WO2005119953A1 - Method for implementing channel estimate in orthogonal frequency division multiplexing (ofdm) system - Google Patents

Method for implementing channel estimate in orthogonal frequency division multiplexing (ofdm) system Download PDF

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Publication number
WO2005119953A1
WO2005119953A1 PCT/CN2005/000757 CN2005000757W WO2005119953A1 WO 2005119953 A1 WO2005119953 A1 WO 2005119953A1 CN 2005000757 W CN2005000757 W CN 2005000757W WO 2005119953 A1 WO2005119953 A1 WO 2005119953A1
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time
ofdm symbol
domain channel
channel information
pilot
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PCT/CN2005/000757
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English (en)
French (fr)
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Shujun Dang
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Huawei Technologies Co., Ltd.
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Application filed by Huawei Technologies Co., Ltd. filed Critical Huawei Technologies Co., Ltd.
Priority to EP05755158.2A priority Critical patent/EP1742402B1/en
Publication of WO2005119953A1 publication Critical patent/WO2005119953A1/zh
Priority to US11/652,758 priority patent/US7688907B2/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2673—Details of algorithms characterised by synchronisation parameters
    • H04L27/2675—Pilot or known symbols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H04L25/023—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols
    • H04L25/0236—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols using estimation of the other symbols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/022—Channel estimation of frequency response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0222—Estimation of channel variability, e.g. coherence bandwidth, coherence time, fading frequency
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H04L25/023—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols
    • H04L25/0232—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols by interpolation between sounding signals
    • H04L25/0234—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols by interpolation between sounding signals by non-linear interpolation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0003—Two-dimensional division
    • H04L5/0005—Time-frequency
    • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0212—Channel estimation of impulse response
    • H04L25/0216—Channel estimation of impulse response with estimation of channel length

Definitions

  • the present invention relates to Orthogonal Multiplexing Frequency Division Multiplexing (OFDM) technology, and more particularly to a method for implementing channel estimation in an OFDM system.
  • OFDM Orthogonal Multiplexing Frequency Division Multiplexing
  • OFDM technology is a frequency division multiplexing technology capable of transmitting high-rate data services.
  • OFDM technology can use a simple equalization algorithm to provide higher frequency efficiency; on the other hand, In a system using OFDM, there is no need to allocate a wider protection bandwidth between adjacent carriers as in traditional frequency division multiplexing (FDM), and mutual interference between subcarriers can be avoided, thereby saving bandwidth.
  • FDM frequency division multiplexing
  • OFDM technology has been widely used in existing communication systems, and this technology has been reflected in the wireless local area network standard. 802.11a and fixed wireless access standard 802.16a.
  • the radio access network of the 3rd Generation Partnership Project (3GPP) and the physical layer of IEEE 802.20 are also considering the use of OFDM technology to build mobile radios with higher frequency efficiency. Communication access system.
  • FIG. 1 shows the networking diagram of a typical frequency cellular multiplexing system.
  • two radio network controllers namely RNC1 and RNC2
  • CN core network
  • BS base stations
  • BS1 and BS3 are connected to RNC1 and BS4
  • BS5 and BS6 are connected to NC2
  • MS mobile stations
  • FIG. 2 is a typical cell omnidirectional antenna multiplexing method, referred to as a cell multiplexing method for short
  • FIG. 3 is a typical cell 120-degree directional antenna multiplexing method, which is referred to as a sector multiplexing method.
  • the data transmission system using OFDM technology has the following advantages: 1) Strong fault tolerance for multipath delay spread.
  • an OFDM symbol includes two parts in the time domain: a data part and a cyclic prefix part.
  • the cyclic prefix part is cyclically generated from the end of the data part, and the time occupied by the data part in the figure is ⁇ . '.
  • the time taken by the cyclic prefix part is.
  • the fault tolerance of OFDM technology is shown as follows: Compared with the duration Ts of an OFDM symbol, the duration of a typical channel impulse response is small, which only takes up a small part of Ts, so it can be increased by adding a smaller cyclic prefix. That is to completely overcome the interference between signals caused by multipath.
  • OFDM technology can recover digital signals carried by strong fading subcarriers by adopting redundant schemes such as channel coding.
  • the OFDM technology has higher spectrum efficiency.
  • the purpose of the channel estimation in the above key technology is: The receiver obtains the frequency domain channel information of the data transmitted by the transmitter through the channel estimation. After obtaining the frequency domain channel information, the receiver can perform processing such as equalization according to the frequency domain channel information to obtain corresponding data. Therefore, the channel estimation technology is an important prerequisite for the receiver to correctly acquire the data.
  • the IEEE 802.11a protocol provides channel estimation techniques. Specifically, in 802.11a systems, The frame structure of the frame is shown in FIG. 5. The beginning of each frame includes a preamble, followed by a variable-length data OFDM symbol. The data OFDM symbol includes user data and signaling. The pilot allocation scheme for 802.11a is shown in Figure 6. In the physical layer selection schemes of 802.11a and 802, 16a, Preamble is used for channel estimation. Specifically, since the receiver knows the data carried by each subcarrier of the preamble transmitted by the transmitter, the channel conditions experienced by each subcarrier of the preamble can be obtained by using the received preamble, and the channel environment changes slowly. In the case of the preamble, the channel conditions experienced by each subcarrier of the Preamble can be regarded as the channel conditions experienced by the subcarrier corresponding to the Preamble according to the OFDM symbol.
  • the solution provided by the 802.11 protocol is to approximate the channel conditions of the data OFDM symbols to the channel conditions of the corresponding Preamble.
  • this solution if the channel environment in the system changes rapidly, this approximation will bring large errors.
  • the relative movement between the receiver and the transmitter will cause the channel environment to change, so This solution will have certain limitations when applied to systems where the channel environment changes rapidly.
  • the current channel changes of mobile wireless communication systems tend to be fast. Obviously, the above scheme is not suitable for use in mobile wireless communication systems.
  • pilot subcarriers are introduced to track channel changes in the 802.11a OFDM implementation, in order to modify the channel conditions experienced by each subcarrier of the Preamble, and use the corrected channel conditions as the corresponding data OFDM
  • the channel value of the subcarrier of the symbol in order to modify the channel conditions experienced by each subcarrier of the Preamble, and use the corrected channel conditions as the corresponding data OFDM
  • This correction cannot fully reflect the rapid change of the channel, and it will still cause a large performance loss.
  • a pilot frequency allocation mode in a time-frequency grid mode is shown in FIG. 7.
