WO2020171755A1

WO2020171755A1 - Serial mimo antenna system comprising a first link and a second link

Info

Publication number: WO2020171755A1
Application number: PCT/SE2020/050158
Authority: WO
Inventors: Pål FRENGER; Martin HESSLER; Jan HEDEREN
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2019-02-20
Filing date: 2020-02-13
Publication date: 2020-08-27

Abstract

The present disclosure relates to an antenna system (100) comprising at least one central unit (101) and at least one antenna unit group. The at least one antenna unit group comprises a plurality of serially connected antenna units (103a, 103b). Each antenna unit (103a, 103b) in the antenna unit group is serially connected to its neighboring antenna unit(s) (103a, 103b) via a first link (108). Each antenna unit (103a, 103b) in the antenna unit group is directly connected to the central unit (101) via a second link (110). Each antenna unit (103a, 103b) in the antenna unit group is adapted to process UE data received from at least one UE (115).

Description

Serial MIMO antenna system comprising a first link and a second link

TECHNICAL FIELD Embodiments herein relate generally to an antenna system, a method performed by an antenna system, a method for setting up an antenna system, a second antenna unit, a method performed by the second antenna unit, a central unit, a method performed by the central unit. More particularly the embodiments herein relate to processing of UE data, for example uplink processing in an at least partly distributed and serial MIMO system.

BACKGROUND

Multiple Input Multiple Output (MIMO) is also referred to as spatial multiplexing and is defined by 3GPP as to be“used to increase the overall bitrate through transmission of two (or more) different data streams on two (or more) different antennas - using the same resources in both frequency and time, separated only through use of different reference signals - to be received by two or more antennas." MIMO may be in various dimensions, such as 2x2, 4x4, 8x8 etc. For example, in 2x2 MIMO, two different data streams are transmitted on two transmitter (TX) antennas and received by two receiver (RX) antennas, using the same frequency and time, separated only by the use of different reference signals.

Massive MIMO, also known as a large-scale antenna system and very large MIMO, is a multi-user MIMO technology where each Base Station (BS) is equipped with a large number of antenna elements, e.g. more than 50 antenna elements, which are being used to serve many User Equipments (UE) that share the same time and frequency band and are separated in the spatial domain. The UE may also be referred to as a terminal. A key assumption is that there are many more base station antenna elements than UEs; at least twice as many, but ideally as many as possible. Massive MIMO offers many benefits over conventional multi-user MIMO. First, conventional multi-user MIMO is not a scalable technology, since it has been designed to support systems with roughly equal numbers of service antenna elements and UEs, and practical implementations typically relies on Frequency-Division Duplex (FDD) operation. The term service antenna element mentioned above is antenna element adapted to serve e.g. a UE. By contrast, in massive MIMO, the large excess of service antenna elements over active UEs in Time Division Duplex (TDD) operation brings large improvements in throughput and radiated energy efficiency. These benefits result from the strong spatial multiplexing achieved by appropriately shaping the signals sent out and received by the base station antenna elements. By applying precoding to all antenna elements, the base station may ensure constructive interference among signals at the locations of the intended UEs, and destructive almost everywhere else. Furthermore, as the number of antenna elements increases, the energy may be focused with extreme precision into small regions in space. Other benefits of massive MIMO include use of simple low-power components since it relies on simple signal processing techniques, reduced latency, and robustness against intentional jamming.

When a base station operating in TDD mode, massive MIMO may exploit the channel reciprocity property, according to which the channel responses are the same in both uplink and downlink. Channel reciprocity allows the base stations to acquire Channel State Information (CSI) from pilot sequences transmitted by the UEs in the UpLink (UL), and this CSI is then useful for both the uplink and the DownLink (DL). The pilot sequence may also be referred to as a sequence of pilot signals, pilot signal sequence or similar. By the law of large numbers, the effective scalar channel gain seen by each UE is close to a deterministic constant. This is called channel hardening. Thanks to the channel hardening, the UEs may reliably decode the downlink data using only long-term statistical CSI, making most of the physical layer control signalling redundant, i.e. low-cost CSI acquisition. This renders the conventional resource allocation concepts unnecessary and results in a simplification of the Medium Access Control (MAC) layer. These benefits explain why massive MIMO has a central position in Fifth Generation (5G). The MAC layer mentioned above is one of two sublayers that make up the data link layer of the Open Systems Interconnection (OSI) model, and provides addressing and channel access control mechanisms that enable several UEs or network nodes to communicate in a network. Flowever, massive MIMO system performances are affected by some limiting factors: Channel reciprocity requires hardware calibration. In addition, the so-called pilot contamination effect is a basic phenomenon which profoundly limits the performance of massive MIMO systems. Theoretically, every UE in a massive MIMO system could be assigned an orthogonal uplink pilot sequence. Flowever, the maximum number of orthogonal pilot sequences that may exist is upper-bounded by the size of the coherence interval, which is the product of the coherence time and coherence bandwidth. Hence, adopting orthogonal pilot sequences leads to inefficient resource allocation as the number of the UEs increases or it is not physically possible to perform when the coherence interval is too short. As a consequence, pilot sequences must be reused across cells, or even within the home cell, for higher cell density. This inevitably causes interference among UEs which share the same pilot sequence. Pilot contamination does not vanish as the number of base station antenna elements grows large, and so it is the one impairment that remains asymptotically. To implement massive MIMO in wireless networks, two different architectures may be adopted:

• Centralized massive MIMO (C-maMIMO), where all the antenna elements 105 are co-located in a compact area at both the base station 102 and UE 115 sides, as shown in fig. 1. It represents the conventional massive MIMO system.

· Distributed massive MIMO (D-maMIMO), where base station antennas 105are geographically spread out over a large area, in a well-planned or random fashion, as shown in fig. 2. In D-MaMIMO, the antenna element may be named Access Point (AP). The antenna units 103 are connected together and to a Central Processing Unit (CPU) 101 through high-capacity backhaul links 110, e.g. fiber- optic cables. A D-maMIMO system is also known as a cell-free massive MIMO system.

Note that even though fig. 1 is exemplified with six UE’s 1 15, the C-maMIMO may comprise any suitable n number of UEs 1 15, where n is a positive integer. Note also that even though fig. 2 is exemplified with five UEs 1 15 and nine antenna elements 105, the D- maMIMO may comprise any suitable n number of UEs 1 15 and m number of antenna elements 105, where n and m are positive integers.

D-maMIMO architecture is one important enabler of network MIMO in future standards. Network MIMO is a terminology that is used for a cell-free wireless network, where all the base stations that are deployed over the coverage area act as a single base station with distributed antenna elements 105. This may be considered the ideal network

infrastructure from a performance perspective, since the network has great abilities to spatially multiplex users and exactly control the interference that is caused to everyone. The distinction between D-maMIMO and conventional distributed MIMO is the number of antenna elements 105 involved in coherently serving a given UE 1 15. In D-maMIMO, every antenna element 105 serves every UE 1 15. Compared to C-maMIMO, D-maMIMO has the potential to improve both the network coverage and the energy efficiency, due to increased macro-diversity gain. This comes at the price of higher fronthaul requirements and the need for distributed signal processing. In D-maMIMO, the information regarding payload data, and power control coefficients, is exchanged via the backhaul network between the antenna elements 105 and the CPU 101. There is no exchange of instantaneous CSI among the antenna elements 105 or the CPU 101 that is CSI acquisition may be performed locally at each antenna element 105.

Due to network topology, D-maMIMO suffers from different degrees of path losses caused by different access distances to different distributed antenna elements 105, and very different shadowing phenomena that are not necessarily better. The antenna elements 105 deployed at the street level are more easily blocked by buildings than antenna elements 105 deployed at elevated locations. Moreover, since the location of antenna elements 105 in D-maMIMO has a significant effect on the system performance, optimization of the antenna locations is crucial. In addition, D-maMIMO potentially system suffers a low degree of channel hardening. As mentioned earlier, the channel hardening property is key in massive MIMO to suppress small-scale fading and derives from the large number of antenna elements 105 involved in a coherent transmission. In D- maMIMO, antenna elements 105 are distributed over a wide area, and many antenna elements 105 are very far from a given UE 1 15. Therefore, each UE 1 15 is effectively served by a smaller number of antenna elements 105. As a result, channel hardening might be less pronounced. This would considerably affect the system performance.

The performance of any wireless network is clearly the availability of good enough CSI to facilitate phase-coherent processing at multiple antennas. Intuitively, acquiring high quality CSI should be easier with a C-maMIMO than in a D-maMIMO where the antenna elements 105 are distributed over a large geographical area. Nevertheless, the macro diversity gain has a dominant importance and leads to improved coverage and energy efficiency.

A problem with a massive MIMO deployment is that a large number of antenna elements 105 generate a large amount of data. This implies that with traditional radio to antenna element interfaces very large capacity fiber network are needed to shuffle this data around. Fiber is both expensive and needs skilled personal for installation. Both of which limit the deployment scenarios for massive MIMO. There is also a scalability issue as different size base-band units are needed to handle different array sizes, e.g. one to handle 32 antenna elements 105 one other for 128 antenna elements 105 etc.

From a practical point of view, a C-maMIMO solution where all antenna elements 105, are placed close together has a number of drawbacks compared to D-maMIMO solution where the antenna elements 105 are distributed over a larger area. These are e.g.

• Very large service variations: UEs 1 15 that happen to be located close to the

central massive MIMO node will experience very good service quality while for UEs 1 15 further away the service quality will degrade rapidly.

• Sensitive to blocking: On high frequency bands in particular the signal is easily blocked by obstacles that obscure the line-of-sight between the UE 1 15 and the C- maMIMO node. In D-maMIMO, a number of antenna elements 105 may be blocked but it requires much larger obstacles to block all antenna elements 105.

• High heat concentration: Due to heat concentration it is difficult to make C- maMIMO nodes very small. In D-maMIMO, each antenna element 105 and its associated processing generates only a small amount of heat and this simplifies miniaturization.

