TECHNICAL FIELD

[0001] The present invention relates to a technical field of wireless communications, and more specifically, to a relay cooperative transmission field.

BACKGROUND

[0002] The relay cooperative transmission technology, as one of the fundamental functions determined by LTE's subsequent development, i.e. LTE-Advanced, has attracted extensive attention. Its main characteristic is to enable a mobile terminal in which multi-antenna technology is hard to be employed to obtain a transmit diversity gain, thereby overcoming the adverse impact of a fading channel on the wireless communication system.

[0003] The relay cooperative transmission method used in the existing 3G/LTE wireless communication system is mainly related to a decoding-and-forwarding (DF for short) relay. The forwarding process of the method as illustrated in Fig. 1 mainly comprises two phases: as illustrated in Fig. 1 (a), in a first phase, a transmitting end (e.g. one user equipment UE) simultaneously transmits data packets to a receiving end (e.g. one base station, eNB) and one relay node (RN for short; the RN herein may be a relay device and may also be another UE); and as illustrated in Fig. 1 (b), in a second phase, the RN decodes the data packets and re-encodes them, and then transmits the re-encoded data packets to the receiving end. At the receiving end, a maximal ratio combining (MRC for short) method is used to combine and decode the signals received in the two phases to obtain the data transmitted by the transmitting end.

[0004] The main problem of the DF method lies in that: the Quadrature Amplitude Modulation (QAM for short) is used in the existing 3G/LTE system, and in a modulation constellation selected according to the 3GPP standard, bits in different positions of one symbol have different reliabilities. Taking 16QAM as an example, each symbol includes 4 bits (bib ₂ b ₃ b ₄ ) and the constellation specified by the 3GPP standard is illustrated in Fig. 2. It can be seen that different values of bits in bi and b ₂ positions are distributed in different quadrants and can be differentiated by the quadrants, while different values of bits in b ₃ and b ₄ positions are distributed in the same quadrant and must be differentiated within the quadrant. Thus, the bits in bi and b ₂ positions have a larger Euclidean distance, that is to say, the bits in bi and b ₂ positions have a higher reliability while the bits in b ₃ and b ₄ positions have a lower reliability. However, since the same symbol as that transmitted at the transmitting end is used in forwarding, i.e. the bits having a lower reliability will have a further reduced reliability after being forwarded, its performance is limited by the bits having the lower reliability, i.e. the bit error rate of the bits in b ₃ and b ₄ positions is a main factor influencing the overall bit error rate of the DF method.

[0005] In the prior art, based on the characteristic that the bit reliabilities in a multi-order QAM modulation are different, some constellation rearrangement based technical solutions are proposed accordingly to equalize the reliability differences among bits, typically for example, a constellation rearrangement based retransmission method used in HARQ. The method can equalize bit reliability differences and achieve the object of reducing transmission errors by storing a same set of modulation constellations at both the receiving end and the transmitting end, selecting different constellations in each retransmission for modulating at the transmitting end based on the feedback from the receiving end, and using a corresponding constellation at the receiving end for demodulating. However, such type of constellation rearrangement based method is not adapted to the actual application scenario of the current relay cooperative transmission. The main reasons include: firstly, corresponding control signaling and feedback signals of the receiving end are needed to indicate how to perform the constellation rearrangement, while the cooperative relay transmission manner is direct forwarding and there is no step of transmitting after receiving a feedback; secondly, the existing 3GPP specification has explicitly specified the constellations used by respective-order QAM modulations, and using a constellation outside the standard may cause a device compatibility problem; additionally, this type of method requires the receiving end and RN to store all possible constellations, while one big advantage of the cooperative relay transmission is that a certain UE may act as the relay node, and in a case that a UE acts as the RN, storing all possible constellations increases the storage requirement of the terminal device and increases the cost for UE; thirdly, this type of method needs to look for the optimal constellation via complicated searching algorithms, which increases the requirement for RN's calculation capabilities and thus it is not adapted to the case that a UE acts as the RN, either.

[0006] Thus, there needs a new method for equalizing bit reliability differences of QAM modulation symbols in the relay cooperative transmission process, and this method should be compatible with the existing standards as much as possible and be adapted to the case that a UE acts as the RN.

