WIRELESS COMMUNICATION METHOD AND WIRELESS COMMUNICATION
`
`DEVICE
`
`BACKGROUND
`
`1. Technical Field
`
`[0001] The present disclosure relates to the field of wireless communication, and in
`
`particular, to wireless communication methods and wireless communication devices in
`
`Machine-Type Communication.
`
`2. Description of the Related Art
`
`[0002] MTC (Machine-Type Communication) is a new type of communication in 3GPP
`
`(The 3rd Generation Partnership Project) in release 12 and is an important revenue
`
`stream for operators and has a huge potential from the operator perspective. Based on
`
`the market and operators' requirements, one of the important requirements of MTC is
`
`improving the coverage of MTC UEs (User Equipments). Thus, MTC will further be
`
`envisioned in release 13, for example, to support coverage enhancement of 15 dB.
`
`This type of coverage enhancement technique is quite useful for some MTC UEs such
`
`as sensors in the basement which have large losses on their signal strengths due to the
`
`penetration losses.
`
`[0003] Repetition is one of key techniques to support MTC UEs in coverage
`
`enhancement. Specifically, for MTC UEs in coverage enhancement, basically each
`
`channel needs to do multiple repetitions (e.g., 100 times). At the receiver side, the
`
`receiver combines all the repetitions of the channel and decodes the information. Thus,
`
`coverage enhancement requirement is reached by signal accumulation and power
`
`enhancement resulting from repetitions.
`
`SUMMARY
`
`[0004] One non-limiting and exemplary embodiment provides an approach to
`
`maximally optimize the system performance in MTC with coverage enhancement.
`
`[0005]
`
`In one general aspect, the techniques disclosed here feature a wireless
`
`communication method, including: transmitting a reference signal and a data signal in a
`
`1
`
`P0625234
`
`

`

`Physical Resource Block (PRB) with a coverage enhancement level, wherein the
`
`number of resource elements transmitting the reference signal in the PRB is determined
`
`by the coverage enhancement level, the channel type and/or the coding rate of the data
`
`signal.
`
`[0006]
`
`It should be noted that general or specific embodiments may be implemented
`
`as a system, a method, an integrated circuit, a computer program, a storage medium, or
`
`any selective combination thereof.
`
`[0007] Additional benefits and advantages of the disclosed embodiments will become
`
`apparent from the specification and drawings. The benefits and/or advantages may be
`
`individually obtained by the various embodiments and features of the specification and
`
`drawings, which need not all be provided in order to obtain one or more of such benefits
`
`and/or advantages.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0008]
`
`Figs. 1A and 1B are schematic diagrams each showing an example of BLER
`
`performance of PUSCH repetitions;
`
`Fig. 2 is a flowchart of a wireless communication method according to an embodiment
`
`of the present disclosure;
`
`Fig. 3 is a flowchart of a wireless communication method according to another
`
`embodiment of the present disclosure;
`
`Fig. 4 is a block diagram showing a wireless communication device according to a
`
`further embodiment of the present disclosure; and
`
`Fig. 5 is a block diagram showing a wireless communication device according to a still
`
`further embodiment of the present disclosure.
`
`DETAILED DESCRIPTION
`
`[0009]
`
`In the following detailed description, reference is made to the accompanying
`
`drawings, which form a part hereof.
`
`In the drawings, similar symbols typically identify
`
`similar components, unless context dictates otherwise.
`
`It will be readily understood that
`
`the aspects of the present disclosure can be arranged, substituted, combined, and
`
`2
`
`P0625234
`
`

