Differential space-time line coding system and method

Abstract

Disclosed are a differential space-time line coding system and method that do not use channel information. A transmitter used in the differential space-time line coding system comprises: a space-time encoder that performs space-time encoding of input symbols; and at least one transmission antenna. The space-time encoder performs space-time encoding of the input symbols without using channel information, and the encoded input symbols are transmitted to a receiver through the transmission antenna.

Description

Differential spatiotemporal line encoding system and method

[0001] The present invention relates to a differential space-time line encoding system and method.

[0002] Among the space-time coding (STC) technologies utilizing multiple transmit / receive antennas, the widely known space-time block code (STBC) transmits block-shaped codes without using channel information and uses channel information estimated at the receiver to achieve maximum space diversity gain. This STBC technology was initially applied to time-invariant channel environments and was not suitable for time-varying ones.

[0003] The space-time line code (STLC) technology, which is currently being developed, is a technology that is completely symmetrical to the existing STBC. It uses channel information at the transmitter, not the receiver, and the receiver provides the same performance as STBC by simply linearly combining the received signals without channel information.

[0004] STLC technology was also initially implemented in a time-invariant channel environment. Like the early STBC technology, this existing STLC technology was developed assuming a time-invariant channel environment, making it difficult to acquire information on time-varying channels, especially those with high mobility.

[0005] Therefore, development of STLC technology suitable for time-varying channel environments is necessary.

[0006] The present invention provides a differential space-time line encoding system and method.

[0007] In order to achieve the above-described object, a transmitter used in a differential space-time line coding system according to one embodiment of the present invention includes a space-time encoder that space-time encodes input symbols; and at least one transmission antenna. Here, the space-time encoder space-time encodes the input symbols without any channel information, and the encoded input symbols are transmitted to a receiver via the transmission antenna. The differential space-time line coding system is characterized in that it is used.

[0008] A transmitter used in a space-time line encoding system according to another embodiment of the present invention comprises a space-time encoder that space-time encodes an input symbol; and at least one transmitting antenna. Here, the space-time encoder space-time encodes a reference symbol as the input symbol to generate a reference STLC signal, normalizes the generated reference STLC signal using a weight, and transmits the normalized reference STLC signal to a receiver via the transmitting antenna.

[0009] A receiver used in a space-time linear encoding system according to one embodiment of the present invention comprises 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 receiving signal matrix, and decodes the formed receiving signal matrix. Here, the receiving signal matrix is ​​determined by a previous receiving signal matrix and input symbols input to the transmitter.

[0010]

[0011] The differential space-time line coding system and method according to the present invention space-time encodes input symbols without using channel information at the transmitter, making encoding simple. Furthermore, the receiver also does not use channel information, making the decoding process simple. Furthermore, the system can provide excellent communication performance even in environments with extreme channel variations. Consequently, the differential space-time line coding system can be suitably used for various mobile communications systems with time-varying channel environments.

[0012] FIG. 1 is a diagram illustrating the concept of a differential space-time line encoding system according to one embodiment of the present invention.

[0013] FIG. 2 is a diagram illustrating the structure of a transmitter according to one embodiment of the present invention.

[0014] FIG. 3 is a diagram illustrating a space-time encoding process according to one embodiment of the present invention.

[0015] FIG. 4 is a diagram illustrating the structure of a receiver according to one embodiment of the present invention.

[0016] FIG. 5 is a diagram illustrating a spatiotemporal decoding process according to one embodiment of the present invention.

[0017] Figure 6 is a drawing showing a constellation diagram.

[0018] Figure 7 is a diagram showing the results of comparing BER performance according to signal-to-noise ratio.

[0019] Figure 8 shows the channel change (f d T s ) is a diagram showing the BER performance.

[0020] FIG. 9 is a diagram illustrating a transmitter of a differential space-time line encoding system according to another embodiment of the present invention.

[0021] FIG. 10 is a diagram illustrating a receiver of a differential space-time line encoding system according to another embodiment of the present invention.

[0022] As used herein, singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "consist of" or "include" should not be construed to necessarily include all components or steps described in the specification, and should be construed to mean that some of the components or steps may not be included, or that additional components or steps may be included. In addition, terms such as "part" and "module" described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware or software, or by a combination of hardware and software.

[0023]

[0024] The present invention relates to a differential space-time line encoding system and method, and is a technology suitable for a time-varying channel environment in mobile communications such as vehicle / train / aircraft / satellite communications.

