CN101061654A - Communication device, communication system and communication method - Google Patents

Abstract

The present invention proposes a communication device. Compared with the traditional sub-band adaptive method, the device can improve the system spectrum utilization rate, especially the spectrum utilization rate under fast fading and channel estimation error, and can reduce the complexity of self-adaptation at the same time. and reduce feedback overhead. In the device, the sub-band AMC parameter selection unit (318) selects the AMC parameters of each sub-band. On the one hand, the adaptive receiving control unit (503) needs to control the adaptive demodulation and decoding unit (311), on the other hand, it also needs to control the parallel-to-serial converter (312) before the adaptive demodulation and decoding , combine the received symbols in the same subband group together for demodulation and decoding.

Description

Communication device, communication system and communication method

technical field

The present invention relates to a communication device, a communication system and a communication method, in particular to an adaptive transmission technology in a subcarrier communication system, that is, a subcarrier communication system, especially a wireless communication Orthogonal Frequency Division Multiplexing (OFDM A communication device, a communication system and a communication method for performing adaptive modulation and coding in the ) system.

Background technique

OFDM technology is currently the mainstream technology for high-speed wireless data transmission. The principle of OFDM technology is to transmit the high-speed data to be transmitted with many orthogonal sub-carriers, and the data rate on each sub-carrier is relatively low. Compared with the usual frequency division multiplexing system, the orthogonality of subcarriers in OFDM makes the system have higher spectrum utilization. In OFDM, the entire signal bandwidth is divided into several very narrow sub-carrier frequency bands, and since the bandwidth of each sub-carrier is smaller than the bandwidth of the channel, flat fading occurs. Thus, flat fading in OFDM is much easier to achieve than in single-carrier systems. Currently, OFDM technology has been successfully applied in Asymmetric Subscriber Data Loop (ADSL), Digital Video Broadcasting (DVB) and Wireless Asynchronous Transfer Mode (WATM) systems.

In order to improve the spectrum utilization of wireless systems, high-speed wireless data transmission in fading channels requires the use of adaptive, high-spectrum utilization transmission technologies. In fading channels, compared with fixed coded modulation, adaptive modulation and coding (AMC) technology can effectively improve system throughput and bit error rate (BER) performance. The so-called throughput here refers to the spectrum utilization rate of the system, that is, the amount of information transmitted per unit spectrum bandwidth per unit time. The basic idea of AMC technology is to adaptively change one or more of the transmission power, symbol transmission rate, constellation size, coding efficiency, and coding mechanism according to the current channel characteristics, and to transmit more information when the channel condition is good to improve the frequency spectrum. Utilization rate, when the channel condition is poor, less information is transmitted to ensure a certain receiving BER requirement.

Before introducing the AMC method in OFDM, first briefly introduce the channel characteristics in OFDM transmission.

Figure 1 shows an example of channel characteristics for OFDM.

Wherein, the two horizontal axes respectively represent the labels of the OFDM symbols in the time domain and the subcarriers in the frequency domain, and the vertical axis represents the channel gain on the corresponding OFDM symbols and subcarriers. Due to the time-domain dispersion and frequency-domain dispersion of the channel during transmission, the OFDM channel has fluctuations in both the time domain and the frequency domain.

As mentioned earlier, the idea of AMC is to change the transmitted modulation and coding parameters according to the current channel characteristics. For OFDM, the adaptation at this time is the adaptation in the time domain and the frequency domain. At present, in terms of adaptive structure, AMC in OFDM can be divided into subcarrier-based AMC and subband-based AMC. The so-called sub-carrier-based AMC means that each sub-carrier is the smallest adaptive unit, and each sub-carrier of OFDM uses different modulation and coding methods for transmission. The disadvantage of subcarrier-based AMC is that the implementation complexity is too high, and there is also the problem of excessive feedback overhead. Generally speaking, methods based on subcarrier AMC are difficult to implement in practical systems. Another adaptive structure in OFDM is the sub-band AMC structure using independent coding, which is the traditional sub-band adaptive method.

FIG. 2 is a schematic diagram of traditional sub-band adaptive modulation and coding.

In this structure, all subcarriers in the OFDM frequency domain are divided into several subbands. The so-called sub-band refers to a sub-carrier group composed of sub-carriers at adjacent positions in the frequency domain. For example, in FIG. 2 , the total number of subbands is N. Then, a coded modulation block is composed of the same subband in several adjacent (in FIG. 2 , the value is M) OFDM symbols. In the traditional sub-band adaptation in FIG. 2 , each coding and modulation block performs coding and modulation parameter estimation and independent coding according to its own channel characteristics. The numbers in each coded modulation block in FIG. 2 indicate the level to which the coded modulation parameters in the coded modulation block belong.

