Performance Analysis of Sub-Rating for Handoff Calls in HCN

Transcription

1 I. J. Counication, Network and Syte Science, 29, 1, 1-89 Publihed Online February 29 in SciRe ( Perforance Analyi of Sub-Rating for Handoff Call in HCN Xiaolong WU 1, in HE 1, Fei WANG 2, Jun ZHENG 3, Ea REGENTOVA 4, Guohun HAO 5 1 Departent of CECS, 2 Departent of EE, California State Univerity, Long Beach, CA, USA 3 Departent of Coputer Science, New exico Intitute of ining and Technology, New exico, USA 4 Departent of Electrical and Coputer Engineering, Univerity of Nevada, La Vega, Nevada, USA 5 National Lab of Software Developent Environent, Beijing Univerity of Aeronautic and Atronautic, Beijing, China Eail:{xwu3, he, fwang3}@culb.edu Received October 3, 28; revied Deceber 28, 28; accepted Deceber 31, 28 Abtract Hierarchical Cellular Network (HCN) offer ore efficient channel utilization and better quality of ervice (QoS) under the high tele-traffic condition copared to the ingle-tier yte. One of the iportant eaure of QoS in HCN a in any ingle-tier yte i the handoff dropping rate. Although the exiting approache uch a guard channel and queuing can reduce forced terination probability, they alo reult in higher new call blocking probability. The channel ub-rating trategy ha found to be an effective technique to reduce the handoff force terination probability while preerving the new call blocking probability in a ingle-tier yte. In thi paper, we propoe a new call adiion control chee for HCN baed on the channel ub-rating. Analytic odel baed on 1-D arkov proce in icrocell and 2-D arkov proce in acrocell are developed. Experiental reult how that our chee achieve lower blocking and forced terination probabilitie copared to the traditional guard channel chee. The effect of channel ub-rating on the voice quality degradation i alo tudied. Reult deontrate that we can etablih a good balance between the forced terination probability and the voice quality degradation by varying the nuber of ub-ratable full-rate channel. Keyword: Sub-Rating, HCN, Handoff, Degradation Ratio 1. Introduction Cellular network ha experienced a rapid growth of the nuber of ubcriber during the pat decade, which place high deand on the yte capacity [1 4]. The cell ize can be reduced to accoodate ore obile uer in a given area and higher frequency re-ue [5]. However, chance of utual interference and cellboundary croing (handoff) in all-cell yte are high [6]. The encountered handoff can degrade one of the eential perforance characteritic of cellular network, i.e., forced terination probability probability of dropping an active call. Handoff call liit the call handling capacity of a cellular yte due to higher delay and liited bandwidth ource. One way of controlling the increae of traffic, while preerving the frequency reue advantage of all-cell yte i to conider hierarchical cellular network (HCN) [7 8]. In HCN, cell of different ize are organized into eparate layer to provide high coverage and capacity over a given ervice area. For exaple, in the two-layer (icro/ acro) hierarchical tructure [9], everal all cell called icrocell with a radii of a few hundred eter are organized a a icrocell layer which i overlaid by a large acrocell whoe radiu i a few kiloeter. In HCN, upon entering the yte, the obile terinal can elect the ervice layer baed on their obility or traffic pattern. For exaple, in the peedinenitive election echani [1], all new and handoff call are firt directed to the icrocell; if there i no channel available in the icrocell, call can be overflowed to the acrocell. On the contrary, in the peed-enitive trategy, the obile terinal traveling at high peed (fat-obility ubcriber) are norally erviced by the acrocell, wherea low-obility ubcriber are handled by the icrocell [4,9 12]. Under the peed-enitive layer election trategy, the overflow operation can be ued to tranfer call to the other layer if there i no ufficient reource in the current ervice layer [13 15]. For call adiion control (CAC) in HCN, handoff call handling i particularly iportant becaue generally the forced terination of an ongoing call i conidered Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

