Abstract:
A transmission/reception method for transmitting a control channel in an Orthogonal Frequency Division Multiplexing (OFDM) system. The transmission method includes generating a plurality of control channels such that control information for demodulation of the plurality of control channels is distributed over information of other control channels; and modulating a data channel and the control channels into a radio signal according to a predetermined transmission scheme, and transmitting the radio signal to a wireless network. The reception method includes receiving a plurality of control channels transmitted via a wireless network; and extracting control information for demodulation of the control channels from other previously received control channels, and performing the demodulation using the control information.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. §119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Mar. 25, 2006 entitled “Apparatus And Method For Transmitting/Receiving Control Channel In An Orthogonal Frequency Division Multiplexing System” and assigned Serial No. 2006-27219, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a transmission/reception apparatus and method for a wireless communication system, and in particular, to an apparatus and method for transmitting/receiving control channels in an Orthogonal Frequency Division Multiplexing (OFDM) system.  
         [0004]     2. Description of the Related Art  
         [0005]     Wireless communication systems have been developed to connect fixed wire networks to mobile terminals. Typical wireless communication systems are mobile communication systems, Wireless Local Area Network (LAN) systems, Wireless Broadband Internet (Wibro) systems, and Mobile Ad Hoc systems.  
         [0006]     Mobile communication, unlike the general wireless communication, is premised on mobility of users. The ultimate goal of the mobile communication is to allow the users to exchange information media using terminals such as mobile phone and radio paging receiver, regardless of time and place.  
         [0007]     In addition, with the rapid progress of communication technologies using mobile terminals, mobile communication systems have been developed to provide not only the general voice call service but also high-speed data services capable of transmitting high-volume digital data such as moving image as well as e-mail and still image.  
         [0008]     An OFDM transmission scheme is one of the typical wireless mobile communication systems employing a multi-carrier transmission scheme, which provides high-speed data services. The OFDM transmission scheme, a scheme for converting a serial input symbol stream into parallel streams and then modulating them with multiple orthogonal subcarriers before transmission, has started to attract attention with the development of Very Large Scale Integration (VLSI) technology since the early  1990 s.  
         [0009]     The OFDM transmission scheme, as it modulates data using multiple orthogonal subcarriers, shows high robustness against a frequency selective multipath fading channel, compared with the conventional single-carrier modulation scheme, and this transmission scheme is suitable for the high-speed data services such as broadcast services.  
         [0010]     The existing OFDM systems have used one control channel. Generally, however, because all users use the control channel, attempts are being made to use multiple control channels in the OFDM system in order to reduce system load. In the following description, it will be assumed that the multiple control channels include a Primary Data Control Channel (PDCCH) and a Secondary Data Control Channel (SDCCH). The SDCCH transmits various control information used for demodulating data channels. The PDCCH transmits control information such as Modulation Coding Scheme (MCS) of the SDCCH, offset information indicating positions of subcarriers, size information of resources, and the like.  
         [0011]      FIG. 1  illustrates the transmission structure of a control channel in a forward link of a general OFDM system. The illustrated exemplary transmission structure uses PDCCH and SDCCH as control channels, and groups the SDCCHs.  
         [0012]     Mobile terminals are classified into a plurality of groups according to the distance from a base station and/or channel environment. The base station encodes and transmits SDCCHs in association with corresponding groups using MCS that mobile terminals in each group can readily detect. For example, if the number of the groups is 3, SDCCHs can be classified into a first SDCCH (G# 1 )  101 , a second SDCCH (G# 2 )  103 , and a third SDCCH (G# 3 )  105 . Control information for demodulation of the first SDCCH G# 1   101 , the second SDCCH G# 2   103 , and the third SDCCH G# 3   105  is transmitted to mobile terminals over a PDCCH  107 .  
         [0013]     Referring to  FIG. 1 , the first SDCCH  101  is encoded using Quadrature Phase Shift Keying (QPSK) as a modulation scheme and rate-(5,1) convolutional coding (or rate-⅕ convolutional coding) as a coding scheme, for the mobile terminals located in the cell boundary having poor channel environment. The second SDCCH  103  is encoded using 16-ary Quadrature Amplitude Modulation (16 QAM) and rate-(3,1) convolutional coding (or rate-⅓ convolutional coding), for the mobile terminals located between the cell boundary and the cell center. The third SDCCH  105  is encoded using 64 QAM and rate-(2,1) convolutional coding (or rate-½ convolutional coding), for the mobile terminals located in the cell center having the best channel environment. Control information  109 ,  111  and  113  transmitted over the PDCCH  107  includes control information such as MCS, offset of subcarriers, and size of used resources, for demodulation of the first to third SDCCHs  101 ,  103  and  105  for the corresponding groups.  
