FR2954642A1 - Method for adaptive transmission of information using digital video broadcasting-satellite-second generation system, involves selecting transmission mode between transmission and receiving devices based on estimated signal to noise ratio - Google Patents

Abstract

The method involves estimating an instantaneous signal to noise ratio for signals received by a set of receiving antennas of a receiving device in a wireless communication system i.e. digital video broadcasting-satellite-second generation (DVB-S2)system, using a signal-to-noise ratio estimation unit. A transmission mode is selected between a transmission device and the receiving device based on the estimated instantaneous signal to noise ratio using a multiple transmission selector. An independent claim is also included for a system for adaptive transmission of information using a multiple input and multiple output antenna, comprising a signal to noise ratio estimation unit.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method and an adaptive transmission system capable of appropriately maintaining a transmission rate and stability in accordance with the present invention. a defined communication environment in DVB-S2 digital television broadcasting using a multiple input multiple output (MIMO) antenna system.

II. BACKGROUND TECHNOLOGY DVB-S2 digital television broadcasting is a second-generation standard for satellite broadcasting that is being developed by a digital television broadcasting (DVB) project.

DVB-S2 technology uses V-BLAST (vertical bell laboratories layered space-time) coding, etc., which is a coding method, to increase the transmission rate and uses a space-time block code. (STBC), etc., to ensure the stability of a signal. V-BLAST coding is a wireless communication technology that does not additionally use a frequency band in a fading environment and can transmit data at a high rate. STBC coding is a wireless communication technology that can achieve space-time diversity gain without subsequently increasing bandwidth simply by using coding in the MIMO antenna system. At the same time, the DVB-S2 encoding has a trade-off relationship in that, when the DVB-S2 encoding using the multiple input and multiple output antenna system uses the STBC encoding, the stability of a signal is ensured but the transmission rate is degraded and, when the DVB-S2 coding uses the V-BLAST coding, the transmission rate of a signal is increased but the stability of the signal is degraded. Therefore, it is preferable to adaptively determine the appropriate coding method and the number of transmit and receive antennas as a function of the communication environments. In this case, in the MIMO antenna system, the manner of determining the signal-to-noise ratio (hereinafter referred to as the signal-to-noise ratio or S / B), also commonly referred to as SNR (for "signal to noise ratio" in English), which is an important index for the communication environment, is very important. However, the detailed and clear standard for the process has not yet been established. III. SUMMARY OF THE INVENTION An object of the present invention is to provide an adaptive transmission method using a MIMO antenna system using an adaptive transmission scheme capable of simultaneously improving signal stability and transmission rate. Another object of the present invention is to provide an adaptive transmission system using the aforementioned adaptive transmission method. In order to solve the technical problem, according to one aspect of the present invention, there is provided an adaptive transmission method using a multiple input multiple output antenna system, comprising: estimating an instantaneous signal-to-noise ratio for signals received in a plurality of receiving antennas; and selecting a transmission mode between a transmitting device and a receiving device according to the instantaneous signal-to-noise ratio. The estimate of the instantaneous signal-to-noise ratio includes any one of the instantaneous minimum signal-to-noise ratio selection among a plurality of instantaneous signal-to-noise ratios measured at the plurality of receiving antennas, the selection of the signal-to-noise ratio. instantaneous maximum noise among the plurality of instantaneous signal-to-noise ratios measured at the plurality of receiving antennas, and selecting an average signal-to-noise ratio obtained by dividing a sum of the plurality of instantaneous signal-to-noise ratios measured at the level of the plurality of receiving antennas by the number of the plurality of receiving antennas. Selecting the transmission mode between the transmission device and the receiving device according to the instantaneous signal-to-noise ratio comprises comparing a predetermined switching level with the instantaneous signal-to-noise ratio for the plurality of transmission modes of the system. digital television broadcasting. The plurality of transmission modes includes STBC 4Txx4Rx, STBC 2Txx2Rx, STBC 2Txx1Rx, BLAST 2Txx2Rx, BLAST 4Txx4Rx, BLAST 8Txx8Rx. According to another aspect of the present invention, there is provided an adaptive transmission method performed by a receiving device using a multiple input and multiple output antenna, comprising: estimating an instantaneous signal-to-noise ratio for received signals in a plurality of receiving antennas; selecting at least one of the number of transmitting antennas and the number of receiving antennas according to the instantaneous signal-to-noise ratio. Selecting at least one of the number of transmitting antennas and the number of receiving antennas based on the instantaneous signal-to-noise ratio compares the instantaneous signal-to-noise ratio with a predetermined switching level to select the transmission mode of the transmission system. digital television broadcasting. The plurality of transmission modes selects an STBC scheme or BLAST scheme as an encoding scheme, without being limited to it. Estimation of the instantaneous signal-to-noise ratio includes: selecting instantaneous signal-to-noise ratio determination schemes; determining the instantaneous signal-to-noise ratio for each of the plurality of receiving antennas; and estimating the instantaneous signal-to-noise ratio of all of the plurality of receiving antennas from the instantaneous signal-to-noise ratio determined for each of the plurality of receiving antennas based on the selected determination scheme. The determination schemes include any of the minimum signal-to-noise ratio selection among a plurality of instantaneous signal-to-noise ratios measured at the plurality of receiving antennas, the selection of the maximum signal-to-noise ratio among the plurality of instantaneous signal-to-noise ratios measured at the plurality of receiving antennas, and selecting an average signal-to-noise ratio obtained by dividing a sum of the plurality of instantaneous signal-to-noise ratios measured at the plurality of received antennas; receiving antennas by the number of the plurality of receiving antennas. The selection of at least one of the number of transmitting antennas and the number of receiving antennas as a function of the instantaneous signal-to-noise ratio comprises: comparing a predetermined switching level with the instantaneous signal-to-noise ratio so as to switch between the plurality of transmission modes; and selecting at least one of the number of transmitting antennas and the number of receiving antennas based on the predetermined selection criteria based on the result of the comparison. The adaptive transmission method performed by a receiving device using a multiple input multiple output antenna further comprises determining an encoding scheme based on the instantaneous signal-to-noise ratio. The adaptive transmission method performed by a receiving device using a multiple input multiple output antenna further comprises transmitting information regarding the number of transmitting antennas for the transmission device. According to another aspect of the present invention, there is provided an adaptive transmission system using a multiple input multiple output antenna system, comprising: a signal / noise ratio estimating unit which estimates an instantaneous signal-to-noise ratio for signals received in a plurality of receiving antennas; and a multiple transmission selector which is connected to the signal / noise ratio estimating unit and selects a transmission mode between a transmitting device and a receiving device according to the instantaneous signal-to-noise ratio. The signal / noise ratio estimation unit estimates any one of the instantaneous minimum signal-to-noise ratio selection, the instantaneous maximum signal-to-noise ratio and an instantaneous average signal-to-noise ratio obtained by dividing a sum of the plurality of instantaneous signal-to-noise ratios measured at the plurality of receiving antennas by the number of the plurality of selected receiving antennas out of a plurality of instantaneous signal-to-noise ratios measured at the plurality of receiving antennas such as the instantaneous signal-to-noise ratio. 7 The multiple transmission selector compares the instantaneous signal-to-noise ratio with the predetermined switching level to select the transmission mode.

