Carrier detection applicable for SISO, MIMO, MISO, and SIMO communications

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 (SISO), 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 determining 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).

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention relates generally to communication systems; and, more particularly, it relates to performing carrier detection within such communication systems.

2. Description of Related Art

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 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.

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

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a diagram illustrating a communication system10that includes a plurality of base stations and/or access points12,16, a plurality of wireless communication devices18-32and a network hardware component34. Note that the network hardware34, which may be a router, switch, bridge, modem, system controller, et cetera provides a wide area network connection42for the communication system10. Further note that the wireless communication devices18-32may be laptop host computers18and26, personal digital assistant hosts20and30, personal computer hosts24and32and/or cellular telephone hosts22and28. The details of the wireless communication devices will be described in greater detail with reference toFIG. 2.

Wireless communication devices22,23, and24are located within an independent basic service set (IBSS) area and communicate directly (i.e., point to point). In this configuration, these devices22,23, and24may only communicate with each other. To communicate with other wireless communication devices within the system10or to communicate outside of the system10, the devices22,23, and/or24need to affiliate with one of the base stations or access points12or16.

The base stations or access points12,16are located within basic service set (BSS) areas11and13, respectively, and are operably coupled to the network hardware34via local area network connections36,38. Such a connection provides the base station or access point1216with connectivity to other devices within the system10and provides connectivity to other networks via the WAN connection42. To communicate with the wireless communication devices within its BSS11or13, each of the base stations or access points12-16has an associated antenna or antenna array. For instance, base station or access point12wirelessly communicates with wireless communication devices18and20while base station or access point16wirelessly communicates with wireless communication devices26-32. Typically, the wireless communication devices register with a particular base station or access point12,16to receive services from the communication system10.

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. 2is a diagram illustrating a wireless communication device200that includes the host device18-32and an associated radio60. For cellular telephone hosts, the radio60is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio60may be built-in or an externally coupled component.

As illustrated, the host device18-32includes a processing module50, memory52, a radio interface54, an input interface58, and an output interface56. The processing module50and memory52execute the corresponding instructions that are typically done by the host device. For example, for a cellular telephone host device, the processing module50performs the corresponding communication functions in accordance with a particular cellular telephone standard.

Radio60includes a host interface62, digital receiver processing module64, an analog-to-digital converter66, a high pass and low pass filter module68, an IF mixing down conversion stage70, a receiver filter71, a low noise amplifier72, a transmitter/receiver switch73, a local oscillation module74, memory75, a digital transmitter processing module76, a digital-to-analog converter78, a filtering/gain module80, an IF mixing up conversion stage82, a power amplifier84, a transmitter filter module85, a channel bandwidth adjust module87, and an antenna86.

It is noted that one or both of the high pass and low pass filter module68and the low noise amplifier72can operate to perform any desired gain and/or attenuation of the inbound RF signal88(i.e., using the low noise amplifier72) or the down-converted version thereof (i.e., using the high pass and low pass filter module68), as indicated by the reference numeral99. A packet gain signal can be provided from one or both of the high pass and low pass filter module68and the low noise amplifier72to 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 antenna86may be a single antenna that is shared by the transmit and receive paths as regulated by the Tx/Rx switch73, 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 device200is compliant.

The digital receiver processing module64and the digital transmitter processing module76, in combination with operational instructions stored in memory75, 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 modules64and76may 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 memory75may 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 module64and/or76implements 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 radio60receives outbound data94from the host device via the host interface62. The host interface62routes the outbound data94to the digital transmitter processing module76, which processes the outbound data94in accordance with a particular wireless communication standard (e.g., IEEE 802.11, Bluetooth, et cetera) to produce outbound baseband signals96. The outbound baseband signals96will 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 converter78converts the outbound baseband signals96from the digital domain to the analog domain. The filtering/gain module80filters and/or adjusts the gain of the analog signals prior to providing it to the IF mixing stage82. The IF mixing stage82converts the analog baseband or low IF signals into RF signals based on a transmitter local oscillation83provided by local oscillation module74. The power amplifier84amplifies the RF signals to produce outbound RF signals98, which are filtered by the transmitter filter module85. The antenna86transmits the outbound RF signals98to a targeted device such as a base station, an access point and/or another wireless communication device200.

