This invention relates generally to the signal combination of multiple RF signals used in wireless communications and specifically to the combination of narrowband and wideband RF signals.
In wireless communication systems, such as cellular-based systems, multiple RF signals are combined for transmission through a single antenna or set of antennas. For example, at a cellular base station or site, multiple carrier signals, such as GSM carriers, for handling wireless communication traffic may be combined to be transmitted through the same antenna system. In such signal applications, it is always desirable to combine signals without significant signal loss or attenuation of the combined signals. Furthermore, it is desirable to minimize the cost and complexity of such signal combining systems.
In a typical GSM wireless system, it may be necessary to combine two or more GSM carriers. For low loss combining of narrowband carriers like GSM carriers, one conventional system uses the outputs of narrowband tunable filters (one filter for each GSM carrier). The outputs from the multiple narrowband filters are then electrically summed. An example of such a combiner design is illustrated in
However, while the combiner design 10 of
In the progression of wireless communication technology and standards, it has become necessary to handle both narrowband and wideband signals and applications. The signal interface for third generation (3G) applications utilizes wideband signal technology such as wideband CDMA or W-CDMA. For example, applications such as UMTS applications, which are the 3G successors to GSM applications, make use of the W-CMDA protocol. Therefore, it is becoming desirable to have a single site, such as a cellular base station, that handles both wideband and narrowband applications. Such co-siting is becoming more frequent at wireless communication sites, and with co-siting, the combining of narrowband and wideband signals is mandatory.
To handle the combination of both narrowband and wideband signals, some systems employ hybrid couplers. For example, a combiner 22 is shown in
Therefore, there is still a need to provide a signal combiner that has low cost and low complexity. There is also a need for a low loss combiner able to combine not only narrowband signals, but also to combine narrowband and wideband signals, such as in co-siting applications.
As noted above, it is desirable to combine RF signals, such as in wireless communication applications, using a low cost and low loss solution while reducing the complexity of the signal combiner. The present invention provides such a low loss combiner solution by eliminating components that had been utilized in prior solutions, and provides a low cost and simple, non-complex combiner. The inventive combiner is also expandable to accommodate additional signals to be combined. Furthermore, the inventive combiner is not only able to combine multiple narrowband signals, such as multiple GSM carriers, but also can handle wideband signals such as W-CDMA signals in a co-siting application.
Referring to
The narrowband signal GSM1 is introduced at signal port 32 and passes through a bandpass filter 40. Bandpass filter 40 has a defined pass band, which is a characteristic band of frequencies that are allowed through or will pass through the filter, as is understood by a person of ordinary skill in the art. Signals outside of the pass band are generally attenuated or rejected by the bandpass filter. The bandpass filter is preferably a tunable bandpass filter that may be tuned such that it will pass the signal input at port 32, such as signal GSM1.
The bandpass filter 40 is coupled to one input of a circulator 42. A circulator is a passive device with three or more ports in which the ports can be accessed in a sequential order, such that when a signal is input into a port, it is presented at the next sequential port. The first port of the circulator is also counted as following the last port in the sequential order. In one embodiment of the present invention as illustrated in
Generally, in the present invention, the circulator 44 has two input ports, ports 1 and 3, and has a single output port, port 2, wherein the signals from the input ports are combined according to the invention. Input port 3 of circulator 42 is coupled to the signal port 34 such that another input signal, such as an additional narrow band signal (GSM2) or a wideband signal (WCDMA1) is introduced into the input port 3 of circulator 42. The signal introduced at input port 3 is presented at the next sequential port, which is input port 1. Bandpass filter 40 is tuned or configured to pass the signal from signal port 32 to the input port 1 of circulator 42. The signal at input port 1 is then presented at output port 2 as noted above. However, the signal at signal port 34 would generally be outside or out of the pass band of filter 40. For example, a second narrowband signal, such as GSM2, might be outside of that pass band. Certainly, a wideband signal, WCDMA1, would be outside the pass band of the bandpass filter 40. Therefore, the input signal from the signal port 34 that is introduced at the circulator input port 3 and passed to the circulator input port 1 is rejected by filter 40. Since the signal from input port 3 is out of the pass band, it is reflected by the bandpass filter 40 at port 1 and then output to the output port 2 of circulator 42 as the next sequential port. Reference arrows illustrated by reference numeral 50 show the path of the signal input that is presented at signal port 34. Reference numeral 52 illustrates the path of the signal presented at signal port 32. Therefore, by the operation of combiner 30, multiple input signals at signal ports 32, 34 are combined at the single output port 36.
