Explain Handoff and power control in 3G system

Power control is one of the main features in 3rd generation cellular CDMA systems. Power control reduces the interference in the system and hence increases the capacity. The basic operation of power control implementation in 3G CDMA systems. The inner loop and the outer loop algorithms are explained where the power commands are sent at a high rate and uncoded resulting in high error rate in receiving them. The problem of errors in the power control commands becomes worse during soft handoff where the terminal communicates with more than one base station simultaneously.

Handoff Action: When a handoff order is received, the mobile station is at DTX high state and stays at that state. If the mobile station is at DTX low state it must enter the DTX high state and wait for 200 ms before taking the handoff action.

Handoff to a digital traffic channel is described as follows:

  1. Turn on signaling tone for 50 ms, turn off signaling tone, turned off transmitter which was operating on the old frequency.

  2. Adjust power, tune to new channel, set stored DVCCs to the DVCC field of the received message.

  3. Set the transmitter and receiver to digital mode, set the transmit and receive rate based on the message-type field.

  4. Set time slot based on the message-type field.

  5. Set the time alignment offset to the value based on the TA field.

  6. Once the transmitter is synchronized, enter the conversation task of the digital traffic channel.

Hand off between two different cells

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