Abstract:
Carrier detection applicable for SISO, MIMO, MISO, and SIMO communications. A novel approach is presented to perform carrier detection for a signal found in any of a wide variety of communication systems including single-input-multiple-output (SISO), multiple-input-multiple-output (MIMO), multiple-input-single-output (MISO) single-input-multiple-output (SIMO), communication systems. This novel approach to performing carrier detection is more robust than those approaches existent in the art. By employing normalization with respect to power in determined a modified correlation function, there is less susceptibility to false detects. Also, this approach is quite robust to any circuitry DC offsets that may undesirably exist within a communication device that undergoes operational changes due to a variety of factors including environmental perturbations and/or changes in processing circuitry within the communication device (e.g., changes in gain control).

Description:
CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS  
     Provisional Priority Claims  
       [0001]     The present U.S. Utility Patent Application claims priority pursuant to 35 U.S.C. § 119(e) to the following U.S. Provisional Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Utility Patent Application for all purposes:  
         [0002]     1. U.S. Provisional Application Ser. No. 60/700,968, entitled “Carrier detection applicable for SISO, MIMO, MISO, and SIMO communications,” (Attorney Docket No. BP4650), filed Wednesday, Jul. 20, 2005 (07/20/2005), pending.  
       Incorporation by Reference  
       [0003]     The following U.S. Utility Patent Applications are hereby incorporated herein by reference in their entirety and made part of the present U.S. Utility Patent Application for all purposes:  
         [0004]     1. U.S. Utility patent application Ser. No. 11/132,939, entitled “Carrier detection for multiple receiver systems,” (Attorney Docket No. BP4159), filed May 19, 2005 (05/19/2005), pending.  
         [0005]     2. U.S. Utility patent application Ser. No. 11/168,793, entitled “Reduced feedback for beamforming in a wireless communication,” (Attorney Docket No. BP4637), filed Jun. 28, 2005 (06/28/2005), pending. 
     
