Analytical Results to Improve the Capacity of A Cellular System In Frequency Selective Rayleigh Fading Channel

Transcription

1 Prvinr Kumr / Interntionl Journl of Engineering n Tehnology Vol. (5), 010, Anlytil Results to Improve the Cpity of A Cellulr System In Frequeny Seletive Ryleigh Fing Chnnel Mr. Prvinr Kumr Deprtment of Eletronis n Communition Engineering Rooree Engineering & Mngement Tehnology Institute, Shmli (IDIA) E-mil: it.prvs@gmil.om Abstrt - One of the biggest rw b of wireless environment is the limite bnwith. However, the users shring this limite bnwith hve been inrese onsierbly by using SDMA tehnique tht n enhne the pity of ommunition system. There re some tehniques tht n inrese the pity of the ellulr system, these re- Spreing Tehnique, Error Control Coing Tehnique, Multipth Diversity Tehnique ( i.e. Re Reeiver), Smrt Antenn Tehnique. In this pper we hve use ll these tehnique n exmine how the pity of ellulr system vry with vrying the ifferent prmeters suh s- the vlue of spreing ftor, the number of Re fingers, the number of interfering ells, vlue of iretivity of Aptive Antenn t bse sttion. In the results we fin tht the pity of ellulr system is vrying with these prmeters. Inex Terms -- BER, Aptive Antenn, DS-CDMA, Error Control Coing, Re Reeiver, Ryleigh Multipth hnnel, SDMA. ITRODUCTIO BER [1] is use to mesure the en to en performne of wireless ommunition system whih quntifies the relibility of ommunition system. SDMA []-[5] with smrt ntenns t the bse sttion n inrese System pity n support rte emning servies. Mobile ommunition systems re urrently hrterize by n ever-growing number of users, whih however is Couple with limite vilble resoures, in prtiulr in terms of usble frequeny spetrum. The SDMA tehnique llows enhning the pity of ellulr system by exploiting sptil seprtion between users. In n SDMA system, the bse sttion oes not trnsmit the signl throughout the re of the ell, s in the se of onventionl ess tehniques, but rther onentrtes power in the iretion of the esire mobile unit, n reues power in the iretions where other units re present. The sme priniple is pplie for reeption. The SDMA tehnique n be integrte with ifferent multiple ess tehniques (FDMA, TDMA, CDMA). A forwr error orretion (FEC) tehnique[6]-[9] nown s onvolutionl oing with Viterbi eoing n improve the pity of hnnel by ing some refully esigne reunnt informtion to the t being trnsmitte through the hnnel. The proess of ing this reunnt informtion is nown s hnnel oing. Convolutionl oing n blo oing re the two mjor forms of hnnel oing. Convolutionl oes operte on seril t, one or few bits t time. Due to refletions from obstles rio hnnel n onsist of mny opies of originlly trnsmitte signls hving ifferent mplitues, phses, n elys. If the signl omponents rrive more thn urtion of one hip prt from eh other, Re Reeiver n be use to resolve n ombine them. The Re Reeiver uses multipth iversity priniple. It is lie re tht res the energy from the multipth propgte signl omponents[10]-[15]. Setion-1 gives the introution of SDMA n Smrt Antenn. The bsi onept of Aptive Antenn is given in setion-. Setion-3 presents the Error Control Coing Tehnique. In setion-4 we hve given the bsi onept of Re reeiver. In setion-5 we hve the Anlytil Results. At the en the setion-6 gives the onlusion. 1. ITRODUCTIO OF SDMA 1.1 SDMA In SDMA number of users shre the sme vilble resoures n re istinguishe only in the sptil imension. In tritionl ellulr systems the bse sttion rite the signl in ll iretion to over the entire re of the ell, ue to this we hve both wste of power n the trnsmission, in the iretions where there re no mobile terminls to reh, of signl whih will be seen s interfering for o-hnnel ells, i.e. ISS :

