KR101075288B1 - Quadrature modulation rotating training sequence - Google Patents

Abstract

A system and method are provided for transmitting a rotational training sequence. The rotational training signal is generated at an orthogonal modulation transmitter. The rotation training signal includes training information transmitted through an in-phase (I) modulation path and training information transmitted through a quadrature (Q) modulation path. The rotational training signal can be generated by initially transmitting training information over the I modulation path and subsequently transmitting the training information over the Q modulation path. Training information transmitted over the I modulation path may include a first symbol having a reference phase (eg, 0 ° or 180 °). The training information transmitted over the Q modulation path will then include a second symbol having a phase that is ± 90 from the reference phase.

Description

Quadrature Modulation Rotation Training Sequence {QUADRATURE MODULATION ROTATING TRAINING SEQUENCE}

The present invention generally relates to modulation of communications, and more particularly to systems and methods for generating an orthogonal modulated rotational training signal for use in the training of receiver channel estimates.

1 is a schematic block diagram of a conventional receiver front end (prior art). Conventional wireless communication receivers have an antenna for converting a radiated signal into a conducted signal. After some initial filtering, the conduction signal is amplified. If a sufficient power level is provided, the carrier frequency of the signal can be converted (downconverted) by mixing the signal with the local transmitter signal. Because the received signal is orthogonally modulated, the signal is demodulated through separate I and Q paths before being combined. After frequency conversion, the analog signal may be converted to a digital signal using an analog-to-digital converter (ADC) for baseband processing. The process may include a Fast Fourier Transform (FFT).

There are several errors that can occur at the receiver that adversely affect the restoration of the predetermined signal and the channel estimates. Errors can arise from passive components such as mixers, filters, and capacitors. Errors can be serious if those errors cause an imbalance between the I and Q paths. In an effort to estimate the channel and thus zero-out some of these errors, communication systems may use a message format that includes a training sequence that may be a repeated or predetermined data symbol. For example, by using an orthogonal frequency division multiplexing (OFDM) system, the same IQ constellation point can be transmitted repeatedly for each subcarrier.

In an effort to save power in portable battery-operated devices, some OFDM systems use only a single modulation symbol for training. For example, the inherent direction in the constellation (eg, the I path) is simulated, while the other direction (eg, the Q direction) is not simulated. The same type of non-directional training can also be used with pilot tones. Note: scrambling a single modulation channel through ± 1 does not rotate the constellation points, and does not provide any stimulation for the orthogonal channel.

In the presence of orthogonal path imbalance that occurs mainly in large bandwidth systems, the power-saving training sequence described above leads to biased channel estimation. Biased channel estimation can align IQ constellations well in one direction (ie, I path), but can provide orthogonal imbalance in the orthogonal direction. It is desirable for any imbalance to be equally distributed in both channels.

이고, 여기서

는 채널의 위상이다. Q 경로는 -sin(wt)를 통해서 하향변환된다. I 경로는

를 통해서 하향변환된다.

및

는 하드웨어 불균형들인데, 각각 위상 에러 및 진폭 에러이다. 저역 통과 필터들(H_I 및 H_Q)은 각각의 경로에 대해 상이하다. 그 필터들은 추가적인 진폭 및 위상 왜곡을 발생시킨다. 그러나, 이러한 추가적인 왜곡들은

및

내에서 럼핑된다(lumped). 주시 : 이러한 두 필터들은 실질적이며, +w 및 -w 모두에 동일한 방식으로 영향을 준다.2 is a schematic block diagram showing orthogonal imbalance at the receiver side (prior art). Although not shown, the transmitter side imbalance is similar. Suppose the Q path is a reference. The impinging waveform is

, Where

Is the phase of the channel. The Q path is downconverted through -sin (wt). I path is

Downconverted through

And

Are hardware imbalances, respectively, phase error and amplitude error. Low pass filters H _I and H _Q are different for each path. The filters generate additional amplitude and phase distortion. However, these additional distortions

And

Lumped in. Note: These two filters are practical and affect both + w and -w in the same way.

Assuming that the errors are small:

)은 Q 경로로부터의 작은 누설이다. 임핑잉 파형의 하향변환 이후에는 다음과 같다:The first component on the right (cos (wt)) is the ideally scaled I path. Second component (

) Is a small leakage from the Q path. After downconverting the impinging waveform:

In the path I:

In the Q path:

Errors result in incorrect interpretation of symbol positions in the orthogonal modulation constellation, which results in incorrectly demodulated data.

Wireless communication receivers tend to cause errors due to lack of tolerances in hardware components associated with mixers, amplifiers, and filters. For quadrature demodulators, these errors can also result in an imbalance between the I and Q paths.

The training signal can be used to correct receiver channel errors. However, training signals that do not simulate both I and Q paths do not solve the imbalance problem between the two paths.

Thus, a method for transmitting an orthogonally modulated rotational training sequence is provided. The rotation training signal is generated by an orthogonal modulation transmitter. The rotation training signal includes not only training information transmitted through an in-phase (I) modulation path but also training information transmitted through a quadrature (Q) modulation path. Orthogonally modulated communication data is generated simultaneously with or subsequent to the training signal. The rotation training signal and quadrature modulated communication data are transmitted.

For example, the rotational training signal can be generated by initially transmitting training information over the I modulation path and then transmitting the training information over the Q modulation path. More specifically, the training information transmitted over the I modulation path may include a first symbol having a reference phase (eg, 0 ° or 180 °). The training information transmitted over the Q modulation path will then include a second symbol having a phase that is ± 90 from the reference phase.

Further details of the method described above, a system for generating a rotational training signal, and other variations of the present invention are provided below.

1 is a schematic block diagram of a conventional receiver front end (prior art).

2 is a schematic diagram showing orthogonal imbalance at the receiver side (prior art).

3 is a schematic block diagram of a wireless communication device having a system for transmitting a rotational training sequence.

4A to 4D are diagrams illustrating a training sequence having orthogonal modulated communication data.

5A and 5B are schematic diagrams showing rotational training symbols as shown in the orthogonal constellation diagram.

6 is a schematic diagram illustrating an example framework for conveying a message having a rotational training signal.

7 is a schematic block diagram illustrating a processing apparatus for transmitting an orthogonal modulation rotation training sequence.

