explain how spread spectrum receivers can exploit multipath diversity using RAKE receivers?
vinoth 17-April-2008 12:10:38 AM
Comments


RAKE receiver is used in spread spectrum communication systems to combine multipath rays and thereby exploit channel diversity. Multipath rays include line of sight rays received directly from the transmitter and rays reflected from objects and terrain.After finger assignment, the time locations of the maxima change slowly, and these locations are tracked by time tracking circuits in each assigned finger. If the multipath rays are separated from each other by at least one chip time of delay, then each path can be resolved separately by the RAKE receiver time tracking circuitry and diversity gain is realized.
Posted by waqqas1


Mobile stations for use in spread spectrum communication systems commonly employ RAKE receivers. A RAKE receiver includes two or more receiver fingers which independently receive radio frequency (RF) signals. Each finger estimates channel gain and phase and demodulates the RF signals to produce traffic symbols. The traffic symbols of the receiver fingers are combined in a symbol combiner to produce a received signal.

A RAKE receiver is used in spread spectrum communication systems to combine multipath rays and thereby exploit channel diversity. Multipath rays include line of sight rays received directly from the transmitter and rays reflected from objects and terrain. The multipath rays received at the receiver are separated in time. The time separation or time difference is typically on the order of several chip times. By combining the separate RAKE finger outputs, the RAKE receiver achieves path diversity.

Generally, the RAKE receiver fingers are assigned to the strongest set of multipath rays. That is, the receiver locates local maxima of the received signal. A first finger is assigned to receive the strongest signal, a second finger is assigned to receive the next strongest signal, and so on. As received signal strength changes, due to fading and other causes, the finger assignments are changed. After finger assignment, the time locations of the maxima change slowly, and these locations are tracked by time tracking circuits in each assigned finger. If the multipath rays are separated from each other by at least one chip time of delay, then each path can be resolved separately by the RAKE receiver time tracking circuitry and diversity gain is realized.
Posted by gsmxprt


Posted: 21-May-2008 03:11:35 AM By: gsmxprt

Mobile stations for use in spread spectrum communication systems commonly employ RAKE receivers. A RAKE receiver includes two or more receiver fingers which independently receive radio frequency (RF) signals. Each finger estimates channel gain and phase and demodulates the RF signals to produce traffic symbols. The traffic symbols of the receiver fingers are combined in a symbol combiner to produce a received signal.

A RAKE receiver is used in spread spectrum communication systems to combine multipath rays and thereby exploit channel diversity. Multipath rays include line of sight rays received directly from the transmitter and rays reflected from objects and terrain. The multipath rays received at the receiver are separated in time. The time separation or time difference is typically on the order of several chip times. By combining the separate RAKE finger outputs, the RAKE receiver achieves path diversity.

Generally, the RAKE receiver fingers are assigned to the strongest set of multipath rays. That is, the receiver locates local maxima of the received signal. A first finger is assigned to receive the strongest signal, a second finger is assigned to receive the next strongest signal, and so on. As received signal strength changes, due to fading and other causes, the finger assignments are changed. After finger assignment, the time locations of the maxima change slowly, and these locations are tracked by time tracking circuits in each assigned finger. If the multipath rays are separated from each other by at least one chip time of delay, then each path can be resolved separately by the RAKE receiver time tracking circuitry and diversity gain is realized.

Posted: 31-December-2008 12:57:18 PM By: waqqas1

RAKE receiver is used in spread spectrum communication systems to combine multipath rays and thereby exploit channel diversity. Multipath rays include line of sight rays received directly from the transmitter and rays reflected from objects and terrain.After finger assignment, the time locations of the maxima change slowly, and these locations are tracked by time tracking circuits in each assigned finger. If the multipath rays are separated from each other by at least one chip time of delay, then each path can be resolved separately by the RAKE receiver time tracking circuitry and diversity gain is realized.