Multimedia Wireless Communication Networks. Architecture and resource management

Transcription

1 Multimedia Wireless Communication Networks Architecture and resource management

2 Multimedia Wireless Networks and Applications High data transmission rate Adapt to high mobility Wide coverage area and seamless roaming among different systems High capacity and low bit cost Efficient resource control to provide QoS for Multimedia Applications Dynamic spectrum assignment Software radio and smart radio that can accommodate multiple systems

3 Access Technology for Multimedia Support LAN access: Ethernet, Fast Ethernet For home user to have high Internet connection: solve the last mile problem. Digital Subscriber Line (DSL) Use regular phone line to achieve high speeds (e.g 1.5Mbps) Cable modem Use TV cable to achieve high speeds. 3G wireless cellular network 144k-384 kbps for high mobility users with wide coverage and, 2Mbps for low mobility users with local coverage. Support of multimedia services a requirement High data transmission rate: 10-20Mbit/s for 4G cellular system and higher rate for WLAN (IEEE b, IEEE a)

4 Interworking Between Different Access Systems

5 Issues of QoS User s expectations and challenges Speed (throughput, bit rate) : Variable link bandwidth due to statistical multiplexing and changing channel conditions. Accuracy (error rate, loss rate): Packet losses due to RF environment and buffer overflow. Latency : Variable queueing delay due to scheduling and RF condition. Availability (blocking, setup time): Control plane signaling and mobile processor capacity. Reliability (call dropping, out rage): Mobility management and network restoration strategy.

6 QoS Engineering for Multimedia Wireless Network Traffic characterization voice, web-browsing, WAP, streaming video Admission control and network resource allocation Server/link scheduling and traffic policing/shaping QoS mapping between networks and between layers Service level agreements and policy management Radio channel selection and bandwidth allocation RF power control and rate control among users RF resource set-up and tear-down strategies Traffic engineering and network design

7 Traffic Management What is traffic management? It is a set of policies and mechanisms that allow a network to efficiently satisfy a diverse range of service requests. It includes admission control, scheduling, buffer management and flow control, which are important to provide QoS.

8 Admission Control To adapt to the multimedia applications in the wireless environment, the admission control must own following attributes: Stability of the provided QoS (blocking/ber/delay) Adaptability in the varying wireless channel condition Ability to be reconfigured and extended for new services Simplicity and minimization of processing time

9 Parameter-Based Admission Control (PBAC) PBAC schemes use a priori traffic specification to determine the parameters of deterministic or stochastic models. Deterministic models, including the peak-rate and worstcase models, reserve bandwidth to meet even the most critical conditions, which results in low bandwidth utilization. Stochastic models utilize the concept of equivalent bandwidth that is based on the statistic approximation of incoming traffic, and ensure that the outrage probability is below the defined threshold. Stochastic models can achieve high bandwidth utilization.

10 Measurement-Based Admission Control (MBAC) MBAC relies on the measurement of actual traffic load and QoS performance in making admission decisions. MBAC provides higher bandwidth utilization and is more suitable to support real-time applications Admission decisions are made by Measuring the actual traffic load of existing flows Using a priori admission policy to determine whether the new flow is admitted or rejected

11 Scheduling Schemes Why do we need scheduler in networks? Various multimedia applications emerge with diverse QoS requirements, e.g. the voice and web browsing have different throughput and delay requirements. To support different QoS requirements, scheduler operates among sessions to ensure that proper resource is allocated for sessions with their QoS requirements.

12 Fair Scheduling Scheduling discipline allocates a resource Intuitively each connection gets no more than what it wants the excess, if any, is equally shared provides protection traffic hogs cannot overrun others automatically builds firewalls around heavy users

13 Scheduling in Wireless Multimedia Networks Various multimedia applications have diverse QoS requirements, e.g. the voice and web browsing have different throughput and delay requirements. The existing wireline scheduling schemes may not be applied to the wireless networks due to the time-varying and location-dependent wireless channels Extra information must be exchanged between mobile station and base station to make the scheduling possible The scheduling scheme must be effective to save the limited battery life of mobile station Handoff and bursty errors could result in unfairness The interference must be considered in CDMA system to meet the required SIR when multiple users are scheduled

14 Components of Scheduler Channel State Monitor/Predictor Session 1 Session 2 Scheduler Transceiver Session N Compensation Ideal Model

15 Components of Scheduler An error free ideal model that describe how the algorithm provides service with error-free channels. A compensation model that provide fairness among sessions depending on their class and requirements (e.g. delay-sensitive interactive applications). Separate packet queues for different sessions that can support, e.g. delaysensitive or error-sensitive. Channel state predictor that detects the channel conditions of all backlogged sessions.

16 Scheduler of TDMA Wireless System Session 1 Time Slot Session 2 Scheduler Session 3 Only a single user is scheduled for transmission in a time-slot.

17 Scheduler of CDMA Wireless System Time Slot Scheduled Transmit Rate Session 1 Session 2 Scheduler Session 3 Multiple users are scheduled for transmission at a time-slot.

18 CDMA Scheduling Algorithms -- Compensation procedure C Assigned Power Index C Power Index Capacity Assigned Power Index The error-free ideal system Iteratively distribute the system power index to obtain high resource utilization Compensated Power Index Given up rate lagging leading leading lagging lagging leading Make the adjustment to achieve fairness

19 Example: Influence of Wireless Environment on Video Unreliability: Unlike wired links, wireless channels are more noisy and have fades, making the BER very high, which can have devastating effect on video quality. Bandwidth Fluctuation: Bandwidth fluctuation may be caused when User moves from WLAN to WWAN (Corresponding bandwidth changes from Mb/s to kb/s) Handoff happens, the new cell may not have enough resource to support the previous service quality interference varies The distance to the base station changes Heterogeneity: In the multicast case, all receivers are forced to receive the same content despite their channel qualities, processing power etc. That means multicast service loses the flexibility of QoS negotiation.

20 Adaptive Wireless Video Transmission Framework The adaptive framework consists of three basic components: Scalable video coding Network-aware end system Adaptive service Sender Side Receiver Side Scablable Video Encoder Scalable Video Representations Scablable Video Encoder Network-aware End System Adaptive Service (Application-aware Networks) Network-aware End System

21 Scalable Video Coding Following example encodes the raw video sequence into three layers: one base layer and two enhancement layer. The base layer can be can be independently decoded and it provides basic video quality. The enhancement layers can only be decoded together with the base layer and they further refine the quality of the base layer. Layered Codec Layer 0 + Layer 2 Layer k/s Decoder 256k/s Decoder 1Mb/s Decoder

22 Network-aware End System and Adaptive Service Network-aware end system consists of two elements: network monitoring and adaptation. Network monitoring Network monitoring aims to collect information about network status, like the available bandwidth and BER. This information could be sent to the end system from the base station. Adaptation By the known network information, the end system may choose what layers video is to be transmitted since multiple enhancement layers in the high BER condition can only result in worse video quality. The objective of adaptive services is to achieve smooth change of perceptual quality in the presence of bandwidth fluctuations in wireless channels. Reserve a minimum bandwidth to meet the demand of the base layer. As a result, the perceptual quality can always be achieved at an acceptable level. Adapt the enhancement layers based on the available bandwidth and the fairness policy. In other words, it scales the video streams based on resource availability and the fairness policy.