KR20050120964A - Apparatus and method for diversity reception using cyclic shift offset - Google Patents

Abstract

The present invention relates to a communication system using Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA). In particular, the present invention relates to an OFDM signal broadcast for a broadcast service. An apparatus and method are provided for obtaining diversity gain. According to the present invention, a diversity gain is obtained at a cell boundary region by applying different cyclic delay offsets for a specific base station, sector, or antenna for a broadcast service in a wireless communication system using an orthogonal frequency division multiplexing scheme.

Description

Diversity Implementation Apparatus and Method Using Cyclic Delay Offset {APPARATUS AND METHOD FOR DIVERSITY RECEPTION USING CYCLIC SHIFT OFFSET}

The present invention uses Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA). The present invention relates to a communication system (hereinafter referred to as an "OFDMA communication system"), and more particularly, to an apparatus and a method for obtaining diversity gain through an broadcast OFDM signal.

Since the cellular cellular mobile telecommunication system was developed in the United States in the late 1970s, AMPS (Advanced Mobile Phone Service), which can be called an analog 1G (1st generation) mobile communication system in Korea, Began to provide voice communication services.

Later, as a 2nd generation (2G) mobile communication system in the mid-1990s, a code division multiple access (CDMA) system was commercialized to provide voice and low-speed data services. Provided.

In addition, the International Mobile Telecommunication-2000 (IMT-2000), a 3rd generation (3G) mobile communication system that has been launched since the late 1990s, aims for improved wireless multimedia services, global roaming, and high-speed data services. Some commercialized services are in operation. In particular, the third generation mobile communication system has been developed to transmit data at higher speed as the amount of data serviced by the mobile communication system increases rapidly.

In addition, it is currently developing from a 3rd generation mobile communication system to a 4th generation (4G) mobile communication system. The 4G mobile communication system is not just a wireless communication service like the previous generation mobile communication systems, but has been standardized for efficient interworking and integration services between a wired communication network and a wireless communication network. Therefore, there is a demand for a technology for transmitting a large amount of data close to the capacity of a wired communication network in a wireless communication network.

Therefore, the fourth generation mobile communication system is actively studying the OFDM scheme as a method useful for high-speed data transmission in wired and wireless channels. The OFDM method is a method of transmitting data using a multi-carrier, and a plurality of sub-carriers having mutual orthogonality to each other by converting symbol strings serially input in parallel. ), That is, a type of multi-carrier modulation (MCM) that modulates and transmits a plurality of sub-carrier channels.

Accordingly, orthogonal frequency division multiplexing (OFDM) has excellent performance in multipath and mobile reception environments. For this reason, attention has been paid to modulation methods suitable for terrestrial digital TV and digital voice broadcasting. Although OFDM has been mainly researched in the communication field, research and development has been conducted in the broadcasting field as it is adopted as a modulation method of the digital voice broadcasting system proposed by the European Broadcasting Union (EBU).

The transmission signal of OFDM is a sum of a number of digital modulation waves. As a modulation method of each carrier, a multi-value modulation method such as QPSK for voice broadcasting and 64QAM, which has excellent band utilization efficiency for terrestrial digital TV broadcasting, is well used. Data transmission by OFDM is performed in units of transmission symbols. Each transmission symbol is composed of a valid symbol interval and a guard interval. The guard interval is a signal interval to reduce the effects of multipath (ghost).

 Comparing OFDM with a single carrier scheme in which transmission bandwidth and bit rate are constant, when transmitting data spread over NC carriers, the duration of one transmission symbol is approximately NC times that of a single carrier scheme. As described above, when the duration of one transmission symbol is significantly longer than that of the single carrier, and a guard interval is added on the time axis, transmission characteristics are less deteriorated even if the multipath (ghost) is increased.

 Since OFDM transmits data spread over the entire transmission band, even if an interference signal exists in a specific frequency band, the influence is limited to some data bits, and the interleaving and error correction codes can effectively improve characteristics. In addition, since the multipath has a strong characteristic, it is possible to construct a single frequency network (SFN) covering a service area with a single frequency by using a plurality of relatively small power transmission stations.

In addition, since OFDM is a multicarrier system in which carriers are aligned at the same frequency interval, nonlinear characteristics exist in a transmission path, and characteristic degradation due to intermodulation is likely to occur. Therefore, it needs to be used in a sufficient linear region. In addition, OFDM has a feature that modulation and demodulation processing by FFT (Fast Fourier Transform) is possible.

The OFDM scheme is a type of multicarrier transmission using multiple carriers, and the transmission period in each channel is increased by the number of carriers. In this case, the frequency selective channel appearing in the wideband transmission is approximated as a frequency non-selective channel without intersymbol interference, so a simple single tap equalizer can compensate.

