Signal Processing - September 2017 - 66
data channels in QPSK modulation, such as noncoherent, semicoherent, and differentially coherent combining techniques [19].
Noncoherent channel combining
Noncoherent channel combining simply adds the magnitudes (or
magnitudes squared) of the correlation outputs of the pilot and
data channels [20]. Similar to the noncoherent integration technique, noncoherent channel-combining technique provides a relatively small SNR increase comparing to the coherent combining
technique and may suffer from the squaring loss [3].
Semicoherent channel combining
Since the relative phase between the data channel and the pilot
channel is either + 90c or - 90c due to the unknown data and
the secondary codes modulating the channels, the integration function output in a complex form can be expressed with
one of the two combinations: R D + jR P and R D - jR P, where
R D ^= R ID + jR QDh and R P ^= R PI + jR QP h are the correlation outputs of data and pilot channels, respectively, and the superscripts
I and Q represent the in-phase and quadrature-phase components, respectively (see Figure 1). Therefore, in the semicoherent
combining, the integration function G ($) returns the combination result of larger magnitude (or magnitude squared) between
the two. In practice, the semicoherently combined output can be
noncoherently integrated to produce the detection variable [19].
detection techniques, since they estimate the relative signs
between the data and pilot channels and between two consecutive correlation outputs. In the study of the optimal detection
technique for GPS L5 signal [21], it is indicated that the optimal
detection technique should utilize all of the constraints given by
the data bit and secondary codes for the coherent channel combining and the coherent integration of correlation outputs. Therefore, the optimal detection technique for weak GNSS signals
requires an additional search for the secondary code and data bits
along the third dimension indexed with h in (3). This may be
an exhaustive search, since the number of possible data bits and
code-chip combinations grows exponentially with N t (= N i Tco) .
When the consecutive correlation outputs are obtained within the
same data bit, the optimal search technique for GPS L5 signals
may only need to perform an additional search for the secondary code, the Neuman-Hoffman (NH) code. To reduce the additional search complexity for the secondary code, a tree structure
of the NH code may be utilized [22], and the characteristic code
of the NH code that has all of the possible code-chip transition
patterns can be used [23]. Table 3 summarizes the detection variables of the channel-combining techniques.
Channel combining technique for in-phase GNSS signals
GPS L1C, Galileo E1 OS, and (candidate) BeiDou B1 signals have the pilot and data channels that are separated by the
spreading codes and transmitted (mostly) in the same phase
Differentially coherent channel combining
(i.e., in-phase) channel. Note that the candidate BeiDou B1
Denoting the unknown phase of the data and pilot channels as {
pilot channel has a QMBOC modulation, in which a small porand { ! 90c, respectively, multiplying the data channel correlation
tion (about 12%) of its power is allocated to the sinBOC(6,1)output, R D, with the complex conjugate of the pilot channel correlamodulated high-frequency component in the quadrature
tion output, R *P, results in an imaginary component (i.e., the resultphase. However, the advantage of combining the two channels
ing phase becomes " 90c). Therefore, in [19], the detection variable
to improve the acquisition sensitivity possibly can be small
with differentially coherent combining is obtained from the magniwhen the signal power is not evenly distributed between the
tude of the imaginary component of the result, i.e., Im " R D R *P , ,
two channels [23]. In addition, combining the two channels
where Im {$} is a function returning the imaginary part.
increases the receiver complexity considerably. For example,
the GPS L1C and (the candidate) BeiDou B1 have 75% of their
Coherent channel combining
signal power in the pilot channel, and the remaining 25% is
and integration for optimal detection
in the data channel. The acquisition performance, in terms
In fact, the semicoherent combining technique and the difof the detection probability in the individual hypothesis test,
ferentially coherent combining technique are only suboptimal
Pd, when the only pilot channel is used is slightly lower than
that when the both channels are used. In
addition, since the pilot channels of GPS
L1C and (the candidate) BeiDou B1 have
Table 3. Detection variables of various channel-combining techniques.
