A. ASYMMETRIC CA
To ameliorate the spectrum capacity in LTE-Advanced systems asymmetric carrier aggregation should be supported in the uplink and downlink channel; meaning that the number of aggregated component carriers in the downlink channel is different from the number of the of aggregated component carriers in the uplink channel. Asymmetric CA procures ambiguity to the LTE-Advanced eNB in downlink component carrier selection because during a random access process, identifying the downlink component carrier to which UE is attached may be difficult. Therefore, the eNB cannot transmit the random access response to the UE without selecting the exact downlink component carrier. We note that, ...view middle of the document...
2) The control channels of different component carriers can be jointly coded and spread in a specified component carrier.
3) Multiple control channels for different component carriers are simultaneously coded and then sent over the entire frequency band formed by a CA scheme. This approach is not suitable for LTE-systems but it exhibits low signaling overhead and high decoding performance in control channels.
C. HANDOVER CONTROL
Since the channel qualifications of two or more adjacent cells for the definite UE may be completely distinct, it is very important to support transmission continuity during the handover procedure with high quality of service (QoS) requirements.
A method is proposed to overcome this problem:
The UE has to measure the performance of only one component carrier in each adjacent cell. The measurement outcome of one component carrier is utilized to estimate the performance of the other component carriers in the corresponding cell. Thus, based on the estimation result, the handover process and transmission configuration can be decided.
D. GUARD BAND SETTING
Guard band is unused portions of the spectrum between frequency bands, for the aim of preventing interference. Here, for the non continuous carrier aggregation, component carriers are well separated so the interference between them is not considered but frequency bands of other systems are still adjacent to each component carrier. In the high-speed mobile environment, adjacent frequency bands will interfere and orthogonality characteristic between them will be lost due to large Doppler frequency shift. Thus, to maintain high spectrum efficiency in data transmission, the guard band setting for a component carrier of both continuous and non continuous CA should be neatly set to restraint this intersystem interference.
Figured 4: BER performance with and without Doppler frequency shift
According to the LTE technical specification, 10 percent of the total system bandwidth should be allocated to set the guard bands...