KR100929067B1 - Data Multiplexing Method in Orthogonal Frequency Division Multiple Access System and Its Transceiver - Google Patents

Abstract

The present invention relates to an OFDM-based wireless communication system, and, when a data transmitter transmits a packet data channel in a data transmission / reception process, adapts according to a code rate of the transmitted packet or an effective SNR of a wireless channel of a corresponding terminal. In general, the present invention relates to a method and a transmission / reception apparatus for selectively using a multiplexing scheme. The adaptive multiplexing method is the same concept as the method for adaptively performing unitary precoding. Examples of the unitary precoded multiplexing method include OFCDM, FFT-S-OFDM, and FFH-OFDM. In addition, the present invention can improve the reception performance of the packet data by adaptively selecting the multiplexing method to transmit and receive the packet data.

Adaptive, Multiplexed, OFDM, Unitary Precoded OFDM

Description

DATA MULTIIPLEXING METHOD IN OFDMA SYSTEM AND TRANSMITTING / RECEIVING APPARATUS THEREOF}

1 is a block diagram of a typical OFDM system transmitter

FIG. 2 illustrates a structure of a transmitter of a general unitary precoded OFDM (OFDM) scheme. FIG.

3A is a diagram illustrating a case where a Hadamard transform is used as a kind of unitary precoding.

3B is a diagram illustrating a case where a fast fourier transform is used as a kind of unitary precoding.

FIG. 3C is a diagram illustrating a case where fast frequency hopping (FFH) is used as a kind of unitary precoding.

4 is a view briefly explaining the concept of a general fast frequency hopping (FFH) introduced in FIG.

5 is a diagram illustrating a performance comparison result of OFDM and OFCDM (MC CDM) when a code rate of a transport block is 1/4

FIG. 6 is a diagram illustrating a performance comparison result of OFDM and OFCDM when a code rate of a transport block is 1/2.

FIG. 7 is a diagram illustrating performance comparison results of OFDM and OFCDM when a code rate of a transport block is 4/5.

8 and 9 are diagrams illustrating a method for adaptively selecting a multiplexing scheme according to a predetermined criterion whenever a transmitter transmits a packet data channel in an OFDM based wireless communication system according to a preferred embodiment of the present invention.

10 illustrates a transmitter structure according to the adaptive multiplexing method of the present invention proposed in FIG. 8 or 9 according to a preferred embodiment of the present invention.

11 illustrates a method for a receiver to receive a packet according to the adaptive multiplexing technique proposed by the present invention according to a preferred embodiment of the present invention.

12 illustrates a receiver structure according to a preferred embodiment of the present invention.

The present invention relates to a communication system using a multiple access scheme, and in particular, each data transmission for improving the reception performance of data transmitted in a system for transmitting and receiving data using a multiple access scheme based on an orthogonal frequency division multiplexing scheme. It relates to a method and a transmission and reception apparatus for selecting and transmitting an optimal multiplexing method according to the conditions.

Recently, in the field of wireless communication systems, orthogonal frequency division multiplexing (OFDM) has been actively studied as a method useful for high-speed data transmission in a wireless channel. The OFDM method is a method of transmitting data using a multi-carrier, and converts a series of symbols input in parallel to each other. In addition, each of them is a kind of multi-carrier modulation (MCM) method that modulates and transmits each of a plurality of sub-carriers, that is, a plurality of sub-carrier channels. .

1 is a block diagram of a typical OFDM system transmitter.

Referring to FIG. 1, the general OFDM system transmitter includes a channel encoder 101, a modulator 102, a serial to parallel 103, an inverse fast Fourier transform, Hereinafter referred to as " IFFT ", a parallel to serial converter 105, and a cyclic prefix inserter 106.

The channel encoder 101 receives a predetermined information bit string as an input and performs channel encoding. In general, a coding unit includes a convolutional encoder, a turbo encoder, a low density parity check (LDPC) encoder, and the like.

The modulator 102 receives the output of the channel encoder 101 as an input and modulates QPSK, 8PSK, 16QAM, and the like. Although omitted in FIG. 1, it is obvious that a rate matching unit for performing a function such as repetition and puncturing may be added between the reference numerals 101 and 102.

The serial-to-parallel converter 103 receives the output of the modulator 102 and converts the signal in parallel. The IFFT 104 receives an output of the serial-to-parallel converter 103 as an input and performs an IFFT operation.

The parallel to serial converter 105 receives the output of the IFFT block and converts the signal back to serial. The cyclic prefix inserter 106 adds a cyclic prefix to the output signal of the parallel-to-serial converter 105.

