Patent Publication Number: US-7587016-B2

Title: MIMO timing recovery

Description:
CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS 
   Provisional Priority Claims 
   The present U.S. Utility Patent Application claims priority pursuant to 35 U.S.C. § 119(e) to the following U.S. Provisional Patent Applications which are hereby incorporated herein by reference in their entirety and made part of the present U.S. Utility Patent Application for all purposes: 
   1. U.S. Provisional Application Ser. No. 60/700,968, entitled “Carrier detection applicable for SISO, MIMO, MISO, and SIMO communications,” filed Wednesday, Jul. 20, 2005 (Jul. 20, 2005), pending. 
   2. U.S. Provisional Application Ser. No. 60/700,967, entitled “MIMO timing recovery,” filed Wednesday, Jul. 20, 2005 (Jul. 20, 2005), pending. 
   Incorporation by Reference 
   The following U.S. Utility Patent Applications is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes: 
   1. U.S. Utility patent application Ser. No. 11/168,793, entitled “Reduced feedback for beamforming in a wireless communication,” filed Jun. 28, 2005 (Jun. 28, 2005), pending. 

   BACKGROUND OF THE INVENTION 
   1. Technical Field of the Invention 
   The invention relates generally to communication systems; and, more particularly, it relates to performing timing recovery for signals within such communication systems. 
   2. Description of Related Art 
   Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof. 
   Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network. 
   For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard. 
   As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna. 
   In many systems, the transmitter will include one antenna for transmitting the RF signals, which are received by a single antenna, or multiple antennas, of a receiver. When the receiver includes two or more antennas, the receiver will select one of them to receive the incoming RF signals. In this instance, the wireless communication between the transmitter and receiver is a single-output-single-input (SISO) communication, even if the receiver includes multiple antennas that are used as diversity antennas (i.e., selecting one of them to receive the incoming RF signals). For SISO wireless communications, a transceiver includes one transmitter and one receiver. Currently, most wireless local area networks (WLAN) that are IEEE 802.11, 802.11a, 802.11b, or 802.11g employ SISO wireless communications. 
   Other types of wireless communications include single-input-multiple-output (SIMO), multiple-input-single-output (MISO), and multiple-input-multiple-output (MIMO). In a SIMO wireless communication, a single transmitter processes data into radio frequency signals that are transmitted to a receiver. The receiver includes two or more antennas and two or more receiver paths. Each of the antennas receives the RF signals and provides them to a corresponding receiver path (e.g., LNA, down conversion module, filters, and ADCs). Each of the receiver paths processes the received RF signals to produce digital signals, which are combined and then processed to recapture the transmitted data. 
   For a multiple-input-single-output (MISO) wireless communication, the transmitter includes two or more transmission paths (e.g., digital to analog converter, filters, up-conversion module, and a power amplifier) that each converts a corresponding portion of baseband signals into RF signals, which are transmitted via corresponding antennas to a receiver. The receiver includes a single receiver path that receives the multiple RF signals from the transmitter. In this instance, the receiver uses beam forming to combine the multiple RF signals into one signal for processing. 
   For a multiple-input-multiple-output (MIMO) wireless communication, the transmitter and receiver each include multiple paths. In such a communication, the transmitter parallel processes data using a spatial and time encoding function to produce two or more streams of data. The transmitter includes multiple transmission paths to convert each stream of data into multiple RF signals. The receiver receives the multiple RF signals via multiple receiver paths that recapture the streams of data utilizing a spatial and time decoding function. The recaptured streams of data are combined and subsequently processed to recover the original data. 
   Within such communication systems that process and extract packets from a received signal, there is typically a need to set make decisions related to the various portions of the packet. For example, when decoding a packet that includes a preamble and a payload (e.g., data), the communication device processing typically needs to determine precisely where the payload portion of the packet is within the overall packet. This may generally be referred to as performing timing recovery. If this decision making is not performed well, then the information contained within the payload portion of the packet may be improperly decoded. 
   Moreover, there are instances where a particular location within either the preamble or the payload is desired to be known to assist in the training of the communication device. For example, portions of the preamble may sometimes be employed to make channel estimates for use in performing channel equalization among other types of compensation that may be performed to overcome the deficiencies of the communication channel through which the signal has traveled. As such, a need continues to exist in the art for better and more effective means by which timing recovery may be performed with respect to a received signal to govern the configuration and set up of such a communication device implemented to process the received signal. More specifically, there exists a need for better and more effective means to determine a particular location at which to begin processing a packet that is extracted from a received signal in an effort to extract information contained therein. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Several Views of the Drawings, the Detailed Description of the Invention, and the claims. Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a diagram of a wireless communication system. 
       FIG. 2  is a diagram of a wireless communication device. 
       FIG. 3  is a diagram of another wireless communication device. 
       FIG. 4  is a diagram of feedback control within a communication device. 
       FIG. 5  is a diagram illustrating an embodiment of an OFDM (Orthogonal Frequency Division Multiplexing) packet that may be processed. 
       FIG. 6  is a diagram illustrating an embodiment of functionality operable to perform timing recovery. 
       FIG. 7  is a diagram illustrating an embodiment of choice logic functionality employed when performed timing recovery. 
       FIG. 8  is a diagram illustrating another embodiment of choice logic functionality employed when performed timing recovery. 
       FIG. 9  is a diagram illustrating an embodiment of functionality operable to support symbol timing recovery processing. 
       FIG. 10  is a diagram illustrating an embodiment of a modified correlation function as a function of samples. 
       FIG. 11A  is a diagram illustrating an embodiment of a single-input-single-output (SISO) communication system. 
       FIG. 11B  is a diagram illustrating an embodiment of a multiple-input-multiple-output (MIMO) communication system. 
       FIG. 11C  is a diagram illustrating an embodiment of a multiple-input-single-output (MISO) communication system. 
       FIG. 11D  is a diagram illustrating an embodiment of a single-input-multiple-output (SIMO) communication system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a diagram illustrating a communication system  10  that includes a plurality of base stations and/or access points  12 ,  16 , a plurality of wireless communication devices  18 - 32  and a network hardware component  34 . Note that the network hardware  34 , which may be a router, switch, bridge, modem, system controller, et cetera provides a wide area network connection  42  for the communication system  10 . Further note that the wireless communication devices  18 - 32  may be laptop host computers  18  and  26 , personal digital assistant hosts  20  and  30 , personal computer hosts  24  and  32  and/or cellular telephone hosts  22  and  28 . The details of the wireless communication devices will be described in greater detail with reference to  FIG. 2 . 
   Wireless communication devices  22 ,  23 , and  24  are located within an independent basic service set (IBSS) area and communicate directly (i.e., point to point). In this configuration, these devices  22 ,  23 , and  24  may only communicate with each other. To communicate with other wireless communication devices within the system  10  or to communicate outside of the system  10 , the devices  22 ,  23 , and/or  24  need to affiliate with one of the base stations or access points  12  or  16 . 
   The base stations or access points  12 ,  16  are located within basic service set (BSS) areas  11  and  13 , respectively, and are operably coupled to the network hardware  34  via local area network connections  36 ,  38 . Such a connection provides the base station or access point  12   16  with connectivity to other devices within the system  10  and provides connectivity to other networks via the WAN connection  42 . To communicate with the wireless communication devices within its BSS  11  or  13 , each of the base stations or access points  12 - 16  has an associated antenna or antenna array. For instance, base station or access point  12  wirelessly communicates with wireless communication devices  18  and  20  while base station or access point  16  wirelessly communicates with wireless communication devices  26 - 32 . Typically, the wireless communication devices register with a particular base station or access point  12 ,  16  to receive services from the communication system  10 . 
   Typically, base stations are used for cellular telephone systems and like-type systems, while access points are used for in-home or in-building wireless networks (e.g., IEEE 802.11 and versions thereof, Bluetooth, and/or any other type of radio frequency based network protocol). Regardless of the particular type of communication system, each wireless communication device includes a built-in radio and/or is coupled to a radio. 
     FIG. 2  is a diagram illustrating a wireless communication device  200  that includes the host device  18 - 32  and an associated radio  60 . For cellular telephone hosts, the radio  60  is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio  60  may be built-in or an externally coupled component. 
   As illustrated, the host device  18 - 32  includes a processing module  50 , memory  52 , a radio interface  54 , an input interface  58 , and an output interface  56 . The processing module  50  and memory  52  execute the corresponding instructions that are typically done by the host device. For example, for a cellular telephone host device, the processing module  50  performs the corresponding communication functions in accordance with a particular cellular telephone standard. 