On the other hand, a system using a multicarrier modulation scheme was first applied to military HF radios in the late 1950s, and the OFDM scheme of overlapping a plurality of orthogonal subcarriers began to develop in the 1970s, but the implementation of orthogonal modulation between multicarriers Since this was a difficult problem, there were limits to the practical application of the system. However, in 1971, Weinstein et al. Announced that modulation and demodulation using the OFDM scheme can be efficiently processed using the Discrete Fourier Transform (DFT).

In addition, the use of guard intervals and the insertion of cyclic prefix guard intervals are known to further reduce the negative effects of the system on multipath and delay spread.

The transmission of OFDM symbols is performed in symbol units, but is affected by previous symbols while OFDM symbols are transmitted through a multipath channel. In order to prevent such OFDM intersymbol interference, a guard interval longer than the maximum delay spread of a channel is inserted between consecutive symbols.

OFDM symbol period ( ) Is the effective symbol period ( ) And the protection interval, and the receiver performs the demodulation by removing the protection interval and taking data during the valid symbol period. In the guard interval, the last interval in the effective symbol interval (to prevent the destruction of orthogonality which may be caused by the delay of subcarriers) ) Is copied and inserted into the signal, which is called a cyclic prefix (CP).

With the insertion of CP, the bandwidth efficiency is ( ) / ( + In this case, the signal-to-noise ratio loss occurs. The length of the effective symbol interval is set so that the signal-to-noise ratio loss due to the insertion of CP is 1% or less. In addition, inter-symbol interference (ISI) and inter-channel interference (ICI) are interposed between adjacent OFDM symbols by inserting a CP longer than a delay spread into a guard interval. Easy to remove

On the other hand, the OFDM technology is a digital audio broadcast (DAB), digital television, digital local area network (WLAN: Wireless Local Area Network (WLAN) and wireless asynchronous transfer mode (WATM) such as digital It is widely applied to transmission technology. In other words, due to the hardware complexity, it is not widely used, but is recently called a Fast Fourier Transform (FFT) and an Inverse Fast Fourier Transform (IFFT). Various digital signal processing technologies, including "IFFT", have been developed and realized.

The OFDM scheme is similar to the conventional Frequency Division Multiplexing (FDM) scheme, but most of all, an optimal transmission efficiency can be obtained in high-speed data transmission by maintaining orthogonality between a plurality of subcarriers. Has the characteristics. In addition, the frequency use efficiency is good and the characteristics of the multipath fading (multipath fading) has the characteristics that can be obtained optimal transmission efficiency in high-speed data transmission.

In addition, because the frequency spectrum is superimposed, frequency use is efficient, strong for frequency selective fading, multipath fading, and protection intervals to reduce the influence of Inter Symbol Interference (ISI). It is possible to design the equalizer structure simply by hardware, and has the advantage of being strong against impulsive noise, and it is being actively used in the communication system structure.

Meanwhile, the multiple access scheme based on the OFDM scheme is the OFDMA scheme. The OFDMA method is a method in which sub-carriers in one OFDM symbol are divided and used by a plurality of users, that is, a plurality of terminals. That's the way. The advantage of OFDMA is that it can provide a variety of frequencies and times to meet the needs of the user. For this reason, the OFDMA scheme can provide various QoS. In addition, OFDMA allocates subchannels of OFDM adaptively according to user's channel environment to maximize capacity and can be used simultaneously with TDMA.

As the communication system using the OFDMA scheme, there is an IEEE 802.16a communication system and an IEEE 802.16e communication system. Here, the IEEE 802.16a communication system is a fixed broadband wireless access (BWA) communication system using the OFDMA scheme. In addition, the IEEE 802.16e communication system is a system that considers the mobility of the terminal in the IEEE 802.16a communication system, the current IEEE 802.16a communication system and IEEE 802.16e communication system 2048-point (2048-point) inverse fast Fourier transform ( IFFT: Inver se Fast Fourier Transform (hereinafter referred to as “IFFT”) is used, and 1702 subcarriers are used.

The IEEE 802.16a communication system and the IEEE 802.16e communication system use 166 subcarriers of the 1702 subcarriers as pilot subcarriers, and 1536 subcarriers except the 166 subcarriers are data. (data) Use as subcarriers. In addition, the 1536 data subcarriers are classified into 48 groups to generate 32 sub-channels, and the sub channels are allocated to a plurality of users according to a system situation.

Here, the sub-channel refers to a channel composed of a plurality of subcarriers, where 48 subcarriers constitute one subchannel. In this case, two communication systems may be considered according to a method of configuring a subchannel.

