Utility Of Signal To Silence Ratio As A Predictive Tool For Enhancing Cross-layer Multimedia Protocols †ϒ Shirish S. Karande, Kiran Misra, Utpal Parrikar and Hayder Radha Department of Electrical & Computer Engineering / 2120 Engineering Building Michigan State University, East Lansing, MI 48824 USA {karandes, misrakir, prabhupa, radha}@egr.msu.edu Abstract – Wireless multimedia applications can benefit significantly by employing cross-layer protocols that recover information from corrupted packets. The performance of such protocols can be improved with the help of Receiver- side Channel State Information (CSI). However, in practice, the bits observed at the link-level do not have an inherent soft-information associated with them. Hence standard physical-layer link quality indications (e.g. the signal strength of each individual bit) cannot be used as CSI. Due to the lack of a practical predictive tool, many standard optimiza- tions for capacity planning, soft-decoding, rate control etc., cannot be practically employed with the considered cross- layer protocols. In this paper we address this important engineering problem. In practice, 802.11b radio devices are capable of measuring the signal power for the first few microseconds ( s μ ) of each packet reception. This measure- ment can be used to associate a coarse Signal-to-Silence (SSR) ratio with each individual packet. This work, investi- gates the practical predictive utility of such coarse measurements. We show that SSRs can be used to provide mean- ingful CSI with a reasonably link/infrastructure invariant model training. Depending upon the specific application, the empirically determined correlation between the SSR indications and the Bit Error Rate (BER) can be utilized in a realtime or non-realtime fashion. We consider two sample applications to illustrate the practical predictive utility of SSRs: (a) We show that SSRs can be used for cross-layer network planning. (b) As the primary contribution of this work, we show that SSRs can be used to provide realtime CSI to improve the error-recovery performance of cross- layer Forward Error Correction (FEC) schemes, especially under dynamic channel conditions. H.264 based simula- tions are used to exhibit the implied improvements for multimedia applications. Index Terms- channel capacity, channel coding, video coding, wireless networks, channel modeling † Part of this work has been presented as [21]-[22]. ϒ This work was supported in part by NSF Award CCF-0515253, NSF Award CNS-0430436, MEDC Grant GR-296, and unrestricted gift from Microsoft Research.