   The radio interface  54  allows data to be received from and sent to the radio  60 . For data received from the radio  60  (e.g., inbound data), the radio interface  54  provides the data to the processing module  50  for further processing and/or routing to the output interface  56 . The output interface  56  provides connectivity to an output display device such as a display, monitor, speakers, et cetera such that the received data may be displayed. The radio interface  54  also provides data from the processing module  50  to the radio  60 . The processing module  50  may receive the outbound data from an input device such as a keyboard, keypad, microphone, et cetera via the input interface  58  or generate the data itself. For data received via the input interface  58 , the processing module  50  may perform a corresponding host function on the data and/or route it to the radio  60  via the radio interface  54 . 
   Radio  60  includes a host interface  62 , digital receiver processing module  64 , an analog-to-digital converter  66 , a high pass and low pass filter module  68 , an IF mixing down conversion stage  70 , a receiver filter  71 , a low noise amplifier  72 , a transmitter/receiver switch  73 , a local oscillation module  74 , memory  75 , a digital transmitter processing module  76 , a digital-to-analog converter  78 , a filtering/gain module  80 , an IF mixing up conversion stage  82 , a power amplifier  84 , a transmitter filter module  85 , a channel bandwidth adjust module  87 , and an antenna  86 . 
   It is noted that one or both of the high pass and low pass filter module  68  and the low noise amplifier  72  can operate to perform any desired gain and/or attenuation of the inbound RF signal  88  (i.e., using the low noise amplifier  72 ) or the down-converted version thereof (i.e., using the high pass and low pass filter module  68 ), as indicated by the reference numeral  99 . A packet gain signal can be provided from one or both of the high pass and low pass filter module  68  and the low noise amplifier  72  to indicate that the gain has settled (i.e., undergone any change, passed through any transient period, and settled to a new steady state operating level for the packet). 
   The antenna  86  may be a single antenna that is shared by the transmit and receive paths as regulated by the Tx/Rx switch  73 , or may include separate antennas for the transmit path and receive path. The antenna implementation will depend on the particular standard to which the wireless communication device  200  is compliant. 
   The digital receiver processing module  64  and the digital transmitter processing module  76 , in combination with operational instructions stored in memory  75 , execute digital receiver functions and digital transmitter functions, respectively. The digital receiver functions include, but are not limited to, digital intermediate frequency to baseband conversion, demodulation, constellation demapping, decoding, and/or descrambling. The digital transmitter functions include, but are not limited to, scrambling, encoding, constellation mapping, modulation, and/or digital baseband to IF conversion. The digital receiver and transmitter processing modules  64  and  76  may be implemented using a shared processing device, individual processing devices, or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory  75  may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module  64  and/or  76  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. 
   In operation, the radio  60  receives outbound data  94  from the host device via the host interface  62 . The host interface  62  routes the outbound data  94  to the digital transmitter processing module  76 , which processes the outbound data  94  in accordance with a particular wireless communication standard (e.g., IEEE 802.11, Bluetooth, et cetera) to produce outbound baseband signals  96 . The outbound baseband signals  96  will be digital base-band signals (e.g., have a zero IF) or a digital low IF signals, where the low IF typically will be in the frequency range of one hundred kHz (kilo-Hertz) to a few MHz (Mega-Hertz). 
   The digital-to-analog converter  78  converts the outbound baseband signals  96  from the digital domain to the analog domain. The filtering/gain module  80  filters and/or adjusts the gain of the analog signals prior to providing it to the IF mixing stage  82 . The IF mixing stage  82  converts the analog baseband or low IF signals into RF signals based on a transmitter local oscillation  83  provided by local oscillation module  74 . The power amplifier  84  amplifies the RF signals to produce outbound RF signals  98 , which are filtered by the transmitter filter module  85 . The antenna  86  transmits the outbound RF signals  98  to a targeted device such as a base station, an access point and/or another wireless communication device  200 . 
   The radio  60  also receives inbound RF signals  88  via the antenna  86 , which were transmitted by a base station, an access point, or another wireless communication device. The antenna  86  provides the inbound RF signals  88  to the receiver filter module  71  via the Tx/Rx switch  73 , where the Rx filter  71  bandpass filters the inbound RF signals  88 . The Rx filter  71  provides the filtered RF signals to low noise amplifier  72 , which amplifies the signals  88  to produce an amplified inbound RF signals. The low noise amplifier  72  provides the amplified inbound RF signals to the IF mixing module  70 , which directly converts the amplified inbound RF signals into an inbound low IF signals or baseband signals based on a receiver local oscillation  81  provided by local oscillation module  74 . The down conversion module  70  provides the inbound low IF signals or baseband signals to the filtering/gain module  68 . The high pass and low pass filter module  68  filters, based on settings provided by the channel bandwidth adjust module  87 , the inbound low IF signals or the inbound baseband signals to produce filtered inbound signals. 
   The analog-to-digital converter  66  converts the filtered inbound signals from the analog domain to the digital domain to produce inbound baseband signals  90 , where the inbound baseband signals  90  will be digital base-band signals or digital low IF signals, where the low IF typically will be in the frequency range of one hundred kHz to a few MHz. The digital receiver processing module  64 , based on settings provided by the channel bandwidth adjust module  87 , decodes, descrambles, demaps, and/or demodulates the inbound baseband signals  90  to recapture inbound data  92  in accordance with the particular wireless communication standard being implemented by radio  60 . The host interface  62  provides the recaptured inbound data  92  to the host device  18 - 32  via the radio interface  54 . 
   As one of average skill in the art will appreciate, the wireless communication device  200  of  FIG. 2  may be implemented using one or more integrated circuits. For example, the host device may be implemented on one integrated circuit, the digital receiver processing module  64 , the digital transmitter processing module  76  and memory  75  may be implemented on a second integrated circuit, and the remaining components of the radio  60 , less the antenna  86 , may be implemented on a third integrated circuit. As an alternate example, the radio  60  may be implemented on a single integrated circuit. As yet another example, the processing module  50  of the host device and the digital receiver and transmitter processing modules  64  and  76  may be a common processing device implemented on a single integrated circuit. Further, the memory  52  and memory  75  may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module  50  and the digital receiver and transmitter processing module  64  and  76 . 
     FIG. 3  is a diagram illustrating a wireless communication device  300  that includes the host device  18 - 32  and an associated radio  60 . For cellular telephone hosts, the radio  60  is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio  60  may be built-in or an externally coupled component. 
   As illustrated, the host device  18 - 32  includes a processing module  50 , memory  52 , radio interface  54 , input interface  58  and output interface  56 . The processing module  50  and memory  52  execute the corresponding instructions that are typically done by the host device. For example, for a cellular telephone host device, the processing module  50  performs the corresponding communication functions in accordance with a particular cellular telephone standard. 
   The radio interface  54  allows data to be received from and sent to the radio  60 . For data received from the radio  60  (e.g., inbound data), the radio interface  54  provides the data to the processing module  50  for further processing and/or routing to the output interface  56 . The output interface  56  provides connectivity to an output display device such as a display, monitor, speakers, et cetera such that the received data may be displayed. The radio interface  54  also provides data from the processing module  50  to the radio  60 . The processing module  50  may receive the outbound data from an input device such as a keyboard, keypad, microphone, et cetera via the input interface  58  or generate the data itself. For data received via the input interface  58 , the processing module  50  may perform a corresponding host function on the data and/or route it to the radio  60  via the radio interface  54 . 
   Radio  60  includes a host interface  62 , a baseband processing module  100 , memory  65 , a plurality of radio frequency (RF) transmitters  106 - 110 , a transmit/receive (T/R) module  114 , a plurality of antennas  81 - 85 , a plurality of RF receivers  118 - 120 , a channel bandwidth adjust module  87 , and a local oscillation module  74 . The baseband processing module  100 , in combination with operational instructions stored in memory  65 , executes digital receiver functions and digital transmitter functions, respectively. The digital receiver functions include, but are not limited to, digital intermediate frequency to baseband conversion, demodulation, constellation de-mapping, decoding, de-interleaving, fast Fourier transform (FFT), cyclic prefix removal, space and time decoding, and/or descrambling. The digital transmitter functions include, but are not limited to, scrambling, encoding, interleaving, constellation mapping, modulation, inverse fast Fourier transform (IFFT), cyclic prefix addition, space and time encoding, and digital baseband to IF conversion. The baseband processing modules  100  may be implemented using one or more processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory  65  may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module  100  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. 