         [0014]     The control information for the first to third SDCCHs  101 ,  103  and  105  is block-coded per group or block-coded at a time, and then inserted into the PDCCH  107  before being transmitted. The control information transmission over the PDCCH, as it groups the SDCCHs, is efficient compared with the use of a single control channel. However, this scheme also inefficiently uses wireless resources because it should transmit control information of all SDCCH groups over one PDCCH.  
       SUMMARY OF THE INVENTION  
       [0015]     An aspect of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a control channel transmission/reception apparatus and method capable of efficiently using frequency resources for control channels in an OFDM system.  
         [0016]     Another aspect of the present invention is to provide an apparatus and method for efficiently transmitting control information for demodulation of control channels when grouping control channels before transmission in an OFDM system.  
         [0017]     According to one aspect of the present invention, there is provided a transmission apparatus for transmitting a control channel in an Orthogonal Frequency Division Multiplexing (OFDM) system. The transmission apparatus includes a transmitter for modulating a data channel and a plurality of control channels into a radio signal according to a predetermined transmission scheme, and transmitting the radio signal to a wireless network; and a control channel processor for controlling an operation of transmitting channel by channel control information for demodulation of each of the control channels over other control channels respectively.  
         [0018]     According to another aspect of the present invention, there is provided a transmission method for transmitting a control channel in an Orthogonal Frequency Division Multiplexing (OFDM) system. The transmission method includes generating a plurality of control channels such that control information for demodulation of the plurality of control channels is distributed over information of other control channels respectively; and modulating a data channel and the control channels into a radio signal according to a predetermined transmission scheme, and transmitting the radio signal to a wireless network.  
         [0019]     According to a further aspect of the present invention, there is provided a reception apparatus for receiving a control channel in an Orthogonal Frequency Division Multiplexing (OFDM) system. The reception apparatus includes a receiver for receiving a data channel and a plurality of control channels, transmitted via a wireless network, according to a predetermined transmission scheme; and a control channel demodulator for extracting control information for demodulation of the control channels from other previously received control channels respectively, and performing the demodulation using the control information.  
         [0020]     According to yet another aspect of the present invention, there is provided a reception method for receiving a control channel in an Orthogonal Frequency Division Multiplexing (OFDM) system. The reception method includes receiving a plurality of control channels transmitted via a wireless network; and extracting control information for demodulation of the control channels from other previously received control channels respectively, and performing the demodulation using the control information. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0022]      FIG. 1  is a diagram illustrating a transmission structure of a control channel in a forward link of a general OFDM system;  
         [0023]      FIG. 2  is a diagram illustrating a transmission structure of control channels in a forward link of an OFDM system according to the present invention;  
         [0024]      FIG. 3  is a block diagram of the structure of a transmission apparatus in an OFDM system according to the present invention;  
         [0025]      FIG. 4  is a flow chart of a process of generating and transmitting control information of each group by a transmission apparatus in a forward link of an OFDM system according to the present invention;  
         [0026]      FIG. 5  is a block diagram of the structure of a reception apparatus in an OFDM system according to the present invention; and  
         [0027]      FIG. 6  is a flow chart of a process of receiving and demodulating control information of a corresponding group by a reception apparatus in a forward link of an OFDM system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0028]     Exemplary embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness.  
         [0029]     Although the number of groups of mobile terminals and SDCCHs is assumed herein to be  3  for convenience, the number of groups of SDCCHs can be extended to N.  
         [0030]     Referring to  FIG. 2 , this embodiment provides a proposed transmission structure of control channels by using PDCCH and SDCCH as control channels, and grouping the SDCCHs such that control information of each group is located in the PDCCH or the SDCCH of a preceding group in the link structure.  
