Performance Analysis of Bandwidth Allocations for Multi-Services Mobile Wireless Cellular Networks *

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1 erformance Analysis of Banwith Allocations for Multi-Serices Mobile Wireless Cellular Networs * Lizhong Li Bin Li Bo Li Xi-Ren Cao Department of Computer Science Department of Electrical an Electronic Engineering Hong Kong Uniersity of Science an Technology, Hong Kong, China Abstract One of the ey challenges in the esign of banwith allocation policies for a multi-serices mobile cellular networ is to guarantee the potentially ifferent Quality of Serice (QoS) requirement from ierse applications, while at the same to ensure that the scarce banwith be utilize efficiently. Complete Sharing (CS) an Dynamic artition (D) schemes hae been shown as iable techniques for managing the banwith. Howeer, there has been no stuy that compares their respectie performance, which is the focus of this paper. Specifically, in this paper, through both analysis an simulation, we emonstrate that both schemes can achiee comparable performance by proper manipulation of control parameters. The traeoff is that D scheme can more easily achiee the target QoS requirement, at the expense of oer-proisioning, thus can potentially lea to less channel efficiency when comparing to a CS base scheme. Inex Terms Banwith allocation, guare channel policy, hanoff, an mobile cellular networs I. INTRODUCTION We hae recently witnesse phenomenal growth in the eelopment an eployment of wireless serices, eient from the proliferation of cellular ata serices an the emerging wireless multimeia applications. This opens up a new research aenue an calls for the re-examination of some of the funamental issues in wireless cellular networs. Various issues such as QoS guarantee hae to be carefully examine. One of the ey elements in proiing QoS guarantee is an effectie banwith allocation policy, which not only has to ensure that the system guarantee potentially ifferent QoS requirements an proie the necessary serice ifferentiation from ierse applications, but at the same time has to fully utilize the scarce wireless banwith aailable in the wireless cellular networs. Moing from a oice-centric macro-cell wireless networ to a multi-serices micro-cell or/an pico-cell wireless networ brings seeral new challenges: ) the characteristics of ata an multimeia applications are typically ifferent from that of oice, e.g., ata traffic usually consumes more banwiths than that of oice, but can be aaptie, thus has less stringent serice requirement; ) The limite wireless resources hae to be utilize effectiely, an fairly allocate to ifferent types of traffic with potentially ifferent serice requirements an serice ifferentiation; ) smaller cell potentially results in more hanoffs, maing it more ifficult to proie the necessary QoS guarantee. Banwith allocation has been extensiely stuie in singleserice wireless cellular networs. The Guare Channel (GC) schemes hae been shown to be effectie for proiing the necessary QoS guarantee in terms of both call termination an call blocing probabilities [-4]. One of the challenges in moing to a multi-serice system is that the limite banwith has to be share among multiple traffics. In [5] a Complete Sharing (CS) an Complete artition (C) schemes were inestigate for two types of traffic, namely narrow-ban an wieban. It assume that wieban traffic oes not hae hanoff. Huang et al propose a moable bounary allocation scheme for oice an ata traffic [6], in which banwith is iie into two sub-pools by two threshols that can be ynamically auste. This facilitates the banwith proisioning for ifferent QoS requirements an is aaptie to the changing traffic. The limitations are that both oice an ata require the same banwith, an there is no serice ifferentiation between oice new calls an hanoff. To the best of our nowlege, there has been no comparatie stuy that inestigates the performance of ifferent banwith allocation schemes for multi-serice wireless cellular networs. This is the focus of this paper. Specifically, we are intereste in obtaining the quantitatie performance measures for ifferent banwith allocation schemes. Although our analysis in this paper focuses on two traffic types, but the eriation an conclusions also proie insight for arbitrary number of traffic types. A ariety of banwith allocation schemes hae been propose to support multiple traffics, which can be classifie as Complete artitioning (C), Complete Sharing (CS) or hybri schemes, epening on how the banwith are allocate among ierse traffic. In this paper, we first exten * The research was supporte in part by grants from Hong Kong Research Gants Council (RGC) uner contracts HKUST 66/00E, N-HKUST 605/0 an HKUST 696/0E /0/$7.00 (C) 00 IEEE 07

