Methods and apparatuses for phase tracking reference signal design

1. A method, comprising:

forming, configured by a network node, a phase tracking reference signal sample sequence utilizing outer-most constellation points corresponding to scheduled modulation order of data channel for discrete Fourier transform spread orthogonal frequency division multiplexing; and

applying orthogonal cover code of length L across L consequent phase tracking reference signal sequence samples in time within a phase tracking reference signal burst to code division multiplex at least one phase tracking reference signal port of a given user equipment.

2. The method according to claim 1 , wherein the phase tracking reference signal sample sequence is further formed by scrambling with a user equipment-specific sequence.

3. The method according to claim 1 , further comprising:

signaling, to a user equipment, the phase tracking reference signal sample sequence configured for the user equipment.

4. The method according to claim 1 , further comprising:

applying the orthogonal cover code to multiple phase tracking reference signal ports among different multi-user multiple-input and multiple-output users with a same physical resource block allocation.

5. The method according to claim 1 , further comprising:

defining a number of the phase tracking reference signal sequence samples based on an amount of allocated physical resource blocks.

6. The method according to claim 5 , wherein the defining further comprises defining the number of phase tracking reference signal sequence samples by using the following equation: ceil(number of scheduled PRBs/R), where R={4,2,1}.

7. The method according to claim 1 , wherein discrete Fourier transform input block comprises N sub-blocks and K phase tracking reference signal sequence samples are split into N groups of length K/N with first group allocated to first K/N samples of sub-block #0, and last group allocated to last K/N samples of sub-block #(N−1).

8. The method according to claim 1 , wherein the forming of the phase tracking reference signal sample sequence further comprises:

user equipment-specifically configuring the phase tracking reference signal burst periodicity and burst length based on at least one of residual frequency offset estimated by the network node, a channel quality indication reported by the user equipment, or information on time-correlation properties of the user equipment's local oscillator phase noise.

9. The method according to claim 1 , wherein the phase tracking is time domain multiplexed with a physical uplink shared data channel.

10. An apparatus, comprising:

at least one processor; and

at least one memory comprising computer program code,

the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to:

form a phase tracking reference signal sample sequence utilizing outer-most constellation points corresponding to scheduled modulation order of data channel for discrete Fourier transform spread orthogonal frequency division multiplexing; and

apply orthogonal cover code of length L across the L consequent phase tracking reference signal sequence samples in time within a phase tracking reference signal burst to code division multiplex at least one phase tracking reference signal port of the apparatus.

11. The apparatus according to claim 10 , wherein the phase tracking reference signal sample sequence is further formed by scrambling with a user equipment-specific sequence.

12. The apparatus according to claim 10 , wherein the at least one memory and computer program code are further configured, with the at least one processor, to cause the apparatus at least to:

signal, to a user equipment, the phase tracking reference signal sample sequence configured for the user equipment.

13. The apparatus according to claim 10 , wherein the at least one memory and computer program code are further configured, with the at least one processor, to cause the apparatus at least to:

apply the orthogonal cover code to multiple phase tracking reference signal ports among different multi-user multiple-input and multiple-output users with a same physical resource block allocation.

14. The apparatus according to claim 10 , wherein the at least one memory and computer program code are further configured, with the at least one processor, to cause the apparatus at least to:

define a number of the phase tracking reference signal sequence samples based on an amount of allocated physical resource blocks.

15. The apparatus according to claim 14 , wherein the at least one memory and computer program code are further configured, with the at least one processor, to cause the apparatus at least to:

define the number of phase tracking reference signal sequence samples by using the following equation: ceil(number of scheduled PRBs/R), where R={4,2,1}.

16. The apparatus according to claim 10 , wherein discrete Fourier transform input block comprises N sub-blocks and K phase tracking reference signal sequence samples are split into N groups of length K/N with first group allocated to first K/N samples of sub-block #0, and last group allocated to last K/N samples of sub-block #(N−1).

17. The apparatus according to claim 10 , wherein the at least one memory and computer program code are further configured, with the at least one processor, to cause the apparatus at least to:

user equipment-specifically configuring the phase tracking reference signal burst periodicity and burst length based on at least one of residual frequency offset estimated by the apparatus, a channel quality indication reported by the user equipment, or information on time-correlation properties of the user equipment's local oscillator phase noise.

18. The apparatus according to claim 10 , wherein the phase tracking is time domain multiplexed with a physical uplink shared data channel.

19. The method according to claim 10 , wherein the phase tracking is frequency domain multiplexed with a physical downlink shared data channel.