Technology: Gigabit Wi-Fi - Do Your Clients Need It?



By Eddie Felmer, Ruckus Wireless. The number of devices joining the home network is increasing all of the time. Think of tablets, smart phones, laptops, desktops, control pads, TVs, security cameras, servers, printers, projectors - the list goes on. Installing a completely wired network is not always practical, so a partially or totally wireless system, will be required in many instances. [caption id="attachment_3557" align="aligncenter" width="600"] A world going Wi-Fi.[/caption] If you have installed a wireless system for any of your customers, then you will have used equipment that conforms to the IEEE 802.11 set of standards. The most common versions of the set are 802.11a, 802.11b, 802.11g, and the newer 802.11n that was published in 2009. 802.11n saw a significant increase in the maximum data rate up to 450Mbps. An evolution of 802.11n is 802.11ac, which is due to be ratified in Q1 2014. In theory this first release (Wave 1) increases the maximum throughput to 1.3Gbps (although it will be a lot less in real life situations), hence its nickname Gigabit Wi-Fi. The second release (Wave 2), to be ratified in the second half of 2014, will theoretically support multi-Gbps throughput up to 6.93Gbps. According to a loose study by In-Stat, 802.11ac devices will reach one billion worldwide by 2015, so the question for the residential custom installer is, do you need to be looking at 11ac, or is 11n sufficient for your clients for now? Technical Advantages 802.11n uses MIMO (multiple-input multiple-output) technology, meaning that multiple antennas can be used to support higher data rates than are possible using a single antenna. 802.11n supports up to three spatial streams. The maximum 450Mbps data rate is only achieved be employing all of these streams using one 40MHz-wide channel. 802.11n is typically used in the 2.4GHz ISM (industrial, scientific and medical) frequency band, although operation in the 5GHz band is optional. The 2.4GHz ISM band is fairly congested, whereas the 5GHz band has much more capacity due to many non-overlapping radio channels and less radio interference. [caption id="attachment_3560" align="aligncenter" width="250"] Comparison of channel capacity of 2.4GHz and 5GHz ISM frequency bands.[/caption] The 802.11ac specification supports the 5GHz band only, and must have a channel bandwidth of 80MHz, with 160MHz being optional in Wave 2. This gives it an advantage over 802.11n, since there is a two-fold performance boost each time the channel width doubles. [caption id="attachment_3559" align="aligncenter" width="290"] The available bandwidth of an ISM band can be divided into 20MHz, 40MHz, 80MHz or 160MHz channels, but the wider channels offer greater performance.[/caption] Another enhancement of 11ac is its support for up to 8 spatial streams (8 streams in parallel between client and access point), as opposed to the 3 supported by 11n. In theory, this again increases the capacity of the network, but in practice it is technically very challenging, which explains why existing premium enterprise-grade 11n access points (APs) support a maximum of 3 streams, and mid-range products only currently support 2 streams. [caption id="attachment_3561" align="aligncenter" width="520"] MIMO in an 8x8:8 configuration (a system that can transmit on 8 antennas and receive on 8 antennas, and which can send or receive 8 data streams).[/caption] 11ac additionally supports multi-user MIMO (MU-MIMO), which means that an AP can talk to multiple clients at the same time. This multiplies airtime efficiency and is useful for clients with fewer spatial streams, and while it does result in less throughput per device, it can still result in tens of Mbps throughput per stream, which is more that current average requirements. [caption id="attachment_3558" align="aligncenter" width="600"] Single-user MIMO versus multi-user MIMO.[/caption] For signal modulation, 11n uses 128-bit QAM, whereas 11ac supports up to 256-bit QAM. This is more efficient and results in throughput gains of up to 33%, but the downside is that it works over very short ranges only (10-12m) and requires very good RF or low interference conditions. Deployment Timelines 11ac is designed as an evolution of 11n rather than a revolution, and is being introduced in two waves. Wave 1 products, introduced in 2013, saw support for 3 spatial streams, 80MHz channels and 256-bit QAM. To be implemented, this first wave of 11ac requires new APs and new client devices. Wave 2 products are planned for 2015, and will support up to 8 spatial streams, 80 and 160MHz channels, 256-bit QAM and MU-MIMO. Taking full advantage of this wave will again require new APs and new client devices. So is it worth jumping in now, or should you wait? Conclusion The single-link and multi-user enhancements supported by IEEE 802.11ac enable several new wireless LAN applications, such as simultaneous streaming of HD video to multiple clients throughout the home, rapid synchronisation and backup of large data files, and wireless display. What you, as an installer, must ask yourself is, do you actually have applications that require more bandwidth than a 3-stream 11n AP/client can deliver today? 11ac products and technologies are just emerging, so you have to decide whether you need to deploy it now or hold back until it is more mainstream. Moreover, will Wave 1 give you all you want, or are you going to have to do a fork-lift replacement of APs and clients in 2-3 years' time? It may be that your existing wireless infrastructure will do for the next couple of years, but if it is likely to be struggling any time soon, then there are some exciting upcoming Gigabit Wi-Fi products that you need to research further. Eddie Felmer is Technical Director - Northern Europe, for Ruckus Wireless. Ruckus Wireless is a pioneer in the wireless infrastructure market, enabling carriers and enterprises to stay ahead of the exploding demand for high-bandwidth applications and services with its smart Wi-Fi products and technologies. www.ruckuswireless.com

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