Novel Signaling Scheme for 1x CDMA based Femtocell Networks

Novel Signaling Scheme for 1x CDMA based cell Networks Kuen Chool Yoo*, Tae Jin Lee** *School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-764, South Korea {kcyoo2000,tjlee}@ece.skku.ac.kr Abstract A cell netwoks can support iosolated coverage area and high data rates for mobile users by using wired lines such as x and other cables for backhaul connectivity. This wireless communication system architecture in the form of a cell cellular network can also support higher bandwidths at lower expense. cell networks can be classified into 3GPP UMTS based wireless networks and 1x CDMA-based wireless networks. In addition, 3GPP UMTS based femtocells are standardized in the form of Home Node-B. However, 1x CDMA-based femtocells are not currently standardized. As a result, operators and communication system vendors are developing and lauching such networks with their own specifications. Various methods of standardization have been supposed for 1x CDMA-based femtocell networks, including one that is directly interconnected with an, another that is interconnected by a Access Gateway, and another that is interconnect with an IMS Core Network. From the viewpoint of an operator seeking to reduce its setup-costs, the adoption of the Access Gateway is preferable. If femtocell networks based on the Access Gateway are adopted, the standardization between the femtocells and Access Gateway is required. Most operators and manufacturers have proposed -based signalling for this standardiztion. However, this signalling technique suffers from some performance problems. In this paper, we propose a novel type of signalling flow and evaluate its performance in comparison with that of -based signal flow. Also, we propose an optimized signalling flow and describe the corresponding performance results. Keywords 1x CDMA based femtocell, Access Gateway, Optimized signaling flow. I. INTRODUCTION The femtocell can be used in a small area such as a home or office environment and is operated a low-power, low-cost cellular base station. Mobile stations can be connected at low-power and the femtocell can use the as the backhaul to provide the mobile stations with high capacity [1]. cells can provide two kinds of radio access environments. The first is the 3GPP UMTS-based femtocell and the other is the 1x CDMA-based femtocell. The 3GPP UMTS-based femtocell is standardized as an Iu-h interface between a Home Node-B and Access Gateway [2]. However, 1x CDMA-based femtocells are being launched by some equipment manufacturers and communication operators without any standardization. For their standardization, various integrations models between 1x CDMA-based femtocells and 1x CDMA Core network have been proposed in the femto forum [3]. By default, because the is used for backhaul connectivity, a Security gateway for Sec tunnelling between the femtocells and core network is configured as a separate node. Three main configurations have been proposed, where the femtocell is connected directly to the, indirectly to the through a gateway such as a -like gateway, or directly to an Protocol Multimedia Subsystem. Of these schemes, the best solution in terms of the costeffectiveness model is to deploy a gateway. The gateway should have various functionalities, such as functions, interconnections for lots of femtocells, No.7-based signalling with and E1/T1-based TDM functions for voice traffic. This method based on a gateway is required to standardize the signalling interface between the femtocells and the ( access Gateway) such as a 3GPP Iu-h interface. Thus, it is necessary to propose the most appropriate interface, because it is not yet standardized. This type of interface uses a secure tunnel such as Sec. The interoperability of two network elements occurs through the, so some appropriate signaling interfaces have been suggested by various manufacturers. Of these proposals, the main method uses a Session Initiation Protocol as the signaling interface and Real Time Protocol as the traffic interface. This approach may be appropriate in terms of the IMS network migration and signaling protocol. However, it has some problems in terms of the compatibility of the existing core network. Therefore, we propose an -based signaling protocol that refers to the 3GPP2 specifications. By comparing the performances of -based signaling and based signaling, we were able to select the most appropriate signaling flow. When an message is delivered, the messages should be transferred as the contents. Therefore, we have to define a type of contents that discriminates the messages. In this way, using on the is an advantage in terms of the use of networks, but differences can occur between the Air Interface flow and flow interconnecting the. Therefore, the basic flow must be modified and additional

