What is the meaning of inverse signal bandwidth?
OK, now it's more clear. In a two ray model, you have tow versions of the signal; the line of sight $u(t)$, and the reflected version $u(t-\tau)$, where $\tau$ is the delay spread of the channel. 

If $\tau&lt;&lt;\frac{1}{B_s} \simeq T_s$, where $B_s$ and $T_s$ are the bandwidth and duration of the signal, then the shift in the reflected version would be very small compared to the symbol duration. So, the LOS version would be received at time $t_0$ up to $t_0+T_s$, and the reflected version would be received at time $t_0+\tau$ up to $t_0+T_s+\tau$. But $\tau&lt;&lt;T_s$, and thus the two versions are received very close to each others. This answers your first question.

As for the second question, the maximum delay spread of the channel is related to something called the coherence bandwidth of the channel. Roughly speaking, the coherence bandwidth $B_c$ is inversely proportional to the maximum delay spread, in this case $\tau$. If the signal bandwidth $B_s\simeq \frac{1}{T_s}&lt;B_c\simeq \frac{1}{\tau}$, then the channel is said to be frequency-flat fading, which means that the channel frequency response remains contact withing the signal bandwidth. In the time domain, this is translated to interference-free channel, since different symbols don't interfere with each others. On the other hand, if $B_s &gt; B_c$, then the channel is called frequency-selective channel, as different frequency components of the signal are affected differently by the channel. In the time domain, this causes inter-symbol interference (ISI), since the maximum delay spread is larger that the symbol duration, and different symbols interfere with each others at the receiver.