HK1071482A

HK1071482A - Single-carrier to multi-carrier wireless architecture

Info

Publication number: HK1071482A
Application number: HK05104010.3A
Authority: HK
Inventors: 马克．A．韦伯斯特; 迈克尔．J．斯尔斯
Original assignee: 英特塞尔美国公司
Priority date: 2001-09-26
Filing date: 2002-09-25
Publication date: 2005-07-15

Description

Single carrier to multi-carrier wireless architecture

Technical Field

The present invention relates to wireless communications, and more particularly, to a wireless communication architecture configured to communicate using a single carrier-multi-carrier mixed waveform structure.

Background

The Institute of Electrical and Electronics Engineers (IEEE)802.11 standard is a family of standards for Wireless Local Area Networks (WLANs) in the 2.4 and 5 gigahertz (GHz) frequency bands that do not require registration. The current 802.11b standard defines different data rates in the 2.4GHz band, including rates of 1, 2, 5.5, and 11 megabits per second (Mbps). The 802.11b standard uses Direct Sequence Spread Spectrum (DSSS) at a chip rate of 11 megahertz (MHz), which is a serial modulation technique. The 802.11a standard defines different and higher data rates of 6, 12, 18, 24, 36 and 54Mbps in the 5GHz band. It should be noted that systems implemented in accordance with the 802.11a and 802.11b standards are incompatible and cannot work together.

A new standard, named 802.11g ("802.11 g recommendation"), is currently being proposed, which is a high data rate extension of the 802.11b standard at 2.4 GHz. It should be noted that the current 802.11g proposal is only a proposal, and it is not yet a fully defined standard. Several significant technical challenges have been presented to date for the new 802.11g proposal. It is desirable to enable 802.11g devices to communicate using higher data rates than standard 802.11b in the 2.4GHz band. What is desired to be accomplished in some configurations is that 802.11b and 802.11g devices can coexist in the same WLAN environment or wireless area without seriously interfering or interrupting each other, regardless of whether they can communicate with each other. It is therefore desirable that 802.11 be backward compatible with 802.11b devices. It is also desirable that 802.11g and 802.11b devices communicate with each other at, for example, the 802.11b rate of either standard.

The impairment to wireless communications, including WLANs, where multiple echoes (reflections) of a signal arrive at a receiver, is multipath distortion. Both single-carrier and multi-carrier systems must include equalizers designed to combat this distortion. The equalizer of a single carrier system is designed based on its preamble and header. Such as different and incompatible wireless signal types, such other types of interference may cause problems with WLAN communications. For example, the bluetooth standard defines an inexpensive short range frequency hopping WLAN. For 802.11 based systems, systems implemented according to the bluetooth standard present a significant source of noise. The preamble is very important for good receiver acquisition. Thus, in the presence of multipath distortion or other types of interference, it is not desirable to lose all of the information when transitioning from single carrier to multi-carrier.

There are several potential problems associated with signal transformation, particularly legacy equipment. The transmitter may experience analog transients (e.g., power, phase, filter delta), power amplifier back-off (e.g., power delta), and power feedback changes for the power amplifier. The receiver may then be subject to Automatic Gain Control (AGC) disturbances due to power variations, spectral variations, multipath effects, Channel Impulse Response (CIR) (multipath) estimation, carrier phase loss, carrier frequency loss, and timing alignment loss.

A Mixed Waveform Configuration for Wireless communications is disclosed in the earlier U.S. provisional patent application serial No. 60/306,438 filed on 7/6/2001, which is incorporated herein by reference in its entirety. The system described in this application reuses equalizer information that is obtained during acquisition of the single-carrier portion of the signal. This technique provides continuity between single-carrier and multi-carrier segments (e.g., orthogonal frequency division multiplexing or OFDM) by fully specifying the transmit waveforms for the single-carrier and multi-carrier segments and specifying the transitions. The waveform allows continuity to be maintained between two signal segments that contain AGC (power), carrier phase, carrier frequency, timing and spectrum (multipath). It is contemplated that it is not necessary to reacquire the signal with the multi-carrier portion of the receiver since the information generated during the duration of the single-carrier portion (preamble/header) is valid and used to begin acquisition of the multi-carrier portion. However, the particular receiver architecture is not discussed.

Described herein is a hybrid carrier transmitter capable of communicating using the proposed hybrid carrier waveform architecture. The term "mixed carrier" is also used herein to refer to a composite signal that is preceded by a single carrier portion and followed by a multi-carrier portion. And the transmitter may be configured to operate in multiple modes of operation, including single carrier, mixed carrier, and multi-carrier. Several receiver architectures are also described that are configured to receive the mixed carrier signal and resolve the combined baseband signals that are combined into the mixed carrier signal.

Disclosure of Invention

A baseband receiver according to one embodiment of the present invention includes: a Channel Impulse Response (CIR) estimation block, gain, phase and timing loops, a Channel Matched Filter (CMF), a single carrier processor and a multi-carrier processor. The CIR estimation section is capable of generating an impulse response signal from a single-carrier segment of the received signal, i.e., a single-carrier signal or a mixed carrier signal, wherein the single-carrier segment has a spectrum that approximates the multi-carrier spectrum. The gain, phase and timing loops adjust the gain, phase, frequency and timing of the received signal to provide an adjusted received signal. The CMF filter filters the adjusted received signal according to the impulse response signal. A single-carrier processor processes the conditioned and filtered received signals to resolve a single-carrier segment of the mixed carrier signal. The single-carrier processor can detect the mixed carrier mode indication in the single-carrier segment and assert a start indication corresponding to an end of the single-carrier segment. The multi-carrier processor can then process the multi-carrier segment of the mixed carrier signal in response to the assertion of the start indication.

In a particular embodiment, a modulation scheme selected from Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) is used to modulate the single-carrier segment, and Orthogonal Frequency Division Multiplexing (OFDM) is used to modulate the multi-carrier segment of the mixed carrier signal.

The baseband receiver may include control logic to select between single carrier, multi-carrier, and mixed carrier modes of operation. In this configuration, the single-carrier processor is configured to process the conditioned and filtered received signal of the single-carrier signal in the single-carrier mode of operation and is configured to process the conditioned and filtered received signal of the mixed carrier signal in the mixed carrier mode of operation. The multi-carrier processor is further configured to process the multi-carrier received signal prior to conditioning and filtering in the mixed carrier mode of operation and to process the multi-carrier segment in the mixed carrier signal in the mixed carrier mode of operation. The multi-carrier processor can operate in a non-coherent mixed carrier mode in which it processes the multi-carrier segment of the received signal prior to conditioning and filtering. In this non-coherent mode, the multicarrier segment may comprise a synchronization field, wherein the multicarrier processor determines the frequency-domain equalizer taps from the synchronization field. The gain, phase and timing loops may produce gain, phase, frequency and timing adjustment parameters, wherein the multicarrier processor is configured to be programmable with a selected combination of the gain, phase, frequency and timing adjustment parameters. The multicarrier processor may also comprise a phase-locked loop with a filter, the phase-locked loop being configured to be programmable using the frequency adjustment parameter. In this case, the multicarrier processor may comprise a timing loop configured to be programmable using the timing adjustment parameter.

In response to detection of the mixed carrier mode indication, the single-carrier processor may assert a freeze (freeze) indication to the gain, phase, and timing loops, wherein the freeze indication aborts operation of the timing, gain, and phase loops at the end of the single-carrier segment of the mixed carrier signal. The baseband receiver may also include a Fast Fourier Transform (FFT) generator and a frequency domain equalizer. The FFT generator converts the impulse response signal into a frequency response signal that is provided to the frequency domain equalizer. Frequency domain is equal toThe equalizer determines a multi-carrier equalized signal based on the frequency response signal. In response to assertion of the start indication, the multicarrier processor uses the multicarrier equalization signal to process the adjusted and filtered received signal multicarrier segment. In one configuration, the multi-carrier processor is coupled to an output of the CMF and the frequency domain equalizer is based on the equation FEQ (ω)_k)＝1/(abs(H(ω_k))²To determine the frequency response based signal H (ω)_k) Multi-carrier equalized signal FEQ (ω)_k) Where "abs" is an absolute value function. In an alternative embodiment, the multi-carrier processor is coupled to an input of the CMF, the single-carrier processor asserts the start indicator one CMF waiting period before the end of the single-carrier segment, and the frequency-domain equalizer is based on the equation FEQ (ω)_k)＝1/H(ω_k) To determine a multi-carrier equalized signal.

