Patent Publication Number: US-2023155742-A1

Title: Hybrid Automatic Repeat Request (ARQ) with Spatial Diversity

Description:
The present disclosure generally relates to wireless systems in which a central processing unit for a base station is coupled to a series of spatially separated transmitting and receiving antenna points via serial interfaces. The present disclosure relates more particularly to handling retransmissions in such wireless systems. 
     BACKGROUND 
     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.  1    provides a conceptual view of a cell-free massive MIMO deployment, comprising a CPU  20  connected to several APUs  22 , via serial links  10 . As seen in the figure, each of several user equipments (UEs)  115  may be surrounded by one or several serving APUs  22 , all of which may be attached to the same CPU  20 , which is responsible for processing the data received from and transmitted by each APU. Each UE  115  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.  FIGS.  2  and  3    provide other views of example deployments of distributed wireless systems. In this scenario shown in  FIG.  2   , multiple APUs  22  are deployed around the perimeter of a room, which might be a manufacturing floor or a conference room, for example. Each APU  22  is connected to the CPU  20  via a “strip,” or “stripe.” More particularly, the CPU  20  in this example deployment is connected to two such stripes, each stripe comprising a serial concatenation of several ( 10 , in the illustrated example) APUs  22 .  FIG.  3    shows an two-dimensional model of a factory floor with densely populated APUs  22  connected to the CPU  20  via several such “stripes” As a general matter, the CPU  20  can target a UE anywhere in the room by controlling one or several APUs  22  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 10 meters, in both x- and y-directions, which means that a UE is never more than about 7 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  FIGS.  1 - 3    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 (5G) wireless networks. 
     Another requirement of 5G 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. 
     In conventional wireless systems, if a transmission from a base station to a wireless device cannot be decoded by the wireless device, the problem is typically resolved by the wireless device asking the base station to transmit the information again, e.g., by sending a negative acknowledgement (NACK) to the base station. The retransmission by the base station can be done with new coding, or with the same coding used for the first transmission. However, this conventional approach may not be optimal for distributed wireless systems as generally described above. 
     SUMMARY 
     The present disclosure describes techniques for reducing the need for retransmissions by a wireless device when operating in a distributed wireless system like those generally described above. 
     An example method, according to some embodiments, is carried out 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. This example method comprises sending a first command to a first one of the two or more antenna processing nodes, the first command instructing the first one of the two or more antenna processing nodes to transmit first data to a wireless device, and, responsive to determining that the wireless device has not successfully decoded the first data, sending a second command to a second one of the two or more antenna processing nodes, the second command instructing the second one of the two or more antenna processing nodes to transmit the first data to the wireless device. If the wireless device remains unable to decode the first information, the controlling node may send an instruction to one or more additional antenna processing nodes to transmit the first data to the wireless device, in some embodiments. 
     Another example method, according to some embodiments, is carried out in an antenna processing node of a distributed wireless system that comprises a controlling node, the antenna processing node, and one or more additional antenna processing nodes, where each of the antenna processing nodes are communicatively coupled to the controlling node but are spatially separated from each other and from the controlling node. This example method comprises receiving, from the controlling node, information corresponding to first data for transmission to a wireless device in a first interval, and storing the information corresponding to the first data, without transmitting it to the wireless device in the first interval. This method further comprises receiving, after the first interval has passed, a command instructing the antenna processing node to transmit the first data to the wireless device in a second interval, and transmitting the first data to the wireless device in the second interval. 
     Another example method, according to some embodiments, is also carried out in an antenna processing node of a distributed wireless system that comprises a controlling node, the antenna processing node, and one or more additional antenna processing nodes, where each of the antenna processing nodes are communicatively coupled to the controlling node but are spatially separated from each other and from the controlling node. This example method comprises receiving, from the controlling node, information corresponding to first data for transmission to a wireless device in a first interval, and storing the information corresponding to the first data, without transmitting it to the wireless device in the first interval. This method further comprises receiving, after the first interval has passed, signaling indicating that information corresponding to the first data may be discarded, and discarding the stored information corresponding to the first data, without transmitting it to the wireless device. 
     Details and variants of the methods summarized above are provided below. Further, controlling node apparatuses and antenna processing node apparatuses configured to carry out the methods summarized above and variants thereof are described in the detailed description below, and illustrated in the attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is an illustration of an example cell-free massive MIMO system. 