2 Prvinr Kumr / Interntionl Journl of Engineering n Tehnology Vol. (5), 010, those ells using the sme group of rio hnnels. Anlogously, in reeption, the ntenn pis up signls oming from ll iretions, inluing noise n interferene. These onsiertions hve le to the evelopment of the SDMA tehnique, whih is bse on eriving n exploiting informtion on the sptil position of mobile terminls. In prtiulr, the rition pttern of the bse sttion, both in trnsmission n reeption is pte to eh ifferent user so s to obtin the highest gin in the iretion of the mobile user. Thus SDMA is reognize s one of the most useful tehniques for improving the pity of ellulr systems. This tehnique llows ifferent users to be serve on the sme frequeny hnnel t the sme time thus improving the spetrl effiieny. 1. Smrt Antenn A smrt ntenn is n ntenn system tht is ble to iret the bem t eh iniviul user, llowing the users to be seprte in the sptil omin. It is not the ntenn tht is smrt, but the ntenn system. The impt of using smrt ntenns epen both on the level of intelligene of the ntenn system n the type of mobile system in whih it is eploye [4] Levels of intelligene Reliztions of smrt ntenns n be ivie into 3 levels of intelligene. These re: Swithe Lobe (SL) This is lso lle swithe bem. It is the simplest tehnique, n omprises only bsi swithing funtion between seprte iretive ntenns or preefine bems of n rry. Phse Arry (PA) By ming the bemforming igitlly, ontinuously moveble bem is estblishe, whih is irete towrs the strongest signl omponent. This is generliztion of the swithe lobe onept n hs n infinite number of possible bem iretions. The optimizing riterion is to mximize the signl level. Aptive Arry (AA) Similr to the phse rry, the bemforming is one igitlly, n min lobe is generte in the iretion of the strongest signl omponent. In ition sie lobes re generte in the iretion of multi pth omponents n nulls in the iretion of interferers. This tehnique will mximize the signl to interferene n noise rtio (SIR). 1.. Type of mobile system In this pper we re using Universl Mobile Teleommunition System (UMTS) [15].. ADAPTIVE ATEA Aptive ntenn provies spot bem for eh user n bse sttion trs eh user in the ell s it moves. It n be seen tht the probbility of bit error is epen on the bem pttern of reeiver, n there is onsierble improvement tht is hieve using high gin ptive ntenns t the bse sttion. In typil ellulr instlltions, D rnges between 3B to10 B. 3. ERROR COTROL CODIG TECHIQUE 3.1 Prmeters of Convolutionl oing The output from the binry soure oul be pplie iretly to the moultor n trnsmitte s the hnnel wve form. oise introues the probbility of error in the etete signl, this being given by bit error probbility ( BEP ). One funtion of the hnnel enoer is to moify the binry strem in suh wy tht errors in the reeive signl n be etete n possibly orrete t the reeiver without the nee to request retrnsmission of messge, it is referre to forwr error orretion (FEC). There re three prmeters, whih efine the onvolutionl oe. These re given s follows: 1. Coe Rte r Rtio of the number of input bits to the number of output bits is nown s oe rte. In this pper we use Coe Rte r 1, whih mens tht there re two output bits for eh input bit.. Constrint Length C L The number of shift require for messge bit to