The multiple transmission selector transmits information relating to the selected transmission mode according to the switching level to the transmission device, the transmitted information relating to the transmission mode including the number of transmitting antennas and channel coding information. The plurality of transmission modes includes STBC 4Txx4Rx, STBC 2Txx2Rx, STBC 2Txx1Rx, BLAST 2Txx2Rx, BLAST 4Txx4Rx, BLAST 8Txx8Rx and the multiple transmission selector selects any one of the plurality of transmission modes. The multiple transmission selector is mounted on the receiving device and transmits to the transmission device the information relating to at least one of the number of transmitting antennas and the channel coding scheme, through the return path between the receiving device and the transmission device. According to embodiments of the present invention, it estimates the instantaneous signal-to-noise ratio of the receiving end in the MIMO antenna system and controls at least one of the coding scheme of the digital television broadcasting system and the number of Antennas of the MIMO antenna system as a function of the estimated instantaneous signal-to-noise ratio, thus enabling data to be transmitted with optimum stability and transmission rate in the given communication environment in the MIMO antenna transmission system. such as DVB-S2, etc. IV. LIST OF FIGURES FIG. 1 is a schematic block diagram for explaining an adaptive transmission system using a multiple input multiple output antenna according to an illustrative embodiment of the present invention; Fig. 2 is a flowchart for explaining an adaptive transmission method using a multiple input multiple output antenna according to an illustrative embodiment of the present invention; and Figures 3 and 4 are graphs for explaining a signal / noise ratio estimation scheme usable in the method and the adaptive transmission system according to the illustrative embodiment of the present invention.

