Link Margin Examples - IEEE Standards Association
IEEE P802.24Smart Grid TAGProjectIEEE P802.24 Smart Grid Technical Advisory GroupTitle TITLE \* MERGEFORMAT Link Margin ExamplesDate Submitted12 September 2016Source[ AUTHOR \* MERGEFORMAT Benjamin Rolfe][ DOCPROPERTY "Company" \* MERGEFORMAT BCA][PO Box 798 Los Gatos CA 95031]Voice:[+1-408-395-7207]Fax:[ Deprecated ]E-mail:ben.rolfe @ ]Re:Sub-1GHz white paper contribution COMMENTS \* MERGEFORMAT AbstractExamples of link margin calculations for 902-928 MHz band and 2.4GHz band using the NIST Small City model.PurposeContribution to white paperNoticeThis document has been prepared to assist the IEEE P802.24. 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.ReleaseThe contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.24.Link Margin Calculations comparing Sub-GHz 915 band to 2.4 GHz bandThe following calculations compare the link loss difference between a sub-1GHz band at 902-928 MHz with the 2.4 GHz band, keeping all other variables equal. The parameters are typical of a commonly available moderately low data rate radio as is popular in many smart grid and IoT related applications such as metering and remote monitoring. It should be noted that other factors beyond propagation loss, including required data rate, would drive selection of a band. For example, the contiguous spectrum available at 2.4 GHz is much larger than what is available in sub-1GHz bands in many regions, and so maximum data rate achievable may limit use of lower frequencies for applications that require high data volumes. Example calculations, based on the NIST link model. The “Small City” model was used as this approximates an urban environment.Conditions:Transmitter antenna height (m)10.0Receiver antenna height (m)3.0Center frequency in MHz915EnvironmentSmall CityFading modeshadowing and fadingStd. Deviation in dB, ?L1.0Percentage of time, X90%Desired link margin in dB, M6.0Transmit power30 dBmReceiver sensitivity --97 dBmResult:Transmit power30.0dBmGains10.0dBLosses129.3dBReceived power-89.3dBmNoise + interference power-120.9dBmMedian received SNR31.6dBProcessing gain0.0dBMedian received EbNo31.6dBRequired EbNo24.0dBExcess7.6dBMargin6.0dBSURPLUS1.6dBDesired link reliability90%Effective link reliability62%Specified link distance1.000kmDistance for desired reliability1.100kmThe second example uses exactly the same parameters, but changes the transmit frequency to use the 2.4GHz license exempt band throughout the world. Changing only the frequency, we see the distance to achieve the same 6dB link margin is reduced by nearly half:Transmit power30.0Gains10.0Losses139.8Received power-99.8Noise + interference power-120.9Median received SNR21.2Processing gain0.0Median received EbNo21.2Required EbNo24.0Excess-2.8Margin6.0SURPLUS-8.8Desired link reliability90Effective link reliability27Specified link distance1.000Distance for desired reliability0.589 ................
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