Abstract:
Disclosed is a radio repeater system that utilizes a number of spatially diverse receiving antennas, a signal measuring system associated with each of the antennas, a weighted signal combining means, with amplification and retransmission. The system operates by monitoring each of receiving antennas and then calculating the weighted inputs in the signal combining subsystem. The calculation of the weighted inputs is performed by any one of a number of methods, including maximum ratio combining (MRC), minimum mean square error combining (MMSE), and other methods.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 60/826,468 filed on Sep. 21, 2006, by Zhu et al, entitled MULTI-ANTENNA UPGRADE FOR A TRANSCEIVER, the contents of which are hereby incorporated by reference as if recited in full herein for all purposes. 
     
    
     BACKGROUND  
       [0002]     The present device is related to the field of radio wave data communication devices in general and radio signal repeaters in particular.  
         [0003]     Wireless Local Area Networking (WLAN) is a popular method of computer communications. Several methods of Wireless Local Area Networking communications exist and are well known in the arts. The frequency and communication protocols are typically defined by a standards body to ensure interoperability between devices. For example, “WiFi” and “WiMax” are common names for frequency and protocols for data transmission standards.  
         [0004]     A repeater is well known in the radio communication arts. The purpose of a repeater is to receive the signal from a transmitting source, amplify the signal, then retransmit the signal to a receiver. The resulting stronger signal from the output of the repeater increases the range in which a receiver can receive a signal.  
         [0005]     When data signals are transmitted, such as WLAN signals, current repeater design involves the reception of the incoming attenuated signal, decoding the signal, and then reencoding the amplified signal. This leads to interoperability problems because the due to the inherent processing capabilities of the repeaters.  
         [0006]     As is well known in the arts, a typical system configuration in a WLAN system is shown in the prior art  FIG. 1 . In this WLAN System  100  an access point  110  transmits data to a single antenna client  120 . Likewise, the single antenna client  120  transmits data to the access point  110 , completing the communications cycle. Typically, the access point  110  is implemented as a wireless router. The client  120  is usually a computer with a plug-in and/or integrated wireless card.  
         [0007]     When data is transmitted from the access point  110  to the client  120  is termed a ‘downlink’  130  of data. When data is transmitted from the client  120  to the access point  110  it is an ‘uplink’  140  of data. The cyclic process of the downlink of data and the uplink of data between the access point  110  and the client  120  creates a communications channel that allows for the exchange of electronic information.  
         [0008]     WLAN systems can suffer from the degradation of signal quality. When signal quality degrades, the ability to transmit information is reduced. Signal quality is determined by a number of factors, including, the power of the transmitter at the access point  110  and the gain of the receiver at the client  120  during the downlink. Other factors affecting signal quality include the distance between the transmitter and receiver, and the topography between the transmitter and receiver. In a metropolitan area, the topography may not only consist of tall buildings but may also include subterranean structures. Also affecting the signal quality is the number of other signals that are transmitting on the same frequency and that interfere with the signal. Signal quality is both spatially and temporally variant with mobile clients and/or access points. There are changing signal characteristics as the client moves from one topography point to another. This variation in signal quality is known as “fading”.  
         [0009]     Fading of the signal, in a scattering environment, is not unusual in a metropolitan area. Fading is uncorrelated in space when the separation is more than ½ wavelength for multi-antenna configurations. (see W. C. Jakes, “New Techniques for mobile radio”, Bell Laboratory Rec., pp. 326-330, December 1970). Transmission of a radio signal becomes uncorrelated in space if the separation is larger than ½ a wavelength.  
