Differential space-time line code system and method

Abstract

Disclosed is a differential space-time trellis code system and method without using channel information. A transmitter used in the differential space-time trellis code system comprises a space-time encoder for space-time encoding input symbols; and at least one transmitting antenna. The space-time encoder space-time encodes the input symbols without using channel information, and the encoded input symbols are transmitted to a receiver through the transmitting antenna.

Description

Technical Field

[0001] This invention relates to a differential space-time line code system and method. Background Technology

[0002] Space-time block code (STBC), a well-known technique in space-time coding using multiple transceiver antennas, transmits block codes without using channel information and achieves maximum spatial diversity gain by using channel information estimated at the receiver. This STBC technique was applied to early time-invariant channel environments and is not suitable for time-varying channel environments.

[0003] The recently developed space-time line code (STLC) technology is a technology that is perfectly symmetrical to the existing STBC. It uses channel information at the transmitting end instead of the receiving end, and the receiving end provides the same performance as STBC by simply combining the received signals without channel information.

[0004] In its early stages, STLC technology was also implemented in time-invariant channel environments. Like the earlier STBC technology, this existing STLC technology was developed based on the assumption of a time-invariant channel environment. Therefore, in time-varying channels, especially for high-speed mobile situations, it is difficult to obtain rapidly changing channel information.

[0005] Therefore, it is necessary to develop STLC technology suitable for time-varying channel environments. Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] The present invention provides a differential space-time line code system and method.

[0008] Technical solutions for solving the problem

[0009] To achieve the objectives described above, a transmitter used in a differential space-time line code system according to an embodiment of the present invention includes: a space-time encoder for space-time encoding of input symbols; and at least one transmit antenna. The space-time encoder, used in the differential space-time line code system, is characterized in that it performs space-time encoding of the input symbols without any channel information, and the encoded input symbols are transmitted to a receiver via the transmit antenna.

[0010] A transmitter used in a space-time line code system according to another embodiment of the present invention includes: a space-time encoder for space-time encoding of input symbols; and at least one transmit antenna. The space-time encoder performs space-time encoding on a reference symbol serving as the input symbol to generate a reference STLC signal, normalizes the generated reference STLC signal using weights, and transmits the normalized reference STLC signal to a receiver via the transmit antenna.

[0011] A receiver used in a space-time line code system according to an embodiment of the present invention includes: at least two receiving antennas; and a space-time decoder that receives space-time encoded STLC symbols from a transmitter having one transmitting antenna through the receiving antennas to form a received signal matrix, and decodes the formed received signal matrix. The received signal matrix is ​​determined by a previously received signal matrix and input symbols input to the transmitter.

[0012] The differential space-time line code system and method of the present invention perform space-time coding of input symbols at the transmitting end without using channel information, thereby simplifying the coding process. Furthermore, since channel information is not used at the receiving end, the decoding process is also simplified, while providing excellent communication performance even in environments with drastically changing channels. Ultimately, the differential space-time line code system is applicable to various mobile communications with time-varying channel environments. Attached Figure Description

[0013] Figure 1 A diagram illustrating the concept of a differential space-time line code system according to an embodiment of the present invention.

[0014] Figure 2 A diagram illustrating the structure of a transmitter according to an embodiment of the present invention.

[0015] Figure 3 A diagram illustrating the space-time coding process according to an embodiment of the present invention.

[0016] Figure 4 A diagram illustrating the structure of a receiver according to an embodiment of the present invention.

[0017] Figure 5 A diagram illustrating the space-time decoding process according to an embodiment of the present invention.

[0018] Figure 6 A diagram showing a constellation.

[0019] Figure 7 A graph showing the performance comparison results based on signal-to-noise ratio and bit error rate (BER).

[0020] Figure 8To illustrate the changes based on channel variation (f) d T s The graph shows the BER performance of ( ).

[0021] Figure 9 A diagram illustrating the transmitter of a differential space-time line code system according to another embodiment of the present invention.

