Mobility performance testing

EE-Evaluation Engineering, June, 2008 by Richard Lu

The rich availability of Wi-Fi connectivity and the universal demand for constant access to voice and data communications are driving consumer and enterprise demand for converged Wi-Fi/ cellular applications and services. Under the banner of fixed-mobile convergence (FMC), these applications promise better access to voice and data services as well as lower communications costs.

Successful delivery of converged services is based on the assumption that wireless IP networks and 802.1 la/b/g/n devices can deliver the underlying quality of service necessary to guarantee a satisfying end-user experience. Critical FMC performance metrics that directly affect user experience are measured by voice quality, dropped calls, and battery life.

These user-experience metrics are directly influenced by Wi-Fi metrics such as data rate, error rate, packet loss, and roam time, which define mobility performances like range, roaming, and hand-in/hand-out. The increasing adoption and deployment of this technology have created the need for a reliable means to ensure the delivery of carrier-grade voice over Wi-Fi to end users.

As a result, extensive testing is required to guarantee that FMC devices and the networks on which they operate can deliver the necessary performance. For mobility performance testing to be effective from quality, coverage, and cost perspectives, test methodologies must accurately recreate the real world in an efficient, repeatable, cost-effective, and scalable manner.

What Is Fixed-Mobile Convergence?

FMC means different things to different groups. For end users, it is the promise of quality fixed services and applications of voice, video, and data being delivered seamlessly over mobile wireless networks to handsets or endpoint devices. For infrastructure vendors, FMC represents a large commercial opportunity to deliver back-end integration products and services, and for service providers, it is an opportunity to develop additional revenue from existing cellular and Wi-Fi network infrastructure investments. To drive increased adoption by end users, the industry must deliver compelling FMC applications and services beyond what are currently available.

One major benefit that FMC provides is the convenience of having one device and phone number for both the mobile network and the home network. With the voice call seamlessly transferred from the cellular network to the home or corporate network, users enjoy continuous communications and benefits from improved coverage of the Wi-Fi network while reducing cellular minute usage.

Location-independent access to data applications also represents a huge draw for potential users. Whether stationary or mobile in any location covered by a cellular or Wi-Fi network, users will have access to Internet-based applications such as e-mail, Web browsing, and online services like banking, news, and entertainment. This ability to use data applications where and when they want will enable significant improvements in personal and professional productivity.

Consumer Satisfaction

In addition to seamless voice and data communications, sustainable consumer demand for FMC services also will be driven by the capability to provide cost savings not available from alternative Wi-Fi and cellular-only services. Existing cellular services have established user experience expectations that new converged services must meet or exceed. For service providers, this means FMC must deliver carrier-grade voice and data services characterized by:

* Optimal voice quality.

* Few or no dropped calls.

* Reliable and high throughput data connectivity.

* Long handset battery life in the standby and active states.

* Seamless voice and data roaming/handoff.

Wi-Fi Mobility Usage Scenarios

The growth in consumer demand for long-range cellular network services has been primarily driven by improvements in mobile voice services and value-added data services like text messaging and Web access. FMC broadens the range of these services indoors where cellular coverage may be less reliable. By moving coverage onto the Wi-Fi network, users have access to potentially much higher-speed services.

However, this Wi-Fi connectivity must at least sustain the mobility and quality of service that cellular users have come to expect. Additionally, converged Wi-Fi/cellular services must support the same or better quality voice and data services while the user is in motion and transferring among the networks. This mobility service requires adequate performance in three key usage scenarios: Wi-Fi range, Wi-Fi roaming, and hand-in/hand-out network handover.

Wi-Fi range, or coverage, is defined as quality voice and data services while the user moves closer to and away from a Wi-Fi Access Point (AP) and is a significant measure of Wi-Fi performance. In contrast to cellular technology, Wi-Fi technology varies the transmission data rate to minimize packet errors.

A Wi-Fi transmitter on the AP or client uses dynamic rate adaptation algorithms to control the transmission data rate on a packet-by-packet basis. These algorithms consider many different network and environmental variables including receive signal strength and packet error rate in deciding to increase or decrease the transmission rate.