Microcell zone concept

Why the microcell zone concept is needed

When sectoring is used to increase capacity, the cell is split into sectors, which increases the number of handoffs and the load on the switching centre (MSC), and also reduces trunking efficiency. The microcell zone concept, proposed by Lee, improves capacity and S/I without extra handoffs.

Microcell zone concept

• A cell is divided into several zones (e.g. 3), each with a low-power, directional zone site (transmitter/receiver) located at the cell edge pointing inward.
• All zone sites are connected by fibre or microwave to a single base station, and they share the same radio equipment and channels of the cell.
• As the mobile moves from one zone to another within the cell, the base station simply switches the channel to the new zone site; the mobile keeps the same channel, so no handoff is processed by the MSC.
• A channel is active only in the zone where the mobile is, so radiation is localised and co-channel interference is reduced. This improves S/I (Lee reports about 18 dB with N = 3 instead of N = 7), giving about 2.33 times capacity of a 7-cell omni system.

          Zone 1
          (Tx/Rx)
            \  /
     ┌────── BS ──────┐
  Zone 2 (Tx/Rx)   Zone 3 (Tx/Rx)
   (links by fibre/microwave to BS)

Advantages: higher capacity, fewer handoffs, better S/I, useful along highways and in urban corridors.