The phase loop may include a phase error detector that generates a phase error signal, a phase filter that receives the phase error signal and generates a phase correction signal, and a phase rotator that adjusts the received signal based on the phase correction signal. Once the freeze indication is asserted, the phase correction signal remains constant. Once the freeze indication is asserted to keep the phase correction signal constant, the phase error detector may set the phase error signal to zero. The gain loop may include a gain error detector that generates a gain error signal, an integrator that receives the gain error signal and generates a gain correction signal, and a multiplier that adjusts the received signal based on the gain correction signal. Once the freeze indication is asserted, the gain correction signal remains constant. Once the freeze indication is asserted to keep the gain correction signal constant, the gain error detector may set the gain error signal to zero. The timing loop may include a time tracking component that receives and adjusts the timing of the received signal and discontinues tracking the received signal when the freeze indication is asserted. The baseband multi-carrier processor may comprise a combiner for combining the multi-carrier equalized signal from the frequency domain equalizer with the frequency response signal based on the received multi-carrier signal.

The baseband receiver may include control logic to select between a single carrier, a multi-carrier, and a mixed carrier mode of operation, wherein in the single carrier mode of operation the single carrier processor is configured to process conditioned and filtered received signals in a single carrier signal, in the mixed carrier mode of operation it is configured to process conditioned and filtered received signals in a mixed carrier signal, and wherein in the multi-carrier mode of operation the multi-carrier processor is configured to process multi-carrier received signals prior to conditioning and filtering, and in the mixed carrier mode of operation it is configured to process conditioned and filtered received signals a multi-carrier segment in the mixed carrier signal.

A wireless Radio Frequency (RF) communication device according to one embodiment of the invention includes an RF transceiver, a baseband transmitter, and a baseband receiver. The RF transceiver converts RF signals from the antenna to baseband signals and converts the baseband signals to RF signals for transmission via the antenna. The baseband transmitter is configured to transmit a mixed carrier signal via the RF transceiver by modulating the single-carrier portion using single-carrier modulation and modulating the multi-carrier portion using multi-carrier modulation. The transmitter filters the single-carrier portion to approximate a multi-carrier power spectrum and formulates a mixed carrier signal to maintain frequency, phase, gain, and timing coherence between the single-carrier and multi-carrier portions. The baseband receiver is implemented in a similar manner as described above.

The RF transceiver is capable of multiple band operation, wherein the RF transceiver operates in a first RF band for single carrier and mixed carrier modes, and wherein the RF transceiver operates on a selected one of a plurality of frequency bands including the first and second RF bands for multi-carrier modes. In one particular embodiment, the first RF band is approximately 2.4 gigahertz (GHz) and the second RF band is approximately 5 GHz.

The baseband transmitter may include a single-carrier transmit processor that generates a single-carrier signal, a multi-carrier transmit processor that generates a multi-carrier signal, a digital filter, and a signal combiner. The digital filter filters the single-carrier signal to have a power spectrum similar to the multi-carrier power spectrum. The signal combiner combines the filtered single-carrier signal and the multi-carrier signal while maintaining phase, gain, and timing alignment. The signal combiner may include a phase multiplier, a digital combiner, and a soft switch. The phase multiplier multiplies the multi-carrier signal with the phase of the last part of the single-carrier part and provides a rotated multi-carrier signal. A digital combiner combines the filtered single-carrier signal with the rotated multi-carrier signal and provides a combined mixed carrier signal. The soft switch then selects the filtered single carrier signal before the end, the combined mixed carrier signal during the transition, and the rotated multi-carrier signal at the end of the transition period. The single-carrier signal may comprise consecutive chips according to a predetermined timing interval, wherein the transition period has a duration equivalent to the predetermined timing interval.

A method of generating a mixed carrier packet for RF transmission according to one embodiment of the present invention includes: the method includes generating a multi-carrier payload using a selected multi-carrier modulation scheme, generating a single-carrier segment including a preamble and a header using a single-carrier modulation scheme, filtering the single-carrier segment to have a power spectrum similar to the power spectrum of the multi-carrier modulation scheme, and combining the filtered single-carrier segment with the multi-carrier payload in a manner that preserves gain, phase, frequency, and timing in the transition to provide a carrier packet.

The combining may include rotating the multi-carrier payload by a phase, wherein the phase is determined from the filtered single-carrier segment. The single-carrier modulation scheme may be Barker (Barker) modulation and the multi-carrier modulation may be in accordance with OFDM, wherein the rotating comprises rotating the OFDM multi-carrier payload by a phase of a last Barker word of the filtered single-carrier segment. The multi-carrier payload may include an OFDM preamble. The combining may also include ramping down (ramp) the filtered single carrier segment while ramping up the multi-carrier payload in transition. The filtered single-carrier segment may have a predetermined chip rate, in which case the method may further comprise sampling the filtered single-carrier segment and the multi-carrier payload at a predetermined sampling rate, and declaring a first full sample of the multi-carrier payload one transition period after a last full sample of the filtered single-carrier segment based on the predetermined chip rate of the filtered single-carrier segment. The combining may also include proportionally combining the respective filtered single-carrier segments and the multi-carrier payload to provide a plurality of samples in the transition time. In one configuration, the predetermined sampling rate is four times the predetermined chip rate, in which case the proportional combining in the transition time includes providing first, second, and third intermediate samples for which the percentages of the filtered single-carrier segment to the multi-carrier payload are 75/25, 50/50, and 25/75, respectively.

A method of acquiring a mixed carrier signal of a single carrier segment followed by a multi-carrier segment according to one embodiment of the invention comprises: determining gain, phase, frequency and timing adjustment parameters of a received baseband signal, adjusting the baseband signal using the adjustment parameters to provide an adjusted baseband signal, determining a CIR estimate while receiving a single-carrier segment of the received baseband signal, filtering the adjusted baseband signal based on the CIR estimate to provide a filtered and adjusted baseband signal, processing the filtered and adjusted baseband signal using a single-carrier processor to obtain a single-carrier segment, detecting a mixed carrier mode identifier in the single-carrier segment and asserting a mixed mode indication, and processing the received baseband signal using a multi-carrier processor to obtain a multi-carrier segment in response to the mixed mode indication.

Processing the received baseband signal using the multicarrier processor may include processing the received baseband signal prior to conditioning and filtering. The method also includes determining, using the multicarrier processor, a second channel frequency response estimate from a preamble portion of the multicarrier segment and filtering the multicarrier segment based on the second frequency response estimate. The method may further comprise using any selected combination of gain, phase, frequency and timing adjustment parameters as at least one start-up parameter by means of the multi-carrier processor to obtain the multi-carrier segment.

A method of acquiring a mixed carrier signal of a single carrier segment followed by a multi-carrier segment according to another embodiment of the invention comprises: determining gain, phase, frequency and timing adjustment parameters of a received baseband signal, adjusting the baseband signal using the adjustment parameters to provide an adjusted baseband signal, determining a CIR estimate while receiving a single-carrier segment of the received baseband signal, converting the CIR estimate to a frequency response signal, programming a frequency domain equalizer using the frequency response signal, filtering the adjusted baseband signal based on the CIR estimate to provide a filtered and adjusted baseband signal, processing the filtered and adjusted baseband signal using a single-carrier processor to obtain a single-carrier segment, detecting a mixed carrier mode identifier in the single-carrier segment and asserting a mixed mode indication and a freeze indication, and in response to the freeze indication, maintaining the gain, phase, frequency and timing adjustment parameters of the single-carrier segment, and in response to the CIR estimate, determining a CIR estimate, and in response to the CIR estimate, determining a mixed mode indication, The phase, frequency and timing adjustment parameters are constant, and the filtered and adjusted baseband signal is processed using a multi-carrier processor employing a frequency domain equalizer in response to the mixed mode indication to obtain multi-carrier segments. Determining gain, phase, frequency and timing adjustment parameters may include determining gain, phase, frequency and timing error values. Keeping the gain, phase, frequency and timing adjustment parameters constant may include setting the gain, phase, frequency and timing error values to zero.

