Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANS) Submission Title: [General Atomics – Interference Analysis of IEEE 802.11a

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANS)

Submission Title: [General Atomics – Interference Analysis of IEEE 802.11a on UWB Systems]

Date Submitted: [November 2002]Revised: [11 November 2002]

Source: [Naiel Askar, Ph.D.; Roberto Aiello, Ph.D.] Company [General Atomics Inc.] Address [General Atomics Photonics Division- Advanced Wireless Group, 10240 Flanders Ct, San Diego, CA 92121-2901] Voice [(858) 457-8700], Fax [(858) 457-8746], E-mail [[email protected]], [Roberto Aiello] E-mail [[email protected]]

Re: [Interference Analysis]

Abstract: [Tutorial]

Purpose: [IEEE 802.15.3SGa Tutorial November 12, 2002]

Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual or organization. The material in this document is subject to change in form and content after further study. The contributor reserves the right to add, amend or withdraw material contained herein.

Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

November 2002

General Atomics-Naiel Askar & Roberto AielloSlide 2

doc.: IEEE 802.15-02/441r1

Submission

Interference Analysis of IEEE 802.11a on UWB Systems

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doc.: IEEE 802.15-02/441r1

Submission

We will see today…

• Interference definitions and policies– Potential interference issue between IEEE 802.11a and UWB due to

overlap in frequency– New policies on interference and co-existence are being developed by

regulatory agencies (FCC) and the IEEE-SA

• Interference analysis is based on principles drawn from the current selection criteria

– Two UWB examples considered: high PRF, single band system and low PRF, multi-band system

• Conclusions and recommendations– Both UWB system examples are affected by 802.11a emission– Spectrum regulators will demand that new standards and incumbents

“equally bear the responsibility” via two-way dialog to “promote coexistence”

– Technical collaboration between15.3a and 802.11a groups need to be established while the15.3a standard is being developed

November 2002


doc.: IEEE 802.15-02/441r1

Submission

Frequency in MHz EIRP in dBm 960-1610

1610-1990 1990-3100 3100-10600

Above 10600

-75.3 -53.3 -51.3 -41.3 -51.3

Frequency Band Maximum Output Power With up to 6dB antenna gain

5.15-5.25GHz 5.25-5.35GHz

5.725-5.825GHz

40mW (2.5mW/MHz) 200mW (12.5mW/MHz) 800mW (50 mW/MHz)

*Source: FCC 02-48, UWB Report & Order *Source: IEEE P802.11a Standard

Potential interference- UWB & 802.11a overlap frequencies

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doc.: IEEE 802.15-02/441r1

Submission

[IEEE objective is to] maximize the use of the spectrum and promote co-existence1

• Both FCC and IEEE-SA’s missions include public good, global needs and interoperability and co-existence

• The FCC requires that devices “…may not cause…” and “…must accept harmful interference” [47 C.F.R. Sec. 15.5(b)]

• “The [Federal Communication] Commission may, consistent with the public interest…make reasonable regulations … governing the interference potential of devices which in their operation are capable of emitting radio frequency energy…[US Comm. Act of 1934, Sec. 5.302]

• “The IEEE-SA provides a standard program that serves the global needs of industry, government and the public. [IEEE-SA Website]

• “It is in the best interest of users and the industry to strive for a level of coexistence with other wireless systems, especially those in similar market spaces”. [802.15.3a PAR]

1 P.Nikolich, C. Stevenson, “Comments of IEEE 802 in response to the commission’s spectrum policy task force inquiry”, July 13, 2002

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doc.: IEEE 802.15-02/441r1

Submission

• FCC and IEEE-SA are currently reviewing policies on interference, sharing and co-existence to update all assumptions for new technologies

• FCC currently reviewing spectrum’s policy to improve spectrum’s scarcity due to current spectrum management policies: “Chairman Powell has formed a Spectrum Policy Task Force charged with conducting a systemic evaluation of existing spectrum policies and with making recommendations as to possible improvements” [FCC Docket 02-135]

