Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03891—Spatial equalizers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
  • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0452—Multi-user MIMO systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/0224—Channel estimation using sounding signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/08—Access point devices
  • H04W88/085—Access point devices with remote components

Definitions

• TITLE Process for processing radio frequency signals received on R antennas, reception process, decoding process, computer program and corresponding system.
• the field of the invention is that of telecommunications.
• the invention relates to communications in the uplink, that is to say in the direction of the mobile terminals (or UE for “User Equipment”) towards a base station (or eNodeB, gNodeB, etc.).
• the invention proposes a new distribution of the functionalities implemented by a radio unit and by a baseband processing unit, for the decoding of radio frequency signals received on a plurality of antennas of a base station.
• the proposed solution applies in particular, but not exclusively, in the context of 5G NR (“New Radio” or “New Radio”) mobile networks.
• a radiofrequency signal received on an antenna undergoes analog processing, analog-to-digital conversion, then digital processing.
• the digital processing can be performed by a baseband processing unit, also called “Base Band Unit” (BBU) or “Distributed Unit” (DU) in English.
• BBU Base Band Unit
• DU Distributed Unit
• the active part of the analog processing can be performed by a “radio unit”, also called “Radio Unit” (RU) or “Remote Radio Head” (RRH) in English. It is recalled for this purpose that within the analog processing part, a passive part can be distinguished, comprising in particular the radiating antenna elements, and an active part, comprising in particular the filters, amplifiers, analog/digital converters, etc.
• RU Radio Unit
• RRH Remote Radio Head
• the base station BTS (“Base Transceiver station”) was connected to the passive elements of the antenna via a coaxial cable, via a limited number of antenna ports (maximum 4).
• the disadvantage of this architecture is the loss of power of the radio frequency signal between the antenna ports and the base station. This also limits the acceptable distance between the BTS and the passive antennas.
• the centralized RAN (Radio Access Network) architecture based on geographical separation of baseband (DU) computing capacities for digital processing, and radio transmitters (RU) for active analog processing, has developed.
• This type of architecture provides both functional benefits, thanks to better coordination between cells at the level of centralized units, and in terms of cost, by pooling the computing capacities of the different cells in common servers.
• several RUs can communicate with a DU.
• the interface between the DU and the RU is called “FrontHaul” in English, and can make it possible to deport the RU up to a maximum distance of 20km to centralize the DUs.
• TXRUs Transceiver Unit
• the evolution of base stations has consisted in bringing the TXRUs closer to the antenna, or integrated into the antenna in an RU radio unit.
• the baseband processing entity DU is thus connected to the RU by an optical fiber, carrying a digital signal, thus limiting the propagation losses associated with the use of a coaxial cable.
• the number of TXRUs has increased significantly over time and can now reach, for 5G, the value of 64 (massive MIMO).
• Open Fronthaul The xRAN Fronthaul Working Group, and more recently the O-RAN Standards Alliance, have supported the full specification of a single, open and interoperable interface between different vendors of RUs and DUs (“Open Fronthaul”).
• the 7.2x split is an adaptation of the 7.2 split specified in 3GPP and which makes it possible to reduce the complexity of the RU by moving processing functions up to the DU level.
• the DU includes the RLC/MAC/PHY-high layers
• the RU includes the layer called PHY-low.
• the PHY-low layer implemented in an RU includes, in addition to the active analog part of the antennas, certain baseband processing (close to the analog part) such as FFT/IFFT or digital beamforming. " in English. The resulting increase in bandwidth on the “open fronthaul” interface can be compensated by compression mechanisms referenced by the O-RAN Alliance.
• FIG. 2 illustrates more precisely the functionalities implemented by the RU 21 and by the DU 22, in the up direction, for the 7.2x split.
• the 7.2x split consists in moving the channel estimation 221 and RE-demapping 222 functionalities (extraction and separation of the resource elements - or "Resource Element (RE) - carrying the data and carrying the reference signals, in particular the DMRS (DeModulation Reference Signal)) in ORAN “Distributed Unit” (O-DU) 22.
• the 7.2x split includes a feature, implemented by O-RU 21, called port reduction 212 (“port reduction”) enabling the number of streams to be transmitted to the O-DU to be reduced.
