new ccna logo

new ccna logo.Diversity coding ( diversitycoding) oPrecoding is a coding technique that makes use of multiple antennas and multiple paths and is discussed in detail in Chapter 3. 802.lln uses the Transmission Beamforming ( TxBF,TransmitBeamForming) technique to adjust and send signals from individual antennas when there are multiple transmission antennas, so that the signal strength can be significantly improved even when the receiver is far from the transmitter. This technique is generally used when there is only a single antenna at the receiving end and it cannot be moved. If the receiver can be moved, the reflection characteristics will change and beamforming will not be adjusted. This adjustment is called ChannelStateInformation (CSI) 0.Spatial multiplexing splits the signal into several low-speed streams and sends them out from different antennas. Each low-speed stream is sent at the samefrequency. The number of low-speed streams is limited to the minimum number of antennas on the transmitter or receiver side. If the AP has 4 antennas and theclient has 2 antennas, then the number of low-speed streams is 2.Although 802.1 In is still a draft standard, the Wi-Fi Alliance is in the process of issuing certificates to 802.1 In devices. The Wi-Fi Alliance is doing this with the interim IEEE 802.1In draft 2.0.802.11H differs from other 802.11 protocol standards in other ways as well. For example, at the physical layer, the approach to sending signals views reflections and interference as advantages rather than problems. Another way to increase throughput is through channel aggregation. In 802.11n, two channels are aggregated together to increase throughput. O802.11n uses 20 MHz and 40 MHz channels, and the 40 MHz channel in 802.11n is actually a combination of two 20 MHz channels adjacent to each other.The client in an 802.11n environment is quite complex and thus 802.11n is combined with OFDM. This allows for the use of more subcarriers in the 48 to 52 range.78 Chapter 6 802.11WLAN Protocol OverviewWith 802.11n,data rates of up to 32Mbit/so