Patent Application
20210119684
The present application claims priority from Finland No. FI20195893, filed Oct. 16, 2019, which is hereby included by reference in its entirety.
The present application relates generally to methods and apparatae for omission of feedback coefficients, for example to meet payload contraints.
In radio communication systems, such as the New Radio currently being defined by 3GPP, feedback of uplink control information (UCI) such as channel state information (CSI) from user equipment (UE) to base station (BS) is used to allow the base station to control the connection between the two. UCI is generally transmitted on an uplink control channel, resources on which are allocated to the UE by the BS. In some instances, a UE may however have more UCI available for transmission than would fit in the allocated resources. A UE may in such cases wait for additional resources to transmit all available UCI, but this approach as drawbacks such as increasing the delay in transferring all UCI and forcing the BS to allocate resources for all UCI available at the UE. Better approaches are hence needed for UCI transfer.
In 3GPP TS 38.214, a method was introduced omit a portions of CSI reports to ensure that the CSI payload would fit in an available resource allocation. This is achieved by dividing a variable part of a number (NRep) of CSI reports configured to be carried in a CSI payload in a slot into 2NRep+1 segments with different priority levels. Segments are then dropped in order of increasing priority until the UCI code rate falls below a threshold, such that the CSI payload fits in the available resource allocation.
The priority levels are described in Table 5.2.3-1 of TS 38.214, reproduced below in Table 1, where Priority 0 indicates highest priority and Priority 2NRep indicates lowest priority.
As may be observed from Table 1, CSI is segmented in accordance with odd and even subbands. However, when frequency compression is introduced, such segmentation is no longer feasible. Accordingly, an alternative segmentation into groups has been agreed as depicted in Table 2. Certain parameters of each CSI report are carried in group 0 with highest priority and other parameters of a CSI reports are split in two groups, group 1 and group 2.
The coefficients of at least some the other parameters may then be restricted to its non-zero coefficients cl,m(λ), where λ∈{0, 1, . . . , RI−1} indicates a layer associated with the coefficient, l∈{0, 1, . . . , 2L−1} a beam associated with the coefficient and m E {0, 1, . . . , M−1} indicates a frequency domain-basis (FD-basis) associated with the coefficient, wherein a FD-basis represents a frequency domain vector selected after frequency domain compression, RI indicates a number of reported layers and L indicates a number of reported beams.
The nonzero coefficients are prioritized from high to low priority according to the index triplet (l, m, λ). The [KNZTOT/2] highest priority coefficients are assigned to group 1 and the └KNZTOT/2┘ lowest priority coefficients are assigned to group 2. The priority level is assigns by the following function:
Prio(cl,m(λ))=2L·RI·π1(m)+RI·π2(l)+λ (1)
wherein π1(m) and π2(l) are FD-basis and beam permutation functions that are applied to each layer λ respectively.
Various aspects of examples of the invention are set out in the claims.
According to a first aspect of the present invention, there is disclosed a method, apparatus and software program product for partitioning channel state information into groups of different priority levels, wherein said channel state information comprises non zero coefficients and said partitioning comprises using at least one permutation function to prioritize said non-zero coefficients substantially based on an amplitude distribution of said non zero coefficients to determine mapping of said non zero coefficients to said groups, and further for omitting zero or more non-zero coefficients in accordance with said amplitude distribution based prioritizing from said groups, and for transmitting remaining non zero coefficients in said groups.
For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:
It is considered that when NCZs are assigned to groups 1 and 2, their assignment depends on the distribution of the coefficients in the bitmap associated with a layer, which may lead to undesirable effects. For example, the average amplitude of the coefficients in group 2 may be significantly larger than those in group 1, meaning that dropping group 2 would cause significant degradation in the PMI representation if the dropped coefficients are the most important ones, i.e., those with the largest amplitude. In another example, All NZCs of a layer might be assigned to a same group, where omitting that group would reduce the actual number of reported layers RI. Thus, in advantageous embodiments of the present invention, permutation functions π1(m) and π2 (l) are provided that mitigate such undesirable effects.
