CN113037664B - Comb-shaped pilot channel estimation and equalization device and method for OFDM system - Google Patents
Comb-shaped pilot channel estimation and equalization device and method for OFDM system Download PDFInfo
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Abstract
The invention discloses a comb-shaped pilot channel estimation and equalization device and method of an OFDM system, wherein the device comprises: an input buffer unit for receiving and buffering the effective input data of the OFDM signal; the pilot frequency storage unit is used for storing a local initial pilot frequency symbol; a channel estimation unit for performing pilot channel response estimation; the IFFT computing unit is used for carrying out IFFT operation to obtain the time domain impulse response of the wireless channel; the intermediate buffer unit is used for buffering a plurality of data in the first time domain impulse response; the data preprocessing unit is used for preprocessing a plurality of data in the first time domain impulse response; the FFT calculating unit is used for estimating frequency domain channel responses by utilizing the preprocessed first data; the data equalization unit is used for carrying out channel equalization; and the output buffer unit is used for buffering and outputting the channel equalization result. The comb-shaped pilot frequency channel estimation and equalization device and method of the OFDM system can reduce the calculation complexity of channel equalization, shorten calculation time delay and improve equalization precision.
Description
Technical Field
The invention relates to the technical field of communication engineering, in particular to a comb-shaped pilot channel estimation and equalization device and method of an OFDM system.
Background
Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation technique widely used in the field of mobile communication, has a high spectrum utilization rate, and can resist multipath interference and wireless channel fading. At a transmitting end of the OFDM system, information bits are mapped to QAM (Quadrature Amplitude Modulation) or PSK (phase-shift keying) symbols after being encoded and interleaved, and after pilot is inserted according to a certain pilot insertion rule, IFFT (Inverse Fast Fourier Transform) operation is performed and a Cyclic Prefix (CP) is added, and then the information bits are transmitted. After the signal reaches the receiving end through the wireless channel, the signal without the cyclic prefix is firstly subjected to Fast Fourier Transform (FFT) operation, and then the pilot symbols inserted by the transmitting end are utilized to complete channel estimation and equalization, so as to compensate the influence of the wireless channel on the signal. Then, QAM or PSK demapping is completed on the equalized data symbols, and the obtained bit data is deinterleaved and decoded to obtain sending information data.
At present, the commonly used pilot insertion method for the OFDM system mainly includes a block pilot structure, a comb pilot structure, and a hybrid pilot structure. The comb-shaped pilot frequency structure can well track the time-varying characteristic of a wireless channel and is a main scheme adopted in a high-speed mobile application scene. The channel estimation and equalization method based on the comb-shaped pilot frequency structure firstly estimates the frequency domain channel response of the pilot frequency position by utilizing the scattered pilot frequency distributed in the signal bandwidth, then estimates the full frequency domain channel response by an interpolation method or an FFT (fast Fourier transform) method, and finally completes the data equalization by utilizing the full frequency domain channel response.
The interpolation method adopts polynomial interpolation or designs a proper low-pass filter as an interpolation filter, and estimates channel responses of other positions of a frequency domain based on the channel response of a pilot frequency position; the FFT method firstly estimates the time domain impulse response of the wireless channel by IFFT operation by utilizing the frequency domain channel response of the pilot frequency position, and then carries out FFT transformation on the time domain impulse response so as to determine the channel responses of other positions of the frequency domain.
However, in practical applications, when the interpolation method is adopted, noise has a large influence on the channel estimation performance, and the problem of discontinuous channel response phase is easily caused. Compared with the interpolation method, although the FFT transformation method can reduce the influence of noise on the channel estimation performance, and avoid the problem of discontinuous channel response phase caused by the interpolation method, and has a better channel equalization effect, the FFT transformation method involves IFFT and FFT operations, resulting in a relatively large computational complexity and processing delay of the FFT transformation method. When the OFDM comb-type pilot channel equalization is completed by adopting an FFT (fast Fourier transform) method, assuming that an OFDM signal comprises N subcarriers and P pilot symbols, P-point IFFT (inverse fast Fourier transform) operation and N-point FFT (fast Fourier transform) operation need to be completed once, and the calculation complexity is obviously improved when the number N of the OFDM subcarriers is larger; meanwhile, from the first effective data input equalizer of the OFDM signal to the last calculation result output equalizer, the time delay is about 4N +2P clock cycles, which exceeds 4 times of the duration of one OFDM signal. In addition, when the OFDM signal contains guard subcarriers, the current method only fills guard symbols on the guard subcarriers without adding pilot symbols, and at this time, the comb-shaped pilot symbols are not uniformly distributed in the whole signal band, which may cause leakage of channel impulse response energy, thereby affecting the channel estimation and equalization accuracy.
Disclosure of Invention
In order to solve some or all technical problems in the prior art, the present invention provides a comb-shaped pilot channel estimation and equalization apparatus and method for an OFDM system.
