Reference signal management
According to an example aspect of the present invention, there is provided an apparatus configured to select a reference signal sequence, determine a number of resource blocks located outside a frequency interval via spectrally extending the signal, and when the number is an odd number, perform exactly one of the following: symmetrically extend a cyclically shifted version of the selected reference signal sequence, or asymmetrically extend the selected reference signal sequence without shifting it, map the extended reference signal sequence to resource blocks located in the frequency interval and resource blocks located outside the frequency interval, perform spectral shaping of a second signal comprising the resource blocks located both inside and outside the frequency interval, and transmit the second signal in uplink direction.
1 . An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:
select a reference signal sequence for a first signal based on a first number of resource blocks located inside a frequency interval;
determine a second number of resource blocks located outside the frequency interval via spectrally extending the first signal, determine whether the second number is an odd number, and based on determining that the second number is an odd number, apply a frequency shift to the first signal and extend the selected reference signal sequence by performing one of the following:
applying a cyclic shift to the selected reference signal sequence and then applying a cyclic extension to the selected reference signal sequence at both ends of the selected reference signal sequence, or
applying a cyclic extension to the selected reference signal sequence, wherein the cyclic extension is by a third number of sequence elements at a first end of the selected reference signal sequence and by a fourth number of sequence elements at a second end of the selected reference signal sequence, wherein the third number of sequence elements is greater than the fourth number of sequence elements, and
map the extended reference signal sequence to the resource blocks located in the frequency interval and the resource blocks located outside the frequency interval, perform spectral shaping of a second signal comprising the resource blocks located both inside and outside the frequency interval, and transmit the second signal in uplink direction.
2 . The apparatus according to claim 1 , wherein the reference signal sequence has the property that cyclically shifted versions of the reference signal sequence are orthogonal with one another.
3 . The apparatus according to claim 2 , wherein the selected reference signal sequence is a Zadoff-Chu sequence, a constant amplitude zero autocorrelation sequence or a computer search based zero autocorrelation sequence.
4 . The apparatus according to claim 1 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to, only in case the second number is an even number, cyclically extend the selected reference signal sequence at both ends with a same number of elements without cyclically shifting the selected reference signal sequence.
5 . The apparatus according to claim 1 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to perform the cyclic shift of the selected reference signal sequence by shifting it by N/(2×m) positions, where N is a number of subcarriers in a resource block and m is spacing between adjacent subcarriers that carry the reference signal sequence, wherein the spacing is an integer number of subcarriers.
6 . The apparatus according to claim 5 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to select a direction for the cyclic shift based on an instruction from a base station node, or based on a direction of the frequency shift, wherein the direction of the cyclic shift is to a decreasing index based on the frequency shift being in an ascending frequency direction or the direction of the cyclic shift is to an increasing index based on the frequency shift being in a descending frequency direction.
7 . The apparatus according to claim 1 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to, when the cyclic extension of the selected reference signal sequence at the first end is by the third number of sequence elements and by the fourth number of sequence element at the second end, cyclically extend the selected reference signal sequence at a first end by (Q−M+N)/(2×m) sequence elements and by (Q−M−N)/(2×m) sequence elements at the second end, where Q is a number of subcarriers of the resource blocks located both inside and outside the frequency interval, M is the number of the subcarriers in the frequency interval, N is a number of subcarriers in a resource block and m is the spacing between adjacent subcarriers that carry the reference signal sequence, wherein the spacing is an integer number of subcarriers.
8 . The apparatus according to claim 1 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to, when the cyclic extension of the selected reference signal sequence at the first end is by the third number of sequence elements and by the fourth number of sequence element at the second end, obtain the extended reference signal sequence from the selected reference signal sequence by a cyclic extension of the selected reference signal sequence by (Q−M+N)/(2×m) elements at the beginning of the sequence and by (Q−M−N)/(2×m)+(M/m−Nzc) elements at the end of the sequence when the frequency shift is in a descending frequency direction, where Q is a number of subcarriers in an entire used allocation, M is a number of the subcarriers in the frequency interval, N is a number of subcarriers in a resource block, Nzc is a length of the selected reference signal sequence, and m is the spacing between adjacent subcarriers that carry the selected reference signal sequence, wherein the spacing is an integer number of subcarriers, wherein the selected reference signal sequence is a Zadoff-Chu sequence.
9 . The apparatus according to claim 1 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to apply the cyclic shift to a Zadoff-Chu sequence as the selected reference signal sequence, and to apply a cyclic extension to the Zadoff-Chu sequence, wherein the cyclic extension is by a fifth number of sequence elements at a first end of the Zadoff-Chu sequence and by a sixth number of sequence elements at a second end of the Zadoff-Chu sequence, where the fifth number of elements equals to (Q−M)/(2×m) and the sixth number of elements equals to (Q−M)/(2×m)+(M/m−Nzc), where Nzc is the length of the Zadoff-Chu sequence, Q is a number of subcarriers in an entire used allocation, M is the number of the subcarriers in the frequency interval and m is the spacing between adjacent subcarriers that carry the selected reference signal sequence, wherein the spacing is an integer number of subcarriers.
