codeigniter - Failed to open stream: HTTP wrapper does not support writeable connection Php

one text

I am working with Php Codeigniter and i am trying to download "xls",But i am getting following error "Failed to open stream: HTTP wrapper does not support writeable connection",My file path is correct but right now unable to download xls file,Here is my current code

$fileName = base_url().'uploads/employee.xlsx';  
$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();
$sheet->setCellValue('A1', 'Id');
$rows = 2;
foreach ($result as $val){
$sheet->setCellValue('A' . $rows, "Hello world");
$rows++;
} 
$writer = new Xlsx($spreadsheet);
$writer->save($fileName);
header("Content-Type: application/vnd.ms-excel");