Carrier Aggregation Discussion

LTE-Advanced New UE Categories[4]
2

LTE-Advanced New UE Categories
 Advanced MIMO (Multiple Input, Multiple Output)[8].
3

 Using higher-order modulation (256-QAM)[8].
4

 CA + MIMO + 256 QAM[9].
5

Carrier Aggregation is the first step of LTE Advanced
 Bandwidth extension by aggregating LTE component
carriers (CC), Up to 5 CC can be allocated in both DL
and UL – 100 MHz aggregated[4].
 For FDD, the CC number in DL should be larger than or
equal to which in UL ; for TDD, the CC number in DL
should be equal to which in UL[3].
6

Carrier Aggregation is the first step of LTE Advanced
 For CA, modes and deployments are as below[4]:
7

Intra-Band Uplink Challenges
 Intra‐band uplink CA signals use more bandwidth and
have higher peak‐to‐average power ratios (PAPRs) than
standard LTE signals because more subcarriers lead to
higher PAPRs[3].
 Large PAPR requires high linearity requirements for PA
and increases power consumption[5].
8

 Thus, for intra-band UL, the temperature drift of
duplexer or filter should be as small as possible. This is
especially important for high channel[6,9].
PA
Normal Temp
High Temp
High Channel
9

 BAW filters are consistent performance over a wide
temperature range. Qorvo LowDrift™ BAW filters
achieve high isolation and low insertion loss to
maximize system performance compared to competing
devices using TC(Temperature Compensated)
SAW/SAW[6]. >0.5 dB of nominal
insertion loss
improvement
10

Inter-band Challenges
 Take B17/B4 combination for example, the B17 3H may
fall in B4 received band, thereby causing desense
issue[4].
11

 The B4 desense is as shown below[4]:
6.8dB due to noise floor
increase
caused by harmonic
0.5 dB due to H3 trap filter
insertion loss
For H3 trap filter, LPF has
smaller IL than BPF[10]12

Consideration for harmonics
 TVS(Transient Voltage Suppression) is often added in
ASM ANT port to avoid making ESD damage ASM.
 TVS limited VBR clips RF signal, causing distortion and
then harmonics aggravates[12].
VBR
RF Signal
waveform
13

 For B17, if 2H noise(about 1400 MHz) exists in PA Vcc
path, the 3H product may aggravate due to IMD
mechanism.
PA
Vcc 2H Noise
IMD2
= 2H Noise + RF
= 3H
14

 Apparently, PA dominates the whole 3H level[10].
15

 Therefore, the PA output impedance should be tuned to
high linearity zone to achieve lower harmonics.
16

 Not only RF signal at PA input, but also 3H product
generated from transceiver.
Transceiver
PA
3H
 If we take PA as:
and take 3H product@PA input as :
we can get PA output 3H product as :
17

 Obviously, as mentioned earlier, the higher 3H product
at PA input leads to higher 3H product at PA output.
 Thus, we can add LPF or notch filter at PA input to
suppress 3H product generated from transceiver,
thereby lowering 3H product at PA output.
18

 For IMD3(3rd order intermodulation) calculation[10] :
 In addition to active devices, passive devices, such as
duplexers, also generate IMD products due to
nonlinearity[10,11].
 For B1/B3 combination CA, 2B1TX – B3TX = B1RX. That
is, B1 and B3 transmitting signals generate IMD
products falling into B1 received bands, thereby
causing desense issue. 19

Transceiver
PA
PA
Aperture
Switch
eLNA
eLNA
ASM
ANT
Tuner
LB Path
ANT 0
LB/MB
Primary
ANT
Tuner Aperture
Switch
ANT 1
LB/MB
Diversity
DSM
eLNA
LB Path
B1TX
B3TX
B1/B3 ANT
B1PRX
B3PRX
eLNA
B1DRX
B3DRX
ASDiV
IMD3
 As shown below, the IMD3 product generated by
quadplexer nonlinearity may interfere B1 RX by
quadplexer, ASDiV limited isolation, and limited ANT-to-
ANT isolation.
20

 Besides, 2B3TX – B1TX = GPS, the IMD3 product may
interfere GPS signal as well by means of limited ANT-to-
ANT isolation.
Transceiver
PA
PA
Aperture
Switch
eLNA
eLNA
ASM
ANT
Tuner
LB Path
ANT 0
LB/MB
Primary
B1TX
B3TX
B1/B3 ANT
B1PRX
B3PRX
ASDiV
IMD3
Diversity
path
To diversity
ANT GPS
21

