CN104168246A - Pilot carrier design method based on iteration average processing - Google Patents

Abstract

The invention belongs to the field of the communication technology and particularly relates to a pilot carrier design method based on iteration average processing under the conditions that a subcarrier is discontinuously available. A pilot symbol applicable to a carrier extension OFDM system is designed based on the concept of iteration average processing specific to the conditions that the subcarrier is discontinuously available. By means of the pilot symbol, the problem that the peak-to-average power ratio of the OFDM system can be solved effectively, and excellent error bit performance can be ensured.

Description

A kind of pilot design method based on iteration average treatment

Technical field

The invention belongs to communication technical field, relate in particular at subcarrier discontinuous available in the situation that, a kind of pilot design method based on iteration average treatment.

Background technology

Cognitive radio technology is to be proposed in 1999 by Joseph Mitola doctor III the earliest, its core concept is to obtain by frequency spectrum perception the frequency spectrum that can use in current time, utilize these frequency spectrums to carry out the transmission of data, thereby greatly improved on the whole the utilance of frequency spectrum.

Based on the thought of cognitive radio, be applied in OFDM (Orthogonal Frequency Division Multiplexing, OFDM) system and go, parton carrier wave will be taken by primary user, and frequency spectrum is no longer available continuously.According to this feature, discontinuous OFDM (Non-Contiguous Orthogonal Frequency Division Multiplexing, NC-OFDM) carry out transfer of data by unappropriated subchannel, and the interference to primary user is avoided in the subcarrier zero setting corresponding to occupied subchannel.

As the OFDM technology in Multicarrier Transmission Technology have the availability of frequency spectrum high, realize simple, be easy to carry out the advantages such as combination with other technology, thereby be extensively subject to the favor of scientific research and engineering field, and obtain extensively popularization as the key technology of 4G.But OFDM technology also has some defects of self, one of subject matter that wherein too high peak-to-average power ratio (Peak-to-Average Power Ratio, PAPR) is the application of restriction ofdm system engineering.

The time domain output of ofdm system shows as the stack of multiple sub-carrier signals, certainly will cause like this composite signal can produce very high PAPR, and this linearity to transmitter power amplifier has proposed very high requirement, has increased the required precision of equipment.Too high power also can cause very large waste simultaneously, and the next generation communication system requiring with high energy efficiency runs in the opposite direction.

For this problem, a lot of scholars are studied, the method of various reduction ofdm system PAPR has been proposed, wherein, document 1 " High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry spreading codes (W.D A, Nassar C R and Z.Wu.IEEE Transactions on Communications, vol.51, iss.7, 1123-1134, July 2003) " a kind of CI-OFDM transmission technology proposed, it utilizes a kind of orthogonal CI code, each parallel data of transmitting on subcarrier are individually expanded on all subcarriers and transmitted simultaneously, the peak value of each subcarrier time domain waveform of modulation is evenly staggered, as OFDM time domain waveform, be to be no longer formed by stacking by the signal of all subcarriers, thereby make between subcarrier transmitted power in theory identical, thereby reduce the PAPR of transmitted signal.

Document 2 " research of carrier wave interference ofdm system signal detection technique (high training. Chengdu: University of Electronic Science and Technology 2011.) " CI-OFDM technology is applied in the discontinuous available situation of subcarrier, design a kind of CI code adding method, proposed discontinuous CI-OFDM system.But this method is only carried out CI expansion to data subcarrier, the existence of the idle sub-carrier causing due to primary user, makes the orthogonality of subcarrier be subject to destruction to a certain degree, and the amplitude that causes PAPR to suppress is less.

But document 1 and document 2 are not concrete to be introduced after experience fading channel, how to design pilot schemes and to carry out actual channel estimation for the feature of NCI-OFDM system.

Document 3 " discrimination of carrier wave interference ofdm system (Lei Jun. electronic information journal .2006, 28 (8): 1400-1402) ", can prove CI-OFDM and single carrier frequency domain equalization (Single Carrier transmission with Frequency Domain Equalization from mathematical angle, SC-FDE) system is equal in fact, transmitted signal does not have clear and definite frequency domain concept in fact, we are difficult to add pilot tone in frequency domain, complete channel estimating, and the lower PAPR of guarantee, therefore conventional Comb Pilot is not suitable for being applied in CI-OFDM system.Slower when variations of fading channels, while being greater than one or several OFDM symbol time, we can adopt block pilot tone, and one is the OFDM symbol of pilot tone entirely, carries out channel estimating.

