Abstract:
Disclosed are an adaptive beamforming apparatus and method that despreads an input signal, and determines whether a symbol of despread signal belongs to a pilot sub-channel or non-pilot sub-channel of the despread signal. One of two beamforming algorithms is accordingly enabled. If the symbol belongs to the pilot sub-channel, a first algorithm is used to calculate a weight vector, and if the symbol belongs to the non-pilot sub-channel, a second algorithm is used to calculate the weight vector. A current weight vector is updated using newly calculated weight vector, and a beam pattern is formed based on the updated weight vector.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an adaptive beamforming apparatus and method, and in particular to an improved weight vector update technique for the adaptive beamforming apparatus and method. 
   2. Background of the Related Art 
   In wireless communication systems, various diversity methods are used to increase the coverage area and capacity of a system. For example, use of a rake receiver architecture provides an effective immunity to the inter-symbol interference (ISI) in multipath propagation environments that cause the same signal to be repeatedly received at an antenna at a plurality of different time intervals. 
   Recently, directive antennas have been used to increase the signal-to-noise ratio (SNR) by increasing the energy radiated to a desired mobile terminal while simultaneously reducing the interference energy radiated to other remote mobile terminals. Such reduction in the interference energy radiated to the other mobile terminals can be achieved by generating spatially selective, directive transmission beam patterns. 
   One of the directive antenna techniques used to achieve such beam patterns is adaptive beamforming, in which the beam pattern produced by beamforming antenna arrays of the base station adapts in response to changing multipath conditions. In such beamforming arrays, the antenna beam pattern is generated so as to maximize signal energy transmitted to and received from an intended mobile terminal. 
   In order to adapt to the change of the multipath condition, each Angle of Departure (AOD) at which energy is to be transmitted from the base station antenna array to the intended mobile terminal must be determined. Each AOD is determined by estimating each Angle of Arrival (AOA) at the base station of signal energy from the mobile terminal. In the adaptive beamforming antenna systems, a weight vector concept is used to estimate an AOA spectrum corresponding to a desired AOD spectrum. 
   A Least Means Square (LMS) algorithm is one kind of adaptive beamforming algorithm, and uses only the pilot channel for transmitting a reference signal (non-blind beamforming algorithm). 
   In the LMS algorithm, the weight vector to minimize a mean square error is calculated using a pilot symbol as a training signal. The weight vector is calculated by the following equation 1 in the LMS algorithm. 
                   w   k     ⁡     (     m   +   1     )       =         w   k     ⁡     (   m   )       -     μ   ⁢           ⁢           r   DPCCH_k     ⁡     (   m   )       ⁡     [         d     k   ,   c       ⁡     (   m   )       -         w   k   H     ⁡     (   m   )       ⁢       r   DPCCH_k     ⁡     (   m   )           ]       H           ⁢     
     ⁢         r   DPCCH_K     ⁡     (   m   )       =       [         r   DPCCH_k   0     ⁡     (   m   )       ⁢       r   DPCCH_k   1     ⁡     (   m   )       ⁢           ⁢   …   ⁢           ⁢       r   DPCCH_k     (     P   -   1     )       ⁡     (   m   )         ]     H       ⁢     
     ⁢         w   k     ⁡     (   m   )       =       [         w   k     (   0   )       ⁡     (   m   )       ⁢       w   k   1     ⁡     (   m   )       ⁢           ⁢   …   ⁢           ⁢       w   k     (     P   -   1     )       ⁡     (   m   )         ]     H               〈     Equation   ⁢           ⁢   1     〉             
 
where w is weight vector, and, is a weight vector update coefficient.
 
   Another adaptive beamforming algorithm is the Constant Modulus Algorithm (CMA). The CMA is a blind adaptive beamforming algorithm that uses a constant envelope signal rather than the training signal. This means that there is no intended amplitude modulation. In the CMA, the weight vector is calculated by the following equation 2. 
                   y   DPCCH_k     ⁡     (   m   )       =         w   k   H     ⁡     (   m   )       ⁢       r   MPCCH_k     ⁡     (   m   )           ⁢     
     ⁢         e   DPCCH_k     ⁡     (   m   )       =     2   ⁢     (         y   DPCCH_k     ⁡     (   m   )       -         y   DPCCH_k     ⁡     (   m   )         |     y     DPCCH_k   ⁢     (   m   )         |         )         ⁢     
     ⁢         w   k     ⁡     (     m   +   1     )       =         w   k     ⁡     (   m   )       -     μ   ⁢           ⁢       r   DPCCH_k     ⁡     (   m   )       ⁢       e   DPCCH_k   *     ⁡     (   m   )                     〈     Equation   ⁢           ⁢   2     〉             
 
