SYSTEM

FIELD OF THE INVENTION

[1] The present invention relates to wireless communication technologies, and more specifically relates to a method and apparatus for processing a DMRS (demodulated reference signal) signal in a LTE (Long-Term Evolution)-based wireless communication system.

BACKGROUND OF THE INVENTION

[2] In the LTE Release 13 protocol, 3GPP (3 Generation Partnership Project) has decided to consider the DMRS enhancement technology to better support downlink multi-user multi-in multi-out (DL MU-M IMO). About this point, there are several candidate schemes where the extended DL DMRS over the DM RS features supported in the technical report TR36.897 are utilized to reduce mutual interference among DMRS ports.

[3] Wherein, in alternative solution 1 proposed by current 3GPP, the OCC (Orthogonal Cover Code) =4, and each physical resource block (PRB) uses 12 resource elements (RE), i.e., making enhancement on the existing antenna ports 7, 8, 11, and 13. This alternative has the following advantages, e.g., smallest reference signal (RS) overhead, no extra RE puncturing, and transparency for MU (multi-user) operation; therefore, it is very likely supported by the 3GPP.

However, the current DMRS pattern will cause power fluctuations issue to the alternative 1 between OFDM symbols where DMRS is multiplexed. This is the so-called power imbalance problem, which should be avoided in reference signal design. In order to solve this problem, the present invention provides a solution of using a new OCC pattern for the extended DM RS ports.

[4] In current LTE protocol, two OCC patterns are provided below:

{wp(i), Wp(3— 0} P ⁼ 7,8,11,13, wherein p indicates an antenna port number;

[5] In alternative solution 1 of the TR36.897, the two OCC patterns rotate between DM RS subcarriers for antenna ports 7, 8, 11, and 13. The sequence for each port is defined by the following Walsh code:

[6] If we rewrite it the Walsh matrix into

[7] then, rotation pattern, w _p (i) and w _p (3— i) can be expressed by [a b c d] and [d c b a] respectively. Suppose there are four multi-user layers (MU layers) and the associated precoding weights for the n ^th transmit antenna at eNB is denoted by z _n = [ ^z n,i ^z n,2 ^z n,3 ^z n,4] ^T ■ Then, as illustrated in Fig. 1, the transmission power of the nth transmitting antenna for four DMRS OFDM symbols in one subframe can be determined by: ¾ι = ^ ( ¾ + l ^dT ¾| ² ) = ^¾ ^««T + dd^z _n

¾!_ = ^ (|f ^T ¾| ² + k ^T Z _n | ² ) = ^zgCftft ^T _{+ cc} T _)Zn

¾ ^S o, ₃ = ^ (k ^T Z _n | ² + | ¾ ^T Z _n | ² ) = ^ ZH( _CC T + ftftT _)Zn

¾ ^S o, ₄ = ^ (|d ^T z„ + |« ^T z _n | ² ) = ^ ^ζ ^ + aa^z _n

[8] Because the pre-coding vector Z _n is dependent on channel conditions, the transmission powers for four symbols are different from each other. The worst case is that Z _n matches one of the sequences in {a, b, c, d}. For example, ifz _n = a = [+1 +1 +1 +1] ^T , then P _S ymboii ^{= P} s mboi4 = 48N _RB and P _s ™boi2 = ^P symboi3 = °< ^{wnich wil1 cause} power fluctuation between OFDM symbols, thereby causing power imbalance between OFDM symbols.

SUMMARY OF THE INVENTION

[9] An objective of the invention is to solve the issue of imbalance between OFDM symbols for DMRS enhancement technology in the existing LTE protocol.

[10] According to a first aspect of the present invention, there is provided a method for processing DMRS signals in a LTE protocol-based base station, wherein before performing OFDMA modulation, the method further comprises:

[11] - performing pattern rotation processing with OCCs on subcarriers corresponding to available DMRS antenna ports so as to reduce power imbalance between OFDM symbols generated subsequently.

[12] According to a second aspect of the present invention, there is provided a method of processing DMRS signals in a LTE-based user equipment, comprising:

[13] performing processing, which reverse to the pattern rotation processing in the method according to the first aspect of the present invention, with OCCs on subcarriers corresponding to available DMRS antenna ports in an OFDM-demodulated data block.

