Patent Publication Number: US-2005135516-A1

Title: Dual antenna receiver for voice communications

Description:
FIELD  
      The present invention relates generally to wireless packet networks, and more specifically to voice communications in wireless packet networks.  
     BACKGROUND  
      Wireless Voice-over-Packet Networks (VoPN) allow packetized voice calls to occur on wireless local area networks (WLAN) or cellular networks. In these networks, voice data is divided into packets, and the packets are transmitted. Many packet networks do not guarantee a minimum latency for packets, which may cause a problem for voice transmission. If one or more packets are delayed due to latency, the voice signal may not be faithfully reproduced on the receiving end of the wireless link. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a dual antenna receiver;  
       FIG. 2  shows a Voice-over-IP architecture;  
       FIG. 3  shows a system diagram in accordance with various embodiments of the present invention; and  
       FIG. 4  shows a flowchart in accordance with various embodiments of the present invention. 
    
    
     DESCRIPTION OF EMBODIMENTS  
      In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views.  
       FIG. 1  shows a dual antenna receiver. Dual antenna receiver  100  includes antennas  102  and  112 , baseband conversion units  104  and  114 , analog-to-digital (A/D) converters  106  and  116 , spatio-temporal processing unit  120 , and maximum likelihood sequence estimation (MLSE) detection block  130 .  
      Antennas  102  and  112  may be directional antennas or an omni-directional antennas. As used herein, the term omni-directional antenna refers to any antenna having a substantially uniform pattern in at least one plane. For example, in some embodiments, one or both of antennas  102  and  112  may be an omni-directional antenna such as a dipole antenna, or a quarter wave antenna. Also for example, in some embodiments, one or both of antennas  102  or  112  may be a directional antenna such as a parabolic dish antenna or a Yagi antenna.  
      Baseband conversion units  104  and  114  convert signals received by antennas  102  and  112  to baseband. In some embodiments, baseband conversion units  104  and  114  may include circuitry to support reception of radio frequency (RF) signals. For example, in some embodiments, baseband conversion units  104  and  114  include circuits to perform “front end” processing such as low noise amplification (LNA), filtering, frequency conversion and the like. Also for example, in some embodiments, baseband conversion circuits  104  and  114  may include clock recovery circuits, symbol timing circuits, and the like. The invention is not limited by the contents or function of baseband conversion units  104  and  114 .  
      Analog-to-digital (A/D) converters  106  and  116  convert the baseband signals output from baseband conversion units  104  and  114  to digital sample streams. For example, the baseband signal corresponding to antenna  102  is converted to digital sample stream y 1 (n), and the baseband signal corresponding to antenna  112  is converted to digital sample stream y 2 (n).  
      Spatio-temporal processing unit  120  linearly combines the two digital sample streams y 1 (n) and y 2 (n). Equation 1 describes the mathematical connection between the output and the input of spatio-temporal processing unit  120 . 
 
 z ( n )= y   1 ( n )   c   1 ( n )+ y   2 ( n )   c   2 ( n )  (1) 
          where: 
            y 1  represents the first antenna digital baseband signal;     y 2  represents the second antenna digital baseband signal;     c 1  represents the first antenna combining coefficients;     c 2  represents the second antenna combining coefficients; and     z represents the combined signal.    
               

      In some embodiments, the combining coefficients c 1  and c 2  may be the matched-filter solution (See Eq. 2, below) to equalize the channel. Equation 2 represents the optimal or near-optimal receiver when the only noise source in the system is white Gaussian noise. 
 
 c   1 ( n )= h   1 *(− n )/σ 1   2  
 
c 2 ( n )= h   2 *(− n )/σ 2   2   (2) 
          where: 
            h 1  represents a first antenna channel estimator; and     h 2  represents a second antenna channel estimator; and     σ 1   2  represents a first antenna noise variance; and     σ 2   2  represents a second antenna noise variance.    
               

