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FER/Throughput Measurement Feedback for 1X EV-DV

FER/Throughput Measurement Feedback for 1X EV-DV. Giridhar D. Mandyam Nokia Research Center. Alan Hsu and Mark Cheng Nokia Mobile Phones. Introduction. 1X EV systems require mobile station feedback for link adaptation

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FER/Throughput Measurement Feedback for 1X EV-DV

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  1. FER/Throughput Measurement Feedback for 1X EV-DV Giridhar D. Mandyam Nokia Research Center • Alan Hsu and Mark Cheng • Nokia Mobile Phones

  2. Introduction • 1X EV systems require mobile station feedback for link adaptation • Due to bandwidth restrictions on uplink, mobile cannot send back full characterization of downlink channel to BTS • Feedback may be restricted to following parameters • Ec/Nt measurement on downlink • Multipath detected • Base station may be able to estimate limited downlink channel conditions from uplink received data • Doppler frequency • Frame error rate on downlink based on ACK/NAK's received on uplink • Degradation in system performance can occur due to incorrect link allocation decisions by base station due to limited feedback

  3. Motivation • Since the BTS has an imperfect characterization of the downlink channel, the mobile may be assigned a modulation and coding method on the downlink which violates the service's QoS requirements • FER in particular • BTS may measure FER from fast ARQ ACK's • Requires reliability at MAC layer • May not be supported depending on configuration of service • Accuracy of measurement affected by • ACK error rate (i.e. erroneous ACK's on uplink) • ACK frequency (i.e. small number of received ACK's on uplink) • BTS may imply FER based on using lookup tables along with available information characterizing downlink channel • Incorrect characterization of dowlink channel can lead to non-ideal link allocation

  4. What is FER/Throughput Measurement Feedback? • Mobile sends bit on uplink - the FER/throughput measurement feedback • Indicates to the base station that measured FER at mobile has been exceeded • Base station can use indication to reduce modulation and coding assignment on downlink to more reliable configuration • Can be viewed as a sort of outer loop power control for forward shared resources

  5. FER Measurement Performance for 1XTREME: 16 QAM, 1 code channel

  6. FER Measurement Performance for 1XTREME: 8-PSK, 1 code channel

  7. FER Measurement Performance for 1XTREME: QPSK, 1 code channel

  8. Summary of Results for FER Measurement • At ACK bit SNR = 8 dB (5% error rate) • 16 QAM resulted in as much as 4.8 dB degradation in FER measurement • 8-PSK resulted in as much as 4.5 dB degradation in FER measurement • QPSK resulted in as much as 3.7 dB degradation in FER measurement • Incorrect FER measurement at BTS could result in downlink throughput degradation • Could result in unnecessary allocations to lower modulation and coding schemes • Evidenced by fact that FER measurement error on ACK channel resulted in overstimated FER

  9. Throughput Test • Test set up • 1-path Rayleigh on downlink at 3 km-hr • BTS using incorrect characterization of downlink channel • Assuming Ped B on downlink • Correct velocity estimate • Mobile sets feedback bit to '1' to indicate throughput is too low • Comparison scenarios • With feedback • Without feedback • Without feedback but with BTS using correct characterization of downlink channel

  10. Throughput Performance

  11. Summary of Results for Throughput Performance • Biggest performance benefits at lower SNR • As much as 2 dB enhancement using feedback • Shown to at least partially correct for imperfect downlink channel characterization at BTS • Comes to within a 1 dB of perfect channel characterization

  12. Recommendations • One bit of feedback be added to 1X EV-DV uplink to indicate excessive FER on downlink shared resource • Base station can use feedback bit to adjust link allocation to mobile • Feedback rate for measurement should be equivalent to maximum adaptation rate

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