The development and future of Wi-Fi - Part 2

The development and future of Wi-Fi - Part 1

Network Administration - In Part 2 of this series, we will continue the discussion by talking about the current state of Wi-Fi and 802.11n technology.

Introduce

In the previous part of this series, we began to introduce the Institute for Electrical and Electronics Engineers (IEEE) and described the development of Wi-Fi technology. In this second part, we will introduce Wi-Fi technology in the most recent form, known as 802.11n.

MIMO

New innovation in 802.11n is the emergence of Multiple Input Multiple Output antennas (MIMO) in Wi-Fi standards. Previous Wi-Fi antenna configurations only use Single Input Single Output (SISO) technology. As its name suggests, MIMO means that there are multiple antennas to receive as well as multiple antennas to transmit data. MIMO is one of three common configurations used for multi-antenna technology. These configurations, as shown in Figure 1, are:

MIMO technology has many benefits for users. First, there are cases where many users have access to the same Wi-Fi resource. For example, in your office there may be a Wi-Fi button located in the waiting room, and you and your colleagues can connect to this button when drinking morning coffee during the coffee break there. Before 802.11n, if there were multiple users accessing the same 802.11n node, the performance would be significantly reduced. With this new technology, each antenna can be assigned to a user and all users (assuming that the number of users is less than or equal to the number of antennas) will not notice a decrease in access speed.

The distribution of antennas

MIMO also has many benefits when there is only one user. Let's go back to the office's scenario scenario. Now assume that only one user is accessing the Wi-Fi button. Although one of your colleagues is using their blackberry cell phone, there is still a short wave being released, or even someone is using a wireless phone. This is an old problem for Wi-Fi. It is a situation in which there is only one person using Wi-Fi but it is very difficult to receive signals because there are too many noise in the environment (electromagnetic noise). MIMO can neutralize this interference by sending the same signal to the same user but on multiple antennas. Users who receive these signals can compare one of the signals together, then decide which signal is real (the signal before being interfered with).

The method for counting this signal interference is called antenna distribution. There are 5 general ways to implement this distribution.

Spatial distribution

When an application uses an antenna distributed spatially, the base station must have multiple antennas, which are physically separated. Usually these antennas will have the same characteristics. The distance between antennas can be any. But often this distance is equivalent to the wavelength of the signal being transmitted. In other cases, antennas can be placed apart into miles. This is the most commonly used antenna distribution scheme that you will see in 802.11n Wi-Fi base stations.

Distributed by style

The pattern distribution is most commonly used with directional antennas. In this antenna distribution scheme, many directional antennas will be placed close to the antenna with a different radiation pattern. This scheme can provide better performance when compared to schemas using a omnidirectional antenna.

Distribution according to polarity

Polarization distribution consists of a pair (or pairs) of antennas, each with an opposite polarity. Since the signals transmitted from one of these antennas have opposite polarity, interference by the signals will also be different. Therefore the receiver will be able to receive better signals, or at least the receiver can use both signals to rebuild the original transmission.

Distributed according to adaptive array

Adaptive arrays consist of an array of antennas that can easily change their polarization patterns. This type of antenna is very expensive and requires a lot of control, and this makes their cost more expensive. For this reason, this type of antenna is hardly suitable for Wi-Fi technology.

Distribution / distribution

Transceiver distribution may occur when a base station has a transmitting antenna and another antenna to receive. There are not many advantages of transceivers in this scheme, although it can save a lot of costs and does not require duplexer duplexers.

Future benefits

We mentioned above that MIMO will bring many benefits to users. But the benefits are not enough, MIMO still has many other benefits.

Dirty Paper Coding

One technology that we find very interesting is the technology called Dirty Paper Coding (DPC). Basically DPC is a mathematical problem and involves coding the signals before transmission. Before explaining what DPC is, allow us to explain what the problem is. Let's go back to the lounge scenario of the office, where you and some of your colleagues are visiting the base station. As I explained earlier, MIMO allows each antenna to be assigned to each user so that each user will use his own base station antenna. However, this makes the signals interfering with each other and reducing the transmission range. At this point the DPC is responsible for solving the problem. Basically, DPC theory tells us that, if you know that both signals are being transmitted, you will know the interference and can change the signals so that the receiver will receive the intended signal.

This may sound simple, but in reality it doesn't work that way. That's because if you change one of the signals, the noise also changes, which in turn requires you to change the other signal, and continue to change the noise. So with complex signals being broadcast on Wi-Fi base stations, it will be very difficult to calculate the required changes for DPC. It is even more difficult to perform fast enough for users to not see delays.

Multi-source for one user

Multi-source for one user (MSSU) means that in this case there is only one user connecting to a MIMO base station. Now, instead of each antenna emitting an identical copy of the data, the data can be split and each antennae can transmit part of the data and can then be reassembled by the receiver. According to the theory of this method, users can receive the same amount of data in half of the time.