[14] According to a third aspect of the present invention, there is provided an apparatus for processing DMRS signals in a LTE protocol-based base station, wherein before performing OFDMA modulation, the apparatus further comprises:

[15] a pattern rotation processing module configured to perform pattern rotation processing with OCCs on subcarriers corresponding to available DMRS antenna ports so as to reduce power imbalance between OFDM symbols generated subsequently.

[16] According to a fourth aspect of the present invention, there is provided an apparatus for processing DMRS signals in a LTE-based user equipment, comprising:

[17] a pattern rotation reverse processing module configured to perform processing, which reverse to the pattern rotation processing in the method according to the third aspect of the present invention, with OCCs on subcarriers corresponding to available DMRS antenna ports in an OFDM-demodulated data block.

[18] The solution according to the present invention may eliminate or reduce the imbalance issue between OFDM symbols for DMRS enhancement technology in the existing LTE protocol.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS [19] The present invention will be understood more comprehensively through the detailed depiction provided below and the accompanying drawings, wherein the same units are represented by the same reference numerals. The drawings are only provided for illustration and therefore not intended to constitute limitation to the present invention, wherein:

[20] Fig. 1 illustrates the OCC rotation pattern in an existing scheme according to the LTE R12 protocol;

[21] Fig. 2 illustrates the OCC rotation pattern obtained after processing DMRS signal based on column permutation according to one embodiment of the present invention;

[22] Fig. 3 illustrates the OCC rotation pattern obtained after processing DMRS signal based on frequency dependent code according to one embodiment of the present invention;

[23] Fig. 4 illustrates a flow diagram of a method for processing DMRS signal in a LTE-based base station according to one aspect of the present invention;

[24] Fig. 5 illustrates a flow diagram of a method for processing DMRS signal in a LTE-based user equipment according to another aspect of the present invention;

[25] Fig. 6 illustrates a block diagram of an apparatus for processing DMRS signal in a LTE-based base station according to one aspect of the present invention;

[26] Fig. 7 illustrates a block diagram of an apparatus for processing DMRS signal in a LTE-based user equipment according to another aspect of the present invention;

[27] It should be mentioned that these figures are intended to illustrate general characteristics of the method, structure and/or material utilized in some exemplary embodiments and make supplementations to the written description provided infra. However, these figures are not drawn proportionally and possibly do not accurately reflect an accurate structure or performance characteristics of any given embodiment, and should not be construed as defining or limiting the scope of the numerical values or attributes covered by the exemplary embodiments. Use of similar or totally identical reference numerals in respective figures is to indicate existence of similar or completely identical units or features.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[28] Although the exemplary embodiments may have various modifications and alternative manners, only some embodiments thereof are illustrated in the drawings as examples, which will be described in detail here. However, it should be understood that it is not intended to limit the exemplary embodiments to the specific forms disclosed here; on the contrary, the exemplary embodiments intend to cover all modifications, equivalent solutions, and alternative solutions within the scope of the claims. Same reference numerals constantly represent same units in depictions of respective drawings.

[29] It should be mentioned before discussing the exemplary embodiments in more detail that some exemplary embodiments are described as processing or methods in the form of flow diagrams. Although a flow diagram depicts respective operations as being sequentially processed, many operations therein may be implemented in parallel, concurrently or simultaneously. Besides, various operations may be re-ordered. When the operations are completed, the processing may be terminated. However, there may comprise additional steps not included in the accompanying drawings. The processing may correspond to a method, a function, a specification, a sub-routine, a sub-program, etc.

[30] The term "wireless device" or "device" used here may be regarded as synonymous to the following items and sometimes referred to as the following items infra: client, user equipment, mobile station, mobile user, mobile end, subscriber, user, remote station, access terminal, receiver, mobile unit, etc., and may describe remote users of wireless resources in the wireless communication network.

[31] Similarly, the term "base station" used here may be regarded as synonymous to the following items and sometimes referred to as the following items infra: node B, evolved-type node B, eNodeB, transceiver base station (BTS), RNC, etc. and may describe a transceiver communicating with the mobile terminal and providing a wireless resource in a wireless communication network crossing a plurality of technical generations. Except the capabilities of implementing the method discussed above, the base station as discussed may have all functions associated with traditional well-known base stations.

