Inlämning av Examensarbete / Submission of Thesis

Per Rosengren; Andreas Nilsson MME 99-07, pp. 64. Department of Telecommunications and Signal Processing, 1999.

The work

Författare / Author: Per Rosengren, Andreas Nilsson
andreasnilsson@dof.se
Titel / Title: Bumblebee Killer
Abstrakt Abstract:

A common problem in GSM terminals is an interfering signal nicknamed
the “Bumblebee”. This interference is generated by the switching nature of
TDMA cellular telephony, the radio circuits are switched on and off with
the radio access rate. In GSM, this frequency is approximately 217 Hz,
This frequency and its harmonics get into the analog microphone signal,
and produce a very annoying periodic noise in the uplink speech.
This thesis contains a study of four differerent software solutions, to suppress
this interference. These four different methods are denoted, Notch filter,
Matched filter, Correlators and Interpolation in frequency. It is shown
that the best result is achieved with the Correlatars.
Since the frequency comlponents of the Bumblebee are well known, it is
possible to estimate the phase and the amplitude of these with Correlators.
This is done by correlating the microphone signal with sinusoids having
the same frequencies as the Bumblebee, hence the name Correlators. By
generating sinusoids with these phase and amplitude estimates, and then
subtracting them from the microphone signal, the Bumblebee is suppressed.
Since it is subtracted in the time domain it is also possible to consider a
recurring pause in the interference caused by the so called idle frame in the
transmission.

Ämnesord / Subject: Telekommunikation - Telecommunications
Signalbehandling - Signal Processing
Nyckelord / Keywords: Speech Enhancement, Correlators, TDMA, Periodic noise, mobile

Publication info

Dokument id / Document id:
Program:/ Programme Magisterprogram i Elektroteknik / Master of Science in Electrical Engineering
Registreringsdatum / Date of registration: 10/20/2005
Uppsatstyp / Type of thesis: D-Uppsats/Magister/Master

Context

Handledare / Supervisor: Ingvar Claesson
Organisation / Organisation: Blekinge Institute of Technology
Institution / School: Department of Telecommunications and Signal Processing

+46 455 780 00
I samarbete med / In co-operation with: Ericsson
Anmärkningar / Comments:

Filen Bumb.pdf innehåller själva uppsatsen.
Följande ljudfiler, med förklaring innehållande deras ref. nr. i uppsatsen, finns bifogade nedan.

[S1]: Interfering signal Bumblebee, recorded in a silent room.
sound file: Bumblebee.wav
[S2]: Cancellation of the Bumblebee with Notch filter. No speech.
sound file: notch_no_speech.wav
[S3]: Cancellation of the Bumblebee with Notch filter in speech.
soundfile: notch_speech.wav
[S4]: Cancellation of the Bumblebee with Correlators where the idle
frame has been considered. No speech.
sound file: corr_no_speech.wav
[S5]: Cancellation of the Bumblebee with Correlators in speech where VAD and
idle have been considered.
sound file: corr_speech.wav
[S6]: Cancellation of the Bumblebee with Correlators in the Half
Rate case where the idle frame has been considered. No speech.
sound file: corr_no_speech_HR.wav
[S7]: Cancellation of the Bumblebee with Correlators in speech in the Half
Rate case where VAD and idle have been considered.
sound file: corr_speech_HR.wav
[S8]: Cancellation of the Bumblebee with interpolation using a 256
FFT. No speech.
sound file: int_no_speech.wav
[S9]: Cancellation of the Bumblebee with interpolation in speech
using a 256 FFT where VAD has been considered.
sound file: sound:int_speech.wav