OVSF code slots sharing and reduction in call blocking for 3G and beyond WCDMA networks

Transcription

1 Davnder S. San, Vn Bayan OVSF code sots sharng and reducton n ca bockng for 3G and beyond WCDMA networks DAVINDER S SAINI, VIIN BALYAN Deartment of Eectroncs and Communcaton Engneerng, Jayee Unversty of Informaton Technoogy,Waknaghat, Dstt. Soan, Hmacha radesh 735 Jayee Insttute of Informaton Technoogy, Sector-8, Dstt. Noda, Uttar radesh 0307 INDIA davnder.san@ut.ac.n vn.bayan@redffma.com Abstract: OVSF (Orthogona Varabe Sreadng Factor) codes are used n WCDMA unk and downnk transmsson for mutrate traffc. The orthogona roerty of these codes eads to code bockng and new ca bockng. Two code (or sot) sharng assgnment schemes are roosed to reduce the effect of code bockng usng OVSF and NOVSF (non bockng OVSF) codes. The schemes favor the rea tme cas as they are gven hgher rorty n a 3G and beyond networks. The beneft of the roosed scheme s the better handng of non quantzed rates comared to other nove snge code and mut code assgnment schemes. Both snge code and mut code otons are anayzed for OVSF as we as NOVSF codes. Smuaton resuts are dscussed to show the benefts of the roosed scheme. Key- Words: OVSF codes, sots, tme sharng, mutexng, snge code assgnment, mut code assgnment, rea tme, code bockng. Introducton Two mortant ssues under research n WCDMA systems are sreadng codes [,] and moduaton[]. Sreadng s the fundamenta oeraton of WCDMA rado nterface. The sreadng codes n WCDMA are of two tyes namey channezaton code and scrambng code. The channezaton codes n WCDMA are OVSF codes. The channes n the forward nk and reverse nk use theses codes for transmsson. OVSF codes are shorter n ength and are made from orthogona functon. The orthogonaty roerty of OVSF codes makes t sutabe for WCDMA. The sgnas from two or more UEs n the reverse nk are transmtted to same BS n the ce from searate ocatons. Ths change n dstance gves rse to change n tme for the sgnas to reach at the BS. The orthogona roerty of the OVSF codes s dsturbed due to dfferent arrva tmes. Hence the OVSF codes are not used for cas searaton n the reverse nk. The facty to hande varabe ca rate s aso ncororated n OVSF codes. In contrast to OVSF codes, scrambng codes are qute ong (wth the exceton of the reverse nk of the short scrambng code). Scrambng codes are generated from the stream caed seudo nose (N) sequences [3]. In WCDMA the requrement s have codes wth hgh vaue of autocorreaton and ow vaue of crosscorreaton. Hgh autocorreaton roertes are desred to recover the ntended sgna and to reduce the effect of mutath sgnas. The ow crosscorreaton roertes are requred to mnmze the effect of nterferng sgnas. The N codes and s (t) + - s (t) + - Fg.. Orthogona sgnas orthogona codes ndvduay do not have both good autocorreaton and good crosscoreaton roertes. Orthogona codes are sets of bnary t t E-ISSN: Issue 4, Voume, Ar 0

2 Davnder S. San, Vn Bayan sequences that have a cross-correaton coeffcent equa to zero. A set of erodc sgnas s (t) and s (t) s orthogona f T 0, s ( t) s ( t) dt = () E 0, = where, E s the energy of the sgna gven by E T = s ( t) dt () 0 In Equaton (), T s the erod of the sgnas s (t) and s (t), and E s the sgna energy as defned n Equaton (). The set of sgnas reresentng the orthogona bnary sequences 00 and 0 s shown n Fgure. The OVSF codes desgned to factate mutrate traffc. Ths s because mute sreadng factor otons. The OVSF codes are generated [4] usng to Wash functons. The codes wth dfferent sreadng factors hande cas wth dfferent rates. One of the mortant roertes of OVSF codes s that, when a code s used, a of ts ancestors and descendants are bocked from assgnment. Ths s requred to assgn orthogona codes to each new ca. The SF of a code decdes the rate of the ca that can be suorted by an OVSF code. Lower s the oston of a code n tree, hgher s SF and vce versa. Once a code s assgned, a ts ancestors and descendants are bocked. It mts the number of OVSF codes. So, OVSF codes shoud be aocated effcenty. Further, the far aocaton of codes become dffcut as the scattered ower rate codes bock hgh rate codes [5-6]. In OVSF based networks, the treatment of voce cas and data cas s dfferent. The voce cas C 5, hand for data traffc, the modes deend uon the scheme used for resource aocaton and affects code bockng whch reduces the sectra effcency of WCDMA system u to 5%. The code bockng aears due to two reasons namey nterna fragmentaton [8]and externa fragmentaton [8]. The nterna fragmentaton s due to quantzed rate handng caacty of OVSF codes. The