[0022] Figure 10 A diagram illustrating a receiver for a differential space-time line code system according to another embodiment of the present invention. Detailed Implementation

[0023] Unless the context clearly indicates otherwise, the singular expressions used in this specification shall include the plural expressions. Terms such as "constituting as" or "comprising" in this specification shall not be construed as necessarily including all constituent elements or steps described in the specification, where some constituent elements or steps may be excluded, or shall be construed as potentially including additional constituent elements or steps. Furthermore, terms such as "...part" or "module" in the specification refer to a unit that performs at least one function or action, which may be implemented by hardware or software, or by a combination of hardware and software.

[0024] This invention relates to a differential space-time line code system and method, which is a technology suitable for time-varying channel environments in mobile communication such as vehicles / trains / aircraft / satellite communications.

[0025] According to one embodiment, the differential space-time line code system can perform space-time coding at the transmitting end without using channel information and transmit the space-time coded symbols through a single transmit antenna, and perform space-time decoding on the symbols received through two receive antennas at the receiving end. This differential space-time line code system provides excellent communication performance even in environments with drastic time variations and can have a very simple structure. Therefore, it is applicable to various mobile communications with time-varying channel environments.

[0026] Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings.

[0027] Figure 1 A diagram illustrating the concept of a differential space-time line code system according to an embodiment of the present invention. Figure 2 A diagram illustrating the structure of a transmitter according to an embodiment of the present invention is provided. Figure 3 A diagram illustrating the space-time coding process according to an embodiment of the present invention is provided. Figure 4 A diagram illustrating the structure of a receiver according to an embodiment of the present invention is provided. Figure 5 A diagram illustrating the space-time decoding process according to an embodiment of the present invention is provided. Figure 6 A diagram showing a constellation.

[0028] Reference Figure 1 The differential space-time line code system of this embodiment may include a transmitter 100 and a receiver 102 that communicate in a time-varying channel environment.

[0029] According to one embodiment, transmitter 100 may use one transmit antenna, and receiver 102 may use two receive antennas. In particular, transmitter 100 may perform space-time coding without using all channel information.

[0030] Next, after observing the structure and operation of the transmitter 100, we will observe the structure and operation of the receiver 102.

[0031] Structure and operation of transmitter 100

[0032] Reference Figure 2 The transmitter 100 may include a space-time encoder 200 and a transmitting antenna. The space-time encoder 200 may include a reference symbol encoder 210 for space-time encoding of reference symbols and a data symbol encoder 212 for encoding data symbols input after the reference symbols.

[0033] According to one embodiment, the space-time encoder 200 can perform space-time encoding and transmission of the reference symbol used as the input symbol without using channel information, and then perform space-time encoding and transmission of the data symbol. That is, unlike existing space-time line code technology that utilizes all channel information at the transmitting end, the differential space-time line code system of the present invention does not use channel information. Nevertheless, as described below, the differential space-time line code system of the present invention can provide superior communication performance compared to existing space-time line codes in time-varying channel environments. This is because the differential space-time line code system does not use channel information, and the differential STLC symbol (STLC signal) after being independently space-time line-coded is normalized before being transmitted to the receiver 102.

[0034] Transmit basic symbols

[0035] When two symbols x1[0] and x2[0] are input sequentially as reference symbols, the reference symbol encoding unit 210 can perform space-time encoding on the symbols x1[0] and x2[0] as described in the following mathematical formula 1 to generate a reference differential STLC signal (the 0th differential STLC symbol, n=0). n is the STLC index.

[0036]

Mathematical Formula 1

[0037]

[0038] Where, symbol x i [0] is any non-zero reference symbol (reference signal) that is not decoded in receiver 102, and vi [0] can be any value as the initial differential STLC coding matrix.

[0039] Next, the reference symbol encoding unit 210 performs power normalization on the reference differential STLC signal in order to limit the power when transmitting the reference differential STLC signal, as described in the following mathematical formula 2.

[0040]

Mathematical Formula 2

[0041]

[0042] Where β is the weight, as shown in the following mathematical formula 3, β[0] can be obtained based on the reference signal.

[0043]

Mathematical Expression 3

[0044]

[0045] Next, the reference symbol encoding unit 210 can transmit the normalized reference differential STLC signal to the receiver 102 via the transmitting antenna. Preferably, the reference symbol encoding unit 210 can transmit s1[0] / β[0] and s2[0] / β[0] to the receiver 102 in sequence.

