Dual-mode radio receiver for receiving narrowband and wideband signals

DETAILED DESCRIPTION The present invention provides an improved dual-mode radio receiver operating in a radio communication system that uses either wideband or narrowband signals.
The radio receiver demodulates wideband and narrowband signals with reduced duplication of receiver components.
The radio receiver has a wideband mode (e.
g.
, the GSM or IS-95 standard) for demodulating wideband signals and a narrowband mode (e.
g.
, the IS-54 or INMARSAT-M satellite communications standard) for demodulating narrowband signals.
A wideband filter apparatus adapted for a wideband mode and having a wide filter bandwidth is provided for filtering radio signals containing alternatively wideband signals and narrowband signals.
When in the wideband mode, the wideband filter apparatus receives radio signals and extracts wideband signals.
The extracted wideband signals are demodulated by well-known methods.
When in the narrowband mode, the wide bandwidth filter apparatus receives radio signals containing narrowband signals and generates filtered signals which contain the narrowband signals in subbands of the wide filter bandwidth.
The filtered signals are digitized and processed with a digital filter.
The digital filter has a narrow filter bandwidth adapted to the narrowband signals and separates the desired narrowband signals by filtering out unwanted flanking signals.
The radio receiver is adapted to perform the extraction of narrowband signals existing in off-center subbands of the wide filter bandwidth.
Furthermore the radio receiver can be adapted to jointly extract two or more different narrowband signals that are at different radio channel frequencies and that are located in different subbands of the wide filter bandwidth.
The extraction of different narrowband signals lying in off-center subbands of the wide filter bandwidth is an important useful feature of the invention claimed herein.
In the parent application, the invention was described to receive narrowband signals lying nominally in the center of the wide filter bandwidth with the undesired flanking signals flanking the desired narrowband signals