   In operation, the radio  60  receives outbound data  94  from the host device via the host interface  62 . The baseband processing module  64  receives the outbound data  88  and, based on a mode selection signal  102 , produces one or more outbound symbol streams  90 . The mode selection signal  102  will indicate a particular mode of operation that is compliant with one or more specific modes of the various IEEE 802.11 standards. For example, the mode selection signal  102  may indicate a frequency band of 2.4 GHz, a channel bandwidth of 20 or 22 MHz and a maximum bit rate of 54 megabits-per-second. In this general category, the mode selection signal will further indicate a particular rate ranging from 1 megabit-per-second to 54 megabits-per-second. In addition, the mode selection signal will indicate a particular type of modulation, which includes, but is not limited to, Barker Code Modulation, BPSK, QPSK, CCK, 16 QAM and/or 64 QAM. The mode select signal  102  may also include a code rate, a number of coded bits per subcarrier (NBPSC), coded bits per OFDM symbol (NCBPS), and/or data bits per OFDM symbol (NDBPS). The mode selection signal  102  may also indicate a particular channelization for the corresponding mode that provides a channel number and corresponding center frequency. The mode select signal  102  may further indicate a power spectral density mask value and a number of antennas to be initially used for a MIMO communication. 
   The baseband processing module  100 , based on the mode selection signal  102  produces one or more outbound symbol streams  104  from the outbound data  94 . For example, if the mode selection signal  102  indicates that a single transmit antenna is being utilized for the particular mode that has been selected, the baseband processing module  100  will produce a single outbound symbol stream  104 . Alternatively, if the mode select signal  102  indicates 2, 3 or 4 antennas, the baseband processing module  100  will produce 2, 3 or 4 outbound symbol streams  104  from the outbound data  94 . 
   Depending on the number of outbound streams  104  produced by the baseband module  10 , a corresponding number of the RF transmitters  106 - 110  will be enabled to convert the outbound symbol streams  104  into outbound RF signals  112 . In general, each of the RF transmitters  106 - 110  includes a digital filter and upsampling module, a digital to analog conversion module, an analog filter module, a frequency up conversion module, a power amplifier, and a radio frequency bandpass filter. The RF transmitters  106 - 110  provide the outbound RF signals  112  to the transmit/receive module  114 , which provides each outbound RF signal to a corresponding antenna  81 - 85 . 
   When the radio  60  is in the receive mode, the transmit/receive module  114  receives one or more inbound RF signals  116  via the antennas  81 - 85  and provides them to one or more RF receivers  118 - 122 . The RF receiver  118 - 122 , based on settings provided by the channel bandwidth adjust module  87 , converts the inbound RF signals  116  into a corresponding number of inbound symbol streams  124 . The number of inbound symbol streams  124  will correspond to the particular mode in which the data was received. The baseband processing module  100  converts the inbound symbol streams  124  into inbound data  92 , which is provided to the host device  18 - 32  via the host interface  62 . 
   As one of average skill in the art will appreciate, the wireless communication device  300  of  FIG. 3  may be implemented using one or more integrated circuits. For example, the host device may be implemented on one integrated circuit, the baseband processing module  100  and memory  65  may be implemented on a second integrated circuit, and the remaining components of the radio  60 , less the antennas  81 - 85 , may be implemented on a third integrated circuit. As an alternate example, the radio  60  may be implemented on a single integrated circuit. As yet another example, the processing module  50  of the host device and the baseband processing module  100  may be a common processing device implemented on a single integrated circuit. Further, the memory  52  and memory  65  may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module  50  and the baseband processing module  100 . 
     FIG. 4  is a diagram of feedback control  400  within a communication device. Initially, a plurality of signals, indicated by reference numeral  410 , is received after undergoing receive filtering and down sampling. Such initial processing as receive filtering and down sampling may be viewed as being performed within an AFE (Analog Front End) of a communication device. In some embodiments, the feedback control  400  may be viewed may be viewed as being performed in a baseband processing module as depicted in some other of the embodiments disclosed herein. 
   Within this feedback control  400 , a symbol timing recovery module  469  is operable to perform symbol timing recovery in accordance with any one of the various embodiments or equivalents described herein. Also, within this feedback control  400 , a coarse/fine frequency estimation module  440  is operable to perform initially coarse frequency estimation and then subsequently fine frequency estimation as governed by PHY (physical layer) control, as indicated by PhySM control input  420 . 
   Also within this feedback control  400 , cyclic prefix (CP) removal of this incoming signal streams may be performed as shown by the CP removal modules  421 - 422 ; the operation of these CP modules  421 - 422  is also governed by PHY control, as indicated by PhySM control input  420 . The CP removal functionality is based on an advance/retard signal  445  provided from a compute SFO (Sampling Frequency Offset) correction module  444  that operates using inputs received from a carrier PLL (Phase Locked Loop)  446  and the coarse/fine frequency estimation module  440 . 
   Thereafter, predictive time-domain (TD) PLL correction is computed using a plurality of TD correction modules  423 - 424  (based on signals received from the carrier PLL  446  that correspond to a previous plurality of received symbols (e.g., previous N−1 st  symbol in one embodiment)). These outputs from the TD correction modules  423 - 424  are then passed to a plurality of FFT (Fast Fourier Transform) modules  425 - 426 . These FFT modules  425 - 426  operate to transform the signal processing from the time domain (T-dom) to the frequency domain (F-dom). An equalize module  430  is operable to perform equalization on the signals received from the FFT modules  425 - 426 . The equalize module  430  may be viewed as performing essentially a channel inversion operation on the signals received from the FFT modules  425 - 426  in an effort to compensate for, at least in part, the imperfections and deleterious characteristics of the communication channel over which a signal has been transmitted and from which the signal has been received. During a first instance, this equalize module  430  may be viewed as performed a 1 st  pass of equalization, in that, the equalize processing may be viewed as being an iterative type process that compensates for any channel induced errors. 
   After this, these equalized signal streams are passed to a plurality of CPE_SFO correction modules  431 - 432  that is operable to apply predictive SFO correction that has been computed using a previous plurality of symbols (e.g., previous n−1 st  symbol in one embodiment) while also considering common phase error (CPE) correction values. The CPE_SFO correction modules  431 - 432  receive input signals from both the compute SFO correction module  444  as well as the carrier PLL  446 . In an initial pass through the, the CPE correction value may be set to a phase of 0 (zero). The streams output from the CPE_SFO correction modules  431 - 432  are then provide to a plurality of symbol demap modules  433 - 434  that is operable to perform the appropriate symbol demapping of each of the symbols of these sequences of discrete values modulation symbols according to the appropriate modulation types (i.e., each modulation type includes a constellation shape and a corresponding mapping). 
   A compute metrics module  450  is operable to compute the CPE correction values. These CPE correction values are then filtered by the carrier PLL  446  before being provided to the CPE_SFO correction modules  431 - 432 . A compute TD correction module  442  then computes the TD PLL correction from the current symbol (e.g., the n th  symbol) for use with respect to the next symbol (e.g., n+1 st  symbol). The compute SFO correction module  444  then computes the SFO correction from the current symbol (e.g., the nth symbol) for use with respect to the next symbol (e.g., n+1 st  symbol). The equalize module  430  is then also adjusted using the SFO correction values that have been calculated using the compute metrics module  450 . 
   The same SFO correction values computed and applied for the predictive SFO correction employed above as applied in conjunction with the CPE correction values from the current symbol (e.g., the n th  symbol). In this pass of the feedback control processing, the CPE correction has the current symbol phase estimate that has been calculated as described above. The plurality of symbol demap modules  433 - 434  is then operable to perform the appropriate symbol demapping of each of the symbols again. After this step, an LMS channel update module  452  is then operable to compute the LMS (Least Means Square) channel update error terms for use by the next symbol (e.g., n+1 st  symbol). The LMS channel update module  452  then is operable to provide updated channel information to a channel estimate module  454  for processing the next symbol (e.g., n+1 st  symbol). 
   The compute metrics module  450  is operable to perform a variety of functions. The compute metrics module  450  is operable to compute the angular phase error, θ(est) or {circumflex over (θ)}, between the outputs of the equalize module  430  and the expected constellation points of the expected modulation (having the expected constellation shape and corresponding mapping). This is employed by the carrier PLL  446  for CFO/SFO tracking by each of the corresponding appropriate modules. 
   The compute metrics module  450  is also operable to compute the error, ΔH k , between a received vector and an expected vector based on an expected constellation point. This is employed by the LMS channel update module  452 . 
   The compute metrics module  450  is also operable to determine a signal type (shown by sig_type) that indicates the modulation type of the SIG field as is known within an OFDM packet employed in accordance with IEEE 802.11n. 