)에 대한 이상적인 성상도 및 불균형 성상도을 나타내는 개략도이다.FIG. 8 shows two different phases of the impinging waveform of FIG. 2 (FIG.

A schematic showing ideal constellations and unbalance constellations for

9 is a graph showing phase imbalance as a function of phase on an impinging waveform.

10 is a flowchart illustrating a method for transmitting a communication training sequence.

Several embodiments are now described with reference to the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such embodiment (s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing these embodiments.

As used in this application, terms such as "component", "module", "system" and the like refer to any of computer-related entities, ie hardware, firmware, a combination of hardware and software, software, or executable software. Intended to. For example, a component may be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and / or a computer. By way of example, both an application running on a computing device and the computing device can be a component. One or more components may exist within a process and / or thread of execution, and a component may be localized on one computer and / or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures stored thereon. The components are for example from a signal having one or more data packets (eg, from one component interacting with another component of the local system, distributed system and / or interacting with another system via a network such as the Internet via a signal). Data) may be communicated via local and / or remote processes.

Various embodiments may be provided through systems that may include a number of components, modules, and the like. Various systems may include additional components, modules, and / or may not include all of the components, modules, etc. described in connection with the drawings. Combinations of these solutions can also be used.

3 is a schematic block diagram of a wireless communication device 300 having a system for transmitting a rotational training sequence. System 302 may include inputs on lines 306a and 306b for receiving information, in-phase (I) modulation path 308, quadrature (Q) modulation path 310, and their I and Q paths 308. And a combiner 312 for respectively combining the signals from 310. Although an RF transmitter is used as an example to illustrate the present invention, it should be appreciated that the present invention can be applied to any communication medium (eg, wireless, wired, optical) capable of carrying orthogonal modulated information. I and Q paths may alternatively be referred to as I and Q channels. The combined signals are provided to amplifier 320 via line 318 and finally to antenna 322 where the signals are radiated. Transmitter 304 may be enabled to transmit a message with a rotational training signal. Training information and Q modulation paths in which rotation training signals, which may also be referred to as quadrature balanced training signals, balanced training signals, balanced training sequences, or unbiased training signals, are transmitted through I modulation path 308. Training information transmitted through 310 is included. Transmitter 304 also transmits orthogonal modulated (not predetermined) communication data. In one aspect, the orthogonally modulated communication data is subsequently transmitted to transmit a rotational training signal. In another example, the training signal is transmitted simultaneously with the communication data in the form of pilot signals. The system is not limited to any particular temporal relationship between the training signal and the quadrature modulated communication data.

4A to 4D are schematic diagrams showing a training signal having orthogonally modulated communication data. 3A and 4A together, in one aspect, the transmitter 304 initially transmits training information over the I modulation path 308 and then trains over the Q modulation path 310. By transmitting the information, the rotation training signal is transmitted. That is, the training signal is capable of transmitting information such as a symbol transmitted only through I modulation path 308 or a series of repeated symbols followed by a transmission of a symbol transmitted only or only through Q modulation path 310 or a repeated series of symbols. Include. Alternative but not shown training information may be initially transmitted over Q modulation path 310 and then over I modulation path 208.

In the case where single symbols are transmitted alternately over the I and Q paths, it is most possible for the transmitter to transmit a rotational training signal with predetermined training information over the I and Q modulation paths. For example, the first symbol may always be (1,0) and the second symbol may always be (0,1).

The rotational training signal described above, which initially transmits the rotational training signal over the I modulation path only, can be achieved by energizing the I modulation path 308 and deactivating the Q modulation path 310. . The transmitter then transmits a rotational training signal over the Q modulation path by transmitting the training information over the I modulation path followed by activating the Q modulation path 310.

5A and 5B show rotational training symbols in a representation in an orthogonal constellation. 3, 4A, and 5A, the transmitter 304 transmits a first symbol having a reference phase through the I modulation path 308, and also (reference phase + 90 °) or (reference). A rotational training signal is generated by transmitting a second symbol with a phase of any one of phase -90 [deg.] Through the Q modulation path 310. For example, the reference phase of the first symbol may be 0 °, in which case the phase of the second symbol may be 90 ° (as shown) or −90 ° (not shown).

However, as described above, it is unnecessary to simply alternate the transmission of symbols over the modulation paths 308/310 to obtain symbol rotation. For example, the first symbol may be transmitted only through (only) I (or Q) modulation paths, and the transmitter may transmit training information simultaneously through both I and Q modulation paths, and I and Q modulated signals These may be combined to provide a second symbol. As another example, the transmitter may simultaneously transmit training information over both I and Q modulation paths, and combine the I and Q modulated signals to provide a first symbol, whereas the second symbol may only be Q (or I) obtained only using the modulation path.

Training symbols can also be rotated by providing symbols each having both I and Q members, as is typically associated with orthogonal modulation, see FIG. 4B. That is, transmitter 304 may transmit training information simultaneously through both I and Q modulation paths 308/310 and combine the I and Q modulated signals to provide a first symbol over line 318. Can be. For example, the first symbol may occupy a position at 45 ° in the constellation, see FIG. 5B. Similarly, the transmitter will simultaneously transmit training information through both I and Q modulation paths 308/310 and combine the I and Q modulated signals to provide a second symbol. For example, the second symbol can be rotated to a position of -45 °, which is orthogonal to the first symbol 45 °.

Thus, in one aspect, the rotation training symbol includes at least a sequence of two symbols with a phase difference of 90 °. However, the system is not limited to a system using only two symbols. In general, an even number of symbols is preferred so that half of the symbols can be generated using the I modulation path and the other half can be generated using the Q modulation path. However, in sequences longer than two symbols, a 90 ° rotation does not need to be performed between all symbols. In other words, there is no particular order of phase between symbols. In one aspect, half of the symbols differ by 90 ° on average from the other half. For example, an ultra wideband (UWB) system uses six symbols that are transmitted prior to transmission of communication data or beacon signals. Therefore, three consecutive symbols may be generated on the I modulation path, followed by three consecutive symbols on the Q modulation path. By using this process, the Q channel needs to be briefly active for only three symbols before returning to the sleep mode.

