Coexistence of Multi-band OFDM and IEEE 802.11a: Interference Measurements

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Coexistence of Multi-band OFDM and IEEE 802.11a
Interference Measurements Date Submitted 12
January, 2004 Source Dave Magee, Mike
DiRenzo, Jaiganesh Balakrishnan, Anuj Batra
Company Texas Instruments Address 12500 TI
Blvd, MS 8649, Dallas, TX 75243 Voice214-480-12
36, FAX [phone], E-Mailmagee_at_ti.com R
e Abstract This document describes the
interference measurement study to investigate the
coexistence of the multi-band OFDM system with
IEEE 802.11a devices. Purpose For discussion
by IEEE 802.15 TG3a. 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(s) or
organization(s). The material in this document is
subject to change in form and content after
further study. The contributor(s) reserve(s) 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.
2
Coexistence of Multi-band OFDM and IEEE 802.11a
Interference Measurements

• Dave Magee, Mike DiRenzo, Jaiganesh Balakrishnan
  and Anuj Batra
• Texas Instruments12500 TI Blvd, MS 8649Dallas,
  TX
• January 13, 2004

3
Motivation

• Goal To characterize the impact of Multi-band
  OFDM UWB interference on a broadband wireless
  system like IEEE 802.11a.
• Note that mandatory mode of the Multi-band OFDM
  proposal does not occupy the U-NII band.
• This study was initiated based on comments by
  members during the ABQ meeting.
• Consider an example Multi-band OFDM UWB system
  that uses the U-NII band.

4
UWB Interferers

• We consider two types of UWB interferers for this
  study.
• (1) a MB OFDM interferer operating on 3 bands and
  with a zero prefix.
• (2) an AWGN interferer.
• Data was captured at the input of the adjustable
  gain stage.
• During the measurements, both interferers were
  calibrated to have the same average power.

5
Test Setup
6
Test Equipment
7
Testing Procedure

• Test procedure
• Configure the IEEE 802.11a device with a data
  rate of 36 Mbps (16 QAM, R ¾).
• Calibrate the IEEE 802.11a to sensitivity (BER
  10-5) in the absence of interference.
• The IEEE 802.11a power level was adjusted to
  different values above sensitivity.
• At these power levels, we measured the maximum
  tolerable interference power level that can be
  tolerated by the IEEE 802.11a devices in order to
  maintain a BER of 10-5.
• Definition Maximum Tolerable Interference Power
  Level (MTIPL) is defined as the interference
  power level that can be tolerated by the IEEE
  802.11a device and still maintain a BER of 10-5.

8
Measurement Data

• The difference in MTIPL between the MB-OFDM and
  AWGN interferers are tabulated for various
  sensitivity levels and their corresponding I/N
  ratios.

Signal Power of 802.11a above sensitivity I/N Difference in MTIPL
10 dB 9.5 dB 0.5 dB
3 dB 0 dB 0.5 dB
2 dB -2.3 dB 0 dB
1 dB -5.9 dB 0 dB
0.5 dB -9.1 dB -1.5 dB
Note that it is challenging to accurately
measure maximum tolerable interferer power at
very small I/N ratios. ? The MB-OFDM and AWGN
interferers have similar impact (within
measurement errors) on IEEE 802.11a victim
receiver.
9
Impact on AGC (1)

• During the last meeting, questions were raised on
  the impact that interference may have on the AGC
  for IEEE 802.11a devices.
• Assumption IEEE 802.11a signal power is 3 dB
  above receiver sensitivity and the UWB interferer
  was transmitting at the maximum tolerable
  interferer power level.

• The performance of packet detection and AGC
  convergence is similar for both UWB interferers
  with the same average power.

10
Impact on AGC (2)

• Assumption
• IEEE 802.11a device operating at 3 dB above
  sensitivity.
• UWB interferer operating at 10 dB higher than the
  maximum tolerable interferer power level.
• The figure illustrates the performance of the AGC
  algorithm in the presence of a UWB interferer.
• AGC convergence and packet detection are not
  affected even when the UWB power level is higher
  than the maximum tolerable interferer power level.

SIFS
Packet Detected
MB-OFDM Interferer
11
Conclusions

• We conducted interference measurements to study
  co-existence between an IEEE 802.11a system and a
  hypothetical Multi-band OFDM UWB system that
  occupies the U-NII band.
• The Multi-band OFDM and AWGN interferers have a
  similar impact (within measurement error) on an
  IEEE 802.11a victim receiver.
• The impulse nature of the Multi-band OFDM
  interference does not adversely affect the packet
  detection circuitry and AGC convergence of the
  IEEE 802.11a victim receiver.

12
Backup slides
13
Measurement Results (1)

• The BER curves for the IEEE 802.11a system are
  shown below as a function of the UWB interference
  power and received signal power.

14
Measurement Results (2)

• The BER curves for the IEEE 802.11a system are
  shown below as a function of the UWB interference
  power and received signal power.

15
Measurement Results (3)

• The BER curves for the IEEE 802.11a system are
  shown below as a function of the UWB interference
  power and received signal power.