ES2357434T3 - SYSTEM AND METHOD FOR THE PERFORMANCE OF PRECODIFICATION IN A WIRELESS COMMUNICATIONS SYSTEM. - Google Patents

Abstract

A base station (102) capable of performing precodes in a wireless communications system (100), comprising: a plurality of codebooks (270), each codebook comprises a plurality of composite precoding matrices generated based on a matrix with a corresponding precoding diversity and a power sharing precoding matrix; and a code book selector (275) that can be operated to select one of the code books (270) for use in a communications session with a subscriber station (111).

Description

Technical Field of the Invention

The present disclosure refers in general to the field of wireless communications and, more specifically, to a system and method for performing precoding in a wireless communication system.

Background of the invention

The multi-input and multi-output wireless communications (MIMO) systems that are currently implemented sometimes use unitary precoding prior to the assignment of data streams to physical antennas in order to create a set of virtual antennas. This allows each keyword to be transmitted from all physical antennas. However, this precoding is performed only for spatial multiplexing.

The article "Limited Feedback Unitary Precoding for spatial Multiplexing Systems" published in IEEE Transactions on Information Theory, Vol. 51, August 8, 2005 on pages 2967-2976 written by David J. Love and Robert

W. Health proposes a quantified precoding system in a multi-input wireless system - multiple outputs (MIMO) through the use of spatial multiplexing modulation techniques in order to improve the resistance of spatial multiplexing. According to this system the optimal precoder is chosen from a finite codebook known to both the receiver and the transmitter and the index of the optimal precoder is transported from the receiver to the transmitter through a low feedback link delay. The simulation results show that the proposed system offers better results than antenna selection and works close to the optimal unit precoding with a minimum amount of feedback.

The article "Limited Feedback Unitary Precoding for orthogonal Space-Time Block Codes" published in IEEE Transactions on signal processing, Vol. 53, No. 1, January 2005 written by David J. Love and Robert W. Health investigates a feedback approach limited that uses a book of precoding matrix codes known a priori by both the transmitter and the receiver. The receiver chooses a codebook matrix based on the current channel conditions and transports the optimal precoding matrix to the transmitter through an error-free zero delay feedback channel. It has been proven that code books designed using this method provide total diversity order in Rayleigh fade channels.

The article "Spatial Multiplexing in Correlated Fading via the Virtual Channel Representation" in IEEE Journal on Selected Areas in Communications, Vol. 21, No. 5, June 2003 written by Zhihong Hong, Ke, Liu, Robert W. Health and Akbar M Sayeed studies the design and performance of spatial multiplexing techniques based on a virtual representation of realistic MIMO fade channels. According to these techniques, the pairwise analysis of error probability (PEP) for the correlative channels is greatly simplified. Unitary precoding is proposed to provide robustness to unknown channel statistics. Non-unitary precoding techniques are proposed to exploit the channel structure when the channel statistics are known to the transmitter.

When the system is using the transmission diversity method, precoding is not available, which results in a decrease in performance. Therefore, there is a need in the art for a system for performing precoding with both spatial multiplexing and the method of transmission diversity in a wireless communication system.

Summary of the Invention

A base station capable of precoding in a wireless communication system is provided. According to an advantageous embodiment of the present disclosure, the base station includes a plurality of code books and a code book selector. Each codebook comprises a plurality of composite precoding matrices that are generated based on a matrix with a corresponding precoding diversity. The codebook selector can be operated to select one of the codebooks for use in a communications session with a subscriber station.

In accordance with another embodiment of the present disclosure, a base station capable of precoding is provided in a wireless communication system that includes a precoder. The precoder can be operated to perform precoding on a plurality of data streams using a composite precoding matrix.

In accordance with another embodiment of the present disclosure, there is provided a method for performing precoding in a wireless communication system that includes the storage of a plurality of code books. Each codebook comprises a plurality of composite precoding matrices that are generated based on a matrix with a corresponding precoding diversity. One of the code books is selected for use in a communications session with a subscriber station.

Before addressing the "Detailed Description of the Invention" below, it would be advantageous to explain the definitions of certain words and phrases used throughout this document: the terms "include" and "understand," as well as their derivatives, mean inclusion without limitation; the term "or," is inclusive, that is to say it means and / or; the term "each" means each of at least a subset of the identified elements; the phrases "associated with" and "associated with this / this / these / these," as well as their derivatives, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with , be communicable with, cooperate with, interleave, juxtapose, be close to, be linked to or with, have, own, or similar property; and the term "controller" means any device, system or part thereof that controls at least one operation, such device may be implemented in hardware, firmware or software, or some combination of at least two of them. It should be noted that the functionality associated with any given controller can be centralized or distributed, either locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those skilled in the art should understand that in many, if not most of the time, such definitions apply to past and future uses of such Defined words and phrases.