10 . The apparatus according to claim 1 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to at least one of: spectrally extend the transmit signal symmetrically on both sides of the frequency interval, or apply, in case the cyclic shift is applied, the cyclic extension to the selected reference signal sequence at both ends of the selected reference signal sequence by a same number of elements.
11 . A method comprising:
selecting a reference signal sequence for a first signal based on a first number of resource blocks located in a frequency interval;
determining a second number of resource blocks located outside the frequency interval via spectrally extending the first signal, determining whether the second number is an odd number, and based on determining that the second number is an odd number, applying a frequency shift to the first signal and extending the selected reference signal sequence by performing one of the following:
applying a cyclic shift to the selected reference signal sequence and then applying a cyclic extension to the selected reference signal sequence at both ends of the selected reference signal sequence, or
applying a cyclic extension to the selected reference signal sequence, wherein the cyclic extension is by a third number of sequence elements at a first end of the sequence and by a fourth number of sequence elements at a second end of the sequence, wherein the third number of sequence elements is greater than the fourth number of sequence elements, and
mapping the extended reference signal sequence to the resource blocks located in the frequency interval and the resource blocks located outside the frequency interval, performing spectral shaping of a second signal comprising the resource blocks located both inside and outside the frequency interval, and transmitting the second signal in uplink direction.
12 . The method according to claim 11 , wherein the reference signal sequence has the property that cyclically shifted versions of the reference signal sequence are orthogonal with one another.
13 . The method according to claim 12 , wherein the selected reference signal sequence is a Zadoff-Chu sequence, a constant amplitude zero autocorrelation sequence or a computer search based zero autocorrelation sequence.
14 . The method according to claim 11 , further comprising: in case the second number is an even number, cyclically extending the selected reference signal sequence at both ends with a same number of elements without cyclically shifting the selected reference signal sequence.
15 . The method according to claim 11 , further comprising: performing the cyclic shift of the selected reference signal sequence by shifting it by N/(2×m) positions, where N is a number of subcarriers in a resource block and m is spacing between adjacent subcarriers that carry the reference signal sequence, wherein the spacing is an integer number of subcarriers.
16 . The method according to claim 15 , further comprising: selecting a direction for the cyclic shift based on an instruction from a base station node, or based on a direction of the frequency shift, wherein the direction of the cyclic shift is to a decreasing index based on the frequency shift being in an ascending frequency direction or the direction of the cyclic shift is to an increasing index based on the frequency shift being in a descending frequency direction.
17 . The method according to claim 11 , further comprising: when the cyclic extension of the selected reference signal sequence at the first end is by the third number of sequence elements and by the fourth number of sequence element at the second end, cyclically extending the selected reference signal sequence at a first end by (Q−M+N)/(2×m) sequence elements and by (Q−M−N)/(2×m) sequence elements at the second end, where Q is a number of subcarriers of the resource blocks located both inside and outside the frequency interval, M is the number of the subcarriers in the frequency interval, N is a number of subcarriers in a resource block and m is the spacing between adjacent subcarriers that carry the reference signal sequence, wherein the spacing is an integer number of subcarriers.
18 . The method according to claim 11 , further comprising: when the cyclic extension of the selected reference signal sequence at the first end is by the third number of sequence elements and by the fourth number of sequence element at the second end, obtaining the extended reference signal sequence from the selected reference signal sequence by a cyclic extension of the selected reference signal sequence by (Q−M+N)/(2×m) elements at the beginning of the sequence and by (Q−M−N)/(2×m)+(M/m−Nzc) elements at the end of the sequence when the frequency shift is in a descending frequency direction, where Q is a number of subcarriers in an entire used allocation, M is a number of the subcarriers in the frequency interval, N is a number of subcarriers in a resource block, Nzc is a length of the selected reference signal sequence, and m is the spacing between adjacent subcarriers that carry the selected reference signal sequence, wherein the spacing is an integer number of subcarriers, wherein the selected reference signal sequence is a Zadoff-Chu sequence.
19 . An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:
select a reference signal sequence based on a first number of resource blocks located inside a frequency interval in an uplink transmission received by the apparatus;
determine a second number of resource blocks located outside the frequency interval via spectrally extending the uplink transmission, determine whether the second number is an odd number, and based on determining that the second number is an odd number, apply a frequency shift to the uplink transmission received by the apparatus and extend the selected reference signal sequence by performing one of the following:
applying a cyclic shift to the selected reference signal sequence and then applying a cyclic extension to the selected reference signal sequence at both ends of the selected reference signal sequence, or
applying a cyclic extension to the selected reference signal sequence, wherein the cyclic extension is by a third number of sequence elements at a first end of the sequence and by a fourth number of sequence elements at a second end of the sequence, wherein the third number of sequence elements is greater than the fourth number of sequence elements, and
employ the extended reference signal sequence in reception of the uplink transmission in the apparatus.
20 . The apparatus according to claim 19 , wherein the at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus to perform the cyclic shift of the selected reference signal sequence by shifting it by N/(2×m) elements, where N is a number of subcarriers in a resource block and m is spacing between adjacent subcarriers that carry the reference signal sequence, wherein the spacing is an integer number of subcarriers.