吉时利_新一代移动通信射频测试技术研讨会_162页.pdf

A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2004 Keithley Instruments,Inc.1RF Test&Measurement RevolutionOFDM Plus MIMOA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.2AgendaThe evolution of communications and an introduction to the test toolsPart One OFDM and SISO radio configurationsThe case for OFDMOFDM Signal Structure,generic and WLAN.MeasurementsOFDM and OFDMAPeak to average ratio considerationsWiMAX and LTEPart Two OFDM and MIMO radio configurationsMIMO Multiple Input Multiple Output Radio TopologyHow it works.MeasurementsChannel ConsiderationsSmart Antenna Systems and Beam Forming ConclusionTechnology Overview and Test Equipment SummaryA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.3The Evolution of RF Technology LTE4GUMB802.11a-b-g-j 802.16e 802.11n 802.16e Wave2SISO MIMOGSM W-CDMA(HSxPA)DVB-HHSPA+GMSK QPSK QAM OFDMcdmaOne cdma2000 1xEV-DV&1xEV-DO MediaFLO3GPP&3GPP2CellularWLAN&WirelessMANSignalBandwidthFrequency200kHz 1.23MHz 5MHz 20MHz 40MHz800MHz 1.8GHz 2.1MHz 2.4GHz 5.8MHzSmart AntennaTraditional Antenna802.16mA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.4Test tools we will use today2800 VSA and 2900 VSGSISOSpectrum Analyzer,Signal GeneratorGSMCDMAWLANWiMAXLTE2800 VSA,2900 VSG+2895MIMOWLANWiMAXLTEA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.5Keithley Simplifies Signal Creationand AnalysisIntroducing the industries only graphically based signal creation and analysis software Signal Meister.Simplifies signal creation allowing users to create signals then optionally add distortion parameters quickly and easilyIncludes signal creation and analysis for 3GPP,3GPP2,WiMAX,WLAN with MIMO configurations and channel distortion.Interfaces to the 2900/2800 series of Keithely vector signal generators and analyzers.A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.6Technology EvolutionSISO2x24x48x8WiFiWiMaxWiMax Wave 22G3G4GWiFi(n)Beam Forming802.16mPhased ArrayA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.7AgendaThe evolution of communications and an introduction to the test toolsPart One OFDM and SISO radio configurationsThe case for OFDMOFDM Signal Structure,generic and WLAN.MeasurementsOFDM and OFDMAPeak to average ratio considerationsWiMAX and LTEPart Two OFDM and MIMO radio configurationsMIMO Multiple Input Multiple Output Radio TopologyHow it works.MeasurementsChannel ConsiderationsSmart Antenna Systems and Beam Forming ConclusionTechnology Overview and Test Equipment SummaryA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.8Traditional Serial Transmission using a SISO radio Only one symbol is transmitted at a time One radio,only one antenna used at a time(e.g.,1 x 1)Antennas constantly switched for best signal pathSingle Data Channel11QI10 01 10 11QIA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.9Why use Orthogonal Frequency Division Multiplex?High spectral efficiency provides more data services.Resiliency to RF interference good performance in unregulated and regulated frequency bands Lower multi-path distortion works in complex indoor environments as well as at speed in vehicles.A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.10High Spectrally Efficiency OFDMGSMW-CDMAHSDPAWLAN802.11a/gWiMax0.52.04.02G(GMSK)3G(CDMA)Bits/Second/HzA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.11Why OFDM?Resiliency to RF interference.The ISM Band(Industrial Scientific and Medical)is a set of frequency ranges that are unregulated.Most popular consumer bands 915MHz Band(BW 26MHz)2.45GHz Band(BW 100MHz)5.8GHz Band(BW 100MHz)Typical RF transmitters in the ISM band include Analog Cordless Phones(900MHz)Microwave Ovens(2.45 GHz)Bluetooth Devices(2.45GHz)Digital Cordless Phones(2.45GHz or 5.8GHz)Wireless Lan(2.45GHz or 5.8GHz).A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.12The Multi-Path ProblemExample:Bluetooth Transmitter&Receiver TX1RX1CeilingFloorMaximum time for signalTo travel D(Distance)Dmultipath DdirectTX to RX 1usSymbol Rate=1MSymbols/sSymbol Duration=1/1E6=1usDdirectMaximum Symbol Delay DdirectTX to RX 3.3usSymbol Rate=300kSymbols/sSymbol Duration=1/300=3.3usDdirectMaximum Symbol Delay 3.3usBut the data throughput is reduced!QI10 01 10 11A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.15Improve the throughput-use more than one carrier!802.11a-g