Patent Publication Number: US-8537771-B2

Title: Method of multiple-input-multiple-output wireless communication

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/734,120 , (U.S. Pat. No. 7,443,818) filed Dec. 15, 2003, which is hereby incorporated in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     A Multiple-Input-Multiple-Output (NIMO) Space-Time-Coding (STC) wireless communication device may implement STC to multiplex data into a plurality of parallel data sequences. The STC device may also include a Space-Time (ST) encoder to encode the data sequences, and a ST decoder to decode received data. The encoded data sequences may be simultaneously transmitted by a plurality of antennas using one frequency channel. 
     A MIMO Multi-Channel (MC) wireless communication device may include a plurality of channel controllers associated with a plurality of Single-Input-Single-Output (SISO) encoders and a plurality of SISO decoders, respectively. Each of the channel controllers may be assigned to a different frequency channel. The MC device may simultaneously transmit and/or receive data over a plurality of different frequency channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanied drawings in which: 
         FIG. 1  is a schematic diagram of a wireless communication system in accordance with some exemplary embodiments of the present invention; 
         FIG. 2  is a schematic illustration of a dual-channel wireless device in accordance with some exemplary embodiments of the invention; and 
         FIG. 3  is a schematic illustration of a flow chart of a method of controllably selecting between a spatial-multiplexing modulation method and a frequency-multiplexing modulation method in accordance with some exemplary embodiments of the invention. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. Moreover, some of the blocks depicted in the drawings may be combined into a single function. 
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits may not have been described in detail so as not to obscure the present invention. 
     Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system&#39;s registers and/or memories into other data similarly represented as physical quantities within the computing system&#39;s memories, registers or other such information storage, transmission or display devices. In addition, the term “plurality” may be used throughout the specification to describe two or more components, devices, elements, parameters and the like. 
     Not withstanding any conventional meaning of the term “modem” (e.g., modulator-demodulator), in this application, unless specifically stated otherwise, the term “modem” may refer to a modulator, e.g., a device able to modulate data frames of signals to be transmitted and/or to a demodulator, e.g., a device able to demodulate data frames of received signals, and/or to a device able to both modulate and demodulate signals. Implementations of modems in accordance with embodiments of the invention may depend on specific applications and design requirements. Furthermore, modems in accordance with some embodiments of the invention may be implemented by separate modulator and demodulator units or in a single modulator/demodulator unit, and such units may be implemented using any suitable combination of hardware and/or software. 
     It should be understood that the present invention may be used in a variety of applications. Although the present invention is not limited in this respect, the circuits and techniques disclosed herein may be used in many apparatuses such as units of a wireless communication system, such as for example, a Wireless Local Area Network (WLAN) communication system and/or in any other unit and/or device. Units of a WLAN communication system intended to be included within the scope of the present invention include, by way of example only, modems, Mobile Units (MU), Access Points (AP), wireless transmitters/receivers, and the like. 
     Types of WLAN communication systems intended to be within the scope of the present invention include, although are not limited to, “IEEE-Std. 802.11, 1999 Edition (ISO/IEC 8802-11: 1999)” standard (“the 802.11 standard”), and more particularly in “IEEE-Std 802.11a-1999 Supplement to 802.11-1999: Wireless LAN MAC and PHY specifications: Higher speed Physical Layer (PHY) extension in the 5 GHz band”, “IEEE-Std 802.11b-1999 Supplement to 802.11-1999, Wireless LAN MAC and PHY specifications: Higher speed Physical Layer (PHY) extension in the 2.4 GHz band”, “IEEE-Std 802.11g-2003 Supplement to 802.11-1999, Wireless LAN MAC and PHY specifications: Further Higher Data Rate Extension in the 2.4 GHz band, Draft 8.2”, and “IEEE-Std 802.11k-2003 Supplement to 802.11-1999: Wireless LAN MAC and PHY specifications: Specification for Radio Resource Measurement, Draft 0.1”, and the like. 
     Although the scope of the present invention is not limited in this respect, the circuits and techniques disclosed herein may also be used in units of wireless communication systems, digital communication systems, satellite communication systems and the like. 
     Devices, systems and methods incorporating aspects of embodiments of the invention are also suitable for computer communication network applications, for example, intranet and Internet applications. Embodiments of the invention may be implemented in conjunction with hardware and/or software adapted to interact with a computer communication network, for example, a LAN, wide area network (WAN), or a global communication network, for example, the Internet. 