  • the pilot OFDM symbols in this mode that is, Preamble, are evenly distributed on the time-frequency plane. Therefore, tracking the channel changes using the pilot OFDM symbols can solve the problem of channel environment changes to a certain extent.
  • a proposal submitted by Siemens to 3GPP RAN1, Tdoc R1-030780 proposes a specific time-frequency grid point pilot allocation mode, a corresponding channel estimation method, and corresponding simulation results. This method specifically uses two one-dimensional interpolation methods.
  • the main object of the present invention is to provide a method for implementing channel estimation in an OFDM system, so as to reduce the performance loss of the receiver when performing channel estimation.
  • a method for implementing channel estimation in an orthogonal multiple channel frequency division multiplexing system includes the following steps:
  • the transmitting end determines the distribution density of pilot OFDM symbols according to the maximum Doppler frequency shift supported by the OFDM system, and transmits pilot OFDM symbols and data OFDM symbols according to the determined distribution density.
  • the receiver estimates the frequency-domain channel information of the OFDM symbol based on the received pilot OFDM symbol.
  • the transmitting end determines the distribution density of pilot OFDM symbols according to the maximum Doppler frequency shift as follows: it is determined by the number of data OFDM symbols between adjacent pilot OFDM symbols, and the adjacent pilots Data between OFDM symbols
  • the number of OFDM symbols is determined by the following formula: Among them, ⁇ is the number of data OFDM symbols between adjacent pilot OFDM symbols, Td is the length of time occupied by the data OFDM symbols, and ⁇ is the maximum Doppler frequency domain supported by the system.
  • the step b includes the following steps:
  • the receiving end obtains time-domain channel information of the pilot OFDM symbol according to the received time-domain pilot OFDM symbol;
  • the frequency-domain channel information at the data OFDM symbols is obtained through estimation.
  • the solution of the present invention determines the distribution density of pilot OFDM symbols in the system by using the maximum Doppler frequency shift supported by the OFDM system, and the receiving end estimates the frequency domain channel information of the data OFDM symbols according to the received pilot OFDM symbols. This makes it possible to achieve better performance in situations where the channel environment changes quickly and in high latency.
  • the solution of the invention enhances the applicability of the data communication system to the channel environment, improves the performance of the actual channel estimation in the OFDM system, and thereby improves the data transmission efficiency of the actual system.
  • Figure 1 is a networking diagram of a typical frequency cellular multiplexing system
  • FIG. 2 is a schematic diagram of a typical cell omnidirectional antenna multiplexing method
  • Figure 3 is a schematic diagram of a typical 120-degree directional antenna multiplexing mode in a cell
  • FIG. 4 is a schematic diagram of OFDM symbols
  • FIG. 5 is a schematic diagram of a frame structure provided by 802.11a;
  • FIG. 6 is a schematic diagram of a pilot allocation scheme of 802.11a
  • FIG. 7 is a schematic diagram of a pilot grid mode
  • 8 is a schematic diagram of a distribution relationship between a pilot OFDM symbol and a data OFDM symbol
  • FIG. 9 is a schematic diagram of a structure of a pilot OFDM symbol
  • FIG. 10 is a schematic structural diagram of data OFDM symbols
  • FIG. 11 is a schematic flowchart of transmitting an OFDM symbol at a transmitting end
  • FIG. 12 is a schematic flowchart of a receiver receiving an OFDM symbol
  • FIG. 13 is a schematic diagram of a numbered segment of an OFDM symbol in a solution of the present invention.
  • FIG. 14 is a schematic diagram of a process of performing channel estimation by a receiving end according to an embodiment of the present invention.
  • FIG. 15 is a flowchart of a channel estimation process corresponding to FIG. 14 in the solution of the present invention
  • FIG. 16 is a flowchart of another channel estimation process in the solution of the present invention
  • FIG. 17 is a schematic diagram of the channel estimation performance obtained by using the solution of the present invention when the number of truncated paths is 32, and the vehicle A channel is 30 kmph;
  • FIG. 18 is a schematic diagram of a channel estimation performance obtained by using the solution of the present invention when the number of truncated paths is 32, and the vehicle A channel is 60 kmph;
  • FIG. 19 is a schematic diagram of a channel estimation performance obtained by using the solution of the present invention when the number of truncated paths is 160, and the vehicle B channel is 30 kmph.
  • the solution of the present invention first sets the distribution density of pilot OFDM symbols according to the maximum Doppler frequency shift supported by the system; the transmitter transmits pilot OFDM symbols and data OFDM symbols according to the distribution density; and the receiver uses the received pilot OFDM Symbol estimation data Frequency-domain channel information for OFDM symbols.
  • the solution of the present invention first determines the distribution density of pilot OFDM symbols according to the maximum Doppler frequency shift supported by the system, that is, the moving speed of the mobile station supported by the system.
  • the frame structure includes pilot OFDM symbols and data OFDM symbols, and the distribution relationship between the pilot OFDM symbols and the data OFDM symbols is shown in FIG. 8. Therefore, determining the distribution density of pilot OFDM symbols is also determining between adjacent pilot OFDM symbols.
  • the number of data OFDM symbols The number of data OFDM symbols between adjacent pilot OFDM symbols depends on how quickly the channel environment changes. More specifically, if the maximum Doppler frequency shift f d ⁇ supported by the system and the maximum moving speed supported by the system The relationship between v max is:
  • ⁇ is the carrier frequency used by the system and c is the speed of light
  • n is the speed of light
  • T d is the length of time occupied by the data OFDM symbol.
  • the length of the pilot OFDM symbol in the solution of the present invention may be the same as the length of the data OFDM symbol, or may be different.
  • pilot OFDM symbols and data OFDM symbols are also composed of a cyclic prefix part and a data part.
  • the cyclic prefix part is generated cyclically from the end of the data part, where the length of the cyclic prefix part and the data part is the part. The number of sample points occupied.
  • the structure of the pilot OFDM symbol is shown in FIG. 9, and the length of the cyclic prefix part is N. w , the length of the data part is ⁇ ⁇ ⁇ ; the structure of the data OFDM symbol is shown in FIG.
  • the length of the cyclic prefix part is N d , cp
  • the length of the data part is N d . data .
  • the length of the data part in the pilot OFDM symbol and the data OFDM symbol may be equal or different.
  • the length of the data part in the pilot OFDM symbol may be ⁇ . Set to less than According to the length of the data part in the OFDM symbol ⁇ , generally, these two values can be set to satisfy the following relationship:
  • the length of the cyclic prefix part in the pilot OFDM symbol and the data OFDM symbol may be equal or different.
