CN104796375B - A kind of channel estimation methods of the SIM OFDM based on pilot tone - Google Patents
A kind of channel estimation methods of the SIM OFDM based on pilot tone Download PDFInfo
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Abstract
The invention discloses a kind of channel estimation methods of the SIM OFDM based on pilot tone, belong to Communication Anti-Jamming Techniques field, the present invention is directed to the technical problem of existing SIM ofdm communications method channel estimation performance difficulty, a kind of insertion low energy pilot frequency sequence on silent subcarriers is proposed to complete the method for channel estimation, in channel estimation, receiving terminal determines pilot frequency locations based on energy measuring, by pilot data, frequency-domain received signal at position and pilot frequency locations carries out initial channel estimation, second of pilot frequency locations detection is carried out again after equilibrium treatment is done to reception signal based on present channel estimate again, so as to be based on current pilot position, frequency-domain received signal at pilot data and pilot frequency locations is updated to channel estimation.The channel estimation and demodulated to frequency-domain received signal Y data that the present invention is used in SIM ofdm systems, had both remained the advantage of SIM ofdm systems in itself, and can use a pilot for channel estimation again, foundation is provided for final detection algorithm.
Description
Technical field
The invention belongs to Communication Anti-Jamming Techniques field, and in particular to a kind of channel estimation of the SIM-OFDM based on pilot tone
Method
Background technology
OFDM (Orthogonal Frequency Division Multiplexing) technology is a kind of radio communication
High speed transmission technology, its general principle are that the data flow of high speed is resolved into the sub-data flow of many low rates, i.e., by signal point
Into many orthogonal subcarriers, it is transmitted simultaneously using these mutually orthogonal subcarriers.The technology utilizes subcarrier logarithm
According to being modulated, the pulse width of symbol is extended, intersymbol interference (Inter-Symbol can be reasonably resistant to
Interference, ISI), improve the performance to anti-multipath fading.Compared with conventional frequency division is multiplexed (FDM), OFDM need not
Special guard band.It is mutually orthogonal between each carrier wave although having overlapping between frequency spectrum.It is former according to orthogonality
Reason is understood, is that interference is not present between each carrier wave, so as to substantially increase the utilization rate of frequency spectrum.
Recently, a kind of new multi-carrier communication mode --- modulate (Subcarrier Index based on sub-carrier indices
Modulation, SIM) ofdm system be suggested.For SIM-OFDM systems, except add SIM modulation modules with
Outside, other the step of and traditional ofdm system do not have any difference.Wherein, most crucial SIM modulation modules employ son
The thought of carrier wave piecemeal.Whole multicarrier is continuously divided into the multiple sub-blocks of size identical first, passes through rope in each sub-block
Draw bit to select wherein several subcarriers (referred to as activating subcarrier) to send data, and remaining subcarrier is not sent
Data (are referred to as silent subcarriers).Because index bit is not sent in itself, but lie in the position letter of activation subcarrier
In breath, so index bit and being not take up frequency spectrum resource.In receiving terminal, rope is obtained with by the position for activating subcarrier
Draw the information of bit.
Existing SIM-OFDM has many advantages, such as compared with traditional ofdm communication method, such as SIM-OFDM systems
Papr is smaller, confrontation inter-sub-carrier interference performance is more preferable, the bit error rate is more low, by selecting different power point
Transmitter energy can also be saved with strategy.Shortcoming is due to employ the mode of piecemeal, and SIM-OFDM systems are without image of Buddha OFDM
It is the same in system, pilot tone is simply inserted on fixed position to complete channel estimation.In SIM-OFDM systems, if each
Fixed position insertion pilot tone in block, can produce the problem of wasting frequency spectrum resource, lose the advantage of itself again.
The content of the invention
The present invention is directed to the technical problem of existing SIM-OFDM communication means channel estimation performance difficulty, it is proposed that Yi Zhong
Low energy pilot frequency sequence is inserted on silent subcarriers to complete the method for channel estimation.So that SIM-OFDM systems were both remained
The advantage of system itself, channel estimation can be used a pilot for again.
