Abstract:
The present disclosure provides a method and a system for antenna sharing for asynchronous TDD radios comprising an integrated antenna with plurality of antennas and a circuit to limit the co-located transmitters signals, a plurality of transmitters, each transmitter operable on a predetermined set of channels and coupled via a respective transmit switch to a combiner and in turn to an antenna, a plurality of receivers, each receivers operable on a predetermined set of channels and coupled via a respective receive switch to a splitter and in turn to an antenna and a switch controller connected to respective transmit and receive switches for asynchronously connecting at least one transmitter and at least one receiver to the antenna for effecting antenna sharing.

Description:
FIELD OF THE INVENTION 
     The present invention relates to methods and systems for antenna sharing and is particularly concerned with asynchronous time-division duplex (TDD) radios. 
     BACKGROUND OF THE INVENTION 
     Referring to  FIG. 1 , there is illustrated a known antenna sharing frequency-division duplex (FDD) radio system. The FDD radio system  10  includes a shared antenna  12  with duplexer  14  having transmit and receive filters,  16  and  18 , respectively. The transmit frequency and receiving frequency needs to be well separated so that the duplexer can have a good isolation between transmit and receive chains. The system also includes an intermediate frequency transceiver  20  having a transmit side  22 , a receive side  24  and a master oscillator  26 . The system also includes a base band component  30  with analog to digital converter  32  and digital down converter  34  on the receive path and digital up converter  36  and digital to analog converter  38  on the transmit path. The base band component  30  includes baseband processor  40 . The FDD radio system  10  of  FIG. 1  typically splits the available bandwidth between the transmit side and the receive side. For the example of  FIG. 1  the transmit side uses 1930 to 1990 MHz, while the receive side uses 1850 to 1910 MHz. 
     As illustrated in  FIG. 1 , frequency-division duplex (FDD) radios can be co-located. Consequently, they have found it desirable to share an antenna. 
     Referring to  FIG. 2 , there is another known antenna sharing system for synchronous time-division-duplex (TDD) where transmit and receive use the same frequency but in different time intervals. All the radios are synchronized in transmit or in receive via a network or a global-positioning-system (GPS). As illustrated in  FIG. 2 , a 10 ms time frame is divided into 4 parts. The first part  60  is for all the base station radios to transmit and all the terminals to receive; the second part  80  is a transition gap to allow transceivers to switch from transmission mode to reception mode; the third part  10  is the time interval that all the terminals can transmit while all the base stations should be in receiving mode; the fourth part  120  is the receive to transmit transition gap. So all the radios are synchronized either in transmission mode or in receiving mode. 
     However, when co-located TDD radios are in asynchronous mode, one radio is in transmit mode with signal strength 23 dBm, while the other is in receiving mode with a desired weaker signal (˜−90 dBm), there requires roughly 110 dB of isolation in between transmitting radio and receiving radio so that the receiver can work properly. 
     Referring to  FIG. 3 , there is graphically illustrated USA TV channel allocation prior to conversion from analog to digital TV transmission. As can be seen Channels  2  to  69  were allocated between 54 MHZ and 806 MHz with gaps  200 ,  202 ,  204  and  206  between 72 MHZ and 76 MHz, 88 MHz and 174 MHz, 216 MHz and 470 MHz and 608 MHz and 614 MHz, respectively. 
     Referring to  FIG. 4 , there is graphically illustrated USA TV channel allocation after conversion from analog to digital TV transmission. As can be seen Channels  2  to  51  were allocated between 54 MHZ and 698 MHz with the same gaps  200 ,  202 ,  204  and  206  between 72 MHZ and 76 MHz, 88 MHz and 174 MHz, 216 MHz and 470 MHz and 608 MHz and 614 MHz, respectively. 
     Systems and methods disclosed herein provide a system for antenna sharing to obviate or mitigate at least some of the aforementioned disadvantages. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved methods and systems for antenna sharing with asynchronous time-division duplex (TDD) radios. 
     Accordingly, the present disclosure provides methods and systems for antenna sharing with asynchronous time-division duplex (TDD) radios for utilization of television broadcast channels with reduced transmit interferences to receivers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be further understood from the following detailed description with reference to the drawings in which: 
         FIG. 1  illustrates in a block diagram a known frequency-division duplex (FDD) radios antenna sharing system; 
         FIG. 2  illustrates another known synchronized time-division duplex (TDD) radios antenna sharing system. The base stations radios are scheduled to transmit in one time interval while terminals are all in receiving mode; terminals radios are scheduled to transmit in another time interval while base station radios are all in receiving mode. 
