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