an approach to the problem of optimizing channel parameters march 2001 vlad oleynik, umbrella...

An approach An approach to the to the

problem of problem of optimizing optimizing

channel channel parametersparameters

An approach An approach to the to the

problem of problem of optimizing optimizing

channel channel parametersparameters

March 2001

Vlad Oleynik, Umbrella TechnologySlide 1

doc.: IEEE 802.11-01/152

Submission

March 2001

Vlad Oleynik, Umbrella Technology

doc.: IEEE 802.11-01/152

Submission

Parameters determining potential Throughput Rate for a given Parameters determining potential Throughput Rate for a given medium statemedium state

• Transmitter Power Levelincrease Signal-to-Interference Ratio (SIR)

• Modulation/Coding (BPSK, QPSK, MBOK, CCK, QAM...)in extreme conditions, an modulation/coding scheme with bigger redundancy (lower bit rate) may have better throughput rate

• Packet Lengthwhen interference is present, smaller packet length

will decreased PER value

Continuous medium monitoring provides the right selection and adjustment of the channel characteristics in real time mode.Continuous medium monitoring provides the right selection and adjustment of the channel characteristics in real time mode.

Slide 2

March 2001


doc.: IEEE 802.11-01/152

Submission

Major determination factorsMajor determination factorsMajor determination factorsMajor determination factors

• Load level of the communication channel(s)• STA density and topology

• Activity Level of WLAN

• distortion from other WLAN

• Noise Interference properties• Noise bandwidth

• Long term / Short term Statistical analyses for medium state

To estimate medium conditions, it is possible to use available measurement parameters which depend on both the medium’s state and the communication channel mode.

To estimate medium conditions, it is possible to use available measurement parameters which depend on both the medium’s state and the communication channel mode.

Slide 3

March 2001


doc.: IEEE 802.11-01/152

Submission

Medium Changes AdaptationMedium Changes Adaptation

To perform medium monitoring it is necessary to have •P sum, summary power level•PhN, phase noise value•PER, time frame statistics

To perform medium monitoring it is necessary to have •P sum, summary power level•PhN, phase noise value•PER, time frame statistics

Packets

Noise/Interference

Phase Noise

Threshold

Psum

D

A B A B A

FG

B A

D

A B

E

A Normal receiving begins. Psum is increased. Phase Noise (PhN) is less then the threshold level

B Packet has been transmitted. Psum is decreasing. Phase Noise exceeds the threshold level

C Interference. Psum is increased. Phase Noise exceeds the threshold level

D Power level of the packet to be transmitted is decreased due to low phase noise level of the previous packet

E Power level of the packet to be transmitted is increased due to high phase noise level of the previous packet

F Packet was lost because of increasing interference level during packet transmission

G Packet was normally received due to high transmission power level

Slide 4

March 2001


doc.: IEEE 802.11-01/152

Submission

Techniques of medium adaptationTechniques of medium adaptation

Measured parameters (Psum, PhN, PER) are used to determine the set (S) of the communication channel characteristics (P, PL, Mod) which are optimal for the given regulation strategy.

Measured parameters (Psum, PhN, PER) are used to determine the set (S) of the communication channel characteristics (P, PL, Mod) which are optimal for the given regulation strategy.

Demodulator

IF DSSS

ProcessorMAC

PER Statistics

TPC processor

Received Signal

Power Level

Psum

Modulator

Phase

Fluctuation

Chips

CLK PhNModulation

Selector

Packet Length Selector

SS

SS

Slide 5

March 2001


doc.: IEEE 802.11-01/152

Submission


Transmitter MediumMonitoring:

PhN, PER, Psum(P, PL, Mod)

Is MediumChanged?

No

Yes

Calculation:New

P, PL, Mod

PhNPsumPER

PMod

P, PL, Mod

UpdatedP, PL, Mod

PL

Receiver

Variations in medium state are represented by parameters (Psum, PhN, PER). They are the basis by which to determine the new parameter set S new = (updated Pmin/P, PL, Mod) optimized to the variable medium.

Variations in medium state are represented by parameters (Psum, PhN, PER). They are the basis by which to determine the new parameter set S new = (updated Pmin/P, PL, Mod) optimized to the variable medium.

Slide 6

March 2001


doc.: IEEE 802.11-01/152

Submission


AP STA

AP's transmission @ S(AP) = (P, PL, Mod)AP

adaptation process

adaptation process

- Measures PhN, Psum, PER

- Determines new AP Set(P, PL, Mod)

Normal frame transmission + next AP Set @ S(STA) = (P, PL, Mod)STA

- Measures PhN, Psum, PER

- Determines new STA Set(P, PL, Mod) AP's transmission + next STA Set

@ S(AP) = (P, PL, Mod)AP

Slide 7

March 2001


doc.: IEEE 802.11-01/152

Submission

Transmitter Power ControlTransmitter Power Control

Us

Un

Usum

Psum = Ps + Pn (1)

Pn/Ps = (Un/Us)2 = sin

2,

From this follows: Pn = Ps * sin2 (2)

Pn/Ps.min = sin2(max)

max – phase fluctuation maximum value, when receiving with necessary PER

is still possible. max is dependent on modulation mode.

