List size reduction for polar decoding

Methods, systems, and devices for wireless communications are described. The user equipment (UE) may initiate a successive cancellation list (SCL) decoding procedure, and may perform the SCL decoding procedure across various nodes (e.g., for each information bit through a decoding tree). At each node, the UE may determine whether a relationship between a first path metric and a second path metric satisfy a threshold. In some examples, the UE may determine whether multiple thresholds are satisfied. If conditions are satisfied (e.g., the relationship between the two path metrics satisfies a threshold), then the UE may decrease a list size of the SCL decoding.

FIELD OF TECHNOLOGY

The following relates to wireless communications, including list size reduction for polar decoding.

BACKGROUND

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support list size reduction for polar decoding. A user equipment (UE) may initiate a successive cancellation list (SCL) decoding procedure, and may perform the SCL decoding procedure across various nodes (e.g., for each information bit through a decoding tree). At each node, the UE may determine whether a relationship between a first path metric and a second path metric satisfy a threshold. In some examples, the UE may determine whether multiple thresholds are satisfied. If conditions are satisfied (e.g., the relationship between the two path metrics satisfies a threshold), then the UE may decrease a list size of the SCL decoding.

A method for wireless communications at a user equipment (UE) is described. The method may include initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics, switching from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics, and outputting the set of multiple information bits according to a result of the successive cancellation list decoding.

An apparatus for wireless communications at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to initiate successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics, switch from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics, and output the set of multiple information bits according to a result of the successive cancellation list decoding.

Another apparatus for wireless communications at a UE is described. The apparatus may include means for initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics, means for switching from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics, and means for outputting the set of multiple information bits according to a result of the successive cancellation list decoding.

A non-transitory computer-readable medium storing code for wireless communications at a UE is described. The code may include instructions executable by a processor to initiate successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics, switch from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics, and output the set of multiple information bits according to a result of the successive cancellation list decoding.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, switching from the first list size to the second list size may include operations, features, means, or instructions for selecting the second list size based on a comparison between the first path metric and a product of the second path metric and a path metric threshold.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, switching from the first list size to the second list size may include operations, features, means, or instructions for selecting the second list size based on a difference between the first path metric and the second path metric.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, switching from the first list size to the second list size may include operations, features, means, or instructions for selecting the second list size based on a ratio between the first path metric and the second path metric.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for selecting the first path metric from the set of path metrics, where the first path metric may have a lowest value of the set of path metrics and the second path metric may have a value that may be higher than the first path metric and lower than the remainder of the set of path metrics of the set of path metrics.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, switching from the first list size to the second list size may include operations, features, means, or instructions for selecting the second list size based on a number of information bits of the set of multiple information bits previously processed during the successive cancellation list decoding satisfying a processing threshold.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, switching from the first list size to the second list size may include operations, features, means, or instructions for selecting the second list size based on a comparison between the first path metric and the second path metric satisfying a first path metric threshold and a second path metric threshold that may be different from the first path metric threshold, the first path metric threshold corresponding to the second list size and the second path metric threshold corresponding to a third list size associated with a third number of decoding paths for the set of multiple information bits.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for updating the first path metric, the second path metric, a number of information bits of the set of multiple information bits previously processed during the successive cancellation list decoding, or any combination thereof and performing the successive cancellation list decoding at a second node of the decoding tree based on the updated first path metric, the updated second path metric, the updated number of information bits previously processed during the successive cancellation list decoding, or any combination thereof, where outputting the set of multiple information bits may be based on performing the successive cancellation list decoding at a set of multiple nodes of the decoding tree including at least the first node and the second node.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the second list size may be smaller than the first list size.

DETAILED DESCRIPTION

Some wireless communications systems may support polar decoding between network entities and user equipments (UEs). A UE may receive downlink signaling (e.g., on a control channel) that is encoded using polar coding. The UE may decode the downlink signaling using a successive cancellation list (SCL) decoding procedure. For the SCL decoding, the UE may (for each node of a decoding tree) maintain a number of lists (e.g., decoding paths) until a full message (e.g., a full set of information bits) is decoded. Maintaining a large list size (e.g., a large number of decoding paths) may result in improved reliability of decoding, but may also result in increased latency (e.g., a large number of cycles to decode the full message). Maintaining a smaller list size (e.g., a smaller number of decoding paths) may increase the speed of decoding and decrease latency, but may result in decreased reliability of decoding. A balanced approach (decreasing a number of cycles without overly decreasing accuracy) may result in efficient and accurate decoding. Some decoding techniques may not support such a balance.

Techniques described herein may support a decoding procedure that reduces latency while maintaining a high level of decoding accuracy. A UE may support polar decoding according to an SCL decoding procedure by selecting a list size based on one or more parameters satisfying one or more thresholds. For example, a relationship (e.g., a difference, a ratio, or any other relationship) between two current best (e.g., lowest) path metrics of a set of path metrics for a current node of the decoding tree may determine whether the UE will sacrifice reliability of the decode by decreasing the list size, or not. Similarly, if a portion of information bits have already been processed, then a large list size may not have much of an impact on successfully decoding remaining information bits.