    
     BACKGROUND OF THE INVENTION  
       [0006]     1. Technical Field of the Invention  
         [0007]     The invention relates generally to communication systems; and, more particularly, it relates to performing carrier detection within such communication systems.  
         [0008]     2. Description of Related Art  
         [0009]     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.  
         [0010]     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.  
         [0011]     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.  
         [0012]     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.  
         [0013]     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.  
         [0014]     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.  
         [0015]     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.  
         [0016]     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.  
         [0017]     Within these types of communication systems, as well as within other types of communication systems, there is oftentimes a need to perform detect of a carrier within a signal received from a communication channel. In detection theory, there is a generally understood relationship between designing a carrier detection apparatus that tries on one hand to reduce false detections of the carrier and on the other hand to maximize the probability of true carrier detections. Also, within many communication devices implemented within modern communication systems, the circuitry and components therein oftentimes undergo modification (sometimes in real time) and adjustment that can generate certain degrees of transients, static DC offsets, and/or transient DC offsets within certain portions of the communication device. For example, in an AFE (Analog Front End) of a communication device that performs certain functions as filtering, frequency conversion, and/or gain control, the modification and adjustment of many of the components required to perform these functions may undesirably generate many of these deleterious effects. Moreover, sometimes a signal received from a communication channel arrives at a communication device with some degree of a DC offset; this is a deficiency in the actual signal received by the communication device and not a deficiency in the actual components of the corn device itself.  
         [0018]     These and other problems that can arise make the challenge of performing carrier detection even more difficult. There seems always to be this balancing between reducing false detections and maximizing the probability of true detections when designing devices operable to perform carrier detection. There seems also continually to be new considerations and trade-offs made available for designers to perform this balancing act in designing means to perform carrier detection. As such, a need continues to exist in the art for better and more effective means by which carrier detection may be performed.  
       BRIEF SUMMARY OF THE INVENTION  
       [0019]     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  
       [0020]      FIG. 1  is a diagram of a wireless communication system.  
         [0021]      FIG. 2  is a diagram of a wireless communication device.  
         [0022]      FIG. 3  is a diagram of another wireless communication device.  
         [0023]      FIG. 4  is a diagram of feedback control within a communication device.  
         [0024]      FIG. 5  is a diagram illustrating an embodiment of an OFDM (Orthogonal Frequency Division Multiplexing) packet that may be processed.  
         [0025]      FIG. 6  is a diagram illustrating an embodiment of functionality operable to perform carrier detection.  
         [0026]      FIG. 7  is a diagram illustrating another embodiment of functionality operable to perform carrier detection.  
         [0027]      FIG. 8  is a diagram illustrating an embodiment of functionality operable to support auto-correlation detection processing.  
         [0028]      FIG. 9  is a diagram illustrating an embodiment of functionality operable to support match filter detection processing.  
         [0029]      FIG. 10  is a diagram illustrating an embodiment of functionality operable to combining carrier detect signals from multiple streams into a single carrier detect signal.  
         [0030]      FIG. 11  is a diagram illustrating an embodiment of a match filter function as a function of samples.  
         [0031]      FIG. 12  is a diagram illustrating another embodiment of a match filter function as a function of samples.  
         [0032]      FIG. 13A  is a diagram illustrating an embodiment of a single-input-single-output (SISO) communication system.  
         [0033]      FIG. 13B  is a diagram illustrating an embodiment of a multiple-input-multiple-output (MIMO) communication system.  
         [0034]      FIG. 13C  is a diagram illustrating an embodiment of a multiple-input-single-output (MISO) communication system.  
         [0035]      FIG. 13D  is a diagram illustrating an embodiment of a single-input- multiple-output (SIMO) communication system.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]      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 .  
         [0037]     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 .  
         [0038]     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 .  
         [0039]     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.  
         [0040]      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.  
         [0041]     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.  
         [0042]     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 .  
         [0043]     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 .  
         [0044]     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).  
         [0045]     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.  
         [0046]     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.  
         [0047]     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).  
         [0048]     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 .  
         [0049]     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.  
         [0050]     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 .  
         [0051]     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 .  
         [0052]      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.  
         [0053]     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.  
         [0054]     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 .  
         [0055]     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.  
         [0056]     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.  
         [0057]     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 .  
         [0058]     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 .  
         [0059]     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 .  
         [0060]     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 .  
         [0061]      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.  
         [0062]     Within this feedback control  400 , a carrier detection module  469  is operable to perform carrier detection 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 .  
         [0063]     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 .  
         [0064]     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.  
         [0065]     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).  
         [0066]     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 .  
         [0067]     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).  
         [0068]     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.  
         [0069]     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 .  
         [0070]     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.  
         [0071]     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.  
         [0072]     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.  