Ps.min = Ps * sin2/ sin

2(max) (3)

From (1) i (2) Ps = Psum/(1 + sin2) (4)

Thus Ps.min = (Psum/(1 + sin2)) * (sin

2/ sin2(max))

And Ps.min/ Ps = sin2/ sin

2(max)

Initial points for min necessary power level calculationInitial points for min necessary power level calculation

Slide 8

March 2001


doc.: IEEE 802.11-01/152

Submission

Transmitter power level adaptationTransmitter power level adaptation

• Transmitter power level adaptation is based on the forecast, which is formed by real time measurement of the propagating condition change

• Signal/Interference Ratio (SIR) - interference level changes involve adequate transmitter power level changes

• Generating a forecast of the minimum necessary power level is based on RSSI and measurement of phase noise fluctuations, taking into account PER statistics • optimum transmission power level is achieved and maintained• adaptation of the transmitter mode to the typical changes of the

medium when affected by changing interferences

Slide 9

March 2001


doc.: IEEE 802.11-01/152

Submission

Packet Length AdaptationPacket Length Adaptation

Packets

Noise/Interference

Phase Noise

Packets

ThresholdPhase Noise

When interference is present, smaller packet length corresponds with decreased PER valueWhen interference is present, smaller packet length corresponds with decreased PER value

Slide 10

March 2001


doc.: IEEE 802.11-01/152

Submission


• Adaptation of the packet length is based on analysis of the recent propagating conditions as well as on the cumulative statistics-based forecast for the given modulation/coding and power level

• Packet length adaptation to achieve maximum throughput rate is suitable for extreme conditions.

• For any extreme condition it is possible to determine the right packet length to provide an advantage in throughput rate

Slide 11

March 2001


doc.: IEEE 802.11-01/152

Submission


Tpack(M)=[TPH+PL/BR(M)] + TACK (1)Tpack(M) data packet transmission time for modulation method M;TPH preamble/header data packet transmission time;PL data packet length, bit;BR(M) bit rate for the selected modulation method M, for PRISM BR=1,2,5.5, or 11 mbpsTACK ACK signal transmission time, for simplicity assume TACK= TPH

TR= PL/ Tpack(M) (2)

PER=1-(1-BER)PL

Tpack(M)={ [ TPH + PL / BR(M) ] + TACK } / {[1 - PER(M)] * (1 - PERACK )} (3)PER(M) – the probability of data packet transmission errorPERACK – the probability of ACK-packet transmission error

PERACK<< PER(M)

Tpack(M)={ [ TPH + PL / BR(M) ] + TACK } / [1 - PER(M)] (4)

And then the data transmission speed taking into account (2) and (4) is:

TR(M) = PL / {[ TPH + TACK + PL / BR(M) ] / [ 1 - BER(M)]PL]} (6)

At a sufficiently high BER value the best average throughput will be achieved by selecting optimal packet length and proper

modulation/coding method (not necessarily with max bit rate) .

Slide 12

March 2001


doc.: IEEE 802.11-01/152

Submission

Packet Length and Modulation/Coding AdaptationPacket Length and Modulation/Coding Adaptation

Light magenta zone - is throughput advantage of 1 Mbps (BER 1e-5) vs

11 Mbps (BER 1e-3)

Zone between - is throughput advantage of 2 Mbps

(BER 1e-4) vs 11 Mbps (BER 1e-3)

Zone between - is throughput advantage of 5.5 Mbps

(BER 1e-4) vs 11 Mbps (BER 1e-3)

PL, Kbit

TR

, M

bp

s

0 2 4 6 8 0

1

2

3

4

5

6

7

At a sufficiently high BER value and for each modulation method there is a packet length which provides the maximum Throughput Rate

At a sufficiently high BER value and for each modulation method there is a packet length which provides the maximum Throughput Rate

BER = 10-5

BER = 10-4

5.5Mbps

BER = 10-5

BER = 10-4

BER = 10-3

11Mbps

BER = 10-5

BER = 10-4

2Mbps

BER = 10-5

BER = 10-4

1Mbps

For the same medium the BER is different for different modulation methods, and modulations with smaller bit rates may have smaller BER values

For the same medium the BER is different for different modulation methods, and modulations with smaller bit rates may have smaller BER values

Slide 13

March 2001


doc.: IEEE 802.11-01/152

Submission

Adaptation of modulation methodsAdaptation of modulation methods

• Adaptation of modulation/coding methods is based on analysis of the current state of the medium and propagation condition forecast including multi-path channels for a given power level and packet length

• Switching modulation method to achieve maximum throughput rate is suitable for extreme conditions.

• For extreme conditions a modulation/coding scheme with bigger redundancy (less bit rate) may have the advantage in throughput rate

Slide 14

an approach to the problem of optimizing channel parameters march 2001 vlad oleynik, umbrella...

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