6 is a diagram illustrating an example frame network for conveying a message having a rotation training signal. 3 and 6, in one aspect, the transmitter 304 is operated in accordance with the OSI model. In this conventional seven-layer model, the transmitter is associated with a physical (PHY) layer. As shown, the transmitter 304 transmits a physical layer (PHY) signal 600 that includes a preamble 602, a header 604, and a payload 606. The transmitter transmits a rotation training signal via the PHY header 604 and transmits orthogonally modulated communication data via the PHY payload 606.

While many communication systems transmit beacon information at relatively slow orthogonal modulation communication data rates, they reserve higher data rates for the transmission of (undetermined) information. Networks operating in accordance with IEEE 802.11 protocols are examples of such systems. Because many wireless communication devices operate on batteries, these units preferably operate in a "sleep" mode when they are not actually transmitting information. For example, the main units or access points may broadcast relatively simple and low data rate beacon signals until the sleeping unit responds.

Pilot signals may be considered a special case of training signals. Although the training signals are typically sent before the data using all subcarriers (all N frequencies in the communication bandwidth), the pilot tones are sent on a subset of the (reserved) frequencies with orthogonal modulated communication data. In a system using OFDM such as UWB, this reserved set is formed of pilot tones. That is, pilot tones are associated with P frequencies and data is associated with the remaining N-P frequencies.

Training signals and pilot signals are similar in that the information content of the transmitted data is typically predetermined or "known" data that allows the receiver to calibrate and perform channel measurements. When receiving communication (undetermined) data, there are three unknowns: the data itself, the channel, and the noise. The receiver cannot correct the noise because the noise changes randomly. Channels are measurements commonly associated with delay and multipath. During relatively short time periods, errors occurring due to multipath can be measured when predetermined data such as training or pilot signals are used. Once the channel is known, this measurement can be used to remove errors in the received communication (not predetermined) data. Therefore, some systems provide a training signal to measure the channel before data decoding begins.

However, the channel may change, for example, when the transmitter or receiver moves in space or the clocks drift. As such, many systems contribute to sending more "known" data along with "unknown" data to track slow changes in the channel. To illustrate the system, it will be assumed that the pilot signals are a subset of the more general class of training signals. In other words, as used herein, training signals refer to both initial training sequences as well as tracking training sequences, referred to as pilot tones in a UWB or 802.11 system. In other words, "initial training" and "tracking training" or "pilot tones" are all types of training signals.

In one aspect, the transmitter 304, following the rotation training signal, transmits a message if the orthogonal modulated communication data is a beacon signal transmitted at the beacon data rate. That is, beacon signals used by many communication systems may be transmitted via rotational training signals. In addition, the transmitter 304 may alternatively or additionally, following the rotational training signal, transmit a message with orthogonally modulated communication data at a communication data rate greater than the beacon data rate.

In one aspect, the transmitter may transmit a combination of rotating and non-rotating training signals and messages. For example, the transmitter 304 may send multi-burst messages including a balanced message, followed by an unbalanced message. For simplicity, the phrase “balanced message” is used to describe a message that includes both a rotation training signal and quadrature modulated communication data. An unbalanced message is a message that includes a non-rotating training signal when training information is transmitted, for example, via an I modulation path but not through a Q modulation path. In this aspect, the unbalanced message also includes a message format signal inserted in the header, for example, indicating that a balanced message (with a rotation training signal) is sent following that unbalanced message. The unbalanced message contains orthogonally modulated communication data, which may be transmitted following the message format signal via the payload. However, the system is not limited to any particular time relationship between the training signal, the message format signal, and orthogonal modulated data. For example, the unbalanced message can be a beacon signal or an initial training message. Alternatively, an unbalanced message can be sent following a balanced message, or the unbalanced messages can be interspersed with the balanced messages.

Considering FIG. 4C, many communication systems, such as systems conforming to IEEE 802.11 and UWB, use multiple subcarriers transmitted simultaneously. In this aspect, the rotational training signal may be possible in the form of pilot signals. For example, P rotation pilot symbols may be generated with (N-P) orthogonal modulated communication data symbols. Each rotation pilot symbol includes 90 ° different training symbols per symbol. Thus, the balance message is transmitted by transmitting N symbols simultaneously with the rotation training signal. In another aspect, fewer rotation pilot symbols are used than P because some of the pilot symbols are non-rotation symbols.

Referring to FIG. 4D, in another aspect of a multi-carrier system, a rotation training signal includes training information for i subcarriers transmitted through an I modulation path but not through a Q modulation path. To include symbols that are generated simultaneously for multiple subcarriers. In addition, the training signal uses training information for the j subcarriers transmitted over the Q modulation path but not over the I modulation path. Subsequently, IQ modulated communication data is generated for the i and j subcarriers following the generation of the training information. In one aspect, the subset of i subcarriers includes "paired subcarriers" or "paired tones", which is a pair of tones at frequency -f and frequency + f. Likewise, the tones of subset j may be made in pairs. Pairing the tones at -f and + f helps to obtain I channel training, Q channel training, and rotational training.

If the sequence of training symbols on any particular subcarrier does not rotate by 90 °, such a system can still be considered when generating a rotational training signal, because the channel estimation averaging technique is used to average adjacent subcarriers. This can be used at the receiver. The overall effect of using adjacent non-rotating I and Q training symbols is then the rotation training signal. In one aspect, the training signal is designed so that odd subcarriers use non-rotating training symbols transmitted over an I modulation path (channel X) and even subcarriers use a Q modulation path (channel X + 90 °).

In another aspect of the invention, the wireless communication device 300 of FIG. 3 includes means (308/310) for rotating a training signal using I and Q modulation paths, and means for generating orthogonally modulated communication data. 308/310 may be considered to include. As above, the training signal may be pilot symbols transmitted simultaneously with the communication data, or the communication data may be transmitted following the rotational training signal. In addition, the apparatus 300 includes means 320/322 for transmitting in RF communication.

Similarly, an unbalanced message can be generated, and orthogonal modulation means 308/310 are used to generate the following: Training information transmitted over the Q modulation path with training information transmitted over the I modulation path. Non-rotating training signal having no; A message format signal indicating that a balance message (with a rotation training signal) will be sent following an unbalanced message; And quadrature modulated communication data.

