MM000888 1 Header Detection to Improve Multimedia Quality over Wireless Networks Syed A Khayam Shirish Karande Muhammad U Ilyas and Hayder Radha Senior Member IEEE Abstract Wireless multimedia studies have revealed that forward error correction FEC on corrupted packets yields better bandwidth utilization and lower delay than retransmissions To facilitate FEC based recovery corrupted packets should not be dropped so that maximum number of packets are relayed to a wireless receiver s FEC decoder Previous studies proposed to mitigate wireless packet drops by a partial checksum that ignored payload errors Such schemes require modifications to both transmitters and receivers and incur packet losses due to header errors In this paper we introduce a receiver based scheme which uses the history of active multimedia sessions to detect transmitted values of corrupted packet headers thereby improving wireless multimedia throughput Header detection is posed as the decision theoretic problem of multihypothesis detection of known parameters in noise Performance of the proposed scheme is evaluated using trace driven video simulations on an 802 11b local area network We show that header detection with application layer FEC provides significant throughput and video quality improvements over the conventional UDP IP 802 11 protocol stack Index Terms Communication Systems Multimedia Communication Video Signal Processing Wireless LAN I INTRODUCTION Wireless communication channels incur unpredictable and time varying packet losses due to fading interference and mobility This data loss is particularly detrimental for realtime communications whose delay constraints generally do not allow retransmission based recovery of lost packets To combat wireless errors and losses emerging multimedia standards have introduced enhanced error resilience and concealment features e g slices in JVT H 264 1 and reversible VLC in MPEG 4 2 For an error resilient application distortion in multimedia quality can be decreased by reducing the amount of data loss at a wireless receiver i e by relaying maximum number of error free and corrupted packets to the multimedia application It is then up to the application to drop or retain the corrupted packets Due to the high error rates of wireless media many errors are not corrected by the physical layer These errors cause checksum failures at higher layers consequently leading to a significant number of packet drops on a link employing a conventional e g TCP UDP IP protocol stack Previous wire less multimedia studies proposed to reduce packet drops by employing a partial checksum which only covers packets headers while payload errors are ignored 3 9 Payload errors are subsequently corrected using forward error correction FEC at the application layer It has been shown that partial protection with FEC requires much lesser FEC redundancy than a conventional protocol stack that drops corrupted packets However schemes using partial checksum incur packet drops due to header errors especially at high data rates Also support of partial checksum requires changes to the standard protocols at the multimedia transmitter and or intermediate network nodes In many realistic scenarios modifications to multimedia servers and intermediate nodes cannot be dictated by the end receivers1 In this paper we propose a receiver based decisiontheoretic approach to relay packets with corrupted headers to wireless multimedia receivers The proposed technique requires no modifications to wireless transmitters and intermediate nodes and only minor modifications are required at the receiver We identify critical header fields CHF that can uniquely differentiate multimedia sessions at a wireless receiver Under the proposed technique wireless multimedia receivers maintain an a priori CHF histogram from previously received error free packets We also propose and employ a likelihood function based on the sample space of the a priori distribution When a corrupted packet is received the a priori distribution and the likelihood function are used to compute the a posteriori distribution Correcting the CHF then reduces to the decision theoretic problem of multihypothesis detection of known parameters in noise 10 in short referred to as header detection in this work We demonstrate the efficacy of the proposed scheme by trace driven video simulations at different data rates and for varying number of video sessions over an 802 11b LAN We show that header detection has high accuracy and negligible false positives After header detection we use FEC 11 at the application layer to correct the corrupted data We show that header detection requires much lesser FEC redundancy than the 802 11b protocol stack We also show that for fixed FEC parameters header detection provides significantly better multimedia quality than the 802 11b protocol stack The rest of this paper is organized as follows Section II details our proposed approach and its variants Section III de Manuscript received February 18 2005 S A Khayam S Karande M U Ilyas and H Radha are with the Department of Electrical and Computer Engineering ECE Michigan State University MSU East Lansing MI 48824 USA e mail khayamsy karandes ilyasmuh radha egr msu edu 1 For instance public domain video web casting is oblivious of the end link communication media and often identical multicast sessions serve heterogeneous users with wired as well as wireless end links MM000888 2 scribes the experimental setup Sections IV V and VI respectively evaluate the throughput FEC and video performances of the proposed scheme Start Receive packet II THE HEADER DETECTION METHODOLOGY The main objective of header detection is to relay maximum number of error free and corrupted packets to a wireless receiver s application layer In this paper we use 802 11b wireless LANs as our performance evaluation test bed We start by identifying critical header fields CHF that can uniquely classify a multimedia session at the receiver and are not liable to change during a multimedia transmission These fields are destination MAC address source and destination IP addresses and source and destination ports More fields can be concatenated to these CHF without any modifications to the proposed methodology Let W denote the CHF of a received packet and let X1 X 2 Xn be the set of all correctly received CHF of the last E packets That is each Xi for 1 i n n represents the CHF of session i The set Xi the set i 1 of all bins of the