Patent Application
20110053536
The present invention relates generally to radio communication systems, and particularly to methods and systems for performing frequency conversion in radio receivers.
Some communication systems, e.g., microwave links, partition the system circuitry between an Outdoor Unit (ODU) and an Indoor Unit (IDU). For example, U.S. Patent Application Publication 2005/0124307, whose disclosure is incorporated herein by reference, describes an indoor unit (IDU) and compact outdoor unit (ODU) having an intermediate frequency/modem circuit, millimeter wave transceiver circuit, and digital interface between the IDU and the ODU.
U.S. Pat. No. 6,844,787, whose disclosure is incorporated herein by reference, describes a system that performs a first modulation at an arbitrary frequency and a second modulation at another arbitrary frequency. In order to achieve this goal, the system demodulates the first modulation using the same reference oscillator signal that was used in the first modulation. In effect, a first modulation is achieved at a first frequency, the first modulation is then demodulated to zero frequency, and, in turn, a second modulation is achieved at a second frequency.
An embodiment of the present invention provides a receiver, including:
a front end, which is configured to down-convert a first Radio Frequency (RF) signal at a first frequency, so as to produce a second signal at a second frequency, lower than the first frequency;
an up-converter, which is configured to up-convert the second signal to produce a third Intermediate Frequency (IF) signal at a third frequency, higher than the second frequency; and
an interface, which is configured to transmit the third signal over a cable for remote demodulation.
In some embodiments, the receiver further includes a reception subsystem, which is configured to receive the third signal from the cable, to down-convert the third signal and to demodulate the down-converted third signal. In an embodiment, the interface is operative to communicate a reference clock signal over the cable together with the third signal, the up-converter is configured to up-convert the second signal using the reference clock signal, and the reception subsystem is configured to down-convert the third signal using the reference clock signal. In a disclosed embodiment, the interface is configured to communicate management information over the cable between the receiver and the reception subsystem. In another embodiment, the receiver is included in an Outdoor Unit (ODU) and the reception subsystem is included in an Indoor Unit (IDU).
In yet another embodiment, the front end includes at least one filter, which is configured to filter the second signal and to provide the filtered second signal to the up-converter. In still another embodiment, the front end includes a frequency source, which is configured to generate at least one Local Oscillator (LO) signal, and the front end is configured to down-convert the first RF signal using the LO signal. In an embodiment, the second signal includes a baseband signal. In a disclosed embodiment, the front end is included in an integrated device, which is separate from the up-converter and is mounted in the receiver.
There is additionally provided, in accordance with an embodiment of the present invention, a method for communication, including:
down-converting a first Radio Frequency (RF) signal at a first frequency, so as to produce a second signal at a second frequency, lower than the first frequency;
up-converting the second signal to produce a third Intermediate Frequency (IF) signal at a third frequency, higher than the second frequency; and
transmitting the third signal over a cable for remote demodulation.
There is also provided, in accordance with an embodiment of the present invention, a production method, including:
obtaining at least first and second identical front end units, which down-convert respective first Radio Frequency (RF) signals in a first frequency band to produce respective second signals in a second frequency band, lower than the first frequency band;
incorporating the first front end unit in a first receiver, which up-converts the second signal produced by the first front end unit to produce a third Intermediate Frequency (IF) signal in a third frequency band, higher than the second frequency band, transmits the third signal over a cable, receives the third signal from the cable, down-converts the third signal and demodulates the down-converted third signal; and
incorporating the second front end unit in a second receiver, which demodulates the second signal produced by the second front end unit.
There is also provided, in accordance with an embodiment of the present invention, a method, including:
producing at least first and second identical front end units, which down-convert respective first Radio Frequency (RF) signals in a first frequency band to produce respective second signals in a second frequency band, lower than the first frequency band;
supplying the first front end unit for use in a first receiver, which up-converts the second signal produced by the first front end unit to produce a third Intermediate Frequency (IF) signal in a third frequency band, higher than the second frequency band, transmits the third signal over a cable, receives the third signal from the cable, down-converts the third signal and demodulates the down-converted third signal; and
supplying the second front end unit for use in a second receiver, which demodulates the second signal produced by the second front end unit.