         [0073]     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.  
         [0074]      FIG. 5  is a diagram illustrating an embodiment of an OFDM (Orthogonal Frequency Division Multiplexing) packet  500  that may be processed.  
         [0075]     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.  
         [0076]     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.  
         [0077]     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.  
         [0078]     In the context of carrier detect functionality and method implemented to perform carrier detection, 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. Each of the OFDM symbols includes a plurality of samples. For example, the OFDM symbol S 2  includes sample  511 , sample  512 , and . . . , sample  519 . 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.  
         [0079]      FIG. 6  is a diagram illustrating an embodiment of functionality  600  operable to perform carrier detection. This embodiment shows a very generic embodiment by which a carrier detect module  610  may be implemented. In some desired embodiments, the carrier detect 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.  
         [0080]     The carrier detect module  610  is operable to receive samples of at least two symbols of an STS of an OFDM packet, as indicated by the reference numeral  605 . The carrier detect module  610  includes an auto-correlation detection module  620  and a match filter detection module  630 . In some instances, the match filter detection module  630  also includes an auto-correlation detection module  635  that is distinct from the auto-correlation detection module  620 , in that, the auto-correlation detection module  635  operates using a relaxed set of parameters when compared to the parameters employed by the an auto-correlation detection module  620 . Operating cooperatively, the auto-correlation detection module  620  and the match filter detection module  630  operate on the samples of at least two symbols of an OFDM packet to generate a carrier detect signal  615 . This carrier detect signal  615  then indicates carrier detect or not (i.e., a carrier signal has been sensed and detected or no carrier signal has been sensed and detected).  
         [0081]      FIG. 7  is a diagram illustrating another embodiment of functionality  700  operable to perform carrier detection. It is noted that this diagram corresponds to an embodiment for use in performing carrier detection within a single received signal stream. This embodiment  700  could also be replicated and employed to perform carrier detection among a number of received signal streams as well. In such a multiple received signal stream embodiment, if the embodiment  700  were replicated (one for each received signal stream), then each embodiment  700  would provide a carrier detect signal for that particular received signal stream, and the results of all of the embodiments  700  (i.e., one for each received signal stream) could be combined for overall carrier detection. For example, in such a multiple received signal stream embodiment, a combining module can be employed to perform the combining functionality according to a desired manner for a given application. At least one such possible embodiment is described below.  
         [0082]     In some desired embodiments, a carrier detect module  710  may be implemented within a baseband processing module  701 . This baseband processing module  701  may be the baseband processing module  100  shown above within other embodiments, or the baseband processing module  701  may include different functionality and capabilities as the baseband processing module  100  shown above.  
         [0083]     Similar to the embodiment described just above, the carrier detect module  710  is operable to receive samples of at least two symbols of an STS of an OFDM packet, as indicated by the reference numeral  705 . In this embodiment, the carrier detect module  710  includes a 1 st  auto-correlation detection module  720 , a match filter detection module  730 , and a 2 nd  auto-correlation detection module  740 . The 1 st  auto-correlation detection module  720  is operable to process the samples of at least 2 symbols of an OFDM packet to generate a first carrier detect signal, and the 2 nd  auto-correlation detection module  740  is operable to process the samples of at least 2 symbols of an OFDM packet to generate a second carrier detect signal. The match filter detection module  730  is operable to process samples of at least 1 symbol of an OFDM packet as compared to a predetermined symbol as determined using match filter parameters corresponding thereto; the match filter detection module  730  is operable to generate a match filter detection signal.  
         [0084]     The carrier detect module  710  also includes at least one embodiment of some logic circuitry and/or logic functional blocks that are operable to process each of the first carrier detect signal, the match filter detection signal, and the second carrier detect signal. For example, in one possible embodiment, the match filter detection signal and the second carrier detect signal are provided to a first logical AND gate  711 . In some alternative embodiments, the first logical AND gate  711  may be replaced by a logical OR gate.  
         [0085]     The output of this first logical AND gate  711  is provided to a second logical AND gate  712  that also receives the first carrier detect signal. The output of this second logical AND gate  712  is a carrier detect signal  715  that indicates carrier detect or not (i.e., a carrier signal has been sensed and detected or no carrier signal has been sensed and detected).  
         [0086]     In another possible embodiment, the match filter detection signal and the second carrier detect signal are provided to the first logical AND gate  711 . The output of this first logical AND gate  711  is provided to a logical OR gate  713  that also receives the first carrier detect signal. The output of this logical OR gate  713  is a carrier detect signal  716  that indicates carrier detect or not (i.e., a carrier signal has been sensed and detected or no carrier signal has been sensed and detected). In this embodiment, either the signal output from the first logical AND gate  711  or the first carrier detect signal output from the 1 st  auto-correlation detection module  720  is sufficient to direct the carrier detect signal  716  to indicate carrier detect or not.  
         [0087]     A designer is given great latitude by which to combine each of the first carrier detect signal, the match filter detection signal, and the second carrier detect signal. Each of these two possible embodiments of logic circuitry may be implemented within a single carrier detect module in some embodiments, and selection may be made regarding which of the two possible embodiments to employ.  
         [0088]     More detail is provided below showing greater detail by which each of these various embodiments of these auto-correlation detection modules and match filter detection modules may be implemented.  
         [0089]      FIG. 8  is a diagram illustrating an embodiment of functionality  800  operable to support auto-correlation detection processing. Modified correlation function calculation  820  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 )  801  and samples of moving window (S 2 )  802 , respectively) that are processed and received after undergoing receive filtering and down sampling, as indicated by reference numeral  810 . 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.  
         [0090]     This modified correlation function calculation  820  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  801  and the samples of window 2  802 .  
         [0091]     A strict auto-correlation function calculation, ρ corr  of using the samples of moving window (S 1 )  801  and samples of moving window (S 2 )  802 , 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: 
 
