Higher Order Impulsive Signals for Short Range Communications

1. Higher Order Impulsive Signals for Short Range Communications Simone Morosi, Dania MarabissiUniversity of Firenze, ItalyJocelyn FiorinaEcole Supérieure d’Electricité, France These results have been obtained the framework of the Network of Excellence NEWCOM and partially presented at PIMRC 2006.

2. UWB communications ULTRA WIDE BAND technology has been presented as a promising way to provide very high speed communication with multiple access. Another potential application is also low data rate networks with positioning capability. It is a solution for new types of local area network. One of the first proposal has been developed by R.A.Scholtz ("Multiple Access with Time-Hopping Impulse Modulation", Milcom’93). It was based on Time Hopping Modulation (TH-PPM, TH-PAM UWB). The basic receiver in UWB is the single user matched filter (SUMF) receiver which is a simple receiver using correlation. It has the advantage to be a relatively easy and low cost receiver.

3. UWB in few words Definition: Fractional Bandwidth Δf/fc > 0.25. Reuse of the band, the UWB signals should act as harmless noise on existing systems. LPI/LPD Technology inherited from radar where UWB exists from a long time; the huge bandwidth provides temporal precision and ranging/localization ability.

4. A glimpse of history Some articles establish the sources of UWB systems in Marconi works. On the other hand, other cite Hedy Lamarr and George Antheil as first example of spread spectrum systems. 1949: Shannon and Pierce, idea of CDMA, a time hopping spread spectrum multiple access system in a bell labs technical memorandum. 1952: Pierce, Hopper, "Non-synchronous time division with holding and with random sampling" 60’s to 80’s: impulses radar development, definition of superwideband in USSR: fractionnal bandwidth >0.1. DARPA and classified research. 92: Withington and Fullerton "An impulse radio communications system", 93: R.A.Scholtz, "Multiple Access with Time-Hopping Impulse Radio“

5. Monocycle A typical pulse: the second derivative of a Gaussian pulse (Scholtz) τn=0.1125ns t

6. Topic of this presentation What we propose here is a formalization of the IR-UWB signals, allowing to propose high order signaling schemes. Classical constellation are usually used for complex value signals, we have generalized the constellation representation to the real value base-band IR-UWB signals. The high order signaling schemes will improve the bit rate because of the higher number of bits per symbol, but also thanks to the symbol time reduction.

7. UWB communications: basis

8. UWB communications: basis TH-PPM UWB am=1 am+1=0 t δ δ Each symbol is composed of Ns frames. Each frame is composed of Nh slots. Ns is called the repetition factor. Nh the frame length. The processing gain of the spread spectrum system is N=Ns.Nh

9. UWB communications: basis TH-PAM UWB am=1 am+1=-1 t

10. SUMF receiver (TH-PAM) SUMF (Single User Matched Filter) reception in TH-PAM. Also called correlator receiver. Received signal : s(t) = y(t) + n(t). t Correlation with the template: t

11. SUMF receiver (TH-PPM) t Correlation with t minus t

12. Constellations

13. Constellations

14. Constellations Introduction of a basis in the signal space to represent and We can choose !!

15. Constellations Symbols in PPM: p1 and p2 ( and ) Symbols in PAM: p1 and -p1 ( and )

16. Constellations 4-PAPM

17. Constellations 8-PAPM MTO Note that

18. Performances

19. Bit rate If we represent an impulse w by 40 samples:

20. Bit rate

21. Bit rate

22. Conclusions We have proposed a formalization which is useful to understand IR-UWB signaling through constellations. Thus we can derive high order signaling schemes which increase the efficiency of IR-UWB. Higher order signaling are highly vulnerable to frequency selective fading which is very strong in UWB-IR indoor applications. Current activities aim at defining proper strategies for these signallinmg schemes in indoor environments.