In a 4G-LTE environment the available bandwidth is split into channels, or component carriers. The standard sizes of these are 1.4, 3, 5, 10, 15 or 20MHz. The operator will split their available bandwith into these component channels and a user will have that channel available - so 20MHz is the maximum available. To get more space, or indeed use the narrower channels better, some way to combine these component carriers will be needed.
To increase the data rate for the given user there are only two options namely, widen the channel or combine channels. This latter option is available in 4G+ and called carrier aggregation. This allows the various channels to be combined up to a maximum of 5 channels. So there is a theoretical maximum channel size of 100MHz. This is theoretical as the MNOs have only 35MHz blocks of bandwidth available to the 2.6GHz 4G network.
Note that different carrier aggregation can be implemented on the up and down links min order to make best use of the available bandwidth
With these basics quite complex carrier aggregation can be used. For the operator a large contiguous bandwidth makes channel aggregation easier and more efficient. Currently the 4G and 5G bandwidth allocated to operators is small and spread over various bands making carrier aggregation both difficult and necessary. It is generally accepted that a contiguous allocation of 100MHz of bandwith would make the transmission of data more efficient. THREE, with their purchase of UKBroadband managed to acquire a significant amount of contiguous bandwidth for 5G thus making their bandwidth management through carrier aggregation simpler. OfCom is promoting some refactoring of broadband in the UK to give more contiguous space.
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