Transcript Why Cross-layer - Quality of Service I

CROSSNET – IT AVEIRO
Plans
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IT- Aveiro Involvement in W2
 Main Involvement – Task2
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MAC definition and Cross-layer design
 Objectives of the task
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1) Identification and transport of relevant cross-layer information (CLI)
2) Definition of a cross-layer (CL) architecture framework
3) Cross-layer strategies between PHY and MAC/RRM strategies
 The following aspects / algorithms will be addressed:
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Enhancement of distributed MAC/scheduling strategies so as to make extensive use of
CL I
Exploitation of multi-user detection schemes, multipacket reception capabilities and
space/components vs MAC/scheduling schemes
Conception of self adaptative MAC/scheduling functionalities able to self-adjust to
time-varying availability or changes in CSI or resources available.
Work will resort to simulations and analysis
Simulations: system level simulator developed under the framework of other projects
will be upgraded
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Why Cross –layer ?
 Main characteristic of wireless networks  randomness
– Network topology is not fixed (users move, enter, leave the
network...)
– Link characteristics vary with time , position
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Why Cross-layer - Quality of Service I
 Trends in telecommunication networks
– Provide end to end quality of service
• different traffic types get different levels of network service
 Characteristics used for QoS
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Bandwidth allocation (bandwidth: misnomer for data rate)
Delay bound
Jitter bound (Jitter = variation in delay)
Loss rate
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Why Cross-layer - Quality of service II
 What are the issues associated with QoS provision?
– Isolation / sharing
• Provision of individualized quality communication guarantees facilitated if different
flows are isolated
Isolation is inherent in circuit switched networks
but
in the current Internet (IP) all flows share all resources at the packet level.
• Ensuring QoS requires isolation
• However too much isolation lower the resource utilization
 To support QoS in IP network, need to emulate the traffic isolation while
sharing resources at the packet level
– Delay bounds
• IntServ requires scheduling to support delay bounds.
• Delay bounds reflect the trade-off between isolation and sharing.
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Why Cross-layer - Quality of Service III
 Provision of QoS services generally involve putting in place
mechanisms that ensure
– Fairness - access to network resources
– Isolation - protection from excessive usage of network resources
from other users
Subject to general goals of
– Efficiency
– Complexity
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Why cross-layer - Quality of Service V
 To reach these goals in packet switched networks requires
collaboration of many components
– Admission Control
– Scheduling
•
Which packet gets transmitted first on the output link significantly
impacts QoS guarantees for different flows.
– Scheduling affects delay, jitter and loss rate.
– Allows protection against misbehaving flows.
– Buffer Management
– Congestion Control
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Why Cross-Layer - QoS and Scheduling
 Scheduling is a major component in the QoS scheme
 There are conflicts in a packet switched network between
– The goal of sharing resources
– The need to provide some flow isolation and fairness to guarantee QoS
 Scheduler designed to maximize throughput does not answer these
objectives
 But these goals and implementation problems are not specific of wireless
networks
– also exist in the wired world to fullfill the quest of QoS provision
 Are there solutions that can be imported?
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QoS and scheduling – Wired vs Wireless I
 There are some fundamental difference between wired and
wireless networks
– Wired networks: can assume time-invariant physical links in most
cases
• Packet schedulers use information from the upper layers(QoS
requirements, forwarding policies,…) to decide about which packets
should be transmitted
Upper layers
Read QoS
requirements / packet
attributes, get
forwarding policies
Scheduler
PHY layer
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QoS and Scheduling – Wired vs Wireless II
 What happens with wireless networks?
– Dynamic topology: user moves around, also enter and leave
– Quality of the wireless channel is typically different for different
users, and randomly changes with time (on both slow and fast time
scales).
– Wireless bandwidth is usually a scarce resource that needs to be used
efficiently (can not overprovision the wireless link).
– Excessive amount of interference and higher error rates are typical.
 A scheduling algorithm that does not account for this variability of
the channel will have low efficiency would be for most scenarios
very poor
 wireless networks require scheduling algorithms that use the PHY layer
information
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QoS and Scheduling V
 To provide QoS in packet switched wireless networks a crosslayer design approach is needed to design schedulers
– Service requirements have to be taken into account
– Physical layer information needs also to be considered
Upper layers
Read QoS
requirements /
packet atributes,
get forwarding
policies
Scheduler
Get Channel State
Information
PHY layer
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thereof uses the information as its sole risk and liability.
Cross-Layer Schemes - Concept
 Concept
QoS
requirements
L3
Read QoS
requirements
/ packet
atributes
RRM
Channel
estimation
Provide CSI
Takes decisions in order to
optimize some cost / revenue
function f(QoS,CSI)
PHY layer
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RRM topics to be investigated
 RRM for MIMO systems
 Which RRM
– Scheduling algorithms (ongoing work)
– Joint scheduling / link adaptation and power assignement
 Phase 1
– Consider the DL  centralized architecture
 Phase 2
– Extend to UL
• Investigation of the different approaches
– Centralized vs distributed
– Still open
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Cross Layer
 Work in paralel with algorithm development
– Impact on architectures
• Signalling required, overhead
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Cross Layer
 Past / Current work
– Scheduling algorithms based on priority function involving CSI and
delay
• SISO and MIMO
– MIMO
• Radio resource reuse through beamforming and scheduling
– Joint design of scheduler and link adapatation (modulation and
coding selection) (ongoing)
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The information in this document is provided as is and no guarantee or warranty is given that the information is fit for any particular purpose. The user
thereof uses the information as its sole risk and liability.