Drawings

The invention may be better understood when the following detailed description of preferred embodiments is considered in conjunction with the following drawings, in which:

fig. 1 is a schematic diagram of a mixed signal packet implemented according to an embodiment of the invention.

Fig. 2 is a simplified block diagram of a mixed carrier signal transmitter incorporating a baseband transmitter implemented in accordance with an embodiment of the present invention.

Fig. 3 is a simplified block diagram of one embodiment of the combiner of fig. 2.

Fig. 4A and 4B are graphs of the phase relationship of an exemplary single-carrier modulation scheme using BPSK or QPSK, respectively.

Fig. 5 is a timing diagram depicting the calibration between single carrier and multi-carrier portions using Barker and OFDM signals.

Fig. 6 is a graph depicting exemplary single carrier signal termination and multi-carrier signal start in an overlap period.

Fig. 7 is a block diagram of a mixed carrier signal receiver incorporating a baseband receiver implemented in accordance with an embodiment of the invention.

Fig. 8 is a block diagram of a baseband receiver similar to the baseband receiver of fig. 7 and implemented in accordance with an alternative embodiment of the present invention.

Fig. 9 is a block diagram of an exemplary OFDM embodiment of the core of fig. 7 and 8.

Fig. 10 is a block diagram of a baseband receiver incorporating an implementation in accordance with an alternative and non-coherent embodiment of the present invention.

Detailed Description

A baseband transmitter and receiver architecture according to one embodiment of the invention achieves coherence during single-carrier to multi-carrier transitions by preserving multi-carrier signal gain, phase, frequency, sample timing, and Channel Impulse Response (CIR) of a single-carrier to mixed-carrier signal. In this way, it is not necessary to resort to the multi-carrier portion of the receiver to reacquire the signal, since the information generated during the duration of the single-carrier portion is valid and used to begin acquisition of the multi-carrier portion. Maintaining and accumulating information also makes the signal more robust in the face of the common interference experienced in wireless communications. A baseband receiver architecture according to an alternative embodiment is also described which does not maintain coherence in the conversion, so that the multicarrier part of the receiver has to acquire the signal completely again after the conversion. Also disclosed is another embodiment of a non-coherent receiver that uses selected information derived from the single-carrier portion of the waveform, such as any selected parameter associated with gain, phase, frequency, or timing. Although the non-coherent architecture is less robust than the coherent architecture, this non-coherent option is easier and less expensive to implement while still maintaining sufficient robustness, thereby enabling a communication system suitable for a variety of applications.

The wireless device described herein operates in the 2.4GHz band in either the 802.11b or 802.11g modes, but may also operate in any of several bands (multi-band) in one or more 802.11a modes, such as 2.4GHz, 5GHz, or any other suitable band. These devices may be configured using any suitable format, such as any type of computer (desktop, portable, laptop, etc.), any type of compatible radio communication device, any type of Personal Digital Assistant (PDA), or any other type of network device, such as a printer, facsimile machine, scanner, hub, switch, router, etc. It is noted that although the 802.11g proposal, the 802.11b standard, the 802.11a standard, or the 2.4GHz band may be used in some embodiments, the invention is not limited to these standards and frequencies. Wireless devices may be configured to communicate with each other at any one of the standard 802.11b rates, including 1, 2, 5.5, and 11Mbps, to maintain backward compatibility with 802.11b devices. The wireless device may be further configured for mixed carrier mode operation to enable use of a mixed signal structure according to any of several embodiments to communicate at different or higher data rates, such as 802.11a rates of the standards of 6, 9, 12, 18, 24, 36, 48, or 54 Mbps.

The mixed signal devices can operate and/or coexist in the same wireless operating area as 802.11b devices, but even when operating in mixed signal mode, these devices do not cause significant interference to each other.

Fig. 1 is a schematic diagram of a mixed signal packet 101 performed in accordance with one embodiment of the present invention. Packet 101 includes a single-carrier portion 103 followed by a multi-carrier portion 105. Single-carrier portion 103 is modulated with a single-carrier modulation scheme and multi-carrier portion 105 is modulated with a multi-carrier modulation scheme. In the embodiments described herein, the single-carrier modulation is Quadrature Phase Shift Keying (QPSK) symbol rate or Binary Phase Shift Keying (BPSK), e.g., according to the 802.11b standard, while the multi-carrier modulation is OFDM, e.g., according to the 802.11a standard. It is understood and contemplated that other single carrier and multi-carrier modulation schemes may be used.

In the illustrated embodiment, the single-carrier portion 103 includes a barker preamble 108 followed by a barker header 111. The barker preamble 108 includes a sync field 107 followed by a Sync Field Delimiter (SFD)109, the barker preamble 108 being configured in accordance with 802.11b for barker modulation. The preamble 108 and barker header 111 may be modulated in BPSK or QPSK, and thus may be transmitted at a rate of 1 or 2 megabits per second (Mbps). The long version of the single carrier portion 103 is transmitted in 192 microseconds (mus) while the short version is transmitted in 96 mus. The multi-carrier portion 105 includes a preamble 113, a data field 115, and a SIF pad 117. The data field 115 is transmitted using OFDM modulation at a data rate selected from typical data rates of 6, 9, 12, 18, 24, 36, 48 or 54 Mbps. The SIF pad characters are transmitted in 6 mus.

The preamble 113, which is used to perform synchronization for OFDM modulation, includes a long synchronization field 119 and a signal field 121. The preamble 113 is transmitted in approximately 12 mus. The long synchronization field 119 includes a pair of 0.8 μ s guard intervals 123, 125 and a pair of 3.6 μ s long training symbols 127, 129. It is thus expected that the total duration of the long synchronization field 119 is 8 mus, which is significantly shorter than the short or long version of the single carrier portion 103, which costs at least 96 mus.

Fig. 2 is a simplified block diagram of a mixed carrier signal transmitter 200 including a baseband transmitter 201 implemented in accordance with one embodiment of the present invention. In one embodiment, the transmitter 201 is configured to operate in several modes, including a single carrier mode (e.g., 802.11b), a mixed carrier mode (802.11g), and several multi-carrier modes (e.g., 802.11 a). The multi-carrier mode may use OFDM modulation on any one of several frequency bands, such as the 2.4 or 5GHz bands. The single-carrier processor or kernel 203 introduces kernel processing functionality whereby a single-carrier signal is configured at a selected chip rate, e.g., barker chips at 11 MHz. The output of the core 203 is provided to the input of a 1: 2 splitter 205. The first output 207 of the splitter 205 is then provided to the input of a single-carrier pulse shaping means 209 (digital filter) which outputs a single-carrier packet at a sample rate of 44 MHz. While the output of single-carrier pulse shaping component 209 is provided to a first input 211 of a 3: 1 Multiplexer (MUX)213, the output of which is coupled to an input of a digital-to-analog converter (DAC) 215.

The analog output of DAC215 is mixed with a Radio Frequency (RF) signal and, as known to those skilled in the art, is transmitted in a wireless medium via antenna 204. In the illustrated embodiment, the analog output of DAC215 is provided to RF system 202, which converts the baseband signal to an RF signal that is asserted in the wireless medium via an antenna. Transmitter 200 also includes control logic 206 coupled to RF system 202 and baseband transmitter 201 to control operation and control particular modes of operation. Control logic 206 controls splitter 205 and MUX213 to select those single carrier packets for the single carrier mode and to select multicarrier packets for the multicarrier mode, and to select mixed carrier packets for the mixed carrier mode of operation.

RF system 202 and control logic 206 may also be configured for multi-band operation. RF system 202 may be configured to transmit packets using a selected one of several RF carrier frequencies, including but not limited to the unlicensed 2.4 and 5 gigahertz (GHz) bands. The 2.4GHz band is also considered for single carrier mode in accordance with 802.11 b. And may also use the 2.4GHz band for mixed carrier mode to provide backward compatibility with legacy 802.11b devices. It is also contemplated to use the 5GHz band for the multi-carrier mode according to 802.11 a. And several different frequency bands including the 2.4GHz and 5GHz frequency bands, as well as any other selected frequency bands, are contemplated for use in the multi-carrier mode (i.e., multi-band operation), regardless of whether the frequency bands are standard frequency bands. For example, the FCC recently approved a modified version of 802.11a to operate in the licensed band near 6 GHz. Thereby allowing for multi-band 802.11a operation.