Combiner 30 may handle multiple narrowband signals (e.g., GSM1, GSM2), as illustrated as well as wideband signals (GSM1, WCDMA1), also illustrated in
Prior to reaching the signal ports 32, 34, the respective input signals might be amplified and thus one or more GSM amplifiers and one or more WCMDA amplifiers (See
Combiner 30 of the present invention reduces the complexity of the combiner as well as reduces its cost. Combiner 30 is low loss and only requires the tuning of a single bandpass filter 40, unlike other solutions as discussed above, that utilize a bandpass filter for each of the combined signals. The use of only one bandpass filter reduces not only the cost, but also the complexity of the combiner. Furthermore, combiner 30 may be utilized to combine both narrowband and wideband signals and introduces losses that are 2 dB lower than the hybrid combiner architecture discussed above with respect to
In accordance with another aspect of the present invention, additional signals might be combined by cascading multiple combiners similar to combiner 30 together. For example, multiple GSM signals might be added together with a W-CDMA signal by cascading the inventive combiners as illustrated in
As illustrated in
In the embodiment illustrated in
Turning now to combiner 60, bandpass filters 40 and 41 might be considered first and second bandpass filters, although as discussed, if additional signals are added, additional bandpass filters may be necessary for each additional stage. Therefore, the present invention is certainly not limited to the embodiments illustrated in
The second port, or output port 2B of circulator 43, is coupled to the third port, or input port 3A of circulator 42. Since bandpass filter 40 has a pass band that is tuned for the input GSM1, the carrier of GSM2 is reflected by filter 40 and provided to the output port 2A of the first circulator 42 to thus combine with the carrier of GSM1. The additional signals that are to be combined take a somewhat similar path and migrate up to port 3A to be presented at the output of port 2A.
The input port 3B of circulator 43 is coupled with the signal port 35, which delivers the wideband signal WCDMA1 to port 3B. The WCDMA1 signal is out of band for both of the pass bands of the first and second bandpass filters, 40, 41. The signal at port 3B is presented at port 1B, and the out-of-band signal is reflected from port 1B to port 2B or, rather, to input port 3A of the first circulator 42. The signal is subsequently presented at port 1A (through port 3A). The signal at port 1A that is out of band with respect to filter 40 is reflected and presented at the output port 2A of circulator 42. In that way, the signals input at the first ports 1A, 1B to each of the circulators 42, 43, and at the third port 3B of the second circulator 43 are all combined as an output at the output port 2A.
For the purposes of isolation, circulators 44, 45 and 47 might be configured as isolators, as shown in
The present invention might also be used for combining signals wherein at least one of the signals is a frequency-hopping signal. For example, some GSM applications might use a GSM carrier that jumps between several frequency channels at a high rate, whereas others of the GSM carriers are at a constant frequency channel. The technique is used to address random external disturbances and increase the robustness of the system. Since the tuning speed of a bandpass filter, such as filter 40, is too slow to adjust to the frequency hopping, which might be on the order of milliseconds, the frequency-hopping GSM signal is introduced at the wideband input port 34, as shown in
For combining a wideband signal with GSM carriers wherein one of the GSM carriers is used with a frequency-hopping technique, the circuit configuration of
Accordingly, the present invention provides a low loss and low cost combiner with reduced complexity for combining not only multiple narrowband signals, but also combining narrowband and wideband signals, such as in co-siting applications. The combiner of the present invention might be incorporated directly into existing base station architecture by coupling it in the signal path to a duplexer, or other combiner, coupled to the antenna system for the base station. While the embodiments set forth herein use GSM and W-CDMA signals as examples, the present combiner is not limited to such signals. Signals from other signal formats and signal protocols might also be combined using the present invention.
In another aspect of the invention, an adjustable line element L might be used, as shown in
Although
Thus, while the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept. For example, the exemplary feed- forward amplifier system described herein has focused on digital filters implemented by switching capacitors to ground, aka digitally commutated filter). However, the principles of the present invention are applicable to other digital filters as well.