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.
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0. 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.
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.
0. 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.
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.
2. The downlink signal constitution method as claimed in
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4. The downlink signal constitution method as claimed in
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9. The downlink signal constitution method as claimed in
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As the pilot symbol assignment becomes denser, the channel estimation performance becomes more excellent but the data rate is decreased. Hence, a trade-off lies between the data rate and the channel estimation performance (i.e., pilot symbol distance).
There exits a pilot symbol distance that optimizes the trade-off between the improved channel estimation and the signal-to-noise ratio (SNR) reduced by data symbols. By varying the pilot symbol distances NF and NT, the values approximate to the optimum with reference to the performance of bit error rate (BER) can be determined. In
In this optimal assignment of pilot symbols, the channel environment and the moving speed of the mobile users are of a great importance as parameters to be considered.
It is an advantage of the present invention to provide an apparatus and method for adaptive pilot symbol assignment and sub-carrier allocation that reduces transmission power and overhead caused by pilot symbols and increases the total data rate on a downlink in an OFDMA-based cellular system.
In one aspect of the present invention, there is provided 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 including: (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 user, and determining a transmission mode of each user according to the user's moving speed, 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; and (d) 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.
In another aspect of the present invention, there is provided a downlink signal constitution method, which is for a cellular system using an orthogonal frequency division multiplexing access method, the downlink signal constitution method including: (a) dividing users into a first user group including high-speed mobile users and a second user group including the rest of the users, in consideration of each user's moving speed and traffic volume; (b) allocating a first sub-carrier band for the first user group, and a second sub-carrier band for the second user group; and (c) assigning pilot symbols to the first and second sub-carrier bands, the pilot symbols assigned to the first sub-carrier band being different in assignment density from the pilot symbols assigned to the second sub-carrier.
In a further aspect of the present invention, there is provided a downlink signal constitution apparatus, which is for a cellular system using an orthogonal frequency division multiplexing access method, the downlink signal constitution apparatus including: a first memory for storing 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 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 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 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; and a time/sub-carrier/antenna mapper for multiplying 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, and mapping the resulting symbols to time, sub-carrier, and antenna by a defined method.
In a still further aspect of the present invention, there is provided a recording medium with a built-in program, which implements a downlink signal constitution method for a cellular system using an orthogonal frequency division multiplexing access method, the program including: a function of 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; a function of 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, channel information, and traffic requirement; a function of determining additional pilot symbols, additionally necessary for a demodulation of the traffic channel, according to the transmission mode and moving speed by users; and a function of 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.
In a still further aspect of the present invention, there is provided a recording medium with a built-in program, which implements a downlink signal constitution method for a cellular system using an orthogonal frequency division multiplexing access method, the program including: a function of dividing users into a first user group including high-speed mobile users and a second user group including the rest of the users, in consideration of each user's moving speed and traffic volume; a function of allocating a first sub-carrier band for the first user group, and a second sub-carrier band for the second user group; and a function of assigning pilot symbols to the first and second sub-carrier bands, the pilot symbols assigned to the first sub-carrier band being different in assignment density from the pilot symbols assigned to the second sub-carrier.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention:
In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.
The symbol assignment method according to the embodiment of the present invention comprises, as shown in
More specifically, the symbol assignment step S100 for common/control channels performs coding, interleaving, and symbol mapping on data of common and control channels, and assigns the mapped symbols to time, frequency, and antennas. Also, fundamental pilot symbols necessary for demodulation of the common and control channels are assigned to time, frequency, and antennas.
The symbol assignment step S200 for traffic channels receives data to be transferred through the traffic channel of each user; determines each user's transmission mode according to the user's moving speed, channel information, and traffic requirement; performs coding, interleaving, and symbol-mapping according to the transmission mode of the user; and assigns the traffic channel symbols of each user to time, frequency, and antennas. Also, pilot symbols additionally necessary for a demodulation of the traffic channel are generated according to the transmission mode by users, and assigned to time, frequency, and antennas.
The traffic channel signal constitution step S300 constitutes the signal of the traffic channel using the traffic channel symbols of each user and the additional pilot symbols output from the step S200.
When the base station has information about the moving speed and channel status of each user, a required number of pilot symbols are inserted, reducing transmission power and overhead caused by pilot symbols.
According to the embodiment of the present invention, the transmitter antennas are divided into basic antennas and additional antennas. The basic antenna refers to an antenna used for transmitting common and control channels, while the additional antenna refers to an antenna additionally used to enhance the transmission rate or performance of the traffic channel of the user.
