Patent Application
20140113576
This application claims the benefit under 35 U.S.C. §119(a) and 37 CFR §1.55 to UK patent application no. GB1218745.6, filed on 18 Oct. 2012, the entire content of which is incorporated herein by reference.
1. Field of the Invention
Examples described in the present application relate generally to radio receivers and down-converting a received signal in a radio receiver. Examples described in the present application also relate to radio access networks, such as Universal Mobile Telecommunication System (UMTS), Universal Terrestrial Radio Access Network (UTRAN), a Long Term Evolution (LTE) network called Evolved UTRAN (E-UTRAN), LTE advanced, a Wideband Code Division Multiple Access (WCDMA), and a High Speed Packet Access (HSPA) network.
2. Description of the Related Technology
In a radio access network (RAN) a base station, or an evolved Node B (eNB) in LTE, assigns radio resources to a user equipment (UE). In time division systems the radio resources are short time periods, such as 1 ms. These periods are termed time slots, frames, or subframes depending on the RAN in which they are used. Alternatively, the radio resources may be radio frequencies. Thus, the base station assigns a certain time slot or a certain radio frequency to the UE to be used in a downlink transmission or in an uplink transmission. It is also possible to define the radio resources in regard to time and frequency. A duplex communication system is a point-to-point system composed of two devices, such as two radio sets, which are able to communicate in both directions simultaneously. The duplex communication system provides a two-way communication channel between the devices. A term multiplexing refers to mediating pair wise communication between more than one pair of devices. The multiplexing enables a number of devices to use the same communication channel in the same time. Time division duplex (TDD) and frequency division duplex (FDD) are known techniques for sharing the communication channel. A half-duplex system allows communication in both directions, but only one direction at a time. Conversely, a full-duplex system allows the communication simultaneously in the both directions.
A signal can be generally characterized in terms of bandwidth and signal-to-noise ratio (SNR). A “wanted” signal is a signal which is similar to an original signal and this original signal is, for example, transmitted signal 112 sent from transmitter subsystem 103. A received signal is a mixture of the wanted signal and unwanted signals, such as leakage signals and blocker signals. Especially full-duplex systems suffer from leakage signals. For example, transmitted signal 112 may include frequencies which at least partly overlap the frequency band of received signal 114. In other words, transmitted signal 112 “leaks” on the frequency band of the received signal 114.
Down-conversion of the received signal is performed using a local oscillator (LO) signal at a carrier frequency generated by a synthesizer (Sx). The synthesizer comprises a phase locked loop with a configurable loop filter. The synthesizer generates phase noise as a side effect. The configurable loop filter affects the spectrum of the phase noise.
The following example discloses how the quality of the LO signal can be enhanced and thus also the quality of the output signal of the receiver can be enhanced.
A LO signal contains unwanted phase noise components that can be classified as “near” and “far” phase noise components. “Near” phase noise components are located at frequencies close to the wanted signal, and they cause reciprocal mixing products with the wanted signal that fall into the bandwidth of the wanted signal and thus deteriorate the quality of a received signal. Conversely, “far” phase noise components are located at frequencies sufficiently remote from the wanted signal, and their reciprocal mixing products with the wanted signal fall outside the wanted signal bandwidth where they do not deteriorate the signal reception. A far phase noise component, however, may interact with other unwanted signals in the same frequency range, such as blockers or transmit leakage signals, and cause reciprocal mixing products that overlap the bandwidth of the wanted signal and thus degrade the quality of the received signal.
Radio transmissions with multiple transmit and receive antennas are referred to as “MIMO” (multiple input multiple output). Multiple antennas can be utilized in various manners. In a first MIMO technique multiple transmit antennas are used to send the same data on the same frequency. In a second MIMO technique multiple receive antennas are used to receive the same data on the same frequency. The above-mentioned first and second technique can be utilized separately or together, i.e. the techniques can also be used simultaneously. Given a sufficiently rich fading channel, MIMO may establish an independent MIMO stream between each transmit- and receive antenna and thus considerably improve the throughput over a radio channel. However, MIMO may be sensitive to reciprocal mixing product appearing in multiple MIMO streams that are correlated. Correlated reciprocal mixing products may result both from utilizing the same LO signal in multiple receivers to process received signals from multiple receive antennas, and from a single receiver down converting the sum of transmit signals from multiple transmit antennas in parallel. The error caused by correlated reciprocal mixing products can severely impair the reception of the MIMO signal.
