The present invention relates to communication systems and methods, and, particularly, to multiple-input-multiple-output (MIMO) communication system and methods.
Carrier to Interference-plus-Noise Ratio (CINR) is an important parameter for any communication system and/or method, and it is particularly difficult to estimate CINR for communication system and methods using multiple-input-multiple-output (MIMO).
In contrast to other transmission and reception schemes, in maximum likelihood (ML) decoded spatial multiplexing (SM), the per-tone post processing CINR is trivial. The formula adopted in the IEEE802.16e for ML decoded vertical SM is provided by Eq. 1:
(1) Eq. 1 gives erroneous results when the matrix H features high correlation. For instance, in the case represented by Eq. 2:
(2) Eq. 1 cannot be modified in a simple manner to accommodate horizontal SM, where multiple CINR estimates are to be produced (one for each stream), as in uplink (UL) collaborative MIMO.
The following US patent applications are believed to represent the most relevant prior art: 20060030364, 20070058603, 20070201568, 20070248151, 20070274409, 20080080459, 20080080634, 20080186915, and 20080240217.
The present invention provides a different formula for ML decoded SM that remedies to aforementioned problems. The proposed method gives a much more accurate CINR estimate that allows superior link mode selection, link adaptation, etc. There is thus a widely recognized need for, and it would be highly advantageous to have, a CINR estimation method and/or system devoid of the above limitations.
According to one aspect of the present invention there is provided a method for calculating channel quality in a multi-stream communication system, the method including the step of calculating the channel quality for a selectable stream of the multi-stream communication system.
According to another aspect of the present invention there is provided a method for assigning a plurality of transmitters to a frequency-time resource in a multi-stream communication system, the method including the steps of: calculating single-stream channel quality for a plurality of selectable streams of the multi-stream communication system, selecting a frequency-time resource, and assigning a plurality of transmitters to the frequency-time resource according to their channel quality.
According to yet another aspect of the present invention there is provided a method for calculating channel quality additionally including estimating at lest one set of error vectors including at least one transmission vector including at least one erroneous element, and where the step of calculating the channel quality uses the estimation of at lest one set of error vectors.
According to still another aspect of the present invention there is provided a method for calculating channel quality where the element includes at least one of a bit, a baud, and a symbol.
Also according to another aspect of the present invention there is provided a method for calculating channel quality where the channel quality includes signal to noise ratio (SNR), or Carrier to Interference-plus-Noise Ratio (CINR), or Signal to Interference-plus-Noise Ratio (SINR).
Additionally according to still another aspect of the present invention there is provided a method for calculating channel quality where the receiver receives the multi-stream signal in the uplink and/or in the downlink.
Further according to another aspect of the present invention there is provided a method for calculating channel quality where the multi-stream communication system includes a Multi-Input-Multi-Output (MIMO) technology, and/or a spatial diversity technology, and/or a spatial multiplexing technology.
Further according to another aspect of the present invention there is provided a method for calculating channel quality where the step of calculating the channel quality includes calculating sets of values corresponding to errors in each stream, and/or constructing at lest one set of error vectors (Âi) from the values.
Yet further according to another aspect of the present invention there is provided a method for calculating channel quality where the step of calculating the channel quality includes the steps of estimating channel response for each antenna, and constructing channel matrix (H) from the channel responses.
Even further according to another aspect of the present invention there is provided a method for calculating channel quality where the step of calculating the channel quality includes calculating a set of values H·e for the i-th stream, where e denotes a matrix element of the error matrix Âi, and calculating the CINR for the selectable stream i according to
Also according to another aspect of the present invention there is provided a method for calculating channel quality where the multi-stream communication system includes a plurality of user terminals, where each of the user-terminals transmits a single stream, and where the multi-stream signal includes the single streams transmitted by the plurality of user-terminals.
Additionally according to another aspect of the present invention there is provided a method for calculating channel quality where at least two of the plurality of user-terminals use the same frequency-time resource.
According to yet another aspect of the present invention there is provided a method for calculating channel quality additionally including the steps of selecting the user-terminals using the same frequency-time resources, and/or selecting the frequency-time resources for use by the plurality of user-terminals.
