Due to cost pressure, device complexity and size issue, most of the digital communication receiver designers try to avoid very sharp Anti- Aliasing filter. And because of that aliasing frequency e.g. image frequency e.g. ghost cell frequency appear inside the digital baseband, which apparently remained un-noticed to the receiver. As receiver is blind about that signal so, it processes the aliasing signal frequency as a desired cell frequency and if the aliasing signal is strong enough, then the initial mobile receiver’s operations like, cell search and camp on etc. will be successfully performed using that aliasing signal. Later, during the uplink transmission time the receiver will discover that it has wrongly camped to an aliasing frequency, as network will not respond to mobile receiver’s message due to mismatch in DL and corresponding UL ARFCN.Here in this paper, a simple, fast and efficient method is proposed to detect the presence of aliasing frequency in the received digital baseband signal. First the dc power at 0 Hz is estimated using I and Q signal average, then that is compared with the dc power after rotating by p radian (e.g. fs/2 – half sampling frequency in case of a twice oversampled received signal). If the estimated dc power before rotation is much higher than the dc power after rotations that will indicate there is no aliasing frequency present in the received digital baseband signal. And in such case, the receiver will process further the received signal, otherwise it will discard or take the appropriate action to combat the aliasing.
AA: Anti-Alias, DCR: Direct Conversion Receiver, RF: Radio Frequency, ADC: Analog to Digital Converter, WCDMA: Wideband Code Division Multiple Access, ARFCN: Absolute Radio-Frequency Channel Number, UL: Uplink, DL: Downlink, UE: User Equipment
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