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Keysight
Solutions for LTE-Advanced Manufacturing Test
Understanding the Requirements for LTE-Advanced
Carrier Aggregation Manufacturing Test
Application
Note
Introduction
Overview
Carrier aggregation (CA), introduced in the 3GPP Release 10 standard, is an important new feature of
LTE-Advanced. Carrier aggregation enables the combining of multiple LTE carriers into a larger, sin-
glechannel bandwidth to increase data rates and throughput. For operators with limited or fragment-
ed spectrum allocations, carrier aggregation is a way to keep pace with the growing data demands on
their networks.
A goal of LTE-Advanced is to preserve backward compatibility with earlier LTE releases. For that
reason, CA in LTE-Advanced is based on the carriers first defined for 3 GPP Release 8. This allows
existing LTE devices to continue operating properly but enables new devices to support the higher
data throughput that CA makes possible. The LTE carriers defined in Release 8 are called component
carriers (CCs). Component carriers can use any of the 3GPP-defined LTE bandwidths--1.4, 3, 5, 10, 15,
or 20 MHz--and up to five CCs can be combined for a theoretical maximum of 100 MHz of bandwidth.
Since most LTE-FDD operators today lack the spectrum to support the widest channels, they are ex-
pected to use the 5 or 10 MHz bandwidths for carrier aggregation. In LTE-Advanced systems based on
frequency division duplex (FDD), the number of CCs aggregated in the uplink must always be less than
or equal to the number of aggregated downlink CCs. The carrier bandwidths can vary--for example, a
5 MHz carrier can be combined with a 10 MHz carrier--as this scenario is most likely to be fielded by
operators.
In systems based on time division duplex (TDD), both the downlink and uplink share the same chan-
nel. As defined in Release 10, the number of aggregated CCs in a TDD system and the bandwidth of
each CC must be the same for the downlink and the uplink. This definition changes in 3GPP Release
11, which introduces TDD support for different uplink and downlink configurations in each frequency
band.
Figure 1. A simplified view of carrier aggregation. Multiple LTE carriers are combined into a larger, single-channel
bandwidth to increase data rates and throughput and to make best use of available spectrum.
03 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
Two types of carrier aggregation are defined for LTE-Advanced in Release 10: intra-band
carrier aggregation and inter-band carrier aggregation. With intra-band CA, aggregated
CCs occupy channels within a single LTE frequency band. These channels may be contig-
uous (adjacent), non-contiguous, or both if more than three CCs are used (Figure 2).
Some chipsets support this feature using only a single receiver. With inter-band CA, the
CCs are located in different frequency bands (Figure 3), and thus two or more receivers
are needed. While this type of CA is more expensive, it is the most likely implementa-
tion for operators because blocks of spectrum are more available to them in different
frequency bands.
LTE-Advanced networks can support carrier aggregation in just the downlink or in both
the downlink and the uplink. Initial deployments are implementing CA in the downlink
only, where internet packet-data traffic is typically heavier.
LTE downlink intra-band carrier aggregation
Channel 1 Channel 2 Channel 3
Single 3GPP frequency band
Figure 2. Intra-band carrier aggregation with contiguous and non-contiguous channels.
LTE downlink intra-band carrier aggregation
Band X Band Y
Channel 1 Channel 2
3GPP frequency band X 3GPP frequency band Y
Figure 3. Inter-band carrier aggregation, which combines channels from different frequency bands.
04 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
Problem
Carrier aggregation brings some new challenges for manufacturers of LTE user equip-
ment (UE) in terms of increased test time and complexity, even though CA does not add
any new categories of test. Just as for other cellular devices, the manufacturing test
process for CA-enabled UEs requires two stages: calibration and verification. Different
test strategies are possible, as explained below.