Firstly, the OFDMA communication system is a communication system aiming to obtain frequency diversity gain by distributing all subcarriers, particularly data subcarriers used in a subchannel, over the entire frequency band. to be. Secondly, the OFDMA communication system is a communication system in which all subcarriers used in a subchannel, in particular data subcarriers, are configured as adjacent subcarriers in a frequency band.

1 is a diagram illustrating the concept of an OFDMA communication system. Referring to FIG. 1, an area in which three adjacent base stations have similar distances may cause a channel from each base station to be a single path, and each path arrives within a time difference of a sample unit. When the terminal receives the broadcast signal in such an area, only the average SNR value is increased and the diversity gain cannot be obtained. For convenience, this area is referred to as a diversity deficiency area.

2 is a view schematically showing the structure of a transmitter according to the prior art. Referring to FIG. 2, first, the transmitter of the OFDMA communication system includes a CRC inserter checker 111, an encoder 113, a symbol mapper 115, and a subchannel. Sub-channel allocator (117), serial to parallel converter (119), pilot symbol inserter (121), inverse fast Fourier transform (IFFT) (Hereinafter referred to as "IFFT") 123, parallel to serial converter 125, guard interval inserter 127, digital to analog converter to analog converter (129), and a radio frequency (RF) processor (131).

First, when user data bits and control data bits to be transmitted are generated, the user data bits and the control data bits are input to the CRC inserter 111. Here, the user data bits and the control data bits will be referred to as "information data bits". The CRC inserter 111 inputs the information data bit, inserts the CRC bit, and outputs the CRC bit to the encoder 113. The encoder 113 inputs the signal output from the CRC inserter 111, codes the signal by using a preset coding scheme, and outputs the encoded signal to the symbol mapper 115. Here, the coding scheme may be a turbo coding scheme or a convolutional coding scheme having a predetermined coding rate.

The symbol mapper 115 modulates the coded bits output from the encoder 113 by using a preset modulation scheme to generate a modulated symbol and outputs the modulated symbols to the subchannel allocator 117. do. Here, the modulation scheme may be a Quadrature Phase Shift Keying (QPSK) scheme or a Quadrature Amplitude Modulation (16QAM) scheme.

Quadrature Phase Shift Keying (QPSK) is a type of phase shift modulation (PSK) that transmits two (0 or 1) transmission signals to be transmitted with the zero phase of the carrier. Unlike binary phase shift modulation (BPSK: binary PSK), which transmits corresponding to the two phases of the phase, it collects two bits of 0 and 1 of the digital signal of two values and transmits them by matching the four phases of the carrier. Say the way.

I.e. (0, 0) at zero phase, (0, 1), in / 2 phase (1, 0), 3 in phase Transmit by matching (1, 1) to the / 2 phase. Unlike binary phase shift modulation, which takes a phase change of a carrier at intervals of 90 degrees and transmits one bit with one symbol, it transmits two bits with one symbol. Quadrature phase shift modulation is also referred to as quadrature PSK.

The four phase shift key can transmit twice the information in the same frequency bandwidth as the two phase shift key. Satellite broadcasting is widely used in the transmission of voice signals and satellite communications.

Quadrature Amplitude Modulation (QAM) is a multi-level modulation method, which is a kind of digital modulation, and uses a combination of both amplitude and phase of a modulated carrier. Analog telephone lines are widely used as high-speed modulators for digital transmission. For example, if the amplitude of 4 values and the phase of 4 values can be determined for each wave to be modulated, 16 information can be transmitted.

For this reason, when the carrier wave is set to 2400Hz, 9600bps transmission is possible. To accurately determine the 16 value at the receiving end, it is necessary to restore the degraded characteristics on the telephone line. This is called automatic equalization. In recent years, automatic equalization technology has been developed, and high-speed modulators such as multi-valued 32-value QAM and 64-value QAM have emerged.

Meanwhile, the sub channel allocator 117 inputs modulation symbols output from the symbol mapper 115 to allocate a sub channel and outputs the sub channel to the serial / parallel converter 119. The serial / parallel converter 119 inputs the serial modulation symbols to which the sub-channels output from the sub-channel allocator 117 are allocated, converts them in parallel, and then outputs them to the pilot symbol inserter 121. The pilot symbol inserter 121 inserts pilot symbols into the parallel-converted modulated symbols output from the serial / parallel converter 119 and outputs the pilot symbols to the IFFT unit 123.

