ase 10 and al- lowed up to five 20-MHz carriers to be aggregated-allowing for a total bandwidth up to 100 MHz. In Release 13, this was extended to support up to 32 carriers, allowing for the total bandwidth to rise to 640 MHz. Note that the aggregated component carrier does not need to be contiguous in frequency domain (meaning each carrier can be from a different band in the available spectrum). This means that, as shown in Figure 10-19, different combinations of inter- and intra-band CA are possible, namely Intra-band CA Using contiguous carrier components (frequencies adjacent to each other) Using noncontiguous carrier components (nonadjacent frequencies) Inter-band CA using noncontiguous carrier components Intra-band contiguous Frequency band A Frequency band B ((Q)) Intra-band noncontiguous Frequency band A Frequency band B Inter-band Frequency band A Frequency band B (a) Carrier Aggregation (b) Dual Connectivity Figure 10-19 Different Types of Carrier Aggregation When a pair of eNBs support CA, only a very small time interval is available to complete the scheduling for all the carrier components participating in sending the data frame. This means that a tightly coupled, low-latency connection is required between these eNBs to schedule and control their contribution. Additionally, they both need to be very closely aligned in time/phase because they are both cooperating to send related data to the UE at the same time. Given these requirements, it is safe to assume that the participating antennas are either co-located or connected to their eNB with a direct link. Specifically, for intra-band contiguous CA, the synchron- ization requirement is SO tight that one can assume that all the antennas in the CA scheme are in- stalled at the same location. Carrier Aggregation synchronization requirements are outlined in Table 10-7. Table 10-7 Time Synchronization Requirement for Transmission Diversity and MIMO Time Alignment Refer- Application Error LTE intra-band noncontiguous CA with or without MIMO or Tx diversity 26