about 88% of the total signal power in the
Detection variable for the l th code phase and m th Doppler-frequency
sinBOC(1,1) and the remaining 12% in
Channel Combining
hypothesis
sinBOC(6,1), a receiver may neglect the
N -1
Z ncc 6l, m@ = / " R D 6h, l, m@ 2 + R P 6h, l, m@ 2 ,
Noncoherent
sinBOC(6,1) component and processes
h=0
only the signal component in sinBOC(1,1)
N -1
Z scc 6l, m@ = / max " R + 6h, l, m@ 2, R - 6h, l, m@ 2 ,,
Semicoherent
at the cost of small sensitivity loss; 1.1 dB
h=0
for GPS L1C and 0.56 dB for (the candiwhere R ! 6h, l, m@ = R D 6h, l, m@ ! jR P 6h, l, m@
date) BeiDou B1 signals.
N -1
Z dcc 6l, m@ = / Im " R D 6h, l, m@ R *P 6h, l, m@,
Differentially coherent
GPS L2C signal has a TDM of data-modh=1
2
ulated civil moderate (CM) code and datamax N - 1
Z cc 6l, m@ =
D 6h@ S D 6h@ R D 6h, l, m@ + jS P 6h@ R P 6h, l, m@ ,
Coherent
free civil long (CL) code of T p = 20 ms
I h/
=0
and T p = 1.5 s, respectively. Since the two
where I = "" D 6h@ S D 6h@, S P 6h@,|h = 0, 1, 2, f, N i - 1 ,
channels are separated in time and the CL
i
i
i
i
66
IEEE SIGNAL PROCESSING MAGAZINE
|
September 2017
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Table of Contents for the Digital Edition of Signal Processing - September 2017
Signal Processing - September 2017 - Cover1
Signal Processing - September 2017 - Cover2
Signal Processing - September 2017 - 1
Signal Processing - September 2017 - 2
Signal Processing - September 2017 - 3
Signal Processing - September 2017 - 4
Signal Processing - September 2017 - 5
Signal Processing - September 2017 - 6
Signal Processing - September 2017 - 7
Signal Processing - September 2017 - 8
Signal Processing - September 2017 - 9
Signal Processing - September 2017 - 10
Signal Processing - September 2017 - 11
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Signal Processing - September 2017 - 13
Signal Processing - September 2017 - 14
Signal Processing - September 2017 - 15
Signal Processing - September 2017 - 16
Signal Processing - September 2017 - 17
Signal Processing - September 2017 - 18
Signal Processing - September 2017 - 19
Signal Processing - September 2017 - 20
Signal Processing - September 2017 - 21
Signal Processing - September 2017 - 22
Signal Processing - September 2017 - 23
Signal Processing - September 2017 - 24
Signal Processing - September 2017 - 25
Signal Processing - September 2017 - 26
Signal Processing - September 2017 - 27
Signal Processing - September 2017 - 28
Signal Processing - September 2017 - 29
Signal Processing - September 2017 - 30
Signal Processing - September 2017 - 31
Signal Processing - September 2017 - 32
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Signal Processing - September 2017 - 34
Signal Processing - September 2017 - 35
Signal Processing - September 2017 - 36
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Signal Processing - September 2017 - 48
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Signal Processing - September 2017 - 58
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Signal Processing - September 2017 - 60
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Signal Processing - September 2017 - 62
Signal Processing - September 2017 - 63
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Signal Processing - September 2017 - 66
Signal Processing - September 2017 - 67
Signal Processing - September 2017 - 68
Signal Processing - September 2017 - 69
Signal Processing - September 2017 - 70
Signal Processing - September 2017 - 71
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Signal Processing - September 2017 - 73
Signal Processing - September 2017 - 74
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Signal Processing - September 2017 - 76
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Signal Processing - September 2017 - 78
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Signal Processing - September 2017 - 80
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Signal Processing - September 2017 - 88
Signal Processing - September 2017 - 89
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Signal Processing - September 2017 - 92
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Signal Processing - September 2017 - 94