         [0092]     E[S 1 , S 2   * ] is the expected value when considering the samples of moving window (S 1 )  801  and samples of moving window (S 2 )  802 ;  
         [0093]     m S     1    is the mean value of the samples of moving window (S 1 )  801 ;  
         [0094]     m S     2    is the mean value of the samples of moving window (s 2 )  802 ;  
         [0095]     P S     1    the power of the samples of moving window (S 1 )  801 ; and  
         [0096]     P S     2    is the power of the samples of moving window (S 2 )  802 .  
         [0097]     It is noted that E[S 1 , S 2   * ] is calculated as a function of each of the samples of moving window (S 1 )  801  and the samples of moving window (S 2 )  802 . 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     .         
 
         [0098]     For comparison, the covariance function calculation, ρ cov , of using the samples of moving window (S 1 )  801  and the samples of moving window (S 2 )  802 , would be performed as follows:  
               
 
         [0099]     σ S     1    is the standard deviation of the noise of the samples of moving window (S 1 )  801 ; and  
         [0100]     σ S     2    is the standard deviation of the noise of the samples of moving window (S 2 )  802 .  
         [0101]     However, the modified correlation function calculation  820  (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           .         
 
         [0102]     As can be seen, the modified correlation function calculation  820  is normalized with respect to the power of each of the samples of moving window (S 1 )  801  and samples of moving window (S 2 )  802 . 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 corr , 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 )  801  and samples of moving window (S 2 )  802 , decreases, then the values of the modified correlation function increases.  
         [0103]     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  850 . Typically, when the samples of moving window (S 1 )  801  and samples of moving window (S 2 )  802 , 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.  
         [0104]     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.  
         [0105]     Also, this embodiments shows how the power of each of the samples of moving window (S 1 )  801  and samples of moving window (S 2 )  802 , undergoes power comparison. Specifically, the power of the samples of moving window (S 1 )  801 , is compared to a 1 st  power threshold as shown in a block  830 ; 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 )  802 , is compared to a 2 nd  power threshold as shown in a block  840 ; this comparison of the power of samples of moving window (S 2 )  802 , is with respect to a 2 nd  power threshold.  
         [0106]     The outputs of each of these blocks  850 ,  830 , and  840  are provided to a combining module  860 . The combining module  860  may be viewed as performing the processing of each of the comparisons being performed in the blocks  850 ,  830 , and  840  to determine whether or not a carrier detect signal  816  indicates that a carrier signal has in fact been detected or not.  
         [0107]     In one possible embodiment, the carrier detect signal  816  indicates carrier detect of a signal being monitored when: (1) the modified correlation function exceeds the modified correlation function threshold, (2) the first power corresponding to the first symbol exceeds the first power threshold, and (3) the second power corresponding to the second symbol exceeds the second power threshold. When all three of these conditions are not met, then the carrier detect signal  816  does in fact indicate carrier detect, and when at least one of these conditions is not met, then the carrier detect signal  816  does not indicate carrier detect.  
         [0108]      FIG. 9  is a diagram illustrating an embodiment of functionality  900  operable to support match filter detection processing. Initially, a plurality of signals, indicated by reference numeral  910 , is received after undergoing receive filtering and down sampling. Analogous to other embodiments, 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.  
         [0109]     Match filter function calculation  920  is performed when operating on the samples of successive different symbols of an OFDM packet (e.g., S 1  and S 2 , as indicated by reference numerals  901  and  902 , respectively).  
         [0110]     The match filter function calculation  920  is performed using the samples of each of the symbols, S 1  and S 2,  as compared to samples of a predetermined symbol. Each of these samples undergoes match filter processing performed with respect to the samples of the predetermined symbol thereby generating a match filter output signal, MF_out. Generally speaking, the n th  sample of each of the symbols, S 1  and S 2 , is processed within the corresponding sample, S known   *  (−n), of the predetermined/known symbol. The received symbol, S 1 , is then correlated with a predetermined/known sequence (e.g., the predetermined/known symbol, S known ) thereby generating a match filter function, ρ MF . This match filter function calculation  920  to generate the match filter function, ρ MF  is performed using the match filter output signal, MF_out, and some of the various characteristics and measures of the predetermined/known symbol. For example, the match filter function, ρ MF , may be calculated as follows:  
           ρ   MF     =       MF_out   -       m     S   1       ·     m     S   known                 P     S   1         ·       P     S   known               ,     where   ⁢     :           
 