The IFFT unit 123 inputs the signal output from the pilot symbol inserter 121 to perform an N-point IFFT and then outputs it to the parallel / serial converter 125. The parallel / serial converter 125 inputs the signal output from the IFFT device 123, converts the signal in series, and outputs the serial signal to the guard interval inserter 127. The guard interval inserter 127 inputs a signal output from the parallel / serial converter 125 to insert a guard interval signal and then outputs the guard interval signal to the digital / analog converter 129.

Here, the guard interval is inserted to remove interference between the OFDM symbol transmitted at the previous OFDM symbol time and the current OFDM symbol transmitted at the current OFDM symbol time when the OFDM symbol is transmitted in the OFDMA communication system. In addition, the guard interval has been proposed in the form of inserting null data of a predetermined interval, but in the form of transmitting null data in the guard interval is the interference between subcarriers when the receiver incorrectly estimates the start point of the OFDM symbol There has been a disadvantage in that the probability of misjudgment of the received OFDM symbol increases.

Therefore, the "cyclic prefix" scheme in which the last predetermined bits of the OFDM symbol in the time domain are copied and inserted into the effective OFDM symbol or the first predetermined bits of the OFDM symbol in the time domain is copied to the valid OFDM symbol. The insert "Cyclic Postfix" method is used.

The digital-to-analog converter 129 inputs the signal output from the guard interval inserter 127 and performs analog conversion, and then outputs the signal to the RF processor 131. The RF processor 131 may include components such as a filter and a front end unit, and may transmit a signal output from the digital-to-analog converter 129 on an actual air. After the RF process, the transmission is performed on the air through a Tx antenna.

In case of broadcasting service in the communication system based on the OFDMA technology, the time delay of the broadcast signal from the neighboring base station or the neighboring sector is within the guard time and the delay of the broadcast signal from the neighboring base station or the neighboring sector due to the multipath combining capability which is a unique feature of the OFDM modulation scheme. Diversity gain is obtained when the time difference is greater than or equal to the sample interval, which is the inverse of the channel bandwidth. However, in the prior art, as shown in FIG. 1, in the cell boundary region, there is an area where a time delay path difference from an adjacent base station or an adjacent sector is within a sample interval, that is, a diversity deficiency area. There is a problem that there is no probabilistic diversity gain but only an increase in the average reception level.

An object of the present invention is to provide diversity gain in a cell boundary region by applying a different cyclic delay offset to a transmission signal of each base station in a communication system based on OFDM / OFDMA technology.

Another object of the present invention is to provide diversity gain in a sector boundary region by applying different cyclic delay offsets to transmission signals of each sector of the same base station in a communication system based on OFDM / OFDMA technology.

Another object of the present invention is to divide a section for a packet service and a section for a broadcast service in one frame structure in an OFDM / OFDMA communication system, and to protect the coverage of each service in order to vary coverage of each service. It is to control the coverage of each service by setting different protection periods of symbols for packet service and packet service differently.

In order to achieve the above object, an embodiment of the present invention provides a data transmission apparatus for implementing broadcast diversity of a mobile terminal in a diversity deficient region, and converts transmission data into a data sequence of a time domain by performing inverse fast Fourier transform. Inverse fast Fourier transformer; A cyclic delay unit for setting a separate cyclic delay time according to a base station for the data sequence of the time domain transformed by the inverse fast Fourier transformer and generating a delay signal according to a given cyclic delay time; And a guard interval inserter for inserting a guard interval with respect to the delay signal generated from the cyclic delay unit.

In one embodiment of the present invention, the cyclic delay unit comprises a cyclic delay unit for setting a separate cyclic delay time according to the base station for the data sequence of the time domain transformed by the inverse fast Fourier transformer; And a cyclic delay offset controller for generating a delay signal according to the cyclic delay time.

In one embodiment of the present invention, the protective section is characterized in that consisting of a cyclic prefix. In one embodiment of the present invention, the base station is characterized in that for transmitting the cyclic delay by the cyclic delay time previously given separately for each base station for the same broadcast data. In one embodiment of the present invention, the data is characterized in that the data further comprises packet service data.

In one embodiment of the present invention, the data is characterized by distinguishing the packet service data from the broadcast service data by performing a cyclic delay. In one embodiment of the present invention, the cyclic delay is characterized in that it is performed differently for each base station. In one embodiment of the present invention, the base station is any one of a plurality of cells in the base station.

Another embodiment of the present invention provides a data transmission apparatus for implementing broadcast diversity of a mobile terminal in a diversity lacking region, comprising: a modulator for modulating transmission data; A cyclic delay unit for setting a separate cyclic delay time according to a base station for the data in the frequency domain converted by the modulator, and generating a delay signal according to the cyclic delay time; And an inverse Fourier transformer for performing inverse Fourier transform on the delay signal generated from the cyclic delay unit.