         FIG. 3  graphically illustrates USA TV channel allocation prior to conversion from analog to digital TV transmission; 
         FIG. 4  graphically illustrates USA TV channel allocation after conversion from analog to digital TV transmission; 
         FIG. 5  illustrates a channel allocation method in accordance with a first embodiment of the present disclosure; 
         FIG. 6  illustrates an asynchronous TDD radio antenna sharing system in accordance with a second embodiment of the present disclosure; and 
         FIG. 7  illustrates another asynchronous TDD radio antenna sharing system in accordance with a third embodiment of the present disclosure. 
         FIG. 8  illustrates yet another asynchronous TDD radio antenna sharing system in accordance with a fourth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 5  there is illustrated a channel allocation method in accordance with a first embodiment of the present disclosure. According to this method three resonant frequencies f 1 , f 2  and f 3  are pre-selected for antenna  220  with each having TV channel frequencies assigned as shown in  FIG. 5 . Each resonant frequency will result one physical antenna piece, for example a half wavelength dipole, so there are 3 physical antennas and each will resonant at one frequency. 3 antennas will mechanically combined together to form one physical antenna. 
     Referring to  FIG. 6  there is illustrated an antenna sharing system for asynchronous TDD radio systems in accordance with a second embodiment of the present disclosure. There are illustrated three asynchronous TDD radios  290 ,  292  and  296  sharing one physically looking antenna  230  and a control switch module  298 . Each TDD radio system,  290  as an example, includes a transmit side  276  and a receive side  282 . 
     In transmission mode, the transmitted signal is amplified by a power amplifier  264  meanwhile the switch controller  298  swings the switch  252  to connect the transmit circuit and switch  258  to disconnect. The signal then goes through an isolator  240  for which one pole is grounded to avoid the signal returns. The signal further goes through a circulator  232  which directs the signal towards the antenna and then radiates into air. 
     In receiving mode, the switch control  298  swings the switch  252  to disconnect while swing the switch  258  to connect. The antenna receives both desired signal and undesired signals including signals from collocated transmitters. Due to the fact that the antenna is optimized at frequency group f 1 , other undesired frequencies are first gated by antenna. The received signals go through the circulator  232 , which passes the signal at frequency f 1  and further reduces the undesired signals at other frequencies. The received signals pass to the bandpass filter  246 , which allows only the desired signal at frequency f 1  to pass and filters out the other undesired signals. 
     In operation, the switch controller  298  extracts transmit and receive timing information from MAC scheduler or the base band module, which TDD system or chipset vendors provide. 
     Thus, in accordance with the embodiment of  FIG. 6  there is provided an antenna system including an integrated antenna  230  which consists of three antenna pieces (refer to  203   a ) with each antenna is designed for one designated frequency band. The integrated antenna  230  is virtually shared by three radios (or transceivers)  290 ,  292  and  294  hence there are three separate antennas co-located in one enclosure and separated each other 0.168 meters. The circulator  232  passes the signal from transmitter  276  towards the antenna, while it blocks the signal going to the receiver  282 . Similar functions are performed by circulators  234  and  238 . The isolator  240  passes the signal from transmitter  276  and converts the signals from the reverse direction to thermo and dissipated through grounding  241 . The tunable band-pass filter  246  band-passes frequencies associated with frequency f 1  and rejects all other frequencies. Preferably the band-pass filter is a 5th order Chebeshev filter and has a bandpass of 70 MHz with 60 dB rejection on adjacent bands. There are similar bandpass filters  248  and  250  for other two radios. The switch controller  298  controls the coupled TDD switches  252  and  258 ,  254  and  260 ,  256  and  262  such that when in transmit mode, for example, the radio  290 , the controller  298  will instruct TDD switch  252  to turn on and TDD switch  258  to turn off, similarly, in receive mode, for the radio  292 , the controller  298  will instruct switch  254  to turn off and  260  to turn on. 
     In practice, the radio  290  is in transmit mode while  292  is in receiving mode. The undesired signal transmitted on frequency f 1  is received by antenna designed on frequency f 2 , which then leaks into receiver  284 . If the undesired signal strength is 23 dBm, the signal is first attenuated 12 dB due to antenna separation, then experiences an insertion loss of 8dB and filter rejection loss 60 dB and 3 dB loss when passed through switch  260 . Hence, the undesired signal is reduced to 23−12−8−60−3=−60 dbm before it gets into receiver  284  and where the receiver further reduces this undesired signal. 
     In accordance with another embodiment there is provided a method including the steps of 1) deciding how many octes N in the desired whole frequency band 2) dividing the whole frequency bands into N groups such that the frequencies among groups have the largest separation 3) designing N antennas with each optimized for one band group 4) integrating N antennas as a whole and enclosing them into one enclosure 4) allocating frequencies to antennas according to each group. 
