LTE TDD What to Test and Why © 2012 LitePoint Corp.

LTE TDD What to Test and Why
© 2012 LitePoint Corp.
© 2 0 1 2 L i t e P o i n t , A T e r a d yn e C o m p a n y. Al l r i g h t s r e s e r ve d .
Agenda
•
•
•
•
•
LTE Overview
LTE Measurements
Testing LTE TDD – Where to Begin?
Building a LTE TDD Verification Plan
Optimizing a LTE TDD Verification Plan
© 2012 LitePoint Corp.
•32
Why LTE? – Something for Everyone
For the user..
Higher Performance (Data Rate)

Instantaneous downlink peak data rate:
150 Mbit/s in a 20MHz downlink spectrum (5 bit/s/Hz)
 Instantaneous uplink peak data rate:
75 Mbit/
Mbit/s iin a 20MH
20MHz uplink
li k spectrum
t
(2
(2.5
5 bit/
bit/s/Hz)
/H )
For the service provider…
Cell capacity – more users per cell
 up to 200 active users per cell (5 MHz) (i.e., 200 active data clients)
1st all-data network: packet-switched
 Simplifies network architecture – no difference between voice & data
© 2012 LitePoint Corp.
•33
Key Features of LTE
Multiple access scheme
Downlink (DL):
• Uplink (UL):
•
OFDMA enables maximum spectrum utilization by the base station
SC-FDMA
SC
FDMA relaxes the linearity requirements for the handset
Multiple Uplink Transmission Modes
FDD:
• TDD:
•
balanced DL / UL data traffic by using different channels
enables asymmetric
y
DL / UL capacity,
p
y, sharing
g a single
g channel
Adaptive Modulation and Coding
LTE dynamically changes modulation based on channel conditions to optimize its capacity
• DL modulations:
QPSK, 16QAM, and 64QAM
• UL modulations:
QPSK and 16QAM
Channel Bandwidth Scalability
Scalable channel bandwidth allows efficient operation in differently-sized allocated spectrum bands
Multiple Antenna Technology – MiMo
Multiple Antenna techniques enables higher data rate, improve network reliability and data capacity
© 2012 LitePoint Corp.
•34
OFDM meets Cellular…
•
LTE is the first cellular standard to use OFDMA modulation
- Combining time and frequency multiplexing, enabling multiple users to
operate in a single time slot
OFDMA
•OFDM Modulation
© 2012 LitePoint Corp.
•35
OFDMA Highlights
•
LTE uses OFDMA for the downlink
- Uses a large number of narrow sub-carriers for
multi-carrier transmission
- “Resource blocks” and “elements”
•Each resource block and element is defined in
“frequency” and “time” (1 block = 180 kHz; 0.5 ms)
- Dynamically assigns these resource blocks to
LTE users, thus improving spectrum utilization
- Subcarrier spacing – 15 kHz compared to
312 .5 kHz for WLAN
•The basic LTE downlink physical resource
can be seen as a time-frequency grid:
© 2012 LitePoint Corp.
•36
SC-FDMA
•
The LTE uplink transmission scheme based on a pre-coded version of OFDMA
known as SC-FDMA (Single Carrier Frequency Division Multiple Access).
•
SC-FDMA operates with a lower Peak to Average Power Ratio (PAPR) than OFDM
- High PAPR requires expensive and inefficient power amplifiers
•
SC-FDMA reduces the linearity
requirement for power amplifier
•
Two LTE UL transmission modes:
- FDD
- TDD
© 2012 LitePoint Corp.
