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EP-3788823-B1 - TRANSMISSION OF UPLINK REFERENCE SIGNALS

EP3788823B1EP 3788823 B1EP3788823 B1EP 3788823B1EP-3788823-B1

Inventors

  • NILSSON, ANDREAS
  • FAXÉR, Sebastian
  • WERNERSSON, Niklas

Dates

Publication Date
20260506
Application Date
20180504

Claims (20)

  1. A method for transmitting uplink reference signals to a network node (300), the method being performed by a terminal device (200), the method comprising: obtaining (S102), from the network node (300), a configuration of transmission of the uplink reference signals, the configuration comprising an indication of a first frequency interval in which the uplink reference signals are to be transmitted; distributing (S108) transmission power available for transmitting the uplink reference signals over the first frequency interval, by allocating more transmission power to frequency parts in the first frequency interval with a first channel quality than to frequency parts in the first frequency interval with a second channel quality, based on channel information for the first frequency interval, wherein the channel information pertains to properties of a radio propagation channel between the terminal device (200) and the network node (300), and the channel information is indicative of the frequency parts in the first frequency interval with the first channel quality and the frequency parts in the first frequency interval with the second channel quality, wherein the second channel quality is less than the first channel quality; and transmitting (S110) the uplink reference signals to the network node (300) in accordance with the distributed transmission power.
  2. The method according to claim 1, wherein the first frequency interval comprises at least two subbands.
  3. The method according to claim 2, wherein the at least two subbands are contiguous.
  4. The method according to claim 3, wherein the transmission power is distributed over at least two of the at least two subbands.
  5. The method according to claim 2, wherein the at least two subbands are non-contiguous.
  6. The method according to claim 2, wherein the transmission power is distributed only over one single subband.
  7. The method according to claim 1, wherein the first frequency interval comprises a single subband.
  8. The method according to claim 7, wherein the terminal device (200) and the network node (300) communicate with each other in a communication system having an active system bandwidth, and wherein the single subband spans the entire active system bandwidth.
  9. The method according to claim 2 or 7, wherein the transmission power is distributed over less than one subband.
  10. The method according to claim 1, wherein the transmission power is distributed so as to be non-zero only for a set of frequency bands in the first frequency interval.
  11. The method according to claim 10, wherein the set of frequency bands define a second frequency interval.
  12. The method according to claim 11, wherein the second frequency interval is contiguous.
  13. The method according to claim 11, wherein the transmission power is uniformly distributed within the second frequency interval.
  14. The method according to claim 11, further comprising: notifying (S106) the network node (300) about the second frequency interval before transmitting the uplink reference signals.
  15. A terminal device (200) for transmitting uplink reference signals to a network node (300), the terminal device (200) comprising processing circuitry (210), the processing circuitry being configured to cause the terminal device (200) to: obtain, from the network node (300), a configuration of transmission of the uplink reference signals, the configuration comprising an indication of a first frequency interval in which the uplink reference signals are to be transmitted; distribute transmission power available for transmitting the uplink reference signals over the first frequency interval, by allocating more transmission power to frequency parts in the first frequency interval with a first channel quality than to frequency parts in the first frequency interval with a second channel quality, based on channel information for the first frequency interval, wherein the channel information pertains to properties of a radio propagation channel between the terminal device (200) and the network node (300), and the channel information is indicative of the frequency parts in the first frequency interval with the first channel quality and the frequency parts in the first frequency interval with the second channel quality, wherein the second channel quality is less than the first channel quality; and transmit the uplink reference signals to the network node (300) in accordance with the distributed transmission power.
  16. The terminal device (200) according to claim 15, wherein the processing circuitry is configured to cause the terminal device (200) to arrange the first frequency interval so that it comprises at least two subbands.
  17. The terminal device (200) according to claim 16, wherein the processing circuitry is configured to cause the terminal device (200) to arrange the two subbands as contiguous subbands.
  18. The terminal device (200) according to claim 17, wherein the processing circuitry is configured to cause the terminal device (200) to distribute the transmission power over at least two of the at least two subbands.
  19. The terminal device (200) according to claim 17, wherein the processing circuitry is configured to cause the terminal device (200) to arrange the two subbands as non- contiguous subbands.
  20. The terminal device (200) according to claim 15, wherein the processing circuitry is configured to cause the terminal device (200) to distribute the transmission power only over one single subband.