2 22 X. L. WU ET AL. le deirable than blocking of a new call. Thu, handoff call have higher priority than new call during the call adiion control proce. Several approache have been propoed for handling handoff call in HCN. Guard channel [3,9,16] are reerved for erving the handoff call in both icrocell and acrocell. Blocked handoff call [1] are queued before there i any free channel available to reduce the force terination probability. Lagrange and Goldewki [1] propoed that only handoff call can overflow fro the icrocell to the acrocell. Chung and Lee [11] propoed a obility-dependent call adiion control chee that new call are accepted according to oe obility-baed acceptance probability while handoff call are aditted when there are free channel available. Thee exiting chee can effectively reduce the handoff call forced terination probability, but at the cot of the increent of new call blocking probability. In [5], a new channel aignent chee called the ubrating i introduced to addre handoff call proble in the Peronal Cellular Syte (PCS). Sub-rating ean that an occupied full-rate channel can be teporarily divided into two channel at the half of the original rate: one to erve the exiting call and the other to erve the handoff requet. By uing the channel ub-rating, it i hown that the forced terination probability i greatly reduced with a light increae of the blocking probability of new call. The channel ub-rating chee wa ued in [17] to iprove the perforance of handoff packet for the cellular radio network. The propoed chee which cobine fixed channel aignent, ub-rating, and directed retry, give a ignificant iproveent in the QoS of the cellular radio network. In [18], Yaanaka and Shiohara applied channel ub-rating for handoff call in CDA cellular network. However, in all of the aforeentioned tudie, the channel ub-rating i only ued in a ingle-tier yte. Even oe preliinary reult about the utilization of ub-rating in HCN were reported in [19], thi paper give a coplete invetigation of the ub-rating trategy for handoff call in HCN. A general two-tier HCN yte odel i conidered in thi paper. Perforance odel are developed for the icrocell layer and acrocell layer repectively. Two iportant QoS erit, new call blocking probability and handoff call forced terination probability, are coputed to evaluate the propoed call adiion control chee. eanwhile, the degraded voice quality due to the half-rate channel i alo invetigated to tudy the effect of the ub-rating on the QoS. Furtherore, the partial ub-rating by decreaing the nuber of ub-ratable full-rate channel i taken into conideration to balance the forced terination probabilitie and the voice quality. The ret of the paper i organized a follow. The propoed CAC trategy with channel ub-rating and unidirectional call overflow i introduced in Section 2. In Section 3, the yte odel and perforance analyi of icro/acro layer are decribed with detail. Nuerical reult are preented in Section 4. Finally, concluding reark are given in Section Call Adiion Control With Sub-Rating The HCN yte upport both fat-obility uer and low-obility uer, e.g. pedetrian. We ue the peedenitive election trategy, i.e., the acrocell handle the fat-obility uer while the icrocell erve the low-obility uer. In the following, we decribe the propoed CAC chee with the channel ub-rating. Notice that oe other technique uch a queuing [5] are orthogonal to the propoed chee thu not invetigated here. The chee i illutrated in Figure 1. In each icrocell, low new or handoff call will be erviced with a full-rate channel if the total nuber of call currently being erviced doe not exceed the full capacity of the icrocell. Otherwie, handoff requet are handled by uing ub-rating that i an occupied full-rate channel but teporarily divided into two channel at a half of the original rate: one to erve the exiting call and the other to erve the new incoing low handoff requet. To reduce the blocking probability of low new call, blocked low new call are allowed to overflow to the overlaying acrocell. In a acrocell, fat new or handoff call and overflowed new low call will be erved with a full-rate channel if the nuber of call exiting doe not exceed the full capacity of the acrocell. Otherwie, new call, including fat new call and overflowed low new call will be blocked, while handoff call including fat handoff call and low handoff call incurred by the overflowed low new call are handled baed on the ub-rating, iilar to thoe at the icrocell layer. The overflow of the fat call fro acrocell to icrocell i not allowed becaue it will incur frequent handoff of the fat call in the icrocell layer due to all ize of a icrocell. Takeback i alo not ued a it need the yte to continuouly onitor the available reource in the icrocell layer [13]. 