Meanwhile, there is a method of transmitting a modulation symbol to be transmitted by a transmitter in a frequency domain by performing a Hadamard transform in a frequency domain using the conventional multiplexing method of OFDM. This method is generally referred to as Multi-Carrier Code Domain Multiplexing (MC-CDM) or Orthogonal Frequency Code Domain Multiplexing (OFCDM).

FIG. 2 is a diagram illustrating a transmitter structure of a general unitary precoded OFDM (OFDM) scheme.

Referring to FIG. 2, the transmitter unit of the general unitary precoded OFDM scheme includes a channel encoder 201, a modulator 202, a unitary precoder 203, and a serial. Serial to Parallel 204, Inverse Fast Fourier Transform (IFFT) 205, Parallel to Serial 206, and CP (Cyclic Prefix) insertion unit 207 is included.

The channel encoder 201 performs channel encoding by receiving a predetermined sequence of information bits. In general, a coding unit includes a convolutional encoder, a turbo encoder, or a low density parity check (LDPC) encoder.

The modulator 202 receives the output of the channel encoder 201 and modulates QPSK, 8PSK, 16QAM, and the like. Although omitted in FIG. 2, it is apparent that a rate matching unit for performing a function such as repetition and puncturing may be added between the reference numerals 201 and 202.

Since the unitary precoder 203 is a general unitary precoder 203, various examples of unitary precoding will be described in detail with reference to FIGS. 3A to 3C.

The serial-to-parallel converter 204 receives the output of the modulator 202 as an input and converts the signals in parallel. The IFFT 205 receives an output of the serial-to-parallel converter 204 as an input and performs an IFFT operation.

The parallel to serial converter 206 receives the output of the IFFT block and converts the signal back to serial. The cyclic prefix inserter 207 adds a cyclic prefix to the output signal of the parallel-to-serial converter 206.

3A to 3C are diagrams illustrating a plurality of examples of the unitary precoder of FIG. 2, and FIG. 3A is a diagram illustrating a case where a Hadamard transform is used as a kind of unitary precoding.

Referring to FIG. 3A, the unitary precoder includes a symbol demultiplexer 311, a Walsh function covering part 312, and a Walsh adder 313.

The symbol demultiplexer 311 receives an output of the modulator 202 of FIG. 2 as an input and converts a serial signal in parallel. The Walsh function covering unit 312 represents a process in which each modulation symbol output from the symbol demultiplexer 311 is Walsh covered or spread by a Walsh code having a predetermined length. The Walsh summing unit 313 is a block representing a process of adding up the outputs of the Walsh function covering unit 312 (that is, the outputs spread by each Walsh function).

3B is a diagram illustrating a case where a fast fourier transform is used as a kind of unitary precoding.

Referring to FIG. 3B, the unitary precoder includes a symbol demultiplexer 321, an FFT 322, and a parallel-to-serial converter 323.

The symbol demultiplexer 321 receives an output of the modulator 202 of FIG. 2 as an input and converts a serial signal in parallel. The FFT 322 receives an output of the symbol demultiplexer 321 as an input and outputs an FFT transform. The parallel-to-serial converter 323 receives the serial signal of the FFT 322 as an input and outputs the converted signal after parallel conversion.

3C is a diagram illustrating a case where fast frequency hopping (FFH) is used as a kind of unitary precoding.

Referring to FIG. 3C, the unitary precoder includes a symbol demultiplexer 331, an FFH linear processor 332, and a parallel-to-serial converter 333.

The symbol demultiplexer 331 receives an output of the modulator 202 of FIG. 2 as an input and converts a serial signal in parallel. The FFH linear processor 332 receives the output of the symbol demultiplexer 331 as an input and then outputs the linear transform after a fast frequency hopping. The fast frequency hopping refers to a technique for mapping different subcarriers for each OFDM sample. The parallel-to-serial converter 333 receives a serial signal of the FFH linear processor 332 as an input and outputs the parallel signal after converting it in parallel.

Meanwhile, among the conventional unitary precoded OFDM multiplexing schemes as described above, the Hadamard Precoded OFDM scheme as an Orthogonal Frequency Code Division Multiplexing (OFCDM) scheme is illustrated in FIG. 3A. The FFT Precoded OFDM scheme will be referred to as an FFT-S-OFDM (FFT Spread OFDM) scheme as shown in FIG. 3B. In addition, as shown in FIG. 3C, the FFH precoded OFDM scheme will be referred to as a fast frequency hopping-OFDM scheme.