In a first aspect, the present invention discloses a comb-type pilot channel estimation and equalization apparatus for an OFDM system, the apparatus comprising:
an input buffer unit for receiving and buffering the effective input data of the OFDM signal;
the pilot frequency storage unit is used for storing a local initial pilot frequency symbol;
a channel estimation unit, configured to perform pilot channel response estimation by using the valid input data and the local initial pilot symbol to obtain a channel response of a pilot position;
an IFFT calculation unit, configured to perform IFFT operation on the channel response of the pilot frequency position to obtain a wireless channel time domain impulse response;
the intermediate buffer unit is used for buffering a plurality of data in the first time domain impulse response of the wireless channel, wherein the number of the buffered data is a preset value;
the data preprocessing unit is used for preprocessing a plurality of data in the first time domain impulse response of the wireless channel;
the FFT calculating unit is used for estimating the frequency domain channel response corresponding to the sub-carrier of the OFDM signal by utilizing the first plurality of data of the preprocessed wireless channel time domain impulse response;
a data equalization unit, configured to perform channel equalization on data symbols using the frequency domain channel response;
and the output buffer unit is used for buffering and outputting the channel equalization result.
In some optional embodiments, the apparatus further comprises:
the data write-in controller is used for controlling the data write-in mode of the input cache unit;
and the data reading controller is used for controlling the data reading mode of the input buffer unit.
In some optional embodiments, the input buffer unit includes:
the dual-port random access memory comprises two dual-port random access memories, the two dual-port random access memories are matched with each other in a ping-pong structure mode, and each dual-port random access memory can simultaneously carry out read operation and write operation.
In some optional embodiments, the intermediate cache unit comprises:
the single-port random access memory comprises two single-port random access memories, the two single-port random access memories are matched with each other in a ping-pong structure mode, and the read operation and the write operation of each single-port random access memory are set to be carried out in a time-sharing mode.
In some optional embodiments, the output buffer unit includes:
a dual-port random access memory including one for caching channel equalization results.
In some optional embodiments, the data preprocessing unit comprises:
the read address generator is used for reading the wireless channel time domain impulse response data from the intermediate buffer unit and reading a cosine value and a sine value corresponding to the twiddle factor from the twiddle factor compression storage subunit;
the twiddle factor compression storage subunit is used for storing cosine values and sine values corresponding to twiddle factors;
the rotation factor transformation subunit is used for transforming the read cosine values and sine values to obtain rotation factors corresponding to the cosine values and the sine values;
and the complex multiplier is used for weighting the twiddle factors obtained by transformation and the read wireless channel time domain impulse response data and sending the weighted result to the FFT calculating unit.
In a second aspect, the present invention also discloses a method for estimating and equalizing a comb-shaped pilot channel of an OFDM system, wherein the method comprises:
a data caching step: receiving and buffering effective input data of an OFDM signal, wherein the effective input data of the OFDM signal is a subcarrier of the OFDM signal;
pilot channel response estimation step: reading a pilot frequency symbol from the effective input data according to the subcarrier serial number, and performing pilot frequency channel response estimation by using the read pilot frequency symbol and a local initial pilot frequency symbol to obtain channel response of a pilot frequency position;
a data transformation step: performing IFFT operation on the channel response of the pilot frequency position to obtain wireless channel time domain impulse response, and caching a plurality of data of the wireless channel time domain impulse response, wherein the number of the cached data is a preset value;
and a full frequency domain channel response estimation step: preprocessing a plurality of data before the wireless channel time domain impulse response, and estimating the frequency domain channel response corresponding to the sub-carrier of the OFDM signal by FFT operation by utilizing the preprocessed plurality of data before the wireless channel time domain impulse response;
a channel equalization step: and carrying out channel equalization on data symbols by using the effective input data and the frequency domain channel response, and caching and outputting a channel equalization result.
In some optional embodiments, in the data buffering step, one valid input data is buffered every clock cycle;
the processing time of the pilot channel response estimation step and the data conversion step is less than or equal to N + N cp One clock cycle, where N represents the number of valid input data and N cp Representing the number of data for caching the wireless channel time domain impulse response;
the processing time of the full frequency domain channel response estimation step and the channel equalization step is less than or equal to N + N cp One clock cycle, where N represents the number of valid input data and N cp And the number of the data for caching the wireless channel time domain impulse response is represented.
In some optional embodiments, performing pilot channel response estimation by using the read pilot symbols and the local initial pilot symbols to obtain a channel response of a pilot position based on the following formula;
wherein H p (i) Indicating the channel response at the pilot location, Y [ Pos ] P (i)]Denotes the Pos-th P (i) 1 valid input data, pos P (i) Denotes the subcarrier number, X, to which the i-1 th pilot symbol belongs P (i) Denotes the i-1 th pilot symbol, [ X ] P (i)] * Represents X P (i) Conjugation of (1).
In some alternative embodiments, channel equalization of data symbols is performed using the effective input data and the frequency domain channel response based on the following formula;
wherein the content of the first and second substances,
indicating the result of channel equalization of the data symbols, Y [ i ]]Represents the i-1 th valid input data, mod represents the remainder-taking operation, H [ (i + N/2P) modN]Indicating the frequency domain channel response for the (i + N/2P) mod N-1 sub-carrier.