         [0111]     MF_out is the match filter output signal generated using one of the received symbols (e.g., S 1 ) and the predetermined/known symbol, S known ;  
         [0112]     m S     1    is the mean value of the symbol, S 1 ;  
         [0113]     m S     known    is the mean value of the predetermined/known symbol, S known ;  
         [0114]     P S     1    is the power of the symbol, S 1 ; and  
         [0115]     P S     known    is the power of the predetermined/known symbol, S known .  
         [0116]     However, by the very design and definition of the predetermined/known symbol, S known , and the design of the STS of an OFDM packet as described herein, the value of m S     known    is zero (i.e., m S     known   =0). Therefore, the match filter function, ρ MF , may be calculated as follows:  
           ρ   MF     =     MF_out         P     S   1         ·       P     S   known               ,       
 
 or alternatively after being squared as follows:  
         ρ   MF   2     =           (   MF_out   )     2         P     S   1       ·     P     S   known           .         
 
         [0117]     Once the match filter function has been (and continues to be) calculated for the samples of the various symbols of the STS of an OFDM packet, match filter function analysis is performed, as shown in a block  950 .  
         [0118]     For example, as shown in a block  951 , the match filter function analysis  950  is operable to perform 1 st  peak identification within the match filter function as shown in a block  951 . This is performed using a 1 st  match filter function threshold (e.g., Th MF1 ). Analogously, the match filter function analysis  950  is operable to perform 2 nd  peak identification within the match filter function as shown in a block  952 . This may be performed using a 2 nd  match filter function threshold (e.g., Th MF2 ).  
         [0119]     Also, as shown in a block  953 , the match filter function analysis  950  is operable to determine the relative difference of magnitude between the 1 st  peak of the match filter function and the match filter function at an expected location of a 2 nd  peak (e.g., Δ P1+Δt     −     P1  ). This may be performed to determine whether the 1 st  peak and the 2 nd  peak are of approximately similar magnitude. This is also determined as a function of the periodicity between the 1 st  peak and the 2 nd  peak. For example, this may be calculated as a function of a difference threshold (which may be represented as Th diff ) that may be selected by a designer. 
 
Δ P1+Δt     −     P1 =|ρ MF   2 (n P1 {tilde over (+)}Δt)−ρ MF   2 (n P1 )|&lt;Th diff , 
 
 where: 
 
         [0120]     ρ MF   2  (n P1 ) is the match filter function corresponding to the sample, n P1 , that corresponds to the 1 st  peak;  
         [0121]     ρ MF   2  (n P1 {tilde over (+)}Δt) is the match filter function corresponding being a predetermined period of time away from the sample, n P1 , associated with the 1 st  peak; this generally will correspond to the location of the that corresponds to the 2 nd  peak that is spaced an approximate period of time (e.g., Δt) from the 1 st  peak (this term Δt may be predetermined in some embodiments, e.g., a particular period of time such as 0.8 μsec); and  
         [0122]     Th diff  is the designer selected threshold employed to compare this function&#39;s difference.  
         [0123]     Alternatively, an actual difference, Δ P1−P2 , between the 1 st  peak and the actual 2 nd  peak can be calculated directly as follows: 
 
Δ P1−P2 =|ρ MF   2 (n P2 )−ρ MF   2 (n P1 )|&lt;Th diff , 
 
 where: 
 
