Now the number of connecting devices exploding!! So the capacity of the systems should grow in the same proportions!! Here comes another savior technique : Multiple access..
These schemes are used to allow a number of mobile users to share simultaneously a finite amount of radio spectrum. The sharing of spectrum is essential as the available spectrum is not going to increase with the number of devices! High capacity can be achieved by simultaneously allocating the available bandwidth/channels to multiple users.
Lets start withe basics! The duplexing techniques. There are two ways
1. Time Division Duplexing : Here multiple users share single radio channel by taking turns in the time domain. Individual users are allowed to access the channel in assigned time slots, and each duplex channel has both a forward time slot and a reverse time slot to facilitate bidirectional communication.
2. Frequency Division Duplexing : Here every user will have two distinct bands of frequencies. The forward band provides traffic from the base station to the mobile, and the reverse band provides traffic from the mobile to the base station.
Now the "Multiple Access".. The following diagram shows the multiplexing techniques.
1. FDMA : Frequency Division Multiple Access
Individual channels are assigned to every user.
2. TDMA : Time Division Multiple Access
First the whole radio spectrum into slots, one user in each slot is allowed to
transmit or receive at any given time.
3. CDMA : Code Division Multiple Access
This is a type of spread spectrum techniques.All the users can use a wide band for entire time but each has a different psuedo-random code assigned.
I hope now some of the terms I mentioned while writing about 3G and 4G standards make more sense.
These schemes are used to allow a number of mobile users to share simultaneously a finite amount of radio spectrum. The sharing of spectrum is essential as the available spectrum is not going to increase with the number of devices! High capacity can be achieved by simultaneously allocating the available bandwidth/channels to multiple users.
Lets start withe basics! The duplexing techniques. There are two ways
1. Time Division Duplexing : Here multiple users share single radio channel by taking turns in the time domain. Individual users are allowed to access the channel in assigned time slots, and each duplex channel has both a forward time slot and a reverse time slot to facilitate bidirectional communication.
2. Frequency Division Duplexing : Here every user will have two distinct bands of frequencies. The forward band provides traffic from the base station to the mobile, and the reverse band provides traffic from the mobile to the base station.
Now the "Multiple Access".. The following diagram shows the multiplexing techniques.
1. FDMA : Frequency Division Multiple Access
Individual channels are assigned to every user.
2. TDMA : Time Division Multiple Access
First the whole radio spectrum into slots, one user in each slot is allowed to
transmit or receive at any given time.
3. CDMA : Code Division Multiple Access
This is a type of spread spectrum techniques.All the users can use a wide band for entire time but each has a different psuedo-random code assigned.
I hope now some of the terms I mentioned while writing about 3G and 4G standards make more sense.
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