In the OFDMA system, one frequency band is divided into a plurality of sub-carrier bands to transmit the traffic channel of each user through the allocated sub-carriers. Namely, the OFDMA system properly allocates a sub-carrier band according to the user's moving speed, channel environment, and traffic requirement, or selects a defined sub-carrier band, determines the number of transmitter antennas according to the user's moving speed, channel environment, and traffic requirement, and then assigns additionally necessary pilot symbols to the allocated sub-carrier band.
More specifically, as illustrated in
The transmission mode and the number of additional antennas are determined in consideration of the user's channel information (i.e., channel status), traffic requirement, and moving speed, in step S220.
In step S230, the system assigns pilot symbols for additional antennas, when the additional antennas are needed according to the transmission mode determined in the step S220.
The additional pilot symbols according to the moving speed of the basic antennas and the additional antennas are then assigned in consideration of the user's moving speed, in step S240.
The system performs coding, interleaving, and symbol mapping using the transmission mode determined in the step S220 and the traffic channel data stored in the step S210 to generate coded, interleaved, and symbol-mapped traffic channel symbols, in step S250.
In the step S220, the transmission mode for each user is determined independently, or the transmission mode for multiple users is determined by optimization in consideration of the total transmission rate, the quality of service, or the total transmission power.
In
In
Referring to
The pilot symbols (NF=5) of the basic antenna (antenna 0) and the common and control channels are transmitted for the first OFDMA symbol, and the traffic channel is transmitted for the other OFDMA symbols. The pilot symbols of the additional antennas (antenna 1, antenna 2, antenna 3) are additionally transmitted. In the meantime, the symbols of the traffic channel can be generated by any one of the following methods: (1) a first method of generating traffic channel symbols previously in consideration of the number of additional pilots; (2) a second method of generating the maximum number of traffic channel symbols and then puncturing at positions to transmit additional pilot symbols; and (3) a third method of generating traffic channel symbols previously in consideration of the number of a part of additional pilot symbols, and then puncturing at positions to transmit the rest of the additional pilot symbols.
The pilot symbols (NF=5) of the basic antenna (antenna 0) and the common and control channels are transmitted for the first OFDMA symbol, and the traffic channel is transmitted for the other OFDMA symbols. The pilot symbols of the additional antenna (antenna 1) are additionally transmitted.
In the meantime, the symbols of the traffic channel can be generated by one of the following methods: (1) a first method of generating traffic channel symbols previously in consideration of the number of additional pilots; (2) a second method of generating the maximum number of traffic channel symbols and then puncturing at positions to transmit additional pilot symbols; and (3) a third method of generating traffic channel symbols previously in consideration of the number of a part of additional pilot symbols, and then puncturing at positions to transmit the rest of the additional pilot symbols.
In summary, there are four cases of pilot symbol assignment in relation to the number of antennas of the traffic channel:
(1) moving at a low speed with one basic antenna—using no additional pilot symbol;
(2) moving at low speed with additional antennas—assigning pilot symbols for additional antennas;
(3) moving at high speed with one basic antenna—additionally inserting pilot symbols for basic antenna in conformity to the high-speed environment; and
(4) moving at high speed with additional antennas—additionally inserting pilot symbols for basic and additional antennas in consideration of the moving speed.
To use the methods illustrated in
In the former case, the mobile station sends a signal (e.g., preamble, pilot, etc.) for channel measurement, and then the base station measures the channel information of the uplink by the respective antennas based on the received signal. The base station acquires channel information of the downlink using the reciprocity of channels because the uplink and the downlink have the same channel information because they use the same frequency band.
Contrarily, in the FDD system, the mobile station previously sends pilots of additional antennas so as to perform a channel estimation of the additional antennas.
Namely,
In
The downlink signal constitution apparatus 100 comprises a common/control channel processor 110, a fundamental pilot symbol generator 120, a traffic channel information memory 130, a traffic channel processor 140, a channel information/traffic requirement/moving speed memory 150, a transmission user and transmission mode determiner 160, an additional pilot symbol generator 170, and a time/sub-carrier/antenna mapper 180.
The common/control channel processor 110 encodes and interleaves the common/control channel information, and maps the coded and interleaved common/control channel information to symbols to generate a coded/interleaved/symbol-mapped common/control channel symbol. The fundamental pilot symbol generator 120 generates a fundamental pilot symbol. The fundamental pilot symbol is a pilot symbol transmitted irrespective of the transmission mode of the traffic channel of the user, and in
The traffic channel information memory 130 stores the user's traffic channel information, and the channel information/traffic requirement/moving speed memory 150 stores the user's channel information, traffic requirement, and moving speed information.
