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. •39 •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