         FIG.  2    illustrates an example deployment of a distributed wireless system. 
         FIG.  3    illustrates another example deployment of a distributed wireless system. 
         FIG.  4    is a block diagram of an example antenna processing node, according to some embodiments. 
         FIG.  5    illustrates a simulation of a factory floor deployment of a distributed wireless system. 
         FIG.  6    is a process flow diagram illustrating an example technique, according to some embodiments. 
         FIG.  7    is a process flow diagram illustrating an example method carried out by a controlling node, according to some embodiments. 
         FIG.  8    is a process flow diagram of an example method carried out by an antenna processing node, according to some embodiments. 
         FIG.  9    is a process flow diagram of another example method carried out by an antenna processing node, according to some embodiments. 
         FIG.  10    is a block diagram of an example controlling node, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Another approach is to implement each link, or “hop,” along the stripes shown in  FIG.  2    as a dielectric waveguide that carries a high-frequency RF signal (e.g., a millimeter-wave signal). As a general matter, this term 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. 
     The techniques disclosed herein are described in the context of the first approach described above, i.e., in systems where a CPU is connected to multiple APUs via a series of serial links. However, these techniques are not necessarily limited to this approach. In such a system, communications along these serial links 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 data towards the CPU, via an upstream serial interface, along with any data that it receives from one or more APUs that are further downstream, via a downstream serial interface. This is seen in  FIG.  4   , which is a block diagram illustrating components of an example APU, here illustrated as antenna processing node  400 . As seen in the figure, the antenna processing node  400  also receives communications for itself and for downstream APUs from the CPU, via the upstream serial interface  432 , and forwards those communications intended for downstream APUs towards those APUs, via the downstream serial interface  434 . 
     The required capacity of the fronthaul network formed by these serial links is proportional to the number of simultaneous data streams that the APUs in the series can spatially multiplex, at maximum network load. The required capacity of the backhaul of the CPU (i.e., the CPUs connection towards the core network) is the sum of the data streams that the serial links connecting the APUs to the CPUs will transmit and receive at maximum network node. The most straightforward way to limit these capacity requirements is to constrain the number the number of UEs that can be served per APU and CPU. Put another way, the capacity of the distributed wireless system to serve UEs may be limited by the maximum capacities of the serial links between the APUs to the CPUs. 
     The use of serial interfaces as described above is generally a good match for downlink (DL) communications, i.e., communications from a base station to one or more UEs. Note that the terms “wireless device,” “user equipment,” and “UEs” are used herein to refer to any wireless devices served by the distributed wireless systems described here, including wireless devices that do not have a “user” as such but that are connected to machines. The serial interfaces described here work well for downlink communications because the same information may be sent to all of the APUs involved in any given transmission to a wireless device. This downlink information may be the bits or data blocks that must be transmitted by the APUs, with each APU involved in the transmission separately performing its own coding, modulation, upconversion, and transmission. There are other possibilities, however, such as the CPU sending to the APUs a time-domain digital representation of a modulated in-phase/quadrature (I/Q) signal, for upconversion and transmission, or the CPU sending to the APUs a frequency-domain digital representation of I/Q symbols, for OFDMA modulation, upconversion, and transmission by the APUs. In any of these cases, when the CPU sends this downlink information to two or more APUs in the chain, it need only send one copy, with each APU forwarding the information further downstream, as necessary. 
     Generally, it is desirable to keep the number of simultaneously active (i.e., transmitting) APUs as low as possible, to minimize power consumption and interference. Thus, while transmitting the same data to a wireless device from multiple APUs, e.g., using transmit diversity with different coding from each APU, could provide better signal coverage, it is desirable to minimize redundant transmissions. 
     In many deployments of distributed wireless systems, moreover, it will likely be the case that, the majority of the time, the signal received by a wireless device from at least one of the APUs alone is of sufficient quality (i.e., subjected to a sufficiently low path loss) that the DL data can be decoded by the wireless device without error. This is illustrated in  FIG.  5   , which shows a simulation of path loss from each of several APUs to a UE at each of the positions represented by dots at the lower portion of the left-hand part of the figure. The right-hand portion of the figure shows a probability density function for the path-gains of links from all APUs to all UE positions outlined, as well as a probability density function for the path-gain of the link from the best APU to each UE position. According to this simulation, selecting the APU with the lowest pathloss, which can be done by the CPU based on signal quality measurements reported to the CPU from the APUs, results in a nearly 100% probability that the pathloss from that APU to the wireless device is equal to the free space pathloss. 
