2. EXECUTIVE SUMMARY CA combinations are divided into intra-band (contiguous and non-contiguous) and inter-band. Aggregated carriers can be adjacent or non-adjacent even at different frequency bands[2]. Inter-band CA provides more flexibility to utilize fragmented spectrum allocations. Thus inter-band CA is an efficient technology to combine their spectrum resources for increased data rates[2].

3. INTRODUCTION LTE offers flexible bandwidth options ranging from 1.4 to 20 MHz using orthogonal frequency-division multiple access (OFDMA) in the downlink and single-carrier, frequency-division multiple access (SC-FDMA) in the uplink[1,2]. OFDM support multiple users (Multiple Access) via TDMA basis only, while OFDMA support either on TDMA or FDMA basis or both simultaneously[1,2].

4. INTRODUCTION SC-FDMA, variant of OFDM, reduces the PAPR between 3- to 9dB compared to OFDMA. Hence, SC-FDMA has smaller PAPR than OFDMA due to merely single carrier. [1,2].

5. INTRODUCTION 3GPP defined a maximum of five component carriers(CC) that can be aggregated. Hence, the maximum aggregated bandwidth is 100 MHz. CA can be used by both LTE frame structures; meaning by both FDD and TDD, and it can be enabled for both DL and UL direction[2]. In FDD, the number of aggregated carriers can be different in DL and UL, which is also referred to as asymmetric configuration. However, the number of UL component carriers is always equal to or lower than the number of DL component carriers.The same requirements apply for TDD[2].

6. 3GPP Release Status for Carrier Aggregation

10. CA Configuration

11. CA schemes may also combine contiguous and non- contiguous elements. One example is the CA_41C_41A scheme, which combines contiguous CA (CA_41C) with a non-contiguous element (41A) for a three-carrier DL CA capable of delivering up to 60 MHz DL bandwidth to the UE[2]. CA_4A-12A is an example of a low and high band CA case that aggregates two DL CCs from Band 4 and Band 12 to provide up to 30 MHz of aggregated bandwidth[2].

12. CA BENEFITS AND PERFORMANCE As mentioned above, the component carrier(CC) can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz[2]. According to Shannon theorem, wider bandwidth leads to larger throughput. Thus, the CA feature increases the bandwidth for a CA- capable UE by aggregating several LTE carriers, thereby increasing the UE’s bit rate. Each of the aggregated carriers is referred to as a CC[2].

13. CA BENEFITS AND PERFORMANCE As shown below, with CA, DL throughput improves[2].

14. UL CA As mentioned above, allocating more CCs to a UE generally results in a higher throughput thanks to the larger bandwidth[2]. However, this is NOT always the case in UL. Increasing the bandwidth does not necessarily result in an increase of data rates if a UE reaches its maximum transmission power[2].

15. UL CA That’s why DL is always larger than UL in CC number. For DL, the more the CC number is, the larger bandwidth will be, thereby increasing throughput. Nevertheless, for UL, the more the CC number is, the larger PAPR will be, thereby aggravating linearity such as EVM. That’s why UL adopts SC-FDMA in LTE[1,2]. Thus, for UL, more CC number does NOT lead to higher throughput necessarily. Because SNR decreases as EVM increases, thereby lowering throughput.

16. UL CA To mitigate the issue, more back-off of the UE transmission power is needed[3]. To control the level of power back-off, MPR(Maximum Power Reduction) is introduced. MPR means the maximum back-off of UE transmission power when ACLR and SEM requirements are just meet[3].

17. UL CA The SEM and ACLR for UL CA are shown as below :

18. UL CA When the RB allocation is wide enough to extend to the second CC, PAPR will increase greatly and hence more MPR is required compared to the single carrier transmission[3].

19. Two close frequencies bands CA In order to support the CA of two low band frequencies, it may be necessary to build devices requiring additional RF hardware to separate the two radio signal paths, and so do the CA of two high band frequencies. The low band and high band case does not have this limitation[2]. Thus, for the CA of two close band frequencies, tight filtering and other interference mitigation design are necessary[2].

20. Two close frequencies bands CA For example, due to the nonlinearity of component, any two close tones will lead to intermodulation products. As long as one of the two closes tones is AM modulated, there is cross-modulation product as well[4].

21. FDD-TDD CA This serving cell is referred to as the primary cell (PCell). In the DL, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC), while in the UL it is the Uplink Primary Component Carrier (UL PCC)[2]. Other serving cells are referred to as secondary cells (SCells) and are used for bandwidth expansion for the particular UE. The Rel-12 TDD-FDD CA design supports either a TDD or FDD cell as the primary cell.

22. RF FRONT END IMPACTS In a single carrier FDD (non-CA) scenario, a duplexer ensures that the transmission on the uplink does not interfere with the reception on the downlink[2]. As shown below, in a dual-band CA, comprising of bands 3 and 1, band 3 UL should not interfere with the DL on band 3(In-band isolation) and band 1(Cross Isolation). So does band 1 UL[2]. In-band Isolation Cross Isolation

23. RF FRONT END IMPACTS For non-CA case, directly connecting two duplexers by one single antenna is allowed because multiple bands will NOT operate simultaneously. For CA case, directly connecting two duplexers together by one single antenna can affect each other’s filter characteristic, thereby losing the isolation that is needed to operate at reference sensitivity[2].

24. RF FRONT END IMPACTS Therefore, for CA case :   Single Antenna : to insert diplexer (LB/HB) or phase shifter(LB/LB, HB/HB).   Multiple Antennas : No diplexer or phase shifter.

25. RF FRONT END IMPACTS In addition, for CA case, you need quadplexer if you want :   Single Antenna   No diplexer, no phase shifter

26. Reference [1] EVM Degradation in LTE Systems by RF Filtering, slideshare [2] LTE Carrier Aggregation Technology Development and Deployment Worldwide [3] Analysis of Maximum Power Reduction of Uplink for Carrier Aggregation in LTE-A System, IEEE [4] TD-SCDMA RD V2.1 Design Meets Rx-Blocking Mask and Sensitivity Requirements, MAXIM [5] Simplifying and Accelerating the Deployment of Carrier Aggregation, Qorvo