Improved Frame Synchronization and Frequency Offset Estimation in OFDM System and its Application to WMAN. and

Transcription

1 Iprove Fre Synchronzton n Frequency Offset Estton n OFD Syste n ts Appcton to WAN Ch. Nn Kshore Heosoft In Pvt. Lt., Hyerb, In n V. Upth Rey Internton Insttute of Inforton Technoogy Gchbow, Hyerb, In Ths work s prt of the WAN project, sponsore by Heosoft In Pvt. Lt.

2 Outne of the Tk Introucton Propose etrc for esttng the sybo bounry --otvton --Anyss --Suton resuts Frequency offset estton Frcton n nteger prts Estton of the bn shft Suton resuts Appcton to WAN Concusons

3 Introucton In OFD, hgh rte t stre s spt nto nuber of pre ow rte t stres, ech of whch outes t sub-crrer. In OFD syste, tng n frequency synchronzton re essent for ntnng orthogonty of the sub-crrers. Prebe structure for OFD oe n 8.6 CP: cycc prefx Aong the sever recenty propose tng gorths, the one suggeste by Sch n Cox [] s robust to frequency offset n chnne phse. Aso, t cn be ppe to OFD oe n 6. The etrc n [] reches pteu, whch y gve rse to soe bguty n the strt of the fre/sybo n the presence of nose n frequencyseectve chnne. 3

4 Propose Tng etrc Conser the secon sybo of the prebe precee by CP. We propose the foowng tng etrc. P R P [ r ] [ r ] R r 3 r - spes of the bse-bn equvent receve sgn - te nex corresponng to the frst spe n wnow of spes - te on spes n the frst hf of the sybo sybo ength R s the receve sgn energy n the secon hf of the bock of spes. For the etrc n [], the nuertor ter s r r P. 4 The enontor ter s se s 3. 4

5 Propose Tng etrc- otvton We ssue e chnne wth no nose n n the CP nterv. Let enote the spe nex esure w.r.t eft bounry of the CP. For the etrc n [] jφ P e L o L o 5 whch, for L, cn be spfe s j e P φ 6 φ s the phse ue to frequency offset, n L s the ength of CP. gntue of P s the cycc utocorreton of the sequence for g zero, whch rens t the se vue for L te nces. For the propose etrc j P e φ L o L o whch cn be spfe s j P e φ L o 7 gntue of P s the cycc utocorreton of the sequence for g -L, whch ttns xu vue when L. 5

6 Propose Tng etrc- otvton cont. The retve vue of the pek copre to those for L epens on the nture of the cycc utocorreton of n o t e o r c A uto Lg vue n spes Norze utocorreton of 6

7 Propose Tng etrc- Anyss We conser AWGN n frequency-seectve chnnes seprtey. AWGN chnne Assung L, n foowng the nyss n [], P cn be expresse s P L o nphseφ { n } 8 n [ P ] E L o 9 [ R ] σ E σ E n n E s the energy n the frst or secon hf of the trnstte sybo. Further, for the vues of uner conserton, E [ P ] E [ Q ] E [ R ] n E [ ] E[ Q ] Q s the squre-root of the tng etrc. 7

8 AWGN chnne cont. For opt L, 9 n gve [ ] E Q opt n for [ ] E Q 4 3 E σ n < L, [ L o ] 4 E σ n The nuertors n 3 n 4 re the cycc utocorreton of the sequence for gs zero n -L, respectvey. Fro the utocorreton of, we note tht the en vue of the tng etrc t the correct sybo bounry s t est.4 tes the en vue t ny other te nstnt n CP. Propose etrc Sch n Cox etrc etrc g n e t h o ft e p tu A Offset fro sybo bounry n spes Coprson of two etrcs for AWGN chnne 8

9 9 Propose Tng etrc- Anyss cont. Frequency-seectve chnne Let hn enote the chnne puse response of ength υ, whose th λ tp hs the rgest power. Conser the cse when correspons to tht prt of CP, where the etrc gven n [] yes pteu. We cn show } { { } ] o o Re o n nphse L L h h L h P > φ υ υ υ [ ] o L P E υ ρ 5 [ ] n n E R E σ ρ σ ρ υ 6 where h E ρ s the power n th tp of the chnne puse response, n υ ρ ρ

10 Frequency-seectve chnne cont. E [ P ] s the convouton of the sequence of tp powers wth the shfte utocorreton sequence of, wth the shft beng L. The pek of the convove output w gn wth the chnne tp hvng the rgest power. Propose etrc Sch n Cox etrc.8 etrc g n e t h o ft e p tu A Offset fro sybo bounry n spes Coprson of two etrcs for SUI- chnne SUI-chnne: Stnfor Unversty Inter chnne oe.

