Source: http://www.google.com/patents/US20030216156?dq=7222078
Timestamp: 2013-12-19 04:24:08
Document Index: 595706421

Matched Legal Cases: ['art 310', 'art 310', 'art 310', 'art 310', 'art 310', 'art 310', 'art 310', 'art 310']

Patent US20030216156 - Apparatus and method for forming a forward link transmission beam of a smart ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method and apparatus for a base station including an antenna array calculates a direction of a weight vector of a transmission beam to maximize in-phase component power for a common channel signal in a transmission channel signal for transmission to a mobile station and to minimize a sum of quadrature-phase...http://www.google.com/patents/US20030216156?utm_source=gb-gplus-sharePatent US20030216156 - Apparatus and method for forming a forward link transmission beam of a smart antenna in a mobile communication systemAdvanced Patent SearchPublication numberUS20030216156 A1Publication typeApplicationApplication numberUS 10/440,195Publication dateNov 20, 2003Filing dateMay 19, 2003Priority dateMay 17, 2002Also published asCN1653720A, CN100454775C, EP1363357A1, EP1363357B1, US7103384, WO2003098837A1Publication number10440195, 440195, US 2003/0216156 A1, US 2003/216156 A1, US 20030216156 A1, US 20030216156A1, US 2003216156 A1, US 2003216156A1, US-A1-20030216156, US-A1-2003216156, US2003/0216156A1, US2003/216156A1, US20030216156 A1, US20030216156A1, US2003216156 A1, US2003216156A1InventorsByung-jin ChunOriginal AssigneeChun Byung-JinExport CitationBiBTeX, EndNote, RefManReferenced by (18), Classifications (14), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetApparatus and method for forming a forward link transmission beam of a smart antenna in a mobile communication systemUS 20030216156 A1Abstract A method and apparatus for a base station including an antenna array calculates a direction of a weight vector of a transmission beam to maximize in-phase component power for a common channel signal in a transmission channel signal for transmission to a mobile station and to minimize a sum of quadrature-phase power component and interference power for other mobile stations inside and outside a cell due to a transmission channel signal for the mobile station. Images(8) Claims(27)
What is claimed is: 1. A transmission beam forming control apparatus of a base station, for forming a transmission beam for a transmission channel signal to be transmitted to a mobile station from an antenna array including a plurality of antenna elements, the apparatus comprising: a transmission beam weight vector calculator for estimating a direction of the mobile station by using a reception signal and a reverse link power control bit received from the mobile station, and calculating a transmission beam weight vector in the estimated direction; and a transmission beam former for applying the calculated transmission beam weight vector to the transmission channel signal and providing the applied transmission channel signal to the antenna array. 2. The transmission beam forming control apparatus of claim 1, wherein the transmission beam weight vector calculator comprises: a first forward link covariance matrix calculator for calculating a forward link covariance matrix estimation value by using a signal received from the mobile station via the antenna array, a reverse link power control value of the mobile station, and a frame error rate; a second forward link covariance matrix calculator for calculating a forward link covariance matrix estimation value for other mobile stations; and an optimal weight vector calculator for calculating an optimal weight vector of the transmission beam from the estimation values output from the first and second forward link covariance matrix calculators and the weight vector for the common channel signal. 3. The transmission beam forming control apparatus of claim 2, wherein the second forward link covariance matrix calculator calculates the weight vector by considering an expected average transmission power value for other mobile stations. 4. The transmission beam forming control apparatus of claim 2, wherein the first forward link covariance matrix calculator comprises: a reverse link covariance matrix estimator for estimating a reverse link covariance matrix by using a signal received from the mobile station via the antenna array and a reverse link power control signal; an AOA (Angle of Arrival) estimator for estimating an arrival angle of a signal from the reverse link covariance matrix value; a beamwidth estimator for determining a beamwidth of a forward link signal by using the reverse link covariance matrix value and the frame error rate; and a forward link covariance matrix synthesizer for synthesizing a forward link covariance matrix by using an output of the AOA estimator and an output of the beamwidth estimator. 5. The transmission beam forming control apparatus of claim 2, wherein the optimal weight vector calculator calculates a transmission beam weight vector for maximizing a signal-to-interference plus noise ratio (SINR) for the forward link beam forming, the SINR being defined as where Pi represents in-phase component power for the common channel signal, Pq represents quadrature-phase component power for the common channel signal, Pexp represents interference power due to the transmission channel signal for other mobile stations located inside a cell serviced by the base station, and Poc represents interference power due to the transmission channel signal for other mobile stations located outside the cell. 6. The transmission beam forming control apparatus of claim 5, wherein the optimal weight vector calculator calculates a weight vector for the transmission beam in accordance with the following equation where represents an optimal weight vector of a transmission beam for the mobile station, M represents the number of mobile stations currently serviced by the base station, Ri represents a transmission covariance matrix for an ith mobile station among M mobile stations serviced by the base station, Roc represents an interference covariance matrix value for mobile stations serviced by other base stations, and wp represents a common beam weight vector. 7. The transmission beam forming control apparatus of claim 2, wherein the optimal weight vector calculator calculates a transmission beam weight vector for maximizing a signal-to-interference plus noise ratio (SINR) for forward link beam forming, the SINR being defined as where Pd represents power of the transmission channel signal, Pexp represents interference power due to the transmission channel signal for other mobile stations located inside a cell serviced by the base station, and Poc represents interference power due to the transmission channel signal for other mobile stations located outside the cell. 8. The transmission beam forming control apparatus of claim 7, wherein a direction of the transmission beam weight vector for maximizing the SINR is calculated by where represents an optimal weight vector of a transmission beam for the mobile station, M represents the number of mobile stations currently serviced by the base station, Ri represents a transmission covariance matrix for an ith mobile station among M mobile stations serviced by the base station, Roc and represents an interference covariance matrix value for mobile stations serviced by other base stations. 