**5. Summary**

44 Will-be-set-by-IN-TECH

As illustrated in the previous section an integration of TK operation into the MIR-UWB system is possible with only minor complexity increase if at most one NBI occurs in each subband. In this case the approach of [42] can be used. It bases on the interplay of the TK operation with a highpass filtering. As illustrated in Fig. 27 only two additional analogue components have to be integrated into each subband of the existing non-coherent MIR-UWB receiver. Thereby, received subband signals are given to TK operation which acts as a frequency-to-DC shifter. The resulting low-frequency signal is afterwards highpass filtered to mitigate interfered signal components without any a priori information of the interference specific carrier frequency. As the bandwidth of the subband signal is larger than the interference bandwidth energy

**Figure 27.** Integration of TK operation into the existing non-coherent MIR-UWB receiver.

the MIR-UWB subband with an SIR of −5 dB.

signal highpass filtering is done after the TK operation.

In the following the potential of interference mitigation with the TK operation is shown for OOK in case of a binary one. An MIR-UWB subband of carrier frequency 5.13 GHz and effective bandwidth 162.5 MHz is considered for SNR = 11 dB. It is assumed that an IEEE 802.11a WLAN signal [47] of bandwidth 20 MHz and of carrier frequency 5.14 GHz interferes

Fig. 28 (a) shows the to one normalized amplitude spectrum of all occurring signal components at the output of TK operation. Thereby, the UWB signal spectrum ranges from DC to 162.5 MHz whereas the lower frequency regions have a higher energy concentration. A similar behaviour occurs for the narrowband WLAN signal. Its corresponding amplitude spectrum ranges from DC to 20 MHz whereas energy is strongly distributed around DC. Furthermore, additional spectral cross components between signal, noise and interference occur which can be ascribed to the non-linearity of the TK operation. To mitigate the WLAN

Fig. 28 (b) illustrates the to one normalized amplitude spectrum after highpass filtering. The used highpass filter is characterised by the order six, a passband ripple of 0.1 dB, a 50 dB stopband attenuation as well as a 50 MHz wide stopband. Obviously, the narrowband WLAN signal is mitigated after highpass filtering. In contrast the subband signal has an

*4.3.3. Integration of Teager-Kaiser operation*

detection might be possible.

This chapter deals with an easy-to-realise non-coherent MIR-UWB system which is a promising approach for high data rate and energy efficient communication over short distances. Due to its low complexity the MIR-UWB system is an alternative to already existing UWB systems for high data rate applications such as Multiband OFDM UWB.

The MIR-UWB system is based on an energy detection receiver. Thus the first part of this chapter deals with the performance of this component. To understand the energy detection receiver we look at the bit and symbol error probability in different wireless channels.

First we introduce a closed form expression of the SEP for an energy detection receiver with *M*-PAM in the AWGN channel. Based on this result, we optimise the interval thresholds to minimise the SEP. Optimal interval thresholds guarantee a minimal SEP for *M*-PAM. In the next step we look into the optimal amplitudes for *M*-PAM using an energy detection receiver. This approach enables to reduce the SEP for *M*-PAM with medium to large degrees of freedom.

To understand the characteristics of the energy detection receiver in fading channels we look into different approaches to model the energy at the receiver. It has been shown, that the flat fading channel model can be used to model the energy at a receiver for a receiver bandwidth *B* > 100 MHz. Based on this assumption we introduce closed form expressions for the SEP of the energy detection receiver with *M*-PAM for different fading statistics such as *Rayleigh*, *Rice* and *Nakagami*-*m*. We also analyse the SEP of an multichannel receiver using different combining techniques. Square Law Combing and Square Law Selection are possible combining schemes for an energy detection receiver. A closed form solution for SLC and SLS is introduced for the AWGN and for the *Rayleigh* fading channel including i.i.d. and correlated fading gains.

The first part ends with the analysis of the SEP in a frequency selective fading channel. Based on *Rayleigh* distributed fading gains, representing a non line-of-sight channel (NLOS), we

#### 46 Will-be-set-by-IN-TECH 46 Ultra-Wideband Radio Technologies for Communications, Localization and Sensor Applications MIRA – Physical Layer Optimisation for the Multiband Impulse Radio UWB Architecture <sup>47</sup>

introduce a closed form expression for the energy detection receiver with *M*-PAM. The result also contains the possibility to analyse the effect of correlated fading gains. This is the case in typical UWB wireless channels. If the fading gains are not *Rayleigh* distributed, we present a numerical solution for any fading distributions. The results of the first part enable a precise prediction of an energy detection receiver with *M*-PAM in many different scenarios.