2 H a n o ff o i c e H a n o ff o i c e N e w o i c e M i x e a t a S h a r e c h a n n e l s K K K Total channel number: C N e w o i c e M i x e a t a K K Total channel number: C c a l l s F i g. ( a ) : D c o n t r o l s c h e m e F i g. ( b ) : D T B R c o n t r o l s c h e m e the moable bounary scheme [6] to consier ifferent banwith consumption by the two traffic types, referre as Dynamic artition (D). We compare this with a CS scheme we propose in [7], calle Dual Threshol Banwith Reseration (DTBR). We compare their respectie performance using both analysis an simulation. The stuy reeals a number of interesting obserations an proies insight in searching more suitable banwith allocation schemes. The rest of the paper is organize as follow. We escribe the D an DTBR schemes in Section. We present the analytical moels in Section, following by the numerical stuies in Section 4. We conclue the paper in Section 5 with iscussions on possible aenue for further stuy. II. BANDWIDTH ALLOCATION STRATEGIES We assume that each cell hae a total of C channels. The banwith requirements for oice calls an ata calls are fixe as an B units, respectiely. A. Dynamic artition (D) Scheme In [6], Haung et al propose a oice an ata integrate system with finite buffers, in which banwiths assigne to oice an ata are separate (i.e., complete partition). The unique feature of this scheme is that the bounary for the partition is moable, thus can effectiely eal with the traffic changes in the system. In this scheme, howeer, hanoff calls were not ifferentiate form new calls, thus the strict requirement of hanoff ropping probability cannot be met. Furthermore it was assume that the ata requires one unit of banwith. We exten the moable bounary scheme to ifferentiate hanoff calls an further tae into account the ifferent banwith requirement. In the new scheme, calle Dynamic artition (D) scheme (see Fig. (a)), among C channels, K channels (oice only area) are resere exclusiely for new/hanoff oice calls an K channels (ata only area) are resere exclusiely for new/hanoff ata calls. The other C K K channels (share area) are fairly share by both oice an ata calls. In orer to maintain a low hanoff ropping probability for oice calls, we further restrict that new oice calls can only use the K out of K oice channels (i.e., Guare Channel policy). But hanoff oice calls can use all the K channels, the hanoff oice will be roppe only if there is no channel aailable in both the oice only area an the share area. New oice call will be reecte if the number of channel occupancy excees the threshol K in the oice only area an there is no ile channel in the share area. Data call (new or hanoff) will be accepte only if there are at least B ile channels in the ata only area or in the share area. B. Dual-Threshol Banwith Reseration (DTBR) The rationale for aopting a CS approach in the propose Dual-Threshol Banwith Reseration (DTBR) scheme [7] (see Fig. (b)) is that it can achiee the maximum channel efficiency, while at the same time still being able to proie serice guarantee an ifferentiation from ierse traffic. In the DTBR scheme, C channels of each cell are iie into three regions by two threshols K an K. When the number of channels occupie is less than the threshol K, then both ata an oice traffic can be amitte into the system; when the number of channels occupie is oer the threshol K, no ata traffic is allowe; when the number of channels occupie is more than the threshol K, then only hanoff oice calls can be allowe. The hanoff oice call will be roppe only if there is no channel aailable. Uner this basic control moel, the hanoff oice gets highest priority, while ata receies lowest serice. The reason is that the ata traffic can tolerate certain egree of serice egraation, while oice cannot. There can be a number of ariations using this basic moel, for example, whether or not to use a queue to further buffer the hanoff request when the requeste channels are not aailable [7]. This has been shown to reuce the hanoff ropping probability [, ]. In this stuy, for simplicity an for fair comparison with the D scheme, we only consier the DTBR scheme without queuing. III. ERFORMANCE ANALYSIS We consier a homogeneous wireless networ where all cells hae the same number of channels an experience the same new an hanoff call arrial rates. In each cell, the arrials of new oice calls, new ata calls, hanoff oice calls 07