Brief description of the drawings

For a better understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which similar reference numbers represent similar parts:

FIGURE 1 illustrates a wireless Orthogonal Frequency Division Multiplexing (OFDM) network that is capable of providing precoded signals in accordance with an embodiment of the present disclosure;

FIGURE 2 illustrates an exemplary base station that is capable of precoding in accordance with an embodiment of the present disclosure;

FIGURE 3 illustrates details of a portion of the signal generator of FIGURE 2 when using total spatial multiplexing in accordance with an embodiment of the present disclosure;

FIGURE 4 illustrates details of a portion of the signal generator of FIGURE 2 when using the transmission diversity method according to an embodiment of the present disclosure;

FIGURES 5 A-D illustrate details of a portion of the signal generator of FIGURE 2 when using partial spatial multiplexing in accordance with some embodiments of the present disclosure;

FIGURES 6 A-B illustrates precoding structures with symbol vector for use by the signal generator of FIGURE 2 when using partial spatial multiplexing according to two embodiments of the present disclosure; Y

FIGURE 7 is a flow chart illustrating a method for performing precoding using the signal generator of FIGURE 2 in accordance with an embodiment of the present disclosure.

Detailed description of the invention

FIGURES 1 to 7, which were discussed above, and the different embodiments used to describe the principles of the present disclosure in this patent document are illustrative only and should not be construed in any way as limiting the scope of the disclosure. Those skilled in the art will understand that the principles of the present embodiment can be implemented in any properly configured wireless network.

FIGURE 1 illustrates a wireless orthogonal frequency division multiplexing network (OFDM) 100 that is capable of providing signals in accordance with an embodiment of the present disclosure. In the illustrated embodiment, the wireless network 100 includes a base station (BS) 101, a base station (BS) 102, and a base station (BS) 103. The base station 101 communicates with the base station 102 and with the station base 103. The base station 101 also communicates with the Internet Protocol (IP) network 130, such as the Internet, a private IP network, or another data network.

The base station 102 provides wireless broadband access to the network 130, via the base station 101, to a first plurality of subscriber stations within the coverage area 120 of the base station 102. The first plurality of subscriber stations includes the station Subscriber (SS) 111, Subscriber Station (SS) 112, Subscriber Station (SS) 113, Subscriber Station (SS) 114, Subscriber Station (SS) 115, and Subscriber Station (SS) 116. In one embodiment For example, the SS 111 can be located in a small business (SB), the SS 112 can be located in a company (E), the SS 113 can be located in a WiFi access point (HS), the SS 114 it can be located in a first residence, the SS 115 can be located in a second residence, and the SS 116 can be a mobile device (M).

The base station 103 provides wireless broadband access to the network 130, via the base station 101, to a second plurality of subscriber stations within the coverage area 125 of the base station 103. The second plurality of subscriber stations includes the subscriber station 115 and the subscriber station 116.

In other embodiments, the base station 101 may be in communication with fewer or more base stations. In addition, while only six subscriber stations are shown in FIGURE 1, it is understood that wireless network 100 can provide wireless broadband access to more than six subscriber stations. It should be noted that the subscriber station 115 and the subscriber station 116 are located at the edge of the coverage area 120 and the coverage area 125. The subscriber station 115 and the subscriber station 116 each communicates with both the base station 102 and with the base station 103 and it can be said that they operate in smooth transfer, as those skilled in the art know.

In an exemplary embodiment, base stations 101-103 can communicate with each other and with subscriber stations 111-116 using a wireless metropolitan area network standard IEEE-802.16, 802.20, or 802.11, such as, for example, a IEEE-802.16e standard. In another embodiment, however, a different wireless protocol may be employed, such as, for example, a HIPERMAN wireless metropolitan area network standard. The base station 101 can communicate through a direct line of sight communication with the base station 102 and with the base station 103. The base station 102 and the base station 103 can each communicate through a communication without direct visibility with base stations 111-116 using OFDM and / or OFDMA techniques.

The base station 102 may provide a service of level T1 to the subscriber station 112 associated with the company and a service of level T1 fractionated to the subscriber station 111 associated with the small business. The base station 102 may provide a wireless return network for the subscriber station 113 associated with the WiFi hotspot, which may be located at an airport, a cafe, a hotel, or a university campus. The base station 102 may provide a digital subscriber line level (DSL) service to the subscriber stations 114, 115 and 116.

