Patent Application
20100267346
1. Field
The present disclosure relates generally to methods and apparatus for control signaling in a communication system, and more specifically to utilizing delta-sigma modulation for control signaling in communication systems having continuous valued measurement and feedback, such as in closed-loop transmit diversity (CL-TD) systems.
2. Background
In many mobile wireless communication systems, system operation uses significant control signaling in both uplink (i.e., a mobile device to a base station) and downlink (i.e., base station to mobile devices) directions. Many of the control signals are continuous-valued in nature, such as phase and power measurements for closed loop transmit diversity (CL-TD) as an example. Effectiveness of such control signaling, however, is often times limited more by control signaling granularity depending on Over the Air (OTA) resource allocation per channel use, than by allowed rate of such channel use. For example, in a UMTS system control channel allocation is one or two bits per channel at a rate of 1500 Hz for just phase adjustment. Assuming 2 bits per channel (i.e., four possible values), phase adjustment via the control signaling in a 360° range can only be quantized into four values at 90° resolution, for example, which also implies a quite significant ±45° error. Thus, such fixed quantization schemes in control signaling imply a fixed amount of error, which becomes particularly acute in situations when a communication device is positioned where maximum phase error occurs.
In general, performance degradation due to quantization depends on types of control signaling in CL-TD systems, each of which has specific cost associated for deviation of quantized signal from continuous-valued signal as well as for fast transition among quantization levels. One method of enhancing the performance of control signaling is by allowing finer resolution with direct quantization, such as with 3 or 4 bits. Such enhancement, however, is at a cost of scarce control channel resources or OTA resources.
Performance enhancement is also possible if the feedback rate can be lowered with an aggregation of multiple channel uses for finer quantization granularity. This enhancement is at the cost of latency, however, and thus limits the effectiveness of closed-loop control, which may or may not be acceptable over fast changing channel conditions. Another possible approach to enhancement is by applying delta modulation for more efficient utilization of the same given OTA resource allocation. This approach, however, involves a tradeoff of quantization step size for conflicting requirements between granularity and slope overload.
According to an aspect, a method for control signaling is disclosed. The method includes: receiving a communication signal, and measuring at least one of a phase and amplitude of the received communication signal to derive a current measurement signal. The method further includes determining a difference signal by subtracting a previously quantized integrated difference signal from the current measurement signal, integrating the difference signal, and then quantizing the integrated difference signal. Finally, the quantized integrated difference signal is transmitted as part of control signaling to a communication device.
According to another aspect, a method for control signaling is disclosed that includes receiving control signaling including control information from a communication device that is a quantized signal formed using delta-sigma modulation. The method further includes filtering the control signaling to obtain the control information, and controlling one of phase and amplitude for a transmitter portion of a wireless device based on the control information.
According to yet another aspect, an apparatus for control signaling is disclosed. The apparatus includes a receive unit configured to receive a communication signal. Also included are a measurement unit configured to measure at least one of a phase and amplitude of the received communication signal to derive a current measurement signal, and an additive calculation unit configured to determine a difference signal by subtracting a previously quantized integrated difference signal from the current measurement signal. The apparatus also includes an integrator configured to integrate the difference signal, a quantization unit configured to quantize the integrated difference signal, and a transmitter unit configured to transmit the quantized integrated difference signal as part of control signaling to a communication device.
According to still a further aspect, an apparatus for control signaling is disclosed. The apparatus includes a receiver unit configured to receive control signaling including control information from a communication device that is a quantized signal formed using delta-sigma modulation. The apparatus also includes a band limiting unit configured to filter the control signaling to obtain the control information, and a control unit configured to control one of phase and amplitude for a transmitter portion of a wireless device based on the control information.
According to another aspect, an apparatus for control signaling is disclosed that includes means for receiving a communication signal, and means for measuring at least one of a phase and amplitude of the received communication signal to derive a current measurement signal. The apparatus also includes means for determining a difference signal by subtracting a previously quantized integrated difference signal from the current measurement signal, means for integrating the difference signal, and means for quantizing the integrated difference signal. Finally, the apparatus includes means for transmitting the quantized integrated difference signal as part of control signaling to a communication device.
According to yet a further aspect, an apparatus for control signaling is disclosed having means for receiving control signaling including control information from a communication device that is a quantized signal formed using delta-sigma modulation. The apparatus also includes means for filtering the control signaling to obtain the control information, and means for controlling one of phase and amplitude for a transmitter portion of a wireless device based on the control information.