Generally speaking, the coding and modulation parameters corresponding to each coding and modulation parameter level have been determined at the initial stage of the system. For example, Table 1 shows the relationship among levels, coding parameters and modulation parameters as an example. But the present invention is not limited to Table 1.

level Encoding parameters Modulation parameters 0 Do not pass Do not pass 1 1/2Turbo BPSK 2 1/2Turbo QPSK 3 3/4Turbo QPSK 4 2/3Turbo 8PSK 5 3/4Turbo 16QAM 6 2/3Turbo 64QAM

Next, Fig. 3 shows the realization block diagram of adopting the traditional sub-band adaptive method in OFDM.

FIG. 3A and FIG. 3B are block diagrams of an OFDM-AMC system in which traditional OFDM and AMC are combined.

Assuming that the communication device (transmitter) in FIG. 3A communicates with the communication device (receiver) in FIG. 3B , a typical example is that FIG. 3A is the base station (AP), and FIG. 3B is the mobile terminal (UE). It is also assumed that the transmission from FIG. 3A to FIG. 3B adopts the AMC mechanism.

At the sending end of Fig. 3A, the information bits to be transmitted first pass through the adaptive modulation and coding unit 301, and the output serial modulation symbols pass through the serial/parallel transform (S/P) device 302 respectively, and the inverse fast Fourier transform (IFFT) Converter 303 transforms the frequency domain symbol into time domain, and then inserts a guard interval after passing through a parallel/serial converter (P/S) converter 304 , which is completed by inserting a guard interval unit 305 . After that, it is sent out through the antenna 306 . After the receiving end of FIG. 3B receives the sending signal from the sending end through the receiving antenna 316, the guard interval added by the sending end is first removed, which is completed by the removing guard interval unit 315, and then through the serial/parallel converter (S/P) device 314, Fast Fourier Transform (FFT) unit 313 transforms time domain symbols into frequency domain, then performs parallel/serial conversion processing through parallel/serial conversion (P/S) unit 312, and finally through adaptive demodulation and decoding unit 311 The output gets the received data.

The adaptive transmission from the sending end in FIG. 3A to the receiving end in FIG. 3B is mainly embodied in the adaptive modulation and coding unit 301 in the sending end and the adaptive demodulation and decoding unit 311 in the receiving end. As mentioned earlier, the meaning of adaptive modulation and coding is to adaptively adjust the parameters of modulation and coding at the sending end according to the current channel characteristics, and use the parameters corresponding to the sending end to perform demodulation and decoding at the receiving end. In a general system, the adaptive parameters required by the adaptive modulation and coding unit 311 come from the feedback from the receiving end. Before each data block is sent, the receiving end first uses the channel estimation unit 319 to estimate the channel currently transmitted from the sending end to the receiving end to obtain the channel characteristics on each subcarrier in OFDM. Then, according to these channel characteristics, the receiving end uses the subband AMC parameter selection unit 318 to determine the modulation and coding parameters used on each subband in OFDM when the current sending end sends data. The adaptive modulation and coding parameters on each sub-band obtained by the sub-band AMC parameter selection unit 318 have two purposes:

(1) Used as the modulation and coding parameters on each subband of OFDM when the current sender sends data. After the sub-band AMC parameter selection unit 318 at the receiving end selects the modulation and coding parameters on each OFDM sub-band, through the parameter sending unit 320 at the receiving end→antenna 316 at the receiving end→antenna 306 at the sending end→the parameter receiving and extracting unit 307 at the sending end Such a feedback path sends these parameters back to the sender. After extracting these parameters, the transmitting end controls the adaptive modulation and coding unit 301 through the AMC control unit 308 .

(2) It is used as a parameter used in demodulation and decoding at the receiving end. In AMC transmission, the receiving end must demodulate and decode the received data according to the same modulation and coding parameters as the sending end to obtain the correct information bits. Therefore, after the subband AMC parameter selection unit 318 obtains the AMC parameter, it also needs to send it to the adaptive demodulation and decoding unit 317, which is temporarily stored by the adaptive demodulation and decoding unit 317, and used as the receiving end for its own Adapt to the control of the demodulation and decoding unit 311 .

In order to more clearly describe the method of using subband AMC in traditional OFDM, the module 309 in FIG. 3A and the module 321 in FIG. 3B are refined in FIG. 4A and FIG. 4B .

FIG. 4A and FIG. 4B show the implementation structure of traditional sub-band adaptive modulation and coding.

