WO2008074209A1 - Method for transmitting data between a transmitting station and a receiving station - Google Patents

Abstract

A method for implementing a high-data-rate orthogonal frequency-division multiplex (OFDM) wireless local area network and the system thereof belong to the wireless communication technical field. In the implementing method and system, a transmitting station transmits data by using different signal modulation modes for OFDM sub channels; in one error correcting code way, the modulation mode used by each sub channel is determined by a receiving station based on the signal-to-noise ratio or channel gain of each OFDM sub channel; the modulation mode information used by each sub channel (sub channel - modulation mode information) is transmitted from the receiving station to the transmitting station through one of the following two ways of: (1) the request-response way between the transmitting station and the receiving station, (2) the receiving station transmitting it to the transmitting station on its own initiative under the case of no request.

Description

 Method of transferring data between a transmitting site and a receiving site

Technical field

 The present invention belongs to the field of wireless communication technologies, and in particular, to an Orthogonal Frequency Division Multiplexing (OFDM) wireless local area network system. Background technique

 With the increasing demand for information in social life, the Internet has become an indispensable part of people's daily life. Wireless LAN has broad development prospects due to its flexible access and no wiring.

 The IEEE 802.il working group proposed a wireless LAN solution for the application requirements of the wireless domain network, which is the 802.11 wireless LAN standard. So far, there are four main standards for the 802.11 WLAN physical layer, namely 802. 11, 802. lib, 802. llg and 802.lla. The standards for the media access (MAC) layer are mainly 802.11 and 802. lle. In terms of physical layer standards, 802.11 defines three working modes of frequency hopping spread spectrum, direct sequence spread spectrum and infrared; 802. lib extends the direct sequence spread spectrum operation mode of 802.11 to make the physical layer the highest data. The rate reaches 11Mbps (the former can only reach 2Mbps); 802.llg further expands 802. lib. On the basis of compatible with 802. lib, it adds OFDM working mode, and the physical layer has the highest data rate of 54Mbps, 802. Lgg and 802. lib both work in the 2. 4G band; 802.11a standard works in the 5G band, using OFDM mode, the physical layer maximum data rate is 54Mbps; 802.llg OFDM mode and 802.11a adopted ^ The same implementation, the difference is only in the working frequency band. In terms of the MAC layer standard, 802.11 defines the way in which the working station occupies the channel in the 802.11 network, that is, through the random competition occupied channel (DCF) and the AP through the central control occupied channel (PCF), 802. lie mainly It is a solution proposed for the user service quality problem of 802.11 network, and proposes the HCF working mode to realize the user service quality in LAN communication.

It should be noted that the current design of the 802.11 system is designed for medium and low data rates, and is not suitable for high-speed data transmission, 'can not meet the requirements of real-time transmission of video (such as high-definition television). While 802.11- 0FDM (which includes 802.11a and 802.11g 0FDM operation) systems can theoretically achieve physical layer data rates as high as 54 Mbps, the implementation of this data rate requires good channel conditions. When the 802.11- 0FDM system works in an indoor environment, there is no direct path between the transmitting site and the receiving site. At the time, the channel has severe frequency selectivity, which greatly limits the performance and data rate of its physical layer.

 In a frequency selective channel, each subcarrier channel of an OFDM system has a different channel gain. If the same modulation method is used for each subchannel, the problem arises: in those subchannels with high channel gain, excessive gain is wasted; and in subchannels with low channel gain, especially Subchannels with deep fading and thus low channel gain can cause serious errors in the transmission sequence. Deep fading in frequency-selective channels makes 802.11-OFDM systems unsuitable for high-order modulation, code rate transmission of data, so that the physical layer is difficult to achieve data rates as high as 54 Mbps in actual corners.

 The present invention proposes a method and system for implementing a high data rate OFDM wireless local area network for a wireless channel having frequency selective fading. In the implementation method and system, the transmitting station (refers to the station that transmits data from the network layer, the same below) uses different modulation modes for different OFDM subcarrier channels when transmitting data; The modulation mode information (subchannel-modulation mode information) to be used by the channel is implemented by the transmitting station and the corresponding receiving station (refer to the station receiving data from the network layer, the same below) at the MAC layer request-response mechanism. Or the receiving station sends the information directly to the transmitting station at the MAC layer; the receiving station determines the signal modulation mode to be used on the subchannels according to the channel gain or the signal to noise ratio of each subchannel of the 0FDM.

