A SELF-ADAPTIVE BANDWIDTH RESERVATION SCHEME FOR 4G MOBILE. WIMAX . Chenn-Jung Huang*, Yi-Ta Chuang**, Chih-Tai Guan*, Dian-Xiu Yang* ...
A SELF-ADAPTIVE BANDWIDTH RESERVATION SCHEME FOR 4G MOBILE WIMAX . Chenn-Jung Huang*, Yi-Ta Chuang**, Chih-Tai Guan*, Dian-Xiu Yang* & You-Jia Chen* . * Department of Computer & Information Science College of Science National Hualien University of Education, Hualien, Taiwan ** Institute of Computer Science and Engineering National Chiao Tung University, Hsinchu, Taiwan . ABSTRACT
. Many mechanisms based on bandwidth reservation have been proposed in the literature to decrease connection dropping probability for handoffs in cellular communications. The handoff events occur at a much higher rate in packet-switched 4G mobile WiMAX networks than in traditional cellular systems. In this paper, a self-adaptive bandwidth reservation schemes, which adopts a probabilistic mobility prediction model to estimate the bandwidth required in neighboring cells, is proposed to reduce the forced termination probability of multimedia handoffs in 4G mobile WiMAX networks. Via cross-layer design, it exploits 4G mobile WiMAX advantages by using the bandwidth reservation. The simulation results show that the proposed scheme can achieve superior performance than the representative bandwidth-reserving schemes in the literature when performance metrics are measured in terms of the forced termination probability for the handoffs, the call blocking probability for the new connections and bandwidth utilization.
. 1. INTRODUCTION
. With the increasing demand for the provision of multimedia applications, such as Voice over IP (VoIP), video conferencing, Video on Demand (VoD), massive online gaming, and peer-to-peer, and many WWW-based applications, a great deal of attention is being paid to resource allocation for providing seamless multimedia access in next generation mobile communication networks The most important driving factor behind this significant rise is the increasing availability of broadband access, based on leased lines using cable modems, fiber optic links, and digital subscriber line (xDSL) access networks. With the popularity of mobile devices such as laptops, palmtops, and cellular phones, connectivity to the world thus becomes available everywhere with wireless network enhanced capability embedded in the mobile devices. Moreover, the advent of the Broadband Wireless Access technology (BWA) makes the above mentioned applications practical in the next generation networks. There are several standards for BWA developed in
1-4244-1284-6/07/$25.00 2007 IEEE
fourth generation technologies, such as IEEE 802.16e (or known as mobile WiMAX) [1-5]. Mobile WiMAX is a desirable candidate for envision of fourth generation network owing to its high data transmission rate and great extension capability for supporting mobility. Mobile WiMAX allows VoIP phone users to communicate seamlessly over metropolitan areas, large hotspots, campus served through WiMAX spectrum, especially in rural and hard-to-reach areas. With the benefit of WiMAX, users are able to access internet resource via the connection to mobile WiMAX when they are not in the hot spot of Wi-Fi (802.11) but still within a mobile WiMAX service area. To support the full mobility, mobile WiMAX creates small cells instead of trying to cover large areas with a single antenna. Since the multimedia applications are very sensitive to the available bandwidth, jitters or delays in the networks, some sorts of service quality guarantees are desperately needed. Internet Engineering Task Force (IETF) Integrated Service (IntServ) working group was formed to meet the demand on Quality of Service (QoS) in the Internet [6]. Under IntServ architecture, each flow adopts the Resource Reservation Protocol (RSVP) to make reservation for the resource before sending data. Although per flow-based QoS may be guaranteed, significant overhead traffic caused by a larger number of connections makes the realization of IntServ unfeasible in wide area networks. In order to maximize the system capacity, one of the most promising ways to solve the trade-off between the QoS provision and the efficient bandwidth utilization is the cross-layer design, which allows different layers to share status information in order to cooperate in the bandwidth reservation management. There are two important Quality-of-Service (QoS) parameters considered in wireless networks, namely the handoff call dropping probability (CDP) and new call blocking probability (CBP). Handoff is a mechanism that a mobile host (MH) is transferred from one base station (BS) to another during an ongoing call and the desired bandwidth should be allocated in the new cell in order to provide QoS guarantee for multimedia traffic. The CDP denotes the likelihood that an ongoing call is forced to terminate during a handoff process when the allocated resources in the new cell are degenerated to an unacceptable level, while the CBP represents the possibility that a new connection request is denied admission into the cellular networks. Accordingly, one of