3. Syte odel and Perforance Analyi 3.1. Syte odel For the analyi purpoe, we introduce the yte odel of the two-tier HCN with the following auption. A acrocell in the acrocell layer i overlaid copletely by N icrocell in the icrocell layer and there i no acrocell-only or icrocell-only area. Cell in the ae layer have the ae hape and ize. Each icrocell contain C channel and each acrocell contain C channel. The fat-obility call are firt directed to a acrocell, while low-obility call are firt directed to a icrocell. The velocity of obile terinal i aued not to change greatly during it call lifetie. The total new call arrival to a cluter fored by a acrocell Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

3 PERFORANCE ANALYSIS OF SUB-RATING FOR HANDOFF CALLS IN HCN 23 and it aociated N icrocell follow a Poion proce with the ean arrival rate. The portion of low new call in total call arrival to a cluter i a. The low/fat handoff call arrival to a given cell at each layer i aued to be an independent Poion proce with the ean arrival rate / h fh, repectively. The overflowed low new call fro the icrocell layer arrive at the overlaying acrocell in accordance with a Poion proce with the ean rate ; and no the low handoff call reulting fro the overflowed low new call arrive at the acrocell in accordance with a Poion proce with the ean rate. h The call holding tie in a acrocell or icrocell i exponentially ditributed with the ean rate 1/ µ. The dwell tie i the obile reidence tie in a given cell. For a low obile, it dwell tie are exponentially ditributed with the ean rate 1/ γ and 1/ γ in the icrocell and acrocell repectively. The dwell tie of a fat obile in the acrocell i exponentially ditributed with the ean rate 1/ γ. Since the arrival proce of the overflowed call i generally not Poion ditributed, above auption are an approxiation ade for analytic tractability. Therefore, the low and fat new call arrival rate can be obtained a 1 n = an; fn = (1 a) n N f (1) Alo we can obtain the channel holding tie of low call in a icrocell (or acrocell) which i exponentially ditributed with the ean rate of 1/ µ = 1/ ( µ + γ ) or 1/ µ = 1/ ( µ + γ ). In the ae anner, we can find that the channel holding tie for fat call in a acrocell i alo exponentially ditributed with ean 1/ µ = 1/ ( µ + γ ) f f. Baed on the yte odel, we can perfor the perforance analyi of the propoed call adiion control trategy in the two-layer HCN. In the analyi, we aue that all full-rate channel are ub-ratable and the odel can be eaily odified for partial ub-rating. The analyi i carried out eparately for the icrocell and acrocell layer Perforance Analyi of the icrocell Layer Baed on the above yte odel, the icrocell layer in the two-layer HCN yte can be odeled a a onedienion arkov proce. The tate tranition diagra of the arkov proce i hown in Figure 2. In thi diagra, a tate i defined a the nuber of call in progre in a icrocell. For i C, ( i ) repreent that there are i full-rate buy channel being occupied in a icrocell. If there are le than C buy channel, the arrived low call (either a new call or a handoff call) i allocated one of thoe free channel. The arkov proce ove fro current tate ( i ) to the next tate ( i + 1) with the rate + n h. The tranition rate fro tate ( i + 1) to ( i ) i given by ( i + 1)µ. n + h n + h n + h h h h 1 C C+1 2C µ 2 µ C µ ( C + 1) µ ( C + 2) µ 2C µ Figure 2. State tranition diagra for the icrocell. For C < i 2C, ( i ) repreent that there are 2C i full-rate buy channel, and 2( i C ) halfrate buy channel. When all full-rate channel in the icrocell layer are buy, the arrived low new call will be blocked while the low handoff call will be erved by ub-rating a full-rate buy channel into two half-rate channel. If i = 2C, all channel are ub-rated, any arrived low hand-off call will be blocked. The arkov proce ove fro ( i ) to ( i + 1) with the rate. The tranition rate fro tate ( i + 1) to ( i ) i given by ( i + 1)µ. The teady tate probability π of tate i ( i ) in a icrocell i given a follow π i = n + h i! µ h i! µ i 1 i 1 π, i C π, C < i 2C 2C h (2) After the noralization condition that = π = 1, it yield π C 2C i C ( + ) ( + ) i C ( ) n h n h h = i +!( µ ) i i i!( µ ) i= i= C + 1 [ ] i 1 i (3) Fro Equation (2) and (3), the repective probabilitie of the new and handoff low call being blocked in a icrocell, P and P, are expreed a 2C i i= C+ 1 nb P nb = π ; P = π (4) hb hb 2C Figure 1. CAC chee with channel ub-rating and unidirectional call overflow. According to the CAC chee decribed in Section 2, the new low call that are blocked at the icrocell layer Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