networks wth non quantzed cas, aways gves wastage of caacty of the code t occues. The caacty wastage s hgh as codes near the root are used where t can reach cose to 00%. The externa fragmentaton s due to scattered vacant codes such that the hgh rate ca s reected deste the system has enough caacty to hande t. Ths aer descrbes tme sot sharng method whch avods the mtaton of code bockng to avod both the mtatons dscussed above. The sot usage benefts are exaned for tradton OVSF codes and non bockng OVSF codes where the codes n dfferent ayers are orthogona to each other. The reference s gven to hande rea tme (rorty) cas. The remander of the aer s organzed as foows. Secton dscusses revew of OVSF and non bockng OVSF based WCDMA systems. Secton 3 gves exanaton of the roosed OVSF sot sharng assgnment scheme for snge code and mute code oton. Secton 4 descrbe NOVSF sot sharng scheme usng snge code and mute codes. Secton 5 gves smuaton arameters and resuts to show the code bockng reducton benefts n the roosed schemes. The aer s concuded n secton 6. Layer Bandwdth SF C 4, C 4, 5 3R 4 6R C, C, C,3 C,4 C,5 C,6 C,7 C,8 3 8R 4 Vacant code Busy code Fg.. OVSF code tree wth sx ayers requre snge code for fu ca duraton at fxed rate, whe the data cas have the fexbty of varabe data rate. The treatment of rea tme and on rea tme cas n most of the systems ncudng GSM, CDMA etc. s dfferent. In [7], the voce cas and rea tme cas are handed wth ether comete arttonng (C) or arta arttonng () methods. The voce traffc, the traffc mode used s Erang Law for both cases C and. On the other Bocked code 4R 8 R 6 0 R 3 OVSF and non bockng OVSF Codes. OVSF Code Tree and code bockng Consder an L ayer (L=8) WCDMA OVSF code tree wth ayer 7 for root and ayer 0 for eaves. The ca data rates and sreadng factor (SF) and for E-ISSN: Issue 4, Voume, Ar 0

3 Davnder S. San, Vn Bayan ayer, [0, L ] are R (R=5 kbs) and L resectvey. Fgure shows OVSF code tree wth sx ayers. There are three ossbe statuses of the codes as exaned beow, Busy code: Code assgned to a ca (marked back n Fgure ). Bocked code: Code bocked (marked gray n Fgure ) due to busy ancestor or descendant. Vacant code: Unoccued code (marked whte n Fgure ) can be assgned to future cas. A code n a ayer s orthogona to codes n the same ayer and a the codes n dfferent branches, but not to the codes n the same branch. As dscussed, f a code s assgned to the ncomng ca, ts ancestors and descendants are bocked from assgnment. In Fgure, code C,7 s beng occued by the ca. Therefore a ts ancestors and descendants are bocked from assgnment. The data rate handed vares from R, R,, 3R wth corresondng code SF =3,6,,. The overa bandwdth transmtted s aways 3R. To make transmtted bandwdth same rresectve of nut cas wth rate R, R,, 3R requre SF= 3,6,.,. The maxmum caacty of the tree s 3R out of whch 5R (sum of bandwdth of back nodes) s currenty used. So the maxmum avaabe caacty s 7R. If a ca wth rate 8R wants vacant code, t w not be handed by the system because there s no vacant code wth caacty 8R. We come to the stuaton n whch a ca s not handed even the system have enough caacty to hande t. Ths s caed code bockng whch eads to ca bockng. There s arge number of code assgnment schemes roosed n terature to reduce code bockng.. Non bockng OVSF (NOVSF) codes The non bockng OVSF (NOVSF) codes [9] rovde zero code bockng. There are two categores of NOVSF codes. The frst category of codes emoy tme mutexng gvng dfferent ncomng ca rates the fexbty of usng tme sots from a snge ayer ony. The ayer used and number of sots er code deends on the tye of ca and maorty. In the second category, the structure of the non bockng OVSF code tree s exacty same as that of OVSF code tree. The codes n dfferent ayers are orthogona to each other (unke tradtona OVSF codes). The SF of the root can be chosen accordng to the tye of wreess network. The aer ams to rovde tme sot usage descrton for two scenaros: () when a cas are treated smary () some cas are gven hgher rorty..3 Exstng code assgnment schemes The code assgnment schemes whch do not ncororate code sharng can be categorzed nto snge code and mut code assgnment schemes. The snge code assgnment scheme used snge code to hande ncomng cas [0]. The eftmost code assgnment (LCA) [], crowded frst assgnment (CFA) [], fxed set arttonng (FS) [] and dynamc code assgnment (DCA) [3] are snge code assgnment schemes. In the eftmost code assgnment scheme, the code assgnment s done from the eft sde of the code tree. In crowded frst assgnment, the code s assgned to a new ca such that the avaabty