         [0031]     The SDCCHs are divided into, for example, 3 groups  201 ,  203  and  205  according to positions of mobile terminals in the cell and/or channel environments, and control information  207 ,  209  and  211  included in the PDCCH and the SDCCH of each group includes an MCS level of the next group, and position (i.e. offset of subcarrier) and size information of the SDCCH. Control information of a first SDCCH  201 , which is a first group, is included in the PDCCH, which is a preceding control channel. Upon receiving the control information of the first group from the PDCCH, a mobile terminal demodulates first SDCCH  201  using the control information. Control information for demodulation of a second SDCCH  203 , which is a second group, is included in preceding first SDCCH  201 . The mobile terminal receives control information from first SDCCH  201  and demodulates second SDCCH  203  using the control information. In the same manner, control information for demodulation of a third SDCCH  205 , which is a third group, is included in second SDCCH  203  of the preceding group. The mobile terminal receives the control information from second SDCCH  203 , and demodulates third SDCCH  205  using the control information. In the course of demodulating the SDCCH of each group, the mobile terminal acquires control information of the SDCCH corresponding to its own Media Access Control (MAC) ID and its own group, and no longer demodulates SDCCHs of other groups.  
         [0032]     With reference to  FIGS. 3 and 4 , a description will now be made of a structure and operation of a transmission apparatus according to the present invention.  
         [0033]     Referring to  FIG. 3 , in the transmission apparatus, an OFDM transmission module  300   a  generates an OFDM symbol by performing Inverse Fast Fourier Transform (IFFT) on packet data, and transmits to a wireless network the control information for demodulation of the SDCCH, provided from a control channel processing module  300   b.  The OFDM transmission module  300   a  includes a channel encoder  301  for channel-encoding packet data received from an undepicted physical layer, a channel interleaver  303  for interleaving the coded packet data, a modulator  305  for modulating the interleaved packet data, a guard tone inserter  307  for inserting guard tones for preventing an out-band signal from serving as interference, and a pilot tone inserter  309  for inserting pilot tones for channel estimation at a mobile terminal.  
         [0034]     Further, the transmission apparatus includes a QPSK spreader  311 , an IFFT processor  313  for transforming a time-domain signal into a frequency-domain signal, a Cyclic Prefix (CP) inserter  315  for inserting a CP in the front of OFDM data to prevent an interference signal, and a Radio Frequency (RF) processor  317  for converting the CP-inserted OFDM signal into an RF signal.  
         [0035]     The control channel processing module  300   b  includes a PDCCH processor  319 , an SDCCH processor  321 , and a controller  323 , and controls a generation and insertion operation for the control information. PDCCH processor  319  generates PDCCH information including control information such as MCS level for an SDCCH of the next group and position (offset of subcarrier) and size information of the SDCCH, connected in the link structure, and delivers the PDCCH information to the IFFT processor  313 . Similarly, SDCCH processor  321  generates control information including MCS level for an SDCCH of the next group and position and size information of the SDCCH, connected in the link structure, and/or SDCCH information for demodulation of a data (traffic) channel in the current group, and delivers the generated information to the IFFT processor  313 . Controller  323  controls an operation of inserting the control information generated from SDCCH processor  321  in the PDCCH or a corresponding position of the SDCCH before transmission.  
         [0036]     Referring to  FIG. 4 , in step  401 , a base station groups mobile terminals into a plurality of groups in association with SDCCHs according to positions of the mobile terminals and/or forward channel conditions. In this case, the base station can group the mobile terminals into a plurality of groups in order of a terminal with a lower Channel Quality Indicator (CQI) (for example, in order of a terminal located in the cell boundary to a terminal located in the cell center). It is assumed in  FIG. 4  that the base station groups terminals and SDCCHs into  3  groups. In step  403 , the base station generates control information including MCS level for a first SDCCH group among the  3  groups, and position (offset of subcarrier) and size information of the SDCCH, and inserts the control information in a PDCCH linked thereto. Similarly, in step  405 , the base station generates control information including MCS level of a second SDCCH group, and position and size information of the SDCCH, and transmits the control information over the first SDCCH of the first group. In step  407 , the base station generates control information including an MCS level of a third SDCCH group, and position and size information of the SDCCH, and transmits the control information over the second SDCCH of the second group. Finally, in step  409 , the base station generates the third SDCCH according to a general operation because there is no next group.  
