University:
College
Course:
College Engineering
Academic year:

2023
Views:

276

Pages:

2
Author:

Dipin K.

Handoff To keep the call active, the Handoff procedure should be completed while the MS (the bus) is in the overlap region. Hard handoff The MS connects with only one BS at a time. And there is usually some interruption in the conversation during the link transition. Soft handoff The two BSs are briefly simultaneously connected to the MU while crossing the cell boundary. As soon as the mobile's link with the new BS is acceptable, the initial BS disengages from the MU. Hard handoff 1. MU temporarily suspends the voice conversation by sending a link suspend message to the old BS. 2. MU sends a handoff request message through an idle time slot of the new BS to the network. 3. The new BS sends a handoff ack message and marks the slot busy. 4. The MU returns the old assigned channel by sending a link resume message to the old BS. MU continues voice communication while the network prepares for the handoff. 5. Upon receipt of a handoff request message, the new BS sends a handoff ack message and reconfigures itself to effect the handoff. 6. The MSC inserts a bridge into the conversation path and bridges the new BS. 7. Finally, the network informs the MU to execute the handoff via both the new and old BSs by sending the handoff execute message. 8. MU releases the old channel by sending an access release message to the old BS. 9. Once the MU has made the transfer to the new BS, it sends the network a handoff complete message through the new channel, and resumes the voice communication. The network removes the bridge from the path and frees up the resources associated with the old channel. Soft Handoff 1. MU sends a pilot strength measurement message to the old BS, indicating the new BS to be added. 2. The old BS sends a handoff request message to the MSC. If the MSC accepts the handoff request, it sends a handoff request message to the new BS. 3. The BS sends a null traffic message to the MU to prepare the establishment of the communication link. 4. The new BS sends a join request message to the MSC. The MSC bridges the connection for the two BSs, so that the handoff can be processed without breaking the connection. 5. The new BS sends a handoff ack message to the old BS via the MSC. The old BS instructs the MU to add a link to the new BS by exchanging the handoff command and handoff complete messages. 6. The old BS and the MSC conclude this procedure by exchangin8 the required handoff information. The quality of the new link is guaranteed by the exchange of the pilot measurement request and the pilot strength measurement message pair between the MU and the new BS. Three issues need to be considered for handoff management:    Handoff detection Channel Assignment Radio link Transfer Handoff detection: Find the suitable time for handoff. Channel Assignment: Assigning required channel and bandwidth for the user to continue the call. Radio link Transfer: Transferring the call from one base station to other is the change of radio link.