According to still another aspect of the present invention there is provided a method for calculating channel quality where the receiver performs at least one of the additional steps described above.
Further according to another aspect of the present invention there is provided a method for calculating channel quality where the channel quality is calculated for a plurality of channels in a vertical spatial multiplexing situation, and where the step of calculating the channel quality includes the steps of calculating a set of values H·e for the i-th stream, where e denotes a matrix element of the error matrix Âi and calculating the CINR for the selectable stream i according to
CINR(H)=min[CINR0(H),CINR1(H)]
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting. Except to the extend necessary or inherent in the processes themselves, no particular order to steps or stages of methods and processes described in this disclosure, including the figures, is intended or implied. In many cases the order of process steps may varied without changing the purpose or effect of the methods described.
Implementation of the method and system of the present invention involves performing or completing certain selected tasks or steps manually, automatically, or any combination thereof. Moreover, according to actual instrumentation and equipment of preferred embodiments of the method and system of the present invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or any combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions.
The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in order to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
In the drawings:
The principles and operation of a method and system for calculating Carrier to Interference-plus-Noise Ratio (CINR), or Signal to Noise Ration (SNR), or Signal to Interference plus noise ratio (SINR), for a data stream in a Multi-Input-Multi-Output (MIMO) system according to the present invention may be better understood with reference to the drawings and accompanying description.
Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.
In this document, an element of a drawing that is not described within the scope of the drawing and is labeled with a numeral that has been described in a previous drawing has the same use and description as in the previous drawings. Similarly, an element that is identified in the text by a numeral that does not appear in the drawing described by the text, has the same use and description as in the previous drawings where it was described.
The CINR formula of the present invention is intended to overcome limitations of the systems currently known in the art as described by the set of Eqs. 3, 4 and 5:
Eqs. 3, 4 and 5 are effective when there is no correlation between the data streams and the calculation of the CINR is performed on the pre-processed received signal, that is, before demodulation. However, when there is correlation between the streams the calculation of the CINR should be performed on the post-processed signal, that is after the demodulation. In this case the CINR calculation as described by Eqs. 3, 4 and 5 is erroneous. The CINR calculation described below describes a method for calculating CINR on the post-processed, or the demodulated, signal.
Reference is now made to
In the MIMO communication system 10 of both
We consider the following mathematical model for the per tone received N×1 signal vector y in SM, is represented by Eq. 6:
y=Hs+ρn Eq. 6:
where
The optimal ML MIMO decoder is best described by the expression for the log-likelihood ratio (LLR) of each transmitted bit is represented by Eq. 7:
Therefore, in uncoded systems the ML estimator Ŝ for the transmitted vector S is represented by Eq. 7:
An error event is preferably defined herein by Eq. 9 in a manner that distinguishes the event of error in s0 from error in s1:
Pr(error in si)=Pr(ŝεBi) Eq. 9:
where:
Applying the union bound, the per stream error probability is bounded by Eq. 10:
Using Eq. 6 and some standard high (pre processing) CINR approximations leads to Eq. 11:
The error probability may be further simplified through the max-log approximation as described by Eq. 12:
Continuing, without loss of generality, with QPSK modulation, and bearing in mind that in QPSK the CINR estimate should satisfy Eq. 13:
Equating the exponentials of Eqs. 12 and 13 gives the approximation described by Eq. 14:
At this point we turn to the determination of the sets Ai. To keep the exposition simple we consider the case of 2 spatial streams. An error in S0 means that the first component in e is nonzero, and may assume any value corresponding to a transition to any other constellation point in the QAM that differs from S0. Moreover, the second component in e may assume any value corresponding to a transition to any other constellation point including zero (zero means that there is no error in S1).
Reference is now made to
is transmitted in s0.
is transmitted in s1.
is transmitted in s0.
is transmitted in s1.
In QPSK the set A0 takes the form of Eq. 15:
It is appreciated that many of the elements in the set A0 are redundant as they lead to the same value of the cost functional ∥He∥.
The first four elements of A0 are an example, and so are the vectors √{square root over (2)}[1,−1]T,√{square root over (2)}[−1,1]T.