Calibrating an intra-band CA device is similar to calibrating any LTE device at a given
frequency. However, more steps may be required to cover the effects of supporting
the aggregated bandwidth--for example, it may be necessary to verify a power ampli-
fier back-off when the device is transmitting multiple CCs. To verify the intra-band CA
device, some manufacturers may use multiple carriers for testing, while others will simply
test using a single carrier and then perform audit checks on a sample basis using multi-
ple carriers.
In the case of inter-band CA, every transmit and receive path must be calibrated individ-
ually. A dual-band device therefore requires two complete calibrations. This effectively
doubles the required calibration time and is a potential cost issue for manufacturing.
After calibration, each transmit and receive path also needs to be verified for proper
operation. Depending on the capabilities of the chipset employed and the test philosophy
of the manufacturer, either serial or parallel test techniques may be used for inter-band
CA verification testing.
In recent years cellular device manufacturing has moved to sequence-based, non-sig-
naling test for both calibration and verification (Figure 4). Using sequenced techniques
has dramatically reduced test times in calibration. Sequenced verification tests are
reducing both test times and the requirement for expensive, over-the-air signaling test
equipment.
These gains are not automatic, however, as chipset providers have to build support into
their chipsets for sequenced, non-signaling test and provide the drivers or complete
software needed to implement these capabilities. Test equipment must be capable of
advanced sequencing and single-acquisition measurements, and it must support the
necessary cellular formats and features--in this case LTE-Advanced carrier aggregation.
Test executive
Non-signaling
tester
Receive/send Chipset control,
RF signals read results
Figure 4. Setup for a non-signaling test is shown.
05 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
Test Requirements
Taking into account the capabilities in the target chipset and the capabilities of the test
equipment, manufacturers of LTE-Advanced CA devices must choose an appropriate
strategy for testing carrier aggregation. Tests may be performed sequentially or in paral-
lel.
Sequential CA testing requires no special test modes in the device chipset other than
the ability to switch between the various component carriers, receivers, or transceivers
(intra-band, inter-band, and uplink/downlink or both). With sequential test, the paths
are tested one at a time employing the same method used to test a standard LTE device.
Parallel CA test requires that both the target device and test equipment support con-
figuration and testing of multiple component carriers, receivers, or transceivers at the
same time. Clearly parallel test can yield significant time savings but comes with greatly
increased complexity and cost.
For intra-band carrier aggregation, the component carriers can be tested either sequen-
tially or in parallel. If the target chipset supports downlink intra-band CA only, then a
vector signal generator (VSG) is sufficient for testing. For sequential testing of intra-band
CA, the target chipset must be able to turn on the component carriers one at a time. The
test setup requires a VSG and vector signal analyzer (VSA) capable of handling a single
LTE carrier with the target bandwidth. The VSG and VSA are switched sequentially to
test each CC.
Parallel testing of intra-band CA is faster but requires more support in the chipset test
mode and more capable test equipment. The target chipset must be able to activate all
receivers or transceivers simultaneously. The test equipment must have a VSG with mod-
ulation bandwidth wide enough to handle all the component carriers. It must also have
a VSA with enough bandwidth to capture all the CCs and with the ability to demodulate
and analyze each of the captured CCs.
For inter-band CA testing, the sequential technique offers many benefits. First, it is rela-
tively simple to implement since the test mode in the target chipset has only to support
testing on one transceiver path at a time (Figure 5). A single command in the chipset
can be used to select the active transceiver path. Thus the same test plan developed
for existing LTE devices can be reused with only the addition of the new command. The
test sequence is then replicated for each transceiver path. Sequential testing in this
case does not require highly complex and expensive test equipment. However, the test
time increases 100% for each additional transceiver path to be tested. In the case of
downlink-only CA, it is likely that the device supports a second receiver for diversity or
MIMO capability. The secondary receiver path may already have been verified and so will
require little additional CA testing.