In another embodiment of the present invention, the cyclic delay unit may include: a cyclic delay unit for setting a separate cyclic delay time according to a base station with respect to a data sequence of a time domain converted by the inverse fast Fourier transformer; And a cyclic delay offset controller for generating a delay signal according to the cyclic delay time. In another embodiment of the present invention, the base station transmits the same broadcast data by performing a shift offset according to a predetermined cyclic delay time for each base station.

In another embodiment of the present invention, the data is characterized in that the data further comprises packet service data. In another embodiment of the present invention, the data is characterized by distinguishing the packet service data from the broadcast service data by performing a shift offset. In another embodiment of the present invention, the shift offset may be performed differently for each base station. In another embodiment of the present invention, the base station is any one of a plurality of cells in the base station.

Another embodiment of the present invention provides a broadcast data transmission method for implementing broadcast data reception diversity of a mobile station in a diversity lacking region, the method comprising: mapping modulation symbols to be transmitted to a subcarrier; Converting modulation symbols mapped to subcarriers into inverse fast Fourier transform into a data sequence of a time domain; And performing a cyclic delay according to a cyclic delay time previously assigned to each base station for each data sequence in the time domain.

In another embodiment of the present invention, the data is transmitted with a cyclic prefix as a guard interval. In another embodiment of the present invention, the base station transmits the same broadcast data by performing a cyclic delay according to a predetermined cyclic delay time for each base station. In another embodiment of the present invention, the data is characterized in that the data further comprises packet service data. In another embodiment of the present invention, the data is characterized by distinguishing the packet service data from the broadcast service data by performing a cyclic delay. In another embodiment of the present invention, the cyclic delay is characterized in that it is performed differently for each base station. In another embodiment of the present invention, the base station is any one of a plurality of cells in the base station.

According to another embodiment of the present invention, in a broadcast data transmission method for implementing broadcast data reception diversity of a mobile station in a diversity lacking region, phases of modulation symbols of a frequency domain by a predetermined shift offset are individually given to each base station. Performing a transition; And performing inverse fast Fourier transform on the modulation symbols on which the phase shift has been performed, and then performing data transmission through a transmission antenna.

In another embodiment of the present invention, the data is transmitted with a cyclic prefix as a guard interval. In another embodiment of the present invention, the base station transmits the same broadcast data by performing a phase shift based on a shift offset previously given for each base station individually.

In another embodiment of the present invention, the data is characterized in that the data further comprises packet service data. In another embodiment of the present invention, the data is characterized by distinguishing the packet service data and the broadcast service data by a shift offset. In another embodiment of the present invention, the shift offset is characterized in that it is performed differently for each base station. In another embodiment of the present invention, the base station is any one of a plurality of cells in the base station.

DETAILED DESCRIPTION A detailed description of preferred embodiments of the present invention will now be described with reference to the accompanying drawings. In addition, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

The present invention uses Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA). Note that the present invention relates to a communication system to be used (hereinafter referred to as an "OFDMA communication system"), which will be described below in terms of an orthogonal frequency division multiple access (OFDMA) scheme.

As described above, OFDMA is a multi-user access scheme for dividing frequency and time to a user. The present invention provides a data transmission / reception apparatus for generating a transmission signal for each base station for obtaining diversity gain in a cell boundary region in an OFDMA communication system. Provide a method. To this end, the present invention generates a transmission signal by assigning different cyclic delay offset (Cyclic Delay Offset) for each cell / sector in the transmitter in the OFDMA communication system. In the diversity deficiency area, when the terminal receives a broadcast signal, only the average SNR value is increased and diversity gain cannot be obtained. Therefore, in the present invention, a cyclic delay offset is given to each base station so that the diversity lacking region obtains a diversity effect, so that a cell having a high average reception SNR in a cell boundary region having a low average signal-to-noise ratio (SNR) The effect of moving toward the central area is to improve the quality of service in the cell boundary area. In this case, the base station may serve and manage one cell, and may serve and manage a plurality of cells, but for convenience of description, it is assumed that one base station manages only one cell.

Hereinafter, the method of implementing the cyclic delay offset and the operation of the receiver will be described.

First, the transmitter structure of the communication system according to the present invention will be described with reference to FIG. 3. Prior to description, FIG. 3 illustrates a conventional transmitter structure in which a cyclic delay unit 126.A and a cyclic delay offset controller 126.B are inserted between the parallel / serial converter 125 and the guard interval 127 in FIG. It shows form. For convenience, only parts to which the present invention is applied are shown, and operations of other parts have been described with reference to FIG.

