October 1-15, 2007A Global Sources Publication

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Evaluating data transfer in HSDPA/W-CDMA nets

NETWORK DIAGNOSTICS

Dr. Michael Leung SMIEEEmichael-hf_leung@agilent.com

A HSDPA/WCDMA network simulator www.agilent.com/ find/e6703T is selected for evaluating the data transfer performance of the HSDPA / WCDMA user equipment (UE). The throughput performance of two different models of HSDPA / WCDMA UEs are measured and presented when they are used alone and as wireless modems for personal computers (PCs).

IntroductionModern mobile devices are capable of transferring an increasing variety of data types that continue to grow in complexity. For example, mobile phones, once used only for trans-mitting/receiving voice data, are now capable of playing and sending music files; capturing and transmitting photographic

images; and even recording and sending video clips [1]. Moreover, they can be used as wireless modems and connect PCs to the Internet. As the designs of these devices get more and more intricate, it becomes increasingly important that engineers can test the performance of each aspect involved in the data transfer.

Designers of mobile devices typically test the efficiency of data transfers from baseband data analysis. A better scenario is to test the device under a real network

environment. However, there are three issues when involving a mobile network in testing. First, the network, such as a high speed downlink packet access (HSDPA) network or wideband CDMA (WCDMA) network, may not be available. Second, if the device is connected to a real network and a problem, for example a link dis- connection or a slow down in throughput, arises, it is very difficult to trace the actual cause which may happen in any of the sub-systems. Also, the real network

itself is time-varying, and the quality that it provides to the UEs is not guaranteed and is hardly reproducible. Therefore, the perfor- mance evaluation of the UE is not quite reliable while connecting the UE to a real network. Figure 1 shows the six subsystems involved in a HSDPA / WCDMA network: Mobile Station/User Equipment, Node B (base station), Radio Net- work Controller (RNC), 3G-Serving GPRS Support Node (3G-SGSN), 3G-Gateway GPRS Support Node (3G-GGSN), and IP server [2].

Figure 1: Subsystems in a WCDMA Network.

Figure 3: IP data throughput analysis at 7.2Mbps data rate

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Figure 2: Replacing Subsystems in a HSDPA / WCDMA Network by the tester.

stable and reproducible network environment.

Throughput testThe Agilent HSDPA/WCDMA net-work emulator has been selected

for data throughput experiments. The test set provides a complete, end-to-end packet data service conforming to the GPRS Packet Data Service described in [3]. The user may connect the test set’s local area network (LAN) port to their computer network and make a complete connection from the UE through the test set to that network. Figure 3 shows the data throughput analysis for 7.2Mbps mobile at Over-The-Air (OTA) & IP data layers

The GPRS service configura- tion supported by the test set provides a number of different Radio Access Bearer configura- tions. The particular configurations studied here are 64k uplink (UL)/ 384K downlink (DL) packet- switch data mode (PSD), and 384k UL/7.2M DL PSD mode. Figure 4 shows the exchange of protocol layers messages between the UE and the wireless tester. The messages indicate that the mobile initiates to make a packet data connection with GPRS attached and PDP (Packet Data Protocol) activation processes.

Figure 4: Protocol logged by the tester when the UE initiates a HSDPA packet switching data connection with GPRS attached and Packet Data Protocol activation processes.

HSDPA/WCDMA Network in a boxIn this paper, we select to use a UE tester (Agilent 8960) that allows evaluating the IP throughput performance of the HSDPA / WCDMA UE. With the tester, the aforementioned problems can be resolved. The tester, with built-in HSDPA / WCDMA network simulator and software verification tools, is designed specifically for HSDPA / WCDMA UE developers who require performing radio/ protocol/software/hardware

design verification and integra-tion, as well as performance evaluation. Figure 2 illustrates how the tester can be used to replace the sub-systems of a HSDPA / WCDMA network. The tester offers realistic network simulation, and provides Internet connectivity with real data traffic flows. Additional capability can also be obtained from extensive real-time protocol logging and analysis tools. Moreover, the tester can serve as a platform for comparing the throughput of different UEs by providing a

Dr. Michael Leung is an Applications Program Manager of Electronic Measurement Group of Agilent Technologies in Asia. Michael is respon- sible for application engineer’s development and customer consult ing on advanced wireless technologies. Michael joined Agilent/Hewlett-Packard in 1997 as technical marketing

Dr. Michael Leung SMIEEEEmail: michael-hf_leung@agilent.com

Biography engineer. Michael then moved to US and UK in the same year as application consultant on 3GPP wireless applications. Later in 2003, he took up the position of senior application consultant and then assumed his present role in 2005. Michael plays a signi- ficant role on Agilent's wireless technology development front for 3G(WCDMA), 3.5G (HSPA) and 3.9G (LTE), protocol research and testing developments in Asia.

During his years of service in Agilent, Michael had gained 4 technical invention awards, contributed over 20 Agilent technical conference papers, and published 10 research papers in various international journals & conference. Michael received his Master of Science and Doctor of Engineering degrees from Hong Kong Polytechnic University in 1998 and 2005 respectively.

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Mobile IP data performance optimization (such as memory size, CPU speed, OS perfor-mance). In the first test, a PC is connected to a UE and uses the UE as a “wireless modem” to down-load files of different sizes from the server via the test set. Figure 5 plots the time taken to download versus the file size for 2 different UEs. It can be observed at downlink data rates of 384k and 7.2M, both UEs have a similar performance and UE #1, with a smaller DL time, has slightly outperformed UE #2. Moreover, the time taken increases linearly with the file size. The raw data rates, computed from the inverse of the slopes of the lines, are approximately 195 kbps and 5000 kbps for the 384k DL and 7.2M DL, respectively. The results show that when the DL speed increases by 6

times from 384k to 7.2M, the actual increase in raw data rate is more than 25 times.

In the second test, the UEs operate alone and download files of different sizes. Figure 6 plots the time taken to download against the file size for the two UEs again. It can be observed that the performances of the UEs are similar to those in the previous case except in one scenario. At a downlink data rate of 7.2M, UE #2 requires a substantially longer time to download files, giving a much lower raw data rate of approximately 1Mbps. Possible causes are lower processing power, operating system efficien- cies, and smaller mobile memory buffer of UE #2. Based on this, we can conclude that the design of UE #1 is better than that of UE #2

Figure 5: Download time versus file size when the UE is connected to a PC and is used as a wireless modem.

in downloading data. Comparing with modem & non-modem conditions & plot data analysis data, it will be much easier to familiar with mobile performance.

ConclusionA 7.2Mbps HSDPA / WCDMA net-work simulator has been used for evaluating the data transfer performance of the HSDPA / WCDMA user equipment (UE). The Agilent 8960 tester provides a stable and reproducible environment for engineers to evaluate the performance of UEs. The simulator has been implemented successfully and the IP data throughput of two different brands of UEs have been measured under two different scenarios. Based on the 8960 tester, engineers can measure and

Figure 6: Download time versus file size when a standalone UE is used.

optimize the performance of the UE much easily.

Authors’ affiliationDr. Michael H.F. Leung, SMIEEE, Applications Program Manager, Application Engineering Organi-zation (AEO), Agilent Technologies Co. Ltd., Hong Kong China

References:[1] 3GPP TS 23.228, IP Multime-

dia Subsystem (IMS); Stage 2

[2] 3GPP TR 23.922, Architecture for an All IP Network

[3] 3GPP TS 23.060, General Packet Radio Service (GPRS) Service description; Stage 2