The UE may initiate an SCL decoding procedure, and may perform the SCL decoding procedure across various nodes (e.g., for each information bit through a decoding tree). At each node, the UE may determine whether a relationship between a first path metric and a second path metric (e.g., the lowest path metrics of the current list size) satisfy a threshold. For instance, the UE may determine whether the first metric is greater than or equal to the product of the second path metric and a threshold path metric value, or may determine whether a difference between the first path metric and the second path metric satisfy a threshold, or may determine whether a ratio between the first path metric and the second path metric satisfy a threshold. If conditions are satisfied (e.g., the relationship between the two path metrics satisfies a threshold), then the UE may decrease the list size (e.g., from L=8 to L=2), resulting in less maintained decoding paths for a next node, and faster decoding of remaining information bits. In some examples, the UE may determine whether multiple thresholds are satisfied. For example, if the relationship between the first and second path metrics satisfies a first (e.g., lower) threshold, then the UE may decrease the list size from a first list size (e.g., L=8) to a second list size (e.g., L=2). If the relationship between the first and second path metrics satisfies a second (e.g., higher) threshold, then the UE may decrease the list size from the first list size (e.g., L=8) to a third list size (e.g., L=1, in which case the UE may perform a successive cancelation decoding, instead of an SCL decoding). In some examples, the UE may only decrease the list size if a number of previously processed information bits satisfies a threshold (e.g., if enough information bits have been processed to render a high number of lists unnecessary).

Aspects of the disclosure are initially described in the context of wireless communications systems. Aspects of the disclosure are further illustrated by and described with reference to wireless communications systems, decoding trees, and flow diagrams. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to list size reduction for polar decoding.

For instance, an access network (AN) or RAN may include communications between access nodes (e.g., an IAB donor), IAB nodes104, and one or more UEs115. The IAB donor may facilitate connection between the core network130and the AN (e.g., via a wired or wireless connection to the core network130). That is, an IAB donor may refer to a RAN node with a wired or wireless connection to core network130. The IAB donor may include a CU160and at least one DU165(e.g., and RU170), in which case the CU160may communicate with the core network130over an interface (e.g., a backhaul link). IAB donor and IAB nodes104may communicate over an F1 interface according to a protocol that defines signaling messages (e.g., an F1 AP protocol). Additionally, or alternatively, the CU160may communicate with the core network over an interface, which may be an example of a portion of backhaul link, and may communicate with other CUs160(e.g., a CU160associated with an alternative IAB donor) over an Xn-C interface, which may be an example of a portion of a backhaul link.

A UE115may initiate an SCL decoding procedure to decode information transmitted using network coding by a network entity or another device. The UE115may perform the SCL decoding procedure across various logical nodes (e.g., for each information bit through a decoding tree). At each node, the UE115may determine whether a relationship between a first path metric and a second path metric (e.g., the lowest path metrics of the current list size) satisfy a threshold.

For instance, the UE115may determine whether the first metric is greater than or equal to the product of the second path metric and a threshold path metric value, or may determine whether a difference between the first path metric and the second path metric satisfy a threshold, or may determine whether a ratio between the first path metric and the second path metric satisfy a threshold.

If conditions are satisfied (e.g., the relationship between the two path metrics satisfies a threshold), then the UE115may decrease the list size (e.g., from L=8 to L=2), resulting in less maintained decoding paths for a next node, and faster decoding of remaining information bits. In some examples, the UE115may determine whether multiple thresholds are satisfied. For example, if the relationship between the first and second path metrics satisfies a first (e.g., lower) threshold, then the UE115may decrease the list size from a first list size (e.g., L=8) to a second list size (e.g., L=2). If the relationship between the first and second path metrics satisfies a second (e.g., higher) threshold, then the UE may decrease the list size from the first list size (e.g., 8L=) to a third list size (e.g., L=1, in which case the UE115may perform a successive cancelation decoding, instead of an SCL decoding). In some examples, the UE may only decrease the list size if a number of previously processed information bits satisfies a threshold (e.g., if enough information bits have been processed to render a high number of lists unnecessary).

FIG.2illustrates an example of a wireless communications system200that supports list size reduction for polar decoding in accordance with one or more aspects of the present disclosure. The wireless communications system200may include a network entity105-aand a UE115-a, which may be examples of corresponding devices described with reference toFIG.1. The network entity105-amay serve one or more UEs115-awithin a geographic coverage area110-a.

The network entity105-amay communicate with the UE115-avia bidirectional communication link205. In some examples, the network entity105-amay perform polar coding for a downlink transmission to the UE115-a. In some examples, the UE115-amay perform polar decoding to decode the downlink transmission. In some examples, the UE115-amay perform successive cancellation (SC) decoding.

In an SC decoding procedure, latency may be caused by sequential processing over a decoding tree. In some examples, the UE115-amay perform successive cancelation list (SCL) decoding210. For SCL decoding, the UE115-amay maintain a list of decoding paths along the decoding tree, and each decoding path may have a path metric (e.g., a penalty value), as described in greater detail with reference toFIG.3). A path metric may be an example of or refer to a metric in a decoder that provides a value for a quality (such as a level or measurement of “correctness”) of the decoder or of the decoding procedure. The path metric may represent a reliability of a decoding path candidate or a probability that the corresponding decoding path candidate is the correct set of decoded bits. The path metric may be based on the determined bit metrics and the bit values selected at each bit channel. The SCL decoder may have a number of levels equal to the number of bit channels in the received codeword. For some coding schemes, a smaller value of a path cost may be associated with a higher quality of the decoder or of the decoding procedure, and a UE may calculate the path metric as an accumulated value over the decoding nodes.