The SIM-OFDM based on pilot tone of present invention channel estimation methods comprise the following steps：
Transmitting terminal：
Step 1-1：Piecemeal processing is carried out to the subcarrier of system, obtains g=N/n sub-block, wherein N represents the son of system
Carrier wave total number, n represent the subcarrier number of each sub-block；
Step 1-2：To each sub-block of system, step 1-2：To each sub-block of system, carried and sent out by activation subcarrier
Data are sent, silent subcarriers carry pilot data, and set the transmit power of activation subcarrier to be more than the transmission of silent subcarriers
Power；
Receiving terminal：
Step 2-1：First time pilot frequency locations judge.Frequency-domain received signal Y uses to be divided with transmitting terminal identical mode
Block, g=N/n sub-block is obtained, contains n subcarrier in each sub-block.After piecemeal, to each piece of progress energy measuring, recognize
The n-k sub-carrier positions for minimum energy in each sub-block are pilot data (in channel estimation, the pilot number of current sub-block
According to for one group of data known to sending and receiving end) where sub-carrier positions, that is, search n-k subcarrier position of minimum energy in each block
Put and be designated as the pilot frequency locations l of current sub-blocki(subscript i is sub-block identifier), by g pilot frequency locations liForm pilot frequency locations collection
Close L1, by pilot frequency locations set L1The frequency-domain received signal Y at pilot frequency locations can be obtainedp1。
Step 2-2：Initial channel estimation.By frequency-domain received signal Yp1, pilot frequency locations set L1Letter is carried out with pilot data P
Estimate to obtain channel estimation value in roadChannel estimation methods include but are not limited to Linear least square estimation (LS), it is linear most
Small mean square error estimation (LMMSE) etc..
Step 2-3：Second of pilot frequency locations judges.The channel estimation value obtained using step 2-2Frequency domain is received and believed
Number Y carries out equilibrium treatment and is equalized signalEqualization methods include but are not limited to brokenly zero balanced (ZF), linear least mean-square
Error balance (LMMSE) etc..Equally, to equalizing signalPiecemeal is carried out using with transmitting terminal identical mode, obtains g=N/n
Individual sub-block, contain n subcarrier in each block.After piecemeal, each sub-block is detected.Detection method is：Each sub-block
Equalizing signal on middle n subcarrierData pilot data P corresponding with current sub-blockiCarry out Euclidean distance djComparison：Wherein i represent i-th of sub-block, j represent i-th of sub-block in j-th of subcarrier, it is believed that it is European away from
From djN-k minimum sub-carrier positions are sub-carrier positions where the pilot data of current sub-block, that is, search Euclidean distance most
Small n-k sub-carrier positions are simultaneously designated as the pilot frequency locations l ' of current sub-blocki(subscript i is sub-block identifier), by g pilot bit
Put l 'iForm pilot frequency locations set L2, based on pilot frequency locations set L2Obtain frequency-domain received signal Yp2；
Step 2-4：Update channel estimation.By frequency-domain received signal Yp2, the obtained pilot bit of pilot data P and step 2-3
Put set L2Carry out channel estimation, the channel estimation value after being updatedChannel estimation methods include but are not limited to ZF,
LMMSE etc..
In summary, by adopting the above-described technical solution, the beneficial effects of the invention are as follows：In existing SIM-OFDM systems
On the basis of, low energy is inserted on silent subcarriers (by setting the transmit power of silent subcarriers to be more than activation subcarrier
Transmit power realize) pilot frequency sequence completes the method for channel estimation, i.e. transmitting terminal inserts low energy on silent subcarriers
Pilot frequency sequence is measured, is detected the position where pilot tone by special detection method in receiving terminal, and combine reception signal
And pilot frequency sequence completes channel estimation.The advantage of this method is both to remain the advantage of SIM-OFDM systems in itself, again may be used
To use a pilot for channel estimation, foundation is provided for final detection algorithm.