 In the system designed by the present invention, the receiving station determines the modulation mode according to the bit error rate of each subchannel under a certain channel error correcting code condition, so that the wireless local area network system can obtain benefits in two aspects: 1) Since the specified error rate can be achieved by each subchannel of the 0FDM under the specified error correction code condition, the system can achieve the specified frame error rate, effectively control the frame loss, and realize the effective transmission of data at the physical layer; (2) For a subchannel with a large channel gain, by using a higher order signal modulation method, the 0FDM' symbol can be transmitted with more bits of data without loss of bit error performance, thereby improving the physical layer. Data rate.

 By adopting the implementation method and system of the present invention, the 0FDM wireless local area network can effectively overcome the frequency selective fading of the channel on the one hand, and can fully utilize the channel gain of each subchannel on the other hand, so that the physical layer can be obtained. A considerable increase in data rate. Summary of the invention

 The present invention has been made in order to achieve the above object. '

According to the present invention, a data rate orthogonal frequency division multiplexing (OFDM) is proposed. The implementation method of the network is characterized by:

 The transmitting station refers to a station that transmits a number of 从 from the network layer, and the same one uses different signal modulation modes in different subchannels when transmitting data through OFDM symbols;

 The corresponding receiving station refers to the station that receives the data from the network layer, and the same one of the transmitting stations provides the information of the modulation mode to be used for each subchannel of the OFDM symbol in a certain error correction code mode. The information is referred to as subchannel-modulation mode information in this patent;

 The receiving station determines the modulation mode to be used by the subchannels in a certain error correction code mode according to the signal to noise ratio or channel gain of each subchannel of the OFDM obtained by the channel estimation;

 The subchannel-modulation mode information is transmitted by the receiving station to the transmitting station in one of two ways: (1) a request-response mode between the transmitting station and the receiving station, and (2) an active transmitting mode of the receiving station;

 The transmission of the subchannel-modulation mode information from the receiving station to the transmitting station can be realized by designing a specific data frame, or by using the information exchange mechanism of the wireless local area network at the MAC layer;

 The method is implemented in an OFDM wireless local area network.

 Preferably, the transmitting station implements a method for transmitting different numbers of data bits by using different order modulation modes for different subchannels, which is implemented by the following processing:

 Each sub-channel flexibly selects the signal modulation mode according to its own signal-to-noise ratio or channel gain; in addition to the BPSK, QPSK, 16QAM, and 64QAM modulation modes already used by the 0FDM WLAN, 256QAM, 128QAM, 32QAM, 8QAM, etc. are also used. the way.

 Preferably, the receiving station determines the modulation mode to be used according to the signal to noise ratio or channel gain of each subchannel of the 0FDM, which is implemented by the following steps:

 The receiving station determines a set of signal to noise ratio or channel gain decision thresholds in advance, and each of the decision thresholds corresponds to a signal modulation mode;

 The signal-to-noise ratio or signal gain of each subchannel is compared with the above signal to noise ratio or channel gain decision threshold to determine the modulation scheme of each subchannel.

 Preferably, the method for implementing the subchannel-modulation mode information from the receiving station to the transmitting station by the request-response manner between the transmitting station and the receiving station is implemented by the following steps: the transmitting station sends a subchannel-modulation request to the receiving station. Data frame-one sub-channel-modulation mode request frame;

The receiving station sends a data containing subchannel-modulation mode information to the transmitting station by means of a response. When the method and system proposed by the present invention are applied to a wireless local area network with a MAC layer presence information interaction mechanism, the transmission of the subchannel-modulation mode information from the receiving station to the transmitting station can utilize the information exchange of the wireless local area network system at the MAC layer. achieve. For example, when it is used in an 802.11 network, it can interact with the MAC layer information specified in the current 802.11 standard or the 802.11 protocol in Table 802.11.

 DCF mode

 {RTS - CTS - } [Frag - ACK - ] Last - ACK

 PS-Poll - ACK

 PS-Poll - [Frag - ACK - ] Last - ACK

 PCF mode

 Data+CF-Poll {+CF-Ack} - Data+CF- Ack - {CF-Ack (no data) }

Data+CF-Poll {+CF-Ack} - CF-Ack (no data) . '

CF-Poll (no data) {+CF-Ack} - Data - {CF-Ack (no data) }

CF-Poll (no data) {+CF-Ack} - Data - ACK

 CF- Poll (no data) {+CF-Ack} - Null (no data)

 Data(dir) {+CF-Ack} - ACK

 Note: {~} means it is sent 0 times or 1 time; '

 [...] means that it is sent 0 or more times;

 [Frag - ACK - ] indicates the fragment transmitted when the DATA frame or Management frame is transmitted in fragmented mode.

 Last indicates the data frame when the DATA frame or Management frame is not transmitted in fragmented mode, or the last fragment when the fragmented mode is transmitted. The Subtype sub-domain of the Frame Control field of the MAC frame for information exchange is newly defined so that it becomes a data frame carrying RSM information and ISM information, and for the MAC frame carrying the ISM information, the corresponding storage is also defined. Subchannel - The data field of the modulation mode letter 1.