   The compute metrics module also receives the appropriate 1 or more coefficients are received as shown by reference numeral  449  that are employed to calculate the location of the expected modulation (constellation and mapping) to which the received signal is symbol demapped. These may be provided via the signal, indicated by reference numeral  449 , that operates by receiving coefficients from a demod_coefcalc module. 
   It is noted that the feedback control  400  within a communication device may be viewed as being implemented within a communication system operating using OFDM (Orthogonal Frequency Division Multiplexing) signaling. 
   Several of the following embodiments are directed towards performing carrier detection when processing an OFDM packet that is processed from a signal that has been received from a communication channel. The carrier detection functionality and methods presented herein are applicable to any of a variety of communication systems including those having more than one receive stream. Generally speaking, these carrier detection functionality and methods may be applied to any received signal. 
     FIG. 5  is a diagram illustrating an embodiment of an OFDM (Orthogonal Frequency Division Multiplexing) packet  500  that may be processed. 
   The OFDM packet  500  may be viewed as including a preamble portion  502  and a data portion  504 . The leftmost portion of the OFDM packet  500  is the demarcation of the start of packet (SOP) and the rightmost portion of the OFDM packet  500  is the demarcation of the end-of-packet (EOP). The preamble portion  502  of the OFDM packet  500  is relatively short in time compared to the overall packet length of the OFDM packet  500 , and corrections and calculations for other system impairments such as carrier frequency detect, carrier recovery, timing recovery, CFO (Carrier Frequency Offset), and others may also need to be calculated during this portion of the transmission. Thus, the amount of time needed to determine such parameters for a received OFDM packet  500  needs to be kept small. 
   The preamble portion  502  may be divided into several training sequences. For example, first a short training sequence (STS) may be received. This is followed by a long training sequence (LTS), signal field (SIG), and an additional short training sequence (MIMO STS). The SIG portion of the preamble may describe the content of data with information provided in a predetermined format. 
   It is also noted here that the preamble portion  502  may include a wide variety of combinations of STSs, LTSs, and SIGs. In addition, the order of each of these various types of training sequences (STSs, LTSs, and SIGs) may be in any desired order within the preamble portion  502 . The particular arrangement of the preamble portion  502  within this diagram is illustrative of just one possible embodiment. Clearly, variations thereof may be implemented without departing from the scope and spirit of the invention. 
   In the context of timing recovery functionality and method implemented to perform such functionality, the operation and processing may be performed on the STS. Each of the portions of the OFDM packet  500  may be viewed as including more than 1 OFDM symbol. For example, the STS of the preamble portion  502  of the OFDM packet  500  may include a plurality of OFDM symbols, shown as S 1 , S 2 , S 3 , . . . , S m . Clearly, the STS could possibly include as few as 2 OFDM symbols in some embodiments. The LTS of the preamble portion  502  of the OFDM packet  500  may also include a plurality of OFDM symbols, shown as L 1 , L 2 , L 3 , . . . , L n . Clearly, the LTS also could possibly include as few as 2 OFDM symbols in some embodiments. 
   Each of the OFDM symbols comprises a plurality of samples. For example, the OFDM symbol S 2  includes sample  511 , sample  512 , and . . . , sample  519 . As another example, the OFDM symbol L 3  includes sample  521 , sample  522 , and . . . , sample  529 . Clearly, this relationship may also be applicable for other of the OFDM symbols as well, in that, each OFDM symbol includes a corresponding plurality of samples, and the total number of samples within each of these symbols may not be identical. 
     FIG. 6  is a diagram illustrating an embodiment of functionality  600  operable to perform timing recovery. This embodiment shows a very generic embodiment by which a timing recovery module  610  may be implemented. In some desired embodiments, the timing recovery module  610  may be implemented within a baseband processing module  601 . This baseband processing module  601  may be the baseband processing module  100  shown above within other embodiments, or the baseband processing module  601  may include different functionality and capabilities as the baseband processing module  100  shown above. 
   This embodiment shows the receiving of multiple streams that may corresponds to a plurality of antennae within a communication device. For example, each of the streams  1 , . . . , n can correspond to a particular antenna within the communication device (e.g., the communication device includes n antennae). Initially, a plurality of signals, indicated by reference numeral  619 , is received after undergoing receive filtering and down sampling. Such initial processing as receive filtering and down sampling may be viewed as being performed within an AFE (Analog Front End) of a communication device. 
   The samples of symbols of a 1 st  stream  605  are provided to a first STR (Symbol Timing Recovery) module  621 . Analogously, the samples of symbols of an n th  stream  606  are provided to an n th  STR module  629 . Each of these STR modules is operable to perform processing of its corresponding received samples of symbols of its corresponding stream to generate a symbol timing recovery signal. For example, the first STR module  621  generates a 1 st  symbol timing recovery signal (e.g., STR 0 ), . . . , and the n th  STR module  629  generates an n th  symbol timing recovery signal (e.g., STRn). All of these symbol timing recovery signals are provided to a choice logic module  630  implemented within the timing recovery module  610 . Each of the symbol timing recovery signals indicates whether or not symbol timing recovery has been in fact performed for that corresponding stream. 
   In some embodiments, the samples of symbols of a 1 st  stream  605  and the samples of symbols of an n th  stream  606  are provided to a carrier detect module  640  that is operable to generate a corresponding plurality of carrier detect signals for each of the receive streams. The carrier detect module  640  may be partitioned to include one carrier detect module for each of the receive streams (e.g., carrier detect module  641  for performed carrier detection on the samples of symbols of a 1 st  stream  605 , . . . and a carrier detect module  649  for performed carrier detection on the samples of symbols of an n th  stream  606 . Each of these corresponding plurality of carrier detect signals is provided to the choice logic module  630  implemented within the timing recovery module  610 . For example, the carrier detect module  640  (or the carrier detect module  641 ) provides a 1 st  stream carrier detect signal (e.g., CDO)  607  to the choice logic module  630 , . . . , and the carrier detect module  640  (or the carrier detect module  649 ) provides an n th  stream carrier detect signal (e.g., CDn)  608  to the choice logic module  630 . 
   In some embodiments, the choice logic module  630  is operable to receive all of these symbol timing recovery signals at approximately the same time as the choice logic module  630  receives the carrier detect signals. Generally speaking, the generation of the symbol timing recovery signals by each of the STR modules may be performed in parallel as the generation of the carrier detect signals by each of the carrier detect modules in a particular communication device. 
   The timing recovery module  610  also receives a packet gain settle signal  609  that indicates whether or not the communication device is operating according to steady-state operating conditions. For example, it is not uncommon for various portions of a communication device to undergo modification (e.g., gain control) to accommodate and process received signals. Sometime, when switching between various settings within other portions of the communication device (e.g. within an AFE (Analog Front End)), undesirable transients may propagate through the communication device. This packet gain settle signal  609  provides indicia as to whether any modifications that have been made within the communication device are completed and the operation of the communication device is settled down to a sufficient degree as not to perturb the processing being performed by the timing recovery module  610 . 
   The choice logic module  630  is operable to receive each of the symbol timing recovery signals corresponding to the multiple streams as well as the carrier detect signals corresponding to the multiple streams. By considering all of these received signals, the choice logic module  630  is operable to select one of the symbol timing recovery signals or a non-symbol timing recovery signal for each of the streams. In some instances, the choice logic module  630  is operable to select a symbol timing recovery signal corresponding to one of the streams to be used as the symbol timing recovery signal for another of the streams. In other words, the symbol timing recovery signal corresponding to a particular stream is not always selected as the symbol timing recovery signal for that particular stream. 
   The choice logic module  630  of the timing recovery module  610  is operable to output a 1 st  stream symbol timing recovery signal (STR 0 _out)  651 , . . . , and n th  stream symbol timing recovery signal (STRn_out)  659 . The timing recovery module  610  is operable to provide either an actual symbol timing recovery signal or a non-symbol timing recovery signal for each of the streams. 
     FIG. 7  is a diagram illustrating an embodiment  700  of choice logic functionality employed when performed timing recovery. In this embodiment, the choice logic functionality is implemented as a MUX (Multiplexor) (i.e., choice logic MUX  730 ). This embodiment is shown as receiving and operating on two streams, but this could clearly be extended up to a larger plurality of streams as well. The inputs to the choice logic MUX  730  are a 1 st  symbol timing recovery signal (STR 0 ) and a 2 nd  symbol timing recovery signal (STR 1 ), and the select signals for the choice logic MUX  730  are a 1 st  carrier detect signal (CD 0 ) and a 2 nd  carrier detect signal (CD 1 ). There are at least 2 modes of operation by which the choice logic MUX  730  may operate to output symbol timing recovery signals for each of these two streams (e.g., STR 0 _out for the 1 st  stream and STR 1 _out for the 2 nd  stream). 
   A table indicating mode 1 of operation (shown by reference numeral  701 ) is provided below. 
   