The technical scheme of the invention has the following main advantages:
the comb-shaped pilot frequency channel estimation and equalization device of the OFDM system of the inventionThe device and the method only need to complete P-point IFFT operation and N/N operation once when carrying out comb-shaped pilot channel estimation and equalization cp Sub N cp Point FFT operation due to N cp N, the calculation complexity can be obviously reduced; meanwhile, the calculation time delay is only 2N +2P + N cp The number of clock cycles is + S, and is less than that of clock cycles of 4N +2P by at least N clock cycles, so that the calculation time delay can be obviously shortened; moreover, the problem of energy leakage caused by non-uniform pilot frequency distribution can be avoided, and the channel estimation and equalization precision is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a comb-type pilot channel estimation and equalization apparatus of an OFDM system according to an embodiment of the present invention;
fig. 2 is a schematic diagram illustrating an arrangement of pilot symbols, data symbols and guard symbols in subcarriers according to an embodiment of the present invention;
fig. 3 is a timing diagram of input data and output data of the comb pilot channel estimation and equalization apparatus according to an embodiment of the present invention;
fig. 4 is a schematic diagram illustrating a timing control manner of each operation step in the comb pilot channel estimation and equalization apparatus according to an embodiment of the present invention;
FIG. 5 is a schematic structural diagram of an input buffer unit according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of a data preprocessing unit according to an embodiment of the present invention, wherein an intermediate buffer unit and an FFT computation unit are further shown.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are only some of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The technical scheme provided by the embodiment of the invention is described in detail below with reference to the accompanying drawings.
In a first aspect, referring to fig. 1, an embodiment of the present invention provides an apparatus for estimating and equalizing a comb pilot channel of an OFDM system, where the apparatus includes:
an input buffer unit for receiving and buffering the effective input data of the OFDM signal;
the pilot frequency storage unit is used for storing a local initial pilot frequency symbol;
a channel estimation unit, configured to perform pilot channel response estimation using the valid input data and the local initial pilot symbol to obtain a channel response of a pilot position;
an IFFT calculation unit, configured to perform IFFT operation on the channel response at the pilot frequency position to obtain a wireless channel time domain impulse response;
the intermediate buffer unit is used for buffering a plurality of data of the wireless channel time domain impulse response, wherein the number of the buffered data is a preset value;
the data preprocessing unit is used for preprocessing a plurality of data in the front of the wireless channel time domain impulse response;
the FFT calculating unit is used for estimating the frequency domain channel response corresponding to the subcarrier of the OFDM signal by utilizing a plurality of data before the preprocessed wireless channel time domain impulse response;
a data equalization unit for performing channel equalization of data symbols using the frequency domain channel response;
and the output buffer unit is used for buffering and outputting the channel equalization result.
Specifically, when the comb pilot channel estimation and equalization apparatus of the OFDM system according to an embodiment of the present invention performs comb pilot channel estimation and equalization, the input buffer unit receives and buffers effective input data of an OFDM signal, where the effective input data of the OFDM signal is a subcarrier of the OFDM signal, and the pilot storage unit stores a local initial pilot symbol; the channel estimation unit reads a pilot frequency symbol from effective input data according to the subcarrier serial number to which the pilot frequency symbol belongs, reads a local initial pilot frequency symbol from the pilot frequency storage unit, and performs pilot frequency channel response estimation by using the read pilot frequency symbol and the local initial pilot frequency symbol to acquire channel response of a pilot frequency position; the IFFT calculation unit performs IFFT operation on the channel response of the pilot frequency position acquired by the channel estimation unit to acquire the wireless channel time domain impulse response based on pilot frequency estimation; the intermediate cache unit caches a plurality of data of the wireless channel time domain impulse response acquired by the IFFT calculation unit, and the number of the cached data is a preset value; the data preprocessing unit reads the cached wireless channel time domain impulse response from the intermediate cache unit to perform data preprocessing; the FFT calculation unit processes the preprocessed wireless channel time domain impulse response through FFT operation and estimates the frequency domain channel response corresponding to the subcarrier of the OFDM signal; the data equalization unit performs channel equalization of data symbols by using the effective input data and the frequency domain channel response; and the output buffer unit buffers and outputs the channel equalization result.
The working principle and process of the comb pilot channel estimation and equalization apparatus of the OFDM system according to an embodiment of the present invention are further described by specific examples below.
Referring to fig. 2, setting:
the OFDM signal comprises N subcarriers, N is an integral power of 2, the number of pilot symbols is P, N can be divided by P, the number of data symbols is S, the number of protection symbols is G, and N = S + G + P; the P pilot symbols are uniformly distributed in the N sub-carriers by taking the N/P sub-carriers as intervals;
0,1, …, N-1 are used to represent the corresponding serial numbers of N sub-carriers of OFDM signal, and the serial number Pos of the sub-carrier to which the pilot symbol belongs P (i) Comprises the following steps:
subcarrier sequence number Pos to which data symbol belongs S (i) Comprises the following steps:
in the formula (I), the compound is shown in the specification,
indicating a rounding down, mod indicating a remainder operation;
except the sub-carriers occupied by the pilot frequency symbols and the data symbols, other sub-carriers in the OFDM signal are filled with protection symbols; the value of the protection symbol is 0, the value of the data symbol is a constellation point after PSK or QAM constellation mapping, the pilot frequency symbol is generated based on a constant modulus sequence, and the (i-1) th pilot frequency symbol X P (i) Is defined as:
where C is an amplitude factor, C is a constant, and r is a constant coprime to N.
In one embodiment of the invention, the pilot frequency is inserted into both the data symbol and the protection symbol, so that the pilot frequency symbols are uniformly distributed in the whole frequency band, the problem of energy leakage caused by non-uniform pilot frequency distribution can be avoided, and the improvement of the channel estimation and equalization precision is facilitated.