SUMMARY

[0007] In order to solve the above problem in the prior art, the present invention proposes a new forwarding method, comprising: performing, before a RN forwards a signal, a rearranging operation on a bit sequence in a QAM modulation symbol, rearranging bits in positions with different reliabilities, and then modulating and transmitting them, while at the receiving end, receiving an original signal transmitted from the transmitting end and the rearranged signal forwarded by the RN, and then using a combining estimation method for decoding.

[0008] Specifically, according to a first aspect of the present invention, there is provided a method for forwarding a multi-order quadrature amplitude modulation signal transmitted by a second device in a first device of a wireless communication system, comprising steps of: receiving an initial multi-order quadrature amplitude modulation signal transmitted from the second device; decoding the initial multi-order quadrature amplitude modulation signal to obtain an initial symbol sequence that contains at least one symbol, the symbol containing a bit sequence that comprises a front portion and a rear portion, wherein a reliability of a bit in the front portion is different from the reliability of a bit in the rear portion; rearranging the front portion and the rear portion of the bit sequence to obtain a rearranged symbol so that at least one bit in the rear portion is contained in positions corresponding to the front portion in the bit sequence of the rearranged symbol and at least one bit in the front portion is contained in positions corresponding to the rear portion; constituting a rearranged symbol sequence with the rearranged symbols; and encoding the rearranged symbol sequence to obtain a rearranged multi-order quadrature amplitude modulation signal and transmitting the rearranged multi-order quadrature amplitude modulation signal.

[0009] Preferably, the multi-order quadrature amplitude modulation signal transmitted by the second device is a 16QAM signal or a 64QAM signal.

[0010] More preferably, when the front portion and the rear portion have a same length, the rearranging is exchanging bits in the front portion with bits in the rear portion.

[0011] Preferably, the first device is a relay device or a user equipment.

[0012] According to a second aspect of the present invention, there is provided a method for receiving a multi-order quadrature amplitude modulation signal in a third device of a wireless communication system, comprising steps of: receiving an initial multi-order quadrature amplitude modulation signal transmitted from a second device; receiving a rearranged multi-order quadrature amplitude modulation signal generated according to the method of the first aspect of the present invention and transmitted from a first device; and performing a combined estimation based decoding operation based on the received initial multi-order quadrature amplitude modulation signal and the rearranged multi-order quadrature amplitude modulation signal.

[0013] Preferably, the combined estimation based decoding operation is a maximum a posteriori method based decoding operation.

[0014] More preferably, the maximum a posteriori method based decoding operation is a logarithmic likelihood ratio based decoding operation.

[0015] More preferably, the logarithmic likelihood ratio based decoding operation comprises: calculating a logarithmic likelihood ratio of each bit in the initial multi-order quadrature amplitude modulation signal and in the rearranged multi-order quadrature amplitude modulation signal, respectively; in accordance with a corresponding relationship in a rearranging operation in the rearranging step of the method according to the first aspect of the present invention, combining the logarithmic likelihood ratio of each bit in the initial multi-order quadrature amplitude modulation signal with the corresponding logarithmic likelihood ratio of each bit in the rearranged multi-order quadrature amplitude modulation signal to obtain a combined logarithmic likelihood ratio of each bit; and performing a decoding operation based on the combined logarithmic likelihood ratio of each bit.

[0016] According to a third aspect of the present invention, there is provided an apparatus for forwarding a multi-order quadrature amplitude modulation signal transmitted by a second device in a first device of a wireless communication system, comprising: a receiving unit configured to receive an initial multi-order quadrature amplitude modulation signal transmitted from the second device; a decoding unit configured to decode the initial multi-order quadrature amplitude modulation signal to obtain an initial symbol sequence that contains at least one symbol, the symbol containing a bit sequence that comprises a front portion and a rear portion, wherein a reliability of a bit in the front portion is different from the reliability of a bit in the rear portion; a rearranging unit configured to rearrange the front portion and the rear portion of the bit sequence to obtain a rearranged symbol so that at least one bit in the rear portion is contained in positions corresponding to the front portion in the bit sequence of the rearranged symbol and at least one bit in the front portion is contained in positions corresponding to the rear portion; a combining unit configured to constitute a rearranged symbol sequence with the rearranged symbols; and an encoding and transmitting unit configured to encode the rearranged symbol sequence to obtain a rearranged multi-order quadrature amplitude modulation signal and transmit the rearranged multi-order quadrature amplitude modulation signal.

[0017] Preferably, the multi-order quadrature amplitude modulation signal transmitted by the second device is a 16QAM signal or a 64QAM signal.