enter the shift register n finlly ome out. In this pper we use Constrint Length CL 3. Constrint Length CL m 1; Where m is the number of shift register 3. Genertor Polynomil Genertor Polynomil shows the wiring of the input sequene with the ely elements to form the output. In this thesis the Genertor Polynomil is [7,5] 8 [111,101] e.g.the output from the rm use the X-or of the urrent input, previous input & the previous to previous input. The Blo igrm of onvolutionl enoer is in Fig. 3 Moulo- Aer Pth 1 v1 Input 0 Output Bits Bits Flip Flop Flip Flop Pth v 0 Fig. 1. Blo Digrm of Convolutionl Enoer Hene the genertor polynomil for pth 1 is : 1 g ( D) 1 D D...(1) Here D enotes the unit ely vrible. The genertor polynomil for pth is : g ( D) 1 D.() If messge polynomil is md, ( ) the output polynomil of pth is : C ( D) g ( D). m( D).(3) ISS :

3 Prvinr Kumr / Interntionl Journl of Engineering n Tehnology Vol. (5), 010, Similrly the output polynomil of pth is : C ( D) g ( D). m( D).(4) 3. Trnsfer funtion of onvolutionl oe Bit error rte performne with using onvolutionl oing n viterbi eoing n be efine by the Trnsfer funtion. To efine the Trnsfer funtion we will efine the stte igrm of onvolutionl oe Stte Digrm (Signl flow grph) Sine the output of the enoer is etermine by the input n the urrent stte of the enoer, stte igrm n be use to represent the enoing proess. The stte igrm is simply grph of the possible sttes of the enoer n the possible trnsition from one stte to nother. Fig.. Stte Digrm for onvolutionl enoer Here ote lines inite tht the input bit is 1 n soli lines inite tht the input bit is 0.The orresponing output is given on the orresponing line. ow the Trnsfer Funtion of onvolutionl oe is given s: 5 D T D ;1;..(5) 1 D TD;1; D D 4D 8D 16D 3 D... Set 1 to get the istne trnsfer funtion, we get T ( D) D D 4D 8D 16D 3 D... (6) The exponent of D on brnh esribes the hmming weight of enoer output orresponing to tht brnh. The exponent of J is lwys equl to 1, sine the length of eh brnh is one. The exponent of enotes the number of 1 s in the informtion sequene for tht pth. (i.e, for input 0, exponent of is 0 n for input 1, it is equl to1). 3.. Free istne of onvolutionl oe The performne of onvolutionl oe epens not only on the eoing lgorithm use but lso on the istne properties of the oe. The most importnt signl mesure of onvolutionl oe s bility to ombt hnnel noise is the istne enote by. The istne of onvolutionl oe is efine s the minimum Hmming istne between ny two oe wors in the oe. A onvolutionl oe with istne n orret t errors if n only if is greter thn t i.e. t. The istne n be obtine quite simply from the Trnsfer funtion of onvolutionl oe. From eqution (6) we hve the following onlusions: There is one oe sequene of weight 5. Therefore 5. There re two oe sequene of weight 6, There re four oe sequene of weight 7,There re eight oe sequene of weight8,. et. 3.3 Viterbi Deoing The Viterbi eoing is the most generl eoing for onvolutionl oe. The Viterbi eoing is n effiient n reursive lgorithm tht performs the mximum lielihoo (ML) eoing. A noisy hnnel uses bit errors t the reeiver. The Viterbi eoer uses the reunny, whih is impose by the onvolutionl enoer, to eoe the bit strem n orret the errors. At first, we explin the vrious terms with respet to Viterbi eoing. 