Publication number | US20020196733 A1 |

Publication type | Application |

Application number | US 10/230,762 |

Publication date | Dec 26, 2002 |

Filing date | Aug 28, 2002 |

Priority date | Nov 25, 1998 |

Also published as | US6463043 |

Publication number | 10230762, 230762, US 2002/0196733 A1, US 2002/196733 A1, US 20020196733 A1, US 20020196733A1, US 2002196733 A1, US 2002196733A1, US-A1-20020196733, US-A1-2002196733, US2002/0196733A1, US2002/196733A1, US20020196733 A1, US20020196733A1, US2002196733 A1, US2002196733A1 |

Inventors | Qiang Shen, Peter Savinsky, Rui Wang, Wen Tong, Dmitry Menyailov, Dmitry Pogorilko, Alexander Garmonov |

Original Assignee | Qiang Shen, Peter Savinsky, Rui Wang, Wen Tong, Dmitry Menyailov, Dmitry Pogorilko, Alexander Garmonov |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (2), Referenced by (8), Classifications (9) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

US 20020196733 A1

Abstract

Method and apparatus for performing complex channel gain estimation from a transformer output and a non-coherent combiner output include a selector, an envelope detector, a weighting unit, a controller, store units, and an averager. The device may perform coherent complex channel gain estimation on link signals for signals transmitted by IS-95 burst randomization, and may operate on a power control group.

Claims(24)

a selector for determining an orthogonal function index from said non-coherent combiner output, and determining a corresponding complex value from said transformer output using said orthogonal function index,

an envelope detector for calculating the squared magnitude of said transformer output, and for generating at least one M-ary real value, wherein M is an integer greater than one,

a weighting unit coupled to said envelope detector for estimating a signal quality coefficient from said at least one M-ary real value and generating at least one weighted symbol by multiplying said signal quality coefficient by said corresponding complex value,

at least one store unit coupled to said weighting unit for storing said at least one weighted symbol,

an averager coupled to said at least one store unit for averaging said at least one weighted symbol, and

a controller coupled to said non-coherent combiner output, said at least one store unit, and said averager, for resetting said at least one store unit and for controlling said averager, thereby determining said complex channel gain estimation.

determining an orthogonal function index from said non-coherent combiner output, and determining a corresponding complex value from said transformer output using said orthogonal function index,

calculating the squared magnitude of said transformer output, and for generating at least one M-ary real value, wherein M is an integer greater than one,

estimating a signal quality coefficient from said at least one M-ary real value and generating at least one weighted symbol by multiplying said signal quality coefficient by said corresponding complex value,

storing said at least one weighted symbol,

averaging said at least one weighted symbol, and

controlling said averager, thereby determining said complex channel gain estimation.

a selector means for determining an orthogonal function index from said non-coherent combiner output, and determining a corresponding complex value from said transformer output using said orthogonal function index,

an envelope detector means for calculating the squared magnitude of said transformer output, and for generating at least one M-ary real value, wherein M is an integer greater than one,

a weighting unit means coupled to said envelope detector means for estimating a signal quality coefficient from said at least one M-ary real value and generating at least one weighted symbol by multiplying said signal quality coefficient by said corresponding complex value,

at least one store unit means coupled to said weighting unit means for storing said at least one weighted symbol,

an averager means coupled to said at least one store unit means for averaging said at least one weighted symbol, and

a controller means coupled to said non-coherent combiner output, said at least one store unit means, and said averager means, for resetting said at least one store unit means and for controlling said averager means, thereby determining said complex channel gain estimation.

a despreader capable of despreading at least one code from said multi-rate signals and obtaining said in-phase and quadrature phase signals;

a transformer coupled to said despreader capable of transforming said in-phase and quadrature phase signals and obtaining a plurality of M-ary complex values, wherein M is an integer greater than one;

a buffer coupled to said transformer capable of storing said plurality of M-ary complex values;

a non-coherent combiner coupled to said transformer, capable of combining said non-coherent portions of said plurality of M-ary complex values;

an estimator coupled to said transformer and said non-coherent combiner, configured to estimate a channel complex gain from said plurality of M-ary complex values and combining said non-coherent portions of said plurality of M-ary complex values; and,

a coherent combiner coupled to said buffer and said estimator, configured to perform maximal ratio combining of said stored plurality of M-ary complex values and said channel complex gain estimation, thereby generating a plurality of real value vectors, said combinations representative of carrier phase of said multi-rate signals.