According to the symmetry principle of Fourier transform, CI-OFDM expands the reduction that has realized time-domain signal PAPR by CI, this just must cause the PAPR of frequency-region signal to raise, show as the signal power maldistribution of each frequency, the signal energy of some frequency can be low especially, after adopting CI expansion, also can there is this phenomenon in pilot tone, the too low channel estimating performance that obviously can affect this frequency of pilot energy on indivedual subcarriers, obviously the equalization that frequency-domain and time-domain signal power is distributed forms contradiction, how under the lower prerequisite of the time-domain signal PAPR that ensures block pilot tone, reduce the lower situation of indivedual frequency pilot signal power as far as possible and become a difficult point, and this also directly has influence on the performance that receiver channel is estimated.

For this situation, the present invention with document 4 " TD-LTE-Advanced mobile communication system design (and Wang Yingmin; Sun Shaohui. Beijing: People's Telecon Publishing House; 2012; 80-87.) " in LTE standard frequency pilot sign be substantially, a kind of pilot design method based on iteration average treatment has been proposed.

Summary of the invention

The present invention proposes a kind of pilot design method based on iteration average treatment, process by the method that iteration is average, frequency pilot sign is being met under the prerequisite that lower PAPR requires, and the equalization of trying one's best of the amplitude on each subcarrier, approaches thereby obtain the performance that ideal communication channel is estimated.

Based on a pilot design method for iteration average treatment, comprise the steps:

S1, obtain random LTE pilot tone: obtain at random one group of N-N _zerolTE pilot tone, wherein, N represents the total number of frequency, N _zerorepresent to be taken frequency points by primary user, available frequency is N-N _zeroindividual;

S2, LTE pilot tone described in S1 is carried out to CI code expansion obtain the pilot signal X through the expansion of CI code that one group of N is _p;

S3, to pilot signal X described in S2 _pthrough to handle averagely, upgrade pilot signal X _pin value;

S4, judge that whether pilot signal transmitted meets PAPR requirement, is specially:

S41, by the pilot signal X upgrading in S3 _pmode with OFDM sends, by IDFT processing, power normalization and interpolation Cyclic Prefix;

The PAPR of the pilot signal sending described in S42, test S41;

S43, pilot signal PAPR thresholding η is set, if PARP < η described in S42 returns to S3, if PARP >=η described in S42 proceeds to S5;

S5, obtain final pilot signal X _final, carry out OFDM transmission.

Further, described in S3, to handle averagely is specific as follows:

Pilot signal X described in S31, search S2 _ptwo frequency positions that middle mould value is minimum and maximum, $\begin{array}{c}i\max =\underset{p}{\max }\left\{\right|X_p\left|\right\}\\ i\min =\underset{p}{\min }\left\{\right|X_p\left|\right\}\end{array},$ Wherein, imax ∈ [1, N], imin ∈ [1, N];

S32, two minimum and maximum mould value described in S31 corresponding pilot signals in frequency position are averaged to processing

S33, order $X_{i\max }=X_{i\min }=\left(\frac{X_{i\max }+X_{i\min }}{2}\right),$ Upgrade pilot signal X _pin value.

Further, η=6.5dB described in S4.

The invention has the beneficial effects as follows:

Can be good at being applicable to the feature of NCI-OFDM system by the block pilot tone after iteration average treatment, taken into account lower PAPR and good channel estimating performance.And because the processing of pilot tone can be before system operation, thus the computing cost can not take system works time, increase system complexity that can be not extra.

Brief description of the drawings

Fig. 1 is PAPR simulation result figure.

Fig. 2 is BER simulation result figure.

Embodiment

Below in conjunction with embodiment and accompanying drawing, describe technical scheme of the present invention in detail.

Present embodiment adopts Matlab2013a emulation platform to carry out running experiment.The NCI-OFDM system that analogue system adopts document 3 to introduce.System parameters: subcarrier N=512, Cyclic Prefix N _g=64, sampling time T _s=0.1us, modulation system is QPSK modulation.

The shared subcarrier of primary user accounts for 20% of total number of sub-carriers, and the shared sub-carrier number of primary user is N _zero=N × 20%.

Pilot tone adopts block pilot tone, and transmitted signal one frame comprises 1 pilot signal and 9 data-signals.

What simulated channel adopted is " COST207 TUx6 " typical urban environment (Typical Urban, TU) channel model, and this channel model has adopted classical Jakes power spectrum and Gauss I type and these two kinds of self-defining power spectrum of Gauss II type.All square time delays of channel expand to 1.0us, and 90% coherence bandwidth is 20kHz.In emulation, the maximum doppler frequency of channel design is 40Hz, and be 11ms coherence time.