 Whether in the request-response mode or in the active transmission mode, the receiving station calculates the signal modulation mode of each of the 0FDM subchannels based on the received physical frame. Before the new subchannel-modulation mode works, the receiving station and the transmitting site are working according to the original working mode.

10 Transmission information, which may be a conventional operation mode in which each subchannel uses the same signal modulation mode, or a subchannel-modulation mode operation mode determined at a certain previous time. When the receiving station calculates the new subchannel-modulation mode information in the atomic channel-modulation mode operation mode, the original working mode is required to perform data transmission on each OFDM subchannel.

 The process of calculating the subchannel-modulation method by the receiving station through the received physical frame is as follows: The receiving station uses the physical frame for channel estimation, and calculates the channel gain of each subchannel or its signal to noise ratio; in a certain error correction code mode Comparing the channel gain or signal-to-noise ratio of each subchannel with a predetermined set of channel gain or SNR thresholds associated with the current error correction code mode, ensuring that each subchannel achieves a certain bit error rate Under the premise of performance, the modulation method with high order is selected as much as possible; each modulation mode is mapped into one bit group, and then these bit groups are placed together to form a data group, which is subchannel-modulation Mode; the calculated subchannel-modulation mode is labeled to indicate the specific working mode. This label is called the scheme number. (If the system defines the information of the error correction code mode and the information of the subchannel-modulation method. For transmission, a scheme number is set for the combination of the subchannel-modulation mode data group and the error correction code mode; The subchannel-modulation mode data group, the error correction code mode (when the system defines the two types of information bundle transmission) and the scheme number are placed in the MAC frame carrying the subchannel-modulation mode information in the agreed format, and sent to the transmitting station.

 The signal-to-noise ratio or channel gain threshold required for the calculation of the subchannel-modulation method for each subchannel of OFDM in a certain error correction code mode can be obtained in advance on the simulation platform by the Monte-Carlo algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

 In the drawings, the same reference numerals are used to refer to the same or similar components. Detailed descriptions of well-known functions and structures incorporated in the present invention are omitted for clarity and conciseness, which may otherwise confuse the subject matter of the present invention.

 Fig.1 System structure and implementation process of subchannel-modulation mode working mode

 Figure 2 Implementation process of transmitting subchannel-modulation mode information in request-response mode

 Figure 3 Transmission of subchannels by active transmission - Implementation of modulation mode information

 Figure 4 Scheme number field, coding mode field and subchannel-modulation mode field of the transmission subchannel-modulation mode information ―

 Figure 5 Implementation method of transmitting data using subchannel-modulation mode working mode Figure 6 Physical frame frame structure and structure of SIGNAL symbol in 802.11-0FDM standard

11 Figure 7 Frame structure of 802.11 system RTS frame

 Figure 8 802.11 system frame structure of CTS frame

 Figure 9 802.11 system implements the frame structure of the RTS+RSM frame requested by the subchannel modulation mode

 Figure 10 802.11 system transmits subchannel-modulation mode information CTS+ISM frame frame structure Figure 11 802.11 standard DATA frame frame structure

 Figure 12 802.11 system ACK frame frame structure

Figure 13 Frame structure of DATA+RSM frame for subchannel-modulation mode request under 802.11 standard Figure 14 Frame structure of ACK+ISM frame for 802.11 system transmission subchannel-modulation method information I ⁵ 80 ² . lie standard DATA frame frame structure '

 FIG. 16 is a frame structure of a DATA+RSM frame that implements a subchannel-modulation method under the 802.1 IE standard. FIG. 17 shows a process for determining a modulation mode to be used by a receiving station to determine a subchannel by a signal to noise ratio decision. FIG. The process of determining the modulation mode to be used for determining the subchannel

 Figure 19 Process of constructing subchannel-modulation mode domain, coding mode domain and scheme number domain in the receiving station Figure 20 Signal-to-noise ratio of different modulation modes in certain error correction code mode obtained by Monte-Carlo algorithm - bit error rate curve specific Implementation

 The present invention considers that different modulation modes are used in each subchannel of OFDM to achieve full utilization of the channel and overcome its frequency selectivity, and each modulation of the order selects a modulation mode. The present invention recommends the following combinations of modulation methods:

 M = { BPSK, QPSK, 8QAM, 16QAM, 32QAM, 64QAM, 128QAM, 256QAM } (1) The advantage of using QAM modulation is that it has good range characteristics and it is easy to extract soft information in the decoding of the receiving end. I. Method for transmitting data by transmitting station according to subchannel-modulation mode working mode The data frame containing subchannel-modulation mode information sent from the receiving station to the transmitting station includes the following data related to subchannel-modulation mode information. Domain: The scheme number field, the coding mode field, and the subchannel-modulation mode field (see Figure 4). The scheme number is implemented by using a number of bits to identify the current subchannel-modulation mode operation mode in a certain error correction code mode; the subchannel-modulation mode domain is composed of K subfields.

