Rake receiver
Encyclopedia
A rake receiver is a radio receiver
designed to counter the effects of multipath fading. It does this by using several "sub-receivers" called fingers, that is, several correlators each assigned to a different multipath component. Each finger independently decodes a single multipath component; at a later stage the contribution of all fingers are combined in order to make the most use of the different transmission
characteristics of each transmission path. This could very well result in higher signal-to-noise ratio
(or Eb/N0) in a multipath environment than in a "clean" environment.
The multipath channel through which a radio wave transmits can be viewed as transmitting the original (line of sight
) wave pulse through a number of multipath components. Multipath components are delayed copies of the original transmitted wave traveling through a different echo path, each with a different magnitude and time-of-arrival at the receiver. Since each component contains the original information, if the magnitude and time-of-arrival (phase) of each component is computed at the receiver (through a process called channel estimation), then all the components can be added coherently to improve the information reliability.
The rake receiver is so named because it reminds the function of a garden rake, each finger collecting symbol energy similarly to how tines on a rake collect leaves.
hardware in them to process and correlate the intended signal. Rake receivers only became common after 16-bit CPUs capable of signal processing became widely available. The rake receiver was patented in the US in 1956, but it took until the 1970s to design practical implementations of the receiver.
Radio astronomers were the first substantial users of rake receivers in the late 1960s to mid-1980s as this kind of receiver could scan large sky regions yet not create large volumes of data beyond what most data recorders could handle at the time. Astropulse
that is part of SETI@Home
project uses a variant of a rake receiver as part of its sky searches—so this kind of receiver is still current for the needs of radio astronomy.
radio devices such as mobile phones and wireless LAN
equipment.
Rake receivers are also used in Radio Astronomy. The CSIRO Parkes Radio Telescope and Jodrell Bank Telescope have 1-bit filterbank recording formats that can be processed in real time or prognostically by software based rake receivers.
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
designed to counter the effects of multipath fading. It does this by using several "sub-receivers" called fingers, that is, several correlators each assigned to a different multipath component. Each finger independently decodes a single multipath component; at a later stage the contribution of all fingers are combined in order to make the most use of the different transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
characteristics of each transmission path. This could very well result in higher signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
(or Eb/N0) in a multipath environment than in a "clean" environment.
The multipath channel through which a radio wave transmits can be viewed as transmitting the original (line of sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
) wave pulse through a number of multipath components. Multipath components are delayed copies of the original transmitted wave traveling through a different echo path, each with a different magnitude and time-of-arrival at the receiver. Since each component contains the original information, if the magnitude and time-of-arrival (phase) of each component is computed at the receiver (through a process called channel estimation), then all the components can be added coherently to improve the information reliability.
The rake receiver is so named because it reminds the function of a garden rake, each finger collecting symbol energy similarly to how tines on a rake collect leaves.
History
Rake receivers must have either a general-purpose CPU or some other form of digital signal processingDigital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
hardware in them to process and correlate the intended signal. Rake receivers only became common after 16-bit CPUs capable of signal processing became widely available. The rake receiver was patented in the US in 1956, but it took until the 1970s to design practical implementations of the receiver.
Radio astronomers were the first substantial users of rake receivers in the late 1960s to mid-1980s as this kind of receiver could scan large sky regions yet not create large volumes of data beyond what most data recorders could handle at the time. Astropulse
Astropulse
Astropulse is a distributed computing project that uses volunteers across the globe to lend their unused computing power to search for primordial black holes, pulsars, and ETI. Volunteer resources are harnessed through Berkeley Open Infrastructure for Network Computing platform...
that is part of SETI@Home
SETI@home
SETI@home is an Internet-based public volunteer computing project employing the BOINC software platform, hosted by the Space Sciences Laboratory, at the University of California, Berkeley, in the United States. SETI is an acronym for the Search for Extra-Terrestrial Intelligence...
project uses a variant of a rake receiver as part of its sky searches—so this kind of receiver is still current for the needs of radio astronomy.
Use
Rake receivers are common in a wide variety of CDMA and W-CDMAW-CDMA
W-CDMA , UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the UMTS family and sometimes used as a synonym for UMTS...
radio devices such as mobile phones and wireless LAN
Wireless LAN
A wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network...
equipment.
Rake receivers are also used in Radio Astronomy. The CSIRO Parkes Radio Telescope and Jodrell Bank Telescope have 1-bit filterbank recording formats that can be processed in real time or prognostically by software based rake receivers.