A second output 217 of the splitter 205 is provided to a mixed carrier pulse shaping component or digital filter 219. The digital filter 219 receives the single carrier preamble and header signals from the core 203 and shapes and filters the signals in a manner that has a similar power spectrum as the multi-carrier signal used for the mixed carrier waveform. In particular, the digital filter 219 comprises a scaled Finite Impulse Response (FIR) filter branch, so that the power spectrum of the single-carrier signal approximates the power spectrum of the multi-carrier signal. In one embodiment, the digital filter 219 uses a time-shaped pulse that is specified in continuous time and generated with an infinite impulse response approximated by a brick wall (brick wall). Preferably, the infinite impulse response is truncated with a continuous time window, where the window is long enough to achieve the desired spectral characteristics (similar to multicarrier modulation), but short enough to reduce complexity. The resulting continuous-time pulse waveform may be sampled at the sampling rate of the DAC215, which in the illustrated embodiment is 44 MHz. For 802.11g, which uses barker and OFDM, the FIR taps are scaled, so the barker preamble and header power spectra approximate the power spectrum of OFDM.

The preamble and header of the mixed carrier output by the digital filter 219 are provided to one input 221 of a combiner 223 which receives the multi-carrier payload from a multi-carrier processor or core 225 at a second input 227. The combiner 223 operates to combine the preamble and header of the mixed carrier with the multi-carrier payload to produce a mixed carrier packet at its output 228, the output 228 being coupled to a second input 229 of the MUX213, as described further below. The core 225 introduces core processing functionality to configure the multicarrier packet at a selected sampling rate, which may be, for example, the 44MHz sampling rate of the DAC 215. The output of core 225 is provided to input 227 of combiner 223 and to a third input 231 of MUX 213. The transmitter 201 is operated in a single carrier mode (e.g., 802.11b) when the control logic 206 controls the splitter 205 to select its first output 207 and controls the MUX213 to select its first input 211, thereby providing the single carrier packet generated by the core 203 and shaped by the pulse shaping component 209 to the DAC 215. The transmitter 201 is operated in mixed signal mode (e.g., 802.11g) when the control logic 206 controls the splitter 205 to select its second output 217 and controls the MUX213 to select its second input 229 to provide the mixed carrier packet from the combiner 223 to the DAC 215. When control logic 206 controls MUX213 to select its third input 231 to provide the multi-carrier packet generated by core 225 to DAC215, transmitter 201 operates in a multi-carrier mode (e.g., 802.11 a).

It is noted that the core 203 may be configured to generate a complete single carrier packet (via the pulse shaping circuit 209) and the core 225 may be configured to generate a complete multi-carrier packet. However, the combiner 223 combines the first portion or preamble and header of the single-carrier signal with the payload portion (e.g., including the preamble 113, data field 115, and SIF 117) of the multi-carrier signal to produce the mixed carrier packet. Single-carrier kernel 203 is also configured to modify header 111 of single-carrier portion 103 to include a bit or field indicating a mixed-carrier operating mode. The mixed carrier mode bit informs the receiver that the packet is a mixed carrier signal rather than a single carrier signal.

Figure 3 is a simplified block diagram of one embodiment of a combiner. The combiner 223 performs phase and time alignment between the single carrier header and preamble received through its input 221 and the multi-carrier payload received through its input 227. The combiner 223 also performs a transition between the end of the single carrier header and the beginning of the multi-carrier payload. The combiner 223 comprises a soft switch 301 that graphically switches the output 228 between the first, second and third terminals 303, 305 and 307, respectively. And the soft switch 301 need not be implemented as a physical or mechanical switch, but instead may be implemented in firmware or digital logic to perform smooth switching between signals during the transition. The first terminal 303 is coupled to an input 221 of a combiner 223 and to a first input 317 of a digital combiner block 309. The second terminal 305 is coupled to an output of a digital combiner unit 309. The third terminal 307 is coupled to an output 315 of the phase rotator 311, which is also provided to a second input 319 of the digital combiner block 309. As described further below, phase rotator 311 rotates or multiplies the multi-carrier signal by a phase angle v, relative to the last portion of the single-carrier signal, in order to maintain phase continuity. During the transition between the complete single-carrier part and the complete multi-carrier part of the mixed carrier signal, the digital combiner 309 combines the single-carrier and multi-carrier signals.

Fig. 4A and 4B are phase relationship diagrams of exemplary single-carrier modulation schemes using BPSK or QPSK, respectively. Fig. 4A is a simplified illustration of a BPSK curve with real and imaginary parts (one of 2 phases) introduced in two quadrants by BPSK. The phase angle Φ is 1 or-1. Fig. 4B is a simplified illustration of a QPSK curve depicting the introduction of real and imaginary parts into all four quadrants (one of the 4 phases) for QPSK. The phase angle Φ is 1, j, -1, or-j. During transmission, certain phases of the signal are ambiguous and thus the absolute phase is also uncertain. The receiver is typically configured to determine and track the phase of the incoming signal. However, for a mixed carrier signal, the relative phase between the single-carrier and multi-carrier portions should be maintained, or otherwise determinable, thereby simplifying the acquisition performed by the receiver. Thus, the multi-carrier signal phase is based on the phase of the last part of the single-carrier signal, thereby simplifying the phase acquisition of the receiver.

Single-carrier signals use Direct Sequence Spread Spectrum (DSSS), which is distinct compared to OFDM multi-carrier signal formats. For CCK-ODFM, any of these BPSK or QPSK formats may be reused for the header. The phase of the last barker word in the 802.11b header determines the phase that the coherent OFDM signal has relative to the OFDM signal generated by the core 225. Referring back to FIG. 3, for CCK-OFDM, phase rotator 311 rotates the OFDM signal by the phase angle of the last barker word (#), and asserts the rotated OFDM signal at its output 315. The rotated OFDM signal is applied to an input 319 of a digital combiner 309 and to a third terminal 307 of the soft switch 301. A phase angle of magnitude 1 corresponds to 0 degrees rotation (no rotation), a phase angle of magnitude j corresponds to 90 degrees rotation, a phase angle of magnitude-1 corresponds to 180 degrees rotation, and a phase angle of magnitude-j corresponds to-90 degrees rotation. A multi-carrier signal such as OFDM is a complex number that contains real and imaginary parts, which may also be referred to as in-phase (I) and quadrature-phase (Q) components, thus mathematically multiplying the I and Q components by-1, j, or-j.

Fig. 5 is a timing diagram depicting the correction between single-carrier and multi-carrier portions using barker and OFDM signals. The timing diagram illustrates the alignment of the OFDM signal portion 501 with the last barker word 503 of the preamble. The first chip of each barker word comprises the first chip of the last barker word 503 shown at 507, where the first chip of each barker word is centered at 1 μ s alignment and each subsequent barker chip of each code word is centered at 1/11 μ s or 91 nanoseconds (ns). For the start of the OFDM signal, the first complete sample of the OFDM signal shown at 509 occurs 1 μ s after the zero phase peak of the first chip of the last barker word in the header and thus 1/11 μ s after the last chip 511 of the last barker word, thus maintaining timing during the conversion. The period between the last chip 511 and the first complete OFDM sample 509 forms an overlap period 513 of 1/11 mus between the last barker word 503 and the first complete sample of the OFDM signal. A scaled OFDM sample 515 is also shown before the first full scale OFDM sample to illustrate the operation of the smooth waveform transition performed by the digital combiner 317. OFDM samples 515 are periodically spread because they occur long before the OFDM samples completely begin. This transition time alignment enables equalizer information and timing information to continue to be communicated between the single-carrier and multi-carrier portions of the mixed carrier signal.