The radio60also receives inbound RF signals88via the antenna86, which were transmitted by a base station, an access point, or another wireless communication device. The antenna86provides the inbound RF signals88to the receiver filter module71via the Tx/Rx switch73, where the Rx filter71bandpass filters the inbound RF signals88. The Rx filter71provides the filtered RF signals to low noise amplifier72, which amplifies the signals88to produce an amplified inbound RF signals. The low noise amplifier72provides the amplified inbound RF signals to the IF mixing module70, which directly converts the amplified inbound RF signals into an inbound low IF signals or baseband signals based on a receiver local oscillation81provided by local oscillation module74. The down conversion module70provides the inbound low IF signals or baseband signals to the filtering/gain module68. The high pass and low pass filter module68filters, based on settings provided by the channel bandwidth adjust module87, the inbound low IF signals or the inbound baseband signals to produce filtered inbound signals.

The analog-to-digital converter66converts the filtered inbound signals from the analog domain to the digital domain to produce inbound baseband signals90, where the inbound baseband signals90will 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 module64, based on settings provided by the channel bandwidth adjust module87, decodes, descrambles, demaps, and/or demodulates the inbound baseband signals90to recapture inbound data92in accordance with the particular wireless communication standard being implemented by radio60. The host interface62provides the recaptured inbound data92to the host device18-32via the radio interface54.

As one of average skill in the art will appreciate, the wireless communication device200ofFIG. 2may be implemented using one or more integrated circuits. For example, the host device may be implemented on one integrated circuit, the digital receiver processing module64, the digital transmitter processing module76and memory75may be implemented on a second integrated circuit, and the remaining components of the radio60, less the antenna86, may be implemented on a third integrated circuit. As an alternate example, the radio60may be implemented on a single integrated circuit. As yet another example, the processing module50of the host device and the digital receiver and transmitter processing modules64and76may be a common processing device implemented on a single integrated circuit. Further, the memory52and memory75may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module50and the digital receiver and transmitter processing module64and76.

FIG. 3is a diagram illustrating a wireless communication device300that includes the host device18-32and an associated radio60. For cellular telephone hosts, the radio60is a built-in component. For personal digital assistants hosts, laptop hosts, and/or personal computer hosts, the radio60may be built-in or an externally coupled component.

As illustrated, the host device18-32includes a processing module50, memory52, radio interface54, input interface58and output interface56. The processing module50and memory52execute the corresponding instructions that are typically done by the host device. For example, for a cellular telephone host device, the processing module50performs the corresponding communication functions in accordance with a particular cellular telephone standard.

Radio60includes a host interface62, a baseband processing module100, memory65, a plurality of radio frequency (RF) transmitters106-110, a transmit/receive (T/R) module114, a plurality of antennas81-85, a plurality of RF receivers118-120, a channel bandwidth adjust module87, and a local oscillation module74. The baseband processing module100, in combination with operational instructions stored in memory65, 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 modules100may 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 memory65may 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 module100implements 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 radio60receives outbound data94from the host device via the host interface62. The baseband processing module64receives the outbound data88and, based on a mode selection signal102, produces one or more outbound symbol streams90. The mode selection signal102will 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 signal102may 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 signal102may 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 signal102may also indicate a particular channelization for the corresponding mode that provides a channel number and corresponding center frequency. The mode select signal102may further indicate a power spectral density mask value and a number of antennas to be initially used for a MIMO communication.

The baseband processing module100, based on the mode selection signal102produces one or more outbound symbol streams104from the outbound data94. For example, if the mode selection signal102indicates that a single transmit antenna is being utilized for the particular mode that has been selected, the baseband processing module100will produce a single outbound symbol stream104. Alternatively, if the mode select signal102indicates 2, 3 or 4 antennas, the baseband processing module100will produce 2, 3 or 4 outbound symbol streams104from the outbound data94.

Depending on the number of outbound streams104produced by the baseband module10, a corresponding number of the RF transmitters106-110will be enabled to convert the outbound symbol streams104into outbound RF signals112. In general, each of the RF transmitters106-110includes 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 transmitters106-110provide the outbound RF signals112to the transmit/receive module114, which provides each outbound RF signal to a corresponding antenna81-85.

When the radio60is in the receive mode, the transmit/receive module114receives one or more inbound RF signals116via the antennas81-85and provides them to one or more RF receivers118-122. The RF receiver118-122, based on settings provided by the channel bandwidth adjust module87, converts the inbound RF signals116into a corresponding number of inbound symbol streams124. The number of inbound symbol streams124will correspond to the particular mode in which the data was received. The baseband processing module100converts the inbound symbol streams124into inbound data92, which is provided to the host device18-32via the host interface62.