4 24 X. L. WU ET AL. are not dropped but overflow to the overlaying acrocell (ee Figure 2). Baed on Equation (3), the aggregate ean arrival rate of the overflowed low new call no fro N icrocell to the overlaying arocell can be deterined a no nb n = NP (5) 3.3. Perforance Analyi of the acrocell Layer Baed on the above auption, the total call flow to an individual acrocell can be divided into the following four portion: 1) fat new call with the arrival rate of ; 2) fat handoff call with the arrival rate of ; 3) fn overflowed low new call with the arrival rate of ; 4) no handoff call reulting fro the overflowed low new call with the arrival rate of. The call tate proce in the arcocell layer can be odeled by a two-dienional arkov proce a hown in Figure 3. For each tate (i,j), i repreent the nuber of fat call including the fat new and handoff call, and j i the nuber of low call including the overflowed low new call and the incurred low handoff call in the acrocell layer. The axiu channel capacity of a acrocell i 2C, which ean i + j 2C. In the tate tranition diagra, h fn and fh fh caue the tate change along the horizontal direction while and no alter the tate change along the vertical direction. h Following the tate tranition diagra in Figure 3 and 4, the equilibriu equation can be derived a follow ( ) π, = µ π 1, + µ π,1 fn fh no h f (6) ( δ A fn + fh + no + h + iµ f ) π i, = ( i + 1) µ f π i+ 1, π + µ π +( δ + ) π, < i < 2C i,1 B fn fh i 1, fh 2C 1, = 2 f 2 C, (7) C µ π (8) ( + + δ + + jµ ) π, = µ π1, fn fh C no h j f j + ( j + 1) µ π +( δ + ) π, < j < 2C π, j+ 1 D no h, j 1 = h,2c 1 2,2C (9) C µ π (1) ( + iµ jµ ) π, = fn fh no h f i j ( i + 1) µ π + ( j + 1) µ π +( + ) π f i+ 1, j i, j+ 1 no h i, j 1 + ( + ) π, < i + j < C fn fh i 1, j ( iµ jµ ) π, = fh h f i j ( i + 1) µ π + ( j + 1) µ π +( + ) π f i+ 1, j i, j+ 1 no h i, j 1 + ( + ) µ π, i + j = C fn fh i 1, j (11) (12) Figure 3. State tranition diagra for a acrocell. Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

5 PERFORANCE ANALYSIS OF SUB-RATING FOR HANDOFF CALLS IN HCN 25 Figure 4. Specific tate in the tate tranition diagra. ( + + iµ + jµ ) π, = ( i + 1) µ π + 1, fh h f i j f i j + ( j + 1) µ π + π + π, C < i + j < 2C i, j+ 1 h i, j 1 fh i 1, j (13) where δ A = 1 for <i<c, δ B = 1 for <i C, δ C = 1 for < j<c, and δ D = 1for <j C. We ue the Gau-Seidel iterative ethod to olve the above linear equation and copute the teady-tate probabilitie π i, j. The probabilitie of fat new call and overflowed low new call blocked in the acrocell layer, P and P, are then expreed a fnb no P = P = π (14) fnb no i, j C i+ j 2C The blocking probabilitie of the fat handoff call and the overflowed low handoff call, P and P, are expreed a P fhb = P ho = i, j i+ j= 2C fhb ho π (15) Fro (14) and (15), the total new and handoff low call blocking probabilitie including icrocell and acrocell, Pnb and P hb can be obtained repectively a P = P P ; P = P + P (1 P ) P (16) nb nb no hb hb nb no ho The arrival rate of low and fat handoff call can be obtained a in [5] uing following three expreion. γ (1 ) = Pnb h µ + γ Phb ; n γ (1 ) = Pno h µ + γ P no ho ; γ (1 ) = f Pfnb fh µ + f Pfhb fn (17) Since the handoff rate and the tead tate probabilitie are utually related, an iterative algorith i eployed here to copute the The Degradation Ratio The ub-rating chee i efficient under the liited channel reource becaue ore handoff call can be erved. However, we need to conider the degradation of the voice quality due to the eployent of ub-rating. In the following, the degradation ratio of voice quality for the icrocell and icrocell layer are evaluated. The expected nuber E[ H ] of the buy channel buy in the icrocell layer i expreed a 2C = E[ H ] i π (18) buy i= i The expected nuber E[ H ub ] of the ub-rated channel in the icrocell layer i obtained a follow 2C = ub i i= C + 1 E[ H ] 2( i C )π (19) The degradation ratio of the voice quality in the icrocell layer, DR, i the portion of the call holding tie that the obile uer experience the degraded voice Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

