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An example of DCC structure. The basic principle of DCC is shown in Figure 5.35(b). When BS2 reduces its pilot-signal transmission power (PP2), the cell boundary moves toward BS2. The area of BS2 decreases, and some MSs that were in the BS2 cell are reallocated to the BS1 cell. At the same time, MSs reconnected to BS1 increase their transmission power (TM) to meet the target power level of BS1 (SL1). This action, however, increases the interference with BS2. BS2 thus raises its target power level (SL2) to improve the local anti-interference characteristics, and BS1 decreases its target power level (SL1). | Initiatives in 4Gmobile Design 311 Measured SIR D_SIR f Update interval SIR t l Signal converter Power limiter U_Pp t Pp t SIRo SM target SIR BS standard power level TPC controller Figure 5.36 An example of DCC structure. The basic principle of DCC is shown in Figure 5.35 b . When BS2 reduces its pilot-signal transmission power PP2 the cell boundary moves toward BS2. The area of BS2 decreases and some MSs that were in the BS2 cell are reallocated to the BS1 cell. At the same time MSs reconnected to BS1 increase their transmission power TM to meet the target power level of BS1 SL1 . This action however increases the interference with BS2. BS2 thus raises its target power level SL2 to improve the local anti-interference characteristics and BS1 decreases its target power level SL1 to balance the volume of interference between cells. These power adjustments take place independently at each BS so that the communication-quality level equals the target quality level. Figure 5.36 shows an example DCC structure at a BS. Only three functions need to be added to a conventional BS calculating the difference from the SIR target calculating updated power level values and determining pilot signal transmission powers and target powers. The DCC control unit is located a layer above the TPC ones. The DCC controls the power levels so the measured SIR level SIR t meets to the SIR target level SIRO. The difference between the measured SIR and the target SIR is sent to a signal converter and used as the update value for the pilot-signal transmission power. The target power level SL t is updated in inverse relation to the update of pilot-signal power assuming that the propagation loss is the same in both the uplink and the downlink. A TPC controller sends the power-up down information to each MS therefore the uplink signal from each one meets SL t . The interval of DCC control can be determined according to the variation in teletraffic and interference. 5.5.6 Evaluation of DCC Figure .