3 an hanoff ata calls are oisson istribute with arrial rate λ n, λ n, λh an λh respectiely. Thus the total oice call arrial rate an ata call arrial rate are λ = λn λh an λ = λn λh respectiely. Since ata can usually tolerate some egree of serice egraation, new ata calls an hanoff ata calls are not istinguishe. Call uration times or call holing times of oice an ata are exponentially istribute with the aerage call uration time / µ r an / µ r. In aition, the hanoff oice an the hanoff ata are exponentially istribute with mean µ h an µ h respectiely. This set of assumptions hae been foun reasonable as long as the number mobiles is much larger than the number of channels in a cell, an hae been wiely use in literature [- 7]. The exponential call holing time has also been shown to be ali for a wie range of systems [8-0]. For simplifying notations, we assume K is a multiple of B. A. Dynamic artition Scheme Scheme D can be moele as a three-imensional Maro chain. It is ergoic [6] if ρ < ( C K ) / B. Let i be the steay probability that there are i new oice calls, hanoff oice calls an ata calls in the system. Let x enote the greatest integer less than or equal to x. The steay-state balance equations of D scheme are shown as below. Case : if i = = = 0, then ( λ () λ ) 000 = µ 00 µ 00 Bµ Case : if 0 i K an 0 < ( C K) K i < C K an 0 < < ( C i ) λ λ λ µ = ( n <, then h ( i ) µ n i, h i,, µ i, ) 00 i, ( ) i,, ( ) i Bµ Case : if 0 i < K an = ( C K) λ λ µ = ( n h ( i ) µ i,, or <, then n i, h i,, ) i, ( ) i µ i,, i, Case 4: If K i K an ( C K ) < = ( λ µ ) = h ( ) µ i i,, λn, λh,, Case 5: if i = K an ( C K ) = K i < C K an = ( C i ) λ, or <, or i = C K an K / B, then i,, then = ( i µ ) = λn, λh,, λ, µ (5) Case 6: if i = C K an K / B, then < () () (4) ( λ µ ) ( ) Bµ i = i, λn i, λh i,, λ i, B. Complete Sharing Scheme DTBR Scheme DTBR can be moele as a two-imensional Maro chain. It is ergoic [6] if ρ < K / B. Let i be the steay probability that there are i oice calls an ata calls in the system. The steay-state balance equations of DTBR scheme are shown as below. If K / B, then 0 i B > C λh, if i B = C iµ ( i ) µ, λh, ( ) Bµ, λh if K < i B < C ( i ) µ, λ, ( ) Bµ, λh if i B = K ( i ) µ, λ, ( ) Bµ, = λ if K < i B < K ( i ) µ, λ, ( ) Bµ, λ, λ if i B = K ( i ) µ, λ, ( ) Bµ, λ, λ λ if 0 < i B < K ( i ) µ,0 Bµ, if i = 0 an = 0 λ λ 0 if i < 0 or < 0 (7) If = K / B, then i 0 λh, iµ ( i ) µ, λh λh ( i ) µ, λ = λh ( i ) µ, λ λ ( i ) µ, λ, λ 0,,, if K K K K (6) if i > C K < i < C K if i = K if 0 < i < K if i = C K if i = 0 if i < 0 (8) 074

4 Both moels can be sole by a recursie technique eelope by Herzog [], which is base on the typical feature of Champan-Kolmogoroff equations that there exist a subset of the state probabilities, calle them bounaries, an all states can be expresse as a function of bounary states. The basic iea of this technique is to choose the bounaries first an to erie the expressions for all remaining state probabilities as functions of the bounary alues, an then sole a reuce system of equations for these bounaries. After that, etermine all state probabilities by means of the bounaries. This has been shown to be suitable for soling a wie class of queuing problems. Due to the length limitation, we omit the etails of the analytical eriations, an leae it to the full length paper []. IV. NUMERICAL RESULTS AND REMARKS In this section, we present numerical results an compare the aboe two schemes. In orer to aliate the accuracy of the analysis, we also eelop an eent-rien simulation. The system performance parameters consiere in this paper are hanoff oice ropping probability, oice call blocing probability, ata call blocing probability an oerall channel utilization. We consier the following system configuration. The total channel number C of each cell is set to be 0 an the banwith requirement of ata calls B is set to be. The ata call intensity ρ is set to be 7, with the aerage arrial rate of λ = 0.007S an the aerage serice rate of µ = 0.00S. This is reasonable for typical Internet type of traffic []. For oice call, the aerage serice rate is assume to be µ = 0.008S, while the oice call intensity can ary from 6 to 6. To alleiate the transient effect, the simulation was run for a long uration in orer to reach the steay state, an the system