As one of average skill in the art will appreciate, the wireless communication device300ofFIG. 3may be implemented using one or more integrated circuits. For example, the host device may be implemented on one integrated circuit, the baseband processing module100and memory65may be implemented on a second integrated circuit, and the remaining components of the radio60, less the antennas81-85, may be implemented on a third integrated circuit. As an alternate example, the radio60may be implemented on a single integrated circuit. As yet another example, the processing module50of the host device and the baseband processing module100may be a common processing device implemented on a single integrated circuit. Further, the memory52and memory65may be implemented on a single integrated circuit and/or on the same integrated circuit as the common processing modules of processing module50and the baseband processing module100.

FIG. 4is a diagram of feedback control400within a communication device. Initially, a plurality of signals, indicated by reference numeral410, 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 control400may 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 control400, a carrier detection module469is operable to perform carrier detection in accordance with any one of the various embodiments or equivalents described herein. Also, within this feedback control400, a coarse/fine frequency estimation module440is 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 input420.

Also within this feedback control400, cyclic prefix (CP) removal of this incoming signal streams may be performed as shown by the CP removal modules421-422; the operation of these CP modules421-422is also governed by PHY control, as indicated by PhySM control input420. The CP removal functionality is based on an advance/retard signal445provided from a compute SFO (Sampling Frequency Offset) correction module444that operates using inputs received from a carrier PLL (Phase Locked Loop)446and the coarse/fine frequency estimation module440.

Thereafter, predictive time-domain (TD) PLL correction is computed using a plurality of TD correction modules423-424(based on signals received from the carrier PLL446that correspond to a previous plurality of received symbols (e.g., previous N-1stsymbol in one embodiment)). These outputs from the TD correction modules423-424are then passed to a plurality of FFT (Fast Fourier Transform) modules425-426. These FFT modules425-426operate to transform the signal processing from the time domain (T-dom) to the frequency domain (F-dom). An equalize module430is operable to perform equalization on the signals received from the FFT modules425-426. The equalize module430may be viewed as performing essentially a channel inversion operation on the signals received from the FFT modules425-426in 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 module430may be viewed as performed a 1stpass 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 modules431-432that is operable to apply predictive SFO correction that has been computed using a previous plurality of symbols (e.g., previous n-1stsymbol in one embodiment) while also considering common phase error (CPE) correction values. The CPE_SFO correction modules431-432receive input signals from both the compute SFO correction module444as well as the carrier PLL446. 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 modules431-432are then provide to a plurality of symbol demap modules433-434that 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 module450is operable to compute the CPE correction values. These CPE correction values are then filtered by the carrier PLL446before being provided to the CPE_SFO correction modules431-432. A compute TD correction module442then computes the TD PLL correction from the current symbol (e.g., the nthsymbol) for use with respect to the next symbol (e.g., n+1stsymbol). The compute SFO correction module444then computes the SFO correction from the current symbol (e.g., the nth symbol) for use with respect to the next symbol (e.g., n+1stsymbol). The equalize module430is then also adjusted using the SFO correction values that have been calculated using the compute metrics module450.

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 nthsymbol). 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 modules433-434is then operable to perform the appropriate symbol demapping of each of the symbols again. After this step, an LMS channel update module452is then operable to compute the LMS (Least Means Square) channel update error terms for use by the next symbol (e.g., n+1stsymbol). The LMS channel update module452then is operable to provide updated channel information to a channel estimate module454for processing the next symbol (e.g., n+1stsymbol).

The compute metrics module450is operable to perform a variety of functions. The compute metrics module450is operable to compute the angular phase error, θ(est) or {circumflex over (θ)}, between the outputs of the equalize module430and the expected constellation points of the expected modulation (having the expected constellation shape and corresponding mapping). This is employed by the carrier PLL446for CFO/SFO tracking by each of the corresponding appropriate modules.

The compute metrics module450is also operable to compute the error, ΔHk, between a received vector and an expected vector based on an expected constellation point. This is employed by the LMS channel update module452.

The compute metrics module450is 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 802.11 n.

The compute metrics module also receives the appropriate 1 or more coefficients are received as shown by reference numeral449that 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 numeral449, that operates by receiving coefficients from a demod_coefcalc module.

