In　heterogeneous　wireless　networks　(HWNs),　a　scheme　called　Joint　Call　Admission　Control　(JCAC)　is　demanding　for　deciding　whether　or　not　an　incoming　service　request　will　be　accepted.　In　this　paper,　we　propose　an　optimal　JCAC　policy　for　HWNs　based　on　semi-Markov　decision　process　(SMDP)　to　achieve　the　optimal　resource　management　scheme　in　terms　of　minimal　the　network　cost　and　acquire　the　required　quality　of　service　(QoS)　of　mobile　user.　Furthermore,　an　improved　value　iteration　algorithm　with　multi-dimensional　threshold　structure　is　presented.　Numerical　results　show　that　the　proposed　JCAC　policy　is　the　overall　optimal　policy.　The　proposed　algorithm　is　effective　for　high　QoS　performance　by　reducing　the　probabilities　of　dropping　and　blocking　calls.　The　optimal　JCAC　policy　is　ratified　by　the　current　trend　in　the　design　of　next　generation　wireless　networks　(NGWNs).　©　2016　SERSC.