Voice-Aware Radio Resource Management

The concept of voice-aware radio resource management is to build upon the measurements used for determining network capacity and topology, and integrate them into the decision-making process for dynamic microcell architectures.

Basic radio resource management is more concerned with establishing minimum levels of coverage while avoiding interference from neighboring access points and surrounding devices. This is more suitable for data networks. Voice-aware RRM shifts the focus towards providing a more consistent coverage that voice needs, often adjusting the nature of the RRM process to avoid destroying active voice calls. Voice-aware RRM is a crucial leg of voice mobility deployments based on microcell technology. (Layered or virtualized deployments do not use the same type of voice-aware RRM, as they have different means of ensuring high voice quality and available resources.)

The first aspect of voice-aware radio resource management is ironically to disable radio resource management. Radio resource management systems work by the access points performing scanning functions, rather similar to those performed by clients when trying to hand off. The access point halts service on a channel, and then exits the channel for a short amount of time to scan the other channels to determine the power levels, identities, and capacities of neighboring access points. These neighboring access points may be part of the same network, or may belong to other interests and other networks. Unlike with client scanning, in which the client can go into power save to inform the access point to buffer frames, however, access point scanning has no good way for clients to be told to buffer frames. Moreover, whereas client scanning can go off channel between the packets of the voice call, only to return when the next packet is ready, an access point with multiple voice calls will likely not have any available time to scan in a meaningful way. In these cases, scanning needs to be disabled. In RRM schemes without voice-aware services, administrators often have to disable RRM by hand, thus nullifying the RRM benefits for the entire network. Voice-aware RRM, however, has the capability to turn off scanning on a temporary basis for each access point, when the access point is carrying voice traffic. There are unfortunately two downsides to this. The first is that RRM is necessary for voice networks to ensure that coverage holes are filled and that the network adapts to varying density. Disabling the scanning portion of RRM disables RRM, effectively, and so voice-aware RRM scanning works best when each given access point does not carry voice traffic for uninterrupted periods of time. Second, RRM scanning is usually the same process by which the access points scan for wireless security problems, such as rogue access points and various i ntrusions. Disabling scanning in the presence of voice leaves access points with voice more vulnerable, which is unacceptable for voice mobility deployments. Here, the solution is to deploy dedicated air monitors, either as additional access points from the same network vendor, but set to monitor rather than serve, or from a dedicated WLAN security monitoring vendor, as an independent overlay solution.

The second aspect of voice-aware radio resource management is in using coverage hole detection and repair parameters that are more conservative. Although doing so increases the likelihood of co-channel interference, which can have a strong downside to voice mobility networks as the network scale and density grows, it is necessary to ensure that the radio resource management algorithms for microcells do not leave coverage holes stand by idle. Coverage holes disproportionately affect the quality of voice traffic over data traffic. Increasing the coverage hole parameters ensures that these coverage holes are reduced. Radio resource management techniques often detect the presence of a coverage hole by inferring them from the behavior of a client. RRM assumes that the client is choosing to hand off from an access point when the loss becomes too high. When this assumption is correct, the access point will infer the presence of a coverage hole by noticing when the loss rate for a client increases greatly for extended periods of time. This is used as a trigger that the client must be out of range, and informs the access point to increase its power levels. It is better for voice mobility networks for the coverage levels to be increased prior to the voice mobility deployment, and then for the coverage hole detection algorithm to be made less willing to reduce coverage levels. Unfortunately, the coverage hole detection algorithms in RRM schemes are proprietary, and there are no settings that are consistent from vendor to vendor. Consult your microcell wireless network manufacturer for details on how to make the coverage hole detection algorithm be more conservative.

The final aspect of voice-aware RRM is for when proprietary extensions are used by the voice client and are supported by the network. These extensions can provide some benefit to microcell deployments, as they allow the network to alter some of the tuning parameters that clients use to hand off. Unfortunately, the aspects of voice-aware radio resource management trade off between coverage and quality of service, and so operating these networks can become a challenge, especially as the density or proportion of network use of voice increases. Monitoring tools for voice quality are especially important in these networks