Computerworld - As the popularity of wireless devices at businesses (Wi-Fi, PDAs and RFID) and in homes (PCs, Bluetooth devices, home entertainment and so on) accelerates, the need for high-quality, high-throughput wireless bandwidth is emerging as a key constraint on growth.
To address this demand, new innovations are needed. Emerging specifications, such as 802.11n and 802.16, open new areas in which Intel has performed extensive research: the use of smart antennas, which can improve signal quality and the distances over which wireless signals operate. Depending on their specific design, smart antennas can also increase the point-to-point or network throughput of wireless devices.
What Are Smart Antennas?
Television and radio broadcasts as we know them use a traditional system of communication:Oone antenna transmits a signal and a second antenna receives it. This configuration is called single-input, single-output (SISO). Many wireless systems today use the same basic design: one antenna at the access point transmits and another, in a notebook computer or other device, receives the data.
New radio technologies are increasingly examining designs in which transmission and reception use multiple antennas at both ends of the communication. This approach is called multiple-input, multiple-output (MIMO), and it is shown in Figure 1. To handle multiple signals, these MIMO systems need greater smarts than simple SISO configurations. As a result, these multiple antenna systems are referred to as smart antenna systems.
The basic principle of smart antennas is that each antenna receives a separate and distinct signal. Depending on how the wireless system is set up, the receiver might combine the signals from multiple signals to improve the quality of data reception; or it might extract multiple data streams to increase bandwidth.
Extending Range by Improving Signal Quality
Technologies that compare the quality of signals from two antennas and choose the stronger one can substantially increase signal quality. Let's examine a common scenario in which a user is working across a Wi-Fi connection in a busy public place. When the Wi-Fi access point transmits data, the signal is subject to fading if an object (such as a person walking by or standing between the two devices) appears between the access point and the receiving device. If both signals were received by a device with two antennas, the device would switch to the better signal if the one it was using began to fade, a technique called switched diversity.
This simple approach monitors the two antennas and switches back and forth as signals gain strength or fade in relation to each other. Signal fade is the
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