[32] The methods discussed infra (some of which are illustrated through flow diagrams) may be implemented through hardware, software, firmware, middleware, microcode, hardware description language or any combination thereof. When they are implemented with software, firmware, middleware or microcode, the program code or code segment for executing essential tasks may be stored in a machine or a computer readable medium (e.g., storage medium). (One or more) processors may implement essential tasks.

[33] The specific structures and function details disclosed here are only representative, for a purpose of describing the exemplary embodiments of the present invention. Instead, the present invention may be specifically implemented through many alternative embodiments. Therefore, it should not be appreciated that the present invention is only limited to the embodiments illustrated here.

[34] It should be understood that although terms "first," "second" might be used here to describe respective units, these units should not be limited by these terms. Use of these terms is only for distinguishing one unit from another. For example, without departing from the scope of the exemplary embodiments, the first unit may be referred to as the second unit, and similarly the second unit may be referred to as the first unit. The term "and/or" used here includes any and all combinations of one or more associated items as listed.

[35] It should be understood that when one unit is "connected" or "coupled" to a further unit, it may be directly connected or coupled to the further unit or an intermediate unit may exist. In contrast, when a unit is "directly connected" or "directly coupled" to a further unit, an intermediate unit does not exist. Other terms (e.g., "disposed between" VS. "directly disposed between," "adjacent to" VS. "immediately adjacent to," and the like) for describing a relationship between units should be interpreted in a similar manner.

[36] The terms used here are only for describing preferred embodiments, not intended to limit exemplary embodiments. Unless otherwise indicated, singular forms "a" or "one" used here further intends to include plural forms. It should also be appreciated that the terms "comprise" and/or "include" used here prescribe existence of features, integers, steps, operations, units and/or components as stated, but do not exclude existence or addition of one or more other features, integers, steps, operations, units, components, and/or a combination thereof.

[37] It should also be noted that in some alternative embodiments, the functions/actions as mentioned may occur in an order different from what is indicated in the drawings. For example, dependent on the functions/actions involved, two successively illustrated diagrams may be executed substantially simultaneously or in a reverse order sometimes. [38] Unless otherwise defined, all terms (including technical and scientific terms) used here have meanings identical to what are generally understood by those skilled in the art within the field of exemplary embodiments. It should also be understood that unless explicitly defined here, those terms defined in commonly-used dictionaries should be interpreted to have meanings consistent in the context of relevant fields, and should not be interpreted according to ideal or too formal meanings.

[39] Some parts of exemplary embodiments and corresponding detailed depictions are provided through software or algorithm in the computer memory and symbols for operating data bits. These descriptions and expressions are descriptions and expressions used by those skilled in the art to effective convey their work substance to other skilled in the art. Like what are generally used, the term "algorithm" used here is envisaged to obtain step sequences consistent with the desired results. The steps are those steps for physically manipulating the physical amounts. Generally, but not essentially, these numbers employ optical, electric, or magnetic signals that can be stored, transmitted, combined, and compared and manipulated by other manners. Mainly out of the reason of general use, it has been proved that it is advantages to refer to these signals sometimes as bits, numerical values, elements, symbols, characters, items, digits, etc.

[40] In the description below, illustrative embodiments may be described with reference to symbol expressions implemented as actions and operations processed by program modules or function modules. The program modules or function processing include routines, programs, objects, data structures, etc. for implementing specific tasks or specific abstract data types, using existing hardware at existing network elements. Such existing hardware may include one or more central processing units (CPU), digital signal processor (DSP), application-specific integrated circuit, field programmable gate array (FPGA) computer, etc.

[41] However, it should be aware that all of these and similar terms should be associated with appropriate physical amounts and are only convenient tags applied to these amounts. Unless otherwise explicitly stated, or it may be apparently seen from the discussion, terms such as "processing," "computing," "determining," or "displaying" refer to the actions and processing of a computer system or a similar electronic computing device, which manipulate data represented as physical and electronic amounts within the register and memory of the computer system and transform them into other data represented as physical amounts within the computer system memory or register or other such kind of information storage, delivery or display devices.

