doc.: 11-04-0012-00-000n-proposal-statistical-channel-error-model.ppt submission jan 2004 ucla -...

Jan 2004

UCLA - STMicroelectronics, Inc.Slide 1

doc.: 11-04-0012-00-000n-proposal-statistical-channel-error-model.ppt

Submission

Proposal for Statistical Channel Error Model

D. Maniezzo, G. Pau, F. Benedetto, F. Cerioli, M . Gerla,W. Zhu, M. Fitz.

UCLA – University of California, Los AngelesValerio Filauro

STMicroelectronics, Inc.

{maniezzo|gpau|beneoet|fcerioli|gerla}@cs.ucla.edu,[email protected], [email protected]

[email protected]

Jan 2004



Submission

Outline

• Introduction• Statistical Channel Model from Testbed

Measurements• Tested Conficuration• Instant PER vs SNR• Channel Model Assumptions• Results• Conclusions and Future Work

Jan 2004



Submission

Introduction• A realistic channel simulation model is mandatory to study a

PHY/MAC layer such as 802.11n that takes into account the channel conditions.

• The channel conditions affect the throughput, the delay and the jitter.

• Goal of the simulator: measure network throughput as a function of MIMO parameters such as: – the geometry of the MIMO system, – the model of the channel, – the distance of the stations, etc;

• A statistical error model gives us a faster simulator than if we integrated TGn Matlab channel model [1] with the selected network simulator.

Jan 2004



Submission

Testbed: 3x4 MIMO System

Jan 2004



Submission

Statistical Channel Model from Testbed Measurements

• From real MIMO measurements from the Narrowband Testbed [2], we derive Packet Error Statistic vs. SNR and use it in the network simulator.

• We select as a network simulator ns-2 but the approach applies to any simulator.

• Test-bed (in UCLA UnWiReD Lab ):– The receiver in fixed location; the transmitter is in different corridor

locations for different experiments– Transmission power is -10 dBm for each transmit antenna. – 24 different S/T coding schemes are tested

• Alamouti: 4PSK, 8PSK, 16QAM, 64QAM.• 3-TX Orthogonal Block Code: 4PSK, 8PSK, 16QAM, 64QAM.• 3-TX Super Orthogonal Block Code with 2 extra bits: 4PSK, 8PSK, 16QAM, 64QAM• 3-TX Super Orthogonal Block Code with 3 extra bits: 4PSK, 8PSK, 16QAM, 64QAM. • 3-TX Super Orthogonal Block Code with 4 extra bits: 4PSK, 8PSK, 16QAM, 64QAM. • 3x4 BLAST: 4PSK, 8PSK, 16QAM, 64QAM.

• The measurements are repeated for different receiver positions to have PER vs. SNR.

Jan 2004



Submission

Testbed Configuration

• Physical layer parameters– Carrier Frequency: 220.5625MHz– Bandwidth: 4KHz – Symbol Rate: 3.2 kbps – Antenna Configuration: Up to 3x4– No mobility

Jan 2004



Submission

Testbed Configuration (cont’d)• Frame Format

The transmitter continuously transmits Long frames with the following structure:– Preamble (300 known symbols): used for frame and carrier synchronization.– Control Frame (Alamouti coded frame): used for transmission of the state

(seed) of the random number generator, which is used to generate the random information bits to be coded.

– Data Block: consists of 24 Data Frames.Each Data Frame

• carries random information bits encoded using one of the 24 Space-Time Coding Schemes.

• consists of 300 symbols (228 of which are data and 72 are pilot symbols). – Silence Period between Long Frames (70 symbols): the transmitter is silent.

The receiver uses this period to estimate the received noise power in the operating frequency band.

…

Jan 2004



Submission

values averaged over a 2 hours experiment

Packet Error Rate vs SNR

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

0 5 10 15 20 25 30 35 40 45

SNR (dB)

PE

R

Alamouti, 16QAM, R=4

Alamouti, 64QAM, R=6

BLAST, QPSK, R=6

BLAST, 16QAM, R=12

BLAST, 64QAM, R=18

Jan 2004



Submission

Channel Model Assumptions• SISO (1x1) instead of MIMO (3x4); single carrier (instead of OFDM)• Propagation model:

– Exp. Path loss model– AWGN– Shadowing– No Fading (it is compensated in the real system by: multiple antenna diversity and multiple frequency

subchannel spreading).