Brief description of the drawings
Fig. 1 is n=2, exemplified by k=1, the schematic diagram of SIM modulation, and wherein X1... X512Represent the transmission number of each sub-block
According to αsRepresent the transmit power of activation subcarrier, P1... P512Represent the pilot data of each sub-block, αPExpression is led silent son and carried
The transmit power of ripple.
Embodiment
To make the object, technical solutions and advantages of the present invention clearer, with reference to embodiment and accompanying drawing, to this hair
It is bright to be described in further detail.
The present invention is based on existing SIM-OFDM systems, unlike existing SIM-OFDM systems, transmitting terminal
Low energy pilot frequency sequence is inserted on silent subcarriers, then in receiving terminal by special detection method by the position where pilot tone
Put to detect and complete channel estimation, wherein involved SIM modulation, send and receive processing etc. with existing SIM-OFDM
System is identical.
Below with (n, k)=(2,1), total subcarrier number N=1024, cyclic prefix CP=64, to sending data
Modulation symbol uses QPSK (4-QAM), using the embodiment that the present invention is introduced exemplified by ZF equilibriums, LMMSE channel estimations.
Transmitting terminal：
The schematic diagram of SIM modulation as shown in Figure 1, specific implementation process are roughly divided into following several steps：
Step 1-1：It is determined that the parameter for the system to be selected, that is, determine subcarrier number N=1024, the son load of each sub-block
Ripple number n=2, how many subcarrier number k=1 is activated in sub-block, sub-block the number g=N/n=512, order of modulation M=4 being divided into.
Then the amount of bits of a frame is calculated according to formula.Index bit length is for wherein any one sub-block：Expression rounds downwards, then a shared m for the index ofdm system of a frame1=p1G=512 positions
Index bit；4-QAM modulation symbols are sent to the subcarrier of activation, for the system of (n, k)=(2,1), can be sent
The modulation bit number of one frame is：m2=gp2=gklog2M=1024, the then total bit number m=m of a frame1+m2=1536.By this
Frame data are divided into two groups, and one group is index bit, and for selecting subcarrier to send data, one group is modulation bit, for modulating
Sent in subcarrier in being activated.
Step 1-2：Conventional SIM modulation is carried out, it is determined that corresponding activation subcarrier (the activation subcarrier of each sub-block
Number is represented with k), then SIM modulation symbols are assigned on corresponding activation subcarrier.
In the present invention, to each sub-block of system, carried by activation subcarrier and send data, silent subcarriers are carried and led
Frequency sets the transmit power of activation subcarrier to be more than the transmission work(of silent subcarriers according to (frequency pilot sign in corresponding diagram)
Rate.In the present embodiment, for the SIM-OFDM systems of (n, k), activation subcarrier, the transmission work(of silent subcarriers can be set
The average normalized of rate meets k αs+(n-k)αP=n, and αs＞ 1, αP＜ 1, wherein αsTo activate the average normalized hair of subcarrier
Send power, αPFor the average normalized transmit power of silent subcarriers.
SIM modulation detailed process be：K subcarrier carries p2Position bit information, each subcarrier carry 1 symbol,
Each symbol is by log2M bit map into 1 M rank signal modulation symbol.According to p in each sub-block1The numerical value of individual bit
Value determines that specific which k is activated subcarrier to send this k M rank signal modulation symbol.