of vacant hgher rate codes n future s more. In the fxed set arttonng, the code tree s dvded nto a number of sub trees accordng to the nut traffc dstrbuton. In dynamc code assgnment scheme, the bockng robabty s reduced usng reassgnments based on the cost functon. The DCA scheme requres extra nformaton to be transmtted to nform the recever about code reassgnments. The ncomng cas are converted nto quantzed rates (f not so). A fast OVSF code assgnment desgn s gven n [4] whch ams to reduce number of codes searched wth otma/subotma code bockng. The code assgnment scheme uses those vacant codes whose arents are aready bocked. Ths eads to occurrence of more vacant codes n grous, whch utmatey eads to ess code bockng for hgher rate cas. The ntegraton of cas s done n [5] for aocaton of OVSF codes when a quantzed or nonquantzed ca arrves, and further, the voce cas and data cas are treated dfferenty as former are deay senstve and ater can be stored n buffer.the snge code assgnment schemes are smer, cost effectve and requre snge rake combner at the BS/UE. The mut code assgnment schemes use mute codes n the OVSF code tree and hence mute rake combners to hande snge ca. It reduces code bockng comared to snge code assgnment schemes but the cost and comexty s more[6,7,8]. The mut-code assgnment schemes rovde addtona beneft of handng nonquantzed (not n the form of R,, [0, L ] data rates. The DCA scheme wth dfferent QoS requrements s gven n [9]. The erformance of fxed and dynamc code assgnment schemes wth bockng robabty constrant s gven n [0]. The throughut erformance s roved to be better n ths aer. The mut rate mut code comact assgnment (MMCA) [] scheme uses the concet of comact ndex to accommodate QoS dfferentated mobe termnas. The maxmay fexbe assgnment scheme [] dscusses two code E-ISSN: Issue 4, Voume, Ar 0

4 Davnder S. San, Vn Bayan assgnments namey rearrangeabe code assgnment and non rearrangeabe code assgnment schemes. It defne fexbty ndex to measure the caabty of assgnabe code set. Both schemes rovde the maxma fexbty for the code tree after each code assgnments. The code/sot sharng n a above schemes further reduces the code bockng. The code assgnment scheme n [3] uses the hgher ayer code sharng on the erodc bass. Ths s sgnfcant requrement for cas wth arge eak to average rato of data rates. The code utzaton s ncreased due to code sharng. Usng de/unused code sots for bursty traffc, the farness and er connecton data rate guarantee s acheved. The code assgnment scheme dscussed n [4] descrbes three schedung termnas. Each ca s aowed to use mute codes n tme sharng manner. The channe senstve agorthm s gven to use mute codes when there are channe errors eadng to bad sgnas. For bad quaty transmsson, codes wth hgher sreadng factors are used. It defnes shared count of ancestors to use the code from artay shared area or fuy shared area. Zero wastage desgns n [5] are defned n whch the rake combner s usage s made dynamc and the amount of rake combners used deend uon the rate tye, wth more combners gven to the rate whch devates sgnfcanty from the quantzed one. The average number of rakes er ca s arbtrary assumed, and f the rakes used for a artcuar ca are ess than the average (whch haens for quantzed or near quantzed cas), the T ref L- Fg.3 Tota tme sots n any one ayer (a) R R R 4R 0R R 3R (b) R R R R R R 4R 3R 0R R 3R (c) R R R R R R R 4 R 5R R R R 3R (d) Ongong ca rorty ca usng unused sots rorty ca usng non rorty ca sots Fg.4. Iustraton of sot usage n a 3 OVSF CDMA system. A cas excet 4R and 6R are non rorty cas. (a) tota vacant codes avaabe (b) Status of the sots at the arrva of 4R rorty ca (c) Status of the sots after handng 4R ca when the system has one rake (d) Status of the sots after handng 4R ca when the system has two rakes (e) Status of the sots after handng 6R ca when the system has two rakes agorthms to suort mutmeda transmssons. The credt management and comensaton mechansm rovdes rate guarantee and far access to mobe unused rakes can be used by future cas. The erformance s sgnfcanty mroved comared to the fxed rate systems. The amount of codes used on E-ISSN: Issue 4, Voume, Ar 0

