CN103973608A - Channel estimating method for single carrier frequency domain equalization in short-wave communication channel - Google Patents
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Abstract
The invention provides a channel estimating method for single carrier frequency domain equalization in a short-wave communication channel, which is used for solving a problem that system transmission efficiency is lowered due to too many pilot-frequency block UW sequences in the prior art. The method comprises the following steps: inserting UW sequence pilot-frequency blocks among data blocks at equal intervals, and calculating by a least squares (LS) algorithm or a linear minimum mean square error (LMMSE) algorithm to obtain channel estimated values of positions of the pilot-frequency blocks; then, obtaining the channel estimated value of each data block by an interpolation algorithm, wherein the channel estimated values are used for completing frequency domain equalization. In the short-wave channels with very tense frequency spectrum resources, the method can be used for effectively reducing the pilot-frequency blocks, so that the frequency spectrum resources of the short-wave channels can be utilized efficiently, and the system transmission efficiency is improved.
Description
Technical field
The invention belongs to New Technology Of Shortwave Communication field, particularly relate to the channel estimation methods for single carrier frequency domain equalization under short wave communication channel (Singl e Carrier Frequency Domain Equalization, SC-FDE).
Background technology
According to the division of the CCIR of Consultative Committee on International Radio (CCIR) (Consultative Committee of International Radio), shortwave refers to that wavelength is at 10m～100m, and frequency is at the electromagnetic wave of 3MHz～30MHz.The radio communication that radiothermy carries out is called short wave communication.Short wave communication is actual refers to that the frequency range of use is 1.5MHz～30MHz, operable frequency range only has 28.5MHz, according to the world, stipulate, each short-wave radio set takies the band width of 3.7kHz, the band width that has now promoted recently short-wave radio set has reached 6kHz～9kHz, but the space of communication is still very crowded, the capacity of communication and the transmission rate of data have been limited to a great extent.
Short wave communication adopts the form of sky wave transmission substantially, namely by ionospheric one or many, reflect into Serial Communication, therefore there is serious multipath effect, statistics shows, multipath way is the highest with the probability of 3 appearance, multidiameter representative value is 2～8ms, becomes the major limitation of short-wave link transfer of data.The sky wave channels could of shortwave is variable-parameter channel, and the transmission stability of signal is poor.Hf radio communication is mainly to rely on ionosphere to carry out distant signal transmission, and ionosphere is that the changeability of parameter is very large as the weakness of signal reflex medium.His feature is path loss, time delay expansion, Noise and Interference, be all with round the clock, frequency, place and constantly changing.Ionospheric variation allows signal produce decline on the one hand, and amplitude and the frequency of decline constantly change.In addition, atmosphere and wireless industrial electrical noise interference are serious.Atmosphere and wireless industrial electrical noise mainly concentrate on radio-frequency spectrum low side, and along with the rising of frequency, intensity reduces gradually.Although low at this noise like interference ratio medium-long wave band of shortwave frequency range, intensity is still very high, has a strong impact on the communication reliability of shortwave, especially impulse type burst noise, often can make transfer of data occur unexpected error, has a strong impact on communication quality.
A new generation's Shortwave Communication System is mainly high speed HF digital communication system, has parallel and two kinds of systems of serial.The main thought of parallel system is that short wave channel is divided into some parallel subchannels, uploads and send a subcarrier respectively at every sub-channels, adopts quadrature modulation, by the method for a plurality of subcarrier parallel transmissions, improves speed, is called again multitone.Typical system has the approach that realizes of French Thomson (thomson) company, adopts OFDM (Frequency Division Multiplexing, OFDM) system, and the number of subcarrier is 79; But OFDM technology transmitting power is disperseed, and signal peak-to-average ratio is very large, and anti-frequency selective fading is poor, be difficult to eliminate intersymbol interference.