The transmission user and transmission mode determiner 160 determines the transmission user and each transmission mode according to a defined method using the information stored in the channel information/traffic requirement/moving speed memory 150. The traffic channel processor 140 reads the traffic channel information stored in the traffic channel information memory 130 according to the transmission mode determined by the transmission user and transmission mode determiner 160, encodes and interleaves the traffic channel information, and maps the coded and interleaved traffic channel information to generate a coded/interleaved/symbol-mapped traffic channel symbol.
The additional pilot symbol generator 170 generates an additional pilot symbol according to the number of antennas and the moving speed determined by each user's transmission mode. The additional pilot symbol is a pilot symbol additionally transmitted other than the fundamental pilot symbol for the respective users, and in
The time/sub-carrier/antenna mapper 180 multiplies the coded/interleaved/symbol-mapped common/control channel symbol generated from the common/control channel processor 110, the coded/interleaved/symbol-mapped traffic channel symbol generated from the traffic channel processor 130, the fundamental pilot symbol generated from the fundamental pilot symbol generator 120, and the additional pilot symbol generated from the additional pilot symbol generator 170 by channel gain information by channels or users, and maps the channel symbols to time, sub-carrier, and antenna by a defined method.
The time/sub-carrier/antenna mapper 180 can use any one of the following methods: (1) a first method of generating traffic channel symbols previously in consideration of the number of additional pilots; (2) a second method of generating the maximum number of traffic channel symbols and then puncturing at positions to transmit additional pilot symbols; and (3) a third method of generating traffic channel symbols previously in consideration of the number of a part of additional pilot symbols, and then puncturing at positions to transmit the rest of the additional pilot symbols.
The output of the downlink signal constitution apparatus 100 is OFDM-modulated through OFDM modulators 200a, 200b, . . . , and 200n, and is subjected to D/A conversion, frequency up-conversion, filtering, and amplification through radio transmitters 300a, 300b, . . . , and 300n, and transmitted via antennas 400a, 400b, . . . , and 400n.
According to the embodiment of the present invention, some of the sub-carriers are allocated according to the traffic requirement and the moving speed by an appropriate method in the downlink of the OFDMA-based cellular system, and then the pilot symbols of the traffic channel of the corresponding sub-carrier are properly assigned by the pilot symbol assignment method according to the moving speed, or the like.
More specifically, referring to
If the moving speed is determined as low in the step S420, then the sub-carriers are allocated according to channel status, traffic requirement, and low-speed determination information, in step S430, and pilot symbols for low speed are assigned to the allocated sub-carriers, in step S450.
If the moving speed is determined as high in the step S420, then the sub-carriers are allocated according to channel status, traffic requirement, and high-speed determination information, in step S440, and pilot symbols for high speed are assigned to the allocated sub-carriers, in step S460.
The pilot symbols assigned in the steps S450 and S460 are output to a data symbol assignment input.
Typically, sub-carrier allocation is achieved by users or data types. Here, the sub-carriers are allocated according to each user's moving speed. In the case of pilot symbol assignment for mobile users in an express train running at a speed of 250 km/h in consideration of the user's quality of service, for example, the pilot symbols are assigned very densely with a small pilot symbol distance, and the number of data symbols to be transmitted is reduced with a deterioration of the data rate. However, for users who are stationary or moving at a speed of less than 120 km/h, the pilot symbols are much more densely assigned than needed, with a deterioration of efficiency. Thus the users can be divided into a user group having a moving speed of 250 km/h and a user group having a moving speed of less than 120 km/h, based on the fact that there is no speed to be considered between 120 and 250 km/h.
In
While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent assignments included within the spirit and scope of the appended claims.
The present invention determines the number of transmit antennas according to each user's moving speed, channel status, or user request, and properly assigns pilot symbols in the downlink of an OFDMA-based cellular system, thereby reducing a transmission power consumption and an overhead caused by pilots.
Furthermore, the present invention 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, based on the fact that the ultrahigh-speed mobile users have a traffic volume almost insignificant to the whole traffic volume, thereby optimizing the transmission power caused by the pilot symbols as well as enhancing the total data rate.
Kim, Kwang-Soon, Chang, Kyung-Hi, Lee, Sok-Kyu
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