  • the length of the cyclic prefix part of the pilot OFDM symbol may be set to be larger than the length N of the cyclic prefix part of the data OFDM symbol.
  • the transmitting end when transmitting, the transmitting end first generates pilot OFDM symbols and data OFDM symbols according to the cyclic prefix part and the data part of the pilot OFDM symbol and the data OFDM symbol.
  • the two symbols are multiplexed in the time domain, and then the generated OFDM symbols are transmitted through a process such as digital-to-analog conversion.
  • the transmitting process at the transmitting end is shown in Figure 11.
  • the receiving end When the receiving end receives the signal transmitted by the transmitting end, it first performs data sampling on the received electromagnetic signal; then, according to the obtained synchronization information, the received sampling data is demultiplexed in the time domain to form the received data. Time-domain pilot OFDM symbols and time-domain data OFDM symbols, and further obtain frequency-domain received signals of the pilot OFDM symbols and data OFDM symbols; and then estimate frequency-domain channel information of the data OFDM symbols based on the pilot OFDM symbols; and according to the data OFDM The channel information in the frequency domain of the symbols is channel-equalized to further recover the data OFDM symbols transmitted by the transmitting end.
  • the receiving process at the receiving end is shown in Figure 12.
  • the frequency domain channel information of the OFDM symbol estimated by the receiving end according to the pilot OFDM symbol data is processed in addition to the existing scheme, and there are two other specific types Processing method: One is to first obtain the time i or channel information at the pilot OFDM symbol according to the received pilot OFDM symbol, and then use the interpolation algorithm to estimate the data at the OFDM symbol based on the time-domain channel information.
  • Time domain Channel information to obtain the frequency domain channel information of the corresponding data OFDM symbol according to the time domain channel information of the data OFDM symbol; another processing method also first obtains the time domain channel information at the pilot OFDM symbol according to the received pilot OFDM symbol The difference is that after obtaining the time-domain channel information at the pilot OFDM symbol, the frequency-domain channel information at the pilot OFDM symbol is obtained according to the information, and then the frequency-domain channel information at the adjacent pilot OFDM symbol is obtained, The interpolation algorithm is used to estimate the frequency domain channel information at the data OFDM symbol.
  • the transmitted OFDM symbols are numbered according to the numbering rules described below:
  • pilot OFDM symbols are numbered sequentially in accordance with the time sequence of transmission, where the pilot OFDM symbols transmitted first are numbered smaller;
  • N data of adjacent pilot OFDM symbols Natural numbering of OFDM symbols: sequentially numbered from 1 to n, where the number of the first transmitted data OFDM symbol is smaller;
  • Number of data OFDM symbols The number of pilot OFDM symbols adjacent to itself and transmitted before itself is multiplied by the number of data OFDM symbols between adjacent pilot OFDM symbols, and then the data OFDM symbols are added in phase. Natural numbering between adjacent pilot OFDM symbols.
  • k-l, k, k + 1 and k + 2 are the numbers of pilot OFDM symbols; n * (k_ 1) + 1 ⁇ . n * (k-1) + n is the number of data OFDM symbols between pilot OFDM symbols k-1 and k; n * k + 1 ... n * k + n is pilot OFDM symbol k Number of data OFDM symbols between k + 1; n * (k + l) + 1 ... n * (k + 1) + n is the pilot OFDM symbol k
  • the frequency-domain signal carried by the i-th subcarrier of the k-th pilot OFDM symbol is A ; then, the frequency-domain signal sequence carried by the k-th pilot OFDM symbol is (Dk'o,, ..., D k , Np, d. Ta).
  • the first processing method that is, the method of first acquiring the time-domain channel information of the data OFDM symbol, and then acquiring the frequency-domain channel information is described in detail below. See FIG. 14 for the processing of this method. The corresponding process is shown in FIG. 15.
  • This processing method is implemented by the following steps: Step 1501: Obtain the time domain of the pilot ORDM symbol according to the received time domain pilot OFDM symbol. Channel response.
  • the time-domain signal sequence received by the k-th pilot OFDM symbol is ⁇ S k ' fi , S k ' ,,-, S K ' Npd , after Fourier transform, such as after fast Fourier transform (FFT), the obtained frequency
  • the domain received signal sequence is ⁇ ,. , ...,! ⁇
  • the frequency-domain signal sequence carried by the k-th pilot OFDM symbol is ( ⁇ , ..., ⁇ J
  • the frequency-domain channel response at the k-th pilot OFDM symbol is ( ⁇ ⁇ V .., ⁇ ), abbreviated as
  • Step 1502 Extract time-domain channel information at the pilot OFDM symbol according to the time-domain channel response at the pilot OFDM symbol.
  • the time-domain channel information includes path delay, path loss, and the like.
  • the information After obtaining the time-domain channel response at the pilot OFDM symbol, in order to reduce channel noise, the information needs to be analyzed to obtain effective channel information.
  • the simple truncation method which can be used when the channel delay range of the wireless transmission environment is known.
  • the other is the adaptive channel information extraction method.
  • the truncation range can be determined according to the delay extension supported by the system. For example, assuming that the channel delay is at most N sampling points, the steps can be directly performed at this time.
  • the time-domain channel response at the pilot OFDM symbol obtained in 1502 (c, ⁇ , truncation, and the truncation range is slightly larger than the number of sampling points corresponding to the maximum delay of the channel, for example, the truncation range is N, and N , ⁇ N.
  • the time-domain channel at the k-th pilot OFDM symbol obtained at this time is (., ⁇ , ..., 0), where the number of 0 is N p , rfato -N '.
  • the selected effective paths need not be continuous. For example, channel information that is valid for that period of time can be selected for a period of time. After the effective channel information is determined, 0 is used to replace the time domain channel response of the pilot OFDM symbol. The time domain channel value is not selected, so that the time domain channel information of the pilot OFDM symbol can be obtained.
  • the foregoing adaptive channel information extraction method may also be simplified, for example, truncation may be incorporated into the method.
  • the simplified method is called an adaptive truncation method.
  • the method first needs to determine the truncation length N.
  • N the time domain channel at the continuous time pilot OFDM symbol can be firstly reacted. .
  • Step 1503 Use time-domain channel information at adjacent pilot OFDM symbols and use a specific interpolation algorithm to estimate time-domain channel information at data OFDM symbols.
  • the time-domain channel information ( ⁇ ...) of the channel at the data OFDM symbol can be further estimated based on the information. , ⁇ ,, ⁇ , ⁇ .. ⁇ , where s is the number of the data OFDM symbol.