Subscriber stations 111-116 may use broadband access to network 130 to access voice, data, video, video teleconference, and / or other broadband services. In an exemplary embodiment, one or more subscriber stations 111-116 can be associated with an access point (AP) of a Wi-Fi WLAN network. Subscriber station 116 may be a number of mobile devices, including a laptop with wireless capability, a personal data assistant, a notebook, a portable device, or other device with wireless capability. Subscriber stations 114 and 115 may be, for example, a personal computer with wireless capability, a laptop, a gateway, or other device.

Dotted lines show the approximate extent of coverage areas 120 and 125, which are shown as approximately circular by way of example and explanation only. It should be clearly understood that the coverage areas associated with the base stations, for example, the coverage areas 120 and 125, may have other shapes, including irregular shapes, s the configuration of the base stations and the variations in the radial environment associated with natural and artificial obstructions.

In addition, the coverage areas associated with the base stations are not constant over time and can be dynamic (expanding or contracting or changing shape) based on changing transmission power levels of the base station and / or the stations Subscribers, weather conditions, and other factors. In one embodiment, the radius of the coverage areas of the base stations, for example, the coverage areas 120 and 125 of the base stations 102 and 103, may extend in the range between about 2 kilometers and about fifty kilometers from the stations base.

As is well known in the art, a base station, such as station 101, 102, or 103, can employ directional antennas to support a plurality of sectors within the coverage area. In FIGURE 1, base stations 102 and 103 are shown approximately in the center of coverage areas 120 and 125, respectively. In other embodiments, the use of directional antennas may place the base station near the edge of the coverage area, for example, at the tip of a conical or pear-shaped coverage area.

The connection to the network 130 from the base station 101 may comprise a broadband connection, for example, a fiber optic line, to the servers located in a central office or other operational presence point of the company. The servers can provide communication to an Internet portal for communications based on the Internet protocol and to a gateway to the public switched telephone network for voice communications. The servers, the Internet portal, and the gateway to the public switched telephone network are not shown in FIGURE 1. In another embodiment, the connection to the network 130 may be provided by different nodes and network equipment.

In accordance with an embodiment of the present disclosure, each base station 101-103 can be operated to precode signals using a composite precoding matrix that provides power sharing and diversity characteristics. The use of this composite precoding matrix allows base stations 101-103 to take advantage of precoding whether spatial multiplexing is used

or the method of transmission diversity. In addition, for an embodiment of the present disclosure, each base station 101-103 may be operated, for each communications session, to select a precoding matrix code book composed from a plurality of possible code books and use one or more of the precoding matrices composed within the codebook selected for that communications session.

FIGURE 2 illustrates an exemplary base station 102 in greater detail in accordance with an embodiment of the present disclosure. Base station 102 is illustrated by way of example only. However, it should be understood that the components illustrated and described with respect to the base station 102 are also part of the base stations 101 and 103. In one embodiment, the base station 102 comprises a controller 225, the channel controller 235, the transceiver interface (IF) 245, radio frequency transceiver unit (RF) 250, and a set of antennas 255.

The controller 225 comprises circuits and a processing memory capable of executing an operating program that controls the general operation of the base station 102. In one embodiment, the controller 225 may be operated to communicate with the network 130. Under normal conditions, the controller 225 directs the operation of the channel controller 235, which comprises a number of channel elements, such as the example channel element 240, each of which performs two-way communication on the transmission channel and the channel reception. A transmission channel (or downlink) refers to outgoing signals from the base station 102 to the subscriber stations 111-116. A receiving channel (or uplink) refers to incoming signals from the subscriber stations 111-116 to the base station 102. The channel element 240 also preferably performs all baseband processing, which includes the processing of any digitized signal received to extract the information or bits of data transported in the received signal, which normally includes demodulation, decoding, and error correction operations, as is known to those skilled in the art. The IF 245 transceiver interface transfers the bidirectional channel signals between the channel controller 235 and the RF transceiver unit 250.

The antenna set 255 transmits the transmission channel signals received from the RF transceiver unit 250 to the subscriber stations 111-116 in the coverage area of the base station 102. The antenna set 255 can also be operated to send to the RF transceiver unit 250 reception channel signals from the subscriber stations 111-116 in the coverage area of the base station 102. According to an embodiment of the present disclosure, the antenna assembly 255 comprises a multisectoral antenna, such as a three sector antenna in which each antenna sector is responsible for transmitting and receiving in a coverage area corresponding to an arc of approximately 120 degrees. Also, the RF transceiver unit 250 may comprise an antenna selection unit for selecting among the different antennas in the antenna set 255 during the transmission and reception operations.