     Of course, for applications where ultra-high reliability is necessary, “nearly 100% probability” is not enough. Further, the signal conditions between a UE and a given APU may change over time, e.g., when an object or person moves around the environment, blocking the signal from the APU, meaning that the most recently received signal quality reports may not always be accurate. This means that if the CPU controls only the “best” APU to transmit the data to the wireless device, the received signal may not always be of sufficient quality to yield a successful decoding by the wireless device of the downlink transmission, in which case the wireless device will transmit a NACK or fail to acknowledge the transmission. 
     In a conventional system, when a wireless device transmits a NACK, the transmitting base station can re-transmit the downlink data, one or more times. Various techniques whereby the wireless device combines information from the original transmission and one or more re-transmissions to improve the probability of a successful decoding are well known—these include so-called Chase combining, where the original transmission and re-transmission include the same information and the wireless device uses maximum-ratio combining (MRC) to improve the effective signal-to-noise ratio, and incremental redundancy, where each re-transmission is coded differently, in such a way that each re-transmission provides additional information to the receiver. 
     Just as in conventional systems, in a distributed wireless system like those described above it may sometimes be the case that an interfering object between a transmitting APU and the target wireless device causes a higher path loss or fading in the channel, such that a retransmission is requested by the targeted wireless device/machine. This interfering object or condition may be relatively slow-moving or slowly changing, such that retransmission from the same APU may experience similar conditions. While soft combining techniques like Chase combining or incremental redundancy may overcome these conditions, further improvements in a distributed wireless system may be gained by modifying conventional re-transmissions in such a way as to take advantage of spatial diversity. 
     In embodiments of the methods and apparatuses disclosed herein, then, an initial transmission to a wireless device is performed by an APU that has been identified as the best candidate for communication to the wireless device, e.g., according to signal-quality or quality-of-service (QoS) metrics maintained for each APU/wireless device combination. According to these embodiments, when the wireless device is unable to successfully decode a downlink and requests a retransmission, the CPU can request an APU having the second-best QoS metric to perform the retransmission. If the wireless device again requests a retransmission, the CPU can request the APU having the third-best QoS metric to perform the second retransmission. This can be repeated until the wireless device acknowledges that it has successfully decoded the transmission, or until the CPU decides to stop further retransmissions, e.g., after a predefined number of retransmissions have occurred, or when the next-best QoS metric is worse than the best QoS metric by a predetermined quantity, etc. At this point, the CPU may start over with the APU having the best QoS metric, in some embodiments. 
     A key benefit of this approach to re-transmissions is that each transmission from a new physical location will result in a new channel from the base station to the device/machine. This will result in a spatial diversity gain. Diversity gain is an efficient way to suppress block error rate (BLER) from slow fading channels, or avoid other fast changes in the radio channel. 
     As noted above, the APUs are connected in series, with each APU obtaining from its upstream serial interface the data it needs from the CPU and forwarding other information downstream to the next APU. Data for a given downlink transmission to a UE can be forwarded to and saved by all the APUs in the chain, in some embodiments, so that each APU already has the data it needs in the event that the APU is asked to perform a transmission or re-transmission to the wireless device. The re-transmission techniques described above thus do not require that the CPU re-send the downlink data on the downstream serial links for each re-transmission. Rather, it only needs to send a command instructing the appropriate APU or APUs to perform the re-transmission. Thus, the re-transmission techniques described here do not substantially increase the required capacity of the downstream serial links. 
     While these techniques require that each APU receive and buffer the downlink data for each downlink transmission, whether or not the APU ultimately transmits the data, the amount of buffering (and the corresponding buffer size) can be limited, since the data is scrapped after a successful decoding in the machine/device. 
       FIG.  6    is a process flow diagram illustrating an example method, according to the technique described in general terms above. The illustrated method begins with the CPU having an ordered list of measured signal quality or estimated path losses associated with a wireless device of interest. This list is shown at block  605 , where it is labeled a “QoS list” and where there is a signal quality (or path loss) value for each of N APUs. For the purposes of this discussion, it is assumed that the quantity associated with APU  1  represents the “best” quantity, in that it is the highest signal quality or the lowest estimated pathloss from among the APUs. In the figure, this best quantity is referred to as the “best QoS.” In the illustrated example, it is assumed that APU  2  has the second best QoS; APU  3  has the third best QoS, and so on. 