     Reference is made to  FIG. 1 , which schematically illustrates a wireless communication system  100  in accordance with an embodiment of the present invention. It will be appreciated by those skilled in the art that the simplified components schematically illustrated in  FIG. 1  are intended for demonstration purposes only, and that other components may be required for operation of the wireless systems, devices and methods described herein. Those of skill in the art will further note that the connection between components in the wireless devices described herein need not necessarily be as depicted in the schematic diagram of  FIG. 1 . 
     Communication system  100  may include wireless communication devices  130  and  110 , which may communicate via a wireless link or channel  120  of wireless communication system  100 . Although the scope of the present invention is not limited in this respect, communication devices  130  and  110  may include wireless modems of computers, and communication channel  120  may be part of a WAN or a LAN. For example, system  100  may be a WLAN system, a Wireless Personal Area Network (WPAN), or a Wireless Wide Area Network (WWAN). 
     Although the scope of the present invention is not limited in this respect, the exemplary communication system shown in  FIG. 1  may be part of a wireless communication system, in which wireless device  130  is a remote unit (RU) and wireless unit  110  is an access point (AP). It will be recognized, however, that in some embodiments of the invention either or both communication devices  130  and  110  may be mobile stations, a personal digital assistant (PDA) and a server, respectively, access points, base stations, or any other device or combination of devices suitable for communicating within communication system  100 . 
     Communication device  110  may include a transceiver  102 , which may include a transmitter and/or a receiver in any suitable configuration. Transceiver  102  may include any suitable transmission and/or reception circuitry known in the art for receiving data transmitted, e.g., by device  130  and/or for transmitting data, e.g., to device  130 , as described below. Transceiver  102  may be implemented, for example, in the form of a single unit or in the form of separate transmitter and receiver units using any suitable combination of hardware and/or software as is known in the art. For example, in the context of the embodiment described with reference to  FIG. 1 , transceiver unit  102  may operate to both transmit and receive signals. 
     Communication devices  130  and  110  may include one or more radio frequency antennas, as is known in the art. For example, device  110  may include an antenna  104  associated with transceiver  102 , and device  130  may include a plurality of antennas, for example, antennas  112 ,  114 , and  116 . Although the scope of the present invention is not limited in this respect, types of antennae that may be used for antenna  104 , antenna  112 , antenna  114 , and/or antenna  116  may include but are not limited to internal antenna, dipole antenna, omni-directional antenna, a monopole antenna, an end fed antenna, a circularly polarized antenna, a micro-strip antenna, a diversity antenna and the like. 
     Wireless device  110  may include a processor  106 , which may be associated with a memory (not shown). Processor  106  may process data packets of signals received by transceiver  102  and/or data packets of signals intended for transmission by transceiver  102 . Wireless device  130  may include a processor  119  associated with a memory (not shown), and a controller  118 . Controller  118  may be able to control the flow of data to/from processor  119  and to selectively provide to either a frequency-multiplexing modem  138  or a spatial-multiplexing modem  132  a data frame to be transmitted, as described in detail below. 
     According to exemplary embodiments of the invention, modem  138  may be able to modulate data to be transmitted and/or demodulate received data based on a Multiple-Input-Multiple-Output (MIMO) frequency multiplexing method, i.e., a MIMO multiplexing method using in parallel a plurality of channels separated in frequency, as is known in the art. For example, modem  138  may implement a MIMO Multi-channel (MC) multiplexing method, as is known in the art. 
     According to exemplary embodiments of the invention, modem  132  may be able to modulate data to be transmitted and/or to demodulate received data based on a MIMO spatial-multiplexing method, i.e., a MIMO multiplexing method simultaneously using a plurality of spatial channels of one frequency, as is known in the art. For example, modem  132  may implement a Space-Time Coding (STC) algorithm, a Space Division Multiplexing (SDM) method, or any other spatial-multiplexing method, as are known in the art. 
     According to exemplary embodiments of the invention, wireless device  100  may also include a plurality of Radio Frequency (RF) paths  134  associated with modem  138  and modem  132 . Paths  134  may be adapted to transmit and receive data via antennas  112 ,  114 , and  116 , as is known in the art. 
     According to exemplary embodiments of the invention, controller  118  may selectively transfer data to be transmitted, e.g., provided by processor  119 , either to modem  138  or to modem  132 , based on a predetermined criterion, as described below. The data may be modulated by the selected modem, and transferred via one or more of paths  134  to an antenna selector  136 . Modem  130  may also control antenna selector  136  to select one or more of antennas  112 ,  114  and  116 , e.g., according to one or more frequency channels implemented by the frequency-multiplexing method, e.g., as is known in the art. Data received from one or more of channels  134 , e.g., via one or more of antennas  112 ,  114 , and  116 , may be demodulated by either modem  138  or modem  132 . For example, data previously modulated according to the STC method may be demodulated by modem  132 , and data previously modulated according to the MC method may be demodulated by modem  138 , e.g., as described below. The demodulated data may be transferred by controller  118  to processor  119 , e.g., as described below. 