   The related art adaptive beamforming methods have various problems. For example, the LMS algorithm converges to an optimal value slowly. Hence, it is difficult to employ the LMS algorithm in fast fading radio environments. Additionally, with regard to CMA, since it is a blind adaptive algorithm, its convergence speed is slower than those algorithms that use the training signals. Also, the convergence characteristics of the CMA are not precisely defined relative to the LMS algorithm. 
   Even though there exist various other beamforming algorithms, most of them are much too complex to apply to the radio systems, as compared to the LMS and CMA. Accordingly, such algorithms are problematic. 
   The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
   It is another object of the present invention to provide an adaptive beamforming apparatus and method capable of producing an optimum beam pattern by accurately estimating the AOA spectrum. 
   It is another object of the present invention to provide an adaptive beamforming apparatus and method capable of improving a system capacity and communication quality by generating an optimum beam pattern to a mobile terminal. 
   To achieve at least the above objects in whole or in parts, there is provided an adaptive beamforming apparatus including a despreader for despreading an input signal, a weight vector calculation module for calculating a weight vector in unit of symbol outputted from the despreader, and a beamformer for generating beam pattern using an output symbol from the despreader and the weight vector from the weight vector calculation module, wherein the weight vector calculation module includes a weight vector estimator for selecting one of two beamforming algorithms according to the type of the output symbol. The beamforming algorithms are LMS and CMA algorithms. 
   The type of the output symbol is determined according to a sub-channel of a DPCCH slot. The DPCCH slot is divided into a pilot sub-channel and a non-pilot sub-channel. The weight vector estimator selects the LMS algorithm if the output symbol belongs to the pilot sub-channel and the CMA algorithm if the output symbol belongs to the non-pilot sub-channel. 
   If the beamforming algorithm is changed from the LMS algorithm to the CMA algorithm, the CMA algorithm uses a last (i.e., previous) weight vector calculated by the LMS algorithm as an initial weight vector thereof. Conversely, if the beamforming algorithm is changed from the CMA algorithm to the LMS algorithm, the LMS algorithm uses a last (i.e., previous) weight vector calculated by the CMA algorithm as an initial weight vector thereof. 
   Additionally, to achieve at least the above objects in whole or in parts, there is further provided an adaptive beamforming method comprising despreading an input signal, determining whether a despread signal is a DPCCH signal, determining whether the symbol belongs to a pilot sub-channel or non-pilot sub-channel of the DPCCH signal, enabling one of two beamforming algorithms if the symbol belongs to the pilot sub-channel, enabling the other one of two algorithms if the symbol belongs to the non-pilot sub-channel, updating the weight vector using a calculated weight vector, and forming a beam pattern based on the updated weight vector. The two beamforming algorithms are LMS and CMA algorithms. 
   If the beamforming algorithm is changed from the LMS algorithm to the CMA algorithm, the CMA algorithm uses a last weight vector calculated by the LMS algorithm as an initial weight vector thereof. If, on the other hand, the beamforming algorithm is changed from the CMA algorithm to the LMS algorithm, the LMS algorithm uses a last weight vector calculated by the CMA algorithm as an initial weight vector thereof. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed Out in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
       FIG. 1  is a radio frame structure illustrating an uplink DPDCH and DPCCH configuration; 
       FIG. 2  is a block diagram illustrating an adaptive beamforming apparatus according to a preferred embodiment of the present invention; 
       FIG. 3  is a diagram illustrating a beamformer of the beamforming apparatus of  FIG. 2 ; and 
       FIG. 4  is a flowchart illustrating an adaptive beamforming method according to a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   A preferred embodiment of the present invention will be described hereinafter with reference to the accompanying drawings. 
   The uplink dedicated physical channel (DPCH) defined by the 3GPP comprises three-layer structure of a super-frame, a radio frame, and a slot. There are two types of DPCHs. The first type is a dedicated physical data channel (DPDCH) for transferring, dedicated data and the second type is a dedicated physical control channel (DPCCH) for transferring control information. 
     FIG. 1  illustrates an uplink radio frame structure according to the 3GPP RAIN specification as used by the preferred embodiment. 
   As shown in  FIG. 1 , an uplink DPCH radio frame includes a plurality of slots (slot# 0 -slot# 14 ). A DPCCH slot includes a pilot field, a transport format combination indicator (TFCI) field, a format byte integer (FBI) field, and a transmit power control (TPC) field. 
     FIG. 2  illustrates an adaptive beamforming apparatus according to a preferred embodiment of the present invention. As shown in  FIG. 2 , the adaptive beamforming apparatus of the present invention preferably includes a first Dedicated Physical Data Channel (DPDCH) despreader  11 A and a Dedicated Physical Control Channel (DPCCH) despreader  11 B for respectively despreading a data channel signal and a control channel signal from a dedicated physical channel signal r DPCH     —     k  received from an antenna (not shown). The apparatus preferably further includes a weight vector calculation module  12  to calculate a weight vector of the signal despread at the DPCCH despreader  11 B in a symbol unit. 
   The weight vector calculation module  12  includes an adaptive weight vector estimator  12 A which estimates the weight vector using different weight vector update algorithms according to a sub-channel of a DPCCH slot. 
   A DPDCH beamformer  13 A is provided to multiply the despread signal with the weight vector calculated at the weight vector calculation module  12  and sum the multiplied signal with identically processed signals. The identically processed signal are respectively received through other antennas. The apparatus further includes a DPCCH beamformer  13 B to multiply the despread signal with the weight vector calculated at the weight vector calculation module and to sum the multiplied signal with identically processed signals that are respectively received through other antennas. Next, a DPDCH data buffer  14  is provided to store output signals from the DPDCH beamformer  13 A, and a channel estimator  15  is provided for compensating the channel using the signal from the DPCCH beamformer  13 B. The apparatus further includes a multiplier  16  for multiplying the output signal from the DPDCH data buffer  14  by the output signal from the channel estimator  15  to compensate the output signal of the DPDCH data buffer  14 . A DPDCH combiner  17  is also provided to combine signals from the multiplier  16  into a frame and a frame buffer  18  is provided to store the frame from the DPDCH combiner  17 . Finally, a second DPDCH despreader  19  is provided to despread the frame from the frame buffer  18  and then output the despread frame. 
     FIG. 3  shows additional detail of the DPCCH beamformer  13 B of the adaptive beamforming apparatus of preferred embodiment. 
   As shown in  FIG. 3 , weight values of the DPCCH beamformer  13 B are continuously updated. The DPCCH beamformer  13 B multiplies signals 
       (       r   DPCCH_k     (   0   )       ∼     r   DPCCH_k     (     P   -   1     )         )       
 