9. The transmission beam forming control apparatus of claim 1, wherein a beamwidth of the transmission beam weight vector is determined according to a frame error rate (FER) during calculation of the transmission beam weight vector. 10. The transmission beam forming control apparatus of claim 1, wherein the transmission beam weight vector calculator minimizes phase mismatching between a common channel signal and the transmission channel signal by dividing power of the transmission channel signal into an in-phase power component and a quadrature-phase power component for the common channel signal, maximizing the in-phase power component and minimizing the quadrature-phase power component. 11. The transmission beam forming control apparatus of claim 1, wherein the transmission beam weight vector calculator calculates a transmission beam weight vector so as to minimize phase mismatching between the common channel signal and the transmission channel signal. 12. A transmission beam forming control method of a base station, for forming a transmission beam for a transmission channel signal to be transmitted to a mobile station from an antenna array including a plurality of antenna elements, the method comprising the steps of: estimating a direction of the mobile station by using a reception signal and a reverse link power control bit received from the mobile station, and calculating a transmission beam weight vector in the estimated direction; and applying the calculated transmission beam weight vector to the transmission channel signal; and providing the applied transmission channel signal to the antenna array. 13. The transmission beam forming control method of claim 12, wherein the transmission beam weight vector calculator calculates a transmission beam weight vector to minimize phase mismatching between a common channel signal and the transmission channel signal. 14 The transmission beam forming control method of claim 12, wherein the transmission beam weight vector calculation step comprises the steps of: calculating a first forward link covariance matrix estimation value by using a signal received from the mobile station via the antenna array, a reverse link power control value of the mobile station, and a frame error rate; calculating a second forward link covariance matrix estimation value for other mobile stations; and calculating an optimal weight vector of the transmission beam from the calculated first and second forward link covariance matrix estimation values and the weight vector for a common channel signal. 15. The transmission beam forming control method of claim 14, wherein the second forward link covariance matrix estimation value calculation step comprises the step of calculating the weight vector by considering an expected average transmission power value for other mobile stations. 16. The transmission beam forming control method of claim 14, wherein the first forward link covariance matrix calculation step comprises the steps of: estimating a reverse link covariance matrix by using a signal received from the mobile station via the antenna array and a reverse link power control signal; estimating an arrival angle of a signal from the reverse link covariance matrix value; determining a beamwidth of a forward link signal by using the reverse link covariance matrix value and the frame error rate; and synthesizing a forward link covariance matrix by using the estimated arrival angle and the determined beamwidth. 17. The transmission beam forming control method of claim 14, wherein the optimal weight vector calculation step comprises the step of calculating a transmission beam weight vector for maximizing a signal-to-interference plus noise ratio (SINR) for forward link beam forming, the SINR being defined as where Pi represents in-phase component power for the common channel signal, Pq represents quadrature-phase component power for the common channel signal, Pexp represents interference power due to the transmission channel signal for other mobile stations located inside a cell serviced by the base station, and Poc represents interference power due to the transmission channel signal for other mobile stations located outside the cell. 18. The transmission beam forming control method of claim 17, wherein the transmission beam weight vector for maximizing the SINR is calculated by where represents an optimal weight vector of a transmission beam for the mobile station, M represents the number of mobile stations currently serviced by the base station, Ri represents a transmission covariance matrix for an ith mobile station among M mobile stations serviced by the base station, Roc represents an interference covariance matrix value for mobile stations serviced by other base stations, and wp represents a common beam weight vector. 19. The transmission beam forming control method of claim 14, wherein the optimal weight vector calculation step comprises the step of calculating a transmission beam weight vector for maximizing a signal-to-interference plus noise ratio (SINR) for forward link beam forming, the SINR being defined as where Pd represents power of the transmission channel signal, Pexp represents interference power due to the transmission channel signal for other mobile stations located inside a cell serviced by the base station, and Poc represents interference power due to the transmission channel signal for other mobile stations located outside the cell. 20. The transmission beam forming control method of claim 19, wherein a direction of the transmission beam weight vector for maximizing the SINR is calculated by where represents an optimal weight vector of a transmission beam for the mobile station, M represents the number of mobile stations currently serviced by the base station, represents a transmission covariance matrix for an ith mobile station among M mobile stations serviced by the base station, and Roc represents an interference covariance matrix value for mobile stations serviced by other base stations. 21. The transmission beam forming control method of claim 12, wherein the transmission beam weight vector calculation step comprises the step of minimizing phase mismatching between a common channel signal and the transmission channel signal by dividing power of the transmission channel signal into an in-phase power component and a quadrature-phase power component for the common channel signal, maximizing the in-phase power component and minimizing the quadrature-phase power component. 22. An apparatus for forming a transmission beam for a transmission channel signal to be transmitted to each of mobile stations in a base station apparatus including an antenna array having a plurality of antenna elements, the base station apparatus communicating with the mobile stations, the apparatus comprising: a reception beam former for separating baseband signals received from the antenna elements according to mobile stations; a base station modem receiver for calculating and extracting a frame error rate and a forward link power control bit for each mobile station from the signals received from the reception beam former; a transmission beam controller for calculating a transmission beam weight vector and transmission beam power for minimizing phase mismatching between a common channel signal and the transmission channel signal by using a separated baseband signal and an output of the base station modem receiver; a transmission channel signal generator for generating data to be transmitted to each mobile station; and a transmission beam former for forming a transmission beam by applying the calculated weight vector to an output of the transmission channel signal generator. 23. The apparatus of claim 22, wherein the transmission beam controller comprises: a transmission beam weight vector calculator for calculating the transmission beam weight vector for minimizing phase mismatching between the common channel signal and the transmission channel signal by using the separated baseband signal and an output of the base station modem receiver; and a transmission beam power calculator for calculating the transmission beam power by using a power control bit for each mobile station. 24. The apparatus of claim 23, wherein the transmission beam weight vector calculator calculates a transmission beam weight vector for maximizing a signal-to-interference plus noise ratio (SINR) for forward link beam forming, the SINR being defined as where Pi represents in-phase component power for the common channel signal, Pq represents quadrature-phase component power for the common channel signal, Pexp represents interference power due to the transmission channel signal for other mobile stations located inside a cell serviced by the base station, and Poc represents interference power due to the transmission channel signal for other mobile stations located outside the cell. 25. The apparatus of claim 24, wherein the transmission beam weight vector calculator calculates the weight vector for the transmission beam in accordance with the following equation where represents an optimal weight vector of a transmission beam for the mobile station, M represents the number of mobile stations currently serviced by the base station, Ri represents a transmission covariance matrix for an ith mobile station among M mobile stations serviced by the base station, Roc represents an interference covariance matrix value for mobile stations serviced by other base stations, and wp represents a common beam weight vector. 26. The apparatus of claim 24, wherein the transmission beam weight vector calculator calculates a transmission beam weight vector for maximizing a signal-to-interference plus noise ratio (SINR) for forward link beam forming, the SINR being defined as where Pd represents power of the transmission channel signal, Pexp represents interference power due to the transmission channel signal for other mobile stations located inside a cell serviced by the base station, and Poc represents interference power due to the transmission channel signal for other mobile stations located outside the cell. 27. The apparatus of claim 26, wherein a direction of the transmission beam weight vector for maximizing the SINR is calculated by where represents an optimal weight vector of a transmission beam for the mobile station, M represents the number of mobile stations currently serviced by the base station, Ri represents a transmission covariance matrix for an ith mobile station among M mobile stations serviced by the base station, and Roc represents an interference covariance matrix value for mobile stations serviced by other base stations.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0030] Several embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness. [0031] The embodiments of the present invention will be described with reference to two different cases. The first case provides a method for calculating an optimal transmission weight vector when there is no dedicated pilot channel and only a common pilot channel exists. The second case provides a method for calculating an optimal transmission weight vector when a dedicated pilot channel exists, e.g., the special case described in conjunction with the prior art. Embodiments of the present invention can be generally applied to a current mobile communication system, such as FDMA, TDMA and CDMA. However, for convenience, the embodiments of the present invention will be described with reference to a CDMA system, especially a 3rd generation CDMA mobile communication system such as a CDMA2000 system and a WCDMA (Wideband CDMA) system. Meanwhile, it will be assumed herein that direction and magnitude of a weight vector for a common beam were previously calculated by known means. [0032]FIG. 1 is a system diagram illustrating an example of a channel model of a forward link smart antenna according to an embodiment of the present invention. Specifically, FIG. 1 illustrates a channel model of a forward link smart antenna on the assumption that M mobile stations MSi (i=1,2, . . . ,M) in a cell are communicating with a base station BS. In FIG. 1, sm (t) represents a forward link traffic channel signal for an mth mobile station MS from a base station BS, hm represents a forward link channel response vector from the base station BS to an mth mobile station MSm, and wm represents a forward link weight vector from the base station BS to an mth mobile station MSm. In addition, channel response vectors from the base station BS to a plurality of mobile stations located in other cells are represented by hoc. [0033] If a forward link signal transmitted from the base station BS to mobile stations via an antenna array comprised of a plurality of antenna elements is defined as s(t), the s(t) becomes a linear combination of a common channel signal sp(t) with a common weight vector wp and a traffic channel signal si(t)(i=1,2, . . . ,M) with an individual transmission weight vector wi(i=1,2, . . . , M). That is, the s(t) can be represented by [0034] Although the common channel signal includes a pilot channel signal, a synchronization channel signal and a paging channel signal, only the pilot channel signal will be designated herein as the common channel signal, for the convenience of explanation. The pilot channel signal sp(t) is a signal transmitted over an omidirectional beam or a sector beam in order to provide time and phase criteria for coherent demodulation to mobile stations in a cell. Therefore, a weight vector wp for the pilot channel signal