5 Davnder S. San, Vn Bayan average s ess than the codes requred for exstng mut code desgns. 3 OVSF based tme sots sharng For a ayer, the number of codes n OVSF code tree s L- and number of sots er code s. It s suffcent to use any one ayer from the code tree for tme sot sharng wth tota L vacant sots. For exame, f ayer 4 s used, there are 8 orthogona codes n the OVSF code tree wth 6 tme sots er code makng tota sots equa to L- (as shown n Fgure 3). The sots n a ayer are denoted by S x, where x s the sot number. The dentfer S x does not deend on ayer number as any ayer can be oted. 3. Sots sharng wth snge code Two ca scenaros are consdered, () genera case: a the cas are treated smary () some ayer cas are gven hgher rorty. 3.. Genera case: A cas are treated smary For a new ca kr, f k consecutve vacant sots are avaabe, the ca s handed. Otherwse the ca s reected. The ca reecton s ony due to nsuffcent sots. 3.. rorty and non rorty cas coexst The cas are dvded nto two categores, namey, rorty cas (-cas) and non rorty cas (Ncas). When a N-ca arrves, the sots are assgned accordng to the rocedure dscussed earer. On the other hand, f -ca wth rate kr arrves, the avaabty of k vacant sots s checked, and f the vacant codes are avaabe ca s handed as dscussed earer. If k vacant sots are not avaabe, the ca can st be handed by aocatng some sots currenty assgned to N-cas. Thus, the rate of the N-ca s reduced at the cost of handng -ca. If at the arrva of a new -ca of rate kr, there are N ongong -cas and N n ongong N-cas wth corresondng used sots S, N and S n, N n resectvey, the agorthm dentfes the otmum N-ca whose some sots can be assgned to the new ca. In our desgn we use snge eve sharng where ony one -ca can share the sots of a N-ca. It may haen that none of exstng N-cas has enough sots and therefore, the sots from two or more ongong cas are requred. For a -ca of kr rate, f the maxmum vacant sots avaabe are k, k < k and there are some N- ongong cas wth at east (k- k ) sots, the -ca ca can be handed wth eve- sharng. However, t w ncrease the tme duraton of ongong Nca. If rates of N-cas are denoted by vector n n n n R = R, R,..., R ] from eft to rght of the code [ Nn tree, otmum N-ca s dentfed n n by R = max( R ), [, N ] R s use to ot n and n ot hande -ca. The requrement of (k-k ) sots of an otmum N-ca guarantee that the exstng N cas has at east haf the sots avaabe for ts own after gvng (k- k ) sots to -ca. Ths mantans farness of caacty dstrbuton between -ca and N-ca. For a th N ca wth rate R, f there are tota S sots out of whch S sots are gven to a - ca, the new rate of N ca becomes R ( S S ) S. 3. Mut code assgnment 3.. Genera case: A cas are treated smary Same as dscussed n secton One or more cas are gven hgher rorty If a rorty ca wth kr rate arrves, fnd the sot avaabty as exaned n secton. If r grous wth suffcent vacant sots are not avaabe, the sots from non rorty cas are used. Let fracton k R k < k s handed by q q<r grous of vacant sots, the rate orton ( k k ) R has to be handed by non rorty busy ca sots. The seecton of busy code deends on number of avaabe rakes and number of rakes used w ncrease eve sharng. One rake s used to hande vacant sots grou and one rake for each N ca whose sots are used. Leve- sharng: number of rakes used -. Leve- sharng: number of rakes used -3 and so on. For remanng ( k k ) sots, arrange N-cas n descendng order of sots assgn to them. If a Nca of maxmum sots (say) k wth k ( k k ) exsts, new ca of rate kr s handed usng k vacant sots and ( k k ) sots of N-ca. Ths s eve- sharng utzng two rakes. If a ca rate s not handed and avaabe rakes are more than used rakes, ncrease eve sharng wth m usng more N-cas t = k = ( k k ), where m denotes N-cas whose sots are used, utzng m+ rakes. Consder a 3 sots OVSF CDMA system as shown n Fgure 4(a), where a the users excet 4R are non rorty users. For a artcuar tme, et the status of the code sots s shown n Fgure 4(b). If a new 6R rorty ca arrves, avaabty of four E-ISSN: Issue 4, Voume, Ar 0

6 Davnder S. San, Vn Bayan vacant sots s checked. As shown n (c) there are 3R rate vacant sots between -4 oston and three R rate sots avaabe at, 5 and 7 ostons resectvey. Ths ca w be handed wthout sharng. If a new ca of rate 0R arrves, vacant sots are not enough to suort t. The assgned sots to N-cas are arranged n descendng order and haf of the sots (requred sots) of these cas are assgned to new ca. As shown n (d), 3R avaabe vacant sots and remanng 7R s rovded by ongong N-cas sots arranged n descendng order0 R,4R,3R,R,R, R and R. The ca s handed usng 3 vacant sots and 5R, R and R sots of 0R, 4R and R rate ca resectvey. 