     
       
         
             
          
             
                 
             
             
               Mode 1 701 
             
          
         
         
             
             
             
             
             
          
             
                 
               CD0 
               CD1 
               STR0_out 
               STR1_out 
             
             
                 
                 
             
             
                 
               0 
               0 
               0 (none) 
               0 (none) 
             
             
                 
               0 
               1 
               STR1 
               STR1 
             
             
                 
               1 
               0 
               STR0 
               STR0 
             
             
                 
               1 
               1 
               STR0 
               STR1 
             
             
                 
                 
             
          
         
       
     
   
   This mode 1  701  of operation provides a non-symbol timing recovery signal for each of the streams when each of the streams receives a carrier detect signal that indicates that no carrier detection has been made (this is shown above as 0 (none)). In this mode 1  701 , when only one of the carrier detect signals indicates that carrier detection has been successful (and the other carrier detect signal indicates no carrier detect), then the symbol timing recovery signal corresponding to the stream that has successful carrier detection is employed as the symbol timing recovery signal for both of the streams. In addition, in this mode 1  701 , when both of the carrier detect signals indicate that carrier detection has been successful, then the symbol timing recovery signal corresponding to each of the streams is employed as the symbol timing recovery signal for that corresponding stream. 
   A table indicating mode 2 of operation (shown by reference numeral  702 ) is provided below. 
   