performance measures were obtaine by aeraging oer the results of 0 inepenent rouns of simulations. Hanoff oice call ropping probability is a ey QoS measures in wireless cellular networs, so in this paper, we set the target of the hanoff oice call ropping probability to be 0 [4], an stuy the system performance uner a wie range of call intensity. For D allocation scheme, among all the sets of threshols ( K, K, K ) that can guarantee target hanoff oice call ropping probability ( 0 ) at ρ = 6, only the one with the highest channel utilization is chosen as representatie here (see [] for etail) to compare with DTBR scheme with ifferent ( K, K ) alues. In the etermination of ( K, K ) alue for DTBR scheme, we first set the alue for K, then change the alue of K from high to low, till the hanoff oice call ropping probability equals to 0 at ρ = 6. Figs. to 5 epict the system performance when λh = 0. λ. Fig. emonstrates that, compare with DTBR scheme, D scheme usually proies much lower hanoff oice call ropping probability when ρ is low. This is because in complete partition D scheme, those oice only channels neee to maintain target hanoff oice call ropping probability at ρ = 6 cannot be share by ata calls, thus results in an oer-proisioning of the banwith when ρ is low. On the contrary, in DTBR scheme, no channels are eicate to oice calls. Except those ( C K ) channels neee to eep target hanoff oice call ropping probability at ρ = 6, all other channels can be share statistically by oice calls an ata calls. Thus when oice call intensity becomes low, because there still exist impacts from ata calls, hanoff oice call ropping probability cannot ecrease rapily. Fig. shows that, among all the cases of DTBR scheme (here for clarity we only present three cases) an D scheme, DTBR with one threshol K = K = 7 has the highest channel utilization. The reason is that, in this case, no priority is gien to new oice calls. Except a small amount of channels ( C K = in this case) are resere for hanoff oice calls to eep target QoS, all other aailable channels can be share by oice calls an ata calls equally. Thus leas to much higher channel utilization. This can further explain that DTBR with K = K = 7 can achiee the lowest ata call blocing probability as obsere from Fig. 4. The high channel utilization an low ata call blocing probability for DTBR with one threshol K = K = 7 is obtaine at the expense of higher new oice call blocing probability, as inicate in Fig. 5. This is because in this case, no priority is gien to new oice calls. New oice calls hae to conten with hanoff oice calls an ata calls to get access. When we increase λh to 0.4λ (i.e., higher user mobility), similar results can be obtaine. These are illustrate in Figs. 6 to 9. Noticeably the main ifference is the selection of the control threshols in both schemes. From the aboe results, in orer to maintain the target hanoff oice call ropping probability, we can raw the following conclusions: () D scheme has the lowest oice hanoff ropping probability an relatie lower ata call blocing probability, while at the same time eeping relatie higher channel utilization. () DTBR scheme with one threshol (i.e., there is no channel resere for new oice call) can achiee the highest channel utilization an the lowest ata call ropping probability. () If more stringent hanoff oice call ropping probability an oice call blocing probabilities are require, DTBR schemes with two threshols yiel the best performance. This is achiee at the expense of lower channel utilization an potentially higher ata call blocing probability. Ⅴ. CONCLUSIONS In this paper, we stuy an compare the performance of two banwith allocation schemes for multi-serice cellular 075

5 networ, namely Dynamic artition (D) an Dual-Threshol Banwith Reseration (DTBR) schemes. From the results obtaine from both analysis an simulation, we can conclue that, by eeping the stringent hanoff oice call ropping probability uner gien traffic loas: () D scheme always has the lowest hanoff oice call ropping probability; () DTBR scheme with one threshol can achiee the highest channel utilization an the lowest ata call blocing probability; () DTBR scheme with two threshols can achiee the lower new oice call blocing probability. There are a number of issues that will be aresse in our future research: ) the banwith allocation schemes iscusse in this paper are static. Howeer as shown in [4,4], ynamic schemes can always achiee better performance; ) the hanoff rates for