In SC or SCL decoding, an amount of latency may be proportional to a number of survival paths on the decoding tree. One way to reduce latency may be to reduce a number of survival paths in SCL decoding210. For instance, if the UE115-amaintains a large list size (e.g., maintains a large number of simultaneous decoding paths of the decoding tree for each node of the decoding tree), the UE115-amay perform a large number of cycles of the SCL decoding210, and may also output decoded information bits with a high probability of accurate decoding. However, the increased accuracy may be achieved at the cost of increased latency.

The UE115-amay be able to reduce latency by reducing list size, resulting in a reduction in a number of cycles in the SCL decoding210. If the UE115-aselectively reduces the list size when conditions are satisfied, as described herein, the UE115-amay reduce latency under conditions in which such a reduction in time will not overly impact the accuracy of the decoding.

As described herein, the UE115-amay achieve power savings (e.g., by reducing a number of cycles of the SCL decoding210) while reducing performance loss of downlink signaling and polar decoding (e.g., for NR control channels (CCHs)). The UE115-amay perform a dynamic list size reduction scheme. For example, the UE115-amay perform single-threshold list size reduction (e.g., as described with reference toFIG.4), or double-threshold list size reduction (e.g., as described in greater detail with reference toFIG.5). In some examples, CCH signal detection may be based on a final path metric (PM) ratio of an SCL decoding210.

In some examples, the UE115-amay perform CCH signal detection based on a final path metric ratio of SCL decoding. For example, as described with reference toFIGS.3-5, the UE115-amay determine (e.g., for each node of a decoding tree) a set of one or more path metrics α for a list size L, where α=[α0, α1, . . . , αL-1]. a lowest (e.g., minimum) value of α for a given node (e.g., a last node in the decoding tree) may be referred to as αminand a highest (e.g., maximum) value of α for the node may be referred to as αmax. In some examples, a final PM ratio may be referred to as αmax/αmin. In some examples, the UE115-amay determine the existence of a CCH signal if αmax/αmin≥γ, where γ≥1 is a predetermined threshold.

The UE115-amay perform a multi-stage decoding. For example, the UE115-amay initialize the SCL decoder with a first list size (e.g., L=2), and may run the CCH signal detection based on the path metric ratio (e.g., perform CCH signal detection if αmax/αmin≥γ. If the CCH signal is detected (e.g., if the decision is true), then the UE115-amay run the SCL decoder with a second list size (e.g., L=8). Otherwise, the UE115-amay terminate the polar coding. This may occur if the CCH signal exists (e.g., a first hypothesis) resulting from a misdetection error (e.g., the decision is false and the CCH signal exists), or if the CCH signal does not exist (e.g., a second hypothesis) resulting from a false alarm error (e.g., the decision is true, and no CCH signal exists. If there is a good separation (e.g., a separation that exceeds a threshold) between two probability density functions (PDFs) of a final path metric ratio, then the techniques described herein may be particularly reliable.

FIG.3illustrates an example of a decoding tree300that supports list size reduction for polar decoding in accordance with one or more aspects of the present disclosure. Decoding tree300may represent a list decoding operation performed by an SCL decoder of list size L=2. Each node320may represent an assigned bit for a decoding path candidate. The SCL decoder may calculate a corresponding bit value305, bit metric310, and path metric315associated with each node320, and may determine the decoding path candidates based on these calculations.

In this specific example of a decoding operation, the SCL decoder may search for an eight bit codeword (e.g., transmitted over eight bit channels). The eight bit codeword may include five frozen bits (e.g., each with a default value of 0), followed by three information bits. A receiver may receive a candidate codeword over a control channel, and may send the candidate codeword to the SCL decoder. Based on the candidate codeword, the SCL decoder may determine a received LLR for each of the eight bit channels. For example, the set of received LLRs may contain LLR values of 2.9, 0.6, −1.8, −2.3, 5.9, 7.6, −1.4, and 2.0 for bit channels 1 through 8, respectively.

The SCL decoder may perform a list decoding operation on the set of received LLRs. Based on the sequential order of decoding, the SCL decoder may first decode node320-a, representing the first bit channel, based on the set of received LLRs. The SCL decoder may determine a decoded LLR of −0.6 for the first bit channel. The SCL decoder may use the decoded LLRs as the bit metrics310for calculating path metrics315during the decoding process. Therefore, the SCL decoder may set the value of the first bit metric310to −0.6. In some cases, a negative value of a decoded LLR may indicate a 1 bit. However, since the expected codeword contains a frozen bit in the first bit channel, the SCL decoder may assign a bit value305of 0 to the first bit channel.