In FIG. 3, the cyclic delay 126.A and the cyclic delay offset controller 126.B show an embodiment implemented in the time domain, and the cyclic delay 126.A and the cyclic delay offset controller 126. B) is characterized in that it is disposed before the guard interval inserter (127). At this time, the operation of the cyclic delay unit 126.A and the cyclic delay offset controller 126.B is expressed by Equation 1 below.

Where f _c is the carrier frequency, _δ f is the subcarrier interval, T _g is the guard time, T _s is the total OFDM symbol interval plus guard time and transmission time T _b , τ is the cyclic delay time, and C _k is the subcarrier It means a modulated signal such as QPSK or 16QAM transmitted. In other words, the cyclic delay 126.A generates a delay signal equal to the shift offset given by the cyclic delay controller 126.B, that is, the cyclic delay time τ. It should be noted that τ, which is a cyclic delay time by the cyclic delay offset controller 126.B, is given differently for each base station. In this case, all of the transmitted data are transmitted by the same broadcast data by the base stations.

That is, the present invention performs a cyclic delay according to Equation 1 by the cyclic delay controller 126.B for the same broadcast data transmitted by the base stations, and then generated by the cyclic delay 126.A. The delay signal is characterized in that for transmitting.

Unlike the cyclic delay 126.A and the cyclic delay offset controller 126.B of FIG. 3, which is an embodiment implemented in the time domain, the phase change is implemented by the cyclic delay and the cyclic delay offset controller in the frequency domain. This is possible.

In the frequency domain, the present invention changes the phase of the subcarrier in proportion to the subcarrier index k by placing the cyclic delay unit 126.A and the cyclic delay offset controller 126.B before the IFFT unit 123. Can be. Equation 2 is the same as Equation 1, and represents the above operation in the frequency domain.

In this case, the operations of the cyclic delay unit 126.A and the cyclic delay offset controller 126.B are as described above, and are transmitted after the phase shift according to the shift offset value occurs.

FIG. 4 is a diagram illustrating a transmission signal to which different cyclic delay offsets are applied according to an embodiment of the present invention on a time axis. FIG. 4 illustrates a result of applying a cyclic delay of τ before inserting a guard interval according to a base station / cell number. The carrier is shown. Each base station having a cyclic delay and a cyclic delay offset controller according to the present invention will generate a cyclically delayed signal of τ ₁ and τ ₂ as shown.

By applying the cyclic delay as described above from the individual base station, the received signal of the user in the cell boundary region seems to have gone through multiple paths, and thus diversity gain can be obtained. Analytically, these gains are as follows.

In the diversity lacking region of FIG. 1, the arrival time from each base station is equal to t _o , and each channel is assumed to be a single path attenuation channel. In the case of a broadcast signal, the modulated signal C _k for each base station is the same. Therefore, if the channel viewed by the receiver is larger than the inverse of the system bandwidth, the values of τ ₁ and τ ₂ -τ ₁ in Equation 3 are separated from each other. As you can, you get diversity gain.

That is, a convolution sum that describes a physical channel in physical processing at the same time but reaches the same point in time. 'Circular Convolution,' a feature of OFDM using IFFT / FFT and guard time. Is replaced by '). Accordingly, as shown in the terminal FFT window of FIG. 4, the receiver operates as if the physical channel is multipath, which is a result according to Equation (3). Here, the received signal r (t) is a signal s ₀ , s ₁ , s ₂ transmitted by cyclically delaying the same signal s (t) for each adjacent base station or sector by cyclic delay offset values 0, τ ₁ , τ ₂ , respectively. Path channel characteristics h ₀ , h ₁ , and h ₂ of the transmitted signals are added to each other after convolution. As can be seen from the result of the equation, it can be shown that the physical channel is multipath for the same signal s.

In the base station allocation of the cyclic delay offset according to the present invention, the cyclic delay offset τ value is for enhancing the diversity effect in the cell overlap region and does not require a large number of offsets. Depending on the configuration of the system, you can create a certain number of offsets, such as 4 or 7, 12 (4 * 3), 21 (7 * 3), and assign them without overlapping adjacent cells / sectors.

5 is a diagram illustrating a frame structure for providing a broadcast service in an OFDM based packet service network according to another embodiment of the present invention.

In this case, a cyclic delay method may be applied to the broadcast symbol. In this case, the protection time of the broadcast symbol may be different from that of the packet service symbol in order to adjust the cell coverage of the broadcast service. In addition, if there is no separate broadcast preamble signal at the beginning of the broadcast section, the receiver of the terminal may use the preamble signal of the packet service section. That is, in order to collect energy of multipaths of neighboring base stations / sectors by estimating transmission delay time of neighboring base stations / sectors, the reception FFT window set for the packet service section may be reset in the broadcast service section.