     
       
         
             
          
             
                 
             
             
               Mode 2 702 
             
          
         
         
             
             
             
             
             
          
             
                 
               CD0 
               CD1 
               STR0_out 
               STR1_out 
             
             
                 
                 
             
             
                 
               0 
               0 
               0 (none) 
               0 (none) 
             
             
                 
               0 
               1 
               STR0 
               STR1 
             
             
                 
               1 
               0 
               STR0 
               STR1 
             
             
                 
               1 
               1 
               STR0 
               STR1 
             
             
                 
                 
             
          
         
       
     
   
   This mode 2  702  of operation also provides a non-symbol timing recovery signal for each of the streams when each of the streams receives a carrier detect signal that indicates that no carrier detection has been made (this is shown above as 0 (none)). In this mode 2  702 , when only one of the carrier detect signals indicates that carrier detection has been successful (and the other carrier detect signal indicates no carrier detect), then the then the symbol timing recovery signal corresponding to each of the streams is employed as the symbol timing recovery signal for that corresponding stream. This may be viewed as being based on the supposition that each of the symbol timing recovery signals is in fact accurate when carrier detection has been successful on at least one of the streams. In addition, in this mode 2  702 , when both of the carrier detect signals indicate that carrier detection has been successful, then the symbol timing recovery signal corresponding to each of the stream is employed as the symbol timing recovery signal for that corresponding stream (this is similar to the mode 1  701 ). 
   Clearly, while this embodiment  700  of choice logic functionality has been illustrated to show processing and operation on two streams, these principles may be extended to operate on higher numbers of streams as well without departing from the scope and spirit of the invention. 
     FIG. 8  is a diagram illustrating another embodiment  800  of choice logic functionality employed when performed timing recovery. In this embodiment, the choice logic functionality is implemented as a MUX (Multiplexor) (i.e., choice logic MUX  830 ). This embodiment is shown as receiving and operating on two streams, but this could clearly be extended up to a larger plurality of streams as well. The inputs to the choice logic MUX  830  are a 1 st  symbol timing recovery signal (STR 0 ) and a 2 nd  symbol timing recovery signal (STR 1 ), and the select signals for the choice logic MUX  830  are a 1 st  carrier detect signal (CD 0 ), a 2 nd  carrier detect signal (CD 1 ), a 1 st  packet gain settle signal (G 0 ), and a 2 nd  packet gain settle signal (G 1 ). In instances where carrier detection is performed relatively late, then the packet gain may not have settled yet (e.g., after having undergone a change, it may still be undergoing some transient type behavior). In each of these embodiments, if carrier detect has not been successful, then regardless of what the gain is, no symbol timing recovery signal is generated. In other words, before an accurate symbol timing recovery signal can be generated, it is highly desirable that the packet gain has settled. 
   There are at least 3 modes of operation by which the choice logic MUX  830  may operate to output symbol timing recovery signals for each of these two streams (e.g., STR 0 _out for the 1 st  stream and STR 1 _out for the 2 nd  stream). Each of these modes considers, at least in part, one or both of the 1 st  packet gain settle signal (G 0 ) and the 2 nd  packet gain settle signal (G 1 ). 
   A table indicating mode 3 of operation (shown by reference numeral  803 ), corresponds to the cases where the 1 st  packet gain settle signal (G 0 ) is less than the 2 nd  packet gain settle signal (G 1 ) (i.e., G 1 &lt;G 1 ). The Table is provided below. 
   
     
       
         
             
          
             
                 
             
             
               (G0 &lt; G1) Mode 3 803 
             
          
         
         
             
             
             
             
             
          
             
                 
               CD0 
               CD1 
               STR0_out 
               STR1_out 
             
             
                 
                 
             
             
                 
               0 
               0 
               0 (none) 
               0 (none) 
             
             
                 
               0 
               1 
               STR0 
               STR0 
             
             
                 
               1 
               0 
               STR0 
               STR0 
             
             
                 
               1 
               1 
               STR0 
               STR0 
             
             
                 
                 
             
          
         
       
     
   
   This mode 3  803  of operation provides a non-symbol timing recovery signal for each of the streams when each of the streams receives a carrier detect signal that indicates that no carrier detection has been made (this is shown above as 0 (none)). In this mode 3  803 , when 1 st  packet gain settle signal (G 0 ) is less than the 2 nd  packet gain settle signal (G 1 ) (i.e., G 1 &lt;G 1 ), then when either one or both of the carrier detect signals indicate that carrier detection has been successful, then the symbol timing recovery signal corresponding to the 1 st  stream (STR 0 ) is employed as the symbol timing recovery signal for both of the streams. 
   A table indicating mode 4 of operation (shown by reference numeral  804 ), corresponds to the cases where the 1 st  packet gain settle signal (G 0 ) is more than the 2 nd  packet gain settle signal (G 1 ) (i.e., G 0 &lt;G 1 ). The Table is provided below. 
   
     
       
         
             
          
             
                 
             
             
               (G0 &gt; G1) Mode 4 804 
             
          
         
         
             
             
             
             
             
          
             
                 
               CD0 
               CD1 
               STR0_out 
               STR1_out 
             
             
                 
                 
             
             
                 
               0 
               0 
               0 (none) 
               0 (none) 
             
             
                 
               0 
               1 
               STR1 
               STR1 
             
             
                 
               1 
               0 
               STR1 
               STR1 
             
             
                 
               1 
               1 
               STR1 
               STR1 
             
             
                 
                 
             
          
         
       
     
   
   This mode 4  804  of operation provides a non-symbol timing recovery signal for each of the streams when each of the streams receives a carrier detect signal that indicates that no carrier detection has been made (this is shown above as 0 (none)). In this mode 4  804 , when 1 st  packet gain settle signal (G 0 ) is more than the 2 nd  packet gain settle signal (G 1 ) (i.e., G 0 &gt;G 1 ), then when either one or both of the carrier detect signals indicate that carrier detection has been successful, then the symbol timing recovery signal corresponding to the 2 nd  stream (STR 1 ) is employed as the symbol timing recovery signal for both of the streams. 
   A table indicating mode 5 of operation (shown by reference numeral  805 ), corresponds to the cases where the 1 st  packet gain settle signal (G 0 ) is approximately equal to the 2 nd  packet gain settle signal (G 1 ) within some desired threshold (i.e., G 0 ≈G 1 ). The Table is provided below. 
   
     
       
         
             
          
             
                 
             
             
               (G0 ≈ G1) Mode 5 805 
             
          
         
         
             
             
             
             
             
          
             
                 
               CD0 
               CD1 
               STR0_out 
               STR1_out 
             
             
                 
                 
             
             
                 
               0 
               0 
               0 (none) 
               0 (none) 
             
             
                 
               0 
               1 
               STR0 
               STR1 
             
             
                 
               1 
               0 
               STR0 
               STR1 
             
             
                 
               1 
               1 
               STR0 
               STR1 
             
             
                 
                 
             
          
         
       
     
   
   This mode 4  804  of operation provides a non-symbol timing recovery signal for each of the streams when each of the streams receives a carrier detect signal that indicates that no carrier detection has been made (this is shown above as 0 (none)). In this mode 5  805 , when 1 st  packet gain settle signal (G 0 ) is approximately equal to the 2 nd  packet gain settle signal (G 1 ) (i.e., G 0 ≈G 1 ), when only one of the carrier detect signals indicates that carrier detection has been successful (and the other carrier detect signal indicates no carrier detect), then the then the symbol timing recovery signal corresponding to each of the streams is employed as the symbol timing recovery signal for that corresponding stream. This may be viewed as being based on the supposition that each of the symbol timing recovery signals is in fact accurate when carrier detection has been successful on at least one of the streams. In addition, in this mode  5   805 , when both of the carrier detect signals indicate that carrier detection has been successful, then the symbol timing recovery signal corresponding to each of the stream is employed as the symbol timing recovery signal for that corresponding stream. 
     FIG. 9  is a diagram illustrating an embodiment of functionality  900  operable to support symbol timing recovery processing. Modified correlation function calculation  920  is performed when operating on the samples of two moving windows of an OFDM packet (e.g., as indicated by samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 , respectively) that are processed and received after undergoing receive filtering and down sampling, as indicated by reference numeral  910 . Such initial processing as receive filtering and down sampling may be viewed as being performed within an AFE (Analog Front End) of a communication device. 
   Each of these streams can be viewed as being one of any number of streams within a communication device for which timing recovery processing is being performed. Clearly, more than 2 streams can be employed in a particular embodiment. 
   For example, the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902  may be viewed as being successive symbols within an OFDM packet. These 2 symbols may both be located within an STS of an OFDM packet. Alternatively, these 2 symbols may both be located within an LTS of an OFDM packet. In even another instance, 1 of these 2 symbols may both be located within an STS of an OFDM packet, and the other 1 of these 2 symbols may both be located within an LTS of an OFDM packet (i.e., 1 symbol in the STS, and 1 symbol in the LTS). This modified correlation function calculation  920  is then performed using the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 . 
   This modified correlation function calculation  920  differs from straight-forward auto-correlation function calculation, in that, the term is normalized with respect to the power of each of the moving windows of each of the samples of window  1   901  and the samples of window  2   902 . 
   A strict auto-correlation function calculation, ρ corr , of using the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 , would be performed as follows: 
               ρ   corr     =         E   ⁡     [       S   1     ,     S   2   *       ]             P     S   1         ·       P     S   2             -       m     S   1       ·     m     S   2             ,         
where:
 