Based on the above setting, the working process of the comb-shaped pilot channel estimation and equalization device is specifically as follows:
and (3) data caching process: an input buffer unit receives and buffers N effective input data of the OFDM signal, wherein the N effective input data are represented by Y (i), i =0,1, …, N-1;
pilot channel response estimation procedure: after N effective input data are stored, the channel estimation unit is used for estimating the subcarrier sequence number Pos to which the pilot frequency symbol belongs P (i) I =0,1, …, P-1 reads the pilot symbol Y [ Pos ] from the input buffer unit P (i)]I =0,1, …, P-1, in combination with local pilot read from pilot storage unitThe starting pilot symbol estimates a channel response of the pilot position by using a channel estimation algorithm, where the channel estimation algorithm may be, for example, a Least Square (LS) channel estimation algorithm, and the channel response of the pilot position is expressed as:
in the formula, H p (i) Channel response, X, indicating pilot position P (i)] * Represents X P (i) According to the constant modulus characteristic of the pilot frequency symbol, satisfies X P (i)[X P (i)] * ＝1；
And (3) data transformation process: channel response H of IFFT computing unit to pilot frequency position p (i) I =0,1, …, P-1 performs P-point IFFT operation to obtain the corresponding time domain sequence h p (i) I =0,1, …, P-1, time domain sequence h p (i) I =0,1, …, P-1 is the wireless channel time domain impulse response based on pilot frequency estimation; since the channel delay spread is typically less than the duration of the cyclic prefix of the OFDM signal, the wireless channel time-domain impulse response h is preserved p (i) First N of cp Number of values and the first N reserved by the intermediate buffer unit cp Caching the numerical values for subsequent operation;
the full frequency domain channel response estimation process: data preprocessing unit to reserve N of buffer cp The time domain impulse response data of each wireless channel is preprocessed based on the preprocessed N cp The FFT calculation unit passes N cp Estimating frequency domain channel responses H (i) corresponding to N subcarriers of the OFDM signal by using point FFT operation, wherein i =0,1, … and N-1;
and (3) channel equalization process: the data equalization unit performs channel equalization of the data symbols by using the full frequency domain channel response estimation result, the output buffer unit buffers the channel equalization result, and after the N channel equalization results are stored, the data equalization unit performs channel equalization of the data symbols according to the serial numbers Pos of the sub-carriers to which the data symbols belong S (i) I =0,1, …, S-1 outputs a result of channel equalization of a data symbol, wherein a channel equalization operation on the data symbol may be performedExpressed as:
in the formula (I), the compound is shown in the specification,
indicating the result of the channel equalization for the data symbol and mod the remainder operation.
The comb-shaped pilot channel estimation and equalization device provided by the embodiment of the invention receives natural sequence data demodulated by FFT and subjected to cyclic prefix removal, and continuously outputs the channel equalization result of S data symbols in each OFDM signal after processing.
Referring to fig. 3-4, since the comb pilot channel estimation and equalization apparatus operates in a streaming input-output manner, in order to reduce the buffer overhead of the intermediate data as much as possible, in an embodiment of the present invention, the timing sequence of each processing process of the comb pilot channel estimation and equalization apparatus is controlled accordingly, so as to ensure that the data generated in each process of each OFDM signal can be used for the processing of the next process in time, thereby reducing the storage overhead of the intermediate data. In fig. 4, step a represents a data buffering process, step b represents a pilot channel response estimation process, step c represents a data transformation process, step d represents a full frequency domain channel response estimation process, and step e represents a channel equalization process.
Specifically, in an embodiment of the present invention, the comb pilot channel estimation and equalization apparatus employs the following timing control method:
in the data caching process, caching effective input data in each clock cycle;
the processing time of the pilot channel response estimation process and the data conversion process is less than or equal to N + N cp One clock cycle;
the processing time of the full frequency domain channel response estimation process and the channel equalization process is less than or equal to N + N cp One clock cycle.
In the data caching process, caching one effective input data in each clock cycle, namely caching N effective input data demodulated by each OFDM signal in N clock cycles, so that the data caching rate can be matched with the data input rate;
making the processing time of pilot channel response estimation process and data conversion process less than or equal to N + N cp And each clock period can ensure that the operation of the pilot channel response estimation process and the data conversion process can be immediately started after the data buffering of each OFDM signal in N clock periods is finished.
Because 2P clock cycles are needed from the first data input to the last calculation result output when the IFFT calculation unit performs P-point IFFT operation, the pilot channel response estimation only needs to perform complex multiplication operation on the received pilot symbols and the local initial pilot symbols and can be completed only by 1 clock cycle, and therefore 2P +1 is not more than N + N cp When P is less than or equal to N/2, i.e. the pilot density is less than 1/2, the processing time constraint can be satisfied, and the pilot density of the OFDM system is usually much less than 1/2, so the above requirements can be satisfied.
The processing time of the full frequency domain channel response estimation process and the channel equalization process is less than or equal to N + N cp In each clock period, when the latter OFDM signal completes the pilot frequency channel response estimation process and the data transformation process in the comb-shaped pilot frequency channel estimation and equalization device, the former OFDM signal also completes the related operation of the full frequency domain channel response estimation process and the channel equalization process, therefore, for each OFDM signal, after the pilot frequency channel response estimation process and the data transformation process are completed, the operation of the full frequency domain channel response estimation process and the channel equalization process can be immediately started to be executed.
Further, referring to fig. 1, the comb-type pilot channel estimation and equalization apparatus further includes:
the data write-in controller is used for controlling a data write-in mode of the input cache unit;
and the data reading controller is used for controlling the data reading mode of the input buffer unit.
Referring to fig. 3, as an example, the data write controller may include: an accumulator, a reverse order conversion unit and a data selector (MUX); the accumulator is respectively connected with the inverted sequence conversion unit and the data selector, the inverted sequence conversion unit is connected with the data selector, and the data selector is connected with the input cache unit.