At the sending end of Fig. 3A, the adaptive modulation and coding unit 301 includes an adaptive coding unit 401, an interleaving unit 402 and an adaptive modulation unit 403, and the data output by the adaptive modulation and coding unit 301 is converted through serial-to-parallel (S/P) After the device 302 is sent to the IFFT device 303. The AMC control unit 308 at the transmitting end controls the adaptive modulation and coding unit 301 according to the modulation and coding parameters of each subband obtained by the parameter receiving and extraction unit 307 from the feedback channel in FIG. 3A . In traditional subband adaptation, each subband in OFDM is independently coded and modulated, that is to say, each subband has its own set of modulation and coding parameters. The AMC control unit 308 controls the adaptive modulation and coding unit 301 through the obtained coding parameter C and modulation parameter M of each subband. At the same time, the AMC control unit 308 can also obtain the number of information bits transmitted in each sub-band according to the coding parameter C and the modulation parameter M, thereby generating a corresponding interleaving matrix Π, and performing the interleaving unit 402 in the adaptive modulation and coding unit 301 control. After the AMC, the sending end obtains the serial data stream 404, which contains the data sent in the sub-bands 1, 2, ... N in order, and the modulation and coding methods are (C ₁ , M ₁ ), (C ₂ , M ₂ ), . . . , (C _N , M _N ). Afterwards, the serial-to-parallel conversion of these data is sequentially mapped to corresponding subbands in OFDM for transmission.

The AMC parameters required by the sender to send each data block come from the feedback from the receiver, that is, before the sender sends each data block, the receiver must first select the AMC parameters for the data block sent by the sender . The process of selecting parameters at the receiving end is as follows: First, channel estimation is performed through the received signal. There are many methods for channel estimation, including pilot-based methods, blind channel estimation, and so on. Afterwards, the channel estimation unit 319 sends the obtained channel characteristics on each OFDM subcarrier to the subband AMC parameter selection unit 318 . The subband AMC parameter selection unit 318 first analyzes the performance of each subband in OFDM based on this, and then selects an appropriate AMC parameter for each subband from the set of candidate AMC parameters. The resulting AMC parameters are sent back to the sending end through the feedback channel on the one hand, used for the actual adaptive modulation and coding operation of the sending end when sending, and on the other hand, used for the adaptive demodulation and decoding control unit of the receiving end 409. At the same time, due to the consideration of time delay, a parameter storage unit 410 is also required to store the currently obtained parameters. The adaptive modulation and decoding unit 311 at the receiving end includes an adaptive demodulation unit 408 , a deinterleaving unit 407 and an adaptive decoding unit 406 .

Compared with subcarrier adaptation, the existing subband-independent coding-based adaptive method shown in Figure 3A to Figure 4B can effectively reduce the complexity of adaptive implementation, and can also effectively reduce the feedback overhead of the system . However, this method still has certain disadvantages: it does not effectively utilize the diversity capability among subbands.

Diversity is an important method to improve the quality of wireless transmission. The so-called diversity, in a nutshell, is that the sending end uses a certain resource to increase information redundancy and try to make the mutually redundant information experience as independent distortion or attenuation as possible, and comprehensively utilize and combine the information at the receiving end to obtain a certain system. performance gain techniques. To put it simply, it is to use multiple channels for transmission at the same time, and the performance loss of one channel at the receiving end can be compensated by other channels.

On the basis of the independent coding method of subbands used in the traditional OFDM adaptive modulation and coding, the patent application of the present invention adds a method of combining subbands into subband groups according to a certain method, and then jointly coding each subband group. This method seems to run counter to the traditional AMC idea, because the traditional AMC method requires independent selection of parameters and encoding for each subband. However, this method introduces diversity between sub-bands, so that greater coding gain can be obtained. In addition, according to the method we give, the selection of modulation and coding parameters in the sub-band group will not cause the loss of transmission throughput compared with the traditional method. Combining the two, adopting the method of this patent application will help to improve the performance of adaptive transmission in OFDM.

Contents of the invention

The problem to be solved by the invention

The purpose of the present invention is to provide a communication device, a communication system and a communication method, wherein firstly all sub-bands in the frequency domain in the sub-carrier communication system are combined into several sub-band groups according to certain rules, and then the sub-bands for each sub-band are selected Compared with the traditional subband adaptive method, it can improve the system spectrum utilization rate, especially the spectrum utilization rate under fast fading and channel estimation error. Accommodates implementation complexity and reduces feedback overhead.

solution to the problem

The structure of the communication device of the present invention includes: a channel estimation unit, which performs channel estimation on each subband; a parameter determination unit, based on the result of the channel estimation, determines modulation parameters and coding parameters for each subband group formed by a plurality of subbands The parameter information sending unit sends the parameter information to the communication object, and the parameter information is the information of the modulation parameter and the encoding parameter determined by the parameter determination unit; the receiving unit receives the received signal containing data, and the The data is the data obtained by the communication object by using the modulation parameter and the coding parameter of the parameter information sent by the parameter information sending unit to modulate and code each subband group; and the data an obtaining unit that demodulates and decodes each of the subband groups using the modulation parameter and the coding parameter determined by the parameter determination unit on the received signal received by the receiving unit, and obtains The data included in the received signal.