• Large and visible installations: C-maMIMO installations may become large,

especially on lower frequency bands. D-maMIMO installations are actually even larger, but the visual impact may be made almost negligible.

• Installation requires personnel with“radio skills”: Installing a complex piece of hardware in a single location requires planning and most probably also proper installation by certified personnel. In a D-maMIMO installation it is less crucial that each and every one of the very many antenna elements 105 is installed in a very good location. It is sufficient that the majority of the antenna elements 105 are installed in good enough locations. The requirements on installation may be significantly relaxed with a D-maMIMO deployment.

• Power limited by regulations, e.g. Specific Absorption Rate (SAR): If the antenna elements 105 are located close together there will be an area close to the installation where electromagnetic wave safety rules apply. This is likely to put limits on the total radiated radio frequency power in many installations. In a D- maMIMO installation, a UE 1 15 may come close to a small number of antenna elements 105, but it is impossible to be physically close to many antenna elements 105 that are distributed over a large area.

There are many significant benefits with D-maMIMO compared to C-maMIMO. But the cabling and internal communication between antenna elements 105 in a D-maMIMO is prohibiting in state-of-the art solutions. It is not economically feasible to connect a separate cable between each antenna element 105, and possibly the APU 103, and a central processing unit 101 , e.g. in a star topology, in a D-maMIMO installation. Either arbitrary or optimal antenna element topology may lead to a prohibitive cost for the backhaul component, as well as installation cost for distributing processing and settings.

Radio Stripes

The actual base stations in a radio stripe system may comprise circuit mounted chips inside a protective casing of a cable or a stripe. The receive and transmit processing of each antenna element 105 is performed next to the actual antenna element 105 itself by an Antenna Processing Unit (APU) 103. Since the total number of distributed antenna elements 105 is assumed to be large, e.g. several hundred, the radio frequency transmit power of each antenna element 105 is very low.

The example in fig. 3 depicts a system mock-up and shows a Light Emitting Diode (LED) radio stripe 301 connected to a box referred to as stripe station 303. This fig. 3 is only used to exemplify how the actual distributed massive MIMO base station may be built. A central processing unit or stripe station 101 connects with one or more radio stripes 301 or distributed MIMO active antenna cables.

The actual radio stripes 301 may comprise tape or adhesive glue on the backside, as in the example of the LED stripes. Or it may simply contain very small per-antenna processing units, i.e. the APU 103, and antenna elements 105 protected by the plastics covering the cable. The APU 103 may be referred to as antenna unit or antenna processor herein.

An observation to make is that both the transmitter and receiver processing may be distributed under certain assumption, e.g. see fig. 4. With low-complexity pre-coding methods such as conjugate beamforming, each antenna element 105 may be equipped with a controlling entity, e.g. the APU 103 that determines the beamforming weights without communicating with all other APUs 103. By using e.g. conjugate beamforming, the beamforming processing required may be performed per-element, or per group of elements (not shown in fig. 4). Fig. 4 shows step 1 where user k sends a pilot

transmission p_k towards the antenna element 105 n on an estimated channel g _n. k and n are positive integers. In step 2 in fig. 4, data with conjugate beamforming is transmitted from the antenna elements 105 towards the UE 1 15. I.e. data signal s_k is sent to user k.

Fig. 5 the operations performed in an APU 103 during DL transmission. The APU 103 receives the data signals for each UE s_k 1 15 for each user k = 1 , K. K is a positive integer. In this example, the data is a frequency domain vector of Quadrature Amplitude Modulation (QAM) symbols. The pre-coding coefficients are also in the general case a frequency domain vector per user k. After pre-coding the sum-signal is processed by an Inverse Fast Fourier Transform (IFFT) in the Orthogonal Frequency Division Multiplexing (OFDM) TX-Processing-step. Fig. 5 shows a RX/TX unit 501 and a demux unit 503. Fig. 5 also shows a TX viewing calculator 505, an OFDM TX-processing unit 508 and an antenna element 105 n. Packet data [s^-.- sJ are input to the RX/TX unit 501 , and packet data [Si , ... s_k] are output from the RX/TX unit 501.

Note that in case the pre-coding is not frequency selective but instead frequency flat, then the IFFT operation may be performed per user in the CPU 101 instead of distributed in the APUs 103.

Fig. 5 shows that, during downlink transmission, each APU 103 needs to receive the data s_k for each user k = 1 , ... , K. The TX antenna weight(s) that were determined during the training period are applied.

The receiver operations in an APU 103 are similar. However, in the UL, all signal components received from the different antenna elements 105 need to be combined.

Also, the received signals for each user /c are represented by soft-bits of some resolution, e.g. 4 bits per hard-bit. In addition to the received signals per UE 1 15, it may be beneficial to also estimate and communicate an estimate of the cannel quality per UE 1 15. The UE 1 15 may also be referred to as a user or the UE 1 15 may be referred to as being associated with a user. When used herein, the term UL direction refers to the direction from an APU 103 to a CPU 101 and the term DL direction refers to the direction from the CPU 101 to the APU 103. Fig. 6 shows UL processing performed in APU103 n. Fig. 6 shows that input to a RX unit 600 is packet data from antenna element 105 n+1 [r_{1 n+1} , ... r_K,n+i]- The input to the RX unit 600 is optionally [SNRi, ... SNR_k] SNR is short for Signal-to-Noise Ratio. Data from the RX unit 600 is input to a demux unit 601. Fig. 6 shows a MUX unit 603 which provides input data to the TX unit 605 as [r_v , r_{k n}]. Fig. 6 shows that output from a TX unit 605 is packet data to antenna element 105 n-1 [r_v , r_{k n}]. Fig.6 shows a RX viewing calculator 608, a OFDM RX processing unit 610 and an antenna element 105 n. Comparing DL fig. 5 and fig. 6 it is noted that in terms of fronthaul communication, the DL is a broadcast channel, i.e. the same signal from CPU 101 to all APUs 103, while the UL processing has a pipe-line structure, i.e. APU„ 103 receives soft information r _n+ for each UE 1 15 /cfrom APU_n+1 103; adds its own soft signal components; and forwards the result to APU„-i 103. This is depicted in fig. 7. Fig. 7 shows the fronthaul in a radio stripe 301 comprising multiple APUs 103. The DL has a broad-case structure while the UL has a pipe-line structure. Fig. 7 shows the CPU 101 on the left side and eight serially connected APUs 103. Note that the radio stripe may comprise any other suitable N number of APUs 103 instead of eight, where N is a positive integer.

To support multiple independent antenna ports that may be used e.g. for pre-coder-based beamforming, parallel daisy chains may bel needed. This results in a spread of interference over an unnecessarily large area. The antenna ports that may be used for pre-coder-based beamforming are distributed in space and not point-shaped.

The UL fronthaul pipe-line structure induces processing delay. The delay increases with the number of APU 103 in a radio stripe 301 , which makes the system non-scalable beyond a certain length.

In each pipe-line step, the APU„ 103 needs receive and process signals from all UEs 1 15. This makes the processing complexity significant for each step in the pipe-line, resulting in increased delay/energy consumption/cost.

Therefore, there is a need to at least mitigate or solve this issue.

SUMMARY An objective of embodiments herein is therefore to obviate at least one of the above disadvantages and to provide an improved antenna system, e.g. an improved MIMO system. It may provide improved uplink processing in an antenna system.

The objective is achieved by the claims.

According to a first aspect, the object is achieved by an antenna system comprising at least one central unit and at least one antenna unit group. The at least one antenna group comprises a plurality of serially connected antenna units. Each antenna unit in the antenna unit group is serially connected to its neighboring antenna unit via a first link.

Each antenna unit in the antenna unit group is directly connected to the central unit via a second link. Each antenna unit in the antenna unit group is adapted to process UE data received from at least one UE.

According to a second aspect, the object is achieved by a method performed by an antenna system. A first antenna unit a second antenna unit and a central unit are comprised in the antenna system. The first antenna unit and the second antenna unit are neighboring antenna units and comprised in an antenna unit group. The first antenna unit is serially connected to its neighboring second antenna unit via a first link. The first antenna unit and the second antenna unit are directly connected to the central unit via a second link. The first antenna unit and the second antenna unit obtain UE data from at least one UE in an uplink direction. The first antenna unit and the second antenna unit process the obtained UE data. The processed UE data is provided from the first antenna unit to its neighboring second antenna unit in the uplink direction and via the first link. The second antenna unit obtains the processed UE data from the neighboring first antenna unit. The second antenna unit combines the processed UE data from the first antenna unit and the UE data processed by the second antenna unit. The combined processed UE data is provided from the second antenna unit to the central unit via the second link or to a neighboring third antenna unit via the first link.

According to a third aspect, the object is achieved by a method for setting up an antenna system. The antenna system comprises at least one central unit and at least one antenna unit group. The at least one antenna unit group comprises a plurality of antenna units. Each antenna unit in the at least one antenna unit group is serially connected to its neighboring antenna unit via a first link. Each antenna unit in the at least one antenna unit group is directly connected to the central unit via a second link.

According to a fourth aspect, the object is achieved by a method performed by a second antenna unit. The first antenna unit, the second antenna unit and the central unit are comprised in an antenna system. The first antenna unit and the second antenna unit are neighboring antenna units and comprised in an antenna unit group. The first antenna unit is serially connected to its neighboring second antenna unit via a first link, and the second antenna unit is directly connected to the central unit via a second link. The second antenna unit obtains UE data from at least one UE and processes the obtained UE data. The second antenna unit provides the processed UE data to the central unit via the second link or to a neighboring third antenna unit via the first link.

According to a fifth aspect, the object is achieved by a second antenna unit. The first antenna unit, the second antenna unit and the central unit are comprised in an antenna system. The first antenna unit and the second antenna unit are neighboring units and comprised in an antenna unit group. The second antenna unit is serially connected to its neighboring first antenna unit via a first link, and the second antenna unit is directly connected to the central unit via a second link. The second antenna unit is adapted to obtain UE data from at least one UE, and to process the obtained UE data. The second antenna unit is adapted to provide the processed UE data to the central unit via the second link or to a neighboring third antenna unit via the first link.