[0018] More preferably, when the front portion and the rear portion have a same length, the rearranging unit exchanges bits in the front portion with bits in the rear portion. [0019] Preferably, the first device is a relay device or a user equipment.

[0020] According to a fourth aspect of the present invention, there is provided an apparatus for receiving a multi-order quadrature amplitude modulation signal in a third device of a wireless communication system, comprising: a receiving unit configured to receive an initial multi-order quadrature amplitude modulation signal transmitted from a second device and a rearranged multi-order quadrature amplitude modulation signal generated according to the method of Claim 1 and transmitted from a first device; and a decoding unit configured to perform a combined estimation based decoding operation based on the received initial multi-order quadrature amplitude modulation signal and the rearranged multi-order quadrature amplitude modulation signal.

[0021] Preferably, the combined estimation based decoding operation performed by the decoding unit is a maximum a posteriori method based decoding operation.

[0022] More preferably, the maximum a posteriori method based decoding operation performed by the decoding unit is a logarithmic likelihood ratio based decoding operation.

[0023] More preferably, the logarithmic likelihood ratio based decoding operation performed by the decoding unit comprises: calculating a logarithmic likelihood ratio of each bit in the initial multi-order quadrature amplitude modulation signal and in the rearranged multi-order quadrature amplitude modulation signal, respectively; in accordance with a corresponding relationship in the rearranging operation in the rearranging step of the method according to the first aspect of the present invention, combining the logarithmic likelihood ratio of each bit in the initial multi-order quadrature amplitude modulation signal with the corresponding logarithmic likelihood ratio of each bit in the rearranged multi-order quadrature amplitude modulation signal to obtain a combined logarithmic likelihood ratio of each bit; and performing a decoding operation based on the combined logarithmic likelihood ratio of each bit.

[0024] In the present invention, rearranging bit positions in the bit sequence of the QAM symbol before the RN forwarding the signal actually exchanges bits having a higher reliability with bits having a lower reliability. That is, it avoids further reduction of the reliability of the bits having the lower reliability during the forwarding process to thereby equalize reliability differences among different bits. Considering that the performance of forwarding is mainly limited by the bits having the lower reliability, the present invention improves the performance of forwarding on the whole. Meanwhile, the operation at the RN is very simple, and it only needs to perform a position arrangement on the bit sequence of the decoded symbol, without adding control signaling or receiving feedback signals, thereby having little impact on the existing standards. Furthermore, the overhead for implementing this operation is very small, and this operation is especially adapted to the case that UE acts as RN. In addition, decoding can be implemented by simply combining corresponding logarithmic likelihood ratios of bits using a combined estimation method at the receiving end, and the calculation overhead at the receiving end is also very small. That is, the present invention achieves a beneficial effect of improving the relay cooperative transmission performance with a small overhead.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] When reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, other features, objects and advantages of the present invention will become more apparent, wherein,

FIGs. 1 (a) and 1 (b) illustrate a forwarding process of a DF method;

FIG. 2 illustrates a 16QAM constellation based on 3GPP specifications; FIGs. 3 (a) and 3 (b) illustrate a process of a relay cooperative transmission method according to the present invention;

FIG. 4 illustrates a signal forwarding flowchart according to the present invention;

FIG. 5 illustrates a signal receiving flowchart according to the present invention;

FIG. 6 illustrates a block diagram of a signal forwarding apparatus according to the present invention; FIG. 7 illustrates a block diagram of a signal receiving apparatus according to the present invention;

FIG. 8 illustrates simulation results of performance comparison between the present invention and the DF method.

[0026] In the accompanying drawings, identical or like reference numerals represent identical or like step features or apparatus/modules.

DETAILED DESCRIPTION OF EMBODIMENTS

[0027] In the following detailed descriptions of preferable embodiments, the appended accompanying drawings constituting a part of the present invention will be referred to. The appended accompanying drawings illustrate by way of example specific embodiments capable of implementing the present invention. The exemplary embodiments are not intended to exhaustively list all embodiments according to the present invention. It can be understood that without departing from the scope of the present invention, other embodiments may be utilized and structural or logical modifications may also be made. Thus, the following detailed descriptions are non-limiting and the scope of the present invention is limited by the appended claims.

