Study Of Blind Channel Estimation For OFDM System

Orithogona l frequency division multiplexing (OFDM) is becoming widely appliedin wireless communication system due to its high rate transmission capability withhigh bandwidth efficiency and its robustness with regard to multi-path fading.It hasbeen used in digital audio broadcasting (DAB) system.d igita l video broadcasting(DVB) system,d igital subscriber line (DSL) standards,a nd wireless LAN standardssuch as European equiva lent HIPRLAN/2.It has also been proposed as the coretechnique for the fourth-generation (4G) wireless mobile communications.The use of differentia l phase-shift keying (DPSK) in OFDM system avoids needto track a time varying channel;it limits the number of bits per symbol and results in a3 db loss in signa l-to-noise ratio (SNR),coherent modulation allows arbitrary signa lconstellations,but efficient channel estimation strategies were required for coherentdetection and decoding. The channel estimation meathods for OFDM system aredicussed. The ma in contents are summa rized as follows:1)The first part of the thesis focuses on the algorithms for channel estimationbased on comb-type pilot in the cyclic prefixing (CP) OFDM system,the channelmatrix can be resolved for postpone matrix and range vector of product,the projectionapproxima tion subspace tracking (PAST) algorithms is introduced to estimationpostpone matrix,the least minimum square (LMS) algorathm is used to estimate rangevector,the channel matrix that corresponde to the pilot signa l frequency channelrespondence is carried out,then,interpolation is used to estimate other carrier wavefrequency channel respondence.Moreover,this text returns kalma n algorithm used forthe channel estimation and used to lead pilot signa l acquires of the channel estimationis the initia l value of the kalma n iterative algorithm ,usege decoded data and latelyreceivedsigna l from orientation renewa l kalma n coefficient,rea lization to actualchannel respondence.2)For place zero OFDM (ZP-OFDM) system,to receive the data matrix adoptionsubspace the decomposition acquire a noise subspace vector,from noise subspace vector constitute Hankel matrix , the sum of the each vector correspond ing Hankelmatrix inner product is formated the new matrix W,the minimum and strange value ofW matrix corresponde to vector is direct ratio channel impact respondence.Studiedapplied recursive least squares (RLS) and LMS in the mea ntime the algorithmresolves towards receiving data matrix to carry out on-line from orientation noisesubspace and adopt iterative algorithm carry out the channel respondence of thechannel blind estimatio n;still discussed the misty coefficient of channel blindestimation is really detemined,imitates through computer and verifies the possibility ofalgorithm realization.3)The independent component analysis(ICA) algorithm is made use to the blindsigna l separation of CP-OFDM system,the receiving signa l matrix is directly madewhite processing,pass ICA iterative agorithm,seek ing the mnimum value of thenonlinearity price function carried out the blind separation of signa l.still discussed inthe mea ntime content of the usage CP-OFDM channel matrix a convolution structurecharacteristic and circulates to move a processing towards receiving signa lmatrix,usa ge ICA algorithm carry out the blind separation of signa l.A norma lizationprocessing is adopted to overcome the misty coefficient problem in the blind algorithm.4)At the flat fading channel under the circumsta nce,the bit error rate(BER) ofOFDM system was made mathematics analysis;still discussed OFDM correspondencesystem,adopt DPSK to modulate over the frequency-selective channel due to theDoppler spreading,deduced the BER of system expression;In the mea ntime, the BERof MIMO-OFDM system adopted the trellis-coded modulation(TCM) is studied.TheBER of system over the flat-fading and rayleigh-fading channels is simulated.