Traffic shifting between UnderLaid and Overlaid Cells.pptx

traffic

1. Traffic shifting between Underlaid and overlaid cells: airtel gabon case 22 th – May. 2020

2. agenda

3. INTRODUCTION The traffic capacity of a cellular network can be increased by adding more frequencies or reducing the frequency re-use distance. One approach is to apply a second frequency re-use pattern, using the existing sites, with a tighter frequency reuse and overlay on the existing pattern. These cells should be restricted in size, making shorter re-use distance possible without causing excessive co-channel or adjacent channel interference. They are termed overlaid (OL) subcells , whereas the original cells, now with the OL subcells associated, are termed underlaid (UL) subcells . By having more frequencies per cell, the network capacity is increased. To manage the traffic between OL/UL subcells , Ericsson has introduced a feature SCLD ( SubCell Load Distribution). This presentation will show us the different steps to tune this solution with 3 new sites of Airtel Gabon Network.

4. SUBCELL LOAD DISTRIBUTION (SCLD ): Description         Subcell load distribution is an Ericsson feature, which aims at keeping mobile stations connected to the UL subcell . The OL subcell is only used, when the traffic load in the UL subcell increases beyond a certain limit. The fundamental idea with OL/UL subcells is that traffic close to the site is moved to the OL subcell , while the traffic closer to the cell border is moved to the UL subcell . By controlling the traffic in this way, the frequencies in the OL subcell can have a tighter reuse.

5. SUBCELL LOAD DISTRIBUTION : Main Parameters         A path loss threshold LOL with a hysteresis LOLHYST and a timing advance threshold TAOL with a hysteresis TAOLHYST , define the serving area of an OL subcell and control the OL/UL subcell change algorithm in Locating . The conditions for changing subcell within a cell are the following: From UL to OL (see figure 3): The downlink path loss L and the filtered timing advance ta shall fulfil the following condition: L <= LOL - LOLHYST and ta < TAOL – TAOLHYST From OL to UL (see figure 3): The downlink path loss L and the filtered timing advance ta shall fulfil the following condition: L > LOL + LOLHYST or ta >= TAOL + TAOLHYST The downlink path loss, L, is given by the expression: L = BSTXPWR - rxlev_dl

6. SUBCELL LOAD DISTRIBUTION : Main Parameters         If parameter TAOL is set to its maximum value the criterion for changing subcells is only controlled by the path loss threshold LOL . If parameter LOL is set to its maximum value the criterion for changing subcells is only controlled by the timing advance threshold TAOL . If LOL and TAOL are set to values somewhere between their maximum and minimum values, the criterion is controlled by both thresholds as described above. If the percentage of the total number of idle full rate capable TCHs in an UL subcell is less than or equal to parameter SCLDLL and the timers of “ subcell change due to bad quality” or “ subcell change due to too many intracell handover” are not activated for the OL subcell , then a subcell change from the UL subcell to the OL subcell will be requested, see figure 2. When the percentage of idle full rate capable TCHs in the UL subcell equals or falls below SCLDLL subcell changes from the UL to the OL subcell are initiated. When the same percentage exceeds SCLDUL then subcell changes from the OL to the UL subcell are initiated. In between no subcell changes are initiated. Figure 2 PS : No SDCCH should be configured in OL subcell , which makes use of Subcell Load Distribution, since it is only applicable to traffic channels. With SCLD activated, only assignment to UL is allowed, which makes SDCCH in the OL subcell inaccessible .

7. SUBCELL LOAD DISTRIBUTION : Main Parameters         LOL : is the path loss threshold for the serving area of the OL subcell within a cell. This parameter is set per OL subcell . TAOL : is the timing advance threshold for the serving area of the OL subcell within a cell. This parameter is set per OL subcell . LOLHYST : is the path loss hysteresis for the serving area of the OL subcell within a cell. This parameter is set per OL subcell . TAOLHYST : is the timing advance hysteresis for the serving area of the OL subcell within a cell. This parameter is set per OL subcell . SCLD is used to activate subcell load distribution in a cell. It is set per cell. SCLDLL defines the percentage of idle full rate capable TCHs in the UL subcell at or below which subcell change from the UL subcell to the OL subcell is attempted. It is set per cell. SCLDUL defines the percentage of idle full rate capable TCHs in the UL subcell above which subcell change from the OL subcell to the UL subcell is attempted. It is set per cell.

8. SUBCELL LOAD DISTRIBUTION : Value range and Default value

9. Airtel Gabon’s 3 new Sites: Configuration         Ericsson has commissioned 3 new sites in Airtel Gabon Network with the below configuration: Cells capacity: 3/3/3 (900GSM) and 5/5/5 (1800GSM) The MBC ( MultiBand Cell) is activated PS: The Multi band cell feature allows transceiver from different frequency band to be used in the same cell, with a BCCH in only one of the frequency bands

10. Airtel Gabon’s 3 new Sites : Parameters tuning After the changes, we can see the traffic on OL SubCell . Traffic UL is reduced to 38% Traffic OL is increased to 94%