Method and system for polar modulating OFDM signals with discontinuous phase

Aspects of a method and system for polar modulating OFDM signals with discontinuous phase may include amplifying an OFDM signal via a plurality of amplifiers such that a combined gain of the plurality of amplifiers comprises a coarse amplitude gain and an amplitude offset gain. A gain of one or more of the plurality of amplifiers may be adjusted to set the coarse amplitude gain, and a gain of one or more remaining ones of the plurality of amplifiers may be adjusted to set the amplitude offset gain. The setting of the coarse amplitude gain and/or the amplitude offset gain may be adjusted dynamically and/or adaptively.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to signal processing for communication systems. More specifically, certain embodiments of the invention relate to a method and system for polar modulating OFDM signals with discontinuous phase.

BACKGROUND OF THE INVENTION

Polar Modulation is related to in-phase (I) and quadrature (Q) modulation in the same way that polar coordinates are related to the Cartesian coordinate system. For polar modulation, the orthogonal I and Q components of an RF signal are converted to a phasor representation comprising an amplitude component and a phase component. In this way, the combined I and Q signal may be generated with one phase change and one amplitude change, whereas separate I and Q modulation may require amplitude and phase modulation for each channel, especially for non-constant envelope modulation modes. In addition, the I and Q modulation approach may require good linearity of the power amplifier, often leading to power inefficient designs that suffer from parameter variability due to factors such as temperature. In contrast, polar modulation may allow the use of very efficient and non-linear amplifier designs for non-constant envelope modulation schemes.

BRIEF SUMMARY OF THE INVENTION

A method and/or system for polar modulating OFDM signals with discontinuous phase, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and system for polar modulating OFDM signals with discontinuous phase. Aspects of a method and system for polar modulating OFDM signals with discontinuous phase may comprise amplifying an OFDM signal via a plurality of amplifiers such that a combined gain of the plurality of amplifiers comprises a coarse amplitude gain and an amplitude offset gain. A gain of one or more of the plurality of amplifiers may be adjusted to set the coarse amplitude gain, and a gain of one or more remaining ones of the plurality of amplifiers may be adjusted to set the amplitude offset gain.

The setting of the coarse amplitude gain and/or the amplitude offset gain may be adjusted dynamically and/or adaptively. The gain of the one or more of the plurality of amplifiers associated with the coarse amplitude gain may switch between unity gain and an arbitrary fixed gain, and the gain of the one or the plurality of amplifiers associated with the amplitude offset gain may be variable and arbitrary or discrete. The amplifier of the plurality of amplifiers associated with the amplitude offset gain may comprise one or more analog amplifiers. The signal may be generated by phase-modulation of a radio-frequency carrier. The combined gain of the plurality of amplifiers may be controlled based on a desired amplitude modulation. An integrated circuit may comprise the plurality of amplifiers.

FIG. 1is a diagram illustrating an exemplary wireless communication system, in accordance with an embodiment of the invention. Referring toFIG. 1, there is shown an access point112b, a computer110a, a headset114a, a router130, the Internet132and a web server134. The computer or host device110amay comprise a wireless radio111a, a short-range radio111b, a host processor111c, and a host memory111d. There is also shown a wireless connection between the wireless radio111aand the access point112b, and a short-range wireless connection between the short-range radio111band the headset114a.

Frequently, computing and communication devices may comprise hardware and software to communicate using multiple wireless communication standards. The wireless radio111amay be compliant with a mobile communications standard, for example. There may be instances when the wireless radio111aand the short-range radio111bmay be active concurrently. For example, it may be desirable for a user of the computer or host device110ato access the Internet132in order to consume streaming content from the Web server134. Accordingly, the user may establish a wireless connection between the computer110aand the access point112b. Once this connection is established, the streaming content from the Web server134may be received via the router130, the access point112b, and the wireless connection, and consumed by the computer or host device110a.

It may be further desirable for the user of the computer110ato listen to an audio portion of the streaming content on the headset114a. Accordingly, the user of the computer110amay establish a short-range wireless connection with the headset114a. Once the short-range wireless connection is established, and with suitable configurations on the computer enabled, the audio portion of the streaming content may be consumed by the headset114a. In instances where such advanced communication systems are integrated or located within the host device110a, the radio frequency (RF) generation may support fast-switching to enable support of multiple communication standards and/or advanced wideband systems like, for example, Ultrawideband (UWB) radio. Other applications of short-range communications may be wireless High-Definition TV (W-HDTV), from a set top box to a video display, for example. W-HDTV may require high data rates that may be achieved with large bandwidth communication technologies, for example UWB and/or 60-GHz communications.