The communication system of the present invention is a communication system including a base station device that transmits modulated and coded data and a communication terminal device that receives the data, and the communication terminal device includes: a channel estimation unit that performs channel estimation for each subband A parameter determination unit, based on the channel estimation result, determines modulation parameters and coding parameters for each subband group formed by a plurality of subbands; a parameter information sending unit, sends parameter information to the base station device, and the parameter information information of the modulation parameter and the encoding parameter determined by the parameter determination unit; a receiving unit that receives a received signal including data transmitted by the base station apparatus by using the parameter information transmitting unit The parameters of the parameter information are used to modulate and encode the data obtained by each of the subband groups; and the data extraction unit uses the modulation parameters of the parameter information for the received signal received by the receiving unit and the coding parameters, demodulate and decode each of the subband groups, and extract the data contained in the received signal, the base station device includes: an adaptive modulation and coding unit, according to the Modulating and coding the modulation parameters and coding parameters of the parameter information sent by the sending unit; and a data sending unit, sending the data modulated and coded by the adaptive modulation and coding unit.

The communication method of the present invention includes the following steps: performing channel estimation for each subband; determining modulation parameters and coding parameters for each subband group formed by a plurality of subbands based on the channel estimation result; sending parameter information by a communication terminal device, The parameter information is the determined information of the modulation parameter and the coding parameter; the base station device receives the parameter information sent by the communication terminal device; the modulation parameter and the coding parameter according to the received parameter information The encoding parameters are used to modulate and encode the data; the base station device transmits the modulated and encoded data; the communication terminal device receives the received signal containing the data sent by the base station device; and the received said The reception signal is demodulated and decoded for each of the subband groups using the modulation parameter and the coding parameter of the parameter information, and the data included in the reception signal is extracted.

Description of drawings

Figure 1 shows an example of the channel characteristics of OFDM;

FIG. 2 is a schematic diagram of adaptive modulation and coding in the prior art;

FIG. 3A is a block diagram showing the structure of the transmitting end of the OFDM-AMC system in the prior art;

FIG. 3B is a block diagram of a receiving end structure of an OFDM-AMC system in the prior art;

FIG. 4A is a schematic diagram of a module including an adaptive modulation and coding unit at a transmitting end in the prior art;

FIG. 4B is a schematic diagram of a module including an adaptive demodulation and decoding unit at a receiving end in the prior art;

FIG. 5A is a schematic diagram of a structure of a transmitting end of an OFDM-AMC system according to an embodiment of the present invention;

FIG. 5B is a schematic diagram of a receiving end structure of an OFDM-AMC system according to an embodiment of the present invention;

FIG. 6A is a schematic diagram of a module including an adaptive modulation and coding unit at a sending end according to an embodiment of the present invention;

FIG. 6B is a schematic diagram of a module including an adaptive demodulation and decoding unit at a receiving end according to an embodiment of the present invention;

FIG. 7 shows a diagram of an adaptive modulation and coding method according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of an example of a subband group according to an embodiment of the present invention;

FIG. 9 is a schematic diagram of an example of a subband group according to an embodiment of the present invention;

FIG. 10 is a schematic diagram of an example of a subband group according to an embodiment of the present invention;

Fig. 11 shows a schematic diagram of performance comparison results between adaptive modulation and coding and traditional adaptive modulation and coding according to an embodiment of the present invention;

Fig. 12 shows a schematic diagram of performance comparison results between adaptive modulation and coding and traditional adaptive modulation and coding according to an embodiment of the present invention.

Detailed ways

The specific implementation manner of the present invention will be described below in conjunction with the accompanying drawings. In order to describe the present invention clearly, the present invention uses an OFDM system as an example for description. The adaptive modulation and coding method of the present invention is also suitable for any sub-carrier communication system using sub-carriers for communication.

The present invention adopts the sub-band independent coding method in the traditional OFDM adaptive modulation and coding, combines the sub-bands into sub-band groups in a certain way, and then performs joint coding on each sub-band group. Moreover, the invention also provides various ways of combining subbands into subband groups, and selection methods of modulation and coding parameters used in joint coding within subband groups. It will be described later.

Fig. 5A and Fig. 5B show the OFDM-AMC system structure for realizing the method of the present invention.

In order to make the description of the present invention clearer, the structures known in the prior art shown in FIGS. .