despreader means for despreading at least one code from said multi-rate signals and obtaining said in-phase and quadrature phase signals;

transformer means coupled to said despreader means for transforming said in-phase and quadrature phase signals and obtaining a plurality of M-ary complex values, wherein M is an integer greater than one, and, wherein M-ary complex values contain non-coherent portions;

buffer means coupled to said transformer means for storing said plurality of M-ary complex values;

non-coherent combiner means coupled to said transformer means for combining said non-coherent portions of said plurality of M-ary complex values;

estimator means coupled to said transformer means and said non-coherent combiner means, for estimating a channel complex gain from said plurality of M-ary complex values and said combination of non-coherent portions of said plurality of M-ary complex values; and,

coherent combiner means coupled to said buffer means and said estimator means, for performing maximal ratio combining of said stored plurality of M-ary complex values and said channel complex gain estimation, thereby generating a plurality of real value vectors, said combinations representative of carrier phase of said multi-rate signals.

despreading at least one code from said multi-rate signals and obtaining said in-phase and quadrature phase signals, using a despreader;

transforming said in-phase and quadrature phase signals and obtaining a plurality of M-ary complex values, wherein M is an integer greater than one, and, wherein M-ary complex values contain non-coherent portions, using a transformer coupled to said despreader;

storing said plurality of M-ary complex values, using a buffer coupled to said transformer;

combining said non-coherent portions of said plurality of M-ary complex values, using a non-coherent combiner coupled to said transformer;

estimating a channel complex gain from said plurality of M-ary complex values and said combination of non-coherent portions of said plurality of M-ary complex values, using an estimator coupled to said transformer and said non-coherent combiner;

performing maximal ratio combining of said stored plurality of M-ary complex values and said-channel complex gain estimation, using a coherent combiner coupled to said buffer and said estimator; and,

generating a plurality of real value vectors from said coherent combiner, said combinations representative of carrier phase of said multi-rate signals.

multiplying a complex conjugate of said channel complex gain estimation to a plurality of corresponding finger outputs and combining all said fingers.