[0046] In summary, the reference symbol encoding unit 210 normalizes the differential STLC signal using weights based on the reference signal and transmits it to the receiver 102. This entire process is illustrated in... Figure 3 The image on the right.

[0047] Transmit data symbols

[0048] If the data symbol to be transmitted as the input symbol is defined as mathematical formula 4 below, then the data symbol encoding unit 212 can generate the nth differential STLC signal as mathematical formula 5 below.

[0049]

Mathematical Expression 4

[0050]

[0051]

Mathematical Expression 5

[0052]

[0053] As shown in Equation 6 below, V[n] can be implemented based on previously encoded differential STLC symbols.

[0054]

Mathematical Expression 6

[0055]

[0056] Referring to mathematical formula 6, it can be seen that the first differential STLC coding matrix V[1] can be obtained from the normalized reference differential STLC signal. Finally, the first differential STLC coding matrix V[1] will reflect the reference signal information, and as a result, the nth STLC coding matrix V[n] will also reflect the reference signal information. That is, the space-time encoder 200 does not use channel information.

[0057] Next, the data symbol encoding unit 212 can perform power normalization on the differential STLC signal. At this time, the weight β used when n = 1 can be defined as shown in the following mathematical formula 7. Therefore, when derived in a similar manner, the weight β used for the nth time is shown in the following mathematical formula 8.

[0058]

Mathematical Expression 7

[0059]

[0060]

Mathematical Expression 8

[0061]

[0062] Referring to Equation 8, it can be confirmed that the weights used for normalization do not depend on channel information and are determined by the input symbol x. k The weight β[n] is determined by the input symbols x1[n] and x2[n]. If a non-constant modulus constellation is used, the nth weight β[n] can be determined by the two input symbols x1[n] and x2[n].

[0063] Next, the data symbol encoding unit 212 can transmit the normalized differential STLC signal to the receiver 102 via the transmitting antenna. Preferably, the data symbol encoding unit 212 can transmit s1[n] / β[n] and s2[n] / β[n] to the receiver 102 in sequence.

[0064] In summary, unlike existing STLC signals that utilize channel information to determine the reference differential STLC signal weights using reference signal information, the data symbol encoding unit 212 determines the weights using the input symbols. Ultimately, the data symbol encoding unit 212 also does not use channel information. This detailed process is illustrated in... Figure 3 middle.

[0065] The overall process at the transmitting end can be summarized as follows: The space-time encoder 200 can perform space-time encoding and normalization on the reference symbol without using channel information, and then transmit it to the receiver 102. Furthermore, it can use the encoded reference symbol or the previously encoded data symbol to perform space-time encoding and normalization on the data symbol input after the reference symbol, and then transmit it to the receiver 102. As described above, since the transmitter 100 does not use channel information, the decoding process is simple, and the transmission of the differential STLC signal to the receiver 102 after normalization can suppress noise. Moreover, excellent communication performance (e.g., bit error rate (BER)) can be achieved by limiting fluctuations in time-varying channel environments.

[0066] Structure and operation of receiver 102

[0067] Reference Figure 4 The receiver 102 includes two receiving antennas and a space-time decoder 400.

[0068] Observing the space-time decoding process, if we define the two received signals (differential STLC signals) initially received through the first and second receiving antennas as r respectively... 11 [n] and r 21 [n], and define the next two received signals (differential STLC signals) as r respectively. 12 [n] and r 22 [n], then the nth received signal matrix is ​​as shown in the following mathematical formula 9. Since the transmitter 100 transmits two differential STLC symbols in sequence, and the receiver 102 receives two STLC symbols respectively through two receiving antennas, the received signal matrix can be expressed as shown in the following mathematical formula 9.

[0069]

Mathematical Expression 9

[0070]

[0071] Where Z[n] is the effective noise, and it can be assumed that the current channel state is similar to the previous channel state ( ).

