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Performance Analysis of Joint Radio Resource Management Strategies for Beyond 3G Networks Hermes Irineu Del Monego #1, Jose´ Manuel Oliveira ¤2, Manuel Ricardo #3 # INESC Porto, Faculdade de Engenharia, Universidade do Porto ¤ INESC Porto, Faculdade de Economia, Universidade do Porto Rua Dr. Roberto Frias, 378, 4200-465, Porto, Portugal 1 [email protected] 2 [email protected] 3 [email protected] Abstract—In beyond 3G networks the user will not be aware networks resources is desired. This will certainly improve the of the access network technology used to provide a telecom- service offered to the users and, at the same time, will increase munications service. Heterogeneous network technologies will be the operators’ revenue. seamlessly integrated in one “common” access network, enabling rd users to move around and continuously receive their subscribed The 3 Generation Partnership Project (3GPP) has defined a services. In a commercial environment, this network evolution generic interconnection architecture between 3G networks and requires that a telecommunications operator jointly manages its WLAN, illustrated in Fig. 1 [1], [2]. The release 8 of 3GPP networks resources to improve the service offered to the users promotes solutions for networks interconnection following a and, at the same time, to increase its revenue. seamless mobility approach, characterized by providing the Starting from the UMTS and WLAN interconnection architec- ture defined by 3GPP, this paper analyzes the performance of a service independently of the technology used to access it. new joint radio resource management strategy, comparing it with Considering the UMTS and WLAN networks interconnec- two well-known strategies used in scenarios where both networks, tion scenario defined by 3GPP, this paper analyzes the per- the UMTS and the WLAN, are interconnected. The new strategy formance of a new joint radio resource management (JRRM) presented in the paper bases its decisions on criteria related to user mobility characteristics and the application characteristics. strategy, comparing it with two well-known strategies used The strategy also introduces the possibility of renegotiating new in scenarios where the user is located in a place covered by calls and reallocating running calls from one access network to different radio access technologies. This new strategy, called another. MTend, bases its behavior in criteria related with user mobility. The performance analysis considers two traffic scenarios. One Additionally, in a scenario of low available resources, the where only real-time applications are running and other which strategy introduces the possibility of renegotiating requests of also introduces TCP applications. The comparison studies show the proposed strategy outperforms the other strategies in what new calls or reallocating existing calls from one network to concerns call blocking probability and applications QoS support. another. The performance analysis presented in this paper only Besides, the proposed strategy tends to reduce the handoffs considers scenarios where the user is static. between networks. In the next section, some important related works are pre- Index Terms—Renegotiation, Reallocation, Resource manage- ment, Heterogeneous wireless networks, Session continuity sented. Section III presents the call admission control mecha- nisms used by the UMTS and WLAN interfaces. Section IV proposes the new strategy for joint management of multi-radio I. INTRODUCTION resources, based on user mobility and the renegotiation or The recent evolutions in telecommunications have been reallocation of calls; this section also describes the decision influenced by the crescent need of users to access their algorithm used to define the interface to which a new call subscribed services in mobile environments. This demand should be allocated. Section V presents the simulation scenario has determined two complementary research lines in this used to analyze and compare the performance of this new area. On one hand, multimode terminals have been deve- joint radio resource management strategy with two other well- loped, being capable to access different network technologies, known strategies. Section VI analyzes in detail the simulation particularly wireless technologies, such as Universal Mobile results. Finally, Section VII presents the conclusions and Telecommunication System (UMTS), Wireless Local Area points out directions for future work. Network (WLAN), or Bluetooth. On the other hand, the inter- connection of different access networks has been researched II. RELATED WORK and defined, enabling call transference from one interface to another, seamlessly to the user. The joint multi-radio resource management is an well In a context where one telecommunications operator accepted research area in telecommunications. It promotes administrates different network technologies in the same solutions for the support of Quality of Service (QoS) classes