the most important QoS issues in providing multimedia traffic in wireless networks is to reduce handoff drops caused by lack of available bandwidth in the new cell while maintaining high bandwidth utilization and low new call blocking rate. In traditional handoffs only signal strength and channel availability are considered, while the following new metrics have been proposed for use in conjunction with signal strength measurements in the envisioned 4G mobile WiMAX networks [11], such as class of traffic, monetary cost, network conditions, include traffic, available bandwidth, network latency, and congestion (packet loss), and conditions of the MH, such as velocity, moving pattern, moving histories, and location information, etc. Moreover, the micro-cell deployments in 4G mobile WiMAX for offering mobility result in higher rate of handoffs. Hence an effective resource mechanism is required for 4G mobile WiMAX networks to deal with complex handoff process in micro-cell environments and varied 4G performance metrics. The remainder of the paper is organized as follows. A primitive bandwidth reservation scheme employed for 4G mobile WiMAX systems is introduced in Section 2. Then Sections 3 states how to incorporate the probabilistic mobility prediction model into the bandwidth-reserving estimator for better performance achievement. Section 4 exhibits the simulation results, where the proposed approach is compared with three representative algorithms in the literature. Conclusions are given in Section 5.
z
The probability that MH will move to a neighboring cell will be larger if the neighboring cell is a hot cell. z The current reserved bandwidth for the neighboring cells. The probability of moving to a neighboring cell is proportional to the bandwidth that the neighboring cell reserves. Based upon the above considerations, the bandwidth reserved in the range of base station B for MH Q located within the range of base station A when the new connection is accepted as shown in Figure. 1., can be derived as follows. (1) BRB = C ⋅ ϕ B (Q ) ⋅ BW (Q ) , where C is a constant, BW (Q ) denotes the minimum bandwidth requested by a MH Q within the range of base station A, ϕ B (Q ) represents the probability that MH Q moves inside the range of base station B.
B
G
Q C
A
F
E
2. A PRIMITIVE ADAPTIVE RESOURCE
D
RESERVATION SCHEME The traffic in cellular networks is usually categorized into the following two classes. Class I traffic denotes real-time multimedia traffic, such as interactive audio and video, while Class II is non-real-time data traffic, such as images and text. The representative bandwidth reservation schemes in the literature anticipate that a Class I connection request will make a handoff into one of its neighboring cells in the future and thus try to reserve some bandwidth in surrounding cells before the connection request is admitted. The Class I connection is forced to be dropped during handoff if its minimum acceptable bandwidth requirement cannot be satisfied in the entering cell. As for Class II traffic, a handoff is always accepted as long as there is any free bandwidth available. Although the above-mentioned bandwidth reservation schemes can effectively reduce the CDP in traditional macrocell wireless networks, whether they fit the requirement of the new metrics defined for processing multimedia handoff in 4G mobile WiMAX is doubtful. We thus propose a primitive resource reservation scheme in this section to aim at reducing overheads among the BSs and reserving bandwidth in an effective manner, effectively decreasing the CDP for the multimedia handoffs in 4G mobile WiMAX, while keeping bandwidth utilization at a reasonable level. The amount of the reserved bandwidth is determined by the following two factors in this work:
Fig. 1: 4G mobile WiMAX architecture with a cluster size equal to seven. 3. PROBABILISTIC MOBILITY PREDICTION BASED BANDWIDTH RESERVATION MECHANISM The probability of the MH Q moves out of the circle is defined by, u u ∞ − x (2) u − r, O ( r ) = xe t dx = 1 + r e t
∫
t
r
t
We assume the moving patterns of the MH are exponentially distributed. Then the probability density function of a MH moving for the distance of r after duration of t becomes, u − r t
, where u is a user-defined constant. Since ∞ , 2πrp (r )dr = 1 p t (r ) = ct e
∫
(3)
(4)
t
0
we have 2
ct =
1 ∞
2π ∫ re 0
and
ur − t
dr
u , t = 2π
(5)
π
2
u −u r t pt (r ) = e t . 2π
u
(6)
The probability of a MH moving into zones A and B G separated by v as shown in Fig. 2 can be respectively obtained by, G ϕ ( L ,v ) , (7) G 1
( )
At L, v =
∫π O (r secθ )dθ t
2π
−
2
and π
( )
2
G 1 Bt L, v = 2π
∫ O) (r sec θ )dθ ϕ( G L,v
where
(8)
.
