Process for blind detection of a synchronization signal for LTE
To detect a cell-specific synchronization signal, a modified correlation approach is used, which removes the need for channel estimation.
1. A method of detecting a synchronization signal from a received signal in an Orthogonal Frequency Division Multiplex (OFDM) based communication system, the method comprising the steps of:
detecting a first primary synchronization signal;
receiving a signal Y from a communication channel, the signal Y being a OFDM signal comprising a set of subcarriers; and
performing a second synchronization detection among a set of M predetermined synchronization sequences S m (m=0 to M−1), the second synchronization detection comprising the further steps of:
for each predetermined sequence S m , computing a vector Z m from the received signal Y in accordance with the formula Z m [i]=S m [i]Y[i], where S m [i], Y[i] and Z m [i] are the element (i) of sequence S m , the received signal Y and the computed vector Z m , respectively;
computing at least one of a vector T m and U m by multiplying the symbol in one subcarrier by the complex conjugate of the symbol in the first or second consecutive subcarriers, respectively; and
maximizing or minimizing a cost function applied on the vector T m or U m in order to determine the particular sequence yielding the best cost function.
2. The method of claim 1 wherein the particular sequence is selected by maximizing the value
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.
3. The method of claim 1 wherein computing a vector T m comprises computing T m according to: T m [i]=Z m [i]×Z m *[i+1].
4. The method of claim 1 wherein computing a vector U m comprises computing U m according to: U m [i]=Z m *[i+2].
5. The method of claim 1 further comprising computing both
T m [i]=Z m [i]×Z m *[i+ 1] and
U m [i]=Z m [i]×Z m *[i+ 2]
and selecting the particular sequence from the maximizing of
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and
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max
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.
6. The method of claim 1 further comprising:
computing U m [i]=Z m [i]×Z m *[i+2]; and
selecting the particular sequence from the maximizing of
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=
arg
max
{
∑
i
=
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2
}
.
7. The method of claim 1 wherein the set of synchronization sequences comprises 168 secondary synchronization sequences or signals, being each carried by a set of 62 subcarriers.
8. The method of claim 1 wherein each sequence comprises interleaved short segments.
9. The method of claim 8 wherein the method is performed first for the detection of the first segment and then subsequently for the detection of the second segment.
10. A method of detecting a synchronization signal from a received signal of a Long Term Evolution (LTE) communication, the synchronization signal comprising a first short segment Y 1 =[Y(0), Y(2), Y(4) . . . , Y(60)] and a second interleaved segment Y 2 =[Y(1), Y(3), Y(5) . . . , Y(61)], the method comprising:
a telecommunication apparatus performing the steps of:
(a) computing the element-wise product of Y 1 with all possible first short segments S 1,m according to Z 1,m [i]=S 1,m [i]Y[2i], for i=0, . . . , 30;
(b) multiplying the i th resulting element by the complex conjugate of the i+1-th element, according to T 1,m [i]=Z 1,m [i]×Z 1,m *[i+1], for i=0, . . . , 29;
(c) selecting the first segment which maximizes
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^
1
,
m
=
arg
max
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1
,
m
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i
]
2
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;
(d) identifying the possible second segment in a predetermined table; and
(e) performing steps (a-c) to select the second segment.
11. An apparatus operative to detect a synchronization signal in an Orthogonal Frequency Division Multiplex (OFDM) based communication system, the apparatus comprising:
a receiver operative to receive a signal Y from a communication channel, the signal being a OFDM signal comprising a set of subcarriers;
a primary detector operative to detect a primary synchronization signal; and
a secondary detector operative to perform a second synchronization detection among a set of M predetermined synchronization sequences S m (m=0 to M−1), by:
for each predetermined sequence S m , computing a vector Z m from the received signal Y in accordance with the formula Z m [i]=S m [i]Y[i], where S m [i], Y[i] and Z m [i] are the element (i) of sequence S m , the received signal Y and the computed vector Z m , respectively;
computing at least one of a vector T m and U m by multiplying the symbol in one subcarrier by the complex conjugate of the symbol in the next one or two consecutive subcarriers, respectively; and
maximizing or minimizing a cost function applied on the vector T m or U m in order to determine the particular sequence yielding the best cost function.