Referring back to fig. 3, the soft switch 301 connects the first terminal 303 to the output 228 of the combiner 223 until after the end of the last barker chip 511, thereby forwarding the last barker word. Then, after the last barker chip 511, the switch 301 switches to connect the output of the digital combiner 309 to the output 228 on the second terminal 305. In the overlap period 513, the digital combiner 309 digitally combines the single-carrier signal at input 317 and the rotated multi-carrier signal at input 319. It should be noted that although in the illustrated configuration the signals are digitally sampled so that a digital combiner is used, analog combiners and other devices are contemplated in alternative embodiments. In one embodiment, digital combiner 309 ramps down the single carrier signal while ramping up the multi-carrier signal. Since both single-carrier and multi-carrier signals are sampled at 44MHz and the calibration is based on barker chips at 11MHz, there are three (3) intermediate samples between the last barker chip 511 and the first full OFDM sample 509 in the overlap period 513. In one embodiment, during the conversion, the digital combiner 309 combines 75% of the barker signal with 25% of the OFDM signal for the first intermediate sample, and 50% of the barker signal with 50% of the OFDM signal for the second intermediate sample, and further combines 25% of the barker signal with 75% of the OFDM signal for the third intermediate sample, wherein the intermediate samples are provided to the output 228 in successive 44MHz periods. Before the first complete OFDM sample 509, soft switch 301 switches to connect terminal 307 with the rotated OFDM sample at output 315 of phase rotator 311 to output 228, and soft switch 301 remains at terminal 307 for the remainder of multicarrier portion 105.

Fig. 6 is a diagram depicting an exemplary termination of a single carrier signal and an OFDM symbol start in an overlap period 513, where the single carrier signal termination is shown by the dashed curve at 601 and shaped as per 802.11b, and the OFDM symbol start is shown at 603 and shaped as per 802.11 a. As illustrated in these figures, the single carrier is terminated in a controlled manner when transitioning from single carrier to multi-carrier. This single carrier termination maintains AGC and minimizes signal power gaps at the time of the impending transition, which in turn minimizes signal degradation by another carrier. The single-carrier termination of the 802.11b segment is similar to the termination of OFDM shaping of 802.11 a. 802.11a specifies a window function for OFDM symbols that defines the termination of a single-carrier segment. The single carrier signal is terminated within a predetermined time window, such as nominally 100 nanoseconds (ns). Furthermore, it is not necessary to flush the single carrier pulse shaping filter completely. The resulting distortion of the last barker word in the header is very small compared to the 11-chip processing gain, thermal noise, and multipath distortion. And the termination can be done either in the digital signal processing or explicitly by analog filtering.

Fig. 7 is a simplified block diagram of a receiver 700 incorporating a baseband receiver 701 implemented according to one embodiment of the invention. Receiver 700 includes an RF system that receives RF signals from a wireless medium through antenna 704 and converts the RF signals to baseband signals. The baseband analog input signal is applied to the input of an analog-to-digital converter (ADC) 703. ADC 703 asserts a corresponding digital baseband signal sampled at a rate of 22MHz to Channel Impulse Response (CIR) estimation block 705, first input 707 of MUX 709, input of time tracking loop block 711, and input of non-coherent Automatic Gain Control (AGC) feedback block 713. As known to those skilled in the art, the receiver 700 converts the RF signal from the wireless channel into a baseband analog input signal via a series of amplifiers, filters, and mixing stages. The gain range of the receiver 700 is typically large in order to detect weak signals (high gain) or reduce strong signals (low gain). The ADC 703 may be implemented with sufficient bit resolution to cover the entire gain range, but typically the ADC 703 is implemented to contain only a sufficient number of bits for the intended resolution of the input baseband signal. An AGC feedback block 713 is used on a feedback line 715 to assert a feedback signal to the RF system 702 in an attempt to resolve the gain of the receiver 700 to a target gain range within the range of the ADC 703. The AGC feedback component 713 is "non-coherent" in that it operates without regard to signal timing, frequency, phase or other parameters, thereby only coarsely resolving the gain for the input signal. The AGC feedback section 713 performs only a coarse gain adjustment.

In a similar manner as described above for transmitter 200, receiver 700 includes control logic 706 coupled to RF system 702 and baseband receiver 706 via control and Select (SEL) signals, which control operation and select one of several operating modes. Receiver 700 may be further configured to operate in a single-carrier mode to receive and acquire single-carrier packets or signals, may be configured to operate in a multi-carrier mode to acquire multi-carrier packets, and may be configured to operate in a mixed-carrier mode to acquire mixed-carrier packets. Receiver 700 may be further configured for multi-band operation, including 2.4 and 5GHz frequency bands as well as other frequency bands as desired. The 2.4GHz band is intended for single carrier and mixed carrier modes to remain compatible with either 802.11b or 802.11b legacy devices. Any selected frequency band may be used for the multi-carrier mode of operation and is also intended to operate using multi-band 802.11 a. It is noted that RF system 202 and control logic 206 may be combined with RF system 702 and control logic 706, and baseband transmitter 200 and baseband receiver 700 may be coupled to the combined RF system and implement an RF transceiver in accordance with one embodiment of the present invention by performing control.

For single carrier and mixed carrier modes of operation, CIR estimation section 705 examines the known preamble in the signal, estimates the wireless channel and outputs a time domain signal hi representing the channel impulse response (and intermediate filters). In one embodiment, CIR estimation section 705 is a FIR filter having a selected number "i" of filter taps. The hi signal is provided to the inputs of a Fast Fourier Transform (FFT) component 717 and a Channel Matched Filter (CMF) component 719. The CMF component 719 programs its branches by performing the conjugate and inverse time functions of the hi signal. CMF component 719 can also include a FIR filter. Essentially, signal distortion due to channel effects is removed by the CMF part 719. The time tracking component 711 is an autonomous digital adjustment filter that checks and adjusts the timing of the digital baseband signal. For example, the time tracking component 711 adjusts the timing based on barker chips of the 802.11b signal. Time tracking block 711 to multiplier 721One input asserts a time adjusted signal which is multiplied by a gain adjust signal KAGC received at the other input of the multiplier, thereby producing a gain adjusted signal. Multiplier 721 asserts this gain adjusted signal to one input of phase rotator 723, which uses a phase adjusted signal e received at its other input^jθPLLTo adjust the signal to produce a phase adjusted signal. Phase rotator 723 asserts the phase adjusted signal to an input of CMF component 719, which removes channel distortion from the signal. An output of the CMF component 719 is coupled to a second input 725 of the MUX 709, an input of the single carrier core 731, an input of the Phase Locked Loop (PLL) phase error component 727, and an input of the AGC gain error component 729. And provides a SEL signal between control logic 706 and single-carrier core 731 to control the operating mode. Although operation is typically controlled by control logic 706, single-carrier core 731 may change the mode of operation from single-carrier to mixed-carrier mode once a mixed-carrier packet is detected.

PLL phase error block 727 detects any phase error at the output of CMF block 719 and provides a corresponding phase error signal Φ_errorAssert to a lead/lag (lead/lag) filter 733, which generates a phase adjustment signal e^jθPLLAnd asserts it to the phase rotator 723. The AGC gain error component 729 compares the signal gain at the output of the CMF component 719 to a predetermined target gain and generates a corresponding gain error signal K to the integrator component 735_error. The integrator component 735 receives this gain error signal K_errorAnd generates a gain adjustment signal K_AGCAnd a gain adjustment signal K_AGCIs provided to multiplier 721. Thus, at least three different loops for single carrier signals are provided in the baseband receiver 701, including a timing loop that focuses on the time tracking loop 711 to adjust timing, a gain loop that focuses on the multiplier 721 to adjust gain, and a phase rotator 723 to adjust gainA phase loop for adjusting frequency and phase. Initially, h from CIR estimation section 705 is used_iThese loops are held constant at nominal values until the signals program the branches of the CMF component 719. After the CMF component 719 is programmed, the loop will be released to resolve and reduce or eliminate timing, gain, phase, and frequency errors in the input signal.

MUX 709 is controlled by the SEL signal to select its first input 707 for a multi-carrier mode of operation, such as 802.11a based grouping. The output of MUX 709 is coupled to the input of a multicarrier core 737 which, as described further below, introduces the necessary processing functions to resolve the timing, frequency, gain, phase and channel response of those multicarrier signals received via ADC 703. The SEL signal from control logic 706 is provided to multicarrier core 737 to control the mode of operation. The remainder of the baseband receiver 701 is bypassed to perform the multi-carrier mode of operation. For single carrier mode of operation, core 731 introduces the necessary processing functions to detect and resolve single carrier packets. The frequency, timing, phase, gain, and filter response are all processed by the loop and CMF component 719, thereby resolving the barker or CCK single carrier signal.