It is noted that the feedback control400within 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. 5is a diagram illustrating an embodiment of an OFDM (Orthogonal Frequency Division Multiplexing) packet500that may be processed.

The OFDM packet500may be viewed as including a preamble portion502and a data portion504. The leftmost portion of the OFDM packet500is the demarcation of the start of packet (SOP) and the rightmost portion of the OFDM packet500is the demarcation of the end-of-packet (EOP). The preamble portion502of the OFDM packet500is relatively short in time compared to the overall packet length of the OFDM packet500, 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 packet500needs to be kept small.

The preamble portion502may 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 portion502may 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 portion502. The particular arrangement of the preamble portion502within 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 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 packet500may be viewed as including more than 1 OFDM symbol. For example, the STS of the preamble portion502of the OFDM packet500may include a plurality of OFDM symbols, shown as S1, S2, S3, . . . , Sm. 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 S2includes sample511, sample512, and . . . , sample519. 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.

FIG. 6is a diagram illustrating an embodiment of functionality600operable to perform carrier detection. This embodiment shows a very generic embodiment by which a carrier detect module610may be implemented. In some desired embodiments, the carrier detect module610may be implemented within a baseband processing module601. This baseband processing module601may be the baseband processing module100shown above within other embodiments, or the baseband processing module601may include different functionality and capabilities as the baseband processing module100shown above.

The carrier detect module610is operable to receive samples of at least two symbols of an STS of an OFDM packet, as indicated by the reference numeral605. The carrier detect module610includes an auto-correlation detection module620and a match filter detection module630. In some instances, the match filter detection module630also includes an auto-correlation detection module635that is distinct from the auto-correlation detection module620, in that, the auto-correlation detection module635operates using a relaxed set of parameters when compared to the parameters employed by the an auto-correlation detection module620. Operating cooperatively, the auto-correlation detection module620and the match filter detection module630operate on the samples of at least two symbols of an OFDM packet to generate a carrier detect signal615. This carrier detect signal615then indicates carrier detect or not (i.e., a carrier signal has been sensed and detected or no carrier signal has been sensed and detected).

FIG. 7is a diagram illustrating another embodiment of functionality700operable 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 embodiment700could 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 embodiment700were replicated (one for each received signal stream), then each embodiment700would provide a carrier detect signal for that particular received signal stream, and the results of all of the embodiments700(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.

In some desired embodiments, a carrier detect module710may be implemented within a baseband processing module701. This baseband processing module701may be the baseband processing module100shown above within other embodiments, or the baseband processing module701may include different functionality and capabilities as the baseband processing module100shown above.

Similar to the embodiment described just above, the carrier detect module710is operable to receive samples of at least two symbols of an STS of an OFDM packet, as indicated by the reference numeral705. In this embodiment, the carrier detect module710includes a 1stauto-correlation detection module720, a match filter detection module730, and a 2ndauto-correlation detection module740. The 1stauto-correlation detection module720is operable to process the samples of at least 2 symbols of an OFDM packet to generate a first carrier detect signal, and the 2ndauto-correlation detection module740is 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 module730is 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 module730is operable to generate a match filter detection signal.

The carrier detect module710also 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 gate711. In some alternative embodiments, the first logical AND gate711may be replaced by a logical OR gate.

The output of this first logical AND gate711is provided to a second logical AND gate712that also receives the first carrier detect signal. The output of this second logical AND gate712is a carrier detect signal715that 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 another possible embodiment, the match filter detection signal and the second carrier detect signal are provided to the first logical AND gate711. The output of this first logical AND gate711is provided to a logical OR gate713that also receives the first carrier detect signal. The output of this logical OR gate713is a carrier detect signal716that 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 gate711or the first carrier detect signal output from the 1stauto-correlation detection module720is sufficient to direct the carrier detect signal716to indicate carrier detect or not.

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.

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.

FIG. 8is a diagram illustrating an embodiment of functionality800operable to support auto-correlation detection processing. Modified correlation function calculation820is performed when operating on the samples of two moving windows of an OFDM packet (e.g., as indicated by samples of moving window (S1)801and samples of moving window (S2)802, respectively) that are processed and received after undergoing receive filtering and down sampling, as indicated by reference numeral810. 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.

This modified correlation function calculation820differs 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 1801and the samples of window 2802.