     It will be noted that wireless device  130  may be implemented by different architectures, as are known in the art. For example, one or more elements of device  130 , e.g., processor  119 , controller  118 , modem  132 , modem  138 , paths  134  and/or antenna selector  136 , may be implemented using any suitable combination of hardware and/or software, and may include any circuit, circuitry, unit or combination of integrated and/or separate units or circuits, as are known in the art, to perform desired functionalities. It is noted that the terms “circuit” and “circuitry” as used herein, may include any suitable combination of hardware components and/or software components, e.g., as described below. 
     Reference is made to  FIG. 2 , which schematically illustrates a dual-channel wireless device  200  in accordance with some exemplary embodiments of the invention. 
     According to some exemplary embodiments of the invention, device  200  may be capable of receiving and/or transmitting data using either a STC modem or a dual-channel modem, as described below. 
     According to exemplary embodiments of the invention, device  200  may include a processor  205  associated with a controller  210 , as described in detail below. Device  200  may also include a dual channel modem  220  and a STC modem  230  associated with controller  210 , respectively, as described below. Device  200  may also include a first RF path  240  and a second RF path  250 , each associated with modem  220  and modem  230 . Path  240  and path  250  may transmit and/or receive data to/from a plurality of antennas, e.g., antennas  290 ,  292  and  294 , via an antenna selection module  280 , as is known in the art. Path  240  and path  250  may include any suitable RF path for transmitting and/or receiving data through a channel, as is known in the art. For example, path  240  may include a transmission (Tx) sub-module  242  and a Receiving (Rx) sub-module  244 , and path  250  may include a Tx sub-module  252  and a Rx sub-module  254 , as are known in the art. 
     According to exemplary embodiments of the invention, modem  220  may include any suitable dual-channel modem for modulating data to be transmitted and/or demodulating received data according to a MC multiplexing method. For example, modem  220  may include a channel selection module  222 , e.g., as is known in the art, to select a frequency channel for transmitting data provided from controller  210 . For example, the frequency channel may be selected based on a physical-carrier sensing mechanism or a virtual-carrier sensing mechanism, as are defined by the 802.11 standard. 
     Module  222  may transfer the data from controller  210  to a first MC-based channel access control module  224  or to a second MC-based channel access control module  226 , e.g., based on the selected frequency channel. Each of modules  224  and  226  may be adapted to control transmission of the data via an individual frequency channel, e.g., using one or more of antennas  290 ,  292  and  294 , as is known in the art. 
     Module  222  may also be adapted to control antenna selection module  280  according to one or more frequency channels implemented by the MC multiplexing method, as is known in the art. For example, module  222  may control selector  280  to assign one or more of antennas  290 ,  292  and  294  for receiving data, e.g., via path  240 , and to assign one or more of antennas  290 ,  292  and  294  for transmitting data, e.g., via path  250 . 
     Module  224  may be associated with a first Single-Input-Single-Output (SISO) encoding module  228  and a first SISO decoding module  229 , and module  226  may be associated with a second SISO encoding module  225  and a second SISO decoding module  227 . Modules  228  and  225  may include any suitable SISO encoding modules, e.g., as are known in the art, adapted to encode the data to be transmitted via paths  240  and  250 , respectively. Modules  229  and  227  may include any suitable SISO decoding modules, e.g., as are known in the art, adapted to decode data received via paths  240  and  250 , respectively. Path  240  and/or path  250  may be assigned individually to a channel, e.g., by module  224  and/or module  226 , such that a data-frame may be transmitted through one of paths  240  and  250 . At least some of antennas  290 ,  292  and  294  may be controllably assigned, e.g., by module  222 , to path  240  or path  250 . Thus, modem  220  may be implemented, for example, to transmit and/or receive data over two frequency channels in parallel, e.g., in full duplex. Module  224  and module  226  may also be adapted to check for an acknowledgment (ACK) frame corresponding to the data-frame transmitted, and transfer to module  222  a signal corresponding to whether an ACK frame was received or not, as is known in the art. Module  224  and module  226  may also be adapted to send an ACK frame corresponding to each data-frame received without errors, as is known in the art. 
     According to exemplary embodiments of the invention, modem  230  may include any suitable modem for modulating data to be transmitted and/or demodulating received data according to a STC multiplexing method. For example, modem  230  may include a STC-based channel access control module  232  adapted to control simultaneous transmission via paths  240  and  250  of the data received from controller  210 , e.g., using one frequency channel, as is known in the art. 