In one embodiment, a priority permutation function is provided that is designed based on typical amplitude histograms of the NZC. Across the frequency division (FD) components, the amplitude of the NZC is significantly larger at the “edges” as compared to the “centre” of the frequency components. This is typical in a DFT transformation of a correlated (i.e., “low-pass”) signal. Therefore, the priority permutation of FD components can be advantageously designed based on prioritizing components in order of typical decreasing average amplitude, by using the following mapping, where N3 is the maximum index number reported in a FD basis indicator:
FD components: {0,1,2, . . . ,N3−−1}→{0,N3−1,1,N3−2,2, . . . }. (2)
This priority permutation π1(m) can be expressed as:
π1(m)=min(2m,2(N3−m)−1) (3)
One skilled in the art will appreciate that a pair of FD components (m, N3−m) may be presumed to have similar amplitudes and thus may be reversed in priority order without departing from the scope the present invention.
If the selected FD basis consists of M<N3 components and the index m is defined in the set: {0, 1, . . . , M−1}, the ‘local’ index m in the right-hand side of equations (3) may be replaced by the ‘global’ index corresponding to the m-th selected FD component in the set: {0, 1, . . . , N3−1}. If km is such index, then the function (3) becomes
π1(m)=min(2k,2(N3−km)−1) (4)
SD beams: {0,1,2, . . . ,2L−1}→{l*,l*+L,l*+1,l*+L+1,l*+2, . . . } mod 2L. (5)
The priority permutation π2(l) be expressed as:
In some embodiments π1(m) may be set in accordance with Eq. 3, Eq. 4 or an equivalent function in combination with π2(l) set in accordance with Eq. 6 or an equivalent function, whereas in other embodiments, π1(m) may be set in accordance with Eq. 3, Eq. 4 or an equivalent function whereas π2(l) may be set to 1 (i.e. no layer permutation) or a different permutation function than provided in Eq. 6. In yet other embodiments, π2(l) may be set in accordance with Eq. 6 or an equivalent function whereas π1(m) may be set to 1 or a different permutation function than provided in Eq. 3 or Eq. 4.
After priorities have been assigned to the NZCs in accordance with priority permutations of at least one Eq. 3, Eq. 4, Eq. 6 or Eq. 6 or equivalent permutations, CSI groups may be omitted in order of increasing priority until the UCI code rate falls below a threshold, such that the CSI payload fits in the available resource allocation.
In certain embodiments, priorities for NZCs are allocated for a frequency domain basis on the basis of a typical amplitude order of a signal, for example a DFT of a correlated signal. In certain embodiments, priorities for NZCs are allocated for a frequency domain basis on the basis of prioritizing coefficients from the edges of the frequency domain inwards until the center coefficient(s) of the frequency domain forms/form the lowest priority coefficient(s). It is noted that no actual measurement of (e.g. instantaneous) amplitudes is foreseen to affect the ordering, as such ordering would require providing information about the ordering in the CSI payload (or through alternative signaling) as well. Thus, the priorities are set substantially in accordance with the amplitudes of the non-zero coefficients, though may not be set exactly in accordance with the amplitudes of the NZCs of an individual CSI report as the amplitudes of the NZCs of an individual CSI report may fluctuate relative to the typical amplitude histogram for the NZCs.
Omission of lowest priority NZCs in correspondence with (a) of
It may be understood that rather than applying any of the disclosed priority permutations on the NZCs or in addition to applying any of the disclosed priority permutations, a priority permutation may also be applied to a bitmap of elements βl,m(λ), where each element of the bitmap indicates whether or not the corresponding coefficient cl,m(λ) is considered to be non-zero or not. As such, for all embodiments where in the preceding non-zero coefficients cl,m(λ) (NZCs) are applied, additional embodiments where the same is applied to bitmap elements βl,m(λ) should be considered disclosed as well.
Embodiments of the invention may be implemented in software (executed by one or more processors), hardware (e.g., an application specific integrated circuit or field programmable gate array), or a combination of software and hardware. In an example embodiment, the software (e.g., application logic, an instruction set) is maintained on any one of various conventional non-transitory computer-readable media.
Although various aspects are set out above, other aspects comprise other combinations of features from the described embodiments, and not solely the combinations described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20195893 | Oct 2019 | FI | national |