[42] It should also be mentioned that the aspect of software implementation of exemplary embodiments is generally encoded on a program storage medium of a certain form or a transmission medium of a certain type. The program storage medium may be magnetic (e.g., floppy or hard disk driver) or optical (e.g., compact disk read-only memory or "CD ROM") storage medium, and may be read-only or randomly access storage medium. Similarly, the transmission medium may be twisted pair, co-axial cable, optical fiber or some other appropriate transmission mediums known in the art. Exemplary embodiments are not limited to these aspects of any given embodiments.

[43] The processors and memory may operate together to run apparatus functions. For example, the memory may store code segments regarding the apparatus functions. The code segment may also be executed by the processor. Besides, the memory may store processing variables and constants for the processor to use. [44] Fig. 4 illustrates a flow diagram of a method for processing DM RS signal in a LTE-based base station according to one aspect of the present invention, wherein as illustrated in Fig. 4:

[45] In step S401, the base station performs pattern rotation processing with OCCs on subcarriers corresponding to available DM RS antenna ports so as to reduce power imbalance between OFDM symbols generated subsequently;

[46] Then, in step S402, the base station performs OFDM modulation to a data block including the pattern rotation processed OCC to generate an OFDM symbol.

[47] In other words, in order to solve the problem of power imbalance between OFDM symbols existing in DM RS enhancement technology of the existing LTE protocol, the base station according to the present invention can generate OFDM symbols by performing pattern rotation processing with the OCC on subcarriers corresponding to the available DMRS antenna ports and then performing OFDM modulation to the data block.

[48] Specifically, the pattern rotation processing process includes, but not limited to, perform a certain degree of transformation to the OCC rotation pattern used by the DMRS, e.g., a transformation based on column permutation and frequency dependent code. Hereinafter, two embodiments of transformation based on column permutation and frequency dependent code are provided below, respectively.

COLUMN PERMUTATION-BASED TRANSFORMATION:

[49] In step S401, the step of performing pattern rotation processing with OCCs on subcarriers corresponding to available DMRS antenna ports comprises:

[50] - performing pattern rotation processing with M=4 DMRS OCCs, as provided by the following expression, on subcarriers corresponding to the available DMRS antenna ports:

{WE ₀ , WE ₁ , WE ₂ , WE ₃ }, (1) wherein, W is a Walsh matrix

wherein E _t is a 4x4 permutation matrix, i.e., the columns of E _t are non-identical to each other and selected from the following set:

and satisfies the following condition:

[51] Hereinafter, the column permutation-based solution will be further illustrated using two embodiments with 4 antenna ports 7/8/11/13 designated for DMRS enhancement in the current LTE protocol:

Embodiment 1:

Wherein E _t is: 0 0 0 0 0 1 1 0

1 0 0 1 0 0 0 0

En = , E ₃ =

0 1 1 0 , E ₂ = 0 0 0 0 0 0 0 0 1 0 0 1

[52] It is apparent that E _t satisfies the condition of equation (2) above. Then, as illustrated in Fig. 2, the OCC rotation pattern is:

WE ₀ = [a b c d] WE ₁ = [d c b a] WE ₂ = [c d a b]

WE, [b a d e]

[53] Here, as illustrated in the equation below, we can easily verify that in the present embodiment, the transmission power for DMRS symbols after column permutation are identical.

iDMRS jDMRS iDMRS 3N RB

symboll ' symboll ' symboll ' symboll z^(aaJ + bb ¹ + cc ^T + dd ^T )z,

[54] If the PRB number is an integer multiple of 4, the rotated DMRS OCC pattern (hereinafter referred to as "OCC pattern") based on the present embodiment eliminates the power fluctuation between different symbols. When the rotated OCC pattern is substituted into the original Walsh matrix, it may be seen in the example that the ports 7/8 still maintain the same rotation pattern (w _p (i), w _p (3— i)} as Releasel2; the DMRS OCC pattern for ports 11/13 is transformed into:

{wu (0- Wn(3 - O. Wn(3 - O.WnCO)

{w ₁₃ (i), w ₁₃ (3 - i), -w ₁₃ (3 - 0- -w ₁₃ (0)

[55] As a preferred solution, because the OCC pattern for ports 7/8 is not changed, the embodiment may be compatible with legacy user equipments (UEs) of Releasel2 or an earlier version in DMRS enhancement technology.