1. Trellis igrm The trellis igrm is the igrm representing trnsition of the stte of shift registers in onvolutionl enoer by ting time xis to the horizontl xis.. Treb epth The treb epth is the number of trellis sttes proesse before the Viterbi eoer mes eision on bit. 3. Hr/soft eision In hr eision, the reeiver elivers hr symbol equivlent to binry 1 to the Viterbi eoer. In soft eision, the reeiver elivers soft symbol multilevele to represent the onfiene in the bit being positive or negtive to the Viterbi eoer. 3.4 Performne Using ViterbiDeoing Bit error rte performne with using onvolutionl oing n viterbi eoing n be efine by the Trnsfer funtion. Agin: TD J D D D D D D J 1 ow T D J D D D D D ; ; ; ; J 1 T D ; J ; J D D D D D ow the bit error rte is written s [9], [15] : BER T D; J; (7) J 1; 1; D BEP 1 BEP 4. RAKE RECEIVER In synhronous DS-CDMA [15]-[17] system for reverse lin mobile to bse sttion) tht supports K tive users the trnsmitting signls in DS-CDMA system given by [17] S( t ) Pb( t ) ( t ) Cos( t )...(8) Where b () t is binry t sequene, () t is pseuornom sequene, P is the power of the trnsmitte signl, is the rrier ngulr frequeny, is the time ely tht ounts for ISS :

4 Prvinr Kumr / Interntionl Journl of Engineering n Tehnology Vol. (5), 010, the l of synhronistion between the trnsmitters n is the phse ngle of the th rrier. The th user s t signl is sequene of unit mplitue retngulr pulse of urtion Tb, ting vlues {-1,+1}.If T is the hip perio n there re hips per bit thus = Tb / T is the spreing ftor for user K. Let the esire user is K=0 n ll other users ontribute to MAI. If the hnnel h () t is multipth Ryleigh frequeny seletive fing hnnel. The ely ifferene between ny two ifferent pths is lrger thn the hip urtion T. The omplex low pss equivlent impulse response of the hnnel is given by L j, l ( )....(9) h t, l e ( t, l ) Where, l l 1 is the phse of the multipth omponent,, l the pth ely, n L is the number of multipth th omponents. l, is mgnitue of the l multipth with Ryleigh istribution. The reeive signl t the input of the reeiver is given by K 1 L r( t) P, l b ( t, l ) 0 l 1 ( t) Cos( t ) Cos( t ) n() t.(10), l, l Using Re Reeiver, with perfet (noiseless) estimtes of the hnnel tp weights with Mximl Rtio Combiner in the system hving M number of fingers, The Coe bit error probbility( BEP ) of Re Reeiver is given s [15]: M M 1 M 1 j 1 1 j j 0 BEP.(11) Where 1 0 M 1 1 LK 1 reb 3D 5 j is ell. Thus the pity of ommunition system with Re Reeiver will ereses with inresing the number of interfering ells. Fig.3. Cpity s funtion of interfering ells (M) 5.. CAPACITY AS A FUCTIO OF SPREADIG FACTOR () In fig.4, t BER vlue of 10 there re 9 users with =3, 4 with =64, 35 with =18. Thus we see tht the pity of ommunition system is inrese with inresing the vlue of Spreing Ftor onsierble. Where D is the iretivity of bse sttion ntenn, r is the oe rte, is the spreing ftor, M is the number of interfering ells, L is the number of multipth, K is the number of users. 5. RESULTS 5.1. CAPACITY AS A FUCTIO OF UMBER OF ITERFERIG CELLS (M)- In Fig.3, the number of multipth L =8, number of users K =3, spreing ftor =3, iretivity of bse sttion ntenn D = 5B, number of fingers M=3, number of interfering ells M =[1,4,6].Coe rte r =1/, Constrint length C =3. At L BER vlue of 10 there re 7 users with 6 interfering ells, 9 users with 4 interfering ells n 13 users with 1 interfering Fig.4. Cpity s funtion of Spreing Ftor () 5.3. CAPACITY AS A FUCTIO OF RAKE FIGERS In fig.5, t BER vlue of 10, there re 6 users with using Re fingers, 9 users with 3 Re fingers n 19 users with 5 Re fingers. Thus pity of ommunition system will inrese with inresing the vlue of Re finger. ISS :