According to an embodiment of the present disclosure, the channel controller 235 also comprises a signal generator 265 comprising a plurality of code books 270, a code book selector 275, a precoder selector 280, a precoder 285 and a fast reverse Fourier transform (IFFT) block 290. Although they are illustrated and described as four separate components, it should be understood that any two or more elements between code book selector 275, precoder selector 280, precoder 285 and the IFFT block 290 may be jointly implemented in a single component without departing from the scope of the present disclosure.

The signal generator 265 can be operated to create a virtual antenna for each signal by precoding the signals before transmission. The signal generator 265 can also be operated to store a plurality of possible code books 270, each of which comprises a plurality of precoding matrices for use in the precoding of the signals. The code book selector 275 can be operated to select one of the code books 270 to be used during any suitable interval. For example, for one embodiment, the code book selector 275 can be operated to select one of the code books 270 to be used once for each communication session with a subscriber station 111-116.

The precoder selector 280 can be operated to select one of the precoding matrices from the selected code book 270 for use in communicating with a subscriber station 111-116 during any suitable interval. For example, for one embodiment, the precoder selector 280 may be operated to select one of the precoding matrices from the selected code book 270 for

5 the use in communication with a subscriber station 111-116 for each transmission time interval (TTI).

The precoder 285 can be operated to precode each signal, or data stream, for a corresponding virtual antenna using the precoding matrix selected by the precoder selector 280. The IFFT block 290 can be operated to perform a fast reverse Fourier transform operation. on

10 each precoded signal. Each precoded transformed signal can be transmitted from a different antenna in the set of antennas 255.

Each precoding matrix of the code books 270 that can be used by the precoder 285 to precode the signals for transmission from the base station 102 may comprise a composite precoding matrix, which is a precoding matrix that is generated based on a matrix with a diversity of precoding and a power sharing precoding matrix. As used herein, a "matrix with a precoding diversity" means a precoding matrix that can be operated to provide transmission diversity. For example, for one embodiment, the matrix with a diversity of precoding may comprise a matrix of unit diversity of cyclic delay. However, it should be understood that the matrix with a diversity of precoding can comprise a matrix of

20 non-unit precoding or other suitable type of unit precoding matrix.

In addition, as used herein, a "power sharing precoding matrix" means a precoding matrix that can be operated to provide power sharing properties for physical antennas 255, such as those associated with spatial multiplexing in which each signal is transmitted in some way through each antenna 255. For example, for one embodiment, the power sharing precoding matrix may comprise a unit precoding matrix based on the Fourier transform. However, it should be understood that the power sharing precoding matrix may comprise a non-unitary precoding matrix or a unitary precoding matrix not based on a Fourier transform. As described in more detail below, each of the code books 270 may comprise composite precoding matrices that are generated based on the same

30 set of power sharing precoding matrices but which are also generated based on a matrix with a diversity of precoding that has a different phase shift compared to the other code books 270.

In one example, a power sharing precoding matrix may comprise a Fourier precoding matrix, of NxN square, which is defined as follows:

image 1

Therefore, a 2x2 Fourier precoding matrix can be expressed as follows:

image 1

Similarly, a 4x4 Fourier precoding matrix can be expressed as follows:

image 1

40 Multiple power sharing precoding matrices that can be used for the generation of composite precoding matrices for a given code book 270 can be defined by entering a shift parameter (g / G) in the matrix of Fourier precoding according to:

image 1

For example, a set of four 2x2 Fourier precoding matrices can be defined considering G = 4. These four matrices of 2x2 with g = 0, 1, 2 and 3 are written as follows:

image2

A cyclic delay diversity scheme can be implemented in the frequency domain with a phase shift of ej�ik applied to the subcarrier k transmitted from the transmission antenna ith 255. The phase shift angle can be defined as:

image 1

10 where Di is the cyclic delay in the samples applied from the ith 255 antenna. It will be understood that other functions can be used to obtain the phase shift in the frequency domain. In addition, for some embodiments, the phase shift for one group of subcarriers can be kept constant and it can be allowed to vary from one group of subcarriers to another.

It can be considered that the cyclic delay diversity is precoded with the following matrix with a diversity of 15 precoding in the case of four transmitting antennas 255:

image 1

For this case, the same symbol is transmitted with the phase shifts depending on the antenna and the frequency from multiple antennas 255. Normally, no phase shift is applied for the symbol transmitted from the first antenna 255. As described above. , you can use different angles of

20 phase shift to generate matrices with a variety of multiple precoding, where each matrix with a diversity of precoding corresponds to a given code book 270.