`

`designed in a wide variety of different configurations, all of which are explicitly
`
`contemplated and make part of this disclosure.
`
`Underlying Knowledge Forming Basis of the Present Disclosure
`
`[0010]
`
`In the repetition as one key technique of coverage enhancement for MTC as
`
`mentioned in the BACKGROUND, long repetitions will last a long time and will ask MTC
`
`UEs to keep active for a long time to be always in a reception state, which will largely
`
`consume UEs' power and occupy many system resources. Therefore, other coverage
`
`enhancement technique such as RS (reference signal) density increase is a useful
`
`assistance to realize coverage enhancement to reduce repetition time.
`
`[0011]
`
`In order to introduce the RS density increase simply, take one PRB (Physical
`
`Resource Block) as an example. One PRB consists of 14 symbols in time domain and
`
`12 subcarriers in frequency domain, and one symbol and one subcarrier form one RE
`
`(Resource Element). That is to say, one PRB has 12 x 14 REs in total.
`
`It is specified in
`
`the standard that some REs are assigned for transmitting some kinds of reference
`
`signals and other REs are assigned for transmitting data signals in one PRB. For a
`
`certain reference signal in a normal usage case, the number of REs assigned for
`
`transmitting it in one PRB and positions thereof are specified in the standard. Thus, the
`
`RS density, that is, the ratio of REs for transmitting the reference signal to total REs in
`
`one PRB, is specified in the standard. Accordingly, RS density increase means
`
`increasing the number of REs for transmitting the reference signal in one PRB.
`
`[0012]
`
`By increasing the RS density, the channel estimation performance and thus
`
`signal quality can be improved, so that repetition times can be reduced for MTC UEs
`
`with coverage enhancement.
`
`[0013] One straightforward solution to apply RS density increase is that all UEs and
`
`all channels assume the maximum RS density, for example 24 CRS (Cell-specific
`
`Reference Signal) REs and 24 DMRS (Demodulation Reference Signal) REs per PRB.
`
`However, based on our observations, some UEs cannot benefit from RS density
`
`increase, but their performance will be impacted. Also, some channels cannot benefit
`
`from RS density increase due to impact on the coding rate. The detailed observations
`
`3
`
`P0625234
`
`

`

`are described below.
`
`[0014] The first observation is based on PUSCH (Physical Uplink Shared Channel)
`
`simulation with varying repetition times and the number of subframes combined at the
`
`receiver side for demodulation. Figs. 1A and 1B are schematic diagrams each showing
`
`an example of BLER (Block Error Rate) performance of PUSCH repetitions.
`
`[0015] As shown in Figs. 1A and 1B, Fig. 1A on the left and Fig. 1B on the right show
`
`simulation curves corresponding to two different repetition cases respectively.
`
`In each
`
`of them, the horizontal axis represents the average SNR (Signal to Noise Ratio) and the
`
`vertical axis represents the average BLER.
`
`In the lower left corner of Fig. 1A and the
`
`lower right corner of Fig. 1B, simulation parameters are given specifically. Simulation
`
`parameters of Fig. 1A and Fig. 1B are same except that repetition time NRep = 8 for Fig.
`
`1A and repetition time NRep =128 for Fig. 1B.
`
`[0016]
`
`Further, as shown in the upper right corner of Fig. 1A and Fig. 1B, a parameter
`
`of Nave represents the number of subframes combined in the receiver side for joint
`
`channel estimation. Specifically, in Fig. 1A, for a case of 8 repetitions, the curve in
`
`dotted line corresponds to the ideal channel estimation and three curves in solid lines
`
`correspond to realistic channel estimations when the number of subframes combined in
`
`the receiver side to do joint channel estimation equals to 1, 4 and 8 respectively.
`
`Similarly, in Fig. 1B, for a case of 128 repetitions, the curve in dotted line corresponds to
`
`the ideal channel estimation and three curves in solid lines correspond to realistic
`
`channel estimations when the number of subframes combined in the receiver side to do
`
`joint channel estimation equals to 1, 4 and 8 respectively.
`
`[0017]
`
`lntuitively, by comparing Fig. 1A and Fig. 1B, no matter whether the ideal
`
`channel estimation or realistic channel estimations, the average SNR of 8 repetitions is
`
`much larger than that of 128 repetitions for a same average BLER. Also, the
`
`performance gap between the ideal channel estimation curve and realistic channel
`
`estimation curves with 4 or 8 subframes combining for the case of 8 repetitions in Fig.
`
`1A is smaller than that for the case of 128 repetitions in Fig. 1B. That is, the
`
`performance gap between the ideal channel estimation curve and the realistic channel
`
`estimation curves becomes large as the number of repetitions increases.
`
`4
`
`P0625234
`
`

