1. Communication Technology Laboratory Wireless Communication Group Partial Channel State Information and Intersymbol Interference in Low Complexity UWB PPM Detection + T. Zasowski, F. Troesch, A. Wittneben 12. MCM of COST 289 October 30-31, 2006 + has been published in part at ICUWB, September 2006, Waltham/Boston, USA

2. 2 Communication Technology Laboratory Wireless Communication Group Outline Introduction –Motivation –Intersymbol Interference aware ML symbol detection with partial channel state information Performance without Intersymbol Interference –ML full, ML IDPD, ML APDP Performance with Intersymbol Interference –ML full,ISI, ML IDPD,ISI, ML APDP,ISI –Energy detector with MLSE Conclusions

3. 3 Communication Technology Laboratory Wireless Communication Group Wireless Body Area Network sufficient link margin (>25dB) within FCC constraints reasonable excess path delay (<20ns) low data rate: throughput < 1Mbps ultra low power consumption: –low duty cycle, i.e. high peak data rate (50Mbps): ISI –low complexity modulation and detection robustness to synchronization errors 2-PPM impulse radio single pulse per bit symbol-wise (energy) detector Goal: get intuition on the impact of partial CSI in the presence of ISI

4. 4 Communication Technology Laboratory Wireless Communication Group Partial Channel State Information full CSI –(discrete) channel impulse response known at the receiver instantaneous power delay profile (IPDP) –only magnitude of the real channel taps known at RX –measured after squaring device of energy detector receiver average power delay profile (APDP) –average power of each channel tap known at RX no CSI –average energy of channel impulse response known at RX

5. 5 Communication Technology Laboratory Wireless Communication Group Discrete System Model 2-PPMchannel Detector S P f observation window

6. 6 Communication Technology Laboratory Wireless Communication Group Intersymbol Interference Aware Symbol-Wise ML Detection with Partial Channel State Info observation vector : one PPM frame statistically independent normal channel taps –diagonal correlation matrices maximum length of discrete channel impulse response: T symbolwise -ML decision variable with partial CSI C PPM frame 1

7. 7 Communication Technology Laboratory Wireless Communication Group Outline Introduction –Motivation –Intersymbol Interference aware ML symbol detection with partial channel state information Performance without Intersymbol Interference –ML full, ML IDPD, ML APDP Performance with Intersymbol Interference –ML full,ISI, ML IDPD,ISI, ML APDP,ISI –Energy detector with MLSE Conclusions

8. 8 Communication Technology Laboratory Wireless Communication Group Special Case: Decision Metrics without ISI full CSI: instantaneous power delay profile: average power delay profile: –for : energy detector ISI metrics in paper

9. 9 Communication Technology Laboratory Wireless Communication Group after the unitary transformation H we obtain the statistically equivalent decision variable –performance independent of "shape" of impulse response excess noise due to excess dimensions ED: Energy Detector uses the decision variable –with a unitary transformation H has no impact on the error performance we choose H such, that without ISI we have for s 1 =-1 same as N/2=1 statistically independent zero mean noise from excess dimensions

10. 10 Communication Technology Laboratory Wireless Communication Group without ISI we obtain for IPDP for ML full as L(s 1 =1) loss for IPDP ML IPDP : Instantaneous Power Delay Profile in the high SNR regime we obtain the approximation compare to ML full

11. 11 Communication Technology Laboratory Wireless Communication Group Performance Results without ISI based on physical system (continuous time) –PPM frame duration T=20ns –10dB-bandwidth B 10 =3GHz uniform power delay profile –max. delay: 10ns equivalent discrete model has N/2=60 i.i.d. normal channel taps energy of each channel realization normalized to 1 –ML full performance same as AWGN –emphasizes impact of PDP minor improvement with IPDP ED performance sufficient

12. 12 Communication Technology Laboratory Wireless Communication Group Outline Introduction –Motivation –Intersymbol Interference aware ML symbol detection with partial channel state information Performance without Intersymbol Interference –ML full, ML IDPD, ML APDP Performance with Intersymbol Interference –ML full,ISI, ML IDPD,ISI, ML APDP,ISI –Energy detector with MLSE Conclusions

13. 13 Communication Technology Laboratory Wireless Communication Group ML full,ISI -Symbol-Wise Detector: Considers ISI energy per bit: impulse crosscorrelation: free Euclidean distance: decision regions adapted to ISI requires three correlators

14. 14 Communication Technology Laboratory Wireless Communication Group ML full -Symbol-Wise Detector: ignores ISI decision variable –mismatched to ISI –requires only one correlator free Euclidean distance: for a=0 we obtain for the loss w.r.t the ISI aware metric optimal without ISI ( ) for a=0 and E h =E g : 1.8dB loss in comparison to ML full,ISI

15. 15 Communication Technology Laboratory Wireless Communication Group decision metric for uniform PDP (energy detector) without additive noise we obtain e.g. for s 1 = -1 High SNR performance of ML APDP (ignores ISI) => ISI causes error floor PPM frame 1

16. 16 Communication Technology Laboratory Wireless Communication Group MLSE : Maximum Likelihood Sequence Estimator uses two decision variables per PPM frame –energy detector: L=L 2 -L 1 simple two-state trellis: very limited instantaneous CSI required: simplified branch metrics –the noise is modelled as normally distributed with nonzero mean potentially removes error floor of ED with ISI note: operates with bit clock (as opposed to sample rate)

17. 17 Communication Technology Laboratory Wireless Communication Group Performance Results: Weak ISI based on physical system (continuous time) –PPM frame duration T=20ns –10dB-bandwidth B 10 =3GHz uniform power delay profile –max. delay: 14ns energy of each channel realization normalized to 1 ISI aware metrics substantially improve performance ML APDP,ISI essentially blanks ISI segment of PPM frame MLSE close to ML APDP,ISI even though max. delay is not known –no error floor

18. 18 Communication Technology Laboratory Wireless Communication Group Performance Results: Strong ISI based on physical system (continuous time) –PPM frame duration T=20ns –10dB-bandwidth B 10 =3GHz uniform power delay profile –max. delay: 17ns energy of each channel realization normalized to 1 ED not applicable due to 10% error floor –MLSE removes error floor ML IPDP,ISI almost as robust to ISI as ML full,ISI –ISI aware metric very efficient MLSE and ML APDP,ISI again have similar performance

19. 19 Communication Technology Laboratory Wireless Communication Group Summary and Conclusions we derived the intersymbol interference aware ML- symbol decision metrics for partial CSI –full CSI (ML full ML full,ISI ) –instantaneous power delay profile (ML IPDP ML IPDP,ISI ) –average power delay profile (ML APDP ML APDP,ISI ) ML APDP,ISI removes the ISI induced error floor of the ED ML full and ML IPDP are suprisingly robust to ISI MLSE performs similar to ML APDP,ISI overall the MLSE seem the most attractive compromise between complexity and performance in our application