The latest upgrade to the family of IEEE 802.11 standards is identified as IEEE 802.11n. Users of this new process will notice two improvements with this improved wireless technology. They will find that significantly greater speeds and ranges can be achieved over the existing standards.
Specifically, 802.11g products, which have a theoretical maximum throughput speed of 54Mbit/sec, typically providing real-world speeds of 22Mbit/sec to 24Mbit/sec. In contrast, IEEE 802.11n networks are providing real-world speeds of 100Mbs to 140Mbs.
The achievable range of IEEE802.11n is harder to quantify because it is affected by many variables, such as physical barriers that could block the signal. However, testing shows that 802.11n equipment typically delivers more than twice the range of 802.11g equipment at any given throughput speed.
The wireless networking topology in a company facility is usually unique to the physical plant and often fills specific niches, such as providing networking in conference rooms, lunch rooms, or in temporary or under-construction office space. In the past, the lack of full deployment of wireless is understandable, given the fact that wired Ethernet provides greater reliability and speeds. In addition, the use of Layer-2 Ethernet switches provides a segmented collision-domain network. On the other hand, wireless-LANs usually provide slower speeds and a shared bandwidth.
The new 802.11n technology is expected to solve the throughput problem for business users, opening the way to the more effective use of far more applications such as wireless voice over IP, and more effective video conferencing sessions.
The question I am most often asked by my students is “How is 802.11n different from the current generations of Wi-Fi?”
The basic answer is that the 802.11n standard uses some new technology and updates some of the existing technologies to give wireless LANs more speed and range. The most notable new technology is called multiple input, multiple output (MIMO). MIMO uses several antennas to move multiple data streams from one place to another. Instead of sending and receiving a single stream of data, MIMO can simultaneously transmit three streams of data and receive two. This allows more data to be transmitted in the same period of time. This technique can also increase range, or the distance over which data can be transmitted.
The underlying capability of MIMO lies in its ability to take multipath reception, which used to be an undesirable and unavoidable byproduct of radio communications, and convert it into a distinct advantage that actually multiplies transmission speed and improves throughput.
Multipath radio reception has always produced undesirable results, no matter what the frequency range used. As an example, you are in a car in downtown Chicago, listening to the radio. You know that your car’s antenna is receiving the direct signal from the station’s transmitter. But, your radio is also receiving additional signals of that same broadcast from many different directions. This phenomenon is caused because buildings, wires, geographical features such as water tanks and other structures, in the area between the sender and the receiver, can reflect or refract those signals. The end result is that each of these additional signals arrives at your car radio via a different path at a slightly different time. These additional signals are always out of phase with the original and will randomly boost or cancel out parts of the original signal.
This phase differential introduces noise and distortion that you can hear as your car moves about the city, in the form of signal fading, intermittent reception, and sudden signal dropouts. In digital communications, these factors can cause a reduction in data speed and an increase in the number of errors.
In the past, adding antennas, as some wireless systems do, helps sort out signals, allowing the receiver to pick the antenna getting the strongest signal at any given point. The selection process is performed through a software algorithm. Different manufactures have offered different products using unique antenna arrays. For instance, one major manufacturer has recently offered products using seven internal antennas, which combine to create up to 127 different antenna patterns. This process is known as diversity reception and although it is not a true MIMO implementation, it is just the beginning of what can be done with multiple antennas.
MIMO, on the other hand, can use the additional signal paths in a positive and productive manner. MIMO can transmit more information and recombine the signals on the receiving end. This process is very much like our ability to use our two ears to readily localize the origin of specific sounds or to isolate and understand one conversation fragment from the midst of assorted cocktail party chatter. Using multiple receivers in this way isn’t a newly discovered phenomenon. It has been used in some radio transmission schemes for at least half a century. But, as with many legacy processes, until recently the amount of signal processing needed has been too expensive to be practical to be implemented in hardware. Now, however, an important factor driving MIMO acceptance today is the availability of inexpensive, high-speed chips that can implement these processes in hardware.
MIMO systems can use spatial multiplexing to distinguish among different signals on the same frequency. Moreover, transmissions can be encoded so that information on each signal can be used to help reconstruct the information on the others. This process is called space-time block coding, and be thought of as a form of parity or other error-detection and –correction.
Although the total acceptance of the IEEE 802.1n standards is still a work in progress, most of the provisions are now being implemented in both private and business networks. A visit to the electronics section of any big-box store will show an amazing range of IEEE 802.11n products available for your home network or small business applications.
Author: David Stahl