These holes must be filled with more APs. This translates into a lower data rate and smaller Wi-Fi cells that can create coverage holes. But lowering transmit power also lowers the signal strength received by the clients. Doing this reduces the number of devices sharing an AP, which can improve performance. This approach is highly inefficient, and subsequently all users sharing this AP experience poorer performance.Īnother common method for Wi-Fi design is to reduce the AP transmit power to make better use of the limited number of channels. Packets are now in the air longer, which means there is a greater chance of losing those packets because they take longer to be received - making them more susceptible to periodic interference. Yet lowering the AP's data rate can actually have the opposite desired effect. They must lower their physical data rate until an acceptable level of packet loss is achieved. Since these antennas always transmit and receive exactly the same in all situations, when interference crops up, these systems only have one option to combat interference. These antennas send and receive transmissions equally in all directions. The vast majority of APs on the market today use omni-directional, dipole antennas. While each of these can be useful in some respect, none of them addresses the fundamental problem of dealing directly with RF interference. Three popular approaches to addressing RF interference include lowering the physical (PHY) data rate, reducing the transmit power of the affected AP or changing the AP's channel assignment. If just one of these signals runs into interference, the ability to spatially multiplex or bond channels, two fundamental 802.11n techniques that help to yield dramatically higher data rates, is effectively eliminated.Ĭommon approaches to dealing with interference ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |