Coexistence Metrics for Wireless Systems

1. Project: IEEE P802.19 Coexistence TAG Submission Title: [Coexistence Metrics for Wireless Systems] Date Submitted: [11 Sep 2002] Source: [Jim Lansford] Company: [Mobilian Corporation] Address: [7431 NE Evergreen Rd, Suite 220, Hillsboro, OR 97124] Voice:[(405) 377-6170], FAX: [ (405) 377-6173], E-Mail:[jimlans@mobilian.com] Re: [ ] Abstract: [This presentation is based on work in progress by the authors for PHY-based metrics for determining coexistence. Metrics based on physical layer characteristics provide a relative measure of the interference between systems that establishes a bound on degradation. More detailed models that take MAC characteristics into account can provide more fidelity, but are much more difficult to develop and verify.] Purpose: [Propose possible metrics to quantify the level of coexistence between two wireless systems.] Notice: This document has been prepared to assist the IEEE P802.19. 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 P802.19. Jim Lansford, Mobilian Corporation

2. Coexistence Metric (CM)for Wireless Systems Jim Lansford Jim.Lansford@mobilian.com Rob Poor r@ember.com PHY models are good first order approximations to quantify interference Parameters are well defined and lead to models that are relatively easy to compute Can give reasonably good estimates of BER/PFR Do not have the fidelity of PHY+MAC models Cannot be used to evaluate latency and jitter Jim Lansford, Mobilian Corporation

3. Terms • Coexistence? • the effects of interference among wireless devices that are physically near one another • Two wireless devices are said to coexist if they can be brought near one another without significant degradation in their performance • The term “significant” is open to interpretation • What is a “coexistence metric?” • A number, typically derived from a model, that quantifies the extent to which device A is expected to interfere with and be interfered by device B. • The level of detail required in the model is debatable, but simple is desirable. Jim Lansford, Mobilian Corporation

4. Goals of a Coex Metric • Quantitative, rather than qualitative • Simple framework • Allows others to use the model easily • Produces intuitive results • Builds upon previous work • Particularly TG2 • Establishes a bound • A relatively simple model should be somewhat pessimistic • More detailed models (e.g., including MAC) should improve results • Use a portable, widely supported framework • Java or Matlab • Open process • Consensus-based • Frequent feedback and revision Jim Lansford, Mobilian Corporation

5. A Physical Model • Similar to TG2 • Provides BER/FER • No MAC behavior • Doesn’t give latency/jitter performance • Doesn’t give detailed throughput, but a bound Jim Lansford, Mobilian Corporation

6. Model parameters • Interference is assumed to appear as AWGN at the detector • Can refine this over time • Signal power • Interference power • Path loss • Spectral coupling (called spectrum factor in TG2) • Signal-to-interference ratio – derived from parameters • Bit error rate – derived from SIR and modulation type • Frame error rate – derived from BER and frame structure of victim Jim Lansford, Mobilian Corporation

7. Path loss • At 2.4GHz, can use TG2 model • L= 20 log(4d/) = 40.23 + 20 log(d) d ≤ 8m = 58.3 + 33 log(d/8) d > 8m Jim Lansford, Mobilian Corporation

8. Spectral coupling • Combined effect of Tx mask of interferer and Rx passband of victim • Quantifies power from interferer that couples to victim’s detector • For FH systems, there would be multiple offsets Area AI Area AF Receiver Passband Coupled power Interferer Spectral Coupling = Area AF / Area AI Jim Lansford, Mobilian Corporation

9. Status • Java applet has been coded • Future work to incorporate: • Compare model to measured results and refine • Add other radios such as UWB • Incorporate effects of duty cycle Jim Lansford, Mobilian Corporation