4 NOVSF based tme sots sharng 4. Snge code assgnment Consder a NOVSF CDMA system wth L (ayer numbers 0 to L-) ayers n the code tree. The code n ayer, [0,L-] s reresented by C,x, L x. The tme frame for code C,x can be reresented as sum of fxed sots of wdth T ref, where T ref reresents the duraton of code tme frame n ayer 0 known as reference tme sot (RTS). For a ayer, the code tme frame can be reresented as sum of RTSs. For a code C,x the sots are S to S, ( x ) +, wth wdth of each sot T x ref. For every ayer, the tota numbers of sots are L-. For a aocaton wthout tme sot usage where a ca can be handed ony f there s at east one vacant code (equvaent to consecutve vacant sots). The dvson of code tme frame nto sots s ustrated n Fgure 5 for,( L ) ayer OVSF code tree. To ustrate code sots sharng benefts, two scenaros of WCDMA systems are consdered () genera case where a the cas are treated smary () one (or more) ayer cas s (are) gven hgher rorty as comared to others. 4.. Genera case: A cas are treated smary Consder fu vacant code tree. For a new ca of rate kr, fnd mn() k. The ca kr uses k vacant sots L of a vacant code, where x and C, x C, = mn(, L ) wth x has at east k vacant sots. If a code C, x, s used and t has, > k vacant sots ntay, the vacant sots of code C, whch, x can be used by future cas are k. If ayer do not have k consecutve vacant sots, fnd the vacant sots n codes of ayer + to L-. If we defne sot utzaton as the rato of sots used by ongong cas to the tota sots avaabe n the OVSF CDMA system, the code sot sharng ncreases sot utzaton and reduce code bockng sgnfcanty. 4.. One or more users are gven hgher rorty When one or more users (ayers) are gven hgher Layer Sots/code n ayer L L L- Sots/code n ayer L L-3 Sots/code n ayer L-. Sots/code n ayer Sots/code n ayer 0 T ref Fg.5. (a) 8 ayer N-OVSF code tree (b) Number of sots/code for each ayer n art (a). ca of rate R, any of the unused sots (consecutve or scattered) n ayer can be used for the new ca. Ths s dfferent from the code rorty, some of the busy sots of the ongong non rorty cas can be utzed for rorty cas. The cometon tme for non rorty cas ncreases as a E-ISSN: Issue 4, Voume, Ar 0

7 Davnder S. San, Vn Bayan [ consequence. Let ayer vectors =,,... ] n n n n and = [,,... L ] reresents rorty and L- non rorty ayers. For non rorty cas a n n n n threshod vector H = [ H, H,... H L ] (sgnfyng maxmum number of tme sots whch can be used by rorty cas) s used to decde whether or not the ncomng rorty ca can be handed by a non rorty ayer n. If the number of sots occued by rorty cass users n ayer n s n n ess than H, some of the busy sots n ayer can be used by the rorty ayer ca. The cometon tme of the of the non rorty ca ncreases (comared to the cometon tme when there s no sot sharng). For a n L codec,, x n, the sot x n utzatonuc, s defned as x n SC, x n UC, x = n (5) In Equaton (5), SC, reresents the sum of sots of busy codes x n C, x n, used by the revous rorty cas (f any). Sot utzaton reresents the fracton of the code caacty utzed by ongong non rorty ca. The code wth the east C, x n vaue of sot utzaton s the canddate for handng of new ca. The am s not to reduce the number of sots sgnfcanty for the ongong busy ca n non rorty ayer. Ths mantans the farness for amount of sots used by ongong non rorty cas. If a te occurs for sot utzaton of two or more busy codes, any one code can be used for rorty ca handng. If the rorty users can be of non quantzed rate nature, consder rorty casses reresented by vector R = [ R, R,... R ]. A rorty users fa n dfferent ayers reresented by ayer [ vector =,,... ], where the rorty users wth rates R w requre tme sots from the rorty ayer k f R k k = mn( k ) for a. Then for a new ca of rate R = kr, the rocedure w be same as for quantzed rate rorty users. Ths may ead to code caacty wastage and may be avoded by the use of mute codes as w be dscussed n secton 4.. To ustrate the deay nduced n cometon of non rorty ca by assgnng ts sots to rorty ca, assume t 0 s the nta cometon tme of the ca handed by the 7 code C, x n non rorty ayer n n, x n n n wth rate R whose busy code threshod s not exceeded. The busy code s dentfed usng the sot utzaton Equaton (5). If a new rorty ca seekng a code n ayer arrves and there s no vacant code n ayer, the nta tme t 0 of the code C n, s dvded nto two comonents x n and( t ). The tme t0 sgnfes the eased tme of 0 t 0 the code C n, when the ca of R x n n t 0 arrves. The roosed desgn ncreases remanng tme ( ) t of 0 t 0 the ca by assgnng R code sots to R rorty ca. Subsequenty, the new remanng tme for ongong non rorty ca after the arrva of R ca becomes n ( t t ) t = 0 0 (6) n Aso, the tota duraton of non rorty ca becomes t 0 + t. If some future rorty ca requres vacant sots and threshod of ths non rorty ca s not exceeded, the number of sots from ths ca can be utzed by rorty ca R. The tme t of the code C n, s dvded nto two x comonents t t. The new remanng tme of the non rorty ca becomes t + t + where t s gven as 0 t t and ( ) n ( ) t t t = (7) n The resut can be generazed for m th eve sharng of non rorty ca n m n R to hande rorty ca R. Therefore the remanng tme becomes where tm s defned as t m = ( t t ) m m n n m = m = m = t + t m (8), E-ISSN: Issue 4, Voume, Ar 0