[0072] Furthermore, if mathematical formulas 5 and 6 are used, the nth transmitted differential STLC signals s1[n] and s2[n] can be rearranged into mathematical formula 10 as follows.

[0073]

Mathematical Formula 10

[0074]

[0075] When mathematical formula 10 is substituted into mathematical formula 9, the received signal matrix can be simplified to the following mathematical formula 11.

[0076]

Mathematical Expression 11

[0077]

[0078] in, Furthermore, if the channels are highly correlated within 4Ts, then it can be assumed that... .

[0079] In this case, if we compare mathematical formula 9 with mathematical formula 11, the received signal matrix can be rearranged into mathematical formula 12, and the effective noise matrix can be rearranged into mathematical formula 13.

[0080]

Mathematical Expression 12

[0081]

[0082]

Mathematical Expression 13

[0083]

[0084] Referring to mathematical formulas 12 and 13, it can be confirmed that the current received signal matrix is ​​determined by the previously received signal matrix and the input symbols of the transmitter 100.

[0085] Next, if the effective noise Z[n] is assumed to be additive white Gaussian noise (AWGN), then the joint maximum likelihood method can be used for decoding. That is, the space-time decoder 400 can use the joint maximum likelihood method to decode the symbols as shown in the following mathematical formula 14.

[0086]

Mathematical Expression 14

[0087]

[0088] The overall space-time decoding process is illustrated in... Figure 5 (See also) Figure 5 It can be confirmed that the received differential STLC signal is decoded without using channel information. That is, it can be confirmed that even if the input symbols are encoded at the transmitter without using channel information, they can still be decoded normally at the receiver.

[0089] In summary, the receiver 102 of the differential space-time line code system of the present invention does not use channel information. Although the differential space-time line code system of the present invention may have slightly higher decoding complexity due to the use of a joint maximum likelihood method, it can achieve excellent communication performance.

[0090] In modulation with non-constant mode constellations, ambiguity exists when using the maximum likelihood method of Equation 14. For example, as... Figure 6 As shown in (a), in the quadrilateral 16-QAM constellation diagram, after the two sign vectors are normalized, they are distinguished only by their phase because they are of the same magnitude. As a result, since x and x' incur the same cost, they are blurred. To avoid this blurring, as... Figure 6 As shown in (b), non-quadrilateral 16-point modulation can be designed with phase rotation (PR) at the four corner symbols in the 16-QAM constellation diagram. Alternatively, as another method to avoid this ambiguity, it can be used as illustrated in... Figure 6 (c) 16-APSK. The inner loop has 4 states and the outer loop has 12 states. The ratio of the size of the inner loop to the size of the outer loop is... The phase angles between the inner and outer rings are π / 2 and π / 6, respectively. As described above, in the figure... Figure 6 In the constellation diagrams of (b) and (c), the phases of the symbols are all different from each other, and the results are not ambiguous during the maximum likelihood method.

[0091] Furthermore, in the maximum likelihood method of mathematical formula 14, It is a 2-by-2 matrix channel, whereas in existing STBC technology it is a 2-by-1 vector channel. Ultimately, the differential space-time line code system of this invention has superior coding gain compared to existing technologies, thereby improving noise performance in Equation 13.

[0092] While the above mentions the use of one transmitting antenna and two receiving antennas, it is also possible to use two or more transmitting antennas and three or more receiving antennas. That is, using one or more transmitting antennas and two or more receiving antennas is sufficient. For example, the use of a 1×2 antenna can be extended to the use of a 2×4 antenna.

[0093] The following will examine the comparative experimental results of the differential space-time line code system of the present invention with those of the prior art.

[0094] Figure 7 To illustrate the comparison results of BER performance based on signal-to-noise ratio, Figure 8 To illustrate the changes based on channel variation (f) d T s A graph showing the BER performance of ( ). The techniques for comparison are specified as follows.

[0095] 1. STBC w / Partial CSIR : Existing STBC systems that use only initial channel information (partial CSIR) at the receiver / 2. STLC w / Partial CSITSTLC systems that use initial channel information (partial CSIT) at the transmitter / 3. difference STBC : Existing differential STBC systems that use only initial channel information (partial CSIR) at the receiver / 4. Differential STLC : A proposed differential STLC system that does not use channel information at the transmitting end (this invention) / 5. STBC w / Full CSIR : Existing STBC systems that ideally utilize all channel information at the receiving end / 6. STLC w / Full CSIT Existing STLC systems that ideally utilize all channel information at the transmitting end.