A strict auto-correlation function calculation, ρcorrof using the samples of moving window (S1)801and samples of moving window (S2)802, would be performed as follows:

E└S1, S2*┘ is the expected value when considering the samples of moving window (S1)801and samples of moving window (S2)802;

mS1is the mean value of the samples of moving window (S1)801;

mS2is the mean value of the samples of moving window (s2)802;

PS1the power of the samples of moving window (S1)801; and

PS2is the power of the samples of moving window (S2)802.

It is noted that E└S1, S2*┘ is calculated as a function of each of the samples of moving window (S1)801and the samples of moving window (S2)802. For example, assuming the samples of S1includes n samples as x1, x2, . . . , xn, and the samples of S2includes n samples as y1, y2, . . . , ynthen the term, E└S1, S2*┘, is calculated as follows:

For comparison, the covariance function calculation, ρcov, of using the samples of moving window (S1)801and the samples of moving window (S2)802, would be performed as follows:

σS1is the standard deviation of the noise of the samples of moving window (S1)801; and

σS2is the standard deviation of the noise of the samples of moving window (S2)802.

However, the modified correlation function calculation820(which is performed for every sample of each of the moving windows as depicted using, S1and S2) is instead calculated as follows:

ρmod_corr=E⁡[S1,S2*]-mS1·mS2PS1·PS2,
or alternatively after being squared as follows:

As can be seen, the modified correlation function calculation820is normalized with respect to the power of each of the samples of moving window (S1)801and samples of moving window (S2)802. This generally results in a smaller value than would either of the strict auto-correlation function calculation, ρcorror the covariance function calculation, ρcorr, 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 (S1)801and samples of moving window (S2)802, 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 block850. Typically, when the samples of moving window (S1)801and samples of moving window (S2)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.

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.

Also, this embodiments shows how the power of each of the samples of moving window (S1)801and samples of moving window (S2)802, undergoes power comparison. Specifically, the power of the samples of moving window (S1)801, is compared to a 1stpower threshold as shown in a block830; this comparison of the power of the symbol, S1, is with respect to a 1stpower threshold. The power of the samples of moving window (S2)802, is compared to a 2ndpower threshold as shown in a block840; this comparison of the power of samples of moving window (S2)802, is with respect to a 2ndpower threshold.

The outputs of each of these blocks850,830, and840are provided to a combining module860. The combining module860may be viewed as performing the processing of each of the comparisons being performed in the blocks850,830, and840to determine whether or not a carrier detect signal816indicates that a carrier signal has in fact been detected or not.

In one possible embodiment, the carrier detect signal816indicates 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 signal816does in fact indicate carrier detect, and when at least one of these conditions is not met, then the carrier detect signal816does not indicate carrier detect.

FIG. 9is a diagram illustrating an embodiment of functionality900operable to support match filter detection processing. Initially, a plurality of signals, indicated by reference numeral910, 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.

Match filter function calculation920is performed when operating on the samples of successive different symbols of an OFDM packet (e.g., S1and S2, as indicated by reference numerals901and902, respectively).

The match filter function calculation920is performed using the samples of each of the symbols, S1and S2, 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 nthsample of each of the symbols, S1and S2, is processed within the corresponding sample, Sknown*(−n), of the predetermined/known symbol. The received symbol, S1, is then correlated with a predetermined/known sequence (e.g., the predetermined/known symbol, Sknown) thereby generating a match filter function, ρMF. This match filter function calculation920to generate the match filter function, ρMFis 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, ρMF, may be calculated as follows:

MF_out is the match filter output signal generated using one of the received symbols (e.g., S1) and the predetermined/known symbol, Sknown;

mS1is the mean value of the symbol, S1;

mSknownis the mean value of the predetermined/known symbol, Sknown;

PS1is the power of the symbol, S1; and

PSknownis the power of the predetermined/known symbol, Sknown.

However, by the very design and definition of the predetermined/known symbol, Sknown, and the design of the STS of an OFDM packet as described herein, the value of mSknownis zero (i.e., mSknown=0). Therefore, the match filter function, ρMF, may be calculated as follows:

ρMF=MF_outPS1·PSknown,
or alternatively after being squared as follows:

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 block950.

For example, as shown in a block951, the match filter function analysis950is operable to perform 1stpeak identification within the match filter function as shown in a block951. This is performed using a 1stmatch filter function threshold (e.g., ThMF1). Analogously, the match filter function analysis950is operable to perform 2ndpeak identification within the match filter function as shown in a block952. This may be performed using a 2ndmatch filter function threshold (e.g., ThMF2).