Receiving terminal：
Step 2-1：First time pilot frequency locations judge.Frequency-domain received signal Y uses to be divided with transmitting terminal identical mode
Block, g=512 sub-block is obtained, contains n=2 subcarrier in each block.After piecemeal, energy inspection is carried out one by one to each piece
Survey ej=| Yi,j|, wherein i represents i-th piece, and j represents j-th of subcarrier in i-th piece, it is believed that minimum energy in each block
N-k=1 sub-carrier positions be current sub-block pilot data PiSub-carrier positions where (i=1,2 ..., 512), search
N-k sub-carrier positions of minimum energy and the pilot frequency locations l of current sub-block is designated as in each blocki(i=1,2 ..., g), by
512 pilot frequency locations liForm pilot frequency locations set L1, by L1The frequency-domain received signal Y at pilot frequency locations can be obtainedp1。
Step 2-2：Initial channel estimation.By frequency-domain received signal Yp1, pilot data P=[Pi]1≤i≤gWith pilot frequency locations collection
Close L1Carry out LMMSE channel estimations and obtain channel estimation value
Step 2-3：Second of pilot frequency locations judges.The channel estimation value obtained using step 2-2Frequency domain is received and believed
Number Y carries out ZF equilibriums and is equalized signalEqually, to equalizing signalDivided using with transmitting terminal identical mode
Block, g=512 sub-block is obtained, contains n=2 subcarrier in each sub-block.After piecemeal, each sub-block is examined one by one
Survey.Detection method is：Data pilot data P corresponding with the block in each block on n subcarrieriCarry out Euclidean distance dj's
Compare：J=1,2, i=1,2 ..., 512, wherein i represents i-th of sub-block, and j represents i-th of sub-block
In j-th of subcarrier, it is believed that Euclidean distance dj1 minimum sub-carrier positions are the pilot data P of current sub-blockiPlace
Carrier position, i.e., by i-th of sub-block, minimum euclidean distance djCorresponding sub-carrier positions are designated as pilot frequency locations l 'i(i=1,
2 ..., g), by g pilot frequency locations l 'iForm pilot frequency locations set L2.By L2The frequency-domain received signal at pilot frequency locations can be obtained
Yp2。
Step 2-4：Update channel estimation.By the frequency-domain received signal Y of pilot frequency locationsp2, pilot data P and step 2-3
Obtained pilot frequency locations set L2Carry out LMMSE channel estimations, the channel estimation value after being updated
If at this time, it is believed that channel estimation can not meet the performance requirement of system twice, renewal channel estimation can be improved
Number, that is, step 2-3 and 2-4 are repeated, when number of repetition is equal to predetermined threshold value T (T span is 1~3), terminated
Repeat, obtain final channel estimation value
The channel estimation value finally given based on the present inventionThe demodulating data to frequency-domain received signal Y can be obtained, below
Detected with ML and sketch its demodulating process：
ML detections space (standard point vector) in one block：
Frequency-domain received signal Y and channel estimation valuePiecemeal is carried out using with transmitting terminal identical mode, obtains g=512
Individual sub-block, contain n=2 subcarrier in each block.ML detections are carried out to each sub-block, calculate each sub-block vector YiWith standard
The vectorial D of point and block of channels vectorThe overall Euclidean distance of product, wherein i represent i-th of sub-block vector.Standard point vector D bags
Containing n=2 data, it is made up of the k=1 modulation symbol after energy distributes and n-k=1 frequency pilot sign, possible group
(symbol j represents imaginary unit in table as shown above for conjunction.).Every kind of combination and specific index bit vector I and modulation symbol
Vectorial Q is corresponding, uses DIQRepresent.According to formulaChoose Euclidean distance minimum one group is hair
Set of symbols is sent, so as to find index bit vector I and modulation symbol vector Q, symbolic solution is modulated to modulation symbol vector Q and reflected
Penetrate to obtain modulation bit.
The foregoing is only a specific embodiment of the invention, any feature disclosed in this specification, except non-specifically
Narration, can alternative features equivalent by other or with similar purpose replaced；Disclosed all features or all sides
Method or during the step of, in addition to mutually exclusive feature and/or step, can be combined in any way.
