Apparatus and method for signal constitution for downlink of OFDMA-based cellular system

Abstract

Disclosed are an adaptive pilot symbol assignment method that flexibly controls the number of transmit antennas according to each user's moving speed, channel status, or user request, and assigns proper pilot symbols in the downlink of an OFDMA (Orthogonal Frequency Division Multiplexing Access) based cellular system; and a sub-carrier allocation method for high-speed mobile that allocates some sub-carriers to assign proper pilot symbols for ultrahigh-speed mobile users, and the rest of the sub-carriers to the other users to assign proper pilot symbols to the users, on the assumption that the ultrahigh-speed mobile users have a traffic volume almost insignificant to the whole traffic volume.

What is claimed is: 
     
       1. A downlink signal constitution method, which is for a downlink of a cellular system using an orthogonal frequency division multiplexing access method, the downlink signal constitution method comprising:
 (a) coding, interleaving, and symbol-mapping data of a common channel and a control channel, and assigning fundamental pilot symbols, necessary for a demodulation of the common channel and the control channel, to time, frequency, and antenna; 
 (b) receiving data to be transmitted through a traffic channel of each to user mobile device, and determining a transmission mode of each user according to the user's moving speed of the mobile device, channel information, and traffic requirement; 
 (c) determining additional pilot symbols, additionally necessary for a demodulation of the traffic channel, according to the transmission mode and moving speed by users of the mobile station; and 
 (d) coding, interleaving, and symbol-mapping the data of the traffic channel according to the transmission mode by users the mobile station, and assigning the mapped symbols and the additional pilot symbols according to time, frequency, and antenna. 
 
     
     
       2. The downlink signal constitution method as claimed in  claim 1 , wherein the assignment of the fundamental pilot symbols for the sub-carriers used by a first user group is different from the assignment of the fundamental pilot symbols for the sub-carriers used by a second user group. 
     
     
       3. The downlink signal constitution method as claimed in  claim 2 , wherein the assignment of pilot symbols for the sub-carriers used by the first user group is denser than the assignment of pilot symbols for the sub-carriers used by the second user group. 
     
     
       4. The downlink signal constitution method as claimed in  claim 3 , wherein the first user group is a higher-speed user group than the second user group, and some of all the sub-carriers is previously allocated for the first user group. 
     
     
       5. The downlink signal constitution method as claimed in  claim 1 , wherein the step (c) of determining the additional pilot symbols includes: using no additional pilot symbol, when the transmission mode of the traffic channel is using only a basic antenna with the moving speed of a the mobile station being less than a reference value; and using pilot symbols for additional antenna, when the transmission mode of the traffic channel is using an additional antenna with the moving speed of the mobile station being less than the reference value. 
     
     
       6. The downlink signal constitution method as claimed in  claim 1 , wherein the step (c) of determining the additional pilot symbols includes: additionally inserting pilot symbols for basic antenna in consideration of the moving speed of a the mobile station, when the transmission mode of the traffic channel is using only a basic antenna with the moving speed of the mobile station exceeding a reference value; and additionally inserting pilot symbols for basic and additional antennas in consideration of the moving speed of the mobile station, when the transmission mode of the traffic channel is using an additional antenna with the moving speed of the mobile station exceeding the reference value. 
     
     
       7. The downlink signal constitution method as claimed in  claim 1 , wherein the step (d) of assigning of the additional pilot symbols includes generating traffic channel symbols previously in consideration of the number of the additional pilots. 
     
     
       8. The downlink signal constitution method as claimed in  claim 1 , wherein the step (d) of assigning of the additional pilot symbols includes generating symbols according to a maximum number of traffic channel symbols, and then puncturing at positions for transmitting the additional pilot symbols. 
     
     
       9. The downlink signal constitution method as claimed in  claim 1 , wherein the step (d) of assigning of the additional pilot symbols includes generating traffic channel symbols previously in consideration of a portion of the number of the additional pilot symbols, and then puncturing at positions for transmitting the rest of the additional pilot symbols. 
     
     
       10. A downlink signal constitution apparatus, which is for a cellular system using an orthogonal frequency division multiplexing access method, the downlink signal constitution apparatus comprising:
 a first memory for storing configured to store traffic channel information of each user; 
 a second memory for storing channel information, traffic requirement, and moving speed information of each user; 
 a transmission user and transmission mode determiner for determining configured to determine a transmission user and a transmission mode according to a defined method using the information stored in the second memory; 
 a traffic channel processor for reading configured to read the traffic channel information stored in the first memory according to the transmission mode determined by the transmission user and transmission mode determiner, and performing coding, interleaving, and symbol-mapping of the traffic channel; 
 an additional pilot symbol generator for generating configured to generate additional pilot symbols necessary for a demodulation of the traffic channel, using the transmission mode determined by the transmission user and transmission mode determiner and the moving speed information stored in the second memory; 
 a time/sub-carrier/antenna mapper for multiplying configured to multiply the traffic channel symbols output from the traffic channel processor and the additional pilot symbols output from the additional pilot symbol generator by a channel gain by channels/users channels, and mapping the resulting symbols to time, sub-carrier, and antenna by a defined method; 
 a common/control control channel processor for receiving common/control configured to receive control channel information, and performing coding, interleaving, and symbol-mapping of the received common/control control channels; and 
 a fundamental pilot symbol generator for generating configured to generate a fundamental pilot symbol necessary for demodulation of the common/control control channels. 
 
     
     
       11. A downlink signal constitution method, which is for a downlink of a cellular system using an orthogonal frequency division multiplexing access method, the downlink signal constitution method comprising:
 coding, interleaving, and symbol-mapping data of a common channel and a control channel, and assigning fundamental pilot symbols, necessary for a demodulation of the common channel and the control channel, to time, frequency, and antenna;   receiving data to be transmitted through a traffic channel of each user, and determining a transmission mode of each user according to the user's moving speed and channel information;   determining additional pilot symbols, additionally necessary for a demodulation of the traffic channel, according to the transmission mode and moving speed by users; and   coding, interleaving, and symbol-mapping the data of the traffic channel according to the transmission mode by users, and assigning the mapped symbols and the additional pilot symbols according to time, frequency, and antenna.   
     
     
       12. A downlink signal constitution apparatus, which is for a cellular system using an orthogonal frequency division multiplexing access method, the downlink signal constitution apparatus comprising:
 a first memory configured to store traffic channel information of each user;   a second memory configured to store channel information, traffic requirement, and moving speed information of each user;   a transmission user and transmission mode determiner configured to determine a transmission user and a transmission mode according to a defined method using the information stored in the second memory;   a traffic channel processor configured to read the traffic channel information stored in the first memory according to the transmission mode determined by the transmission user and transmission mode determiner, and performs coding, interleaving, and symbol-mapping of the traffic channel;   an additional pilot symbol generator configured to generate additional pilot symbols necessary for a demodulation of the traffic channel, using the transmission mode determined by the transmission user and transmission mode determiner and the moving speed information stored in the second memory;   a mapper configured to multiply the traffic channel symbols output from the traffic channel processor and the additional pilot symbols output from the additional pilot symbol generator by a channel gain by channels, and maps resulting symbols to time, sub-carrier, and antenna by a defined method;   a control channel processor configured to perform coding, interleaving, and symbol mapping of received control channels; and   a fundamental pilot symbol generator configured to generate a fundamental pilot symbol necessary for demodulation of the control channels.