According to a sixth aspect, the object is achieved by a method performed by a central unit. The first antenna unit, the second antenna unit and the central unit are comprised in an antenna system. The central unit is directly connected to the first antenna unit and the second antenna unit via a second link. The central unit obtains processed UE data from the first antenna unit or from the second antenna unit in an uplink direction and via the second link.

According to a seventh aspect, the object is achieved by the central unit. The first antenna unit, a second antenna unit and the central unit are comprised in an antenna system. The first antenna unit and the second antenna unit are neighboring antenna units and comprised in an antenna unit group. The central unit is directly connected to the first antenna unit and the second antenna unit via a second link. The central unit is adapted to obtain processed UE data from the first antenna unit or from the second antenna unit in an uplink direction and via the second link.

Embodiments herein afford many advantages, of which a non-exhaustive list of examples follows:

An advantage of the embodiments herein is that they provide a way to enable UL pipe-line processing in an antenna system, e.g. in the form of a radio stripe, without limiting the maximum number antenna units, e.g. due to UL processing delay.

Another advantage of the embodiments herein is that they reduce the complexity of the antenna system compared to existing antenna systems.

A further advantage of the embodiments herein is that they provide reduced and controllable delay in the antenna system.

Another advantage of the embodiments herein is that it provides increased flexibility in the UL processing. A further advantage of the embodiments herein is that they reduce energy consumption in the antenna system.

Another advantage of the embodiments herein is that an antenna unit can bypass other antenna units when it has completed its processing and provide its processed data directly to the central unit.

Another advantage of the embodiments herein is that they increase the coverage of the antenna system. A further advantage of the embodiments herein is that the processing requirement on each antenna unit is reduced.

Another advantage of the embodiments herein is that the antenna units in the antenna unit group can operate in parallel. The embodiments herein are not limited to the features and advantages mentioned above. A person skilled in the art will recognize additional features and advantages upon reading the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will now be further described in more detail by way of example only in the following detailed description by reference to the appended drawings illustrating the embodiments and in which:

Fig. 1 is a schematic drawing illustrating an example of a centralized massive

MIMO architecture.

Fig. 2 is a schematic drawing illustrating an example a distributed massive MIMO architecture.

Fig. 3 is a schematic drawing illustrating an example of a massive MIMO radio stripe system.

Fig. 4 is a schematic drawing illustrating an example of that by using e.g.

conjugate beamforming the beamforming processing required may be performed per-antenna unit.

Fig. 5 is a schematic drawing illustrating an example of that during downlink

transmission each APU need to receive the data s_k for each user k = 1 ,

K. The TX antenna weight(s) that were determined during the training period are applied.

Fig. 6 is a schematic drawing illustrating an example of UL processing performed in APU n.

Fig. 7 is a schematic drawing illustrating an example of front-haul in a radio stripe comprising of multiple APUs. The DL has a broad-case structure while the UL has a pipe-line structure.

Fig. 8a is a schematic block diagram illustrating an example of an antenna system Fig. 8b is a schematic block diagram illustrating an example of an antenna system Fig. 9 is a signalling diagram illustrating an example of a method

Fig. 10 is a schematic drawing illustrating an example of a radio stripe fronthaul structure comprising a“pipe-line” data bus and a“direct-line data bus”. Fig. 1 1 is a schematic drawing illustrating an example of UL receiver pipe-line processing for different UEs starts in different antenna units.

Fig. 12 is a schematic drawing illustrating an example of assigning different UL RX pipe-line lengths for different signals to minimize the collision probability of transmission on the direct-line data bus.

Fig. 13 is a schematic drawing illustrating an example of processing of multiple

streams from a single UE.

Fig. 14 is a schematic drawing illustrating an example of a printed circuit board (PCB). Fig. 15 is a flow chart illustrating a method

Fig. 16 is a flow chart illustrating a method

Fig. 17 is a flow chart illustrating a method

Fig. 18 is a flow chart illustrating a method.

Fig. 19a is a schematic block diagram illustrating an example of a second antenna unit Fig. 19b is a schematic block diagram illustrating an example of a second antenna unit Fig. 20a is a schematic block diagram illustrating an example of a central unit

Fig. 20b is a schematic block diagram illustrating an example of a central unit.

The drawings are not necessarily to scale and the dimensions of certain features may have been exaggerated for the sake of clarity. Emphasis is instead placed upon illustrating the principle of the embodiments herein.

DETAILED DESCRIPTION Fig. 8a depicts an example of an antenna system 100 in which embodiments herein may be implemented. The antenna system 100 comprises a central unit 101 and a plurality of antenna units 103. The antenna system 100 may be referred to as a serial system, a serial MIMO system, a MIMO system, or a serial massive MIMO system etc. The term plurality refers to two or more. The plurality of antenna units 103 may be referred to as an antenna unit group. The antenna unit group comprises a plurality of antenna units 103. There may be one or multiple antenna unit groups in the antenna system 100. An antenna unit group may be referred to as a radio stripe.

The central unit 101 may be a Central Processing Unit (CPU). The central unit 101 may be described as a central unit adapted to perform processing. The central unit 101 may be referred to as a main unit or a control unit or a processing unit. The central unit 101 may be described as being a central to each of the antenna units 103 in the antenna unit group. There may be one or multiple central units 101 in the system. The central unit 101 may be adapted to be connected to one or multiple antenna unit groups in the antenna system 100.

Fig. 8b shows an example of the antenna system 100 of fig. 8a with one antenna unit group (indicated with a dotted box) comprising two antenna units 103, i.e. a first antenna unit 103a and a second antenna unit 103b, however the antenna unit group may comprise any n suitable number of antenna units 103, where n is a positive integer larger than 1. Thus, the term plurality refers to two or more, multiple etc. When the reference number 103 is used herein without the letters a or b, it refers to any of the first antenna unit 103a and second antenna unit 103b. The plurality of antenna units 103 in the antenna unit group are serially connected to each other, i.e. the antenna units 103 in the antenna unit group are connected one after the other, one after another, consecutively, etc. A serial connection may be seen as the opposite of or the contrast to a parallel connection. One single data stream is transmitted in a serial connection, while several data streams are transmitted simultaneously in a parallel connection The antenna system 100 may be co-located in one shared unit, box, frame, casing, cover, structure etc. The central unit 101 may also be co-located with the antenna unit group in the shared unit or it may be adapted to be connected to the shared unit, i.e. the central unit 101 may be located in a distance to the antenna unit group. Each antenna unit 103 in the antenna unit group may also be referred to as an APU, an antenna unit 103 adapted to perform processing e.g. of UE data, an antenna unit 103 having processing capacity, an antenna unit 103 comprising a processing unit. Each antenna unit 103 in the antenna unit group may be adapted to be connected to one or a plurality of antenna element(s) 105, or adapted to control one or a plurality of antenna element(s) 105. The antenna element(s) 105 are adapted to transmit and/or receive UE data to and/or from one or more UE(s) 115. The antenna elements(s) 105 maybe be an interface between the UE(s) 1 15 and the antenna unit 103. The term antenna element 105 refers to the physical antenna. The UE 1 15 may also be referred to as a user herein. One UE 1 15 may be adapted to transmit and/or receive UE data to one or more antenna units 103 via the respective antenna elements 103. Only one UE 1 15 is exemplified in figs. 8a and b for the sake of simplicity. A UE 1 15 may also be referred to simply as a device. The UE 1 15, e.g. a Long Term Evolution (LTE) UE or a 5G/NR UE, may be a wireless communication device which may also be known as e.g., a wireless device, a mobile terminal, wireless terminal and/or mobile station, a mobile telephone, cellular telephone, or laptop with wireless capability, just to mention some further examples. The abbreviation NR used above is short for New Radio. The UE 1 15 may be a device by which a subscriber may access services offered by an operator’s network and services outside operator’s network to which the operator’s radio access network and core network provide access, e.g. access to the Internet. The UE 1 15 may be any device, mobile or stationary, enabled to communicate over a radio channel in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device, Internet of Things (IOT) device, terminal device, communication device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The UE 1 15 may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another UE, a server, a laptop, a Personal Digital Assistant (PDA), or a tablet, Machine- to-Machine (M2M) device, device equipped with a wireless interface, such as a printer or a file storage device, modem, or any other radio network unit capable of communicating over a radio link in a communications system.

The UE 1 15 is enabled to communicate wirelessly within the antenna system 100. The communication may be performed e.g. between two devices, between a devices and a regular telephone, between the UE 1 15 and a network node, between the UE 1 15 and an antenna unit 103, between the UE 1 15 and the central unit 101 , between network nodes, and/or between the devices and a server via the radio access network and possibly one or more core networks and possibly the internet.

The central unit 101 is adapted to be connected to at least one of the plurality of antenna units 103 in the antenna unit group via a first link 108. Using the example in fig.8b, the central unit and the second antenna unit 103b are adapted to be connected to each other via the first link 108, and the first antenna unit 103a and the second antenna unit 103b are adapted to be connected to each other via the first link 108. Each antenna unit 103 is adapted to be connected to its neighboring antenna unit 103 via the first link 108. The first link 108 may be referred to as a pipe-line, a data bus, a UL data bus, a UL pipe-line.

Each antenna unit 103 in the antenna unit group is adapted to be directly connected to the central unit 101 via a second link 110. Using other words, the antenna units 103 and the central unit 101 are adapted to be connected to the second link 1 10. The second link 1 10 may be referred to as a direct link, a shared data bus, a shared UL data bus, a direct-line, a UL direct-line, a shared link, a shared direct-line etc. Using the example in fig. 8b, the second antenna unit 103b is directly connected to the central unit 101 via the second link 1 10, and the first antenna unit 103a is directly connected to the central unit 101 via the second link 1 10.