   E└S 1 ,S* 2 ┘ is the expected value when considering the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 ; 
   m S     1    is the mean value of the samples of moving window (S 1 )  901 ; 
   m S     2    is the mean value of the samples of moving window (S 2 )  902 ; 
   P S     1    is the power of the samples of moving window (S 1 )  901 ; and 
   P S     2    is the power of the samples of moving window (S 2 )  902 . 
   It is noted that E└S 1 ,S* 2 ┘ is calculated as a function of each of the samples of moving window (S 1 )  901  and the samples of moving window (S 2 )  902 . For example, assuming the samples of S 1  includes n samples as x 1 , x 2 , . . . , x n , and the samples of S 2  includes n samples as y 1 , y 2 , . . . , y n , then the term, E└S 1 ,S* 2 ┘, is calculated as follows: 
   
     
       
         
           
             E 
             ⁡ 
             
               [ 
               
                 
                   S 
                   1 
                 
                 , 
                 
                   S 
                   2 
                   * 
                 
               
               ] 
             
           
           = 
           
             
               
                 
                   
                     x 
                     1 
                   
                   ⁢ 
                   
                     y 
                     1 
                     * 
                   
                 
                 + 
                 
                   
                     x 
                     2 
                   
                   ⁢ 
                   
                     y 
                     2 
                     * 
                   
                 
                 + 
                 
                   ⋯ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     x 
                     n 
                   
                   ⁢ 
                   
                     y 
                     n 
                     * 
                   
                 
               
               n 
             
             . 
           
         
       
     
   
   For comparison, the covariance function calculation, ρ cov , of using the samples of moving window (S 1 )  901  and the samples of moving window (S 2 )  902 , would be performed as follows: 
               ρ   cov     =         E   ⁡     [       S   1     ,     S   2   *       ]       -       m     S   1       ·     m     S   2               σ     S   1       ·     σ     S   2             ,         
where:
 
   ρ S     1    is the standard deviation of the noise of the samples of moving window (S 1 )  901 ; and 
   ρ S     2    is the standard deviation of the noise of the samples of moving window (S 2 )  902 . 
   However, the modified correlation function calculation  920  (which is performed for every sample of each of the moving windows as depicted using, S 1  and S 2 ) is instead calculated as follows: 
               ρ   mod_corr     =         E   ⁡     [       S   1     ,     S   2   *       ]       -       m     S   1       ·     m     S   2                 P     S   1         ·       P     S   2               ,         
or alternatively after being squared as follows:
 
   
     
       
         
           
             ρ 
             mod_corr 
             2 
           
           = 
           
             
               
                 
                   ( 
                   
                     
                       E 
                       ⁡ 
                       
                         [ 
                         
                           
                             S 
                             1 
                           
                           , 
                           
                             S 
                             2 
                             * 
                           
                         
                         ] 
                       
                     
                     - 
                     
                       
                         m 
                         
                           S 
                           1 
                         
                       
                       · 
                       
                         m 
                         
                           S 
                           2 
                         
                       
                     
                   
                   ) 
                 
                 2 
               
               
                 
                   P 
                   
                     S 
                     1 
                   
                 
                 · 
                 
                   P 
                   
                     S 
                     2 
                   
                 
               
             
             . 
           
         
       
     
   
   As can be seen, the modified correlation function calculation  920  is normalized with respect to the power of each of the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 . This generally results in a smaller value than would either of the strict auto-correlation function calculation, ρ corr , or the covariance function calculation, ρ cov , thereby providing for less susceptibility to false carrier detects. By generating a smaller number, a carrier signal is a bit more difficult to detect, but this will provide for a more robust approach that reduces false carrier detects while also providing a very accurate carrier detect signal indicating that a carried signal is in fact detected (or sensed). Generally speaking, as the power of each of the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 , decreases, then the values of the modified correlation function increases. 
   The modified correlation function is monitored over a predetermined number of samples, and the modified correlation function is compared to a modified correlation function threshold as shown in a block  950 . Typically, when the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 , are correlated, then the modified correlation function climbs to reach a peak and then decreases over a region before climbing again to a subsequent peak. 
   A designer is given great flexibility in how to implement these the criterion or criteria required to be met before declaring that carrier detect has been performed. For example, any of the thresholds employed herein can be modified. In some instances, the thresholds can be lowered when accompanied with requiring more consecutive peaks be detected within the modified correlation function threshold. 
   Once the modified correlation function has been (and continues to be) calculated for the samples of the various symbols of the stream containing this OFDM packet, modified correlation function analysis is performed, as shown in a block  950 . 
   As shown in a block  951 , the modified correlation function is compared to a symbol timing recovery threshold (e.g., Th STR ). Also, as shown in a block  952 , a peak value (or a starting value) of the modified correlation function is identified (e.g., ρ AC     —     start   2  (n AC     —     start )). This peak value (or starting value) (e.g., ρ 2   AC     —     start   2 (n AC     —     start )) is identified when the modified correlation function exceeds the symbol timing recovery threshold (e.g., Th STR ) and when the modified correlation function is substantially non-increasing. It is noted that the modified correlation function need not necessarily be decreasing; if the modified correlation function is flat (e.g., neither increasing nor decreasing), this is sufficient to meet the criterion of this parameter. 
   As shown in a block  953 , over a region which it is determined that the modified correlation function is in fact decreasing, a mid-point of the decreasing region of the modified correlation function is identified that, when biased by a predetermined amount, is less than the peak value of the modified correlation function. This mid-point is really a mid-point that is biased by a certain degree; this may be viewed as being performed to ensure that the mid-point is sufficiently less than the peak value (or starting value) (e.g., ρ 2   AC     —     start   2 (n AC     —     start )). This could be expressed mathematically as follows:
 
(ρ 2   AC     —     mp   2 ( n   AC     —     mp )+bias)&lt;ρ AC     —     start   2 ( n   AC     —     start ), where:
 
   ρ AC     —     start   2 (n AC     —     start ) is the modified correlation function at this peak value (or starting value) which is located as sample, n AC     —     start ; 
   ρ AC     —     mp   2 (n AC     —     mp ) is the modified correlation function at this mid-point value which is located as sample, n AC     —     mp ; and 
   bias is an offset bias value selected by a designer. 
   As shown in a block  954 , an end-point of the decreasing region of the modified correlation function is identified that, when scaled by a predetermined scaling factor, is less than the peak value (or starting value) (e.g., ρ AC     —     start   2 (n AC     —     start )) of the modified correlation function. This could be expressed mathematically as follows:
 
