Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-05-15
2001-04-10
Ghebretinsae, Temesghen (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S349000, C370S335000
Reexamination Certificate
active
06215814
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a RAKE receiver of a radio system using a Code Division Multiple Access (CDMA) method.
BACKGROUND OF THE INVENTION
In radio systems, diversity methods of different kinds are used for increasing the coverage area and/or capacity of the system. As to this publication, space diversity, i.e. antenna diversity, polarization diversity and multipath diversity are of interest. Space diversity signifies that antennas are positioned sufficiently far from each other to achieve a sufficient decorrelation between signals received via the separate antennas. An interesting kind of polarization diversity is implicit polarization, when a signal is sent on one polarization level, but received by cross-polarized antennas. Multipath diversity signifies a diversity created by multipath propagated signal components, this diversity being usable in a system, such as a CDMA system, in which the bandwidth of a signal is much wider than the coherent bandwidth of a channel.
In a CDMA system, a RAKE receiver is used for separating multipath propagated signal components at the reception. In general, the signal components must then be separated from each other at least by one part of a spreading code used, i.e. by a chip. The RAKE receiver comprises RAKE fingers and, in each of these fingers, despreading and diversity combination take place. In addition, the receiver comprises a delay estimator having a matched filter for each antenna branch and an allocation block for the RAKE fingers. In the matched filter, a signal, received by a spreading code used for signal spreading, is correlated by different delays, the timing of the spreading code then being changed for instance in steps of one chip. When the correlation is high, a multipath propagated signal component is found, which can then be received by the delay found.
On the radio path, the signal will include, besides the wanted signal, also noise and interference caused by other users or systems. In systems utilizing diversity, the influence of noise and interference can be decreased for instance by Maximal Ratio Combining (MRC) method, according to which method signals received via separate antennas are weighted in proportion to the signal power in the separate antenna branches. However, this method presupposes that the interference of each antenna is independent. This pre-supposition is not always true in practical cellular radio networks, but it is conceivable that the same interference is present at each antenna.
There is no such restriction on Interference Rejection Combining (IRC) method. However, the method has been used only in systems utilizing Time Division Multiple Access (TDMA) method, these systems often being incapable of separating multipath propagated signal components. IRC method signifies here an adaptive beam forming (optimal combination of signals), by which the signal power is maximized in proportion to the power of interference and noise, i.e. a Signal-to-Interference-and-Noise Ratio (SINR) is maximized.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is thus a RAKE receiver using IRC. This is achieved by the RAKE receiver presented below. This RAKE receiver comprises at least two antenna branches for receiving a radio signal; at least one RAKE finger connected to the antenna branches for processing a multipath propagated signal component of the radio signal; a delay estimator connected to the antenna branches for searching for a delay of at least one multipath propagated signal component and for allocating a RAKE finger for processing the found multipath propagated signal component and for informing said RAKE finger of the found delay; the RAKE finger comprising: a channel estimator for generating an impulse response of the channel of the multipath propagated signal component found by means of a known pilot part included in the radio signal of each antenna branch; an interference estimator for generating an interference signal, included in the radio signal of each antenna branch and consisting of interference and noise, by subtracting from the received radio signal a regenerated wanted radio signal, which regenerated wanted radio signal is obtained by means of the known pilot part and the estimated impulse response of the channel; a despreader connected to each antenna branch for despreading the pilot part included in the multipath propagated signal component by using a known spreading code by a delay as informed by the delay estimator; a despreader connected to each antenna branch for despreading the data part included in the multipath propagated signal component by using the known spreading code by a delay as informed by the delay estimator. The RAKE finger also comprises: a weighting coefficient part for providing each antenna branch with weighting coefficients maximizing the Signal-to-Interference-and-Noise Ratio (SINR); a multiplier for multiplying the pilot part, despread by the despreader in each antenna branch, by a weighting coefficient; a multiplier for multiplying the data part, despread by the despreader in each antenna branch, by a weighting coefficient; an antenna branch summer for combining the despread pilot parts, received via the separate antenna branches and multiplied by the weighting coefficient, to one pilot signal; an antenna branch summer for combining the despread data parts, received via the separate antenna branches and multiplied by the weighting coefficient, to one data signal; and the RAKE receiver further comprises a RAKE finger summer for combining the data signals of the RAKE fingers operating by different delays to a sum data signal representing the received bits.
Objects of dependent claims are presented in the preferred embodiments of the invention.
The invention is based on that a RAKE receiver using IRC is formed.
The RAKE receiver of the invention provides the E
b
/l
o
ratio of a signal (energy per bit divided by power density of interference) with a value up to two decibels better than a conventional RAKE receiver using MRC.
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Copy of International Search Report for PCT/FI99/00749.
Muszynski Peter
Neffling Toni
Tiirola Esa
Ylitalo Juha
Altera Law Group LLC
Ghebretinsae Temesghen
Nokia Networks Oy
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