Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/0204—Channel estimation of multiple channels
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/0224—Channel estimation using sounding signals
  • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals

Definitions

• the present disclosure is directed towards communication systems. More particularly, it is directed towards systems and methods for channel estimation in telecommunication systems, such as wired, wireless and optical telecommunication systems.
• MIMO systems are increasingly prevalent in communication systems, such as wireless or optical communication systems.
• MIMO systems employ multiple ports at the transmitting end and the receiving end of a communication medium (e.g., air in wireless systems or optical fiber in optical systems) to improve the data communication rate of the communication between the transmitting and receiving ends while holding radio bandwidth and power constant.
• a communication medium e.g., air in wireless systems or optical fiber in optical systems
• a MIMO transmitter transmits an outgoing symbol signal stream using multiple transmit ports by demultiplexing the outgoing signal stream into multiple signal streams and transmitting the signal streams from separate transmit ports over a potentially noisy communication channel (e.g., air or fiber) .
• MIMO exploits the multiple signal propagation paths between the transmit ports and the receive ports to increase throughput, reduce bit error rates, and reduce transmission power of the transmitted symbols .
• Successful decoding and reconstruction of the signal streams received by the multiple receive ports of the MIMO receiver into the transmitted symbol signal stream typically includes estimating or modeling the noisy channel over which the signal streams are transmitted and received by the MIMO system.
• a system and method includes generating an m x n t input symbol matrix P for transmission over a communication channel via a transmitter having n t transmit ports, where m is greater than n t ; determining an m x n r output symbol matrix Y received at n r receive ports of a receiver in response to the transmission of the input symbol matrix P over the communication channel; generating a 2n t xm pseudo-inverse matrix P ⁇ based on the input symbol matrix P ; and, estimating a first channel matrix H and a second channel matrix G for the communication channel using the pseudo-inverse matrix P ⁇ and the output symbol matrix Y.
• 1 identifies one or more nodes in the given level of the tree .
• the communication channel is a wireless medium and the n t transmit ports and the n r receiving ports are antennas.
• the communication channel is a wired communication channel and the transmit ports and the receive ports are data ports interconnected with each other via wires.
• the communication channel is an optical communication channel and the transmit ports and the receive ports are optical data ports interconnected via an optical fiber .
• FIG. 1 illustrates an example of a MIMO system in accordance with an aspect of the disclosure.
• FIG. 2 illustrates a widely-linear block-diagram representation of a MIMO system in accordance with an aspect of the disclosure.
• FIG. 3 illustrates another widely-linear block- diagram representation of a MIMO system in accordance with an aspect of the disclosure
• FIG. 4 illustrates an example process for estimating channel matrices of a MIMO system in a widely- linear framework in accordance with an aspect of the disclosure .
• FIG. 5 illustrates a block-diagram relationship for estimating channel matrices using the process illustrated in FIG. 4.
• FIGS. 6A-6B illustrate an example for constructing a tree for determining a pilot matrix in accordance with an aspect of the disclosure.
• FIG. 7 illustrates an example of an apparatus for implementing various aspects of the disclosure.
• the term, "or” refers to a nonexclusive or, unless otherwise indicated (e.g., “or else” or “or in the alternative") .
• words used to describe a relationship between elements should be broadly construed to include a direct relationship or the presence of intervening elements unless otherwise indicated. For example, when an element is referred to as being “connected” or “coupled” to another element, the element may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Similarly, words such as “between”, “adjacent”, and the like should be interpreted in a like fashion.
• FIG. 1 illustrates a block diagram of a MIMO communication system 100 according to one embodiment of the present disclosure.
• the MIMO communication system 100 includes a MIMO transmitter 110 and a MIMO receiver 120.
• the MIMO transmitter 110 includes a plurality of transmit ports 112 to 114, and the MIMO receiver 120 includes a plurality of receive ports 122 to 124.
• the MIMO transmitter 110 is configured to generate a plurality of signal streams ti to t T from a transmit bit sequence 140 for transmission over the MIMO channel 130.
• the MIMO receiver 120 is configured to generate an output bit sequence 150 by recovering the original transmit bit sequence 140 from a plurality of signal streams r 1 to r R received from the MIMO channel 130.
• each of the transmit ports 112 to 114 in the MIMO transmitter 110 transmits a signal stream t ⁇ over a MIMO channel 130, where the index i ranges from 1 to T, which indicates the total number of the transmit ports 112 to 114.
• an ith transmit port may transmit a signal stream ti such that the first transmit port 112 transmits a signal stream ti while the last transmit port 114 transmits a signal stream t T .
