Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-03-30
2001-12-18
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S553100, C455S339000, C455S131000, C375S350000
Reexamination Certificate
active
06332083
ABSTRACT:
The present invention relates generally to the reception of receive signals at a receiver, such as the receive portion of a radio telephone operable in a cellular communication system. More particularly, the present invention relates to receiver apparatus, and an associated method, which digitizes receive signals at an IF (intermediate frequency) stage of the receiver, thereby to permit increased portions of the signal processing elements of the receiver to be performed in a digital domain. Such increased signal processing in the digital domain permits improved performance of the receiver and also permits simplification of receiver construction, particularly when the receiver forms a portion of a multi-mode device, such as a multi-mode, radiotelephone.
BACKGROUND OF THE INVENTION
A communication system permits the communication of information between two or more communication stations. The communication stations are connected by a communication channel upon which a communication signal is transmitted. The communication signal includes the information which is to be communicated between the communication stations. In a two-way communication system, a communication station includes both a transmitter portion and a receiver portion operable to transmit and to receive respectively, communication signals. Thereby, information can be both transmitted and received at a single communication station. In a duplex communication system, communication signals can be both transmitted and received concurrently, or seemingly concurrently.
A radio communication system is a communication system in which the communication channel formed between the communication stations is a radio channel defined upon a portion of the electromagnetic spectrum. When a communication station operable in such a communication system includes both a transmitter portion and a receiver portion, the communication station forms a radio transceiver, capable of two-way radio communication with another communication station. Because communication signals can be transmitted between radio transceivers on radio channels, wireline connections are not required to effectuate communications in a radio communication system. Thereby, communications are possible by way of a radio communication system when formation of a wireline connection between the communication stations would be impractical.
A cellular communication system is an exemplary radio communication system. Cellular communication systems, constructed according to various standards, have been installed throughout significant portions of the world. A subscriber to a cellular communication system is able to communicate telephonically by way of a radio transceiver, typically referred to as a mobile station, when the mobile station is positioned within an area encompassed by the communication system. Telephonic communication of both voice information and data information is permitted in such networks.
Various cellular communication system standards have been developed, and existing cellular communication systems are constructed pursuant to such standards. And, various new proposed standards have been set forth pursuant to which additional cellular communication systems are to be constructed. Various of the standards which define various ones of the cellular communication systems are operable in different manners and require different apparatus, both to form the network infrastructure of such systems, as well as the mobile stations operable therein.
Various mobile stations have been constructed to be operable in more than one cellular communication system. Dual-mode mobile stations, for instance, are available to permit a user to communicate alternately by way of two different cellular communication systems. More generally, multi-mode mobile stations have been developed to permit their operation in multiple different types of cellular communication systems. The mobile station typically must include circuitry specifically constructed for each of the different cellular communication systems in which the mobile station is operable. Because signals generated and received pursuant to operation of the different cellular communication systems are operable, variously, at different frequency ranges, with different modulation schemes, and coding schemes, etc., little of the circuitry required of the mobile station to permit its operation in the different communication systems can be shared. That is to say, significant portions of the circuit paths of the receive and transmit portions of the mobile station required for its operation in the various communication systems cannot be shared. Separate, but functionally redundant, circuit elements are required for the different circuit paths to permit operation of the mobile station in the various communication systems.
Such duplication increases the complexity of the mobile station as well as the cost of the mobile station.
Also, in a typical radio receiver, even a radio receiver operable in a digital communication scheme, significant portions of the receiver circuitry operate on analog signals. Only after the received signals are converted to a base band frequency are the signals typically converted to digital form to permit digital processing thereof.
With advances in digital circuitry, processing of signals in a digital, rather than an analog, domain would permit both better and more cost-efficient processing of the signals.
A manner by which to facilitate processing of signals generated during operation of a communication system in a digital, rather than an analog, domain, would therefore be advantageous.
A manner by which to permit sharing of increased portions of the circuitry of a multi-mode radio device would also be advantageous.
It is in light of this background information related to radio devices that the significant improvements of the present invention have evolved.
SUMMARY OF THE INVENTION
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to digitize receive signals at an IF (intermediate frequency) stage of a receiver, such as the receiver portion of a cellular radiotelephone. By digitizing the receive signals at an IF, rather than base band, frequency, increased portions of processing performed by the receiver are in the digital, rather than analog, domain. Such digitizing of the signals at an IF frequency permits simplification of the construction of the device and also permits improvement in the performance of the device.
In one implementation, apparatus is provided for a multi-mode radiotelephone operable in two or more radio communication systems. Signals provided to the multi-mode radiotelephone are digitized at an IF stage of the receiver portion of the radiotelephone. The RF (radio frequency) and IF stages of the receiver portion of the radiotelephone are shared elements. That is, the RF stage and IF stage are common to the circuitry which is used to receive signals generated by network infrastructure of the various communication systems. Circuit simplification and cost efficiencies concomitant therewith result.
In one aspect of the present invention, receive signals received at a receiver are converted in frequency to an IF frequency level and then applied to a &Sgr;&Dgr;ADC (sigma-delta analog-to-digital converter). The &Sgr;&Dgr;ADC exhibits a signal transfer function and a noise transfer function. The two transfer functions are dissimilar with one another. When a signal is applied to the ADC, the signal is digitized. Quantization noise generated during digitizing of the signal is shifted in frequency. Such shifting in frequency facilitates processing of the informational content of the digitized receive signal as, once shifted in frequency, the noise is readily filtered.
In another aspect of the present invention, the &Sgr;&Dgr;ADC forms a portion of the IF stage of a multi-mode radiotelephone. Signals converted into IF frequencies are applied to a bandpass filter which exhibits a bandpass of frequencies corresponding to the widest frequency band of the two or
Hsu Ken
Shi Zhongming
Gary Erika A.
Maung Nay
Nokia Mobile Phones Limited
Patel Milan I.
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