should be able to entirely cover the inside of a cell or the inside of a sector. In the present examples, it is assumed that the wp is previously calculated through known means. What is provided is a method for calculating transmission weight vectors wi(i=1,2, . . . ,M) for traffic channel signals si(t)(i=1,2, . . . ,M) transmitted to each of the mobile stations in the cell, by an optimal criterion. For convenience, the description will be limited to a method for calculating a transmission weight vector wm for an mth mobile station MSm among M mobile stations. Of course, transmission weight vectors for the other mobile stations can also be calculated in the same method. Therefore, it is possible to independently calculate transmission weight vectors for the respective mobile stations. [0035] When a base station transmits a signal s(t) over a radio channel, a signal rm(t) received at an mth mobile station MSm can be represented by [0036] In Equation (2), * denotes a conjugate operator, and H denotes a Hermitian operator. [0037] The signal rm(t) is divided into a pilot channel signal rp(t), a traffic channel signal rd(t) for an mth mobile station MSm, and an interference signal rimp(t) indicating a signal transmitted to other mobile stations but flowed into or provided to an mth mobile station MSm, as illustrated in Equation (3). [0038] Power of each signal received at an mth mobile station MSm shown in Equation (3) can be expressed by Equation (4) below. In Equation (4), Pp represents power of a pilot channel signal, Pd represents power of a traffic channel signal, and Pimp represents power of an interference signal. [0039] In Equation (4), Rm represents a forward link transmission covariance matrix for an mth mobile station MSm and is Rm=[hmhm H], and Sp represents power of a pilot channel signal transmitted from a base station and is Sp=E[|si(f)|2]. In addition, Si represents power of a forward link traffic channel signal transmitted from a base station to an ith mobile station MSi and is Si=E[|si(f)|2], and Sm represents power of a forward link traffic channel signal transmitted to an mth mobile station MSm. [0040] When there is no dedicated pilot channel and only a common pilot channel exists, a weight vector wp applied to a common pilot channel is generally different from a weight vector wm applied to a traffic channel, thus causing phase mismatching between a pilot channel signal and a traffic channel signal received at an mth mobile station MSm, illustrated in Equation (3). Here, phase variation due to sp(t) and sm(t) of the signal is excluded. [0041] However, since a traffic channel is synchronized by a pilot channel, a common pilot channel signal becomes a phase criterion in a mobile station. Therefore, of the traffic channel signal of Equation (3), a component phase-matched to the pilot channel signal acts as a signal component, while a component phase-mismatched to the pilot channel signal acts as an interference component. Herein, the component phase-matched to the pilot channel signal is referred to as �in-phase component,� and the component phase-mismatched to the pilot channel signal is referred to as �quadrature-phase component.� Considering this, the traffic signal power Pd of Equation (4) can be divided into in-phase power Pi and quadrature-phase power Pq, as shown in Equation (5) below. [0042] In Equation (5), w′p is [0043] and represents a normalized weight vector of a pilot channel. [0044] Meanwhile, of the s(t) transmitted from the base station BS, an interference signal rexp(t) indicating a traffic channel signal [0045] to be transmitted only to an mobile station MSm but flowed out to other mobile stations MSi (i=1,2, . . . ,M) in a cell, and an interference signal roc(t) indicating the traffic channel signal flowed out to mobile stations belonging to other cells can be represented by [0046] Power of the inference signals due to outflow of a signal to other mobile stations inside and outside the cell can be defined as [0047] In Equation (7), Roc, denotes a forward link transmission covariance matrix for mobile stations within other cells, and can be represented by [0048] In addition, a thermal noise generated within a mobile station can be considered together with interference signals from other mobile stations, and the thermal noise can be given by Pth=σth 2 Equation (8) [0049] A weight vector for a transmission beam is calculated using the enumerated signal and interference power. First, in order to calculate a direction of a weight vector for a transmission beam for an mth mobile station MSm, a signal-to-inference plus noise ratio (SINR) for forward link beam forming (FLBF) is defined as [0050] The [0051] is not a value that can be actually measured in a corresponding mobile station MSm. However, in order to maximize the [0052] in Equation (9), it is necessary to minimize the sum of a quadrature-phase component power Pq and interference powers Pexp and Poc indicating a signal transmitted to a corresponding mobile station MSm but flowed out to other mobile stations inside and outside a cell while maximizing in-phase component power Pi, for a phase of a pilot channel signal serving as a phase criterion during coherent detection. As a result, from the viewpoint of the overall system, actual [0053] is increased in a mobile station MSm. Therefore, it is possible to define the SINR of Equation (9) instead of using the actual [0054] If a transmission beam weight vector wm for maximizing [0055] is calculated through the definition, the calculated value becomes an optimal weight vector [0056] for minimizing phase mismatching between a pilot channel signal and a traffic channel signal and also minimizing power of an interference signal for other mobile stations, thereby achieving objects of the present invention. [0057] In addition, the [0058] becomes a function of only a transmission beam weight vector wm for an mth mobile station MSm when a common beam weight vector wp is given. As a result, it is possible to independently optimize the transmission beam weight vector according to mobile stations. Particularly, it can be understood from Equation (9) that [0059] depends upon only a direction of a forward link channel response vector wm regardless of magnitude of a forward link channel response vector wm from a base station to a corresponding mobile station and a forward link traffic channel signal Sm for the corresponding mobile station. From this, it can be noted that it is possible to independently calculate direction and magnitude of the forward link channel response vector wm. [0060] In Equation (9), a calculation result obtained by selecting the optimal forward link weight vector [0061] as a value for maximizing [0062] becomes [0063] For covariance matrixes used in Equation (10), other means, for example, a forward link covariance matrix fed back from a mobile station MSm to a base station BS or its equivalent information can be used. When there is no information fed