         [0010]     A way to reduce signal fading is to employ multiple antennas that are separated by more than one half of a wavelength. It is well known in the arts that the use of multiple antennas improves signal quality for either the access point or the client. When signals are transmitted from multiple antennas, there is a decrease in the risk of fading. Multiple antennas also allow incoming signals to be combined to produce a stronger signal. When multiple antennas are used for both the access point  110  and the client  120 , this configuration is known as “MIMO” (multiple in, multiple out).  
         [0011]     As shown in prior art  FIG. 2 , a passive MIMO type radio subsystem  200  consists of a signal path  205 , signal processing module  210 , and a phase antenna array interface  215 , and multiple antennas  220 ′,  220 ″,  220 ″′. Downlink data is transmitted on the signal path  205  and processed by the module  210 . The signal is then fed to the antenna array and transmitted on the antennas  220 .  
         [0012]     As shown in prior art  FIG. 3 , an active MIMO type radio subsystem  300  consists of a signal path  305 , a signal processing module  310 , several antennas  320 ′,  320 ″, and  320 ″′. Downlink data is transferred from signal path  305  to the antennas  320 , alternately uplink data is transferred from antennas  320  to the signal processing module.  
         [0013]     Therefore, to increase the signal strength of single antenna systems and by complementing them with MIMO efficiencies; a repeater with MIMO capabilities is proposed that can be easily installed in front of the transmitting WLAN. This repeater configuration is termed a “multi-antenna extender”.  
       SUMMARY  
       [0014]     The inventive subject matter overcomes problems in the prior art by providing a multi-antenna extender with the following qualities, alone or in combination:  
         [0015]     The features of the multi-antenna extender are at least two input antennas, a processor controller, a radio frequency combiner, a summation module, and a radio frequency transmitter. The processor controller may be configured to read the signal value on each of the input antennas and then create a new signal using various algorithms as implemented in software or firmware in the processor controller. These algorithms include the maximum ratio combining (MRC), and the minimum mean square error combining (MMSE) with interference suppression. Methods of using the multi-antenna extender are also described that illustrates the position of the device for the purpose of extending the radio signal strength.  
         [0016]     These and other embodiments are described in more detail in the following detailed descriptions and the figures.  
         [0017]     The foregoing is not intended to be an exhaustive list of embodiments and features of the present inventive subject matter. Persons skilled in the art are capable of appreciating other embodiments and features from the following detailed description in conjunction with the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a prior art block diagram of Access Point and a Single Client System.  
         [0019]      FIG. 2  is a prior art block diagram of a MIMO antenna system that uses a passive antenna array.  
         [0020]      FIG. 3  is a prior art block diagram of a MIMO antenna system that uses an active antenna array.  
         [0021]      FIG. 4  is a block diagram of the multi-antenna extender configured to downlink information from the access point to the computer.  
         [0022]      FIG. 5  is a block diagram of the multi-antenna extender configured to uplink radio signals from the computer to the access point.  
         [0023]      FIG. 6  is a block diagram of the multi-antenna extender configured to select between “n” antenna inputs based on signal strength.  
         [0024]      FIG. 7  is a block diagram of the multi-antenna extender configured to use a weighting of values of “n” receiving antennas.  
         [0025]      FIG. 8  is a generalized flowchart showing the calculation and weighting of the factors in the RF combiner.  
         [0026]      FIG. 9  is a generalized flowchart showing the calculation and weighting of the factors in the RF combiner using the maximum ratio combining algorithm.  
         [0027]      FIG. 10  is a generalized flowchart showing the calculation and weighting of the factors in the RF combiner using the minimum mean square error method, with interference suppression.  
         [0028]      FIG. 11  shows a configuration of the multi-antenna extender where two extenders are used to allow a greater distance between the access point and the client.  
         [0029]      FIG. 12  shows a configuration with a multiple of multi-antenna extenders arranged in parallel to increase the bandwidth of the transmission path. 
     