FIG. 4 is a diagram briefly explaining a concept of a general fast frequency hopping (FFH) introduced in FIG. 3A.

Referring to FIG. 4, a fast frequency hopping scheme will be described by comparing the difference between the conventional frequency hopping technique and the fast frequency hopping technique for one OFDM symbol time through an example in which the FFT size M is four.

Block 401 of FIG. 4 shows a multi-carrier modulation apparatus of a frequency hopping scheme of a conventional symbol unit for four OFDM sample times. Also, reference numerals 405 to 408 illustrate a multi-carrier modulation apparatus of the fast frequency hopping technique.

In the existing frequency hopping scheme on the left side of FIG. 4, input data is the same for four OFDM sample times, and output signals are output one at every sample time. Since the conventional frequency hopping scheme is mapped to a fixed subcarrier within one OFDM symbol time, blocks 401 to 404 are the same for four sample times.

However, in the postal fast frequency hopping scheme of FIG. 4, the mapping of subchannel data and actual subcarriers is changed by M to M switches at every sample time. The subcarriers to which the first subchannel of the reference 405 is mapped are [1 4 2 3] and the subcarriers to which the second subchannel of the reference 406 is mapped are [4 3 1 2] and the third subchannel of the reference 407 is mapped. The subcarrier is mapped to [2 1 3 4] and the subcarrier to which the fourth subchannel of reference numeral 408 is mapped is [3 2 4 1]. This mapped method is called a hopping pattern of each subchannel.

As described above, the relative performance of OFDM and Unitary Precoded OFDM (OFDM) shows relatively good performance when the code rate is low. Then, at a very high code rate, that is, a code rate of 4/5, unitary precoded OFDM shows better performance. Despite the above characteristics, there is a problem in the conventional mobile communication system that only one of OFDM or Unitary Precoded OFDM (OFDM) technology is used for the packet data transmission channel.
Accordingly, there is a need to improve the performance of a transceiver using OFDM and unitary precoded OFDM by improving the adaptive multiplexing scheme of an OFDMA communication system.

Therefore, in the present invention, in order to improve the reception performance in transmitting and receiving packet data in an OFDM-based wireless communication system, instead of using only one of OFDM and Unitary Precoded OFDM techniques, both techniques may be applied to a situation. It provides a method and a transmission and reception device adaptively adapted to suit.

Accordingly, according to an embodiment of the present invention, in an orthogonal frequency division multiple access system in which a base station transmits a data packet to a terminal and the terminal performs packet communication in an area of the base station, a data transmission method of the base station is required for scheduling. Collecting information, performing scheduling based on the collected information, comparing a code rate and a threshold value of data to be transmitted to a selected terminal, selecting a suitable multiplexing method according to the comparison result, and selecting the selected multiplexing And transmitting the packet data using the scheme.

In addition, according to an embodiment of the present invention, in an orthogonal frequency division multiple access system in which a base station transmits a data packet to a terminal and the terminal performs packet communication in an area of the base station, a data transmission method of the base station is required for scheduling. Collecting information, performing scheduling based on the collected information, acquiring an effective signal-to-noise ratio (SNR) corresponding to a transport packet of a selected terminal for unitary precoded OFDM and OFDM, respectively; Comparing the effective signal-to-noise ratio for the unitary precoded OFDM with the effective signal-to-noise ratio for the OFDM, selecting a multiplexing scheme suitable for each of the selected terminals according to the comparison result, and using the selected multiplexing scheme And transmitting the data.

In addition, according to an embodiment of the present invention, in an orthogonal frequency division multiple access system in which a base station transmits a data packet to a terminal and the terminal performs packet communication in the area of the base station, the data reception method of the terminal includes: Checking whether the received packet data is received; searching for a multiplexing scheme used for the received packet data; and demultiplexing the received packet data using the found multiplexing scheme. Characterized by including.

In an embodiment of the present invention, in a base station apparatus of an orthogonal frequency division multiple access system, a base station transmits a data packet to a terminal through adaptive data multiplexing, and the terminal performs packet communication in an area of the base station. A unit for converting the modulation symbols to be transmitted in a frequency domain in a frequency domain, a transfer unit capable of performing transfer to the unitary converter, and a control unit for determining whether to transfer the transfer unit according to a multiplexing method; It is characterized by including.

In another aspect of the present invention, in the terminal apparatus of the orthogonal frequency division multiple access system, a base station transmits a data packet to a terminal through adaptive data multiplexing, and the terminal performs packet communication in an area of the base station. And an inverse unit transform unit for performing inverse unit transform on the received modulation symbols in a frequency domain, and a control unit for determining whether to operate the inverse unit transform unit according to a multiplexing scheme.