Compared with the traditional OFDM-AMC structure shown in Figure 3A and Figure 3B, the OFDM-AMC system of the present invention has the following differences:

(1) The subband group AMC parameter selection unit 504 included in the module 505 in FIG. 5B as a parameter selection unit selects the AMC parameter of the subband group, and the subband group AMC parameter included in the module 321 in FIG. 3B The band AMC parameter selecting unit 318 is to select the AMC parameter of each sub-band. This is because in the traditional OFDM-AMC system, the subband adaptive modulation and coding unit is the subband, but in the OFDM-AMC system of the present invention, the subband group is the adaptive modulation and coding unit. In the present invention, all subbands in the frequency domain in OFDM are combined into several subband groups through combination patterns, and then adaptive modulation and coding are performed on each subband group. Moreover, in the OFDM-AMC system of the present invention, in Fig. 5B, what is transmitted in such a feedback link as parameter sending unit 320 → receiving end antenna 316 → sending end antenna 306 → sending end parameter receiving and extracting unit 307 is used as parameter information The AMC parameters about the subband group, instead of the AMC parameters about the subbands in OFDM-AMC as shown in FIG. 3 , the parameter information is information about modulation parameters and coding parameters.

(2) The adaptive transmission control unit 501 in the transmitting end replaces the AMC control unit 308 in FIG. 3A . In the technology of the present invention, the transmitting end performs adaptive modulation and coding on subband groups in OFDM, and the subband groups are formed by combining subbands in OFDM according to a combination pattern. Therefore, on the one hand, the adaptive transmission control unit 501 needs to control the AMC of the subband group in the adaptive modulation and coding unit 301, and on the other hand, it also needs to control the serial/parallel conversion (S/P ) device 302 controls, so that the information bits sent in each subband group can be mapped to the corresponding subband in OFDM after coding and modulation for transmission.

(3) The adaptive reception control unit 503 in the receiving end replaces the adaptive demodulation and control unit 317 in FIG. 3B . On the one hand, the adaptive reception control unit 503 needs to control the adaptive demodulation and decoding unit 311 as the data acquisition unit; The unit 312 performs control to combine the received symbols in the same subband group together for demodulation and decoding.

Module 502 in FIG. 5A and module 505 in FIG. 5B can be refined into FIG. 6A and FIG. 6B .

FIG. 6A and FIG. 6B are schematic diagrams showing the implementation structure of the method proposed by the present invention.

At the sending end, the difference from the traditional subband adaptation in FIG. 4A is that the unit of adaptive modulation and coding is a subband group rather than a subband. At this time, the output 603 of the adaptive modulation and coding unit 301 is in order Contains the data sent in subband groups 1, 2, ... K, and its modulation and coding methods are (C ₁ , M ₁ ), (C ₂ , M ₂ ), ..., (C _K , M _K ), where K is the total number of subband groups divided in OFDM. In addition, in addition to controlling the AMC operation, the transmitting end also needs to perform serial/parallel conversion in the serial/parallel converter (S/P) device 302 according to the combination pattern of the subbands stored in the combination pattern storage unit 601. control, so that the information bits sent in each subband group can be mapped to corresponding subbands in OFDM for transmission after encoding and modulation.

At the receiving end, the difference from the traditional subband adaptation in FIG. 4B is that the unit of adaptive demodulation and decoding is a subband group rather than a subband. In addition, in addition to controlling the adaptive demodulation and decoding operations, the receiving end also needs to perform the parallel/serial conversion (P/S) converter 312 according to the combination pattern of the subbands stored in the combination pattern storage unit 605. The parallel/serial conversion is controlled, so that the received symbols in the same subband group of OFDM are combined together for demodulation and decoding. In addition, as shown in FIG. 6B , the subband group AMC parameter selection unit 504 is also different from that in FIG. 4B . In Fig. 6B, on the basis of the parameters of each OFDM subband selected by the parameter selection unit 411, the parameter selection unit 606 of the subband group selects each OFDM subband group according to the combination pattern stored in the combination pattern storage unit 607. adaptive parameters.

Fig. 7 shows a process flowchart for implementing an adaptive coding and modulation method according to an embodiment of the present invention. Specifically, the realization process of the technology of the present invention is as follows:

In the first step, the receiving end determines the adaptive modulation and coding parameters in each subband group in OFDM at the sending end, and feeds them back to the sending end. This process includes channel estimation at the receiving end (step 901), selection of adaptive parameters for each OFDM subband (step 902), selection of adaptive parameters for each subband group of OFDM (step 903), and parameter feedback (step 921).

(1) The channel estimation in step 901 can use existing general methods, such as pilot-based channel estimation, blind channel estimation and so on.

(2) The selection of adaptive parameters for each subband of OFDM in step 902 refers to considering the modulation and coding parameters used for adaptive transmission of each subband in OFDM under the traditional independent coding of each subband. Due to the independent coding, the parameters in each sub-band are different according to their channel characteristics.