Single-carrier kernel 731 is used to parse single-carrier portion 103 and multi-carrier kernel 737 is used to parse multi-carrier portion 105 of mixed carrier packet 101 to perform a mixed carrier mode of operation. MUX 709 is controlled by the SEL signal and selects its second input 725 to provide the output of CMF block 719 to core 737. However, for mixed carrier mode of operation, core 737 does not attempt to resolve single-carrier portion 103 and core 737 is disabled before core 731 issues a START control signal. The core 731 parses the single-carrier portion 103 of the input signal, just as if the input signal were a normal single-carrier packet. Core 731 detects the mixed mode bit in header 111 of single-carrier portion 103 and enables the mixed carrier mode of operation. If the mixed carrier packet is represented by a mode bit, then the coreThe core 731 issues a FREEZE control signal to the PLL phase error block 727, AGC gain error block 729, and time tracking block 711 at the end of the single carrier portion 103. Assertion of the FREEZE signal will cause the PLL phase error component 727 to phase error signal phi_errorSet to zero, thereby holding the phase adjustment signal e^jθPLLThe current level of the current voltage. And assertion of the FREEZE signal also causes AGC gain error component 729 to apply gain error signal K_errorSet to zero, thereby maintaining the gain adjustment signal K_AGCThe current level of the current voltage. In addition, assertion of the FREEZE signal also stops operation of the time tracking component 711, thereby disabling time tracking adjustments. Freezing these parameters will preserve the phase, frequency, gain, and sampling timing derived from the single carrier waveform to use as the starting point for the multi-carrier waveform.

Core 731 enables operation of core 737 at the beginning of the multicarrier payload by asserting a START signal. Core 737 has its own gain, phase/frequency, and time tracking loops, as described further below. In the single-carrier portion 103 of the partially mixed signal, the FFT section 717 converts the time impulse response signal hi into a corresponding frequency domain signal H (ω). The H (ω) signal is the frequency response of the wireless channel and is provided to an input of a frequency domain equalizer (FEQ) calculation section 739. FEQ calculating section 739 calculates the frequency domain equalizer branch according to the following equation:

where the subscript "k" is an index that indicates the "tone" or "subcarrier" associated with the multicarrier signal. To OFFor DM, ω_kThe subcarrier frequencies of the OFDM signal of interest are indicated. For each subcarrier of the OFDM signal, the FEQ operates as a single-tap frequency domain equalizer that removes gain and phase distortion produced by the wireless channel. Since the baseband receiver 701 maintains CIR estimates from single-carrier to multi-carrier waveforms, a single-carrier preamble is used as the FEQ for the core 737. Thereby preserving signal coherence during the transition from the single-carrier portion to the multi-carrier portion of the mixed signal.

Fig. 8 is a block diagram of a baseband receiver 801 implemented in accordance with an alternative embodiment of the invention. The remainder of the receiver, such as the RF system 702 and the control logic 706, are not shown in the figure, but operate in a similar manner. The baseband receiver 801 is similar to the baseband receiver 701 and may be replaced, but the output of the phase rotator 723 is coupled to the second input 725 of the MUX 709 instead of the output of the CMF component 719. The operation is substantially similar, except that the latency via the CMF component 719 is accounted for by asserting the FREEZE and START signals before the end of the single-carrier portion 103. Further, FEQ calculating section 739 calculates the frequency domain equalizer branch according to the following equation 2:

from a computational point of view, the equation for calculating the FEQ for the baseband receiver 801 is somewhat simpler than the equation for calculating the baseband receiver 701. However, the baseband receiver 701 need not determine when to assert both the FREEZE and START signals by determining latency through the CMF component 719.

Fig. 9 is a block diagram of an exemplary OFDM embodiment of core 737. It is contemplated that other multicarrier cores may also be considered depending on the particular multicarrier modulation scheme used. The OFDM signal output by the MUX 709 is supplied to a combiner 901, which combines a frequency adjustment signal F_ADJAnd provides a frequency adjustment signal to the timing adjustment component 903. Timing adjustment component 903 receives a frequency error signal at another input and provides a timing adjustment signal to one input of multiplier 905. The multiplier 905 multiplies the output of the timing adjustment section 903 with the gain adjustment signal K_AGCMultiplies and asserts a gain adjustment signal to the input of the fine tuned guard interval component 907. The fine guard interval part 907 mitigates inter-symbol interference (ISI) by performing an operation, and provides its time domain output signal to the FFT part 909, which FFT part 909 converts the time domain signal into a frequency response signal. The frequency response signal is provided to an input of a combiner 911, which receives the frequency domain equalizer branch FEQ (ω) from the FEQ calculation block 739_k)。

The combiner 911 asserts a channel adjust signal to the input of the soft decision component 913, the input of the gain error component 915, and the input of the phase error component 917. The gain error block 915 provides a gain error signal to an integrator 919, which provides a gain adjustment signal K_AGCIs asserted to multiplier 905. The phase error section 917 asserts a phase error signal to a lead/lag filter section 921 which asserts a frequency error signal to the timing adjustment section 903 and to a complex digitally controlled oscillator (CNCO) circuit 923. CNCO 923 produces a frequency adjustment signal F which is supplied to combiner 901_ADJ. And the CNCO circuit 923 adjusts the frequencies and phases of all subcarriers of the OFDM signal.

The gain error block 915, integrator 919, and multiplier 905 form a gain tracking loop 925 of an OFDM-based core 737 that adjusts the gain of the OFDM signal. Phase error section 917, lead/lag filter 921, CNCO circuit 923, combiner901 and timing adjustment block 903 form a frequency, phase and timing tracking loop 927 that adjusts the frequency, phase and timing of the OFDM signal. Core 737 begins processing the multi-carrier portion of the mixed carrier signal from the point where the FREEZE signal ceases the single carrier loop when the START signal is asserted. Thus, even though OFDM core 737 includes its own multi-carrier gain, frequency, phase and time tracking loop, these multi-carrier loops can track the gain, frequency, phase and time parameters determined for single-carrier portion 103 by the single-carrier loop. Since the transmitter maintains coherency during the transition from the single-carrier to the multi-carrier portion of the mixed carrier signal, coherency is also maintained between the single-carrier and multi-carrier processor portions of the baseband receiver. Furthermore, since the mixed-carrier digital filter 219 of the transmitter 201 performs power spectrum approximation, the CIR estimate obtained by the CIR estimation section 705 in the single-carrier portion 103 is applicable to the multi-carrier portion 103 of the mixed carrier signal 101. Thus, the frequency domain equalizer branch FEQ (ω) from the FEQ calculating section 739_k) Associated with the multi-carrier portion 105, thereby removing gain and phase distortion of the wireless channel. Thus, coherent conversion will occur between the single-carrier and multi-carrier portions of the mixed-signal packet 101 in the baseband receiver 701 or 801.

The OFDM core 737 may be implemented in a standard manner to include a deinterleaving and depuncturing block 929, a branch metric calculation block 931, a viterbi decoder 933, and a descrambler 935, which outputs the recovered signal information to a local Medium Access Control (MAC) device.

Fig. 10 is a block diagram of a baseband receiver 1001 embodying an alternative and non-coherent embodiment of the present invention. The single-carrier portion of the baseband receiver 1001 operates in a manner substantially identical to the baseband receivers 701 and 801, and therefore will not be described here. Baseband receiver 1001 includes a single-carrier core 1003 that operates similarly to core 731, but does not assert the FREEZE control signal. Instead, core 1003 may issue a START signal to a multi-carrier core 1005 upon detecting mixed-carrier packet 101. Core 1005 operates in a similar manner to core 737 described above, but receives input directly from ADC 703 rather than from CMF block 719 or phase rotator 723. Thus, core 1005 must re-acquire frequency, phase, gain, sample timing, and CIR estimates directly from the multi-carrier portion 105, e.g., from the 8 μ s OFDM long synchronization field 119 of the OFDM preamble 113 portion of mixed carrier packet 101.