The plurality of antenna units 103 in the antenna unit group may be distributed in that they may be geographically spread out over an area. The distance between the antenna units 103 in the plurality may be any suitable distance. The distance may be the same between all antenna units 103 in the antenna unit group or the distance may be different. The antenna units 103 in the antenna unit group may be uniformly or irregularly distributed in the antenna unit group. For example, the distance between the first antenna unit 103a and the second antenna unit 103b may be between 0,1 -10m, it may be between 1 -8m, it may be between 2-6m, it may be between 3-5m etc. The distance may be associated with the wavelength of the signals that are conveyed over the first link 108 between the antenna units 103. For example, the distance may be associated with l, l/2, l/4 etc., where l represents the wavelength. The distance between the antenna units 103 in the associated with a size of the location in which the antenna system 100 is adapted to installed in. For example, the antenna system 100 may be installed in a building, a factory, a shopping mall, a sports arena etc.

In case the antenna system 100 comprises a plurality of antenna unit groups, then the plurality of antenna unit groups may be distributed in that they may be geographically spread out over an area, or they may be at the same geographical area. The distance between the plurality of antenna unit groups may be any suitable distance. The distance may be the same between all antenna unit groups or the distance may be different. The antenna units 103 in the antenna unit group may be uniformly or irregularly distributed in the antenna unit group. For example, the distance between the first antenna unit group and the second antenna unit groups may be between 0,1 -10m, it may be between 1 -8m, it may be between 2-6m, it may be between 3-5m etc. The distance may be associated with the wavelength of the signals that are conveyed over the first link 108 between the antenna units 103. For example, the distance may be associated with l, l/2, l/4 etc., where l represents the wavelength. The distance between the antenna unit group in the associated with a size of the location in which the antenna system 100 is adapted to installed in. For example, the antenna system 100 may be installed in a building, a factory, a shopping mall, a sports arena etc.

Fig. 9 is a signalling diagram illustrating an example of a method. The method

exemplified in fig. 9 comprises at least one of the following steps, which step may be performed in any suitable order than described below: Step 200

The central unit 101 may determine which antenna unit group and which of the plurality of antenna units 103 and that should be a starting point for processing on the first link 108 and may send instructions to this determined antenna units 103 to be the starting point for processing on the first link 108. The processing may be processing of UE data, e.g. data received from one or multiple UEs 1 15. Processing may also be referred to as handling, calculating, analysing, treating etc. The determined antenna unit 103 receives the instructions from the central unit 101.

Some or all antenna units 103 in the antenna unit groups may participate in the

processing. For example, the antenna unit 103 determined to be the starting point on the first link 108 may be antenna unit 103 number five in an example with seven antenna units 103, i.e. antenna units 103 one, two, three, four and five participates in the processing and antenna units 103 six and seven does not participate in the processing. In this example, antenna unit 103 one is the neighbour to the central unit 101 , i.e. the antenna unit 103 being located closest to the central unit 101 compared to the other antenna units 103.

In the example in fig. 9, the first antenna unit 103a is the determined starting point for the processing of the UE data. In another example, the starting point of the processing may be pre-co nfigu red in the relevant antenna unit 103, i.e. the central unit 101 may not take any decision or send any instructions.

The number of antenna units 103 from and including the starting point and the central unit 101 may be referred to as a processing path or a length of a processing path. The processing path has a length of 2 in the example in fig. 9, i.e. two antenna units 103. The processing length may be described as the number of antenna units 103 that performs processing of UE data. The processing of all UE data will start at the same time, at the beginning of the UL slot. They will all finish at different times since they have different processing length. Hence, there will be no collisions on the second link 1 10, i.e. the shared broadcast channel/direct line, between the antenna units 103 and the central unit 101. If the direct line 1 10 is anyway occupied, then one of the UE data might as well be processed for a few extra steps while waiting for the direct line 1 10 to become free.

Step 202 may not be time critical. Step 200 may or may not be done for each UL transmission.

Step 201

The UE 101 may provide UE data to the first antenna unit 103 and the second antenna unit 103b. The UE data may also be referred to as UE signals, UE information, UE parameters, UL signals, UL UE signals, UL signals, UE UL transmission. The first antenna unit 103 and the second antenna unit 103b may receive or obtain the UE data from the UE. The UE data may be described as being transmitted“over-the-air” to the first antenna unit 103a and the second antenna unit 103b.

In an example where the first antenna unit 103a is not the starting point of the processing, then the UE data may be referred to as accumulated UE data, i.e. it may be a combination of processed UE data from antenna units 103 being located further away from the central unit 101 compared to the first antenna unit 103a. In other words, the processed UE data is accumulated as the processing path moves closer to the central unit 101.

The UE data obtained by the first antenna unit 103a may be the same or different than the UE data obtained by the second antenna unit 103b. The UE data obtained by the antenna units 103 is data from the same UE 1 15. The UE 1 15 transmits UE data that is received by many (potentially all) different antenna units 103. These UE data need to be combined. But, the system may process UE data from multiple signals at the same time. Signals from different UEs may not be combined.

The UE data obtained by the first antenna unit 103a may be referred to as first UE data. The UE data obtained by the second antenna unit 103b may be referred to as second UE data. Steps 202-203

The first antenna unit 103a and the second antenna unit 103b may process the UE data. This may also be described as the first antenna unit 103a and the second antenna 103b may perform UL reception processing. Step 204

The first antenna unit 103a may provide the processed UE data to the second antenna unit 103b via the first link 108. The second first antenna unit 103b may obtain the processed UE data from the first antenna unit 103a. This step may be described as the first antenna unit 103 forwards the processed UE data via the first link 108, e.g. a pipe-line, to the second antenna unit 103b.

Step 205

The second antenna unit 103b may combine the processed UE data and the processed UE data obtained from the first antenna unit 103a. The result of the combining may be referred to as combined UE data. Thus, the second antenna unit 103b may combine its locally processed UE data with the UE data received on first link 108 from the first antenna unit 103a. Step 206

The second antenna unit 103a may provide the combined UE data to the central unit 101 via the second link 1 10, i.e. the direct-line. It is the second antenna unit 103b which is the neighbour to the central unit 101 that provides the combined UE data to the central unit 101. This step may be only performed by the last antenna unit 103 in the antenna unit group. Step 207

The central unit 101 receives the combined UE data from the second antenna unit 103b and utilizes it. The utilization may be for example that the central unit 101 may perform more high level processing, i.e. more advanced processing, and adopt interfaces internal in the stripes towards more general, i.e. high level, interfaces.

Fig. 10 is a schematic drawing illustrating an example of a radio stripe fronthaul structure comprising a first link 108, e.g. a pipe-line data bus, and a second link 1 10, e.g. a direct- line data bus. The first link 108 may also be referred to as a UL receiver processing data bus and the second link 1 10 may also be referred to as a shared UL data bus.

In fig. 10, the central unit 101 is exemplified by a CPU and the plurality of antenna units 103 are exemplified by APUs. The reference number 101 will be used when referring to the CPU and the reference number 103 will be used when referring to an APU in the example of fig. 10. Fig. 10 shows an example with eight APUs 103, i.e. APU

where N is a positive integer. APU 103 number n-1, n and n+1 are enlarged in the lower part of fig. 10.

In addition to the first link 108, e.g. the pipe-line data bus, that connects each APU 103 with its’ neighboring APUs 103, the APUs 103 and the CPU 101 are also connected to a second link 1 10, e.g. a shared data bus denoted direct-line.

All transmissions on the second link 1 10, e.g. the direct-line data bus may be coordinated by the CPU 101 . The transmissions on the second link 1 10, e.g. the direct-line data bus, may be based on a Listen-Before-Talk (LBT) protocol, or some other collision avoidance protocol, e.g. ALOHA, etc.

Note that in some embodiments the APUs 103 controls a single antenna element while in other embodiments an APU 103 control multiple antenna elements 105.

The processing of different UE data in the first link 108, e.g. the UL receiver pipe-line, may starts in different APUs 103, e.g. the UL processing of user k starts in APU 103 no where n_k are all different for k = 1 , ... , K. This is schematically depicted in fig. 11 where the processing of signals from users UEi , UE₂, and UE₃ 1 15 starts in APU 103

, n₂, and /¾, respectively. Using different starting points for the first link 108, e.g. pipe-line starting points, for different UEs 1 15 allows each APU 103 to only process a limited number of signals, typically 1 , in each pipe-line step.

In fig. 1 1 , the APU„ 103 calculates the UE data, e.g. the signal components, [r r₂, r_K ] locally. When the receiver pipe-line processing reaches APU„ 103 it will receive all accumulated signal components from its neighboring APU_n+i 103, denoted [r_{1 n+1}, r_2,n+ , r_K,n+i]. Now APU„ 103 may combine every signal component it has calculated locally with the accumulated signal components. In case the combination comprise an additional operation then the APU„ 103 calculates r_{Kn =} r_k + r_kn+ for k = 1 , , K. Note that other combination operations are also possible.

By ensuring that not all received signals reach the APU„ 103 in the same pipe-line step the amount of processing per pipe-line step may be reduced. This may enable the pipe line 108 to be clocked faster. It may also require less internal storage in the APU„ 103 for storage of the locally computed received signal components.

The pipe-line processing starting APU 103 for each user k is determined by the CPU 101 based on e.g. UE position, average path loss, etc. This may be determined based on UL training. E.g. the APU 103 with the best average path gain determined and the starting point may be selected as a certain number of APUs 103 further ahead in the pipe-line 108. Each APU 103 may compute the received UE data, e.g. signal component, r_k, k = 1 , K in the order they are needed in the pipe-line processing.

The APU 103 may selectively compute the received UE data, e.g. signal component, r_k, k = 1 , ... , for UEs 1 15 that may be accumulated in the UL pipe-line processing by that APU 103. Referring to fig. 11 :

• APU„i 103 computes the internal RX signals component r_k in the order {r r₃, r₂}

• APU„ 103 computes {r₃, r₂}

• APU„ 103 computes {r₂}

• APU„ 103 computes { } The number of UL receiver processing pipe-line steps may be different for different UEs 1 15. The number of UL reception pipe-line steps for each UE 1 15 k may be determined in dependence of e.g.