12 (K is the number of subcarriers used by the OFDM system to transmit data), each subfield consists of several bits, indicating the signal modulation mode to be used for the corresponding subcarrier channel. In this patent, these subfields are called ModType. The sub-domain; the coding mode field is implemented by using a number of bits, and is used to identify the current error correction code mode, which is marked with a virtual frame, when the error correction code mode information used by the system definition is bundled with the subchannel-modulation mode information. The data field exists. Otherwise, the domain does not exist, and the error correction code mode information is transmitted to the transmission by other means.

 An implementation of data bit-modulation mapping

 Site. When a single error correcting code is used between the transmitting station and the receiving station, the receiving station does not have to transmit error correcting code information to the transmitting station.

 Each data bit group in the ModType subfield of the subchannel-modulation mode field represents a signal modulation mode, and the physical layer uses the modulation mode M shown in the formula (1) as an example, and Table 2 shows that 4 bits are used. The data set to represent the real-time scheme of a data bit-modulation mode mapping when the modulation mode is used. In this mapping scheme, NULL means no data is transferred. Each data bit group in the coding mode domain is mapped to an error correction code mode. Each data bit group in the scheme number field represents a scheme number.

After obtaining the subchannel-modulation mode information, the transmitting station can calculate a subchannel-bit allocation table, and can determine the number of data bits to be transmitted by one OFDM symbol. Let the 0FDM system send data with K subcarriers, and the number of transmitted bits is: W b _K , and the number of transmitted bits of one OFDM symbol is:

B = ∑b _k (2) The process of transmitting data using the subchannel-modulation mode of the transmitting station is shown in Figure 5. It is completed in three steps: In the first step, the transmitting station splits the encoded data sequence. Into several B ratios a special data set (when the last data set is less than B bits, it is padded by data - such as padding 0 - to lengthen it to B bits); the second step is to construct each B bit data set into an OFDM symbol; In three steps, each OFDM symbol is sequentially placed in a physical frame to perform data transmission.

 In the process of constructing a B-bit data set into one OFDM symbol, the B-bit data is first allocated to different sub-channels according to the sub-channel-bit allocation table, and then the data bits are mapped in each sub-channel by a specified modulation method. The complex-valued symbol is finally transformed into a time-domain OFDM symbol by an FFT transform.

 When transmitting data in the subchannel-modulation mode, the transmitting station must write the scheme number of the currently used subchannel-modulation scheme to the beginning of the physical frame it transmits, so that the corresponding receiving station is in the physical This information can be known in advance before demodulation of the data symbols in the frame for demodulation of these data symbols. The following takes the frame structure of the physical frame of the 802.11-OFDM system as an example, and writes the scheme number of the subchannel-modulation scheme to the physical frame to be sent.

 Correspondence between the physical frame rate domain bit group and the frame body data working mode of the 802.11- 0FDM system

表 4 速率域比特组与方案号对应的一个例子

Table 4 An example of the rate domain bit group corresponding to the scheme number

14 Implementation method.

 The physical frame frame structure of the 802.11-OFDM system is shown in FIG. 6. It consists of a physical frame header, a SIGNAL symbol and a data symbol. The SIGNAL symbol is used to provide the receiving station with modulation about its frame data. Information such as code rate and length. The 802.11-OFDM standard corresponds the bit group in the SIGNAL symbol rate domain to the eight physical layer data rates defined by it, since each physical layer data rate corresponds to a specific signal modulation scheme and convolutional code. The code rate, thus achieving the correspondence between the data bit group and the modulation mode-code rate, and the corresponding relationship is shown in Table 3. Since only 16 of the four 4-bit groups are used, the remaining 4-bit groups can be used to represent the scheme number of the subchannel-modulation scheme. For example, we can use the four 4-bit groups starting with 0 to represent the subchannel- The four scheme numbers of the modulation scheme, Table 4 gives an example of realizing the correspondence of this bit group-scheme number.

 In this way, by the correspondence between the rate domain bit group and the subchannel-modulation scheme scheme number, the receiving station can quickly determine the subchannel-modulation mode used by the data symbol of the physical frame according to the rate domain bit group when the data is received. Further, the demodulation of the data symbols is smoothly achieved. Method for transmitting subchannel-modulation mode information from receiving station to transmitting station

 The receiving station transmits the subchannel-modulation mode information to the transmitting station in two ways, namely: the request-response mode and the receiving station active transmission mode.