(15)
Based on Eq. (10), the bandwidth reserved at base station B for MH Q located at base station A as shown in Fig. 1 can be expressed by, (16) BRB = C ⋅ PB (Q) ⋅ BW (Q) , where C is a constant, BW (Q) denotes the minimum bandwidth requested by MH Q within range of base station A, PB (Q ) represents the probability that the MH Q moves inside the range of base station B.
t
G G w× v wv
( G)
,
1 2 u − R1 secθ Pe (Q) = ( R1 sec θ ) dθ 1 + R1 sec θ e t 2π θ∫4 t
ϕ L, v = arcsin G G
.
(9)
G v
G w
Fig. 3: Range of the communication in a fixed base station A and B. 4. SIMULATION RESULTS
G Fig. 2: Zones A and B separated by v . G Here w denotes the vector perpendicular to L as shown in Fig. 2. Now assume a MH Q is located within fixed base station A as shown in Fig. 3, the probability of MH Q moving to communicatable position within the range of base station B is, as follows. PB (Q) = PLA (Q) − Pa (Q) − Pb (Q) − Pd (Q) − Pe (Q)
,
(10)
where the probability of passing through line LA , PLA (Q ) , is expressed by, π 2
1 PLA (Q) = 2π
∫πO (R secθ )dθ t
−
.
(11)
1
2
Besides, the probabilities of MH Q moving to areas a, b, d and e can be obtained via the following four equations, θ u , (12) 1 u − t R sec θ 1
Pa (Q ) =
2π
∫π 1 + t R sec θ e
1
1
−
( R1 sec θ )dθ
2
π
Pb (Q) =
1 2π
1 Pd (Q) = 2π
2
2
θ3
u
u
∫ 1 + t R θ
2
, − R2 sec θ sec θ e t ( R 2 sec θ ) dθ
(13)
,
(14)
u
u − R3 secθ ∫π 1 + t R3 secθ e t ( R3 secθ )dθ − 2
A series of simulations were conducted to compare the proposed probabilistic mobility prediction based bandwidth reservation scheme (MBR), with the fixed reservation scheme (FR), and the scheme without bandwidth reservation (NR). Meanwhile, the rate-based borrowing scheme (RBB) is also compared with the proposed work because it was reported that the RBB scheme achieves better performance than other representative bandwidth allocation and reservation schemes in the literature, such as the scheme presented. The RBB scheme not only allows the new calls and handoff connections to borrow bandwidth form existing multimedia connections, but also reserves 15% of bandwidth exclusively for Class I handoff connections. In the NR scheme, no bandwidth is reserved for handoff connections in each cell. If there is no bandwidth available when the MH moves to the new coverage area, the handoff call is disconnected and a forced termination occurs. As for the FR approach, a set of channels called guard channels are preserved in each cell to provide a way of prioritizing handing off calls on new call originations by setting aside a fixed bandwidth to support handing off users. New call originations cannot be assigned bandwidth from the guard channel pool. The guard channels are set to 20% of the whole bandwidth for the FR scheme in our simulations. The connections in the simulations are divided into two classes. A Class I traffic, which is a multimedia connection, is allowed to move to a neighboring cell only when the unallocated bandwidth in the target cell exceeds the requested bandwidth. A data connection of Class II