Many desirable communications standards that may be utilized over the wireless connection between the access point112band the wireless radio111, and/or the short-range wireless connection between the headset114aand the short-range radio111bmay be using Orthogonal Frequency Division Multiplexing (OFDM) based technology. Exemplary communication standards may comprise IEEE 802.11a/g, commonly referred to as Wireless LAN; Multiband UWB; WiMAX IEEE 802.16; and UMTS LTE (Universal Mobile Telecommunications System—Long Term Evolution). In accordance with various embodiments of the invention, more power-efficient power amplification may be implemented in such systems.

FIG. 2is an exemplary complex signal diagram, in accordance with an embodiment of the invention. Referring toFIG. 2, there is shown a real axis and an imaginary axis that may span the complex plane. There is also shown an amplitude axis. A plurality of exemplary complex signal vectors202,204and206, associated with amplitudes A(1), A(2) and A(3), respectively, may also be illustrated. Each complex signal vector may be defined by an amplitude and a phase angle from the origin of the complex plane. For illustrative purposes, only the angle φ(2) for the vector204may be illustrated. Alternatively, as illustrated inFIG. 2, each complex signal vector may be described in terms of an in-phase component I(t) along the real axis and a quadrature component Q(t) along the imaginary axis, as illustrated for the complex signal vector206.

A general complex transmit signal may be decomposed into an in-phase and quadrature component. A modulated transmit signal s(t) may be, for example, given by the following relationship:
s(t)=A(t)cos(wctφ(t))=I(t)cos(wct)+Q(t)sin(wct)  (1)
where A(t) may be an amplitude and φ(t) may be an angle modulated onto a carrier cos(wct). The first form in equation (1) may be written in terms of an in-phase and quadrature component, I(t) and Q(t), respectively. The various signal components may be given by the following relationships:
I(t)=A(t)cos(φ(t))
Q(t)=A(t)sin(φ(t))
A(t)=√{square root over (I2(t)+Q2(t))}{square root over (I2(t)+Q2(t))}
φ(t)=tan−1(Q(t)/I(t))

FIG. 3is an exemplary amplitude diagram for a complex signal, in accordance with an embodiment of the invention. Referring toFIG. 3, there is shown an amplitude levels axis and a quantized amplitude levels axis. The amplitude levels axis may be similar to the amplitude axis inFIG. 2and may be obtained from a complex signal, for example, as illustrated inFIG. 2. In an exemplary case, there may be M different amplitude levels for a certain complex signal over a certain time interval, where each amplitude A(t) may correspond to a different instance in time, in general.

With an increasing number of amplitude levels and/or a large range of amplitudes for a given complex signal, it may become more efficient in some instances to implement N fixed amplitude levels together with, for example, an analog and continuous amplitude offset, rather than generate a large dynamic range of amplitudes in a single amplifier. In these instances, the set of amplitudes {A(t)} may be mapped onto a smaller set of amplitudes {A′1, A′2. . . , A′N}. In addition, each amplitude may be associated with an offset value d(t), which may be used to define the amplitude level A(t) from a given level A′n. Hence, the amplitudes may be related as illustrated in the following relationship:
A(t)=A′n+d(t);n∈1, . . . , N
Hence, the amplitudes A′nmay be considered analogous to the quantization of the amplitudes A(t) with a quantization error d(t). An exemplary quantization process may be illustrated inFIG. 3. For example, the amplitude levels A(t) may be quantized, or associated with, a nearest level A′non the quantized constellation amplitude levels axis. For example, the amplitude levels A(1) and A(M−1) may be quantized to A′1, as illustrated. Similarly, the amplitude levels A(M−1) and A(4) may be quantized to A′N, A(2) may be quantized to A′N-1, etc.

For example, the amplitude level A(M) may be quantized to the quantized amplitude level A′2. Associated with the amplitude level A(M) may also be an amplitude offset d(M).

FIG. 4is block diagram of an exemplary OFDM system, in accordance with an embodiment of the invention. Referring toFIG. 4, there is shown a polar amplitude modulation system400, comprising multipliers402and404, an adder406, an amplitude control block408, a plurality of amplifiers, of which amplifiers410,412,414and416may be illustrated, and OFDM baseband processor420, and a coarse amplitude select block418. There is also shown a normalized in-phase signal I′(t), a normalized quadrature signal Q′(t), an in-phase carrier cos(wct), a quadrature carrier sin(wct), a quantized Amplitude A′, quantized constellation amplitude levels A′1, A′2and A′N, an amplitude offset dA, and a transmit signal s(t).

