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8960 in Wireless Device Design News

Series 2 Issue 1

GAN Mobile Phones: What Needs To Be Tested?

The generic access network (GAN) is the 3GPP standard for cellular network and wireless local area network convergence. For operators of cellular mobile networks, GAN promises greater network capacity and improved quality of indoor cellular coverage, without requiring an entirely new cellular infrastructure.

For users of mobile phones, GAN offers the benefits of a fixed broadband network, including higher data rates than currently available on GPRS and W-CDMA networks. In fact, GAN may provide a single phone that can replace separate fixed and mobile devices for home, office, and outdoor use. The technology is expected to stimulate competition—for example, mobile operators teaming up with fixed-line operators to offer bundled cellular and fixed-line Internet services as an alternative to voice over IP.

Ultimately convergence of the mobile and fixed domains means more choices for users. However, success is always a result of positive user experience, and that is particularly true for GAN, which relies heavily on the mobile phone’s ability to deliver high quality voice and data while making seamless handovers between cells and between different radio access networks. Yet conformance specifications remain limited in scope, with only a small number of handover tests and no coverage of application performance and data throughput. As a designer of GAN phones, you will need to test well beyond the current specifications to get a device that is ready for customer use.

GAN system components

Figure 1 shows a proposed system architecture for GAN. Implementation requires adding several new components to the existing network:

  • a wireless local area network, which can be based on wireless LAN or Bluetooth technology;
  • dual-mode, GAN-enabled phones that can detect the wireless LAN and also make transitions to and from the GERAN or UTRAN cellular networks; and
  • a network element called the generic access network controller (GANC), which is similar to a base station controller and connects to the cellular operator’s core network and (at the front end) to the Internet through the wireless LAN access points. The GANC includes an integral security gateway (SEGW) through which the GAN phone securely connects.
  Figure 1. Proposed system architecture for GAN
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All GAN phones must conform to the 3GPP standards and deliver reliable performance. Conformance tests focus primarily on discovery and registration, ensuring crucial interoperability between GAN devices and the SEGW and GANC, and several handover-related tests are included as well. No mandates exist, however, for measuring such things as the performance of data services running simultaneously, dual transfer mode performance when a data session is interrupted by a voice call, or the performance of services that take advantage of the higher bandwidth offered by GAN. You’ll need to develop your own strategy for determining application performance, data throughput, and voice quality.

The 8960 running the E6701A Lab Application, with GAN emulation capability, is a valuable tool that can help you verify performance in all these areas using realistic test scenarios.

Complex radio environment

Handling the simultaneous radio environments is perhaps the greatest challenge for a GAN phone. Although there are several modes in which GAN-enabled phones can operate, the most common is GAN-preferred. In this mode the phone always chooses the GAN over a GERAN or UTRAN unless no GAN signal is available; only then does it transfer to the alternative networks.

The GAN phone must be able to demonstrate that it can detect both GAN and GERAN/UTRAN services and connect to both, handing in and out of each service while an active call or active data session is in progress. To do this, the phone must provide adjacent cell information; that is, it must measure and report the suitability of adjacent cells. The GANC is configured to emulate a GERAN cell so that it can be identified by the phone. Figure 2 shows how this is done using the 8960. Note that the GANC is required to indicate its capabilities—for attach/detach, GPRS availability, and Dual Transfer Mode support in this case. The GAN phone must likewise indicate its capabilities.

  Figure 2. GANC emulation of a GERAN
cell using the Agilent 8960
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When the GAN phone discovers a GAN cell, it establishes a preference for that cell over others by reporting the GAN cell’s power at maximum. In contrast, traditional cell selection methods generally look for the cell that actually has the highest power as well as low interference. Despite the phone’s preference for the GAN cell, however, it must still continue to measure adjacent GERAN and UTRAN cells, in case GAN coverage is lost. A GAN measurement report indicating GERAN/UTRAN coverage is shown in Figure 3.

  Figure 3. Even when a mobile phone is connected
to the GAN, it still measures adjacent
GERAN/UTRAN cells.
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Other challenges

Other challenges for a GAN phone are presented by the voice and data services. In a GAN system, voice is sent using IP packets that contain encapsulated, GSM-encoded voice information. That means GAN must deal with issues similar to those in a VoIP network: delay, latency, lost packets, dropped packets, reordering of packets, and so on. For example, when GAN changes codec rate to protect the voice under varying RF conditions, it bases the change on the number of lost packets—not on power or interference levels, as is the case in the GERAN. Voice quality testing is important to ensure a suitable user experience with GAN.

Similarly, data throughput testing is required. With multiple applications such as music, video, web browsing, and SMS or MMS running simultaneously, the phone has to do more things at once, which entails prioritizing and executing functions quickly. Peak processor usage is already a common source of problems in mobile phones, and GAN only adds to the burden. As processor speed improves, GAN data rates will increase and are expected to surpass HSPA. Data throughput testing can tell you how well your phone is performing under all this pressure.

Battery life

Battery life is another factor to consider. A typical GSM phone has 5-6 hours of calling time, and a WCDMA phone about half of that. A WLAN phone has even less calling time, because WLAN standards were not written for small portable devices with very small batteries.

These figures are obviously not good enough for a GAN phone intended to replace all of a user’s mobile and fixed communication devices. Moreover, the GAN phone has to monitor not just one network, but the GERAN, UTRAN and GAN, causing even more drain on the battery. Adequate battery life is crucial to the success of a GAN phone. The 8960 used in conjunction with Agilent’s Wireless Test Manager, mobile communications DC source, and Device Characterization Software makes a system for measuring battery current drain and analyzing the impact at key usage points.

As the demand for GAN-compatible phones grows, you’ll want to be certain that your design can keep up with the technology. The 8960 is ready to help you meet the challenge.

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