Wi-Fi networks in 5 GHz: a few observations
There is a lot of talk in the air about 802.11ac; and accordingly, there is also a lot of talk about 5 GHz Wi-Fi networks.
Lisa Phifer recently wrote a tech note on Webtorial discussing this current topic. It was great talking to her as always on hot topics in Wi-Fi. From these types of conversations and from firsthand experience with many enterprise Wi-Fi network deployments, some salient points stand out for me pertaining to operation of Wi-Fi networks in the 5 GHz band. They are as follows.
Benefits of 5 GHz band
The topic of 5 GHz Wi-Fi is often associated with the impending 802.11ac Wi-Fi standard. However, it is important to underscore that all the key benefits of the 5 GHz band are present even today with the existing 802.11n networks. However, certain economic and interoperability factors have held this option back for some time. However, these issues are fading and over time viability of the 5 GHz band for enterprise Wi-Fi will continue to rise.
Following are clear benefits of the 5 GHz band:
- 5 GHz is free from non-Wi-Fi interference: Virtually all known non-Wi-Fi RF interference sources operate in the 2.4 GHz band – microwave oven, Bluetooth, non-Wi-Fi wireless video cameras, non-DECT cordless phones, etc. The only well-known non-Wi-Fi interference source in the 5 GHz band is the 5.8 GHz cordless phone (channel numbers 149,153,157,161, 165), which by the way is also fast disappearing due to more popular DECT 6.0 phones which operate in the 1.9 GHz frequency band (called DECT in many parts of the world, where it operates in the 1.8 GHz frequency band). As a result, the 5 GHz band offers a clean radio environment for Wi-Fi without nuisance from virtually all non-Wi-Fi interference sources.
- Tighter cell packing for higher capacity: Traditionally, Wi-Fi networks have been designed first for coverage and secondly for capacity. That has favored the 2.4 GHz band due to higher range of radio signals (in the 2.4 GHz band) compared to those in the 5 GHz band (radio waves travel longer at smaller frequency). However, growing use of Wi-Fi as de facto enterprise access technology requires higher capacity per unit area in addition to coverage. High capacity mandates a pico-cell architecture so that more cells can be packed in a given area thereby increasing its wireless access capacity. Tighter cell packing requires a higher number of non-overlapping channels and the 5 GHz band offers more than 20 non-overlapping channels compared to 3 or 4 in the 2.4 GHz band.
Practical challenges in 5 GHz operation
- Smaller coverage per cell results in higher total cost: 5 GHz networks require more APs to cover the same area because of the smaller range of the 5 GHz signals compared to the 2.4 GHz signals. More APs also require more Ethernet drops and cable runs which add to the cost of Wi-Fi deployment. In the past, this has favored the 2.4 GHz band. However, as the reliance on Wi-Fi in the enterprises increases, more investment should flow into the Wi-Fi infrastructure and this economic hurdle should disappear paving the way for more 5 GHz networks.
- All wireless clients are not 5 GHz capable: There is still significant population of clients that are only 2.4 GHz capable, particularly in the mobile form factor. Enterprises are required to operate 2.4 GHz networks so that these clients are not deprived of wireless network access. However, with ever increasing mobile devices which now support 5 GHz radios; this interoperability hurdle should also should fade away in near future.
Current and medium term reality
2.4 GHz is not EOL yet, but 5 GHz should be leveraged to the extent possible. Dual band (2.4 GHz and 5 GHz) networks will continue to be around for some time. Enterprises should take advantage of the good characteristics of the 5 GHz band described above to the extent possible, while not prematurely writing off the 2.4 GHz networks. Following are a few guidelines for dual band network design:
- 5 GHz should be standardized for clients running mission critical applications. Whenever possible, mission critical application should be supported on 5 GHz and devices for mission critical applications should be standardized for 5 GHz operation. Note that many enterprises currently run VoIP over Wi-Fi in 5 GHz.
- Techniques such as band steering can be used to move clients running mission critical applications (e.g. certain corporate SSID) to 5 GHz radio. However, brute force band steering should be avoided, otherwise the 5 GHz network may get congested and the 2.4 GHz network could remain underutilized.
- 2.4 GHz coverage should still be supported, for both corporate applications and for guest access to cater to 2.4 GHz only devices, or to cater to areas where there may be holes in the 5 GHz coverage due to small cell size in the 5 GHz band, or to cater to clients which are not steered to 5 GHz because of congestion on the 5 GHz radios.
- Good coverage in 5 GHz will typically result in higher AP density allowing introduction of additional functionality on some of the AP radios. If dual-radio APs are deployed (mainstream today) there is no additional benefit if all 2.4 GHz radios on those APs are activated in dense AP deployment. Beyond a certain point, the co-channel interference in 2.4 GHz band will be too high to manage in high density deployments. The excess radios can be effectively used to provide security monitoring without introducing additional cost. APs with band unlocked, software defined radios offer the highest flexibility and efficiency for deploying 5 GHz/2.4 GHz/security in Wi-Fi networks.
What does 5 GHz operation have to do with 802.11ac?
802.11ac is 5 GHz only technology, but 802.11n also has 5 GHz option. If you deploy an 802.11ac AP (or 802.11ac radio on the AP for that matter), it will necessarily operate in 5 GHz. If you use 802.11n, it has option to operate in 5 GHz band. The difference between 802.11ac and 802.11n is support for high link rates in the 802.11ac, if your network needs them. However, the benefits, challenges and strategies for 5 GHz network operation are similar in both.
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