RAKE Receiver
Definition: A receiver technique which uses several baseband correlators to individually process several signal multipath components. The correlator out-puts are combined to achieve improved communications reliability and performance.
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© 1999 DR. ERNEST SIMO - SPACE2000
Rake Receiver
Application:
In IS-95, both the base station and mobile receivers use RAKE receiver techniques. Each correlator in a RAKE receiver is called a RAKE-receiver finger. The base station combines the outputs of its RAKE-receiver fingers noncoherently. i.e., the outputs are added in power. The mobile receiver combines its RAKE-receiver finger outputs coherently, i.e., the outputs are added in voltage. At the time of this writing, mobile receivers had 3 RAKE-receiver fingers and base station receivers had 4 or 5 depending on the equipment manufacturer. There are two primary methods used to combine the RAKE-receiver finger outputs. One method weights each output equally and is, therefore, called equal-gain combining. The second method uses the data to estimate weights which maximize the Signal-to-Noise Ratio (SNR) of the combined output. This technique is known as maximal-ratio combining. In practice, it is not unusual for both combining techniques to perform about the same.
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© 1999 DR. ERNEST SIMO - SPACE2000
Rake Receiver
Example: The word "RAKE" is not an acronym and, in fact, is not always capitalized as it is in this writing. RAKE derives its name from its inventors Price and Green in 1958. When a wideband signal is received over a multipath channel, the multiple delays appear at the receiver as depicted in the figure below. By attaching a "handle" to the plot of the multipath returns, a picture of an ordinary garden rake is created. It is from this picture that the RAKE receiver gets its name.
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© 1999 DR. ERNEST SIMO - SPACE2000
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