Mobile Communications and Digital Signal Processing.
Mobile communications and digital signal processing.
Introduction to mobile radio communications.
Spread spectrum.
Modulation techniques.
Introduction.
Mobile communication has seen an unprecedented increase in the number of users over the past years. Its success in part is due to the various technologies that have been developed. It is not unlike other stationary communication systems in many respects however it does differ in others, one obvious one being the environment the signal and data propagate over.
The generic mobile communication system.
Basically this is a transmitter and a receiver see figure Generic mobile communication. There are many varied and complex techniques associated with such a system the figure serves as a basic introduction. As the signal is communicating over spatial (unguided media) it may encounter obstacles.
[pic]
Figure. Generic mobile communication.
Spread spectrum techniques.
A number of techniques are used in mobile communications that are described as spread spectrum techniques, named because they increase the bandwidth required. This effectively increases the bit rate of the signal and gives the signal a unique characteristic.
• Example the data to be transmitted say a '1' is purposely increased in the number of bits transmitted. • A four times increase could change a '1' into say '1010' • The pattern used depends on the "spreading code" used • Obviously here the bit rate has increased by four but the data is still only '1
Direct sequence spread spectrum. (DS-SS).
The basic technique is shown in the figure basic spread spectrum where two bits of a data signal m(t) are spread by the so called spreading code s(t) here multiplication of the two signals is shown see figure Basic DS-SS using multiplication.
[pic]
Figure. Basic DS-SS using multiplication.
Another way to implement DSSS is to XOR the data stream with the spreading, often the spreading code is a Pseudo noise
Introduction to mobile radio communications.
Spread spectrum.
Modulation techniques.
Introduction.
Mobile communication has seen an unprecedented increase in the number of users over the past years. Its success in part is due to the various technologies that have been developed. It is not unlike other stationary communication systems in many respects however it does differ in others, one obvious one being the environment the signal and data propagate over.
The generic mobile communication system.
Basically this is a transmitter and a receiver see figure Generic mobile communication. There are many varied and complex techniques associated with such a system the figure serves as a basic introduction. As the signal is communicating over spatial (unguided media) it may encounter obstacles.
[pic]
Figure. Generic mobile communication.
Spread spectrum techniques.
A number of techniques are used in mobile communications that are described as spread spectrum techniques, named because they increase the bandwidth required. This effectively increases the bit rate of the signal and gives the signal a unique characteristic.
• Example the data to be transmitted say a '1' is purposely increased in the number of bits transmitted. • A four times increase could change a '1' into say '1010' • The pattern used depends on the "spreading code" used • Obviously here the bit rate has increased by four but the data is still only '1
Direct sequence spread spectrum. (DS-SS).
The basic technique is shown in the figure basic spread spectrum where two bits of a data signal m(t) are spread by the so called spreading code s(t) here multiplication of the two signals is shown see figure Basic DS-SS using multiplication.
[pic]
Figure. Basic DS-SS using multiplication.
Another way to implement DSSS is to XOR the data stream with the spreading, often the spreading code is a Pseudo noise