## 4 Methodology  
The error and congestion resilient video streaming scheme is demonstrated for IEEE 802.16, which is the standardized version of WiMAX wireless broadband technology [50]. WiMAX continues to be rolled out in parts of the world that do not benefit from existing wired infrastructures or cellular networks. WiMAX is also cost effective in rural and suburban areas in some developed countries. It is designed to provide effective transmission at a cell's edge by the allocation to a mobile user of sub-channels with separated frequencies to reduce co-channel interference. The transition to the higher data rates of IEEE 802.16 m [51] indicates the technological route by which WiMAX will respond to the technological advances of its competitors, especially LTE. However, we modeled version IEEE 802.16e-2005 (mobile WiMAX), of which IEEE 802.16-2009 is an improved version [52], as this is backwards compatible with fixed WiMAX (IEEE Project P802.16d), which still remains the most widely deployed version of WiMAX. Time Division Duplex (TDD) (Figure 1) and effective scheduling of time slots between MSs through TDMA (not to be confused with AL packet scheduling as described in this paper) increases spectral efficiency. Figure 2 provides a closer look at the frame and sub-frame structure within which are contained per-MS data bursts. (For simplicity, the MS to BS sub-frame structure is illustrated.) Within each data burst are WiMAX packets, which at the MAC sub-layer are called Protocol Data Units (PDUs) and consist of a MAC header, MAC Service Data Unit (MSDU), and a CRC, as shown in Figure 3. An MSDU corresponds to a packet passed to the MAC layer from higher layers in the protocol stack, most immediately from the transport layer. It consists of an IP packet with typical IP/UDP/RTP headers attached, though, in practice, packet header compression is normally employed over wireless links in order to reduce the heard overhead. The payload of this network packet will contain an NALU and additional rateless channel coding data added at the application layer, as described below.  
Figure 1: Worldwide Interoperability for Microwave Access (WiMAX) frame divided into two sub-frames separated by a guard interval, namely the downlink (DL) sub-frame from a base-station (BS) to mobile stations (MSs), and an uplink (UL) sub-frame following in time from the MSs to the BS. The time direction consists of successive Orthogonal Frequency-Division Multiple Access (OFDMA) symbols, while the frequency direction is assigned to data bursts on a per-MS basis (OFDMA is a refinement of Orthogonal Frequency Division Multiplexing (OFDM) that in mobile WiMAX allows more flexible sub-channelization in the frequency dimension). (Additional preamble, burst mapping, and ranging signaling is also present. For more details refer to [50].)  
As a whole, the WiMAX video-streaming scheme, Figure 4, comprises three components: (1) source-coded data partitioning of the video bitstream; (2) adaptive rateless channel coding; and (3) AL packet scheduling. This Section now describes these three components. As analyzed in Section 1, the first two of these are error resilience measures, while the third, supports congestion resilience. Therefore, the following description of the methodology is split into error resilience and congestion resilience. The  
Figure 3: WiMAX burst structure showing MAC Service Data Unit (MSDU) packets. The DL-Burst is similar, except that there are additional headers included prior to the MAC PDUs. (PAD = padding, as the PDU size is variable.)  
Figure 2: Sub-frame structure showing per-MS data bursts (numbered from 1 to z). (FCH = frame control header, RTG = receive/transmit transition gap, TTG = transmit/receive transition gap.)  
error-resilience description includes the way that the source packets (NALUs) are mapped to the underlying broadband wireless MAC and PHY layers.