In this step, it is first necessary to determine an alternative adaptive parameter set, such as the parameter sets in Table 1 and Table 2. Then, according to the current channel characteristics of each sub-band, appropriate modulation and coding parameters are selected for it, and the corresponding number of transmission information bits is determined at the same time. Here, there are many existing methods for selecting parameters according to channel characteristics, such as the method based on the lowest SNR of the subband, the method based on the average SNR of the subband, the method based on capacity, and the method based on the average SNR combined with other statistical characteristics method, and so on. In this implementation example, we take the method based on the average signal-to-noise ratio as an example to make a brief description.

The method based on the average signal-to-noise ratio is as follows: firstly, the threshold value of signal-to-noise ratio required for each modulation and coding parameter (as shown in Table 2) is determined by theoretical analysis or simulation method, and the throughput capacity is various The spectral utilization rate corresponding to the coded modulation parameter is numerically equal to the product of the coded efficiency and the number of bits contained in each symbol. Then, for each subband, the average signal-to-noise ratio over its internal subcarriers is calculated. Finally, a modulation and coding parameter whose threshold value is lower than the average SNR and has the highest throughput is selected for the subband as the modulation and coding parameter in the subband. Table 2 shows the relationship among coding parameters, modulation parameters, signal-to-noise ratio threshold and throughput capability of each level. For example, when the average signal-to-noise ratio in the sub-band is 0, 2, 4, 6, 8, according to the parameters shown in Table 2, the levels corresponding to the selected modulation and coding parameters are 1, 1, 2, 3, respectively. 4. Correspondingly, the number of information bits allocated in the sub-band is also determined (the value thereof is equal to the product of the total number of sub-carriers in the sub-band and the throughput corresponding to the selected modulation and coding parameters). grade encoding parameters modulation parameters SNR Threshold (dB) Throughput (bps/Hz) 0 do not pass do not pass -∞ 0 1 1/2 Turbo BPSK -0.4 0.5 2 1/2 Turbo QPSK 2.2 1 3 3/4 Turbo QPSK 5.2 1.5 4 2/3 Turbo 8PSK 7.6 2 5 3/4 Turbo 16QAM 10.9 3 6 2/3 Turbo 64QAM 14.5 4

(3) The adaptive parameter selection of each OFDM subband group in step 903, in the traditional adaptive method, each OFDM subband is independently modulated and coded. However, in the method of the present application, the unit of adaptive transmission is a subband group rather than a subband. Therefore, firstly, all subbands in the OFDM frequency domain are combined into several subband groups according to a certain combination method (or combination pattern). The method of combination may be: the method of combining adjacent subbands, the method of combining interval subbands, the method of combining all subbands, and the method of combining according to other rules. The method of combining adjacent subbands, that is, the method of selecting a plurality of adjacent subbands on the frequency axis is a method of combining several adjacent subbands into a subband group, as shown in FIG. 8 . Figure 8 is an example of combining adjacent subbands. In addition, the subband group has a combination pattern of subbands, and the subbands are composed of the same number of subcarriers at adjacent positions in the frequency domain within a certain number of subcarrier modulation symbols.

In Figure 8, the N subbands in the same position in the time domain and the frequency domain in OFDM are combined into several subband groups, and the subbands with adjacent frequency domain positions are combined into a subband group, that is, under the same hatching pattern in the figure The subbands belong to the same subband group.

In addition, the method of combining subbands at intervals, that is, the method of selecting multiple subbands at predetermined intervals in the subbands arranged on the frequency axis, is a method of combining several subbands at intervals to form a subband group, see Figure 9 . FIG. 9 is an example of combining interval subbands.

In FIG. 9 , alternately selected subbands in the OFDM frequency domain are combined into the same subband group, that is, the subbands under the same hatch pattern in the figure belong to the same subband group.

In addition, the method of combining all subbands, that is, the method of selecting all subbands for each predetermined time domain, is to combine all subbands in the frequency domain into one subband group, see FIG. 10 . Figure 10 is an example of all subband combinations.

In FIG. 10 , all N subbands in the same position in the time domain and frequency domain in OFDM are combined into one subband group.

In addition, in the method of combining according to other rules, after the modulation and coding parameters of each subband in the subband group and the number of allocated information bits are determined, the number of information bits allocated in the subband group and the joint coding parameters can be determined as follows : (1) first sum the number of information bits allocated in each sub-band as the number of information bits allocated in the entire sub-band group; (2) then select the largest modulation level in each sub-band as the unified modulation in the sub-band group The modulation method used, and then the coding efficiency is determined by the number of information bits allocated in the subband group and the modulation method.