In other words, when simultaneously providing a packet service and a broadcast service, the preamble section of the broadcast service may be selectively provided. That is, the preamble 2 may be implemented by including the preamble 2 which is a separate preamble from the preamble 1 or by delaying the preamble 1 to a certain degree. At this time, the delay time in the preamble 2, that is, the shift offset is implemented differently for each base station, and the present invention is applied.

 Meanwhile, as will be described later, the FFT window in the CP removal block may be changed in the broadcast section during the reception operation. As such, the channel of the broadcasting section has a different packet service section and channel characteristics, and therefore, a channel must have a preamble or pilot tone dedicated to the broadcasting section. In addition, there is no difference in operation from that of a general OFDM cellular system except that subcarrier mapping / demapping is performed for each base station / cell and the same broadcast data is received.

6 is a flowchart illustrating operations of a transmitter and a receiver according to an embodiment of the present invention. First, in the case of the transmitting end, data generation (S1), CRC addition and channel encoding (S2), modulation and subcarrier mapping (S3), and pilot insertion, which are operations in a typical transmission apparatus, are performed (S4).

In the case of the time domain, the present invention performs an IFFT and a cyclic shift as described above (S5), and then applies a shift offset as represented by Equation 1 (S6).

On the other hand, if the present invention is made in the frequency domain, the shift offset is applied before performing the IFFT and the cyclic shift, that is, after the pilot insertion (S4). This is represented by equation (2). After the shift offset is applied, parallel-to-serial conversion and CP, that is, cyclic prefix are added (S7), and finally transmission is performed through the RF and the transmit antenna (S8).

Meanwhile, in the case of the receiving end, the diversity gain according to the present invention is obtained through a demodulation process. Hereinafter, the process will be described in more detail.

Data transmitted through the channel from the transmitter is subjected to the normal reception process by the receiver. That is, the data collected by the receiving antenna passes the RF process (S9) and then performs synchronization (S10).

At this time, assuming that the difference in arrival time of the multipath is within the guard time, the continuous time channel of Equation 3 is equivalently converted into a discrete time model as shown in Equation 4 below. Where n ₁ and n ₂ are normalized values of τ ₁ and τ ₂ to the sampling interval, which is the inverse of the system bandwidth. For reference, in the absence of a cyclic delay, Equation 4 becomes h (n) = (h ₁ + h ₂ + h ₃ ) δ (n) so that it becomes a single path so that there is no diversity gain and only the average power of the received signal is increased. do.

After passing through the channel, the frequency-domain received signal passing through the FFT block of the receiver can be expressed by Equation 5 (S11).

In order to recover the information bits in the receiver, the received data in the frequency domain undergoes a demodulation process of Equation 6 considering channel estimation. At this time, pilot separation and channel measurement are performed (S12), and submapping and demodulation of the subcarrier are performed (S13). In addition, since the transmission information bits are determined by collecting the soft information spread over the entire subcarriers through the channel decoding and the deinterleaving process of the receiver (S14), as shown in Equation 7, the average power of the received signal is increased as well as the multipath. Diversity gain is also obtained (S15).

 The present invention is to generate a transmission signal by assigning different cyclic delay offset (Cyclic Delay Offset) for each cell / sector in the OFDMA communication system transmitter as described above, for convenience of description, one base station manages only one cell It was assumed that. In addition, in the present invention, when there are a plurality of transmit antennas in a communication system based on the OFDMA technology, a diversity gain may be provided by applying a different cyclic delay offset to each transmit antenna as described above. In addition, the present invention can increase the coverage by applying different cyclic delay offset to the transmission signal of the adjacent broadcast station in order to increase the coverage of the broadcast service in the OFDMA communication system. The transmission method according to the present invention is particularly useful for a broadcast service. As described above, the reception level is increased so that diversity gain does not need to be obtained toward the cell center, and diversity gain is obtained in a cell boundary region having a lower reception level. The overall performance is improved.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described. However, various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, according to the present invention, since the lack of diversity region moves from the cell boundary region to the center of the cell having a relatively high reception signal level, the present invention can increase the cell coverage as a whole.

1 is a diagram illustrating a concept of an OFDMA communication system.

2 is a view schematically showing the structure of a transmitter according to the prior art;

3 is a diagram illustrating a cyclic delay unit and a cyclic delay offset controller according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a transmission signal to which different cyclic delay offsets are applied on a time axis according to an exemplary embodiment of the present invention.

5 is a diagram illustrating a frame structure for providing a broadcast service in an OFDM based packet service network according to another embodiment of the present invention.