• IEEE 802.19 Coexistence TAG: “… will develop and maintain policies defining the responsibilities of 802 standards developers to address issues of coexistence with existing standards and other standards under development”. “The informal definition shall be “the ability of one system to perform a task in a given shared environment in which other systems have an ability to perform their tasks and may or may not be using the same set of rules” [IEEE COEX 02/023r0]

The challenge is to find equitable new rules that improve overall efficiency

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doc.: IEEE 802.15-02/441r1

Submission

• Both FCC’s and IEEE’s goal is to increase global efficiency– Maximize network capacity– Maximize spectral efficiency– Maximize economic efficiency

• “New users and incumbent users should equally bear the responsibility for adopting technologies designed to maximize the use of the spectrum and promote coexistence” [Nikolich, 2002]

• “Rather than simply saying your transmitter cannot exceed a certain power, we instead would utilize receiver standards and new technologies to ensure that communication occurs without interference, and that the spectrum resource is fully utilized.” [Powell, Oct 30, 2002]

• Therefore the complex question of 802.11a and UWB interference should be addressed by both sides

802.11a and UWB interference needs to be reciprocally evaluated to define scenario of maximum efficiency

November 2002


doc.: IEEE 802.15-02/441r1

Submission

Interference metric: Signal to Interference Ratio Margin (MSIR)

UWB

802.11a

1

2 TxPWR -PathLoss

SIR Req

4

SIR Margin

• MSIR is the excess signal power at the receiver over what is required for a given performance

MSIR (dB) = UWB Tx Power - 11a Tx Power - (UWB path loss - 11a path loss) - Required SIR

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doc.: IEEE 802.15-02/441r1

Submission

STEP1 : UWB peak Tx power, system dependent (1 of 3)

• Peak Tx power (dBm) = FCC Limit + 10*log(BW^2/PRF)1

• 2 example architectures will be considered

Example1 Example2

Duty Cycle, PRF High Low

Frequency Bands One Multiple

Processing Gain

(per band)

Multiple pulses per bit One or more bits per pulse

PRF (per band) Raw bit rate*pulses per bit

Raw bit rate/bits per pulse / no. of bands

1 See backup slide for more details

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doc.: IEEE 802.15-02/441r1

Submission

STEP1 : UWB examples shown in frequency and time (2 of 3)

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STEP 1: UWB TX power- Assumptions (3 of 3)

Example1 Example2

Raw Bit Rate (Mbps) 150 150

BW (GHz) (per band) 3 0.5

No of bands 1 6

Pulses per bit (per band)

15 1

PRF (per band) (MHz) 2250 25

Tx Peak Power (dBm) -5 -1 (per band)

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doc.: IEEE 802.15-02/441r1

Submission

STEP 2: 802.11a Tx power

• Utilize the 5.25-5.35 GHz band parameters– Total Tx power is 23 dBm

– Out of band emissions – 41 dBm/ MHz

• For 5.15 - 5.25 and 5.725 - 5.825 GHz bands, apply correction factors to MSIR of +7 and -6 dB respectively

Frequency Band Maximum Output Power With up to 6dB antenna gain

5.15-5.25 GHz 5.25-5.35 GHz

5.725-5.825 GHz

40 mW (2.5mW/MHz) 200 mW (12.5mW/MHz) 800 mW (50 mW/MHz)

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doc.: IEEE 802.15-02/441r1

Submission

STEP 3: Difference in path lossUWB Tx

UWBRx

11a Tx

dINT

dSIG

•Depends on relative distance –Some applications need < 1 ft. separation–Performance will depend on relative distance

• Adapted Selection Criteria numbers to reflect our example

Selection Criteria Example Value Correction Factor

11a Tx Power +15 dBm +23 dBm -8 dB

UWB Rx Level -6 dB 0 -6 dB

UWB/11a distance ratio

10:1 (required) 33:1(desired)

