Patent Description:
The term "cell-free massive MIMO" has been used to refer to a massive Multiple-Input Multiple-Output (MIMO) system where some or all of the transmitting and receiving antennas for a base station are geographically distributed, apart from the base station. Each of the transmitting and receiving points may be referred to as an "antenna point," "antenna processing node," or "antenna processing unit. " These terms may be understood to be interchangeable for the purposes of the present disclosure, with the abbreviation "APU" being used herein. These APUs are communicatively coupled to and controlled by a controlling node, which is spatially separate from some or all of the APUs, may be referred to interchangeably as a "central processing node" or "central processing unit" - the abbreviation "CPU" is used herein.

<FIG> provides a conceptual view of a cell-free massive MIMO deployment, comprising a CPU <NUM> connected to several APUs <NUM>, via serial links <NUM>. As seen in the figure, each of several user equipments (UEs) <NUM> may be surrounded by one or several serving APUs <NUM>, all of which may be attached to the same CPU <NUM>, which is responsible for processing the data received from and transmitted by each APU. Each UE <NUM> may thus move around within this system without experiencing cell boundaries.

Systems described herein include at least CPU and two or more APUs spatially separated from each other and from the CPU. These systems, which may be considered examples of cell-free massive MIMO deployments, will be called distributed wireless systems herein. <FIG> and <FIG> provide other views of example deployments of distributed wireless systems. In this scenario shown in <FIG>, multiple APUs <NUM> are deployed around the perimeter of a room, which might be a manufacturing floor or a conference room, for example. Each APU <NUM> is connected to the CPU <NUM> via a "strip," or "stripe. " More particularly, the CPU <NUM> in this example deployment is connected to two such stripes, each stripe comprising a serial concatenation of several (<NUM>, in the illustrated example) APUs <NUM>. <FIG> shows an two-dimensional model of a factory floor with densely populated APUs <NUM> connected to the CPU <NUM> via several such "stripes" As a general matter, the CPU <NUM> can target a UE anywhere in the room by controlling one or several APUs <NUM> that are closest to the UE to transmit signals to and receive signals from the UE. In this example deployment, the APUs are spaced at <NUM> meters, in both x- and y-directions, which means that a UE is never more than about <NUM> meters away from one (or several) APUs, in the horizontal dimension.

It will be appreciated that the distribution of base station antennas into APUs as shown in <FIG> can provide for shorter distances between the base station antennas and the antenna(s) for any given UE served by the base station, in many scenarios. This will be an enabler for the use of higher carrier frequencies, and thereby higher modulation/information bandwidths, both of which are key expectations for fifth-generation (<NUM>) wireless networks. More particularly, new frequency bands in the millimeter-wave (mmW) range are introduced for <NUM>. Even higher frequency bands are envisioned for <NUM>, with operating frequencies up to several hundred GHz. These high frequencies present challenges in radio propagation but are well suited for cell-free massive MIMO deployments, since all users can be very close to a base station in such systems. Wall penetration is bad at these high frequencies, which is beneficial if trying to build an isolated indoor system. A key advantage of these higher frequency bands is that there are several GHz of contiguous frequency bands available. This enables very high UE bitrates, e.g., in the tens of Gbps, or higher.

Another requirement of <NUM> networks is that they support a high quality-of-service (QoS). To achieve this, it is necessary that the radio link between the mobile/device/machine (UE) and the base station be highly reliable and support low-latency communications. This is especially the case for industrial scenarios, for example, where mission-critical real-time communication is needed for communications with or between machines equipped with devices. Here again, the type of network discussed herein is seen as a good candidate for ultra-reliable networks, since they can provide more than one radio link between the UE and the infrastructure network. The following background art documents are also referred to. SSB stands for synchronization signal blocks.

<CIT>, relates to a communication method and system for converging a 5th-Generation (<NUM>) communication system for supporting higher data rates beyond a 4th-Generation (<NUM>) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the <NUM> communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method of configuring a reference signal to manage backhaul (BH) links in an integrated access and BH (IAB) is provided. The method includes providing channel measurement and reporting information, and using the channel measurement and reporting information to discover and maintain backup BH links.

3GPP contribution by <NPL>, discloses Integrated Access and Backhaul for NR.

3GPP contribution by <NPL>, discloses extensions of SSBs for inter-lAB-node discovery and measurement.

<CIT>, discloses a method of operating an Integrated Access Backhaul, IAB, wherein The IAB node is arranged to communicate backhaul traffic wirelessly with a parent node and a child node. The method comprises: receiving a duplexing pattern configuration message from the parent node; transmitting a duplexing pattern configuration message to the child node; receiving a duplexing pattern configuration acknowledgment message from the child node; after receiving the duplexing pattern configuration acknowledgment message from the child node, applying a duplexing pattern contained within the duplexing pattern configuration message received from the parent node; and transmitting a duplexing pattern configuration acknowledgement message to the parent node.

<CIT>, discloses a method and apparatus for indication of resource ports in a communication system is disclosed. In one embodiment, a method performed by a first wireless communication node, includes: receiving resource configuration information from a second wireless communication node in a communication system; and determining at least one muting resource set according to the resource configuration information.

A distributed wireless system according to embodiments described herein comprises a controlling node and two or more antenna processing nodes communicatively coupled to the controlling node but spatially separated from each other and from the controlling node. An example method in the controlling node comprises controlling a first subset of the antenna processing nodes to transmit synchronization signal blocks (SSBs) having a first SSB identifier, the first subset including one or more of the antenna processing nodes, and controlling a second subset of the antenna processing nodes to transmit SSBs having a second SSB identifier, the second subset including one or more of the antenna processing nodes and being disjoint with the first subset, wherein the method further comprises: receiving, via one or more of the antenna processing nodes, a random access request from a wireless device; and selecting an antenna processing node for one or more subsequent transmissions by mapping a timeslot in which the random access request was transmitted to an SSB identifier, identifying at least one antenna processing node transmitting SSBs with that SSB identifier, and selecting the antenna processing node for subsequent transmissions from among the identified at least one antenna processing node.

An example controlling node apparatus according to embodiments described herein, for use in a distributed wireless system that comprises the controlling node and two or more antenna processing nodes communicatively coupled to the controlling node but spatially separated from each other and from the controlling node, comprises interface circuitry configured to send information to and receive information from a plurality of antenna processing nodes, as well as processing circuitry operatively coupled to and configured to control the interface circuitry. The processing circuitry is configured to control a first subset of the antenna processing nodes to transmit SSBs having a first SSB identifier, the first subset including one or more of the antenna processing nodes, and to control a second subset of the antenna processing nodes to transmit SSBs having a second SSB identifier, the second subset including one or more of the antenna processing nodes and being disjoint with the first subset, wherein the processing circuitry is further configured to receive, via one or more of the antenna processing nodes, a random access request from a wireless device; and select an antenna processing node for one or more subsequent transmissions by mapping a timeslot in which the random access request was transmitted to an SSB identifier, identifying at least one antenna processing node transmitting SSBs with that SSB identifier, and selecting the antenna processing node for subsequent transmissions from among the identified at least one antenna processing node.

Variations of the above-summarized method and apparatus are described in detail below, as are corresponding systems, computer program products, and computer-readable media.

Benefits of the techniques and apparatus disclosed herein include that they facilitate the locating of the APU having the lowest pathloss to each UE making a random access attempt in a distributed wireless system. Using these techniques, the UE is able to direct its beamforming towards the APU with lowest path loss and the CPU will select the best beam from the selected APU to serve the UE. This will result in lower path loss for each UE, and thus faster and more reliable communication. In addition, overall system capacity is improved due to lower interference level.

Additional details and further advantages are described below, and illustrated in the attached figures.

