5/17/2023 0 Comments Wifi signal strengthOf course, the spread in throughput is widest for low RSSI values where the connection is less reliable. The graph clearly shows that a single RSSI value can result in a wide range of throughput measurements, even for the same access point! For example, it turns out an RSSI value around -75 dBm on AP6 can result in anything between 5 Mbps and 45 Mbps. However, does this also mean we can predict the throughput based on the RSSI? In other words, can we assess the actual performance of an access point based on the reported RSSI values, like many tools do? Multiple access points (all with similar characteristics) are plotted.Īt first glance, there seems to be a clear correlation between RSSI and throughput: the higher the RSSI, the higher the throughput. The data points show the RSSI values and throughput results for a single Wi-Fi client device on multiple locations. The picture below shows data from such a test. Since we store both the actual throughput result and the RSSI value for each measurement, we can easily correlate the two. These locations are chosen in such a way that the complete RSSI scale (-90 dBm up to -25 dBm) is generally covered. In such tests we measure the real application –layer throughput on a fixed set of locations within a house environment. For example, if a transmitted packet is not acknowledged, some Wi-Fi devices immediately fall back to a lower modulation while others will try to retransmit at the same modulation (and only fall back after some retries).Īll this makes the relationship between RSSI and link throughput a lot less predictable! Reality CheckĪt Excentis, we perform a lot of Wi-Fi throughput testing. While current access points often have three antennas sending at the maximum allowed power, many mobile devices are limited to one antenna and limit their output strength on purpose to save battery energy.įurthermore, just how and when to switch between different modulations varies between Wi-Fi chipsets. Until we start using Wi-Fi access points as smartphones, this is not very likely. To use the RSSI at one side of a link as a metric for the throughput of that link, means assuming the Wi-Fi link is symmetrical. While ‘ full-duplex gigabit ethernet‘ may accurately describe the real-life performance of a wired link, the performance of a single Wi-Fi link may change from 1 Gbps to 1 Mbps and back within a matter of seconds.Īs long as the chosen modulation is based on the received signal quality, RSSI should still be a good metric for performance, right? True, but there seems to be a lot more to the story!įirst of all, RSSI is pure receive-side metric, while modulation happens at the transmitting side. Wi-Fi transmitters constantly adjust their traffic modulation in response to varying conditions, such as changes in attenuation or interference levels. Since Wi-Fi operates in a rapidly changing wireless environment, it is highly dynamic in nature. Most Wi-Fi access points (or APs) even register RSSI values of all their connected client devices and a lot of popular Wi-Fi planning tools (like Ekahau, NetSpot, TamoGraph and AirMagnet Survey Express) use this signal strength measurements to create heatmaps and predict Wi-Fi coverage and throughput. This information is then used to give the user some knowledge about the Wi-Fi signal quality in the form of the well known signal bars. Wi-Fi devices continuously measure the amount of power carried by incoming traffic and report it back to the operating system of the device. This signal can be Wi-Fi, a mobile network connection or any other wireless protocol. RSSI is a measurement of the amount of power in a received radio signal. In other words, big investment decisions in Wi-Fi infrastructure turn out to be based on paltry data at best. This blog post will show that the Received Signal Strength Indication or RSSI of a link (which is basically a numeric value for the number of bars) doesn’t correlate well with the throughput that can be achieved on that link. To make things worse, a lot of professional Wi-Fi planning and comparison tools use this same signal strength metric as a substitute for Wi-Fi throughput! We’ve all had situations where 4 or more bars are lighting up, but websites are still loading agonizingly slow. But more often than not, the amount of bars doesn’t give us a good indication of the quality of our connection. To check our Wi-Fi signal reception, we tend to look at the signal notification icon of our devices: the more bars, the better the signal.
0 Comments
Leave a Reply. |