5 Prvinr Kumr / Interntionl Journl of Engineering n Tehnology Vol. (5), 010, spreing ftor (t BER 10 there re 9 users with 10 =3n 35 with =18), Re fingers (t BER there re 6 users with M= n 19 users with M=5), iretivity of ntenn (t BER 10 there re 7 users with D =4B n 17 users with D =8B). REFERECES Fig.5. Cpity s funtion of Re Fingers (M) 5.4. CAPACITY AS A FUCTIO OF DIRECTIVITY OF BASE STATIO ATEA ( D ) In fig.6, t BER vlue of 10 there re 7 users with iretivity of bse sttion ntenn 4 B, 11 users with iretivity of bse sttion ntenn 6 B n 17 users with iretivity of bse sttion ntenn 8 B. Thus the pity of ommunition system with Re reeiver will inrese with inresing the vlue of iretivity of bse sttion ntenn. [1] Bit Error Rte : Funmentl Conepts n Mesurement Issues, From Jnury 003 High Frequeny Eletronis Copyright 003 Summit Tehnil Mei, LLC [] Error Performne Anlysis to Inrese Cpity of A Cellulr System Using SDMA, By M. M. Hossin, J. Hossin. Journl of Teleommunitions, Volume 1, Issue 1, Februry 010. [3] Aril Jobsen, SMART ATEAS for DUMMIES, Telenor AS 5/07/00. [4] Enrio Burhini, SDMA I MOBILE RADIO SYSTEMS: CAPACITY EHACEMET I GSM & I 95. [5] Prvinr Kumr et l., BER Anlysis to Inrese Cpity of A Cellulr System Using SDMA Over Multipth Ryleigh Fing Chnnel, Interntionl Journl on Computer Siene n Engineering, Vol- 0,0.-04, 010, pp [6] J. G. Prois, Digitl Communitions, MGrw-Hill, ew-yor, [7]T.S. Rppport, Wireless Communitions Priniples n Prtie, Prentie Hll, ew Jersey,1996. [8] RTL implementtion of Viterbi eoer Mster s thesis Performe in Computer Engineering by WEI CHE Reg nr LiTH- ISY-EX--06/3886--SE, Linöping June 0, 006. [9] PPT on The viterbi lgorimth by A. J. Hn Vin. Institute for Experimentl Mthemtis, Ellernstrsses Essen-Germny [10]Tommi Heiil, Re Reeiver, Postgrute Course in Rio Communitions Autumn 004. [11] BER Anlysis of Re Reeiver in Ryleigh Fing Chnnels, Chen Wei WuLinyn Mengn, wuhn University of Tehnology, Chin. [1] An Effiient Re Reeiver Design for WCDMA System. The 3 r Interntionl Tehnil Conferene on Ciruits/Systems, Computers n Communitions (ITC-CSCC -008). [13] Ber Performne Simultion of Re Reeiver for WCDMA System e-thesis by LEE LI YIG, 11 My 007. [14] A ovel Re Reeiver Design for Wiebn Wireless Communitions, Konstntinos B. Bltzis John. Shlos, Springer Siene+Business Mei, LLC 007. [15] Prvinr Kumr et l., BER Performne Anlysis of Re reeiver in Ryleigh Fing Chnnel for UMTS environment, Interntionl Journl of Engineering Siene n Tehnology, Vol. (6), pp June010. [16] Wiebn DS-CDMA for ext-genertion Mobile Communitions Systems, IEEE Communition Mgzine September,1998 [17] J.Cheng, n.c.beulieu Aurte DS-CDMA bit-error probbility lultion in Ryleigh fing, IEEE on wireless Communitions, vol. 1, no.1, pp. 3-15, Jn.00 Fig.6. Cpity s funtion of ntenn iretivity ( D ). 6. COCLUSIO For the figures 3 pity of ellulr system will erese by inresing the interfering ells (t BER 10 there re 7 users with 6 interfering ells n 13 users with 1). From Fig. 4, 5, 6, pity of ellulr system will inrese by inresing, Mr. Prvinr Kumr reeive his B.Teh Degree in Eletronis n Communition Engineering from Iel Institute of Tehnology, Ghzib (U.P). He hs one M.Teh. in Digitl Communition (D.C) from Amber Institute of Tehnology (AIT), Geet Colony, Delhi. He hs yers of tehing experiene. His tehing n reserh interests re in the re of wireless ommunition. He is woring s n Assistnt Professor in Rooree Engineering n Mngement Tehnology Institute (REMTeh.), Shmli (U.P). ISS :