         [0124]     ρ MF   2 (n P1 ) is the match filter function corresponding to the sample, n P1 , that corresponds to the 1 st  peak;  
         [0125]     ρ MF   2 (n P2 ) is the match filter function corresponding to the sample, np P2 , that corresponds to the 2 nd  peak; and  
         [0126]     Th diff  is the designer selected threshold employed to compare this function&#39;s difference.  
         [0127]     Also, as shown in a block  954 , the match filter function analysis  950  is operable to determine whether match filter function falls below 3 rd  match filter function threshold between 1 st  and 2 nd  peak of the match filter function.  
         [0128]     This 3 rd  match filter function threshold may be represented as Th fall , and this operation in the block  954  may be expressed mathematically as follows: 
 
ρ MF   2 (n P1 )−ρ MF   2 (n v )&gt;Th fall , 
 
 where: 
 
         [0129]     ρ MF   2 (n P1 ) is the match filter function corresponding to the sample, n P1 , that corresponds to the 1 st  peak;  
         [0130]     ρ MF   2 (n v     1   ) is the match filter function corresponding to the sample, n v     1   , that corresponds to a particular distance (e.g. in terms of samples) along the match filter function from the 1 st  peak (this sample, n v     1   , and its distance from the sample, n P1 , may be predetermined and/or selected by a designer); and  
         [0131]     Th fall  is the designer selected threshold employed to compare this difference.  
         [0132]     Then, as shown in a block  955 , the match filter function analysis  950  is operable to identify a predetermined number of peaks of match filter function after 1 st  peak and 2 nd  peak. The number of peaks to be identified may be selected by a designer (e.g., N peaks). This is to ensure that the match filter function is in fact periodic over a reasonable amount of time.  
         [0133]     Also, this embodiments shows how the power of each of the symbols, S 1  and S 2,  undergoes power comparison. Specifically, the power of the symbol, S 1 , 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 symbol, S 2,  is compared to a 2 nd  power threshold as shown in a block  940 ; this comparison of the power of the symbol, S 2 , is with respect to a 2 nd  power threshold.  
         [0134]     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 the symbols, S 1  and S 2,  in fact comport sufficiently with the predetermined/known symbol as indicated by a match filter detection signal  916 . The match filter detection signal  916  indicates whether each of the symbols, S 1  and S 2,  sufficiently corresponds to the predetermined/known symbol.  
         [0135]     In one possible embodiment, the match filter detection signal  916  indicates sufficient match filter correlation between a received symbol and a predetermined/known symbol when: (1) the first peak of the match filter function exceeds the first match filter function threshold, (2) the second peak of the match filter function exceeds the second match filter function threshold, (3) the difference in magnitude between the first peak and the second peak is less than a difference threshold, (4) the match filter function falls below a third match filter function threshold between the first peak and the second peak, (5) the first power corresponding to the first symbol exceeds a corresponding first power threshold, (6) and the second power corresponding to the second symbol exceeds a corresponding second power threshold.  
         [0136]     Also, as indicated by the dotted lines, this functionality  900  may be implemented to process only one symbol (shown as S 1 ) at a time. If desired, to provide for some efficiency between the functionality  800  and the functionality  900 , the samples of each of the symbols, S 1  and S 2 , may be provided simultaneously to borrow on certain of the parallel type processing. For example, each of the functionality  800  and the functionality  900  perform power threshold comparison.  
         [0137]     It is also noted that unique and different power thresholds may be employed for each of these corresponding threshold comparisons being performed in each of the embodiments of the functionality  800  of the  FIG. 8  and the functionality  900  of the  FIG. 9 . A designer is provided significant freedom and latitude to select the particular thresholds employed herein.  
         [0138]     It is also noted that any embodiment that employs multiple auto-correlation modules (e.g., the functionality  700  of the  FIG. 7 ), different sets of parameters may be employed for each of those auto-correlation modules. For example, a 1 st  auto-correlation module may employ a 1 st  plurality of parameters such that its decision-making criteria is more stringent than a 2 nd  auto-correlation module that employs a 2 nd  plurality of parameters. The use and selection of certain thresholds employed by each of these auto-correlation modules ensures that they operate differently and may provide carrier detect signals indicating carrier detect under slightly different conditions.  
