LTE Advanced: 3GPP Solution for IMT-Advanced

5.6 Band Combinations for Carrier Aggregation

Basically the same band combinations as with the downlink carrier aggregation in Chapter 4 are considered for the uplink carrier aggregation. The use of two uplinks causes additional considerations for the interference and some band combinations may need to be used only with the downlink carrier aggregation. The 3GPP performance work will cover first the downlink band combinations with them being simpler than the uplink ones. The uplink will have some additional issues due to the following:

• It is not desirable to exceed the maximum transmission power thus the power on each of the uplinks on the average is reduced by 3 dB compared to the single carrier UE transmission power.
• The two transmitters may cause additional issues that impact out of band or spurious emissions and thus additional maximum power reduction is likely to be needed.
• In some cases the uplink transmission band may be too close to a downlink reception band. For example the use of the European 1800 MHz and 2100 MHz bands is problematic. The 2100 MHz band uplink transmission band edge at 1920 MHz is only 40 MHz apart from the downlink band edge at 1880 MHz for 1800 MHz band downlink and thus would cause TX noise to leak to the downlink reception band as shown in Figure 5.15. Such a band combination has not been proposed so far for use in LTE carrier aggregation. Also the harmonics in the case of some bands may be a potential reason to limit the carrier aggregation to take ...