    
     DETAILED DESCRIPTION  
       [0030]     Representative embodiments according to the inventive subject matter are shown in FIGS.  1  to  12  wherein similar features share common reference numerals.  
         [0031]     In certain respects, the inventive subject matter provides a Multiple Input Multiple Output (MIMO) capabilities to an existing single antenna WLAN environment. The inventive subject matter also provides a cost effective method of upgrading a computing network to provide MIMO capabilities.  
         [0032]      FIG. 4  depicts a block diagram  400  as shown with the multi-antenna extender  430  operating in “downlink” mode in accordance with the inventive subject matter. WLAN signals  420 ′,  420 ″, and  422  are generated by the access point (‘ap’)  412  and transmitted on the access point antenna  414 . A portion of the signals transmitted on the access point antenna  414  are received by the multi-antenna extender receiving antennas  432 ′,  432 ″, whereas another portion of the signals transmitted are received by the single antenna client  452 . Although two multi-antenna extender antennas  432 ′,  432 ″ are shown it is generally understood that any practical number of antennas may be implemented.  
         [0033]     The ap-mae physical distance  490  from the access point  412  to the multi-antenna extender  430  can be increased since the received signal strength on the multi-antenna extender consists of processing the received WLAN signals  420 ′ and  420 ″ simultaneously using a MIMO type subsystem as shown in the prior art.  
         [0034]     The multi-antenna extender  430  then retransmits the signal  440  from the multi-antenna extender  430  to the antenna of the single-antenna client (“sac”)  450 . Physically, the mae-sac distance  470  can be relatively small and in all likelihood is a line of site connection. This short physical mae-sac distance  470  results in a low loss of signal strength.  
         [0035]     Now referring to  FIG. 5 . In  FIG. 5 a  block diagram  500  is shown with the multi-antenna extender  430  operating in “uplink” mode. The sac  450  transmits on the antenna  452  the uplink signal  510 ′,  510 ″. The uplink signal  510 ′, 510 ″ is received by the multi-antenna extender  430  via the multiple antennas  432 ′,  432 ″ and retransmitted on the single antenna  434  as signal  505 . This signal is received by the single antenna ap  412  by the antenna  414 .  
         [0036]     Now referring to  FIG. 6 .  FIG. 6  being the preferred embodiment of the multi-antenna extender  430 . The system diagram  600  of the multi-antenna extender consists of the physically diverse antennas  610 ′, 610 ″ receiving radio signals  605 ′,  605 ″′. Connected to the physically diverse antennas  610 ′,  610 ″ are energy meters  620 ′, 620 ″ respectively. The output of the energy meters  620 ′, 620 ″ is the signal strength  625 ′, 625 ″ for each signal respectively. The signal strength  625 ′,  625 ″ is connected to the n-input comparator  630 . The output of the n-input comparator is a switch signal  635  that controls a multi-selector switch  640 . The multi-selector switch  640  controls the pathway of the radio signals  605  to signal amplifier  650 . The signal amplifier  650  consists of an input and an output. The output of the signal amplifier  650  is a signal transmitted on the antenna  660 .  
         [0037]     The term “connected to” may be, but is not limited to, an electrical, optical, or wireless connection between the objects being connected.  
         [0038]     During operation the n-input comparator continually samples outputs from each energy meter  620 ′,  620 ″ . . .  620   N . When the signal value for one energy meter  620  exceeds the others, the multi-selector switch  640  selects the corresponding antenna  610  with the highest signal value. The radio signal  605  is then passed through to the signal amplifier and transmitted on antenna  660 .  
         [0039]     Now referring to  FIG. 7 , which depicts another embodiment of the multi-antenna extender. Radio signals  710 ′, 710 ″ are received by antennas  720 ′,  720 ″ that are spatially diverse. The radio signals  720 ′ and  720 ″ are input to a processor controller  740  and the RF combiner  780 . The RF combiner  780  is connected to a Power Amplifier  790  and an antenna  800 .  
         [0040]     The processor controller  740  has a number of radio input signals  730 ′, 730 ″ corresponding to each receiving antenna. Software within the processor controller  740  continuously measures the input signals  730 ′, 730 ″ generating weighting factors  750 ′, 750 ″. The weighting factors  750 ′,  750 ″ are connected to the RF Combiner  780 .  
         [0041]     The RF combiner  780  has two sets of inputs and one output. The first set of inputs to the RF combiner are the radio input signals  730 ′,  730 ″ and the second set of inputs are the weighting factors form the processor controller  740 . The combiner output  785  from the RF Combiner  780  is a weighted sum of the received signals from the radio input signals  730 ′,  730 ″.  
         [0042]     The combiner output  785  is connected to a power amplifier  790  that transmits and repeats the radio signal on the antenna  800 . The antenna  800  transmits the repeated signal  810 . The repeated signal being a weighted combination of the radio input signals  730 ′ and  730 ′.  
         [0043]     This implementation is shown with two antennas for simplicity, but any number of antennas may be utilized for the desired reception and amplification of the radio input signal.  
         [0044]     Now referring to  FIG. 8  which is a generalized flowchart of an embodiment as shown in  FIG. 7 . Here the processor/controller program ( 1000 ) in the processor controller  740  scans each of the antennas  730 ′,  730 ″ (Steps  1010 ,  1020 ,  1030 ) and stores the signal of each antenna (Step  1040 ) in the processor controller  740 . After the signal of each antenna has been measured, then the computed antenna weights (Step  1050 ) are generated. The computed antenna weights  1050  are then applied to the RF Combiner  780  as weighting factors  750 ′,  750 ″.  
         [0045]     Now referring to  FIG. 9 , showing an embodiment of the processor/controller program  1000  as illustrated in  FIG. 8  utilizing the maximum ratio combining (MRC).  
         [0046]     The desired signal x 1  (e.g. the signal that leaves the antenna at the transmitter) arrives at each of the receiving antennas Y 1 , Y 2 , (etc) with varying levels. The signals Y 1 , Y 2  as measured by the multi antenna extender as the signal input. The desired signal x 1  arrives at each antenna with a different power and signal phase because of different channel coefficients h 11  and h 21 . 
 