`

`[0018]
`
`In particular, when observing the average BLER = 10'1 as an example, by
`
`comparing the ideal channel estimation curve with the curve for the case of Nave = 8 as
`
`indicated by the bidirectional arrow, it can be easily found that the channel estimation
`
`gain is only about 1 dB for the case of 8 repetitions as shown in Fig. 1A and reaches up
`
`to 6 to 7 dB for the case of 128 repetitions as shown in Fig. 18. That is to say, the
`
`channel estimation gain is quite limited in case of a small repetition time but large in
`
`case of a large repetition time.
`
`[0019]
`
`It is noted that, although the simulation results come from the uplink simulation,
`
`the above observation is also valid for downlink cases. Namely, the channel estimation
`
`performance improvement will largely increase BLER performance in lower SlNR
`
`(Signal to Inference plus Noise Ratio) scenario (e.g., as shown in Fig. 1B) but only have
`
`a small effect on performance in relatively higher SlNR scenario (e.g., as shown in Fig.
`
`1A).
`
`[0020]
`
`So from the above observation, it is meaningful to increase RS density for a
`
`large repetition time or long repetitions (a higher coverage enhancement level) which
`
`has relatively lower SlNR as shown in Fig. 18, instead of zero or a small repetition time
`
`or no or short repetitions (no or a lower coverage enhancement level) which has
`
`relatively higher SlNR as shown in Fig. 1A.
`
`[0021] The second observation is based on EPDCCH (Enhanced Physical Downlink
`
`Control Channel) examples as follows.
`
`[0022] As one example, assuming that EPDCCH is transmitted with one PRB which
`
`has 120 available REs, DCI (Downlink Control Information) size is 26 bits with CRC
`
`(Cyclic Redundancy Check) and modulation is QPSK (Quadrature Phase Shift Keying),
`
`equivalent coding rate thereof is around 26/(120 x 2) = 0.108, which is quite low.
`
`In that
`
`case, in order to increase RS density, some REs assigned for transmitting data signals
`
`are usually used for transmitting RS, which seems to have no big impact on the coding
`
`rate. For example, using 12 data REs for transmitting RS additionally will make the
`
`coding rate changed to 26/((120 - 12) x 2) = 0.120, which is still very low. And the
`
`change amount of the coding rate is 0.012, which is also very low.
`
`[0023] As another example, assuming EPDCCH is transmitted with one ECCE
`
`5
`
`P0625234
`
`

`

`(Enhanced Control Channel Element) which could carry 36 REs, DCI size is also 26 bits
`
`with CRC and modulation is QPSK, equivalent coding rate thereof is 26/(36 x 2) = 0.361,
`
`which is relatively high as compared with the above example.
`
`In this case, replacing 3
`
`or 6 data REs for RS REs will make the coding rate changed to 26/((36 - 3) x 2) = 0.394
`
`or 26/((36 - 6) x 2) = 0.433, which is also relatively high as compared with the above
`
`example. And, the change amount of the coding rate is 0.033 or 0.072, which is
`
`correspondingly high. Thus, replacing 3 or 6 data REs for RS REs would have some
`
`impact on BLER performance.
`
`In that case, the channel estimation gain resulting from
`
`the RS density increase may be smaller than a loss caused by the increased coding
`
`rate.
`
`[0024] Therefore, from the above observation, it can be found that RS density
`
`increase is more reasonable in a case of a low coding rate (e.g., the former example)
`
`than a case of a high coding rate (e.g., the latter example), because it has almost no
`
`impact on the low coding rate but UE (User Equipment) can benefit from the channel
`
`estimation performance improvement resulting from the RS density increase.
`
`[0025]
`
`It is noted that, although the results of the above observation are based on
`
`downlink examples, the above observation is also valid for uplink cases.
`
`[0026] Based on the above two observations, we need to consider in which conditions
`
`the RS density increase is meaningful when adopting the RS density increase, so as to
`
`maximally optimize system performance.
`
`[0027]
`
`In an embodiment of the present disclosure, there is provided a wireless
`
`communication method 20 as shown in Fig. 2. Fig. 2 is a flowchart of a wireless
`
`communication method according to an embodiment of the present disclosure. As
`
`shown in Fig. 2, the wireless communication method 20 includes a step S201 of
`
`transmitting a reference signal and a data signal in a PRB with a coverage
`
`enhancement level.
`
`In the wireless communication method 20, the number of resource
`
`elements transmitting the reference signal in the PRB is determined by the coverage
`
`enhancement level, the channel type and/or the coding rate of the data signal.
`
`[0028]
`
`Specifically, as described above, one PRB includes 12 x 14 REs in total, some
`
`of which are assigned for transmitting the reference signal (RS) and another some of
`
`6
`
`P0625234
`
`