7 is a schematic block diagram illustrating a processing apparatus for transmitting an orthogonal modulation rotation training sequence. Processing apparatus 700 includes an I path modulation module 702 having an input on line 704 for receiving information and an input on line 706 for receiving I control signals. I path modulation module 702 has an output on line 708 for providing I modulated information. Q path modulation module 710 has an input on line 712 for receiving information and an input on line 714 for receiving Q control signals. Q path modulation module 710 has an output on line 716 for providing Q modulated information.

The combiner module 718 has inputs on lines 708 and 716 for receiving I and Q modulated information, respectively, and an output on line 720 for providing an orthogonally modulated RF signal. Controller module 722 has outputs on lines 706 and 714 for providing I and Q control signals, respectively. The controller module 722 controls I and Q to generate messages with rotational training signals including orthogonally modulated communication data, as well as training information transmitted over the I modulation path and training information transmitted over the Q modulation path. Use signals The functions performed by the modules described above will not be described repeatedly for simplicity as they are similar to the functions performed by the apparatus of FIG. 3.

detail of fuction

As described above, the rotation training signal of the present invention can be used to modify conventional systems that use only the I modulation path for training in an effort to save power. Such a system can be modified by momentarily enabling the Q modulation path during the second portion of the training sequence. This solution uses only a little more power, while simulating both I and Q channels during the training sequence.

Alternatively, an unbalanced message with a non-rotating training signal can be used for the beacon, while balanced messages are used for high data rates along with the rotating training signals. Such a solution may require that the receiver be programmed to associate rotating training signal messages with a high data rate and unbalanced messages with beacons. In order to eliminate the need for the receiver to "guess" the type of training signal to be received, information for informing the receiver of the type of training sequence to be followed may be inserted in the preamble.

In another variation, conventional unbalanced messages may be used as the first burst in multi-burst transmissions. With multi-burst transmission, the receiver can easily know in each burst the type of training sequence to appear in subsequent bursts. Then, typically, the first burst may be an unbalanced message and all subsequent bursts may be balanced messages. Such messages may be selectively enabled and used only, for example, if provided by both the transmitter and the receiver. In this way, the present invention can achieve backward compatibility with existing devices.

Another solution that is not backward compatible is to change all training sequences, including the beacon's training sequence, so that the training sequence is always balanced. In this variant, the receiver does not need to operate on two different types of training signals.

As an example, analysis is provided under improvements that can be obtained in a conventional UWB-OFDM system by adding a balance message with rotation training signals. Typically, the training sequence is a repeated OFDM symbol. This means that the same constellation point is repeatedly transmitted for each subcarrier. The natural direction (eg, I path) in the constellation is simulated while the other direction (eg, Q path) is not simulated. Errors associated with such a system are presented in the background above.

에 대한 이상적인 성상도 및 불균형 성상도을 나타내는 도면이다. 위상 불균형은

=10°이다(진폭 불균형을 갖지 않음). 주시 : 그 불균형은 각도들이 0° 및 90°일 때 가장 강하지만, 각도가 45° 및 135°일 때는 거의 존재하지 않는다. 그 이유는 불균형 자체가 임핑잉 파의 위상이 I 및 Q 경로들 사이의 중간에 있을 때 대략 45°를 보상하기 때문이다. 임핑잉 파형의 각도는 데이터 및 채널 양쪽 모두에 의존적이고, 0°와 360° 사이의 임의의 값을 취할 수 있다.8 shows two different phases of the impinging waveform of FIG.

A diagram showing ideal constellations and unbalance constellations for. Phase imbalance

= 10 ° (without amplitude imbalance). Note: The imbalance is strongest at angles of 0 ° and 90 °, but rarely present at angles of 45 ° and 135 °. This is because the imbalance itself compensates approximately 45 ° when the phase of the impinging wave is in the middle between the I and Q paths. The angle of the impinging waveform depends on both the data and the channel and can take any value between 0 ° and 360 °.

=0)으로 정렬되도록 하는 각도를 임핑잉 파형이 갖는다고 가정하면, 그 I 방향은 0°의 에러로 정확히 추정될 것이다. 그러나, Q 방향은 10°만큼 벗어날 것이다. 백색 부가 가우시안 잡음(AWGN) 에서, 이는 Q 방향에 놓인 성상도 포인트들에 대한 과도한 에러들을 초래한다. 만약 다른 한편으로 임핑잉 파형이

=45°의 각도(I 및 Q 사이의 중간)를 갖는다면, 불균형은 거의 존재하지 않는다.For example, all training symbols are in the I direction (

Assuming that the impinging waveform has an angle that causes it to align 0 = 0), its I direction will be accurately estimated with an error of 0 °. However, the Q direction will deviate by 10 °. In white additive Gaussian noise (AWGN), this results in excessive errors for constellation points lying in the Q direction. If on the other hand the impinging waveform

If there is an angle (middle between I and Q) of = 45 °, there is almost no imbalance.

9 is a graph showing phase imbalance as a function of phase on an impinging waveform. The solid line on the figure shows the phase imbalance in case of repeated training sequences. The dashed line represents the case of the rotation training sequence. For AWGN and for BER uncoded QPSK of 10 ⁻⁵ , the loss for unbalance (depending on the phase of the impinging waveform) that varies between 0 ° and 10 ° is between 0 dB and 1.5 dB.

^ｏ만큼 벗어날 것이다. 그들은 상당히 더 많은 에러들을 초래할 것이다.Analysis may begin on a simpler problem of time domain modulations such as Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA) in AWGN. It is assumed that the training sequence has all the symbols that lie on the I axis (I channel). After transmission on the AWGN channel, the axis can rotate about direction X in the orthogonal 2D plane (depending on the channel phase). By having all the training symbols aligned in direction X, direction X is properly estimated and any data symbol in that direction is placed on the appropriate axis (after rotation). However, the symbols in orthogonal direction Y are from the ideal position

^o it will escape much. They will cause considerably more errors.

Since all training symbols lie on the X axis, the channel estimate is H = angle (X).

The error in the X direction is angle X-H = 0.

이다.The error in the Y direction is angle (Y) -90 ° -H =

to be.

This analysis assumes that the training sequence rotates constantly so that the I and Q channels are simulated identically. In this case, the average channel has a phase that is no longer aligned only in the X direction. It will also be aligned in the Y direction for half of the time.

The channel estimate is now H = [angle (X) + angle (Y) -90 °] / 2.