6 26 X. L. WU ET AL. quality [2]. The ean degradation ratio of the voice quality, E[DR ], can be expreed a 2C H buy 2( i C ) H i i ub i= C + 1 E [ DR ] = E [ ] = π (2) Siilarly the ean degradation ratio of the voice quality in the acrocell layer, E[DR ], can be obtained a P nb C 2( i + j C ) ( i+ j) i, j ( i+ j) = C + 1 [ ] = E DR π (21) 4. Nuerical Reult In thi ection, nuerical reult derived fro the odel developed in Section 3 are preented to quantify the perforance of the propoed chee. The reult are copared to the chee with guard channel and unidirectional call overflow propoed in [9], referred a Shan3 in the plot. If otherwie not pecified, the paraeter and their value ued for the experient are thoe hown in Table 1 [11,21], where C g and C G are the nuber of guard channel reerved in the icrocell and acrocell for Shan3 chee. Table 1. Paraeter and their value. Paraeter Value Paraeter Value 1 / µ 11 N 4 1/ γ 15 C g 1 1/ γ 3 C G 1 1/ γ 6 C 5 f a.8 C Cae 1: Full Sub-Rating In thi part, we preent the experiental reult generated fro the odel developed in Section 3 where all the full-rate channel are conidered to be ub-ratable. Figure 5 plot the low/fat new call blocking probabilitie and low/fat handoff call forced terination probabilitie under variou total new call arrival rate for the propoed chee and Shan3 Schee. For Shan3 chee, we invetigate the perforance with different guard channel nuber. It can be een fro Figure 5(b) & (d) that the low/fat handoff call forced terination probabilitie of the propoed chee are alot zero and alo uch lower than thoe of Shan3, even in the cae that two guard channel are reerved for handoff call. Figure 5(a) & (c) reveal that when the nuber of guard channel i et to one, the new fat call blocking probability of Shan3 are alot the ae a that of the propoed chee while the new low call blocking probability of Shan3 i lightly higher than that of the propoed chee when the nuber of guard channel i et to two. The reaon i that the propoed chee allow the icro-acro overflow of the new low call when P hb P fnb P fhb (a) (b) Propoed Shan3(C g = C G = 1) Shan3(C g = C G = 2) (c) (d) Figure 5. Perforance coparion of the propoed chee with the Shan3 chee, P nb, (b) P hb, (c) P fnb, (d) P fhb. Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

7 PERFORANCE ANALYSIS OF SUB-RATING FOR HANDOFF CALLS IN HCN 27 Degradation Ratio icrocell layer acrocell layer Figure 6. The degradation ratio of the icrocell and acrocell layer. there i no free channel in the icrocell. For Shan3 chee, although reerving ore guard channel can greatly reduce the handoff call forced terination probability, the new call blocking probability alo increae ignificantly. The reult deontrate that the propoed chee achieve better perforance for both new and handoff call than Shan3 chee in all cae. By eploying channel ub-rating trategy, the propoed CAC chee can aively reduce the probability of forced terination of handoff call while aintaining the new call blocking probability a low a poible. Under the channel ub-rating trategy, when call are in progre, the obile uer i expected to experience the degraded voice quality due to the half-rate channel. Figure 6 plot the correponding degradation ratio of the voice quality in the icrocell and acrocell layer of Figure 5. Reult indicate that the low and fat obility ubcriber experience the degraded voice quality for a very hort period of the total channel holding tie when the total new call arrival rate i.1 call/econd. A the total new call arrival rate increae, the degradation ratio increae correpondingly. When the total new call arrival rate reache.8 call/econd, the degradation ratio for the icrocell and acrocell are about 1% and 8%, repectively. To reduce the degradation ratio, we can decreae the nuber of full-rate channel that can be ub-rated which in turn increae the handoff call forced terination probability. Next we will invetigate partial ub-rating to balance the forced terination probabilitie and the voice quality Cae 2: Partial Sub-Rating In thi part, we preent the experiental reult when only partial full-rate channel can be ub-rated. The nuber of ub-ratable full-rate channel i denoted a C /C for the icrocell/acrocell. Figure 7 plot the low and fat handoff call forced terination probabilitie and degradation ratio for the icrocell and acrocell layer under variou C and C. The total new call arrival rate i et to.5 call/econd. It can be een that the handoff call forced terination probability drop rapidly a the nuber of ub-ratable