Before revision: Alternatively a bus can use modulation or encoding such as PAM4 which groups 2 bits into symbols which are then transferred instead of the bits themselves, and allows for an increase in data transfer speed without increasing the frequency of the bus.
After revision: Alternatively a bus can use modulation or encoding such as URL which groups 2 bits into symbols which are then transferred instead of the bits themselves, and allows for an increase in data transfer speed without increasing the frequency of the bus.