[56] Generally, besides embodiment 1, in order to support legacy user equipments of Releasel2 and an earlier version in DMRS enhancement technology, another restricted condition for selecting E _t is to ensure that the resulted OCC rotation pattern for ports 7/8 is same with that in Releasel2 protocol.

Embodiment 2:

[57] In the present embodiment, E _t is:

[58] Likewise, E _t also satisfies the condition of equation (2). The OCC rotation pattern is:

WE ₀ = [a b c d] [d a b c]

WE ₂ [c d a b]

WE ₃ [b c d a]

[59] It may be seen that the OCC rotation pattern has a cyclic shift form, and it may also be easily verified that the OCC rotation pattern based on this embodiment also eliminates the power fluctuation between different symbols, and does not change the rotation pattern of the port 7/8 defined in Releasel2.

12

[60] Because the DMRS enhancement technology has — = 3 Res in one PRB per OFDM symbol, the method of column permutation can only achieve power balance in PRBs with a number of integer multiples of 4. This also requires certain degree of limitation on channel frequency selectivity. In other words, it is required that the channel frequency selection characteristics are approximately unchanged in 4 PRBs. In order to solve this problem, another solution based on frequency dependent code is proposed, which may relax the limitation on channel frequency selectivity in the column permutation-based solution.

FREQUENCY DEPENDENT CODE-BASED SOLUTION:

[61] In the present solution, in step S401, the step of performing pattern rotation processing with OCCs on subcarriers corresponding to available DMRS antenna ports comprises:

- performing pattern rotation using M DMRS OCCs on subcarriers corresponding to the available DMRS antenna ports, the OCC pattern is rotated using the expression below:

{diag{/ ₀ } , diagifj W, ··· , diagi/ J W} ,

where diag{/ _m } denotes a diagonal matrix with the vector f _m as a diagonal element, where f _m = [f _m ,o fm,i fm.i fmj], m = 0,— . M - l satisfies

F ^H F = /, wherein

[62] To further illustrate the present solution, expression of current OCC rotation patterns [a b e d] and [d c b a] are provided below:

1 0 0 0- 0 1 0 0

[a b c d] = W = diag{/ ₀ } W

0 0 1 0

-0 0 0 1-

[63] Where f ₀ = [1 1 1 l] , f = [1 —1 —1 l]. The expression above may indicate the rotation pattern used in the current Releasel2 version. For the transmission layer on each antenna port, there is a different frequency dependent code. For example, [1 1] correspond to antenna ports 7/13, [1 —1] corresponds to antenna ports 8/11. Therefore, the transmission power of the first OFDM symbol can be ex ressed as:

_D DMRS

symboll

3W _RB

\Fdiag{a}z.

= ¾H _diag{a} H _F H _Fdiag{a}Zi

(4)

[64] where F Consider the following condition (5),

[65] it is very clear that without a specific assumption to F, _s ° mboii depends on the vector a. If the equation (5) can be satisfied, i.e., the columns of F matrix are orthogonal to each other, a constant-modulus property of the elements in a may be used to obtain i.e., boil does not depend on its time-domain OCC code a. It is also the case for _s ™boi2' ^P symboi3 ^{a nd P} symboi4.- ^{In otner} words, when F ^H F = I, four DMRS symbols in one subframe have the same transmission power.

[66] The OCC pattern of the present solution is illustrated in Fig. 3, wherein in order to make F ^H F = / valid, M should be greater than or equal to 4.

[67] The present solution will be further illustrated using the following two embodiments:

Embodiment 3:

[68] Preferably, in order to be compatible with legacy user equipments, the OCC pattern on the subcarriers corresponding to the ports 7/8 must be consistent with the pattern of the current Releasel2. Therefore, the first two columns of the matrix F should be:

[69] For example, when M=6, F matrix is set to:

where t = e ^{"; r} / ³ .

[70] With the F matrix above, because the first two columns of the F matrix are identical to the OCC pattern of the existing R12 version, user equipments of Releasel2 and earlier versions may be compatible in DMRS enhancement technology, and meanwhile, the issue of power imbalance between OFDM symbols where the DMRS is located is eliminated. EMBODIMENT 4

[71] When M=9, F matrix is provided

where s = e ^{";2 r} / ⁹ .