As an example, the data read controller may include: a calculator, a reverse order transformation unit and a data selector (MUX); the calculator is respectively connected with the inverted sequence conversion unit and the data selector, the inverted sequence conversion unit is connected with the data selector, and the data selector is connected with the input cache unit.
Further, referring to fig. 3, as an example, the input buffer unit includes:
the dual-port random access memory comprises two dual-port random access memories, the two dual-port random access memories are matched with each other in a ping-pong structure mode, and each dual-port random access memory can simultaneously carry out read operation and write operation.
Based on the aforementioned setting, the storage depth of the dual port random access memory (dual port RAM) of the input buffer unit may be set to N.
Further, on the basis of the foregoing setting, and the configuration of the input buffer unit, the data write controller, and the data read controller that are specifically set, the input buffer unit may adopt the following data write method:
the first dual-port random access memory receives the demodulated OFDM signals (m =0,1, …) of 4m +1 and 4m +3, wherein the OFDM signals of 4m +1 are written in sequence according to the natural sequence address 0,1, …, N-1, and the OFDM signals of 4m +3 are written in sequence according to the inverted sequence address rev n (0),rev n (1),…,rev n (N-1) sequentially written, where N = log 2 N，rev n (i) Representing the inverted sequence value of the parameter i in an n-bit representation mode;
the second dual-port random access memory receives the demodulated OFDM signals (m =0,1, …) of 4 < m + > 2 and 4 < m + > 4, wherein the OFDM signals of 4 < m + > 2 are written in sequence according to natural sequence addresses 0,1, …, N < -1 >, and the OFDM signals of 4 < m + > 4 are written in sequence according to inverted sequence addresses rev n (0),rev n (1),…,rev n (N-1) writing in sequence.
On the basis of the aforementioned setting and the specific configurations of the input buffer unit, the data write controller, and the data read controller, the input buffer unit may adopt the following data reading modes:
when input data is stored in a natural order in a dual port random access memory, rev is applied at the output port n [Pos P (i)]For the sequential reading of pilot symbols, i =0,1, …, P-1, in rev n [Pos S (i)]For sequential reading of data symbols, i =0,1, …, S-1.
When input data is stored in a reversed order in a dual port random access memory, pos is applied to the output port P (i) Reading pilot symbols, i =0,1, …, P-1, at Pos S (i) Read data symbols, i =0,1, …, S-1.
Further, as an example, the intermediate cache unit includes:
the single-port random access memories comprise two single-port random access memories, the two single-port random access memories are matched with each other in a ping-pong structure mode, and the reading operation and the writing operation of each single-port random access memory are set to be carried out in a time-sharing mode.
The intermediate buffer unit receives the results arranged in the reverse order, i.e. h, from the IFFT computation unit p (rev l (0)),h p (rev l (1)),…,h p (rev l (P-1)), wherein l = log 2 P，rev l (i) Represents the inverted order value of the parameter i in the l-bit representation.
Based on the aforementioned setting, the storage depth of the single-port random access memory (single-port RAM) of the intermediate cache unit may be set to N cp 。
Further, on the basis of the foregoing setting and the structure of the specifically set intermediate cache unit, the intermediate cache unit may adopt the following data reading and writing modes:
the first single-port random access memory is used for buffering intermediate calculation results (m =0,1, …) corresponding to the 2m +1 th OFDM signal, and the first N in the natural order arrangement are selected from output data of the IFFT calculation unit cp The data is written with the corresponding natural sequence number as the groundAddress writing, switching to a read mode after data writing is finished, and switching to a write-back mode until data is written next time;
the second single-port random access memory is used for buffering the intermediate calculation result (m =0,1, …) corresponding to the 2mth +2 OFDM signal, and selects the first N in the natural sequence from the output data of the IFFT calculation unit cp And the data is written by taking the corresponding natural sequence number as a write address, and is switched to a read mode after the data is written, and the write-back mode is switched until the data is written next time.
Further, as an example, the output buffer unit includes:
and the dual-port random access memories comprise one memory for caching the channel equalization result.
On the basis of the aforementioned setting and the structure of the specifically set output buffer unit, the output buffer unit may adopt the following data read-write modes:
for the 2m +1 th OFDM signal (m =0,1, …),
the write address of is i, and Pos are generated in sequence after N data are received S (i) I =0,1, …, S-1 is used as a read address, and the channel equalization result of S data symbols is output;
for the 2m +2 OFDM signal (m =0,1, …),
is rev n (i) When N data are received, rev is generated in sequence n [Pos S (i)]I =0,1, …, S-1 as a read address, and outputs a result of channel equalization for S data symbols.
Further, referring to fig. 4, the data preprocessing unit may include:
the read address generator is used for reading wireless channel time domain impulse response data from the intermediate cache unit and reading cosine values and sine values corresponding to the twiddle factors from the twiddle factor compression storage subunit;
the twiddle factor compression storage subunit is used for storing cosine values and sine values corresponding to twiddle factors;
the rotation factor transformation subunit is used for transforming the read cosine values and sine values to obtain rotation factors corresponding to the cosine values and the sine values;
and the complex multiplier is used for weighting the twiddle factors obtained by transformation and the read wireless channel time domain impulse response data and sending the weighted result to the FFT calculating unit.