Description

- [0001]This is a division of U.S. patent application Ser. No. 09/200,080 filed Nov. 25, 1998, now pending.
- [0002]This invention relates generally to the field of wireless communications systems and, more particularly, to apparatus and methods for recovering carrier phase of multi-rate signals.
- [0003]In typical wireless communication systems a Cell Site Modem (CSM) is used for communication between the base station and the mobile station. Among other things, the CSM recovers the carrier phase of the link signal from the mobile to base station. Carrier phase recovery (sometimes referred to as phase referencing) is the operation of extracting a phase coherent reference carrier from a received carrier.
- [0004]The base station transmits a pilot channel as a reference channel. This allows the mobile station to acquire the timing of the forward channel and thus provides a phase reference for the mobile station. However, the IS-95 standard does not provide for the mobile station transmitting a reference channel to the base station. Therefore the base station must use the link signal to estimate the carrier phase.
- [0005]Generally, CSMs use non-coherent demodulation. The drawback of this method is the signal to noise ratio degradation at each demodulator. In addition, non-coherent demodulation prevents rake receivers from using more sophisticated combining methods to achieve higher combining gain for a multipath fading channel.
- [0006]Coherent demodulation provides a better signal to noise ratio than non-coherent techniques. However, it is difficult to recover carrier phase when the link signal is the only signal to work from. Carrier recovery used for coherent demodulation is complicated further by the fact that IS-95 uses a data burst randomizer to transmit multi-rate data.
- [0007]When the signal received by the base station is at the full rate, conventional systems and methods of carrier recovery for coherent demodulation may be employed. However, when the signal received by the base station is a series of random bursts, each burst having the length of one power control group (i.e. 6 Walsh symbols in IS-95), conventional CSMs do not effectively estimate carrier phase for use in coherent demodulation. This is because conventional CSMs do not perform complex (i.e. magnitude and phase) channel gain estimation on a single power control group. Thus, sufficient gains are difficult to achieve for the different data rates.
- [0008]Others have attempted to recover carrier phase from the mobile to base station link signal using phase locked loop systems. However these systems do not provide adequate carrier phase. Phase locked loop systems require continuous signal input and cannot operate at lower transmission rates when signals become intermittent. While more gain may be achieved for full rate transmissions, losses can occur for other lower transmission rates. Systems which utilize tentative non-coherent demodulation and moving average complex estimation also require continuous signal input and experience similar problems at lower rate transmissions.
- [0009]Other proposals which utilize aided symbol or aided signal technologies require modification of IS-95 standard devices and methods. These proposals would be incompatible with, the existing wireless communication infrastructure.
- [0010]Accordingly there exists a need for systems and methods of performing coherent complex channel gain estimation on link signals which is effective for signals transmitted by IS-95 burst randomization.
- [0011]There also exists a need for such systems which operate on a power control group.
- [0012]Accordingly it is an object of the present invention to provide systems and methods for performing coherent complex channel gain estimation on link signals which is effective for signals transmitted by IS-95 burst randomization.
- [0013]It is also an object of the present invention to provide systems and methods which operate on a power control group.
- [0014]In accordance with the teachings of the present invention, these and other objects may be accomplished by the present invention, which is a system for performing complex channel gain estimation from a transformer output and a non
**10**coherent combiner output. A selector determines an orthogonal function index from the non-coherent combiner output, and may use the orthogonal function index to determine a corresponding complex value from the transformer output. - [0015]An envelope detector may calculate the squared magnitude of the transformer output and generate M-ary real values, where M is an integer greater than one. A weighting unit coupled to the envelope detector may estimate a signal quality coefficient from the M-ary real values and generating weighted symbols by multiplying the signal quality coefficient by the corresponding complex value.
- [0016]Store units may be coupled to the weighting unit for storing the weighted symbol. Also, an averager may be coupled to the store units for averaging the weighted symbols. A controller may be coupled to the non-coherent combiner output, the store units, and the averager, for resetting the store units and for controlling the averager, thereby determining complex channel gain estimation.
- [0017]Another embodiment of the present invention is a system for performing carrier phase recovery of multi-rate signals which include in-phase and quadrature phase portions. An embodiment of the present invention includes a despreader capable of despreading at least one code from the multi-rate signals. The despreader is also capable of despreading the inphase and quadrature phase signals of the multi-rate signals.
- [0018]This embodiment also includes a transformer which is coupled to the despreader. The transformer is capable of transforming the in-phase and quadrature phase signals and obtaining a plurality of M-ary complex values, where M is an integer greater than one.
- [0019]A buffer, non-coherent combiner, and estimator are coupled to the transformer. The buffer is capable of storing the plurality of M-ary complex values. The non-coherent combiner is capable of combining the non-coherent portions of the plurality of M-ary complex values. The estimator is both coupled to the transformer and the non-coherent combiner. The estimator is configured to estimate a complex channel gain from the plurality of M-ary complex values and the non-coherent combining of the plurality of M-ary complex values of all fingers (branches).
- [0020]In addition a coherent combiner is coupled to the buffer and the estimator. The coherent combiner is configured to perform maximal ratio combining of the stored plurality of M-ary complex values and the channel complex gain estimation. The output of the coherent combiner is a plurality of real value vectors.
- [0021]The invention will be more clearly understood by reference to the following detailed description of an exemplary embodiment in conjunction with the accompanying drawings, in which:
- [0022][0022]FIG. 1 is a general block diagram of a coherent, maximal-ratio combining System in accordance with the present invention.
- [0023][0023]FIG. 1B is a flowchart diagram illustrating the operation of the system in accordance with the present invention.
- [0024][0024]FIG. 2 is a diagram of the non-coherent combiner.
- [0025][0025]FIG. 3 is a diagram of the coherent combiner.
- [0026][0026]FIG. 4A is a diagram of the channel complex gain estimator.
- [0027][0027]FIG. 4B is a flowchart diagram illustrating the operation of the channel complex gain estimator in accordance with the present invention.
- [0028][0028]FIG. 5 is a table showing an example of the contents used in the complex gain estimator.
- [0029]The conventional technology of code division multiple access (CDMA) employs a technique that allows users to simultaneously share the same radio frequency band. It achieves this by modulating the radio frequency signal with a spreading sequence known as a pseudonoise (PN-code) digital signal. Other pseudo-random sequences (i.e. codes) can be mixed to the signals to make them more resistant to noise, multi-path propagation, fading, and time jitter. For example a code that reduces the effect of multi-path propagation, time jitter (imprecise implementation errors) is an orthogonal code. In the preferred embodiment, a Walsh coded orthogonal spectrum is received. However, other types of orthogonal codes are well known. Thus, the Walsh codes can be supplemented by other orthogonal codes and still be within the scope of the present invention.