• port reduction 212 port reduction
• the ORAN "Radio Unit” (O-RU) 21 would transmit a number of streams IQ equal to the number of reception branches R to the O-DU 22, whereas the number of spatial layers v to be detected is often much lower.
• SU-MIMO single PUSCH
• MU-MIMO PUSCHs
• this pre-coding 212 (performed by the O-RU) cannot rely on the DMRS-based channel estimation 221 (performed by the O-DU), since this would require sending all of the R flow to the O-DU 22 (DMRS signals being carried by each PUSCH channel), which is contradictory with the aim of reducing the number of ports.
• the port reduction must be based on other reference signals, for example, the SRS transmitted in the up direction with a relatively high periodicity (of the order of 40 ms).
• the O-DU 22 estimates the channel based on SRS signals and sends it back to the O-RU (beam creation option called “channel information based beamforming” in the O-RAN standard ) or sends the “port reduction” pre-coding coefficients directly to the O-RU (beam creation option called “weights based beamforming” in the O-RAN standard).
• An advantage of the 7.2x split is to be able to co-locate, in the DU 22, the equalization 223 and decoding 224 functionalities, which allows the implementation of advanced receivers with interference subtraction involving a decoding feedback loop .
• a disadvantage of the 7.2x split is having pre-coding coefficients for port 212 reduction less up-to-date than if this pre-coding was based on DMRS channel estimation, since DMRS are part of the transmission of PUSCHs (they give an instant picture of the channel and the interference). A major difficulty therefore appears for the 7.2x split for the reception of the PUSCH(s) in the up direction.
• the invention proposes a solution which does not have all the drawbacks of the prior art, in the form of a method for processing radio frequency signals received on R antennas, with R 3 2, implementing a radio unit communicating with a baseband processing unit.
• such a method comprises, implemented by the radio unit:
• Such a method further comprises, implemented by the baseband processing unit:
• the proposed solution is therefore based on a new distribution of functionalities between a radio unit (located as close as possible to the antenna structure of a base station) and a baseband processing unit (located at the foot of the base station, or in a data center close to the base station, for example within a radius of 20 km).
• the channel estimation is implemented by the radio unit. It can therefore be implemented from DMRS-based reference signals, which allows a more precise estimation of the transmission channel, and improves the quality of the projection. In particular, it offers an interesting solution for the reception of the PUSCH channel(s) in the uplink.
• Equalization and decoding are for their part implemented by the baseband processing unit, which allows advanced reception processing, in particular iterative processing based on the subtraction of the estimated interferences.
• the solution notably proposes a projection technique implemented by the radio unit, making it possible to reduce the quantity of signals intended for the baseband processing unit.
• the projection is implemented on a vector of R complex samples obtained from the R frequency representations (one sample for each frequency representation).
• the sample corresponding to this useful resource element i.e. to this sub-carrier of an OFDM symbol
• the R frequency representations are identified in each of the R frequency representations.
• a useful resource element carries one or more data symbols
• a reference resource element carries one or more reference symbols.
• a reference signal identifies the set of reference symbols that can be used for channel estimation.
• said at least one control information transmitted from the radio unit to the baseband processing unit belongs to the group comprising:
• the control information transmitted by the radio unit is notably used by the baseband processing unit to estimate the interference and the signal received.
• the transmission of at least one piece of control information is implemented for a set of resource elements.
• the quantity of control information transmitted from the radio unit to the baseband processing unit is limited, if the channel is approximately constant over several resource elements (RE).
• the covariance matrix K ] therefore represents noise plus interference before projection.
• the matrix K x therefore represents the noise plus interference resulting after projection.
• the transmission of at least one piece of control information transmits, for example:
• a suitable filter whitening The noise resulting from the application of the projection G not being white, the projection can be followed by a whitening of the noise, as presented in the second example.
• the vector y 1 of L samples projected at the output of the projection is expressed in the form: with y 1 EC a vector of size with I L an identity matrix of size L x L, representing the noise plus interference resulting after projection and bleaching.
• This projection has the particularity of being without loss of information on the useful signal x.