     Referring to  FIG. 7  there is another illustrated antenna sharing system for asynchronous TDD radios in accordance with a third embodiment of the present disclosure. The antenna  300  is a wide band antenna that can transmit and receive in multiple frequencies. The TDD radio systems  360  and  362  illustrate three TDD radios and each radio is a pair of a transmitter and a receiver, more precisely  340  and  352 ,  342  and  354 ,  344  and  356 . 
     The transmit side  360  includes separate transmitters  340 ,  342  and  344  for each resonant frequency f 1 ,  12  and f 3 , respectively. Which in turn are coupled via respective power amplifiers  326 ,  328  and  330 , switches  314 ,  316  and  318  to a combiner  304 . The combiner  304  is coupled to master circulator  302  connected to the shared antenna  300 . The receive side  362  includes a splitter  306  which coupled to the master circulator  302  and split the signal into plurality of signals that are fed into plurality of bandpass filters  320 ,  322  and  324  respectively. Which are in turn coupled via switches  334 ,  336  and  338  and low-noise amplifiers  346 ,  348  and  350  to respective receivers  352 ,  354  and  356 . 
     In operation, the switch controller  332  is driven by the MAC scheduler of the TDD radio system. Note that while  FIG. 7  shows switches  314  and  316  closed on the transmit side and switch  334  closed on the receive side, all of the switches can be in either a closed or open state at any given point in time. 
     In accordance with the embodiment of  FIG. 7 , there is another antenna system including an integrated antenna  300 , a circulator  302  which passes all the transmitted signals through toward the antenna and blocks all the transmitted signals toward receivers, a combiner  304 , which combines all the signals in transmission direction, a plurality of isolators  308 ,  310  and  312  which block the transmitted signals to return to plurality of power amplifiers  326 ,  328  and  330 . A splitter splits the received signal into a plurality of signals that is fed into each receiver chain respectively, followed by tunable band-pass filters  320 ,  322  and  324  that further limit the undesired signals get into each receiver chain, a plurality of TDD switches  314 ,  316 ,  318  and  334 ,  336  and  338  and a switch controller  332 , which will turn off each of plurality of transmitters when the corresponding receiver is in receiving mode. The integrated antenna  300  is either one piece of metal resonates in multiple frequencies or plural pieces of metal and each resonates at a desired frequency and all pieces of antenna mechanically integrated together and enclosed within one enclosure physically looks like one antenna. 
     Referring to  FIG. 8  there is illustrated yet another antenna sharing system for asynchronous TDD radio systems in accordance with a fourth embodiment of the present disclosure. The fourth embodiment is similar to that of  FIG. 7 , but the transmit side  398  is modified with the addition of feed forward paths  379  and  341  for transmit signals at carrier frequencies f 3  and f 2 , respectively. Each feed forward path  379  and  341  includes an amplifier  376  and  388  and phase shifters  378  and  340 , respectively coupled another combiner  374  to the splitter  380 . The combiner  374  cancels the undesired signals from the co-located transmitters by subtracting the coupled versions of the transmitted signals from the received signal r(t), the output of combiner  374  is r(t)−s 2 (t)−s 3 (t). 
     In operation, the switch control  366  controls respective ones of transmit switches  342 ,  344  and  346  and receive switches  368 ,  370  and  372 . So that one transmitter or one receiver is coupled to the antenna at any given moment. Separation of the transmitted and received channels can greatly increase the isolation between the transmit and receive sides of co-located radios. 
     The feedback paths provided in embodiment two further reduce interference between transmit and receive sides. 
     In accordance with the embodiment of  FIG. 8 , there is another antenna sharing system including an integrated antenna  370 , a circulator  372 . a combiner  373 , which will combine plurality of signals from plurality of transmitters. The combined signal passes though the circulator  372  and radiates into the air through antenna  370 . Although circulator  372  is intended to block all transmitted signals leaking into the receiver chain, some of transmitted signal still pass through circulator toward receivers. Therefore another combiner  374  is equipped to cancel them by subtracting the coupled versions of the transmitted signals from the received signal r(t), the output of combiner  374  is then r(t)−s 2 (t)−s 3 (t). The splitter  380  slits the signal into plurality of signals each further cleaned up by a band-pass filter  350 ,  352 , and  354  with each respective signal going to the next stage of receiving process. 
     Numerous modifications, variations and adaptations may be made to the particular embodiments described above without departing from the scope patent disclosure, which is defined in the claims.