Abstract:
A novel wide null forming system achieves both wide bandwidth and beam width null through employing an antenna array to receive and transmit signals to which a complex null weight vector, calculated by perturbation program, is applied. The novel wide null forming system includes a multiple-element antenna array for receiving or transmitting signals. Multiple conditioning units matching the number of elements is present to condition the signals for proper reception and analysis, after which a series of complex multiplier processors adds complex weights. After being weighted each constituent beam is combined in an adding processor to form one composite beam for use by the user.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims the benefit, pursuant to 35 U.S.C. §119(e), of U.S. provisional application Ser. No. 61/381,381, filed Sep. 10, 2010. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to archite ctures and methods of wireless communication systems. More specifically, but without limitation thereto, the present invention pertains to a communication system and method that allows an antenna element to create a radiation notch when transmitting or receiving radio waves in order to improve gain and signal strength in a desired direction while reducing or eliminating interference from undesired sources and directions. 
         [0004]    2. Prior Art 
         [0005]    The following is a tabulation of some prior art that presently appears relevant: 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 U.S. Patents 
               
             
          
           
               
                 Patent Number 
                 Kind Code 
                 Issue Date 
               
               
                   
               
               
                 5,579,016 
                   
                 1996 Nov. 26 
               
               
                 6,970,722 
                 B1 
                 2005 Nov. 29 
               
               
                 7,117,018 
                 B2 
                 2006 Oct. 03 
               
               
                   
               
             
          
         
       
     
       Non-Patent Literature Documents 
       [0000]    
       
         Wei Wei, Ma Hong, Sun Mingquan, Communications and networking in China, 2-6. ChinaCom &#39;06. First International Conference On, “An Improved adaptive Null Forming Algorithm in Wireless Communication” (2006) 
       
