Hi Subhakanta jena
Good Rx level and bad Rx quality is due to interference as know in GSM/LTE or pollution in WCDMA systems;
the latter is due to many servers having almost the same signal strengtht without any being significantly dominant compared to the others (usually more than 5 radiolinks) and all of them being low.
to fix it you just need to create a dominant server thanks to physical actions on site and neighbors. Also make sure radio parameters are not incriminated (wrong location/mobility parameters like CIO,Qoffset,…)