[72] Because only the first column of the F matrix is identical to the OCC pattern of the existing Releasel2 version, the legacy user equipments of Releasel2 and earlier version associated with port 7 can be compatible in the DMRS enhancement technology.

[73] Fig. 5 illustrates a flow diagram of a method for processing DMRS signal in a LTE-based user equipment according to another aspect of the present invention. As illustrated in Fig. 5,

[74] In step S501, the user equipment performs demodulation processing to an OFDM symbol from a base station to obtain an OFDM demodulated data block;

[75] Afterwards, in step S502, the user equipment performs processing, which is reverse to the pattern rotation processing in the LIE protocol-based base station as described above with reference to Fig. 3, with OCCs on subcarriers corresponding to available DMRS antenna ports in the OFDM-demodulated data block.

[76] In other words, in order to solve the problem of power imbalance between OFDM symbols existing in the DMRS enhancement technology of the existing LIE protocol, the base station according to the present invention may generate an OFDM symbol by performing pattern rotation processing with the OCC pattern on subcarriers corresponding to the available DMRS antenna ports and then performing OFDM modulation to the data block including the pattern rotation processed OCC to generate an OFDM symbol for transmission. Correspondingly, in order to restore the original OCC on the subcarriers corresponding to the available DMRS antenna ports, the user equipment needs to perform processing, which is reverse to the pattern rotation processing in the LIE protocol-based base station as described above with reference to Fig. 3, with OCCs on subcarriers corresponding to available DMRS antenna ports in the OFDM-demodulated data block. Therefore, to those skilled in the art, it is easy to derive a reverse processing in a known processing process, which will not be detailed here.

[77] Fig. 6 illustrates a block diagram of an apparatus for processing DMRS signals in a LTE-based base station according to one aspect of the present invention, as illustrated in Fig. 4, comprising:

[78] A pattern rotation processing module 601 is configured to perform pattern rotation processing with OCCs on subcarriers corresponding to available DMRS antenna ports so as to reduce power imbalance between OFDM symbols generated subsequently;

[79] An OFDM modulating module 602 is configured to perform OFDM modulation to a data block including the pattern rotation processed OCC to generate an OFDM symbol.

[80] In other words, in order to solve the problem of power imbalance between OFDM symbols existing in DMRS enhancement technology of the existing LTE protocol, the base station according to the present invention may generate OFDM symbols by performing pattern rotation processing with the OCC pattern on subcarriers corresponding to the available DMRS antenna ports and then performing OFDM modulation to the data block.

[81] Specifically, the pattern rotation processing process includes, but not limited to, perform a certain degree of transformation to the OCC rotation pattern used by the DMRS, e.g., a transformation based on column permutation and frequency dependent code. Hereinafter, two embodiments of transformation based on column permutation and frequency dependent code are provided below, respectively.

COLUMN PERMUTATION-BASED TRANSFORMATION:

[82] In the present solution, the pattern rotation processing module 601 is specifically for:

[83] - performing pattern rotation processing with M=4 DMRS OCCs, as provided by the following expression, on subcarriers corresponding to the available DMRS antenna ports:

{WE ₀ , WE ₁ , WE ₂ , WE ₃ } (1) wherein, W is a Walsh matrix

wherein E _t is a 4x4 permutation matrix, i.e., the columns of E _t are non-identical to each other and selected from the following set:

and satisfies the following condition:

[84] Hereinafter, the column permutation-based solution will be further illustrated using two embodiments with 4 antenna ports 7/8/11/13 designated for DMRS enhancement in the current LIE protocol:

Embodiment 1:

[85] Wherein E _t is:

[86] It is apparent that E _t satisfies the condition of equation (2) above. Then, as illustrated in Fig. 2, the OCC rotation pattern is:

WE ₀ = [a b c d]

WE ₁ = [d c b a]

WE ₂ = [c d a b] WE ₃ = [b a d c]

[87] Here, as illustrated in the equation below, we can easily verify that in the present embodiment, the transmission power for DMRS symbols after column permutation are identical.

pDMRS _ pDMRS _ pDMRS _ pDMRS _ °"RB ( _ηη Ί , J , _ΓΓ Ί , ,/,/ΤΛ ,, symboll ^— symboll ^— symboll ^— symboll ^— ^ n ^{uu †} ™ ^{† †} ) ^£ n