 In the request-response mode, the transmitting station may request to obtain the subchannel-modulation mode information by directly transmitting a subchannel-modulation method request (RSM) frame to the receiving station at the MAC layer, and the receiving station passes the subchannel-modulation mode information ( The ISM) frame responds to the RSM frame by tB and transmits the subchannel-modulation mode information to the transmitting station. The RSM frame includes a subchannel-modulation mode request indication, and the ISM frame includes subchannel-modulation mode information, which uses the scheme number field, the coding mode domain, and the subchannel-modulation mode domain shown in FIG. . In the active transmission mode, when the receiving station does not receive the RSM frame of the transmitting station but receives other data frames from the transmitting station, the receiving station may calculate the subchannel-modulation mode information from the data frame, and use the ISM frame to Information is sent to the launch site.

In the process of data transmission, the WLAN system may have an information interaction mechanism at its MAC layer due to the needs of channel allocation and the like. For example, in an 802.11 network that uses random competition and polling to allocate channels, there is such a MAC layer information interaction mechanism. When the system proposed by the present invention is applied to such a network, the information exchange mechanism of the MAC layer can be utilized to implement the transmission of the subchannel-modulation mode information from the receiving station to the transmitting station. Here, the request-response mode and the master of the active delivery mode The difference is that the request-response mode uses a complete MAC layer interaction between the transmitting and receiving sites, while the active transmission mode only uses the response of the receiving site to the transmitting site in the MAC layer information interaction.

 In the 802.11 network, the interaction between the RSM information and the ISM information can be implemented through the information interaction of the MAC layer. For this reason, the Frame Control domain of the MAC frame for information interaction in the 802.11 standard and the 802. lie standard can be The Subtype sub-domain or the Type sub-domain is newly defined to be a data frame carrying RSM information and ISM information. For the MAC frame carrying the ISM information, a corresponding data field for storing the sub-channel-modulation mode information is defined. The following is a method for implementing the request and response of the subchannel-modulation method by using the RTS-CTS information interaction of the MAC layer and the DATA-ACK information interaction in the 802.11 network, and other types of MAC layer information in the 802.11 system. The implementation of the request and response of the implementation of the subchannel-modulation method can be similarly derived.

 Sub-channel-modulation method request and response implementation method under RTS-CTS information interaction

 In order to solve the hidden node problem in wireless networks, the 802.11 system designed the RTS-CTS working mode at the MAC layer. The frame structure of the RTS frame and the structure of its Frame Control field are shown in Figure 7. The Subtype ^ field of the Frame Control field is assigned the value of 1011. The frame structure of the CTS frame and the structure of its Frame Control field are shown in Figure 8. The Subtype subfield has a value of 1100.

其中用 Subtype=0011来表示 这是一个 RTS+RSM帧（一般性地， Subtype子域也可定义为其它保留值）。 By redefining its Subtype subfield for the RTS frame, a new MAC frame can be defined for the system: RTS+RSM frame. Figure 9 gives

Where Subtype=0011 is used to indicate that this is an RTS+RSM frame (generally, the Subtype subfield can also be defined as other reserved values).

 By redefining the Subtype subfield of the CTS frame, and adding the Scheme Number field, the Subchannel-Modulation Information field and the Code Type field (when the system defines the error correction code mode) The CTS+ISM frame can be defined for the system when the information is bundled with the subchannel-modulation mode information. Figure 10 shows an example of implementing a CTS+ISM frame, where Subtype=0100 is used to indicate that this is a CTS+ISM frame (generally, the Subtype subfield can also be defined as other reserved values). The coding mode field is marked with a virtual frame, and its meaning is the same as the virtual frame in Figure 4.

 Through the RTS+RSM frame and the CTS+ISM frame defined above, the system can implement the subchannel-modulation request and response in the RTS-CTS information interaction.

 DATA-ACK information interaction subchannel-modulation method request and response implementation method

 Consider first the case when the 802.11 system adopts the MAC layer defined by the 802.11 standard.

 In the 802.11 standard, when a transmitting station transmits a DATA frame through the MAC layer, the receiving station receives it correctly.

16 An ACK response must be made afterwards. The frame structure of the DATA frame and the structure of its Frame Control field are shown in Figure 11. The Subtype subfield of the Frame Control field is assigned the value 0000, and the value of the Type field is noted as Data.

The frame structure of the ACK frame and the structure of its Frame Control field are shown in Figure 12. The assignment of the Subtype subfield is 1101, and the value of the Type field is noted as Control.

