In　this　paper,　the　bit-error-rate　performance　(BER)　is　analyzed　for　primary　single-input　multiple-output　(SIMO)　network　in　cognitive　radio　(CR)　environment.　In　underlay　mode,　secondary　network　shares　the　same　spectrum　occupied　by　primary　network,　which　inevitably　generates　interference　for　primary　network.　With　the　assumption　that　there　is　one　transmit　antenna　and　two　receive　antennas　in　primary　network,　both　distributed　interference　subtraction　(DIS)　scheme　and　our　proposed　Dempster-Shafer　theory　based　signal　combining　(DSC)　scheme　are　considered　to　mitigate　interference　at　primary　receiver.　Simulations　are　performed　for　BER　performance　comparisons　between　these　two　schemes.　The　results　show　that　compared　with　DIS,　DSC　achieves　more　performance　gains　and　is　more　robust　against　interference.