received through P antennas, after being despread, with corresponding weight vectors 
       (       w   k     (   0   )       ∼     w   k     (     P   -   1     )         )       
 
at respective multipliers (M 0 ˜M p−1 ). The DPCCH beamformer  13 B then sums the multiplication results at a summer  21 . The weight vectors of the signals inputted to the DPDCH beamformer  13 A are processed in the same manner.
 
   An operation of the above-structured adaptive beamforming apparatus will next be described. 
   Once the radio signal r DPCH     —     k  is received through the antenna, the signal r DPCH     —     k  is despread by the first DPDCH despreader  11 A and DPCCH despreader  11 B. The signal despread by the DPCCH despreader  11 B is then transmitted to the DPCCH beamformer  13 B and the weight vector calculation module  12 . The weight vector calculation module  12  calculates a weight vector of the signal outputted from the DPCCH despreader  11 B in a unit of a symbol. 
   The uplink DPCCH frame consists of 15 slots, each of which is divided into a pilot sub-channel and a non-pilot sub-channel. 
   According to the preferred embodiment, two beamforming algorithms, i.e., a non-blind beamforming algorithm and a blind beamforming algorithm are used for forming the beam pattern. If the operative beamforming algorithm is converted from a first beamforming algorithm to a second beamforming algorithm, a last weight vector calculated by the first beamforming algorithm is used as an initial weight vector of the second beamforming algorithm. During calculation of the weight vector, the adaptive weight vector estimator  12 A selects one of the LMS and CMA algorithms according to a type of sub-channel of the DPCCH slot, i.e., a pilot sub-channel and a non-pilot sub-channel. Thus, the adaptive weight vector estimator  12 A enable the LMS algorithm relative to the pilot sub-channel and enables the CMA for the non-pilot sub-channel. The LMS and CMA algorithms used by the preferred embodiment are identical to those expressed as equations 1 and 2 of the related art. 
   The initial weight vector is set to 0. The weight vector for a first symbol of the pilot sub-channel is thus calculated on the basis of the initial value of 0. The weight vector is continuously updated in reference to the previous weight vector. Also, the weight vector of a first symbol in the non-pilot sub-channel, is calculated on the basis of the weight vector of the last symbol in the pilot sub-channel and the weight vector of the next symbol is continuously calculated by referring to the weight vector of the previous symbol as the initial weight vector. 
   Here, the weight vector calculation module  12  refers to frame and slot numbers that are provided by a DSP or an upper layer for updating the weight vector. 
   The weight vectors 
       (       w   k     (   0   )       ∼     w   k     (     P   -   1     )         )       
 