[0025] According to one embodiment, the differential space-time line coding system can space-time encode symbols without using channel information at a transmitter, transmit the space-time encoded symbols through a single transmit antenna, and space-time decode the symbols received through two receive antennas at a receiver. This differential space-time line coding system can provide excellent communication performance even in environments with extreme time-dependent channel variations and can have a very simple structure. Therefore, it can be suitably used for various mobile communications with time-varying channel environments.

[0026]

[0027] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings.

[0028] FIG. 1 is a diagram illustrating the concept of a differential space-time linear encoding system according to one embodiment of the present invention, FIG. 2 is a diagram illustrating the structure of a transmitter according to one embodiment of the present invention, and FIG. 3 is a diagram illustrating a space-time encoding process according to one embodiment of the present invention. FIG. 4 is a diagram illustrating the structure of a receiver according to one embodiment of the present invention, FIG. 5 is a diagram illustrating a space-time decoding process according to one embodiment of the present invention, and FIG. 6 is a diagram illustrating a constellation diagram.

[0029] Referring to FIG. 1, the differential space-time line encoding system of the present embodiment may include a transmitter (100) and a receiver (102) that communicate in a time-varying channel environment.

[0030] In one embodiment, the transmitter (100) may use one transmit antenna, and the receiver (102) may use two receive antennas. In particular, the transmitter (100) may perform space-time encoding without using all channel information.

[0031] Below, the structure and operation of the transmitter (100) will be examined, and then the structure and operation of the receiver (102) will be examined.

[0032] Structure and operation of transmitter (100)

[0033] Referring to FIG. 2, a transmitter (100) includes a space-time encoder (200) and one transmission antenna, and the space-time encoder (200) may include a reference symbol encoder (210) that space-time encodes a reference symbol and a data symbol encoder (212) that encodes a data symbol input after the reference symbol.

[0034] According to one embodiment, the space-time encoder (200) can space-time encode and transmit a reference symbol as an input symbol without using channel information, and then space-time encode and transmit a data symbol. That is, unlike the conventional space-time line coding technology that uses the entire channel information at the transmitter, the differential space-time line coding system of the present invention does not use channel information. Nevertheless, as described below, the differential space-time line coding system of the present invention can provide better communication performance than the conventional space-time line coding technology in a time-varying channel environment. This is because the differential space-time line coding system normalizes (standardizes) space-time line-encoded differential STLC symbols (STLC signals) independently of the channel information and then transmits them to the receiver (102).

[0035] Basic symbol transmission

[0036] When two symbols (x1[0], x2[0]) are sequentially input as reference symbols, the reference symbol encoding unit (210) can space-time encode the symbols (x1[0], x2[0]) as in the following mathematical expression 1 to generate reference differential STLC signals (0th differential STLC symbols, n=0). n is an STLC index.

[0037]

[0038] Here, the symbol x i [0] is an arbitrary reference symbol (reference signal) that is not 0 and is not decoded in the receiver (102), and v i [0] can be any value as the initial differential STLC encoding matrix.

[0039] Next, the reference symbol encoding unit (210) can power normalize the reference differential STLC signal as in the following mathematical expression 2 in order to limit power when transmitting the reference differential STLC signal.

[0040]

[0041] Here, β is a weight, and β[0] can be obtained based on the reference signal as in the following mathematical expression 3.

[0042]

[0043] Continuing, the reference symbol encoding unit (210) can transmit the normalized reference differential STLC signals to the receiver (102) via the transmission antenna. Preferably, the reference symbol encoding unit (210) can sequentially transmit s1[0] / β[0] and s2[0] / β[0] to the receiver (102).

[0044] In summary, the reference symbol encoding unit (210) normalizes the differential STLC signal with a weight based on the reference signal and transmits it to the receiver (102). This overall process is shown in the right figure of Fig. 3.

[0045] Data symbol transmission

[0046] If the data symbol to be transmitted as an input symbol is defined as in the following mathematical expression 4, the data symbol encoding unit (212) can generate the nth differential STLC signal as in the following mathematical expression 5.

[0047]

[0048]

[0049] Here, V[n] can be implemented with previously encoded differential STLC symbols as shown in Equation 6 below.

[0050]

[0051] Referring to Equation 6, it can be seen that the first differential STLC encoding matrix V[1] can be obtained from the normalized reference differential STLC signal. Consequently, the first differential STLC encoding matrix V[1] reflects the reference signal information, and as a result, the nth STLC encoding matrix V[n] also reflects the reference signal information. In other words, the space-time encoder (200) does not use channel information.

[0052] Next, the data symbol encoding unit (212) can power-normalize the differential STLC signal. At this time, the weight (β) used when n = 1 can be defined as in mathematical expression 7 below. Therefore, if derived in a similar manner, the nth weight (β) used is as in mathematical expression 8 below.

