Saturday, April 30, 2011

STATE-OF-THE-ART RESEARCH | Multimedia over Mobile WiMAX

Generally, real-time multimedia streaming poses significant challenges in wireless networks due to the time-varying nature of wireless channels, limited bandwidth, channel state fluctuation, inevitable bit error and packet loss, ambient noise, and interferences. Many solutions have been proposed to deal with the challenges for real-time media streaming over generic wireless networks. Research focusing on network resource allocation such as proposed effective solutions for improving performance of delay sensitive multimedia streaming over wireless local area networks (WLANs). These solutions used different error resilient protection techniques such as packetization and retransmissions to different media quality layers to achieve best effort multimedia quality with rate or delay constraints. Efficient network resource allocation problem as joint optimal selection of transmission strategies across PHY, MAC, and APP layers, which maximized multimedia quality or perceived peak signal noise ratio (PSNR) subject to rate and delay constraint. This approach to determine optimal cross-layer strategies based on classification and machine learning. Optimal MAC layer retry limits were predicted for various video packets transmitted over 802.11a WLANs, according to the perception importance of each video packet and current channel conditions. The unicast and multicast video streaming optimization problems over WLANs were addressed, where hybrid automatic repeat request (ARQ) combining PHY layer forward error correction (FEC) and link layer retransmission were described for unicast flows, and the multicast optimization problem was solved via combining progressive source coding and low layer FEC. Another hybrid ARQ scheme combing Reed–Solomon (RS) coding and rate compatible punctured convolution (RCPC) coding for H.263 coded wireless video streaming was proposed.
Unfortunately, cross-layer optimization with specific WiMAX consideration for multimedia streaming was not extensively discussed in most of the researches. A queuing-theoretic and optimization-based model for radio resource management in IEEE 802.16-based multiservice broadband wireless access (BWA) networks was proposed. Joint bandwidth allocation (BA) and connection admission control (CAC) were performed with packet level and connection level QoS consideration. They further presented the architecture for integrating hot spot 802.11 WLANs with 802.16 based multihop wireless mesh infrastructure to relay WLAN traffic to Internet. In that approach, the bandwidth allocation was presented with a bargaining game formulation for fair resource allocation, and an admission control policy was proposed to maximize the utilities for different types of connections. Via simulation, the effectiveness of rtPS, nrtPS, and BE in managing traffic sources, and the results highlighted that the rtPS scheduling service was a very robust scheduling service for meeting the delay requirements of multimedia applications.Addressed resource allocation problems regarding dynamic subcarrier allocation, adaptive power allocation, CAC, and capacity planning in OFDMA wireless metropolitan areas networks (WMAN). Research in Ref. [18] proposed an adaptive bandwidth allocation and admission control scheme for polling service (PS) in an IEEE 802.16-based WMAN. A noncooperative game was proposed, admission control policy was described, and the solution was determined by the Nash equilibrium for the amount of bandwidth allocated to a new connection, ensuring QoS for all connections in the system. Focused on scheduling and resource allocation in a cross-layer fashion. The principles of joint scheduling and resource allocation for IEEE 802.16 operating in adaptive modulation coding (AMC) mode were described, and the critical roles played by physical layer considerations, especially inter-cell interference estimation and channel state awareness were discussed. However, those mentioned researches focused on binary data transmission in mobile WiMAX, and transmission strategy optimization for multimedia content was not fully considered.Studied the performance of voice packet transmissions and BS resource utilization using the three types of scheduling services in IEEE 802.16-based backhaul networks. They demonstrated that while the UGS achieves the best latency performance, the rtPS service could utilize the BS resource more efficiently and flexibly, trading-off between packet transmission performance and BS resource allocation efficiency. According to their studies, the appropriate choice of the frame size was important in both the rtPS and ertPS services to reduce delay and packet loss. Similar research regarding VoIP over WiMAX was found. However, they specifically considered the characteristics of VoIP. Content-based unequal error protection (UEP) for video/image streaming was not considered. A good scheduling control was the key field to support coexisting real-time and nonreal-time traffic flows in mobile WiMAX. They especially suggested that for H.264/AVC-based scalable video coding, it was crucial to separate different video layer packets into different connections with different treatment of protection and retransmission. However, this was based on the assumption that no adaptive resource allocation exists in each connection, which may cause significant overhead on multiple connections’ management.
Since IEEE 802.16e-based mobile WiMAX is a relatively new development, very few protocol compliant resource allocation strategies with respect to multimedia streaming have been proposed in literature. The challenges for multimedia streaming over WiMAX networks entail the definition of a MAC effectively supporting multimedia streaming while efficiently exploring limited radio resources . The IEEE 802.16e standard already has build-in QoS features to support different classes of services, therefore, the radio resource allocation strategies and the scheduling algorithms for multimedia streaming between BS and SS are left open to specific vendor implementations. On the other hand, most of the previous works regarding wireless multimedia focus on traditional layer based UEP, and inequality between Position and Value (P–V) information has largely been ignored. Detailed description of position and value diversity in multimedia streaming. To sum up, the joint consideration of multimedia content and resource allocation with protocol compliance will provide significant potentials for improving delay sensitive media quality performance over standardized mobile WiMAX.
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