updated at the weight vector calculation module  12  are preferably provided to the respective DPDCH beamformer  13 A and DPCCH beamformer  13 B. In the DPCCH beamformer  13 B, the weight vectors are respectively multiplied with the input signals 
       (       r   DPCCH_k     (   0   )       ∼     r   DPCCH_k     (     P   -   1     )         )       
 
at the respective multipliers (M 0 ˜M P−1 ). Recall that the input signals are signals received through P antennas and then despread. The multiplication result values are summed at the summer  21 . The weight vectors 
       (       w   k     (   0   )       ∼     w   k     (     P   -   1     )         )       
 
are also multiplied with the signals received through the antennas and the multiplication results are summed in the DPDCH beamformer  13 A.
 
   The output signal of the DPDCH beamformer  13 A is temporally stored in the DPDCH data buffer  14  and the output signal of the DPCCH beamformer  13 B is used for estimating a channel at the channel estimator  15 . 
   The DPDCH data stored in the DPDCH data buffer  14  is next compensated with the output of the channel estimator  15  at the multiplier  16 , and is then combined to a frame at the DPDCH combiner  17 . The frame from the DPDCH combiner  17  is temporally stored in the frame buffer  18 , and is then outputted after being despread at the second DPDCH despreader  19 . 
   The adaptive beamforming method according to a preferred embodiment of the present invention will now be described with reference to FIG.  4 .  FIG. 4  is a flowchart illustrating an adaptive beamforming method according to a preferred embodiment of the present invention. 
   As shown in  FIG. 4 , a despread symbol is first received from the DPCCH despreader  11 B, at step S 101 . Next, the weight vector calculation module  12  determines whether or not the symbol is in the pilot sub-channel of the DPCCH slot, as shown in step S 102 . If the symbol belongs to the pilot sub-channel, the weight vector calculation module  12  enables the LMS algorithm at step S 103 , and then calculates the weight vector using the LMS algorithm at step S 104 . On the other hand, if the symbol is in the non-pilot sub-channel, the weight vector calculation module  12  enables the CMA algorithm at step S 105 , and calculates the weight vector using the CMA algorithm at step S 106 . 
   If the pilot sub-channel transitions to the non-pilot sub-channel, the weight vector of the last symbol in the pilot sub-channel is used for calculating the weigh vector of the first symbol in the non-pilot sub-channel. If, on the other hand, the non-pilot sub-channel transitions to the pilot sub-channel, the weight vector of the last symbol of the non-pilot sub-channel is used for calculating the weight vector of the first symbol of the pilot sub-channel. 
   The system and method for adaptive beamforming according to the preferred embodiment have many advantages. For example, the adaptive beamforming apparatus and method of the preferred embodiment perform the weight vector update using both the LMS and CMA algorithms respectively for the pilot and non-pilot sub-channels such that it is possible to effectively reduce the interferences radiated from other mobile terminals by spatial filtering effect, resulting in increase of system capacity and coverage area. 
   Moreover, since LMS and CMA algorithms are simple relative to other beamforming algorithms, the adaptive beamforming apparatus and method of the preferred embodiment can be effectively employed to a smart antenna system. 
   Furthermore, in the adaptive beamforming apparatus and method of the preferred embodiment, the weight vector can be precisely calculated using an effective one of the LMS and CMA algorithms according to the situation such that the channel estimation accuracy can be enhanced using the reliable weight vector. 
   The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.