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Message started by aaron_do on Aug 5^th, 2008, 11:59pm

Title: IEEE standard Specs
Post by aaron_do on Aug 5^th, 2008, 11:59pm

Hi all,

i'm working on the IEEE 802.15.4 standard, and the spec for interference is +0 dB at 5 MHz offset and +30 dB at +10 MHz offset. Is this the total integrated interfering power, or is it the maximum power of a sinusoid at a fixed offset.

The reason i'm asking is that the likelihood of receiving a pure sinusoid with 30 dB more power than the desired signal is very low. More likely, that 30 dB higher power is spread over a broad band making it easier to filter.

thanks,
Aaron

Title: Re: IEEE standard Specs
Post by loose-electron on Aug 7^th, 2008, 2:01pm

What you are referrring to is the spectral mask requirements of the system tests.

Thats a system requirement that you need to meet. Will the system actually see that exact signal scenario? Probably not, but this is how they specify the spectral rejection charateristics that are required.

You get a similar set of requirements on a lot of RF systems. The GSM cell requirements are written in a similar fashion.

Title: Re: IEEE standard Specs
Post by aaron_do on Aug 8^th, 2008, 12:16am

Hi,

thanks for the reply. I understand that it is a spectrum mask. However, when we do a frequency domain plot I think we usually either use PSD, or power at a single frequency. The spectrum mask usually covers a band. So for 802.15.4 the adjacent and alternate channel interference requirements are +0 dB and +30 dB.

So taking the +0dB case, assume we receive -85 dBm. Is the interferer:

1) -85 dBm at 5 MHz offset
2) -85 dBm/Hz from 5 MHz onwards (very unlikely)
3) -85 dBm spread over a frequency band (for example 2 MHz) leading to -148 dBm/Hz.

I guess (1) and (3) don't lead to very different receiver specs. However, the second part of my question is, can we assume that to meet standard requirements, the total interference power is -85 dBm + -55 dBm?

thanks,
Aaron

Title: Re: IEEE standard Specs
Post by RFICDUDE on Aug 8^th, 2008, 4:33am

It is a tough question because it depends entirely on how vendors interpret the spec. Your question is reasonable and you do need to know the right answer since it is probably not reasonable to design a filter to handle a sinusoidal interfer at the closest mask offset.

If the industry does not have a defined measurement for compliance then you will have to ask vendors how they test compliance or look into the details of any automated test equipment that performs the measurement.

If you can't find any measurement information. Then the reasonable thing to do is to consider what range of other standards operate in the band of interest and come up with a worst case scenario based on the most narrowband interferer being as close it could get to the mask edge.

Title: Re: IEEE standard Specs
Post by RFICDUDE on Aug 8^th, 2008, 7:16am

Here is a coexistance oriented paper that does discuss your issue; however, I think even they had to assume some sort of practical interfer scenario because the spec is too vauge.

Yong-Kuk Park; Won-Gi Jeon; Hae-Moon Seo; Yeon-Kuk Moon; Jaeho Kim; Byoung-Chul Song; Kwang-Ho Won; Myung-Hyun Yoon; Jun-Jae Yoo; Seong-Dong Kim, "RF Receiver Specifications of Ubiquitous Network for Coexistence with Various Wireless Devices in 2.4GHz ISM-band," Communications, 2005 Asia-Pacific Conference on , vol., no., pp. 595-599, 03-05 Oct. 2005

Title: Re: IEEE standard Specs
Post by aaron_do on Aug 8^th, 2008, 8:20pm

thanks. I'll check out the paper.

Aaron

Title: Re: IEEE standard Specs
Post by loose-electron on Aug 11^th, 2008, 1:08pm

For a particular specification you can also send an inquiry to the working group for the spec, or the industry alliance group asking for clarification.

Title: Re: IEEE standard Specs
Post by didac on Aug 11^th, 2008, 1:57pm

Hi,
The 802.15.4 defines the signal at the adjacent and the alternate channels as a 802.15.4 O-QPSK PHY signal as defined elsewhere in the specs modulated with a PN so I think that it's total power over the channel BW.
Other thing if it is something like a Zigbee compliant receiver, then I don't know if Zigbee Alliance has a test document so you can put the Zigbee logo on it.
The worst interfering case in this band is a microwave oven, in fact I remember a whitepaper about wi-fi errors with microwave ovens operating nearby(something like 70-80% of packet loss in the worst situation).