[0028] FIGs. 3 (a) and 3 (b) illustrate a process of a relay cooperative transmission method according to the present invention. Without loss of generality, the 16QAM modulation is used in this embodiment, and likewise the present invention may be conveniently adapted to other-order QAM signals. For example, in case of 64QAM, each symbol includes 6 bits (bib ₂ b ₃ b ₄ b ₅ b ₆ ), while bits in bi and b ₂ positions also have a higher reliability than bits in other positions, wherein the problem of reliability differences among bits also exists, and the bit position rearranging method according to the present invention also can achieve the effect of equalizing the reliability differences among bits.

[0029] As illustrated in FIG. 3 (a), in the first phase of the forwarding process, the transmitting end (e.g. a user equipment, UE) simultaneously transmits an original signal to the receiving end (e.g. a base station, eNB) and a Relay Node (RN for short; the RN herein may be a relay device and may also be another UE). Without loss of generality, the original signal transmitted herein contains one 16QAM symbol sequence that contains one 16QAM symbol Xi (bib ₂ b ₃ b ₄ ); and as illustrated in FIG. 3 (b), in the second phase of the forwarding process, the RN decodes a data packet to obtain the originally transmitted symbol Xi (b-ib ₂ b ₃ b ₄ ), and then divides the bit sequence of Xi into two portions, i.e. a front portion including (b1 b2) and a rear portion including (b3b4). Bits in the two portions have different reliabilities, wherein bits in the front portion (bib ₂ ) have a higher reliability. The two portions are rearranged to generate a rearranged symbol ½ so that the front portion in x _x at least includes one bit originally included in the rear portion (b ₃ b ₄ ), and the rear portion in x _x at least includes one bit originally included in the front portion (bib ₂ ), for example, in various forms such as (bib ₃ b ₂ b ₄ ), (b ₄ b ₂ bib ₃ ) or (b ₄ b ₃ b ₂ bi), etc., and then the rearranged symbol ½ is re-modulated and transmitted to the receiving end. When the symbol sequence contained by the original signal includes a plurality of symbols, the above described rearranging operation shall be performed on each symbol, and then the rearranged symbols are combined into a new symbol sequence in accordance with the order of the original symbol sequence, and then the new symbol sequence is modulated and transmitted.

[0030] In this embodiment, a more preferable solution is that in a rearranging operation, when the front portion and the rear portion have a same length, the front portion and the rear portion are exchanged, i.e. the positions of b-ib ₂ and b ₃ b ₄ are exchanged to obtain x _x (b ₃ b ₄ b-ib ₂ ). The implementation of this preferable solution is the simplest and the effect of equalizing reliability differences among bits is the most notable.

[0031] FIG. 4 illustrates a specific method for forwarding data at RN according to the above relay cooperative transmission process:

[0032] S41 . receiving an initial multi-order quadrature amplitude modulation signal transmitted from a second device;

[0033] S42. decoding the initial multi-order quadrature amplitude modulation signal to obtain an initial symbol sequence that contains at least one symbol, the symbol containing a bit sequence that comprises a front portion and a rear portion, wherein the reliability of a bit in the front portion is different from the reliability of a bit in the rear portion;

[0034] S43. rearranging the front portion and the rear portion of the bit sequence to obtain a rearranged symbol so that at least one bit in the rear portion is contained in positions corresponding to the front portion in the bit sequence of the rearranged symbol and at least one bit in the front portion is contained in positions corresponding to the rear portion;

[0035] S44. constituting a rearranged symbol sequence with the rearranged symbols;

[0036] S45. encoding the rearranged symbol sequence to obtain a rearranged multi-order quadrature amplitude modulation signal and transmitting the rearranged multi-order quadrature amplitude modulation signal.

[0037] However, at the receiving end, after having received the original signal Xi (bib ₂ b ₃ b ₄ ) transmitted from the transmitting end and the rearranged signal ½ (b ₃ b ₄ bib ₂ ) forwarded by the RN, the present invention proposes decoding by using combined estimation based soft information combining technique at the receiving end. Since the receiving end has already known the corresponding relationship between the bit sequences of X1 and ½ , employing the combined estimation method may sufficiently utilize the received information to obtain better performance.

[0038] Specifically, the decoding may be implemented by employing a plurality of combined estimation based methods, such as a maximum likelihood (ML for short) method, a maximum a posteriori (MAP for short) method, etc. In view of the large calculation overhead of the ML method, the MAP method is preferred in this embodiment for decoding.

