Cancellation of humming GSM mobile telephone noise

A sometimes annoying problem in the most internationally widespread cellular telephone system, the GSM system, is an interfering signal generated by the switching nature of TDMA cellular telephone system. A humming noise originating from the speech frames, equivalent to 160 samples of data corresponding to 20 ms at 8 kHz sampling rate is sometimes clearly audible. This paper describes a study of two different software solutions designed to suppress such interference internally in the mobile handset. The methods are Notch filtering, which is performed on a sample-per-sample basis, and speech frame noise cancellation, which is an alternative method employing correlators and subtraction, similar to active noise control [(B. Widow and S.D. Stearns, 1985), (M.Kuo and D.R. Morgan, 1996)].