8 Davnder S. San, Vn Bayan The dscusson n the secton deas wth users wth rates n the form of. If a new rorty ca of rate kr, k requres code, the k consecutve vacant sots are searched for codes n ayer k. If the vacant sots are not avaabe, the codes n ayer are searched and k > vacant sots n ayer are utzed to hande the new ca. If vacant sots are not resent, k number of busy sots used by non rorty cas are used as dscussed above. 4. Mut code assgnment Consder an OVSF system equed wth r rake combners. We ustrate mut code assgnment for two cases as for snge code assgnment. 4.. Genera case Consder fu vacant code tree. For a new ca of rate kr, fnd mn() k. If there are q q r codes n ayer wth some vacant sots each, rovdng tota k vacant sots the fracton of kr rate handed by ayer codes s k R. The baance rate k R=(k-k )R s to be handed by codes n the ower ayers (-, ). Startng wth ayer -, check the avaabty of maxmum q =r-q codes for fndng k vacant sots. The rocedure can be reeated t ayer to fnd the k vacant sots. Therefore mut code scheme uses the vacant sots of maxmum r dfferent codes to hande new ca. 4.. One or more users are gven hgher rorty There are two ossbtes () the ca requres code from the non rorty ayer () the ca requres code from the rorty ayer. If a non rorty ca kr requres codes (sots) from the non rorty ayer n (say) and f there are q q r codes (consecutve or scattered) wth some vacant sots and a q codes rovdes tota k (or k k <k) vacant sots, the fracton of kr rate handed by ayer Sots used by non rorty users Sots used by rorty users (,4) (,4) (6,4) (6,8) 3 3 (a) Sots avaabe for future cas (b) (,4) (,4) (6,4) (6,7) 3 3 (c) (d) Fg.6. Iustraton of sot usage n 6 ayer NOVSF CDMA systems. A cas excet 4R and 6R are non rorty cas. (a) Status of the sots at the arrva of 4R rorty ca (b) Status of the sots after handng 4R ca when the system has one rake (c) Status of the sots after handng 4R ca when the system has two rakes (d) Status of the sots after handng 6R ca when the system has two rakes E-ISSN: Issue 4, Voume, Ar 0

9 Davnder S. San, Vn Bayan n codes s kr (or k R) as dscussed n secton 3... However, f a rorty ayer ca requres sots n rorty ayer and sots are avaabe then assgn new ca to them. If vacant sots are nsuffcent to hande ca of rate kr, then ca w be handed usng sots n both rorty and non rorty ayers. If a code n rorty MC,m ayer L C, m, m has number of vacant sots avaabe, the tota number of vacant sots of codes n rorty ayer used to hande ca of rate kr q s MC, x. The baance rate =, x L k R=(k-k )R s to be handed by q q ( r ) codes n the non rorty ayer q n n where n n n ) z z = mn( <. In ower most non rorty ayer (say) n L, number of rakes avaabe s r L = q. The tota number of sots st requred (k L- ) can be formuated as k = L = t k k (9) The tota numbers of codes whch can be used n n ayer are gven by L q = L = L r q (0) If a the non rorty ower ayers are unabe to hande the rate kr, the vacant sots are searched n q hgher ayers.e. MC k, the vacant = m=, x m sots are searched n hgher non rorty ayers n n n = mn( ) > n ascendng order of L + L L + ayer number. If ayer n L + z denotes the uermost non rorty ayer, the number of rakes avaabe n n L + z ayer s r q. The number of sots t+ z avaabe at ayer n = L + z s k L + z = k L + z = k. If the number of sots requred s ess than k L-+z, the ca s handed. If there are nsuffcent codes (vacant sots) avaabe even n uermost non n n rorty ayer, the ayers to be checked L + L + z for the threshod of number of busy codes. The rocedure gven n secton can be used for usng few vacant sots for ncomng rorty ca. Consder a sx ayer NOVSF code tree as wth the status of the codes as shown n Fgure 6(a). In ayers 4 and 5, the varabe (a,b) reresents that a number of code sots are used by non rorty users and b number of code sots are used by rorty users. In other ayers the varabe c on a artcuar code reresents c number of vacant sots for that code whch can be used for future cas. Let the users wth rates 4R and 6R are rorty users. If a new user wth rate 4R arrves and the system s equed wth one rake, the ca requre sharng of sots as there s no grou of 4 consecutve vacant sots. If threshod for non rorty ayer s -, 4 vacant sots of code C 4, ayer are used and the status of the code tree s shown n Fgure 6(b). If the system s equed wth two rakes, codes C,6 and C,5 are used as shown n Fgure 6(c). If a new user wth rate 6R arrves codes C, and C 4, are used as shown n Fgure 6(d). 