V. DETAILED DESCRIPTION Advantages and features of the present invention and methods for obtaining them will be explained from illustrative embodiments described below in detail with reference to the accompanying drawings. However, the present invention is not limited to an illustrative embodiment described below, but will be implemented in different forms. Illustrative embodiments are provided by way of example only so that those skilled in the art can fully understand the description of the present invention and the scope of the present invention. Therefore, the present invention will be defined exclusively by the scope of the appended claims. At the same time, the terms used in the present invention are intended to explain illustrative embodiments, rather than to limit the present invention. In the description, a singular word may also be used as a plural word unless specifically indicated. The terms "includes" and / or "including" used herein do not exclude the existence or addition of one or more other components, steps, operations and / or elements. Fig. 1 is a schematic block diagram for explaining an adaptive transmission system of a DVB-S2 system to which an adaptive transmission scheme including an STBC encoding and a V-BLAST encoding according to an illustrative embodiment of the present invention is applied. . Fig. 2 is a flowchart for explaining an adaptive transmission method in a DVB-S2 system to which an adaptive transmission scheme according to an illustrative embodiment of the present invention is applied. Referring to Fig. 1, the adaptive transmission system to which the adaptive transmission scheme of the present invention is applied is connected to a receiving side device of a DVB-S2 system 100 using a MIMO antenna system and is configured to estimating a signal-to-noise ratio for a plurality of receive-side receiver-receiving antennas and selecting any one of multiple transmission modes based on the estimated signal-to-noise ratio. In the present embodiment, the adaptive transmission system is connected to the receiving-side device (hereinafter referred to as the receiving device) of a wireless communication system using a MIMO antenna system and comprises a communication unit. a signal-to-noise ratio estimation 180 which estimates the signal-to-noise ratio for the plurality of receiver antennas of the receiving device and a multiple transmission selector 190 which selects the number of transmitting antennas, the number of receiving antennas, or the two, depending on the value of a signal-to-noise ratio received from the signal-to-noise ratio estimation unit 180. The multiple transmission selector 190 may be installed to transmit information regarding the number of antennas transmitters selected to a transmission-side device (hereinafter referred to as a transmission device) and to transmit information concerning the number of transmitters selected receivers to the receiving device. The adaptive transmission system 100 according to the illustrative embodiment may be configured to include the transmission device, the receiving device, the signal / noise ratio estimating unit 180 and the multi-transmission selector 190. The transmission comprises an encoder 110 which encodes transmission data (TX DATA), a plurality of mappers 120 which map a stream of encoded transmission data into a data symbol, 11 and a plurality of transmitting antennas 130 (Tx 1 to Tx n) which transmits a coded transmission data signal. The transmitting device may further comprise a configuration unit that executes an inverse fast Fourier transform on output signals of the mapper, transforms a parallel data stream into a serial data stream, or inserts a cyclic prefix (CP) into the serial data flow.

In the present illustrative embodiment, the encoder 110 in the transmission device is implemented as the space-time block (STB) based coder and the BLAST coding ("bell laboratories"). layered space-time ").

The receiving device comprises a plurality of receiving antennas 150 (Rx 1 to Rx n) receiving external signals, a plurality of de-mappers 160 which de-map a mapped data stream to a received data symbol and a decoder 170 which decodes the received data stream and outputs the received data (RX DATA). In addition, the receiving device comprises the signal / noise ratio estimation unit 180 which performs the signal / noise ratio detection on each receiving antenna 150.

For convenience of explanation, the plurality of transmitting antennas 130 (Tx 1 to Tx n) is called a transmitting antenna (Tx) and the plurality of receiving antennas 150 (Rx 1 to Rx n) is called a receiving antenna (Rx ).

The signal / noise ratio estimation unit 180 measures the instantaneous signal-to-noise ratio for the plurality of receiving antennas to estimate the instantaneous signal-to-noise ratio (S / N ratio) of the receiving device (see S22 of FIG. Figure 2). The estimated value is transmitted to the multi-transmission selector 190. The multi-transmission selector 190 selects the transmission mode according to the signal-to-noise ratio estimate value received from the signal-to-noise ratio estimation unit 180 At this time, the multiple transmission selector 190 compares the estimated instantaneous signal-to-noise ratio with a predetermined switching level so as to switch between a plurality of transmission modes (see S24 of FIG. 2) and selects any one of modes of transmission according to the results of the comparison (see S26 of Figure 2). In another illustrative embodiment, the multiple transmission selector 190 can select the transmission mode encoding scheme, select the number of transmitting antennas (Tx) and the number of receiving antennas (Rx), or select the number transmitting antennas (Tx) and the number of receiving antennas (Rx) together with the coding scheme.