Serial system adopts the send mode of single carrier wave, because only adopting a carrier wave, also referred to as single-tone.Data send with serial mode modulation, and symbol width is short, reach higher speed, and as 2.4kbps, intersymbol interference will be very serious.In real work, need to adopt suitable balancing technique to resist intersymbol interference.For short wave communication field, the most conventional balancing technique is balanced (SC-TDE) technology of single carrier wave time domain.But the raising along with message transmission rate, when transmission bandwidth more approaches the coherence bandwidth of channel, time dispersive will be more serious, now receive signal with in comprised experience decay and time delay multipath ripple, cause frequency selective fading, thereby cause serious intersymbol interference.If alone time domain equalization reduces intersymbol interference, need more filter tap just can obtain acceptable portfolio effect, be difficult to like this reach the requirement of real-time, and along with the increase of multidiameter delay expansion, complexity of equalization even can increase by exponentially.
A kind of method of effectively anti-multipath being disturbed of single carrier frequency domain equalization (SC-FDE) band technical broadband wireless transmission, be compared to OFDM (OFDM) technology, it is low that single carrier frequency domain equalization has peak-to-average force ratio, anti-frequency selective fading is strong, can reach under the same conditions higher transmission rate and the lower error rate, be compared to general single carrier wave time domain balancing technique, complexity also reduces greatly, and uses and transmit higher speed.Yet, different channel circumstances on systematic function impact need not, correct channel estimation methods becomes the key of SC-FDE.At present, too many for pilot blocks UW sequence number in the channel estimation methods of the single carrier frequency domain equalization under short wave channel, cause channel estimation calculation amount large, greatly reduce system efficiency of transmission.Therefore, provide a kind of our research emphasis that more reasonably becomes for the channel estimation methods of the single carrier frequency domain equalization under short wave channel.
Summary of the invention
The object of the present invention is to provide a kind of for single-carrier frequency-domain equalization channel method of estimation under short wave communication channel, for solve that prior art exists because pilot blocks UW sequence number is too many to such an extent as to reduce the problem of system efficiency of transmission.
Technical scheme of the present invention is: a kind of channel estimation methods for single carrier frequency domain equalization under short wave communication channel, it is characterized in that, and comprise the following steps:
First input traffic is modulated, deblocking, and between data block, insert UW sequence pilot frequency piece;
Then adopt least-squares algorithm (LS) or least mean square algorithm (LMMSE) to calculate UW sequence pilot frequency piece channel estimation value;
Finally by interpolation algorithm, calculate the channel estimation value of all data blocks in data.
Wherein, described interpolation algorithm is for being interpolation algorithm, linear interpolation algorithm, second order interpolation algorithm or three Based on Interpolating Splines nearby.
Wherein, the insertion method that inserts UW sequence pilot frequency piece between described data block is specially: data block head and the tail insert respectively a UW sequence pilot frequency piece, uniformly-spaced insert UW sequence pilot frequency piece between data block.Also can be interpreted as data block on average to insert in the interval between UW sequence pilot frequency piece.
Wherein, described UW sequence pilot frequency block length is greater than the maximum multipath time delay symbolic number of channel.
Preferably, a kind of channel estimation methods for the single carrier frequency domain equalization under short wave communication channel, be specially: in data flow, frame data are divided into x piece, every block length is d, insertion UW sequence pilot frequency piece n piece, every block length are w, a frame data total length L=n*w+x*d, adjacent two UW sequence pilot frequency interblock gap c=x/ (n-1) blocks of data piece, c is greater than 0 integer.
It should be noted that, interpolation algorithm should be selected the different interpolation algorithm of complexity according to the decay speed degree of channel.For example at channel multi-path time delay, Doppler frequency shift and doppler spread, hour can adopt linear interpolation algorithm or second order interpolation algorithm, when channel multi-path time delay is larger, when Doppler frequency shift and doppler spread are larger, can adopt the high-order interpolation algorithms such as three spline interpolations (Spline).
