© 2002 - Diego Ragazzi© 2002 - Diego Ragazzi

"Minimum transmission power" "Minimum transmission power" algorithmalgorithm

for OFDM-based flexible systemsfor OFDM-based flexible systems

Diego Ragazzi Diego Ragazzi diego.ragazzi@cefriel.it

Morena Minto Morena Minto mor.ena@tiscalinet.it

CEFRIELCEFRIELVia Fucini 2Via Fucini 2

20133 Milano, Italy20133 Milano, Italy

Luigi Agarossi Luigi Agarossi luigi.agarossi@philips.com

Luca Giangaspero Luca Giangaspero luca.giangaspero@philips.com

PHILIPS RESEARCH MONZAPHILIPS RESEARCH MONZAVia Casati 23Via Casati 23

20052 Monza - MI, Italy20052 Monza - MI, Italy

Workshop on Broadband Wireless Ad-Hoc Networks and Services12th-13th September 2002, ETSI, Sophia Antipolis, France

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SummarySummary

The Wind-Flex System

Flexibility, Adaptivity, Reconfigurability

The Supervisor Unit

Proposed Algorithm

Simulation Results

Standardisation Issues

Future Developments

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Wind-Flex System (1/3)Wind-Flex System (1/3)

A flexible radio interface for short-range high-speed wireless

networking

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Wind-Flex System (2/3)Wind-Flex System (2/3)

WIND (Wireless INDoor)17 GHz high-speed modem

True 100Mbps High spatial density (> 5Mb/s/m2)

FLEX (FLEXible)Adaptive and re-configurable

Real-time system optimisationMeet QoS requirements given the channel condition with the minimum power (TX and processing)

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Wind-Flex System (3/3)Wind-Flex System (3/3)System parameters Values

Coverage range (omnidirectional antenna, BER 10-6 , code 1/2) LOS: 100 m (QPSK), 30 m (64QAM)NLOS: 10 m (QPSK), 4 m (64QAM)

Radio Interface optimization strategyMeet QoS requirements given channel conditions with the minimum transmitted/processing power

RF parameters Values Baseband parameters Values

Frequency 17.1-17.3 GHz Modulation schemeOFDM with variable number of SC excision

Channel BW 50 MHz Modulation adaptivity Per frame, per user

Number of channels 4Subcarriers modulation schemes

BPSK, QPSK, 16QAM, 64QAM

Subcarrier spacing 390.625 KHzActive OFDM carriers number

100

Max peak EIRP 23 dBm Pilot carriers 0

Max average EIRP 10 dBm OFDM useful symbol length2.56 s

Receiver sensitivity -85 dBm Guard interval200 ns

   Coding scheme Turbo code

   Turbo code scheme Parallel convolutional

   Turbo codes polynomial (13, 15) octal

   Coding rates 1/2, 2/3, 3/4

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Wind-Flex flexibility conceptWind-Flex flexibility concept

• FLEXIBILITY– “umbrella concept” encompassing a set of

independently occurring features, such as adaptivity and reconfigurability

• ADAPTIVITY– dynamic adjustment of parameters depending on both

• multimedia services (traffic conditions, QoS)• time-varying channel response

• RECONFIGURABILITY – ability to rearrange system parts at

architectural/structural level• programmable digital signal processing (FPGA, general-

purpose processor and/or their combinations) to implement radio interfaces and upper layer protocols

• SW controlled network configuration

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The Supervisor UnitThe Supervisor Unit

The “Supervisor” is the basic control unit of any adaptive system, meant to perform at run-time a pre-defined system optimisation

In the Wind-Flex modem, it must fit the requirements of the MAC layer (BER, bit-rate) given the channel conditions with the MINIMUM TRANSMIT POWER

Turbo Enc OFDM Mod

Turbo Dec Channel estimator

LNA

MAC

HPA

Channelcondition

QoS

““SUPERVISOR”SUPERVISOR”““SUPERVISOR”SUPERVISOR”

OFDM Demod

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The Supervisor AlgorithmThe Supervisor Algorithm

Target_Rate

Feedback_mode

Estimated |Hi|2

(M,C)

P

NON and their positions

MAC PHY

““SUPERVISOSUPERVISOR”R”

““SUPERVISOSUPERVISOR”R”

M: Constellation sizeC: Code rate

Inputs and Outputs:MAC_return

Constraints:M and Pi will be the same for all ON SCsBlock length is not considered as an indipendent input

Target_BERService_mode

Actual_BERActual_Rate

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It is based on the sub-carrier switching concept