 By redefining its Subtype subfield for the DATA frame, the DATA+RSM frame that implements the subchannel-modulation mode request function can be defined for the system. Figure 13 shows an example of implementing a DATA+RSM frame, where Subtype=1101 is used. Indicates that this is a DATA+RSM frame (generally, the Subtype subfield can also be defined as other reserved values).

 By redefining the Subtype subfield of the ACK frame and adding the scheme number field, the subchannel-modulation mode field, and the coding mode field, the ACK+ISM frame implementing the subchannel-modulation mode transmission function can be defined for the system. Figure 14 shows an example of implementing an ACK+ISM frame, where Subtype=0101 is used to indicate that this is an ACK+ISM frame (generally, the Subtype subfield can also be defined as other reserved values). The coding mode field is marked with a virtual frame, and its meaning is the same as the virtual frame in Figure 4.

 Thus, through the DATA+RSM frame and the ACK+ISM frame defined above, the system can implement the subchannel-modulation method request and response in the DATA-ACK information interaction.

 Secondly, consider the case when the 802.11 system 3^ uses the MAC layer defined by the 802. lie standard.

 The frame structure of the DATA frame defined by the 802, lie standard and the structure of its Frame Control field and QoS Control field are shown in Figure 15. Note that since the DATA frame needs to be normally acknowledged, the Ack Policy subfield of its QoS Control field shall be set to 00, indicating Normal Ack. By redefining the Subtype subdomain of its Frame Control field, the DATA+RSM frame under the 802. lie protocol can be defined. Figure 16 shows an example of implementing a DATA+ RSM frame under the 802. lie protocol, where Subtype=1101 is used. Indicates that this is a DATA+RSM frame.

 Since the 802. lie standard adopts the same frame structure of the ACK frame as the 802.11 standard, the ACK+ISM frame can be constructed in the same manner as the 802.11 standard, thereby implementing the subchannel-modulation method request and response. . Next, an implementation method of actively transmitting the subchannel-modulation method information by the receiving station by using the RTS-CTS information interaction of the MAC layer and the DATA-ACK information interaction in the 802.11 network is given, through other types in the 802.11 system. The MAC layer information interaction implementation method for realizing the active transmission of the subchannel-modulation mode information can be similarly derived.

17 Realization method for active transmission of subchannel-modulation mode information under RTS-CTS information interaction

 The transmitting station first sends an RTS frame to the receiving station, and the receiving station then responds with the CTS+ISM frame shown in FIG. 10 (generally, its Subtype subfield can also be defined as other reserved values), and the subchannel-modulation method is adopted. Information is transmitted to the launch site.

 Implementation method of active transmission of subchannel-modulation mode information under DATA-ACK information interaction

 The transmitting station first sends a DATA frame to the receiving station, and the receiving station then responds with the ACK+ISM frame shown in FIG. 14 (generally, its Subtype subfield can also be defined as other reserved values), and the subchannel-modulation method is adopted. Information is transmitted to the launch site. Third, the receiving station determines the modulation mode of each subchannel according to the channel information

 The receiving station performs channel estimation on the transmission channel through the physical frame transmitted by the transmitting station, thereby determining the modulation mode to be adopted for each OFDM subchannel in a certain error correcting code mode.

 The current transmitting station and the receiving station may agree to use only one fixed error correcting code mode, or may decide to select one of several optional error correcting code modes for data transmission by the receiving station. After the error correcting code mode is determined, the receiving station can determine the mode of operation of the subchannel-modulation mode to be used based on the signal to noise ratio or channel gain of each subchannel obtained from the result of the channel estimation.

 When the receiving station receives a physical frame from the transmitting station, it can perform channel estimation on the channel between the transmitting station and the receiving station to obtain the channel coefficients of each subchannel of the OFDM. Since the time domain signal to noise ratio can be obtained, the signal to noise ratio on each subchannel of the OFDM signal in the frequency domain can be obtained. Let OFDM signals have a total of W subcarriers, wherein the number of working subcarriers is N', and the number of subcarriers for transmitting information data is N'-K precarriers for implementing other functions of the system. Let the channel coefficients of the ^ subcarrier channels be ^

对各子信道釆用不同的调制方式的目的是为了： 在一定的纠错码方式下， 使各子信道在达到指定的误码性能的前提下尽可能地传输较多的数据比特。误码 性能指标取决于接收站点在接收数据时所要达到的误帧率， 在系统设计时设定。 (& - 1,2,... , Κ), when the receiving station works, the time domain signal-to-noise ratio is SN ?,, it is not difficult to derive the signal-to-noise ratio of each subchannel of the OFDM signal:

The purpose of using different modulation modes for each subchannel is to: In a certain error correction code mode, each subchannel transmits as many data bits as possible under the premise of achieving the specified error performance. The error performance indicator depends on the frame error rate that the receiving station should achieve when receiving data, which is set during system design.

