Wi-Fi operational range depends on factors such as the frequency band, modulation technique,
transmitter power output, receiver sensitivity, antenna gain and type, and propagation and interference characteristics in the environment. At longer distances, speed is typically reduced.
Transmitter power Compared to cell phones and similar technology, Wi-Fi transmitters are low-power devices. In general, the maximum amount of power that a Wi-Fi device can transmit is limited by local regulations, such as
FCC Part 15 in the US.
Equivalent isotropically radiated power (EIRP) in the
European Union is limited to 20
dBm (100 mW). Wi-Fi, however, has higher power compared to some other standards designed to support
wireless personal area network applications. For example, Bluetooth provides a much shorter
propagation range between 1 and 100 metres (1 and 100 yards) and so in general has a lower power consumption. Other low-power technologies such as
Zigbee have fairly long range, but much lower data rate. The high power consumption of Wi-Fi makes battery life in some mobile devices a concern.
Antenna On wireless routers with detachable antennas, it is possible to improve range by fitting upgraded antennas. An access point compliant with either
802.11b or 802.11g, using the stock
omnidirectional antenna might have a range of 0.1 km. The same radio with an external semi-parabolic antenna (15 dB
gain) with a similarly equipped receiver at the far end might have a range of over 32 km. Higher gain rating (
dBi) indicates deviation from a theoretical, perfect
isotropic radiator toward a
directional antenna, and therefore the antenna can project or accept a usable signal further in particular directions, as compared to a similar output power on a more isotropic antenna. For example, an 8 dBi antenna used with a 100 mW driver has a similar horizontal range to a 6 dBi antenna being driven at 500 mW. This assumes that radiation in the vertical direction is not useful for communications.
MIMO (multiple-input and multiple-output) Wi-Fi 4 and higher standards allow devices to have multiple antennas on transmitters and receivers. Multiple antennas enable the equipment to exploit
multipath propagation on the same frequency bands, giving higher speeds and more than doubled range. The Wi-Fi 5 standard uses the 5 GHz band exclusively, and is capable of multi-station WLAN throughput of at least 1 gigabit per second, and a single station throughput of at least . This standard uses several signal processing techniques such as multi-user MIMO and spatial multiplexing streams, and wide channel bandwidth (160 MHz) to achieve its gigabit throughput.
Radio propagation With Wi-Fi signals,
line-of-sight usually works best, but signals can absorb, reflect,
refract,
diffract and
fade through and around structures, both man-made and natural. Wi-Fi signals are very strongly affected by metallic structures (including
rebar in concrete,
low-e coatings in glazing), rock structures (including
marble) and water (such as found in vegetation). Due to the complex nature of radio propagation at typical Wi-Fi frequencies, particularly around trees and buildings, algorithms can only approximately predict Wi-Fi signal strength for any given area in relation to a transmitter. Performance associated with
long-range Wi-Fi is more easily predicted, since longer links typically operate line-of-sight from towers that transmit above the surrounding foliage.
Distance records Distance records (using non-standard devices) include in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about of data between the mountain-tops of
El Águila and Platillon. The
Swedish National Space Agency transferred data , using 6 watt amplifiers to reach an overhead
stratospheric balloon.
Interference Wi-Fi connections can be blocked or the
network throughput lowered by having other devices in the same area. Wi-Fi protocols are designed to share the
radio bandwidth reasonably fairly. To minimize collisions with Wi-Fi and non-Wi-Fi devices, Wi-Fi employs
Carrier-sense multiple access with collision avoidance (CSMA/CA), where transmitters listen before transmitting and delay transmission of packets if they detect that other devices are active on the channel, or if noise is detected from adjacent channels or non-Wi-Fi sources. Nevertheless, Wi-Fi networks are still susceptible to the
hidden node and
exposed node problems. A standard speed Wi-Fi signal occupies five channels in the 2.4 GHz band.
Adjacent-channel interference can be caused by overlapping channels. Any two channel numbers that differ by five or more, such as 2 and 7, do not overlap. Channels 1, 6, and 11 are the only
group of three non-overlapping channels in North America. However, whether the overlap is significant depends on physical spacing. Channels that differ by four interfere a negligible amountmuch less than reusing channels (which causes
co-channel interference)if transmitters are at least a few metres apart. In Europe and Japan where channel 13 is available, using Channels 1, 5, 9, and 13 for
802.11g and
802.11n is viable and
recommended. However, multiple 2.4 GHz 802.11b and 802.11g access points default to the same channel on initial startup, contributing to congestion on certain channels. Wi-Fi pollution, or an excessive number of access points in the area, can prevent access and interfere with other devices' use of other access points, as well as decreasing overall
signal-to-noise ratio (SNR). These issues can become a problem in high-density areas, such as large apartment complexes or office buildings with multiple Wi-Fi access points. It is also an issue when municipalities or other large entities (such as universities) seek to provide large area coverage. Other devices use the 2.4 GHz band: and, in some countries,
amateur radio, all of which can cause significant additional interference. On some 5 GHz bands interference from radar systems can occur in some places. Access points that support those bands employ
dynamic frequency selection, which listens for radar, and if detected, will not permit transmission on that band. These bands can be used by low-power transmitters without a licence, and with few restrictions. However, while unintended interference is common, users who have been found to cause deliberate interference (particularly for attempting to locally monopolize these bands for commercial purposes) have been issued large fines.
Throughput Various layer-2 variants of IEEE 802.11 have different characteristics. Across all flavours of 802.11, maximum achievable throughputs are either given based on measurements under ideal conditions or in the layer-2 data rates. This, however, does not apply to typical deployments in which data are transferred between two endpoints, of which at least one is typically connected to a wired infrastructure. This means that typically data frames pass an 802.11 (WLAN) medium and are converted to 802.3 (Ethernet) or vice versa. Due to the difference in the frame (header) lengths of these two media, the packet size of an application determines the speed of the data transfer. This means that an application that uses small packets (e.g., VoIP) creates a data flow with higher overhead and lower
information rate. Other factors that contribute to the overall application data rate include the energy with which the wireless signal is received. The latter is determined by distance and by the configured output power of the communicating devices. The same references apply to the attached throughput graphs, which show measurements of
UDP throughput measurements. Each represents an average throughput of 25 measurements (the error bars are there, but barely visible due to the small variation), is with specific packet size (small or large), and with a specific data rate ( – ). Markers for traffic profiles of common applications are included as well. This text and measurements do not cover packet errors but information about this can be found at the above references. The table below shows the maximum achievable (application-specific) UDP throughput in the same scenarios (same references again) with various WLAN (802.11) flavours. The measurement hosts have been 25 metres (yards) apart from each other; loss is again ignored. == Hardware ==