- [0030]In accordance with the present invention, a system decorrelates the unique codes mixed with the carrier signals. In addition, the system can use the link signal to estimate the carrier phase. FIG. 1 illustrates a system in accordance with the present invention for using the recovered carrier phase of multi-rate signals. The apparatus shown may be used at a wireless network base station, mobile station, or any other wireless communication station such as a communication satellite.
- [0031]The received signals, which include in-phase (I) and quadrature (Q) components, are applied to the inputs of a despreader
**20**. The despreader**20**decorrelates the PN-code from the received signals. The output of the despreader is the orthogonal (i.e. Walsh) codes in complex form. - [0032]A transformer
**30**is coupled to the output of the despreader**20**. The transformer**30**operates on the I and Q phase components of the orthogonal signals using a Fast Hadamard Transform (a type of Discrete Fourier Transform). Those skilled in the art will appreciate that other known transforms may be used instead of the Fast Hadamard Transform, such as Fast Walsh Transform, Fast Rademacher Transform, Fast Hartley Transform and the like, and still be within the scope of the invention. The output of the transformer is the complex orthogonal spectrum with M-ary complex values, where M is an integer (e.g. 64). - [0033]A delay unit
**40**is also coupled to the transformer**30**. The delay unit**40**stores the orthogonal spectrums (within one power control group) from the transformer**30**for further processing after the channel complex gain estimation is available. A complex gain estimator**70**determines the channel complex gain estimation from the output values of each finger output (i.e. the output of the transformer**30**and noncoherent combiner**60**). Once the complex estimation is ready, the delay**40**feeds the stored data to a coherent combiner**50**with the corresponding complex gain estimate. For example, the delay**40**unit may store the complex signal for up to a 6 Walsh symbol duration. The 6 Walsh symbol spectrum in one power control group can use the same one estimate or use several estimates, depending on the implementation. - [0034]A noncoherent combiner
**60**is also coupled to the output of the transformer**30**. The noncoherent combiner**60**performs diversity combining to all branches of the orthogonal spectrum with noncoherent output. One method of obtaining diversity combining of noncoherent values is to use equal gain combining. However other methods for performing noncoherent diversity combining can be used and still be within the scope of the invention. - [0035]The coherent combiner
**50**is coupled to the delay**40**and the complex gain estimator**70**. The coherent combiner**50**performs diversity combining to all branches with coherent output. This can be accomplished by performing maximal ratio combining on all branches with complex gain weights. Maximal ratio combining is accomplished by multiplying the complex conjugate of the complex gain estimate to the corresponding finger output and then combining all the fingers. The coherent combiner output is the real value vector of M (e.g. M=64) elements for M-ary orthogonal modulation. FIG. 1B is a flowchart diagram illustrating the operation of the coherent, maximal ratio combining system and further illustrates the signal flow and processing of the complex value input in accordance with the present invention. - [0036][0036]FIG. 2 is a detailed diagram of the noncoherent combiner
**60**. The envelope detector**100**performs on each finger output M-ary complex value, which is the output of the transformer**30**. A summer**110**sums the M-ary complex values of each finger from each envelope detector**100**and returns a M-ary real value by computing the square of the magnitude of each complex value. Other fingers**120**may also be coupled to the summer**110**. The output is thus the diversity combining of all the branches of the orthogonal spectrum with noncoherent output. - [0037][0037]FIG. 3 is a detailed diagram of the coherent combiner
**50**. A conjugator**150**returns the complex conjugate of the channel estimation**160**coming from the estimator**70**. The complex conjugate is then multiplied with the delayed orthogonal spectrums**170**by a multiplier**175**, where the delayed orthogonal spectrum comes from the delay**40**. The multiplied output**180**is then summed by a summer**200**. Other fingers**190**may also be summed together. The real part of the complex value from the summer**200**is then obtained using a real value unit**210**. The output is the diversity combination of all the branches of the orthogonal spectrum with coherent output. - [0038][0038]FIG. 4 is a detailed description of the complex gain estimator. A selector
**300**takes the noncoherent combiner**60**output and the transformer**30**output of the corresponding finger and determines the orthogonal function index. This index is corresponding to the maximum value of the orthogonal spectrum received from the non-coherent combiner**60**, and is used to select a corresponding complex value from the transformer**30**output. The output of the selector**300**is the complex value corresponding to that orthogonal function index in the transformer**30**output. The index may be a Walsh index, Gold index, Rademacher index, Hartley index, or the like and still be within the scope of the invention. The corresponding element in the transformer**30**output is fed into a store unit**310**after being weighted by a weighting unit**320**. - [0039]An envelope detector
**360**calculates the squared magnitude of the complex value from the transformer**30**and returns M-ary real values, where M is an integer (e.g. 64). The weighting unit**320**estimates the signal quality (e.g. signal to noise ratio) from the output of the envelope detector**360**and uses this estimation (in the form of weighting coefficients) to weigh the selector**300**output. The weighting unit**320**can be a simple multiplier. It may optionally be omitted, thus creating a weighting factor of one. Those skilled in the art will realize that various noise quality coefficients may be determined from a signal. The preferred embodiment uses a signal to noise ratio coefficient determined by dividing**323**the average**322**and maximum value**321**of the output from the envelope detector - [0040]The store unit
**310**may be a shift register with a tapped delay line, or other memory device, with a size of N, where N is the number of symbols in one power control group. For example, if Walsh symbols are used N may be equal to 6. However since other types of symbols can be used and still be within the scope of this invention and other symbols have different size power control groups, N may be any integer. The symbols may be Walsh symbols, Gold symbols, Rademacher symbols, Hartley symbols, or the like and still be within the scope of the invention. These complex values are then selectively fed into an averager**330**according to certain control logic from a controller**340**. The controller**340**unit counts the symbol index, and at the end of every N symbols (i.e. one power control group), resets the contents of the store unit (i.e. resets the memory or shift register). It also controls which elements of the store unit**310**are used in the channel gain estimation according to the index the system is operating on. FIG. 4B is a flowchart diagram illustrating the operation of the channel estimator and further describes the signal flow through the channel estimator in accordance with the present invention. - [0041]The averager
**330**averages the contents of the store unit**310**. The controller**340**decides which contents the averager**330**will use in the averaging. For example, four summing operators perform averaging over different sets of Walsh symbol values as shown in FIG. 5. - [0042]In the table shown in FIG. 5, B
_{l }(i=1, 2, . . . 6) are the contents in the store unit**310**. They are selectively used in the averager according to each Walsh symbol the channel estimation is for. Note that there are N=6 Walsh symbols in one power control group according to the IS-95 standard. Optionally, the control signal**370**to the averager**330**can be omitted, which means all N(=6) Walsh symbols in one power control group use one channel gain estimation which is the average of all N contents from the store unit**310**. Those skilled in the art will realize that a more sophisticated weighted summation (filtering) can be used in place of the simple averager**330**shown. Also, tap adaptation (i.e. adjusting the poles and/or zeros) of such filtering may also be utilized. - [0043]Having described the invention, what is claimed as new and secured by Letters Patent is:

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Referenced by

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US7430257 * | Apr 24, 2002 | Sep 30, 2008 | Lot 41 Acquisition Foundation, Llc | Multicarrier sub-layer for direct sequence channel and multiple-access coding |

US7593449 | Jan 8, 2007 | Sep 22, 2009 | Steve Shattil | Multicarrier sub-layer for direct sequence channel and multiple-access coding |

US7965761 | Dec 5, 2008 | Jun 21, 2011 | Lot 41 Acquisition Foundation, Llc | Multicarrier sub-layer for direct sequence channel and multiple-access coding |

US8254325 * | Jul 1, 2010 | Aug 28, 2012 | Telefonaktiebolaget Lm Ericsson (Publ) | Multi-path timing tracking and impairment modeling for improved grake receiver performance in mobility scenarios |

US9485063 | Dec 14, 2015 | Nov 1, 2016 | Genghiscomm Holdings, LLC | Pre-coding in multi-user MIMO |

US20070211786 * | Jan 8, 2007 | Sep 13, 2007 | Steve Shattil | Multicarrier Sub-Layer for Direct Sequence Channel and Multiple-Access Coding |

US20090110033 * | Dec 5, 2008 | Apr 30, 2009 | Lot 41 Acquisition Foundation, Llc | Multicarrier sub-layer for direct sequence channel and multiple-access coding |

US20110002232 * | Jul 1, 2010 | Jan 6, 2011 | Jaroslaw Niewczas | Multi-path timing tracking and impairment modeling for improved grake receiver performance in mobility scenarios |

Classifications

U.S. Classification | 370/208, 375/E01.032 |

International Classification | H04B1/712, H04B1/7117, H04L27/00 |

Cooperative Classification | H04L2027/0067, H04B1/7117, H04B1/712 |

European Classification | H04B1/712 |

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