The multi-transmission selector 190 transmits the information concerning at least one of the selected transmission mode, the coding scheme and the numbers of transmitting antennas (Tx) and receiving antennas (Rx) respectively to the transmission device and the device reception. The multiple transmission selector 190 may transmit the information regarding the number of transmitting antennas to the transmission device through a return channel between the receiving device and the transmission device. Here, the return path may include information about the instantaneous signal-to-noise ratio of the receiving device. A procedure for selecting the transmission mode, the coding scheme, the number of transmitting antennas, the number of receiving antennas, or a combination thereof, depending on the estimation value of the signal / noise will be described in more detail. When signals are transmitted in the DVB-S2 system, it is assumed that the transmitted symbol vector is

X = (xi x2, At this point, the N received symbol vectors r can be represented as follows:

r = H x + v where H represents a matrix N x M or nR x nT having a complex value as an element and v represents a noise symbol vector. M or nR represents the number of receiving antennas and N or nT represents the number of transmitting antennas.

The received symbol vector r corresponds to a case of using the V-BLAST coding ("vertical bell laboratories layered space-time") as the initial system in order to estimate the signal-to-noise ratio in an initial state when the signal is transmitted in the DVB-S2 system.

The above case uses a randomly generated training sequence to estimate the instantaneous signal-to-noise ratio of each receiving antenna, if it is assumed that the path is fully estimated.

If the instantaneous signal-to-noise ratio is obtained at each receiving antenna through the received signal and the training sequence received from the plurality of receiving antennas (Rx), it depends on the following equations 1 and 2 .

Equation 1 x IHx1 • = 2 'i = 1, 2, ..., nR l -H ,. xi Equation 2 y, [dB] = 101ogio p, In equation 1, Hi represents an ith line of a matrix H, nR x nT, x represents a learning sequence, and yi represents the signal received at the level of the ith receiving antenna. pi represents the instantaneous signal-to-noise ratio of the receiving antenna, the numerator formula represents the power value of the transmission signal obtained by performing the channel compensation for the learning sequence x, and the denominator formula is the noise power value which subtracts the transmission signal from the received signal y. i represents the index of the receiving antenna. Equation 2 is an equation that transforms pi into a scale in decibel (dB).

Figure 1 schematically shows the matrix nR x nT as H 11, H n 1, H 1n and H nn, for convenience. H 11 represents the channel characteristics between the transmitting antenna No. 1 and the receiving antenna No. 1, Hn1 represents the channel characteristics between the transmitting antenna No. 1 and the receiving antenna No. 1, H 1n represents the channel characteristics between the transmitting antenna No. 1 and the receiving antenna No. n, and Hnn represents the channel characteristics between the transmitting antenna No. n and the receiving antenna No. n.

Then, it is assumed that the selected transmission mode information through the estimated signal-to-noise ratio using the training sequence is completely transmitted to the transmission end through the return path.

Then, when the transmission mode is defined, the manner of coupling the measured signal-to-noise ratio to nR receiving antennas (Rx) is important. In the present embodiment, the following three modes are used.

The first mode is a method for obtaining an average signal / noise ratio measured at the level of the nR receiving antennas. The second mode is a method of selecting the minimum signal-to-noise ratio at the nR receiving antennas. The third mode is a method of selecting the maximum signal-to-noise ratio at the nR receiving antennas. By arranging these methods, they can be represented according to the following equations 3, 4 and 5. Equation 3

1 nx ri Yi nR i = 1 Equation 4 F2 = min41, Yz, ..., YnR} 10 Equation 5 F3 = max fyl, y2, ..., YnR} As shown in equations 3 to 5, Pi represents the instantaneous signal-to-noise ratio of the

A plurality of receiving antennas (i comprises natural numbers from 1 to 3) can be determined based on an average value of the instantaneous signal-to-noise ratio obtained by dividing a sum of the instantaneous signal-to-noise ratios of each receiving antenna

20 by the number nR of receiving antennas, the minimum instantaneous signal-to-noise ratio among the nR receiving antennas or the maximum instantaneous signal-to-noise ratio among the nR receiving antennas.