WLAN example250 kbps symbol rate*48 sub-carriers*6 coded bits/sub-carrier*coding rate=54 MbpsLow symbol rate per carrier *multiple carriers =high data rate(for 64QAM)?Symbol Rate Carrier SpacingQI312.5kHzIQIQ312.5kHzIQ312.5kHzIQ312.5kHzDigital filtering creates a sin x spectrax .Carrier spacing aligned with spectra nulls keeps carriers orthogonalA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.16Parallel Symbols QIIQIQIQ10 01 10 1101 10 11 10 11 00 10 10A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.17Parallel Symbols QIIQIQIQ10 01 10 11IFFTTofdm_symbolAdd IQ waveformA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.18Delays in the channelDdirectTX1RX1CeilingFloorChannelTofdm_symbolTofdm_symbolRofdm_symbolDelayA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.19The guard interval and cyclic prefixLengthen without discontinuityCopy and Paste1/8A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.20Building a simple OFDM signalA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.21Examine the Signal in the Frequency DomainBW=FFT Size x Symbol Rate=512 x 10k=5.12MHzUsed Subcarriers x Symbol Rate=482 x 10k=4.82MHzSuppressed Carrier-241 to-1 Subcarriers1 to 241 SubcarriersA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.22Examine the Signal in the Frequency Domain10kHz10kHz10kHzSpacing=Symbol RateA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.23Example:WLAN(802.11a/g)Modulation Technique OFDMBandwidth 16.25MHzNumber of sub-carriers 52Sub-carrier numbering-26 to+26Pilot sub-carriers-21,-7,+7 and+21(BPSK)Sub-carrier BW 312.5kHzPacket Structure Preamble Header Data Block SUB Carrier Modulation Types-BPSK,QPSK,16-QAM or 64-QAM A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.24WLAN Signal GenerationA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.25Frequency Domain 802.11g16.25MHzSubcarrier-26Subcarrier26A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.26Key OFDM MeasurementsA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.27EVM-Constellation DisplayIs a Composite of all OFDM Sub-carriersQIf1f2f3f4fnIndividual Sub-carriersConstellation Display16QAMBPSKQPSKA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.28EVMError Vector MagnitudeA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.29Carrier Feed ThroughA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.30Pilot Carriers Not all of the sub-carriers are used to transmit data.Pilot sub-carriers are used to transmit training symbols throughout the duration of the packet.The receiver uses this information to correct for impairments such as phase variation,clock differences between transmitter and receiver,amplitude variation,and even assist in channel estimation.Pilots are transmitted using BPSK modulation.A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.31Channel FlatnessTX1RX1CHANNEL!fdBfdBfdBRX can equalize orin a closed loop systemSend information back to TX.QPSK16QAMA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.32OFDM to OFDMAOFDM used by WLAN and WiMAX Fixed(802.16d)as a modulation technique is not multi user all sub-carriers in a channel are used to facilitate a single link.OFDMA used by WiMAX mobile(802.16e)and LTE(3GPP Release 8)assigning different number of sub-carriers to different users.A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.33WiMAX(Mobile)sub-channels Frequency Domain.Subchannel0Subchannel1.SubchannelnfA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.34The Physical Channels are Different from the Logical ChannelsA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.35kk+1k+4k+5k+6k+7k+8k+9k+10k+2k+3OFDM Symbol NumberPre-ambleDL-MapUL BurstDL BurstTransitionGapTransitionGapSub Channel Number0.nSymbol Transmission verses TimeRemember OFDM allows us to transmit symbols in parallel.An OFDM symbol period is a group of parallel symbols.A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.36The WiMAX Symbol MapA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.37WiMAX putting it all togetherFrame(t)Down Link(DL)Up Link(UL)Transition GapPreambleDL 1DL xSub ChannelsDL yOFDM Symbol(t)=(1/Carrier Spacing)+Guard IntervalUseful Time(t)=FFT SizeGuardInterval(t)OFDM Symbol(t)FFT Size=1/Carrier Spacing1/41/81/161/32Guard Interval(t)1/41/81/161/32Guard Interval(t)Symbol MapA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.38Creating