In addition, UW sequence length is greater than the maximum multipath time delay symbolic number of channel, could estimate the gain transformations of channel completely.The number of UW sequence pilot frequency piece and the number of length and data block and length should be analyzed design according to the situation of channel, and every UW sequence pilot frequency piece can be realized timing estimation, frequency deviation estimation and channel estimating.
The invention provides for single-carrier frequency-domain equalization channel method of estimation under short wave communication channel, the method is uniformly-spaced inserted UW sequence pilot frequency piece between data block, utilize least-squares algorithm (LS) or least mean square algorithm (LMMSE) to calculate the channel estimation value that obtains pilot blocks position, then by interpolation algorithm, obtain the channel estimation value of each data block location, in order to complete frequency domain equalization.In the very nervous channel of this frequency spectrum resource of short wave channel, the method has greatly reduced the quantity of pilot blocks, and better the frequency spectrum resource of radiothermy channel, reduces channel estimation calculation amount, improves system efficiency of transmission.
Accompanying drawing explanation
Fig. 1 is the schematic flow sheet for the single carrier frequency domain equalization under short wave channel of the embodiment of the present invention.
Fig. 2 be the embodiment of the present invention for the single carrier frequency domain equalization channel estimation methods schematic diagram under short wave channel.
Fig. 3 be the embodiment of the present invention for the single carrier frequency domain equalization channel estimation methods intermediate waves channel parameter under short wave channel.
Fig. 4 be the embodiment of the present invention for the single carrier frequency domain equalization channel estimation methods frame assumption diagram under short wave channel.
Fig. 5 be the embodiment of the present invention for the single carrier frequency domain equalization channel estimation methods under short wave channel, channel fading frequency spectrum is carried out to Interpolate estimation figure.
Embodiment
Below in conjunction with accompanying drawing and embodiment, the present invention is described in detail.Should be appreciated that specific embodiment described herein, only in conjunction with in order to explain the present invention, does not limit the present invention.
Single-carrier wave frequency domain equalization technology, with symbolic blocks structure transmitted signal, need to insert Cyclic Prefix and carry out frequency domain equalization in data block.Single-carrier frequency domain equalization system transmits frame by frame, and the structure chart that is applicable to short wave communication based on single-carrier wave frequency domain equalization technology as shown in Figure 1.In general single-carrier frequency domain equalization system, in each data block, all need to insert a Cyclic Prefix, Cyclic Prefix is commonly used UW sequence (Unique Word, unique word sequence are generally chu sequence, frank-zadaff, PN sequence etc.) and unloaded data.Because shortwave narrowband channel spectrum resource is very nervous, narrow band channel medium frequency bandwidth only has 3.7kHz, if will waste very much frequency spectrum resource according to inserting UW sequence in every blocks of data.Propose on this problem patent herein, utilize less UW sequence to obtain the channel estimation value of UW sequence location, then by interpolation algorithm, obtain the channel estimation value in all data block location.
The short wave channel of selecting is in the present embodiment the severe short wave channel that international wireless Advisory Board (CCIR) proposes, and wherein parameter is Fig. 3.
In the transmitter of the present embodiment, first the data flow of input is carried out to modulation treatment, then data are divided into 12, finally four UW sequences are inserted in 12 blocks of data.Each inserts a UW sequence head and the tail, middle with in the interval data inserting equating, as shown in Fig. 4 frame assumption diagram, then with this frame structure, at short wave channel, transmits.
In the present embodiment, data are 3kHz in channel width, and adopting QPSK transmission rate is 4.8kbps, in the frame structure of data, UW sequence length is 64 symbols, DATA is 256 symbols for transmitting data length, and wherein UW sequence number is 4,12 of DATA data block numerical digits.
