**5. Conclusions**

12 Will-be-set-by-IN-TECH

*d*int

In [17], we have proposed two advanced (low data rate) transmission schemes based on *M*-ary Walsh-modulation, namely repeated Walsh (R-Walsh) and spread Walsh (S-Walsh). For both schemes, the fast Walsh Hadamard transformation can be used to efficiently implement the demodulator. Whereas the more implementation friendly R-Walsh transmission is favorable for data rates of up to 180 kbps (*M* = 8 or *M* = 16), S-Walsh transmission with *M* ≥ 32 is an

In [15], we have compared R-Walsh transmission with *M*-PPM. It has been shown that R-Walsh works well with a 1-bit quantization. Fig. 13 shows that in the case of Walsh modulation, the quantization loss (compared to the full resolution case) is only about 1.5 dB — independently of *M* and *N*s. However, if a strong near-far effect is present, *M*-PPM

non-coherent detection in multipath, *T*int =32 ns

number of repetitions *N*s

**Figure 13.** Quantization loss due to a one-bit ADC versus the number of repetitions *N*<sup>s</sup> at *p*<sup>b</sup> = 10−<sup>3</sup> for

*M =* 2 *M =* 4 *M =* 8 *M =* 16 *M =* 32

Uncoordinated Piconet 2

**Figure 12.** The SOP test geometry with a single co-channel interference

outperforms R-Walsh with respect to the MA-performance.

*M*-PPM

*M*-Walsh

*M*-Walsh and *M*-PPM in multipath channels (analytical estimation).

1-b

quantization

 loss in dB

**4.4. Power efficient Walsh-modulation**

option for higher data rates.

Desired Piconet 1

Receiver *d*ref

> We have derived concepts for energy efficient impulse radio UWB systems with a low transceiver complexity. These concepts are especially suitable for wireless sensor networks operating at low data rates. The *E*b/*N*0-performance of non-coherently detected 2-PPM and DPSK is very similar. It differs by 3 dB in favour of DPSK. However, if the multipath combining should take place in the analog domain, i.e., by means a simple integrate and dump filter, the difficulty to realize analog broadband delays makes it almost impossible to use differential detection and thus DPSK. On the contrary, digital receiver implementations enable advanced modulation schemes and offer superior interference rejection capabilities. With low-resolution ADCs, only a small quantization loss is observed. Compared to the full-resolution case, a one-bit receiver shows a higher MUI suppressing capability. Sigma-Delta ADCs can be considered as attractive candidates for the analog to digital conversion. Our results show that the full resolution performance can be obtained for an oversampling rate of 4.