[0053] [Correction pursuant to Rule 91, July 29, 2024]

[0054]

[0055] Referring to Equation 8, the weights for normalization do not depend on channel information and are the input symbol x k It can be confirmed that it is determined by [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].

[0056] Next, the data symbol encoding unit (212) can transmit the normalized differential STLC signals to the receiver (102) via the transmission antenna. Preferably, the data symbol encoding unit (212) can sequentially transmit s1[n] / β[n] and s2[n] / β[n] to the receiver (102).

[0057] In summary, the data symbol encoding unit (212) determines the reference differential STLC signal weights based on input symbols, unlike conventional STLC signals where the weights are determined based on channel information. Consequently, the data symbol encoding unit (212) also does not use channel information. This detailed process is illustrated in Fig. 3.

[0058] To summarize the overall process of the transmitter, the space-time encoder (200) space-time encodes and normalizes a reference symbol without using channel information and transmits it to the receiver (102), and space-time encodes and normalizes a data symbol input after the reference symbol using the encoded reference symbol or a previously encoded data symbol and then transmits it to the receiver (102). In this way, since the transmitter (100) does not use channel information, the decoding process is simple, and since the differential STLC signal is normalized and then transmitted to the receiver (102), noise can be suppressed and variability can be limited in a time-varying channel environment, thereby realizing excellent communication performance (e.g., BER (bit error rate)).

[0059]

[0060] Structure and operation of the receiver (102)

[0061] Referring to FIG. 4, the receiver (102) includes two receiving antennas and a space-time decoder (400).

[0062] Looking at the space-time decoding process, the two reception signals (differential STLC signals) initially received through the first reception antenna and the second reception antenna are each r 11 [n] and r 21 Define [n] and then the two received signals (differential STLC signals) are each r 12 [n] and r 22When defined as [n], the nth reception signal matrix is ​​as shown in the following mathematical expression 9. Since the transmitter (100) sequentially transmits two differential STLC symbols and the receiver (102) receives two STLC symbols through two reception antennas, the reception signal matrix can be expressed as the following mathematical expression 9.

[0063]

[0064] Here, Z[n] is the effective noise, and the current channel state is similar to the previous channel state ( ) can be assumed.

[0065] Meanwhile, the nth transmitted differential STLC signals (s1[n] and s2[n]) can be organized as in Equation 10 below using Equations 5 and 6.

[0066]

[0067] By substituting mathematical expression 10 into mathematical expression 9, the received signal matrix can be simplified into mathematical expression 11 below.

[0068] [Correction pursuant to Rule 91, July 29, 2024]

[0069] Here, , and if the channels are highly correlated within 4Ts. It can be assumed that.

[0070] In this case, by comparing mathematical expressions 9 and 11, the received signal matrix can be organized into mathematical expression 12 below, and the effective noise matrix can be organized into mathematical expression 13 below.

[0071]

[0072]

[0073] Referring to mathematical expressions 12 and 13, it can be confirmed that the current received signal matrix is ​​determined by the previous received signal matrix and the input symbols of the transmitter (100).

[0074] Next, assuming that the effective noise (Z[n]) is additive white Gaussian noise (AWGN), decoding may be possible using the joint maximum likelihood technique. That is, the spatiotemporal decoder (400) may decode symbols as in the following mathematical expression 14 using the joint maximum likelihood technique.

[0075]

[0076] This overall spatiotemporal decoding process is illustrated in Figure 5. Referring to Figure 5, it can be confirmed that the received differential STLC signals are decoded without using channel information. In other words, even if the transmitter encodes the input symbols without using channel information, the receiver can successfully decode them.

[0077] In summary, the receiver (102) of the differential space-time line coding system of the present invention does not use channel information. However, the differential space-time line coding system of the present invention can have excellent communication performance, although the decoding complexity may be slightly increased due to the use of the joint maximum likelihood method.

[0078] In terms of modulation with non-constant modulus constellations, there is an ambiguity when using the maximum likelihood technique of Equation 14. For example, in a rectangular 16-QAM constellation as illustrated in (a) of Fig. 6, when two symbol vectors are normalized, their magnitudes are the same and can be distinguished only by their phases, resulting in ambiguity since x and x' incur the same cost. To avoid this ambiguity, a non-rectangular 16-point modulation can be designed with four corner symbols having phase rotation (PR) at the 16-QAM constellation points as illustrated in (b) of Fig. 6. In addition, as another method to avoid this ambiguity, 16-APSK can be used as illustrated in (c) of Fig. 6. The inner ring has four states and the outer ring has 12 states. The ratio of the sizes of the inner ring to the outer ring is , and the phase angles of the inner and outer rings are π / 2 and π / 6, respectively. In this way, the phases of the symbols in the constellations shown in (b) and (c) of Fig. 6 are all different from each other, and as a result, there can be no ambiguity during the maximum likelihood technique.

