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] Voice:[214-480-1236], FAX: [972-761-6966], E-Mail:[magee@ti.com] Re: [] 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. Dave Magee et al., Texas Instruments

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 Dave Magee et al., Texas Instruments

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. Dave Magee et al., Texas Instruments

4. Multi-band OFDM Interferer AWGN Interferer 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. Dave Magee et al., Texas Instruments

5. Test Setup Dave Magee et al., Texas Instruments

6. Test Equipment Dave Magee et al., Texas Instruments

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. Dave Magee et al., Texas Instruments

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. * 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. Dave Magee et al., Texas Instruments

9. SIFS Start of Packet AGC Locked Packet Detected Packet Detected MB-OFDM Interferer AWGN Interferer 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. Dave Magee et al., Texas Instruments

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 Dave Magee et al., Texas Instruments

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. Dave Magee et al., Texas Instruments

12. Backup slides Dave Magee et al., Texas Instruments

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. Dave Magee et al., Texas Instruments

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. Dave Magee et al., Texas Instruments

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. Dave Magee et al., Texas Instruments