     Module  232  may also be capable of multiplexing the data to be transmitted, e.g., to provide two parallel sequences to be simultaneously transmitted via paths  240  and  250 , respectively. Module  232  may be associated with a MIMO encoding module  236  and a MIMO decoding module  234 . Module  236  may include any suitable MIMO encoding module, e.g., as is known in the art, adapted to encode the two data sequences provided from module  232 . Module  234  may include any suitable MIMO decoding module, e.g., as is known in the art, adapted to decode data received simultaneously via paths  240  and  250 . Module  232  may also be capable of demultiplexing decoded data provided from module  234 , as is known in the art. Thus, modem  230  may be implemented to transmit or receive a data-frame via one channel on both path  240  and path  250  simultaneously. 
     Module  232  may also be adapted to check if an ACK frame, corresponding to the data-frame transmitted, is received, as is known in the art. Module  232  may also be adapted to send an ACK frame corresponding to each data-frame correctly received, as is known in the art. 
     According to exemplary embodiments of the invention, controller  210  may include a selection module  211  to select between either frequency-multiplexing modulation method, which may be implemented using modem  220 , or spatial-multiplexing modulation method, which may be may be implemented by modem  230 , based on the predetermined criterion, as described in detail below. 
     According to exemplary embodiments of the invention, controller  210  may also include a Tx frame queue module  212  able to buffer data provided from processor  205 , as is known in the art. Controller  210  may also include a Tx control module  213  associated with queue module  212  and selection module  211 . Queue module  212  may provide Module  213  with a data-frame, e.g., when a channel is available for transmission. Module  213  may selectively transfer the data-frame to either module  222  or module  232 , in accordance with the modulation method selected by module  211 . If, for example, the frequency-multiplexing modulation method is selected by module  211 , module  213  may transfer the data-frame to module  222 . Conversely, if the spatial-multiplexing modulation method is selected by module  211 , module  213  may transfer the data-frame to module  232 . Module  222  or module  232  may provide Tx control module  213  with a signal corresponding to whether an ACK frame corresponding to a transmitted data frame was received. If an ACK frame was not received, Tx control module may be able to re-send the data-frame through a different channel, as is known in the art. 
     According to exemplary embodiments of the invention, controller  210  may also include an Rx flow control module  214  to transfer demodulated data provided from module  226 , module  232  and/or module  224  to a Rx frame queue module  215 , as is known in the art. Module  215  may be able to buffer the data provided from module  214  and to transfer the buffered data to processor  205 , as is known in the art. 
     According to some exemplary embodiments of the invention, it may be required to provide device  200  with information identifying the modulation method, e.g., the frequency-multiplexing modulation method or the spatial-multiplexing method, used for modulating a data-frame to be received by device  200 . This may be performed, for example, by transmitting to device  200 , e.g., before switching between multiplexing methods, a training sequence including information corresponding to the selected multiplexing method. 
     According to other embodiments of the invention, it may not be required to inform device  200  of the multiplexing method used for modulating the data. In such other embodiments, device  200  may be adapted to detect the multiplexing method used to modulate the received data. For example, modules  229  and  227  may be capable of decoding only data-frames previously encoded according to the MC multiplexing method, and module  234  may be capable to decode only data-frames previously encoded according to the STC multiplexing method. 
     Although the above discussion refers to a dual-channel wireless communication device, e.g., device  200 , it will be appreciated by those skilled in the art that device  200  may be modified to implement a communication device of n channels, for example, by replacing paths  240  and  250  with n RF paths, by modifying modem  230  to implement an n-channel STC-based multiplexing method, and by replacing modem  220  with a suitable n-channel modem, e.g., including n MC channel access control modules, n SISO encoding modules and n SISO decoding modules. 
     According to some embodiments of the invention, module  211  may select either the frequency-multiplexing modulation method or the spatial-multiplexing modulation method based on a channel quality value. For example, the channel quality may be evaluated based on data provided to module  211  from module  214  and/or module  213 , as described below. 
     According to some exemplary embodiments of the invention, the channel quality may be evaluated in relation to the number of data-frames that are transmitted by device  200  compared to the number of such data-frames that are acknowledged by, for example, an ACK frame, as described above. The channel quality value may be expressed in terms of a percentage, for example, a Packet Error Rate (PER) percentage, which may be, for example, the number of data-frames for which an ACK frame has not been received, over the number of data-frames transmitted in a particular period. In some embodiments, a success/fail rate of transmitted data-frames may be measured or calculated over an interval of, for example, a most recent group of data-frames that were transmitted, for example, the last 100 or 1000 data-frames transmitted, if desired. In other embodiments, a success/fail rate or a PER may be calculated over a given time period. Thus, for example, module  211  may evaluate the channel quality based on the PER percentage, e.g., related to previously transmitted data-frames. Other measures or periods of calculations may be used. 