The SCL decoder may update the path metric315according to an accumulation of LLRs. The SCL decoder may select a preferred (e.g., best) path if a (e.g., absolute) path metric has a best (e.g., lowest or minimum) value. The SCL decoder may subtract the absolute value of a bit metric310from the path metric315if the SCL decoder assigned a bit value305not indicated by the LLR. In this way, the path metric315indicates unreliability of that decoding path. In this case, the SCL decoder assigned a 0 bit to the first bit channel, despite the LLR indicating a 1 bit (e.g., because the LLR has a negative value). Therefore, the SCL decoder may subtract the absolute value of the bit metric310(i.e., 0.6) from an initial value of the path metric315(i.e., 0). As the first bit channel of the expected codeword contains a frozen bit, both decoding path candidates of the L=2 SCL decoder may assign a 0 bit to this first decoded bit channel.

The SCL decoder may continue the decoding process for the next four frozen bits, indicated by nodes320-b,320-c,320-d, and320-e. Since the expected codeword contains frozen bits in the first five bit channels, the SCL decoder may assign bit values305of 0 to each of these bit channels. The SCL decoder may update the path metric315based on each bit metric310that does not indicate a 0 bit (e.g., the first bit metric of −0.6 and the third bit metric of −1.4). For each bit metric310that indicates the assigned bit, the SCL decoder may not update the path metric315.

For the sixth bit channel, the SCL decoder may process two decoding path candidates due to the expected codeword containing an information bit in the sixth bit channel. Node320-fmay represent a bit value305of 0, while node320-gmay represent a bit value305of 1. Since the SCL decoder has a list size of L=2, one decoding path candidate may assign a bit value305of 0, and the other decoding path candidate may assign a bit value305of 1, for the sixth bit channel. The bit metric310may have a value of −3.5, which may indicate a 1 bit. Therefore, the SCL decoder may accumulate path metric for the decoding path candidate including node320-fby 3.5, while the SCL decoder may not decrease the path metric for the decoding path candidate including node320-g. At this point in the decoding process, the SCL decoder may identify the decoding path candidate including node320-gas the most likely path corresponding to the codeword based on the current path metric315.

The SCL decoder may proceed to decoding the seventh bit channel. To decode the seventh bit, a first decoding path (e.g., the decoding path including node320-f) may process the bit values305and LLRs indicated by nodes320-hand320-i, and may calculate the corresponding bit metrics310and path metrics315. Additionally, a second decoding path (e.g., the decoding path including node320-g) may process the bit values305and LLRs indicated by nodes320-jand320-k, and may calculate the corresponding bit metrics310and path metrics315. In some cases, the SCL decoder may keep the number of decoding path candidates equal to the list size. For example, the SCL decoder may prune the paths with path metrics315of −11.1 and −10.5.

As described with reference toFIG.3path metric may be accumulated, and a best path metric may be selected based on a (e.g., absolute) lowest (e.g., minimum) path metric value. Although illustrated with reference to a list size of L=2, similar techniques may be applied for higher or lower list sizes (e.g., L=8, L=2, etc.). In some examples, as described in greater detail with reference toFIG.4, a UE may dynamically change (e.g., reduce) its list size if one or more conditions are satisfied (e.g., based on a relationship between two path metrics, such as the two lowest path metrics).

FIG.4illustrates an example of a flow diagram400that supports list size reduction for polar decoding in accordance with one or more aspects of the present disclosure. Flow diagram400may implement, or be implemented by, aspects of wireless communications system100, wireless communications system200, or decoding tree300. For example, a UE (e.g., a UE115including an SCL decoder) may communicate with a network entity (e.g., a network entity105). The UE may perform SCL decoding (e.g., as described with reference toFIGS.2-3), and may dynamically change its list size while performing SCL decoding of downlink messages (e.g., or sidelink messages).

At405, the UE may initialize its SCL decoder to perform SCL decoding on a set of bits (e.g., including one or more information bits). The UE may initialize the SCL decoder according to a first list size (e.g., L=8). The first list size may be associated with a first number of decoding paths of a decoding tree (e.g., for L=8 the SCL decoder may maintain 8 decoding paths). Each decoding path may be associated with a path metric. For example, the absolute path metrics at a particular (e.g., current) node of the decoding tree may be represented by absolute α=[α0, α1, . . . , αL-1]. In some examples, the UE may initialize the SCL decoder according to one or more threshold values (e.g., a number of information bits that have been processed I, or a path metric threshold value Athr).

At410, the UE may determine whether one or more parameters satisfy one or more conditions. In some examples, the UE may determine whether a relationship between a first metric value (e.g., and αmin,2) satisfy a condition or rule. In some examples, αmin,1may represent a first or best (e.g., lowest) path metric value of α=[α0, α1, . . . , αL-1] and may represent a second or second-best (e.g., next lowest after of α=[α0, α1, . . . , αL-1]. The UE may select the first and second path metrics from the set of path metrics α. In some examples, the first path metric has a lowest value of the set of path metrics and the second path metric has a value that is higher than the first path metric and lower than the remainder of the set of path metrics of the set of path metrics. In some examples, αmin,1=min α, and αmin,2=min (α/{αmin,1}). If the parameters do not satisfy the conditions, then the UE may maintain the list size (e.g., without reducing the list size), and may determine whether decoding is completed at420. If the parameters do satisfy the conditions, then the UE may reduce the size (L) at415(e.g., may select a second list size based on the parameter satisfying the conditions).