full-rate channel increae. On the other hand, the degradation ratio for the icrocell and acrocell layer becoe higher with the increent of the nuber of ub-ratable full-rate channel. Therefore to eet the QoS requireent of the yte on the handoff call forced terination probability and degradation ratio of the voice quality, the nuber of ub-ratable full-rate channel ut be carefully choen to achieve the bet tradeoff. In Figure 8, we copare the perforance of propoed chee under partial ub-rating with that of Shan3 chee for variou total new call arrival rate, where C, C, C g and C G are both et to 1. The reult deontrate that the propoed chee outperfor the guard channelbaed Shan3 chee. Even in thi cae, only one fullrate channel i allowed to be ub-ratable. 5. Concluion A call adiion control chee for HCN ha been propoed in thi paper which incorporate the channel ub-rating and one-way call overflow. By ub-rating the occupied channel to create new half-rate channel for the handoff call, the forced terination of handoff call are expected to be greatly reduced. eanwhile, the icro-to-acro overflow wa introduced to reduce the blocking probability of low new call. We developed analytic odel to evaluate the perforance of the propoed chee. Experiental reult have hown that the propoed chee baed on channel ub-rating achieve better perforance for both new and handoff call copared to the chee baed on guard channel. P hb E[DR ] C 2 C 2 (a) (c) 5 C 5 C 1 1 P fhb C C 5 C Figure 7. Perforance etric of the propoed chee under variou C and C, (a) P hb, (b) P fhb, (c) E[DR ], (d) E[DR ]. E[DR ] C (b) (d) 1 1 Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

8 28 X. L. WU ET AL. P nb P hb P fnb P fhb Propoed Shan (a) (a) (b) (c) P (d) (d) Figure 8. Perforance coparion of the propoed chee under partial ub-rating with Shan3 chee for variou, C =C =C g =C G =1, (a) P nb, (b) P hb, (c) P fnb, (d) P fhb. The penalty of the ub-rating i the degradation of voice quality during the tie when the channel are ub-rated to accoodate the handoff call. Our reult indicated that there i a tradeoff between handoff call forced terination probability and degradation ratio of the voice quality when the channel ub-rating i eployed. By aigning the appropriate nuber of the ub-ratable full-rate channel, we can achieve good balance between the handoff call forced terination and the voice quality degradation. 6. Reference [1] D. Hong and S. S. Rappaport, Traffic odel and perforance analyi for cellular obile radio telephone yte with prioritized and no-protection handoff procedure, IEEE Tranaction on Vehicular Technology, Vol. 35, pp , [2] Y. S. Hwang, Y. N. Han, and Y. H. Ki, Perforance analyi of ixed voice/data ervice in a acrocell-baed PCS network, IEICE Tranaction on Fundaental, Vol. E81-A, pp , [3] X. Liu and A. O. Fapojuwo, Perforance analyi of hierarchical cellular network with queuing and uer retrial, International Journal of Counication Syte, Vol. 19, pp , 26. [4] S. S. Tang and W. Li, odeling and analyi of hierarchical cellular network with bidirectional overflow and take-back trategie under generally ditributed cell reidence tie, Telecounication Syte, Vol. 32, pp , 26. [5] Y. B. Lin and A. R. Noerpel, The ub-rating channel aignent trategy for PCS hand-off, IEEE Tranaction on Vehicular Technology, Vol. 45, pp , [6] K. ahehwari and A. Kuar, Perforance analyi of icrocellization for upporting two obility clae in cellular wirele network, IEEE Tranaction on Vehicular Technology, Vol. 49, pp , 2. [7] C. Hartannn and O. Schelegelilch, Hierarchical cell tructure with adaptive radio reource anageent, in Proceeding IEEE Vehicular Technology Conference, pp , 2. [8] X. Yang and. Guizani, Optial paging load balance with total delay contraint in acrocell-icrocell hierarchical cellular network, Vol. 5, No. 8, pp , 26. [9] W. H. Shan and P. Z. Fan, Perforance evaluation of a hierarchical cellular yte with obile velocity-baed bidirectional call-overflow chee, IEEE Tranaction on Parallel and Ditributed Syte, Vol. 14, pp , 23. [1] X. Lagrange and P. Godlewki, Teletraffic analyi of a hierarchical cellular network, in Proceeding IEEE Vehicular Technology Conference, pp , [11] S. Chung and J. Lee, obility-dependent call adiion control in hierarchical cellular network, Coputer Counication, Vol. 25, pp , 2. Copyright 29 SciRe. I. J. Counication, Network and Syte Science, 29, 1, 1-89

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