Description

TECHNICAL FIELD Embodiments presented herein relate to a method, a terminal device, a computer program, and a computer program product for transmitting uplink reference signals. BACKGROUND In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed. Some communications networks are deployed for time-division duplexing (TDD). One benefit with TDD (compared to frequency-division duplexing; FDD) is that TDD enables reciprocity based beamforming, which can be applied both at the network-side (i.e. for downlink; DL) and the user-side (i.e. for uplink; UL). For reciprocity based DL transmission terminal devices at the user-side might transmit Sounding Reference Signals (SRSs) which a network node at the network-side might use to estimate the radio propagation channel between the network node and the terminal device. The channel estimate might then be used at the network node to find optimal precoding weights for coming DL transmission to the terminal device, for example by using so-call eigen-beamforming. The SRS should preferably span the full operational frequency bandwidth of the communication network to facilitate frequency selective precoding and/or frequency selective scheduling. The system performance for reciprocity based DL beamforming might be limited by poor SRS coverage, which deteriorates the channel estimation quality. In communication networks utilizing comparatively high frequency bands (e.g. at millimeter wavelengths (mmW), i.e. near and above 30 GHz) the link budget for SRS could be comparatively high, partly due to the higher carrier frequency (where path loss is higher) and larger bandwidths (leading to less power spectral density; PSD) for the SRSs). Different methods have been proposed improve the SRS link budget. One example is frequency hopping, which is illustrated in Fig. 1(a), where the SRSs are allocated different resource in frequency for different orthogonal frequency-division multiplexing (OFDM) symbols. For frequency hopping, different parts of the frequency band are sounded in different OFDM symbols, which means that the PSD will increase for the SRS. Another example is to repeat the same SRS over multiple OFDM symbols, as illustrated in Fig. 1(b), where the SRSs are allocated resource in the entire frequency interval for each OFDM symbol, which will increase the processing gain of the SRS as more and more OFDM symbols are decoded. Yet another example is that the network node notifies the terminal device to only transmit SRS on a certain part of the frequency band, which will increase the PSD of the SRS. SRS transmission might be applied for DL reciprocity based operations, such that the radio propagation channel in the DL direction can be estimated frequently. If the SRS transmission is periodic, it commonly configured using high layer signaling (such as radio resource control; RRC) and could therefore not be updated very quickly, for example in order to track fast fading. However, it might be possible for the network node to adapt the SRS transmission to a more robust scheme, as for example the ones illustrated in Figs. 1(a) and 1(b), to combat long term channel properties, for example high path loss. One drawback with the two methods illustrated in Fig. 1 is that is that multiple OFDM symbols are needed for the SRS transmission. This will increase overhead and latency. Further, decreasing the sounding bandwidth of the SRS leads to that the network node will only have channel estimations for a fraction of the frequency band. If the radio propagation channel is frequency selective it is possible that the sounded frequency band belongs to the comparatively bad parts of the frequency band, which will decrease the link budget for the SRS as well as the DL performance. Hence, there is still a need for mechanisms enabling improved channel estimation. In US 2011/0098054 A1 is described systems and methodologies that facilitate configuring a sounding reference signal transmission in a wireless communication environment. A UE can employ coordinated multi-point transmission and/or reception such that multiple cells collaborate to transmit data to the UE and/or receive data from the UE. To support the coordinated multi-point transmission and/or reception, the UE can transmit a sounding reference signal that is configured to enable reliable reception of the sounding reference signal by members of a cooperating set. In addition, configuration of the sounding reference signal can be coordinated to enable more efficient transmission and utilization of the sounding reference signal. Configuration of the sounding reference signal can be based upon information exchanged between the multiple cells. Moreover, the multiple cells can coordinate to set and control a transmit power of the sounding reference signal. SUMMARY An object of embodim