DL CA introduces New Requirements
 With DL CA, all potential transmit frequencies must be
prevented from injecting excessive noise into all
operating receive channels. So do all operating receive
channels[1].
 These two new requirements are often referred to as a
need for “cross isolation”, which should be at least 50
dB[1-2].
22

 Additionally, to prevent unwanted loading, all
filters must have their impedances adjusted so that,
for any given filter, the parallel combination of all
the other filters looks like an open circuit. These
requirements drive changes in FDD hardware[1].
 Thus, connecting multiple duplexer paths can affect the
filter characteristic of all duplexers, thereby causing
you to lose transmit and receive path isolation required
to operate at system sensitivity[3].
23

 Besides, for TDD DL CA, if band operation is NOT
synchronized, adequate cross isolation must be
ensured[1].
24

 In the case of aggregation of a TDD band with an
FDD band, the FDD band is commonly used as p-
cell (transmitting band) and the filtering in the TDD
band needs to be enhanced as in the case of un-
synchronized TDD-TDD DL CA. If the TDD band
is used as p-cell, the Rx of the FDD duplexer needs
to be enhanced to create high rejection at the TDD
Band[1].
 For DL intra-band CA, there is no impact on UE
filtering, for either contiguous or non-contiguous
CA because intra-band CA passes all the channels to be
aggregated through the same power amplifier and
filtering[1].
25

Inter-Band Architecture Options
 Each band can be on a separate antenna and antenna-
to-antenna isolation is used to ensure sufficient cross
isolation. The major drawback to this method is the
lack of space for the required number of antennas[1].
26

 A second option is to use a switch to simultaneous
close connections to multiple paths, in that proper
impedance loading must be maintained both with the
switch closed and the switch opened. So this method
needs phase shifters to prevent unwanted loading[1,7].
27

 The third option is using a combination of high pass
and low pass filtering, a diplexer can be used to
combine any band in one frequency range with any
band in a second frequency range. This technique
works best when there is substantial frequency spacing
between the two separate frequency ranges, e.g.
separating “low” bands from “mid or high” bands[1].
28

 Alternately, band pass filters can be combined into
a “multiplexer” that provides a common antenna
port but individually filters each Tx and Rx band.
This is the preferred technique when the bands to
be aggregated are close to each other in frequency[1].
29

 For a multiplexer, both in-band isolations and cross
isolation need to be supported and at least 50 dB. And
filter impedances need to be adjusted to prevent
loading. These requirements results in higher insertion
loss than individual duplexers due to more poles and
zeros[1].
 As shown right, the ANT port matching should be
wideband enough to cover band A and B, thereby
increasing insertion loss due to lower Q factor[1].
30

 High out of band reflection enables filters to be
connected in parallel with minimal impedance loading,
so better in band and cross band isolation[1].
 Thus, FBAR multiplexers have lower insertion loss,
higher spurious rejection, and higher in band and cross
band isolation than SAW multiplexers[1].
31

 Nevertheless, using the multiplexer reduces the throw
count of the band select switch, which can be a
significant benefit due to lower switch insertion loss
and complexity. This is especially beneficial to non-CA
band[1].
32

Reference
[1] Multiplexers as a Method of Supporting Same-Frequency-Range Down Link Carrier
Aggregation, AVAGO
[2] LTE Carrier Aggregation Technology Development and Deployment Worldwide
[3] ABCs of Carrier Aggregation
[4] Carrier Aggregation: Fundamentals and Deployments , Keysight
[5] EVM Degradation in LTE Systems by RF Filtering
[6] Addressing Carrier Aggregation Challenges Using Multiplexer Solutions, Qorvo
[7] FRONT-END MODULE FOR CARRIER AGGREGATION MODE, US Patent
[8] Delivering on the LTE Advanced promise, Qualcomm
[9] Carrier Aggregation What’s New in Mobile CA? Qorvo
[10] RF Advanced (Level 3) – RF System-Training Note, Murata
[11] Development of High Linearity Duplexers with Low Passive Intermodulation Component,
TAIYO
[12] ESD Protection Device Solutions in the vicinity of RF antenna -No Harmonic Noise, Murata
33

Carrier Aggregation Discussion

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