Specifically, when the data preprocessing unit performs data preprocessing, the read address generator generates a correct read address, on one hand, data is read from the intermediate buffer unit, on the other hand, the twiddle factor is read from the twiddle factor compression storage subunit, and the two are multiplied and then output to the FFT calculating unit.
The FFT computing unit can adopt a pipeline structure, serial continuous input of data streams is supported, output data are arranged in an inverted order, and the time delay from the first effective data input FFT computing unit to the last calculation result output FFT computing unit is 2N cp One clock cycle.
Based on the aforementioned setting, the data preprocessing unit may adopt the following address generation manner:
in N clock cycles, the read address 0,1, …, N is cyclically generated cp -1 reading data from the intermediate buffer unit until N/N is completed cp Finishing the reading of the wheel data;
acquiring the twiddle factor in N clock cycles
Wherein N =0,1, …, N-1,u = log 2 N cp Represents N cp The corresponding bit width size.
Since the twiddle factor satisfies e -j2πk/N And the value of (= cos (2 pi k/N) -sin (2 pi k/N)) can be conveniently compressed and stored by utilizing the periodicity and symmetry of sine and cosine functions of the real part and the imaginary part of the twiddle factor.
Therefore, in an embodiment of the present invention, a twiddle factor compression storage subunit and a twiddle factor transformation subunit are provided, the twiddle factor compression storage subunit only stores values of cos (2 π k/N) and sin (2 π k/N) in the range of k =0,1.
TABLE 1 twiddle factor mapping relationship and transformation relationship table
In Table 1, the first column parameter k is rev u (n mod N cp )·「n/N cp And k ' is generated through the second column transformation and is used as a read address of the twiddle factor compression storage subunit, cos (2 pi k '/N) and sin (2 pi k '/N) are obtained, and then the read positive cosine value is mapped into a real part and an imaginary part of the twiddle factor according to the mapping relation described by the third column and the fourth column.
The data of the intermediate buffer unit is weighted and sent to the FFT calculating unit according to the mode, and finally the full-frequency-domain channel response H (i) arranged in place, i =0, rev can be obtained n (1),…,rev n (N-1) sequentially generating a read address (i-N/2P) modN, i =0, rev according to equation 5 n (1),…,rev n (N-1), read Y [ (i-N/2P) modN]Completing channel equalization operation to obtain channel equalization result
And sent to the output buffer unit.
In a second aspect, an embodiment of the present invention provides a method for estimating and equalizing a comb pilot channel of an OFDM system, where the method can be implemented by using the apparatus for estimating and equalizing a comb pilot channel of an OFDM system, and includes the following steps:
a data caching step: receiving and buffering effective input data of an OFDM signal, wherein the effective input data of the OFDM signal is a subcarrier of the OFDM signal;
pilot channel response estimation step: reading a pilot frequency symbol from effective input data according to the subcarrier serial number, and performing pilot frequency channel response estimation by using the read pilot frequency symbol and a local initial pilot frequency symbol to obtain channel response of a pilot frequency position;
a data transformation step: performing IFFT operation on the channel response of the pilot frequency position to obtain wireless channel time domain impulse response, and caching a plurality of data of the wireless channel time domain impulse response, wherein the number of the cached data is a preset value;
and a full frequency domain channel response estimation step: preprocessing a plurality of data in front of the wireless channel time domain impulse response, and estimating the frequency domain channel response corresponding to the subcarrier of the OFDM signal by FFT operation by utilizing the preprocessed data in front of the wireless channel time domain impulse response;
a channel equalization step: and carrying out channel equalization on data symbols by using the effective input data and the frequency domain channel response, and caching and outputting a channel equalization result.
Based on the aforementioned setting for the OFDM signal, the method specifically includes the steps of:
a data caching step: receiving and buffering N valid input data of the OFDM signal, wherein the N valid input data are represented by Y (i), i =0,1, …, N-1;
pilot channel response estimation step: after N effective input data are stored, the pilot frequency symbols belong to the subcarrier sequence numbers Pos P (i) I =0,1, …, P-1 reads the pilot symbol Y [ Pos P (i)]I =0,1, …, P-1, and combines the local initial pilot symbol, and estimates and obtains the channel response of the pilot position by using a channel estimation algorithm, where the channel estimation algorithm may be a Least Squares (LS) channel estimation algorithm, and the channel response of the pilot position is expressed as:
in the formula, H p (i) Channel response, X, indicating pilot position P (i)] * Represents X P (i) Conjugate of (2)According to the constant modulus characteristic of the pilot frequency symbol, X is satisfied P (i)[X P (i)] * ＝1；
A data transformation step: channel response to pilot position H p (i) I =0,1, …, P-1 performs P-point IFFT operation to obtain the corresponding time domain sequence h p (i) I =0,1, …, P-1, time domain sequence h p (i) I =0,1, …, P-1 is the wireless channel time-domain impulse response based on pilot frequency estimation, and the reserved wireless channel time-domain impulse response h p (i) Front N of cp Number of values and for the first N reserved cp Caching the numerical values;
and a full frequency domain channel response estimation step: for N of reserved buffer cp The time domain impulse response data of each wireless channel is preprocessed based on the preprocessed N cp Time domain impulse response data of a radio channel by N cp Estimating frequency domain channel responses H (i) corresponding to N subcarriers of the OFDM signal by using point FFT operation, wherein i =0,1, … and N-1;
a channel equalization step: utilizing the full frequency domain channel response estimation result to carry out channel equalization of the data symbols, caching the channel equalization result, and after the N channel equalization results are stored, according to the subcarrier serial numbers Pos to which the data symbols belong S (i) I =0,1, …, S-1 outputs a channel equalization result of a data symbol, where a channel equalization operation on the data symbol may be expressed as:
in the formula (I), the compound is shown in the specification,
indicating the result of the channel equalization for the data symbol and mod the remainder operation.