The optimal mode of transmission among several

25 transmission modes can be obtained depending on the change of communication environments by using the most appropriate scheme for each communication environment among the three schemes for determining the instantaneous signal-to-noise ratio

The plurality of transmission modes considered in the present embodiment utilize different coding schemes as well as different numbers of transmitting antennas and receiving antennas as a function of the instantaneous signal-to-noise ratio value. For example, the plurality of transmission modes according to the present invention may comprise STBC 4Txx4Rx, STBC 2Txx2Rx, STBC 2Txx1Rx, BLAST 2Txx2Rx, BLAST 4Txx4Rx, BLAST 8Txx8Rx and so on. When an exemplary selection of one of a plurality of transmission modes is represented by the following equation as a function of the instantaneous signal-to-noise ratio, it may be represented as the following Table 1.

Table 1 N ° Tx if Pi <rl1 STBC 4 Tx x 4 RX if neither Pi <'i STBC 2 Tx x 2 RX if r12 <Pi <~ 1s STBC 2 Tx x 1 RX if r ~ 3 <ù Pi <rl4 BLAST 2 Tx x 2 RX if rl4 <ù Pi <rl5 BLAST 4 Tx x 4 RX if rl5 <ù Pi <r16 BLAST 8 Tx x 8 RX if Pi> _ r16 In Table 1, ni represents the switching level that is predefined experimentally or according to a standard. i is a natural number from 1 to 6. Each switching level ni may be the minimum value or the threshold value of the signal-to-noise ratio 18 required in several modes of transmission of the DVB-S2 system. The switching level can not be easily applied when dynamically changing or adapting the transmission mode in the coding scheme and the grouping of antennas between the antennas. As an example, when Pi is between the optionally defined switching level ranges, for example n1 and r1, because the communication environment is in a poor environment such as a low instantaneous signal-to-noise ratio, the Adaptive transmission of the present embodiment selects STBC 4Txx4Rx so as to increase stability. In other words, when Pi is between the optionally defined switching level ranges n1 and rie, the adaptive transmission system provides the information concerning the number of antennas used for each transmission device and each receiving device so that four antennas transmitters and four receiving antennas are used in the DVB-S2 transmission system. Further, when the switching level Pi for the predetermined instantaneous signal-to-noise ratio is set between 115 and 116, because the communication environment is good, the adaptive transmission system selects BLAST 8Txx8Rx as a transmission mode so that transmit data with high transmission rate and thus cope with changing communication environments. Successively, when Pi is again set between switching levels r1 and r1, the adaptive transmission system switches the transmission mode to STBC 4Txx4Rx, thereby enabling data to be transmitted and received with appropriate stability and transmission rate. for each communication environment. With the present embodiment, the adaptive transmission system adopts, for example, the STBC transmission mode 4Txx4Rx having the minimum SNR value as the basic transmission mode and adapts the change of communication environments of so that it can be adaptively switched to other transmission modes by using information relating to the number of antennas obtained from the transmission system. Although it is described that switching to the transmission mode according to the fact that the instantaneous signal-to-noise ratio is set to any switching level indicated in Table 1, the difference between switching to the transmission mode can be occur depending on whether the instantaneous signal-to-noise ratio is obtained by any one of the three methods. For example, the switching scheme of the transmission mode following the contents described in Table 1 by obtaining the instantaneous signal-to-noise ratio using the maximum signal-to-noise ratio scheme can transmit data at the transmission rate which is generally greater than the scheme obtaining the instantaneous signal-to-noise ratio using the minimum signal-to-noise ratio scheme and switching the transmission mode accordingly. Figures 3 and 4 are graphs for explaining a signal / noise ratio estimation scheme for use in the method and adaptive transmission system according to an illustrative embodiment of the present invention. As shown in FIG. 3, the minimum signal-to-noise ratio diagram shows the bit error rate (also known as BER for "Bit Error Rate") minimum, that is, the best bit rate performance. bit error throughout the region of a ratio of bit energy to noise power density (denoted Eb / No thereafter). However, the minimum signal-to-noise ratio method shows that the minimum number of bits, i.e. the lowest average bits in a region of Eb / No, is about 5 to 40 as shown in FIG. 3. The results can be obtained by synthesizing the signal-to-noise ratios at the receiving antenna on the basis of the receiving antenna having the minimum signal-to-noise ratio when the signal-to-noise ratios are synthesized at the receiving antennas. Therefore, the transmission method using the minimum signal-to-noise ratio scheme can make bit error rate (BER) performance good, but tends to reduce the number of transmission bits. At the same time, as shown in FIGS. 3 and 4, although the scheme of the maximum signal-to-noise ratio renders the bit error rate performance the lowest in the entire Eb / No region, it tends to increasing the number of medium bits more than the average bit number of the minimum signal-to-noise ratio scheme or the average signal-to-noise ratio scheme in about 5 to 40 Eb / No regions.