Also, as shown in a block953, the match filter function analysis950is operable to determine the relative difference of magnitude between the 1stpeak of the match filter function and the match filter function at an expected location of a 2ndpeak (e.g., ΔP1+Δt−P1). This may be performed to determine whether the 1stpeak and the 2ndpeak are of approximately similar magnitude. This is also determined as a function of the periodicity between the 1stpeak and the 2ndpeak. For example, this may be calculated as a function of a difference threshold (which may be represented as Thdiff) that may be selected by a designer.
ΔP1+Δt−P1=|ρMF2(nP1{tilde over (+)}Δt)−ρMF2(nP1)|<Thdiff,
where:

ρMF2(nP1) is the match filter function corresponding to the sample, nP1, that corresponds to the 1stpeak;

ρMF2(nP1{tilde over (+)}Δt) is the match filter function corresponding being a predetermined period of time away from the sample, nP1, associated with the 1stpeak; this generally will correspond to the location of the that corresponds to the 2ndpeak that is spaced an approximate period of time (e.g., Δt) from the 1stpeak (this term Δt may be predetermined in some embodiments, e.g., a particular period of time such as 0.8 μsec); and

Thdiffis the designer selected threshold employed to compare this function's difference.

Alternatively, an actual difference, ΔP1−P2, between the 1stpeak and the actual 2ndpeak can be calculated directly as follows:
ΔP1−P2=|ρMF2(nP2)−ρMF2(nP1)|<Thdiff,
where:

ρMF2(nP1) is the match filter function corresponding to the sample, nP1, that corresponds to the 1stpeak;

ρMF2(nP2) is the match filter function corresponding to the sample, npP2, that corresponds to the 2ndpeak; and

Thdiffis the designer selected threshold employed to compare this function's difference.

Also, as shown in a block954, the match filter function analysis950is operable to determine whether match filter function falls below 3rdmatch filter function threshold between 1stand 2ndpeak of the match filter function.

This 3rdmatch filter function threshold may be represented as Thfall, and this operation in the block954may be expressed mathematically as follows:
ρMF2(nP1)−ρMF2(nv)>Thfall,
where:

ρMF2(nP1) is the match filter function corresponding to the sample, nP1, that corresponds to the 1stpeak;

ρMF2(nv1) is the match filter function corresponding to the sample, nv1, that corresponds to a particular distance (e.g. in terms of samples) along the match filter function from the 1stpeak (this sample, nv1, and its distance from the sample, nP1, may be predetermined and/or selected by a designer); and

Thfallis the designer selected threshold employed to compare this difference.

Then, as shown in a block955, the match filter function analysis950is operable to identify a predetermined number of peaks of match filter function after 1stpeak and 2ndpeak. 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.

Also, this embodiments shows how the power of each of the symbols, S1and S2, undergoes power comparison. Specifically, the power of the symbol, S1, is compared to a 1stpower threshold as shown in a block930; this comparison of the power of the symbol, S1, is with respect to a 1stpower threshold. The power of the symbol, S2, is compared to a 2ndpower threshold as shown in a block940; this comparison of the power of the symbol, S2, is with respect to a 2ndpower threshold.

The outputs of each of these blocks950,930, and940are provided to a combining module960. The combining module960may be viewed as performing the processing of each of the comparisons being performed in the blocks950,930, and940to determine whether or not the symbols, S1and S2, in fact comport sufficiently with the predetermined/known symbol as indicated by a match filter detection signal916. The match filter detection signal916indicates whether each of the symbols, S1and S2, sufficiently corresponds to the predetermined/known symbol.

In one possible embodiment, the match filter detection signal916indicates 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.

Also, as indicated by the dotted lines, this functionality900may be implemented to process only one symbol (shown as S1) at a time. If desired, to provide for some efficiency between the functionality800and the functionality900, the samples of each of the symbols, S1and S2, may be provided simultaneously to borrow on certain of the parallel type processing. For example, each of the functionality800and the functionality900perform power threshold comparison.

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 functionality800of theFIG. 8and the functionality900of theFIG. 9. A designer is provided significant freedom and latitude to select the particular thresholds employed herein.

It is also noted that any embodiment that employs multiple auto-correlation modules (e.g., the functionality700of theFIG. 7), different sets of parameters may be employed for each of those auto-correlation modules. For example, a 1stauto-correlation module may employ a 1stplurality of parameters such that its decision-making criteria is more stringent than a 2ndauto-correlation module that employs a 2ndplurality 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.