06 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
Test Requirements (continued)
Test executive
Test Tx/Rx 1
Test Tx/Rx 2
Test complete
Test UE supporting two band
equipment inter-carrier CA+ 2 Rx/Tx paths
Tx/Rx 1
Tx/Rx 2
Figure 5. The sequential technique is relatively simple to implement for inter-band CA testing since
the test mode in the target chipset has only to support testing on one transceiver path at a time.
Test times can be greatly affected by the measurement technique used to verify the
receiver path. Today, most chipsets use some form of a single-ended bit error ratio (BER)
test in which the test equipment transmits a known data pattern on the downlink and the
target device then determines its receive path error rate. These tests require the capture
of a relatively large number of data packets to assure reliable measurement results.
The single-ended BER measurement can dominate the overall verification test time of
the device. For a device that supports intra-band CA, using this measurement technique
can double the test time for each additional receiver path tested. The market trend,
however, is to implement much faster measurement techniques for receiver performance
evaluation. Typically some sort of signal-to-noise ratio measurement is performed by the
target device (chipset) on a carrier wave (CW) signal applied to the downlink. Because
these measurements can be made very quickly, they eliminate the long receiver test
times and make the sequential test approach more competitive.
The parallel method of inter-band CA testing is much more complex. The test mode in
the target chipset must be able to activate all the transceiver paths in the device at the
same time (Figure 6). The test equipment must be duplicated for each transceiver path
being tested in parallel, which makes this approach more complex and expensive. The
benefit of parallel testing, however, is that the time required to test multiple transceivers
in an inter-band CA device is the same as for a single transceiver device. Since the num-
ber of new radio systems in chipsets continues to increase, the pressure to reduce test
time may trigger a move to the parallel technique.
07 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
Test flow
Test Tx/Rx 1 Test Tx/Rx 2
Test complete
UE supporting two band
inter-carrier CA+ 2 Rx/Tx paths
Test Tx/Rx 1
equipment
Test
equipment Tx/Rx 2
Figure 6. The parallel method of inter-band CA testing is more complex but can reduce test times
significantly. because multiple devices can be tested in the same amount of time that it takes to
test a single device.
08 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
Solution
The Keysight Technologies, Inc. E6640A EXM Wireless Test Set is designed for high
throughput device calibration and non-signaling-based verification testing of LTE-Ad-
vanced and other cellular and wireless LAN devices. The EXM supports the requirements
of carrier aggregation testing by integrating up to four complete test sets in a single,
compact chassis (Figure 7). Each test set (called a TRX) contains a complete VSG, VSA,
and RF input/output (RFIO) with frequency coverage up to 6 GHz and bandwidths up to
160 MHz.
The EXM test set is compatible with the Keysight EXT manufacturing test set, using the
same command structure and building on the EXT's wide range of supported measure-
ments. Additionally, the EXM offers faster measurements, increased ARB and analyzer
capture memory, more sequencing steps, and enhanced sequencing capabilities. A high
performance quad-core controller enables full performance, even when the EXM is
equipped with the maximum four TRXs.
Each TRX in the EXM has its own 4-port RFIO section that makes it easier to test CA-en-
abled LTE-Advanced devices (Figure 8). Two full-duplex RFIO ports connect directly to
full-duplex devices and support simultaneous downlink and uplink testing. Two user-con-
figurable half-duplex ports can be set to either input or output functions. The internal
VSG and VSA can be switched to any of these four ports, which allows multiple devices
with multiple antenna ports to be connected without external switching. Rugged type-N
connectors are used for all RF connections and BNC connectors for trigger connections,
making the EXM test set ready to handle the rigors of manufacturing.
Figure 7. The EXM supports the requirements of LTE-Advanced carrier aggregation testing with up
to four complete test sets in a single, compact chassis.
Figure 8. Each TRX in the EXM has its own 4-port RFIO section including two full-duplex ports and
two user-configurable half-duplex ports.
