Using the 8960 emulator to evaluate audio/video data transfer over HSDPA/WCDMA networks
This "Product How-To" article focuses how to use a certain product in an embedded system and is written by a company representative.
Modern 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 transmitting/receiving voice data, are now capable of playing and sending music files, capturing and transmitting images, and even recording and sending video clips.
Moreover, they can be used as wireless modems that connect PCs to the Internet. As the designs of these devices get more and more intricate, it becomes increasingly important that engineers test the performance of each aspect involved in the data transfer.
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| Figure 1. There are six subsystems involved in an HSDPA/W-CDMA network. |
Designers of mobile devices typically test the efficiency of data transfers from baseband data analysis. A better scenario is to test the device in a real network environment. However, there are three issues involving mobile networks during test.
First, the network - for instance, a high-speed downlink packet access (HSDPA) network or W-CDMA - may not be available. Second, if the device is connected to a real network and a problem arises (e.g. a link disconnection or a slow down in throughput), it is very difficult to trace the actual cause in any of the subsystems.
Also, the real network itself varies over time, and the quality it provides to user equipment (UE) is not guaranteed and reproducible. Thus, performance evaluation of the UE is not reliable while connecting it to a real network.
Figure 1 above shows the six subsystems involved in an HSDPA/W-CDMA network: the UE, Node B (base station), radio network controller, 3G-Serving GPRS Support Node, 3G-Gateway GPRS Support Node and IP server.
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| Figure 2. The tester offers realistic network simulation, and provides Internet connectivity with real data traffic flows. |
Network in a box
The Agilent
8960 allows evaluation of IP throughput performance of
HSDPA/W-CDMA UE. The tester has a built-in HSDPA/ W-CDMA network
simulator and software verification tools, and is designed specifically
for HSDPA/ W-CDMA UE developers who require performing radio/protocol/
HW/SW design verification and integration, as well as performance
evaluation.
Figure 2 above shows how the tester can be used to replace the subsystems of a HSDPA/W-CDMA 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 stable and reproducible network environment.
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| Figure 3. The UE initiates an HSDPA PSD connection with GPRS-attached and packet data protocol activation processes. |
Throughput test
Agilent's HSDPA/W-CDMA network 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.
The user may connect the test set's LAN port to their computer network and make a complete connection from the UE through the test set to that network. The GPRS service configuration supported by the test set provides a number of different Radio Access Bearer configurations. The particular configurations studied here are 64k uplink (UL)/384k downlink (DL) packet-switch data (PSD) mode, and 64k UL/3.6M DL PSD mode.
Figure 3 above shows the exchange of protocol layer messages between the UE and the wireless tester. The messages indicate that the cellphone initiates to make a packet data connection with GPRS-attached and packet data protocol activation processes. In the first test, a PC is connected to a UE and uses it as a wireless modem to download files of different sizes from the server via the test set.
Figure 4 below plots the time taken to download vs. the file size for two different UEs. It can be observed at DL data rates of 384Kbps and 7.2Mbps that both UEs have similar performance and that UE1 has slightly outperformed UE2.
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| Figure 4. At DL data rates of 384Kbps and 7.2Mbps, UE1 has slightly outperformed UE2. |
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 195Kbps and 5,000Kbps for the 384Kbps DL and 7.2Mbps DL, respectively. The results show that when the DL speed increases by six times from 384Kbps to 7.2Mbps, the actual increase in raw data rate is increased more than 25 times.
In the second test, the UEs operate alone and download files of different sizes. Figure 5 below plots the time taken to download against the file size for the two UEs. The performances of the UEs are similar to those in the previous case, except in one scenario.
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| Figure 5. At a DL data rate of 7.2Mbps, UE2 requires a substantially longer time to download files, giving a much lower raw data rate of approximately 1Mbps. |
At a DL data rate of 7.2Mbps, UE2 requires a substantially longer time to download files, giving a much lower raw data rate of approximately 1Mbps - possible causes of which are lower processing power and smaller mobile memory buffer in UE2.
Thus, we can conclude that the design of UE1 is better than that of UE2 in downloading data. Comparing modem and non-modem conditions and plot data analysis, it will be much easier to familiar with mobile performance.
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. With the 8960 tester, engineers can measure and optimize the performance of the UE more easily.
Michael Leung is Applications Program Manager at Agilent Technologies Inc.
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