back from the mobile station to the base station, the base station can estimate signals received from mobile stations. A detailed description of this will be made later. A signal γm received from an mth mobile station MSm was introduced to calculate wm for maximizing [0064] and then additionally control a phase between a common beam and a transmission beam. [0065] A description has been made of a method for calculating an optimal weight vector when there is no dedicated pilot channel and only a common pilot channel exists. However, when a dedicated pilot channel exists, a weight vector for the dedicated pilot channel serving as a phase criterion during coherent detection is identical in phase to a weight vector applied to a traffic channel. Therefore, if a dedicated pilot channel exists, a phase mismatching problem between the dedicated pilot channel and the traffic channel does no occur. Thus, Equation (5) can be written as P i =P d =w m H R m S m w m Equation (11) Pq=0 [0066] Therefore, [0067] for forward link beam forming is defined as [0068] When the dedicated pilot channel exists, an optimal weight vector for a traffic channel represents a value for maximizing [0069] Of Equation (12) and is calculated by [0070] As described above, for forward link beam forming according to presence/absence of the dedicated pilot channel, forward link transmission covariance matrixes Rm(m=1,2, . . . ,M) and Roc, i.e. [0071] and [0072] are required as illustrated in Equation (13). So far, a reverse link (RL) related signal and a forward link (FL) related signal have not been distinguished for purposes of simplicity, since they may not be confused. However, henceforth, a superscription �FL� will be used for a forward link and a superscription �RL� will be used for a reverse link, for signal distinguishment. As stated above, if such information is provided from a mobile station, the information can be used as it is. In contrast, if the information is not provided, a base station must estimate a forward link covariance matrix from a signal received from a mobile station. However, since a reverse link covariance matrix [0073] is obtained from the received reverse link signal, the base station is required to first estimate transmission power [0074] of a mobile station MSm and to eliminate the estimated transmission power. [0075] In the current mobile communication standard, a base station BS has no way to directly receive transmission power [0076] of a mobile station MSm. Instead, the base station BS can indirectly estimate transmission power [0077] of a mobile station MSm, using a reverse power control bit transmitted to the mobile station MSm every slot for reverse link power control. [0078]FIG. 2 is a diagram illustrating an example of estimating reverse link transmission power according to an embodiment of the present invention. Specifically, FIG. 2 illustrates an example of estimating transmission power [0079] of a mobile station MSm from a reverse link power control bit. In FIG. 2, [0080] means a reverse link power control bit that a base station BS transmits to an mth mobile station MSm every slot fk(k=1,2, . . . ) As illustrated in FIG. 2, transmission power of a mobile station is increased or decreased in a predetermined ratio according to [0081] The transmission power [0082] of a mobile station is calculated by [0083] In Equation (14), �Increment� represents a transmission power ratio (dB) that increases or decreases according to a reverse link power control bit, and So represents initial transmission power. Equation (14) provides a value that the base station BS can calculate, and through this, the base station can estimate transmission power of a mobile station. Equation (14) is given on the assumption that no error occurs during transmission and demodulation of the reverse link power control bit. However, even when an error occurs during transmission of the reverse link power control bit, an actual value can be immediately recovered through feedback of the reverse link power control bit. [0084] When power [0085] of a reverse link traffic channel received from an mth mobile station is estimated, a transmission covariance matrix [0086] for a reverse link channel from the mth mobile station can be calculated from the estimated power. In addition, AOA and beamwidth are estimated from the transmission covariance matrix [0087] for a reverse link channel received from the mth mobile station. Further, a transmission covariance matrix [0088] for a forward link channel to an mth mobile station can be estimated by synthesizing a covariance matrix considering a difference between transmission and reception frequency bands from the estimated AOA and beamwidth. [0089] Even for a transmission covariance matrix Roc for mobile stations in other cells, a similar method can be used. However, it can be difficult to individually detect transmission power of mobile stations inside and outside a cell. In this case, it is necessary to previously determine expected average values of a transmission covariance matrix Roc for mobile stations inside and outside other cells. Generally, since it is assumed that interference from other cells is spatially uniform, the expected average value can be applied without any problem. [0090] A description has been made of a method of simultaneously considering a phase mismatching problem between a common pilot channel signal and a traffic channel signal and an interference problem for other mobile stations when a dedicated pilot channel is not provided. Another method of calculating a direction of an optimal transmission beam weight vector through forward link beam forming considering an interference problem when the dedicated pilot channel is provided. From now on, a description will be made of a process of calculating magnitude of a transmission beam weight vector using forward link power control (FLPC). [0091] Equation (15) shows an example of [0092] for forward link power control on an mth mobile station MSm in a cell. [0093] The [0094] is a value that can directly measured by an mth mobile station MSm. The [0095] for forward link power control can be defined differently according to systems. In the present example, since a forward link power control function provided in an existing CDMA system will be applied as is, a detailed definition of [0096] is not important. [0097] An mth mobile station MSm compares a target value of the [0098] with its current bit measured value, and determines a forward link power control bit [0099] according to the comparison result. A base station BS receives the forward link power control bit [0100] over a reverse link channel, and determines signal power [0101] of a forward traffic channel, i.e., magnitude of a weight vector for a transmission beam, according to a value of the received forward link power control bit. [0102] By calculating a direction of an optimal weight vector of each mobile station through forward link beam forming and independently