[0039] Without loss of generality, a logarithmic likelihood ratio (LLR for short) method is preferred in this embodiment for decoding and the other MAP based decoding methods are also adapted to the decoding steps of the present invention.

[0040] Firstly, in the first phase of the forwarding process, the signal received at the receiving end may be represented as: [0041] where ^ is the received signal; hi is a channel response from the transmitting end to the receiving end; and ni is noise of a channel.

[0042] Correspondingly, the logarithmic likelihood ratio LLR (x-,) of a symbol Xi may be calculated by:

LLR _l (x _l ) = logP{y _l \s _i ) = (y.-V,) ²

2σ ²

[0043] where logP represents a conditional probability operation; s, represents all possible values of the symbol x-i, and for 16QAM, i=1~16; and σ ²

represents noise power.

[0044] Then, the logarithmic likelihood ratio LLR (b _j ) of each bit in the symbol may be calculated by:

_LLRi ( _b ) ₌ log ¹ '^ - ¹ = log—!- = log—^- _

^{Λ 11 &} P(y _l \b _j =Q) ∑ P( _yi \s _k ) ∑ exp(LL¾( _¾ ))

¾;¾ ^■ =« ¾;¾=o

[0045] where s, and S _k respectively represent all possible values of the symbol xi when b _j =1 and all possible values of the symbol xi when b _j =0, for 16QAM, j=1 ~4.

[0046] So far, the logarithmic likelihood ratio of each bit in the original signal received in the first phase is obtained, and then based on the similar method, the logarithmic likelihood ratio of each bit in the rearranged signal received in the second phase can be calculated:

[0047] Firstly, the signal model is :

y ₂ =h ₂ -x ₁ +n ₂

[0048] where y ₂ is the received signal; h ₂ is a channel response from the RN to the receiving end; and n ₂ is noise of a channel.

[0049] Then, the logarithmic likelihood ratio of the symbol ½ is calculated by:

LLR ₂ (x _l ) =

[0050] where logP represents a conditional probability operation ; s _t represents all possible values of the symbol ½ , and for 1 6QAM, i=1 ~1 6; and ^σ represents noise power.

[0051] Then, the logarithmic likelihood ratio of each bit is calculated by:

[0052] where s _t and ¾ respectively represent all possible values of the symbol ½ when ¾ =1 and all possible values of the symbol ½ when b _j =0, and for 1 6QAM, j=1 ~4.

[0053] Finally, the logarithmic likelihood ratios of bits in corresponding positions in the symbols received in the two phases are combined, and for symbols xi (bib ₂ b ₃ b ₄ ) and ½ (b ₃ b ₄ bib ₂ ), the combined logarithmic likelihood ratios of the bits are:

LLR{b _x ) = LLR _X (b _l ) + LLR ₂ (¾ ) _>

LLR(b ₂ ) = LLR ₁ (b ₂ ) + LLR ₂ (b ₄ ) ,

LLR (b ₃ ) = LLR _l (b ₃ ) + LLR ₂ (¾ ) _>

LLR (b ₄ ) = LLR _l (b ₄ ) + LLR ₂ (b ₂ ) . [0054] Then, Turbo decoding is performed on the combined logarithmic likelihood ratios of the bits LLR (b _t ) (i = 1, 2, 3, 4) .

[0055] FIG. 5 illustrates a specific method for performing decoding operation at the receiving end according to the above decoding steps:

[0056] S51 . receiving an initial multi-order quadrature amplitude modulation signal transmitted from a second device;

[0057] S52. receiving a rearranged multi-order quadrature amplitude modulation signal generated according to the method of Claim 1 and transmitted from a first device;

[0058] S53. performing a combined estimation based decoding operation based on the received initial multi-order quadrature amplitude modulation signal and the rearranged multi-order quadrature amplitude modulation signal.

[0059] An apparatus corresponding to the above method provided by the present invention is introduced below in conjunction with block diagrams, but the illustration will be simplified in view of the corresponding relationship between the unit/device features in the apparatus and the step features in the above method.