Removing redundant elements and neglecting vectors that correspond to far transitions, the sets A0 and A1 may be approximated by the set of Eqs. 16:
Thus, the per stream CINR estimation method takes the form of the set of Eqs. 16:
Therefore, the joint CINR (for the case of vertical SM) is provided by of Eq. 18:
The following key points are emphasized:
(1) The proposed method is consistent with the linear decoder CINR in the case the columns of H are orthogonal (where the linear decoder is optimal).
Thus, considering (ill conditioned) matrix 18:
and the CINR of stream 1 is 0.
It is appreciated that this result is obtained from the proposed method, as implied from the first elements in A0 and A1 respectively.
(2) From implementation point of view, the proposed CINR algorithm is best implemented through the ML decoder itself. It is appreciated that the minimum of the cost functional ∥He∥2 may be computed using the kernel of the ML algorithm
The two per tone CINR metrics are tested on vertical SM on constant fading channel, defined by randomly generated channel matrix with given correlation (from 0 to 1 with step 0.1). White noise is added to the product according to SNR.
Reference is now made to
The random source bits are modulated and passed through the channel. For every channel correlation point and CINR point, BER (bit error rate) and the two CINR estimators are measured. Since the fading channel being used is constant, the measured CINR should be related to measured BER according to the BER(CINR) dependency in an AWGN channel. Bearing in mind the above arguments, the CINR measurement error is defined as the difference between the measured CINR and the CINR value that corresponds to the measured BER in an AWGN channel. The CINR error is measured about the working point (BER 1E-3 to 1E-5).
In
Reference is now made to
The CINR derivation in above refers to QPSK modulation. The same derivation may be applied to the QAM16 and QAM64. In higher modulations there are more transition options, however the QPSK transitions sets A0 and A1 are good enough approximations for the QAM16/64 transition sets, as can be seen from
Reference is now made to
The process described by the flow diagram of
The term “channel quality” refers to calculating CINR, or SINR, or SNR, etc.
The term “multi-stream communication system” refers to a communication system including a receiver using a plurality of antennas. For example, using a MIMO antenna system, such as the MIMO communication system 10 of
The term “single selectable stream” refers to a selection of a single stream of the multi-stream communication system. The process calculates the channel quality for the selected stream. Preferably, the process can select and calculate channel quality for any stream of the multi-stream system.
The method for calculating channel quality preferably includes the following steps:
Offline, in this respect, means that the error matrices Ai can be assessed for a MIMO configuration of [M×N] antennas in advance. The appropriate set of error matrices Ai can thereafter be selected by the base-station 14 of
Online, in this respect, means that the channel matrix H is evaluated in real-time, or near real-time, for example using pilot signals, and the CINR is calculated according to the evaluated channel matrix H.
It is appreciated that the receiver is typically a base-station receiving an uplink transmission and the channel quality is calculated for the uplink transmission. However, the receiver can also receive downlink transmissions, and the channel quality can be calculated for the downlink transmission.
It is appreciated that for high SNR, the CINR calculated according to Eq. 19 is practically independent of the modulation technique. Therefore, it is sufficient to assess the error matrices Ai for a simple modulation technique, such as QPSK, and ten use the same error matrices Ai for higher modulation techniques such as QAM16, QAM 64, etc.
It is also appreciated that the CINR calculation technique is useful for situations of mixed modulations. That is, for a MIMO system with streams of different modulation. For example, when the two transmitters 20 of
For transmitters transmitting a single stream each and in a horizontal manner, such as the transmitters 20 of
It is expected that during the life of this patent many relevant Communication devices and systems will be developed and the scope of the terms herein, particularly of the terms “SNR”, “SINR”, “CINR”, MIMO, “spatial multiplexing” and “spatial diversity”, is intended to include all such new technologies a priori.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.
The present application claims priority from U.S. provisional patent application 61/019,313, filed Jan. 7, 2008, the contents of which are hereby incorporated by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2009/050027 | 1/6/2009 | WO | 00 | 7/7/2010 |
Number | Date | Country | |
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61019313 | Jan 2008 | US |