Testing c2k Mobile Stations Using a Digitally Generated Faded Signal

Transcription

1 Testing c2k Mobile Stations Using a Digitally Generated Faded Signal

2 Agenda Overview of Presentation Fading Overview Mitigation Test Methods

3 Agenda Fading Presentation Fading Overview Mitigation Test Methods

4 Fading Overview Large Scale Path Loss Small Scale Path Loss Tx/Rx Separation Short Time Short Motion Free space path loss Inverse square Rayleigh Distribution

5 Fading Overview Overview - Large scale Buildings Mountain Signal level Time Free space path loss (log-normal) average attenuation, exponentially proportional to distance Shadowing (diffraction) secondary wavelets wrap around large objects

6 What is fading? The effect of the environment on the Tx signal at the Rx Multipath time delayed copies of the signal Doppler shift spreading of the spectrum Attenuation atmosphere reduces signal amplitude Why is it important? Enables engineers to test the receiver (BER/BLER) under realistic channel conditions

7 Fading Overview Overview - Small scale Multipath propagation NLOS LOS NLOS Doppler shift caused by angle of arrival relative to motion of receiver

8 Fading Overview QPSK Signal in Rayleigh Deep Fade QPSK Pilot Signal with no deep Rayleigh fade fade

9 Fading Overview Time spreading time frequency TX Impulse Signal strength Received Impulses Delay time T m Max excess delay Fourier Transform F 0 ~ 1/T m F 0 Coherence bandwidth Symbols Frequency selective 1 Flat fading

10 Fading Overview Time variance time frequency Fourier Transform 0 T o Coherence time T 0 ~ 1/f d f c -f d f c f c + f d F d = Doppler spread Symbols 1 Slow fading Fast fading

11 Fading Overview Reduced signal-to-noise ratio (SNR) large scale, flat fading, slow fading Intersymbol interference (ISI) frequency selective fading Must account for total fading margin in link budget analysis Receiver Tu Transmitter Tx 1 2 Time 3 Rx 1 2 Time 3 ISI causes symbol spreading Delay spread

12 Agenda Fading Overview Mitigation Test Methods

13 Mitigation Error correction interleaving and coding Diversity in time in space in frequency Device design Rake receiver

14 Mitigation Effects of Direct Spreading Jamming Signal Data PN Sequence Generator Demod PN Sequence Generator Data

15 Agenda Fading Overview Mitigation Test Methods

16 Test Methods Rayleigh Threshold ( ) S f f fc < 2 f fc fd 1 d 1 f f c = carrier freq, f d = Doppler spread f d Fade Nonfade period f c -f d f c f c + f d No line of sight Deep fades separated by half-wavelength on average Worst-case scenario

17 Test Methods Rician ray α ν S(f) πf d if f 1 f P c Ry f < f f d d f c 2 + P, where Rc δ[(f fc) θ ] P Ry = coefficient of powerof Rayleighcomponent Rc f d P Rc = coefficient of powerof Riciancomponent Fc - fd Fc + 0.7fd fc Fc + fd θ Rc = angle of arrival of Rician direct path Rayleigh + direct path Good for rural areas K factor ratio between direct path and NLOS paths

18 Test Methods Suzuki Signal power Log-normal Rayleigh Log-normal + Rayleigh fading Rayleigh represents small scale fading Log-normal represents largescale fading Antenna displacement (or time)

19 Test Methods cdma2000 MS Fading Tests Channel Section Test Broadcast control channel Demodulation performance in multipath fading Demodulation performance in multipath fading Demodulation performance in multipath fading with closed loop power control (FPC_MODE = ' 000' ) Forward traffic channel Demodulation performance in multipath fading with closed loop power control (FPC_MODE = ' 010' ) Demodulation performance in multipath fading with closed loop power control (FPC_MODE = ' 000', ' 001', and ' 010' ) Demodulation performance in multipath fading with closed loop power control (FPC_MODE = ' 000' ) and transmit diversity Demodulation performance in multipath fading with closed loop power control (FPC_MODE = ' 010' ) and transmit diversity