     
         [0007]    In the field of wireless communications and satellite communications design, beam forming is a well-known technique for improving signal quality and transmission integrity. Utilizing antenna arrays employing multiple 
         [0008]    feed elements, beam forming is used to improve antenna directivity and gain significantly for both transmitting and receiving ends as all power is concentrated into a narrower beam of radio signals. Additionally, beam forming provides beam steering capability. These sorts of advantages translate into several things. Improving directivity and gain means improved signal strength for both transmission and reception functions due to signal concentration. Beam steering capability means that the antenna can focus its signals into a beam and point the signal in a desired direction, rather than radiating in all directions that the antenna is pointing. This not only does this reduce signal leakage, but also gives the user the ability to send the signal where they desire. 
         [0009]    The massive proliferation of digital devices and radio frequency-based communications has led to increasing demand for wireless communication technologies. Additionally, competition for bandwidth and coverage among service providers becomes more intense. Finite amounts of digital and physical space means that there is bandwidth usage overlap, or lack of geostationary orbit (GEO) slots for satellites, the most desirable slots for communications satellites. The satellites must be placed 2° apart due to the possibility of interference, considering different companies may share the same bandwidth. As a result, competition for coverage areas is very high, necessitating research into better methods for interference isolation, leading to another technique called null forming. 
         [0010]    Null forming is a method of forming a radiation notch in a desired direction, able to be used by both transmitting and receiving ends. Null forming creates an area where the radiation does not transmit, essentially creating a signal blind spot to shape coverage. On the other hand, null forming for the receiver entails rejection of interference from certain directions.  FIG. 1  shows a radiation pattern using an older single null forming technique, with a null formed on −2°. As shown in  FIG. 1 , previous methods of single null forming produce very narrow nulls both in spatial and in frequency terms. Such results limit the benefits of null forming for two aspects. First, the function of a radiation null depends on the precise location of the target. A little spatial variation of the target will lead it out of the null range, voiding the rejection. Second, the null position is very sensitive to frequency. Even a small variation of the operating frequency will shift the null position. Thus, the single null forming technique only works for narrow band signals. Otherwise, only part of the interference is rejected while the rest still causes signal leakage. As a result, previous single null forming techniques only work for precisely located narrow band signals. This is often inadequate for wireless communication applications. 
         [0011]    As a result, research has been performed to find a way to create wider nulls that meet the demanding requirements for wireless communications use. For example, U.S. Pat. Nos. 6,970,722 (2005), 7,117,018 (2006) both attributed to Lewis. Although he claims he could steer a wide deep null, Lewis&#39;s patent concentrates on steering a null rather than how to form a wide null. And admittedly, in Wei Wei et al.&#39;s paper, “An Improved adaptive Null Forming Algorithm in Wireless Communication”, the author successfully broadens the null width. However, the improvement is not good enough for today&#39;s demanding requirements. 
         [0012]    The present invention is a null forming technique aimed at creating a system that addresses the shortcomings of previous inventions. The present invention is capable of both wide null forming and beam steering capabilities, combining the innovations secured by both Lewis and Wei into a single system. 
       SUMMARY OF THE INVENTION 
       [0013]    In accordance with one embodiment, the present invention provides a dynamic communication system that focuses on creating a series of wide nulls by an antenna system to either prevent signal transmission in certain directions or to reduce incoming interference from undesired directions while maintaining beam steering capability. 
         [0014]    More specifically, the present invention is a null forming system for either receiving or transmitting signals. The receiving system is comprised of multiple antenna elements forming an array, a series of signal pre-processors, a series of complex multiplier processors, and an adder processor. The system functions by receiving radio signals via the antenna elements, which are then “conditioned” to a usable signal via the pre-processors. The signals then enter the complex multiplier processor, where each constituent signal is assigned a null weight vector and undergoes a complex perturbation program until the weight vectors meet a desired set of requirements. The signals are then summed in the adding processor. 
         [0015]    On the other hand, the null forming processor for transmission of signals comprises 1 to N splitter, a series of complex multipliers, a series of transmitting post-processors, and a multiple element antenna array. The transmitting system functions as such: the signal to be transmitted to an external source enters the 1 to N splitter where the constituent signal is split into multiple channels. Then, the signals are complex-multiplied, given a weight vector, and run through a perturbation program just like the receiving array. A post-processor re-conditions the signal for transmission, with the antenna elements broadcasting the signal to a desired external receiver. 
         [0016]    An alternative embodiment of the present invention aims to combine the function of the complex multiplier processor and adding processor into a single central processor. The rest of the embodiment remains the same, with the array elements feeding or receiving signals to and from a pre- or post-processor. 
         [0017]    Another alternative embodiment is using the same setup as the previous embodiment, with the addition of an extra module. A dynamic optimizer is added for real-time re-calculation of signals as they are handled within the central processor. The addition of this module allows the null forming system to dynamically re-adjust the nulls based on real-time conditions. 
       Advantages 
       [0018]    With the proposed algorithm to calculate weights for antennas, the null forming system may produce null patterns with the following advantages: wide null width, wide bandwidth capability, steerable nulls, cooperative null forming and beam forming. 
         [0019]    Further advantages and applications of embodiments will become clear to those skilled in the art by examination of the following detailed. Reference will be made to the attached sheets of drawing that will first be described briefly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  illustrates a radiation pattern of prior art in which a single null is formed; 
           [0021]      FIG. 2  depicts performance of present architecture at the same frequency with  FIG. 1 ; 
           [0022]      FIG. 3  shows performance of present architecture at a different frequency; 
           [0023]      FIG. 4  presents receiving diagram of proposed architecture; 
           [0024]      FIG. 5  presents transmitting diagram of proposed architecture; 
           [0025]      FIG. 6  illustrates an alternative embodiment for both receiving and transmitting; 
           [0026]      FIG. 7  demonstrates an alternative embodiment with real-time processing; 
           [0027]      FIG. 8  shows diagram of optimization process. 
       