flows are required. These modifications of the signaling flow between the femtocells and can limit the performance and interoperability. In this paper, an -based signal flow is proposed and its performance is evaluated. Then, a comparative analysis is performed on this and another signaling flow. The use of another signaling approach between the femtocell and modifies the existing Interface flow, and the -based signaling flow needs to be defined. The performance of this flow is evaluated and a comparative analysis is performed on the -based signal flow. This approach based on the existing interface can be easily applied to the signaling interface between the and. In this paper, Section 2 describes the two kinds of network architecture for the femtocells and simplified protocol stack. Section 3 describes the two kinds of signaling flow based on 1x CDMA. Section 4 describes the two kinds of simulation environment and compares the simulation results of the proposed signaling flows. Finally, Section 5 provides a summary of the merits and demerits of the two kinds of signaling flow and shows which is the better scheme. II. FEMTOCELL SYSTEM ARCHITECTURE A femtocell is generally installed indoors or in an office area and is connected to a wireless core network through a or cable network[5]. In addition, because it uses an insecure network, the signaling and traffic information are forwarded through an Sec tunnel. In this environment, an interface such as a gateway can be configured for the sake of its interoperability with the existing Macro network. In this paper, two methods of connecting the and femtocells are considered. In the comparison of the performance, we propose an appropriate signaling flow. From the femtocells to Security Gateway, Sec is enabled by default. The signaling for uses. The received messages should be changed to Interface messages. Because recognizes the as one of the s, to achieve signaling with the, the functions of the need to be modified. Because the femtocell includes most of the features of the or, the message body, which contains the parameters, should be forwarded to the. Security Gateway Type (Sec Sec) The receives the messages and then parses the parameters within them. In other words, the should provide a decision function to determine what kind of parameters exist. Figure 2 shows the overall protocol stack for the -based network. The layer delivers the messages of the Interface related to CC(Call Control), RR(Radio Resource management), and MM(Mobile Management). The should support a lot of femtocells through signaling. In addition, is used as the transport layer. [ ] / Gateway [ ] / Figure 2. Protocol Stack based on signaling Figure 3 shows the -based cell network configuration. The network refers to the Transport layer of 3GPP2 and interoperates with the existing. Its interoperability with the is the same as that of the based architecture. Because the -bearers s interface delivers the network traffic through the, this scheme is basically the same as -based signaling. Security Gateway Type (Sec) - based Figure 3. cell Architecture based on signaling The transport layer protocol uses as the -based signaling approach. To perform the performance evaluation, the transport layer protocol uses. The -based protocol stack for the femto network configuration is the same as that shown in Figure 4, and the traffic is the same as the -based traffic. [ CC/ MM/RR] / Gateway [ CC/ MM/RR] / Figure 1. cell Architecture based on Signaling Figure 4. Protocol Stack based on signaling

The 1x CDMA cell network described in this paper minimizes the modification of the legacy CDMA Core Network and the is recognized as one of the s. Therefore, the cell network can be installed without any modification of the existing communication network. Figure 5 shows the overall -based cell network and legacy CDMA network. This cell network configuration, without any modification to the existing legacy system, enables a cell network to be installed rapidly. through a trans-coding function. Figure 7 shows the -based signaling flow proposed in this paper. MS1 MS2 Origination Message cell Udp_CMService Req CMService Req Udp_ Udp_Assignment Complete Assignment Complete Udp_ Udp_ Security Gateway Type (Sec) - based HLR / Udp_ Udp_Assignment Complete Assignment Complete Alert with Information Udp_ Figure 7. -based Signaling Flow Figure 5. -based 1xCDMA cell Network and Legacy System Figure 6 shows the overall -based cell network architecture. It is configured as shown in Figure 5. The modifications of the existing network are minimized or even unnecessary. The -based signaling should translate the Messages and their contents into Messages and parameters. In this process, the can transmit the Message to the. In the same way, the Message is transmitted only to the femtocell at which the subscriber is registered, and the should support a database containing the subscriber s and femtocell s identities. The performs operations that convert the Message and Contents into a No.7-based Message and parameters. Figure 8 shows the -based signaling flow. cell Security Gateway Type (Sec) HLR / MS1 MS2 cell Origination Message INVITE 200 OK ACK CMService Req Assignment Complete MESSAGE Request cell INVITE Figure 6. -based 1x CDMA cell Network and Legacy System III. FEMTOCELL NETWORK S SIGNALING FLOW The -based signaling flow is similar to the 3GPP3 flow; only the parameters for the bearer setup are different. The paging message for incoming call setup is only delivered to the femtocell at which the subscriber is registered, not to all of the femtocells. To perform these functions, a database that can store the subscriber information and the femtocell s identity is required. These informations should be included when the Location Update is performed. Also, a function that converts the -based signaling to No.7-based signaling is required in the. The functionality that converts the -based traffic into PCM-based traffic is performed in the Alert with Info 180 ringing 200 OK Assignment Complete ACK INFO Figure 8. -based Signaling Flow IV. SIMULATION ENVIRONMENT AND RESULTS