In some examples, the UE may determine that the parameters satisfy the condition based on a comparison between one of the path metrics, and a product of the other path metric and the path metric threshold value Athr. For instance, if αmin,2≥Athr·αmin,1, then the UE may consider the conditions satisfied, and may reduce the size (L) at415.

In some examples, the UE may determine that the parameters satisfy the conditions based on a difference between the first path metric and the second path metric. For instance, the UE may determine whether αmin,2−αmin,1satisfies a threshold value. If so, the UE may consider the conditions satisfied, and may reduce the size (L) at415.

in some examples, the UE may determine that the parameter satisfy the conditions based on a ratio between the first path metric and the second path metric. For instance, the UE may determine whether

amin,2amin,1
is greater than a threshold value, or may determine whether

amaxamin≥γ.
If so, then the UE may consider the conditions satisfied, and may reduce the size (L) at415.

In some examples, the UE may determine whether the parameters satisfy a condition based on a number of information bits previously processed during the successive cancelation list decoding satisfying a threshold. For example, at410, the UE may determine whether 1≥IThr. For example, if a large number of information bits have been already processed, then the likelihood that decreasing the list size will negatively impact an output message may be relatively small, whereas if only a small number of information bits have been previously processed, then decreasing the list size prematurely may result in decreased performance. In some examples, the size of I may have an inverse relationship to a ratio between the first and second path metrics. For example, for small values of I,

amin,2amin,1
may be large (e.g., an integer value greater than 1). In some examples, for larger values of I,

amin,2amin,1
may be close to 1.

At415, if the parameters satisfy the one or more conditions at410, the UE may reduce the list size (L). For example, the UE may reduce the list size from L=8 to L=2. In some examples, a message error rate (MER) of a dynamic list size reduction scheme (e.g., as described herein) may be bounded between MERs (e.g., an MER for L=2 and L=8.

At420, the UE may determine whether the decoding is completed. If not, the UE may update parameters at425. For example, the UE may update a value for αmin,2or both (e.g., from a new set of path metrics for the next node on the decoding tree). The UE may update a value for I, one or more thresholds (e.g., IThr, AThr, etc.), or both. The UE may update the parameter values based on having completed operations at410,415, and420, for a first node (e.g., any node on the decoding tree). The UE may then update the parameters at425, and determine whether the updated parameters satisfy the conditions at410for a next node in the decoding tree. At420, the UE may determine whether the decoding is completed. If the decoding is completed, at430, the UE may output the most likely message based on the dynamic list size reduction and SCL decoding described herein.

In some examples (e.g., as described with reference toFIG.4), the UE may perform a single-threshold list size reduction scheme. The UE may balance performance and latency (e.g., for fading channels), which may result in a list reduction probability (e.g., about a ninety percent list reduction probability at an MER of 10-3. This may result in significant cycle savings, compared to the case where a higher list size (e.g., L=8) is used throughout the SCL decoding. In some examples, the UE may perform the dynamic SCL decoding based on multiple thresholds, and multiple possible list size reductions, as described in greater detail with reference toFIG.5.

FIG.5illustrates an example of a flow diagram500that supports list size reduction for polar decoding in accordance with one or more aspects of the present disclosure. Flow diagram400may implement, or be implemented by, aspects of wireless communications system100, wireless communications system200, or decoding tree300. For example, a UE (e.g., a UE115including an SCL decoder) may communicate with a network entity (e.g., a network entity105). The UE may perform SCL decoding (e.g., as described with reference toFIGS.2-3), and may dynamically change its list size while performing SCL decoding of downlink messages (e.g., or sidelink messages).

At505, the UE may initialize its SCL decoder to perform SCL decoding on a set of bits (e.g., including one or more information bits). The UE may initialize the SCL decoder according to a first list size (e.g., L=8). The first list size may be associated with a first number of decoding paths of a decoding tree (e.g., for L=8 the SCL decoder may maintain 8 decoding paths). Each decoding path may be associated with a path metric. For example, the path metrics at a particular (e.g., current) node of the decoding tree may be represented by α=[α0, α1, . . . , αL-1]. In some examples, the UE may initialize the SCL decoder according to one or more threshold values (e.g., a number of information bits that have been processed I, or a path metric threshold value Athr). The UE may initialize the SCL decoder to polar decode one or more signals received on a channel.

At510, the UE may determine whether one or more parameters satisfy one or more first conditions. In some examples, the UE may determine whether a relationship between a first path metric value (e.g., and a second path metric value (αmin,2) satisfies the first conditions. In some examples, αmin,1may represent a first or best (e.g., lowest) absolute path metric value of α=[α0, α1, . . . , αL-1] and may represent a second or second-best (e.g., next lowest after of α=[α0, α1, . . . , αL-1]. The UE may select the first and second path metrics from the set of path metrics a. In some examples, the first path metric has a lowest value of the set of path metrics and the second path metric has a value that is higher than the first path metric and lower than the remainder of the set of path metrics of the set of path metrics. In some examples, αmin,1=min α, and αmin,2=min(α/{αmin,1}). If the parameters do not satisfy the first conditions, then the UE may maintain the list size (e.g., without reducing the list size), and may determine whether decoding is completed at530. If the parameters do satisfy the conditions, then the UE may determine whether the parameters satisfy one or more second conditions at515.