    
    
       [0028]      
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 DRAWINGS-Reference Numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 202 
                 Radiation pattern plane 
                 302 
                 Radiation pattern plane 
               
               
                   
                 cut of 19.95 GHz 
                   
                 cut of 18.55 GHz 
               
               
                 402 
                 Receiving antenna array 
                 404 
                 Receiving pre-processor 
               
               
                 406 
                 Complex multiplier 
                 408 
                 Adder 
               
               
                 502 
                 Transmitting 
                 504 
                 Transmitting 
               
               
                   
                 antenna array 
                   
                 post-processor 
               
               
                 508 
                 1 to N splitter 
                 602 
                 Antenna array 
               
               
                 604 
                 Signal processor 
                 606 
                 Central processor 
               
               
                 702 
                 Dynamic optimizer 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    Prior works on null forming systems, like shown in  FIG. 1 , are mostly static, which means some fixed complex weights derived by a non-perfect process are applied to process signals, and they suffer from the following deficiencies: inability to adapt to environmental changes, narrow beam width, and narrow bandwidth. 
         [0030]    Narrow beam width means a spatially narrow beam, while narrow bandwidth is a narrow beam in frequency.  FIG. 1  shows a radiation pattern plane cut of prior null forming works. In the figure, horizontal axis represents geographical distance in terms of angle which is a popular scale in satellite communication. The vertical axis represents radiation power, in dB. Narrow beam width is obvious in  FIG. 1  that at −2° position, where a deep null is formed, −10 dB beam width is merely 0.01°. In another respect, narrow bandwidth means the radiation notch is only valid at certain frequencies, 19.95 GHz in this case, and any change in frequency will lead to malfunction of the nulling system. Since satellites may move around their orbital slots in relation to the ground and usually possess a wide bandwidth, previous single null forming provides limited help to alleviate the problem nulling signals in certain directions. Additionally, satellites with single null forming capability lack the ability to dynamically adjust to environmental factors. One example of an environmental factor that can affect signal transmission is the Doppler Effect. If the relative velocity between a source and a destination is created or changed, variations of Doppler frequency will be introduced, leading to a different operation frequency. This phenomenon is relatively normal in wireless communications, considering that satellites are in motion, mobile ground terminals are used, among other things. As a result, if a static narrow bandwidth null is formed, the system may be prone to failure, as the null is geared for a certain frequency. Thus, single null forming systems do not adequately fulfill the role needed by current demands. 
         [0031]    However, with the current invention, these disadvantages may be mitigated or eliminated altogether. In  FIG. 2 ,  202  Radiation pattern plane cut of 19.95 GHz shows the same radiation plane cut with  FIG. 1  but using this wide null forming system. It is clear that at −2° position two nulls, but not limited to 2, are formed adjacently, and these nulls together form a larger one whose beam width is almost 0.4°. Such a null width is wide enough to cover any satellite orbital slot wiggle relative to a ground observer. Any change greater than that will lead the signal to another orbital slot, which is a different topic not presently covered. Through such a means, narrow beam width deficiency is overcome. 
         [0032]    Additionally, this wide null forming mechanism remains working at a different frequency. In  FIG. 3 , radiation pattern plane  302  cut of 18.55 GHz shows a radiation pattern under the same setting with in  FIG. 2  except at a different frequency. The nulls formed at −2° and 2° move a little but still cover the desired directions. Thus, null performance at −2° working at 18.55 GHz is unaffected. The forming of multiple nulls via the present invention helps overcome the bandwidth deficiency issue of single null systems. In other words, even wide band signals, like TV programs, could utilize benefits of nulling to shape their coverage. 