     As shown at block  610 , the actions taken begin with transmitting a downlink transmission to a wireless device from the APU with the best QoS. More specifically, the CPU may instruct the APU with the best QoS (as determined by the list maintained by the CPU) to transmit a block of data to the wireless device. In the illustrated example, this is APU  1 . This instruction may accompany or follow the transfer of the block of data or a corresponding representation of the transmission to APU  1 , via the chain of serial links interconnecting the CPU and the APUs. As noted above, the data corresponding to this downlink transmission may be received and stored by all of the APUs in the chain, whether or not they are ultimately instructed to perform the downlink transmission. 
     As shown at block  620 , the CPU next determines whether the wireless device has reported that it has successfully decoded the downlink transmission, e.g., by signaling an acknowledgement (ACK) or negative acknowledgement (NACK). If it has, the stored data corresponding to the downlink transmission may be cleared from each APU&#39;s buffers—this may be in response to an instruction from the CPU, in some embodiments. 
     If the wireless device did not successfully decode the first transmission, on the other hand, a retransmission is needed. As shown at block  630 , the CPU considers whether there are more qualified APUs in the QoS list that have not yet attempted the downlink transmission. In some embodiments or instances, this may be as simple as determining whether there is another next-best APU in the list. In others, this may involve evaluating the QoS associated with the APU having the next-best APU (in this case, APU  2 ) to determine whether the QoS meets some predetermined condition, e.g., being above a particular level, or being no more than a predetermined amount worse than the best QoS, or being among the APUs with the best N QoS parameters, where Nis a predetermined number. If there is another APU in the QoS list, the downlink transmission is performed by the APU having the best QoS among those APUs that have not yet been used for this downlink transmission, as shown at block  640 . Once again, this may be in done in response to an explicit instruction from the CPU. Notably, the CPU does not have to send the downlink data again, as it was previously stored by the APUs. 
     After the retransmission is performed, the procedure returns to block  620 , to determine whether this transmission is successfully decoded. Again, if it was, the APU&#39;s memory buffers are cleared, as shown at block  650 , and the procedure ends. In many cases, the wireless device&#39;s combining of the original transmission and the first re-transmission will produce an effective signal-to-noise-plus-distortion ratio (SNDR) that is high enough for a successful decoding of the downlink transmission. However, in some cases this second decoding attempt will also fail, e.g., when a momentary fade obscures the UE&#39;s signal from both the first and second best APUs. In this case, the steps sown at blocks  630 ,  640 , and  620  may repeat until there are no longer any more APUs (or qualified APUs) in the QoS list. At this point, as shown by the “No” path leading out of block  630 , the entire procedure may be repeated, starting with the APU having the best QoS. 
       FIG.  7    is a process flow diagram illustrating an example method according to the techniques described above, in this case focusing on the operations carried out 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. Again, here the terms “controlling node” and “antenna processing nodes” are used interchangeably with the terms “CPU” and “APU,” respectively. 
     The method illustrated in  FIG.  7    includes, as shown at block  720 , sending a first command to a first one of the two or more antenna processing nodes, the first command instructing the first one of the two or more antenna processing nodes to transmit first data to a wireless device. This may be preceded, in some embodiments, by selecting the first one of the two or more antenna processing nodes based on an estimated signal quality metric corresponding to the wireless device for each of the two or more antenna processing nodes, as shown at block  715 . This may comprise, for example, determining that the first one of the two or more antenna processing nodes has a best estimated signal quality metric corresponding to the wireless device, out of all of the antenna processing nodes. 
     As shown at block  730 , in response to a determination by the controlling node that the wireless device has not successfully decoded the first data, the controlling node sends a second command to a second one of the two or more antenna processing nodes. This second command instructs the second one of the two or more antenna processing nodes to transmit the first data to the wireless device. Once again, this may be preceded in some embodiments, by the step of selecting the second one of the two or more antenna processing nodes based on estimated signal quality metrics, e.g., by determining that the first one of the two or more antenna processing nodes has a the second one of the two or more antenna processing nodes has a next best estimated signal quality metric for the wireless device, compared to the first one of the antenna processing nodes. The determining that the wireless device has not successfully decoded the first data may comprise, in some embodiments receiving an indication of such from the first one of the two or more antenna processing nodes; this indication may comprise a request for retransmission or a “NACK” sent by the wireless device and forwarded to the controlling node by the first one of the antenna processing nodes, in some embodiments. 