The OFDM baseband processor420may comprise suitable logic, circuitry and/or code that may be enabled to generate an OFDM baseband signal, comprising an in-phase signal I′(t) and a quadrature signal Q′(t). The normalized in-phase signal may be given by I′(t)=I(t)/A(t)=cos(φ). Similarly, the normalized quadrature signal may be given by Q′(t)=Q(t)/A(t)=sin(φ). The normalized in-phase signal I′(t) may be multiplied with an in-phase carrier cos(wct) in multiplier402. The normalized quadrature signal Q′(t) may be multiplied with a quadrature carrier sin(wct) in multiplier404. In adder406, the signals may be summed to generate an output signal at the adder406that may be given by the following relationship:
I′(t)cos(wct)−Q′(t)sin(wct)=cos(wct+φ)  (2)
In this instance, the output signal of the adder406may be a normalized version of the transmit signal s(t), as may be illustrated by comparing equation (2) with equation (1).

The coarse amplitude modulation may be achieved by enabling a desirable combination of amplifiers, for example amplifiers410,412and414. The amplitude control block408may comprise suitable logic, circuitry and/or code that may be enabled to generate output signals that may correspond to a quantized coarse amplitude level A′n:n∈{1 . . . N} and an amplitude offset d(t) as a function of a desired amplitude level. The quantized amplitude level may be communicatively coupled to the coarse amplitude select block418. The coarse amplitude select block418may comprise suitable logic, circuitry and/or code that may be enabled to select the gain of the amplifiers410,412and414to generate a desired amplitude levels. In one embodiment of the invention, the amplifiers410,412and414, for example, may be toggled between unit amplification and a suitable gain. In this instance, the quantized amplitude level A′1, for example when A′1<A′2< . . . <A′N, may be achieved by setting amplifier410to a gain of A′1while all the other amplifiers may remain at unit gain. The gain A′2, for example, may be set by setting a gain A′1in amplifier410and a gain of A′2−A1′ in amplifier2while the other amplifiers may remain at unit gain. Similarly, any of the N quantized amplitude levels may be achieved by setting desirable amplification gains in the plurality of amplifiers, for example amplifier410,412and414. In addition, the amplitude control block408may also control a gain at amplifier416. The amplifier416may comprise suitable logic, circuitry and/or code that may be enabled to set a gain d(t) as a function of the input provided by the amplitude control408.

FIG. 5is a flow chart of an exemplary polar amplitude modulation process in an OFDM system, in accordance with an embodiment of the invention. Given a desired amplitude level A, the amplitude quantization process in accordance with an embodiment of the invention may be started in step502. In step504, the desired amplitude level may be written in terms of a coarse quantized amplitude level A′nand an amplitude offset d(t): A(t)=A′n+d(t):n∈{1, . . . , N}. Based on the quantized amplitude level A′nε{A1, . . . , AN}, which may be chosen from a set of amplitudes, a set of amplifiers, for example amplifiers410through414, may be set to achieve coarse polar amplitude modulation in step506. In step508, another amplifier, for example amplifier416may be used to generate the amplitude offset d(t). Step510may complete one cycle of amplitude adjustment, according to various embodiments of the invention.

In accordance with an embodiment of the invention, a method and system for polar modulating OFDM signals with discontinuous phase may comprise amplifying an OFDM signal, for example the output signal of adder406, via a plurality of amplifiers, for example amplifiers410,412,414and416such that a combined gain of the plurality of amplifiers comprises a coarse amplitude gain A′n, and an amplitude offset gain d(t). A gain of one or more of the plurality of amplifiers may be adjusted to set the coarse amplitude gain A′n, and a gain of one or more remaining ones of the plurality of amplifiers may be adjusted to set the amplitude offset gain d(t).

The setting of the coarse amplitude gain and/or the amplitude offset gain may be adjusted dynamically and/or adaptively, for example through the coarse amplitude select block418and/or the amplitude control block408. The gain of the one or more of the plurality of amplifiers associated with the coarse amplitude gain may switch between unity gain and an arbitrary fixed gain, and the gain of the one or more of said remaining ones of the plurality of amplifiers associated with the amplitude offset gain may be variable and arbitrary or discrete, as explained forFIG. 4. The one or more of said remaining ones of the plurality of amplifiers associated with the amplitude offset gain, for example amplifier416, may comprise one or more analog amplifiers. The signal may be generated by phase-modulation of a radio-frequency carrier. The combined gain of the plurality of amplifiers may be controlled based on a desired amplitude modulation, as described forFIG. 4. An integrated circuit may comprise the plurality of amplifiers.

Another embodiment of the invention may provide a machine-readable storage, having stored thereon, a computer program having at least one code section executable by a machine, thereby causing the machine to perform the steps as described above for a method and system for polar modulating OFDM signals with discontinuous phase.