[88] If the PRB number is an integer multiples of 4, the rotated DMRS OCC pattern (hereinafter referred to as "OCC pattern") based on the present embodiment eliminates the power fluctuation between different symbols. When the rotated OCC pattern is substituted into the original Walsh matrix, it may be seen in the example that the ports 7/8 still maintain the same rotation pattern (w _p (i), w _p (3— i)} as Releasel2; the DMRS OCC pattern for ports 11/13 is transformed into:

[w _l (i), W (3 - O. Wn(3 - O.WnCO)

{w ₁₃ (i), w ₁₃ (3 - i), -w ₁₃ (3 - 0- -w ₁₃ (0)

[89] As a preferred solution, because the OCC pattern for ports 7/8 is not changed, the embodiment may be compatible with legacy user equipments (UEs) of Releasel2 or an earlier version in DMRS enhancement technology.

[90] Generally, besides embodiment 1, in order to support legacy user equipments of Releasel2 and an earlier version in DMRS enhancement technology, another restricted condition for selecting E _t is to ensure that the resulted OCC rotation pattern for ports 7/8 is same with that in Releasel2 protocol.

Embodiment 2:

[91] In the present embodiment, E _t is:

[92] Likewise, E _t also satisfies the condition of equation (2). The OCC rotation pattern is:

WE ₀ = [a b c d] WE ₁ = [d a b c] WE ₂ = [c d a b]

WE ₃ = [b c d a]

[93] It may be seen that the OCC rotation pattern has a cyclic shift form, and it may also be easily verified that the OCC rotation pattern based on this embodiment also eliminates the power fluctuation between different symbols, and does not change the rotation pattern of the port 7/8 defined in Releasel2.

12

[94] Because the DMRS enhancement technology has — = 3 Res in one PRB per OFDM symbol, the method of column permutation can only achieve power balance in PRBs with a number of integer multiples of 4. This also requires certain degree of limitation on channel frequency selectivity. In other words, it is required that the channel frequency selection characteristics are approximately unchanged in 4 PRBs. In order to solve this problem, another solution based on frequency dependent code is proposed, which may relax the limitation on channel frequency selectivity in the column permutation-based solution.

FREQUENCY CORRELATION CODE-BASED SOLUTION:

[95] In the present solution, the pattern rotation processing 601 is configured to:

- perform pattern rotation using M DMRS OCCs on subcarriers corresponding to the available DMRS antenna ports, the OCC pattern is rotated using the expression below:

{diag{/ ₀ } , diagifj W, ··· , diagfJ J W}

where diag{/ _m } denotes a diagonal matrix with the vector f _m as a diagonal element where, f _m = [f _m , ₀ f _m f _m , ₂ f _m , ₃ ], m = 0, ··· . M - 1 satisfies

F ^H F = /, wherein

,o - I.I - 1,2 - 1,3 -

[96] To further illustrate the present solution, expression of current OCC rotation patterns [a b e d] and [d c b a] are provided below.

0 0

1 0

[a b d] diag{/ ₀ } W

0 1

0 0

[97] where f ₀ = [1 1 1 l] , f = [1 —1 —1 l]. The expression above may indicate the rotation pattern used in the current Releasel2 version. For the transmission layer on each antenna port, there is a different frequency dependent code. For example, [1 1] correspond to antenna ports 7/13, [1 —1] corresponds to antenna ports 8/11. Therefore, the transmission power of the first OFDM symbol can be expressed as: rjDMRS 3M RB

symboll (|/ ₀ diag{ }z _n | ² + l/Vdiagiajz

3M RB

Fdiag{ }z _;

-≡z* d\ag{a} ^H F ^H Fd\ag{a}z, (4) where F = /o Consider the following condition (5),

fi [98] it is very clear that without a specific assumption to F, _s ° mboi _i depends on the vector a. If the equation (5) can be satisfied, i.e., the columns of F matrix are orthogonal to each other, a constant-modulus property of the elements in a may be used to obtain i.e., boil does not depend on its time-domain OCC code a. It is also the case for _s ™boi2' ^P s mboi3 ^{a nd P} symboi4.- ^{In otner} words, when F ^H F = I, four DMRS symbols in one subframe have the same transmission power .