     As discussed above, in some instances a single re-transmission may not be adequate, in that the wireless device is still unable to successfully decode the downlink transmissions. In these instances, in some embodiments, the method may further comprise determining, after sending the second command, that the wireless device has again been unable to successfully decode the first data, and sending a third command to a third one of the two or more antenna processing nodes, where the third command instructs the third one of the two or more antenna processing nodes to transmit the first data to the wireless device. This is not illustrated in  FIG.  7   ; it will be appreciated that this is simply a repetition of the operation shown in block  730 , but for the “next-best” antenna processing node. 
     The method illustrated in  FIG.  7    further comprises the step of signaling the two or more antenna processing nodes, after determining that the wireless device has successfully decoded the first data, where this signaling indicates that information corresponding to the first data may be discarded. This is shown at block  740 . 
     As discussed above, the techniques described herein need not substantially burden the serial links connecting the controlling node to the antenna processing nodes, since the downlink information to be transmitted to the wireless device can be sent by the controlling node just once, to the first antenna processing node in the chain, with that antenna processing node and each subsequent node in the chain forwarding the downlink information to the next antenna processing node. Thus, in some embodiments, the method shown in  FIG.  7    begins with the step of, prior to sending the first command, sending information corresponding to the first data to every one of the two or more antenna processing nodes. This is shown at block  710 . In other embodiments, this information might be sent along with the first command. 
       FIG.  8    is a process flow diagram illustrating a method, complementing that shown in  FIG.  7   , as carried out in an antenna processing node of a distributed wireless system that comprises a controlling node, the antenna processing node, and one or more additional antenna processing nodes. As in the previous examples, each of the antenna processing nodes is communicatively coupled to the controlling node but spatially separated from each other and from the controlling node. This particular method corresponds to an instance where the antenna processing node does not perform the original transmission of first data to a wireless device, but performs a re-transmission. 
     The method shown in  FIG.  8    begins with the antenna processing node receiving, from the controlling node, information corresponding to first data for transmission to a wireless device in a first interval. This is shown at block  810 . The method further comprises storing the information corresponding to the first data, without transmitting it to the wireless device in the first interval, as shown at block  820 . As shown at block  830 , the antenna processing node receives, after the first interval has passed, a command instructing the antenna processing node to transmit the first data to the wireless device in a second interval. The antenna processing node then transmits the first data to the wireless device in the second interval, as shown at block  840 . 
     In some embodiments, the antenna processing node may be configured to automatically discard the information for the first transmission, after performing the re-transmission. In other embodiments, the antenna processing node may instead wait until it receives signaling from the controlling node indicating that the information may be discarded, as shown at block  850 , before discarding the information, as shown at block  860 . 
       FIG.  9    is a process flow diagram illustrating another method complementing that shown in  FIG.  7   , again as carried out in an antenna processing node of a distributed wireless system that comprises a controlling node, the antenna processing node, and one or more additional antenna processing nodes. This particular method corresponds to an instance where the antenna processing node receives data corresponding to a downlink transmission to a wireless device, but neither performs the original transmission or a re-transmission of the data. This method might be performed at the same time the method of  FIG.  8    is being performed by a different antenna processing node in the same chain, or by the same antenna processing node at a different time, for instance. 
     The method of  FIG.  910    begins, as shown at block  910 , with the antenna processing node receiving, from the controlling node, information corresponding to first data for transmission to a wireless device in a first interval. The antenna processing node stores the information corresponding to the first data, without transmitting it to the wireless device in the first interval, as shown at block  920 . After the first interval has passed, the antenna processing node receives signaling indicating that information corresponding to the first data may be discarded, as shown at block  930 . Finally, as shown at block  940 , the antenna processing node discards the stored information corresponding to the first data, without transmitting it to the wireless device. 