In some examples, the first conditions and second conditions may be associated with list size reductions of different granularities. For example, if the parameters satisfy the first conditions at510, and satisfy the second conditions at515, then the UE may reduce the list size (L) from a first value to a second value (e.g., from L=8 to L=1) at525. However, if the parameters satisfy the first conditions at510but do not satisfy the second conditions at515, then the UE may reduce the list size (L) from the first value to a third value (e.g., from L=8 to L=2) at520. This additional granularity may support improved flexibility, accuracy, and latency at the UE.

In some examples, the UE may determine that the parameters satisfy the condition based on a comparison between one of the path metrics, and a product of the other path metric and the path metric threshold value Athrat510, and Bthrat515. For instance, Athrand Bthrmay be predetermined, preconfigured, or standardized thresholds, where 1≤Athr<Bthr. If αmin,2≥Athr·αmin,1, then the UE may consider the first conditions satisfied. If αmin,2≥Bthr·αmin,1, then the UE may further consider the second conditions satisfied, and may reduce the list size (L) to the second value at525(e.g., L=1, where the UE performs SC decoding with a list size of 1, instead of SCL decoding). If αmin,2≥Athr·αmin,1, but αmin,2<Bthr·αmin,1, then the UE may reduce the size (L) from L=8 to L=2 at520.

As described with reference toFIG.4, the UE may determine whether the parameters satisfy the first conditions at510, the second conditions at515, or both, based on a relationship between the first path metric (e.g., αmin,1) and the second path metric (e.g., αmin,2). For example, the UE may determine whether a ratio between the first path metric and the second path metric satisfies a first threshold value at510and a second threshold value at515, or may determine whether a difference between the first path metric and the second path matric satisfies a first threshold at510and a second threshold at515.

In some examples, the UE may determine whether the parameters satisfy first condition and a second condition based on a number of information bits previously processed during the successive cancelation list decoding satisfying a threshold. For example, at410, the UE may determine whether I≥IThr,1at510, and may determine whether I≥IThr,2at515.

At530, the UE may determine whether the decoding is completed. If not, the UE may update parameters at545. For example, the UE may update a value for αmin,2or both (e.g., from a new set of path metrics for the next node on the decoding tree). The UE may update a value for I, or one or more thresholds (e.g., IThr,1, IThr,2, AThr, BThr, etc.), or both. The UE may update the parameter values based on having completed operations at510,515,520, and/or525, for a first node (e.g., any node on the decoding tree). The UE may then update the parameters at545, and determine whether the updated parameters satisfy the first conditions at510, the second conditions at515, or both, for a next node in the decoding tree. At530, the UE may determine whether the decoding is completed. If the decoding is completed, then the UE may output the most likely message based on the dynamic list size reduction and the SCL decoding described herein.

In some examples, a double-threshold list size reduction scheme (e.g., as described with reference toFIG.5) may perform well on fading channels. At an operating SNR, a transition from L=8 to L=1 may occur as frequently as or more frequently than a transition from L=8 to L=2. For aggregation levels greater than 2, single-threshold list size reduction or double-threshold list-size reduction schemes may result in list reduction probabilities that depend (e.g., primarily) on a target BLER. List size reduction schemes may reduce a number of cycles for decoding (e.g., resulting in decreased latency), but without the constant false alarm rates of consistently using a smaller list size (e.g., without initially starting the SCL decoding at a lower list size).

The communications manager620, the receiver610, the transmitter615, or various combinations thereof or various components thereof may be examples of means for performing various aspects of list size reduction for polar decoding as described herein. For example, the communications manager620, the receiver610, the transmitter615, or various combinations or components thereof may support a method for performing one or more of the functions described herein.

In some examples, the communications manager620may be configured to perform various operations (e.g., receiving, obtaining, monitoring, outputting, transmitting) using or otherwise in cooperation with the receiver610, the transmitter615, or both. For example, the communications manager620may receive information from the receiver610, send information to the transmitter615, or be integrated in combination with the receiver610, the transmitter615, or both to obtain information, output information, or perform various other operations as described herein.

The communications manager620may support wireless communications at a UE in accordance with examples as disclosed herein. For example, the communications manager620may be configured as or otherwise support a means for initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The communications manager620may be configured as or otherwise support a means for switching from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The communications manager620may be configured as or otherwise support a means for outputting the set of multiple information bits according to a result of the successive cancellation list decoding.

By including or configuring the communications manager620in accordance with examples as described herein, the device605(e.g., a processor controlling or otherwise coupled with the receiver610, the transmitter615, the communications manager620, or a combination thereof) may support techniques for decoding procedures resulting in reliable decoding, improved reception of control signaling, more reliable communication, decreased latency, more efficient use of available resources, and improved user experience.

The device705, or various components thereof, may be an example of means for performing various aspects of list size reduction for polar decoding as described herein. For example, the communications manager720may include an SCL decoding manager725, a list size switching manager730, an information bit manager735, or any combination thereof. The communications manager720may be an example of aspects of a communications manager620as described herein. In some examples, the communications manager720, or various components thereof, may be configured to perform various operations (e.g., receiving, obtaining, monitoring, outputting, transmitting) using or otherwise in cooperation with the receiver710, the transmitter715, or both. For example, the communications manager720may receive information from the receiver710, send information to the transmitter715, or be integrated in combination with the receiver710, the transmitter715, or both to obtain information, output information, or perform various other operations as described herein.