• UL processing delay requirement: UEs 1 15 with short delay requirements use a small number of UL reception pipe-line steps. The degradation in UL receiver efficiency may e.g. be compensated for by using a more robust modulation and coding format.

• UL signal quality, e.g. average SNR, average Signal to Interference & Noise Ratio (SINR), average path loss: E.g. UEs 1 15 close to the radio stripe processing chain may have a very good radio channel situation and therefore they may not many

UL reception pipe-line steps.

• UL spectral efficiency, e.g. modulation and coding scheme: During low load it may not be necessary to optimize spectral efficiency. Instead, other things may be optimized that result in lower spectral efficiency requirements, e.g. enabling UEs 1 15 to use low modulation and thereby use less back-off in transmit power amplifiers resulting in reduced power consumption.

• Scheduling of direct-line capacity: Since the accumulated received UE data will be transmitted on the direct-line 1 10 from the last processing APU 103 to the CPU 101 it may be beneficial to ensure that this direct-line channel usage does not occur at the same time for different UEs 1 15.

The number of UL reception processing pipe-line steps per UE 1 15 may be pre determined, e.g. decided by the CPU 101. The number of UL reception processing pipe line steps may be a random variable, e.g. depending on the accumulated SINR, or signal strength, or channel gain, etc.. For example, an APU 103 may determine that no further UL processing is required for a UL signal once a certain condition is fulfilled, e.g. a minimum number of processing step is performed and/or a signal quality measurement exceeds a certain threshold, etc. When an UL signal has been processed in the UL pipe-line 108 for the selected number of steps, the’’last APU in the pipe-line processing chain” may sends the signal directly to the CPU 101. Different uplink reception pipe-line processing length for each UE 101 may be used in order to ensure that transmissions on the second link 1 10, e.g. the direct-line communication bus, from the APUs 103 to the CPU 101 does not collide. The second link length, e.g. the pipe-line processing length, may have an upper/lower bound in-order to align with the UL/DL slots. This is depicted in fig. 12. In fig. 12, UEi 1 15 has low delay requirements and 4 pipeline steps, UE₂ 1 15 has medium SINR and 7 pipeline steps and UE₃ has low SINR and 10 pipeline steps. Fast line usage on the second link 1 10 may be as follows: { 0 , 0, 0, 0, r_u 0, 0, r₂, 0, 0, r₃ } where there are no collisions due to different pipe-line lengths for the different UEs 1 15. The number of pipeline steps may be described as the number of processing steps or the number of APUs 103 processing UE data from one UE 1 15. In other words, one UE 1 15 may provide UE data to a number of APUs 103, and the ones that are from the starting point to the ending point of the processing length may constitute the number of pipeline steps.

The second link 1 10, e.g. the direct line transfer, may take longer time than an UL RX processing pipe-line step and it may also depend on the amount of data, e.g. the bandwidth of the UL transmission that needs to be transmitted from the last processing APU 103 to the CPU 101 . In this case the usage of different pipe-line processing length for different UEs 1 15 may still assure that the second line 1 10, e.g. the direct-line, is highly utilized and that the probability of a collision or APU 103 stalling when waiting for direct line bus to become available on the second link 1 10, e.g. the direct-line data bus, is low.

A UE 1 15 may transmit multiple layers or streams of UE data and these streams/layers may be treated like separate UEs 1 15, see fig. 13. Fig. 13 shows an example with UE stream 1 (solid arrows) and UE stream 2 (dotted arrows). Fig. 13 also shows that there may be different starting points 114 for processing of different streams to facilitate UL pipeline processing. The starting point for one of UE stream 1 is APU_n0 and the starting point for UE stream 2 is APU_n0-i · The UE 1 15 is exemplified to provide UE data to 1 1 APUs 103 in UE stream 1 and to 10 APUs 103 in UE stream 2. The second link usage, e.g. the fast line usage, exemplified in fig. 13 may be as follows: {0, 0, 0, 0, 0, 0, 0, 0, 0, r₂, h}. There are no collisions on the second link 1 10, e.g. the direct line, due to different first link lengths, e.g. pipeline lengths, for different streams.

Unutilized APUs 103 or under-utilized APUs 103 may be de-activated to reduce power consumption. Both the central unit 101 , the APU 103 or a combination of this may decide to de-activate the unutilized APUs 103 or under-utilized APUs 103. For example, a threshold may be sent from the central unit 101 and the APU 103 may compare, for example, a reference signal measurement and the threshold to determine if it should be deactivated. The antenna system 100 may be implemented on a printed circuit board (PCB), as exemplified in fig. 14. Electrical connectors for UL, DL, power, clock, etc. may be used for communicating between CPUs 101 . In the example in fig. 14, some electrical connectors are“non-solid” while some are“solid”, as seen in the bottom view of fig. 14. At least some of the“non-solid” connectors may be used for the first link 108, e.g. the UL RX pipe-line bus, while at least some to the“solid” connectors may be used for the second link 110, e.g. the direct-line communication bus. The tow view of fig. 14 shows an example with a 10x10 APU chip with integrated antennas. 28 GHz and A/2=5,4mm.

An antenna system 100 may comprise one or multiple groups of antenna units 103, e.g. in the form of a grid or matrix or array etc. Thus, one antenna unit group may be connected to one or more other antenna unit group to form a larger antenna system 100, e.g. an antenna network. In an antenna system comprising a plurality of antenna unit groups, then each antenna unit group may be associated with a respective central unit 101. Or, multiple antenna unit groups may be associated with a shared central unit 101 .

In other words, multiple antenna unit groups may share the same central unit 101. A central unit 101 may be associated with one or multiple antenna unit groups. Thus, the antenna system 100 may comprise one or a plurality of central units 101 . In case there is a plurality of central units 101 , then the central units 101 may be adapted to cooperate with each other, e.g. to communicate with each other. In the border area between central units 101 a single UE 1 15 can be utilizing one antenna unit group from one central unit 101 and another antenna unit group from another central unit 101. Then the central units 101 may be adapted to be connected and handle the coordination, e.g. one central unit 101 may act as a master unit and the other may be acting as slave unit.

With one central unit 101 for each antenna unit group, the processing capacity of each central unit 101 does not have to be so large since it handles a lower number of antenna units 103. With a shared central unit 101 , the number of central units 101 will be reduced in the antenna network, e.g. reduced network complexity, reduced cost, reduced number of units etc.

The method described above will now be described seen from the perspective of the antenna system 100. Fig. 15 is a flowchart describing the present method performed by the antenna system 100. A first antenna unit 103a, a second antenna unit 103b and a central unit 101 are comprised in the antenna system 100. The first antenna unit 103a and the second antenna unit 103b are neighboring antenna units and comprised in an antenna unit group. The first antenna unit 103a is serially connected to its neighboring second antenna unit 103b via a first link 108. The first antenna unit 103a and the second antenna unit 103b are directly connected to the central unit 101 via a second link 1 10. The method comprises at least one of the following steps to be performed by the antenna system 100, which steps may be performed in any suitable order than described below:

Step 1601

This step corresponds to step 201 in fig. 2. Obtaining, at the first antenna unit 103a and the second antenna unit 103b, UE data from at least one UE 1 15 in an uplink direction.

Step 1602

This step corresponds to steps 202 and 203 in fig. 2. Processing the obtained UE data at the first antenna unit 103a and the second antenna unit 103b.

Step 1603

This step corresponds to step 203 in fig. 2. Providing the processed UE data from the first antenna unit 103a to its neighboring second antenna unit 103b in the uplink direction and via the first link 108.

Step 1604

This step corresponds to step 204 in fig. 2. Obtaining, at the second antenna unit 103b, processed UE data from the neighboring first antenna unit 103a via the first link 108.

Step 1605

This step corresponds to step 205 in fig. 2. This may be an optional step. Combining, at the second antenna unit 103b, the processed UE data from the first antenna unit 103a and the UE data processed by the second antenna unit 103b.

Step 1606

This step corresponds to step 206 in fig. 2. This may be an optional step. Providing the combined processed UE data from the second antenna unit 103b to the central unit 101 via the second link 1 10 or to a neighboring third antenna unit 103 via the first link 108. A method for setting up an antenna system 100 is exemplified in fig. 16. The antenna system 100 comprises at least one central unit 101 and at least one antenna unit group. The at least one antenna unit group comprises a plurality of antenna units 103a, 103b.

The method comprises at least one of the following steps, which steps may be performed in any suitable order than described below:

Step 1701

Each antenna unit 103a, 103b in the at least one antenna unit group 103a, 103b may be serially connected to its neighboring antenna unit 103a, 103b via a first link 108.

Step 1702

Each antenna unit 103a, 103b in the antenna unit group may be directly connected to a central unit 101 via a second link 1 10.

Step 1703

This may be an optional step. Two or more antenna unit groups may be connected to each other. Each antenna unit group comprises a plurality of serially connected antenna units 103a, 103b.

Step 1704

This may be an optional step. One central unit 101 may be connected to each antenna unit group.

Step 1705

This may be an optional step. One central unit 101 may be connected to multiple antenna unit groups.

The method described above will now be described seen from the perspective of the second antenna unit 103a. Fig. 17 is a flowchart describing the present method performed by the second antenna unit 103b. A first antenna unit 103a, a second antenna unit 103b and a central unit 101 are comprised in the antenna system 100. The first antenna unit 103a and the second antenna unit 103b are neighboring antenna units and comprised in an antenna unit group. The first antenna unit 103a is serially connected to its neighboring second antenna unit 103b via a first link 108. The first antenna unit 103a is directly connected to the central unit 101 via a second link 1 10. The method comprises at least one of the following steps to be performed by the second antenna unit 103b, which steps may be performed in any suitable order than described below: Step 1801

This step corresponds to step 201 in fig. 2. The second antenna unit 103b obtains UE data from at least one UE 1 15.