09 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
How To Test Intra-Band CA
For downlink intra-band carrier aggregation testing, the EXM supports a VSG arbitrary
waveform bandwidth of 160 MHz. The Keysight N7625B Signal Studio software can be
used to create LTE-Advanced waveforms with up to five component carriers. Since only
bands above 3400 MHz have bandwidths greater than 160 MHz, the EXM can cover
nearly all LTE carrier aggregation bands completely with a single arbitrary waveform.
With its 160 MHz bandwidth, the EXM supports contiguous and non-contiguous in-
tra-band CA for up to five 20 MHz carriers.
For uplink intra-band CA testing the EXM also supports an RF analysis bandwidth of up
to 160 MHz (Figure 9). An EXM test set equipped with a single TRX can be connected
to two LTE-Advanced devices that support either downlink-only or downlink and uplink
intra-band CA at the same time (Figure 10). RFIO 1 is connected to one device's main LTE
antenna port and RF3 I/O is connected to the device's GPS input antenna port. RFIO 2 is
connected to the second device's main LTE antenna port and RF4 I/O is connected to the
GPS input antenna port.
This configuration allows sequential pingpong testing of the two devices including the
alternate receive-only paths, which are the GPS receiver paths in this example.
LTE uplink intra-band 20 MHz BW carrier aggregation
Channel 1 Channel 2 Channel 3 Channel 4 Channel 5
E6640A capture BW up to 160 MHz
Figure 9. The EXM supports up to five contiguous and non-contiguous LTE carriers for CA testing.
UE 1
Main Tx/Rx
Downlink up to 160 MHz source arb BW
GPS
Channel 1 Channel 2 Channel 3 Channel 4 Channel 5
UE 2
Uplink up to 160 MHz analyzer capture BW Main Tx/Rx
Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 GPS
Figure 10. Each TRX in the EXM has its own 4-port RFIO section including two full-duplex ports
and two user-configurable half-duplex ports.
10 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
How To Test Intra-Band CA
For this test configuration the VSG creates the intra-band downlink signal that is applied
to each device's main LTE input while the VSA captures the uplink intra-band CA signal
transmitted from the device (if the device supports uplink intra-band CA). The VSG also
creates a GPS waveform for testing the device's GPS path. While one device is being
tested, the second device is being connected to the TRX. Switching in the TRX's RFIO
controls the sequential testing of the first device's main LTE antenna path and GPS
receiver path and the transition to the second device. This setup allow the connection
time of the second device to be hidden during the test time of the first device once the
production flow starts.
By replicating the test configuration shown in Figure 10, an EXM equipped with a full
complement of four TRXs can connect eight LTE-Advanced devices supporting in-
tra-band downlink and uplink CA simultaneously and test four of them in parallel using a
sequential test methodology (Figure 11).
In this test configuration, the RFIO capabilities of each TRX are used to test a re-
ceive-only path in one device--here, the GPS receiver path--in addition to the main LTE
antenna port. As that device is being tested, a second device is connected to the TRX.
All four TRXs are executing this test procedure in parallel.
Once again, the switching in each TRX's RFIO allows sequential testing of the main LTE
antenna path and the GPS receiver path for one device and then allows switching to a
second device. Thus the connection time of each device is hidden during the test time
of the previous device once the production flow starts. A very high density of test is
achieved with this configuration enabling high throughput in minimal space.
UE 1 UE 2 UE 3 UE 4 UE 5 UE 6 UE 7 UE 8
Figure 11. An EXM equipped with four TRXs can connect eight LTE-Advanced devices and test the
downlink/uplink CA capability in four of them in parallel using sequential test methodology.
11 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
How To Test Intra-Band CA
Using a single TRX, two devices supporting downlink-only inter-band carrier aggregation
can be tested sequentially (Figure 12). The internal RFIO switching capabilities of the
EXM reduce the complexity of the external fixture for this scenario. This setup enables
ping-pong testing so that the load time of the second device is hidden during the test
time of the first.