a SignalFrame(t)Down Link(DL)Up Link(UL)Transition GapPreambleDL User 1DL User xSub ChannelsDL User yOFDM Symbol(t)=(1/Carrier Spacing)+Guard IntervalUseful Time(t)=FFT SizeGuardInterval(t)OFDM Symbol(t)FFT Size=1/Carrier Spacing1/41/81/161/32Guard Interval(t)1/41/81/161/32Guard Interval(t)A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.39Time Domain MeasurementPreambleUser SlotA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.40Frequency Domain Transient EffectsWith TransientsGated on SlotA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.41Peak to Average Ratio for WiMAX and WLANGMSK QPSK QAM OFDMPAR10-134-93-41A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.42Gain Compression IssuesGain compression is illustrated graphically in figure 1.The 1dB Gain Compression point is the input power level that causes the actual amplifier output level to be 1dB less than the extrapolated linear small signal behavior.figure 1.1dB Gain CompressionA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.43Random Phase Addition of Multi-carrier QAM 64 Waveforms Since each sub-carrier transmits their symbols in the same channel the instantaneous signal power due to random phases can add up constructively or they can cancel out.This means that the range of signal powers that the RF amplifier has to generate is widely varying and very dynamic.This is what creates the high peak to average ratio(PAR)Summed QAM 64 vectorsA.Vector phase summationB.Vector phase cancellationA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.44Effects of Gain Compression in OFDM SignalsWaveforms having a large PAR can severely stress an RF amplifier causing it to distort during peaks.The issue for measurement instrumentation is that it is not always easy to tell whether an amplifier is being stressed into compression because the signals are so noise like.802.11A 64QAM signal with 0%compression in zero span802.11A 64QAM signal with 20%compression in zero spanA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.45Effects of Gain Compression in OFDM Signals There are obvious degradations to the signal as viewed in the frequency domain as distortion increases,but it is difficult to derive a quantitive measure that would provide the designer feedback to optimize the circuit.802.11A 64QAM signal with 0%compression802.11A 64QAM signal with 20%compressionA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.46Quantifying Gain Compression for OFDM SignalsThe noise like nature of OFDM signals means that in order to extract useful information from the signal a statistical description of the waveforms power levels is required.For these types of signals a complimentary cumulative distribution function(CCDF)is required.CCDF curves can specify completely the power characteristics of the signals that are transmitted in a communications channel.Figure 2.CCDF curve of 802.11A 64QAM signal-No Compression.Notice the Y-axis is in percent and the x-axis is in dB relative to the average power.This signal spends almost 1%of its time at 8dB above the average power.A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.47Quantifying Gain Compression for OFDM SignalsFigure 3.CCDF curve of 802.11A 64QAM signal with 10%compression.The compressed signal is noticeable on the CCDF curve but there can be no way to make a measurement of compression levels.This signal spends almost 1%of its time at 7.25dB above the average power.The addition of Gain Compression in this amplifier has affected the CCDF curve but not in any way that you could reliably indicate the level of gain compression.A G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.48Symbol to WaveformOFDM Parallel Symbol Transmissionsf1f2f3f4fnOFDM Symbol PeriodMultiple carriers will transmit multiple symbols in parallel.Carriers may have different modulations BPSK,QPSK 64QAM.I waveformQ waveformA G R E A T E R M E A S U R E O F C O N F I D E N C E Copyright 2007-2008 Keithley Instruments,Inc.49Quantifying Gain Compression for OFDM Signals Compare the measured time-domain signal with a reference signal and plot the difference as a function of input magnitude.The reference signal is an ideal time-domain waveform,constructed from the demodulated symbol targets using an IFFT.Time domain errors are measured as a function of input mag