By Jeff Kabachinski, MS-T, BS-ETE, MCNE
The newest version of wireless networks is just around the corner. New IEEE802.11ac (11ac) wireless products are expected to start to roll out by the end of summer or fall this year. “Not again!” you might say. “We just finished upgrading to 11n!” (That’s IEEE802.11n.) There will be a lot of discussion about upgrading as 11ac starts to show up in wireless adapters and access points (AP). The intent of this month’s installment of “Networking” is to help arm you with the concepts and terminology surrounding 11ac and also so you can be a part of those discussions.
11ac makes some giant strides beyond 11n. 11ac focuses solely on the 5 GHz spectrum, rather than get involved in any way with the overcrowded 2.4 GHz spectrum. That is probably the first good decision the IEEE committee made—to stay out of troubled waters. One of the things that make the 2.4 GHz range so congested is the amount of wireless backhauling. Backhauling occurs when an AP sends data beyond the targeted end receiver. It may find certain pathways are typically blocked due to excess traffic and knows if it goes to an out-of-the-way location, that location may have a cleaner and cheaper route to the end destination. This is called backhauling and adds to the total amount of traffic on the network. Maybe this is why flying from Baltimore to New Orleans is cheaper if you go through San Francisco first!
11ac makes some giant strides beyond 11n and focuses solely on the 5 GHz spectrum, rather than get involved with the overcrowded 2.4 GHz spectrum.
There will be essentially two slightly different versions of the 11ac standard. Some wireless equipment manufacturers will jump on the first or draft version to be ahead of the competition. We might see early adopters releasing products in the second half of this year, as mentioned above. It is expected that the second or final standard is to be completed in early 2014. Other manufacturers, like Motorola for instance, will wait for the final standard to occur and will most likely have products available by late 2014 or early 2015.
No matter what you think about upgrading to 11ac, it will happen eventually over the next several years. Therefore, expect a mixed 11n and 11ac environment to deal with for quite some time. 11ac brings very-high-throughput possibilities as the fifth generation of wireless networking. Besides ensuring that 11ac installations are backward compatible, clinical/biomedical engineering departments will also need to make sure that the hospital’s wired network can handle the higher data rates and extra traffic that the speedy wireless network will bring.
Here are three major concepts to be aware of:
Quadrature amplitude modulation, or QAM, refers to the number of ways a symbol may be encoded. It is a scheme to pack more bits into each transmission. QAM makes use of four different amplitudes to represent each chip or piece of a symbol. A symbol is a digital one or zero—the basis of digital communications. 16 QAM creates a symbol of 4-bits through 16 different signal points in terms of variation of amplitude and phase. The more bandwidth that can be provided will allow more ways to represent a chip, thus allowing more chips. More chips equals more symbols, and more symbols equals more data. With 11ac this can go up to 256 QAM playing its part in allowing 11ac wireless systems the ability to reach 7 Gigabits per second (Gbps) rates.
At the moment, it looks as though this may be short-range speeds in the neighborhood of 20 to 30 feet, and rates of 3.4 Gbps will be more typical. It has been compared to throwing darts at a dartboard. With a dartboard divided into four equal spaces, it is not difficult to consistently hit a particular quadrant. As that approaches 256 slices, or dartboard partitions, the pathway needs to be clear to get the best shots. This means no noise, interference, or multi-paths to deal with and a high signal-to-noise ratio (S/N) to be as accurate as possible to consistently hit a particular 1/256th of the dartboard.
Steering the Beams
It also highly depends on the skill of the dart thrower. In 11ac this is in the beamforming. In addition, the more bandwidth you have will also help—or the larger the dartboard. This facilitates the newer technologies—the increased skill of the dart thrower.
Beamforming is a method to use at least two antennas to steer a transmitted radio beam in a predetermined direction, effectively ignoring surrounding interfering signals and noise. Signals sent on separate antennas can rejoin at the receiving antennas to constructively add up. Phases of the transmitted beams are adjusted to steer the beams, thus providing overall gain at the receiver. In 11n an AP uses beamforming for transmitting signals to increase overall gain and S/N ratios. With more gain and higher S/N ratios, higher data rates can be achieved while reducing the number of retries. Knowing the recipient and the channel state information (CSI) also helps the transmitter estimate and compute the steering matrix control data applied to the signals being transmitted.
Beamforming is a method to use at least two antennas to steer a transmitted radio beam in a predetermined direction.
Beamforming does add a little overhead to the system as it sends out sounding packets to gather CSI. This is done continually as the CSI changes as the AP or the wireless adaptor move and the steering matrix needs adjusting. Note that especially by adding multiple-input and multiple-output (MIMO) techniques, the added time for sounding and computing still pales to the overall beneficial aspects from beamforming.
MIMO was the basis for 11n. Wi-Fi Certified 802.11n APs have dual-band radios that use three MIMO antennas to carry 450 Mbps (called 3×3 MIMO for three transmit and three receive antennas where each pair carries a third of the signal, or 150 Mbps). MIMO is still being used but taken a step further in 11ac as multiple user MIMO (MU-MIMO). MU-MIMO is also fun to say—as in “Moo-Me-Moe.” If your institution is headed to 11ac and someone from IT is wandering around muttering MU-MIMO, don’t worry; they are working on the next iteration!
MIMO has to do with antennas. Adding more antennas allows the use of space division multiplexing (SDM), providing intelligent antenna systems the ability for improved transmission speeds and better quality with longer-distance radio frequency connections.
Single-user MIMO (SU-MIMO) means one wireless connection per AP. As mentioned earlier, in 11n, a 3×3 antenna array can allow three simultaneous data links or three diverse data streams for a max of 450 mbits/s. Although so much of this is dependent on clear and wide bandwidth, you won’t get the fastest speeds at the longest distances. MU-MIMO in 11ac allows up to four wireless devices to be simultaneously served by one AP. This reduces congestion while allowing more end users to get connected.
11ac brings a major technology upgrade with somewhat minimal changes. The benefits of these improvements are needed in today’s data-rich communication demands, such as transmitted video where HD Wi-Fi displays need 1.5 to 3 Gbps data rates. The added CSI discovery and consequential recomputing time needed to continually form beams is outweighed by the benefits of using this very-high-throughput schemology (the science of creating new schemes and processes)—the fifth generation of wireless networking. 24×7 Networking March 2013
Jeff Kabachinski, MS-T, BS-ETE, MCNE, has more than 20 years of experience as an organizational development and training professional. He is the director of technical development for Aramark Healthcare Technologies in Charlotte, NC.