이다.The error in the X direction is angle (X) -H =

to be.

/2이다.The error in the Y direction is angle (Y) -90 ° -H =

/ 2.

The dashed line curve in the figure shows the phase imbalance in each direction. The dashed line curve is essentially 0.5 times the solid line curve.

Each direction (X and Y) now shares half of the quadrature imbalance burden. The loss is 0 dB to 0.5 dB, corresponding to a 5 ° maximum imbalance on each axis. The gain varies between 0 dB and 1 dB. Note: In the presence of an LOS channel (AWGN), most carriers can be aligned in the same phase and reduced by 1.5 dB in case of repeated training sequences. In the same scenario, the reduction is only 0.5 dB for the rotational training sequence, which is a 1 dB gain. However, because the phase noise and / or residual frequency offset change the phase of the impinging waveform, the phase imbalance varies between 0 ° and 10 °. Errors are partially smoothed. In the case of high data rates, diversity may not be sufficient to compensate for excessive errors that regularly hit the subcarriers. The effect on high data rates is more important.

Implementation of a rotational training sequence does not necessarily mean any greater hardware complexity at the receiver or transmitter. In the receiver, a rotation of 90 ° before accumulation is performed by exchanging I and Q channels and sign-inverting one of them. This can be done in the time domain (when all frequencies are rotated in the same way) or in the more general case the Fourier domain.

및

의 불균형을 갖기보다는 오히려

및

의 불균형이 I 및 Q 채널 각각에서 획득된다.Using the notation of the 2003 IEEE publication "Compensation of IQ imbalance in OFDM system" (Jan Tubbax et al.), The author refers to an imbalance in the middle between the I and Q channels,

And

Rather than having an imbalance of

And

An imbalance of is obtained in each of the I and Q channels.

Orthogonal unbalanced distortion received signal in the absence of any channel and noise can be represented through the transmission signal by the following equation:

및

는 직교 불균형 왜곡을 특징짓는 복소량들(complex quantities)이다. 이들은 아래와 같이 제공된다:Where x is a complex transmit signal, x ^* is a complex conjugate, y is a complex receive signal,

And

Is complex quantities that characterize orthogonal unbalance distortion. These are provided as follows:

When they are 1 and 0, respectively, the received signal is the same as the transmitted signal.

The time domain modulation case in AWGN will be discussed again using this more formal description. If there is no noise but there is an AWGN channel with coefficient c, then the received signal before unbalance is cx and the received signal after unbalance is:

Deflection training sequence

If a training sequence constituting symbols ± u, i.e. a training sequence that is always aligned in u's own direction in the 2D plane, is transmitted, two possible received symbols are obtained:

을 획득하기 위해서 각각 적용된다.For simplicity but without loss of generality, assuming that vector u is a unitary vector for estimating a channel, digital de-rotation of + u ^* and -u ^* is channel estimation.

Are applied to obtain each.

On the left side of the addition operator, a channel (or approximately) is obtained, but noise or bias occurs on the right side. This noise disappears when more and more training symbols are averaged, and it only remains when white noise disappears. Thus, the estimation of the channel is biased when a training sequence is aligned that is only aligned with the symbol u.

When the transmission of data x begins, for example, a metric entering the Viterbi decoder is obtained by multiplying the received signal by the complex conjugate of the channel (the match filter of the channel).

이다.therefore,

to be.

이다.And after removing some of the quantities of the second order,

to be.

The first component in the above metric formula is ideally a positive real scalar proportional to the channel energy multiplied by the original constellation point. However, the second and third components of the formula are unnecessary noise generated by the deflection. Their noise variance is equal to:

And, when no other noise source is present, the signal-to-noise ratio (SNR) is as follows:

This noise does not have a distribution of white Gaussian noise, but if several symbols arrive from different independent channels c _i (multi-paths in CDMA, or interleaving, etc.), after the symbols are combined, Slow convergence to white Gaussian noise is obtained. This SNR may be approximately 10-20 dB. In the case of data rates operating at low SNR, this additional noise may not be a problem. However, for high data rates operating at high SNRs, this additional noise has a significant adverse effect.

Unbiased Training Sequence

If half of the symbols are sent in the orthogonal direction of orthogonal u denoted by v rather than transmitting the entire training sequence aligned in the u's inherent direction, the average of the channel estimate is obtained as follows:

이기 때문에 사라진다. 이제, 메트릭은 다음과 같다:Right deflection is when these two unitary vectors are orthogonal

Because it disappears. Now, the metric is:

Half of the orthogonal imbalance noise disappears. SNR is improved by 3dB (if no noise is present):

OFDM

In OFDM, the formula for the received symbol hardly changes except that the entire OFDM symbol should be considered as a vector of symbols:

Here, the vectors are indicated by bold letters, and the (·) operation is an element-wise product between the two vectors. Channel c is the Fourier domain version of the channel. This equation can be expressed as follows:

Here, the index m represents a vector mirrored over the subcarriers. Contributors to the received symbol at only frequency (+ f) are channels and symbols at symmetrical frequencies (+ f and -f). The two symmetric subcarriers (+ f and -f) can be separated and the received symbol for the subcarrier (+ f) can be expressed as follows:

Here, index m represents a channel or symbol at frequency -f. The main difference between this formula and the formula in the case of TDMA or CDMA is that distortion is now produced by channels and signals at different frequencies, i.e., frequency (-f). This can have a significant adverse effect on a particular received symbol if the symmetrical frequency has a much stronger channel or a much stronger signal. Thus, these issues may be more problematic in OFDM.

Deflection training sequence

Assuming that the pilot tone transmitted at frequency (+ f) is u and the pilot tone transmitted at frequency (-f) is u _m , the deflection training sequence does not properly rotate the pilot tones, thereby causing deflection in channel estimation. Generates:

Then, the metric received at frequency (+ f) can be expressed as follows:

이 매우 강할 수 있기 때문이다. 그 잡음 항들은 이제 주파수(-f)에서 채널의 강도에 의존하며, 중요할 수 있다. 주파수(-f)는 비터비 디코더를 혼동시킬 수 있는 간섭자로서 동작하는데, 그 비터비 디코더는 많은 간섭을 갖는 약한 메트릭을 양호한 메트릭으로 종종 해석할 수 있다.In the above formula, the fourth (noise) term can no longer be ignored because the channel

Because this can be very strong. The noise terms now depend on the strength of the channel at frequency (-f) and may be important. The frequency (-f) acts as an interferer that can confuse the Viterbi decoder, which can often interpret the weak metric with much interference as a good metric.

