livro cisco 200-301

livro cisco 200-301.data rate, QPSK is used in conjunction with Barker coding. At 5.5 Mbit/s data rate, QPSK also works, but is encoded as CCK-16. At llMbit/s data rate, QPSK also works, but is encoded as CCK-128O(7) OFDM OFDM is not considered as a spread spectrum technology but is used for modulation purposes in wireless networks. Using OFDM technique, the highest data rate can be obtained and data corruption due to interference can be suppressed to the maximum extent. OFDM defines a number of channels in a frequency range. These channels are further divided into more small bandwidth subcarriers. The channel bandwidth is 20MHz and the subcarrier bandwidth is 300KHZ.The end result is that each channel is divided into 52 subcarriers. Each subcarrier has a lower data rate, but data can be sent in parallel through the subcarriers at the same time. This is how higher data rates are achieved.OFDM is not used in 802.11b, because 802.11b devices use DSSS technology. Both 802.11g and 802.11a use the14 Chapter 1 Introduction to Wireless Networking ConceptsOFDM, but they are applied slightly differently because 802.llg is used to work with 802.11b devices in the 2.4GHz range. Chapter 2 explains the differences in implementing OFDM implementations.2. MIMOMIMO is a technology used in the new 802.11n specification. Although the 802.11n specification has not yet been approved by the IEEE as of this writing, many vendors are already shipping their products and claiming support for the specification. However, you still need to know something about this technology. A device using MIMO technology uses multiple antennas to send signals in addition to multiple antennas to receive signals (usually two or three)° MIMO technology provides data rates above 100Mbit/s by sending multiple streams of data on a single channel at the same time. That is, if data rates above 100 Mbit/s are desired, multiple data streams should be sent over a bonded channel rather than a single channel. With advanced signal processing, data can be recovered after two or more spatial streams have been sent.By using MIMO technology, an AP can talk to a non-MIMO capable (non-MIMO.capable) device and still gain about 30% in performance over a standard 802.3. dynamic rate shifting