A modulation-and-coding scheme (MCS) is a scheme for transmitting a signal. A modulation-and-coding scheme may be selected in link adaption, where a transmitter attempts to maximize a throughput to a receiver by selecting the highest-order modulation format and coding scheme that meets a required measure of quality, such as a bit error rate, for a given radio link. The radio link may be characterized by a pathloss of the received signal, interference by signals coming from transmitters, the sensitivity of the receiver, etc. Examples for modulation schemes are QPSK (quadrature phase shift keying), providing a low spectral efficiency but low demands on signal quality, and 64 QAM (quadrature amplitude modulation), resulting in a better spectral efficiency but requiring a better signal quality. Examples for coding are convolutional codes or Turbo codes with code rates. For example, a low code rate of ⅓ may carry only one bit of information in three transmitted bits, and a high code rate of 9/10 may carry nine bits of information in ten transmitted bits. In general, a higher code rate results in a higher data throughput but requires a better signal quality than a lower code rate. A modulation-and-coding scheme that employs QPSK or 64 QAM in combination with a predetermined coding rate may be referred to as “QPSK-based” or “64 QAM-based”.
Designing a synthesizer with good phase noise performance at both near and far frequency offsets is inefficient, as it increases the power consumption, which is especially problematic in a battery-powered UE such as a cell phone. There is need for a more efficient solution to prevent degradation of a received signal in a receiver of the UE, wherein the degradation is caused by phase noise.
A preferred embodiment of the invention aims to prevent or mitigate degradation of a received signal with low power consumption.
In a first exemplary embodiment there is a method of enhancing quality of a received signal in a receiver, the method comprising: determining input information that comprises at least one of the following pieces of information: a modulation-and-coding scheme of the received signal; a multiple-antenna configuration; a signal quality estimate of the received signal; a frequency separation between the received signal and a transmitted signal; and selecting a bandwidth value on the basis of the input information; using the bandwidth value for generating a local oscillator signal; and shaping the received signal with the local oscillator signal.
In one embodiment of the method, the bandwidth value controls a bandwidth of a phase noise component in the local oscillator signal.
In one embodiment of the method, the using of the bandwidth value comprises a selection of an oscillator core.
In one embodiment of the method, the generating of the local oscillator signal comprises a frequency division operation.
In one embodiment of the method, the generating of the local oscillator signal comprises use of a feedback loop.
In one embodiment of the method, the input information comprises at least two of the following pieces of information:
the modulation-and-coding scheme of the received signal
the multiple-antenna configuration
the signal quality estimate of the received signal
the frequency separation between the received signal and a transmitted signal.
In one embodiment of the method, the selecting is performed taking into account the at least two pieces of information.
In one embodiment of the method, the signal quality estimate is a channel quality indicator.
In one embodiment of the method, the frequency separation is determined on the basis of a threshold value.
In one embodiment of the method, the frequency separation is determined on the basis of on a band used by the receiver, the band comprising an uplink frequency band and a downlink frequency band.
In one embodiment of the method, the selecting comprises use of a conditional clause.
In one embodiment of the method, the conditional clause comprises at least one predefined threshold values.
In a second exemplary embodiment of the invention there is an apparatus, comprising at least one processor and at least one memory including computer program code, the at least one processor and the computer program code configured to, with the at least one processor, cause the apparatus to perform, at a user equipment, at least the following: determining input information that comprises at least one of the following pieces of information: a modulation-and-coding scheme of the received signal; a multiple-antenna configuration; a signal quality estimate of the received signal; a frequency separation between the received signal and a transmitted signal; and selecting a bandwidth value on the basis of the input information; using the bandwidth value for generating a local oscillator signal; shaping a received signal with the local oscillator signal to enhance quality of the received signal in a receiver.
In one embodiment of the apparatus, the bandwidth value controls a bandwidth of a phase noise component in the local oscillator signal.
In one embodiment of the apparatus, the using of the bandwidth value comprises a selection of an oscillator core.
In one embodiment of the apparatus, the generating of the local oscillator signal comprises a frequency division operation.
In one embodiment of the apparatus, the generating of the local oscillator signal comprises use of a feedback loop.
In one embodiment of the apparatus, the input information comprises at least two of the following pieces of information:
the modulation-and-coding scheme of the received signal
the multiple-antenna configuration
the signal quality estimate of the received signal
the frequency separation between the received signal and a transmitted signal.
In one embodiment of the apparatus, the selecting is performed taking into account the at least two pieces of information.