`

`which are used for transmitting the data signal. For example, the RS may be a DMRS
`
`which is used to demodulate the transmitted signals containing the data in a UE
`
`(receiver side). However, the RS is not limited to a certain RS such as DMRS and may
`
`be all kinds of RSs. For example, when the wireless communication method 20 is used
`
`in MTC, the RS may be a CRS.
`
`[0029]
`
`Furthermore, for example, in MTC with coverage enhancement, a coverage
`
`enhancement level is defined to indicate the level or degree of coverage enhancement.
`
`The higher the coverage enhancement level is, the larger the coverage enhancement is.
`
`In more particular, when employing repetitions to implement coverage enhancement,
`
`the coverage enhancement level may also be represented by the repetition time. That
`
`is to say, the more the repetition time employed is, the larger the coverage
`
`enhancement is and thus the higher the coverage enhancement level is.
`
`[0030]
`
`In addition, with respect to repetitions, it is well known that the repetition time
`
`may indicate the time the RS and the data signal are transmitted repeatedly in
`
`subframes or in PRBs. One subframe consists of two slots, each of them contains 7
`
`symbols in time domain, which is same as one PRB. However, one PRB corresponds
`
`to 12 subcarriers in frequency domain, and one subframe depends on the bandwidth in
`
`frequency domain. Thus, repetition in subframes means repetition in time domain only
`
`and repetition in PRBs means repetition in both time domain and frequency domain.
`
`It
`
`is noted that, although not exemplified here, repetition may also be implemented in
`
`frequency domain only.
`
`[0031] Thus, according to an embodiment of the present disclosure, in the wireless
`
`communication 20, the coverage enhancement level may be represented by the
`
`repetition time of transmission of the reference signal and the data signal in time domain
`
`and/or in frequency domain.
`
`[0032] Note that, the repetition as one of key techniques for coverage enhancement is
`
`only for illustration, the techniques for coverage enhancement are not limited to the
`
`repetition, and other techniques may be used to implement coverage enhancement.
`
`When employing other techniques, the coverage enhancement level may be
`
`represented by other parameters instead of the repetition time.
`
`7
`
`P0625234
`
`

`

`[0033]
`
`Further, the wireless communication method 20 is suitable for MTC, but not
`
`limited to MTC.
`
`It can be applied to any wireless communication with coverage
`
`enhancement.
`
`[0034] As described above, the number of REs transmitting the RS in the PRB may
`
`be determined by the coverage enhancement level, the channel type and/or the coding
`
`rate of the data signal. That is, one of or any combination of the three parameters are
`
`used to implement RS density increase. The details of the three parameters will be
`
`discussed later.
`
`[0035] With the wireless communication 20, by increasing RS density based on the
`
`coverage enhancement level, the channel type and/or the coding rate of the data signal,
`
`signal quality is improved and the power consumption for UEs with coverage
`
`enhancement is reduced.
`
`[0036] According to an embodiment of the present disclosure, in the wireless
`
`communication 20 as shown in Fig. 2, the number of resource elements transmitting the
`
`reference signal in the PRB for a larger coverage enhancement level may be more than
`
`that for a smaller coverage enhancement level.
`
`[0037]
`
`Specifically, as found in the first observation above, since the communication
`
`with a larger coverage enhancement level (e.g., a larger repetition time) has relatively
`
`low SlNR as shown in Fig. 18 and the channel estimation performance improvement
`
`will largely increase its BLER performance, it is meaningful to increase RS density in
`
`this case, that is, more RS REs in the PRB should be used for transmitting the RS.
`
`Meanwhile, the communication with a smaller coverage enhancement level (e.g., a
`
`smaller repetition time) has relatively higher SlNR as shown in Fig. 1A and the channel
`
`estimation performance improvement only have small effect on its BLER performance, it
`
`is meaningless to increase RS density in this case, that is, less RS REs in the PRB
`
`should be used for transmitting the RS.
`
`[0038]
`
`In order for those skilled to understand more easily, PDSCH (Physical
`
`Downlink Shared Channel) is taken as an example.
`
`In the following, Table 1 shows an
`
`exemplary usage of REs for transmitting the RS in the PRB based on the coverage
`
`enhancement level.
`
`8
`
`P0625234
`
`