 In order to determine the modulation mode to be adopted by the signal-to-noise ratio of each subchannel, the system has previously calculated a set of signal-to-noise ratio thresholds for the corresponding error correction code mode and the set error performance index.

18 Each value corresponds to a signal modulation mode, indicating that when the signal-to-noise ratio of the subchannel is greater than or equal to the threshold, if the corresponding modulation mode is adopted, the subchannel can achieve an error better than the set index. Code performance.

 Let the system adopt the modulation method: { (0), A / (l), ..., AfCP)}, where the number in parentheses indicates the modulation order, 3⁄4 the highest modulation order, (0> indicates If the data is not transmitted, and the signal-to-noise ratio threshold corresponding to the modulation method is 5 (Μθ7)) (Definition: . S(M(0)) = 0), then the signal-to-noise ratio calculated by equation (3) is The modulation method to be used for each subchannel can be calculated by the following formula:

Mod _k = arg max{S( (^)) | SNR _k ≥ S(M(p)), ρ = 0 - · , Ρ} (k = l,2,- - ,K) (4) where Arg max represents an argument parameter corresponding to the maximum value in the sequence.

In the actual system, since the value is determined from _N ', 57, the subchannel-modulation method can also be determined by comparing the square value of the channel gain with a corresponding set of threshold values.

通过信噪比比较和信道增益比较确定子信道所要采用的调制方式的过程分 别如图 17和图 18所示。 Mod _k 1,2, -'-, Ρ} ( 1,2 ., ) (5)

The process of determining the modulation mode to be used for the subchannel by the comparison of the signal to noise ratio and the channel gain is shown in Figs. 17 and 18, respectively.

 After receiving the modulation scheme of each subchannel, the receiving station maps it into a data bit group and puts it into the subchannel-modulation mode domain as shown in FIG. When the system defines the error correction code mode information and the subchannel-modulation mode information bundle transmission, it is also required to map the current error correction code mode into a data bit group and put it into the coding mode domain. Next, the receiving station determines a scheme number for the error correction code mode and the subchannel-modulation scheme, and writes it into the scheme number field. Finally, the scheme number field, the coding mode field (if it exists) and the subchannel-modulation mode field are placed together in the data frame of the transmission sub-channel-modulation mode information. The process of constructing the subchannel-modulation mode domain, the coding mode domain, and the scheme number domain by the modulation mode of each subchannel is as shown in FIG. 19. In the figure, the coding mode field is marked with a virtual frame, and its meaning is the same as the virtual frame in FIG. The meaning. So far, the sub-channel _ modulation mode information to be transmitted to the transmitting station is obtained at the receiving station. Method for determining signal to noise ratio decision threshold

 The signal-to-noise ratio decision threshold required in the determination of the receiving station subchannel-modulation mode can be obtained in advance on the simulation platform by the Monte-Carlo algorithm. The following is a practical example of using the Matlab platform to calculate the signal-to-noise ratio threshold of various modulation modes in a certain error-correcting code mode by Monte-Carlo algorithm.

19 The wireless local area network system adopts the modulation mode set M shown in the formula (1), and the channel error correction code adopts the 3/4 code rate specified by 802.11a/802.llg, the 64-state convolutional code, and assumes the receiving end. Soft decision Viterbi decoding is employed. In the additive white noise (AWGN) channel, we obtain a signal-to-noise ratio (SNR)-bit error rate (BER) curve for each modulation method in M by the Monte-Carlo algorithm. Finally, we get the signal-to-noise ratio-bit error rate curve for various modulation modes as shown in Figure 20.

Let the system require the physical layer to achieve a bit error rate of 10 - ⁴ , ' then from Figure 20, we get a set of signal to noise ratio values (in dB) corresponding to 10 - ⁴ as:

 [ 3.5, 6.5, 10.2, 12.8, 16.7, 18.4, 22.3, 24.0 ]

 Join the way of not transmitting data, and get the corresponding threshold:

 [ 0.0, 3.5, 6.5, 10.2, 12.8, 16.7, 18.4, 22.3, 24.0 ]

 Convert it to an absolute multiple:

 [ 0.00, 2.24, 4.47, 10.47, 19.05, 46.77, 69.18, 169.82, 251.19 ] Thus, when the system uses the 3/4 code rate convolutional code defined by 802.11a/802.11g, the receiving station is determined. A set of SNR decision thresholds required for the modulation scheme to be used for the OFDM subchannel. Substituting it into equation (5), a corresponding set of channel gain decision thresholds can be further obtained.

 While the invention has been described in terms of the preferred embodiments of the present invention, it will be understood that various modifications, changes and changes may be made to the inventions without departing from the spirit and scope of the invention. Therefore, the present invention should not be limited by the foregoing embodiments, but by the appended claims and their equivalents.

