Hierarchical Cellular Structure in UMTS
1 Answer
  • In UMTS, to enable world wide coverage and roaming, coverage area is divided hierarchically into layers as illustrated in Figure 7.
  • The higher layers cover bigger area than the lower layers.
  • The highest layer achieves worldwide coverage by using satellites.
  • The lower layers are the macro layer, micro layer, and pico layer. They constitute the UTRAN.
  • Each layer consists of several cells. The lower the layer the smaller the cells.
  • Thus, the macro layer is responsible for nationwide coverage with macro cells.
  • Micro layer has microcells which are used for additional coverage in the urban environment.
  • Pico layer forms picocell. They are employed in buildings or “hotspots” such as airports or train stations.

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Figure 7: Different environments in UMTS

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