5Ghz IEEE 802.11a For Interference Avoidance (01-Aug-2009)

TECHNICAL BRIEF

5Ghz IEEE 802.11a

For Interference Avoidance

Abstract:

The proliferation of wireless devices in the 2.4GHz ISM (Industrial, Scientific, and Medical) unlicensed spectrum has created significant sources of interference for 802.11bg networks. Although sophisticated temporal, spectral, and spatial interference mitigation techniques are available, the most common and simplest method for interference mitigation is simple spectral avoidance; i.e. channel change or band shift.

IEEE 802.11bg networks offer 11 different channels (13 channels for European ETSI) spaced 5 MHz apart in the 2.4000 to 2.4835 GHz spectrum (note: transmission signal is 22 MHz therefore adjacent channels are overlapping).

In cases where a simple channel change is not sufficient to avoid interference, a band shift from 2.4Ghz (802.11bg) ISM to 5Ghz (802.11a) UNII (Unlicensed National Information Infrastructure) may be required. If the network is not designed for dual band 802.11abg operation, then an upgrade of the clients and/or the infrastructure may be required.

This leads to the question addressed by this paper; "will 5GHz become equally congested as designers search for "quiet" spectrum?"

Targeted at an electronics retail environment this paper discusses several consumer electronic interference devices. None the less, much of the analysis is applicable to generic environments. Finally it is out of the scope of this paper to discuss the benefits of multi-band networks for time sensitive multimedia applications (e.g. data/voice/video).

Summary

Although the 802.11a 5GHz UNII band is unlicensed; it is the assertion of this paper that interference levels in this band will remain relatively low compared to ISM 2.4GHz for the foreseeable future. Furthermore, 5 GHz offers several sustainable benefits with respect to interference mitigation:

1). Interference Avoidance - 802.11a 5GHz UNII has up to 300MHz of available spectrum for interference avoidance vs. 83MHz in 2.4GHz ISM.

2). Bluetooth & ZigBee (IEEE 802.15.4) Devices - Bluetooth (Instat estimates over 800M devices shipping in 2008) and IEEE 802.15.4 (e.g. ZigBee) operate in the 2.4GHz ISM band. There are no plans to shift
to 5GHz.

3). Cordless Phones - Current 5.8 GHz handsets will transition to the recently FCC approved DECT 6.0
Unlicensed Personal Communications Services (UPCS) spectrum at 1.920-1.930 GHz (see cordless phone section below).

4). Wavelength Dependent Applications - Wavelength dependent applications such as microwave ovens and low energy lighting (e.g. 2.45 GHz sulfur lighting magnetrons) will not shift to 5.8 GHz.

5). Physics - Propagation absorption characteristics at 5GHz will curtail widespread wireless appliance migration to this band (especially in residential environments).

6). Connectivity - Reduced antenna apertures at 5GHz decre...