  • (..., ⁇ ⁇ ⁇ , ⁇ ) can be used to estimate the value of 4 relieve+ ,,., Where j is the natural numbering of data OFDM symbols in those data OFDMs between two adjacent pilot OFDM symbols.
  • the value of 4+ can be estimated by 2-1 Lagrangian interpolation, and the typical estimation formula is
  • ⁇ represents the time-domain channel value at the i-th sampling point at the k + m-th pilot OFDM symbol
  • n represents The number of data OFDM symbols between two adjacent pilot OFDM symbols.
  • n represents the number of data OFDM symbols between two adjacent pilot OFDM symbols.
  • n represents the number of data OFDM symbols between two adjacent pilot OFDM symbols.
  • Step 1504 Use the time-domain channel information at the data OFDM symbol to obtain frequency-domain channel information at the data OFDM symbol.
  • the s-th data in the time domain is obtained.
  • the time-domain information at the OFDM symbol is used to obtain the s-data OFDM symbol information.
  • Another channel estimation processing method of the solution of the present invention is as follows: firstly obtain the frequency domain channel information of the pilot OFDM symbol, and then obtain the frequency domain channel information of the data OFDM symbol according to the information. This process is shown in Figure 16, which corresponds to the following steps:
  • Step 1601 Obtain the time-domain channel response at the pilot OFDM symbol according to the received time-domain pilot OFDM symbol.
  • This process is the same as step 1501 in the above processing method.
  • Step 1602 Extract time-domain channel information at the pilot OFDM symbol from the time-domain channel response of the channel at the pilot OFDM symbol.
  • the time-domain channel information includes path delay and path attenuation. This process is also the same as step 1502 in the above processing method.
  • Step 1603 Use the obtained time-domain channel information at the pilot OFDM symbol to obtain an alignment. Frequency domain channel information at which OFDM symbols should be piloted.
  • Step 1604 Use frequency-domain channel information at adjacent pilot OFDM symbols, and use interpolation to estimate frequency-domain channel information at data OFDM symbols.
  • the interpolation method used in step 1604 may be a 2 /-1-time L interpolation method.
  • the frequency domain channel information at the OFDM symbol including the pilot subcarrier is used as the frequency domain channel information at the OFDM symbol adjacent to the OFDM symbol and containing data.
  • the solution of the present invention can achieve better performance in the case of changing channel environment and high delay.
  • the truncation path number is 32
  • the channel estimation results in the case of Vehicle A channel and 30 kmph are shown in FIG. 17, and the performance loss is less than 0.3 dB
  • the channel estimation results in the case of A channel and 60kmph are shown in FIG. 18, and the performance loss is less than l.ldB.
  • the performance loss of the channel estimation obtained by using the solution of the present invention is less than 0.7 dB compared to the ideal channel estimation.