During the test procedure (Figure 12), the first device is tested on both the downlink
and the uplink using RFIO 2. The VSG output is then switched to the second band and
channel, and routed to the device's second receive path using the RF4 I/O port. During
this time, a second device is being connected to the TRX's RFIO 1 and RF3 I/O ports,
thus hiding the load time within the first device's test time. Once the test is completed on
the first device, the VSG (changed back to the first band and channel) and the VSA are
switched to RFIO 1. The VSG output is then switched to the second band and channel
and routed to the device's second receive path using the RF3 I/O port. Another device
can be connected during the second device's test time and the pattern repeated.
UE 1
Tx/Rx 1
Rx 2
UE 2
Tx/Rx 1
Rx 2
Figure 12. For inter-band CA testing, a single TRX can connect to two devices and test them se-
quentially, thereby reducing the complexity of external fixturing required for the test.
UE 1 UE 2
Band 1 Channnel 1 Band 2 Channnel 1 Band 1 Channnel 1 Band 2 Channnel 1
Downlink Downlink Downlink Downlink
E6640A RFIO 2 E6640A RFIO 1 E6640A RFIO 2 E6640A RFIO 1
Band 1 Band 2 Band 1 Band 2
Ch 1 Ch 1 Ch 1 Ch 1
Switch from Switch from Switch from
TRX RFIO 2 TRX RFIO 2 TRX RFIO 1
to RF4 I/O to RFIO 1 to RF3 I/O
Uplink Uplink
E6640A RFIO 2 E6640A RFIO 2
Band 1 Band 1
Ch 1 Ch 1
Figure 13. This setup allows ping-pong testing of inter-band carrier aggregation.
12 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
How To Test Intra-Band CA
If a single device supports both downlink and uplink inter-band carrier aggregation,
then it can be sequentially tested with a single TRX using the RFIO 1 and RFIO 2 ports
(Figure 14). The first band and channel are tested on RFIO 2 and then the VSG and VSA
are switched to RFIO 1 to test the second band and channel. If the device supports any
receive-only paths, then the RF3 I/O and RF4 I/O ports on the test set can be used to
send the VSG to these antenna ports on the device. In this example, the RF3 I/O port is
routed to the GPS antenna port of the device.
Parallel testing of LTE-Advanced devices that support inter-band carrier aggregation
is possible with the EXM. Using two TRXs, both the downlink and uplink for two bands
in a single device can be tested in parallel (Figure 15). The VSG and VSA of each TRX
are used to create two downlink signals and to analyze both uplink transmitters in the
device. In this example UE 1 is connected to the RFIO 2 ports from two TRXs with each
testing the downlink and uplink in one frequency band at the same time.
Switching from RFIO 2 to the RFIO 1 ports in both TRXs allows the same test to be
performed on the second device, UE 2. This ping-pong configuration allows the load time
of the second device to be hidden during the test time of the first device. A receive-only
path such as the GPS receiver shown here can also be connected using the half duplex
ports. Two such receive-only paths can be connected and tested using a sequential
switching plan for the VSG.
Band 1 Channnel 1 Band 2 Channnel 2
UE with
Downlink Downlink inter-band
E6640A RFIO 2 E6640A RFIO 1
carrier
Switch aggregation
Band 1 Band 1
Ch 1
from Ch 1
TRX Tx/Rx 1
FRIO 2
to
Tx/Rx 2
Uplink RFIO 1 Uplink
E6640A RFIO 2 E6640A RFIO 1
GPS
Band 1 Band 1
Ch 1 Ch 1
Figure 14. A single TRX can sequentially test a device that supports both downlink and uplink
inter-band carrier aggregation.
13 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
How To Test Intra-Band CA
Tx/Rx 1
UE 1 with
inter-band Tx/Rx 2
carrier
aggregation GPS
Tx/Rx 1
UE 2 with
inter-band Tx/Rx 2
carrier
aggregation GPS
Figure 15. Using two TRXs and parallel testing, the EXM can quickly test both the downlink and the
uplink for two bands in a single device.