•37
LTE-FDD & LTE-TDD
FDD
•
•
downlink and uplink traffic is transmitted simultaneously at separate carrier frequencies
is the preferred mode by most cellular systems,
systems wherever paired spectrum is available –
easy transition from existing 3G networks
TDD
•
•
•
transmission in uplink and downlink is at the same carrier frequency
is a good option where spectrum (carriers) availability is lower
is necessary when pair spectrum is not available
FDD
fDL
TDD
fUL
fDL/UL
time
© 2012 LitePoint Corp.
time
•38
LTE-FDD vs. LTE-TDD
The two versions of LTE are actually quite similar
• The only differences are in the physical layer, enabling support of both
TDD and FDD with a single chipset
•
- All major LTE chipset vendors have released chipsets that support both FDD
and TDD
Parameter
LTE-FDD
LTE-TDD
Paired spectrum
Requires spectrum pairs – TX
and RX on different frequencies
No spectrum pair required – TX and
RX on the same frequency
UL / DL asymmetry
Data capacity determined by
spectrum allocations
Possible to dynamically change
UL / DL to meet capacity demand
Guard interval impact on
data capacity
Increasing guard interval (due to
distance from base station) does
not impact data capacity
Increasing guard interval (due to
distance from base station) reduces
data capacity
© 2012 LitePoint Corp.
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•LTE Growth – China and LTE-TDD will play a key
role
•2011
•2016
•It
It is
i expected
t d that
th t by
b 2016,
2016 Chi
China M
Mobile
bil will
ill representt over 15 percentt off the
th total
t t l LTE
market, with its TDD LTE deployment.
© 2012 LitePoint Corp.
•Source: Signals and Systems Telecom 4/2012
•40
New Challenges in LTE – More Bands
Band
33 to 41
Frequency
Channel
Range
Bandwidths
<2.69
69 G
GHz
1.4, 3, 5, 10,
15 20 MH
15,
MHz
Mode
TDD
•More bands means more test time
© 2012 LitePoint Corp.
•41
New Challenges in LTE – More Configurations
•
LTE has many configurations to test – more test time
- Per channel…
Modulation
RB Config
PWR Levels
QPSK
50,0
4
QPSK
12,0
4
QPSK
12,38
2
QPSK
1,0
1
QPSK
1,24
1
QPSK
1 49
1,49
1
16 QAM
50,0
2
16 QAM
12,38
2
16 QAM
12 0
12,0
2
16 QAM
50,0
1
64 QAM
50,0
1
•LTE threatens to reduce test throughput…
© 2012 LitePoint
Corp.
Higher
cost test?
•42
New Challenges in LTE – More Bandwidth
Spectrum Emission Mask (SEM): 6.6.2.1
• Adjacent Channel Leakage Ratio (ACLR): 6.6.2.3
•
•SE
SE M
Mask
k
•Limit: -25 dB
•20 MHz
Channel
•25 MHz
•25 MHz
•SEM = 70 MHz Total Bandwidth
© 2012 LitePoint Corp.
•43
Testing LTE: Key Requirements
RF Frequency Range
• The test equipment must support the frequency bands 698 MHz - 2690 MHz
• The test equipment must support handsets with an increasing number of antennas
VSA / VSG Bandwidth
• The test equipment
q p
must have at least 20 MHz VSA/VSG bandwidth
- LTE requires support for six channel bandwidths (from 1.4 to 20 MHz)
- With LTE-Advanced, this requirement will become 100 MHz
- >70 MHz required for single-shot LTE ACLR & Spectrum Emission Mask testing
MiMo Technology
•
•
Support for accurate MiMo testing is necessary in both R&D and MFG
I particular,
In
ti l it iis essential
ti l tto h
have multiple
lti l VSA / VSG ports
t for
f DL / UL MIMO signal
i
l
Transmission Schemes
•
•
Supportt two
S
t
transmission
t
i i
schemes
h
f downlink
for
d
li k and
d uplink
li k (OFDMA,
(OFDMA SC
SC-FDMA)
FDMA)
Support two transmission modes (FDD and TDD)
© 2012 LitePoint Corp.
•44
Testing LTE TDD: Where to Begin?
•
LTE complexity introduces more than
10x configurations to test
- Testing every scenario is not practical
•
In production, we are looking to validate
manufacturing quality
•
Goal is to exercise the mobile as much
as possible while minimizing test time
© 2012 LitePoint Corp.
•45
Testing LTE TDD: Where to Begin?