• the method further comprises the transmission, from the radio unit to the baseband processing unit, of a type of projection implemented.
• the radio unit transmits to the baseband processing unit an indicator indicating the type of control information transmitted, whether the projection is a projection followed or not by whitening, etc.
• the baseband processing unit knows the type of projection implemented.
• the baseband processing unit can inform the radio unit of the functionalities implemented by the baseband processing unit. For example, if the baseband processing unit implements DMRS-based channel estimation, it can inform the radio unit, which knows that it is not necessary to transmit control information in this case.
• the invention also relates to a method for receiving radio frequency signals on R corresponding antennas, R 3 2, implemented by a radio unit, comprising:
• reception method could of course comprise the different characteristics relating to the processing method as implemented by the radio unit, which can be combined or taken separately.
• the characteristics and advantages of the reception method are the same as those of the processing method as implemented by the radio unit described above.
• the invention relates to the corresponding radio unit.
• the invention also relates to a method for decoding radiofrequency signals received on R corresponding antennas, R 3 2, implemented by a baseband processing unit, comprising: - reception of at least one piece of control information transmitted by the radio unit, obtained from an estimate of the radiofrequency signal transmission channel implemented by the radio unit,
• Such a decoding method could of course comprise the different characteristics relating to the processing method as implemented by the baseband processing unit, which can be combined or taken separately.
• the characteristics and advantages of the decoding method are the same as those of the processing method as implemented by the baseband processing unit described previously.
• the invention relates to the corresponding baseband processing unit.
• the invention also relates to one or more computer programs comprising instructions for the implementation of a processing, reception or decoding method as described above when this or these programs are executed by at least one processor .
• the invention finally relates to a system comprising at least one radio unit, configured to process radiofrequency signals received on R antennas, with ff>2, and at least one corresponding baseband processing unit.
• the radio unit comprises:
• the baseband processing unit comprises:
• FIG. 1 illustrates different options for the separation of functionalities between the radio and baseband processing units, according to 3GPP;
• FIG 3 shows the main steps implemented by a radio unit and a baseband processing unit according to a particular embodiment of the invention
• FIG 4 shows the simplified structure of a radio unit according to a particular embodiment
• FIG. 5 shows the simplified structure of a baseband processing unit according to a particular embodiment.
• the general principle of the invention is based on a new distribution of functionalities between the RU and the DU, according to which the RU implements a pre-coding / port reduction functionality based on accurate channel estimation, and the DU implements equalization and decoding functionality, allowing for advanced receive processing.
• the RU implementing the active part of the analog processing
• the DU implementing the digital processing
• the DU can be located at the foot of the antenna structure, or in a remote data center, for example located 15-20 km from the RU.
• a DU can serve several RUs (“pooling of resources”).
• a time-frequency resource is a frequency (sub-band) and time (one or more OFDM symbols) granularity.
• a sub-band can range from a resource element (a subcarrier of an OFDM symbol), also called “Resource Element” or RE in English in the 3GPP standards, to a resource block (12 REs), also called “Physical Resource Block” or PRB in English, or to several PRBs.
• the base station receives different radiofrequency signals on R antennas, corresponding to the transmission, by at least one terminal or UE, of a physical channel PUSCH (“Physical Uplink Shared Channel”).
• a PUSCH channel can include several spatial layers v.
• a slot having a duration of 0.5 ms for a spacing between sub-carriers of 30 Khz in the “New Radio” standard several physical PUSCH channels can in particular be transmitted from different terminals. These can be multiplexed in frequency, time, space (MU-MIMO).
• physical channel is meant here a channel of the physical layer originating from a specific user who provides the means of transmitting by radio data/reference signals originating from the MAC layer (or from transport channels).
• FIG. 3 presents the main steps implemented by an RU 31 and by a DU 32 according to one embodiment of the invention, in the uplink.
• Steps implemented by the RU We consider for example R antennas, or R reception branches, with R 3 2, each receiving a different version of the same signal, corresponding to the combination of signals transmitted by at least one user terminal UE, for example a PUSCH. Each antenna r, with R 3 r 3 2 therefore receives a radio frequency signal.