In still another aspect, a computer program product comprising a computer-readable medium is disclosed. The medium includes code for causing a computer to receive a communication signal, code for causing a computer to measure at least one of a phase and amplitude of the received communication signal to derive a current measurement signal, and code for causing a computer to determine a difference signal by subtracting a previously quantized integrated difference signal from the current measurement signal. The medium also includes code for causing a computer to integrate the difference signal, and code for causing a computer to quantize the integrated difference signal; and code for causing a computer to transmit the quantized integrated difference signal as part of control signaling to a communication device.
In still one more aspect, a computer program product comprising a computer-readable medium is disclosed. The medium includes code for causing a computer to receive control signaling including control information from a communication device that is a quantized signal formed using delta-sigma modulation, and code for causing a computer to filter the control signaling to obtain the control information. The medium further includes code for causing a computer to control one of phase and amplitude for a transmitter portion of a wireless device based on the control information.
The presently disclosed apparatus and methods serve to enhance the performance of mobile wireless communication systems and OTA resource utilization by improving the effectiveness of continuous-valued control signaling for closed-loop operations, including but not limited to CL-TD, in both uplink (UL) and downlink (DL) directions.
Referring to
Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the access point. In the example, antenna groups each are designed to communicate to access terminals in a sector of the areas covered by access point 100.
In communication over forward links (or downlinks) 120 and 126, the transmitting antennas of base station or access point 100 may utilize beamforming in order to improve the signal-to-noise ratio of forward links for the different access terminals 116 and 122. In addition, a base station or an access point using beamforming to transmit to access terminals scattered randomly through its coverage causes less interference to access terminals in neighboring cells than an access point transmitting through a single antenna to all its access terminals.
An access point may be a fixed or base station used for communicating with the terminals and may also be referred to as an access point, a Node B, or some other terminology. An access terminal may also be called an access terminal, user equipment (UE), a wireless communication device, terminal, access terminal or some other terminology. Additionally, the system in
It is noted that the system of
Accordingly, the presently disclosed methods and apparatus serve to enhance mobile wireless communication systems performance and/or OTA resource utilization by improving the effectiveness of continuous-valued control signaling for closed-loop operations, including but not limited to CL-TD, in both DL and UL without requiring additional signaling overhead and receiver-transmitter coordination. To achieve this improvement, a delta-sigma (Δ-Σ) approach is utilized. This approach solves the fundamental problem of direct quantization for CL-TD phase feedback, by allowing the feedback channel to be used much more efficiently. Based on an assumption that CL-TD allocated feedback channel bandwidth can often be significantly higher than actualphase control signal bandwidth, a delta-sigma scheme allows CL-TD to exchange excess bandwidth for bit width.
Receiver 202 includes a receive unit 208 that receives a signal over the channel 202. Block 208 feeds the signal to a phase measurement unit 210 configured to measure the phase of the incoming signal and output a current phase measurement 212. The signal may include pilot tones or symbols that may be used by unit 210 to measure the phase of the incoming signal.
The current phase measurement 212 is input to a delta-sigma modulator 214. Both a difference calculation and an integration are performed within the delta-sigma modulator. Regarding the difference calculation, additive calculation unit 216 receives the current phase measurement 212 and subtracts a previously quantized integrated difference signal 218 (or, stated another way, adds the negative of the quantized integrated difference signal) that is fed back (i.e., a negative feedback loop input) from the output of a quantization unit 220 to achieve a difference signal 222. Thus, delta-sigma modulator 214 includes at least unit 216, integrator 224, and the feedback input 218 from quantization unit 220. It is noted that the quantized integrated difference signal 218 may be converted from the digital signal output by quantization unit 220 to an analog signal, or from the digital signal to another digital signal prior to subtraction from the current measured phase dependent on whether the delta-sigma modulator 214 is configured as a digital or analog modulator (of which both are contemplated by the present disclosure).
Difference signal 222 is input to the integration portion of the delta-sigma modulator 214, illustrated by noise shaping integrator 224, which performs an integration of the difference signal 222 as well as noise shaping. In an aspect, the noise is shaped to an upper band, and integrator function is akin to a filter, such as low pass filter, or other suitable processes for shaping the noise. It is noted that the delta-sigma modulator 214 may be configured as a first order modulator as illustrated by
The integrated output of noise shaping integrator 224 is input to the quantization unit 220 to quantize the integrated signal. In an aspect, the quantization may be 2 bit/sample quantization, but one skilled in the art will appreciate that the quantization may be less (i.e., 1 bit quantization) or more (i.e., greater than 2 bit quantization). The quantized output (i.e., the quantized integrated signal) for phase control (e.g., 2 bit) is input to a transmission unit 226 for transmission over the channel 204, and in particular over control or OTA channels to transmitter 206. The quantized signal output by unit 220 is the feedback portion of system 200 providing feedback signaling to the transmitter 206 to enable phase adjustment or control by the transmitter 206.