calculating desired base station transmission power through forward link power control, a smart antenna adopting a forward link beam forming algorithm proposed herein can achieve a desired SINR with minimum base station transmission power, as compared with an omnidirectional antenna or a sector antenna. Thus, it is possible to increase the number of available mobile stations in a cell, contributing to an increase in subscriber capacity, an object of the smart antenna. [0103] A detailed description will now be made of an embodiment of the present invention with reference to the accompanying drawings. [0104]FIG. 3 is a detailed block diagram illustrating an example of components of a base station transmission apparatus with an antenna array according to an embodiment of the present invention. As illustrated, the transmission apparatus for a base station includes an antenna array 300, an RF (Radio Frequency) part 310, a transmission beam former 320, a transmission beam controller 330, a common channel signal generator 340, a transmission channel signal generator 350, a reception beam former 360, and a base station modem receiver 370. It is assumed that the base station is currently communicating with M mobile stations in the cell. [0105] It is assumed that the antenna array 300 is comprised of N identical antenna elements. An antenna array can be classified into a transmission antenna array and a reception antenna array. Here, a description will be made with reference to the transmission antenna array. However, a hardware structure of the antenna array is commonly designed such that it can be jointly used for both transmission and reception by use of a duplexer. The antenna array 300 transmits transmission beams formed by the transmission beam former 320, and provides RF signals received from several mobile stations inside and outside a cell to the RF part 310. [0106] The RF part 310 is comprised of N RF units corresponding to the N antenna elements of the antenna array 300, and each RF unit is connected to its associated antenna element. Each RF unit, though not illustrated, includes a low-noise amplifier, a frequency down converter, and an analog-to-digital (A/D) converter. The RF part 310 converts RF signals received from mobile stations via the antenna array 300 into a baseband digital reception signal x. [0107] The reception beam former 360 converts the baseband digital reception signal x output from the RF part 310 into beams zi(i=1,2, . . . ,M) formed as to mobile stations, and provides the output beams to the base station modem receiver 370. The reception beam former 360 serves as a spatial filter capable of amplifying or eliminating a signal based on a direction of a signal received from each mobile station via the antenna array 300. When a RAKE receiver, not shown for purposes of simplicity, is used to eliminate an interference signal due to multipath fading, the reception beam former 360 can be positioned before or after a demodulator in each finger of the RAKE receiver. [0108] The base station modem receiver 370 modulates the beams zi(i=1,2, . . . ,M) output from the reception beam former 360 into voice or data signals of corresponding mobile stations. In addition, the base station modem receiver 370 restores forward link power control bits [0109] transmitted from corresponding mobile stations and measures SINR for the corresponding mobile stations, thereby determining reverse link power control bits [0110] Moreover, the base station modem receiver 370 restores a forward link FER transmitted from a corresponding mobile station by help of an upper layer. [0111] The transmission beam controller 330 calculates weight vectors for controlling forming of transmission beams, and includes a common beam weight vector calculator 331, a transmission beam weight vector calculator 333, a common beam power calculator 335 and a transmission beam power calculator 337. In embodiments of the present invention, the calculators can be optionally implemented by hardware or software. [0112] The transmission beam former 320 includes a common beam former 323 for forming a common beam, M transmission beam formers 325 for forming transmission beams for M mobile stations, and N adders 321 for forming M forward transmission beams by adding the common beam to the M transmission beams, and then providing the formed forward transmission beams to the N RF units corresponding thereto. [0113] A detailed description will now be made of an operation of forming transmission beams by a base station having the structure stated above. [0114] RF signals received from several mobile stations inside and outside the cell through N antenna elements of the antenna array 300 are converted into baseband digital reception signal x by the RF part 310, and then provided to the reception beam former 360 and the transmission beam weight vector calculator 333. The transmission beam weight vector calculator 333 calculates forward link transmission covariance matrixes [0115] in the above-stated method by receiving the baseband digital reception signal x from the RF part 310 and the reverse link power control bits [0116] from the base station modem receiver 370. When a dedicated pilot channel is not provided, the forward link transmission covariance matrix is calculated using Equation (10) above. In contrast, when the dedicated pilot channel is provided, the forward link transmission covariance matrix is calculated using Equation (13) above. Therefore, the transmission beam weight vector calculator 333 can be designed to include both of the two calculation methods so that it can optionally use one of the two calculation methods. In an embodiment of the present invention, the transmission beam weight vector calculator 333 can be designed to include only a calculation method corresponding to a particular system. In this method, the transmission beam weight vector calculator 333 calculates optimal transmission beam weight vectors wi(i=1,2, . . . ,M) for the mobile stations on a real-time basis, and provides the optimal transmission beam weight vectors to the corresponding transmission beam formers 325. [0117] The transmission beam power calculator 337 calculates transmission beam powers Si(i=1,2, . . . ,M) for the mobile stations by receiving the forward link power control bits [0118] from the base station modem receiver 370, and provides the calculated transmission beam powers to the transmission channel signal generators 350. Each transmission channel signal generator 350 generates transmission channel signals si(i=1,2, M) by multiplying the transmission channel signals having a unit magnitude by square roots of the transmission beam powers Si(i=1,2, . . . ,M), and provides the generated transmission channel signals to the corresponding transmission beam former 325. [0119] The transmission beam formers 325 form transmission beams by multiplying optimal transmission beam vectors wi(i=1,2, . . . ,M) for the mobile stations by the