Power Management in SDR

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1 Power Management in SDR Max Robert, Jeffrey H. Reed Mobile and Portable Radio Research Group (MPRG) Virginia Tech September 14, 2004

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Power Management in SDR. Max Robert, Jeffrey H. Reed Mobile and Portable Radio Research Group (MPRG) Virginia Tech September 14, 2004. Overview. Power fundamentals Overview of approaches Current state of technology Power management for SDR Operation states Interface descriptions - PowerPoint PPT Presentation

Transcript of Power Management in SDR

Page 1: Power Management in SDR

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Power Management in SDR

Max Robert, Jeffrey H. ReedMobile and Portable Radio Research Group (MPRG)Virginia TechSeptember 14, 2004

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Overview

Power fundamentals Overview of approaches Current state of technology Power management for SDR

Operation states Interface descriptions

Conclusion

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Power Basics

Terms: α: switching activity C: capacitance V: voltage f: operating frequency

Fixed attributes Switching activity (algorithm-specific) C is fixed

Attributes open to modification V, f

2P CV f

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Software-controlled power

Some attributes are determined at design time and cannot be changed at run-time Compiler optimizations Waveform design

Attributes that can change at runtime Operating voltage Operating frequency Timing control

Thread management in the case of processors Active components

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General Power Management Power management split into three principal

categories Previous work on each section varies in depth

H ardw are

O perating System /Environm ent

Application

- Thread priority a lgorithm s- Dynam ic Voltage Scaling (D VS) a lgorithm s- Dynam ic Frequency Scaling (D FS) a lgorithm s- Policy selection a lgorithm s

- Advanced C onfiguration and Pow er In terface (ACPI)- O perating System Pow er M anagem ent (O SPM )

- M ulti-vo ltage H W (C rusoe)- M ulti-frequency H W (C PU s, FPG As, ASIC s)- F lexib le RF- E ffic ient com pilers- A lternate data flows

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Software-Controlled Attributes

Timing management Thread priority in the case of a GPP or (sometimes) DSP Bus/message management in system

Algorithm may optimize wait times to cluster work for component Voltage and Frequency selection are related

Higher voltage will allow higher frequencies Optimal voltage for frequency not necessarily the best choice

Voltage switching may be slower than frequency switching May desire to maintain operating range for quick response

Active component selection is a subset Set voltage or frequency to zero for that component

Flexible RF Still unclear what attributes of the RF will be software-controlled

Mixer bias, filter BW, others Framework- and application-based strategies need to be sufficiently

flexible to allow smooth integration of flexible RF control

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Application & Hardware

Significant previous research Adaptive management algorithms Advanced power hardware-level power

management techniques Application- and HW-based strategies well

suited for static applications Current way of developing power-saving

strategies Fixed waveform

Can be optimized to specific platform

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Operating System/Environment

Software structure necessary to support power management functionality Standard interface

Switch between different states i.e.: sleep (several levels), active

States not necessarily limited to sleep modes Standard management structure

Maintain state of all devices in system State machine for describing system

Unified structure for handling associated devices

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State-of-the-Art

Development limited to PC needs Power management for laptops

Sleep mode management BIOS-based management

BPM (BIOS power management) Has no awareness of the user’s (or

application’s) needs Operating-system based management

OSPM (OS power management) Current de-facto standard

Most publications today are algorithms for the efficient switching between states using OSPM

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ACPI

Advanced Configuration and Power Interface State machine used to describe

machine configuration States associated with different parts of

the system Common interface provided to enact

changes in the state of the system

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ACPI States Basic set of

states Cx

CPU states Dx

States for peripheral device

Modem Network card Screen Hard drive

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Interface Descriptions

Multiple standardized interfaces provided Example

AcpiEnterSleepStatePrep AcpiEnterSleepState AcpiLeaveSleepState

Provides common interface for the change of states for the system

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OSPM

Operating System Power Management Model describing partitioning of power

consumption management Operating system determines when to

trigger power management features BIOS determines how to perform power

management features

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OSPM/ACPI

OSPM and ACPI integrated OSPM provides

mechanism for selection of mode

Kernel initiates action

ACPI provides common interface to hardware

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Power Management For SDR

SDR places challenges different from classic communications system Can support application swapping Needs to support wide set of devices