In addition, in an orthogonal frequency division multiple access system, an embodiment of the present invention collects information necessary for scheduling, performs scheduling based on the collected information, compares a code rate and a threshold value of data to be transmitted to a selected terminal, A base station that selects a suitable multiplexing method according to the comparison result and transmits packet data using the selected multiplexing method; and receives a data packet through adaptive data multiplexing from the base station to perform packet communication in the area of the base station. And a terminal for checking whether the packet data has been received, searching for the multiplexing scheme used for the received packet data if the packet data is received, and demultiplexing the packet data using the found multiplexing scheme. It is characterized by including.

In addition, in an orthogonal frequency division multiple access system, an embodiment of the present invention collects information necessary for scheduling, performs scheduling based on the collected information, and calculates an effective signal-to-noise ratio (SNR) corresponding to a transport packet of a selected terminal. A multiplexing scheme obtained for unitary precoded OFDM and OFDM, respectively, and comparing the effective signal-to-noise ratio for the unitary precoded OFDM and the effective signal-to-noise ratio for the OFDM. And a base station for transmitting packet data using the selected multiplexing scheme, receiving a data packet through adaptive data multiplexing from the base station, performing packet communication in the area of the base station, and receiving the packet data. Check, if the packet data is received the Search for the multiplexing scheme used for the packet data, and characterized in that it comprises a station for demultiplexing the packet data using the searched multiplexing scheme a.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the preferred embodiment of the present invention. Like reference numerals refer to the same elements as shown in the drawings, even though they may be shown on different drawings, and in the following description, detailed descriptions of related well-known functions or constructions are unnecessary. If it is determined that it can be blurred, the detailed description thereof will be omitted. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

Unitary Precoded OFDM is a broad concept that includes OFCDM, FFT-S-OFDM, and FFH-OFDM. 5 to 7 are comparative data between OFDM and OFDCDM, but OFDCDM, FFT-S-OFDM, and FFH-OFDM all have the same characteristics. Accordingly, the attached FIGS. 5 to 7 may be referred to as simulation data between OFDM and unitary precoded OFDM.

The performance of the two multiplexing techniques introduced above, namely OFDM and Unitary Precoded OFDM, is not always superior to the other one, but its relative performance depends on various factors. Among the various causes, the code rate of the transmission data block and the frequency selectivity of the channel may be considered as the main causes of the change in relative performance. Accordingly, the results of comparing OFDM and OFCDM according to code rate and frequency selectivity of the channel will be described with reference to FIGS. 5 through 7.

FIG. 5 is a diagram illustrating a performance comparison result of OFDM and OFCDM (indicated as "MC CDM" in FIGS. 5 to 7) when a code rate of a transport block is 1/4. 4 to 6, "EG" denotes equal gain paths, and "UEG" denotes non-equal gain paths. The X axis of the graph represents a bit energy / total noise (Eb / Nt), and the Y axis represents a packet error rate (PER).

As shown in FIG. 5, when the code rate of the transport block is 1/4, OFDM can perform better performance than OFCDM (MC CDM). In addition, the degree of performance difference can be seen that the frequency selectivity (Frequency Selectivity) is different, that is, the change in the number of paths.

FIG. 6 is a diagram illustrating a performance comparison result of OFDM and OFCDM when a code rate of a transport block is 1/2.
Referring to FIG. 6, the X axis of the graph represents a bit energy / total noise (Eb / Nt), and the Y axis represents a packet error rate (PER). As shown in FIG. 6, when the code rate of the transport block is 1/2, OFDM can perform better performance than OFCDM (MC CDM). In addition, the degree of performance difference can be seen that the frequency selectivity (frequency selectivity) is changed, that is, the change in the number of paths.

Referring to FIG. 7, the X axis of the graph represents a bit energy / total noise (Eb / Nt), and the Y axis represents a packet error rate (PER). As shown in FIG. 7, when the code rate of the transport block is 4/5, OFCDM performs better than OFDM. In addition, the degree of performance difference can be seen that the frequency selectivity (frequency selectivity) is changed, that is, the change in the number of paths.

8 and 9 are diagrams illustrating a method of adaptively selecting a multiplexing scheme based on a predetermined criterion whenever a transmitter transmits a packet data channel in an OFDM based wireless communication system according to a preferred embodiment of the present invention. .

8 and 9 are divided into FIG. 8 or 9 according to a criterion in which a base station adaptively selects a multiplexing scheme in a forward direction, that is, a method for data transmission from a base station to a terminal according to a preferred embodiment of the present invention. First, the method is as follows.

