bscriber presses the Call but- ton, the call is connected. 5.3.4 Handover or Handoff During a call the quality of the connection is continuously monitored and the transmission power of the MS and BS is adjusted to keep the quality at a sufficient level while at the same time keeping the transmission power as low as possible. When an MS moves close to the border of a cell, the transmission power is adjusted to the maximum allowed for that cell. As an MS moves fur- ther away from the BS, the S/N of the channel decreases and the error rate increases. If the quality falls below a predetermined level, a new channel is allocated in a neighboring cell and both the BS and the MS are requested to switch to the new channel at the same time instant. The cellular network has analyzed the measuring results before the switch and estimated the quality between the MS and neighbor cells. The best alternative is selected for a new cell. 5.3.5 MS Transmitting Power During the planning phase of a cellular network, the maximum transmitting power for each cell is defined. This power is dependent on the desired cell size and on geographic conditions. The transmitting power of the common Mobile Communications control channel of the BS is adjusted to a level that is high enough to cover the cell area but not higher than necessary. During a call the network, to minimize interference between cells that use the same frequency, continu- ously controls the transmitting power of the MS and the BS. This also saves the battery of the MS. 5.4 Mobile Communication Systems So far we have looked at the generic operation of cellular mobile radio sys- tems because of the importance of these systems. However, there are many other important mobile communication systems, and we briefly introduce some of them in this section. 5.4.1 Cordless Telephones Cordless phones were originally developed for the residential market and they were designed to cover only one local area such as a house and garden. They support only local mobility and should not be conside