         [0139]      FIG. 10  is a diagram illustrating an embodiment of functionality  1000  operable to combining carrier detect signals from multiple streams into a single carrier detect signal  1010  (e.g., a final carrier detect signal). As can be seen, multiple carrier detect signals are provided to a combining module  1060 . Each of these carrier detect signals can be viewed as corresponding to a stream. For example, a carrier detect signal  1001  corresponds to a stream  1 , a carrier detect signal  1002  corresponds to a stream  2 , and a carrier detect signal  1003  corresponds to a stream  3 . Generally speaking, carrier detect signals corresponding to n streams can be received by the combining module  1060 , as shown by a carrier detect signal  1009  corresponds to a stream n. Any number of streams (i.e., as few as 2 streams) can be employed.  
         [0140]     Each of these carrier detect signals may be generated using any of the embodiments described herein for a single stream. For example, each carrier detect signal may be generated using functionality of  FIG. 6 ,  FIG. 7 , and/or  FIG. 8 .  
         [0141]     The combining module  1060  can employ any desired means of performing combining of the multiple carrier detect signals into a carrier detect signal  1010 . In some embodiments, logic circuitry (which can include AND and OR gates, as desired in the implementation) can be employed to make a final decision of carrier detection based on the success/failure of each of the streams.  
         [0142]      FIG. 11  is a diagram illustrating an embodiment  1100  of a match filter function as a function of samples. This embodiment  1100  may assist the reader in identifying the various portions of the match filter function with respect to the functionality  900  of the  FIG. 9  that supports match filter detection processing.  
         [0143]     When processing the samples of successive symbols (e.g., S 1  and S 2 ) within the STS of an OFDM packet as compared to the samples of a predetermined/known symbol, S known , the match filter function, ρ MF   2 (n), typically rises to peaks and falls to valleys over the samples (e.g., which may be depicted by n) of the successive symbols (e.g., S 1  and S 2 ) as a function of the correlation (as determined by the match filter detection processing).  
         [0144]     Many of the variables employed with respect to the description of the previous diagram are shown in this diagram, and these are referenced again for the assistance of reader as follows:  
         [0145]     ρ MF   2 (n P1 ) is the match filter function corresponding to the sample, n P1 , that corresponds to the 1 st  peak;  
         [0146]     ρ MF   2 (n P2 ) is the match filter function corresponding to the sample, n P2 , that corresponds to the 2 nd  peak;  
         [0147]     ρ MF   2 (n v     1   ) is the match filter function corresponding to the sample, n v     1   , that corresponds to a particular distance (e.g. in terms of samples) along the match filter function from the 1 st  peak (this sample, n v     1   , and its distance from the sample, n P1 , may be predetermined and/or selected by a designer);  
         [0148]     Δ P1−P2  is the actual difference between the 1 st  peak and the 2 nd  peak;  
         [0149]     Δ P1+Δt     −     P2  is the difference between the 1 st  peak and the match filter function at an expected location of a 2 nd  peak; and  
         [0150]     Δt is the time period difference between the 1 st  peak and an expected location of the 2 nd  peak (this may easily be expressed as a function of samples as well).  
         [0151]     Also, certain degrees of robustness may be designed into the functionality of any such of the processing that is performed. As one example, when performing match filter function calculation across a plurality of samples, certain criteria may be designed in to allow for a certain amount of failure of correlation while nevertheless providing a match filter detection signal indicating correlation between a received symbol and a predetermined/known symbol. As one embodiment, say N correlations are determined in M collects and corresponding match filter function calculations, then this may be deemed as being sufficient to provide a match filter detection signal indicating correlation between a received symbol and a predetermined/known symbol. However, when less than N correlations are determined in M collects and corresponding match filter function calculations, then this may be deemed as NOT being sufficient to provide a match filter detection signal indicating correlation between a received symbol and a predetermined/known symbol. Certain degrees of robustness, in allowing for a certain degree of imperfectness, in the processing of each of the various calculations and analyses performed herein are certainly within the scope and spirit of the invention.  
