15-02-2009, 12:43 PM
To achieve a better Eb/N0 (bit energy to noise ratio) than todays Rake receiver, a better estimation of the radio
channel is needed. This paper proposes to reach this goal with
artificial neural networks, which are used for detecting all multipaths
in a direct sequence spread spectrum signal.The
output of the adaptive neual net is an estimation of the channel
response. To increase the Eb/N0 of direct sequence spread spectrum
signals, Rake receivers consist of up to 6 demodulators, which
demodulate the strongest few echoes of the signal. Their output signals
are collected. The result is a higher stability against noise.The
presented work is also based on using not only one path for
reconstructing the transmitted bit stream but nearly all paths. The
received PN (pseudo noise) radio signal is sampled with a rate of about
four times the chip rate of the PN signal and passed through a
despreader that correlates it with the original PN sequence.In
contrast to a conventional receiver, the correlation is made for every
delay, realized in a correlator bank whose output is given to a neural
network. As neural net, a perceptron with backpropagation is used, with
the task to detect all the multipaths in the correlated signal. With
conventional filters the problem of detecting only the multipath peaks
and not the peaks due to crosscorrelation of a PN sequence with an
inverted PN sequence - occuring whenever a bit change from 1 to -1 or
inverse - is nearly impossible to handle. The output of the net is the
estimated response of the actual channel. With this information
containing the delay and the attenuation of each propagation path, the
transmitted bit stream can easily be rebuilt. .
channel is needed. This paper proposes to reach this goal with
artificial neural networks, which are used for detecting all multipaths
in a direct sequence spread spectrum signal.The
output of the adaptive neual net is an estimation of the channel
response. To increase the Eb/N0 of direct sequence spread spectrum
signals, Rake receivers consist of up to 6 demodulators, which
demodulate the strongest few echoes of the signal. Their output signals
are collected. The result is a higher stability against noise.The
presented work is also based on using not only one path for
reconstructing the transmitted bit stream but nearly all paths. The
received PN (pseudo noise) radio signal is sampled with a rate of about
four times the chip rate of the PN signal and passed through a
despreader that correlates it with the original PN sequence.In
contrast to a conventional receiver, the correlation is made for every
delay, realized in a correlator bank whose output is given to a neural
network. As neural net, a perceptron with backpropagation is used, with
the task to detect all the multipaths in the correlated signal. With
conventional filters the problem of detecting only the multipath peaks
and not the peaks due to crosscorrelation of a PN sequence with an
inverted PN sequence - occuring whenever a bit change from 1 to -1 or
inverse - is nearly impossible to handle. The output of the net is the
estimated response of the actual channel. With this information
containing the delay and the attenuation of each propagation path, the
transmitted bit stream can easily be rebuilt. .