traffic can be granted to switch to a neighboring cell as long as the target cell possesses any unused bandwidth. Additionally, a new connection of Class I real-time traffic is allowed to borrow bandwidth from Class II non real-time connections in the same cell if the unallocated bandwidth in the current cell is smaller than the minimum bandwidth that the new Class I traffic requests in the proposed work. A similar approach was taken to effectively reduce the new call blocking probability of real-time traffic. The bandwidth requirement for each connection is randomly selected within the range of the maximum and the minimum bandwidth requirement listed in Table 1. Both the class and the location of each MH are randomly selected at the initial state. Each MH is given a speed characteristic, which decides the time spent in a cell, in order to simulate handoffs. If a hot cell neighbors with the cell that a MH is located at, then the MH has a probability of 0.5 to move to the neighboring hot cell, and a probability of 0.1 to one of other neighboring cells. On the other hand, each MH will move to one of the six neighboring cells with equal probability if no neighboring hot cell exists. Table 1: Multimedia traffic parameters used in the simulations. Traffic Bandwidth Average Example Requiremen Call Class t Duration Class I
30 Kbps
3 minutes
Voice Service
CBP for combined Class I and II traffic. The call blocking probability for the new connections in the RBB and the proposed MBR schemes is apparently improved owing to the channel borrowing technique. Meanwhile, the effectiveness of adaptive bandwidth reservation contributes to the better performance achieved in the proposed MBR scheme as illustrated in Figs. 6 and 7. The NR scheme has the highest CBP for new connections because it reserves fixed bandwidth for multimedia handoff connections and results in reduced free bandwidth that be assigned to for new connections. NR
FR
RBB
MBR
CDP for 0.18 class I traffic 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 0.01
0.02
0.05
0.1
0.2
0.5
1
New call arrival rate (requests/second)
Fig. 4: Call dropping probability for Class I traffic in the four schemes. NR Overal CDP
FR
RBB
MBR
0.14 0.12 0.1
Class I
256 Kbps
5 minutes
Video-Phone
Class I
1~4 Mbps
10 minutes
Video Service
0.08 0.06 0.04 0.02 0
Class II
Class II
Class II
5-20 Kbps 64~512 Kbps 1~5 Mbps
30 Seconds
Remote Login 3 minutes
0.01
E-mail, Paging
& Data on
Ftp
Figure 4 shows the comparison of call dropping probability (CDP) for multimedia handoffs (Class I), and Fig. 5 illustrates the CDP for combined Class I and II traffic. We can see from Fig. 5 that the CDP for multimedia handoffs is the lowest for the proposed MBR scheme when traffic load is high. Besides, the CDP for combined Class I and II traffic in MBR scheme is still lower than the other three schemes as shown in Fig. 5. The FR has the worst performance as expected since it does not reserve bandwidth for the handoffs at all. As for the RBB scheme, its fixed bandwidth reservation mechanism is still inferior to the dynamic bandwidth reservation approach taken in this work, although it uses bandwidth borrowing technique to lower down the CDP for handoffs. Figure 6 shows the CBP for the new multimedia connections in the four schemes, and Fig. 7 illustrates the
0.05
0.1
0.2
0.5
1
New call arrival rate (requests/second)
Fig. 5: Call dropping probability for combined Class I and II handoffs in the four schemes. NR
Demand 2 minutes
0.02
FR
RBB
MBR
0.6 CBP for class I traffic 0.5 0.4 0.3 0.2 0.1 0 0.01
0.02
0.05
0.1
0.2
0.5
1
New call arrival rate (requests/second)
Fig 6: Call blocking probability for Class I traffic in four schemes.
NR Overal CBP
FR
RBB
probability for new connections, call dropping probability for the handoffs, and bandwidth utilization are compared. Subsequent research will investigate the feasibility of applying intelligent tools such as neural networks, fuzzy logic and genetic algorithms into the proposed scheme to further improve the accuracy of the motion prediction for the mobile.