Hanns-Ulrich Dehner, Holger Jäkel, Martin Braun and Friedrich K. Jondral *Communications Engineering Lab, Karlsruhe Institute of Technology (KIT), Germany*

[1] Abramowitz, M. & Stegun, I. [1964]. *Handbook of mathematical functions with formulas, graphs, and mathematical tables*, Applied mathematics series, Dover Publications. [2] Batra, A. [2008]. *Multiband OFDM Physical Layer Proposal for IEEE 802.15 Task Group 3a*,

MIRA – Physical Layer Optimisation for the Multiband Impulse Radio UWB Architecture 47

[3] Bober, M., Moorfeld, R. & Jorswieck, E. [2011]. Performance of Energy Detection in NLOS frequency-selective Fading Channels, *Proc. of IEEE International Symposium on Personal,*

[4] Cassioli, D., Win, M. Z. & Molisch, A. F. [2002]. The ultra-wide bandwidth indoor channel: from statistical model to simulations, *IEEE Journal on Selected Areas in*

[5] Dehner, H., Jäkel, H., Burgkhardt, D. & Jondral, F. K. [2010]. The Teager-Kaiser Energy Operator in Presence of Multiple Narrowband Interference, *IEEE Communications Letters*

[6] Dehner, H., Jäkel, H., Burgkhardt, D., Jondral, F. K., Moorfeld, R. & Finger, A. [2010]. Treatment of temporary narrowband interference in noncoherent multiband impulse radio UWB, *Proc. of IEEE Mediterranean Electrotechnical Conference*, pp. 1335 – 1339. [7] Dehner, H., Jäkel, H. & Jondral, F. K. [2011a]. Narrow- and broadband Interference Robustness for OOK/BPPM based Energy Detection, *Proc. of IEEE International*

[8] Dehner, H., Jäkel, H. & Jondral, F. K. [2011b]. On the modified Teager-Kaiser energy operator regarding narrowband interference, *Proc. of IEEE Wireless Telecommunications*

[9] Dehner, H., Koch, Y., Jäkel, H., Burgkhardt, D., Jondral, F. K., Moorfeld, R. & Finger, A. [2010]. Narrow-band Interference Robustness for Energy Detection in OOK/PPM, *Proc.*

[10] Dehner, H., Linde, M., Moorfeld, R., Jäkel, H., Burgkhardt, D., Jondral, F. K. & Finger, A. [2009]. A low complex and efficient coexistence approach for non-coherent multiband

[11] Dehner, H., Moorfeld, R., Jäkel, H., Burgkhardt, D., Finger, A. & Jondral, F. K. [2009]. Multi-band Impulse Radio – An Alternative Physical Layer for High Data Rate UWB Communication, *Frequenz, Journal of RF-Engineering and Telecommunications* Vol. 63(No,

[12] Dehner, H., Romero, A., Jäkel, H., Burgkhardt, D., Moorfeld, R., Jondral, F. K. & Finger, A. [2009]. Iterative coexistence approaches for noncoherent multi-band impulse radio

[13] Digham, F. F., Alouini, M.-S. & Simon, M. K. [2007]. On the Energy Detection of Unknown Signals Over Fading Channels, *IEEE Transactions on Communications* 55(1): 21–24. [14] ECC [2006]. ECC decision of 24 march 2006 on the harmonised conditions for devices using ultra-wideband (UWB) technology in bands below 10.6 GHz, *Technical Report* . [15] Eisenacher, M. [2006]. Optimierung von Ultra-Wideband-Signalen (UWB), *Dissertation, Forschungsberichte aus dem Institut für Nachrichtentechnik der Universität Karlsruhe (TH),*

UWB, *Proc. of IEEE International Conference on Ultra-Wideband*, pp. 734 – 738.

**6. References**

IEEE P802.15-03/268r1.

Vol. 14(No, 8): 716 – 718.

*Conference on Communications*.

*of IEEE International Conference on Communications*.

impulse radio UWB, *Proc. of IEEE Sarnoff Symposium*.

*Symposium*.

9-10): 200–204.

*Band 16, 2006* .

*Indoor and Mobile Communications (PIMRC)*.

*Communications* 20(6): 1247–1257.

Since the MIR-UWB system is highly sensitive to interference, the second part of the chapter considers three different aspects regarding an efficient interference mitigation.

The first aspect deals with the analysis of the interference robustness of an OOK and BPPM specific energy detection receiver being the essential component of the non-coherent MIR-UWB receiver. Thereby, taking into account thermal noise a general frame work is presented which can be used to give statements on the detector's interference robustness for an interference with arbitrary bandwidth. Furthermore, possible system parameters can be identified to increase the detector's interference robustness.

The second aspect considers the coexistence capability of the MIR-UWB system. Thereby, various easy-to-realise adaptive coexistence-based approaches are presented. Starting with a static coexistence approach a DAA coexistence approach for temporary NBI is presented being integrated into the system specific initialisation and data phase. The proposed method allows a reliable adaptive mitigation of temporary NBI. A further adaptive coexistence approach bases on image-based thresholding which can be integrated into the initialisation phase of the MIR-UWB system. Based on an exemplary interference scenario the potential to efficiently mitigate multiple interferences of different interference power is shown.

Lastly, the third aspect focuses on the analytical investigation of the potential to mitigate NBI inside an energy detection receiver. Hereby, the TK operation as well as a modified TK operation is analysed. It is shown that for a narrowband baseband signal the output of the TK operation is characterised by a larger energy concentration in the lower frequency range. In contrast, for the modified TK operation further spectral components occur for higher frequencies. A subsequent analysis of one NBI in the bandpass domain shows that the TK operation acts like a frequency-to-DC shifter. This reveals the potential to mitigate a single NBI without the knowledge of the NBI's carrier frequency. In contrast, for the modified TK operation additional spectral components at twice the NBI's carrier frequency occur making interference mitigation critical. In case of multiple NBI further spectral components occur at the TK operation's output which can be ascribed to the mutual interference influences. Due to a possible distribution of the spectral components within the total MIR-UWB subband interference mitigation depends on the interference position inside the MIR-UWB subband.
