Carrier aggregation (CA) allows the combination of multiple component carriers to increase bandwidth and throughput. CA can be intra-band, combining contiguous or non-contiguous carriers within a band, or inter-band, combining carriers across frequency bands. Inter-band CA provides more flexibility to utilize fragmented spectrum. The LTE standard defines a maximum of five component carriers for CA. CA improves downlink throughput by increasing bandwidth but may not always increase uplink throughput due to limitations of UE maximum power. Close frequency band CA and FDD-TDD CA require additional RF components to separate signal paths and prevent interference between bands.

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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].
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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].
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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].
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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].
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6. 3GPP Release Status for Carrier Aggregation
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7. 3GPP Release Status for Carrier Aggregation
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8. 3GPP Release Status for Carrier Aggregation
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9. 3GPP Release Status for Carrier Aggregation
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10. CA Configuration
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11. CA Configuration
 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].
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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].
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13. CA BENEFITS AND PERFORMANCE
 As shown below, with CA, DL throughput improves[2].
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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].
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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.
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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].
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17. UL CA
 The SEM and ACLR for UL CA are shown as below :
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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].
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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].
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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].
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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.
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22. ANT
Matching
PA
Duplexer
LNA
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
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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].
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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.
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25. RF FRONT END IMPACTS
 In addition, for CA case, you need quadplexer if you
want :
 Single Antenna
 No diplexer, no phase shifter
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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
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