The delta-sigma modulator 214 with negative feedback from quantization unit 220 maintains the average number of digital bit values at the output equal to the phase measurement signal's percentage of full scale. This is otherwise known in the art as pulse density modulation (PDM). This delta-sigma modulation technique serves to shape the conversion noise of modulator 214 to a high input-sample frequency band, which is away from the frequency band of interest in which the phase control signal resides.
A receiver unit 228 receives the phase control signal over channel 204 and inputs the signal to a filtering or band limiting unit 230. Since delta-sigma modulation is used in formation of the signal, there is a higher level of phase quantization noise resulting from this type of modulation. This noise is removable by simple band limiting (e.g., a low pass filter) with band limiting unit 230, as the noise is in the high input-sample frequency band, which is away from the frequency band of interest in which the phase control signal resides. The result of band limiting in unit 230 is therefore the intended phase control signal is much less correlated with the noise, and may then be input to a phase control unit 232 to control the phase of transmission of a transmit unit 234, which transmits signals to the receiver 202 over channel 204. This completes the closed-loop, feedback system illustrated by
It is noted that in an aspect, the band limiting unit 230 may be configured to feature dynamic adjustment of the bandwidth (i.e., a variable bandwidth), rather than merely a set bandwidth. Dynamic adjustment can be configured to vary the filter bandwidth of unit 230 based on detection of changes in the channel. For example, if the changes in the channel 204 are slower, such as in the case of a simple repeating pattern, the channel is likely not changing and the bandwidth of unit 230 could be clamped down to a lower bandwidth to eliminate noise (e.g., taking an average or the DC level of the signal). Conversely, in cases of faster changing channel conditions, the bandwidth of unit 230 could be expanded dependent on how fast channel conditions are changing. Dynamic adjustment of the bandwidth of unit 230 would allow better optimization of the performance of the closed loop system.
By employing delta-sigma modulation in the system of
The proposed delta-sigma modulation of CL-TD control signaling is applicable to not only phase control, but power or amplitude control as well. Thus, in an example of power or amplitude control, the phase control, phase measurement and phase quantization units, could be substituted with amplitude control, measurement, and quantization functionalities. It is further noted that other values beyond merely phase or amplitude control are also contemplated as the apparatus and methodologies disclosed herein are applicable to any control aspects that may be implemented or availed with continuous-valued measurement and feedback.
It is noted that some systems may develop a slight complication with phase measurement given 360° (2π radians) periodicity. In particular, phase measurements may exhibit fast artificial transition near 0° and 360° because of wrap-around. This is not an issue for direct quantization, which treats phase measurements individually. Delta-sigma modulation, however, looks at a sequence of phase measurements for efficient utilization of control channel. Thus, in the present system, it may be desirable not to include artificial transition of phase measurement signal. Accordingly, in another aspect, the system of
At the transmitter 206, the received phase feedback (i.e., the quantized integrated difference signal) may be unwrapped before performing band limiting at the transmitter 206, as indicated by unit 306. Finally, system 200 may include wrapping of the actual phase control within the 360° range prior to transmission of signals by transmit unit 232. This wrapping is performed by unit 308. The signals received at receiver 202 are then unwrapped by the phase measurement and unwrap unit 302.
After the phase or amplitude are measured, a process in block 406 involves determining a difference signal by subtracting a previously quantized integrated signal from the one of the measured phase and amplitude to determine a difference signal. This process in block 406 may be implemented, for example, by additive block 216 in the example of
After determination of the difference signal, this signal is then integrated as shown by block 408. The process of block 408 may also include noise shaping of the difference signal to filter out noise, for example. Noise shaping integrator 224 may implement these processes in block 408, for example. Furthermore, it is noted that the processes of block 406 and 408 effect delta-sigma modulation of the phase or amplitude measurement.
After block 408, flow proceeds to block 410 where the integrated difference signal is quantized. Quantization may be performed, as an example, by phase quantization block 220 in the example of
The method 400 is repeated continuously to provide a continuous control feedback signal (i.e., the quantized integrated difference signal) to another communication device to be used for phase or amplitude control, as two examples. It is noted that method 400 may be utilized in both uplink and downlink directions for sending feedback information to another wireless device.