both oice an ata following conention hae been assume gien, as there lacs aequate moel that can erie hanoff rates base on other parameters such as new call arrial rates an mobility, similar to those in [0]. We are currently woring on the ynamic control policy base on the D scheme, an the online parameters estimation algorithm propose in [5] seems to be a iable technique. Finally, we will be consiering more realistic ata arrial using TC traffic, an exploring the self-similar behaior of the ata arrial obsere in []. REFERENCES [] R. Guerin, Queuing-blocing systems with two arrial streams an guare channels, IEEE Transactions on Communications. Vol. 6, No., February 988. [] R. Ramee, R. Nagaraan an D. Towsley, On optimal call amission control in cellular networs, IEEE Infocom 96, San Francisco, March 996. [] B. Li, C. Lin an S. Chanson, Analysis of a hybri cutoff priority scheme for multiple classes of traffic in multimeia wireless networs, ACM/Baltzer Journal of Wireless Networs, Vol. 4, No. 4, August 998. [4] S. Wu, K. Y. M. Wong an B. Li, A ynamic call amission policy with precision QoS guarantee using stochastic control for mobile wireless networs, IEEE/ACM Transactions on Networing, Vol. 0, No., April 00. [5] B. Epstein an M. Schwartz, Reseration strategies for multimeia traffic in a wireless enironment, IEEE VTC 95. [6] Y.-R. Haung, Y.-B. Lin an J. M. Ho, erformance analysis for oice/ata integration on a finite mobile systems, IEEE Transactions on Vehicular Technology, Vol. 49, No., February 000 [7] H.-L. Wu, L.-Z. Li, B. Li, L. Yin, I. Chlamtac an B. Li, On hanoff performance for an oice/ata integrate cellular system, part II: ata buffer case, IEEE IMRC 00, Lisbon, ortugal, Sept 00. [8] Y. Fang an I. Chlamtac, Teletraffic analysis an mobility moeling of CS networs, IEEE Journal on Selecte Areas in Communications, Vol. 7, No. 7, July 999. [9] Y. Fang, Y.-B. Lin an I. Chlamtac, Channel occupancy times an hanoff rate for mobile computing an CS networs, IEEE Transactions on Computer, Vol. 47, No. 6, June 998. [0] Y.-B. Lin, erformance moeling for mobile telephone networs, IEEE Networs, No/Dec 997. [] Herzog, L. Woo, K.Chany, Solution of queuing problems by a recursie technique, IBM Journal of Research Deelopment, May 975. [] B. Li, L.-Z. Li, B. Li an X.-R. Cao, On hanoff performance for an integrate oice/ata cellular system, to appear in ACM/Kluwer Journal of Wireless Networs,00. [] M. Cheng an L.-F. Chang, Wireless ynamic channel assignment performance uner pacet ata traffic, IEEE Journal on Selecte Areas in Communications, Vol. 7, No. 7, July 999. [4] X. Luo, B. Li, I. Thng, Y.-B. Lin an I. Chlamtac, A measurement-base pre-assignment scheme with connection-leel QoS support for multiserice mobile networs, IEEE Transactions on Wireless Communications, Vol., No., Mach 00 [5] B. Li, L. Yin, K. Y. Michael Wong an S. Wu, An efficient an aaptie banwith allocation scheme for mobile wireless networs base on online local parameter estimations, ACM/Kluwer Journal of Wireless Networs, Vol. 7, No., March/April 00 [6] L. Kleinroc, Queueing systems, Vol.: Theory. NewYor: Wiley, 975 Hanoff oice call ropping probability.e-0.e-04.e-05.e-06.e-07 D: K=5 K=0 K= DTBR: K=9 K=9 DTBR: K=8 K= DTBR: K=K= Figure. Hanoff oice call ropping probability of D an DTBR schemes when λ = 0. λ. Channel utilization h D: K=5 K=0 K= DTBR: K=9 K=9 DTBR: K=8 K= DTBR: K=K= Figure. Channel utilization of D an DTBR schemes when λ = 0.. h λ 076

6 Data call blocing probability D: K=5 K=0 K= DTBR: K=9 K=9 DTBR: K=8 K= DTBR: K=K= Figure 4. Data call blocing probability of D an DTBR schemes when λ = 0.. h λ Channel utilization D: K=5 K=0 K=8 DTBR: K=9 K=7 DTBR: K=8 K=0 DTBR: K=K= Figure 7. Channel utilization of D an DTBR schemes when λ = h λ New oice call blocing probability.e00.e-0.e-0.e-0.e-04.e-05 D: K=5 K=0 K= DTBR: K=9 K=9 DTBR: K=8 K= DTBR: K=K= Figure 5. Voice call blocing probability of D an DTBR schemes when λ = 0.. h λ Data call blocing probability D: K=5 K=0 K=8 DTBR: K=9 K=7 DTBR: K=8 K=0 DTBR: K=K= Figure 8. Data call blocing probability of D an DTBR schemes when λ = h λ Hanoff oice call ropping probability.e-0.e-04.e-05.e-06.e-07 D: K=5 K=0 K=8 DTBR: K=9 K=7 DTBR: K=8 K=0 DTBR: K=K= Figure 6. Hanoff oice call ropping probability of D an DTBR schemes when λ = 0. 4λ. h New oice call blocing probability.e00.e-0.e-0.e-0.e-04.e-05 D: K=5 K=0 K=8 DTBR: K=9 K=7 DTBR: K=8 K=0 DTBR: K=K= Figure 9. Voice call blocing probability of D an DTBR schemes when λ = h λ 077