Revving Up Mesh
Networks with 802.11n
802.11n networks promise greater
data throughput and capacity at a cost-effective price.
Wi-Fi technology has emerged to become a highly relevant
technology. Large enterprises use it to provide broadband
connections throughout a corporate campus. Municipalities and public
safety agencies have deployed it to support critical municipal
functions, such as video surveillance, meter reading and traffic
control. And telecom and cable service providers are using it as a
way to create loyalty and offload heavy data traffic – offering
their customers free wireless broadband access via laptops and smart
phones. Most importantly, consumers are demanding Wi-Fi's
availability nearly everywhere.
Fortunately, the demand for Wi-Fi services is peaking at the same
time new high-capacity Wi-Fi networks are beginning to proliferate.
Most current Wi-Fi network deployments are based on the 802.11a/b/g
standards, which only reach burst data rates of 54 Mbps for 802.11g.
Moreover, the standards were never created with large coverage areas
in mind – making large deployments problematic and expensive. But
the adoption of 802.11n Wi-Fi is dramatically changing the
capabilities and economics of the mesh networking business as it
bumps Wi-Fi’s theoretical performance 10-fold and increases the
range three times that of the 802.11g standard.
According to Chip Yager, general manager for the Motorola Mesh
Networks Product Group, “The number of applications that Wi-Fi
networks can support is multiplying. 802.11n technology expands the
capacity of Wi-Fi communications. High capacity 802.11n mesh
networks support multiple users and multiple applications, leading
to faster ROI.”
That capability is particularly important to outdoor mesh
networks, which have been successful in smaller zones but have
difficulty being deployed longer range without a significant number
of access points and expense, said Roger Skidmore, technical
director with Motorola.
“Business models are more viable now with 802.11n than they were
before when it comes to the outdoor mesh network,” Skidmore said.
“With 802.11n, you are increasing the ability to backhaul data in a
meshing situation. That is the problem that has always plagued mesh
networks from a cost-effective point of view in terms of delivering
the high-performance applications such as video and VoIP people have
come to expect.”
In September 2009, the IEEE officially ratified the 802.11n
standard, but this comes three years after the Wi-Fi Alliance began
certifying Draft N products and six years after the first draft
version of the standard. Today, some 600 Draft N products have been
released since June 2007 –primarily used by consumers in the home
and enterprise networks. The upside to this is that the new wireless
networking standard will work with the existing WiFi certified Draft
N wireless products because all of the standard’s hardware
specifications were agreed upon back in 2007. Draft N equipment can
now be updated via software updates to the new standard but will
depend on manufacturers making firmware updates available.
An official standard, however, raises the comfort level of
enterprises and other entities desiring to roll out mesh networks as
they now can deploy equipment that won’t be obsolete, Skidmore said.
The question now is: What do enterprises, governments and service
providers need to understand in their quest to harness the
capabilities of 802.11n technology for outdoor networks?
“802.11n promises a lot of things, but there are so many
different technical combinations,” Skidmore said. “One thing we are
really investing a lot of time in is looking at how customers can
obtain the right combination to achieve the full benefit of the
standard. Without proper planning, an investment in 802.11n might
only yield a minor improvement over older Wi-Fi technology.”
One aspect entities should keep in mind when considering an
802.11n deployment is the technology’s speed and range capabilities.
While the technology’s theoretical data speed is 10 times that of
802.11g technology and offers three times more the range, the peak
rate most experts talk about is 300 Mbps maximum with real word
speeds clocking in around 100 Mbps, depending on the configuration
of the network.
“The industry is already a good ways along in getting to that 10
times number but it will come in subsequent improvements,” said
Lorne Liechty, software engineer with Motorola. “Chipset vendors say
they will be implementing additional options, and we’ll gradually
see more and more acceptance on the consumer device side, and we’ll
see a phasing out of the older network elements so people can
leverage more and more of the standard.”
Indeed, ABI Research predicts that WiFi chip sales will reach one
billion in 2010 and five billion by the end of the following year,
with 802.11n chipsets being the dominant protocol shipped, noted ABI
analyst Philip Solis. The technology driving this stunning uptake in
the market is MIMO (multiple-input/multiple-out). Continuing
improvements in MIMO technology allow 802.11n networks to
progressively rev up the range and speed of a network. The 802.11n
standard offers many options for MIMO, and draft devices are still
just scratching the surface of what’s available.
This is how MIMO works: An 802.11n radio can include multiple
transmit antennas and paths. Multiple spatial data streams can be
transmitted at the same time, on the same channel by different
antennas. The data streams are then combined from the multiple
receivers using advanced signal processing, yielding a significant
jump in range and speed.
While most devices may not include all of the MIMO technology
options of the 802.11n standard, the 802.11n network still has the
ability to greatly improve data speeds for subscriber units and
offer better coverage. Most entities aren’t planning to rip out
their current generation of 802.11a/b/g equipment immediately but
rather expand their existing networks with 802.11n technology. That
means legacy client devices will still be operating on the new
802.11n network, Liechty said.
But there are a number of technical considerations network
planners need to keep in mind, such as engineering for interference
mitigation between legacy and the new 802.11n technology and
ensuring the network design accommodates the increased RF coverage
capabilities. Incorporating technologies such as maximal ratio
combining (MRC), offers better connectivity for clients because it
incorporates multiple receive antennas to reconstruct signals,
thereby reducing error and giving clients a stronger connection.
“MRC is not part of the N standard, but the hardware requirements
for MIMO allow you to get MRC with less investment than what was
necessary with legacy equipment,” noted Liechty.
Other technical capabilities network planners need to take into
consideration include capabilities like channel boding – the ability
to combine two adjacent channels into a single 40 MHz channel – and
frame aggregation. The new 802.11n standard provides an option for
combining multiple data frames ready for transmission into a single
data frame to help with network backhaul functions.
And finally, while the data rates offered to 802.11n subscribers
can be outstanding, they are useless unless the mesh layer itself
can provide the same or greater speed connection back to the wired
network, Skidmore said.
In all, 802.11n is an exciting development for mesh networks that
with proper engineering reduces the amount of equipment needed while
offering a better broadband experience. Skidmore concludes, “802.11n
finally brings the higher capacity and throughput that people have
come to expect, and it can now be done in a way that is cost
effective.” -Motorola Ezine Article 2009