22.8 Multipath Performance

In many applications such as Wireless Local Area Network (WLAN) and indoor radio, the received signal contains components which have traveled from the transmitter to the receiver via multiple propagation paths with differing delays; this phenomenon is called multipath propagation ^{[2] , [15]}.

The components arriving via different propagation paths may add destructively, resulting in deep frequency-selective fading. Conventional narrow-band systems fail catastrophically if a multipath-related null, defined below, coincides with the carrier frequency.

In the applications mentioned above, the distance between the transmitter and receiver is relatively short, i.e., the attenuation of the telecommunications channel is moderate. The effect which limits the performance of communications in such an environment is not the additive channel (thermal) noise N ₀ but deep frequency-selective fading caused by multipath propagation. In these applications, the most important system parameter is the sensitivity to multipath.

In Sections 22.5 and 22.6, we have concluded that the noise performance of differentially coherent DCSK, even with orthonormal basis functions, in a single-ray AWGN channel is worse than that of coherent conventional narrowband modulation schemes. However, DCSK has potentially lower sensitivity to multipath, because

• the demodulation is performed without carrier synchronization, and

• the transmitted signal is a wide-band signal which cannot be completely canceled by a multipath-related null.

Following the IEEE 802.11 WLAN standard ^[16], we set the RF channel bandwidth to 17 MHz in all simulations in the remainder of this chapter. To illustrate the wideband property of chaotic modulation schemes,...