`

`Table 1
`
`Coverage
`Enhancement
`
`Level
`
`lllllllllllllllilllllllllilllllllllllllll
`
`One or two
`
`Two or four
`
`DMRS
`
`DM RS
`
`DMRS (two
`or four
`
`REs Maximum
` DMRS (two
`
`ports: 12
`REs
`
`ports: 24
`REs
`
`RS
`
`Configuration
`
`ports, 24
`REs) +
`CRS (two
`ports, 16
`REs) = 40
`REs
`
`or four
`
`ports, 24
`REs) +
`CRS (four
`ports, 24
`REs) = 48
`
`DMRS REs
`+ maximum
`
`CRS REs +
`
`CSl-RS
`
`REs > 48
`
`REs
`
`
`
`[0039]
`
`In Table 1, the first line gives five different coverage enhancement levels 1-5
`
`and the second line shows RS configurations corresponding to the coverage
`
`enhancement levels 1-5, respectively. Here, it is assumed that the coverage
`
`enhancement level 1 indicates the smallest level (e.g., the smallest repetition times) and
`
`the coverage enhancement level 5 indicates the largest level (e.g., the largest repetition
`
`times).
`
`[0040]
`
`In a case of the smallest coverage enhancement level 1, the smallest number
`
`of REs in the PRB is used for transmitting the RS, that is, the smallest RS density is
`
`employed since there is potentially no channel estimation gain resulting from RS density
`
`increase in this scenario as discussed previously. For example, as shown in Table 1,
`
`one or two DMRS ports, i.e., 12 DMRS REs, may be used as RS REs here.
`
`[0041]
`
`In a case of the coverage enhancement level 2 which is larger than the
`
`smallest coverage enhancement level 1, the number of REs for transmitting the RS in
`
`the PRB may be increased from the case of the smallest coverage enhancement level 1.
`
`For example, as shown in Table 1, two or four DMRS ports, i.e., 24 DMRS REs, may be
`
`used as RS REs here. 24 DMRS REs is the maximum DMRS RE configuration.
`
`[0042]
`
`In a case of the coverage enhancement level 3 which is larger than the
`
`coverage enhancement level 2, the number of REs for transmitting the RS in the PRB
`
`may be further increased from the case of the coverage enhancement level 2. For
`
`example, as shown in Table 1, in addition to two or four DMRS ports, i.e., 24 DMRS
`
`REs, two CRS ports, i.e., 16 CRS REs, may be used as RS REs here. That is to say,
`
`P0625234
`
`