Referring to FIG. 8, in step 801, the scheduler of the packet transmitter collects information necessary for scheduling. Typically, the information required for scheduling may include a quality of service (QoS) level of each user traffic, a current channel state of each user, and a traffic amount of each user to transmit.

In step 802, the scheduler of the packet transmitter collects information necessary for scheduling and then performs scheduling. As a result of the scheduling, it is determined at what time the packet data of which user is to be transmitted at what data rate. One user may be selected according to the system, and several may be selected at the same time. The fact that the data rate described above is determined means that the amount of data is determined for what time period. In addition, in a general mobile communication system, a modulation order (eg, QPSK, 8PSK, 16QAM, etc.), a code rate, etc. are determined together with the data rate for each user.

After the scheduling is determined as described above, in step 803 to 805, a multiplexing scheme to be used for packet data transmission of each selected user is determined. Steps 803 to 805 may be referred to as essential contents of the present invention. In step 803, the transmitter determines whether the code rate of the data packet determined according to the scheduling result is larger or smaller than a predetermined threshold value (hereinafter referred to as "T_r"). The reason for selecting the multiplexing scheme according to the code rate as described above is that the performance of OFDM and Unitary Precoded OFDM (OFDM) is sensitively affected by the code rate. This is as shown in the experimental results of FIGS. 5 to 7. Accordingly, the present invention proposes a method of selecting a multiplexing method based on a threshold of a code rate predetermined in a packet data transmitter.

According to the determination in step 803, if the code rate is not greater than T_r, OFDM is determined in a multiplexing manner as in step 804. In step 805, in the opposite case, unitary precoded OFDM (OFDM) is determined by a multiplexing scheme. Operation 806 represents a process of transmitting packet data according to the multiplexing scheme determined in operations 803 to 805.

FIG. 9 is a diagram illustrating a process of adaptively determining a multiplexing scheme using criteria different from those of FIG. 8 according to a preferred embodiment of the present invention.

Referring to FIG. 9, in step 901, the scheduler of the packet transmitter collects information necessary for scheduling. Typically, the information required for scheduling may include a quality of service (QoS) level of each user traffic, a current channel state of each user, and a traffic amount of each user to transmit.

In step 902, the scheduler of the packet transmitter collects information necessary for scheduling and then performs scheduling. As a result of the scheduling, it is determined at what time the packet data of which user is to be transmitted at what data rate. The selected user may be one or several may be selected at the same time depending on the system. The above means that the data rate is determined, which means that the amount of data is determined for what time. In addition, in the general mobile communication system, modulation order (QPSK, 8PSK, 16QAM, etc.), code rate, etc. are determined together with the data rate for each user.

After the scheduling is determined as described above, in step 903 to 906, a multiplexing scheme to be used for packet data transmission of each selected user is determined. Steps 903 to 906 may be referred to as essential contents of the present invention. Another criterion for determining the adaptive multiplexing method proposed by the present invention is the effective SNR. That is, it is a method of selecting a multiplexing method having a higher effective SNR by considering which value is higher for OFDM and Unitary Precoded OFDM (Unitary Precoded OFDM).

The effective SNR for OFDM is denoted as SNR _eff _OFDM, and the effective SNR for unitary precoded OFDM (Unitary Precoded OFDM) is denoted as SNR _eff _ Unitary. In general, since the wireless channel of each user can be measured by each terminal, the terminal can know the SNR _eff _OFDM and SNR _eff _Unitary. Accordingly, in order for the base station to know the two SNR _eff _OFDM and SNR _eff _Unitary values, there may be a method in which each UE feeds back the SNR _eff _OFDM and SNR _eff _Unitary to the base station. Alternatively, there may be a method in which each UE feeds back only one SNR value but feeds back a preferred multiplexing method together.

In step 903, the base station obtains the SNR _eff _OFDM and SNR _eff _ Unitary values for each UE in the same manner as described above. The following describes how to calculate commonly used SNR _eff _OFDM and SNR _eff _Unitary. But there are other ways.

Equation 1 generally shows a method of obtaining SNR _eff _ Unitary.

Equation 2 generally shows a method of obtaining SNR _eff _OFDM. In Equation 2, N _data represents the number of sub-carriers used to transmit _data in one OFDM symbol. SNR [k] represents the SNR of each sub-carrier. C () represents the AWGN capacity formula and C ^-1 () Denotes the inverse of C ().

