The Impact of Adjacent Channel Interference in Multi-Radio Systems using IEEE 802.11

Abstract

A promising approach for improving the capacity of Wireless Mesh Networks is by making use of multiple non-overlapping RF channels. Multi-channel protocols have the advantage that several devices can transmit in parallel within a collision domain on distinct channels. When using IEEE 802.11b/g/a most protocol designers assume 3 and 12 non-overlapping channels, respectively. However, this simplified assumption does not hold. We present results from measurements that show that the number of available non-interfering channels depends on the antenna separation, PHY modulation, RF band, traffic pattern and whether single-or multi-radio systems are used. The problem is caused by Adjacent Channel Interference (ACI) where nearby transmitters "bleed over" to other frequencies and either cause spurious carrier sensing or frame corruption. For nearby transceivers, as in the factory defaults of multi-radio devices, this results in at most two noninterfering channels, one within 2.4 GHz and the other within the 5 GHz band. Only if the distance between the antennas is increased, non-interfering channels within the bands themselves become available. Moreover, our comparison of single-and multiradio systems allows us to isolate ACI from board crosstalk and radiation leakage of which only the multi-radio systems seem to suffer. Finally, we show how a packet-level simulator can be improved to realistically incorporate ACI. With the help of this simulator more confident statements about the performance of various multi-channel protocols can be made.

Measurements and Evaluations for an IEEE 802.11a Based Carrier-Grade Multi-radio Wireless Mesh Network Deployment

“…Based on this assumption measurements were only conducted with Tx values between 10 dBm to 15 dBm. In comparison to other previously published work, such as [9] and [10], the following results show every combination of Tx and DR with T and RSSI, respectively. As explained in detail in Section II-A for every calculated sample meanμ, CI is also be provided.…”

“…Additionally, their assumption has already been disproved by many researchers, such as [7] [9] [10], ACI issues must be taken into account when conducting multi-radio measurements with IEEE 802.11a hardware. One of the most important pieces of work in relation to this issue are the results of Nachtigall et al [9]. They demonstrated that the number of available non-interfering channels depends on both the antenna separation and the Physical Layer (PHY) modulation.…”

Rumours and good practices in community networks wireless links

“…However, for the 40 MHz link, the impact is less than when it overlaps with 20 MHz links. This is probably due to the mechanism CSMA/CA which in this case has less spurious carrier sensing and less frames are corrupted ( [2,3]). …”

“…Many works (e.g., [1][2][3][4][5][6][7][8][9]) study different characteristics of WiFi in practice, but still more practical tests and a larger set of experiments are needed. For example, most of the works are focused only on the 2.4 MHz band or only study a reduced set of aspects of the 5GHz band.…”

Utilizing Multiple Channels With Fewer Radios in Wireless Mesh Networks

“…Therefore, separating APs into different channels may decrease cochannel interference. However, in nonoverlapping channels, an 802.11-based multiradio device suffers board crosstalk, radiation leakage, and adjacent channel interference [5], [32], [33]. These problems are hardware dependent [5] and can be alleviated by utilizing hardware and radio frequency (RF) techniques such as shielding, bandpass filters, and antenna separation by distances or orientations [32], [33].…”