      In some embodiments, the combining coefficients c 1  and c 2  may be selected to maximize the SIR (Signal to Interference Ratio), and in other embodiments c 1  and c 2  may be selected to reduce, or even minimize, the Mean Square Error (MSE). In some embodiments, MLSE detection block  130  may not be included when c 1  and c 2  are selected to reduce MSE. In still further embodiments, the coefficients c 1  and c 2  may be selected to whiten spatial and temporal interference.  
      Embodiments that whiten spatial and temporal interference may reduce latency in packet-based networks and enable Voice-over-Packet Networks (VoPN). For example, if the performance of a cellular network is interference-limited, meaning strong interfering signals from neighbouring basestations or other sources degrade the target signal-to-noise ratio and thus degrade the data throughput to the handset, the interfering signals may increase the packet error rate and cause a reduction in throughput. In very crowded network conditions, such as an urban area, the strong interferers may be especially dominant and can degrade throughput to the point where wireless VoPN cannot be implemented. In various embodiments of the present invention, spatio-temporal processing using a dual antenna receiver may be used to enhance interference identification and cancellation. The dual antenna receiver may detect the interfering signals by weighting them according to duration and strength, subsequently cancel out the interference, and reduce latency enough to enable wireless VoPN.  
      Dual antenna receiver  100  may be utilized in any environment suitable for spatio-temporal processing. For example, in some embodiments, dual antenna receiver  100  may be useful as a receiver in a packet-based network such as a General Packet Radio Service (GPRS/EGPRS) network or the like. The receiver may be employed in a handset, a base station, or any other portion of a wireless network capable of receiving signals using a dual antenna receiver.  
       FIG. 2  shows a Voice-over-IP architecture. Architecture  200  includes mobile stations  210  and  220 , and radio access networks (RANs)  250  and  260 . Mobile station  210  communicates with RAN  250  through uplink channel  230 , RAN  250  communicates with RAN  260  through internet protocol (IP) network  270 , and RAN  260  communicates with mobile station  220  through downlink channel  240 .  
      Architecture  200  shows voice communications in a single direction between two mobile stations. For example, mobile station  210  receives voice information from a microphone, and sends the voice information to mobile station  220 , which ultimately plays the voice on a speaker. This unidirectional communication is shown for simplicity only. In some embodiments, bi-directional voice communications take place. In these embodiments, both mobile stations  210  and  220  may send and receive voice data.  
      Mobile stations  210  and  220  may be any type of mobile station capable of packet-based communications. For example, in some embodiments, mobile stations  210  and  220  may be cellular handsets. Also for example, in other embodiments, mobile stations  210  and  220  may be part of laptop computers or other appliances capable of working with voice signals.  
      In operation, the microphone in mobile station  210  converts the voice into data. Voice encoder  212  encodes data from the microphone into voice packets. The voice packets are converted into GPRS/EGPRS packets at  214 . GPRS packets are prepared for transmission and transmitted by mobile transmit path  216  in mobile station  210 . The GPRS packets travel through uplink channel  230  to a base station receiver in RAN  250 . RAN  250  converts the received GPRS packets to IP packets and passes them through IP network  270  to RAN  260 . RAN  260  converts the IP packets back to GPRS packets and transmits the GPRS packets through downlink channel  240  to mobile station  220 . Mobile station  220  receives the GPRS packets using dual antenna receiver  226 , which in some embodiments, uses a spatio-temporal algorithm to detect the GPRS packet with much less error than a conventional receiver. The GPRS packets are then converted to voice packets at  224 , decoded by voice decoder  222  and played by the speaker.  
      The architecture shown in  FIG. 2  utilizes a dual antenna receiver in a mobile station to increase packet-switched network capacity, and to improve its quality of service (QoS) in Packet Switching (PS), as measured by delay or latency. By improving QoS, the use of a dual antenna receiver in architecture  200  may reduce the packet delay, and enable or improve VoPN or VoIP.  
      In some embodiments, each receiver capable of receiving communications may include a dual antenna receiver. For example, in some embodiments, the base station receiver in RAN  250  may utilize a dual antennal receiver. Also in some embodiments, mobile station  210  and RAN  260  may include dual antenna receivers.  
       FIG. 3  shows a system diagram in accordance with various embodiments of the present invention. Electronic system  300  includes antennas  102  and  112 , baseband conversion units  104  and  114 , and A/D converters  106  and  116 , all of which are described above with reference to  FIG. 1 . Electronic system  300  also includes digital signal processor (DSP)  340 , display device  350 , memory device  360 , modulator  330 , radio frequency (RF) conversion unit  320 , and antenna switch  310 .  
      Digital signal processor  340  receives the digital baseband sample streams from A/D  106  and A/D  116 . In some embodiments, DSP  340  implements the spatio-temporal processing described above with reference to spatio-temporal processing unit  120  ( FIG. 1 ). In some embodiments, DSP  340  may also implement maximum likelihood sequence estimation. As shown in  FIG. 3 , DSP  340  communicates with display device  350  and memory device  360  using bus  342 .  