There are several possible approaches for implementing the interconnections between the CPU in a distributed wireless system and the APUs that it controls. One approach is to implement the interconnections between the CPUs and the APUs as a high-speed digital interface, e.g., such as a high-speed Ethernet connection. With this approach, information to be transmitted by a given APUs is sent from the CPU to the APU as digital baseband information. This digital baseband information is then up-converted to a radiofrequency (RF) signal in the APU, for transmission over the air. In the other direction, RF signals received from a UE are downconverted in the APU and converted to digital form before being sent over the digital link to the CPU, for further processing. Some concerns that arise with this approach include power consumption and heat dissipation. The high-speed digital serial interfaces required for this approach may dominate the power consumption needs for the APUs; typically this power will be supplied to the APUs through the serial links themselves, which means that the CPU may be providing the DC power for all of the APUs in such a system.

Another approach is to implement each link, or "hop," along the stripes shown in <FIG> as a dielectric waveguide that carries a high-frequency RF signal (e.g., a millimeter-wave signal). With this approach, the CPU can provide an already modulated and upconverted RF signal to each APU, for transmission by the APU when required. As a general matter, the term "dielectric waveguide" as used herein may include any sort of dielectric waveguide, which would include such things as conventional RF waveguides, which are metallic pipes and in which the dielectric substance within the pipe is often simply air. However, more cost-effective solutions have been developed for short- and medium-range applications; these solutions may comprise an inexpensive plastic dielectric that is metallized, e.g., so as to form a "pipe" surrounding the dielectric material or so as to form two parallel plates separated by the dielectric material. These inexpensive dielectric waveguides may provide suitable performance over links that are several meters, or even dozens of meters, long.

An advantage of this approach is that the RF-based interface circuitry may consume less power than the serial digital interfaces described above. Less processing power is required in each APU as well, further reducing the power consumption of the system.

The following detailed description is focused on the second approach described above, i.e., on systems where a CPU is connected to multiple APUs via a series of dielectric waveguides. However, the inventive techniques described herein are not limited to such a system.

<FIG> is a block diagram of one embodiment of a wireless communication network <NUM> ("network <NUM>") that includes a dielectric waveguide-based distributed radio system configured to provide one or more types of communications services to User Equipments (UEs) <NUM>, according to some embodiments of the presently disclosed invention. For example, the network <NUM> operates as an access network, providing access to one or more external networks <NUM>, such as the Internet.

While <FIG> depicts five UEs <NUM>-<NUM> through <NUM>-<NUM>, no limitation attends the depiction, as the number of UEs <NUM> connected to the network <NUM> varies over time. As with the UEs <NUM>, <FIG> and other ones of the accompanying figures may depict elements that are the same or at least broadly similar for purposes of discussion using suffixed reference numbers. However, this specification refers to suffixes only when necessary for clarity. Thus, the reference number "<NUM>" without suffixing may be used to refer to a given UE in singular form, or to given UEs in plural form. The same holds for other drawing reference numbers depicted with suffixing in any of the figures.

The term "UE" encompasses essentially any type of wireless communication apparatus that is configured to make use of the network <NUM>-i.e., to communicate via wireless attachment to the network <NUM>. Example types or categories of UEs include smartphones, feature phones, laptops, tablets, or other personal computing devices. Other examples include Machine Type Communication (MTC) devices or Internet-of-Things (IoT) devices, such as sensors and controllers. The UEs <NUM> served by the network <NUM> may be of the same type or a mix of various types and the mix may change with time. One or more UEs <NUM> served by the network <NUM> may be embedded, e.g., in a vehicle, and one or more may be stationary. For example, the network <NUM> may be an indoor deployment targeting UEs <NUM> within a building or may be outdoors in an urban area with foot traffic and vehicle traffic.

The network <NUM> in an example embodiment is configured according to Third Generation Partnership Project (3GPP) specifications. In at least one embodiment, the network <NUM> is a Fifth Generation (<NUM>) New Radio (NR) network, according to the corresponding 3GPP specifications. See the specifications referred to as 3GPP Release <NUM> and newer. However, the architecture of the network <NUM> has wider applicability than <NUM> NR deployments and <NUM> NR stands only as one example.

Different "parts" of the network <NUM> include a Radio Access Network (RAN) part <NUM>, also referred to as the RAN <NUM>, and a Core Network (CN) part <NUM>, also referred to as the CN <NUM>. While not necessarily germane to the specific techniques described herein, the CN <NUM> provides authentication, mobility-management, and external-network interfacing functions, in support of providing communication services to the UEs <NUM>, while the RAN <NUM> provides the air interface(s) by which the UEs <NUM> are "connected" to the network <NUM>.

The illustrated RAN <NUM> includes a central processing unit (CPU) <NUM> and one or more antenna processing units (APUs) <NUM>, e.g., APUs <NUM>-<NUM> through <NUM>-<NUM>. As noted above, a CPU <NUM> might also be referred to as a "controlling node," while an APU <NUM> may be referred to as an antenna processing node. A characteristic arrangement contemplated herein is that a CPU <NUM> and one or more APUs <NUM> form a "chain" <NUM> of serially interconnected or interlinked entities. In <FIG>, the CPU <NUM> anchors two distinct chains, a first chain <NUM>-<NUM> that includes the APUs <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> in series, and a second chain <NUM>-<NUM> that includes the APUs <NUM>-<NUM> and <NUM>-<NUM> in series. Another CPU might anchor only a single chain, or more than two chains.

The entities constituting each chain <NUM> are interconnected via dielectric waveguide (DWG) links <NUM>. For example, for the chain <NUM>-<NUM>, the CPU <NUM> couples to the APU <NUM>-<NUM> via a first DWG link <NUM>-<NUM>, the APU <NUM>-<NUM> couples to the APU <NUM>-<NUM> via a second DWG link <NUM>-<NUM>, and the APU <NUM>-<NUM> couples to the APU <NUM>-<NUM> via a third DWG link <NUM>-<NUM>. For the chain <NUM>-<NUM>, the CPU <NUM> couples to the APU <NUM>-<NUM> via a first DWG link <NUM>-<NUM>, and the APU <NUM>-<NUM> couples to the APU <NUM>-<NUM> via a second DWG link <NUM>-<NUM>. The length of each link is determined as needed by the deployment scenario, and need not be consistent through the system.

Each chain <NUM> has a directional sense, with the direction going away from the CPU <NUM> being referred to as the "downstream" direction, and with the direction going towards the CPU <NUM> being referred to as the "upstream" direction. Using this nomenclature, the CPU <NUM> generates "outbound" radio carrier signals and propagates them into the chain <NUM> in the downstream direction, for over-the-air (OTA) transmission by one or more of the APUs <NUM> in the chain <NUM>. Conversely, radio carrier signals received via OTA reception by given ones of the APUs <NUM> are propagated in the chain <NUM> in the upstream direction, for conveyance to the CPU <NUM> for processing-e.g., down-conversion and demodulation.

Saying that a radio carrier signal is "propagated" in the chain <NUM> refers to DWG-conveyance of the radio carrier signal over one or more successive "hops" or "links" in the chain <NUM>. Each DWG link <NUM> in the chain constitutes one serial hop or link. Radio carrier signals propagated in the chain <NUM> may also be referred to as "guided" radio carrier signals or "distributed" radio carrier signals to emphasize that they are conveyed via DWGs. With this in mind, one way to understand operation of the chain <NUM> is that the CPU <NUM> generates outbound radio carrier signals, which are then propagated downstream in the chain <NUM>, as far as needed, for OTA transmission by one or more of the APUs <NUM> in the chain <NUM>. In the opposite direction, radio carrier signals received by given APUs <NUM> via OTA reception are propagated upstream in the chain <NUM> to the CPU <NUM>.