[0079] Also, in the maximum likelihood technique of Equation 14, This is a 2-by-2 matrix channel, whereas the existing STBC technology uses a 2-by-1 vector channel. Consequently, the differential space-time line coding system of the present invention has superior coding gain compared to the existing technology, and thus can improve the noise aspect of Equation 13.

[0080] While the above mentioned use of one transmit antenna and two receive antennas, it is also possible to use two or more transmit antennas and three or more receive antennas. That is, it is sufficient to use one or more transmit antennas and two or more receive antennas. For example, the use of a 1x2 antenna could be extended to use a 2x4 antenna.

[0081]

[0082] Below, we will examine the results of a comparative experiment of the differential space-time line encoding system of the present invention and conventional technologies.

[0083] Figure 7 is a diagram showing the results of BER performance comparison according to signal-to-noise ratio, and Figure 8 is a diagram showing the results of channel change (f d T s ) is a diagram showing the BER performance. The technologies to be compared are specified as follows.

[0084] 1.STBC w / partial CSIR: Existing STBC system that utilizes only initial channel information (partial CSIR) at the receiver / 2.STLC w / partial CSIT: STLC system that utilizes initial channel information (partial CSIT) at the transmitter / 3.Differential STBC: Existing differential STBC system that utilizes only initial channel information (partial CSIR) at the receiver / 4.Differential STLC: Proposed differential STLC system that does not use channel information at the transmitter (the present invention) / 5.STBC w / full CSIR: Existing STBC system that ideally utilizes all channel information at the receiver / 6.STLC w / full CSIT: Existing STLC system that ideally utilizes all channel information at the transmitter

[0085] Referring to Figure 7, it can be confirmed that the BER performance of the present invention is closest to the BER performance (STBC w / full CSIR and STLC w / full CSIT) when rapidly changing channel information is ideally known. In other conventional technologies, the BER performance degradation is very serious in the case of the STBC system and the STLC system. In other words, it can be confirmed that the differential space-time line coding system of the present invention has excellent BER performance even without using channel information.

[0086] Referring to Fig. 8, for the existing STLC system, the channel change (f d Ts ) increases, the BER performance deteriorates very sensitively, while the differential space-time line coding system of the present invention is very robust to increasing channel variations, similar to ideal system performance. While the existing STLC system maintains BER performance up to a channel variation of about 0.0007, the differential space-time line coding system of the present invention can be confirmed to maintain BER performance up to a channel variation of about 0.01.

[0087] FIG. 9 is a diagram illustrating a transmitter of a differential space-time line encoding system according to another embodiment of the present invention, and FIG. 10 is a diagram illustrating a receiver of a differential space-time line encoding system according to another embodiment of the present invention.

[0088] Referring to FIG. 9, the transmitter (100) of the present embodiment includes a frequency converter (900), a space-time encoder (902), and one transmission antenna, wherein the space-time encoder (902) has a reference symbol encoder (910) and a data symbol encoder (912).

[0089] Compared to the transmitter (100) of FIG. 2, the transmitter (100) of the present embodiment further includes a frequency converter (900).

[0090] The frequency converter (900) converts the reference symbol / data symbol into a symbol in the frequency domain by Fourier transforming, and the space-time encoder (902) space-time encodes the symbol in the frequency domain. The operation of the space-time encoder (902) is identical to that of FIG. 2 except that it is in the frequency domain. Therefore, a description of the encoding process will be omitted.

[0091] Referring to FIG. 10, the receiver (102) of the present embodiment includes two receiving antennas, a space-time decoder (1000), and an inverse frequency converter (1002).

[0092] Compared with the receiver (102) of FIG. 4, the receiver (102) of the present embodiment further includes a reverse frequency converter (1002).

[0093] The space-time decoder (1000) decodes symbols in the same process as in the above embodiment except that it is in the frequency domain, and the inverse frequency converter (1002) converts symbols in the frequency domain into symbols in the time domain. Since the decoding process is the same, a detailed description thereof is omitted.

[0094]

[0095] Meanwhile, the components of the aforementioned embodiments can be easily understood from a process perspective. That is, each component can be understood as a separate process. Furthermore, the processes of the aforementioned embodiments can be easily understood from the perspective of the device components.

