# 9.7 DL C/I calculation

The relationship between the contributors of the interference in a <span data-highlighted="true" data-vc="highlighted-text"><span class="_kqswh2mm"><span class="_5pioz8co _189e1dm9 _1il9buyh _19lc184f _d0altlke" data-testid="definition-highlighter">OFDMA</span></span></span> network is illustrated in Figure 205.

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/unnbaZSt0cBNUjLT-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/unnbaZSt0cBNUjLT-image.png)

<div class="rich-media-item mediaSingleView-content-wrap image-align-start css-1a1u2lj" data-layout="align-start" data-media-vc-wrapper="true" data-node-type="mediaSingle" data-renderer-start-pos="114" data-vc="media-single" data-width="651" data-width-type="pixel" id="bkmrk-figure-205%3A-illustra"><div class="css-1la7nta"><div data-alt="" data-collection="contentId-493433" data-context-id="493433" data-file-mime-type="image/png" data-file-name="05.png" data-file-size="170636" data-height="491" data-id="e8cb68c2-ae83-41d4-a083-39c49ab6e5ee" data-node-type="media" data-renderer-start-pos="115" data-type="file" data-width="1280"><div class="_2rko18qm _vchhusvi _kqswh2mm _ect4ttxp _p12f1osq _c71l1osq _1bsb1qmm _4t3ine4n _1hlmd0i9 _1rquusvi _eg541i5c _mts3kb7n _1ntskb7n _yfmhtlke _5sb1v00u new-file-experience-wrapper" data-media-vc-wrapper="true" data-testid="media-card-view" id="bkmrk-figure-205%3A-illustra-1"><div class="_1reo15vq _18m915vq _2rko18qm _1e0c1txw _kqswh2mm _p12f1osq _1bsb1osq _4t3i1osq _c71l1osq media-file-card-view" data-cursor="pointer" data-test-media-name="05.png" data-test-progress="1" data-test-source="cache-remote" data-test-status="complete" data-testid="media-file-card-view"><div class="_kqswstnw _1bsb1osq _4t3i1osq _1e0c1txw _2lx21bp4 _1bah1h6o _4cvr1h6o align-center" data-testid="ImageRendererWrapper">![](blob:https://ecowiki.atlassian.net/fbe8444f-f68b-4f41-9ec1-42ff0182cd8c#media-blob-url=true&id=e8cb68c2-ae83-41d4-a083-39c49ab6e5ee&collection=contentId-493433&contextId=493433&width=1280&height=491&alt=&clientId=113268fe-fe5b-4bc3-8ff3-07965dbf1d18)**Figure 205: Illustration of the interference mechanism in the <span data-highlighted="true" data-vc="highlighted-text">OFDMA</span> module**</div></div></div></div></div></div>Figure 205 illustrates the interference mechanism in the <span data-highlighted="true" data-vc="highlighted-text">OFDMA</span> module where the inter-system or also called self interference is noted “Iinter” and the interference from an “external” interference system is referred to as “Iext”. In the SEAMCAT <span data-highlighted="true" data-vc="highlighted-text">OFDMA</span> implementation, the term “<span data-highlighted="true" data-vc="highlighted-text"><span class="_kqswh2mm"><span class="_5pioz8co _189e1dm9 _1il9buyh _19lc184f _d0altlke" data-testid="definition-highlighter">BS</span></span></span>” and “cell” have the same meaning.

The C/I calculation in DL is calculated as

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/2H0tMho2bCQfjWI3-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/2H0tMho2bCQfjWI3-image.png) (Eq. 46)

where *C(j,k)* is the received power at the *k*-th user from the serving <span data-highlighted="true" data-vc="highlighted-text">BS</span>, i.e., the *j*-th <span data-highlighted="true" data-vc="highlighted-text">BS</span>

 [![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/NcomB4g5dDE29cIZ-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/NcomB4g5dDE29cIZ-image.png) (Eq. 47)

and where is the power of resource block and effective\_pathloss is defined as in Section ‎7.6.1.

*I(j,k)* is the sum of the interference power

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/16QOzYuspvxgVUEK-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/16QOzYuspvxgVUEK-image.png) *(Eq. 48)*

where

- *I<sub data-renderer-mark="true">inter</sub> (j,k)* is the adjacent cell interference (i.e. from the same victim system, i.e. denoted inter-system interference;
- *I<sub data-renderer-mark="true">ext</sub>(j,k)* is the interference from external interfering system(s) in adjacent channel, i.e interference power into this resource block including ACIR;
- *N* is the noise floor.

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/E05qrBEezkC8ZewO-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/E05qrBEezkC8ZewO-image.png) (Eq. 49)

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/cS3vTfveJSwqZmQn-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/cS3vTfveJSwqZmQn-image.png) (Eq. 50)

*I<sub data-renderer-mark="true">ext</sub>(j,k)* is the interference to the the victim <span data-highlighted="true" data-vc="highlighted-text"><span class="_kqswh2mm"><span class="_5pioz8co _189e1dm9 _1il9buyh _19lc184f _d0altlke" data-testid="definition-highlighter">UE</span></span></span><sub data-renderer-mark="true">j,k</sub> from N interfering link transmitters (ILT). Note that the ACIR (Adjacent Channel Interference Ratio) is implicitly taken into account when both unwanted and blocking mechanism are summed in the computation. The unwanted and blocking are defined as follow

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/l4eVEfGvRS9WRObD-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/l4eVEfGvRS9WRObD-image.png) (Eq. 51)

for each of the victim <span data-highlighted="true" data-vc="highlighted-text">UE</span><sub data-renderer-mark="true">j,k</sub>’s frequency where the DL information is received. The ILT can be any generic systems or a <span data-highlighted="true" data-vc="highlighted-text">BS</span>/UEs of a cellular system.

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/ukjJtFKHzgtevug8-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/ukjJtFKHzgtevug8-image.png) (Eq. 52)

at the victim system frequency. Where *N<sub data-renderer-mark="true">RB</sub>* is the number of RBs (i.e. subcarriers) requested per <span data-highlighted="true" data-vc="highlighted-text">UE</span>, and M is the maximum number of RBs per <span data-highlighted="true" data-vc="highlighted-text">BS</span>.

[![image.png](https://wiki.cept.org/uploads/images/gallery/2026-04/scaled-1680-/tDL20QHBK4maLtNj-image.png)](https://wiki.cept.org/uploads/images/gallery/2026-04/tDL20QHBK4maLtNj-image.png) (Eq. 53)

where *NoiseFigure<sub data-renderer-mark="true"><span data-highlighted="true" data-vc="highlighted-text">UE</span></sub>* is the noise figure of a <span data-highlighted="true" data-vc="highlighted-text">UE</span>.