5 Smuaton resuts Consder L=8 ayer OVSF code tree as n the downnk of OVSF System. For smuaton, foowng casses of users are consdered wth rates R, R,.. 8R resectvey. The arrva rateλ s assumed to be osson s dstrbuted wth mean vaue varyng from 0-4 cas er unt of tme. Ca duraton s exonentay dstrbuted wth mean vaue of 3 unts of tme. The maxmum caacty of the tree s 8R (R s 7.5kbs). Smuaton s done for 5000 users and resut s average of ten smuatons. There are 8 ossbtes for arrva cas rates R,, [0,7]. We assume that there are two sub cases (a) ayer,,3 users are gven hgher rorty and these users make 0% of the arrva dstrbuton and 80% of the cas are non rorty cas (b) ayer,,3 users are rorty users and these make 80% of the arrva dstrbuton aong wth 50% non rorty cas. The owermost ayers (,,3 etc.) are chosen for rorty as rea tme cas are generay are rorty cas. It s assumed that the users wth two or more dfferent rorty ayers are not gven rorty wthn themseves (though the rovson can be made for the same aso). The threshod for number of busy codes n non rorty ayer, s 7- (threshod for ayer 7 s as there s ony one code). For quantzed users system, et λ, [0,7] s the average arrva rate of th cass cas. The average servce tme (denoted by, / µ whereµ s average servce rate) s assumed to be for a arrva casses. The traffc oad for the th cass of users s gven by ρ q = λ / µ q. Consder that there are G, =0,,, 7 servers n the th ayer corresondng to G number of vacant codes. The tota codes (servers) n the system assumng eght set of casses are the gven by vector G={G 0,G,G,G 3,G 4,G 5,G 6,G 7 }. The q E-ISSN: Issue 4, Voume, Ar 0

10 Davnder S. San, Vn Bayan maxmum number of servers used to hande new ca s equa to the number of rake combners. The code bockng for the th cass s defned by shown n Fgure. 7. The NOVSF rovdes zero code bockng; therefore resuts are not shown for ths scheme. % Inc reas e n rorty Ca Handed % Increase n rorty Ca Handed Average Traffc Load (a) rorty Cas=0%,Non-rorty Cas=80% SC-TH=0% SC-TH=40% SC-TH=60% rorty Cas=0%,Non-rorty Cas=80% MC-TH=0% MC-TH=40% MC-TH=60% Average Traffc Load (c) % Inc reas e n rorty Ca Handed % Increase n rorty Ca Handed rorty Cas=80%,Non-rorty Cas=0% SC-TH=0% SC-TH=40% SC-TH=60% Average Traffc Load (b) rorty Cas=80%,Non-rorty Cas=0% MC-TH=0% MC-TH=40% MC-TH=60% Average Traffc Load (d) Fg. 7 Comarson of ercentage of rorty ca handed n snge code (a),(b) and mut codes (c),(d) desgns for arrva rates dstrbuton: rorty Cas=0%, Non-rorty Cas=80%, and rorty Cas=80%, Non-rorty Cas=0% B G ( ρ q ) / G! = G n ( ρ ) / n n= q! () Defneλ q as the average arrva rate of a cas n the system and s gven byλ = 7 q = 0λq. The average code bockng for quantzed users s 7 0 ( λ / λ ) () B = = q nq B Three threshod eves are consdered for snge code and mut codes Threshod=0% Threshod=40% Threshod=60% As the threshod ncreases sot utzaton ncreases for snge code and mut codes assgnment as 6 Concuson Rea tme cas are gven hgher rorty n a 3G and beyond systems. The code bockng s the maor mtaton of OVSF based 3G systems whch ead to ca bockng n both rea tme and non rea tme cas. The code sots sharng schemes are roosed to reduce the code bockng for rea tme cas whch gves reducton n ca bockng. The use of mute rakes aong wth the code sharng facty can be used to make rea tme ca bockng cose to zero. The code sharng (tme sharng) s the comcated task and may requre ot of effort. Work can be done E-ISSN: Issue 4, Voume, Ar 0

11 Davnder S. San, Vn Bayan to otmze the assgnment of code sots for dfferent order of rorty wthn rorty users. References: [] E.H. Dnan and B. Jabbar, Sreadng codes for drect sequence CDMA and wdeband CDMA ceuar networks, IEEE Communcatons Magazne, 998. [] Sreadng and Moduaton (FDD), 3G TS 5.3 (V6.0.0). Technca Secfcaton (Reease 6), Technca Secfcaton Grou Rado Access Network, 3G, 003. [3] R.L. ckhotz, D.L. Schng and L.B. Msten, Theory of sread sectrum communcatons-a tutora, IEEE Transacton on Communcatons, Vo. 30, 98, [4] F. Adach, M. Sawahash, K. Okawa, Tree structured generaton of orthogona sreadng codes wth dfferent engths for forward nk of DS-CDMA mobe rado, IEEE Eectronc Letters, Vo. 33, 987, [5] J. S. Chen, W. C. Chang, N. C. Wang, and Y. F. Huang, Adatve oad baance and handoff management strategy for adatve antenna array wreess networks, n roceedngs of th WSEAS Internatona Conference of