Closely associated with mobility management is radio resource management or RRM, the process which ensures that the optimum radio channel is used by an M-ES. Optimum means that the channel provides the most reliable performance while not interfering with either other CDPD or cellular users. Non-interference with cellular voice customers is of paramount importance, since CDPD is a service overlaid on the existing cellular voice network.
Contrary to cellular voice systems, in which cell handoff is controlled by the system,3.22 the CDPD system requires that the mobile device manage its own use of radio resources. This is necessary because of the bursty nature of the packet-switched access to CDPD services; the mobile generally does not transmit long enough for the system to accurately measure its RF reception from multiple MDBSs.
The CDPD system periodically broadcasts information to assist the mobile in evaluating its current channel against alternative channels provided in adjacent cells. Prior to transmitting, the M-ES evaluates alternative channels to ensure that it uses the best channel. In a properly tuned system, the best channel will be in the same cell as the channel assigned to a similarly-located cellular voice handset.
The radio resource management scheme in CDPD also controls the power level used by the mobiles by broadcasting a so-called power product. The theory is that RF signals are reciprocal between two points; if one transceiver informs the other transceiver of the power level it is transmitting at, the second transceiver can calculate the power level it must use, based on the received signal strength.
CDPD radio resource management is defined by Part 405 of the CDPD System Specification [CDPD95] and is described in Chapter 5.