`

`there are 40 RS REs in total in the PRB in this case.
`
`[0043]
`
`In a case of the coverage enhancement level 4 which is larger than the
`
`coverage enhancement level 3, the number of REs for transmitting the RS in the PRB
`
`may be further increased from the case of the coverage enhancement level 3. For
`
`example, as shown in Table 1, two or four DMRS ports, i.e., 24 DMRS REs, as well as
`
`four CRS ports, i.e., 24 CRS REs, may be used as RS REs here. That is to say, there
`
`are 48 RS REs in total in the PRB in this case. 24 CRS REs is the maximum CRS RE
`
`configuration.
`
`[0044]
`
`In a case of the largest coverage enhancement level 5, the number of REs for
`
`transmitting the RS in the PRB may be further increased from the case of the coverage
`
`enhancement level 4. For example, as shown in Table 1,
`
`in addition to the maximum
`
`DMRS RE configuration, i.e., 24 DMRS REs, as well as the maximum CRS RE
`
`configuration, i.e., 24 CRS REs, REs assigned for another RS such as CSl-RS
`
`(Channel State Information Reference Signal) may be used as RS REs here. That is to
`
`say, there are more than 48 RS REs in total in the PRB in this case.
`
`[0045] With the RS configuration based on the coverage enhancement level in Table
`
`1, UE which cannot benefit from RS density increase will have no performance loss.
`
`[0046]
`
`It is noted that, the classification of coverage enhancement levels and
`
`corresponding RS configurations in Table 1 are only for the purpose of illustration, and
`
`the present disclosure is not limited thereto. The classification of coverage
`
`enhancement levels and corresponding RS configurations may be varied depending on
`
`specific practice.
`
`[0047]
`
`Further, although determination of the number of RS REs in a PRB based on
`
`the coverage enhancement level is explained specifically taking PDSCH as an example,
`
`the present disclosure is not limited thereto. The present disclosure is also suitable for
`
`15 PUSCH for example, and is even applicable to any kinds of downlinks and uplinks.
`
`[0048]
`
`By determining the number of RS REs in a PRB based on the coverage
`
`enhancement level, the wireless communication 20 can avoid increasing RS density
`
`unnecessarily and impacting original performance for UEs with a smaller coverage
`
`enhancement level due to increased overhead and coding rate.
`
`10
`
`P0625234
`
`

`

`[0049] According to an embodiment of the present disclosure, in the wireless
`
`communication 20 as shown in Fig. 2, at least a part of the reference signal transmitted
`
`in the PRB may reuse existing CRS, DMRS, CSl-RS and/or other existing reference
`
`signals.
`
`[0050] Reusing these existing RSs means not only using REs assigned for
`
`transmitting these existing RSs in the PRB but also using these signals for channel
`
`estimation. Specifically, RE configurations in a PRB for legacy RSs such as CRS,
`
`DMRS, CSl-RS and the like are predefined in the standard. These legacy RSs can be
`
`reused for increasing RS density.
`
`[0051]
`
`For a MTC UE for example, depending on the specific requirement of RS
`
`density increase, the RS used for MTC may reuse existing CRS, DMRS, CSl-RS, that is,
`
`REs for transmitting the RS for MTC in the PRB may directly apply CRS REs, DMRS
`
`REs, CSl-RS REs and so on. For example, as shown in Table 1, for the coverage
`
`enhancement levels 1 and 2, DMRS is reused. When it is required to increase RS
`
`density for the coverage enhancement levels 3 and 4, CRS is additionally reused.
`
`When it is required to further increase RS density for the coverage enhancement level 5,
`
`DMRS, CRS and CSl-RS are all reused.
`
`In addition to REs of legacy RS, signals of
`
`these legacy RSs may be directly used for the MTC.
`
`[0052]
`
`By reusing legacy RSs for the RS in the wireless communication 20, existing
`
`RSs could be utilized as much as possible and increasing many additional RS REs is
`
`avoided, thus the resource utilization ratio is guaranteed.
`
`[0053] According to an embodiment of the present disclosure, in the wireless
`
`communication 20 as shown in Fig. 2, at least a part of the reference signal transmitted
`
`in the PRB may be transmitted in resource elements used for transmitting the data
`
`signal.
`
`[0054]
`
`Specifically, when legacy RSs cannot be used for MTC for example, some REs
`
`assigned for transmitting the data signals can be used for transmitting the RS. For
`
`example, it is assumed that only DMRS REs are available for PDSCH case in Table 1.
`
`Accordingly, in case of the coverage enhancement level 3, in addition to the maximum
`
`DMRS RE configuration, i.e., 24 DMRS REs, 16 REs assigned for transmitting data
`
`1 1
`
`P0625234
`
`