Consider an example case where the APU <NUM>-<NUM> in the chain <NUM>-<NUM> operates as a serving base station for the UE <NUM>-<NUM> and the CPU <NUM> generates a radio carrier signal conveying user traffic for the UE <NUM>-<NUM>. The CPU <NUM> has a DWG interface that couples it to one end of the DWG link <NUM>-<NUM> and it uses that interface to propagate the generated radio carrier signal into the DWG link <NUM>-<NUM> as an outbound radio carrier signal targeting the UE <NUM>-<NUM>. In turn, the APU <NUM>-<NUM> includes an "upstream" DWG interface that couples it to the other end of the DWG <NUM>-<NUM>, and it receives the outbound radio carrier signal via its upstream DWG interface. Because the outbound radio carrier signal targets a UE <NUM> that is served by the APU <NUM>-<NUM>, the APU <NUM>-<NUM> performs an OTA transmission of the radio outbound carrier signal.

Consider a similar example, but where the outbound radio carrier signal targets the UE <NUM>-<NUM>, which is served by the APU <NUM>-<NUM>. In this case, the APU <NUM>-<NUM> propagates the outbound radio carrier signal to the next hop in the chain <NUM>-<NUM>, which is the DWG link <NUM>-<NUM> that couples the APU <NUM>-<NUM> to the APU <NUM>-<NUM>. In turn, the APU <NUM>-<NUM> propagates the outbound radio carrier signal to the next hop in the chain <NUM>-<NUM>, which is the DWG link <NUM>-<NUM> that couples the APU <NUM>-<NUM> to the APU <NUM>-<NUM>.

Now consider the inbound case, where and given APU <NUM> within a chain <NUM> receives an OTA transmission from a UE <NUM> that it serves. That is, the given APU <NUM> receives an uplink radio carrier signal from the UE <NUM>. The given APU <NUM> couples the received uplink radio carrier signal into the DWG link <NUM> on its upstream side - facing the CPU <NUM> - for propagation in the chain <NUM> in the upstream direction as an inbound radio carrier signal for the CPU <NUM>. Any intervening APUs <NUM> in the upstream direction between the given APU <NUM> and the CPU <NUM> perform respective next-hop propagations of the inbound radio carrier signal towards the CPU <NUM>.

As such, each APU <NUM> can transmit and receive via its DWG interfaces, for propagation of radio carrier signals within the chain <NUM>-i.e., waveguide conveyance in the downstream or upstream direction of the chain <NUM>. Further, each APU <NUM> includes or is associated with an antenna array <NUM>, for OTA transmission of radio carrier signals, referred to as downlink (DL) transmission, and OTA reception of radio carrier signals, referred to as uplink (UL) reception.

All APU operations may be managed and controlled by the CPU <NUM>, e.g., by the CPU <NUM> distributing control signaling in the chain <NUM> for the included APUs <NUM>. In one or more embodiments, each APU <NUM> operates in TDD fashion, such that it performs OTA reception mutually exclusive from OTA transmission and, with respect to one DWG to which it is coupled, it performs DWG reception mutually exclusive from DWG transmission.

Each DWG link <NUM> comprises at least one DWG-that is, the term "DWG link" as used herein refers to at least one dielectric waveguide. In at least one embodiment, each DWG link <NUM> comprises a parallel pair of DWGs, with each DWG in the parallel pair being dedicated to a different radio-carrier-signal polarization. Relating this example arrangement to <FIG>, the DWG link <NUM>-<NUM> is an upstream link with respect to the APU <NUM>-<NUM> and it includes a parallel pair of DWGs, and the DWG link <NUM>-<NUM> is a downstream link with respect to the APU <NUM>-<NUM> and it includes a parallel pair of DWGs. Of course, with respect to the APU <NUM>-<NUM>, the DWG link <NUM>-<NUM> is an upstream link and the DWG link <NUM>-<NUM> is a downstream link for the APU <NUM>-<NUM>.

Using two or more parallel DWGs in each DWG link <NUM> allows separate radio carrier signals to propagate simultaneously over the DWG link <NUM>, e.g., for different polarizations and/or greater signal capacity in the chain <NUM>. For example, in <FIG>, consider the case where each DWG link <NUM> in the chain <NUM>-<NUM> includes a single DWG for each polarization that is in use. That means that one series set of DWGs is available in the entire chain <NUM>-<NUM> for use in transmitting or receiving radio carrier signals of the involved polarization, at least in a TDD implementation.

In at least one arrangement, the DWG links <NUM> within a chain <NUM> comprise <NUM> x N parallel DWGs, where the APUs <NUM> in the chain <NUM> are interleaved and every N:th APU <NUM> is connected to the same DWG pair. Also, such arrangements would gain a capacity increase and increased robustness by terminating the chain <NUM> with a CPU <NUM> at each end. For example, one of the terminating CPUs <NUM> could take over for the other one, if needed, using the same set of series-connected DWGs, or the DWG links <NUM> in the chain <NUM> could have respective sets of series-connected DWGs for each of the CPUs <NUM>, such that one of the CPUs <NUM> acts as a master CPU on one of the sets of series-connected DWGs while the other CPU <NUM> acts as a master CPU on the other one of the sets of series-connected DWGs. Of course, the APUs <NUM> would be configured to support such operation.

With TDD operation of the CPU <NUM>, APUs <NUM>, and DWG links <NUM> in one chain <NUM>-<NUM>, conveying radio carrier signals in the downlink direction of the chain <NUM>-<NUM> is mutually exclusive from conveying them in the upstream direction. As such, all of the UEs <NUM> served by the chain <NUM>-<NUM> "share" the radio-carrier-signal bandwidth in time, with only one UE <NUM> being served at a time. To change this, the chain <NUM>-<NUM> can include more than one DWG in each DWG link <NUM>, for each polarization in use, such that a first series set of DWGs in the chain <NUM>-<NUM> can be used to serve a given UE <NUM> at a given time instant, while a second series set of DWGs in the chain <NUM>-<NUM> in parallel with the first set can be used to serve another given UE <NUM> at the same time.

However, whether each of the DWG links <NUM> that form the series sets of DWGs individually comprise single DWGs or two or more DWGs in parallel, the DWG-based connection arrangement offers distinct advantages. For example, using digital interfaces for the serial interconnections in the chain <NUM> would raise serious issues with respect to power consumption and complexity of the serial interconnections and the APUs <NUM>, particularly when targeting very high bit rates for the traffic exchanged with the UEs <NUM> served by the network <NUM>. At a minimum, the use of digital interfaces would require each APU <NUM> to include corresponding analog-to-digital converters and digital to analog converters.

Further, as noted, the APUs <NUM> as contemplated herein need not perform any modulation, demodulation, or frequency-shifting, meaning that the radio carrier signals they transmit over the air are the same ones they received from the CPU <NUM> via downstream propagation in the chain <NUM>, subject, of course, to any transmit beamforming applied by the APU <NUM>. Similarly, and APU <NUM> may perform reception beamforming but, besides that, the OTA-received radio carrier signal incoming to the APU <NUM> is the same carrier radio signal that the APU <NUM> propagates in the upstream direction as an inbound radio signal for the CPU <NUM>.

As a further advantageous simplification used in one or more embodiments of the APUs <NUM>, the DWG interfaces included in the APUs <NUM> operate in TDD fashion with respect to each DWG included in a corresponding DWG link <NUM>-<NUM>. That is, with respect to a single DWG, the DWG interface transmits and receives on a mutually exclusive basis. This arrangement reduces complexity, e.g., the need for diplexers and other frequency-multiplexing circuitry. And, as noted, the APUs <NUM> need not perform frequency-conversion or shifting for the radio carrier signals they handle.