Unbiased Training Sequence

이고, 2개의 잡음 항들은 아래의 메트릭을 얻기 위해 수학식으로부터 제거된다:In the case of an unbiased training sequence, the channel estimate is

And two noise terms are removed from the equation to obtain the following metric:

The improvement is clear. However, it is difficult to evaluate the benefits of the 480 megabytes per second (Mbps) data rate in UWB-OFDM without the simulation in the actual channel model. Note that for these high data rates the devices are expected to have LOS or nearly LOS and therefore the deviations of the channel at frequencies + f and -f are not expected to be too large. However, a difference of 3 dB or more in channel strength is very possible.

Orthogonal imbalance of the transmitter

및

가 전송기 측에서의 불균형 계수들로서 나타난다면, 전송기의 출력은 다음과 같이 표현될 수 있고:Orthogonal imbalances also appear at the transmitter and add to the distortion. if

And

If is represented as the imbalance coefficients at the transmitter side, the output of the transmitter can be expressed as follows:

) 이후에 다음을 획득한다:Receiver receives channel (c) and distortion (

After) you get:

The above analysis is applicable to TDMA / CDMA, c ^* is replaced with c ^* _m, there is applied to the OFDM If x ^* is replaced by x _m ^* (i.e., the values of the frequency (-f)).

The problem of orthogonal imbalance at both the transmitter and receiver remains the same as described above, but with different values for the imbalance coefficients that are a function of the channel. If the second order quantities are ignored and c _m ^* is not excessively strong or weaker than c, then:

Noise from distortion is increased. Using an unbiased training sequence helps to remove some of the terms that contribute to noise on the metrics as described above.

Sending an unbiased training sequence can be accomplished in a conventional UWB system by sending a first portion of the training sequence using the I path and sending a second portion over the Q path. Although the unbiased training signal (non-rotating training signal) is used for beaconing to save power by turning off the Q channel, the particular signal inserted in the preamble can inform the receiver of the type of training sequence. Alternatively, the receiver can automatically detect the training sequence being sent. This is not a difficult task because it is sufficient to find a few strong sub-carriers to determine if the transmission is the same or rotated by 90 °.

As described earlier, pilot tones are considered to be special case training sequences because many conventional systems use pilots that are transmitted in a unique direction in the complex plane. When pilot tones are tracked, a deflection occurs constantly along that direction. Better pilots are obtained by changing all OFMD symbols by 90 ° or by rotating some pair of subcarriers (± f) by 90 ° relative to another pair of subcarriers (on different frequencies) within the same OFDM symbol. This change in pilot tones is simple and has almost zero cost. When the clocks between the transmitters and receivers drift, the pilot tones have the potential to compensate for some of the deflection introduced through the initial deflection training sequence when an unbalanced training signal is used. In other words, maintaining a deflection (non-rotation) training sequence while simultaneously generating rotation pilot sequences reduces deflection in most environments.

Simulations were performed to measure the effect of orthogonal imbalance with or without the balance training sequence. In the case of an imbalance on the TX side of 10% (0.4 dB) in amplitude and 10 ° in phase, and in the same amount of imbalance on the receiver side, the gain for the highest data rate (480 Mbps) is almost 1 dB. Even larger gains can be expected if more types of losses occur that result in the need for higher SNR. The higher the SNR, the greater the gain that can be obtained using a balanced training sequence.

10 is a flowchart illustrating a method for transmitting a communication training sequence. Although the method is shown as a sequence of numbered steps for clarity, the number does not necessarily indicate an order of steps. Some of these steps may be omitted, may be performed in parallel, or may be performed without the necessity of maintaining a strict sequence order. The method begins at step 1000.

In step 1002, a rotation training signal is generated at an orthogonal modulation transmitter. Typically, predetermined or known information is transmitted as the training signal. In step 1002a, training information is transmitted over an I modulation path, and in step 1002b, training information is transmitted over a Q modulation path. In step 1004, orthogonal modulated communication data is generated. Step 1004 may be performed following step 1002 or may be concurrent with the performance of step 1002. In one aspect, a beacon signal is generated at step 1004 at a beacon data rate. Alternatively, information is generated at step 1004 at a communication data rate greater than the beacon data rate. In step 1006, a rotation training signal and quadrature modulated communication data are transmitted. Typically, the generation and transmission of symbols or information occurs almost simultaneously.

In one aspect, transmitting the rotational training signal at step 1006 includes initially transmitting training information over an I modulation path and subsequently transmitting training information over a Q modulation path. For example, initially generating training information via the I modulation path (step 1002a) may include energizing the I modulation path but not including activating the Q modulation path. Subsequently, generating the training information via the Q modulation path subsequent to generating the training information via the I modulation path includes activating the Q modulation path. Alternatively, the training information may be sent in the reverse order. More specifically, generating training information via the I modulation path at step 1002a may include generating a first symbol having a reference phase. Subsequently, generating training information via the Q modulation path in step 1002b includes generating a second symbol having a reference phase of + 90 ° or a phase of -90 °.

In another aspect, in step 1002b training information is generated over a Q modulation path using subsequent substeps (not shown). In step 1002b1, training information is simultaneously generated through the I and Q modulation paths, and in step 1002b2, the I and Q modulated signals are combined to provide a second symbol. Alternatively or additionally, generating training information via an I modulation path may include substeps (not shown). In step 1002a1 training information is simultaneously generated over both I and Q modulation paths, and in step 1002a2 the I and Q modulated signals are combined to provide a first symbol.

In another aspect, the transmitting step (step 1006) includes substeps. In step 1006a, a physical layer (PHY) signal including a preamble, a header, and a payload is constructed. Note that this configuration typically occurs as a response to receiving information to be sent in the corresponding MAC format. In step 1006b, a rotation training signal is transmitted through the PHY header, and in step 1006c, IQ modulated communication data is transmitted through the PHY payload.

