Inter Symbol Interference Analysis

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Register to read the introduction… Morse first noticed it on the transatlantic telegraph cables transmitting messages using dots and dashes and it has not gone way since. He handled it by just slowing down the transmission. Amplitude

Figure 8 101101 transmitted data
Figure 8 shows a data sequence, 1,0,1,1,0, which wish to be sent. This sequence is in form of square pulses. Square pulses are nice as an abstraction but in practice they are hard to create and also require far too much bandwidth. Amplitude


Figure 9 Received data
Figure 9 shows each symbol as it is received. It also shows what the transmission medium creates a tail of energy that lasts much longer than intended. The energy from symbols 1and 2 goes all the way into symbol 3. Each symbol interferes with one or more of the subsequent symbols. The circled areas show areas of large interference.
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Then faster chips came and allowed to do signal processing controlling ISI and transmission speeds increased accordingly.
2.3 Multipath propagation
Multipath propagation is caused by multipath receptions of the same signal. in city environment or indoors signal travels along different path from transmitter (Tx) to receiver (Rx). * Signal components received at slightly different times (delay) * These components are combined at Rx * Results as a signal that varies widely in amplitude, phase or polarization
2.3.1 Multipath fading
When the components add destructively due to phase differences amplitude of the received signal is very small. At the other times the components add constructively the amplitude of received signal is large. This amplitude variations in the received signal called signal fading, are due to the time-variant characteristics of the channel.
Relative motion between Tx and Rx (or surrounding objects causing e.g. reflection) causes random frequency modulation.

Figure 11 Multipath propagation
Each multipath component has different Doppler shift. The Doppler shift can be calculated by using: fd=Vλcosα V is the velocity of the

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