The comb-shaped pilot channel estimation and equalization method provided by an embodiment of the present invention continuously outputs the channel equalization result of S data symbols in each OFDM signal after processing by receiving the natural sequence data demodulated by FFT and subjected to cyclic prefix removal.
Further, for each OFDM signal at eachThe data generated in the step can be used for the processing of the next step in time so as to reduce the storage overhead of intermediate data; in the comb-shaped pilot channel estimation and equalization method, in the data caching step, one effective input data is cached in each clock period; the processing time of the pilot channel response estimation step and the data conversion step is less than or equal to N + N cp A clock cycle; the processing time of the full frequency domain channel response estimation step and the channel equalization step is less than or equal to N + N cp One clock cycle.
It can be seen that, when performing the comb pilot channel estimation and equalization, the comb pilot channel estimation and equalization apparatus and method of the OFDM system according to an embodiment of the present invention only need to complete a P-point IFFT operation and N/N operations once cp Sub N cp Point FFT operation due to N cp N, the calculation complexity can be obviously reduced; meanwhile, the calculation time delay is only 2N +2P + N cp The number of clock cycles is + S, and is less than that of clock cycles of 4N +2P by at least N clock cycles, so that the calculation time delay can be obviously shortened; moreover, the problem of energy leakage caused by non-uniform pilot frequency distribution can be avoided, and the channel estimation and equalization precision is improved.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. In addition, "front", "rear", "left", "right", "upper" and "lower" in this document are all referred to the placement state shown in the drawings.
Finally, it should be noted that: the above examples are only for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (8)
1. An apparatus for comb pilot channel estimation and equalization in an OFDM system, the apparatus comprising:
an input buffer unit for receiving and buffering the effective input data of the OFDM signal;
the pilot frequency storage unit is used for storing a local initial pilot frequency symbol;
a channel estimation unit, configured to perform pilot channel response estimation by using the valid input data and the local initial pilot symbol to obtain a channel response of a pilot position;
an IFFT calculation unit, configured to perform IFFT operation on the channel response of the pilot frequency position to obtain a wireless channel time domain impulse response;
the intermediate buffer unit is used for buffering a plurality of data in the first time domain impulse response of the wireless channel, wherein the number of the buffered data is a preset value;
the data preprocessing unit is used for preprocessing a plurality of data in the first time domain impulse response of the wireless channel;
the FFT calculating unit is used for estimating the frequency domain channel response corresponding to the subcarrier of the OFDM signal by utilizing the first data of the preprocessed wireless channel time domain impulse response;
a data equalization unit, configured to perform channel equalization on data symbols using the frequency domain channel response;
the output buffer unit is used for buffering and outputting a channel equalization result;
the FFT calculation unit estimates the frequency domain channel response corresponding to the sub-carrier of the OFDM signal by FFT operation by utilizing the first data of the preprocessed wireless channel time domain impulse response;
wherein, setting: the OFDM signal comprises N subcarriers, N is an integral power of 2, the number of pilot symbols is P, N can be divided by P, the number of data symbols is S, the number of protection symbols is G, and N = S + G + P; the P pilot symbols are uniformly distributed in the N sub-carriers by taking the N/P sub-carriers as intervals;
0,1, …, N-1 are used to represent the corresponding serial numbers of N sub-carriers of OFDM signal, and the serial number Pos of the sub-carrier to which the pilot symbol belongs P (i) Comprises the following steps:
subcarrier sequence number Pos to which data symbol belongs S (i) Comprises the following steps:
in the formula (I), the compound is shown in the specification,
indicating a rounding down, mod indicating a remainder operation;
except the sub-carriers occupied by the pilot frequency symbols and the data symbols, other sub-carriers in the OFDM signal are filled with protection symbols; the value of the protection symbol is 0, the value of the data symbol is a constellation point after PSK or QAM constellation mapping, the pilot frequency symbol is generated based on a constant modulus sequence, and the (i-1) th pilot frequency symbol X P (i) Is defined as:
wherein C is an amplitude factor, C is a constant, and r is a constant coprime to N;
performing pilot channel response estimation by using the read pilot symbols and the local initial pilot symbols based on the following formula to obtain channel response of a pilot position;
wherein H p (i) Channel response, Y [ Pos ], indicating pilot position P (i)]Denotes the Pos th P (i) 1 valid input data, pos P (i) Denotes the subcarrier number, X, to which the i-1 th pilot symbol belongs P (i) Denotes the i-1 th pilot symbol, [ X ] P (i)] * Represents X P (i) Conjugation of (1);
performing channel equalization of data symbols using the valid input data and the frequency domain channel response based on the following formula;
wherein the content of the first and second substances,
indicating the result of channel equalization of the data symbols, Y [ i ]]Representing the i-1 st valid input data, mod represents the remainder taking operation, H [ (i + N/2P) mod N]Indicating the frequency domain channel response for the (i + N/2P) th mod N-1 sub-carrier.
2. The apparatus for comb pilot channel estimation and equalization for OFDM system as claimed in claim 1, wherein said apparatus further comprises:
the data write-in controller is used for controlling the data write-in mode of the input cache unit;
and the data reading controller is used for controlling the data reading mode of the input buffer unit.