•
What to test in mobile manufacturing verification:
-
•
Physical layer RF measurements
TX power
TX modulation quality
TX frequency
TX / RX timing
RX sensitivity (min / max)
What NOT to test in mobile
manufacturing verification
- Software
- Digital Design
- Redundant (overlapping) tests or configurations
© 2012 LitePoint Corp.
•46
LTE UE Transmitter Tests
Measurement
Why is this Important?
TX Power
LTE network performance is highly dependent on accurate
power control
p
Error Vector Magnitude
Primary TX quality measurement – detects distortions that will
ultimately degrade accurate transmission of data
Frequency Error
Critically important to avoid communication interference
ACLR
Ensures that transmission does not interfere with neighboring
channels
Occupied Bandwidth
Confirms that signal is contained within channel allocation
Spectrum Emissions Mask
Ensures that signal in adjacent channels rolls off to minimize
interference
Carrier Leakage
An indication of mismatch in the I/Q modulator
Transmit Time Mask
Verifies UE timing accuracy – particularly important for LTE
TDD since the UL/DL are on the same frequency
In-Band Emissions for
non-allocated RBs
Ensures that a UE’s assigned RBs (within a channel) do not
interfere with the unassigned RBs in the channel
•3GPP Measurements
© 2012 LitePoint Corp.
•47
LTE UE Receiver Tests
•
TX measurements give direct access to the signal via the UE antenna
•
Unlike TX measurements
measurements, RX signal quality issues remain buried until the
signal is fully decoded
Measurement
Notes
RX Bit Error Rate (BER)
Fundamental test of a receiver’s ability to decode the inbound
signal. Typically performed at both min & max RX input power
RX Sensitivity (RSSI)
Receive signal strength is a parameter often measured as part
of calibration.
calibration Since the initial TX power level is calculated per
the measured RSSI, accuracy of this measurement directly
impacts UE power transmission
•3GPP Measurements
© 2012 LitePoint Corp.
•48
LTE Test Plan Development
•
Several different approaches to develop a test plan:
- Use the 3GPP standard’s recommendations
- Use
U th
the IC manufacturer’s
f t
’ recommendations
d ti
- Use historical data from similar devices
- Apply some reasonable logic to look for
likely failure modes and apply 3GPP spec conditions
© 2012 LitePoint Corp.
•49
Building a LTE TDD TX Verification Test Plan
Per-Band
Per
Band / Per-Channel
Per Channel
A “reasonable” LTE test plan covered in 21 configurations
Showing config 1-11
•Varies in RB Offset for
RB = 1, QPSK channel
Parameters
TX Power
Modulation
RB
RB Offset
DL Power
Measurements
Power
EVM
EVM Flatness
Frequency Accuracy
Carrier Feedthrough
TX Time Mask
Occupied Bandwidth
ACLR
SEM
In-Band Emissions for
Non-Allocated RBs
© 2012 LitePoint Corp.
•Varies TX Power
for RB = 12 QPSK channel
Test Configuration
1
2
3
4
5
6
7
8
9
10
11
+23
+23
+23
+23
+3.2
-30
-40
+23
+3.2
-30
-40
QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK
1
1
1
12
12
12
12
12
12
12
12
0
24
49
0
0
0
0
38
38
38
38
-57
-57
-57
-57
-57
-57
-57
-57
-57
-57
-57
1
2
3
4
5
6
7
8
9
10
11
•RB Offset
Extremes
•50
Building a LTE TDD TX Verification Test Plan
Per-Band
Per
Band / Per-Channel
Per Channel
A “reasonable” LTE test plan covered in 21 configurations
Showing config 12-21
•Min / Max
Power
•for QPSK
RB = 50
Parameters
TX Power
Modulation
RB
RB Offset
DL Power
Measurements
Power
EVM
EVM Flatness
Frequency Accuracy
Carrier Feedthrough
TX Time Mask
Occupied Bandwidth
ACLR
SEM
In-Band Emissions for
Non Allocated RBs
Non-Allocated
© 2012 LitePoint Corp.