Description

一种在正交多路频分复用系统中实现信道估计的方法 技术领域
本发明涉及正交多路频分复用 （OFDM )技术， 更确切地说是涉及 一种在 OFDM系统中实现信道估计的方法。 发明背景
OFDM技术作为具有传输高速率数据业务能力的频分复用技术， 一 方面， 相对于传统的单载波技术而言， OFDM技术能够利用简单的均衡 算法提供较高的频傅效率； 另一方面， 在采用 OFDM的系统中， 不需要 像传统的频分多路复用 （FDM )那样在相邻的载波之间分配较宽的保护 带宽， 就可以避免子载波之间的相互干扰， 从而节省了带宽。
目前， OFDM技术已被广泛应用在现有的通信系统中， 且该技术已 经体现在无线局域网标准.802.11 a及固定无线接入标准 802.16a中。另夕卜， 在移动无线通信接入系统中， 第三代合作伙伴计划（3GPP )的无线接入 网、 IEEE 802.20的物理层也正在考虑使用 OFDM技术， 以构建具有更 高频率效率的移动无线通信接入系统。
图 1所示为一个典型的频率蜂窝复用系统的组网图。 其中， 两个无 线网络控制器（ NC ), 即 RNC1和 RNC2, 与核心网 （CN )相连， 一 些基站（BS )分别与这两个 RNC相连，其中， BS1、 BS2及 BS3与 RNC1 相连， BS4、 BS5及 BS6与 NC2相连， 两台移动台 （MS ), 即 MS1、 MS2,与这些基站保持无线连接。 图 2为典型的小区全向天线复用方式， 简称为小区复用方式， 图 3为典型的小区 120度定向天线复用方式， 筒 称为扇区复用方式。 采用了 OFDM技术的数据传输系统具有以下优点： 1 )对多径延迟扩展具有较强的容错性。 如图 4所示， 一个 OFDM 符号时域上包括两个部分： 数据部分和循环前缀部分， 循环前缀部分由 数据部分的末端循环生成， 图中数据部分占用的时间为 ^。'。， 循环前缀 部分占用的时间为 。 OFDM技术的容错性表现在： 与一个 OFDM符 号的持续时间 Ts相比， 典型信道冲击响应的持续时间^ [艮小， 只占用 Ts 中一个很小的部分， 因此可以通过增加较小的循环前缀， 即 以完全克 服由多径引起的信号之间的干扰。
2 )对频率选择性衰落具有较强的容错性。 OFDM技术通过采用信 道编码等冗余方案， 可以恢复强衰落子载波所携带的数字信号。
3 )采用了简单的均衡算法。 由于 OFDM技术采用频域传递信号， 而信道的作用在频域上表现为简单的乘法，从而使采用 OFDM技术的数 据传输系统在执行信号均衡时， 只需要一个筒单的单抽头均衡器即可实 现。
4 )相对于 FDM技术而言， OFDM技术具有较高的频谱效率。
虽然采用 OFDM技术的数据传输系统具有上述优点，但是要使上述 优点能够在系统的实际应用中完全体现出来， 更重要的是能使系统正常 工作， 必须要解决以下关键技术： 频率同步、 符号同步、 帧同步、 信道 估计和均衡等。 这些关键技术与系统的实际使用环境密切相关， 也与系 统的网络配置要求密切相关。
上述关键技术中的信道估计的目的在于： 接收方通过信道估计得到 发射方发射的数据的频域信道信息。 在得到该频域信道信息后， 接收方 就可以根据该频域信道信息进行均衡等处理，以得到相应的数据。 因此， 信道估计技术是接收方正确获取数据的重要前提。
IEEE 802.11a协议提供了信道估计技术。 具体来说， 802.11a系统中 的帧结构如图 5所示， 每帧的开始包括一个前导符号（Preamble ), 其后 是不定长的数据 OFDM符号，该数据 OFDM符号包括用户数据和信令。 802.11a的导频分配方案则如图 6所示。 在 802.11a和 802,16a的物理层 选择方案中， 是利用 Preamble进行信道估计。 具体来说， 由于接收机知 道发射机所发射的 Preamble的每个子载波所承载的数据， 因此， 利用接 收到的 Preamble即可得到该 Preamble的每个子载波所经历的信道条件， 在信道环境变化緩慢的情况下， Preamble的每个子载波所经历的信道条 件即可认为是与该 Preamble相应的 ^：据 OFDM符号相应的子载波所经 历的信道条件。
也就是说， 802.11协议所提供的这种方案是将数据 OFDM符号的信 道条件近似为相应的 Preamble的信道条件。对于这种方案来说， 如果系 统中的信道环境变化较快， 则这种近似会带来较大的误差， 另外， 由于 接收机与发射机之间的相对运动会引起信道环境的变化, 因此说， 该方 案在应用于信道环境变化较快的系统中会有一定的局限性。 目前的移动 无线通讯系统的信道变化往往较快， 显然在移动无线通讯系统中不适合 采用上述方案。
另外， 虽然在 802.11a的 OFDM实现方案中引入了导频子载波对信 道的变化进行跟踪， .以修正 Preamble的每个子载波所经历的信道条件， 并将修正后的信道条件作为相应的数据 OFDM符号的子载波的信道值 , 但是这种修正不能完全反映信道的快速变化， 仍然会弓 I起较大的性能损 失。
为解决上述方案的不足，业界提出了时频格点方式的导频分配模式， 这种分配模式如图 7所示。 该方式中的导频 OFDM符号， 即 Preamble, 在时频平面上均匀分布， 因此，利用导频 OFDM符号跟踪信道的变化在 一定程度上可以解决信道环境变化的问题。 目前，西门子公司提交给 3GPP RAN1的一篇提案 Tdoc R1 - 030780 中， 提出了一种具体的时频格点方式的导频分配模式， 与之对应的信道 估计方法， 以及相应的仿真结果。 该方法具体是采用两次一维插值的方 法， 首先在时域上进行 3 次 Lagrange插值， 然后在频域上进行 7 次 Lagrange插值， 以获得时频平面上传送数据的子载波的信道条件。 西门 子提供的仿真结果显示： 相对于理想的信道估计， 西门子的信道估计方 案对于 PA3、 PB3、 VA30信道有 0.5 - 0.7dB的性能损失， 对于 VB30信 道， 在 BLER = 0.13处甚至出现了地板。 所以说， 如果信道为大延迟信 道， 采用西门子的信道估计方法会表现出较大的性能损失。 发明内容
有鉴于此，本发明的主要目的在于提供一种在 OFDM系統中实现信 道估计的方法， 以减小接收方在进行信道估计时的性能损失。
为达到以上目的， 本发明的技术方案是这样实现的： 一种在正交多 路频分复用系统中实现信道估计的方法， 该方法包括以下步驟：
a.发射端根据正交多路频分复用 OFDM 系统所支持的最大多普勒 频移，确定导频 OFDM符号的分布密度，并按照所确定的分布密度发射 导频 OFDM符号及数据 OFDM符号；
b.接收端根据收到的导频 OFDM符号估计数据 OFDM符号的频域 信道信息。
所述步驟 a中，所述发射端根据最大多普勒频移确定导频 OFDM符 号的分布密度为： 通过相邻导频 OFDM符号之间的数据 OFDM符号的 个数确定， 且相邻导频 OFDM符号之间的数据 OFDM符号的个数通过 下述公式确定：
Figure imgf000006_0001