In one embodiment of the apparatus, the signal quality estimate is a channel quality indicator.
In one embodiment of the apparatus, the frequency separation is determined on the basis of a threshold value.
In one embodiment of the apparatus, the frequency separation is determined on the basis of on a band used by the receiver, the band comprising an uplink frequency band and a downlink frequency band.
In one embodiment of the apparatus, the selecting comprises use of a conditional clause.
In one embodiment of the apparatus, the conditional clause comprises at least one predefined threshold values.
In one embodiment of the apparatus, the apparatus comprises a signal shaper for shaping the received signal.
In one embodiment of the apparatus, the signal shaper comprises an oscillator and at least one the following devices: a mixer, divider, a phase detector, a loop filter, a phase locked loop.
In a third exemplary embodiment of the invention there is a non-transitory computer readable medium comprising a set of computer readable instructions stored thereon, which, when executed by a processing system, cause the processing system to carry out a method of enhancing quality of a received signal in a receiver, the method comprising: determining input information that comprises at least one of the following pieces of information:
a modulation-and-coding scheme of the received signal;
a multiple-antenna configuration;
a signal quality estimate of the received signal;
a frequency separation between the received signal and a transmitted signal; and selecting a bandwidth value on the basis of the input information; using the bandwidth value for generating a local oscillator signal; and shaping the received signal with the local oscillator signal.
For a more complete understanding of examples and embodiments of the present invention, reference is now made to the following description taken in connection with the accompanying drawings in which:
Generally speaking, the determining 301 results in one or more pieces of the input information and those pieces of information are used when selecting 302 the bandwidth value.
For example, the determining 301 of the input information may comprise determining a signal quality estimate of the received signal. The signal quality estimate may be, for example, a channel quality indicator or a signal-to-noise ratio. When the determining 301 results in one piece of the input information (such as the signal quality estimate of the received signal) the selecting 302 of the bandwidth value is performed on the basis of that piece of information.
The steps of determining 301 and selecting 302 are discussed in more detail in the following embodiments and examples.
In one embodiment the selecting 302 is performed taking into account the at least two pieces of the input information:
the modulation-and-coding scheme of the received signal;
the multiple-antenna configuration;
the signal quality estimate of the received signal;
the frequency separation between the received signal and a transmitted signal.
In one embodiment, the selecting 302 is performed taking into account the modulation-and-coding-scheme and the multiple-antenna configuration. In one embodiment the selecting 302 is performed taking into account the modulation-and-coding-scheme and the signal quality estimate. In one embodiment the selecting 302 is performed taking into account the multiple-antenna configuration and the signal quality estimate.
In addition to above-mentioned embodiments, there are embodiments in which the selecting 302 comprises at least three pieces of information. For example, the selecting 302 can be performed taking into account the modulation-and-coding-scheme, the multiple-antenna configuration, and the signal quality estimate.
The selecting 302 results in the bandwidth value that is used for generating the oscillator signal. In one embodiment the selecting 302 comprises selecting an alpha value. The alpha value may be the bandwidth value, but usually the alpha value is a kind of coefficient which is needed in calculation of the bandwidth value. A low alpha value may correspond to a narrow bandwidth value and a high alpha value may correspond to a high bandwidth value. An alpha value effects, in one way or other, to a bandwidth value and the bandwidth value effects to the local oscillator signal, and finally, the received signal is frequency-converted in the receiver with the local oscillator signal. Therefore, the alpha value should be selected so that it enhances the quality of the received signal.
For example, a high-order MCS requires high signal quality. In one embodiment, the selecting 302 results in a high alpha value and a high bandwidth value for the high-order MCS. In another embodiment, the high bandwidth value is selected because of MIMO. In one embodiment, a narrow bandwidth value is selected for a low-order MCS that requires only a low signal quality and is mainly used at a cell edge, where blocker signals from an adjacent cell are strong. Alternatively, the narrow bandwidth value is selected when the number of blocker signals is high.
In one embodiment, the pieces of the input information are stored in a memory and those information pieces are readable by an apparatus performing the method. The determining 301 may mean in practice, for example, that a character string “QPSK” is read from the memory and thus the modulation-and-coding scheme is determined to be QPSK-based.