The distributed radio system illustrated in <FIG> comprises several antennas processing units (APU) <NUM>, which are connected to a single central processing unit (CPU) <NUM>, using serial links <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, etc. More particularly, each APU <NUM> is connected to at least one neighboring APU <NUM> and/or to CPU <NUM> via a pair of dielectric waveguides <NUM> that carries the RF signal. Two dielectric waveguides <NUM> may be used for each link so that an APU can be provided (or provide) different RF signals for each of two antenna polarizations. Of course, more than two dielectric waveguides may be used to link neighboring units, in some embodiments.

At each end of each dielectric waveguide, the RF signal received from or transmitted into the dielectric waveguide is converted to or from an electrical signal with a dielectric waveguide interface antenna. These antennas, which may in some cases be very simple conductive elements, launch the RF signals into the dielectric waveguides and pickup RF signals from the dielectric waveguides. The length of each dielectric waveguide <NUM> is set by the deployment scenario and is therefore not a fixed length.

In a system like that illustrated in <FIG>, communications along the links interconnecting the CPU and the APUs may be described as "upstream" and "downstream" communications, where upstream communications are communications in the direction towards the CPU while downstream communications are in the opposite direction, i.e., away from the CPU. In the upstream direction, each APU thus sends its own received radio signal towards the CPU, when requested, via an upstream dielectric waveguide interface. It may also forward, via the upstream dielectric waveguide interface, radio signals it receives, via a downstream dielectric waveguide interface, from an APU that is further downstream in the chain of APUs. In the other direction, the APU receives from the CPU or an upstream APU, via the upstream dielectric waveguide interface, a radio signal for transmitting to one or more UEs. It may also receive, via the upstream dielectric waveguide interface, radio signals for forwarding, via the downstream dielectric waveguide interface, to one or more APUs further downstream.

<FIG> depicts an APU <NUM> in an example embodiment. The APU <NUM> includes two sides in a functional sense, labeled in the diagram as SIDE <NUM> and SIDE <NUM>. One is the upstream side facing towards the CPU <NUM> controlling the chain <NUM> in which the APU <NUM> operates and the other side is the downstream side facing away from the CPU <NUM>.

The APU <NUM> includes "A" elements for a first radio-carrier-signal polarization and "B" elements for a second radio-carrier-signal polarization-e.g., horizontal and vertical polarizations. These may be referred to as "Part A" and "Part B" in the discussion that follows. Correspondingly, the antenna array <NUM> comprises a small antenna matrix for each polarization. Only the A matrix is visible in the diagram. Each antenna matrix provides beamforming gain and thus improve the link budget between the APU <NUM> and the UEs <NUM> that it serves, along with improves the interference situation in implementations where multiple chains <NUM> use the same radio carrier frequencies. Example matrix dimensions are <NUM> x <NUM> for <NUM> radio carrier signals, with the antenna elements <NUM> spaced at lambda/<NUM> (<NUM>).

The example APU <NUM> further includes antenna circuitry <NUM> that interfaces with the antenna array <NUM>, a dielectric waveguide interface <NUM>, and control circuitry <NUM> that may exchange control signaling on the upstream side and on the downstream side of the APU <NUM>. For example, the CPU <NUM> may output control signaling for the APUs <NUM> in the chain <NUM> and each APU <NUM> in the chain may transfer some or all such signaling onto the next APU <NUM> in the chain. The signaling may be common to the A and B parts of the APU <NUM> or may be separate for the A and B parts, e.g., coordinated but separate signaling for A and B radio-carrier-signal polarizations handled by the APU <NUM>. <FIG> illustrates such a case, where <NUM>-1A denotes upstream-side control signaling associated with the A part of the APU <NUM>, <NUM>-1B denotes upstream-side control signaling associated with the B part of the APU <NUM>, <NUM>-2A denotes downstream-side control signaling associated with the A part of the APU <NUM>, and <NUM>-2B denotes downstream-side control signaling associated with the B part of the APU <NUM>. Of course, this example not limiting and other control signaling arrangements are contemplated.

In similar A/B fashion, the DWG interface <NUM> of the APU <NUM> connects to two DWGs in each direction. That is, on SIDE <NUM> of the APU <NUM>, the DWG interface <NUM> provides DWG coupling for two DWGs constituting the SIDE-<NUM> DWG link <NUM>-<NUM>. These two SIDE-<NUM> DWGs are denoted as <NUM>-1A and <NUM>-1B, corresponding to the A and B parts of the APU <NUM>. Likewise, the DWG interface <NUM> provides DWG coupling for two DWGs <NUM> constituting the SIDE-<NUM> DWG link <NUM>-<NUM>. These two SIDE-<NUM> DWGs are denoted as <NUM>-2A and <NUM>-2B, corresponding to the A and B parts of the APU <NUM>.

The DWG <NUM>-1A on SIDE <NUM> "maps" to the DWG <NUM>-2A on SIDE <NUM>, meaning that in relay operation, the APU <NUM> couples radio carrier signals incoming to the APU <NUM> from the DWG <NUM>-1A over to the DWG <NUM>-2A, and vice versa. The same cross-side mapping applies for the DWGs <NUM>-1B and <NUM>-2B. In at least one embodiment, the <NUM>-1A/<NUM>-2A pairing of DWGs handles a first radio-carrier-signal polarization, such as horizontal polarization, and the <NUM>-1B/<NUM>-2B pairing of DWGs handles a second radio-carrier-signal polarization, such as vertical polarization. With TDD operation, only one DWG on either side of the APU <NUM> is needed per polarization.

Assuming that SIDE <NUM> is the upstream side of the APU <NUM>, in downlink (DL) operation, also referred to as outbound operation, the DWGs <NUM>-1A and <NUM>-1B carry corresponding outbound radio carrier signals of "A" and "B" polarization, originated from the CPU <NUM> and propagated in the chain <NUM> towards the APU <NUM>. If the APU <NUM> is operating as a relay station, its DWG interface <NUM> couples these outbound radio signals over to SIDE <NUM> of the APU <NUM>, into the DWGs <NUM>-2A and <NUM>-2B, for the next APU <NUM> in the chain <NUM>. Conversely, in base-station or transceiver mode, the DWG interface <NUM> of the APU <NUM> couples the outbound radio carrier signals incoming on DWGs <NUM>-1A and <NUM>-1B into the antenna circuitry <NUM>, for OTA transmission from the antenna array <NUM> (the A and B antenna matrixes in <FIG>).

Assuming, again, that SIDE <NUM> is the upstream side of the APU <NUM>, in uplink (UL) operation, also referred to as inbound operation, relay-station operation of the APU <NUM> involves the APU <NUM> receiving inbound radio carrier signals on its downstream side (SIDE <NUM>), i.e., on the DWGs <NUM>-2A and <NUM>-2B, where these signals were received via OTA reception by another APU <NUM> that is downstream in the chain <NUM>. The APU <NUM> couples these inbound signals into the SIDE-<NUM> DWGs <NUM>-1A and <NUM>-1B, for propagation towards the CPU <NUM>. For base-station mode UL operation, the APU <NUM> receives an UL radio carrier signal from a UE <NUM> and couples it into its SIDE <NUM> DWG interface, for propagation towards the CPU <NUM> as an inbound radio carrier signal.

Another point worth emphasizing is that the A/B segregations shown in <FIG> aid discussion, but they are not meant to suggest limitations on how an APU <NUM> may be implemented with respect to multiple polarizations. At least some aspects may be integrated.

Other example elements illustrated in the APU <NUM> of <FIG> include a signaling interface <NUM> of the control circuitry <NUM>, which may include two respective control interfaces <NUM>, with the interface <NUM>-<NUM> for control-signaling connectivity on the upstream side of the APU <NUM> and the interface <NUM>-<NUM> for control-signaling connectivity on the downstream side of the APU <NUM>. For example, the CPU <NUM> generates control signaling to control the APUs <NUM> included in a chain <NUM>, such as TDD-related control signaling that determines the relay-station and base-station operations of individual APUs <NUM> in the chain <NUM>. Such signaling may flow via serial control-signaling links between the CPU <NUM> and the successive APUs <NUM> in the chain <NUM>, with the APU <NUM> closest to the CPU <NUM> receiving control signaling directly from the CPU <NUM> and passing all or some of it along to the next APU <NUM>, and so on.