其中， η为相邻导频 OFDM符号之间的数据 OFDM符号的个数， Td为数据 OFDM符号所占用的时间长度， ^ 为系统支持的最大多普 勒频域。
所述步骤 b包括以下步骤：
bll.接收端根据接收到的时域导频 OFDM符号获取导频 OFDM符 号的时域信道信息；
bl2.根据导频 OFDM符号的时域信道信息提取导频 OFDM符号处 的时域信道信息；
bl3.根据相邻导频 OFDM符号的时域信道信息， 通过估计得到数 据 OFDM符号处的频域信道信息。
本发明方案通过利用 OFDM 系统所支持的最大多普勒频移对系统 中导频 OFDM符号的分布密度进行确定， 并由接收端根据收到的导频 OFDM符号估计数据 OFDM符号的频域信道信息， 使得在信道环境变 化较快、 以及高延迟的情形下都可以取得较好的性能。 本发明方案加强 了数据通讯系统对信道环境的适用性，提高了 OFDM系统中实际信道估 计的性能， 从而提高了实际系统的数据传输效率。 附图简要说明
图 1为典型的频率蜂窝复用系统的组网图；
图 2为典型的小区全向天线复用方式示意图；
图 3为典型的小区 120度定向天线复用方式示意图；
图 4为 OFDM符号示意图；
图 5为 802.11a提供的帧结构示意图；
图 6为 802.11a的导频分配方案示意图；
图 7为导频格点方式示意图； 图 8为导频 OFDM符号和数据 OFDM符号之间的分布关系示意图； 图 9为导频 OFDM符号的结构示意图；
图 10为数据 OFDM符号的结构示意图；
图 11为发射端发射 OFDM符号的流程示意图；
图 12为接收机接收 OFDM符号的流程示意图； '
图 13为本发明方案中 OFDM符号的编号片断示意图；
图 14 为本发明实施例中接收端进行信道估计的一种处理经过示意 图；
图 15为本发明方案中与图 14对应的信道估计处理流程图； 图 16为本发明方案中另一种信道估计处理的流程图；
图 17为截断径数为 32时， Vehicle A信道、 30kmph情形下， 采用 本发明方案得到的信道估计性能仿真示意图；
图 18为截断径数为 32时， Vehicle A信道、 60kmph情形下， 釆用 本发明方案得到的信道估计性能仿真示意图；
图 19为截断径数为 160时， Vehicle B信道、 30kmph情形下， 采用 本发明方案得到的信道估计性能仿真示意图。 实施本发明的方式 '
本发明方案首先根据系统所支持的最大多普勒频移设置导频 OFDM 符号的分布密度； 发射方根据该分布密度发射导频 OFDM符号和数据 OFDM符号； 接收方则根据接收到的导频 OFDM符号估计数据 OFDM 符号的频域信道信息。
下面结合附图及具体实施例对本发明方案作进一步详细的说明。 本发明方案首先要根据系统所支持的最大多普勒频移， 即系统所支 持的移动台移动速度，确定导频 OFDM符号的分布密度。与现有技术相 同， 帧结构包括导频 OFDM符号和数据 OFDM符号， 导频 OFDM符号 和数据 OFDM符号分布关系如图 8所示， 因此确定导频 OFDM符号的 分布密度也就是确定相邻导频 OFDM符号之间的数据 OFDM符号的个 数。 相邻导频 OFDM符号之间的数据 OFDM符号的个数依赖于信道环 境的变化快慢程度， 更明确地说， 如果系统所支持的最大多普勒频移 fd^与系统支持的最大移动速度 vmax之间的关系为：
V
f = f .— ,
J rf.max J c ，
C
其中， Λ为系统所使用的载波频率， c 为光速， 则两个相邻导频 OFDM符号之间的数据 OFDM符号的个数 n在一般情况下应满足以下 条件：
n - d -fd^ < 也即" .7 / <^
2 c 2
其中， ： Td为数据 OFDM符号所占用的时间长度。
与现有技术相同，本发明方案中的导频 OFDM符号的长度可以与数 据 OFDM符号的长度相同， 也可以不同。 与通常的 OFDM符号一样， 导频 OFDM符号和数据 OFDM符号也是由循环前缀部分和数据部分构 成， 循环前缀部分由数据部分的末端循环生成， 其中， 循环前缀部分与 数据部分的长度即为该部分占用釆样点的个数。其中，导频 OFDM符号 的结构如图 9所示， 其中的循环前缀部分的长度为 N。w , 数据部分的长 度为 Λ^αία ; 数据 OFDM符号的结构如图 10所示， 其中的循环前缀部分 的长度为 Nd,cp , 数据部分的长度为 Nd.data。 通常导频 OFDM符号与数据 OFDM符号中数据部分的长度可以相 等， 也可以不等， 本发明方案中， 为了減少导频 OFDM符号对系统资源 的占用， 可以将导频 OFDM符号中数据部分的长度 ^。设置为小于数 据 OFDM符号中数据部分的长度^， 一般来说，可以将这两个数值设 置为满足以下关系：
Np,data = -~-Nd<data ; 式中的 " = 0,1,……。 通常导频 OFDM符号与数据 OFDM符号中循环前缀部分的长度可 以相等， 也可以不等， 本发明方案中， 为了增强多径延迟对导频 OFDM 符号的负面影响，可以将导频 OFDM符号的循环前缀部分的长度 设 置为大于数据 OFDM符号的循环前缀部分的长度 N 。
基于上述对导频 OFDM符号及数据 OFDM符号的设置， 发射端在 发射时， 首先会根据导频 OFDM符号和数据 OFDM符号的循环前缀部 分及数据部分生成导频 OFDM符号和数据 OFDM符号， 然后在时域上 对这两个符号进行复用，之后通过数模转换等过程将生成的 OFDM符号 发射出去。 发射端的发射过程如图 11所示。
接收端在接收到发射端发射的信号时， 首先对接收到的电磁信号进 行数据采样； 之后依据已经获得的同步信息， 对接收到的采样数据在时 域上进行解复用，形成接收到的时域导频 OFDM符号和时域数据 OFDM 符号， 并进一步获取导频 OFDM符号和数据 OFDM符号的频域接收信 号； 再依据导频 OFDM符号估计数据 OFDM符号的频域信道信息； 并 根据数据 OFDM符号的频域信道信息进行信道均衡，进一步恢复发射端 所发射的数据 OFDM符号。 接收端的接收过程如图 12所示。
在接收端对接收到的信号进行处理的过程中， 对于接收端依据导频 OFDM符号估计数据 OFDM符号的频域信道信息来说， 除了按照现有 方案进行处理之外， 具体还有两种其他的处理方法： 一种是首先才艮据接 收到的导频 OFDM符号获取导频 OFDM符号处的时 i或信道信息， 再根 据该时域信道信息，并利用插值算法估计出数据 OFDM符号处的时域信 道信息，从而根据数据 OFDM符号的时域信道信息得到对应数据 OFDM 符号的频域信道信息； 另一种处理方法同样首先根据接收到的导频 OFDM符号获取导频 OFDM符号处的时域信道信息， 所不同的是， 在 得到导频 OFDM符号处的时域信道信息后， 再根据该信息得到导频 OFDM符号处的频域信道信息， 之后根据相邻导频 OFDM符号的频域 信道信息， 并利用插值算法估计出数据 OFDM符号处的频域信道信息。
为便于对这两种处理方法进行描述，对发射的 OFDM符号按照如下 所述的编号规则进行编号：
导频 OFDM符号的编号： 对导频 OFDM符号按照发射的时间顺序 顺次编号， 其中， 先发射的导频 OFDM符号的编号较小；
相邻导频 OFDM符号之间的 n个数据 OFDM符号的自然编号：从 1 到 n顺次编号， 其中， 先发射的数据 OFDM符号的编号较小；