         [0037]     With reference to  FIGS. 5 and 6 , a description will now be made of a structure and operation of a reception apparatus according to the present invention.  
         [0038]     Referring to  FIG. 5 , a down-conversion &amp; analog-to-digital (A/D) conversion block  601  converts a signal received via a wireless network into a baseband signal, and converts the analog baseband signal into a digital signal. The digital signal is delivered to a CP remover  503 , and the CP remover  503  removes from the received signal a CP contaminated due to propagation delay and multiple paths. A Fast Fourier Transform (FFT) processor  505  transforms an input time-domain signal into a frequency-domain signal, and a despreader  507  QPSK-despreads the frequency-domain signal and outputs tones of each signal, assuming that a QPSK-spread signal is transmitted from a transmission apparatus. Therefore, if the transmission apparatus uses a different spreading scheme, the reception apparatus also has a despreader supporting the corresponding spreading scheme.  
         [0039]     Despreader  507  delivers the tones of the despread signal to a pilot tone extractor  509 , which extracts pilot tones from the tones of each signal, delivers the extracted pilot tones to a channel estimator  513 , and delivers the remaining signal tones to a data tone extractor  511 . Data tone extractor  511  extracts data tones from the input signal tones, and sends the extracted data tones to a demodulator  515 . Channel estimator  513  estimates a channel using the pilot tones, and delivers the channel estimated value to demodulator  515 . Demodulator  515  performs demodulation on the data tones using the channel estimated value delivered from channel estimator  513 , and the demodulated signal is deinterleaved by a deinterleaver  517  and then input to a decoder  519 . Decoder  519  restores the transmitted signal by decoding the input signal.  
         [0040]     A PDCCH/SDCCH signal, which has passed through FFT processor  505  in the foregoing reception process, is delivered to a control channel demodulator  521 . Control channel demodulator  521  demodulates control information received from a control channel, i.e. PDCCH/SDCCH, and delivers the demodulated control information to demodulator  515 . Demodulator  515  then demodulates not only the traffic channel but also the SDCCH using the control information received from the PDCCH/SDCCH.  
         [0041]     Referring to  FIG. 6 , in step  601 , a receiver of a mobile terminal receives PDCCH information including control information # 1  for demodulation of an SDCCH of the next group, and then demodulates the PDCCH information. In step  603 , the receiver demodulates an SDCCH of a first group using the control information # 1  thereby acquiring SDCCH information of the corresponding group and also acquiring control information # 2  for demodulating an SDCCH of a second group. In step  605 , the receiver determines if a MAC ID detected from the demodulate SDCCH of the first group is identical to a MAC ID of the corresponding mobile terminal, and if the detected MAC ID is identical to the MAC ID of the corresponding mobile terminal, the receiver demodulates data tones of a traffic channel using the SDCCH information of the first group in step  607 . If the detected MAC ID is not identical to the MAC ID of the corresponding mobile terminal in step  605 , the receiver demodulates the SDCCH of the second group using control information # 2  in step  609  thereby acquiring SDCCH information of the corresponding group and also acquiring control information # 3  for demodulating an SDCCH of a third group.  
         [0042]     In step  611 , the receiver determines if a MAC ID detected from the demodulated SDCCH of the second group is identical to the MAC ID of the corresponding mobile terminal, and if the detected MAC ID is identical to the MAC ID of the corresponding mobile terminal, the receiver demodulates data tones of the traffic channel using the SDCCH information of the second group in step  613 . However, if the detected MAC ID is not identical to the MAC ID of the corresponding mobile terminal in step  611 , the receiver demodulates the SDCCH of the third group using control information # 3  in step  615  thereby acquiring SDCCH information of the corresponding group. In step  617 , the receiver determines if a MAC ID detected from the demodulated SDCCH of the third group is identical to the MAC ID of the corresponding mobile terminal, and if the detected MAC ID is identical to the MAC ID of the corresponding mobile terminal, the receiver demodulates data tones of the traffic channel using the SDCCH information of the third group in step  619 .  
         [0043]     As can be understood from the foregoing description, the present invention reduces the amount of control information for the SDCCHs, transmitted over the PDCCH in a forward link of the OFDM system, thereby facilitating efficient management of PDCCH/SDCCH control channels.  
         [0044]     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as further defined by the appended claims.