## 1 Introduction  
Despite increases in capacity, broadband wireless systems still suffer from limitations in bandwidth capacity [1], leading to congestion at a base-station's (BS's) output buffer to its mobile stations (MSs). To reduce the risk of buffer overflow, this paper proposes a customized packet-scheduling regime for data-partitioned video streams. However, taking measures to reduce the impact of congestion at a BS buffer is only one part of the story of how to achieve resilient video streaming over wireless links, which are prone to error bursts [2], leading to a lack of synchronization between video encoders and decoders. In fact, the proposed packet-scheduling regime takes place within the context of a video streaming system that makes use of two measures to counteract the impact of errors: (1) source-coded error resilience [3], _i.e._, within the video codec, in the form of data partitioning [4]; and (2) channel-coded adaptive Forward Error Correction (FEC) combined with error-control signaling [5]. However, these measures are powerless against packet drops through buffer overflow. Unfortunately, due to the predictive nature of video coding [6], most packet losses also have an effect that extends in time until the decoder is reset (intra refreshed). One source-coded error resilience scheme, data partitioning, in its current form, is vulnerable to congestion due to the number of small packets that are produced. Data partitioning, which is a form of layered error resilience, can provide graceful degradation of video quality and, as such, has found an application in mobile video streaming [4]. In an H.264/Advanced Video Coding (AVC) codec [7], when data partitioning is enabled, every slice is divided into three separate partitions: partition-A has the most important data, including motion vectors (MVs); partition-B contains intra coefficients; and partition-C contains inter coefficients, the least important data in terms of reconstructing a video frame at the decoder. These data are packed into three types of Network Abstraction Layer units (NALUs) output by the codec. The importance of each NALU-bearing packet is identified in the NALU header. Though it is possible to aggregate (or segment) NALUs [8] before encapsulation in Internet Protocol (IP)/User Datagram Protocol (UDP)/Real-time Transport Protocol (RTP) packets, when data partitioning is in use, this would be to neglect the advantages of retaining smaller partition-A and -B bearing packets because smaller packets have a lower probability of channel error. Therefore, in this paper each NALU is assigned to its own packet, prior to the addition of network protocol headers. To reduce the risk of buffer overflow for data-partitioned video streams, this paper proposes a packet-scheduling method, which can work in addition to other channel error protection methods, one of which is the adaptive rateless channel coding that is described in Section 2. Packet-scheduling schemes, which are referred to in Section 3, act irrespective of physical-layer (PHY-layer) data scheduling and may be independent of the data-link Medium Access Control (MAC) sub-layer (though some other schemes do indeed intervene at the MAC sub-layer). The proposed packet-scheduling method works by smoothing the packet-scheduling times across one or more video frame intervals,according to allowable latency. Packets are allocated a scheduling time for output to a BS buffer in proportion to their size. As such, the scheduling method is relatively simple to implement, which is one of its attractions owing to the need to reduce latency for interactive services such as mobile video-conferencing and video telephony. In the paper, the potential value of the application-layer (AL) scheduling approach is demonstrated in simulations that take account of PHY-layer packetization and scheduling. The paper also comments on video-content-dependent packetization issues as an aid to others planning AL packet scheduling or video-smoothing algorithms [9].