In other embodiments, the baseband receiver 1001 serves as the multicarrier loop start point using any selected combination of gain, phase, frequency, or timing parameters determined by the gain, phase, and timing loops of the single carrier portions of the receiver. For example, the timing parameters determined by the time tracking component 711 may be programmed into the timing adjustment component 903 of the core 737, and/or the frequency parameters determined by the lead/lag filter 733 may be programmed within the lead/lag filter 921 to simplify multi-carrier acquisition performed by the core 737. Although the gain and phase parameters from the single-carrier loop may also be used in the multi-carrier core, these parameters have been determined from the preamble portion (e.g., OFDM long synchronization field 119) of multi-carrier portion 105 of mixed-signal packet 101 at the time the CIR estimate is determined.

Furthermore, the non-coherent embodiments are backward compatible with single carrier 802.11b mode radios and are capable of operating in conjunction with the proposed 802.11g mixed carrier waveform described herein. However, non-coherent embodiments are not as robust as coherent embodiments because they do not use as much information as is generated in the single-carrier portion of the signal, and instead rely on the relatively short and long synchronization portions of the OFDM signal. Thus, compared to the coherent embodiment, the non-coherent embodiment has a slightly lower sensitivity but a larger packet error rate. Nonetheless, the non-coherent embodiment provides acceptable performance by using a simpler and cheaper design.

Although the system and method according to the present invention has been described herein in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be reasonably included within the spirit and scope of the invention.

Claims

1. A baseband receiver, comprising:

a Channel Impulse Response (CIR) estimation section capable of generating an impulse response signal based on a single-carrier segment of a received signal, i.e., a single-carrier signal or a mixed carrier signal, wherein the single-carrier segment has a spectrum approximating a multi-carrier spectrum;

a gain, phase and timing loop that adjusts the gain, phase, frequency and timing of the received signal to provide an adjusted received signal;

a Channel Matched Filter (CMF) coupled to the CIR estimation block, the filter filtering the adjusted received signal based on the impulse response signal;

a single carrier processor that processes the conditioned and filtered received signals to resolve single carrier segments of the mixed carrier signal, said single carrier processor further capable of detecting a mixed carrier mode indication in a single carrier segment and asserting a start indication corresponding to an end of a single carrier segment; and

a multi-carrier processor capable of processing multi-carrier segments of a mixed carrier signal in response to the start indication assertion.

2. The baseband receiver of claim 1, wherein a modulation scheme selected from Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) is used to modulate the single-carrier segment, and wherein Orthogonal Frequency Division Multiplexing (OFDM) is used to modulate the multi-carrier segment of the mixed carrier signal.

3. The baseband receiver of claim 1, further comprising:

control logic coupled to the single carrier processor and the multi-carrier processor to select between single carrier, multi-carrier, and mixed carrier modes of operation;

the single carrier processor is configured to process the conditioned and filtered received signal of one single carrier signal in a single carrier mode of operation and to process a single carrier segment of the conditioned and filtered received signal of the mixed carrier signal in a mixed carrier mode of operation; and

the multi-carrier processor is configured to process the multi-carrier received signal prior to the adjusting and filtering in the multi-carrier mode of operation and to process the multi-carrier segment of the mixed carrier signal in the mixed carrier mode of operation.

4. The baseband receiver of claim 3, wherein the multi-carrier processor operates in a non-coherent mixed carrier mode, wherein said multi-carrier processor processes the multi-carrier segment of the received signal prior to conditioning and filtering.

5. The baseband receiver of claim 4, further comprising:

a multi-carrier segment comprising a synchronization field, and

the multi-carrier processor determines the frequency domain equalizer taps from the synchronization field.

6. The baseband receiver of claim 5, further comprising:

a gain, phase and timing loop for generating gain, phase, frequency and timing adjustment parameters; and

the multicarrier processor is configured to be programmable in conjunction with a selected combination of gain, phase, frequency and timing adjustment parameters.

7. The baseband receiver of claim 6, further comprising:

the multicarrier processor comprising a phase locked loop with a filter, the phase locked loop being configured to be programmable in conjunction with a frequency adjustment parameter; and

the multicarrier processor comprises a timing loop configured to be programmable in conjunction with a timing adjustment parameter.

8. The baseband receiver of claim 1, further comprising:

in response to detecting the indication of the mixed carrier mode, the single-carrier processor further declaring a freeze indication to the gain, phase, and timing loops that halts operation of the timing, gain, and phase loops at an end of a single-carrier segment of the mixed carrier signal;

a Fast Fourier Transform (FFT) generator that converts the impulse response signal into a frequency response signal that is provided to the frequency domain equalizer;

a frequency domain equalizer coupled to the FFT generator that determines a multi-carrier equalized signal based on the frequency response signal; and

the multicarrier processor processes the multicarrier segment of the adjusted and filtered received signal using the multicarrier equalization signal in response to the assertion of the start indication.

9. The baseband receiver of claim 8, further comprising:

the multi-carrier processor is coupled with one output end of the CMF; and

the equalizer is according to equationTo determine the frequency response based signal H (ω)_k) Multi-carrier equalized signal FEQ (ω)_k)。

10. The baseband receiver of claim 8, further comprising:

the multi-carrier processor is coupled with one input end of the CMF;

the single carrier processor declares a start indication one CMF wait period before the end of the single carrier segment; and

frequency domain equalizer according to equationTo determine the frequency response based signal H (ω)_k) Multi-carrier equalized signal FEQ (ω)_k)。

11. The baseband receiver of claim 8, wherein said phase loop comprises:

a phase error detector coupled to an output of the CMF and generating a phase error signal;

a phase filter coupled to the phase error detector, said filter receiving the phase error signal and generating a phase correction signal; and

a phase rotator coupled to the signal path of the received signal and adjusting the received signal based on the phase correction signal;

wherein the phase correction signal remains constant once the freeze indication is asserted.

12. The baseband receiver of claim 11, wherein

Once the freeze indication is asserted while the phase correction signal is held constant, the phase error detector sets the phase error signal to zero.

13. The baseband receiver of claim 8, wherein said gain loop comprises:

a gain error detector coupled to the CMF output and generating a gain error signal;

an integrator coupled to the gain error detector, the integrator receiving the gain error signal and generating a gain correction signal; and

a multiplier coupled to the signal path of the received signal and adapted to adjust the received signal in accordance with the gain correction signal;

wherein the gain correction signal remains constant once the freeze indication is asserted.

14. The baseband receiver of claim 13, wherein the gain error detector sets the gain error signal to zero upon assertion of the freeze indication to hold the gain correction signal constant.

15. The baseband receiver of claim 8, wherein the timing loop includes a time tracking component that receives and adjusts the timing of the received signal, and wherein said time tracking component discontinues tracking the adjustment of the received signal upon assertion of the freeze indication.

16. The baseband receiver of claim 8, wherein the multicarrier processor comprises a combiner for combining the multicarrier equalized signal from the frequency domain equalizer with the frequency response signal based on the received multicarrier signal.

17. The baseband receiver of claim 8, further comprising:

control logic coupled to the single carrier processor and the multi-carrier processor, the control logic selecting between single carrier, multi-carrier, and mixed carrier operating modes;

the single carrier processor is configured to process the conditioned and filtered received signal in the single carrier signal in a single carrier mode of operation and to process the conditioned and filtered received signal in the mixed carrier signal in a mixed carrier mode of operation; and

the multi-carrier processor is configured to process the multi-carrier received signal prior to the conditioning and filtering in the multi-carrier mode of operation and to process the multi-carrier segment of the conditioned and filtered received signal in the mixed carrier mode of operation.

