livro ccna 200-301 pdf

livro ccna 200-301 pdf.11 8-code slice encoding 4-bit CCK encoding DSSS quadrature phase shift keyingAmplitude modulation is one of the easy to understand modulation methods. Amplitude modulation sends information based on the amplitude of the signal. For example, +5V is 1, -5V is 0. Due to external factors, the amplitude of the signal may change, which in turn will change the information you are sending. Therefore AM is not a suitable solution for sending important data. However other factors, like frequency and phase, are unlikely to change. 802.11b is all about using phase to modulate data. In particular, BPSK and QPSK are also used in 802.11b.(5) BPSKRemember that the phase is the timing between the peaks of the signal. In fact, this concept needs to be expanded further so that you really understand the concepts of BPSK and QPSK. First look at the waveform in Figure IV. This waveform, or motion, occurs in exactly one cycle time.1.2 Basic Topics 13Figure 1-4 illustrates the next step in determining phase. The phase is the difference between two waveforms of the same frequency. If the two waveforms peak at the same moment, they are said to be in phase ( imphase), or 0. If the two waveforms peak at different moments, they are said to be out of phase ( gt-o^phase). Phase-Shift Keying ( PSK, Phase-ShiftKeying) represents information by changing the phase of a signal.BPSK is the simplest type of PSK modulation. In BPSK, the two phases used differ by 180' BPSK can be modulated by 1 bit per symbol. In simple terms, this means that 180. phase shift is 1, and 0. phase shift is 0, as shown in Figure 1-5.Figure 1.5 Phase Shift Coding802.11 also uses Quadrature Phase Shift Keying (QPSK, QuadraturePhase-ShiftKeying), which is discussed below.(6) QPSK is coded at 1 bit per symbol in BPSK. This coding method is only suitable for low data rate cases. QPSK has the ability to encode 2 bits per symbol, which means that QPSK is twice the effective data rate of BPSK in the same bandwidth. At 2Mbit/s data rate, QPSK is compatible with BPSK.