• the RU 31 performs a processing 311r on the radiofrequency signal received on each antenna r, making it possible to obtain a frequency representation of the radiofrequency signal received on each antenna r.
• Each frequency representation is formed from a set of complex samples.
• reception of the radiofrequency signal is understood to mean anything that corresponds to the active part of the analog processing (filtering, amplification, frequency transposition), without the analog-to-digital conversion, the analog-to-digital conversion 3112 of the radiofrequency signal received, the suppression 3113 of the guard interval if a guard interval has been inserted before transmission, the transformation 3114 from the time domain to the frequency domain of the digital signal, delivering a frequency representation of the radio frequency signal received.
• the RU 31 also implements a de-mapping 312 of the R frequency representations, also called RE-demapping.
• de-mapping makes it possible to separate the resource elements carrying data, called useful resource elements, from the resource elements carrying the reference signals, called reference resource elements.
• a useful resource element can carry v data symbols and a reference resource element can carry v reference symbols, including at least one non-zero reference symbol, with v > 1 the number of spatial layers used for data transmission and reference signals.
• the RU 31 also implements an estimation 313 of the transmission channel of the radiofrequency signals and of the covariance of the noise plus interference affecting the radiofrequency signals, from said at least one reference signal extracted from the de-mapping 312, for example a DMRS.
• the data carried by the useful resource elements can then be filtered by the RU to reduce the size of the useful signal, taking into account the channel estimate and the covariance of noise plus interference 313.
• the RU 31 performs a projection 314 of the R complex samples associated with this useful resource element (ie of the R complex samples obtained respectively of each of the R representations frequencies corresponding to this subcarrier - one sample per frequency representation) on L complex samples, called projected samples, taking into account the channel estimation and the covariance of the noise plus interference 313, with R > L 3 v. More precisely, the same useful resource element /c (associated with a particular OFDM symbol) is considered for each reception branch, ie the same time-frequency position in the R radiofrequency signals received, to construct a vector y of R complex samples.
• the projection step 314, also called precoding or port reduction, is described below in more detail.
• the index of the resource element k (or the frequency index per subcarrier and the index of the OFDM symbol) is omitted for the sake of simplifying the notations.
• the covariance matrix K] represents noise plus interference before projection.
• the projection matrix G makes it possible to reduce the dimensions of the vector of the complex samples received y while attempting to keep sufficient statistics (without loss of information) on the transmitted symbols x for their reception.
• the matched filter is known to provide sufficient statistics in the presence of white noise by projecting the received signal and the noise onto the subspace of the useful signal.
• the projection 314 is not followed by whitening of the noise.
• the projection matrix GEC LxR is applied to the vector y, by the RU 31, to reduce the model to a dimension L, and to obtain at the output of the projection 314, a vector of complex samples, called projected samples y 1st CL : with
• the matrix therefore represents the noise plus interference resulting after projection.
• the vector y 1 of L projected samples can thus be transmitted to the DU 32 for the user data, via the DU/RU (“fronthaul”) interface, for example by an optical fiber.
• Control information for this user data can also be transmitted to the DU 32, for example by optical fiber, so that the DU 32 can reconstruct the interference and the received signal.
• the RU 31 can transmit to the DU 32 via the "fronthaul", per resource element k or for a set of resource elements during which the channel (precoded) is approximately constant, and by PUSCH:
• the projection 314 can be followed by whitening of the noise.
• the projection matrix G can be defined as proposed below.
• the network of reception antennas of dimension R, is linear and that the antennas are uniformly spaced (for example by half a wavelength).
• a direction of arrival/departure of the signal can be associated with a DFT vector of dimension R (where each coefficient of the DFT corresponds to a multiplicative factor to be applied to a different reception antenna for the formation of a reception beam in a given direction).
• the set of orthonormal DFT vectors forms an orthonormal basis of the received signal commonly used to analyze the directions of arrival of the signal in reception.
• H is the estimated channel from the DMRSs at the RU.
• K the noise plus interference covariance matrix
• H the estimated channel from the DMRSs at the RU.
• a direction (DFT vector) u t is better than another direction u 2 if and only ll II
• H w Hl can be estimated as the matrix R-dimensional identity. This makes it possible to estimate H w Hl, using an estimator of the type j; ⁇ Li yw ,k yl k — IR using N samples received (bleached).