The above three instantaneous signal-to-noise estimation schemes can be combined with the adaptive transmission scheme as described above with reference to FIGS. 1 and 2. In other words, by selecting the appropriate transmission mode for the transmission environments. communication among a plurality of transmission modes through the aforementioned adaptive transmission scheme, it is possible to select and use any of the instantaneous signal-to-noise ratios estimated by the minimum signal-to-noise ratio schema, the maximum signal-to-noise ratio and the average signal-to-noise ratio pattern. With the present illustrative embodiment, it is finally possible to perform the selection of the transmission mode according to the estimation scheme of the instantaneous signal-to-noise ratio at the receiving device, thus making it possible to increase the possibility of selecting the optimal transmission mode. The best illustrative embodiments of the present invention will be described with reference to the detailed description and drawings as described above. Here, specific terms have been used, but they are simply used for the purpose of describing the present invention and are not used to qualify the meaning or limit the scope of the present invention, which is defined in the appended claims. Therefore, those skilled in the art will appreciate that various modifications are made and other equivalent embodiments are possible. Accordingly, the scope of effective technical protection of the present invention is to be determined by the spirit of the appended claims.

Claims (9)

REVENDICATIONS1. An adaptive transmission method using a multiple input multiple output antenna, comprising: estimating (S22) an instantaneous signal-to-noise ratio for signals received by a plurality of receiving antennas (150); and selecting (S26) a transmission mode between a transmitting device and a receiving device according to the instantaneous signal-to-noise ratio. An adaptive transmission method according to claim 1, wherein the estimate of the instantaneous signal-to-noise ratio (S22) comprises any one of the selection of the minimum instantaneous signal-to-noise ratio among a plurality of measured instantaneous signal-to-noise ratios. by the plurality of receiving antennas (150), selecting the maximum instantaneous signal-to-noise ratio from the plurality of instantaneous signal-to-noise ratios measured by the plurality of receiving antennas (150), and selecting a signal-to-noise ratio mean noise obtained by dividing a sum of the plurality of instantaneous signal-to-noise ratios measured by the plurality of receiving antennas (150) by the number of antennas included in the plurality of receiving antennas (150). An adaptive transmission method according to claim 1, wherein the selection of the transmission mode (S26) between the transmission device and the reception device according to the signal / noise ratio comprises comparing (S24) a predetermined switching with the instantaneous signal-to-noise ratio so as to switch among the plurality of transmission modes. An adaptive transmission method according to claim 3, wherein the plurality of transmission modes comprises STBC 4Txx4Rx, STBC 2Txx2Rx, STBC 2Txx1Rx, BLAST 2Txx2Rx, BLAST 4Txx4Rx and BLAST 8Txx8Rx. An adaptive transmission system using a multiple input multiple output antenna, comprising: a signal / noise ratio estimation unit (180) which estimates an instantaneous signal-to-noise ratio for a signal received by a plurality of antennas receivers; and a multiple transmission selector (190) which is connected to the signal-to-noise ratio estimation unit and selects a transmission mode between a transmission device and a reception device according to the instantaneous signal-to-noise ratio. An adaptive transmission system according to claim 5, wherein the signal / noise ratio estimating unit (180) estimates any of the instantaneous minimum signal-to-noise ratio selection, instantaneous signal-to-noise ratio maximum and a mean instantaneous signal-to-noise ratio obtained by dividing a sum of the plurality of instantaneous signal-to-noise ratios measured by the plurality of receiving antennas (150) by the number of antennas included in the plurality of receiving antennas selected from a plurality of instantaneous signal-to-noise ratios measured by the plurality of receiving antennas (150), such as the instantaneous signal-to-noise ratio. The adaptive transmission system according to claim 5, wherein the multiple transmission selector (190) compares the instantaneous signal-to-noise ratio with the predetermined switching level to select the transmission mode. An adaptive transmission system according to claim 7, wherein the multiple transmission selector (190) transmits information relating to the selected transmission mode according to the switching level to the transmission device, the transmitted information relating to the transmission mode comprising the number of transmitting antennas and channel coding information. An adaptive transmission system according to claim 7, wherein the plurality of transmission modes comprises STBC 4Txx4Rx, STBC 2Txx2Rx, STBC 2Txx1Rx, BLAST 2Txx2Rx, BLAST 4Txx4Rx and BLAST 8Txx8Rx, and the multiple transmission selector selects any one of the plurality of transmission modes.