Also as described above, a power sharing precoding matrix, P, and a matrix with a precoding diversity, D, can be used to generate a composite precoding matrix, C, for the case of four transmitting antennas 255 as it's shown in the following:

image 1

In another embodiment, the order of multiplication of matrices D and P can be changed, which results in a transposition of the composite precoding matrix, or CT, as shown below:

image 1

5 Since C represents a power sharing precoding matrix (which transforms virtual antennas into physical antennas) and a matrix with a precoding diversity (which introduces a cyclic time delay or equivalent frequency offset), the utilization of C as a precoder produces delays for physical antennas. On the other hand, the use of the transposition of this matrix, or CT, causes delays for virtual antennas. Therefore, in order to enter frequency selectivity, when the same symbol is entered

10 within precoder 285, virtual antennas are delayed relative to each other.

In addition, when a single symbol is entered into precoder 285, precoder 285 can be operated to multiply the symbol by a weight vector, w, which is not orthogonal to any line of the composite precoding matrix. For example, when w = [1 1 1 1] T, w is equal to the first line of the composite precoding matrix and is therefore orthogonal to the other lines. In the same way, when they are entered

15 different symbols within the precoder 285, the physical antennas are delayed in relation to each other because a symbol is transmitted through a virtual antenna.

In an example where two transmitting antennas 255 are used, a composite precoding matrix can be defined as follows:

image 1

20 The symbols, T1 and T2, transmitted from the two physical antennas 255 are as follows:

image 1

Composite precoding matrices can be developed for other transmission diversity schemes, such as frequency space block coding (SFBC), switched frequency transmission diversity (FSTD) ), switched time transmission diversity (TSTD) or a combination of these schemes. For example, in the case of the SFBC for two transmitting antennas 255, the symbols transmitted from the two antennas 255 and the two adjacent subcarriers may be presented as:

image 1

where T11 and T21 denote the symbols transmitted from antenna 1 and antenna 2 on the first subcarrier of 10 OFDM and T12 and T22 denote the symbols transmitted from antenna 1 and antenna 2 on the second subcarrier of OFDM.

In another example, in the case of the FSTD for two transmitting antennas 255, the symbols transmitted from the two antennas 255 and the two adjacent subcarriers may be presented as:

image 1

15 where T11 and T21 denote the symbols transmitted from antenna 1 and antenna 2 on the first subcarrier and T12 and T22 denote the symbols transmitted from antenna 1 and antenna 2 on the second subcarrier.

In another example, in the case of the FSTD transmission for four transmission antennas 255, the symbols transmitted from the four antennas 255 on four subcarriers may be presented as:

image 1

image3

If we assume that φ2 = 2φ1 and φ3 = 3φ1, the above expression can be simplified as follows:

image 1

Therefore, as was previously shown with the cases of two and four antennas, the use of a composite precoding matrix produces a scheme that modulates in amplitude the different antennas 255 with orthogonal signals.

In another embodiment, a combination of SFBC and FSTD can be used in the case of four transmitting antennas 255, as follows:

image 1

where Tij represents a symbol transmitted through the antenna ith and the subcarrier jth (i = 1,2,3,4 and j = 1,2,3,4) in the case of four transmitting antennas 255.

10 In addition, it will be understood that the SFBC can be combined with the cyclic delay diversity (CDD) or the phase shift diversity for the case of four transmission antennas as follows:

image 1

where Tij represents a symbol transmitted through the antenna ith and the subcarrier jth (i = 1,2,3,4 and j = 1,2) in the case of four transmitting antennas 255 for the hybrid schemes of SFBC and CDD.

15 In the case of TSTD, the four symbols transmitted in four time slots from the four transmission antennas 255 on the same subcarrier can be presented as:

image 1

where Tij represents a symbol transmitted through the antenna ith and the time slot jth or the symbol of OFDM (i = 1,2,3,4 and j = 1,2,3,4) for the case of four antennas of transmission 255.

In an embodiment of the present disclosure, as described above, a plurality of code books 270 are stored in a signal generator 265. For one embodiment, the composite precoding matrices for each code book 270 may be based on a matrix with a different precoding diversity. For example, a first code book, CB1, can be based on a power sharing precoding matrix without any diversity precoding. This is equivalent to all

10 phase shifts in the matrix with a diversity of precoding are zeros (i.e., the matrix with a diversity of precoding is a diagonal matrix with Is on the diagonal and all other elements fixed in zeros). A offset parameter can be used to generate a plurality of precoding matrices based on a single power sharing precoding matrix. An example of this code book 270 with four precoding matrices in the case of two transmitting antennas 255 can be

15 file as follows:

image 1

Another code book, CB2, can be obtained by adding diversity precoding within the composite precoding matrices. A set of composite precoding matrices for this code book 270 can be obtained as follows:

image 1

The code book, CB2, comprising multiple composite precoding matrices can be presented as follows:

image 1

Similarly, other code books 270 can be obtained using different phase shifts in the

A matrix with a diversity of precoding, D. For example, for a given embodiment, a first code book 270 can be provided without delay, such as the code book, CB1, described above, a second book of codes can be provided. 270 codes with a relatively small delay, and a third code book 270 with a relatively large delay can be provided.