 Y 1 =x 1 *h 11 +n 1
 
 Y 2 =x 1 *h 21 +n 2
 
         [0047]     The received signals are also corrupted by noise n 1  and n 2 . The channel coefficients h 11  and h 21  can be computed with a channel estimator. The MRC algorithm then performs the combining of the incoming signals after weighting each signal path with a factor that is proportional to the square root of its signal to noise ratio snr 1  and snr 2 . In addition, the weighting also aligns the phase of the incoming signals. Therefore the weighting factors are: 
 
 W 1=sqrt(snr1)*exp(− j *angle( h 11))
 
 W 2=sqrt(snr2)*exp(− j *angle( h 21))
 
 Where angle( ) is the phase of the argument. The combined signal to be amplified and forwarded becomes 
 
 Z=W 1 *Y 1 +W 2 *Y 2
 
         [0048]     Now referring to  FIG. 9  showing the flowchart implementing the maximal ratio combining (MRC) algorithm. In the first step, the signal strength is computed on receiving antennas Y 1 , Y 2  (Step  1120 ), next the one sided noise power spectral density No is computed (Step  1125 ), the signal to noise ratio of each antenna input is then computed snr 1 , snr 2  (Step  1130 ). Next the channel estimator coefficients are determined h 11 , h 21  (Step  1135 ). The weighting factors are then determined by multiplying the signal to noise ratio snr 1 , snr 2  by the phase angle (Step  1140 ). The weighting factors are then set in the RF combiner (Step  1145 ).  
         [0049]     Now referring to  FIG. 10 , showing an embodiment of the processor controller program  1000  as illustrated in  FIG. 8  utilizing the minimum mean square error combining (MMSE) with interference suppression.  
         [0050]     The MMSE algorithm can be used to mitigate the effect of interference. The signals Y 1 , Y 2  as measured by the multi antenna extender (MAE) as the signal input. The desired signal x 1  arrives at each antenna with a different power and signal phase because of different channel coefficients h 11  and h 21 . In addition to the desired signal x 1  arriving at the repeater, an interference signal x 2  may also arrive at the MAE with different power and signal phases because of channel coefficients h 12  and h 22 . Therefore, the signals Y 1 ,Y 2  are represented by: 
 