– Error Model: from the measurements we set a look-up table that gives the PER vs. SNR.

• Scaling from 4Khz band and 200Mhz carrier to 5Mhz and 2.4Ghz: As a first approximation, for a given encoding scheme, the error rates are dependent only on SNR.

• As a first approximation, bit errors are assumed to be randomly and uniformly distributed in a frame; packet error rate is computed based on packet length. Future work will investigate error burstiness

• Note: One caveat is that at higher speeds, and using OFDM, better, more robust codes could be used. Anyway, current 4Khz results will provide a conservative estimation

Jan 2004



Submission

Channel Model Assumptions (cont’d)

Doppler effects:– Doppler effects are present as people move in the environment

changing the multipath characteristics and thus causing a drift in carrier frequency (with possible extra errors). This effect is negligible in an indoor slow mobility scenario.

Multipath fade changes and obstruction of direct ray:– In this simplified model we didn’t take into account the relatively

slow change in attenuation caused by people moving in the environment.

– In the future, careful monitoring of this attenuation in the experiment could be used to set up a proper 2 state Markov Chain to capture these effects.

Jan 2004



Submission

MAC/PHY Wireless Model in ns2

MACMAC

netIFnetIFRadioRadio

Propagation Propagation ModelModel

Wireless ChannelWireless Channel

Received PowerReceived Power

Free SpaceShadowing

ErrorModel

Jan 2004



Submission

Experimental Scenarios

• We simulate the following scenarios proposed by TGn Usage Models workgroup:– Residential (#1)

– Residential IBSS (#2)

– Enterprise (#4)

– Hot Spot (#6)

• Note: the same scenarios were simulated in [3] by ST-Microelectronics (without error model).

Jan 2004



Submission

Simulation Set-up

• ns-2.26 • MAC: STMicroelectronics extension “MAC

b/QoS” [3]• PHY:

– Data Rate: 300Mbps– TX power: 17 dbm

• Channel:– 300Mbps– Exp. Path loss model + AWGN + Shadowing + error

model• Simulation time 60 secs

Jan 2004



Submission

Results - Scenario #1

0.00E+00

2.00E+06

4.00E+06

6.00E+06

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1.00E+07

1.20E+07

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ORIGINAL ERROR MODEL

Jan 2004



Submission


0.00E+00

1.00E+06

2.00E+06

3.00E+06

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Jan 2004



Submission


0.00E+00

5.00E+05

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Jan 2004



Submission


0.00E+00

2.00E+05

4.00E+05

6.00E+05

8.00E+05

1.00E+06

1.20E+06

1.40E+06

1.60E+06

1.80E+06

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70

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Jan 2004



Submission

Future Work• More realistic measurements will be available shortly from a new

2.4Ghz testbed.• More experiments will be conducted to evaluate error burstiness and

obtain a more accurate dependence of packet error probability on packet size.

• A two states Markov chain error model will be developed to take into account the time correlation of the errors (e.g. attenuation caused by people moving in the environment).

• The knowledge of time correlation between errors will be exploitedfor optimal parameter setting (eg, fragment aggregation size).

• Model parameterization will be used to limit the size of the look-up table (ie PER vs. SNR) as the system becomes more complex

Jan 2004



Submission

References

[1] 11-03-0940-01-000n.doc TGn Channel Model, November 2003.

[2] Narrowband Testbed webpage:http://www.ee.ucla.edu/~fitz/NBTestbed/NBtestbed.html

[3] “802.11-TGn Usage Models Simulation Results”, Valerio Filauro, Liwen Chu – STMicroelectronics Inc.IEEE802.11-03-0841-00-000n.doc

doc.: 11-04-0012-00-000n-proposal-statistical-channel-error-model.ppt submission jan 2004 ucla -...

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