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.

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In recent years the research of opportunistic protocols for wireless mesh networks gained lots of attention. A great number of protocols like Extreme Opportunistic Routing (ExOR) and Multiuser Diversity Forwarding (MDF) was proposed. Most of the performance evaluations were conducted in a constant bit-rate environment. This paper presents simulation results of the performance of existing opportunistic protocols as well as a new opportunistic protocol called Hybrid Opportunistic Routing (HOR) in a constant-and multi-rate environment. In a constantrate environment with a slow fading channel ExOR outperforms MDF and HOR by around 20%. This is mainly due to its small signaling overhead. ExOR is also the best choice in a fast fading channel. However, here HOR is able to outperform MDF. In a multi-rate environment our proposed ETT-RCA rate control algorithms outperforms the existing Adaptive Auto Rate Fallback (AARF) significantly. AARF is only suitable for short, high quality links. The biggest problem with ExOR is that is cannot be used together with ETT-RCA. In a slow fading channel MDF with ETT-RCA is the best choice. It outperforms ExOR with AARF by multiple times (up to 360%). In a fast fading channel HOR with ETT-RCA is the best choice for mediumdistances (e.g. 80% and 330% higher throughput than MDF with ETT-RCA and ExOR AARF). Only for very large distances ExOR with AARF is able to offer the highest throughput. Here in the multi-rate environment the degrees of freedom (candidate and bit-rate selection) are too large for ExOR and AARF.

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