how to eliminate inteference with handphone signal?

Hi:
i'm using 868Mhz transmitter to transmit data. And i found that the trasmission distance is not far as what i expected. The range is about only 100m... so, how to eliminate the inteference?

What do you mean by intereference?

If it is loss of signal then use an antenna that is longer. At least 1/4 of the wavelenghth of the transmitted wave. You can also increase transmission distance if you increase the power of the transmitter.

If there is noise in the transmission, and you are using AM, try using another technique like FM or Pulse Modulation.