数据 OFDM符号的编号： 与自身相邻、 且先于自身发射的导频 OFDM符号的编号与相邻导频 OFDM符号之间的数据 OFDM符号个数 相乘， 然后加上该数据 OFDM符号在相邻导频 OFDM符号之间的自然 编号。
采用上述编号规则的一段 OFDM符号的编号片断如图 13所示， 图 中， k - l、k、k+ 1及 k + 2为导频 OFDM符号的编号； n*(k_ 1 ) + 1 ··.··· n* (k-1) +n为导频 OFDM符号 k- 1与 k之间的数据 OFDM符号的 编号； n*k + 1…… n*k + n为导频 OFDM符号 k与 k + 1之间的数据 OFDM 符号的编号； n* (k+l) + 1...... n* (k+1) +n为导频 OFDM符号 k
+ 1与 k + 2之间的数据 OFDM符号的编号。
基于上述编号， 假设第 k个导频 OFDM符号的第 i个子载波所承载 的频域信号为 Α; , 则第 k个导频 OFDM符号所承载的频域信号序列为 (Dk'o， ，…， Dk,Np,d。ta )。
下面首先对第一种处理方法，即先获取数据 OFDM符号的时域信道 信息， 再获取频域信道信息的方法作详细说明。 该方法的处理经过参见 图 14, 其所对应的流程如图 15所示， 该处理方法通过以下步驟实现： 步骤 1501、 根据接收到的时域导频 OFDM符号获取导频 ORDM符 号处时域的信道反应。
假如第 k 个导频 OFDM 符号接收的时域信号序列为 {Sk'fi,Sk',,-,SK'Npd , 经过傅立叶变换， 比如经过快速傅立叶变换（FFT) 后， 得到的频域接收信号序列为^,。 ，…,!^ ), 由于第 k个导频 OFDM符号所承载的频域信号序列为 ( ^ ^,...,^^ J , 因此第 k个导 频 OFDM 符号处的频域信道反应为（^ ^v..,^^), 简记为
Dk,0 Dk,\ D ,Np a
( , ,..., ,J。 将得到的频域反应 ( 0, 15-5 ^)进行傅立叶逆 变换， 比如进行快速傅立叶逆变换（IFFT), 即可得到第 k个导频 OFDM 符号处信道的时域信道反应， 简记为（ 。， ，…， ）。
步驟 1502、根据导频 OFDM符号处的时域信道反应提取导频 OFDM 符号处的时域信道信息。 该时域信道信息包括径的延迟、 径的衰耗等。
在得到导频 OFDM符号处的时域信道响应后， 为减少信道噪声，还 需要对这些信息进行分析， 以获取有效的信道信息。
信道信息获取方法有两种， 一种是简单截断法， 可以在已知无线传 输环境信道延迟范围的情况下使用； 另一种是自适应的信道信息提取方 法。
对于简单截断法来说， 可以根据系统所支持的时延扩展来确定截断 范围， 比如， 假设信道的延迟最多为 N个采样点， 此时可以直接对步骤 1502中得到的导频 OFDM符号处的时域信道反应（c ,^, 进行 截断，且截断的范围略大于信道的最大延迟对应的采样点的个数，比如， 截断范围为 N，，且 N，≥N。此时得到的第 k个导频 OFDM符号处的时域 信道为 ( 。,^, ...,0) , 其中， 0 的个数为 Np,rfato - N'。 自适应的信 道信息提取方法具体来说，是通过对一段时间连续接收到的导频 OFDM 符号的时域信道反应 ( 。， ，…，(^ )进行分析，并选择其中的一部分最 强径作为有效径， 所选择的有效径不必是连续的。 比如， 在一段时间中 可以选择 作为该段时间有效的信道信息。在确定了有效信 道信息之后，用 0来代替导频 OFDM符号的时域信道反应中未被选中的 时域信道值， 这样， 即可获得导频 OFDM符号的时域信道信息。
另外， 还可以对上述自适应的信道信息提取方法进行简化， 比如， 可以在该方法中融入截断。 将筒化后的方法称为自适应的截断法， 具体 来说， 该方法首先需要确定截断长度 N，， 在确定 N，时， 可以首先对连 续时间的导频 OFDM符号处的时域信道反应 。）进行分析， 以确定其能量集中的区域， 并将该区域所对应的长度作为 N，， 该 N，即 为所确定的截断长度， 获取 N，之前所对应的所有时域信道值， 然后用 0 来代替导频 OFDM符号处的时域信道反应中未被选中， 也即 N，之后所 有的时域信道值， 从而确定了时域信道信息。
步骤 1503、 利用相邻导频 OFDM符号处的时域信道信息， 并利用 特定的插值算法估计出数据 OFDM符号处的时域信道信息。
在获取了导频 OFDM符号处的时域信道信息 (cf, ^,0,…,0)之 后，可以根据该信息进一步估计出数据 OFDM符号处信道的时域信道信 息 (^^^...,^,,Ο,·..^ , 式中 s为数据 OFDM符号的编号。
具体来说， 可以利用（...,^ Κ^^,·.·)来估计 4„+，,.的值， 式中 j为数据 OFDM符号在相邻两个导频 OFDM符号之间的那些数据 OFDM 中的自然编号。
估计 4„+,的值可以采用 2 - 1 次拉格朗日插值， 典型的估计公式
Figure imgf000014_0001
其中， ^表示第 k + m个导频 OFDM符号处第 i个采样点处的时 域信道值， 表示第 k + j个数据 OFDM符号处第 i个采样点处的 时域信道值， n表示两个相邻导频 OFDM符号之间的数据 OFDM符号 的个数。
当采用一次拉格朗日插值， 即线性插值时， 上述公式可以简化为：
Ck +j = Ck,i +
n + 1
其中， 表示第 k个导频 OFDM符号处第 i个采样点处的时域信道 值， 4„+ ,,.表示第 k*n + j个数据 OFDM符号处第 i个采样点处的时域信 道值， n表示两个相邻导频 OFDM符号之间的数据 OFDM符号的个数。
还可以采用 2/ - 1次对数拉格朗日插值， 典型的估计公式如下： ln(4"w,,)
Figure imgf000014_0002
其中， 表示第 k + m个导频 OFDM符号处第 i个采样点处的时 域信道值， 4 表示第 k*n + j个数据 OFDM符号处第 i个采样点处的 时域信道值， n表示两个相邻导频 OFDM符号之间的数据 OFDM符号 的个数。 同样， 当采用一次对数拉格朗日插值， 即对数线性插值时， 上面的 公式可以简化为： ln(4 ) = ¥ ) + ^ · (1 +1,,) - 1η( 》 其中， 表示第 k个导频 OFDM符号处第 i个采样点处的时域信道 值， 4„+,;表示第 k*n + j个数据 OFDM符号处第 i个采样点处的时域信 通过上述任何一个公式， 都可以估计得到 «, .., ,)的值， 在其 后面添加 Nd,data - N'个 0, 就可以得到 (« ,..., (^,,Ο ,.,Ο)。
步骤 1504、 利用得到的数据 OFDM符号处的时域信道信息得到该 数据 OFDM符号处的频域信道信息。
具体来说,就是对得到的时域的第 s个数据 .OFDM符号处的时域信 得到笫 s个数据 OFDM符号处信
Figure imgf000015_0001
道的频域反应 。
Figure imgf000015_0002
本发明方案另外一种信道估计处理方法为：首先获取导频 OFDM符 号的频域信道信息，然后根据该信息获取数据 OFDM符号的频域信道信 息。 该过程参见图 16, 对应以下步骤：
