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© 2002 - Diego Ragazzi "Minimum transmission power" algorithm for OFDM-based flexible systems Diego Ragazzi

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Presentation on theme: "© 2002 - Diego Ragazzi "Minimum transmission power" algorithm for OFDM-based flexible systems Diego Ragazzi"— Presentation transcript:

1 © Diego Ragazzi "Minimum transmission power" algorithm for OFDM-based flexible systems Diego Ragazzi Morena Minto CEFRIEL Via Fucini Milano, Italy Luigi Agarossi Luca Giangaspero PHILIPS RESEARCH MONZA Via Casati Monza - MI, Italy Workshop on Broadband Wireless Ad-Hoc Networks and Services 12 th -13 th September 2002, ETSI, Sophia Antipolis, France

2 - 2 - Summary The Wind-Flex System Flexibility, Adaptivity, Reconfigurability The Supervisor Unit Proposed Algorithm Simulation Results Standardisation Issues Future Developments

3 - 3 - Wind-Flex System (1/3) A flexible radio interface for short-range high-speed wireless networking

4 - 4 - 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 optimisation Meet QoS requirements given the channel condition with the minimum power (TX and processing)

5 - 5 - Wind-Flex System (3/3) System parametersValues 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 strategy Meet QoS requirements given channel conditions with the minimum transmitted/processing power RF parameters ValuesBaseband parametersValues Frequency GHzModulation scheme OFDM with variable number of SC excision Channel BW50 MHzModulation adaptivityPer frame, per user Number of channels4 Subcarriers modulation schemes BPSK, QPSK, 16QAM, 64QAM Subcarrier spacing KHz Active OFDM carriers number 100 Max peak EIRP23 dBmPilot carriers0 Max average EIRP10 dBmOFDM useful symbol length 2.56  s Receiver sensitivity-85 dBmGuard interval 200 ns Coding schemeTurbo code Turbo code schemeParallel convolutional Turbo codes polynomial(13, 15) octal Coding rates1/2, 2/3, 3/4

6 - 6 - Wind-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

7 - 7 - The 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 EncOFDM Mod Turbo Dec Channel estimator LNA MAC HPA Channel condition QoS“SUPERVISOR” OFDM Demod

8 - 8 - The Supervisor Algorithm Target_Rate Feedback_mode Estimated |H i | 2 (M,C) P N ON and their positions MAC PHY “SUPERVISOR” M: Constellation size C: Code rate Inputs and Outputs: MAC_return Constraints: M and P i will be the same for all ON SCs Block length is not considered as an indipendent input Target_BER Service_mode Actual_BERActual_Rate

9 - 9 - 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 (N ON ) 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)

10 Algorithm Description (2/2) Load channel condition Sort channel gains in descending order Consider the previously derived SNR threshold and N ON which guarantee the target BER and bit-rate Derive the minimum required P i for the N ON -th SC “Switch-off” unused SCs and compute TX power as N ON * P i Load channel condition Sort channel gains in descending order Consider the previously derived SNR threshold and N ON which guarantee the target BER and bit-rate Derive the minimum required P i for the N ON -th SC “Switch-off” unused SCs and compute TX power as N ON * P i Load channel condition Sort channel gains in descending order Consider the previously derived SNR threshold and N ON which guarantee the target BER and bit- rate Derive the minimum required Pi for the N ON -th SC “Switch-off” unused SCs and compute TX power as N ON * P i Load channel condition Sort channel gains in descending order Consider the previously derived SNR threshold and N ON which guarantee the target BER and bit-rate Derive the minimum required P i for the N ON -th SC “Switch-off” unused SCs and compute TX power as N ON * P i Load channel condition Sort channel gains in descending order Consider the previously derived SNR threshold and N ON which guarantee the target BER and bit-rate Derive the minimum required Pi for the NON-th SC “Switch-off” unused SCs and compute TX power as N ON * P i

11 Preliminary Results (1/4)

12 Preliminary Results (2/4)

13 Preliminary Results (3/4)

14 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

15 Standardisation Issues The 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 GHz frequency band is in line with: ETSI TR v2.2.1 CEPT/T/R CEPT/ERC/REC The ITU study group JRG 8A-9B proposed further 400MHz extension from 17.3 to 17.7 GHz For USA and Japan similar bandwidth are generically allocated for radio communications (*)

16 Future 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


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