Microwave Engineering Europe - June 2008 - (Page 28)

28 BLUETOOTH Figure 3: A usage scenario used by the ECC to determine interference protection levels for IMT-2000 services. Figure 4: In the scenario shown in Figure 3, the ECC required a separation distance of 36 cm to protect the IMT-2000 services. density (PSD), and it made no assumptions about the transmitter’s signal characteristics. Hence, any interfering energy with PSD higher than the protection limit speciﬁed in this report was concluded to have the potential to interfere with IMT-2000 client stations. The protection limit was derived in the following manner. The maximum allowable interferer power level at the receiver of the IMT-2000 subscriber unit (without causing degradation) was found to be -115 dBm/MHz. For the use case shown in Figure 3, where a protection distance of 36 cm is considered, a free space path of ≈30 dB (at 2.5 GHz) results in transmit PSD protection limit of -115+30 = -85 dBm/MHz to provide adequate protection to the IMT-2000 client station. Note that in the above example, the ECC determined that a separation distance of 36 cm was appropriate to take into account a foreseen frequent scenario where a UWB device operating may be on a desk in an ofﬁce environment, not far from a potential victim IMT-2000 mobile station. This analysis can be validly extended to the coexistence requirement between WiMAX and the Bluetooth AMP. In the US, 802.11 radios are allowed to transmit up to +20 dBm in 2.4-2.484 GHz, while it can transmit up to -41 dBm/MHz in the adjacent bands allocated to IMT-2000 services. This means that to avoid interference at 36 cm distance, the 2.4 GHz 802.11 AMP device would need to limit the emission levels to -85 dBm/MHz in the adjacent WiMAX bands. (Note that the WiMedia UWB AMP will be operating above 6 GHz.) In the light of the above observations, industry leaders are now suggesting a coexistence mechanism be added in 2.4 GHz Bluetooth so that it does not transmit during WiMAX operation. If next-generation WPANs use the 802.11 AMP to link desktop peripherals, then, the results will dramatically exacerbate the interference situation. For example, if a user receives a streaming video WiMAX transmission on a mobile handset, and the nearby desktop connections start transferring a ﬁle to an iPod (or a printer), the WiMAX video connection will stop and the user will be staring at a blank screen. Measurements A set of measurements were performed in Staccato Communications’ lab to quantify the interference effect. Figure 5 shows the measurement set ups. All measurements were performed in a lab environment using conducted cables. The spectrum analyzer (SA) settings were Figure 5: Measurement set up to determine potential interference from the 802.11 AMP (top) and UWB AMP (bottom). Microwave Engineering Europe ● June 2008 ● www.mwee.com http://www.mwee.com

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Microwave Engineering Europe - June 2008 Contents Comment News Cover Feature Designing and Simulating a Wireless LAN Antenna 60GHz: Achieving the Ultimate Wireless Dream New Radar Developments Include HFETs to Challenge DMOS/LDMOS and a 77-GHz CMOS PA for Automotive Applications Testing Raises Concerns Over 802.11-Based High-Speed Bluetooth IP2 & IP3 Design Considerations with Direct Conversion I/Q Demodulator Receiver Products Calendar

Microwave Engineering Europe - June 2008

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