Variety of needs and states Difficult to narrow to small, well-defined set of

states Requires sophisticated power control

structures Applications can be more predicable than PC

Possible to determine “fast enough” speed

Blind throttle for the application may not be enough

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State Support

ACPI supports mesh state machine Assumes basic device states can be throttled

Linear transitions (throttle) are a subset of the mesh state machine

S 1 S 2 S n

S 1 S 2 S n

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Problems with Mesh SM

Assumes that all transitions are fundamentally “equal” Does not take into account QoS issues related with

state change Example:

Voltage and frequency are fundamentally linked Increased voltage will allow a higher set of

frequency settings to be supported Throttle transitions based on the assumption that lowest

possible voltage is supported for the desired frequency If a change in voltage incurs a higher time delay

than a change in frequency, could lead to unplanned additional latencies

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Rate-Change Support in Communications

Example (802.11b): Support alternate processing speeds for different

sections of received frame

Benefits Minimizes required computing power Provides ability to discard frame before high-speed

processing is necessary

PLC P Prefix PLC P Payload

1M bps (P ream ble+H eader) 11M bps PSD U

192us typ ically ~400us

Pro

cess

ing

C W

SlowFast

Tra

nsiti

on

Tra

nsiti

on

D ecision po in t: d iscard fram e?

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Rate Change and SDR

Waveform takes place of “user” in SDR Latencies associated with change of state need to be

taken into account State switching needs to be in order of microseconds

Millisecond-level switches may be too slow for some waveforms

Ideally, should cluster state changes into transition state Example:

Crusoe TM5400 automatically controls voltage and frequency settings

Slow ramp in voltage for up-frequency changes followed by fast frequency change

Fast down frequency change followed by slow voltage change Changes performed automatically

Possible for some equipment to leave change requests up to the application

Voltage regulator can have a significant impact on the transition speeds in core operating voltage

May be too slow (ms+) for some waveforms

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State Machine Description

Break down state machine into slow-change states and related fast-change states Provides application

with ability to change states quickly during waveform operation

Also supports sleep or standby operation

V 3F3,1 F3,2 F3,3

V 1F1,1 F1,2 F1,3

V 2F2,1 F2,2 F2,3

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Sample Operation

Fast operation Can cycle between 500 and

700 MHz 500 MHz may be more

efficient at 1.5V May choose not to

transition, since change to 600 or 700 MHz expected soon

Can still transition to lower powers Support significantly lower

power consumption levels Same concept can apply to

other devices FPGAs, ASICs, CCMs, DSPs

1.2V100 200 300

1.8V500 600 700

1.5V300 400 500

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Common Interface

Design of common interface will have to wait until conceptual framework is finalized Will rely on ACPI to determine appropriate

interfaces Will also rely heavily on SCA 3.0 interface

specifications SCA 3.0 concentrates on non-CORBA interface

descriptions Challenging task

Generic nature of hardware makes static definition of interfaces unlikely

Will most likely require a generic structure May be able to leverage AML

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Application-Level Power Management

Algorithm development Field of research currently has large number of

contributions Primarily concentrating on PC-based systems

ACPI/OSPM Clear from OEPM that SDR will have some

unique characteristics Optimization strategies will be based on the

permutations possible by conceptual framework

This research venue cannot proceed until conceptual framework is complete

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Conclusion

Some concepts in power management are fairly mature PC power management Voltage and frequency scaling Policies and algorithms

Current state-of-the-art does not cover all needs of SDR Unique issues related to nature of SDR

Actively developing techniques to resolve these issues

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Acknowledgement

This work is funded by the DCI Postdoctoral Research Fellowship and the MPRG Affiliates Program