Equation 3 typically shows another method of obtaining SNR _eff _OFDM. Β is a constant, N _u represents the total number of subcarriers (sub-carrier) and γ _k represents the SNR of the k-th sub-carrier (Sub-carrier). In step 904, the SNR _eff _OFDM and SNR _eff _ Unitary values are obtained as in step 903, and then the magnitudes of the two values are compared.

In step 906, if the resultant SNR _eff _ Unitary of step 904 is greater than the SNR _eff _ OFDM, the unitary precoded OFDM is selected in a multiplexing manner. Otherwise, OFDM is selected in a multiplexing manner as shown in step 905. In step 907, the packet data is transmitted according to the multiplexing scheme determined as described above.

10 is a diagram illustrating a transmitter structure according to the adaptive multiplexing method of the present invention proposed in FIG. 8 or 9 according to a preferred embodiment of the present invention.

Referring to FIG. 10, a transmitter according to an adaptive multiplexing method includes a channel encoder 1001, a modulator 1002, a unitary converter 1003, a switch 1004, a controller 1005, and a serial-to-parallel conversion. A unit 1006, an IFFT 1007, a parallel-to-serial converter 1008, and a CP inserter 1009.

The channel encoder 1001 receives a predetermined information bit string as an input and performs channel encoding. In general, a coding unit includes a convolutional encoder, a turbo encoder, or a low density parity check (LDPC) encoder. The modulator 702 receives the output of the channel encoder 701 as an input and modulates QPSK, 8PSK, 16QAM, and the like. Although omitted in FIG. 7, it is apparent that a rate matching unit for performing repetition and puncturing may be added between the reference numerals 1001 and 1002.

The switching unit 1004 performs switching by controlling by the control unit 1005 whether to use OFDM or unitary precoded OFDM (Unity Precoded OFDM) in a transmission multiplexing scheme. The controller 1005 controls the transfer unit 1004 through the process of FIG. 8 or 9. If the switching unit 704 is switched to the unit conversion unit 1003 by the controller 1005, the unitary precoder operates. That is, to be transmitted in the OFCDM, FFT-S-OFDM or FFH-OFDM scheme described with reference to FIG. 2.

The unitary conversion unit 1003 is configured as shown in FIG. 3, and the operation thereof is also the same. When the switching unit 1004 is directly switched to the serial-to-parallel converter 1006 by the controller 1005, the transmitter does not operate the unitary converter 1003.

The serial-to-parallel converter 1006 serves to make a serially input signal in parallel. IFFT 1007 receives the output of the serial-to-parallel converter 1006 and performs an IFFT operation. The parallel-to-serial converter 1008 converts the parallel output of the IFFT 1007 to serial. The CP inserter 1009 adds a cyclic prefix to the output signal of the parallel-to-serial converter 1008.

On the other hand, although not shown in Figure 10, the size of the matrix corresponding to the unitary converter 1003 is variable according to the given size of the output of the serial-to-history converter 1006. Also, as the size of the matrix is variable, a plurality of unitary precoders may be used. However, the transmitter does not necessarily need to be configured with a plurality of unitary precoders, and a plurality of operations may be performed with one precoder.

For example, assuming that the size of the output of the serial to troop converter 1006 is 16 (which means that the number of subcarriers allocated to the transmitter is 16), this is an input of the serial to troop converter 1006. Means that the size is 16. In this case, the size of the precoder matrix of the unitary conversion unit 1003 may be 16, two 8-digits (or two calculations one by one), four four-digits (or four calculations by one). May be used, or two two (or eight) operations may be used.

On the other hand, the method proposed in the present invention is not necessarily limited to only forward transmission. It may be similarly used for reverse transmission, that is, data transmission from the terminal to the base station. However, as in most systems, since the scheduling is a base station, as shown in FIG. 8 or 9, the scheduling is directly performed, and the terminal receives scheduling information from the base station in the reverse direction instead of applying an adaptive multiplexing method. Thereafter, it can be seen that the UE is slightly different from the method of adaptively selecting the multiplexing method according to the same criteria as described above when the UE is allowed to transmit data.

11 is a diagram illustrating a method for a receiver to receive a packet according to the adaptive multiplexing technique proposed by the present invention according to a preferred embodiment of the present invention.

Although FIG. 11 is described with reference to forward packet transmission (based on transmitting a packet from a base station to a terminal), it should be noted that the proposed method may be similarly used for reverse packet transmission.

Referring to FIG. 11, in step 1101, each terminal continuously checks whether its own packet has been received. Step 1101 is the same as the operation in the conventional packet data system. That is, it is a process of determining whether the packet allocated to itself is being transmitted while continuously monitoring the packet data control channel transmitted in the forward direction.