For this particular example, the code book selector 275 can select the second code book 270 that uses a lower value for φ in the array with a precoding diversity for a low mobility user that requires selective multi-user frequency programming . A smaller φ will produce a minor phase shift from one subcarrier to the next for transmission from multiple 5 antennas 255 that provide upward fades and downward fades over a group of subcarriers suitable for selective multi-user frequency programming. It is also possible to select a constant phase shift by a group of subcarriers. A user with low mobility can also dynamically select a composite precoding matrix from the second codebook 270 that produces maximum signal quality because the dynamic selection of an array of

10 composite precoding is quite reliable at low speeds.

Also, for this particular example, the code book selector 275 can select the third code book 270 which uses a higher value for φ in the matrix with a diversity of precoding for a high mobility user requiring a transmission diversity . A larger φ will produce a larger phase shift from one subcarrier to the next for transmission from multiple antennas 255 that provide

15 frequency diversity. A user with high mobility can also select a fixed composite precoding matrix from the third codebook 270 because dynamic selection of the composite precoding matrix may not be beneficial due to feedback delays of the precoder selection indication.

FIGURE 3 illustrates details of a portion of signal generator 265 when using multiplexing.

Total space according to an embodiment of the present disclosure. As used herein, "total spatial multiplexing" refers to the situation in which signal generator 265 is generating signals based on a specified number of data streams that is equal to the number of transmission antennas in the set. of antennas 255.

For the illustrated embodiment, the signal generator 265 comprises a precoder 285 that can be operated to

25 receive four data streams 310 (S1, S2, S3 and S4) from four virtual antennas 305 (VA1, VA2, VA3 and VA4). In addition, a set of antennas 255 comprises four antennas. However, it will be understood that the signal generator 265 may comprise any other suitable number of virtual antennas 305, each of which may be operated to provide a data stream 310, based on the number of antennas in a set of antennas.

255

30 Precoder 285 can be operated to receive a composite precoding matrix 315 from precoder selector 280. Precoder 285 can be operated to apply composite precoding matrix 315 to each of the data streams 310 received from a created virtual antenna 305 in order to generate four precoded signals 320 (T1, T2, T3 and T4). The IFFT block 290 can be operated to perform a fast reverse Fourier transform on each of the precoded signals 320 to generate a precoded signal

Transformed 330 for transmission through a corresponding physical antenna in the set of antennas 255.

In an example of the case of spatial multiplexing of four data streams in a 4x4 system, the column matrix of the symbol, S, is multiplied by the composite precoding matrix, C, to give a column vector, T, of symbols that are they will transmit from physical antennas 255, as follows:

image4

FIGURE 4 illustrates details of a portion of the signal generator 265 when using transmission diversity in accordance with an embodiment of the present disclosure. For an example of a transmission of

transmission diversity in the case of four transmitting antennas 255 and any number of receiving antennas, the column matrix of the symbol, S, comprising the same symbol is multiplied by the transposition of the composite precoding matrix, C, to give a column vector, T, of symbols transmitted from the four physical antennas 255, as follows:

image2

FIGURES 5A-D illustrate details of a portion of signal generator 265 when using partial spatial multiplexing in accordance with some embodiments of the present disclosure. As used herein, "partial spatial multiplexing" refers to the situation in which the signal generator 265 10 is generating signals based on a specific number of data streams that is greater than one but less than the number of transmitting antennas in the set of antennas 255. It will be understood that the embodiments illustrated in FIGURES 5A-D are examples for explanatory purposes and that other suitable embodiments can be implemented.

As shown in FIGURE 5A, in the case of a spatial multiplexing of two data streams 310, for example, in a 4x4 or 4x2 system, the column vector of the symbol, S, can be generated by repeating two two flow symbols S1 and S2 as below.

image 1

The symbol vector is multiplied by the composite precoding matrix, C, to give a column vector, T, of symbols that will be transmitted from physical antennas 255, as follows:

image3

As shown in FIGURE 5B, in the case of spatial multiplexing of two data streams 310, for example, in a 4x4 or 4x2 system, the information is transmitted through two virtual antennas 305. Virtual antennas 305 are They can select based on the quality information of the virtual antenna channel. For example, when two data streams 310 are transmitted through the first and third virtual antennas 305, the symbol vector can be written as follows:

image 1

The symbol vector is multiplied by the 4x4 precoding matrix, C, to generate a column vector, T, of symbols that will be transmitted from physical antennas 255, as follows:

image 1

As shown in FIGURE 5C, in the case of spatial multiplexing of three data streams 310, for example, in a 4x4 or 4x3 system, the information is transmitted through three virtual antennas 305. The antennas