To this end, the control circuitry <NUM> in one or more embodiments comprises one or more microprocessors, Digital Signal Processors (DSPs), Field Programmable Gate Arrays (FPGAs), or Application Specific Integrated Circuits (ASICs), or any mix thereof. The control circuitry <NUM> may include or be associated with memory or other computer-readable media, and may operate according to the execution of stored computer program instructions.

In at least one embodiment, the DWGs <NUM> comprising the DWG links <NUM> have a conductive exterior <NUM> that provides an electrical connection for exchanging control signaling between the CPU <NUM> and the adjacent APU <NUM>, and between adjacent APUs <NUM>. The conductive exterior <NUM> comprises, for example a metallic coating or a conductive sheathing. In other embodiments, dedicated wired connections independent of the DWG links <NUM> electrically interconnects the CPU <NUM> and the APUs <NUM>. In either case, the control signaling includes, for example, TDD control signaling and mode control signaling, according to which the CPU <NUM> determines which APUs <NUM> transmit or receive OTA radio carrier signals at what times. Thus, the control signaling provides for operation of the APUs <NUM> as a distributed antenna system, where the CPU <NUM> schedules the transmission and/or reception of user traffic from respective UEs <NUM> served by the chain <NUM>, via respective ones of the APUs <NUM> in the chain <NUM>.

Each APU <NUM> may also include or be associated with a power management unit (PMU) <NUM>. The PMU <NUM> provides operating power for the antenna circuitry <NUM>, the DWG interface <NUM>, and the control circuitry <NUM>, for example. In at least some embodiments, the PMU <NUM> is controllable by the CPU <NUM> via the control signaling. In addition to the conductive exteriors <NUM> of the DWGs in the DWG links <NUM> carrying the control signaling, the conductive exteriors <NUM> also may be used to supply operating power, e.g. DC voltage down the chain <NUM> of APUs <NUM>.

In a Power-over-Ethernet (POE) example, a <NUM> volt direct-current (VDC) power signal is carried via the conductive coatings <NUM> included in the respective DWG links <NUM>. However, lower operating voltages may be used, e.g., to facilitate full monolithic integration of the circuitry comprising each APU <NUM>. To some extent, the voltage drops incurred on the successive interconnections used to carry the control signaling down the chain <NUM> of APUs <NUM> may dictate the voltage level of the DC power signal and the PMU <NUM> of each APU <NUM> may include DC/DC converters, as needed, to provide the particular operating voltages needed within the APU <NUM>.

While carrying the control signaling over the power feed may be advantageous in terms of reduced complexity and parts count, the arrangement should be understood as a non-limiting example for the control-signaling interconnections. More broadly, the control signaling arrangement may be implemented as a parallel, low-frequency serial peripheral interface (SPI), with the CPU <NUM> outputting control signaling for respective ones of the APUs <NUM> via the SPI.

Each APU <NUM> has, for example, a unique identifier that allows the CPU <NUM> to identify which APU <NUM> is targeted by particular control signaling. Application Specific Integrated Circuits (ASICs) or other integrated circuitry used within each APU <NUM> may, for example, be fused with a unique identifier that fixes the APU's identity. Dynamic or configurable identities also may be used in one or more embodiments. An APU <NUM> that receives control signaling not targeted to it would pass it along the next control-signaling hop in the chain <NUM>, in the downstream direction. Likewise, upstream control signaling would pass from APU <NUM> to APU <NUM> in the chain <NUM>, as needed, to reach the CPU <NUM>.

As noted, the CPU <NUM> uses the control signaling to, among other things, control the state of each APU <NUM> in the chain <NUM>. Here, the possible states may be relay mode, base-station mode, and standby mode, as set under control of the CPU <NUM>.

<FIG> illustrates an example arrangement for the CPU <NUM> in one or more embodiments. The CPU <NUM> includes DWG interfaces <NUM>, including receiving and transmitting circuitry <NUM> and <NUM>, for coupling into the DWGs that comprise its DWG link <NUM> into the first APU <NUM> of a chain <NUM> of APUs <NUM> controlled by the CPU <NUM>. In at least one embodiment, the DWG interface(s) <NUM> of the CPU <NUM> use antennas <NUM> to transmit outbound radio carrier signals into the associated DWG link <NUM> and to receive inbound radio carrier signals from the associated DWG link <NUM>. The antennas <NUM> may be placed for lateral feeding into the associated DWG link <NUM>, and the same arrangement may be implemented in each of the APUs <NUM>, for coupling with their respective upstream and downstream DWG links <NUM>.

The CPU <NUM> also includes processing circuitry <NUM>, including baseband radio processing circuitry <NUM> for baseband processing of outbound and inbound signals corresponding to the outbound and inbound radio carrier signals. The CPU <NUM> further includes control circuitry <NUM> configured for controlling operation of the CPU <NUM> and for controlling one or more chains <NUM> of APUs <NUM> that are coupled to the CPU <NUM>. To that end, the control circuitry <NUM> is associated with one or more control-signaling interfaces, e.g., SPI circuitry. The control circuitry <NUM> or the processing circuitry <NUM> at large also may be associated with one or more network interfaces <NUM>, e.g., that support backhaul connections for carrying user traffic and related network-control signaling between the CPU <NUM> and one or more supporting nodes in the CN <NUM>.

The processing circuitry <NUM> in one or more embodiments includes or is associated with storage <NUM>, e.g., for storing configuration data <NUM> associated with the operation of the CPU <NUM> and/or one or more computer programs ("CP" in the diagram) <NUM> comprising computer program instructions, the execution of which by one or more microprocessors or other types of digital processors configure such processors as said processing circuitry <NUM>. That is, the processing circuitry <NUM> may be fixed circuitry or programmed circuitry and, in at least one embodiment, the processing circuitry <NUM> is at least partly realized by one or more microprocessors being specially adapted according to their execution of computer program instructions stored in the storage <NUM>. These computer program instructions, whether stored in storage <NUM> or stored or communicated elsewhere, may be understood as constituting a computer program product. Such computer program products are in themselves embodiments of the presently disclosed invention.

Correspondingly, the storage <NUM> provides for at least temporary storage of the computer program(s) <NUM> and also may provide working memory for program execution. Broadly, the storage <NUM> comprises one or more types of computer-readable media, with non-limiting examples including any one or more of SRAM, DRAM, NVRAM, FLASH, EEPROM, and Solid State Disk (SSD).

The CPU <NUM> also includes radiofrequency receive (RX) circuitry <NUM> and transmit (TX) circuitry <NUM> that is associated with the baseband radio processing circuitry <NUM> and with the DWG interfaces <NUM>. In cooperation with the baseband radio processing circuitry <NUM>, the CPU <NUM> uses the TX circuitry <NUM> to generate outbound radio carrier signals for output via the DWG interface(s) <NUM>. Likewise, the CPU <NUM> uses the RX circuitry <NUM> to process inbound radio carrier signals received via the DWG interface(s) <NUM>. In this regard, the CPU <NUM> can be understood as providing all modulation and frequency up-conversion processing for outbound radio carrier signals conveyed in the chain <NUM> of APUs <NUM>, and providing all demodulation and frequency down-conversion processing for inbound radio carrier signals conveyed in the chain <NUM> of APUs <NUM>.

<FIG> is a block diagram illustrating more details of part A of APU <NUM>. Again, it should be understood that example APU <NUM> may comprise a substantially identical part B, which supports a different antenna polarization. <FIG> focuses on an example implementation of the DWG interface <NUM> and the antenna circuitry <NUM>. The antenna circuitry <NUM> includes first radiofrequency circuitry <NUM> and the DWG interface <NUM> includes second radiofrequency circuitry <NUM>.