3. The apparatus for comb pilot channel estimation and equalization in an OFDM system as claimed in claim 2, wherein the input buffer unit comprises:
the dual-port random access memory comprises two dual-port random access memories, the two dual-port random access memories are matched with each other in a ping-pong structure mode, and each dual-port random access memory can simultaneously carry out read operation and write operation.
4. The apparatus for comb pilot channel estimation and equalization in an OFDM system according to claim 1, wherein the intermediate buffer unit comprises:
the single-port random access memory comprises two single-port random access memories, the two single-port random access memories are matched with each other in a ping-pong structure mode, and the read operation and the write operation of each single-port random access memory are set to be carried out in a time-sharing mode.
5. The apparatus for comb pilot channel estimation and equalization in an OFDM system according to claim 1, wherein the output buffer unit comprises:
a dual-port random access memory including one for caching channel equalization results.
6. The apparatus for comb pilot channel estimation and equalization in an OFDM system according to any of claims 1-5, wherein said data pre-processing unit comprises:
the read address generator is used for reading the wireless channel time domain impulse response data from the intermediate buffer unit and reading a cosine value and a sine value corresponding to the twiddle factor from the twiddle factor compression storage subunit;
the twiddle factor compression storage subunit is used for storing cosine values and sine values corresponding to twiddle factors;
the rotation factor transformation subunit is used for transforming the read cosine values and sine values to obtain rotation factors corresponding to the cosine values and the sine values;
and the complex multiplier is used for weighting the twiddle factors obtained by transformation and the read wireless channel time domain impulse response data and sending the weighted result to the FFT calculating unit.
7. A method for estimating and equalizing a comb-type pilot channel of an OFDM system, the method comprising:
a data caching step: receiving and buffering effective input data of an OFDM signal, wherein the effective input data of the OFDM signal is a subcarrier of the OFDM signal;
pilot channel response estimation step: reading a pilot frequency symbol from the effective input data according to the subcarrier serial number, and performing pilot frequency channel response estimation by using the read pilot frequency symbol and a local initial pilot frequency symbol to obtain channel response of a pilot frequency position;
a data transformation step: performing IFFT operation on the channel response of the pilot frequency position to obtain wireless channel time domain impulse response, and caching a plurality of data of the wireless channel time domain impulse response, wherein the number of the cached data is a preset value;
and a full frequency domain channel response estimation step: preprocessing a plurality of data before the wireless channel time domain impulse response, and estimating the frequency domain channel response corresponding to the sub-carrier of the OFDM signal by FFT operation by utilizing the preprocessed plurality of data before the wireless channel time domain impulse response;
a channel equalization step: carrying out channel equalization of data symbols by using the effective input data and the frequency domain channel response, and caching and outputting a channel equalization result;
wherein, setting: the OFDM signal comprises N subcarriers, N is an integral power of 2, the number of pilot symbols is P, N can be divided by P, the number of data symbols is S, the number of protection symbols is G, and N = S + G + P; the P pilot symbols are uniformly distributed in the N sub-carriers by taking the N/P sub-carriers as intervals;
the numbers corresponding to the N sub-carriers of the OFDM signal and the sub-carrier numbers Pos of the pilot symbols are represented by 0,1, …, N-1 P (i) Comprises the following steps:
subcarrier sequence number Pos to which data symbol belongs S (i) Comprises the following steps:
in the formula (I), the compound is shown in the specification,
indicating a rounding down, mod indicating a remainder operation;
except the sub-carriers occupied by the pilot frequency symbols and the data symbols, other sub-carriers in the OFDM signal are filled with protection symbols; the value of the protection symbol is 0, the value of the data symbol is a constellation point after PSK or QAM constellation mapping, the pilot frequency symbol is generated based on a constant modulus sequence, and the (i-1) th pilot frequency symbol X P (i) Is defined as follows:
wherein C is an amplitude factor, C is a constant, and r is a constant coprime to N;
performing pilot channel response estimation by using the read pilot symbols and the local initial pilot symbols based on the following formula to obtain channel response of a pilot position;
wherein H p (i) Channel response, Y [ Pos ], indicating pilot position P (i)]Denotes the Pos th P (i) 1 valid input data, pos P (i) Denotes the subcarrier number, X, to which the i-1 th pilot symbol belongs P (i) Denotes the i-1 th pilot symbol, [ X ] P (i)] * Represents X P (i) Conjugation of (1);
performing channel equalization of data symbols using the valid input data and the frequency domain channel response based on the following formula;
wherein the content of the first and second substances,
indicating the result of channel equalization of the data symbols, Y [ i ]]Represents the i-1 st valid input data, mod represents the remainder taking operation, H [ (i + N/2P) mod N]Indicating the frequency domain channel response for the (i + N/2P) th mod N-1 sub-carrier.
8. The method for comb pilot channel estimation and equalization for an OFDM system as claimed in claim 7, wherein in the data buffering step, one valid input data is buffered every clock cycle;
the processing time of the pilot channel response estimation step and the data conversion step is less than or equal to N + N cp One clock cycle, where N represents the number of valid input data and N cp Representing the number of data for caching the wireless channel time domain impulse response;
the processing time of the full frequency domain channel response estimation step and the channel equalization step is less than or equal to N + N cp One clock cycle, where N represents the number of valid input data and N cp And the number of the data for caching the wireless channel time domain impulse response is represented.
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