Step 1802

This step corresponds to step 202 in fig. 2. The second antenna unit 103a processes the obtained UE data.

Step 1803

This step corresponds to step 204 in fig. 2. The second antenna unit 103a provides the processed UE data to the central unit 101 via the second link 1 10 or to a neighboring third antenna unit 103 via the first link 108.

Step 1804

This step corresponds to step 204 in fig. 2. The second antenna unit 103b may obtain, from a neighboring first antenna unit 103a in an uplink direction, a processed UE data which the first antenna unit 103a has processed.

Step 1805

This step corresponds to step 205 in fig. 2. The second antenna unit 103b may combine the processed UE data from the first antenna unit 103a and the processed UE data which has been processed by the second antenna unit 103b.

Step 1806

This step corresponds to step 206 in fig. 2. The second antenna unit 103b may provide the combined processed UE data to the central unit 101 via the second link 1 10 or to a neighboring third antenna unit 103 via the first link 108.

The method described above will now be described seen from the perspective of the central unit 101. Fig. 18 is a flowchart describing the present method performed by the central unit 101. A first antenna unit 103a, a second antenna unit 103b and a central unit 101 are comprised in the antenna system 100. The first antenna unit 103a and the second antenna unit 103b are comprised in an antenna unit group. The first antenna unit 103a is serially connected to its neighboring second antenna unit 103b via a first link 108. The first antenna unit 103a and the second antenna unit 103b are each directly connected to the central unit 101 via a second link 1 10. The method comprises at least one of the following steps to be performed by the central unit 101 , which steps may be performed in any suitable order than described below:

Step 1900

This step corresponds to step 200 in fig. 2. The central unit 101 may provide information to the first antenna unit 103a indicating that it should be a starting point for processing of UE data on the first link 108.

Step 1901

The central unit 101 obtains processed UE data from the first antenna unit 103a or from the second antenna unit 103b in an uplink direction and via the first link 108.

Step 1902

This step corresponds to step 206 in fig. 2. The central unit 101 may obtain combined processed UE data from the first antenna unit 103a or from the second antenna unit 103b in an uplink direction and via the second link 1 10. The combined processed UE data may be a combination of UE data processed by the second antenna unit 103b and UE data processed by the first antenna unit 103a. Step 1903

The central unit 101 may communicate with one or more antenna unit groups in the antenna system 100.

To perform the method steps described above the second antenna unit 103b may comprises an arrangement as shown in fig. 19a. The first antenna unit 103a, a second antenna unit 103b and a central unit 101 are comprised in an antenna system 100. The first antenna unit 103a and the second antenna unit 103b are neighboring units and comprised in an antenna unit group. The first antenna unit 103a is serially connected to its neighboring second antenna unit 103b via a first link 108. The first antenna unit 103a is directly connected to the central unit 101 via a second link 1 10. The second antenna unit 103b is adapted to, e.g. by means of an obtaining unit 1901 , obtain UE data from at least one UE 1 15.

The second antenna unit 103b is adapted to, e.g. by means of a processing unit 1902, process the obtained UE data.

The second antenna unit 103b is adapted to, e.g. by means of a providing unit 1903, provide the processed UE data to the central unit 101 via the second link 1 10 or to a neighboring third antenna unit 103 via the first link 108.

The first antenna unit 103a may be adapted to, e.g. by means of the obtaining unit 1902, obtain, from a neighboring first antenna unit 103a in an uplink direction, a processed UE data which the first antenna unit 103a has processed.

The second antenna unit 103b may be adapted to, e.g. by means of a combining unit 1904, combine the processed UE data from the first antenna unit 103a and the processed UE data which has been processed by the second antenna unit 103b.

The second antenna unit 103bmay be adapted to, e.g. by means of the providing unit 1903, provide the combined processed UE data to the central unit 101 via the second link 1 10 or to a neighboring third antenna unit 103 via the first link 108.

Fig. 19 depicts two different examples in panels a) and b), respectively, of the

arrangement that the second antenna unit 103b may comprise. In some embodiments, the second antenna unit 103b may comprise the following arrangement depicted in fig. 19a.

The embodiments herein in the second antenna unit 103b may be implemented through one or more processors, such as a processor 1905 in the second antenna unit 103b depicted in fig. 19a, together with computer program code for performing the functions and actions of the embodiments herein. A processor, as used herein, may be understood to be a hardware component. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the first antenna unit 103a. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the first antenna unit 103a.

The second antenna unit 103b may comprise a memory 1906 comprising one or more memory units. The memory 1906 is arranged to be used to store obtained information, store data, configurations, schedulings, and applications etc. to perform the methods herein when being executed in the second antenna unit 103b.

The second antenna unit 103b may receive information from, e.g., the central unit 101 and/or a first antenna unit 103a, through a receiving port 1907. In some embodiments, the receiving port 1907 may be, for example, connected to one or more antenna elements 105 in second antenna unit 103b. In other embodiments, the second antenna unit 103b may receive information from another structure in the antenna system 100 through the receiving port 1907. Since the receiving port 1907 may be in communication with the processor 1905, the receiving port 1907 may then send the received information to the processor 1905. The receiving port 1907 may also be configured to receive other information.

The processor 1905 comprised in the second antenna unit 103b may be further configured to transmit or send information to e.g., the first antenna unit 103a and/or the central unit 101 and/or the UE 1 15 and/or another structure in the antenna system 100, through a sending port 1908, which may be in communication with the processor 1905, and the memory 1906.

The obtaining unit 1901 , the processing unit 1902, the providing unit 1903, the combining unit 1904, and the other units 1900 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g., stored in memory, that, when executed by the one or more processors such as the processor 1905, perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application- Specific Integrated Circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a-Chip (SoC). The different units 1900-1904 described above may be implemented as one or more applications running on one or more processors such as the processor 1905.

Thus, the methods according to the embodiments described herein for the second antenna unit 103b may be respectively implemented by means of a computer program 1909 product, comprising instructions, i.e., software code portions, which, when executed on at least one processor 1905, cause the at least one processor 1905 to carry out the actions described herein, as performed by the second antenna unit 103b. The computer program 1909 product may be stored on a computer-readable storage medium 1910. The computer-readable storage medium 1910, having stored thereon the computer program 1909, may comprise instructions which, when executed on at least one processor 1905, cause the at least one processor 1905 to carry out the actions described herein, as performed by the second antenna unit 103b. In some embodiments, the computer-readable storage medium 1910 may be a non-transitory computer-readable storage medium, such as a CD ROM disc, or a memory stick. In other embodiments, the computer program 1909 product may be stored on a carrier containing the computer program 1909 just described, wherein the carrier is one of an electronic signal, optical signal, radio signal, or the computer-readable storage medium 1910, as described above.

The second antenna unit 103b may comprise a communication interface configured to facilitate communications between the second antenna unit 103b and other nodes or devices, e.g., the first antenna unit 103a, the central unit 101 , the UE 1 15, or another structure. The interface may, for example, include a transceiver configured to transmit and receive radio signals over an air interface in accordance with a suitable standard.

The second antenna unit 103b may comprise the following arrangement depicted in fig. 19b. The second antenna unit 103b may comprise a processing circuitry 1905, e.g., one or more processors such as the processor 1905, in the first antenna unit 103a and the memory 1906. The second antenna unit 103b may also comprise a radio circuitry 1911 , which may comprise e.g., the receiving port 1907 and the sending port 1908. The processing circuitry 1905 may be configured to, or operable to, perform the method described herein, in a similar manner as that described in relation to fig. fig. 19a. The radio circuitry 191 1 may be configured to set up and maintain at least a wireless connection with the second antenna unit 103b. Circuitry may be understood herein as a hardware component.

Hence, embodiments herein relate to the second antenna unit 103b operative to operate in the antenna system 100. The second antenna unit 103b may comprise the processing circuitry 1905 and the memory 1906, said memory 1906 containing instructions executable by said processing circuitry 1905, whereby the first antenna unit 103a is further operative to perform the actions described herein in relation to the second antenna unit 103b. To perform the method steps described above the central unit 101 may comprises an arrangement as shown in fig. 20a. The first antenna unit 103a, a second antenna unit 103b and a central unit 101 are comprised in an antenna system 100. The first antenna unit 103a and the second antenna unit 103b are comprised in an antenna unit group. The first antenna unit 103a is serially connected to its neighboring second antenna unit 103b via a first link 108. The first antenna unit 103a and the second antenna unit 103b are directly connected to the central unit 101 via a second link 1 10.

The central unit 101 is adapted to, e.g. by means of an obtaining unit 2001 , obtain processed UE data from the neighboring first antenna unit 103a or from the second antenna unit 103b in an uplink direction and via the first link 108.

The central unit 101 is adapted to, e.g. by means of the obtaining unit 2001 , obtain combined processed UE data from the first antenna unit 103a or from the second antenna unit 103b in an uplink direction and via the second link 1 10. The combined processed UE data is a combination of UE data processed by the second antenna unit 103b and UE data processed by the first antenna unit 103a.

The central unit 101 may be adapted to, e.g. by means of a providing unit 2002, provide information to the first antenna unit 103a indicating that it should be a starting point for processing of UE data on the first link 108.

The central unit 101 may be adapted to, e.g. by means of a communicating unit 2003, communicate with one or more antenna unit groups in the antenna system 100. Fig. 20 depicts two different examples in panels a) and b), respectively, of the

arrangement that the central unit 101 may comprise. The central unit 101 may comprise the following arrangement depicted in fig. 20a.

The embodiments herein in the central unit 101 may be implemented through one or more processors, such as a processor 2007 in the central unit 101 depicted in fig. 20a, together with computer program code for performing the functions and actions of the embodiments herein. A processor, as used herein, may be understood to be a hardware component. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the central unit 101. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the central unit 101.