In an example case, the antenna array <NUM> includes sixteen antenna elements for transmission and/or reception beamforming, and the first radiofrequency circuitry <NUM> includes a corresponding block of radiofrequency circuitry per antenna element of the antenna array <NUM>. Each block includes a switch <NUM>, a power amplifier (PA) <NUM>, a low noise amplifier (LNA) <NUM>, a switch <NUM>, a beamforming circuit element <NUM>, and a splitter/combiner (S/C) <NUM>.

The second radiofrequency circuitry <NUM> comprises respective DWG coupling circuits <NUM>-<NUM> and <NUM>-<NUM>. Each DWG coupling circuit <NUM> provides for transmit/receive coupling via an associated antenna <NUM> into a DWG <NUM>. To the extent that the APU <NUM> supports more than one DWG <NUM> per DWG link <NUM>, it will have a DWG coupling circuit <NUM> per DWG <NUM>. Going back momentarily to <FIG>, the depicted APU <NUM> would include two DWG coupling circuits <NUM> on SIDE <NUM>, one for the SIDE-<NUM> A connection and one for the SIDE-<NUM> B connection, and two DWG coupling circuits <NUM> on SIDE <NUM>, one for the SIDE-<NUM> A connection and one for the SIDE-<NUM> B connection.

Further, as seen in <FIG>, each DWG coupling circuit <NUM> on one side of the APU <NUM> is paired with-coupled to-a corresponding DWG coupling circuit <NUM> on the other side of the APU <NUM>. That is, each DWG coupling circuit <NUM> on the upstream side of the APU <NUM> has a corresponding DWG coupling circuit <NUM> on the downstream side of the APU <NUM>. These complementary pairings, the upstream/downstream pairings, provide for the coupling of radio carrier signals from an upstream DWG <NUM> into a corresponding downstream DWG <NUM>-i.e., next-hop conveyance. In the diagram, transfer circuitry <NUM> provides such coupling between the DWG coupling circuit <NUM>-<NUM> and the DWG coupling circuit <NUM>-<NUM>.

For relay operation of an outbound radio signal and assuming that SIDE <NUM> is the upstream side of the APU <NUM> and that SIDE <NUM> is the downstream side, an outbound radio carrier signal appears on the DWG <NUM>-<NUM> and the switch <NUM> of the DWG coupling circuit <NUM>-<NUM> (upstream coupler) is set for receiving, such that the outbound radio carrier signal radiates from the upstream DWG <NUM>-<NUM> and is coupled to the input of the LNA <NUM> of the upstream coupler. The LNA <NUM> of the upstream coupler outputs the outbound radio carrier signal with amplification and applies it to an S/C <NUM> of the transfer circuitry. In turn, the S/C <NUM> applies the outbound radio carrier signal to the input of a PA <NUM> of the DWG coupling circuit <NUM>-<NUM> (downstream coupler). The PA <NUM> outputs the outbound radio carrier signal with power amplification, and a switch <NUM> of the downstream coupler is set for transmission, meaning that the outbound radio carrier signal is launched via the antenna <NUM> of the downstream coupler into the downstream DWG <NUM>-<NUM>.

For relay operation of an inbound radio signal and assuming that SIDE <NUM> is the upstream side of the APU <NUM> and that SIDE <NUM> is the downstream side, an inbound radio carrier signal appears on the DWG <NUM>-<NUM> and the switch <NUM> of the downstream coupler is set for receiving, such that the inbound radio carrier signal radiates from the downstream DWG <NUM>-<NUM> and is coupled to the input of the LNA <NUM> of the downstream coupler. The LNA <NUM> of the downstream coupler outputs the inbound radio carrier signal with amplification and applies it to an S/C <NUM>. In turn, the S/C <NUM> applies the outbound radio carrier signal to the input of a PA <NUM> of the upstream coupler. The PA <NUM> of the upstream coupler outputs the inbound radio carrier signal with power amplification, and the switch <NUM> of the upstream coupler is set for transmission, meaning that the inbound radio carrier signal is launched via the antenna <NUM> of the upstream coupler into the upstream DWG <NUM>-<NUM>.

For base-station operation with respect to an outbound radio carrier signal received at the APU <NUM> via the upstream coupler, the S/C <NUM> applies outbound radio carrier signal to a SW <NUM> that couples it into an S/C <NUM> of the antenna circuitry <NUM>. The S/C <NUM> and S/Cs <NUM> split/distribute the outbound radio signal into the respective per-antenna blocks. In embodiments where the APU <NUM> performs transmit beamforming, the split radio carrier signal into each of the antenna blocks is weighted by the beamforming element <NUM> and the switches <NUM> and <NUM> are set for transmission, meaning that the split and weighted radio carrier signal passes to the input of the PA <NUM>, for power amplification and OTA transmission from the associated antenna element.

For base-station operation with respect to an OTA radio carrier signal received at the APU <NUM> via its antenna array <NUM>, the switches <NUM> and <NUM> of each antenna block are set for receive, meaning that an antenna-received radio carrier signal appears at the input of the LNA <NUM> in each block, which provides low-noise amplification for the antenna-received radio carrier signal and applies it to the beamforming element <NUM>. In embodiments of the APU <NUM> that perform receive beamforming, the beamforming element <NUM> applies a weighting to the radio carrier signal output from the LNA <NUM> and provides it to a respective one of the S/Cs <NUM>, which combine the radio carrier signals incoming from each of the antenna blocks. Correspondingly, the S/C <NUM> forms a combined radio carrier signal, e.g., a combination of the weighted radio carrier signals output from the respective beamforming elements <NUM> of the antenna blocks and couples the combined radio carrier signal into the switch <NUM>, which is set for inbound base-station operation and, therefore, couples it into the S/C <NUM>.

In turn, the S/C <NUM> couples the combined radio carrier signal to the PA <NUM> of the upstream coupler, which provides power amplification for it and applies it to the switch <NUM> of the upstream coupler. The switch <NUM> is configured for transmission, meaning that the combined radio carrier signal from the PA <NUM> of the upstream coupler is launched into the upstream DWG <NUM>-<NUM>, as an inbound radio carrier signal, for propagation in the chain <NUM> towards the CPU <NUM>.

It will be understood that the selective operation of the SWs <NUM>, <NUM>, <NUM>, and <NUM>, as well as other modally-controlled elements of the first and second radiofrequency circuitry <NUM> and <NUM> of the APU <NUM> are controlled within the APU <NUM> by the control circuitry <NUM> of the APU <NUM>, in dependence on the operational state of the APU <NUM>. In turn, the control circuitry <NUM> of the APU <NUM> controls the operational state of the APU <NUM> in dependence on the control signaling targeted to it by the CPU <NUM>. In this respect, the various SWs and S/Cs within the radio frequency circuitry <NUM> and <NUM> can be considered as part of the control circuitry <NUM>.

Similarly, the beamforming solutions used by the APU <NUM> for transmit and/or receive antenna beamforming-i.e., the dynamically configured sets of antenna weights collectively applied by the beamforming elements <NUM> of the antenna blocks-may be determined by the CPU <NUM> and conveyed to the APU <NUM> via the control signaling. As such, the control circuitry <NUM> of the APU <NUM> includes or interfaces to the beamforming elements <NUM>, to set the per-antenna weights applied to the radio carrier signals incoming from the antenna array <NUM> or outgoing to the antenna array <NUM>.