1:1 20 dB (required)

Path Loss Difference (dB) +6

• Path loss difference equivalent to dSIG :dINT of 2:1• Assume line of sight propagation loss • Path loss of both systems will be frequency independent • The UWB antenna gain will compensate for differences in path loss

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doc.: IEEE 802.15-02/441r1

Submission

STEP 4: Required SIR at the receiver

• SIR value is system / application dependent – Acceptable throughput/BER

– UWB modulation

– Receiver implementation

– Received signal level

• For Example 1 assume – SIR (dB) = 6 - Processing gain

• For Example 2 assume – For the band with interference SIR (dB) = 6 dB

– For other bands SIR (dB) = 6 dB - 30dB (depends on filtering rejection)

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doc.: IEEE 802.15-02/441r1

Submission

Calculated SIR Margin: From the two examples

Example 1 Example 2

Interferer In-band In-band Out-of-band

MSIR -28.5 -36.3 -6.3

• Implications– A challenge for engineering ingenuity– The Example 1 single-band system is more resistant to interference

than Example 2 multi-band system when interference is in band– The Example 2 system is more resistant when interference is

out-of-band

askarn

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Submission

Possible remedy: Avoid 802.11a

Example 1 Example 2

Limit spectrum below 802.11a (3.1 - 5 GHz)

May not achieve enough processing gain

Select from above and below

Limit spectrum above 802.11a (6 -10.7 GHz)

May be difficult in current technology

Select from above and below

Adaptive band selection

Reduce bandwidth when interference is present

Select bands based on interference

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Submission

Another remedy: RF notch filters

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Submission

Interference canceling in the digital domain

• Approaches such as Minimum Mean Square Error (MMSE) have been successfully utilized in CDMA for interference cancellation up to 30 dB

• Needs 4 - 7 bits extra in ADC dynamic range• Digital processing at high frequencies > 1 GHz• Cost and power consumption will be an issue

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doc.: IEEE 802.15-02/441r1

Submission

Conclusions and recommendation

• PHY performance analysis performed according to principle on current selection criteria

– 802.11a interference with UWB will not be trivial to resolve– Mitigation of interference from 802.11a devices should be designed in from

day 1– We have considered interference avoidance, RF notch filters, digital

approaches• Effects of UWB on 802.11a remain to be investigated

• Spectrum regulators will demand that new standards and incumbents “equally bear the responsibility” via two-way dialog to “promote coexistence”

• Technical collaboration between 802.15.3a and 802.11a groups need to be established while the 802.15.3a standard is being developed

• Opportunities– Promote transmitter power control on all 802.11a devices– Joint IEEE 802.15.3a & 802.19 work effort to address UWB interference and

co-existence for long term

November 2002


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Submission

Additional Material for Backup

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doc.: IEEE 802.15-02/441r1

Submission

Spreadsheet CalculationsParameters Value UnitFCC Limit -41.25 dB11a TX Power 23 dBm2:1 distance diff 6 dBSIR required Nominal 6 dBUncoded rate 150 MbpsExample1 Example1 BW 3000 MHzprocessing gain 15PRF 2250 MHz TX Power -5.23 dBmRequired SIR -5.8 dBMargin -28.5 dBExample 2BW per band 500 MHzNo of freqs. 6Bits per symbol 1PRF 25 MHz TX Power -1.25 dBmRequired SIR 6.0 dBMargin -36.3 dB

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doc.: IEEE 802.15-02/441r1

Submission

Tx peak power calculation

• Tx peak power = FCC limit * BW / Duty Cycle• Duty Cycle = PRF * Pulse width• BW ~= 1/Pulse width• Tx Peak power = FCC Limit *BW^2/ PRF

Documents

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANS) Submission Title: [General Atomics – Interference Analysis of IEEE 802.11a