Simulating time-varying conditions in a wireless network

Abstract

Time-varying conditions in a wireless network are simulated using an architecture that includes an enclosure for shielding a wireless device under test (“DUT”) from electromagnetic interference, including other wireless devices; and at least one of: (1) a communications traffic generating device operable to generate communications traffic having selected characteristics; and (2) at least one dynamically adjustable attenuator in communication with the wireless device and the traffic generator. Embodiments of the architecture include wireless test equipment for testing operating range, roaming and capacity. The attenuator is used to adjustably attenuate signals between the device and the traffic generator over time during a test, whereby motion of the device is simulated. By connecting multiple access points, each associated with a dynamically adjustable attenuator, it is possible to force the DUT to roam between access points. The communications traffic generating device can be used to vary traffic over time during a test in order to test capacity, prioritization and admission control. For example, the communications traffic generator may include phone and data client emulators which simulate different traffic types that can be independently varied over time during a test.

Description

FIELD OF THE INVENTION [0001] This invention relates generally to the field of test equipment, and more particularly to testing responses to time-varying conditions in a wireless network. BACKGROUND OF THE INVENTION [0002] New wireless technology is being developed and deployed to provide support for voice and multimedia services in both residential and enterprise environments. Wireless Local Area Network (“WLAN”) devices, for example, are being developed in conjunction with IEEE 802.11 standards to support packetized voice communications such as Voice over Internet Protocol (“VoIP”). There are technological hurdles that must be overcome in order to support voice and multimedia on WLANs because the technology was initially designed to support simple data communications. In particular, voice and multimedia applications can be more sensitive to jitter, delay and packet loss than data communications applications. IEEE 802.11 specifies protocols and techniques for overcoming some of the...

AI Technical Summary

Benefits of technology

[0004] In accordance with the invention, technology for simulating time-varying conditions in a wireless network includes an enclosure for shielding a wireless device under test (“DUT”) from electromagnetic interference; a communications traffic generator operable to generate communications test traffic having selected characteristics; and a dynamically adjustable attenuator in communication with the wireless device and the traffic generator, the attenuator being operable to adjustably attenuate signals between the device and the traffic generator over time during a test, whereby motion of the device is simulated. By connecting multiple access points, at least one of which is in communication with a separate dynamically adjustable attenuator, it is possible to force the DUT to roam between access points. Further, phone and data client emulators can be employed to simulate support of variable numbers of client devices which can be changed during a test, including individual motions of those devices.

[0005] One advantage of the invention is the ability to simulate motion in order to test range. Manually testing response to motion in open-air is time consuming and inaccurate. Further, static tests carried out at a series of distances can be automated, but fail to account for the effects of rate of motion. Hence, the present invention offers the efficiency and accuracy of an automated test and also simulates selectable rates of motion.

[0006] Another advantage of the invention is the ability to use simulated motion to cause and test roaming. Roaming time is a significant metric to voice communications because each time a phone roams it is subjected to a burst of lost packets. In general, bursty packet loss has a more deleterious effect on voice quality than uniform, distributed packet loss because CODECS are capable of correcting or regenerating limited numbers of lost packets in a given portion of a transmission. This is significant because in WiFi networks where the density of access points is relatively high roaming can occur every few seconds at normal walking velocity, potentially resulting in unacceptable performance. In order to reduce the deleterious effects of bursty packet loss caused by roaming the IEEE and the WiFi Alliance may specify a 50-msec limit on roaming time. To meet the 50-mSec roaming time requirement, the IEEE is developing a new standard, 802.11r, which will define a fast roaming algorithm. 802.11r in turn relies on another new standard, 802.11k, which helps the phone discover neighboring access points and query their status in preparation for a fast roam. 802.11r also relies on the security standard, 802.11i, to support pre-authentication so that the lengthy authentication process can be avoided during a fast roam. The present invention provides an efficient, accurate and automated technology for testing both equipment and communications protocols.

[0007] Yet another advantage of the invention is the ability to simulate a load of both data and voice clients, and to change the number of clients during a test in order to test capacity, e.g., access point capacity. One aspect of the protocols developed to support voice communications on WLANs is implementation of Quality of Service (“QoS”) controls. QoS controls include admission control protocols to limit the number of simultaneous calls though a single access point, and priority protocols to process packets according to assigned levels of priority. For example, an admission control protocol may prevent admittance of a new voice or data client if there is insufficient bandwidth to support that new client. Similarly, in the case of packet forwarding and drop decisions preference may be given to voice packets because voice applications tend to be more susceptible to packet loss, delay and jitter. By simulating selectable numbers of voice and data clients, and changing the number of clients during a test, the invention advantageously facilitates testing such protocols and the devices in which the protocols are implemented.

Problems solved by technology

Manually testing response to motion in open-air is time consuming and inaccurate.

Further, static tests carried out at a series of distances can be automated, but fail to account for the effects of rate of motion.

In general, bursty packet loss has a more deleterious effect on voice quality than uniform, distributed packet loss because CODECS are capable of correcting or regenerating limited numbers of lost packets in a given portion of a transmission.

This is significant because in WiFi networks where the density of access points is relatively high roaming can occur every few seconds at normal walking velocity, potentially resulting in unacceptable performance.

Similarly, in the case of packet forwarding and drop decisions preference may be given to voice packets because voice applications tend to be more susceptible to packet loss, delay and jitter.

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