As seen in <FIG>, the same or similar RF-circuit building blocks are used to implement the antenna circuitry <NUM> and the DWG interface <NUM>. Notably, the elimination of frequency-conversion blocks and mixed-mode circuits from the radio-carrier-signal paths within the APU <NUM> relaxes the requirements on the integrated-circuit process choices available for implementation of these parts of the APU <NUM>. As a further advantage, the absence of filters from the radio-carrier-signal paths within the APUS <NUM> enables full monolithic integration of the circuit elements comprising the antenna circuitry <NUM> and the DWG interface <NUM>.

In a dielectric-waveguide-based distributed wireless system as described above, in sending the modulated RF signal across the waveguide, the CPU is generally limited to sending only one signal at a time in each waveguide. This problem could partly be mitigated by using parallel waveguides, but this makes the system more bulky and costly. In normal operation, then, the distributed wireless system is operated in such a way that only one APU is active at a time, preferably the one having the lowest pathloss to the UE(s) involved in the communication.

In a <NUM> network, when a UE wants to attach to the network, it starts by looking for a synchronization signal block (SSB). The SSB blocks indicates cell timing and when the UE can do a random-access attempt. In a <NUM> system employing NR FR2 (frequency range <NUM>), the UE has beamforming and multiple antenna panels to choose between. The UE uses the SSB to find its optimum antenna panel and the beamforming related to that panel. If an SSB originates from multiple APUs, signals from multiple APUs and reflections reach the UE, which might choose a non-optimal panel and beamforming direction. The UE will then use this direction for random access.

Likewise, the distributed base station consisting of several APUs as described above will look for the random access message transmitted by the UE and select the APU(s) with best signal strength. If the UE has selected a non-optimum panel/beam direction, this will cause the system to use a non-optimum APU for communication, resulting in both degraded UE link performance and overall worse system performance.

In many cases the APU also have beamforming, to improve the link budget. Thus, there is a need to identify the APU and, if applicable, the beam of this APU having the lowest path loss to a UE who want to access the network. Similarly, the UE should select its best panel and beam. The use of the same SSB for multiple APUs, however, may make it difficult to find the best APUs and beams for communication.

A feature in NR is to use beams to divide the cell and thus improve coverage and throughput. For initial access, the beams are identified by using unique SSB index. According to several of the techniques described herein, physically separated APUs are grouped, and the NR beam feature is reused by providing unique SSBs to each group. By grouping the APUs in a manner such that the members of a given group are separated from one another by relatively large distances, compared to the typical link distance, the UE can more readily find the APU which provides the UE with the lowest path loss and direct its random access attempt towards that APU.

To further improve the link budget, beamforming can be applied in each APU. Initial access can then be made using wide beams, with a beam refinement procedure subsequently applied, where closed-loop feedback from the UE is used to find the best beam. In some embodiments of the techniques and systems described herein, the SSB index may be used to also identify the optimal beam during initial access. Note that utilizing this approach may implicate a tradeoff between system capacity, which is increased by the use of narrower and/or more optimally directed beams, and access delay.

Another feature in NR is carrier aggregation. Wide carriers can be built by aggregating multiple narrower carriers. One of them is the primary component carrier and the rest are secondary component carriers. By designating a different carrier among a given group of carriers as the primary component carrier in each of several different APU stripes, another degree of freedom to identify each APU becomes available.

The techniques and systems described herein are discussed in terms of NR and FR2. It is foreseen, however, that similar systems may be implemented also at higher frequencies, where the same techniques may be used.

<FIG> illustrates the concept of a SSB burst set, which is used in NR to facilitate beam sweeping so that beamforming gain can be achieved during the initial UE access. In normal NR operation, the SSB is sent in different directions during the first <NUM> milliseconds of the burst set. Then a UE who wishes to access the network makes a random-access attempt at a time indicated in each SSB. Thus, the time of the UE random access attempt indicates which direction is most favorable for the UE.

<FIG> shows portions of an example signaling during one SSB period of <NUM>. Here, twelve SSBs, numbered SSB3-SSB7 and SSB10-SSB15 are used in the SSB burst set, and are transmitted in slots <NUM>-<NUM> and slots <NUM>-<NUM>. In the figure, the SSBs transmitted in slots <NUM>-<NUM> are shown. The corresponding slots for random access attempts are slots <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> - in <FIG>, slot <NUM>, which is used for random access attempts corresponding to SSB2 and SSB, is shown. The remaining slots in the <NUM>-slot structure may be allocated to control channel signaling, uplink and downlink shared channels, and reference signals.

In normal NR operation, beamforming is used by the base station both when sending SSBs and listening for a random access (RA). As can be seen in <FIG>, there is some system capacity loss due to the SSB and random access operations; in the illustrated example, twelve slots are dedicated to SSB transmissions and for corresponding random access attempts. Thus, generally it is desirable to minimize the number of unique SSBs.

According to several of the techniques described herein, the NR SSB burst set concept is reused, but adapted for use in grouping the APUs, such that the APUs in a given group use the same SSB, but a different SSB is used for each group. If the groups are formed so that the APUs within a given group (and thus using the same SSB) are physically separated, e.g., by as much as possible given the overall system layout, this provides a way of identifying the APU having the lowest path loss to a UE.

For example, in a system like the one illustrated in <FIG>, the APU closest to the CPU on the left-hand stripe might be grouped with the most remote APU on the right-hand stripe, with the next closest APU on the left-handed stripe grouped with the second most remote APU on the right-hand stripe, and so on. Since the SSBs are sent consecutively and the random access attempts are made consecutively, this allocation of SSBs can be done in such a way that there is only one active APU on a stripe, for a given SSB transmission.

Another way to assist in identifying the best APU or APUs to use in serving a given UE is to reuse the NR CA concept. <FIG> shows the CA concept in frequency domain. In carrier aggregation, a wide carrier is built out of multiple narrower component carriers (CCs). One is the primary component carrier (PCC) and is used for initial access and signaling. Secondary component carriers (SCCs) are then added when the capacity of the PCC is insufficient. The idea here is to split the available bandwidth used in a distributed wireless system like those described above into multiple CCs. Then each of the APUs within a given group (which may be using the same SSB), can use a different CC as the PCC. In this way we have yet another degree of freedom in distinguishing between and identifying APUs. In addition, the control signaling is spread more evenly across the frequency domain, enabling more system capacity.

<FIG> may be used to illustrate an example where both SSBs and primary component carriers are used to distinguish between APUs. The example deployment illustrated there has APUs deployed on a grid, with a distance of <NUM> meters between each APU, in both directions of the two-dimensional grid. As an example, each APU on a given stripe may be assigned to a different SSB group, corresponding to different SSB identifiers. Thus, for example, the furthest APU from the CPU on each stripe might be assigned to use a first SSB, the next furthest APU assigned to use a second SSB, and so on. As another example, the ordering might be reversed when moving from one stripe to the next, to increase the minimum distance between two APUs having the same SSB. In addition, multiple component carriers might be used, with a different PCC used among neighboring stripes. Thus, for example, the operating bandwidth might be divided into five component carrier bands, with the left-most stripe being assigned the lowest-frequency component carrier as the PCC, the next stripe using the next lowest-frequency component carrier as the PCC, and so on, with this pattern being repeated until all stripes are assigned a PCC.

If every APU on a given stripe is assigned to a different SSB groups, there will be <NUM> SSB groups, with <NUM> members in each group. Each group will have two members assigned to each of the five component carriers, for use as a PCC. Thus, there <NUM> combinations of SSB and PCC, with only two members assigned to each combination. In the illustrated example, these assignments can easily be made in such a way that the members in each of these pairs are separated from one another by at least <NUM> meters. Thus, a UE listening for each of the SSBs on each of the component carriers is likely to observe a considerably stronger strength from one of the APUs in a given pair than from the other. Likewise, one APU in any given pair is likely to observe a much greater signal strength than the other when receiving a random access attempt in a corresponding random access opportunity. The chance of misidentifying the best APU or APUs for maintaining a link with the UE is greatly reduced.

