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EP-4736348-A1 - CALIBRATION OF REPEATERS IN A WIRELESS NETWORK

EP4736348A1EP 4736348 A1EP4736348 A1EP 4736348A1EP-4736348-A1

Abstract

There is provided techniques for calibrating repeaters in a wireless network, the method is performed by a network node. The method comprises configuring the repeaters with patterns, wherein each of the patterns defines a sequence of non-zero complex-valued gains one of the repeaters is to apply over time during bidirectional sounding. The method comprises obtaining bidirectional channel response measurements for each of the patterns from bidirectional sounding as performed by a first transceiver device and a second transceiver device configured to wirelessly communicate with each other without and via the repeaters in the wireless network. The method comprises determining compensation factors, one per repeater, as a function of linear combinations of the bidirectional channel response measurements. There is one linear combination of bidirectional channel response measurements per pattern. The method comprises calibrating the repeaters by configuring the repeaters with the compensation factors.

Inventors

  • FRENGER, Pål
  • VIEIRA, Joao
  • LARSSON, ERIK G.

Assignees

  • Telefonaktiebolaget LM Ericsson (publ)

Dates

Publication Date
20260506
Application Date
20230630

Claims (20)

  1. CLAIMS 1. A network node (200) for calibrating ^ repeaters (300a:300N) in a wireless network (100a:100c), wherein the network node (200) is configured to: configure the repeaters (300a:300N) with at least ^ patterns, wherein each of the ^ patterns defines a sequence of non-zero complex-valued gains one of the repeaters (300a:300N) is to apply over time during bidirectional sounding; obtain bidirectional channel response measurements for each of the at least ^ patterns from bidirectional sounding as performed by a first transceiver device (110a) and a second transceiver device (110b) configured to wirelessly communicate with each other without and via the repeaters (300a:300N) in the wireless network (100a:100c); determine compensation factors, one per repeater (300a:300N), as a function of linear combinations of the bidirectional channel response measurements, wherein there is one linear combination of bidirectional channel response measurements per pattern; and calibrate the repeaters (300a:300N) by configuring the repeaters (300a:300N) with the compensation factors.
  2. 2. The network node (200) according to claim 1, wherein each of the patterns is taken as a respective row from one and the same orthonormal matrix.
  3. 3. The network node (200) according to claim 2, wherein the orthonormal matrix has ^ columns and ^ rows.
  4. 4. The network node (200) according to claim 1 or 2, wherein the orthonormal matrix is any of: a unimodular matrix, a Hadamard matrix, a DFT matrix.
  5. 5. The network node (200) according to any of claims 2 to 4, wherein coefficients of the linear combinations are given by matrix entries per row of the orthonormal matrix.
  6. 6. The network node (200) according o any preceding claim, wherein the compensation factors are based on channel properties ^ of a wireless direct link between the first transceiver device (110a) and the second transceiver device (110b).
  7. 7. The network node (200) according to claim 6, wherein the compensation factors are based on transmitter gains ^^ , ^^ and receiver gains ^ ^ ,^ ^ at the first transceiver device (110a) and the second transceiver device (110b) as estimated from the channel properties ^ of said wireless direct link.
  8. 8. The network node (200) according to claim 7, wherein the network node (200) further is configured to: configure the repeaters (300a:300N) to keep their phases unrotated during a first bidirectional sounding performed between the first transceiver device (110a) and the second transceiver device (110b).
  9. 9. The network node (200) according to claim 7 or 8, wherein the network node (200) further is configured to: configure the repeaters (300a:300N) to rotate their phases 180 degrees during a second bidirectional sounding performed between the first transceiver device (110a) and the second transceiver device (110b).
  10. 10. The network node (200) according to claims 8 and 9, wherein the channel properties ^ of said wireless direct link are estimated as a function of the first bidirectional sounding and the second bidirectional sounding.
  11. 11. The network node (200) according to claim 6, wherein the channel properties of said wireless direct link are obtained from the first transceiver device (110a) and the second transceiver device (110b).
  12. 12. The network node (200) according to any preceding claim, wherein the network node (200) further is configured to: track a drift in calibration error of the repeaters (300a:300N) by estimating a change in compensation factor between consecutive occasions in which the repeaters (300a:300N) are calibrated.
  13. 13. The network node (200) according o claim 12, wherein the network node (200) further is configured to: select the ^ repeaters (300a:300N) from a set of ^ ^ ^ repeaters based on the drift in calibration error of the ^ repeaters (300a:300N).
  14. 14. The network node (200) according to claim 13, wherein the ^ repeaters (300a:300N) are selected by their drift in calibration error being larger than a threshold value.
  15. 15. The network node (200) according to any preceding claim, wherein each of the repeaters (300a:300N) is configured for communication in a forward direction and a reverse direction, wherein each of the repeaters (300a:300N) comprises forward path circuitry (360a) for communicating in the forward direction and reverse path circuitry (360b) for communicating in the reverse direction, and wherein the repeaters (300a:300N) are by the network node (200) configured to apply the compensation factors to either the forward path circuitry (360a) or the reverse path circuitry (360b).
  16. 16. The network node (200) according to claim 15, wherein the forward path circuitry (360a) for repeater ^, where ^ ൌ 1,… ,^, has a complex-valued gain ^ ^ , wherein the reverse path circuitry (360b) for repeater ^ has a complex-valued gain ^ ^ , and wherein the compensation factor for repeater ^ is a function of a ratio between ^ ^ and ^ ^ .
  17. 17. A system comprising ^ repeaters (300a:300N) to be calibrated in a wireless network (100a:100c), wherein the repeaters (300a:300N) are configured to: receive configuration from a network node (200) with at least ^ patterns according to which the repeaters (300a:300N) are to change their complex-valued gains over time during bidirectional sounding; operate according to the configuration whilst, for each of the at least ^ patterns by the complex-valued gains of the repeaters (300a:300N) being changed over time in accordance with the at least ^ patterns, taking part in the bidirectional sounding between a first transceiver device (110a) and a second transceiver device (110b) configured to wirelessly communicate w each other without and via the repeaters (300a:300N) in the wireless network (100a:100c); receive compensation factors from the network node (200), one per repeater (300a:300N); and apply the compensation factors during subsequent operation.
  18. 18. The system according to claim 17, wherein each of the repeaters (300a:300N) is a dual-antenna repeater (300a:300N).
  19. 19. The system according to claim 17 or 18, wherein each of the repeaters (300a:300N) is configured for communication in a forward direction and a reverse direction, wherein each of the repeaters (300a:300N) comprises forward path circuitry (360a) for communicating in the forward direction and reverse path circuitry (360b) for communicating in the reverse direction, and wherein the compensation factors are to be applied to either the forward path circuitry (360a) or the reverse path circuitry (360b).
  20. 20. The system according to claim 19, wherein the forward path circuitry (360a) for repeater ^, where ^ ൌ 1,… ,^, has a complex-valued gain ^ ^ , wherein the reverse path circuitry (360b) for repeater ^ has a complex-valued gain ^ ^ , and wherein the compensation factor for repeater ^ is a function of a ratio between ^ ^ and ^ ^ .