10 virtual 305 can be selected based on the quality information of the virtual antenna channel. For example, when three data streams 310 are transmitted through the first, third and fourth virtual antennas 305, the symbol vector can be written as follows:

image 1

The symbol vector is multiplied by the 4x4 precoding matrix, C, to generate a column vector, T, of symbols that will be transmitted from physical antennas 255, as follows:

image 1

As shown in FIGURE 5D, three data streams 310 can be transmitted through four virtual antennas 305. The column vector of the symbol, S, is generated by repeating the first flow symbols and 20 by not repeating the seconds. and third flow symbols, as follows:

image 1

In this configuration, the first data stream 310 also benefits from the additional transmission diversity. The symbol vector is multiplied by the composite precoding matrix, C, to give a column vector, T, of symbols that will be transmitted from physical antennas 255, as follows:

image2

FIGURES 6A-B illustrate symbol vector precoding structures 600,650 for use by signal generator 265 when using spatial multiplexing according to two embodiments of the present disclosure.

10 For the embodiment shown in FIGURE 6A, the symbol vector precoding structure 600 may correspond to a transmission time interval (TTI) or a frequency resource block. The illustrated embodiment includes six symbols of OFDM 605a-f; however, it will be understood that each TTI or frequency resource block may comprise any suitable number of OFDM 605 symbols.

For the embodiment in which the symbol vector precoding structure 600 corresponds to a TTI,

15 pop the OFDM 605 symbols assigned to virtual antennas 305 during the TTI as shown. Similarly, for the embodiment in which the vector symbol precoding structure 600 corresponds to a frequency resource block, the OFDM symbols 605 assigned to the virtual antennas 305 from sub-carrier to sub-carrier on the resource block are skipped of frequency assigned for transmission.

In the illustrated embodiment, the symbol for flow 1 (S1) is repeated in the first and fourth symbols of OFDM 605a

20 and 605d, the symbol for flow 2 (S2) is repeated in the second and fifth symbols of OFDM 605b and 605e, and the symbol for flow 3 (S3) is repeated in the third and sixth symbols of OFDM 605c and 605f . Therefore, each of the streams is allowed to experience additional transmission diversity while spatial multiplexing is also provided.

For the embodiment shown in FIGURE 6B, the vector symbol precoding structure 650 may

25 correspond to a TTI or a frequency resource block. The illustrated embodiment includes six OFDM 655a-f symbols; however, it will be understood that each TTI or frequency resource block may comprise any suitable number of OFDM 655 symbols.

In the illustrated embodiment, three data streams 310 are transmitted through three virtual antennas 305. For the embodiment in which the vector symbol precoding structure 650 corresponds to a TTI, the antennas

30 virtual 305 used for transmission change from symbol of OFDM 655 to symbol of OFDM 655. Similarly, for the embodiment in which the vector precoding structure symbol 650 corresponds to a block of frequency resources, virtual antennas 305 used for transmission change from OFDM subcarrier to subcarrier.

For the illustrated example, virtual antennas 2, 3 and 4 are used for flow 1 (S1), flow 2 (S2) and flow 3 (S3),

35 respectively, in the first and fifth symbols of OFDM 655a and 655e. In the second and sixth symbols of OFDM 655b and 655f, virtual antennas 1, 3 and 4 are used for flow 1, flow 2 and flow 3, respectively. In the third symbol of OFDM 655c, virtual antennas 1, 2 and 4 are used for flow 1, flow 2 and flow 3, respectively. In the fourth symbol of OFDM 655d, virtual antennas 1, 2 and 3 are used for flow 1, flow 2 and flow 3, respectively.

FIGURE 7 is a flow chart illustrating a method 700 for performing precoding using signal generator 265 in accordance with an embodiment of the present disclosure. Initially, the base station 102 receives a request for a communications session from a subscriber station, such as the subscriber station 111 (step 705 of the process).

The code book selector 275 selects a code book 270 for the communications session based on the feedback received from the subscriber station 111 (step 710 of the process). The precoder selector 280 selects a composite precoding matrix 315 from the selected code book 270 based on feedback from the subscriber station 111 (step 715 of the process).