Communcaton, 008, [6] J. S. Chen, N. C. Wang, Z. W. Hong and Y.W. Chang, An adatve oad baance strategy for sma antenna based wreess networks, WSEAS Transacton on Communcaton, Vo.8, No.7, 009, [7] G. Budura, C. Bant, A. Budura, and E. Marza, Traffc modes and assocated arameters n GSM/(E)GRS networks, WSEAS Transacton on Communcaton, Vo. 8, No.8, 009, [8] C. M. Chao, Y. C. Tseng and L. C. Wang, Reducng nterna and externa fragmentaton of OVSF codes n WCDMA systems wth Mute Codes, IEEE Transacton on Wreess Communcaton, Vo.4, [9] H. Çam, Nonbockng OVSF Codes and enhancng network caacty for 3G wreess and beyond systems, Seca Issue of Comuter Communcatons on 3G Wreess and Beyond for Comuter Communcatons, Vo. 6, No.7, 003, [0] E. Dahman and K. Jama, Wde-band servces n a DS-CDMA based FLMTS system, n roceedngs of IEEE Vehcuar Technoogy Conference, No. 3, 996, [] Y.C. Tseng, C.M. Chao and S.L. Wu, Code acement and reacement strateges for wdeband CDMA OVSF code tree management, n roceedngs of IEEE GLOBECOM, Vo., 00, [] J.S. ark and D.C. Lee, Enhanced fxed and dynamc code assgnment oces for OVSF- CDMA systems, n roceedngs of IEEE ICWN, 003, [3] T. Mnn and K.Y. Su, Dynamc Assgnment of orthogona varabe sreadng factor codes n W-CDMA, IEEE Journa of Seected Areas n Communcaton, Vo. 8, No.8, 998, [4] V. Bayan and D. S. San, Vacant codes groung and fast OVSF code assgnment scheme for WCDMA networks, Srnger Journa of Teecommuncaton Systems, 0, DOI 0.007/s [5] V. Bayan and D. S. San, Integratng new cas and erformance mrovement n OVSF based CDMA Networks, Internatona Journa of Comuters & Communcaton, Vo.5, No.,,0, [6] W.T. Chen, H.C. Hsao and Y.. Wu, A nove code assgnment scheme for W-CDMA systems, n roceedngs of IEEE Vehcuar Technoogy Conference, 00, Vo., [7] J. S. ark, L. Huang, D. C. Lee, and C.C. Jay Kuo, Otma code assgnment and ca admsson contro for OVSF-CDMA systems constraned by bockng robabtes, n roceedngs of IEEE GLOBECOM, Vo.5, 004, [8] Y. Yang and T. S.. Yum, Mutcode mutrate comact assgnment of OVSF Codes for QoS dfferentated termnas, IEEE Transacton on Vehcuar Technoogy, Vo. 54, No. 6, 005, [9] B. J. Chang and. S. Chang, Mutcode-based WCDMA for reducng waste rate and reassgnments n mobe ceuar communcatons, Comuter Communcaton, Vo. 9, No., 006, [0] H. W. Ferng, H. L. C. Shung and D. Y. C. Tsung, An OVSF code tree artton ocy for WCDMA systems based on the Mut-Code aroach, n roceedngs of IEEE Vehcuar Technoogy Conference, 005, No., [] F. A.. Cruz, J. L. A. Vazquez, A. J. Segun and L. O Guerrero, Ca admsson and code aocaton strateges for WCDMA Systems wth mutrate traffc, IEEE Journa of Seected E-ISSN: Issue 4, Voume, Ar 0

12 Davnder S. San, Vn Bayan Areas n Communcatons, Vo.4, 006, [] Y. Yang and T. S.. Yum, Maxmay fexbe assgnment of orthogona varabe sreadng factor codes for mutrate traffc, IEEE Transacton on Wreess Communcaton, Vo. 3, No. 3, 004, [3] A.C. Kam, T. Mnn, and K.Y. Su, Suortng rate guarantee and far access for bursty data traffc n WCDMA, IEEE Journa of Seected Areas n Communcaton, Vo. 9, No., 00,. 30. [4] L. Xu, X. Shen, and J.W. Mark, Dynamc bandwdth aocaton wth far schedung for WCDMA systems, IEEE Transacton on Wreess Communcatons,Vo.9, No., 00, [5] D.S.San, Reducng wastage caacty n OVSF based CDMA networks usng dynamc rake combners, WSEAS Transacton on Communcaton, Vo. 0, No.6, 009, Davnder S San was born n Naagarh, Inda n January 976. He receved B.E degree n eectroncs and teecommuncaton engneerng from Coege of Engneerng Osmanabad, Inda n 998. He receved M.Tech degree n communcaton systems from Indan Insttute of Technoogy (IIT) Roorkee, Inda n 00. He receved hd degree n eectroncs and communcaton from Jayee Unversty of Informaton Technoogy Waknaghat, Inda n 008. He s wth Jayee Unversty of Informaton Technoogy Wakhnaghat snce une 00. Currenty, he s Assocate rofessor n eectroncs and communcaton deartment. Hs research areas ncude Channezaton (OVSF) codes and otmzaton n WCDMA, routng agorthms and securty ssues n MANETs. Vn Bayan receved B.E degree n Eectroncs & Communcaton wth honors Inda n 003 and M.Tech degree n Eectroncs & Networkng from LaTrobe Unversty, Bundoora, Mebourne, Austraa n 006. He has been wth RKGIT, Ghazabad affated to U..Technca Unversty, Lucknow, Uttar radesh, Inda as a Lecturer for years. He was assocated wth Jayee Unversty, Wakhnaghat, Inda as a Senor Lecturer. He s currenty workng as a Senor Lecturer n Jayee Insttute of Informaton Technoogy, Noda, Inda and ursung hs h.d on Effcent Snge Code Assgnment n OVSF based WCDMA Wreess Networks. E-ISSN: Issue 4, Voume, Ar 0