20

Claims

Rights request A method for transmitting data between a transmitting station and a receiving station in an Orthogonal Frequency Division Multiplexing (OFDM) OFDM wireless local area network, the method comprising:  The receiving station determines the modulation mode information to be used by each subchannel in a certain error correction code mode according to the signal to noise ratio or the channel gain of each subchannel obtained by the channel estimation;  The modulation mode information to be used by the receiving station to transmit the subchannels to the transmitting station; the transmitting station modulates and transmits the data by using modulation mode information to be used by each subchannel transmitted from the receiving station. : . ': ' ' '  2. The method according to claim 1, wherein: the modulation mode information to be used by the receiving station to transmit the subchannels to the transmitting station is implemented in one of two ways: (1) transmitting station and receiving station Request-response mode, (2) The active delivery mode of the receiving site.  3. The method according to claim 1 or 2, wherein: the modulation mode information to be used by the receiving station to transmit each subchannel to the transmitting station is implemented by one of two ways: (1) by design specific The data frame is implemented; (2) using the information exchange mechanism of the wireless local area network at the MAC layer.  4. The method according to claim 1, wherein: the modulation mode information indicates one or more of the following modulation modes: BPSK, QPSK, 16QAM, 64QAM, 256QAM, 128QAM> 32QAM and 8QAM.  5. The method according to claim 1, wherein: the receiving station determines a modulation to be used for each subchannel in a certain error correction code mode according to a signal to noise ratio or a channel gain of each subchannel obtained by channel estimation. The steps of the mode information include:  The receiving station determines a set of signal to noise ratio or channel gain decision thresholds in advance, and each of the decision thresholds corresponds to a signal modulation mode;  The signal-to-noise ratio or channel gain of each subchannel is compared with the signal to noise ratio or channel gain decision threshold to determine the modulation scheme of each subchannel.  The method according to claim 2, wherein the step of implementing the modulation mode information used by the receiving station to transmit the subchannels to the transmitting station by the request-response mode between the transmitting station and the receiving station comprises: The transmitting station sends a subchannel-modulation method including a subchannel-modulation method request to the receiving station. Request frame  The receiving station transmits a subchannel-modulation mode information frame containing subchannel-modulation mode information through the A. transmitting station.  The method according to claim 6, characterized in that the frame structure of the subchannel-modulation mode request frame includes a flag bit for requesting subchannel-modulation mode information from the receiving station.  8. The method according to claim 6, wherein: the frame structure of the subchannel-modulation mode information frame includes a subchannel-modulation mode of each subchannel in an error correction code mode. Information.  9. The method according to claim 1, wherein: the step of implementing the modulation mode information used by the receiving station to transmit the subchannels to the transmitting station by the active transmission mode of the receiving station comprises:  The transmitting station transmits a data frame that does not include a subchannel-modulation mode request to the receiving station; the receiving station transmits a subchannel-modulation mode information frame including subchannel-modulation mode information to the transmitting station.  The method according to claim 9, wherein: the frame structure of the subchannel-modulation mode information frame includes a subchannel-modulation mode signal of each subchannel in a certain error correction code mode. •interest.  11. The method according to claim 3, wherein: the specific data frame refers to a specific data frame having a subchannel-modulation mode request function or a specific subchannel-modulation mode information function.  12. The method according to claim 11, wherein: the frame structure of the specific data frame includes a flag bit requesting subchannel-modulation mode information from the receiving station.  The method according to claim 11, wherein: the frame structure of the specific data frame includes subchannel-modulation mode information of each subchannel in a certain error correction code mode.  14. The method according to claim 3, wherein: the step of implementing the modulation mode information used by the receiving station to transmit the subchannels to the transmitting station by using the information exchange mechanism of the WLAN at the MAC layer comprises:  There is information interaction between the transmitting site and the receiving site at the MAC layer; During the MAC layer information exchange process, when the transmitting station sends the corresponding MAC frame to the receiving station, the request for the subchannel-modulation mode is marked in the MAC frame at the same time; During the MAC layer information exchange process, the receiving station, when responding to the de-C frame of the transmitting station, places the sub-channel-modulation mode information into the response frame and transmits it to the transmitting station.  The method according to claim 14, wherein: the frame structure of the MAC frame includes a flag bit for requesting subchannel-modulation mode information from the receiving station.  The method according to claim 14, wherein: the frame structure of the response frame includes subchannel-modulation mode information of each subchannel in a certain error correction code mode.  17. The method according to claim 1, wherein: the Orthogonal Frequency Division Multiplexing (OFDM) OFDM wireless local area network is an 802.11 network. twenty three