If the spatial multiplexing is being used by the base station 102 (process step 720), the precoder 285 precodes each data stream 310 received from a virtual antenna 305 by applying the selected composite precoding matrix 315 to generate precoded signals 320 (step 725 of the process). However, if the transmission diversity is being used by the base station 102 (process step 720), the precoder 285 precodes each data stream 310 received from a virtual antenna 305 by applying the composite precoding matrix transposition 315 selected to generate 320 precoded signals (step 730 of the process).

The IFFT block 290 performs an IFFT operation on the precoded signals 320 to generate a transformed precoded signal 330 for each precoded signal 320 (step 735 of the process). Each transformed precoded signal 330 is transmitted through a corresponding physical antenna in the set of antennas 255 (step 740 of the process).

If the communications session has not ended (step 745 of the process), the precoder selector 280 may select the same or another precoding matrix 315 based on the additional feedback from the subscriber station 111 (step 715 of the process), and the Continuous method as before. However, once the communications session is over (step 745 of the process), the method comes to an end.

In this way, precoding can be performed if spatial multiplexing or transmission diversity is used in the wireless network 100. In addition, improved precoding can be provided by selecting a code book 270 for each communication session that is custom-made. for that communications session. For example, a user with low mobility may have composite precoding matrices 315 selected from a codebook, while a user with high mobility may have composite precoding matrices 315 selected from another codebook.

Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications within the scope of the appended claims.

Claims (16)

one.

 A base station (102) capable of precoding in a wireless communication system (100), comprising:

a plurality of code books (270), each code book comprises a plurality of composite precoding matrices generated based on a matrix with a corresponding precoding diversity and a power sharing precoding matrix; and a code book selector (275) that can be operated to select one of the code books (270) for use in a communications session with a subscriber station (111).

2.

 The base station (102) according to claim 1, further comprising a precoder selector (280) that can be operated to select one of the precoding matrices of the codebook selected for use in communication with the subscriber station (111) .

3.

 The base station (102) according to claim 2, further comprising a precoder (285) that can be operated to precode a plurality of data streams (310) based on a selected composite precoding matrix (315).

Four.

 The base station (102) according to claim 3, wherein the precoder (285) can also be operated to precode a single data stream based on a transposition of the selected composite precoding matrix (315).

5.

 The base station (102) according to claim 2, wherein the precoder selector (280) can also be operated to select one of the precoding matrices composed of the codebook selected for use in communication with the subscriber station (111) for Each transmission time interval.

6.

 The base station (102) according to claim 1, wherein the matrix with a diversity of precoding comprises a matrix with a diversity of precoding of cyclic delay.

7.

 The base station (102) according to claim 1, wherein the composite precoding matrices have also been generated based on a corresponding power sharing precoding matrix, wherein the power sharing precoding matrix comprises a base precoding matrix to the Fourier transform.

8.

 The base station (102) according to claim 1, wherein the plurality of codebooks (270) comprises a first codebook and a second codebook, wherein the matrix with a diversity of precoding corresponds to the first codebook that does not it provides phase shift, and the matrix with a diversity of precoding corresponds to the second codebook that provides a phase shift.

9.

 A method (700) for performing precodes in a wireless communication system, comprising:

the storage of a plurality of code books (270), where each code book comprises a plurality of composite precoding matrices generated based on a matrix with a corresponding precoding diversity and a power sharing precoding matrix; and the selection (710) of one of the code books (270) for use in a communications session with a subscriber station (111).

10.

 The method (700) according to claim 9, further comprising the selection (715) of one of the precoding matrices composed of the selected codebook (270), for use in communication with the subscriber station (111).

eleven.

 The method (700) according to claim 10, further comprising the precoding (725, 730) of a plurality of data streams (310) based on a selected composite precoding matrix (315).

12.

 The method (700) according to claim 11, further comprising the precoding (725, 730) of a single data stream (310) based on a transposition of the selected composite precoding matrix (315).

13.

 The method (700) according to claim 9, further comprising the selection of one of the precoding matrices composed of the selected code book (270), for use in communicating with the subscriber station (111) for each time interval of transmission.

14.

 The method (700) according to claim 9, the matrix with a diversity of precoding comprises a matrix with a diversity of precoding of cyclic delay.

fifteen.

 The method (700) according to claim 9, wherein the composite precoding matrices have also been generated based on a corresponding power sharing precoding matrix, wherein the matrix of

The power sharing precoding comprises a precoding matrix based on a Fourier transform. 16. The method (700) according to claim 9, wherein the plurality of codebooks (270) comprises a first codebook and a second codebook, wherein the matrix with a diversity of precoding corresponds to the first codebook that does not provide phase shift, and where the matrix with a diversity of 10 precoding corresponds to the second codebook that provides phase shift.