In another aspect, in step 1001a a multi-burst transmission with an unbalanced message is sent (step 1001b), followed by a rotation training signal (step 1006). An unbalanced, i.e., unbalanced message comprises a non-rotating training signal having training information (step 1001b1) transmitted over an I modulation path but no training information (step 1001b2) transmitted over a Q modulation path. The imbalance message includes a generated message format signal (step 1001b3) indicating that the rotation training signal is sent following that imbalance message. Orthogonally modulated communication data is generated in step 1001b4. In another aspect, generating the rotation training signal in step 1002 includes generating P rotation pilot symbols, and generating the orthogonally modulated communication data in step 1004 includes (NP) communication data symbols. Generating them. Subsequently, the transmission in step 1006 includes transmitting N symbols simultaneously.

In another variation, generating the rotation training signal at step 1002 includes generating symbols for multiple subcarriers simultaneously. More specifically, step 1002a uses training information transmitted over the I modulation path rather than the Q modulation path for the i subcarriers. In step 1002b, the training information transmitted over the Q modulation path rather than the I modulation path is used for the j subcarriers. Subsequently, generating orthogonally modulated communication data in step 1004 includes generating orthogonally modulated communication data for the i and j subcarriers subsequent to generation of the training information. In one aspect, each i subcarrier is adjacent to the j subcarrier.

More formally, the channel estimated by subcarrier i is:

(1)

(One)

Almost the same channel is estimated by adjacent subcarriers j with pilot rotated 90 ° as follows:

(2)

(2)

Note: The symbol for complex numbers j in the equation should not be confused with subset j. The deflection is then automatically removed after averaging over the subcarriers, ie after averaging the results of (1) and (2).

The flowchart described above may be interpreted as a representation of a computer-readable medium storing instructions for transmitting an orthogonal modulation rotation training sequence. The instructions for transmitting the rotational training signal will correspond to steps 1000-1006 as described above.

Systems, methods, apparatuses, and processors have been provided for enabling the transmission of orthogonally modulated rotational training signals at a wireless communication device transmitter. Examples of specific communication protocols and formats have been provided to illustrate the present invention. However, the present invention is not limited to these examples only. Other variations and embodiments of the invention will occur to those skilled in the art.

Claims (38)