In this example in receiver, by what receive, carry out piecemeal processing, then by FFT computing, be converted into frequency domain data, then carry out channel estimation process.Wherein 4 UW sequences obtain respectively the channel estimation in frequency domain value H_esti=[H_esti1 of 4 UW sequence locations according to channel estimation in frequency domain algorithm, H_esti6, H_esti11, H_esti16], then H_esti sequence is used three battens (Spline) interpolation algorithm to carry out interpolative data, between UW piece, insert respectively 4 data, can obtain altogether 12 interpolative data H_esti=[H_esti2, H_esti3, H_esti4, H_esti5, H_esti7, H_esti8, H_esti9, H_esti10, H_esti12, H_esti13, H_esti14, H_esti15], these data are just respectively as the channel estimation value of 12 blocks of data piece DATA.Fig. 5 is that a frequency spectrum carries out Interpolate estimation figure.
In the present embodiment, UW sequence length 64 durations are 13.4ms, are greater than the maximum multipath time delay in short wave channel completely, can obtain channel estimation value by UW sequence; A DATA sequence length is that 256 durations are 54ms, and within this time period, channel fading is very slow, supposes that the gain of channel does not change, and as a blocks of data, carries out channel estimating and frequency domain equalization below.
In the present embodiment, after the channel estimation value to each blocks of data, then carry out frequency domain equalization, frequency domain equalization algorithm can use various frequency domain equalization algorithms.For example: ZF (ZF) equilibrium, least mean-square error balanced (MMSE) and some feedback equalization algorithms can directly be used channel estimation value.If adaptive algorithm, interpolation can be obtained to channel estimation value and as initial value, bring in formula directly utilization into and can reduce iterations, can reducing step-length simultaneously, to make to obtain result more accurate.
In the present embodiment, data after frequency domain equalization are carried out to IFFT computing and be converted to time-domain signal, then signal is modulated and is recovered binary signal by judgement.
As can be seen from the above-described embodiment, the embodiment of the present invention utilizes interpolation algorithm can reach good transmission result under the prerequisite that improves efficiency of transmission.And along with the increase of multidiameter delay expansion, frequency domain equalization complexity is compared to time domain equalization and greatly reduces, and interpolation algorithm will be saved more UW sequence compared to general algorithm when multidiameter delay ratio is larger, the advantage that efficiency of transmission improves is also more obvious.And single-carrier wave frequency domain equalization technology phase ratio orthogonal frequency division multiplex system, peak-to-average force ratio is lower, and anti-frequency selective fading ability is strong, under identical condition, can reach higher transmission rate and the lower error rate.
Claims (5)
1. for a channel estimation methods for single carrier frequency domain equalization under short wave communication channel, it is characterized in that, comprise the following steps:
First input traffic is modulated, deblocking, and between data block, insert UW sequence pilot frequency piece;
Then adopt least-squares algorithm or least mean square algorithm to calculate UW sequence pilot frequency piece channel estimation value;
Finally by interpolation algorithm, calculate the channel estimation value of all data blocks in data.
2. by a kind of channel estimation methods for single carrier frequency domain equalization under short wave communication channel described in claim 1, it is characterized in that, described interpolation algorithm is interpolation algorithm, linear interpolation algorithm, second order interpolation algorithm or three Based on Interpolating Splines nearby.
3. by a kind of channel estimation methods for single carrier frequency domain equalization under short wave communication channel described in claim 1, it is characterized in that, the insertion method that inserts UW sequence pilot frequency piece between described data block is specially: data block head and the tail insert respectively a UW sequence pilot frequency piece, uniformly-spaced insert UW sequence pilot frequency piece between data block.
4. by a kind of channel estimation methods for single carrier frequency domain equalization under short wave communication channel described in claim 1, it is characterized in that, described UW sequence pilot frequency block length is greater than the maximum multipath time delay symbolic number of channel.
5. by a kind of channel estimation methods for single carrier frequency domain equalization under short wave communication channel described in claim 1, it is characterized in that, in described channel estimation methods, design parameter is: in data flow, frame data are divided into x piece, every block length is d, insertion UW sequence pilot frequency piece n piece, every block length are w, a frame data total length L=n*w+x*d, adjacent two UW sequence pilot frequency interblock gap c=x/ (n-1) blocks of data piece, c is greater than 0 integer.
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