• the projection then consists, according to this example, in the succession of the following two steps:
• the projection matrix G can therefore be V ⁇ K j 2 , of dimension L x R.
• the vector y 1 of L projected samples can thus be transmitted to the DU 32 for the user data, via the DU/RU (“fronthaul”) interface, for example by an optical fiber.
• Control information for this user data may also be transmitted to the
• the DU 32 for example by the optical fiber, so that the DU 32 can reconstruct the received signal.
• the control information is deduced from the reception of the reference signals which may be DMRS, which differs from the 7.2x option presented in the prior art.
• At least one control information is transmitted to the baseband processing unit 32, for example in an optical fiber.
• the L projected samples are also transmitted to the baseband processing unit 32, for example in an optical fiber.
• the DU 32 can thus receive the L projected samples transmitted by the radio unit 31 for a resource element k, as well as control information 321, as presented in the two examples above, for each channel PUSCH.
• control information of the channel matrix H, projection matrix G, product GH type can be uploaded 321 from the RU to the DU for the resource element k or for a set of resource elements during which the (precoded) channel is approximately constant.
• a covariance matrix K from the RU to the DU for an OFDM symbol, or for a set of X OFDM symbols (for example 14 OFDM symbols, ie a duration of 0.5 ms for a spacing between sub-carriers of 30 kFlz). This assumes that the covariance of noise plus interference is the same over the whole band for a duration of X OFDM symbols.
• the DU 32 can then implement an equalization 322 of the L projected samples, taking account of the control information 321.
• the control information 321 makes it possible in particular to reconstruct the interference and signal models received, in order to be able to implement an equalization .
• the DU 32 implements a processing 323 j of the equalized symbols, for each user j, 1 £ ) ⁇ ] ⁇
• the purpose of the equalization is to process the interference between spatial layers in order to estimate/detect the transmitted symbols.
• / is proportional to the ith row of the matrix
• the DU receives the vector y 1 and the control information comprising for example the product G b H.
• Different techniques can in particular be implemented to inform the DU 32 of the type of projection implemented by the RU 31.
• the DU knows that the projection implemented by the RU is followed (or not) by a bleaching by configuration, or because it receives a message from the RU indicating to the DU the implementation (or not ) bleaching, etc.
• the DU can choose an option (“simple” projection or projection with bleaching), and inform the RU of the chosen option.
• the processing of equalized symbols is a conventional processing.
• a feedback loop with equalization 322 can be provided.
• equalization can be performed jointly or disjointly by PUSCH.
• a feedback loop between the decoding of all users and the equalization of users is possible in the case of an advanced receiver.
• such a radio unit comprises at least one memory 41 comprising a buffer memory, at least one processing unit 42, equipped for example with a programmable calculation machine or a dedicated calculation machine, for a processor P, for example, and controlled by the computer program 43, implementing steps of the reception method according to at least one embodiment of the invention.
• the code instructions of the computer program 43 are for example loaded into a RAM memory before being executed by the processor of the processing unit 42.
• the processor of the processing unit 42 implements the steps of the reception method described above, according to the instructions of the computer program 43, to:
• each frequency representation being formed of a set of complex samples
• such a baseband processing unit comprises at least one memory 51 comprising a buffer memory, at least one processing unit 52, equipped for example with a programmable calculating machine or a dedicated calculation, for example a processor P, and controlled by the computer program 53, implementing steps of the decoding method according to at least one embodiment of the invention.
• the code instructions of the computer program 53 are for example loaded into a RAM memory before being executed by the processor of the processing unit 52.
• the processor of the processing unit 52 implements steps of the decoding method described above, according to the instructions of the computer program 53, to:

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Power Engineering (AREA)
• Radio Transmission System (AREA)

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• 2021
  • 2021-06-04 FR FR2105929A patent/FR3123773A1/fr not_active Withdrawn
• 2022
  • 2022-06-03 EP EP22735013.9A patent/EP4348873A1/de active Pending
  • 2022-06-03 WO PCT/FR2022/051058 patent/WO2022254160A1/fr active Application Filing

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