In step 1102, if it is determined in step 1101 that its own packet is received, the terminal performs a receiving process of a packet data channel. At this time, the UE should search which of the multiplexing methods used for the packet transmission (either OFDM or Unitary Precoded OFDM).

Two methods are possible to achieve step 1102 above. First, there is a method in which the base station informs the terminal of the multiplexing scheme used through the packet data control channel.

As another method, there may be a method of promising between the transceivers in advance which multiplexing scheme is used based on a specific code rate. In this case, if only the code rate information is known, the receiver may know which multiplexing scheme has been transmitted by the transmitter. For example, a method that promises to use OFDM below 1/2 Code Rate and OFCDM above.

Step 1103 is a process of demodulating the packet data channel transmitted thereto according to the multiplexing method found in step 1102.

12 illustrates a receiver structure according to a preferred embodiment of the present invention.

Referring to FIG. 12, the CP remover 1201, the serial-to-parallel converter 1202, the fast Fourier transform (hereinafter referred to as “FFT”) 1203, and the parallel-to-serial converter 1204. ), An inverse unit converter 1205, a controller 1206, a demodulator 1207, and a channel decoder 1208.

The CP remover 1201 removes the CP from the received signal. The received signal from which the CP has been removed is converted into a parallel signal by the serial-to-parallel converter 1202 and then input to the FFT 1203. The output of the FFT 1203 is converted into a serial signal by the parallel to series converter 1204. The inverse unit transform unit 1205 is a block that performs inverse unit transform. The inverse unitary transformer 1205 determines whether to operate the inverse unitary transformer or to pass through the inverse unitary transformer under the control of the controller 1206. The output of the inverse unit converter 1205 is input to a demodulator 1207. The output of the demodulator 1207 is input to the channel decoder 1208, and the final information is obtained through a channel decoding process.

On the other hand, although not shown in FIG. 12, the size of the matrix corresponding to the inverse unit transformer 1205 is variable according to a given size of the output of the parallel-to-serial converter 1204, as described with reference to FIG. As the size of the matrix is variable, a plurality of unitary precoders may be used. However, the receiver does not necessarily need to be configured with a plurality of unitary precoders, and a plurality of operations may be performed with one precoder. For example, assuming that the size of the output of the parallel-to-serial converter 1204 is 16, 16 may be used as the size of the precoder matrix of the inverse unitary converter 1205, or two 8-byte (or One operation twice), four four (or four times one) may be used, and eight two (or eight times one) may be used.

The adaptive multiplexing method proposed by the present invention can be usefully used even in a system using HARQ. In general, packet transmission in a system using a hybrid automatic repeat request (HARQ) is often a high code rate for the initial transmission. Therefore, in the case of retransmission using unitary precoded OFDM (Unitary Precoded OFDM) during initial transmission according to the rule proposed by the present invention, the reception performance can be effectively increased by using OFDM. In addition, the rule for determining the multiplexing may be used by adaptively changing the multiplexing scheme in the initial transmission and retransmission according to the effective SNR instead of the code rate as described above.

Meanwhile, in order to simplify the HARQ operation, once the multiplexing scheme is determined based on the code rate or the effective SNR in the initial transmission, a method of using the same scheme as the multiplexing scheme in the initial transmission may be used when retransmitting. As described above, in the HARQ, the adaptive multiplexing method proposed by the present invention can be used, and in other applications, the multiplexing method can be used based on two criteria proposed by the present invention, that is, a code rate or an effective SNR. Obviously, the decision can be made selectively to increase the reception performance of packet transmission.

The present invention has been described in detail so far, but the embodiments mentioned in the process are merely illustrative and are not intended to be limiting, and the present invention is not limited to the technical spirit of the present invention provided by the following claims. Within the scope of not departing from the field, component changes to the extent that can be replaced evenly from the present invention will fall within the scope of the present invention.

In the present invention operating as described in detail above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

The present invention improves the adaptive multiplexing scheme of an OFDMA communication system to improve the performance of a transceiver using OFDM and unitary precoded OFDM, thereby improving transmission and reception performance of wireless packet data transmission.