`

`signals may be used now for transmitting the RS instead of CRS REs. The cases of the
`
`coverage enhancement levels 4 and 5 will be similar with the case of the coverage
`
`enhancement level 3.
`
`[0055] Therefore, based on the availability of legacy RSs and the number of RS REs
`
`to be increased, all of the RS may reuse legacy RSs, a part of the RS may reuse legacy
`
`RSs and the rest of the RS may be transmitted in some data REs in the PRB, or all of
`
`the RS may be transmitted in some data REs in the PRB.
`
`[0056] According to an embodiment of the present disclosure, in the wireless
`
`communication as shown in Fig. 2, the number of resource elements transmitting the
`
`reference signal in the PRB for a higher coding rate is less than that for a lower coding
`
`rate.
`
`[0057]
`
`Specifically, as found in the second observation above, since there is almost
`
`no impact on a low coding rate when increasing RS density, RS density increase is
`
`more reasonable in a case of a low coding rate than a case of a high coding rate. That
`
`is to say, more RS REs in the PRB should be used for transmitting the RS in a case of a
`
`low coding rate, meanwhile less RS REs in the PRB should be used for transmitting the
`
`RS in a case of a high coding rate.
`
`[0058]
`
`By determining the number of RS REs in a PRB based on the coding rate, the
`
`wireless communication 20 can avoid increasing RS density unnecessarily and causing
`
`performance loss to UEs with a high coding rate.
`
`[0059] According to an embodiment of the present disclosure, in the wireless
`
`communication 20 as shown in Fig. 2, the data signal may be used for transmitting
`
`PDSCH or PUSCH, and the usage of resource elements for transmitting the reference
`
`signal in the PRB may be indicated by MCS indicated in DCI, which is transmitted in
`
`Physical Downlink Control Channel (PDCCH) or EPDCCH.
`
`[0060]
`
`Specifically, in order for those skilled to understand more easily, PDSCH is still
`
`taken as an example in which it is assumed that PDSCH is transmitted with one PRB
`
`with 120 available REs, and the modulation is QPSK. The usage (configuration) of RS
`
`in this case may be indicated in MCS which is indicated in DCI transmitted in PDCCH or
`
`EPDCCH.
`
`In the following, Table 2 shows an example of RS density increase based on
`
`12
`
`P0625234
`
`

`

`the coding rate indicated by MCS (Modulation and Coding Scheme).
`
`Table 2
`
`MCS Index
`
`Modulation
`Order
`
`TBS Index
`
`COdinQ Rate
`
`Increased
`Number of RS
`REs
`
`24REs
`
`MES
`
`24REs
`
`—— 0-067
`
`0-134
`
`0-167
`
`WES
`
`[0061]
`
`In Table 2, the first column lists out MCS indices 0-9, and the second column
`
`gives the modulation order which equals to 2 for QPSK here. Further, the third column
`
`shows TBS (Transport Block Size) indices 0-9 which correspond to MCS indices 0-9 of
`
`the first column one by one and respectively indicates different sizes of data, i.e.,
`
`different numbers of bits of data. Based on the number of bits indicated by each TBS
`
`index as well as conditions assumed above, the corresponding coding rate of each TBS
`
`index may be calculated through the same computation method as that in the second
`
`observation above. The fourth column gives the calculated coding rates respectively
`
`corresponding to TBS indices 0-9. For example, TBS index 0 and MCS index 0
`
`correspond to a coding rate of 0.067, TBS index 1 and MCS index 1 correspond to a
`
`coding rate of 0.1, TBS index 2 and MCS index 2 correspond to a coding rate of 0.134,
`
`TBS index 3 and MCS index 3 correspond to a coding rate of 0.167, TBS index 4 and
`
`13
`
`P0625234
`
`

