Real-time digital signal processing: implementations, ... changes in the input signal is limited by its internal clock rate, so that it may be slow to
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Speech
samples
Transmitter
filter
Speech
encoder
CRC
Interleave
Modulation
Convolutional
encoder
Rayleigh
fading
Gaussian
noise
Receiver
filter
Synchronize
Demodulation
Equalizer
Deinterleave
Viterbi
decoder
Speech
decoder
CRC
Speech
samples
Transmitter
Receiver
Figure 9.22 Simplified wireless communication system
Convolutional coding provides error correction capability by adding redundancy bits
to the information bits. The convolutional encoding is usually implemented by either
the table-lookup method or by the shift register method. Figure 9.23 shows a rate
one-half (1/2) convolutional coder.
The convolutional encoder shown in Figure 9.23 can be expressed using the following
two polynomial generators:
b
0
1 È x È x
3
È x
5
9:7:1
and
b
1
1 È x
2
È x
3
È x
4
È x
5
,
9:7:2
where È denotes the modulo two adder, an XOR operation. For the rate 1/2 convolu-
tional encoder, each input information bit has two encoded bits, where bit 0 is generated
by (9.7.1) and bit 1 by generator (9.7.2). This redundancy enables the Viterbi decoder
to choose the correct bits under noisy conditions. Convolutional encoding is often
represented using the states. The convolutional encoder given in Figure 9.23 has a
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PRACTICAL DSP APPLICATIONS IN COMMUNICATIONS
Summary :
Speech samples Transmitter filter Speech encoder CRC Interleave Modulation Convolutional encoder Rayleigh fading Gaussian noise Receiver filter Synchronize Demodulation Equalizer Deinterleave Viterbi decoder Speech decoder CRC Speech samples Transmitter Receiver Figure 9.22 Simplified wireless communication system Convolutional coding provides error correction capability by adding redundancy bits to the information bits.
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conolutional,encoder,speech,figure,bits,bit,923,decoder,two,using,encoding,crc,information