The central unit 101 may further comprise a memory 2008 comprising one or more memory units. The memory 2008 is arranged to be used to store obtained information, store data, configurations, schedulings, and applications etc. to perform the methods herein when being executed in the central unit 101.

The central unit 101 may receive information from, e.g., the first antenna unit 103a, and/or the second antenna unit 103b and/or the UE 1 15, through a receiving port 2009. In some embodiments, the receiving port 2009 may be, for example, connected to one or more antennas in central unit 101 . In other embodiments, the central unit 101 may receive information from another structure in the antenna system 100 through the receiving port 2009. Since the receiving port 2009 may be in communication with the processor 2007, the receiving port 2009 may then send the received information to the processor 2007.

The receiving port 2009 may also be configured to receive other information.

The processor 2007 in the central unit 101 may be further configured to transmit or send information to e.g., the first antenna unit 103a, and/or the second antenna unit 103b, and/or the UE 1 15, and/or another structure in the antenna system 100, through a sending port 2010, which may be in communication with the processor 2007, and the memory 2008. The obtaining unit 2001 , the providing unit 2002, the communicating unit 2003, and the other units 2004 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g., stored in memory, that, when executed by the one or more processors such as the processor 2007, perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a- Chip (SoC).

The different units 2001 -2004 described above may be implemented as one or more applications running on one or more processors such as the processor 2007.

Thus, the methods according to the embodiments described herein for the central unit 101 may be respectively implemented by means of a computer program 2011 product, comprising instructions, i.e., software code portions, which, when executed on at least one processor 2007, cause the at least one processor 2007 to carry out the actions described herein, as performed by the central unit 101. The computer program 201 1 product may be stored on a computer-readable storage medium 2012. The computer- readable storage medium 2012, having stored thereon the computer program 201 1 , may comprise instructions which, when executed on at least one processor 2007, cause the at least one processor 2007 to carry out the actions described herein, as performed by the central unit 101. In some embodiments, the computer-readable storage medium 2012 may be a non-transitory computer-readable storage medium, such as a CD ROM disc, or a memory stick. In other embodiments, the computer program 7201 product may be stored on a carrier containing the computer program 201 1 just described, wherein the carrier is one of an electronic signal, optical signal, radio signal, or the computer-readable storage medium 2012, as described above.

The central unit 101 may comprise a communication interface configured to facilitate communications between the central unit 101 and other nodes or devices, e.g., the first antenna unit 103a, the second antenna unit 103b, the UE 1 15, or another structure. The interface may, for example, include a transceiver configured to transmit and receive radio signals over an air interface in accordance with a suitable standard. In other embodiments, the central unit 101 may comprise the following arrangement depicted in fig. 20b. The central unit 101 may comprise a processing circuitry 2007, e.g., one or more processors such as the processor 2007, in the central unit 101 and the memory 2008. The central unit 101 may also comprise a radio circuitry 2013, which may comprise e.g., the receiving port 2009 and the sending port 2010. The processing circuitry 2007 may be configured to, or operable to, perform the method described herein, in a similar manner as that described in relation to fig. 20a. The radio circuitry 2013 may be configured to set up and maintain at least a wireless connection with the central unit 101. Circuitry may be understood herein as a hardware component.

Hence, embodiments herein also relate to the central unit 101 operative to operate in the antenna system 100. The central unit 101 may comprise the processing circuitry 2007 and the memory 2008, said memory 2008 containing instructions executable by said processing circuitry 2007, whereby the central unit 101 is further operative to perform the actions described herein.

Some embodiments herein will now be further described with some non-limiting examples. An antenna system 100 comprising at least one central unit 101 and at least one antenna unit group comprising a plurality of serially connected antenna units 103a, 103. Each antenna unit 103a, 103b in the antenna unit group is serially connected to its neighboring antenna unit 103a, 103b via a first link 108. Each antenna unit 103a, 103b in the antenna unit group is directly connected to the central unit 101 via a second link 1 10.

The second link 1 10 may be adapted to convey broadcast information from one of the antenna units 103a, 103b to at least some of the other antenna units 103a, 103b in the antenna unit group. Each antenna unit 103a, 103b in the antenna unit group may be adapted to process UE data from at least one UE 1 15.

Each antenna unit 103a, 103b may be adapted to receive an accumulated or combined UE data from its neighboring antenna unit 103a, 103b in an uplink direction via the first link 108. Each antenna unit 103a, 103b may be adapted to combine every UE data which it has locally processed with the received accumulated UE data.

The central unit 101 may be adapted to determine which of the antenna units 103a, 103b in the antenna unit group that shall be a starting point for the processing of UE data.

Each antenna unit 103a, 103b in the antenna unit group may be adapted to process UE data in an order they are needed, or each antenna unit 103a, 103b in the antenna unit group may be adapted to select which UE data and in which order it should process UE data.

A number of processing steps for processing UE data in the first link 108 may be the same or different for different UEs 1 15. A number of processing steps for processing UE data in the first link 108 may be a random number or a pre-determined number, e.g. determined by the central unit 101 .

When the antenna unit 103a, 103b being the neighbor to the central unit 101 has completed the processing of UE data, then it may send the processed data directly to the central unit 101 via the second link 1 10.

A processing length for the first link 108 may have at least one of an upper and/or lower boundary aligned with uplink/downlink slots. Different UE data may have different processing lengths on the first link 108.

When a UE 1 15 is adapted to transmit multiple UE data to at least one of the multiple antenna units 103a, 103b, then the at least one antenna unit 103a, 103b may be adapted to treat the multiple UE data as coming from separate UEs 1 15.

An unutilized or under-utilized antenna unit 103a, 103b in the antenna unit group may be adapted to be deactivated. At least one of the central unit 101 , the first antenna unit 103a and the second antenna unit 103b may be adapted to determine that an unutilized or under-utilized antenna unit 103a, 103b in the antenna unit group should be deactivated. A non-solid electrical connector at the central unit 101 may be used for the first link 108. A solid electrical connector at the central unit 101 may be used for the second link 1 10.

The antenna units 103a, 103b in the antenna unit group may be each adapted to control at least one antenna element 105.

The control unit 101 may be adapted to control transmissions on the second link 1 10.

The antenna unit 103 in the antenna unit group which is a neighbor to the central unit 101 may be connected to the central unit 101 via the first link 108.

The first link 108 may be a UL data bus or a UL pipe-line.

The second link 1 10 may be a shared UL data bus or a UL direct-line.

The antenna units 103a, 103b may be APUs.

The antenna system 100 may be at least one of: a distributed system, a semi-distributed system, a fully distributed system, a distributed radio stripe system, a semi-distributed radio stripe and pin system, or a pin system etc.

The antenna system 100 may be a MIMO system or a massive MIMIO system.

The antenna system 100 may comprise two or more antenna unit groups. Each antenna unit group may be adapted to be connected to a central unit 101 or multiple antenna unit groups may be adapted to be connected to the same central unit 101.

The antenna system 100 may comprise two or more central units 101. Each central unit 101 may be adapted to be associated with one antenna unit group or to multiple antenna unit groups.

A computer program comprising may instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any one of the above embodiments. A carrier may comprise the computer program and the carrier may be one of an electronic signal, optical signal, radio signal or computer readable storage medium.

The present mechanism may be implemented through one or more processors, such as a processor in the second antenna unit arrangement depicted in fig. 19a and fig. 19b and a processor in the central unit arrangement depicted in fig. 20a and fig. 20b, together with computer program code for performing the functions of the embodiments herein. The processor may be for example a Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC) processor, Field-programmable gate array (FPGA) processor or micro processor. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the first antenna unit 103a and/or the central unit 101. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code can furthermore be provided as pure program code on a server and downloaded to the first antenna unit 103a, the second antenna unit 103b and/or the central unit 01.

The embodiments herein relate to a distributed and MIMO system comprising a central unit 101 and two or more serially connected antenna units 103. The antenna units 103 communicate through a first link 108, e.g. a pipe-line data bus, when performing UL reception processing. In addition to the first link 108, the antenna units 103 may also send information, e.g. received and processed UL signals, on a second link 100, e.g. a shared direct-line data bus, directly to the central unit 101 , e.g. when UL reception processing is ready.

The same physical connectors used for DL broadcast may be used also for second link communication, e.g. direct-line communication, between antenna units 103 and the central unit 101 during UL time-slots.

The second link 1 10, e.g. the direct-line data bus, may be used to broadcast information from one antenna unit 103 to several other antenna units 103.

The embodiments herein relate to uplink processing in a distributed and serial MIMO system. The embodiments herein relate to uplink processing of signals in a distributed and serial massive MIMO system comprising a first link 108 and a second link 1 10, e.g. a pipe-line and a direct-line.

Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used. All references to a/an/the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and/or where it is implicit that a step must follow or precede another step.

Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate. Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following description.

In general, the usage of“first”,“second”,“third”,“fourth”, and/or“fifth” herein may be understood to be an arbitrary way to denote different elements or entities, and may be understood to not confer a cumulative or chronological character to the nouns they modify, unless otherwise noted, based on context.

Several embodiments are comprised herein. It should be noted that the examples herein are not mutually exclusive. Components from one embodiment may be tacitly assumed to be present in another embodiment and it will be obvious to a person skilled in the art how those components may be used in the other exemplary embodiments

The embodiments herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the embodiments. A feature from one embodiment may be combined with one or more features of any other embodiment.

The term“at least one of A and B” should be understood to mean“only A, only B, or both A and B.”, where A and B are any parameter, number, indication used herein etc. It should be emphasized that the term“comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It should also be noted that the words“a” or“an” preceding an element do not exclude the presence of a plurality of such elements.

The term“configured to” used herein may also be referred to as“arranged to”,“adapted to”,“capable of” or“operative to”.

It should also be emphasised that the steps of the methods may, without departing from the embodiments herein, be performed in another order than the order in which they appear herein.