Claims (6)
1. a kind of channel estimation methods of the SIM-OFDM based on pilot tone, it is characterised in that comprise the following steps：
Transmitting terminal：
Step 1-1：Piecemeal processing is carried out to the subcarrier of system, obtains g=N/n sub-block, wherein N represents the subcarrier of system
Total number, n represent the subcarrier number of each sub-block, and determine the activation subcarrier of system；
Step 1-2：To each sub-block of system, being carried by activation subcarrier and send data, silent subcarriers carry pilot data,
And the transmit power of activation subcarrier is set to be more than the transmit power of silent subcarriers；
Receiving terminal：
Step 2-1：First time pilot frequency locations judge：
Using with transmitting terminal identical partitioned mode, frequency-domain received signal Y is divided into g sub-block；
Pilot frequency locations of the n-k sub-carrier positions of minimum energy in each block as current sub-block are searched, by leading for g sub-block
Frequency position forms pilot frequency locations set L1, based on pilot frequency locations set L1Obtain the frequency-domain received signal Y at pilot frequency locationsp1, its
Middle k represents the number of activation subcarrier；
Step 2-2：Initial channel estimation：Based on frequency-domain received signal Yp1, pilot frequency locations set L1Channel is carried out with pilot data P
Estimation obtains channel estimation value
Step 2-3：Second of pilot frequency locations judges：
Based on channel estimation valueEquilibrium treatment is carried out to frequency-domain received signal Y and is equalized signal
Using with transmitting terminal identical partitioned mode, by equalizing signalIt is divided into g sub-block；
Equalizing signal is calculated respectivelyEach sub-block in data pilot data corresponding with current sub-block on n subcarrier it
Between Euclidean distance, search pilot frequency locations of the n-k minimum sub-carrier positions of Euclidean distance as current sub-block, it is sub by g
The pilot frequency locations of block form pilot frequency locations set L2, based on pilot frequency locations set L2Obtain frequency-domain received signal Yp2；
Step 2-4：Update channel estimation valueBased on frequency-domain received signal Yp2, pilot frequency locations set L2Carried out with pilot data P
Channel estimation, the channel estimation value after being updated
2. the method as described in claim 1, it is characterised in that in the step 1-2, set activation subcarrier, silent son to carry
The average normalized of the transmit power of ripple meets k αs+(n-k)αP=n, and αs＞ 1, αP＜ 1, wherein αsFor the flat of activation subcarrier
Normalize transmit power, αPFor the average normalized transmit power of silent subcarriers.
3. method as claimed in claim 1 or 2, it is characterised in that step 2-3 and 2-4 are repeated, until number of repetition is big
In or equal to predetermined threshold value T.
4. method as claimed in claim 3, it is characterised in that the span of the predetermined threshold value T is 1~3.
5. method as claimed in claim 1 or 2, it is characterised in that channel estimation methods described in step 2-2 and/or 2-4 are：
Linear least square estimation method or Linear Minimum Mean-Square Error Estimation method.
6. method as claimed in claim 1 or 2, it is characterised in that the equalization processing method described in step 2-3 is：Broken zero
Equalization methods or linear minimum mean-squared error equalization methods.
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| CN106656875B (en) * | 2017-02-21 | 2019-04-26 | 电子科技大学 | Channel estimation methods for sub-carrier indices modulation ofdm system |
| CN107147483B (en) * | 2017-06-21 | 2019-08-02 | 电子科技大学 | A kind of SIM-OFDM system communicating method based on pilot frequency design modulation |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103595685A (en) * | 2013-11-27 | 2014-02-19 | 电子科技大学 | SIM-OFDM communication method |
| CN103634260A (en) * | 2013-12-06 | 2014-03-12 | 电子科技大学 | SC-IFDMA (single carrier-interleaved frequency division multiple access) communication method based on SIM (subscriber identity module) modulation |
| US8942303B1 (en) * | 2013-11-22 | 2015-01-27 | SiTune Corporation | Pilot assisted channel estimation |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8942303B1 (en) * | 2013-11-22 | 2015-01-27 | SiTune Corporation | Pilot assisted channel estimation |
| CN103595685A (en) * | 2013-11-27 | 2014-02-19 | 电子科技大学 | SIM-OFDM communication method |
| CN103634260A (en) * | 2013-12-06 | 2014-03-12 | 电子科技大学 | SC-IFDMA (single carrier-interleaved frequency division multiple access) communication method based on SIM (subscriber identity module) modulation |
Non-Patent Citations (1)
| Title |
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| A High Energy Efficient Scheme with Selecting Sub-carriers Modulation in OFDM System;Zhao Long 等;《Communications (ICC), 2012 IEEE International Conference on》;20120615;5711–5715 * |
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