The communications manager720may support wireless communications at a UE in accordance with examples as disclosed herein. The SCL decoding manager725may be configured as or otherwise support a means for initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The list size switching manager730may be configured as or otherwise support a means for switching from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The information bit manager735may be configured as or otherwise support a means for outputting the set of multiple information bits according to a result of the successive cancellation list decoding.

FIG.8shows a block diagram800of a communications manager820that supports list size reduction for polar decoding in accordance with one or more aspects of the present disclosure. The communications manager820may be an example of aspects of a communications manager620, a communications manager720, or both, as described herein. The communications manager820, or various components thereof, may be an example of means for performing various aspects of list size reduction for polar decoding as described herein. For example, the communications manager820may include an SCL decoding manager825, a list size switching manager830, an information bit manager835, a path metric manager840, an information bit threshold manager845, an updating manager850, or any combination thereof. Each of these components may communicate, directly or indirectly, with one another (e.g., via one or more buses).

The communications manager820may support wireless communications at a UE in accordance with examples as disclosed herein. The SCL decoding manager825may be configured as or otherwise support a means for initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The list size switching manager830may be configured as or otherwise support a means for switching from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The information bit manager835may be configured as or otherwise support a means for outputting the set of multiple information bits according to a result of the successive cancellation list decoding.

In some examples, to support switching from the first list size to the second list size, the path metric manager840may be configured as or otherwise support a means for selecting the second list size based on a comparison between the first path metric and a product of the second path metric and a path metric threshold.

In some examples, to support switching from the first list size to the second list size, the path metric manager840may be configured as or otherwise support a means for selecting the second list size based on a difference between the first path metric and the second path metric.

In some examples, to support switching from the first list size to the second list size, the path metric manager840may be configured as or otherwise support a means for selecting the second list size based on a ratio between the first path metric and the second path metric.

In some examples, the path metric manager840may be configured as or otherwise support a means for selecting the first path metric from the set of path metrics, where the first path metric has a lowest value of the set of path metrics and the second path metric has a value that is higher than the first path metric and lower than the remainder of the set of path metrics of the set of path metrics.

In some examples, to support switching from the first list size to the second list size, the information bit threshold manager845may be configured as or otherwise support a means for selecting the second list size based on a number of information bits of the set of multiple information bits previously processed during the successive cancellation list decoding satisfying a processing threshold.

In some examples, to support switching from the first list size to the second list size, the path metric manager840may be configured as or otherwise support a means for selecting the second list size based on a comparison between the first path metric and the second path metric satisfying a first path metric threshold and a second path metric threshold that is different from the first path metric threshold, the first path metric threshold corresponding to the second list size and the second path metric threshold corresponding to a third list size associated with a third number of decoding paths for the set of multiple information bits.

In some examples, the updating manager850may be configured as or otherwise support a means for updating the first path metric, the second path metric, a number of information bits of the set of multiple information bits previously processed during the successive cancellation list decoding, or any combination thereof. In some examples, the updating manager850may be configured as or otherwise support a means for performing the successive cancellation list decoding at a second node of the decoding tree based on the updated first path metric, the updated second path metric, the updated number of information bits previously processed during the successive cancellation list decoding, or any combination thereof, where outputting the set of multiple information bits is based on performing the successive cancellation list decoding at a set of multiple nodes of the decoding tree including at least the first node and the second node.

In some examples, the second list size is smaller than the first list size.

The communications manager920may support wireless communications at a UE in accordance with examples as disclosed herein. For example, the communications manager920may be configured as or otherwise support a means for initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The communications manager920may be configured as or otherwise support a means for switching from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The communications manager920may be configured as or otherwise support a means for outputting the set of multiple information bits according to a result of the successive cancellation list decoding.

By including or configuring the communications manager920in accordance with examples as described herein, the device905may support techniques for decoding procedures resulting in reliable decoding, improved reception of control signaling, more reliable communication, decreased latency, more efficient use of available resources, and improved user experience.

At1005, the method may include initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The operations of1005may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1005may be performed by an SCL decoding manager825as described with reference toFIG.8.

At1010, the method may include switching from the first list size to a second list size at a first node of the decoding tree based on a first path metric and a second path metric of the set of path metrics, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The operations of1010may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1010may be performed by a list size switching manager830as described with reference toFIG.8.

At1015, the method may include outputting the set of multiple information bits according to a result of the successive cancellation list decoding. The operations of1015may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1015may be performed by an information bit manager835as described with reference toFIG.8.

At1105, the method may include initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The operations of1105may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1105may be performed by an SCL decoding manager825as described with reference toFIG.8.

At1110, the method may include selecting a second list size based on a comparison between a first path metric and a product of a second path metric and a path metric threshold. The operations of1110may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1110may be performed by a path metric manager840as described with reference toFIG.8.

At1115, the method may include switching from the first list size to a second list size at a first node of the decoding tree, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The operations of1115may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1115may be performed by a list size switching manager830as described with reference toFIG.8.