During parallel testing of devices supporting downlink inter-band CA, the downlink
signals from the TRX may need to be tightly synchronized. This requirement comes from
the Release 10 standard, which specifies a single uplink timing advance value for all
component carriers. This means that the base station transceivers for different carriers
should be at the same location to avoid different propagation delays. The effect of this
requirement from the physical layout of the network is that test equipment generating
the required downlink signals must be synchronized.
The EXM supports tight synchronization between two TRXs. All synchronization occurs
internally so no external connections are required. Typical performance is around 30 ns
accuracy between downlink signals, which is more than sufficient for to meet the syn-
chronization requirement.
A fully configured EXM with four TRXs installed can parallel-test two devices supporting
dual inter-band carrier aggregation, and the EXM can connect two more such devices
during test (Figure 16). Using the same configuration that was shown in Figure 15, one
device is tested on two channels in two different bands through two transceivers using
two TRXs. Another device can be connected during testing.
With four TRXs, two devices can be tested in parallel while each is parallel-tested in
both supported bands for carrier aggregation. As before, the RFIOs in the TRXs also
allow connection of up to two more receive-only paths for each device. In this example,
one of the RF I/O ports is being used to test the GPS receive path in each device.
14 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
How To Test Intra-Band CA
UE 1 UE 2 UE 3 UE 4
Figure 16. A fully configured EXM with four TRXs can test two inter-band CA devices in parallel
while connecting to two additional devices.
Summary
The limited amount of spectrum available worldwide is leading most LTE-Advanced op-
erators to implement inter-band carrier aggregation even though this feature increases
the cost of the UE and reduces battery life. Many LTE-TDD operators have wider blocks
of spectrum and may choose to implement wider (up to 20 MHz) bands of intra-band CA.
In the near term, most implementations will be downlink-only as this limits the complexi-
ty of implementation and matches customer usage patterns for packet data.
Although carrier aggregation enables operators to combine available blocks of spectrum
to achieve the throughput and efficiency benefits of LTE-Advanced, carrier aggregation
adds to the calibration and verification effort required in the UE production process.
Manufacturers will most likely adopt sequential methods of carrier aggregation testing
at first since this approach reduces both the complexity of the test mode in the target
device and the capability required of the test equipment. Moreover, the industry move
towards faster receiver test metrics will reduce the receiver test time, helping to miti-
gate the additional testing required for downlink carrier aggregation support. With the
inevitable increase in the complexity of cellular devices, pressure to reduce test time will
continue to mount. This pressure could drive the market to implement faster but more
complicated parallel testing.
To meet these new test challenges in an efficient and cost-effective manner, the Keysight
E6640A EXM Wireless Test Set supports both sequential and parallel carrier aggregation
test processes without the need for additional test equipment. The EXM can provide high
density test capability by offering up to four complete test sets in a single package. Each
test set includes a flexible four-port RFIO section that reduces complex and expensive
external switching.
With four test sets in a single compact package, the EXM helps manufacturers reduce
capital costs by offering a smaller test footprint and shared use of a single internal
controller, timing reference, and internal power supply. Additionally, the EXM delivers the
highest levels of throughput based on industry-standard measurement science devel-
oped for Keysight X-series analyzers and wireless test sets.
15 | Keysight | Understanding the Requirements for LTE-Advanced Carrier Aggregation Manufacturing Test - Application Note
The Power to Accelerate Wireless Design and Test
Keysight is a leader in wireless test, focused on the highest-performance design and
test of wireless devices and cell sites, with application-focused platforms optimized for
existing and emerging standards. Adding to this optimal R&D and field support, Keysight
allows engineers to better understand the intricacies of the continuously evolving wire-
less industry so you can accelerate your development of products.
To learn more about Keysight's suite of test and measurement products please visit:
www.keysight.com/find/powerofwireless.
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