[0096] In addition, the technical contents described above may be implemented in the form of program commands that can be executed through various computer means and recorded on a computer-readable medium. The computer-readable medium may include program commands, data files, data structures, etc., alone or in combination. The program commands recorded on the medium may be those specially designed and configured for the embodiments or may be 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 floptical disks, and hardware devices specially configured to store and execute program commands, such as ROMs, RAMs, and flash memories. Examples of program commands include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The hardware devices may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

[0097] The above-described embodiments of the present invention are disclosed for the purpose of illustration, and those skilled in the art with common knowledge of the present invention will be able to make various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes, and additions should be considered to fall within the scope of the following patent claims.

Claims

1. A space-time encoder that space-time encodes input symbols; and comprising at least one transmitting antenna, A transmitter used in a differential space-time line encoding system, characterized in that 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 transmission antenna.

2. In the first paragraph, the space-time encoder, A reference symbol encoding unit that spatiotemporally encodes a reference symbol as the input symbol without using channel information; and A transmitter used in a differential space-time line encoding system, characterized by including a data symbol encoding unit that space-time encodes a data symbol as the input symbol using information of the encoded reference symbol.

3. In the second paragraph, the reference symbol encoding unit generates a reference differential STLC signal by space-time encoding the reference symbol without using channel information, and normalizes the generated reference differential STLC signal using a weight. A transmitter used in a differential space-time line coding system, characterized in that the normalized reference differential STLC signal is transmitted to the receiver through the transmitting antenna.

4. In the third paragraph, the weight is obtained based on the reference symbol without using channel information. A transmitter used in a differential space-time line coding system, wherein the receiver comprises at least two receiving antennas.

5. In the second paragraph, the data symbol encoding unit generates a first differential STLC signal by multiplying the encoded reference symbol and the first data symbol, and normalizes the generated first differential STLC signal using the first weight. A transmitter used in a differential space-time line coding system, wherein the normalized first differential STLC signal is transmitted to the receiver through the transmitting antenna, and the first weight is determined by the first data symbol and does not use channel information.

6. In the fifth paragraph, the data symbol encoding unit generates a second differential STLC signal by multiplying the first differential STLC signal and the second data symbol input after the first data symbol, and normalizes the generated second differential STLC signal using the second weight. A transmitter used in a differential space-time line coding system, wherein the normalized second differential STLC signal is transmitted to the receiver through the transmitting antenna, and the second weight is determined by the second data symbol and does not use channel information.

7. In paragraph 1, Further comprising a frequency conversion unit for converting the input symbol into a frequency domain input symbol, A transmitter used in a differential space-time line encoding system, characterized in that the space-time encoder space-time encodes input symbols in the frequency domain.

8. A space-time encoder that space-time encodes the input symbol; and comprising at least one transmitting antenna, A transmitter used in a space-time line encoding system, characterized in that the space-time encoder space-time encodes a reference symbol as the input symbol to generate a reference STLC signal, normalizes the generated reference STLC signal using a weight, and transmits the normalized reference STLC signal to a receiver through the transmission antenna.

9. In paragraph 8, the weight is obtained based on the reference symbol without using channel information. A transmitter used in a space-time line coding system, wherein the receiver comprises at least two receiving antennas.

10. At least two receiving antennas; and A space-time encoded STLC symbol is received from a transmitter having one transmit antenna through the receive antennas to form a reception signal matrix, and a space-time decoder is included to decode the formed reception signal matrix. A receiver used in a space-time line coding system, wherein the received signal matrix is determined by a previous received signal matrix and input symbols input to the transmitter.

11. A receiver used in a space-time line coding system, characterized in that in the 10th paragraph, the space-time encoded STLC symbols are generated by encoding the input symbols by the transmitter without using channel information.

12. In the 10th paragraph, the space-time encoded STLC symbols are encoded by applying a previous space-time encoded STLC symbol to a current input symbol by the transmitter and are generated by normalizing the encoded input symbol using a weight. A receiver used in a space-time line coding system, characterized in that the above weights are determined by the input symbols.

13. A receiver used in a space-time line coding system, characterized in that the previous space-time coded STLC symbol in the 12th paragraph is space-time coded without using channel information.

14. A receiver used in a space-time precoding system, characterized in that in claim 10, the space-time decoder decodes the received signal matrix using a joint maximum likelihood technique.

15. In paragraph 14, A receiver used in a space-time line encoding system, characterized in that it further includes a frequency inverse transform unit that inversely frequency transforms the decoded reception signal matrix in the frequency domain into a signal in the time domain.

Images