There is additionally provided, in accordance with an embodiment of the present invention, a production method, including:
obtaining at least first and second identical front end units, which down-convert respective first Radio Frequency (RF) signals in a first frequency band to produce respective second Intermediate Frequency (IF) signals in a second frequency band, lower than the first frequency band;
incorporating the first front end unit in a first receiver, which transmits the second signal produced by the first front end unit over a cable, receives the second signal transmitted over the cable, down-converts the received second signal and demodulates the down-converted second signal; and
incorporating the second front end unit in a second receiver, which demodulates the second signal produced by the second front end unit using circuitry that is collocated with the second front end unit.
There is also provided, in accordance with an embodiment of the present invention, a method, including:
producing at least first and second identical front end units, which down-convert respective first Radio Frequency (RF) signals in a first frequency band to produce respective second Intermediate Frequency (IF) signals in a second frequency band, lower than the first frequency band;
supplying the first front end unit for use in a first receiver, which transmits the second signal produced by the first front end unit over a cable, receives the second signal transmitted over the cable, down-converts the received second signal and demodulates the down-converted second signal; and
supplying the second front end unit for use in a second receiver, which demodulates the second signal produced by the second front end unit using circuitry that is collocated with the second front end unit.
The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:
Some radio communication systems use split-mount configurations, in which a Radio Frequency (RF) front end is mounted in an Outdoor Unit (ODU), a modem is mounted in an Indoor Unit (IDU), and the ODU and IDU are connected by a cable. Other communication systems use single-mount configurations, in which both the RF front end and the modem are mounted in a single enclosure.
Embodiments of the present invention that are described hereinbelow provide improved receiver designs, which enable the use of a common RF front end unit type for both split-mount and single-mount system configurations. In some embodiments, the RF front end unit receives an RF signal and down-converts it to a low frequency, typically to baseband. In a single-mount configuration, the receiver comprises a demodulator, which demodulates the signal produced by the RF front end unit. In a split-mount configuration, on the other hand, the low-frequency output of the front end unit is up-converted to IF and then sent over the cable for remote demodulation. In alternative embodiments, the RF front end unit produces an Intermediate Frequency (IF) signal. In a split-mount configuration, the IF signal produced by the front end unit is sent over the cable. In a single-mount configuration, the IF signal is demodulated in the ODU, e.g., using additional down-conversion or direct IF sampling.
The receiver designs described herein enable equipment manufacturers to handle (e.g., specify, design, buy, produce, stock, test, integrate, install, operate and/or troubleshoot) only a single type of RF front end unit, and to use these front end units in both split-mount and single-mount system configurations. As a result, manufacturing and stocking costs are reduced.
ODU 24 comprises an RF front end unit 40, which down-converts the received RF signal to low frequency, typically to baseband. As will be shown below, front end 40 is a common building block that is used in both split-mount and single-mount system configurations. An alternative configuration, which uses a common front end that produces an IF signal, is shown in
Front end 40 comprises a down-converting mixer 44 and a frequency source 48 (e.g., a Phase-Locked Loop—PLL). (In a typical implementation, front end 40 may comprise additional components and functions, which are not related to carrying out the disclosed techniques. These elements are not shown in the figures for the sake of clarity.) Frequency source 48 generates a suitable Local Oscillator (LO) signal and provides it to mixer 44. The mixer down-converts the RF signal by mixing it with the LO signal. In some embodiments, front end 40 comprises a low-pass filter 52, which filters the output of mixer 44 so as to suppress out-of-band signals. Thus, front end unit 40 produces a baseband signal that is ready for baseband processing by a demodulator.
As will be shown in
Mixer 56 thus produces an IF signal, at a frequency that is higher than the frequency of the signal produced by front end 40. The frequency of the IF signal can be set to any suitable value, such as, for example, 140 MHz. Mixer 56 up-converts the baseband signal by mixing it with a suitable LO signal provided by a frequency source 60, e.g., a PLL. The ODU may comprise a filter (e.g., band-pass or low-pass filter, not shown) for filtering the IF output of mixer 56, as well as various other components such as amplifiers and n-plexers. The IF signal is provided to a cable interface 64, which sends the signal over cable 32 to the IDU.
IDU 28 comprises a cable interface 76, which receives the IF signal from cable 32. The IDU comprises a down-converting mixer 80, which down-converts the IF signal to low frequency (e.g., baseband). Mixer 80 down-converts the IF signal by mixing it with a LO signal produced by a frequency source 84, e.g., a PLL. The signal produced by mixer 80 is filtered by a low-pass filter 88 and provided to a demodulator 92. The demodulator demodulates the baseband signal so as to extract the data. The data is provided as output to a user or host system (not shown). In an alternative embodiments, IDU 28 may demodulate the IF signal using direct IF sampling instead of down-converting it to baseband.