MBR
0.6 0.5 0.4 0.3 0.2 0.1
6. REFERENCE
0 0.01
0.02
0.05
0.1
0.2
0.5
1
New call arrival rate (requests/second)
[1]
Fig 7: Call blocking probability for combined class I and II traffics in the four schemes. The bandwidth utilization of various mechanisms is given in Fig. 8. The bandwidth utilization is defined as: Bandwidth Utilization =
∑ Used bandwidth of each cell ∑ Maximum bandwidth of each cell for each cell
for each cell
NR
.
(17)
FR
RBB
MBR
Bandwidth 1.2 utilization 1 0.8 0.6 0.4 0.2 0 0.01
0.02
0.05
0.1
0.2
0.5
1
New call arrival rate (requests/second)
Fig. 8: Bandwidth utilization comparison for the four schemes. The proposed MBR scheme still outperforms the other three schemes in bandwidth utilization due to the efficient usage of adaptive bandwidth reservation mechanism. RBB scheme uses bandwidth borrowing technique to achieve higher bandwidth utilization than the NR and FR schemes. Bandwidth utilization is the poorest in the FR scheme since it always reserves fixed bandwidth in each cell which is not necessarily used by the handoffs. 5. CONCLUSION In this work, an effective bandwidth reservation scheme is proposed to reduce forced termination of multimedia handoffs in the 4G mobile WiMAX systems via cross-layer design. A probabilistic mobility prediction model is employed to compute the amount of reserved bandwidth for the handoffs in the expected target cells. This work also tries to decrease the call blocking probability of new connections by using a channel borrowing technique. The simulation results show that both the proposed work performs better then the fixed reservation scheme, the scheme without reservation, and the rate-based borrowing scheme when call blocking
C. Cicconetti, C. Eklund, L. Lenzini, and E. Mingozzi, “Quality of Service Support in IEEE 802.16 Networks,” IEEE Network Magazine, 20(2), 2006. [2] D.-H. Cho, J.-H. Song, M.-S. Kim, and K.-J. Han, “Performance Analysis of the IEEE 802.16 Wireless Metropolitan Area Network,” Proc. First Int’l Conf. Distributed Frameworks for Multimedia Applications, 2005, pp. 130-137. [3] A. Ghosh, D.R. Wolter, J.G. Andrews, and R. Chen, “Broadband Wireless Access with WiMax/802.16: Current Performance Benchmarks and Future Potential,” IEEE Comm. Magazine, 43(2), 2005, pp. 129-136. [4] C. Hoymann, “Analysis and Performance Evaluation of the OFDM-Based Metropolitan Area Network IEEE 802.16,” Computer Networks, 49(3), 2005, pp. 341-363. [5] IEEE P802.16/Cor1/D2, Corrigendum to IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, IEEE, 2005. [6] J. Gozdecki, A. Jajszczyk, R. Stankiewicz, “Quality of service terminology in IP networks,” IEEE Communications Magazine, 41(3), 2003, pp. 153-159. [7] J.-M. Chung, and H. M. Soo, “A Jitter analysis of homogeneous traffic in differentiated services networks,” IEEE Communications Letters, 7(3), 2003, pp. 130-132. [8] W. Liu, X. Chen, Y. Fang and J. M. Shea, “Courtesy piggybacking: supporting differentiated services in multihop mobile ad hoc networks,” IEEE Transactions on Mobile Computing, 3(4), 2004, pp. 380-393. [9] M. Ma, “A cost-based scheduling algorithm for differentiated service on WDM optical networks,” IEEE Communications Letters, 7(9), 2003, pp. 460-462. [10] M. Karaliopoulos, R. Tafazolli, and B. G. Evans, “Providing differentiated service to TCP flows over bandwidth on demand geostationary satellite networks,” IEEE Journal on Selected Areas in Communications, 22(2), 2004, pp. 333-347. [11] J. McNair, and Z. Fang, “Vertical handoffs in fourth-generation multinetwork environments,” IEEE Wireless Communications, 11(3), 2004, pp. 8-15.