In one embodiment, the determining 301 comprises determining the modulation-and-coding scheme, which is used with the received signal, and selecting 302 comprises a condition clause. This condition clause includes at least one IF-THEN clause or IF-THEN-ELSE clause. Example:
In one embodiment, the determining 301 also takes into account a signal quality estimate and selecting 302 comprises a condition clause that includes, for example, three different alpha values. In this embodiment the signal quality estimate is a channel quality indicator (CQI) and the signal quality estimate includes an estimated signal-to-noise ratio SNR intended for channel quality reporting. A user equipment reports the CQI to a base station, i.e. the value of SNR is available in the memory of the user equipment. Example:
In one embodiment, the determining 301 starts with determining the modulation-and-coding scheme after which the determining 301 continues with determining the signal quality estimate. Example:
As can be seen in the above examples, a condition clause may include one or more nested IF-THEN clauses, or nested IF-THEN-ELSE clauses.
In one embodiment, determining 301 comprises determining the signal quality estimate and determining the modulation-and-coding scheme, and selecting 302 comprises a condition clause including two conditions. The first condition could be “SNR>21 dB?” and the second condition could be “MCS QPSK-based?”. In addition, alpha may have a default value. Example:
In the above examples the conditional clauses include only one predefined threshold value (21 dB). It is, however, possible that a conditional clause includes at least two predefined values. Generally speaking, the conditional clause includes at least one variable which is compared to at least one threshold value.
In one embodiment, determining 301 comprises determining a frequency separation between the received signal and the transmitted signal, wherein the frequency separation is measured in Megahertz and stored in a “MinFS” variable. In the following example also the duplex mode is taken into account. In more detail, a “FDD-mode” variable has value TRUE only if the duplex mode is FDD. Example:
The frequency separation may be defined as a duplex distance between a transmit frequency and a receive frequency. When considering E-UTRA bands usable in FDD, the condition “FS<45 MHz” is true for E-UTRA bands 8, 17, and 20, and the condition is false for the E-UTRA bands 1, 4 and 10, for example. In one embodiment, determining the frequency separation comprises determining, whether a device that is designed to operate in E-UTRA bands 1, 4, 8, 10, 17 and 20, is currently operating in band 8, 17 or 20. Example of the embodiment:
It should be noted that while the use of the abovementioned E-UTRA bands may imply use of FDD mode, future bands may be allocated to support both TDD and FDD simultaneously. As the two previous examples indicate, a small alpha value and correspondingly a small bandwidth value may be selected if the frequency separation between the received signal and the transmitted signal is small.
The following embodiments can be utilized with apparatus 411 (in
The following embodiments describe the composition of apparatus 401 (in
The present invention further comprises a computer readable medium. That medium stores a set of instructions which, when executed, causes an apparatus (such as apparatus 401) to perform the steps described in
The present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The hardware may be, for example, a chip, a modem, or some other apparatus which includes or is coupled to at least memory and at least one processor. The application logic, software or instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a “computer-readable medium” may be any media or means that contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. A computer-readable medium may comprise a computer-readable storage medium that may be any media or means that contain or store the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.
When not otherwise mentioned, “one embodiment” in the above refers to “one embodiment of the present invention”. The exemplary embodiments can store information relating to various processes described herein. This information can be stored in one or more memories, such as a hard disk, optical disk, magneto-optical disk, RAM, and the like.
All or a portion of the exemplary embodiments can be conveniently implemented using one or more general purpose processors, microprocessors, digital signal processors, micro-controllers, and the like, programmed according to the teachings of the exemplary embodiments of the present invention, as will be appreciated by those skilled in the computer and/or software art(s). Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as will be appreciated by those skilled in the software art. In addition, the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits, field-programmable gate arrays (FPGAs) or by interconnecting an appropriate network of conventional component circuits, as will be appreciated by those skilled in the electrical art(s). Thus, the exemplary embodiments are not limited to any specific combination of hardware and/or software.
Stored on any one or on a combination of computer readable media, the exemplary embodiments of the present invention can include software for controlling the components of the exemplary embodiments, for driving the components of the exemplary embodiments, for enabling the components of the exemplary embodiments to interact with a human user, and the like. Such software can include, but is not limited to, device drivers, firmware, operating systems, development tools, applications software, and the like. Such computer readable media further can include the computer program of an embodiment of the present invention for performing all or a portion (if processing is distributed) of the processing performed in implementing the present invention. Computer code devices of the exemplary embodiments of the present invention can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes and applets, complete executable programs, Common Object Request Broker Architecture (CORBA) objects, and the like.
The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1218745.6 | Oct 2012 | GB | national |