FIG. 10is a diagram illustrating an embodiment of functionality1000operable to combining carrier detect signals from multiple streams into a single carrier detect signal1010(e.g., a final carrier detect signal). As can be seen, multiple carrier detect signals are provided to a combining module1060. Each of these carrier detect signals can be viewed as corresponding to a stream. For example, a carrier detect signal1001corresponds to a stream1, a carrier detect signal1002corresponds to a stream2, and a carrier detect signal1003corresponds to a stream3. Generally speaking, carrier detect signals corresponding to n streams can be received by the combining module1060, as shown by a carrier detect signal1009corresponds to a stream n. Any number of streams (i.e., as few as 2 streams) can be employed.

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 ofFIG. 6,FIG. 7, and/orFIG. 8.

The combining module1060can employ any desired means of performing combining of the multiple carrier detect signals into a carrier detect signal1010. In some embodiments, logic circuitry (which can include 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.

FIG. 11is a diagram illustrating an embodiment1100of a match filter function as a function of samples. This embodiment1100may assist the reader in identifying the various portions of the match filter function with respect to the functionality900of theFIG. 9that supports match filter detection processing.

When processing the samples of successive symbols (e.g., S1and S2) within the STS of an OFDM packet as compared to the samples of a predetermined/known symbol, Sknown, the match filter function, ρMF2(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., S1and S2) as a function of the correlation (as determined by the match filter detection processing).

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:

ρMF2(nP1) is the match filter function corresponding to the sample, nP1, that corresponds to the 1stpeak;

ρMF2(nP2) is the match filter function corresponding to the sample, nP2, that corresponds to the 2ndpeak;

ρMF2(nv1) is the match filter function corresponding to the sample, nv1, that corresponds to a particular distance (e.g. in terms of samples) along the match filter function from the 1stpeak (this sample, nv1, and its distance from the sample, nP1, may be predetermined and/or selected by a designer);

ΔP1−P2is the actual difference between the 1stpeak and the 2ndpeak;

ΔP1+Δt−P2is the difference between the 1stpeak and the match filter function at an expected location of a 2ndpeak; and

Δt is the time period difference between the 1stpeak and an expected location of the 2ndpeak (this may easily be expressed as a function of samples as well).

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.

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.

FIG. 12is a diagram illustrating another embodiment1200of a match filter function as a function of samples. This embodiment is somewhat analogous to the embodiment11of theFIG. 11, with a difference being that the embodiment1200depicts m peaks and m-1 valleys of a match filter function as a function of samples.

The embodiment11of theFIG. 11shows two consecutive peaks, and the embodiment12of theFIG. 12generally 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 theFIG. 11above) could be employed such as:

(1) ρMF2(nPm), the match filter function corresponding to the sample, nPm, that corresponds to the mthpeak;

(2) the actual difference between the 1stpeak (2ndpeak, and/or (m-1)thpeak) and the mthpeak;

(3) the difference between the 1stpeak (2ndpeak, and/or (m-1)thpeak) and the match filter function at an expected location of a mthpeak; and

(4) the time period difference between the 1stpeak (2ndpeak, and/or (m-1)thpeak) and an expected location of the mthpeak (this may easily be expressed as a function of samples as well).

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.).

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).

FIG. 13Ais a diagram illustrating an embodiment of a single-input-single-output (SISO) communication system1301. A transmitter (TX1311) having a single transmit antenna communicates with a receiver (RX1321) having a single receive antenna.

FIG. 13Bis a diagram illustrating an embodiment of a multiple-input-multiple-output (MIMO) communication system1302. A transmitter (TX1312) having multiple transmit antennae communicates with a receiver (RX1322) 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 RX1322, a first antenna receives A′+B′ and a second antenna receives A″+B″. The RX1322includes the appropriate functionality to perform the extraction and generation of a signal that is a best estimate of the transmitted signal A+B.

FIG. 13Cis a diagram illustrating an embodiment of a multiple-input-single-output (MISO) communication system1303. A transmitter (TX1313) having multiple transmit antennae communicates with a receiver (RX1323) having a single receive antenna.

FIG. 13Dis a diagram illustrating an embodiment of a single-input-multiple-output (SIMO) communication system1304. A transmitter (TX1314) having a single transmit antenna communicates with a receiver (RX1324) having multiple receive antennae. A SIMO communication system may be viewed as being the opposite of a MISO embodiment.

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.

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.