[0096] Reference Figure 7 It can be confirmed that the BER performance of the present invention is closest to the BER performance when the rapidly changing channel information is ideally known (STBC w / full CSIR and STLC w / full CSIT). For other prior art STBC and STLC systems, the BER performance deteriorates significantly. That is, it can be confirmed that the differential space-time line code system of the present invention has excellent BER performance even without using channel information.

[0097] Reference Figure 8 It can be seen that, for existing STLC systems, as the channel changes (f d T s The BER performance deteriorates very sensitively with increasing channel variation, whereas the differential space-time line code system of this invention exhibits similar robustness to ideal system performance with increasing channel variation. It can be confirmed that, in the case of existing STLC systems, BER performance is maintained up to a channel variation of 0.0007, whereas the differential space-time line code system of this invention maintains BER performance up to a channel variation of 0.01.

[0098] Figure 9 A diagram illustrating the transmitter of a differential space-time line code system according to another embodiment of the present invention is provided. Figure 10 A diagram illustrating a receiver for a differential space-time line code system according to another embodiment of the present invention.

[0099] Reference Figure 9 The transmitter 100 in this embodiment includes a frequency conversion unit 900, a space-time encoder 902 and a transmitting antenna, wherein the space-time encoder 902 has a reference symbol encoding unit 910 and a data symbol encoding unit 912.

[0100] When with Figure 2 When comparing the transmitter 100 with the transmitter 100, the transmitter 100 of this embodiment also includes a frequency conversion unit 900.

[0101] The frequency conversion unit 900 performs a Fourier transform on the reference symbol / data symbol to convert it into a symbol in the frequency region, and the space-time encoder 902 performs space-time encoding on the symbol in the frequency region. The operation of the space-time encoder 902 is similar to that in the frequency region, except for the frequency region aspect. Figure 2 The operations are the same as those in [the previous section]. Therefore, a description of the encoding process is omitted.

[0102] Reference Figure 10 The receiver 102 in this embodiment includes two receiving antennas, a space-time decoder 1000, and an inverse frequency conversion unit 1002.

[0103] and Figure 4 When comparing with the receiver 102, the receiver 102 in this embodiment also includes an inverse frequency conversion unit 1002.

[0104] The space-time decoder 1000 decodes symbols using the same process as in the embodiment described above, except for the frequency region, and the inverse frequency conversion unit 1002 converts the symbols in the frequency region into symbols in the time region. Since the decoding process is the same, the following description is omitted.

[0105] Furthermore, the constituent elements of the foregoing embodiments are easily understood from the perspective of the processing flow. In other words, each constituent element can be understood as a processing step. Moreover, the processing flow of the foregoing embodiments is also easily understood from the perspective of the device constituent elements.

[0106] Furthermore, the aforementioned technical content can be implemented as program instructions executable by various computer means and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., individually or in combination. The program instructions recorded on the medium may be specifically designed and configured for the embodiments, or may be instructions well-known and available to those skilled in the art of computer software. Examples of computer-readable recording media include: magnetic media such as hard disks, floppy disks, and magnetic tapes; optical media such as CD-ROMs and DVDs; magneto-optical media such as floppy disks; and hardware devices specifically configured to store and execute program instructions, such as read-only memory (ROM), random access memory (RAM), and flash memory. Examples of program instructions include not only machine language code generated by a compiler, but also high-level language code executed by a computer using an interpreter. The hardware device may be configured to operate as one or more software modules for performing the operations of the embodiments, and vice versa.

[0107] Industrial applicability

[0108] The embodiments of the present invention are disclosed for illustrative purposes only. For those skilled in the art to which this invention pertains, various modifications, alterations, and additions can be made within the concept and scope of the present invention, and such modifications, alterations, and additions should be considered to fall within the protection scope of the patent claims.