       FIG.  10    is a block diagram illustrating an example controlling node apparatus  1000 , according to some embodiments. Controlling node apparatus  1000 , which may also be referred to as simply controlling node  1000 , includes a processing circuit  1010 , which in turn includes one or more processors  1004 , controllers, or the like, coupled to memory  1006 , which may comprise one or several types of memory, such as random-access memory, read-only memory, flash memory, etc. Stored in memory  1006  may be computer program code for execution by processor(s)  1004 , including program code configured to cause the controlling node  1000  to carry out any one or more of the techniques described herein, such as the methods discussed above in connection with  FIG.  7   . It will be appreciated that the computer program code, whether instantiated in memory  1006  or stored or communicated elsewhere, may be regarded as a “computer program product,” and that embodiments of the presently disclosed invention include such computer program products. 
     Controlling node  1000  further comprises serial interface circuitry  1020  operatively coupled to the processing circuit  1010 . Serial interface circuitry  1020  includes at least one serial interface  1022  configured to transmit data to and receive data from one or several antenna processing nodes connected in series, via a serial link connected to the serial interface  1022 . In some embodiments, the serial interface circuitry  1020  may comprise a second serial interface  1024 , configured to transmit data to and receive data from a second set of antenna processing nodes connected in series, via a serial link connected to the second serial interface  1024 . Thus, the controlling node  1000  may be able to separately control two (or more) “stripes” or “chains” of antenna processing nodes, through respective serial interfaces. 
     While not shown in  FIG.  10   , in some embodiments the controlling node  1000  may be collocated with or include an antenna processing node or comparable functionality, e.g., as shown in  FIG.  4   . From a functional standpoint, this collocated antenna processing node functionality may be treated in the same manner as other antenna processing nodes in a series. 
     Referring again to  FIG.  4   , this figure is a block diagram illustrating an example antenna processing node  400 , according to some embodiments. Antenna processing node  400  includes radio circuitry  410  and antennas  415 , processing circuit  420 , and serial interface circuitry  430 , which includes a first serial interface  432 , facing “upstream” towards a controlling node, as well as a second serial interface  434 , facing “downstream,” towards one or more subsequent antenna processing nodes. It will be appreciated that when antenna processing node is the last antenna processing node in a chain, the second serial interface  434  is unused. 
     Radio circuitry  410  includes receive (RX) and transmit (TX) functionality for communicating with one or more wireless devices via antennas  415 . For downlink communications, i.e., radio communications to one or more wireless devices, the radio circuitry  410  includes TX circuitry  414  configured to receive baseband information relayed to the radio circuitry  410  from a controlling node, via the upstream serial interface  432  and the processing circuit  420 . TX circuitry  414  includes upconverter circuits, power amplifier circuits, and filter circuits to convert this baseband information to radio frequency and condition it for transmission to one or more wireless devices. For uplink communications, i.e., radio communications from one or more wireless devices, the radio circuitry  410  includes RX circuitry  412  configured to receive wireless transmissions via antennas  415 , amplify, filter, and downconvert the received transmissions, and sample the downconverted transmissions to obtain soft information corresponding to the received wireless transmission. This soft information may be in the form of I-Q samples, for instance, and may be interchangeably referred to as soft bits or soft bit information. 
     Processing circuit  420  includes one or more processors  424 , controllers, or the like, coupled to memory  426 , which may comprise one or several types of memory, such as random-access memory, read-only memory, flash memory, etc. Stored in memory  426  may be computer program code for execution by processor(s)  424 , including program code configured to control the radio circuitry  410  and serial interface circuitry  430  and to cause the antenna processing node  400  to carry out any one or more of the techniques described herein, such as the methods discussed above in connection with  FIGS.  8  and  9   . Again, it will be appreciated that the computer program code, whether instantiated in memory  426  or stored or communicated elsewhere, may be regarded as a “computer program product,” and that embodiments of the presently disclosed invention include such computer program products. 
     Reference has been made herein to various embodiments. However, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the claims. For example, the method embodiments described herein describes example methods through method steps being performed in a certain order. However, it is recognized that these sequences of events may take place in another order without departing from the scope of the claims. Furthermore, some method steps may be performed in parallel even though they have been described as being performed in sequence. 
     In the same manner, it should be noted that in the description of embodiments, the partition of functional blocks into particular units is by no means limiting. Contrarily, these partitions are merely examples. Functional blocks described herein as one unit may be split into two or more units. In the same manner, functional blocks that are described herein as being implemented as two or more units may be implemented as a single unit without departing from the scope of the claims. 
     Hence, it should be understood that the details of the described embodiments are merely for illustrative purpose and by no means limiting. Instead, all variations that fall within the range of the claims are intended to be embraced therein.