•Tests Absolute
Power Setting
•Min / Max
Power for 16
QAM
•Min / Max
Power for 16
QAM
•RB = 12
•RB = 50
Test Configuration
12
13
14
15
16
17
18
19
20
21
+23
-40
+6.4
-5.6
+23
-40
+23
-40
+23
-40
QPSK QPSK QPSK QPSK 16QAM 16QAM 16QAM 16QAM 16QAM 16QAM
50
50
50
50
12
12
12
12
50
50
0
0
0
0
0
0
38
38
0
0
-57
-57
-57
-57
-57
-57
-57
-57
-57
-57
12
13
14
15
16
17
18
19
20
21
•RB Offset
Extremes
•51
Optimizing the TX Test Plan
•Configurations 1, 3, 12, & 20 test the extremes of modulation and RB allocations / offsets
•Configuration 4 is a “typical” use case
Parameters
TX Power
Modulation
RB
RB Offset
DL Power
Measurements
Power
EVM
EVM Flatness
Frequency Accuracy
Carrier Feedthrough
TX Time Mask
Occupied Bandwidth
ACLR
SEM
In-Band Emissions for
Non-Allocated RBs
Test Configuration
1
2
3
4
5
6
7
8
9
10
11
12
+23
+23
+23
+23
+3.2
-30
-40
+23
+3.2
-30
-40
+23
QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK
1
1
1
12
12
12
12
12
12
12
12
50
0
24
49
0
0
0
0
38
38
38
38
0
-57
-57
-57
-57
-57
-57
-57
-57
-57
-57
-57
-57
1
2
3
4
5
6
7
8
9
10
11
12
No Need for MidChannel Offset
Covered by
Config 21
Already Tested Band
Edges in Configs 1 & 3
13
-40
QPSK
50
0
-57
13
Covered by
Config 21
14
+6.4
QPSK
50
0
-57
14
15
-5.6
QPSK
50
0
-57
15
Can be covered
by any absolute
power setting
16
+23
16QAM
12
0
-57
16
17
-40
16QAM
12
0
-57
17
18
+23
16QAM
12
38
-57
18
19
-40
16QAM
12
38
-57
19
20
+23
16QAM
50
0
-57
20
21
-40
16QAM
50
0
-57
21
Covered by Config 20 &
21, do not need mid-RB
•Configurations we
definitely want to keep
© 2012 LitePoint Corp.
•52
Condensed Test Plan
Reduced to 7 TX configurations
• Added RX tests
• Increases number of measurements while reducing test time
•
Parameters
TX Power
Modulation
RB (UL / DL)
RB Offset
DL Power
Measurements
Power
EVM
EVM Flatness
Frequency Accuracy
Carrier Feedthrough
TX Time Mask
Occupied Bandwidth
ACLR
SEM
In-Band Emissions for
N All t d RB
Non-Allocated
RBs
Measurements
RX BER
© 2012 LitePoint Corp.RX Level
Test Configuration
T1
T2
T3
T4
T5
T6
T7
+23
+23
+23
+23 +3.2 +23
-40
QPSK QPSK QPSK QPSK QPSK 16QAM 16QAM
1
1
12
50
12
12
50
0
49
24
0
24
0
0
-57
-57
-57
-94
-57
-25
-60
TX1 TX2 TX3 TX4 TX5 TX6 TX7
MPR MPR
MPR
RX1
RX2
RX3
•53
LTE TDD Manufacturing Test
•
LTE increases test complexity 5 to 10X
- More measurements, more antennas, wider bandwidth, higher
g
p
performance
- IQxstream’s unique architecture makes LTE test simple and fast
•
Test plan development for LTE needs to focus on exercising the mobile
device with the minimum test time
•
A test plan can be created to maximize
the coverage of the device by using the
test equipment in an efficient manner
- Number of configurations take more test time than number of tests
- Scale test plan to multi-DUT through turnkey non-signaling solutions
- No sacrifice in product quality with shorter per-DUT test times
© 2012 LitePoint Corp.
•54