As a method for transmitting a communication training sequence (communication training sequence), Generating a rotational training signal at a quadrature modulation transmitter, wherein the training signal includes training information transmitted over an in-phase (I) modulation path and training information transmitted over a quadrature (Q) modulation path; Generating orthogonal modulated communication data; And Transmitting the rotation training signal and quadrature modulated communication data; Method of transmitting a communication training sequence. The method of claim 1, wherein transmitting the rotational training signal comprises: Initially transmitting training information over the I modulation path; And Subsequently transmitting training information over the Q modulation path; Method of transmitting a communication training sequence. The method of claim 1, wherein generating the orthogonal modulated communication data comprises a group consisting of a beacon signal generated at a beacon data rate and communication data generated at a communication data rate greater than the beacon data rate. Generating data selected from Method of transmitting a communication training sequence. The method of claim 1, Generating the rotational training signal comprises simultaneously generating symbols for a plurality of subcarriers, Simultaneously generating symbols for the plurality of subcarriers, for i subcarriers, use training information transmitted over the I modulation path rather than the Q modulation path; for j subcarriers, by using training information transmitted over the Q modulation path rather than the I modulation path, Wherein generating the orthogonally modulated communication data comprises generating orthogonally modulated communication data for the i subcarriers and the j subcarriers subsequent to the generation of the training information. Method of transmitting a communication training sequence. The method of claim 1, Generating training information over the I modulation path comprises generating a first symbol having a reference phase; Generating training information via the Q modulation path includes generating a second symbol having a phase selected from the group consisting of the reference phase + 90 ° and the reference phase -90 °. Method of transmitting a communication training sequence. The method of claim 5, wherein generating training information through the Q modulation path comprises: Simultaneously generating training information over both the I modulation path and the Q modulation path; And Combining I and Q modulated signals to provide the second symbol, Method of transmitting a communication training sequence. The method of claim 5, wherein generating training information through the I modulation path includes: Simultaneously generating training information over both the I modulation path and the Q modulation path; And Combining I and Q modulated signals to provide the first symbol; Method of transmitting a communication training sequence. The method of claim 1, wherein transmitting the rotation training signal and quadrature modulated communication data comprises: Constructing a physical layer (PHY) signal comprising a preamble, a header, and a payload; Transmitting the rotational training signal through the PHY header; And Transmitting the orthogonal modulated communication data via the PHY payload; Method of transmitting a communication training sequence. The method of claim 2, wherein initially transmitting training information through the I modulation path includes: Energizing the I modulation path; And Not activating the Q modulation path, Wherein the transmitting of the training information through the Q modulation path following the transmitting of the training information through the I modulation path includes activating the Q modulation path. Method of transmitting a communication training sequence. The method of claim 1, wherein generating the rotational training signal comprises transmitting predetermined training information through the I modulation path and transmitting predetermined training information through the Q modulation path. Method of transmitting a communication training sequence. The method of claim 1, Transmitting the rotational training signal and orthogonally modulated communication data after multi-burst transmission with an unbalanced message, The imbalance message is A non-rotating training signal having training information transmitted through the I modulation path but no training information transmitted through the Q modulation path; A message format signal indicating that a rotation training signal is sent following the imbalance message; And Including orthogonal modulated communication data, Method of transmitting a communication training sequence. The method of claim 1, Generating the rotation training signal comprises generating P rotation pilot symbols; Generating the orthogonal modulated communication data includes generating (N-P) communication data symbols; Transmitting the rotational training signal and the orthogonal modulated communication data includes transmitting N symbols simultaneously. Method of transmitting a communication training sequence. A processing device for transmitting an orthogonally modulated rotational training sequence, comprising: An in-phase (I) path modulation module having an input for receiving information, an input for receiving I control signals, and an output for providing I modulated information; A quadrature (Q) path modulation module having an input for receiving information, an input for receiving Q control signals, and an output for providing Q modulated information; A combiner module having inputs for receiving the I modulated information and the Q modulated information and an output for providing an orthogonal modulated signal; And A controller module having outputs for providing the I control signals and the Q control signals, The controller module uses the I control signals and the Q control signals, A rotation training signal comprising training information transmitted over an I modulation path and training information transmitted over a Q modulation path, and Generating orthogonal modulated communication data, Processing unit. A communication system for transmitting an orthogonally modulated rotational training sequence, comprising: A transmitter having an input for receiving information, an in-phase (I) modulation path, a quadrature (Q) modulation path, and a combiner for combining signals from the I modulation path and the Q modulation path, The transmitter transmits a rotation training signal including training information transmitted through the I modulation path and training information transmitted through the Q modulation path. The transmitter for transmitting quadrature modulated communication data and the rotational training signal, Communication system. 15. The system of claim 14, wherein the transmitter transmits the rotational training signal by initially transmitting training information over the I modulation path and subsequently transmitting training information over the Q modulation path. Communication system. 15. The apparatus of claim 14, wherein the transmitter transmits orthogonal modulated communication data as data selected from the group consisting of beacon signals generated at a beacon rate and communication data generated at a rate greater than the beacon data rate, Communication system. 15. The method of claim 14, The transmitter generates a rotational training signal by simultaneously generating symbols for multiple subcarriers, The rotation training signal is, for i subcarriers, use training information transmitted over the I modulation path rather than the Q modulation path; for j subcarriers, by using training information transmitted over the Q modulation path rather than the I modulation path, Wherein the transmitter generates orthogonally modulated communication data for the i subcarriers and the j subcarriers subsequent to the generation of the training information. Communication system. 15. The apparatus of claim 14, wherein the transmitter transmits a first symbol having a reference phase through the I modulation path and further selects from the group consisting of the reference phase + 90 ° and the reference phase -90 ° through the Q modulation path. Transmitting the rotational training signal by transmitting a second symbol having a phase that becomes Communication system. 19. The apparatus of claim 18, wherein the transmitter simultaneously transmits training information over both the I modulation path and the Q modulation path, and combines an I modulated signal and a Q modulated signal to provide the second symbol. Communication system. 19. The apparatus of claim 18, wherein the transmitter simultaneously transmits the training information through both the I modulation path and the Q modulation path and combines the I modulated signal and the Q modulated signal to provide the first symbol. , Communication system. 15. The method of claim 14, The transmitter transmits a physical layer (PHY) signal including a preamble, a header, and a payload, transmits the rotation training signal through the PHY header, and transmits the orthogonally modulated communication data through the PHY payload. Transmitted, Communication system. The method of claim 15, The transmitter initially transmits the rotational training signal over the I modulation path by activating the I modulation path and not activating the Q modulation path, The transmitter subsequent to transmitting training information through the I modulation path, transmitting the rotational training signal through the Q modulation path by activating the Q modulation path, Communication system. 15. The apparatus of claim 14, wherein the transmitter transmits a rotational training signal having predetermined training information over the I modulation path and the Q modulation path. Communication system. 15. The method of claim 14, The transmitter transmits an unbalanced message, and multi-burst messages comprising the rotation training signal and orthogonal modulated data, The imbalance message is A non-rotating training signal having training information transmitted through the I modulation path but no training information transmitted through the Q modulation path; A message format signal indicating that a rotation training signal is sent following the imbalance message; And Including orthogonal modulated communication data, Communication system. 15. The apparatus of claim 14, wherein the transmitter generates orthogonal modulated communication data having P rotation pilot symbols and (N-P) communication data symbols and simultaneously transmits N symbols. Communication system. A computer-readable medium storing instructions for transmitting a rotational training signal, the instructions comprising: Instructions for generating a rotational training signal at a quadrature modulation transmitter, wherein the rotational training signal includes training information transmitted over an in-phase (I) modulation path and training information transmitted over a quadrature (Q) modulation path; Instructions for generating orthogonal modulated communication data; And Instructions for transmitting the rotational training signal and quadrature modulated communication data; Computer-readable media. A communication device for transmitting a rotational training signal, Means for rotating a training signal using an in-phase (I) modulation path and a quadrature (Q) modulation path; Means for generating orthogonal modulated communication data; And Means for transmitting, Communication device. 28. The system of claim 27 wherein the rotational training signal is initially transmitted over the I modulation path and subsequently transmitted over the Q modulation path. Communication device. 28. The system of claim 27, wherein the orthogonally modulated communication data is transmitted as data selected from a group consisting of a beacon signal generated at a beacon data rate and communication data generated at a rate greater than the beacon data rate, Communication device. 28. The system of claim 27, wherein the rotation training signal comprises symbols generated simultaneously for multiple subcarriers, Simultaneously generated symbols for the plurality of subcarriers, training information transmitted over the I modulation path rather than the Q modulation path, for i subcarriers; for j subcarriers, the training information is transmitted through the Q modulation path instead of the I modulation path, Here, orthogonal modulated communication data is generated for the i subcarriers and the j subcarriers subsequent to generation of the training information. Communication device. 28. The method of claim 27, The training information transmitted over the I modulation path includes a first symbol having a reference phase; The training information transmitted over the Q modulation path includes a second symbol having a phase selected from the group consisting of the reference phase + 90 ° and the reference phase-90 °, Communication device. 32. The system of claim 31, wherein the training information is transmitted simultaneously over both the I modulation path and the Q modulation path and combined to provide the second symbol. Communication device. 30. The system of claim 29, wherein the training information is transmitted simultaneously over both the I modulation path and the Q modulation path and combined to provide a first symbol. Communication device. 28. The method of claim 27, The rotational training signal is transmitted via a physical layer (PHY) message header; IQ modulated communication data is sent via the PHY message payload, Communication device. The method of claim 28, Training information is initially transmitted over the I modulation path using the active I modulation path and not using the active Q modulation path, The training information is subsequently transmitted over the Q modulation path using an active Q modulation path, Communication device. 29. The method of claim 27, wherein the rotational training signal includes predetermined training information transmitted over the I modulation path and the Q modulation path. Communication device. 28. The method of claim 27, Means for generating an unbalanced message, The imbalance message generating means, Means for generating a non-rotational training signal having training information transmitted over the I modulation path but no training information transmitted over the Q modulation path; Means for generating a message format signal indicating that a rotation training signal is sent following the imbalance message; And Means for generating orthogonal modulated communication data; Communication device. 28. The method of claim 27, P rotating pilot symbols are generated with (N-P) orthogonal modulated communication data symbols, N symbols are transmitted at the same time, Communication device.

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