Covilhã, 30 June Atílio Gameiro Page 1 The information in this document is provided as is and no guarantee or warranty is given that the information is

Covilhã, 30 June Atílio Gameiro Page 1

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.

project confidential

CROSSNET – IT AVEIRO CROSSNET – IT AVEIRO PlansPlans




IT- Aveiro Involvement in W2

Main Involvement – Task2– MAC definition and Cross-layer design

Objectives of the task

– 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:– 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




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




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 – Bandwidth allocation (bandwidth: misnomer for data rate)– Delay bound– Jitter bound (Jitter = variation in delay)– Loss rate




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.




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




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




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?




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

Scheduler

PHY layer

Upper layersRead QoS requirements / packet attributes, get forwarding policies




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




QoS and Scheduling V

To provide QoS in packet switched wireless networks a cross-layer design approach is needed to design schedulers– Service requirements have to be taken into account– Physical layer information needs also to be considered

Scheduler

PHY layer

Upper layers

Get Channel State Information

Read QoS requirements / packet atributes, get forwarding policies




Cross-Layer Schemes - Concept

Concept

RRM

PHY layer

L3

Channel estimation

Provide CSI

QoS requirements

Read QoS requirements / packet atributes

Takes decisions in order to optimize some cost / revenue function f(QoS,CSI)




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




Cross Layer

Work in paralel with algorithm development– Impact on architectures

• Signalling required, overhead




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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Covilhã, 30 June Atílio Gameiro Page 1 The information in this document is provided as is and no guarantee or warranty is given that the information is