步骤 1601、 根据接收到的时域导频 OFDM符号获取导频 OFDM符 号处时域的信道反应。
该过程与上述处理方法中的步骤 1501相同。
步骤 1602、 从导频 OFDM符号处信道的时域信道反应提取导频 OFDM符号处的时域信道信息。 该时域信道信息包括径的延迟、 径的衰 该过程同样与上述处理方法中的步骤 1502相同。
步骤 1603、 利用得到的导频 OFDM符号处的时域信道信息得到对 应导频 OFDM符号处的频域信道信息。
步骤 1604、 利用相邻导频 OFDM符号处的频域信道信息， 并利用 插值方法估计数据 OFDM符号处的频域信道信息。
在步骤 1604中采用的插值方法可以是 2/ - 1次 L插值方法。 另夕卜， 接将包含导频子载波的 OFDM符号处的频域信道信息作为与该 OFDM 符号相邻、 且包含数据的 OFDM符号处的频域信道信息。
本发明方案可以在信道环境变化情形以及高延迟情况下取得的较好 的性能。 具体来说， 通过本发明方案， 相对于理想的信道估计来说， 在 截断径数为 32时， Vehicle A信道、 30kmph情形下的信道估计结果如图 17所示， 性能损失小于 0.3dB; Vehicle A信道、 60kmph情形下的信道 估计结果如图 18所示， 性能损失小于 l.ldB。 在截断径数为 160时， 在 Vehicle B信道、 30kmph的情形下， 如图 19所示， 采用本发明方案得到 的信道估计相对于理想信道估计来说， 性能损失也小于 0.7dB。
以上所述仅为本发明方案的较佳实施例， 并不用以限定本发明的保 护范围。

Claims

权利要求书
1、一种在正交多路频分复用系统中实现信道估计的方法，其特征在 于， 该方法包括以下步骤：
a.发射端根据正交多路频分复用 OFDM 系统所支持的最大多普勒 频移，确定导频 OFDM符号的分布密度， 并按照所确定的分布密度发射 导频 OFDM符号及数据 OFDM符号；
b.接收端根据收到的导频 OFDM符号估计数据 OFDM符号的频域 信道信息。
2、根据权利要求 1所述的方法， 其特征在于所述步骤 a中， 所述发 射端根据最大多普勒频移确定导频 OFDM符号的分布密度为：通过相邻 导频 OFDM符号之间的数据 OFDM符号的个数确定，且相邻导频 OFDM 符号之间的数据 OFDM符号的个数通过下述公式确定：
Figure imgf000017_0001
其中， n为相邻导频 OFDM符号之间的数据 OFDM符号的个数， Td为数据 OFDM符号所占用的时间长度， 皿为系统支持的最大多普 勒频域。
3、根据权利要求 1所述的方法，其特征在于所述步骤 a进一步包括： 将导频 OFDM符号数据部分长度 N„与数据 OFDM符号数据部分长度
^. 的关系设置为：
Np,data = jrNd,dala ', 式中的 " = 0,1,……。
4、根据权利要求 1所述的方法，其特征在于所述步驟 a进一步包括： 将导频 OFDM符号循环前缀部分的长度设置为大于数据 OFDM符号循 环前缀部分的长度。
5、根据权利要求 1所述的方法， 其特征在于， 所述步骤 b包括以下 步骤：
bll.接收端根据接收到的时域导频 OFDM符号获取导频 OFDM符 号的时域信道信息；
bl2.根据导频 OFDM符号的时域信道信息提取导频 OFDM符号处 的时域信道信息；
bl3.根据相邻导频 OFDM符号的时域信道信息， 通过估计得到数 据 OFDM符号处的频域信道信息。
6、根据权利要求 5所述的方法， 其特征在于， 所述步骤 bll包括以 下步骤：
bill.根据接收到的时域导频 OFDM符号获取导频 OFDM符号的频 域接收信号；
12.根据导频 OFDM符号的频域接收信号， 以及发射端发射的导 频 ODFM符号的频域信号， 得到导频 OFDM符号处的频域信道信息； bll3. 对得到的导频 OFDM符号的频域信道信息进行傅立叶逆变 换， 得到导频 OFDM符号处的时域信道信息。
7、根据权利要求 5所述的方法， 其特征在于所述步骤 bl2中， 所述 接收端 4艮据导频 OFDM符号的时域信道信息提取导频 OFDM符号处的 时域信道信息为：从步骤 Ml得到的导频 OFDM符号处的时域信道信息 中， 根据系统所支持的时延扩展确定截断范围， 获取该截断范围所对应 的时域信道值，并用 0代替导频 OFDM符号处的时域信道信息中被截去 的时域信道值。
8、根据权利要求 5所述的方法， 其特征在于所述步骤 bl2中， 所述 接收端才艮据导频 OFDM符号的时域信道信息提取导频 OFDM符号处的 时域信道信息为：通过分析连续时间的导频 OFDM符号处的时域信道信 息确定时域信道中一条以上的最强径， 获取该最强径所对应的时域信道 值，并用 0代替导频 OFDM符号处的时域信道信息中未被选中的时域信 道值。
9、根据权利要求 5所述的方法， 其特征在于所述步骤 bl2中， 所述 接收端根据导频 OFDM符号的时域信道信息提取导频 OFDM符号处的 时域信道信息为：通过分析连续时间的导频 OFDM符号处的时域信道信 息^定截断范围， 获取该截断范围所对应的时域信道值， 并用 0代替导 频 OFDM符号处的时域信道信息中未被选中的时域信道值。
10、根据权利要求 5所述的方法， 其特征在于， 所述步驟 bl3包括： 接收端通过对相邻导频 OFDM符号的时域信道信息进行插值估计，得到 数据 OFDM符号处的时域信道信息； 之后通过对数据 OFDM符号的时 域信道信息进行傅立叶逆变换， 得到相应的频域信道信息。
11、根据权利要求 10所述的方法， 其特征在于， 所述接收端通过对 相邻导频 OFDM符号的时域信道信息进行插值估计为：采用 11 - 1次对 数拉格朗日插值方法进行插值估计。
12、根据权利要求 5所述的方法， 其特征在于， 所述步骤 M3包括： 接收端根据得到的导频 OFDM符号的时域信道信息得到相应的频域信 道信息；之后通过对相邻导频 OFDM符号处的频域信道信息进行插值估 计， 得到数据 OFDM符号处的频域信道信息。
13、 根据权利要求 10或 12所述的方法， 其特征在于， 所述接收端 通过对相邻导频 OFDM符号的时域信道信息进行插值估计为：采用 21 - 1次拉格朗日插值方法或 1次拉格朗日插值方法进行插值估计。
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CN116074162A (zh) * 2021-11-01 2023-05-05 大唐移动通信设备有限公司 信道估计和/或感知参数估计方法、装置、设备及可读存储介质

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CN100359959C (zh) 2008-01-02
KR20070036117A (ko) 2007-04-02
US20070183519A1 (en) 2007-08-09
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EP1742402A1 (en) 2007-01-10
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