ABBREVIATIONS

MIMO Multiple Input Multiple Output

MU-MIMO Multi-user MIMO

UE User Equipment

CPU Central Processing Unit

APU Antenna Processing Unit

HW Hardware

Claims

1. An antenna system (100) comprising:

at least one central unit (101 ) and at least one antenna unit group, wherein the at least one antenna unit group comprises a plurality of serially connected antenna units (103a, 103b),

wherein each antenna unit (103a, 103b) in the antenna unit group is serially connected to its neighboring antenna unit(s) (103a, 103b) via a first link (108),

wherein each antenna unit (103a, 103b) in the antenna unit group is directly connected to the central unit (101 ) via a second link (1 10), and

wherein each antenna unit (103a, 103b) in the antenna unit group is adapted to process User Equipment, UE, data received from at least one UE (1 15).

2. The antenna system (100) according to claim 1 , wherein the second link (1 10) is adapted to convey information from one of the antenna units (103a, 103b) to at least one of the other antenna units (103a, 103b) in the antenna unit group.

3. The antenna system (100) according to either of the preceding claims, wherein each antenna unit (103a, 103b) is adapted to receive combined UE data from its neighboring antenna unit (103a, 103b) in an uplink direction via the first link (108), and

wherein each antenna unit (103a, 103b) is adapted to combine every UE data which it has locally processed with the received combined UE data from the neighbouring antenna unit (103a, 103b). 4. The antenna system (100) according to any of the preceding claims, wherein the central unit (101 ) is adapted to determine which of the antenna units (103a, 103b) in the antenna unit group that shall be a starting point for the processing of UE data.

5. The antenna system (100) according to any of the preceding claims, wherein each antenna unit (103a, 103b) in the antenna unit group is adapted to process the UE data in an order they are needed; or

wherein each antenna unit (103a, 103b) in the antenna unit group is adapted to select which UE data and in which order it should process the UE data. 6. The antenna system (100) according to any of the preceding claims, wherein a number of processing steps for processing the UE data is the same or different for different UEs (1 15). 7. The antenna system (100) according to any of the preceding claims, wherein a number of processing steps for processing UE data is a random number or a pre-determined number.

8. The antenna system (100) according to any of the preceding claims, wherein when the antenna unit (103a, 103b) being a neighbor to the central unit (101 ) has completed the processing of the UE data, then it sends the processed data directly to the central unit (101 ) via the second link (1 10).

9. The antenna system (100) according to any of the preceding claims, wherein a processing length for the first link (108) has at least one of an upper and lower boundary aligned with at least one of uplink and downlink slots.

10. The antenna system (100) according to any of the preceding claims, wherein different UE data have different processing lengths for the first link (108).

1 1 . The antenna system (100) according to any of the preceding claims, wherein when the UE (1 15) is adapted to transmit multiple UE data to at least one of the

plurality of antenna units (103a, 103b) in the at least one antenna unit group, then the at least one antenna unit (103a, 103b) is adapted to treat the multiple UE data as coming from separate UEs (1 15).

12. The antenna system (100) according to any of the preceding claims, wherein an unutilized or under-utilized antenna unit (103a, 103b) in the antenna unit group is adapted to be deactivated, and

wherein at least one of the central unit (101 ), a first antenna unit (103a) and a second antenna unit (103b) are adapted to determine that an unutilized or under-utilized antenna unit (103a, 103b) in the antenna unit group should be deactivated.

13. A method performed by an antenna system (100), wherein a first antenna unit (103a), a second antenna unit (103b) and a central unit (101 ) are comprised in the antenna system (100),

wherein the first antenna unit (103a) and the second antenna unit (103b) are neighboring antenna units and comprised in an antenna unit group,

wherein the first antenna unit (103a) is serially connected to its neighboring second antenna unit (103b) via a first link (108),

and wherein the first antenna unit (103a) and the second antenna unit (103b) are directly connected to the central unit (101 ) via a second link (1 10),

the method comprising:

obtaining ( 201 , 1601 ), at the first antenna unit (103a) and the second antenna unit (103b), User Equipment, UE, data from at least one UE (1 15) in an uplink direction;

processing (202, 203, 1602) the obtained UE data at the first antenna unit (103a) and the second antenna unit (103b);

providing (204, 1603) the processed UE data from the first antenna unit (103a) to its neighboring second antenna unit (103b) in the uplink direction and via the first link (108); and

obtaining ( 204, 1604), at the second antenna unit (103b), processed UE data from the neighboring first antenna unit (103a);

combining ( 205, 1605), at the second antenna unit (103b), processed UE data from the first antenna unit (103a) and the UE data processed by the second antenna unit (103b); and

providing (206, 1606) the combined processed UE data from the second antenna unit (103a) to the central unit (101 ) via the second link (1 10) or to a neighboring third antenna unit (103) via the first link (108).

14. A method for setting up an antenna system (100), wherein the antenna system (100) comprises at least one central unit (101 ) and at least one antenna unit group, wherein the at least one antenna unit group comprises a plurality of antenna units (103a, 103b), the method comprising:

connecting (1401 ) each antenna unit (103a, 103b) in the at least one antenna unit group (103a, 103b) serially to its neighboring antenna unit (103a, 103b) via a first link (108); and

connecting (1402) each antenna unit (103a, 103b) in the at least one antenna unit group directly to the central unit (101 ) via a second link (1 10). 15. The method according to claim 14, comprising:

connecting (1403) two or more antenna unit groups to each other, wherein each antenna unit group comprises a plurality of serially connected antenna units (103a, 103b).

16. The method according to any of claims 14-15, comprising:

connecting (1704) one central unit (101) to each antenna unit group; or connecting (1705) one central unit (101 ) to multiple antenna unit groups.

17. A method performed by a second antenna unit (103b),

wherein a first antenna unit (103a), the second antenna unit (103b) and a central unit (101 ) are comprised in an antenna system (100),

wherein the first antenna unit (103a) and the second antenna unit (103b) are neighboring antenna units and comprised in an antenna unit group;

and wherein the second antenna unit (103b) is directly connected to the central unit (101 ) via a second link (1 10),

the method comprising:

obtaining ( 201 , 1801 ) User Equipment, UE, data from at least one UE (1 15); processing (202, 1802J the obtained UE data; and

providing (204, 1803) the processed UE data to the central unit (101 ) via the second link (1 10) or to a neighboring third antenna unit (103) via the first link (108).

18. The method according to claim 17, comprising:

obtaining ( 204, 1804), from the neighboring first antenna unit (103a) in the uplink direction, processed UE data which the first antenna unit (103a) has processed;

combining (205, 1805) the processed UE data from the first antenna unit

(103a) and the processed UE data which has been processed by the second antenna unit (103b); and

providing (206, 1806) the combined processed UE data to the central unit (101 ) via the second link (1 10) or to the neighboring third antenna unit (103) via the first link (108). 19. A second antenna unit (103b),

wherein the first antenna unit (103a) and the second antenna unit (103b) are neighboring units and comprised in an antenna unit group,

wherein the second antenna unit (103b) is serially connected to its neighboring first antenna unit (103a) via a first link (108),

the second antenna unit (103b) is adapted to:

obtain User Equipment, UE, data from at least one UE (1 15); process the obtained UE data; and to

provide the processed UE data to the central unit (101 ) via the second link (1 10) or to a neighboring third antenna unit (103) via the first link (108).

20. The second antenna unit (103b) according to claim 19, adapted to:

obtain, from the neighboring first antenna unit (103a) in the uplink direction, a processed UE data which the first antenna unit (103a) has processed;

combine the processed UE data from the first antenna unit (103a) and the processed UE data which has been processed by the second antenna unit (103b); and to provide the combined processed UE data to the central unit (101 ) via the second link (1 10) or to the neighboring third antenna unit (103) via the first link (108).

21 . A method performed by a central unit (101 ),

wherein a first antenna unit (103a), a second antenna unit (103b) and the central unit (101 ) are comprised in an antenna system (100),

and wherein the central unit (101 ) is directly connected to the first antenna unit (103a) and the second antenna unit (103b) via a second link (1 10),

the method comprising:

obtaining ( 206, 1901 ) processed User Equipment, UE, data from the first antenna unit (103a) or from the second antenna unit (103b) in an uplink direction and via the second link (1 10). 22. The method according to claim 21 , comprising: obtaining (206, 1902) combined processed UE data from the first antenna unit (103a) or from the second antenna unit (103b) in the uplink direction and via the second link (1 10), wherein the combined processed UE data is a combination of UE data processed by the second antenna unit (103b) and UE data processed by the first antenna unit (103a).

23. The method according to any of claims 21 -22, comprising:

providing (200, 1900) information to the first antenna unit (103a) indicating that it should be a starting point for processing of UE data on the first link (108).

24. The method according to any of claims 21 -23, comprising:

communicating (1903) with one or more antenna unit groups in the antenna system (100).

25. A central unit (101 ),

wherein the first antenna unit (103a) and the second antenna unit (103b) are neighboring antenna units and comprised in an antenna unit group.

the central unit (101 ) being adapted to:

obtain processed User Equipment, UE, data from the first antenna unit (103a) or from the second antenna unit (103b) in an uplink direction and via the second link (1 10).

26. The central unit (101 ) according to claim 25, adapted to:

obtain r combined processed UE data from the first antenna unit (103a) or from the second antenna unit (103b) in the uplink direction and via the second link (1 10), wherein the combined processed UE data is a combination of UE data processed by the second antenna unit (103b) and UE data processed by the first antenna unit (103a).

27. The central unit (101) according to either of claims 25-26, adapted to:

provide information to the first antenna unit (103a) indicating that it should be a starting point for processing of UE data on the first link (108). 28. The central unit (101 ) according to any of claims 25-27, adapted to: communicate with one or more antenna unit groups in the antenna system

(100).

29. A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any one of claims 13 and/or 14-16 and/or 17-18 and/or 21 -23. 30. A carrier comprising the computer program of claim 29, wherein the carrier is one of an electronic signal, optical signal, radio signal or computer readable storage medium.