Still another technique that may be used in some embodiments of the presently disclosed techniques and systems is to use the relationship between NR SSB and channel state information reference signal (CSI-RS) set to identify a suitable APU/beam pair for every UE. According to this approach, the UE first selects the beamforming direction according to its reception of an SSB, and then triggers the random access procedure. If this random access is successful, the BS will select one beam from one of the APUs to serve this UE. This beam might not be the optimum beam. But, after having the selected beam from the selected APU after the random access procedure, the UE can continuously do measurements, at the direction of the base station. Since there will be several active APUs in one cell, the SSB and non-zero-power (NZP) CSI-RS mapping could let the base station identify the APU and the best beam of that APU, according to UE measurement report. According to 3GPP TS <NUM>, V15. <NUM>, there are a maximum <NUM> NZP CSI-RS resources, and maximum <NUM> NZP CSI-RS resources per cell. There are a maximum <NUM> CSI-RS configurations. In addition, there are a maximum of <NUM> NZP CSI-RS resource sets and a maximum of <NUM> NZP CSI-RS resources per CSI-RS resource configuration. For each CSI-RS resource set, there are a maximum of <NUM> NZP CSI-RS resources, a maximum of <NUM> NZP CSI-RS resources per resource set and a maximum of <NUM> NZP CSI-RS resources per cell. Finally, there are a maximum of <NUM> CSI SSB resource sets per resource configuration. The information element associatedSSB in Radio Resource Control (RRC) signaling can be used for SSB and CSI mapping.

<FIG> is a process flow diagram illustrating an example method according to several of the techniques described above. The illustrated method is performed by a controlling node of a distributed wireless system that comprises the controlling node and two or more antenna processing nodes communicatively coupled to the controlling node but spatially separated from each other and from the controlling node. The method comprises, as shown at block <NUM>, the step of controlling a first subset of the antenna processing nodes to transmit synchronization signal blocks (SSBs) having a first SSB identifier, the first subset including one or more of the antenna processing nodes. As shown at block <NUM>, the controlling node controls a second subset of the antenna processing nodes to transmit SSBs having a second SSB identifier, the second subset including one or more of the antenna processing nodes and being disjoint with the first subset. It will be appreciated that this technique can be extended to accommodate a third, fourth, and additional subsets of antenna processing nodes and corresponding SSB identifiers, in various deployments. Thus, a method like the one shown in <FIG> may further comprise controlling one or more additional disjoint subsets of the antenna processing nodes to transmit SSBs having respective additional SSB identifiers.

Each subset (referred to as a "group" in the description of several detailed examples above) may include one, two, several, or many antenna processing nodes. As was also discussed above, the allocation of antenna processing nodes into these subsets, or groups, may be done in such a way to maximize, to the greatest extent possible or practical, the minimum distance between any two members of the same subset.

In some embodiments, the distributed wireless system is a dielectric-waveguide-based system as was described in detail above. In these embodiments, controlling the antenna processing nodes to transmit the SSBs as shown in blocks <NUM> and <NUM> may comprise including the SSBs in radio signals sent to the respective antenna processing nodes via one or more dielectric waveguides, for transmission by the respective antenna processing nodes. The respective antenna processing nodes may be instructed when to transmit using control signaling sent separately to the APUs, e.g., via the control signaling mechanisms and techniques described above in connection with <FIG>. In these embodiments where the SSBs are included in radio signals sent to the antenna processing nodes via the waveguides, the the SSBs having the first SSB identifier are and the SSBs having the second identifier are time-multiplexed in the radio signals within an SSB burst period, e.g., as in the example shown in <FIG>.

The method illustrated in <FIG> is not necessarily limited to systems utilizing dielectric waveguides. Systems using digital serial links to interconnect the controlling node and the antenna processing nodes might also benefit from some or all of the techniques described herein. In a system employing digital serial links instead of dielectric waveguides, controlling the various antenna processing to send the appropriate SSB identifiers (in the corresponding appropriate time slots) may comprise including the SSB identifiers in digital baseband information sent to the antenna processing nodes, in some embodiments. In others, controlling the antenna processing nodes to send the appropriate SSB identifiers might instead include configuring the antenna processing nodes with SSB identifier information, via a control channel sent over the digital serial links, with the antenna processing nodes inserting their respective SSB identifiers into appropriate parts of the signal waveforms generated and transmitted by the antenna processing nodes.

In some embodiments of the method illustrated generally in <FIG>, the first subset and the second subset each include two or more antenna processing nodes, and the technique described above for distinguishing between antenna processing nodes by the primary component carrier (PCC) they use is employed. In some of these embodiments, then, controlling the first subset of the antenna processing nodes to transmit SSBs having the first SSB identifier comprises controlling each member of the first subset to transmit the SSBs having the first SSB identifier on a different component carrier than all other members of the first subset, and controlling the second subset of the antenna processing nodes to transmit SSBs having the second SSB identifier comprises controlling each member of the second subset to transmit the SSBs having the second SSB identifier on a different component carrier than all other members of the second subset. This component carrier on which a given SSB is transmitted may be considered the PCC for that antenna processing. More generally, the antenna processing nodes can be controlled in such a way that the members of a given subset (transmitting SSBs with the same identifier) are assigned to use different component carriers for the PCC to the extent possible. Thus, for example, a subset having ten antenna processing nodes may be controlled in such a way that two members of the subset are assigned to each of five component carriers, for use as the PCC.

The method shown in <FIG> is for facilitating the selection by the system of the best antenna processing node (or nodes) to serve a given wireless device, or UE. In some embodiments or instances, then, the method further comprises, as shown at block <NUM>, the step of receiving, via one or more of the antenna processing nodes, a random access request from a wireless device. The method still further comprises, in these embodiments or instances, the step of selecting an antenna processing node for one or more subsequent transmissions by mapping a timeslot in which the random access request was transmitted to an SSB identifier, identifying at least one antenna processing node transmitting SSBs with that SSB identifier, and selecting the antenna processing node for subsequent transmissions from among the identified at least one antenna processing node. This is shown at block <NUM>. In some instances, more than one antenna processing node transmitting SSBs with that SSB identifier may be identifier, in which case selecting the antenna processing node for one or more subsequent transmissions may comprise selecting the "best" antenna processing node, e.g., selecting the one that observed the highest signal strength for the random access request.

In some of these embodiments, the method further comprises identifying which component carrier was used by the wireless device to transmit the random access request, as shown at block <NUM>. In these embodiments, selecting the antenna processing node for one or more subsequent transmissions from among the identified at least one antenna processing nodes comprises selecting an antenna processing node that transmitted SSBs on the identified component carrier. In many instances, this may narrow the antenna processing nodes down to a single identified antenna processing, or to just a few, among which the one observing the best signal strength for the random access request might be selected.

Claim 1:
A method, in a controlling node of a distributed wireless system that comprises the controlling node and two or more antenna processing nodes communicatively coupled to the controlling node but spatially separated from each other and from the controlling node, the method comprising:
controlling (<NUM>) a first subset of the antenna processing nodes to transmit synchronization signal blocks, SSBs, having a first SSB identifier, the first subset including one or more of the antenna processing nodes;
controlling (<NUM>) a second subset of the antenna processing nodes to transmit SSBs having a second SSB identifier, the second subset including one or more of the antenna processing nodes and being disjoint with the first subset,
characterized in that the method further comprises:
receiving (<NUM>), via one or more of the antenna processing nodes, a random access request from a wireless device; and
selecting (<NUM>) an antenna processing node for one or more subsequent transmissions by mapping a timeslot in which the random access request was transmitted to an SSB identifier, identifying at least one antenna processing node transmitting SSBs with that SSB identifier, and selecting the antenna processing node for subsequent transmissions from among the identified at least one antenna processing node.