For a better understanding of 3G systems and basics of 4G systems, it is essential to understand the concept of modulation and different modulation techniques.
Lets understand the word first!! I traced back to the origin of this word, It seems that people from 15th and 16th century defined it as "regulate, measure off properly, measure rhythmically; play, play upon," or "act of regulating according to measure or proportion" . This word was used in context of music those days. Though we are discussing it in telecommunication systems, the purpose and meaning of ''modulation remains the same."
It is necessary to understand modulation before we start discussing 4G as we are going to encounter words like orthogonal frequency modulation in that standard.
Lets start with analog modulation. Two basic techniques of modulation.
1. Amplitude modulation : Here the frequency of the modulated signal is kept constant while the amplitude is varied by the message signal. Thus, AM signals have all their information in the amplitude of the carrier.
2. Frequency Modulation : In this technique, the amplitude of the modulated carrier signal is kept constant while its frequency is varied by the modulating message signal. Thus, FM signals have all their information in the phase or frequency of the carrier.FM is a part of a broader technique called Angle Modulation.
Now lets move on to Digital Modulation. In digital systems, the modulating signal is represented as a sequence of pulses/symbols where each symbol has m finite states Each symbol represents n bits of information, where n = log2m bits/symbol.
There are four major classes of Digital modulation techniques.
1. Linear Modulation Techniques : The amplitude of the transmitted signal varies linearly with the modulating digital signal. These techniques are bandwidth efficient.
2. Constant Envelope Modulation : The amplitude of the carrier is constant, regardless of the variation in the modulating signal. These are power efficient.
3. Combined Linear and Constant Envelope Modulation Techniques : Here digital baseband data may be sent by varying both the envelope and phase (or frequency) of an RF carrier. These are efficient techniques in terms of power and bandwidth.
4. Spread Spectrum Modulation Techniques : Spread spectrum techniques employ a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth.
Lets understand the word first!! I traced back to the origin of this word, It seems that people from 15th and 16th century defined it as "regulate, measure off properly, measure rhythmically; play, play upon," or "act of regulating according to measure or proportion" . This word was used in context of music those days. Though we are discussing it in telecommunication systems, the purpose and meaning of ''modulation remains the same."
It is necessary to understand modulation before we start discussing 4G as we are going to encounter words like orthogonal frequency modulation in that standard.
Lets start with analog modulation. Two basic techniques of modulation.
1. Amplitude modulation : Here the frequency of the modulated signal is kept constant while the amplitude is varied by the message signal. Thus, AM signals have all their information in the amplitude of the carrier.
2. Frequency Modulation : In this technique, the amplitude of the modulated carrier signal is kept constant while its frequency is varied by the modulating message signal. Thus, FM signals have all their information in the phase or frequency of the carrier.FM is a part of a broader technique called Angle Modulation.
Now lets move on to Digital Modulation. In digital systems, the modulating signal is represented as a sequence of pulses/symbols where each symbol has m finite states Each symbol represents n bits of information, where n = log2m bits/symbol.
There are four major classes of Digital modulation techniques.
1. Linear Modulation Techniques : The amplitude of the transmitted signal varies linearly with the modulating digital signal. These techniques are bandwidth efficient.
2. Constant Envelope Modulation : The amplitude of the carrier is constant, regardless of the variation in the modulating signal. These are power efficient.
3. Combined Linear and Constant Envelope Modulation Techniques : Here digital baseband data may be sent by varying both the envelope and phase (or frequency) of an RF carrier. These are efficient techniques in terms of power and bandwidth.
4. Spread Spectrum Modulation Techniques : Spread spectrum techniques employ a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth.