physical location, a joint and efficient management of those while optimizing the usage of resources. mechanism to obtain the available UMTS load factor for both IP Based Network Operator link directions. The load factor for the uplink direction is given by: HA XN 1 ´UL = (1 + i) ¢ ; (1) PDG 1 + W GGSN j=1 (Eb=N0)j ¢Rj ¢vj where N is the number of stations, vj is the activity factor of WAG station j at physical layer, Eb=N0 is the signal-to-noise ratio, SGSN W is the chip rate, Rj is the bit rate of station j and i is the RNC intercell interference observed by station j. WCDMA/UMTS The load factor for the downlink direction is given by: XN (E =N ) ´ = v b 0 j ¢ [(1 ¡ ® ) + i ] ; (2) WLAN AN DL j W=R j j j=1 j User where ®j is the channel orthogonality of the station j, while Fig. 1. 3GPP generic architecture for the interconnection of 3G and WLAN ij is the signal of other cells received by station j. For vj; ®j networks and ij we used commonly accepted values proposed in [6]. The load factor is controlled to be always below a limit represented by ´max (´max < 1). In most of the UMTS A strategy based on service classes is proposed in [3], where systems, the ´max value is not higher than 0:75, for both the authors use two policies: the first policy gives priority to directions, the uplink and the downlink [6], [7]. In our work, voice calls in GERAN and interactive traffic in UTRAN; the we assumed that the operator applies this value for ´max in second inverts the choice. According to the authors, when the both direction. mobile stations are close to the cell there is no difference In the UMTS interface, a new call specifies the minimum between both strategies. On the other side, when the distance QoS requirements that should be satisfied by the network. This to the cell increases, more transmission errors may occur due request includes values for different QoS parameters, such as to WCDMA characteristics, leading to a higher degradation in the bit rate. A new call is accepted by the call admission UTRAN users. In this case, the first policy is the most efficient control mechanism, either in the uplink or in the downlink, one. when the load factor is below ´max after integrating the new Two other strategies commonly used in this context are call. the load balancing (LBal) and the coverage area (CovAr) strategies, which will be used for comparison with the strategy B. WLAN Interface proposed in this paper. The LBal strategy is characterized by Comparing with UMTS, the WLAN interface usually offers directing calls to the interface with lowest load, maintaining a higher bandwidth and a smaller cell coverage area. On the the interfaces balanced [3], [4], [5]. other hand, the radio access in WLAN is most of the times The CovAr strategy directs calls preferentially to the inter- uncertain, being based on the transmission silence time [8]. face associated to smaller area cell. For example, in hotspots The strategy used for obtaining the available bandwidth the calls are directed firstly to the WLAN network until it in the WLAN interface consists on monitoring the channel saturates, and then to the UMTS network [4]. occupation ratio, which determines the channel capacity for The use of JRRM techniques to cope with multi-RAT and transmit [9]. New calls are only admitted in WLAN when the multi-hop networks of the same or different administrative requested bandwidth is below the available bandwidth. The entities, in the context of the Ambient Networks concept, is WLAN available bandwidth, in bit/s, is given by: covered in [?], [?]. The presented solution is characterized L ¢ (R ¡ R ) by being scalable, flexible and applicable to Personal Area Bw = th o ; (3) Networks (PANs) and Body Area Networks (BANs), as well W LAN T as to large operator networks. where L is the average packet size, T is the average time for having success in transmission and Rth is the network III. SINGLE INTERFACE CALL ADMISSION CONTROL threshold, which is a parameter controlled by the operator [9]. The following two sections present the call admission The network occupation factor is given by: control mechanisms used by the UMTS and WLAN network t technologies for managing new calls. busy Roi = ® ¢ + (1 ¡ ®) ¢ (Roi¡1 ); (4) ¢t A. UMTS Interface where tbusy is the busy state time, ¢t is the window size In UMTS, the load factor estimates the amount of supported measurement time, and ® is the importance of the current traffic per base station site; in [6], the authors describe the sample i. When the RTS/CTS mechanism is not used, T is given by: reallocation mechanisms require the monitoring of each access network so that their level of congestion can be evaluated. T = DIF S + T [EP ] + SIF S + ACK: (5) The renegotiation mechanism consists of two renegotiation tries. In a case where the first try does not succeed, the On the other hand, when the RTS/CTS mechanism is used, system enables the application to reduce again the resources T is given by: requested.

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