Table 1 Summary of notations

${\lambda }_w^{dca}$

Mean arrival rate of new WLAN-only calls in a double coverage area

${\lambda }_c^{dca}$

Mean arrival rate of new cellular-only calls in a double coverage area

${\lambda }_c^{coa}$

Mean arrival rate of new cellular-only calls in a cellular only area

${\lambda }_{wc}^{dca}$

Mean arrival rate of new dual access calls in a double coverage area

${\lambda }_{wc}^{coa}$

Mean arrival rate of new dual access calls in a cellular only area

${\lambda }_{wc}^{c\to c}$

Mean arrival rate of horizontal handoff dual access calls

${\lambda }_c^{c\to c}$

Mean arrival rate of horizontal handoff cellular only calls

${\lambda }_{wc}^{w\to c}$

Mean arrival rate of upward vertical handoff calls

${\lambda }_{wc}^{c\to w}$

Mean arrival rate of downward vertical handoff calls

T ^dca

Residence time in a double coverage area

T ^coa

Residence time in a cellular only area

$p^{coa\to dca}$

Probability of a user moving from a cellular only area to a double coverage area

$p^{coa\to coa}$

Probability of a user moving from a cellular only area to a neighbor cellular only area

T _v

Call duration

$T_{wc,dca}^{ca}$

Cell residence time of dual access calls accepted by the cellular network in a double coverage area

$T_{c,dca}^{ca}$

Cell residence time of cellular only calls accepted by the cellular network in a double coverage area

$T_{wc,coa}^{ca}$

Cell residence time of cellular only calls accepted by the cellular network in a cellular only area