At1120, the method may include outputting the set of multiple information bits according to a result of the successive cancellation list decoding. The operations of1120may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1120may be performed by an information bit manager835as described with reference toFIG.8.

At1205, the method may include initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The operations of1205may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1205may be performed by an SCL decoding manager825as described with reference toFIG.8.

At1210, the method may include selecting a second list size based on a difference between a first path metric and a second path metric. The operations of1210may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1210may be performed by a path metric manager840as described with reference toFIG.8.

At1215, the method may include switching from the first list size to the second list size at a first node of the decoding tree, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The operations of1215may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1215may be performed by a list size switching manager830as described with reference toFIG.8.

At1220, the method may include outputting the set of multiple information bits according to a result of the successive cancellation list decoding. The operations of1220may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1220may be performed by an information bit manager835as described with reference toFIG.8.

At1305, the method may include initiating successive cancellation list decoding for a set of multiple information bits according to a first list size, where the first list size is associated with a first number of decoding paths of a decoding tree for the set of multiple information bits, and where each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics. The operations of1305may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1305may be performed by an SCL decoding manager825as described with reference toFIG.8.

At1310, the method may include selecting a second list size based at least in part on a ratio between a first path metric and a second path metric. The operations of1310may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1310may be performed by a path metric manager840as described with reference toFIG.8.

At1315, the method may include switching from the first list size to the second list size at a first node of the decoding tree, where the second list size is associated with a second number of decoding paths of the decoding tree for the set of multiple information bits, and where the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics. The operations of1315may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1315may be performed by a list size switching manager830as described with reference toFIG.8.

At1320, the method may include outputting the set of multiple information bits according to a result of the successive cancellation list decoding. The operations of1320may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of1320may be performed by an information bit manager835as described with reference toFIG.8.

Aspect 1: A method for wireless communications at a UE, comprising: initiating successive cancellation list decoding for a plurality of information bits according to a first list size, wherein the first list size is associated with a first number of decoding paths of a decoding tree for the plurality of information bits, and wherein each decoding path of the first number of decoding paths is associated with a respective path metric of a set of path metrics; switching from the first list size to a second list size at a first node of the decoding tree based at least in part on a first path metric and a second path metric of the set of path metrics, wherein the second list size is associated with a second number of decoding paths of the decoding tree for the plurality of information bits, and wherein the first path metric and the second path metric have lower path metric values than a remainder of the set of path metrics; and outputting the plurality of information bits according to a result of the successive cancellation list decoding.

Aspect 2: The method of aspect 1, wherein switching from the first list size to the second list size comprises: selecting the second list size based at least in part on a comparison between the first path metric and a product of the second path metric and a path metric threshold.

Aspect 3: The method of any of aspects 1 through 2, wherein switching from the first list size to the second list size comprises: selecting the second list size based at least in part on a difference between the first path metric and the second path metric.

Aspect 4: The method of any of aspects 1 through 3, wherein switching from the first list size to the second list size comprises: selecting the second list size based at least in part on a ratio between the first path metric and the second path metric.

Aspect 5: The method of any of aspects 1 through 4, further comprising: selecting the first path metric from the set of path metrics, wherein the first path metric has a lowest value of the set of path metrics and the second path metric has a value that is higher than the first path metric and lower than the remainder of the set of path metrics of the set of path metrics.

Aspect 6: The method of any of aspects 1 through 5, wherein switching from the first list size to the second list size comprises: selecting the second list size based at least in part on a number of information bits of the plurality of information bits previously processed during the successive cancellation list decoding satisfying a processing threshold.

Aspect 7: The method of any of aspects 1 through 6, wherein switching from the first list size to the second list size comprises: selecting the second list size based at least in part on a comparison between the first path metric and the second path metric satisfying a first path metric threshold and a second path metric threshold that is different from the first path metric threshold, the first path metric threshold corresponding to the second list size and the second path metric threshold corresponding to a third list size associated with a third number of decoding paths for the plurality of information bits.

Aspect 8: The method of any of aspects 1 through 7, further comprising: updating the first path metric, the second path metric, a number of information bits of the plurality of information bits previously processed during the successive cancellation list decoding, or any combination thereof; and performing the successive cancellation list decoding at a second node of the decoding tree based at least in part on the updated first path metric, the updated second path metric, the updated number of information bits previously processed during the successive cancellation list decoding, or any combination thereof, wherein outputting the plurality of information bits is based at least in part on performing the successive cancellation list decoding at a plurality of nodes of the decoding tree comprising at least the first node and the second node.

Aspect 9: The method of any of aspects 1 through 8, wherein the second list size is smaller than the first list size.

Aspect 12: A non-transitory computer-readable medium storing code for wireless communications at a UE, the code comprising instructions executable by a processor to perform a method of any of aspects 1 through 9.

The term “determine” or “determining” encompasses a variety of actions and, therefore, “determining” can include calculating, computing, processing, deriving, investigating, looking up (such as via looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” can include receiving (such as receiving information), accessing (such as accessing data in a memory) and the like. Also, “determining” can include resolving, obtaining, selecting, choosing, establishing and other such similar actions.