`

`MCS index 4 correspond to a coding rate of 0.233, TBS index 5 and MCS index 5
`
`correspond to a coding rate of 0.3, TBS index 6 and MCS index 6 correspond to a
`
`coding rate of WA, TBS index 7 and MCS index 7 correspond to a coding rate of 0.433,
`
`TBS index 8 and MCS index 8 correspond to a coding rate of 0.5, and TBS index 9 and
`
`MCS index 9 correspond to a coding rate of 0.567.
`
`[0062] Based on the above discussion, the number of RS REs in the PRB for a higher
`
`coding rate should be less than that for a lower coding rate since the RS density
`
`increase hardly impact the lower coding rate and UE can benefit from the channel
`
`estimation improvement resulting from the RS density increase without suffering from
`
`increased coding rate.
`
`[0063]
`
`In Table 2, the fifth column gives increased number of RS REs in different
`
`cases. Specifically, in cases of low coding rates of 0.067, 0.1 and 0.134 respectively
`
`indicated by MCS index 0, 1 and 2, largest RE density increase is employed, i.e., 24
`
`REs are added for transmitting the RS in the PRB.
`
`In cases of medium coding rates of
`
`0.167, 0.233 and 0.3 respectively indicated by MCS index 3, 4 and 5, medium RE
`
`density increase is employed, i.e., 12 REs are added for transmitting the RS in the PRB.
`
`In cases of large coding rates of WA, 0.433, 0.5 and 0.567 respectively indicated by
`
`MCS index 6, 7, 8 and 9, RE density increase is not employed, i.e., no RE is added for
`
`transmitting the RS in the PRB. Thus, the usage of REs for transmitting the RS (or the
`
`RS density increase) in the PRB can be indicated by MCS as shown in Table 2.
`
`[0064] Note that, the increased number of RS REs (e.g., 24 or 12 REs) in Table 2 is
`
`only for the purpose of illustration and the present disclosure is not limited thereto.
`
`Further, although PDSCH is taken as an example here, the present disclosure is not
`
`limited thereto. The present disclosure is also suitable for PUSCH for example, and is
`
`even applicable to any kinds of downlink and uplink data.
`
`[0065]
`
`In addition, as discussed before, the added 24 or 12 REs in this example may
`
`reuse legacy RSs, may be transmitted in some data REs in the PRB, or may partially
`
`reuse legacy RSs and partially be transmitted in some data REs in the PRB.
`
`[0066]
`
`By indicating the usage of REs for transmitting the RS in the PRB by MCS,
`
`there is no need to set a new signaling to indicate the RS usage.
`
`14
`
`P0625234
`
`

`

`[0067] According to an embodiment of the present disclosure, in the wireless
`
`communication 20 as shown in Fig. 2, the usage of resource elements transmitting the
`
`reference signal in the PRB may be configured by Radio Resource Control (RRC), may
`
`be predefined or may be recommended by a user equipment through Channel Quality
`
`Indicator (CQI).
`
`[0068]
`
`Specifically, although an example that the usage of REs for transmitting the RS
`
`in the PRB is indicated by MCS is given above, the present disclosure is not limited
`
`thereto. The detailed usage of increased RS REs may also be configured by RRC or
`
`predefined. Alternatively, UE may also recommend the RS density increase through
`
`CQI. Since RRC and CQI are existing signaling like MCS and configurations thereof
`
`are well known to those skilled in the art, no more details thereof will be discussed here
`
`for avoiding redundancy. Similarly, there is no need to set a new signaling to indicate
`
`the RS usage in this case.
`
`[0069] As mentioned previously, the number of REs transmitting the RS in the PRB
`
`may be determined by the channel type of the data signal. That is to say, different
`
`channel may use different RS density.
`
`[0070] According to an embodiment of the present disclosure, in the wireless
`
`communication 20 as shown in Fig. 2, the data signal may be used for transmitting
`
`PDCCH or EPDCCH, and the usage of resources elements transmitting the reference
`
`signal in the PRB may be indicated by SIB (System Information Block) or may be
`
`specified.
`
`[0071]
`
`Specifically, PDCCH and PDSCH are taken as an example.
`
`In general, it is
`
`assumed that PDCCH has a quite low coding rate, for example, uses one PRB to
`
`transmit DCI of 26 bits, but PDSCH uses a relatively high coding rate so as to
`
`guarantee the throughput.
`
`In this case, PDSCH usually use a normal RS density while
`
`PDCCH may use increased RS density. Thus, the channel performance of PDSCH will
`
`not be impacted. Meanwhile, PDCCH almost has no performance loss as well but can
`
`benefit from the channel estimation performance improvement resulting from the RS
`
`density increase.
`
`[0072]
`
`In addition, the detailed usage of RS REs for PDCCH may be indicated by SIB.
`
`15
`
`P0625234
`
`

`

`Alternatively, the detailed usage of RS REs for PDCCH may be specified for example in
`
`specification. For example, for the purpose of simplicity, the maximum RS density (e.g.,
`
`24 CRS REs plus 24 DM