# Qiskit: simulate a circuit using a backend noise model

from qiskit import *

def random_bitstring_generator(bit_number, backend):

bitstring = ""

one_qubit_random_bit_generator_circuit = QuantumCircuit(1, 1)
one_qubit_random_bit_generator_circuit.h(0)
one_qubit_random_bit_generator_circuit.measure(0, 0)

for _ in range(bit_number):
counts = execute(one_qubit_random_bit_generator_circuit, backend, shots=8192).result().get_counts()
bit = list(counts.keys())[0]
bitstring += bit

return bitstring

backend = BasicAer.get_backend('qasm_simulator')

print(random_bitstring_generator(1024, backend))

1. How can i insert a noise model replicating IBM melbourne quantum machine for the circuit execution on simulator
2. Is there a way to be able export the sequence received as output to an text/csv file

1. Add this code to your current code. This creates a simulator backend with the noise model from ibmq_16_melbourne.
from qiskit.providers.aer import QasmSimulator

ibmq_melbourne = provider.get_backend('ibmq_16_melbourne')
backend = QasmSimulator.from_backend(ibmq_melbourne)

print(random_bitstring_generator(1024, backend))

1. Your output is already a string. If you want to dump that in a file, you can do this (this is a general Python question, not related to Qiskit:
with open("output.txt", "w") as text_file:
text_file.write(random_bitstring_generator(1024, backend))


Note: If you are trying generate a random number generator, probably you should have a look to qiskit.providers.ibmq.random.

1. https://qiskit.org/documentation/tutorials/simulators/2_device_noise_simulation.html
2. bitstring is a string, you can manipulate it and save it using Python commands.