To evaluate the two different methods, we need to build a simulation environment, as well as simulators that perform the functions and femtocell functions. The femtocell simulator should be able to encapsulate the signaling information into the Message, load the message into the layer and run a lot of femtocell applications simultaneously. In addition, after a certain duration, each session should be released. The Simulator interoperates with the and issues paging messages for the purpose of terminating the call-setups. Typically, it supports No.7-based protocols and issues Request Messages. The simulators do not support the issuing of voice payloads, but does support information delivery for a radio traffic channel and circuit channel. The is composed of various applications, including the Stack, No.7 Stack and UNIX Server. To implement most of the functions of the, it comprises three parts, interoperability with multiple femtocells, interoperability with the using No.7 protocols and session management and information handling for the femtocell identity and mobile stations. Figure 9 shows the virtual environment used to evaluate the -based signaling flow. The function exists between the femtocell simulator and. Simulator Gateway Simulator The simulation is started at the femtocell simulator and the simulator sends Response Messages and a Message. The performance of the was measured by the sar utility. This utility can measure the CPU load. In order to measure the performance of the modules supporting the major functions within the, the top utility was used. The hold time for all of the call sessions was set to 50 seconds and the registration for all MS(Mobile Station)s was completed before call-setup. Table 1. Simulation paramters Parameter Value Total cell Number 100,000 Total Mobile Station Number 500,000 Average call duration 50 second Busy Hour Call Atempt 10,000 20,000 40,000 60,000, 80000, 100000 Although the CPU Load can depend on the server s specifications, the performance evaluation result that was measured by the top utility shows a difference according to the amount of processing. In other words, we confirmed that after the received the Message, the percentage CPU occupation increased according to the amount of Message processing. The CPU occupation pertaining to the function modules interoperating with the was similar for both kinds of signaling flow. parser Emulator 70 60 50 d a 40 o L U P30 C 44.3 28 46.7 30 54.3 38 57.2 58.2 40 42 60.3 45 20 10 0 -bas ed 10000 20000 40000 60000 80000 100000 BHCA(Busy Hour Call Atempt) Figure 9. -based Signaling Flow simulation Environment Figure 11. Load Comparison for BHCA The environment for -based signaling flow is shown in Figure 10. Simulator Message Encoder Figure 10. Gateway parser -based Signaling Flow simulation Environment Simulator Emulator CC/ MM/ RR In the case where the number of femtocells is small, the difference in performance between the two signaling flows is small, but as the number of femtocells increases, the difference becomes greater. To install more femtocells at one, we can configure other kinds of expensive hardware platform. However, by modifying the signaling flow, we can acquire the result. d a o L U P C 90 80 70 60 50 40 30 20 10 0 15.1 10.2 S -bas ed 30.5 20.3 40.5 25 10000 20000 40000 60000 80000 100000 cell Number 51.7 33.5 65.7 48.4 77.5 63.1 Figure 12. Load Comparison for cell number

V. CONCLUSION The easiest way to install a 1x CDMA-based femtocell networks is to use an. For this network configuration, two kinds of signaling interface between the and femtocells can be used, -based or proposed -based signaling. Typically, -based signaling has been used, but in this paper we proposed the -based signaling interface. Also, through the performance evaluation of the two signaling flows, we showed that proposed -based signaling is more efficient and provides superior performance. When a Core Network is migrated to an IMS Core Network, -based signaling may be helpful for the operator. However, this method has some performance problems, whereas -based signaling improves the performance of the. We demonstrated that -based signaling is superior in terms of the development time and cost. Also, in terms of the signaling flow, it is the easier of the two signaling flows. The present results may be helpful for the future standardization of signaling. ACKNOWLEDGMENT This research was supported by Contela Inc. and the simulation was performed in their laboratory. REFERENCES [1] ㅠ Vikram Chandrasekhar and Jeffrey G.Andrews, cell Networks: A Survey, IEEE Communication Magazine, September 2008. [2] 3GPP TS 25.467 V8.1.0, UTRAN architecture for 3G Home NodeB April 2009. [3] http://www.femtoforum.org [4] 3GPP2 A.S00012-C Version 2.0 Interoperability Specification () for cdma2000 Access Network Interface [5] Mostafa Zaman Chowdhury, Won Ryu, Eunjun Rhee, and Yeong Min Jang, Handover between Macrocell and cell for UMTS based Networks, in Proc. of 2009 ICACT Conference, pp 1-3 Feb 2009