18. A wireless Radio Frequency (RF) communication device, comprising:

an RF transceiver which converts an RF signal from the antenna into a baseband signal and converts the baseband signal into an RF signal transmitted via the antenna;

a baseband transmitter coupled to the RF transceiver, the baseband transmitter configured to modulate the single-carrier portion using a single-carrier modulation scheme and to modulate the multi-carrier portion using a multi-carrier modulation scheme to transmit a mixed carrier signal via the RF transceiver, the transmitter filtering the single-carrier portion to approximate a multi-carrier power spectrum, the transmitter further formulating the mixed carrier signal to maintain frequency, phase, gain, and timing coherence between the single-carrier and multi-carrier portions; and

a baseband receiver coupled to an RF transceiver, comprising:

a Channel Impulse Response (CIR) estimation section capable of generating an impulse response signal based on a received baseband signal from the RF transceiver, the received baseband signal comprising a single carrier segment of a single carrier signal or a mixed carrier signal, wherein the single carrier segment has a power spectrum approximating a multi-carrier power spectrum;

a gain, phase and timing loop that adjusts gain, phase, frequency and timing of the received baseband signal and provides an adjusted received signal;

a single carrier processor coupled to the CMF that processes the conditioned and filtered received signals to resolve the single carrier portion of the mixed carrier signal, the single carrier processor capable of detecting the mixed carrier mode indication in the single carrier portion and asserting a start signal corresponding to an end of the single carrier portion; and

a multi-carrier processor capable of processing a multi-carrier portion of the mixed carrier signal in response to assertion of the start signal.

19. The wireless RF communication device of claim 18, wherein a modulation scheme selected from Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) is used to modulate the single-carrier segment, and wherein Orthogonal Frequency Division Multiplexing (OFDM) is used to modulate the multi-carrier segment of the mixed carrier signal.

20. The wireless RF communication device of claim 18, wherein the baseband receiver includes a single-carrier mode of operation in which the single-carrier processor processes the conditioned and filtered received signal to resolve a single-carrier received baseband signal, and a multi-carrier mode of operation in which the multi-carrier processor processes a multi-carrier received baseband signal.

21. The wireless RF communication device of claim 18 wherein the baseband receiver further comprises:

a single carrier receive processor that asserts a freeze signal in response to detection of the mixed carrier mode indication, the freeze signal suspending operation of the gain, phase and timing loops;

a Fast Fourier Transform (FFT) section for converting the impulse response signal into a frequency response signal;

a frequency domain equalizer for generating a multi-carrier equalized signal based on the frequency response signal; and

a multicarrier receiver processor responsive to the open-ended signal for processing the multicarrier portion of the adjusted and filtered received signal using the suspended gain, phase and timing loops and the CMF and using a multicarrier equalization signal.

22. The wireless RF communication device of claim 21 wherein the baseband receiver further comprises:

the single carrier processor is configured to process the conditioned and filtered received signal in the single carrier signal in a single carrier mode of operation and to process a single carrier segment of the conditioned and filtered received signal in the mixed carrier signal in a mixed carrier mode of operation; and

23. The wireless RF communication device of claim 22, wherein the RF transceiver is capable of multi-band operation, wherein the RF transceiver operates in a first RF band for single carrier and mixed carrier modes, and wherein the RF transceiver operates on a selected one of a plurality of frequency bands including the first frequency band and a second RF band for multi-carrier modes.

24. The wireless RF communication device of claim 23, wherein the first RF band is approximately 2.4 gigahertz (GHz) and wherein the second RF band is approximately 5 GHz.

25. The wireless RF communication device of claim 18 wherein the baseband transmitter further comprises:

a single carrier transmitting processor for generating single carrier signal;

a multi-carrier transmit processor for generating a multi-carrier signal;

a digital filter coupled to the single carrier transmit processor, said filter filtering the single carrier signal to have a power spectrum similar to the multi-carrier power spectrum; and

a signal combiner coupled to the digital filter and the multi-carrier transmit processor, the combiner combining the filtered single-carrier signal with the multi-carrier signal while maintaining phase, gain, and timing alignment.

26. The wireless RF communication device of claim 25, wherein the signal combiner further comprises:

a phase multiplier that multiplies the multi-carrier signal by the phase of the last portion of the single-carrier portion and provides a rotated multi-carrier signal;

a digital combiner that combines the filtered single carrier signal with the rotated multi-carrier signal and provides a combined mixed carrier signal; and

a soft switch that selects the filtered single-carrier signal prior to termination, the combined mixed carrier signal during a transition period, and the rotated multi-carrier signal at the end of the transition period.

27. The wireless RF communication device of claim 26, wherein the single-carrier signal comprises successive chips according to a predetermined timing interval, and wherein the transition period has a duration equivalent to the predetermined timing interval.

28. A method of generating a mixed carrier packet for Radio Frequency (RF) transmission, comprising:

generating a multi-carrier payload using a selected multi-carrier modulation scheme;

generating a single-carrier segment comprising a preamble and a header using a single-carrier modulation scheme;

filtering the single-carrier segment to have a power spectrum approximating a power spectrum of the multi-carrier modulation scheme, an

The filtered single-carrier segment and the multi-carrier payload are combined in a manner that preserves gain, phase, frequency, and timing in the transition, thereby providing a carrier packet.

29. The method of claim 28, wherein said combining comprises rotating the multi-carrier payload by a phase determined from the filtered single-carrier segment.

30. The method of claim 29, the single-carrier modulation scheme comprising barker modulation and the multi-carrier modulation scheme comprising Orthogonal Frequency Division Multiplexing (OFDM), wherein the rotating comprises rotating the OFDM multi-carrier payload by a phase that is a last barker word phase of the filtered single-carrier segment.

31. The method of claim 30, wherein the multi-carrier payload comprises an OFDM preamble.

32. The method of claim 29, wherein the combining comprises ramping down the single-carrier segment while ramping up the multi-carrier payload in transition.

33. The method of claim 32, the filtered single-carrier segment having a predetermined chip rate, the method further comprising:

sampling the filtered single carrier segment and the multi-carrier payload at a predetermined sampling rate; and

the combination comprises: declaring a first complete sample of the multi-carrier payload based on a predetermined chip rate of the filtered single-carrier segment for a transition period after a last complete sample of the filtered single-carrier segment.

34. The method of claim 33, wherein said combining further comprises proportionally combining the respective filtered single-carrier segments and the multi-carrier payload to provide the plurality of samples during the transition time.

35. The method of claim 34, wherein the predetermined sampling rate is four times the predetermined chip rate, and wherein said proportionally combining at the transition time comprises providing first, second, and third intermediate samples for which the percentages of the filtered single-carrier segment to the multi-carrier payload are 75/25, 50/50, and 25/75, respectively.

36. A method for acquiring a mixed carrier signal of a single carrier segment followed by a multi-carrier segment, comprising:

determining gain, phase, frequency and timing adjustment parameters of the received baseband signal;

adjusting the baseband signal using the adjustment parameters to provide an adjusted baseband signal;

determining a Channel Impulse Response (CIR) estimate while receiving a single carrier segment of the received baseband signal;

filtering the adjusted baseband signal based on the CIR estimate to provide a filtered and adjusted baseband signal;

processing the filtered and adjusted baseband signal using a single carrier processor to obtain a single carrier segment;

detecting a mixed carrier mode identifier in a single carrier segment and asserting a mixed mode indication; and

in response to the mixed mode indication, a multicarrier processor is used to process the received baseband signal to obtain a multicarrier segment.

37. The method of claim 36, wherein said processing the received baseband signal using a multi-carrier processor comprises processing the received baseband signal prior to said adjusting and filtering.

38. The method of claim 37, further comprising:

determining, using the multi-carrier processor, a second channel frequency response estimate from a preamble portion of the multi-carrier segment; and

filtering the multicarrier segment based on the second frequency response estimate.

39. The method of claim 38, further comprising: any selected combination of gain, phase, frequency and timing adjustment parameters is used as at least one starting parameter by means of the multi-carrier processor to obtain the multi-carrier segment.

40. A method for acquiring a mixed carrier signal of a single carrier segment followed by a multi-carrier segment, comprising:

converting the CIR estimate to a frequency response signal;

using this frequency response signal to program the frequency domain equalizer;

detecting a mixed carrier mode identifier in a single carrier segment and declaring a mixed mode indication and a freeze indication;

in response to the freeze indication, keeping the gain, phase, frequency and timing adjustment parameters constant; and

in response to the mixed mode indication, the filtered and adjusted baseband signal is processed using a multi-carrier processor employing a frequency domain equalizer to obtain multi-carrier segments.

41. The method of claim 40, further comprising:

determining gain, phase, frequency and timing adjustment parameters comprises determining gain, phase, frequency and timing error values; and

the keeping gain, phase, frequency and timing adjustment parameters constant includes setting gain, phase, frequency and timing error values to zero.