      Display device  350  may be any type of display device. For example, in some embodiments, display device  350  may a color display device, and in other embodiments, display device  350  may be a monochrome display device. Further, in some embodiments, display device  350  may be omitted.  
      Memory  360  represents an article that includes a machine readable medium. For example, memory  360  represents a random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), read only memory (ROM), flash memory, or any other type of article that includes a medium readable by DSP  340 . Memory  360  may store instructions for performing the execution of the various method embodiments of the present invention. Memory  360  may also store data associated with the state or operation of electronic system  300 .  
      In some embodiments, modulator  330  receives and modulates digital information from DSP  340 . The digital information modulated by modulator  330  may be voice information in the form of GPRS packets. Radio frequency (RF) conversion unit converts signals provided by modulator  330  to an appropriate frequency for transmission. For example, in some embodiments, RF conversion unit  320  may include circuits to support frequency up-conversion, and an RF transmitter. The invention is not limited by the contents or function of RF conversion unit  320 .  
      Electronic system  300  also includes antenna switch  310  coupled between antenna  112 , baseband conversion unit  114 , and RF conversion unit  320 . When electronic system is receiving signals, antenna switch  310  couples antenna  112  to baseband conversion unit  114 , and dual antenna reception occurs as described above. When electronic system  200  is transmitting signals, antenna switch  310  couples antenna  112  to RF conversion unit  320 , and antenna  112  is used as a transmitting antenna. In this manner, electronic system  300  implements a dual antenna receiver and a single antenna transmitter.  
      Electronic system  300  may be any system capable of including two antennas. Examples include, but are not limited to: a cellular handset, laptop computer, home audio or video appliance, or the like. Electronic system  300  may also be a mobile station in a wireless network, or may be included as a portion of a radio access network (RAN), such as RAN  250  ( FIG. 2 ).  
      Dual antenna receivers, spatio-temporal processing units, and other embodiments of the present invention can be implemented in many ways. In some embodiments, they are implemented in various integrated circuits as part of a voice capable wireless appliance. In some embodiments, design descriptions of the various embodiments of the present invention are included in libraries that enable designers to include them in custom or semi-custom designs. For example, any of the disclosed embodiments can be implemented in a synthesizable hardware design language, such as VHDL or Verilog, and distributed to designers for inclusion in standard cell designs, gate arrays, or the like. Likewise, any embodiment of the present invention can also be represented as a hard macro targeted to a specific manufacturing process.  
       FIG. 4  shows a flowchart in accordance with various embodiments of the present invention. In some embodiments, method  400  may be used to receive voice data in a GPRS wireless network. In some embodiments, method  400 , or portions thereof, is performed by a dual antenna receiver or electronic system, embodiments of which are shown in the various figures. Method  400  is not limited by the particular type of apparatus or software element performing the method. The various actions in method  400  may be performed in the order presented, or may be performed in a different order. Further, in some embodiments, some actions listed in  FIG. 4  are omitted from method  400 .  
      Method  400  is shown beginning at block  410  in which first and second GPRS signals are received using two antennas. At  420 , the first and second signals are converted to two baseband signals. At  430 , the two baseband signals are digitized, and at  440 , the two baseband signals are linearly combined. At  450 , received GPRS packets are converted to voice packets.  
      In some embodiments, the linear combining operation of block  440  is performed by a spatio-temporal processing unit such as spatio-temporal processing unit  120  ( FIG. 1 ). In some embodiments the two digital baseband signals are combined using a matched-filter solution for channels associated with the two antennas. For example, combining coefficients may be selected that correspond to those shown in equation 2, above. In other embodiments, the two digital baseband signals are combined using combining coefficients selected to increase a signal to interference ratio (SIR). In some embodiments, the two digital baseband signals are combined using combining coefficients selected to reduce mean squared error (MSE). In still further embodiments, the two digital baseband signals are combined using combining coefficients selected to whiten spatial and temporal interference.  
      Although the present invention has been described in conjunction with certain embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention. For example, although the various embodiments of the present invention have been described using voice communications, they are equally applicable to video communications. Such modifications and variations are considered to be within the scope of the invention and the appended claims.