 Y 1 =x 1 *h 11 +x 2 *h 12 +n 1
 
 Y 2 =x 1 *h 21 +x 2* h 22+ n 2
 
         [0051]     In matrix notation, the above becomes: 
 
 Y=Hx+n 
 
         [0052]     Where Y=[Y 1  Y 2 ]ˆT, x=[x 1  x 2 ]ˆT, n=[n 1  n 2 ]ˆT, and H=[hij] a 2×2 matrix whose entry in the ith row and jth column is hij (ˆT means that the vector is transposed).  
         [0053]     The weighting coefficients W=[W 1  W 2 ] are computed so as to minimize the signal to interference plus noise ratio (SINR). It is well known in the art that the MMSE solution is given by: 
 
 W =( Hˆ*H+No I )ˆ(−1) Hˆ* 
 
         [0054]     Where ˆ* denotes transpose conjugate, No is the one-sided power spectral density, and I is a 2×2 identity matrix. W is then the first row of W.  
         [0055]     Now referring to  FIG. 10  showing the flowchart  1150  implementing the minimum mean square estimation algorithm (MMSE) with interference suppression.  
         [0056]     In the first step, the signal strengths are measured on receiving antennas Y 1 , Y 2  (Step  1160 ), next the one sided noise power spectral density No is computed (Step  1165 ), next determine and store the Channel Estimator Coefficients h 11 , h 12 , h 21 , h 22  (Step  1175 ). The next stop calculates the weighting factors by taking the first row of the resulting matrix W from the matrix calculation (Hˆ*H+NoI)ˆ(−1)Hˆ*. (Step  1180 ). The weighting factors are then output to  750 ′, 750 ″ (Step  1185 ).  
         [0057]     Additional embodiments of the processor controller program includes: a) the regeneration of the signal prior to forwarding; b) a translation in frequency prior to forwarding; c) processing of input signals and forwarding on multiple antennas; d) use of directional antennas.  
         [0058]     Now referring to  FIGS. 11 and 12  each showing different configurations of multi-antenna extenders to improve communications performance.  
         [0059]     In  FIG. 11 a  system  1200  consists of an access point  1210  with a transmitting antenna  1220 . A local multi-antenna extender  1230  consists of “n” local receiving antennas  1240 ′,  1240 ″ and one transmitting antenna  1250 . A remote multi-antenna extender  1270  consists of “n” remote receiving antennas  1280 ′,  1280 ″ and a single remote transmitting antenna  1290 . The signal  1295  from the single remote transmitting antenna  1290  is transmitted to the single-antenna client  1300  antenna  1310 .  
         [0060]     Now referring to  FIG. 12 a  bank of local multi-antenna extenders  1410  are configured near the access point  1400  and a bank of remote multi-antenna extenders  1420  are configured near the single antenna client  1430 . In this configuration the signal path begins at the access point antenna  1402  which is transmitted to each of the local multi-antenna extenders  1410 ′,  1410 ″,  1410 ″′, etc. receiving antennas  1414 ′,  1414 ″,  1414 ″′. The signal is forward on the antennas  1412 ′,  1412 ″,  1412 ″′, after being internally processed in the local multi-antenna extender  1410 . The forwarded signals are received by the multiple antennas  1422  located on each remote multi-antenna extenders  1420 . The forward signal is processed and transmitted to the single access client  1430  with antenna  1432 .  
         [0061]     Persons skilled in the art will recognize that many modifications and variations are possible in the details, materials, and arrangements of the parts and actions which have been described and illustrated in order to explain the nature of this inventive concept and that such modifications and variations do not depart from the spirit and scope of the teachings and claims contained therein.  
         [0062]     All patent and non-patent literature cited herein is hereby incorporated by references in its entirety for all purposes.