Massive carrier aggregation in LTE-advanced pro: impact on uplink control information and corresponding enhancements

3GPP began standardization of carrier aggregation (CA) in LTE-A Rel. 10 to combine up to five component carriers (CCs) for facilitating wider transmission bandwidth of 100 MHz. Further enhancements followed in Rel. 11 and Rel. 12 to enable features such as aggregation of carriers between time-division duplex (TDD) and frequency-division duplex (FDD) frame structures. In LTE-A Pro Rel. 13, massive CA enhancements were defined to combine more than five CCs with the initial focus on the downlink. While the benefits of CA have been evident, operating an even larger number of downlink carriers results in increased overhead on the uplink as there is a need to send the combined control information for all the CCs. In this article we give an overview of the standardized enhancements, their impact on uplink control information overhead and its transmission, new control channel formats and their link level investigation in 3GPP-defined simulation assumptions.