         [0152]     It is noted that the carrier detect functionality and methods presented herein are applicable to any of a wide variety of communication systems including those particularly depicted and described below. Generally speaking, any signal received from a communication channel may be processing using carrier detect functionality and methods presented herein.  
         [0153]      FIG. 12  is a diagram illustrating another embodiment  1200  of a match filter function as a function of samples. This embodiment is somewhat analogous to the embodiment  11  of the  FIG. 11 , with a difference being that the embodiment  1200  depicts m peaks and m-1 valleys of a match filter function as a function of samples.  
         [0154]     The embodiment  11  of the  FIG. 11  shows two consecutive peaks, and the embodiment  12  of the  FIG. 12  generally shows how a match filter function as a function of samples can have m peaks and m-1 valleys. If desired, a designer could select any number of peaks to be detected and processed. Each of these peaks could have its own particular thresholds to meet to satisfy as being a “peak” in the detection process. If desired, analogous parameters (as discussed within the  FIG. 11  above) could be employed such as:  
         [0155]     (1) ρ MF   2 (n Pm ), the match filter function corresponding to the sample, n Pm , that corresponds to the m th  peak;  
         [0156]     (2) the actual difference between the 1 st  peak (2 nd  peak, and/or (m-1) th  peak) and the m th  peak;  
         [0157]     (3) the difference between the 1 st  peak (2 nd  peak, and/or (m- 1 ) th  peak) and the match filter function at an expected location of a m th  peak; and  
         [0158]     (4) the time period difference between the 1 st  peak (2 nd  peak, and/or (m-1) th  peak) and an expected location of the m th  peak (this may easily be expressed as a function of samples as well).  
         [0159]     Other parameters could be employed as well when employing an embodiment that operates using more than merely 2 detected peaks. For example, this could include the detection of the total number of peaks and/or valleys of the match filter function. If desired, some additional function of the peak and/or valley totals could be employed (e.g., a certain number of peaks needs to be identified, a certain number of valleys needs to be identified, etc.).  
         [0160]     A designer is provide a wide latitude of how to implement the detection processing using the match filter function. For example, in one instance, if more time is available and/or allowed in a preamble to perform carrier detection, then an absolute peak detection threshold (i.e., the criterion used to affirm an actually detected peak in the match filter function) can be lowered when combined with some other functionality such as requiring 3 or more peaks to be detected besides only 2. For example, the total number of peaks that must be detected can be modified as desired (i.e., requiring 3 or generally, X, versus only 2).  
         [0161]      FIG. 13A  is a diagram illustrating an embodiment of a single-input-single-output (SISO) communication system  1301 . A transmitter (TX  1311 ) having a single transmit antenna communicates with a receiver (RX  1321 ) having a single receive antenna.  
         [0162]      FIG. 13B  is a diagram illustrating an embodiment of a multiple-input-multiple-output (MIMO) communication system  1302 . A transmitter (TX  1312 ) having multiple transmit antennae communicates with a receiver (RX  1322 ) 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  1322 , a first antenna receives A′+B′ and a second antenna receives A″+B″. The RX  1322  includes the appropriate functionality to perform the extraction and generation of a signal that is a best estimate of the transmitted signal A+B.  
         [0163]      FIG. 13C  is a diagram illustrating an embodiment of a multiple-input-single-output (MISO) communication system  1303 . A transmitter (TX  1313 ) having multiple transmit antennae communicates with a receiver (RX  1323 ) having a single receive antenna.  
         [0164]      FIG. 13D  is a diagram illustrating an embodiment of a single-input-multiple-output (SIMO) communication system  1304 . A transmitter (TX  1314 ) having a single transmit antenna communicates with a receiver (RX  1324 ) having multiple receive antennae. A SIMO communication system may be viewed as being the opposite of a MISO embodiment.  
         [0165]     Within communication devices that receive and process multiple signals (e.g., SIMO and MIMO), the carrier detection functionality and methods described herein may be performed for each of the receive paths within such a communication device. These carrier detect signals may then be provided to a combination block that is operable to generate a final carrier detect signal that considers each of the carrier detect signals provided from each of the receive paths. Such a combination block may certainly also receive other inputs that assist in and govern the processing to generate the final carrier detect signal.  
         [0166]     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.