What is Carrier aggregation cross carrier scheduling in LTE?

Question

WHY there is not resource allocation in carrier aggregation . there is resource allocation only on PCC ? how to debug this issue

Answer 1

When LTE carrier aggregation is used, it is necessary to be able to schedule the data across the carriers and to inform the terminal of the DCI rates for the different component carriers. This information may be implicit, or it may be explicit dependent upon whether cross carrier scheduling is used.

Enabling of the cross carrier scheduling is achieved individually via the RRC signalling on a per component carrier basis or a per terminal basis.

When no cross carrier scheduling is arranged, the downlink scheduling assignments achieved on a per carrier basis, i.e. they are valid for the component carrier on which they were transmitted.

For the uplink, an association is created between one downlink component carrier and an uplink component carrier. In this way when uplink grants are sent the terminal or UE will know to which uplink component carrier they apply.

Where cross carrier scheduling is active, the PDSCH on the downlink or the PUSCH on the uplink is transmitted on an associate component carrier other than the PDCCH, the carrier indicator in the PDCCH provides the information about the component carrier used for the PDSCH or PUSCH.

It is necessary to be able to indicate to which component carrier in any aggregation scheme a grant relates. To facilitate this, component carriers are numbered. The primary component carrier is numbered zero, for all instances, and the different secondary component carriers are assigned a unique number through the UE specific RRC signalling. This means that even if the terminal or user equipment and the base station, eNodeB may have different understandings of the component carrier numbering during reconfiguration, transmissions on the primary component carrier can be scheduled.

Answer 2

Carrier Aggregation in LTE: It Extends the maximum transmission bandwidth, up to 100 MHz, by aggregating up to five LTE carriers – also known as component carriers (CCs)

And motivation for carrier aggreagations are:
– Achieve wide bandwidth transmissions
– Facilitate efficient use of fragmented spectrum
– Efficient interference management for control channels in heterogeneous networks

Carrier agrreagation can be of 3 types:

 1. Intra band contiguous allocation
 2. Intra band non-contiguous allocation
 3. Inter band non contiguous allocation

So, in carrier aggregation we are aggregating component carriers(CCs).

Resources can be assigned to a UE in two ways:

 1. Same-carrier scheduling – separate PDCCH for each CC
 2. Cross-carrier scheduling – common PDCCH for multiple CCs 
     Main motivation for cross carrier scheduling is:
        – Load balancing
        – Interference management for control channels in heterogeneous networks
    PCell(Primary serving cell) can not be cross scheduled, it is always scheduled
    through its own PDCCH

For example : In the below image,CC1 of Macro Cell would cause high interference to CC1 of pico cell, therefore pico cell uses CC2 for PDCCH messages to schedule PDSCH transmission on CC1 . And Macro cell uses CC1 to schedule PDSCH transmission on both CC1 and CC2