[99] The OCC pattern of the present solution is illustrated in Fig. 3, wherein in order to make F ^H F = / valid, M should be greater than or equal to 4.

[100] The present solution will be further illustrated using the following two embodiments:

Embodiment 3:

[101] Preferably, in order to be compatible with legacy user equipments, the OCC pattern on the subcarriers corresponding to the ports 7/8 must be consistent with the pattern of the current Releasel2. Therefore, the first two columns of the matrix F must be:

[102] For example, when M=6, F matrix is set to:

-+1 -1 t ⁵ _t ioJ where t = e ^{"; r} / ³ .

[103] With the F matrix above, because the first two columns of the F matrix are identical to the OCC pattern of the existing Releasel2 version, user equipments of Releasel2 and earlier versions may be compatible in DM RS enhancement technology, and meanwhile, the issue of power imbalance between OFDMs symbols where the DM RS is located is eliminated.

EMBODIMENT 4

[104] When M=9, F matrix is provided as:

where s = e ^{";2 r} / ⁹ .

[105] Because only the first column of the F matrix is identical to the OCC pattern of the existing Releasel2 version, the legacy user equipments of Releasel2 and earlier version associated with port 7 can be compatible in the DMRS enhancement technology.

[106] Fig. 7 illustrates a flow diagram of an apparatus for processing DMRS signal in a LTE-based user equipment according to another aspect of the present invention. As illustrated in Fig. 5, the apparatus comprises:

[107] an OFDM demodulation module configured to perform demodulation processing to an OFDM symbol from a base station to obtain an OFDM demodulated data block;

[108] a pattern rotation reverse processing module configured to perform processing, which is reverse to the pattern rotation processing in the LIE protocol-based base station as described above with reference to Fig. 3, with OCCs on subcarriers corresponding to available DMRS antenna ports in the OFDM-demodulated data block.

[109] In other words, in order to solve the problem of power imbalance between OFDM symbols existing in the DMRS enhancement technology of the existing LIE protocol, the base station according to the present invention may generate an OFDM symbol by performing pattern rotation processing with the OCC pattern on subcarriers corresponding to the available DMRS antenna ports and then performing OFDM modulation to the data block including the pattern rotation processed OCC for transmission. Correspondingly, in order to restore the data block before OFDM demodulation on the subcarriers corresponding to the available DMRS antenna ports, the user equipment needs to perform processing, which is reverse to the pattern rotation processing in the LIE protocol-based base station as described above with reference to Fig. 3, with OCCs on subcarriers corresponding to available DMRS antenna ports in the OFDM-demodulated data block. Therefore, to those skilled in the art, it is easy to derive a reverse processing in a known processing process, which will not be detailed here. [110] It should be noted that the present disclosure may be implemented in software or a combination of software and hardware; for example, it may be implemented by a dedicated integrated circuit (ASIC), a general-purpose computer, or any other similar hardware device. In an embodiment, the software program of the present disclosure may be executed by a processor so as to implement the above steps or functions. Likewise, the software program of the present disclosure (including relevant data structure) may be stored in a computer readable recording medium, for example, a RAM memory, a magnetic or optical driver, or a floppy disk, and similar devices. Besides, some steps of functions of the present disclosure may be implemented by hardware, for example, a circuit cooperating with the processor to execute various functions or steps.

[111] To those skilled in the art, it is apparent that the present disclosure is not limited to the details of the above exemplary embodiments, and the present disclosure may be implemented with other forms without departing from the spirit or basic features of the present disclosure. Thus, in any way, the embodiments should be regarded as exemplary, not limitative; the scope of the present disclosure is limited by the appended claims, instead of the above depiction. Thus, all variations intended to fall into the meaning and scope of equivalent elements of the claims should be covered within the present disclosure. No reference signs in the claims should be regarded as limiting the involved claims. Besides, it is apparent that the term "comprise/comprising/include/including" does not exclude other units or steps, and singularity does not exclude plurality. A plurality of units or means stated in the apparatus claims may also be implemented by a single unit or means through software or hardware. Terms such as the first and the second are used to indicate names, but do not indicate any particular sequence.

[112] Although exemplary embodiments have been specifically illustrated and described above, those skilled in the art will understand that without departing from the spirit and scope of the claims, their forms and details may change somewhat. Here, the protection as sought is defined in the appended claims.