Method 500 includes a first block 502 including a process of receiving a control signaling including control information from a communication device that is a quantized signal formed using delta-sigma modulation. This process may be implemented by receive block 228 shown in
After receipt of the control signaling, the signaling is filtered to obtain the control information as shown in block 504. In an aspect, the filtering is low pass filtering to remove noise resultant from delta-sigma modulation in the upper frequency bands from the desired control information in lower frequency. The process of block 504 is implementable by a device such as band limiting unit 230 shown in
Once the control information has been obtained, a next block 506 illustrates controlling one of phase and amplitude for a transmit portion of a wireless device based on the control information. This process of block 506 may be effected by phase control unit 232, which provides control of certain aspects of transmit portion 234, as an example from
It will be appreciated by those skilled in the art that the method 500 may be carried out for either an uplink or a downlink in either in a base station or a mobile device. The salient application of method 500, however, is at reception end of a feedback control link for controlling aspects of transmission in the reverse direction, as in a CL-TD system.
In particular, means 602 communicates the received signal to a means 608 for measuring phase or amplitude of the received signal. In the example of phase measurement, means 608 may be implemented by phase measurement block 210 in the example of
Means 608 sends the phase or amplitude measurement to a means 610 for determining a difference signal by subtracting a previously quantized integrated signal from the one of the measured phase and amplitude to determine a difference signal. Means 610 may be implemented, for example, by additive block 216 in the example of
After determination of the difference signal, this difference signal is then integrated by means for integrating the difference signal 614. Means 614 may also include noise shaping of the difference signal to filter out noise, for example. Means 614 may be implemented by noise shaping integrator 224, for example, or equivalent functional circuit to integrate a signal. Furthermore, it is noted that the combination of means 610 and 614 effect delta-sigma modulation of the phase or amplitude measurement.
Apparatus 602 also includes the means 612 for quantization, which quantizes the integrated difference signal determined by means 614. Means 612 may be implemented, as an example, by phase quantization block 220 in the example of
Additionally, it is noted that apparatus 602 may also be in communication with a processor 618, such as a DSP, which among other things reads and/or writes one or more programmable instructions (or program code) to a memory device 620. Processor 618 and memory 620 may be in communication with the other means or modules within apparatus 602 as indicated by coupling to bus 606. It is noted that the present apparatus may be implemented in hardware, software, firmware, or any combinations thereof. It will also be appreciated by those skilled in the art that apparatus 602 may be used for either uplink or downlink feedback control signaling in either in a base station or a mobile device.
The control signaling received by means 704 is then communicated to a means 708, for filtering the control signaling to obtain the control information. In an aspect, means 708 may be configured to employ low pass filtering to remove noise resultant from delta-sigma modulation in the upper frequency bands from the desired control information in lower frequency. Means 708 is implementable by a device such as band limiting unit 230 shown in
Once the control information has been obtained by means 708, this information is passed on to a means 710 for controlling one of phase and amplitude for a transmit portion of a wireless device based on the control information. Means 710 may be effected by phase control unit 232, which provides control of certain aspects of transmit portion 234, as an example from
Additionally, it is noted that apparatus 702 may also be in communication with a processor 712, such as a DSP, which among other things reads and/or writes one or more programmable instructions to a memory device 714. Processor 712 and memory 714 may be in communication with the other means or modules within apparatus 702 as indicated by coupling to bus 706. It is noted that the present apparatus may be implemented in hardware, software, firmware, or any combinations thereof. It will also be appreciated by those skilled in the art that apparatus 702 may be used for control of either uplink or downlink signaling utilizing received feedback in either in a base station or a mobile device.
As disclosed the present apparatus and methods employing delta-sigma modulation afford CL-TD performance that is not limited by direct quantization resolution considering stationary case with constant phase adjustment from receiver to transmitter not happen to align with any of available phase options. Additionally, CL-TD performance is the present disclosure not limited by capacity of feedback channel considering a stationary case when a receiver (e.g. 202) keeps sending the same phase adjustment command to transmitter (e.g. 206). Of further note, the presently disclosed apparatus and methods afford CL-TD phase feedback signaling that consists of information not only in individual command, but also in sequence of phase adjustment commands.
Moreover, the presently disclosed apparatus and methods engender a signaling approach that allows control precision to not be limited by signaling quantization resolution. Also, the present apparatus and methods allow control accuracy to not be limited by choice of signaling quantization constellation, allow control signaling to be truly effective by fully utilizing control channel capacity, and result in a reduction of the control signaling that is more effective and provides better system performance.
While, for purposes of simplicity of explanation, the disclosed methodologies are shown and described herein as a series or number of acts, it is to be understood that the processes described herein are not limited by the order of acts, as some acts may occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with the subject methodologies disclosed herein.
Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the examples disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The various illustrative logical blocks, modules, and circuits described in connection with the examples disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
In one or more exemplary aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. In addition, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
The word “exemplary” as used herein is intended to mean “serving as an example, instance, or illustration.” Any example described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other examples.
The previous description of the disclosed examples is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of the invention. Thus, the present disclosure is not intended to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
