T. Zasowski, F. Troesch, A. Wittneben 12. MCM of COST 289 October 30-31, 2006

1. 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 Communication Technology Laboratory Wireless Communication Group

2. Outline • Introduction • Motivation • Intersymbol Interference aware ML symbol detection with partial channel state information • Performance without Intersymbol Interference • MLfull, MLIDPD, MLAPDP • Performance with Intersymbol Interference • MLfull,ISI, MLIDPD,ISI, MLAPDP,ISI • Energy detector with MLSE • Conclusions Communication Technology Laboratory Wireless Communication Group

3. 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 Wireless Body Area Network • 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 Communication Technology Laboratory Wireless Communication Group

4. 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 Communication Technology Laboratory Wireless Communication Group

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

6. 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 Communication Technology Laboratory Wireless Communication Group

7. Outline • Introduction • Motivation • Intersymbol Interference aware ML symbol detection with partial channel state information • Performance without Intersymbol Interference • MLfull, MLIDPD, MLAPDP • Performance with Intersymbol Interference • MLfull,ISI, MLIDPD,ISI, MLAPDP,ISI • Energy detector with MLSE • Conclusions Communication Technology Laboratory Wireless Communication Group

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

9. 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 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 s1=-1 ED: Energy Detector same as N/2=1 statistically independent zero mean noise from excess dimensions Communication Technology Laboratory Wireless Communication Group

10. without ISI we obtain for IPDP for MLfull as L(s1=1)<0 causes a decision error => loss for IPDP in the high SNR regime we obtain the approximation compare to MLfull MLIPDP: Instantaneous Power Delay Profile Communication Technology Laboratory Wireless Communication Group

11. based on physical system (continuous time) PPM frame duration T=20ns 10dB-bandwidth B10=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 MLfull performance same as AWGN emphasizes impact of PDP Performance Results without ISI • minor improvement with IPDP • ED performance sufficient Communication Technology Laboratory Wireless Communication Group

12. Outline • Introduction • Motivation • Intersymbol Interference aware ML symbol detection with partial channel state information • Performance without Intersymbol Interference • MLfull, MLIDPD, MLAPDP • Performance with Intersymbol Interference • MLfull,ISI, MLIDPD,ISI, MLAPDP,ISI • Energy detector with MLSE • Conclusions Communication Technology Laboratory Wireless Communication Group

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

14. 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 MLfull-Symbol-Wise Detector: ignores ISI • optimal without ISI ( ) • for a=0 and Eh=Eg: 1.8dB loss in comparison to MLfull,ISI Communication Technology Laboratory Wireless Communication Group

15. decision metric for uniform PDP (energy detector) without additive noise we obtain e.g. for s1= -1 High SNR performance of MLAPDP (ignores ISI) PPM frame 1 => ISI causes error floor Communication Technology Laboratory Wireless Communication Group

16. uses two decision variables per PPM frame energy detector: L=L2-L1 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) MLSE : Maximum Likelihood Sequence Estimator Communication Technology Laboratory Wireless Communication Group

17. Performance Results: Weak ISI • based on physical system (continuous time) • PPM frame duration T=20ns • 10dB-bandwidth B10=3GHz • uniform power delay profile • max. delay: 14ns • energy of each channel realization normalized to 1 • ISI aware metrics substantially improve performance • MLAPDP,ISI essentially blanks ISI segment of PPM frame • MLSE close to MLAPDP,ISI even though max. delay is not known • no error floor Communication Technology Laboratory Wireless Communication Group

18. Performance Results: Strong ISI • based on physical system (continuous time) • PPM frame duration T=20ns • 10dB-bandwidth B10=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 • MLIPDP,ISI almost as robust to ISI as MLfull,ISI • ISI aware metric very efficient • MLSE and MLAPDP,ISI again have similar performance Communication Technology Laboratory Wireless Communication Group

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