An example of this process is as follows: Suppose a subband group contains four subbands A, B, C, and D, and the number of subcarriers contained in each subband is 512, and the coding and modulation parameter levels corresponding to each subband are: 0, 1, 2, 3. Then it can be obtained: the number of information bits allocated in each subband group of A, B, C, and D is respectively: 512*0=0 for A, 512*0.5=256 for B, and 512*1=2 for C 512, for D is 512*1.5=768. Therefore, the total number of information bits in the subband group is 0+256+512+768=1536. Afterwards, 8PSK, the highest modulation level in each subband group of A, B, C, and D (here, subband D corresponds to the highest modulation level) is selected as a unified modulation parameter in the entire subband group. Correspondingly, the coding efficiency adopted by the uniform coding in the subband group is 1536/(512*3*4)=1/4.

Here, the estimated number of transmitted information bits in the four subbands A, B, C, and D is summed as the number of information bits transmitted in the subband group. In actual operation, a weighting operation can also be performed on the value. For example, considering that the channel changes quickly and the error of the estimated channel characteristics will be large, then the sum of the transmission information bits in the four subbands A, B, C, and D is weighted by 0.9, that is: subband group The total number of information bits is (0+256+512+768)*0.9=1536*0.9≈1382.

(4) The parameter feedback in step 921, after the receiving end obtains the adaptive parameters of each OFDM subband group, sends it back to the sending end through the feedback channel, so that the sending end can perform actual operations according to this parameter.

In the second step, the sending end allocates a corresponding number of information bits to be transmitted for each sub-band group according to the adaptive parameters in each OFDM sub-band group fed back by the receiving end, and performs a joint operation in each sub-band group according to the corresponding parameters. Coding and modulation (step 911). For example, according to the situation assumed above, joint modulation and coding are adopted for the subband group composed of four subbands A, B, C, and D, and the modulation and coding parameters are 8PSK and 1/4Turbo codes respectively. Next, assign the modulated symbols to corresponding subbands in OFDM according to the subband combination pattern for transmission (step 912). It specifically includes the serial/parallel conversion of the serial/parallel converter 302 , the inverse fast Fourier transform of the IFFT 303 , the parallel/serial conversion of the parallel/serial converter 304 , and the guard interval insertion of the guard interval unit 305 .

In the third step, at the receiving end, at first, after removing the guard interval of the guard interval unit 315, the serial/parallel conversion of the serial/parallel converter 314, the fast Fourier transform of the FFT device 313, and the parallel/parallel conversion of the parallel/serial converter 312 Serial conversion, simultaneously by controlling the parallel/serial converter 312 according to the subband combination pattern the data in each subband group of OFDM received is extracted (step 904), and then, according to the data in each subband group obtained in the first step The adaptive parameters of each subband group are adaptively demodulated and decoded, and the original data to be finally sent is obtained (step 905).

The present invention combines and jointly encodes each sub-band in OFDM, effectively utilizes the diversity capability between sub-bands, thereby effectively improving the system spectrum utilization rate, especially the spectrum utilization rate under fast fading and channel estimation errors, At the same time, it reduces the complexity of adaptive implementation and the feedback overhead.

Fig. 11 shows a diagram of performance comparison results between the method of the present invention and the traditional method under different feedback delays.

Fig. 12 shows a schematic diagram of performance comparison results between the method of the present invention and the traditional method under different channel estimation errors.

Among them, the signal bandwidth of the OFDM system used in the simulation is 10MHz, and the total number of subcarriers is 1024, which is divided into 16 subbands, and each subband spans 8 OFDM symbols in the time domain. The component recursive systematic convolution (RSC) polynomial formula of the Turbo code is (13,11) _oct , and the decoding uses 4 iterations, and the maximum a posteriori probability (MAP) algorithm. The system adopts ARQ. The channel model used in the simulation is M.1225 vehicle channel model A. In specific implementation, the method of combining all subbands is adopted, and the parameter estimation method based on the average signal-to-noise ratio is adopted for a single subband. f _d τ and MSE in Figure 11 and Figure 12 represent the product of the maximum Doppler frequency shift and the feedback time delay, and the channel estimation error, respectively. See Figure 2 for the traditional method. From the results in Figure 11 and Figure 12, it can be seen that no matter in the ideal case (f _d τ = 0, no MSE), or in the case of fast fading (with f _d τ) or channel estimation error (with MSE), the same as Compared with the traditional method, the method proposed by the present invention has a certain performance gain. In addition, at this time, all 16 subbands are combined into one subband group, and the feedback overhead is reduced to 1/16 of the original.

Although the preferred embodiments of the present invention have been shown above, those skilled in the art will understand that various modifications, substitutions and changes can be made to the present invention without departing from the spirit and scope of the present invention. Therefore, the present invention should not be limited by the above-described embodiments.