Claims

1. A transmitter for use in a differential space-time line code system, characterized in that, include: A space-time encoder performs space-time encoding on the input symbols; and At least one transmitting antenna, The space-time encoder performs space-time encoding on the input symbols without using channel information, and the encoded input symbols are transmitted to the receiver through the transmit antenna.

2. The transmitter for a differential space-time line code system according to claim 1, characterized in that, The space-time encoder includes: The reference symbol coding unit performs space-time coding on the reference symbol, which is the input symbol, without using channel information; and The data symbol encoding unit uses the encoded reference symbol information to perform space-time encoding on the data symbols that serve as input symbols.

3. The transmitter for a differential space-time line code system according to claim 2, characterized in that, The reference symbol encoding unit performs space-time coding on the reference symbol without using channel information to generate a reference differential space-time line code signal, and then normalizes the generated reference differential space-time line code signal using weights. The normalized reference differential space-time line code signal is transmitted to the receiver through the transmitting antenna.

4. The transmitter for a differential space-time line code system according to claim 3, characterized in that, The weights are derived based on the reference symbol without using channel information. The receiver includes at least two receiving antennas.

5. The transmitter for a differential space-time line code system according to claim 2, characterized in that, The data symbol encoding unit generates a first differential space-time line code signal by multiplying the encoded reference symbol with a first data symbol, and normalizes the generated first differential space-time line code signal using a first weight. The normalized first differential space-time line code signal is transmitted to the receiver through the transmit antenna, and the first weight is determined by the first data symbol without using channel information.

6. The transmitter for a differential space-time line code system according to claim 5, characterized in that, The data symbol encoding unit generates a second differential space-time line code signal by multiplying the first differential space-time line code signal with a second data symbol input after the first data symbol, and normalizes the generated second differential space-time line code signal using a second weight. The normalized second differential space-time line code signal is transmitted to the receiver through the transmit antenna, and the second weight is determined by the second data symbol without using channel information.

7. The transmitter for a differential space-time line code system according to claim 1, characterized in that, It also includes a frequency transformation unit that performs frequency transformation on the input symbols to generate a frequency region of input symbols. The space-time encoder performs space-time encoding on the input symbols in the frequency region.

8. A transmitter for use in a space-time line code system, characterized in that, include: A space-time encoder performs space-time encoding on the input symbols; and At least one transmitting antenna, The space-time encoder performs space-time encoding on the reference symbol used as the input symbol to generate a reference space-time line code signal, normalizes the generated reference space-time line code signal using weights, and transmits the normalized reference space-time line code signal to the receiver through the transmitting antenna.

9. The transmitter for use in a space-time line code system according to claim 8, characterized in that, The weights are derived based on the reference symbol without using channel information. The receiver includes at least two receiving antennas.

10. A receiver for use in a space-time line code system, characterized in that, include: At least two receiving antennas; and A space-time decoder receives space-time encoded space-time linecode symbols from a transmitter with a transmit antenna via the receive antenna to form a received signal matrix, and then decodes the formed received signal matrix. The received signal matrix is ​​determined by the previously received signal matrix and the input symbols input to the transmitter.

11. The receiver for use in a space-time line code system according to claim 10, characterized in that, The space-time encoded space-time line code symbol is generated by the transmitter by performing space-time encoding on the input symbol without using channel information.

12. The receiver for use in a space-time line code system according to claim 10, characterized in that, The space-time encoded space-time line code symbol is generated by applying the previously space-time encoded space-time line code symbol to the current input symbol through the transmitter, and by normalizing the encoded input symbol using weights. The weights are determined by the input symbols.

13. The receiver for use in a space-time line code system according to claim 12, characterized in that, The previously space-time encoded space-time line code symbol is space-time encoded without using channel information.

14. The receiver for use in a space-time line code system according to claim 10, characterized in that, The space-time decoder uses a joint maximum likelihood method to decode the received signal matrix.

15. The receiver for use in a space-time line code system according to claim 14, characterized in that, It also includes an inverse frequency transformation unit, which performs an inverse frequency transformation on the decoded received signal matrix in the frequency region to convert it into a signal in the time region.

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