Description

CALIBRATION OF REPEATERS IN A WIRELESS NETWORK The project leading to this application has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101013425. TECHNICAL FIELD Embodiments presented herein relate to a method, a network node, a computer program, and a computer program product for calibrating repeaters in a wireless network. Embodiments presented herein further relate to a method, a system of repeaters, a computer program, and a computer program product for the repeaters to be configured. BACKGROUND Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a multiple-input multiple-output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO systems, or just MIMO for short. Cellular massive MIMO, also known as co-located massive MIMO, operating in time- division duplexing (TDD) relies on channel reciprocity to obtain downlink (DL) channel estimates at the access points (APs) from uplink pilots transmitted by the user equipment (UEs). Channel reciprocity is key to harvest most performance gains, since training the channel in the UL requires a pilot overhead that is proportional to the number of antenna ports at the UE side of the link, which is much smaller compared to training the channel in the DL which requires a pilot overhead that is proportional to the number of antenna ports at the APs. Moreover, in such reciprocity-based operation, there is no need for feedback of the measured DL channels to the AP side, as is required in systems that perform explicit DL channel estimation such as non-reciprocal frequency-division duplex (FDD) systems. Throughout this disclosure, reciprocity-based massive MIMO with TDD operation is considered. One challenge of co-located massive MIMO is to efficiently serve UEs in unfavorable locations. One example of this is scenarios with outdoor-to-indoor communications, where indoor UEs are served by APs located outdoors. Another example of this is scenarios in rural environments, where only a small number of channel scatters (e.g., physical objects in the environment) exits, and where the path loss can be very high. Some of the issues resulting from these challenges will be disclosed next. One issue pertains to coverage degradation. In outdoor-to-indoor communications, coverage degradation is due to an additional path loss from signal propagation through walls and windows. In rural environments coverage degradation is due to electromagnetic shadowing from large objects (plus lack of alternative scatterers). The former is especially an issue in buildings that have thick walls containing sheet metal and/or concrete reinforcement bars, or windows with energy-saving coatings, or both. One issue pertains to that richness of the electromagnetic channel might be compromised. In outdoor-to-indoor communications, if the only significant propagation path from an AP located outdoors to a UE located indoors is through a window, the resulting channel will be effectively rank one, also known as a key-hole channel, irrespective of how many antennas the AP and the UE have, and irrespective of how much local scattering there is around the AP and the UE. The issue is aggravated in a multi-user scenario, where many UEs are served through such a keyhole channel. In the rural environments scenario, one issue is that there are only few reliable scatterers between the AP and the UE. Some attempts to mitigate these issues involve installation and use of active repeaters that amplify the signal between the AP and the UE. Other attempts to mitigate these issues involve the use of reflecting intelligent surfaces (RIS) that essentially function as a repeater but without amplification (though with some beam steering capability). A repeater might be regarded as a transceiver device that amplifies the incoming radio-frequency (RF) field and re-transmits it instantaneously. Different types of repeaters exist. Single-antenna repeaters use the same antenna for reception and transmission and require the use of a circulator or similar device to isolate the outgoing wave from the incoming. Single-antenna repeaters have limited amplification by the transmit/receive (Tx/Rx) isolation circuit (e.g., circulator). Further, single-antenna repeaters lack beamforming capabilities (since there is only a single-antenna, and its antenna pattern needs to be wide enough to simultaneously cover both the direction in which the AP is located and the direction in which potential UEs are located). The former results in energy-inefficient communications, in general. For example, if the repeater is installed in the outer part of a building to enable outdoor-to-indoor communications, then the energy that effectively ente