     According to some embodiments of the invention, the channel quality may be expressed in terms of Cyclic Redundancy Check (CRC) error percentage, which may be, for example, the number of data-frames received, e.g., by module  214 , with an incorrect CRC, over the number of data-frames received in a particular period. Thus, for example, module  211  may evaluate the channel quality based on the CRC error percentage, e.g., related to previously received data-frames. 
     According to some exemplary embodiments of the invention, one or more frames received by module  214  may include quality related information, e.g., as defined by the 802.11k standard. For example, if open loop signaling is implemented, e.g., as defined by the 802.11k standard, the quality related information may be part of a preamble of a received data-frame. Additionally or alternatively, for example, if closed loop signaling is implemented, e.g., as defined by the 802.11k standard, the quality related information may be part of a received management frame. 
     According to other exemplary embodiments of the invention, a predetermined training sequence may be received by device  200 , e.g., at a predetermined time interval, as is known in the art. Module  211  may evaluate the channel quality based on the training sequence as received by device  200 . For example, module  211  may evaluate the channel quality based on a comparison of the training sequence as provided from module  214  and the predetermined training sequence. 
     According to some embodiments of the invention, module  211  may select either the frequency-multiplexing modulation method, e.g., as may be implemented by modem  220 , or the spatial-multiplexing modulation method, e.g., as may be implemented by modem  230 , based on the channel quality value. Thus, for example, the data frame may be selectively modulated using either the frequency-multiplexing modulation method or the spatial-multiplexing modulation method based on the predetermined criterion. The selection may be performed using any suitable selection method, e.g., as described below. 
     Reference is made to  FIG. 3 , which schematically illustrates a flow chart of a method of controllably selecting between the spatial-multiplexing modulation method and the frequency-multiplexing modulation method in accordance with an exemplary embodiment of the invention. 
     As indicated at block  302 , the method may include selecting a pre-determined modulation method, e.g., the spatial-multiplexing modulation method. 
     As indicated at block  304 , the channel quality corresponding to a channel estimation related to the pre-determined modulation method may be evaluated, and a channel quality value corresponding to a channel estimation related to the predetermined modulation method may be provided, e.g., as described above. 
     According to some exemplary embodiments, the channel quality may be evaluated at a predetermined time interval. For example, the channel quality may be evaluated during a channel scanning process, as is known in the art. 
     As indicated at block  306 , the method may include comparing the channel quality value to a predetermined reference quality value, e.g., a minimum quality value. A modulation method may be selected based on the comparison between the channel quality value and the reference quality value. For example, the predetermined modulation method, e.g., the spatial-multiplexing modulation method, may be selected if the channel quality value is at least equal to the reference quality value. 
     As indicated at block  308 , the frequency-multiplexing modulation method may be selected if the channel quality value is less than the reference quality value. The channel quality value corresponding to the predetermined modulation method may be re-evaluated periodically, e.g., according to the predetermined time interval, and compared to the reference quality value, as indicated at block  304 . 
     Thus, according to this exemplary embodiment, the spatial-multiplexing modulation method may be selected, e.g., by module  211  ( FIG. 2 ), if the channel quality value corresponding to the spatial-multiplexing modulation method is at least equal to the reference quality value. The frequency-multiplexing modulation method may be selected, e.g., by module  211  ( FIG. 2 ), if the channel quality is less than the reference quality value. 
     It will be appreciated by those skilled in the art that the device system and/or method, according to embodiments of the invention, may be implemented to achieve a relatively stable and relatively high throughput in an open environment, i.e., an environment characterized by relatively low multi-path effects, as well as in a closed environment, i.e., an environment characterized by relatively high multi-path effects. This may be achieved, for example, by selectively switching between the spatial-multiplexing modem and the frequency-multiplexing modem, as described above. 
     Embodiments of the present invention may be implemented by software, by hardware, or by any combination of software and/or hardware as may be suitable for specific applications or in accordance with specific design requirements. Embodiments of the present invention may include units and sub-units, which may be separate of each other or combined together, in whole or in part, and may be implemented using specific, multi-purpose or general processors, or devices as are known in the art. Some embodiments of the present invention may include buffers, registers, storage units and/or memory units, for temporary or long-term storage of data and/or in order to facilitate the operation of a specific embodiment. 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.