The PAPR thresholding η=6.5dB arranging when iteration average treatment.

Step 1: obtain at random one group of N-N _zerothe LTE pilot tone of being introduced as document 4 of dimension, wherein N represents the total number of frequency, N _zerorepresent to be taken frequency points by primary user, available frequency is N-N _zeroindividual.

Step 2: to N-N _zerothe pilot tone of dimension is carried out N-N _zerothe IDFT computing of point, then by this N-N _zerodimension data is mapped to N-N _zeroon individual available subcarrier, and zero setting on all the other unavailable subcarriers, the pilot tone X through the expansion of CI code that one group of N ties up obtained _p.

Step 3: search for pilot signals X _ptwo frequency positions that middle mould value is minimum and maximum, are averaging the pilot value of these two positions, and upgrade respectively the pilot value of these two positions with mean value.

Step 4: by the pilot signal X after upgrading _pmode with OFDM sends, and by IDFT processing, power normalization, interpolation Cyclic Prefix, tests the now PAPR of pilot signal transmitted, if be less than η, jumps to step 3.

Step 5: iteration is complete, obtains final pilot signal X _final, carry out OFDM transmission.

The PAPR of transmitted signal is carried out to emulation testing, and the symbolic number of emulation is 100000, and simulation result as shown in Figure 1.

Relatively two curves are known, and pilot tone is carried out after iteration average treatment, compare the pilot tone PAPR that does not average processing and obtain raising to a certain extent, but what bring is that channel estimating performance has obtained significant raising.As shown in Figure 2, through the random LTE pilot tone through CI expansion of pilot tone being carried out after iteration average treatment, compare processing, in the time that BER is 1e-4, there is the performance gain of 4dB left and right.

One of ordinary skill in the art will appreciate that realizing all or part of step that above-described embodiment method carries is can carry out the hardware that instruction is relevant by program to complete, described program can be stored in a kind of computer-readable recording medium, this program, in the time carrying out, comprises step of embodiment of the method one or a combination set of.

In addition, the each functional unit in each embodiment of the present invention can adopt the form of hardware to realize, and also can adopt the form of software function module to realize.If described integrated module realizes and during as production marketing independently or use, also can be stored in a computer read/write memory medium using the form of software function module.

The above-mentioned storage medium of mentioning can be read-only memory, disk or CD etc.

Claims (3)

1. the pilot design method based on iteration average treatment, is characterized in that, comprises the steps:

S1, obtain random LTE pilot tone: obtain at random one group of N-N _zerolTE pilot tone, wherein, N represents the total number of frequency, N _zerorepresent to be taken frequency points by primary user, available frequency is N-N _zeroindividual;

S2, LTE pilot tone described in S1 is carried out to CI code expansion obtain the pilot signal X through the expansion of CI code that one group of N is _p;

S3, to pilot signal X described in S2 _pthrough to handle averagely, upgrade pilot signal X _pin value;

S4, judge that whether pilot signal transmitted meets PAPR requirement, is specially:

S41, by the pilot signal X upgrading in S3 _pmode with OFDM sends, by IDFT processing, power normalization and interpolation Cyclic Prefix;

The PAPR of the pilot signal sending described in S42, test S41;

S43, pilot signal PAPR thresholding η is set, if PARP < η described in S42 returns to S3, if PARP >=η described in S42 proceeds to S5;

S5, obtain final pilot signal X _final, carry out OFDM transmission.

2. a kind of pilot design method based on iteration average treatment according to claim 1, is characterized in that: described in S3, to handle averagely is specific as follows:

Pilot signal X described in S31, search S2 _ptwo frequency positions that middle mould value is minimum and maximum, $\begin{array}{c}i\max =\underset{p}{\max }\left\{\right|X_p\left|\right\}\\ i\min =\underset{p}{\min }\left\{\right|X_p\left|\right\}\end{array},$ Wherein, imax ∈ [1, N], imin ∈ [1, N];

S32, two minimum and maximum mould value described in S31 corresponding pilot signals in frequency position are averaged to processing

S33, order $X_{i\max }=X_{i\min }=\left(\frac{X_{i\max }+X_{i\min }}{2}\right),$ Upgrade pilot signal X _pin value.

3. a kind of pilot design method based on iteration average treatment according to claim 1, is characterized in that: η=6.5dB described in S4.