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Signal Processing - September 2017 - 97
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Signal Processing - September 2017 - 99
Signal Processing - September 2017 - 100
Signal Processing - September 2017 - 101
Signal Processing - September 2017 - 102
Signal Processing - September 2017 - 103
Signal Processing - September 2017 - 104
Signal Processing - September 2017 - 105
Signal Processing - September 2017 - 106
Signal Processing - September 2017 - 107
Signal Processing - September 2017 - 108
Signal Processing - September 2017 - 109
Signal Processing - September 2017 - 110
Signal Processing - September 2017 - 111
Signal Processing - September 2017 - 112
Signal Processing - September 2017 - 113
Signal Processing - September 2017 - 114
Signal Processing - September 2017 - 115
Signal Processing - September 2017 - 116
Signal Processing - September 2017 - 117
Signal Processing - September 2017 - 118
Signal Processing - September 2017 - 119
Signal Processing - September 2017 - 120
Signal Processing - September 2017 - 121
Signal Processing - September 2017 - 122
Signal Processing - September 2017 - 123
Signal Processing - September 2017 - 124
Signal Processing - September 2017 - 125
Signal Processing - September 2017 - 126
Signal Processing - September 2017 - 127
Signal Processing - September 2017 - 128
Signal Processing - September 2017 - 129
Signal Processing - September 2017 - 130
Signal Processing - September 2017 - 131
Signal Processing - September 2017 - 132
Signal Processing - September 2017 - 133
Signal Processing - September 2017 - 134
Signal Processing - September 2017 - 135
Signal Processing - September 2017 - 136
Signal Processing - September 2017 - 137
Signal Processing - September 2017 - 138
Signal Processing - September 2017 - 139
Signal Processing - September 2017 - 140
Signal Processing - September 2017 - 141
Signal Processing - September 2017 - 142
Signal Processing - September 2017 - 143
Signal Processing - September 2017 - 144
Signal Processing - September 2017 - 145
Signal Processing - September 2017 - 146
Signal Processing - September 2017 - 147
Signal Processing - September 2017 - 148
Signal Processing - September 2017 - 149
Signal Processing - September 2017 - 150
Signal Processing - September 2017 - 151
Signal Processing - September 2017 - 152
Signal Processing - September 2017 - 153
Signal Processing - September 2017 - 154
Signal Processing - September 2017 - 155
Signal Processing - September 2017 - 156
Signal Processing - September 2017 - 157
Signal Processing - September 2017 - 158
Signal Processing - September 2017 - 159
Signal Processing - September 2017 - 160
Signal Processing - September 2017 - 161
Signal Processing - September 2017 - 162
Signal Processing - September 2017 - 163
Signal Processing - September 2017 - 164
Signal Processing - September 2017 - 165
Signal Processing - September 2017 - 166
Signal Processing - September 2017 - 167
Signal Processing - September 2017 - 168
Signal Processing - September 2017 - 169
Signal Processing - September 2017 - 170
Signal Processing - September 2017 - 171
Signal Processing - September 2017 - 172
Signal Processing - September 2017 - 173
Signal Processing - September 2017 - 174
Signal Processing - September 2017 - 175
Signal Processing - September 2017 - 176
Signal Processing - September 2017 - 177
Signal Processing - September 2017 - 178
Signal Processing - September 2017 - 179
Signal Processing - September 2017 - 180
Signal Processing - September 2017 - 181
Signal Processing - September 2017 - 182
Signal Processing - September 2017 - 183
Signal Processing - September 2017 - 184
Signal Processing - September 2017 - 185
Signal Processing - September 2017 - 186
Signal Processing - September 2017 - 187
Signal Processing - September 2017 - 188
Signal Processing - September 2017 - 189
Signal Processing - September 2017 - 190
Signal Processing - September 2017 - 191
Signal Processing - September 2017 - 192
Signal Processing - September 2017 - 193
Signal Processing - September 2017 - 194
Signal Processing - September 2017 - 195
Signal Processing - September 2017 - 196
Signal Processing - September 2017 - Cover3
Signal Processing - September 2017 - Cover4
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