( k·ρ   AC     —     ep   2 ( n   AC     —     ep ))&lt;ρ AC     —     start   2 ( n   AC     —     start ), where:
 
   ρ 2   AC     —     start   2 (n AC     —     start ) is the modified correlation function at this peak value (or starting value) which is located as sample, n AC     —     start ; 
   ρ AC     —     ep   2 (n AC     —     ep ) is the modified correlation function at this end-point value which is located as sample, n AC     —     ep ; 
   k is a scaling factor selected by a designer. 
   It is noted that each of the processing operations performed within the various sub-blocks within the modified correlation function analysis  950  may be considered to determine the rate of fall of the modified correlation function over this decreasing region. 
   Also, this embodiments shows how the power of each of the samples of moving window (S 1 )  901  and samples of moving window (S 2 )  902 , undergoes power comparison. Specifically, the power of the samples of moving window (S 1 )  901 , is compared to a 1 st  power threshold as shown in a block  930 ; this comparison of the power of the symbol, S 1 , is with respect to a 1 st  power threshold. The power of the samples of moving window (S 2 )  902 , is compared to a 2 nd  power threshold as shown in a block  940 ; this comparison of the power of samples of moving window (S 2 )  902 , is with respect to a 2 nd  power threshold. In some embodiments, these power thresholds are the same; in other embodiments, they may be different. 
   The outputs of each of these blocks  950 ,  930 , and  940  are provided to a combining module  960 . The combining module  960  may be viewed as performing the processing of each of the comparisons being performed in the blocks  950 ,  930 , and  940  to determine whether or not a signal timing recovery signal (STR)  941  indicates that symbol timing recovery has been successful or not. This signal timing recovery signal (STR)  941  is then provided to a choice logic module. 
   The combining module  960  also receives a packet gain settle signal  909  that indicates whether or not the communication device is operating according to steady-state operating conditions. For example, it is not uncommon for various portions of a communication device to undergo modification (e.g., gain control) to accommodate and process received signals. Sometime, when switching between various settings within other portions of the communication device (e.g. within an AFE (Analog Front End)), undesirable transients may propagate through the communication device. This packet gain settle signal  909  provides indicia as to whether any modifications that have been made within the communication device are completed and the operation of the communication device is settled down to a sufficient degree as not to perturb the processing being performed by the combining module  960 . 
   In one possible embodiment, the signal timing recovery signal (STR)  941  that is provided to choice logic module indicates successful signal timing recovery has been achieved when: (1) the modified correlation function exceeds the symbol timing recovery threshold, (2) the rate of fall of the modified correlation function exceeds a rate of fall threshold, (3) the first power corresponding to the samples of moving window (S 1 )  901  exceeds the first power threshold, and (4) the second power corresponding to the samples of moving window (S 2 )  902  exceeds the second power threshold. Again, in some instances, these power thresholds are the same; in other embodiments, they are different. 
     FIG. 10  is a diagram illustrating an embodiment  1000  of a modified correlation function as a function of samples. This diagram shows one possible embodiment of many of the various calculations that are performed with respect to the functionality  900  of the  FIG. 9  that is operable to support symbol timing recovery processing. 
   Generally speaking, this diagram shows the modified correlation function, ρ mod     —     corr   2 (n), as a function of sample, n. The modified correlation function, ρ mod     —     corr   2 (n), typically will rise and flatten out as the symbols of the STS of an OFDM packet are typically well correlated. When the LTS is encountered and processed, the symbols located therein are not typically well correlated. As such, the modified correlation function, ρ mod     —     corr   2 (n), typically falls and flattens out because of this characteristic of the symbols within the LTS of an OFDM packet. The rate of increase of the modified correlation function, ρ mod     —     corr   2 (n), and the rate of fall  1004  over a decreasing region of the modified correlation function, ρ mod     —     corr   2 (n), may be identical. As can be seen, the modified correlation function is monotonically decreasing starting when considering this region depicted by the rate of fall  1004 . 
   For example, the symbols within the STS of an OFDM packet may be correlated very well leading to a very rapid rise of the modified correlation function, ρ mod     —     corr   2 (n). However, the symbols within the LTS of an OFDM packet may be somewhat correlated initially and then very poorly correlated thereafter leading to a relatively slow rate of fall  1004 . Alternatively, the symbols within the LTS of an OFDM packet may very poorly correlated from the very beginning leading to a very precipitous rate of fall  1004 . 
   The following points are also identified within the  FIG. 10 : 
   ρ AC     —     start   2 (n AC     —     start ) (peak value)  1001  is the modified correlation function at this peak value (or starting value) which is located as sample, n AC     —     start ; 
   ρ AC     —     mp   2 (n AC     —     mp ) (mid-point)  1002  is the modified correlation function at this mid-point value which is located as sample, n AC     —     mp ; and 
   ρ AC     —     ep   2 (n AC     —     ep ) (end-point)  1003  is the modified correlation function at this end-point value which is located as sample, n AC     —     ep . 
   The reader is encouraged consider the  FIG. 10  in conjunction with the description of the functionality  900  of the  FIG. 9  that is operable to support symbol timing recovery processing. The  FIG. 10  is intended to provide a clearer representation of the calculations performed within and according to the functionality of the  FIG. 9 . 
     FIG. 11A  is a diagram illustrating an embodiment of a single-input-single-output (SISO) communication system  1101 . A transmitter (TX  1111 ) having a single transmit antenna communicates with a receiver (RX  1121 ) having a single receive antenna. 
     FIG. 11B  is a diagram illustrating an embodiment of a multiple-input-multiple-output (MIMO) communication system  1102 . A transmitter (TX  1112 ) having multiple transmit antennae communicates with a receiver (RX  1122 ) having multiple receive antennae. Looking only at 2 of the plurality of antennae at either end of the communication channel, a first antenna transmits A and a second antenna transmits B. At the RX  1122 , a first antenna receives A′+B′ and a second antenna receives A″+B″. The RX  1122  includes the appropriate functionality to perform the extraction and generation of a signal that is a best estimate of the transmitted signal A+B. 
     FIG. 11C  is a diagram illustrating an embodiment of a multiple-input-single-output (MISO) communication system  1103 . A transmitter (TX  1113 ) having multiple transmit antennae communicates with a receiver (RX  1123 ) having a single receive antenna. 
     FIG. 11D  is a diagram illustrating an embodiment of a single-input-multiple-output (SIMO) communication system  1104 . A transmitter (TX  1114 ) having a single transmit antenna communicates with a receiver (RX  1124 ) having multiple receive antennae. A SIMO communication system may be viewed as being the opposite of a MISO embodiment. 
   While some of these embodiments presented above (e.g.,  FIG. 11A  and  FIG. 11C ) show receivers processing only a singular stream, the principles presented above with respect to symbol timing recovery processing may be applied. While multiple symbol timing recovery signals are not generated in such single stream embodiments thereby requiring the choice logic functionality described above with respect to other embodiments, the various embodiments of symbol timing recovery processing may nevertheless be employed to assist in performing timing recovery for a singular received signal. 
   In view of the above detailed description of the invention and associated drawings, other modifications and variations will now become apparent. It should also be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.