20 Test Methods cdma2000 MS Receiver Testing standard setup AWGN Generator Tx BTS Emulator Channel Simulator Σ MS Under Test Tx/Rx Rx

21 Test Methods Example test Demodulation of Forward Traffic Channel in multipath Case Radio Configuration Channel Simulator Configuration Number (8 km/h, 2 paths) (30 km/h, 1 path) (100 km/h, 3 paths) (8 km/h, 2 paths) (30 km/h, 1 path) (100 km/h, 3 paths) Verify that the FER stays below a certain value under standard channel simulation conditions Parameter Units Test 1 Test 2 Test 3 Îor/Ioc db 8 Parameters Band Classes Vehicle 0, 2, 3, 5, 7, 9, Speed 10, 11 and 12 [km/h] Band Classes 1, 4, 6 and 8 Number of Paths Path 2 Power (Relative to Path 1) [db] Path 3 Power (Relative to Path 1) [db] Delay from Path 1 to Delay from Path 2 to Delay from Path 3 to Channel Simulator Configuration N/A 0 0 N/A N/A N/A N/A -3 N/A N/A N/A 2 2 N/A N/A N/A N/A 14.5 N/A N/A Pilot E c I or db -7 (1): (1): (1): Traffic Ec db (2): (2): (2): Ior (3): (3): (3): Îoc dbm/ 1.23MH -63 Data Rate bps 9600 (1): 6.8 (1): 9.4 (1): 11.4 TrafficEb db (2): 6.8 (2): 9.4 (2): 11.4 Nt (3): 5.7 (3): 6.9 (3): 7.7 Channel Simulator 1 Configuration (1): BC 5 and 11; (2): BC 0, 2, 3, 7, 9, 10 and 12; (3): BC 1, 4, 6 and 8.

22 Test Methods Conversion Loss and Noise Calibration RF In ADC Loss Digitized sample Rayleig Log-normal h Rician Add fading DAC Loss Add AWGN RF Out Errors from conversion loss increase uncertainty Measure output power Add noise Measure total power Adding calibrated noise is difficult and time-consuming Average Process must be repeated for any change in power!

23 Test Methods All digital fading simulator DUT RF Digital bus Reconfigurable FPGA technology Intuitive user interface Digital connectivity ease of use and error reduction Test Set or Signal Generator 1) Test Set or Signal Generator generates baseband signal. 2) Baseband waveform is sent to PC over digital bus 3) Signal is faded and AWGN is added in PC 4) Baseband signal is sent back to Test Set for upconversion to RF

24 Test Methods All digital calibrated and integrated noise Signal Source RF Output Power Meter old method Power Meter AWGN Source Conventional RF Fader Directional Couplers Power Meter Combiner Directional Coupler Faded RF Signal with AWGN Digital bus new method PC Test Set

25 Testing Preconfigured setups for major cell standards

26 Test Methods Fading with call processing 8960 Series 10 Test Set with W-CDMA and cdma2000 Lab Applications High Speed Digital Bus Baseband Studio for Fading Fade real-time signals coming from 8960 DUT RF Faded signals to DUT

27 References Bernard Sklar; Rayleigh Fading Channels in Mobile Digital Communication Systems Part I: Characterization; IEEE Communications Magazine; July 1997 Bernard Sklar; Rayleigh Fading Channels in Mobile Digital Communication Systems Part II: Mitigation; IEEE Communications Magazine; July 1997 Theodore Rappaport; Wireless Communications: Principles and Practices; Prentice Hall PTR; 1996 Victor Shtrom, Jose Tellado, A. Paulraj; Designing MIMO systems for reliable coverage in non-los wireless links; RF Design; October 2002 Wally Rasmussen; Simulating the Complex Multipath Signal Conditions of the Mobile Radio Environment; Hewlett-Packard Wireless Communications Symposium;

28 For more information, please visit ww.agilent.com/find/basebandstudio

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