[0060] FIG. 6 illustrates a block diagram of an apparatus S60 for forwarding a multi-order quadrature amplitude modulation signal transmitted by a second device in a first device of a wireless communication system, the forwarding apparatus S60 comprising:

[0061] a receiving unit 6001 configured to receive an initial multi-order quadrature amplitude modulation signal transmitted from the second device;

[0062] a decoding unit 6002 configured to decode the initial multi-order quadrature amplitude modulation signal to obtain an initial symbol sequence that contains at least one symbol, the symbol containing a bit sequence that comprises a front portion and a rear portion, wherein a reliability of a bit in the front portion is different from the reliability of a bit in the rear portion;

[0063] an rearranging unit 6003 configured to rearrange the front portion and the rear portion of the bit sequence to obtain a rearranged symbol so that at least one bit in the rear portion is contained in positions corresponding to the front portion in the bit sequence of the rearranged symbol and at least one bit in the front portion is contained in positions corresponding to the rear portion.

[0064] a combining unit 6004 configured to constitute a rearranged symbol sequence with the rearranged symbols;

[0065] an encoding and transmitting unit 6005 configured to encode the rearranged symbol sequence to obtain a rearranged multi-order quadrature amplitude modulation signal and transmit the rearranged multi-order quadrature amplitude modulation signal. [0066] Preferably, the multi-order quadrature amplitude modulation signal transmitted by the second device is a 16QAM signal or a 64QAM signal.

[0067] Preferably, when the front portion and the rear portion have a same length, the rearranging unit exchanges bits in the front portion with bits in the rear portion.

[0068] Preferably, the first device is a relay device or a user equipment.

[0069] FIG. 7 illustrates a block diagram of an apparatus S70 for receiving a multi-order quadrature amplitude modulation signal in a third device of a wireless communication system, the receiving apparatus S70 comprising:

[0070] a receiving unit 7001 configured to receive an initial multi-order quadrature amplitude modulation signal transmitted from a second device and a rearranged multi-order quadrature amplitude modulation signal generated according to the method of the present invention and transmitted from a first device;

[0071] a decoding unit 7002 configured to perform a combined estimation based decoding operation based on the received initial multi-order quadrature amplitude modulation signal and the rearranged multi-order quadrature amplitude modulation signal.

[0072] Preferably, the combined estimation based decoding operation performed by the decoding unit is a maximum a posteriori method based decoding operation.

[0073] More preferably, the maximum a posteriori method based decoding operation performed by the decoding unit is a logarithmic likelihood ratio based decoding operation.

[0074] More preferably, the logarithmic likelihood ratio based decoding operation performed by the decoding unit comprises: calculating a logarithmic likelihood ratio of each bit in the initial multi-order quadrature amplitude modulation signal and in the rearranged multi-order quadrature amplitude modulation signal, respectively; in accordance with a corresponding relationship in the rearranging operation in the rearranging step of the method according to the present invention, combining the logarithmic likelihood ratio of each bit in the initial multi-order quadrature amplitude modulation signal with the corresponding logarithmic likelihood ratio of each bit in the rearranged multi-order quadrature amplitude modulation signal to obtain a combined logarithmic likelihood ratio of each bit; performing a decoding operation based on the combined logarithmic likelihood ratio of each bit.

[0075] To prove the efficiency of the present invention, a simulation experiment is conducted for comparison between the present invention and the existing DF method. 16QAM and 64QAM modulations are used in the simulation, wherein for 64QAM, the rearranged bit sequence is (b ₄ b ₅ b ₆ b-ib ₂ b ₃ ); 1/3 Turbo code with a length of 3460 bits is adopted; in the adopted channel model, it is assumed that the UE-to-RN channel has a 5db gain compared to other channels.

[0076] The simulation results are illustrated in FIG. 8. It can be seen that in the case of 16QAM and 64QAM, the performance of the present invention is obviously better than that of the existing DF method. The simulation results can prove that compared with the existing method, the forwarding method proposed in the present invention achieves the objective of improving the relay cooperative transmission performance and solves the problem existing in the prior art.

[0077] Embodiments of the present invention are described above, but the present invention is not limited to particular systems, devices and specific protocols, and those skilled in the art can make various variations or modifications within the scope of the appended claims.

[0078] Those of ordinary skill in the art may understand and implement other modifications of the disclosed embodiments by studying the specification, disclosed contents and accompanying drawings, and the appended claims. In the claims, the term "comprising", "containing" or "including" does not exclude other elements and steps; and the term "a" or "an" does not exclude a plural concept. In the present invention, the terms "first" and "second" are used for identifying names but not for representing any specific order. In the actual application of the present invention, one component may perform the functions of a plurality of technical features referred to in the claims. Any reference numerals in the claims should not be construed as the limiting to the scope.