11 Sutons Sutons re use to verfy the utty of the nyss n prectng the en of the peks. Suton set up SNR9.4 B, CP3, 8, Frequency offset.5 en n stnr evton of the peks of Frst n secon peks refer to the rgest n next rgest peks Chnne Type en Stnr Devton Theory Sutons Sutons Frst Pek Secon Pek Frst Pek Secon Pek Frst Pek Secon Pek AWGN SUI SUI SUI Precte vues re cose to those obtne fro the sutons. Stnr evtons, estte fro the sutons, re pproxtey one-tenth of the ens. en vue of the secon pek s pproxtey se n the cses.

12 Frequency Offset Estton Let ε enote the norze frequency offset, esure n unts of sub-crrer spcng. After the sybo bounry s estte, the phse fference between the two hves of the receve sybo s ˆ φ πε, n ˆ φ nge P 7 opt If the ctu norze frequency offset s ore thn sub-crrer spcng, sy ε δ, then the frequency offset estte fro 7 w be εˆ δ 8 where s the even nteger cosest to δ. The nteger frequency offset s estte fro bn shft, n the over offset s copute s ε ˆ ˆ ε bn 9

13 Estton of the Bn Shft The receve OFD sybo s frst copenste wth frcton offset c exp j ˆ ε / N r,,,..., N π. opt Let the DFTs of c n trnstte sybos be N C k c exp jπ k / N, k,,..., N N N A k o exp jπ k / N, k,,..., N N Snce the OFD sybo s oe wth ony even crrers, Ak s zero for o vues of k. The cross correton of Ck n Ak for g s RAC Ck A k, 3 k The g corresponng to the rgest n gntue vue gves the esre bn shft. 3

14 Estton of the Bn Shft cont. Uner the ssupton tht sgn n nose re uncorrete, we cn show c RAC exp jπ / 4 Copute the - pont DFT of c n eterne the coeffcent whose gntue s the rgest. Choose s the estte of the bn shft. Perfornce of the gorth s stue usng sutons. en n stnr evton of the frcton frequency offset estte ctu frequency offset s.5 Chnne Type en Stnr Devton AWGN.5. SUI SUI SUI The estte of the bn shft hs been foun to be n the 5 trs. 4

15 Appcton to the OFD oe n 8.6 Appy the tng etrc choosng 64 frst. Let be the spe nex where the pek of the etrc s observe. Estte the frcton n nteger prts of the frequency offset the frcton prt w be wthn ± n the bn shft w be n nteger utpe of 4, n ppy the copenston to the receve sybo wth estte offset. Appy the tng etrc choosng 8. Let be the spe nex where the pek of the etrc s observe. Estte the resu frequency offset. Estte the ength of CP fro Q[ - o 64] where Q[x] enotes the quntzton of x to the nerest vue of one of the 4 possbe CPs. Suton resuts: The CP estte hs been foun to be 3 n the 5 trs for the cse of AWGN, SUI-, n SUI- chnnes n n 4 trs for the cse of SUI-3 chnne. 5

16 Appcton to the OFD oe n 8.6 cont etrc g n e t h o ft e p tu A Spe nex w.r.t the energy etecton nstnt Tng etrc urng st n n sybos of the prebe for SUI- chnne en n stnr evton of the frcton frequency offset estte couns 3 n 4 correspon to the esttes n the frst n secon sybos of the prebe, n ctu frequency offset s.5 Chnne Type AWGN SUI- SUI- SUI-3 Preter Frcton Frequency Offset Resu Frequency Offset en SD..6 en SD.4.57 en SD..34 en SD

17 Concusons We hve presente new etho of sybo synchronzton n frequency offset estton for the OFD systes. The propose etho yes shrp pek t the correct sybo bounry, n t s robust to frequency offset n chnne phse. The etho hs been nyze for the cse of AWGN n SUI chnnes. The theoretcy precte en vues of the peks uner conserton re shown to gree cosey wth those obtne fro the sutons. The perfornce of the tng synchronzton gorth s copre wth the etho of [] for both AWGN n SUI chnnes usng sutons. The perfornce of the propose etho n esttng the sybo bounry, frequency offset n CP ength, when ppe to the OFD oe of WAN n the ownnk, s ustrte through sutons Ref. []. T.. Sch n D.C. Cox, Robust frequency n tng synchronzton for OFD, IEEE Trns. Counctons, vo. CO-45, pp. 63-6, Dec