Prior art which is related to this technical field can e.g. be found by the technical specifications TS 36.211 current version: 9.0.0), TS 36.212 (current version 9.0.0), and TS 36.213 (current version: 9.0.1) of the 3GPP, and by the contributions according to document R4-093091, document R4-093220 and document R4-093439 of the working group 4 of the 3GPP related to radio access networks.
The following meanings for the abbreviations used in this specification apply:    3GPP: 3rd Generation Partnership Project    CC: Component Carrier    DL: Downlink    eNB: evolved Node B (eNode B)    GSM: Global System for Mobile Communication    HARQ: Hybrid Automatic Repeat Request    ICIC: Inter-Cell Interference Coordination    LTE: Long Term Evolution    OFDMA: Orthogonal Frequency Division Multiple Access    PBCH: Physical Broadcast Channel    PCFICH: Physical Control Format Indicator Channel    PDCCH: Physical Downlink Control Channel    PDSCH: Physical Downlink Shared Channel    PHICH: Physical HARQ Indicator Channel    PS: Public Safety    PSS: Primary Synchronization Channel    PUSCH: Physical Uplink Shared Channel    RRC: Radio Resource Control    SC-FDMA: Single Carrier Frequency Division Multiple Access    SFN: Sub-Frame Numbering    SSS: Secondary Synchronization Channel    TTI: Transmission Time Interval    UE: User Equipment    UL: Uplink
In recent years, 3GPP's LTE as the upcoming standard is under particular research. The base station of LTE is called eNodeB. LTE is expected to be based on OFDMA in downlink and SC-FDMA in uplink. Both schemes allow the division of the uplink and downlink radio resources in frequency and time, i.e. specific frequency resources will be allocated for certain time duration to the different UE. The access to the uplink and downlink radio resources is controlled by the eNode B that controls the allocation of the frequency resources for certain time slots.
As a further development of LTE, an extension of transmission bandwidth is considered. This evolution of LTE, referred to as LTE-advanced, aims at exploiting spectrum allocations up to 100 MHz. Though, this bandwidth extension is made while preserving spectrum compatibility, which is achieved with so-called carrier aggregation, where multiple component carriers are aggregated to provide the necessary bandwidth.
However, by e.g. referring to the example of lower and upper 700 MHz frequency band as used in the United States, when all DL CCs of two different frequency bands (e.g. Band 12 and Band 14, see FIG. 1) or when all DL CCs of a small duplex gap band are active at the same time, potential transmit and receive intermodulation products potentially cause intermodulation-based duplex interference into the eNB's own receiver(s) (and potentially also into the receivers of other networks or devices).
If (which may be an even more probable case) the different aggregated carriers have separate RF hardware/chains, intermodulation duplex interference is either avoided by so-called diplexers—which are at their technical limits in case of wide LTE channels—, or by costly additional antennas.
FIG. 1 illustrates this problem of intermodulation duplex interference—inter-frequency band, where eNB self-interference is caused by combining Band 12 and Band 14 on a same antenna polarization plane, in which case a hardware-based solution (i.e. using diplexer) can be quite challenging. However, as indicated above, FIG. 1 only serves as an example for illustrating the problem which is not restricted to the case of Band 12/Band 14 caused interference.
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