Claims (12)

1, a kind of communicator comprises:

Channel estimating unit is carried out channel estimating to each subband;

The parameter determining unit based on the result of described channel estimating, is determined modulation parameter and coding parameter to each subband group that is formed by a plurality of subbands;

The parameter information transmitting element sends to communication object with parameter information, and described parameter information is the described modulation parameter determined by described parameter determining unit and the information of described coding parameter;

Receiving element, reception comprises the received signal of data, described data are for by described modulation parameter and the described coding parameter of communication object by the parameter information that uses described parameter information transmitting element and sent, come each described subband group is modulated and encoded and the data that obtain; And

Data obtain the unit, the received signal that described receiving element is received, described modulation parameter and described coding parameter that use is determined by described parameter determining unit are separated mediation decoding to each described subband group, and obtain to be contained in the described data of described received signal.

2, communicator according to claim 1 also comprises:

The pattern memory cell, storage in advance is used to choose the pattern of the subband that constitutes described subband group, wherein,

Described parameter determining unit is determined described modulation parameter and described coding parameter to each described subband group, and described subband group is formed by the subband of choosing based on the described pattern that is stored in described pattern memory cell.

3, communicator according to claim 2, wherein,

Described parameter determining unit is determined described modulation parameter and described coding parameter to each the described subband group that is made of described pattern, and described pattern is used to be chosen at a plurality of subbands adjacent on the frequency axis.

4, communicator according to claim 2, wherein,

Described parameter determining unit is determined described modulation parameter and described coding parameter to each the described subband group that is made of described pattern, and described pattern is used for choosing a plurality of subbands from the subband that is arranged on the frequency axis with predetermined interval.

5, communicator according to claim 2, wherein,

Described parameter determining unit is determined described modulation parameter and described coding parameter to each the described subband group that is made of described pattern, and described pattern is used for each predetermined time domain is chosen all subbands.

6, communicator according to claim 1, wherein,

Described parameter determining unit is obtained described modulation parameter to each subband in the described subband group, and will be defined as the described modulation parameter of described subband group in the highest described modulation parameter of being obtained of described modulation parameter middle grade.

7, communicator according to claim 1, wherein,

Described parameter determining unit is determined described coding parameter, is assigned to described subband group so that can distribute to the information bit of all subbands in the described subband group.

8, communicator according to claim 1, wherein,

Described parameter determining unit is determined described coding parameter, so that the result's that the summation of the information bit that can distribute to all subbands in the described subband group is weighted information bit is assigned to described subband group, described weighting is carried out each described subband group.

9, a kind of base station apparatus of the communication object as the described communicator of claim 1, this base station apparatus comprises:

The adaptive modulation and coding unit according to the described modulation parameter and the coding parameter of the described parameter information that is sent by described transmitting element, is modulated and is encoded data; And

Data transmission unit, will by described adaptive modulation and coding unit modulate and encode after data send.

10, a kind of communication system comprises: base station apparatus, and the data after will modulating and encode send; And communication terminal, receive described data,

Described communication terminal comprises:

Channel estimating unit is carried out channel estimating to each subband;

The parameter determining unit based on the result of described channel estimating, is determined modulation parameter and coding parameter to each subband group that is formed by a plurality of subbands;

The parameter information transmitting element sends to described base station apparatus with parameter information, and described parameter information is the described modulation parameter determined by described parameter determining unit and the information of described coding parameter;

Receiving element receives the received signal comprise data, and described data are for by the parameter of described base station apparatus by the parameter information that uses described parameter information transmitting element and sent, comes each described subband group is modulated and encoded and the data that obtain; And

Data extracting unit to the received signal that described receiving element receives, is used the described modulation parameter and the described coding parameter of described parameter information, and each described subband group is separated to be in harmonious proportion decipher, and extract the described data that are contained in described received signal,

Described base station apparatus comprises:

The adaptive modulation and coding unit is modulated and is encoded according to the described modulation parameter of the described parameter information that is sent by described transmitting element and coding parameter; And

Data transmission unit, will by described adaptive modulation and coding unit modulate and encode after data send.

11, a kind of communication means may further comprise the steps:

Each subband is carried out channel estimating;

Based on the result of described channel estimating, each subband group that is formed by a plurality of subbands is determined modulation parameter and coding parameter;

Communication terminal sends parameter information, and described parameter information is the information of determined described modulation parameter and described coding parameter;

Base station apparatus receives the described parameter information that described communication terminal sends;

According to the described modulation parameter and the described coding parameter of the described parameter information that is received, data are modulated and encoded;

Described base station apparatus send modulate and encode after data;

Communication terminal receives the received signal that comprises described data that is sent by described base station apparatus; And

To the described received signal that is received, use the described modulation parameter and the described coding parameter of described parameter information, each described subband group is separated to be in harmonious proportion decipher, and extract the described data that are contained in described received signal.

12, communication means according to claim 11 also comprises:

Storage in advance is used to choose the step of the pattern of the subband that constitutes described subband group, wherein,

Each described subband group is determined described modulation parameter and described coding parameter, and described subband group is formed by the subband of choosing based on the described pattern of being stored.

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