transmission channel signals si(i=1,2, . . . ,M). The transmission beams formed in this manner are provided to the adders 321 associated with the N antenna elements of the antenna array 300. [0120] A weight vector for a common beam is determined by the common beam weight vector calculator 331 and the common beam power calculator 335. The common beam weight vector calculator 331 previously calculates a common beam weight vector wp capable of covering a cell or a sector, and provides the calculated common beam weight vector to the common beam former 323. Meanwhile, the common beam power calculator 335 previously calculates common beam power Sp, and provides the calculated common beam power to the common channel signal generator 340. The common channel signal generator 340 generates a common channel signal sp by multiplying a common channel signal having a unit magnitude by a square root of the common beam power Sp, and provides the generated common channel signal to the common beam former 323. [0121] The common beam former 323 multiplies the common channel signal sp by the common beam weight vector wp, and provides its output to the adders 321 associated with the N antenna elements of the antenna array 300. [0122] The adders 321 form base station transmission signal vectors s(t) by summing up outputs of the common beam former 323 and the transmission beam formers 325, and provide their outputs to the corresponding RF units of the RF part 310. The transmission signal vectors s(t) from the base station to the mobile stations are converted into RF signals by the RF units 310 after being power-amplified through a D/A converter, a frequency up converter and a power amplifier, and then transmitted to the mobile stations in the cell over forward link channels through the antenna array 300. [0123]FIG. 4 is a detailed block diagram illustrating an example of components of the transmission beam weight vector calculator 333 shown in FIG. 3. Specifically, FIG. 4 illustrates an apparatus and method for estimating forward link covariance matrixes for M mobile stations MSi(i=1,2, . . . ,M) from a reverse link base station reception signal vector x. Although the forward link covariance matrix can be estimated from the reverse link base station reception signal vector as mentioned above, it can also be directly fed back from the mobile stations or can be calculated using other methods. In addition, it should be appreciated by those skilled in the art that although the transmission beam weight vector calculator 333 is realized by hardware in FIG. 4, it can also be implemented by software without departing from the scope of the present invention. [0124] Referring to FIG. 4, the transmission beam weight vector calculator 333 includes M forward link covariance matrix calculators 400 associated with M mobile stations MSi(i=1,2, . . . ,M), M optimal weight vector calculators 420, and an other cell covariance matrix calculator 410. Each forward link covariance matrix calculator 400 is comprised of a reverse link covariance matrix estimator 401, an AOA estimator 403, a beamwidth estimator 405, and a forward link covariance matrix synthesizer 407. [0125] The reverse link covariance matrix estimator 401 first calculates a covariance matrix [0126] for an ith mobile station MSi by receiving the baseband digital reception signal vector x. Further, the reverse link covariance matrix estimator 401 estimates mobile station transmission power [0127] using a reverse link power control bit [0128] and then calculates a reverse link transmission covariance matrix [0129] of an ith mobile station from the estimated mobile station transmission power. The reverse link covariance matrix estimator 401 provides the calculated reverse link covariance matrix to the AOA estimator 403 and the beamwidth estimator 405. The AOA estimator 403 and the beamwidth estimator 405 calculate an AOA estimation value AOAi and a beamwidth estimation value BWi for a corresponding mobile station from the reverse link covariance matrix estimation value [0130] and provide the calculated AOAi and BWi to the forward link covariance matrix synthesizer 407. In an abnormal state where FER is increased abruptly for some reason, the beamwidth estimator 405 detects the abrupt increase in the FER from a forward link [0131] received from a mobile station and then increases or decreases the beamwidth by a predetermined value, thereby appropriately coping with the abnormal state. [0132] The forward link covariance matrix synthesizer 407 synthesizes a forward link covariance matrix estimation value [0133] from the AOA estimation value AOAi and the beamwidth estimation value BWi, and provides the synthesized forward link covariance matrix estimation value to the optimal weight vector calculator 420. In an FDD (Frequency Division Duplexing) system where a transmission frequency band is different from a reception frequency band, a difference between the transmission frequency and the reception frequency is compensated for in the forward link covariance matrix synthesizer 407. [0134] The other cell covariance matrix calculator 410 calculates a covariance matrix estimation value Roc for interference to mobile stations in other cells due to a transmission channel signal for an ith mobile station MSi, by receiving the baseband digital reception signal vector x, and providing the calculated covariance matrix estimation value to the optimal weight vector calculator 420. Estimation of the reverse link covariance matrix and the other cell covariance matrix can be performed using a known technique. For example, a method disclosed in �Performance Analysis of CDMA Mobile Communication Systems using Antenna Arrays�, B. Suard, A. Naguib, G, Xu, A. Paulraj, Proc. ICASSP, 1993, which is incorporated herein by reference, can be used. [0135] The optimal weight vector calculator 420 calculates an optimal weight vector wi in accordance with Equation (10) or Equation (11) by receiving a forward link covariance matrix estimation value Ri for an ith mobile station MSi from the forward link covariance matrix calculator 400, an estimation value Roc from the other cell covariance matrix calculator 410, and a common beam weight vector wp from the common beam weight vector calculator 331, and then provides the calculated optimal weight vector to the transmission beam former 325. [0136]FIG. 5 is a diagram illustrating an example of the transmission beam former 325 for an mth mobile station MSm according to an embodiment of the present invention. If it is assumed that the antenna array of the base station includes N antenna elements, the transmission beam former 325 includes N complex multipliers 510 associated with the antenna elements. A transmission beam weight vector wm for an mth mobile station MSm is divided into N elements associated with the antenna elements, and then applied to the corresponding complex multipliers 510. It is well known that the wm can be represented by wm=[wm,1wm,2 . . . wm,N−1wm,N]T. The complex multipliers 510 complex-multiply a traffic channel signal sm(f) for an mth mobile station MSm by the elements of the weight vector wm, and provide their outputs to the corresponding adders 321. [0137] Although the transmission beam former 325 for an mth mobile station MSm is illustrated in FIG. 5, transmission beam formers for other mobile stations also have the same structure. Also, common beam formers for other mobile stations have the same structure as the common beam former 323. [0138]FIG. 6 is a graph illustrating a forward link transmission beam pattern according to the prior art in terms of magnitude and degree, and FIG. 7 is a graph illustrating a forward link transmission beam pattern according to an embodiment of the present invention in terms of magnitude and degree. FIGS. 6 and 7 are based on the assumption that the number of forward link transmission beams is 2 in a base station's linear antenna array that has 4 antenna elements and a gap between the antenna elements is half a wavelength. Specifically, FIG. 6 illustrates a forward link transmission beam pattern formed by considering only AOA and beamwidth from a signal received at the base station from the mobile station, and FIG. 7 illustrates a forward link transmission beam pattern formed according to an embodiment of the present invention. It is further assumed in FIGS. 6 and 7 that forward link transmission beams 610 and 710 shown by solid lines are for AOA=−40� and beamwidth=20�, and forward link transmission beams 620 and 720 also shown by solid lines are for AOA=−0� and beamwidth=20�. [0139] It can be understood that compared with the forward link transmission beam pattern illustrated in FIG. 6, the forward link transmission beam pattern illustrated in FIG. 7 has interference reduced by about 3 to 4 dB within a non-transmission angle range. That is, when a forward link transmission beam is formed according to the disclosed embodiments of the present invention, it is possible to increase the amount of subscriber capacity by the same amount as the reduction in the interference signal. [0140] As described above, the disclosed embodiments of the present invention can form an optimal transmission beam for minimizing phase mismatching between a common beam and a transmission beam and also minimize interference to other mobile stations due to the transmission beam. That is, the invention can achieve high performance forward link transmission, and contribute to an increase in bandwidth capacity of a mobile communication system, improvement in call quality, and a reduction in transmission power of a mobile station. [0141] While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS [0022] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: [0023]FIG. 1 is a system diagram illustrating an example of a channel model of a forward link smart antenna according to an embodiment of the present invention; [0024]FIG. 2 is a diagram illustrating an example of estimating reverse link transmission power according to an embodiment of the present invention; [0025]FIG. 3 is a detailed block diagram illustrating an example of components of a base station transmission apparatus with an antenna array according to an embodiment of the present invention; [0026]FIG. 4 is a detailed block diagram illustrating an example of components of a transmission beam weight vector calculator according to an embodiment of the present invention; [0027]FIG. 5 is a diagram illustrating an example of a transmission beam former according to an embodiment of the present invention; [0028]FIG. 6 is a graph illustrating a forward link transmission beam pattern according to the prior art in terms of magnitude and degree; and [0029]FIG. 7 is a graph illustrating a forward link transmission beam pattern according an embodiment of the present invention in terms of magnitude and degree.
Referenced byCiting PatentFiling datePublication dateApplicantTitleUS7043272 *Dec 26, 2001May 9, 2006Electronics And Telecommunications Research InstituteApparatus for forward beamforming using feedback of multipath information and method thereofUS7548764 *Feb 3, 2006Jun 16, 2009Cisco Technology, Inc.Method and system for generating multiple radiation patterns using transform matrixUS7551611 *Sep 19, 2006Jun 23, 2009Sanyo Electric Co., Ltd.Radio apparatusUS7671800 *Dec 6, 2006Mar 2, 2010Samsung Electronics Co., LtdBeamforming apparatus and method in a smart antenna systemUS7688879 *Jan 14, 2005Mar 30, 2010Samsung Electronics Co., Ltd.Method and apparatus for forming a beamUS8064407 *Dec 29, 2005Nov 22, 2011Zte CorporationMethod and equipment for realizing smart antenna in WCDMA systemUS8068874 *Feb 6, 2006Nov 29, 2011Hitachi, Ltd.System and method for correcting signal deviations in a radio over fiber networkUS8086178 *Apr 20, 2006Dec 27, 2011Shanghai Ultimate Power Communications Technology Co., Ltd.Beam-forming method for realizing interference suppressionUS8130862Nov 16, 2005Mar 6, 2012Intellectual Ventures Holding 40 LlcPrecoding system and method for multi-user transmission in multiple antenna wireless systemsUS8165533 *Apr 2, 2009Apr 24, 2012Samsung Electronics Co., Ltd.Apparatus and method for beamforming based on generalized eigen-analysis in multiple input multiple output wireless communication systemUS8195240 *Apr 15, 2008Jun 5, 2012Cisco Technology, Inc.Hybrid time-spatial multiplexing for wireless broadcast messages through antenna radiation beam synthesisUS8433355Apr 13, 2006Apr 30, 2013Interdigital Technology CorporationMethod and apparatus for generating loud packets to estimate path lossUS8477874 *Dec 30, 2008Jul 2, 2013Mobilicom Ltd.Method, device and system of wireless communicationUS20090011755 *Jan 10, 2007Jan 8, 2009Zion HadadCellular System and MethodUS20090252250 *Apr 2, 2009Oct 8, 2009Samsung Electronics Co. Ltd.Apparatus and method for beamforming based on generalized eigen-analysis in multiple input multiple output wireless communication systemUS20100020901 *Jul 5, 2007Jan 28, 2010Samsung Electronics Co., Ltd.Method and apparatus for transmitting signal in communication systemUS20120021737 *Sep 24, 2009Jan 26, 2012Zte CorporationMethod for improving call success rate and base station system thereofWO2006055719A2 *Nov 16, 2005May 26, 2006Univ TexasPrecoding system and method for multi-user transmission in multiple antenna wireless systems* Cited by examinerClassifications U.S. Classification455/562.1, 455/561International ClassificationH04B7/06, H04B7/26, G01S3/74, H04B1/00, H04B7/10, H04W16/28, H04B7/02Cooperative ClassificationG01S3/74, H04B7/0617, H04W16/28European ClassificationH04W16/28, H04B7/06C1BLegal EventsDateCodeEventDescriptionFeb 18, 2010FPAYFee paymentYear of fee payment: 4May 19, 2003ASAssignmentOwner name: SAMSUNG ELECTRONICS CO., LTD., KOREA, REPUBLIC OFFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CHUN, BYUNG-JIN;REEL/FRAME:014089/0419Effective date: 20030517RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google