         [0033]    The physical system used to achieve these multiple nulls for satellite communications is depicted in  FIG. 4 , an embodiment of wide null system applied to signal receiving. First, receiving antenna array  402 , comprised of multiple antenna elements, namely N in  FIG. 4 , is employed to receive incoming signals. These signals are then processed and “conditioned” through receiving pre-processor  404 . Receiving pre-processor  404  may comprise any of the following: low noise amplifiers, down converters, and analog to digital converters. Low noise amplifiers are used to amplify incoming signals after transmitting through long distance. Down converters are used to convert high frequency signals to processable low frequency signals, for example, from 19.55 GHz to 32 MHz. Due to the current technical limits of carrier signal broadcast, they can only be transmitted in high frequencies. Analog to digital converters are used to transform analog signals into digital signals (of course, all processes here can be done in analog, but digital processing is used in this embodiment). 
         [0034]    After all signals are transformed into digital domain, complex multiplier  406  will be used to apply specially calculated null weight vectors, W 1  to W N , to the digitized signals. The null weight vectors are generated by an adaptive perturbation program which continues to probe different null weight vectors until one set of vector satisfies requirements. In other words, the perturbation program will apply an initial set of null weight vectors to incoming signals and calculate radiation patterns. If the derived radiation pattern meets the requirement, the set of null weight vector will be passed to use. If not, current null weight vector will be modified, with recalculation of the radiation pattern until a suitable radiation patterned is found, as shown in  FIG. 8 . Then adder processor  408  will sum up all signals into a final output signal. 
         [0035]    Previous demonstration is all about receiving signals, to which the transmitting of signals with the null forming system is very similar.  FIG. 5  is an exemplary block diagram of null forming system for transmission. Transmission process is a reverse version of receiving one, from bottom to top, if looked at  FIG. 5 . First, instead of an adder  408 , 1 to N splitter  508  is used to deliver the same source digital signal to N channels (again, this process can also be done in analogue format, but digital implementation is demonstrated here). Then a complex null weight vector, W 1  to W N , will be applied through complex multiplier  406 . The complex null weight vector is calculated using the perturbation program explained previously, and if using the same frequency and radiation pattern with receiving, transmission uses the same null weight vector too. Afterwards, transmitting post-processor  504 , typically including digital to analog converters, up converters, and low noise amplifiers, will prepare and recondition weighted signals for transmission. Digital to analog converters are used to convert digital signals to analog signals for transmit; up converters are used to add high frequency carriers to the just converted signals; low noise amplifiers are used to amplify signals for long distance transmission. Lastly, all signals will go through transmitting antenna  502  for transmission. 
       Alternative Embodiment 
       [0036]    Another embodiment is shown in  FIG. 6 . With currently developed technologies, all digital computations, such as previously discussed complex multiplication and summation, can be integrated in one central processor. For example, a microprocessor, including but not limited to, a digital signal processor (DSP), or a field programmable gate array (FPGA) may all be suitable candidates. Since these alternations only affect the digital domain, it can be applied to both transmit and receive functions. 
         [0037]    For receiving, antenna array  602  receives incoming signals. Signal processor  604  performs the same function receiving pre-processor  404 . Central processor  606  does the job of complex multiplication and summation as combination of complex multiplier  406  and adder  408 . 
         [0038]    For transmit functions, central processor  606  performs the job of splitter and complex multiplication as complex multiplier  406  and  1  to N splitter  508 . Signal processor  604  performs the same function as post-processor  504 . Antenna array  602  transmits outbound signals. 
       Alternative Embodiment 2 
       [0039]    In this alternative embodiment, dynamic optimizer  702  is added as an additional module to the null forming system. As depicted in  FIG. 7 , the null forming system contains N number of antenna elements  702 , connected to an equal number of signal processors  604 , which in turn are all connected to central processor  606 . Dynamic optimizer  702  is connected to central processor  606 . Dynamic optimizer  702  is employed to calculate null weight vectors in real time. From an operational standpoint, dynamic optimizer  702  read signals from signal processor  604 . Optimizer  702  then uses these signals to perturb null weight vectors until the set of complex vectors meets given requirements.