6 is a flowchart illustrating operations of a transmitting end and a receiving end according to an embodiment of the present invention.

Claims (29)

A data transmission apparatus for transmitting broadcast information in an orthogonal frequency division multiple communication system or an orthogonal frequency division multiple access communication system, An inverse fast Fourier transformer for converting transmission data into inverse fast Fourier transforms and converting the data into a data stream in a time domain; A cyclic delay unit for generating a delay signal according to a preset value according to a base station for the data sequence of the time domain converted by the inverse fast Fourier transformer; And And a guard interval inserter for inserting a guard interval with respect to the delay signal generated from the cyclic delay unit. The cyclic delay offset controller of claim 1, wherein the cyclic delay unit sets a separate cyclic delay time according to a base station with respect to a data sequence of a time domain converted by the inverse fast Fourier transformer and a delay signal according to the cyclic delay time. And a circulating delay unit to generate. The apparatus of claim 1, wherein the guard interval comprises a cyclic prefix. The wireless data transmission apparatus of claim 1, wherein the base station transmits the same broadcast data by performing a cyclic delay based on a cyclic delay time previously given for each base station. 4. The apparatus of claim 3, wherein the data is data including packet service data. 6. The apparatus of claim 5, wherein the data distinguishes the packet service data from the broadcast service data by performing a cyclic delay. The wireless data transmission apparatus of claim 6, wherein the cyclic delay is performed differently for each base station. 2. The apparatus of claim 1, wherein the base station is any one of a plurality of cells in the base station. A data transmitting apparatus for transmitting broadcast information to a terminal in an orthogonal frequency division multiple communication system or an orthogonal frequency division multiple access communication system, A modulator for modulating the transmission data; A cyclic delay unit for generating a delay signal according to a preset value according to a base station with respect to the data in the frequency domain converted by the modulator; And And an inverse Fourier transformer for performing inverse Fourier transform on the delay signal generated from the cyclic delay unit. 10. The apparatus of claim 9, wherein the cyclic delay unit comprises a cyclic delay offset controller for setting a separate cyclic delay time according to a base station with respect to a data sequence of a time domain converted by the inverse fast Fourier transformer, and a delay signal according to the cyclic delay time. And a circulating delay unit to generate. 10. The apparatus of claim 9, wherein the base station transmits the same broadcast data by performing a shift offset according to a cyclic delay time previously given for each base station individually. 10. The apparatus of claim 9, wherein the data is data including packet service data. 12. The apparatus of claim 11, wherein the data distinguishes the packet service data from the broadcast service data by performing a shift offset. The wireless data transmission apparatus of claim 12, wherein the shift offset is performed differently for each base station. 10. The apparatus of claim 9, wherein the base station is any one of a plurality of cells in the base station. A broadcast data transmission method for transmitting broadcast information to a terminal in an orthogonal frequency division multiple communication system or an orthogonal frequency division multiple access communication system,  Mapping modulation symbols to be transmitted to subcarriers;  Converting modulation symbols mapped to subcarriers into inverse fast Fourier transform into a data sequence of a time domain; And  And performing a cyclic delay according to a cyclic delay time previously assigned to each base station for each data sequence in the time domain. 17. The method of claim 16, wherein the data is transmitted with a cyclic prefix as a guard interval. 17. The method of claim 16, wherein the base station transmits the same broadcast data by performing a cyclic delay based on a predetermined cyclic delay time for each base station. 17. The method of claim 16, wherein the data is data including packet service data. 20. The method of claim 19, wherein the data distinguishes the packet service data from the broadcast service data by performing a cyclic delay. 21. The method of claim 20, wherein the cyclic delay is performed differently for each base station. 17. The method of claim 16, wherein the base station is any one of a plurality of cells in the base station. A broadcast data transmission method for transmitting broadcast information to a terminal in an orthogonal frequency division multiple communication system or an orthogonal frequency division multiple access communication system, Performing phase shifting of the modulation symbols in the frequency domain by a shift offset previously given for each base station; And And performing an inverse fast Fourier transform on the modulation symbols on which the phase shift has been performed, and then performing data transmission through a transmission antenna. 24. The method of claim 23, wherein the data is transmitted with a cyclic prefix as a guard interval. 24. The method of claim 23, wherein the base station transmits the same broadcast data by performing a phase shift based on a shift offset previously given to each base station separately. 24. The method of claim 23, wherein the data is data including packet service data. 27. The method of claim 26, wherein the data distinguishes the packet service data from the broadcast service data by a shift offset. 28. The method of claim 27, wherein the shift offset is performed differently for each base station. 24. The method of claim 23, wherein the base station is any one of a plurality of cells in the base station.