Hi Ganesh,
sorry but you mixed up the "old" Gateway that carries out CPI-C services within the SAP world SAP Gateway - SAP Library with our "new" SAP Gateway that is responsible to enable OData Service for the SAP Business Suite.
Unfortunately we (SAP) have not followed the Highlander Principle here 
.
While the "old" Gateway is part of every SAP ABAP application server but can also be installed stand-alone the "new" SAP Gateway (formerly known as SAP NetWeaver Gateway whith less options to be mixed up) is based on ABAP technology either deployed as a bunch of AddOns (at least IW_BEP, GW_CORE and IW_FND) or as of 7.40 as a software component SAP_GWFND.
So you are right.
You have to uninstall your standalone Gateway, install an ABAP server and add the SAP Gateway AddOns to it or you go for an installation of a SAP NetWeaver 7.40 system.
If possible I would recommend to use the latter.
Best Regards,
Andre