FEATURE: Three Rs spell user satisfaction for WiFi

Data transfer rates often grab headlines but vendors of WiFi wireless networking gear are realizing that there's more to user satisfaction than data throughput rates, which in many cases exceed the rates supported by the various versions of the 802.11 standard. Exceeding standards is nothing new as it's happened many times in the electronics industry and will happen again and again. It's important to point to other factors that can be just as critical to the consumer's relative satisfaction with WiFi products.

Remembering the three R's
There are three basic "R"s when it comes to WiFi networking and I'm not talking about Reading, wRiting and 'Rithmatic. The WiFi "R"s, all of which are essential to effective wireless networks, are Range, Rate and Robustness.

All three are important because poor performance on any one metric can negate good performance from the other two. A very high data throughput rate looks good on paper, but if the effective reach of the 802.11 signals is so poor that users can't consistently connect to the network, then users won't be satisfied in the long run.  

Failing to maintain connectivity with a WiFi network could be related to the third R, robustness. WiFi operates in the unlicensed 2.4 MHz ISM band of the spectrum where several other wireless technologies also operate and where household appliances can contribute their own RF interference. If the WiFi equipment in a network is not able to combat interfering signals--if it is not robust enough--high data throughput rates will be unattainable for the simple reason that users will have a hard time staying connected to the network. Needless to say, this is not a good formula for customer satisfaction.

Ensuring range
At least in residential wireless networking, the ideal would be for one WiFi access point (AP) or one router to have enough range to cover an entire house. Businesses can implement multiple APs to ensure coverage throughout a facility, but this type of a network configuration could be a bit tricky for most homeowners. Some suppliers of WiFi equipment can rightfully claim they provide whole-house coverage, but if a manufacturer is looking to enhance the range of its WiFi gear, it has several alternative solutions to choose from, some exotic and others more practical.

Increasing the transmit power of the wireless signals while improving the signal sensitivity at the receiver end of the channel is the most straightforward way of enhancing the effective range of a WiFi network. But care must be exercised when taking such a course because the increased energy content in the WiFi transmit signals can have other effects which may mitigate any improvements in range. For example, increasing the energy content in WiFi signaling can also increase the noise level in these same signals, increasing the difficulty receivers may have when the signals arrive at the other end of the channel. There may actually be a reduction in the receivers' ability to reject interference that bleeds over into the 2.4 MHz band from adjacent channels.

Better rates
Several techniques have been employed to increase data throughput rates beyond those supported by the 802.11g and other versions of the WiFi standard. Packet aggregation and packet bursting are two particularly effective techniques which have few, if any, negative side effects.

As the name implies, packet aggregation combines packets that carry data in a WiFi network. This lengthening of the payload-carrying capacity of a packet reduces the non-payload overhead that must be tacked onto each packet for it to be transmitted and received correctly. If three packets are combined into one, for example, the overhead for transmitting the data contained in the original three packets has been reduced by two-thirds. Packets can be aggregated up to 4,000 bytes, or approximately three times the length of normal packets. Benchmarks have shown that packet aggregation can improve data throughput rates on a WiFi network by as much as 30 percent.

Although packet aggregation can be particularly effective at increasing throughput rates, the network's transmitters should have a certain level of intelligence in order to sense the overall traffic conditions on the network. Otherwise, packet aggregation can actually decrease the network's throughput. This occurs when traffic on the network has bogged down the transfer rate to 11 Mbps or less. At this point and below, the longer packets produced by packet aggregation actually slow down traffic on the network even further.

Another rate-increasing technique, packet bursting, is actually defined in the 802.11e version of the WiFi standard. Similarly to packet aggregation, bursting reduces overhead traffic on the network and thereby increases the effective transmission rate for payload data traffic. Bursting operates at the Media Access Control (MAC) layer of an 802.11 network. It reduces overhead by reducing to a minimum the Distributed Interframe Space (DIFS) and the back-off period that separates packets on the network. In this way, bursting delivers more data without increasing traffic on the network, avoiding some of the collision problems that increased traffic can cause.

Rounding out robustness
Increased robustness, or greater immunity to both in-band and out-of-band RF interference, has a double whammy effect. It can impact positively both the throughput rate as well as the range of a WiFi network. Equipment manufacturers must be aware of the probable sources of RF interference and design-in countermeasures. Interference to 802.11 signals can come from household appliances or from other wireless technologies like Bluetooth or UltraWideband (UWB). In addition, separate WiFi networks in close proximity can cause adjacent channel interference (ACI) for each other.

For out-of-band interference, digital filtering on receiver inputs can improve robustness. And, when possible, collaborative power control among wireless technologies that share the 2.4 MHz band can be quite effective. With the rapid convergence of wireless technologies in today's marketplace, this is becoming much more feasible. For example, more and more wireless smartphones are being equipped with WiFi and Bluetooth capabilities. In this type of device, the two technologies can coordinate their use of the wireless spectrum to the benefit of both.

Happy Users
For WiFi equipment manufacturers looking to build market share, user satisfaction is essential. Unfortunately, it's not one-dimensional. Data throughput rates will always receive an unfair share of attention, but other metrics like range and robustness are just as essential to ensuring happy customers. And the only way to add to a customer base is to retain the hard-fought users a manufacturer has already earned.

D'Andre Ladson is the WLAN subsystem manager for Texas Instruments Residential Gateway and Embedded Systems (RGES) business unit. Ladson manages new product development, expanding current product lines, monitoring market trends and extending the company's roadmap.