Subject : Wireless Network

Topic : Planning and Design of Wide-Area Networks

Difficulty : Medium

• In a multipath propagation environment, the multiple versions of a signal arrive at more than one chip interval apart from each other.

• The mobile receiver can recover the signal by correlating the chip sequence with the dominant received signal.

• The remaining signals are treated as noise.

• In order to achieve better performance, the receiver attempts to recover the signals from multiple paths and then combine them with suitable delays. This is the principle of operation of the RAKE receiver used in IS-95 system

• The wireless Channel generates multiple copies of the same signal due to multipath effects, each with a different amount of time delay ($δ_1,δ_2$..etc.), and attenuation factors ($a_1,a_2$, etc.).

• At the receiver, the combined signal is demodulated.

• The demodulated chip stream is then fed into multiple correlators, each delayed by a different amount.

• These signals are then combined using weighting attenuator factors ($a_1',a_2'$, etc.) estimated from the Channel characteristics.