Each of the frequency sources in the ODU and IDU generates an LO signal that is locked to a certain reference clock signal. Any suitable clock frequency, such as 10, 40 or 100 MHz, can be used.
In some embodiments, frequency source 60 in the ODU and frequency source 84 in the IDU generate LO signals that are locked to a common reference clock signal. In other words, up-conversion from baseband to IF in the ODU, and down-conversion from IF back to baseband in the IDU, are performed using LO signals that are locked to the same reference clock signal. Performing up- and down-conversion using the same reference clock signal improves the receiver performance, e.g., reduces frequency offsets and combines I/Q imbalances to allow easier compensation by the host. Receiver 20 comprises a reference clock generator 68, which generates the common reference clock signal. In the example of
When both ODU and IDU use the same reference clock signal, the signal is transferred over cable 32. In the example embodiment of
In some embodiments, ODU 24 and IDU 28 may exchange management data with one another over cable 32. In the example of
In receiver 100, an RF signal is received by antenna 36 and down-converted to baseband by RF front end 40, similarly to the operation of receiver 20 of
As can be seen in the figure, receiver 100 uses the same type of RF front end unit 40 used in receiver 20. Since demodulator 92 is collocated with RF front end 40, the signals sent over cable 108 are digital. Thus, baseband-to-IF up-conversion and IF-to-baseband down-conversion are eliminated.
The configurations of receivers 20 and 100 are example configurations, which were chosen purely for the sake of conceptual clarity. In alternative embodiments, any other suitable configuration can also be used. For example, in a split-mount configuration, the ODU and IDU may generate separate reference clock signals instead of transferring a common reference clock signal over the cable. Additionally or alternatively, the receiver may use separate cables for transferring the received (IF) signal, clock signals and/or management data. RF front end 40 may comprise any other suitable down-conversion circuitry. For example, the RF front end may comprise two or more mixers that down-convert the received RF signal in multiple conversions instead of performing direct conversion to baseband.
The different elements of receivers 20 and 100 may be implemented using discrete components, Radio Frequency Integrated Circuits (RFICs), Monolithic Microwave Integrated Circuits (MMICs) or any other suitable hardware. In particular, front end 40 may be fabricated in an integrated device or unit, which can be mounted in both split-mount and single-mount receivers. The term “integrated device” refers to any kind of package, board or other means of fabricating and assembling the elements of front end 40. For example, the front end can be fabricated in a dedicated IC (e.g., an RFIC or MMIC), or on a dedicated Printed Circuit Board (PCB) or other substrate.
Cable interface 64 sends the IF signal over cable 32 to IDU 28, at a cable transmission step 122. Cable interface 76 in the IDU receives the IF signal from the cable. In some embodiments, cable interfaces 64 and 76 multiplex and de-multiplex a common reference clock signal and/or management data over the cable, together with the IF signal.
In the IDU, mixer 80 down-converts the IF signal received over the cable to baseband, at a second down-conversion step 126. Filter 88 filters the down-converted signal. Demodulator 92 demodulates the baseband signal produced by mixer 80, at a demodulation step 130. The demodulated data is provided as output.
As noted above, the disclosed receiver configurations enable a receiver manufacturer to manufacture both split-mount and single-mount receivers using the same type of RF front end unit. In a possible manufacturing process, a device manufacturer produces multiple front end units (e.g., in RFICs). The device manufacturer may supply the front end units to one or more system integrators (e.g., receiver manufacturers) for use in both split-mount and single-mount receiver configurations.
In some embodiments, both split-mount and single-mount receivers are constructed using a common type of RF front end unit, which down-converts the received RF signal to IF. In split-mount configurations, the IF signal produced by the front end is sent over the cable to the IDU for remote demodulation. In single-mount configurations, the IF signal is demodulated locally (i.e., using circuitry that is collocated with the front end in the ODU). Demodulation of the IF signal in the ODU may be performed, for example, using an additional down-conversion or using direct IF sampling.
The front end may also comprise an IF filter 172 (e.g., a low-pass or band-pass filter), which filters out undesired signals. The IF signal produced by front end unit 164 is provided to cable interface 64, which sends the signal over cable 32 to the IDU. Any suitable split-mount IDU, such as IDU 28 of
The split-mount and single-mount receivers of
Although the embodiments described herein mainly address the design of split-mount and single-mount receivers using a common type of RF front end, the methods and systems described herein can also be used in various other applications.
It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.
