Carrier Aggregation Concept: Single vs. Multiple Carriers
LTE Advanced achieves its extremely high data rates by increasing the effective bandwidth of the radio channel; the bigger the channel, the more data it can carry.
LTE Advanced radio channels are still limited to a maximum bandwidth of 20MHz, in order to provide backwards compatibility with non-LTE-Advanced devices; however, multiple channels can be logically grouped together through carrier aggregation, up to a total of 100MHz. Data is sent in parallel over the individual physical channels, allowing more bits to be transmitted in a given amount of time.
The aggregated channels may be adjacent in the radio spectrum; they may be separated within the same band, or they may be taken from different bands. This flexibility gives the operator the ability to offer significantly higher data rates to their subscribers.
By combining these slices of spectrum into a large aggregated channel, the operator can compete effectively with other service providers, without acquiring large chunks of spectrum.