Discard the Modulation/Code Rate (M,C) couples not

satisfying Target_Rate considering all sub-carriers (SCs)

turned ON

For each useful couple:

Compute the minimum number of SCs (NON) to

achieve the Target_Rate

Derive, from the simulated curves (AWGN channel),

the SNR threshold to get the Target_BER

Compute the minimum power required to shift all the

SCs over the threshold, based on the current channel

status (look at the “worst case” SC)

Choose the couple corresponding to the minimum total

power

Algorithm Description (1/2)Algorithm Description (1/2)

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Algorithm Description (2/2)Algorithm Description (2/2)

Load channel conditionSort channel gains in Sort channel gains in descending orderdescending orderConsider the previously derived Consider the previously derived SNR threshold and NSNR threshold and NON ON which which guarantee the target BER and guarantee the target BER and bit-ratebit-rate

Derive the minimum required PDerive the minimum required Pii for the Nfor the NONON-th SC-th SC““Switch-off” unused SCs and Switch-off” unused SCs and compute TX power as Ncompute TX power as NONON* P* Pii

Load channel conditionLoad channel conditionSort channel gains in Sort channel gains in descending orderdescending orderConsider the previously derived Consider the previously derived SNR threshold and NSNR threshold and NON ON which which guarantee the target BER and guarantee the target BER and bit-ratebit-rateDerive the minimum required Pi for the NON-th SC““Switch-off” unused SCs and Switch-off” unused SCs and compute TX power as Ncompute TX power as NONON* P* Pii

Load channel conditionLoad channel conditionSort channel gains in Sort channel gains in descending orderdescending orderConsider the previously derived SNR threshold and NON which guarantee the target BER and bit-rateDerive the minimum required Pi Derive the minimum required Pi forfor the Nthe NONON-th SC-th SC““Switch-off” unused SCs and Switch-off” unused SCs and compute TX power as Ncompute TX power as NONON* P* Pii

Load channel conditionLoad channel conditionSort channel gains in descending orderConsider the previously derived Consider the previously derived SNR threshold and NSNR threshold and NON ON which which guarantee the target BER and guarantee the target BER and bit-ratebit-rate

Derive the minimum required PDerive the minimum required Pii for the Nfor the NONON-th SC-th SC““Switch-off” unused SCs and Switch-off” unused SCs and compute TX power as Ncompute TX power as NONON* P* Pii

Load channel conditionLoad channel conditionSort channel gains in Sort channel gains in descending orderdescending orderConsider the previously derived Consider the previously derived SNR threshold and NSNR threshold and NON ON which which guarantee the target BER and guarantee the target BER and bit-ratebit-rateDerive the minimum required Pi Derive the minimum required Pi for the NON-th SCfor the NON-th SC“Switch-off” unused SCs and compute TX power as NON* Pi

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Preliminary Results (1/4)Preliminary Results (1/4)

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Preliminary Results (2/4)Preliminary Results (2/4)

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Preliminary Results (3/4)Preliminary Results (3/4)

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Preliminary results (4/4)Preliminary results (4/4)

Remarks:

apart from the channel induced impairments the

system is assumed to be ideal

the most important contribution to the reduction

of the power is the variable number of active

SCs

the algorithm is based on a worst case design

criterion the minimum power is overestimated

other choices could improve performances but

also complexity

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Standardisation IssuesStandardisation IssuesThe Wind-Flex system may be considered as fitting the requirements of ETSI/BRAN HIPERLINK project, that“will provide short-range very high-speed interconnection of HIPERLANs and HIPERACCESS, e.g. up to 155 Mbit/s over distances up to 150 m. Spectrum for HIPERLINK is available in the 17 GHz range.” (*)

The 17.1-17.3 GHz frequency band is in line with: ETSI TR 101 031 v2.2.1CEPT/T/R 22-06 CEPT/ERC/REC 70-03

The ITU study group JRG 8A-9B proposed further 400MHz extension from 17.3 to 17.7 GHzFor USA and Japan similar bandwidth are generically allocated for radio communications

(*) http://www.etsi.org/frameset/home.htm?/technicalactiv/hiperlan/hiperlan2.htm

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Future DevelopmentsFuture Developments

Derive the real BER of the whole coded OFDM symbol from the different SNRs of the various sub-carriers

This will allow better performances, as the metric used to evaluate the minimum required power will not be based on the “worst case” sub-carrier

Implement the presented algorithm, or an improved version, in a prototype demonstrator