Claims (14)

In the orthogonal frequency division multiple access system in which a base station transmits a data packet to a terminal and the terminal performs packet communication in the area of the base station, in the data transmission method of the base station, Collecting information necessary for scheduling and performing scheduling through the collected information; Comparing a code rate and a threshold of data to be transmitted to a selected terminal, and selecting a multiplexing method according to the comparison result; And transmitting the packet data using the selected multiplexing scheme. The method of claim 1, wherein the multiplexing scheme is And when the code rate of the data to be transmitted is smaller than the threshold, the unitary precoded OFDM scheme is selected. If the code rate of the data to be transmitted is larger than the threshold, the OFDM scheme is selected. In the orthogonal frequency division multiple access system in which a base station transmits a data packet to a terminal and the terminal performs packet communication in the area of the base station, in the data transmission method of the base station, Collecting information necessary for scheduling and performing scheduling through the collected information; Acquiring an effective signal-to-noise ratio (SNR) corresponding to the transport packet of the selected terminal for unitary precoded OFDM and OFDM, respectively; Comparing the effective signal-to-noise ratio for the unitary precoded OFDM with the effective signal-to-noise ratio for the OFDM, and selecting a multiplexing scheme for each of the selected terminals according to the comparison result; Transmitting packet data using the selected multiplexing scheme. The method of claim 3, wherein the multiplexing scheme, If the effective signal-to-noise ratio for the unitary precoded OFDM is greater than the effective signal-to-noise ratio for the OFDM, the unitary precoded OFDM scheme is selected, and the effective signal-to-noise ratio for the OFDM is less than the effective signal-to-noise ratio for the OFDM. If it is selected by the OFDM scheme. In an orthogonal frequency division multiple access system in which a base station transmits a data packet to a terminal and the terminal performs packet communication in the area of the base station, in the method of receiving data of the terminal, Checking whether packet data has been received, If the packet data is received, searching for a multiplexing scheme used for the received packet data; Demultiplexing the received packet data using the searched multiplexing scheme. The method of claim 5, wherein the multiplexing scheme, And at least one of unitary precoded OFDM and OFDM. In the base station apparatus of the orthogonal frequency division multiple access system for transmitting a data packet to the terminal through the adaptive data multiplexing and the terminal performs packet communication in the area of the base station, A unitary converter for performing unitary transform on the modulation symbols to be transmitted in the frequency domain; A transfer unit capable of performing transfer to the unitary conversion unit; And a control unit for determining whether to perform the switching unit according to a multiplexing method. The method of claim 7, wherein the multiplexing scheme, A base station apparatus comprising at least one of unitary precoded OFDM or OFDM. In the terminal apparatus of the orthogonal frequency division multiple access system for transmitting a data packet to the terminal through the adaptive data multiplexing and the terminal performs packet communication in the area of the base station, An inverse unit transform unit for performing inverse unit transform on the received modulation symbols in a frequency domain; And a controller configured to determine whether to operate the inverse unit converter according to a multiplexing method. The method of claim 9, wherein the multiplexing scheme, And at least one of unitary precoded OFDM and OFDM. In the orthogonal frequency division multiple access system, Collect information necessary for scheduling, perform scheduling through the collected information, compare the code rate and the threshold value of the data to be transmitted to the selected terminal, select a multiplexing method according to the comparison result, and use the selected multiplexing method A base station for transmitting packet data Receives data packets from the base station through adaptive data multiplexing to perform packet communication in the area of the base station, confirms whether packet data has been received, and is used for the received packet data if received. And a terminal for searching for a multiplexing scheme and demultiplexing the packet data using the searched multiplexing scheme. The method of claim 11, wherein the multiplexing scheme, Orthogonal precoded OFDM if the code rate of the data to be transmitted is smaller than the threshold, and select OFDM if the code rate of the data to be transmitted is greater than the threshold. In the orthogonal frequency division multiple access system, Collecting information necessary for scheduling and performing scheduling through the collected information, and obtaining an effective signal-to-noise ratio (SNR) corresponding to a transport packet of a selected terminal for unitary precoded OFDM and OFDM, respectively, A base station for comparing the effective signal-to-noise ratio for pre-coded OFDM with the effective signal-to-noise ratio for OFDM, selecting a multiplexing scheme for each of the selected terminals according to the comparison result, and transmitting packet data using the selected multiplexing scheme; , Receives data packets from the base station through adaptive data multiplexing to perform packet communication in the area of the base station, confirms whether packet data has been received, and is used for the received packet data if received. And a terminal for searching for a multiplexing scheme and demultiplexing the packet data using the searched multiplexing scheme. The method of claim 13, wherein the multiplexing scheme, If the effective signal-to-noise ratio for the unitary precoded OFDM is greater than the effective signal-to-noise ratio for OFDM, the unitary precoded OFDM is selected. Orthogonal frequency division multiple access system, characterized in that the selected.

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