• each of the receive ports 122 to 124 receives a signal stream j from the MIMO channel 130, where the index j ranges from 1 to R, which indicates the total number of the receive ports 122 to 124.
• a j-th receive port may receive a signal stream ⁇ j such that the first receive port 122 receives a signal stream r 1 while the last receive port 124 receives a signal stream r R .
• the transmitter 110 and the receiver 120 may include any suitable number of ports for implementing a MIMO configuration.
• the term "stream" refers to a sequence of signals or data.
• the signal stream t ⁇ may include one or more signals (e.g., symbols) that are transmitted in sequence.
• the signal stream j may include one or more signals (e.g., symbols) that are received in sequence.
• the MIMO system may be a wireless MIMO system, a wired MIMO system, or an optical MIMO system. Where the MIMO system is implemented as a wireless MIMO communication system (as shown in the example of FIG. 1), the ports 112-114 and 122-124 may be antennas and the MIMO channel 130 may be a wireless medium, such as air.
• the ports 112-114 and 122-124 may be wired or optical ports, and the MIMO channel 130 may include wires (e.g., traces) or optical fibers.
• the transmitter 110 is configured to encode the transmit bit sequence 140 for error detection and correction.
• the transmit bit sequence 140 By encoding the transmit bit sequence 140, errors that may arise during transmission of the bit sequence 140 through the MIMO channel 130 may be detected and corrected at the receiver 120.
• the encoded bit sequence may be divided into a T number of bit streams for modulation and transmission as signal streams ti to t Tr respectively.
• the number T of encoded bit streams are mapped (e.g., modulated) into a set of symbols on a constellation plane prior to transmission over the communication medium 130.
• transmitter 110 may generate symbols ⁇ to x T , respectively, by mapping the respective bit streams to points on a constellation plane.
• transmitter 110 may be configured to apply any suitable modulation technique such as a pulse amplitude modulation (PAM) , a binary phase shift keying (BPSK) , or the like.
• PAM pulse amplitude modulation
• BPSK binary phase shift keying
• the transmitter 110 is configured to convert the symbol streams to analog RF signals that are transmitted over the MIMO channel 130.
• the transmit ports 112 to 114 may receive and transmit analog RF signals as the signal streams ti to t T , respectively, over the MIMO channel 130.
• the transmit ports 112 to 114 may be configured to receive the symbol streams and convert the symbol streams to analog RF signals for transmission as the signal streams t ⁇ to t T , respectively, over the MIMO channel 130.
• the MIMO channel 130 serves as a transmission medium for the signal (e.g., symbol) streams.
• the transmit ports 112 to 114 transmit signal streams ti to t T , respectively, the signal streams ti to t T may be subject to a channel condition, such as interference as well as noise, and received as signal streams r 2 to r R in the receive ports 122 to 124, respectively.
• the present disclosure provides systems and methods for estimating and processing the MIMO system (such as MIMO system 100 of FIG. 1) as a widely- linear (WL) system.
• MIMO system such as MIMO system 100 of FIG. 1
• WL widely- linear
• y is assumed to depend not only on the input signal stream x but also on the conjugate of the input signal stream x * , where the exponent *, as used herein, generally denotes the complex conjugate.
• a widely-linear (WL) system is one that is linear in terms of both the actual input signal stream x and its conjugate signal stream x * , as opposed to a strictly- linear system that is linear only with respect to the input signals x .
• WL estimation of MIMO systems in accordance with various aspects disclosed herein may provide at least an egual or better processing performance over traditional strictly-linear processing, because strictly-linear systems may be understood as a specific case of the more general widely-linear systems.
• WL processing achieves significant performance improvements over the traditional strictly-linear processing in the presence of rotationally variant (or improper) input symbols in the MIMO system.
• it remains a challenge to estimate the underlying physical MIMO system in a WL framework, or, in other words, to systematically estimate the channel matrices of the widely-linear system.
• Various aspects of the present disclosure describe a systematic approach for implementing systems and methods for estimating MIMO systems such as the MIMO system 100 of FIG. 1 in a WL framework.
• the systems and methods disclosed herein may be advantageously applied to model and improve the processing performance of existing MIMO systems.
• FIG. 2 illustrates a block diagram example of a MIMO system 200 expressed in a widely linear framework in accordance with one or more aspects of the disclosure.
• the channel matrices H and G of the WL framework illustrated in Eq. (1) above are estimated by transmitting a number m of training
• the least-square (LS) estimate H of the WL system matrix H may be obtained as:
• H YP+ (5)
• P is referred to herein as the pseudo-inverse pilot matrix of the augmented pilot matrix P and, furthermore, the exponent —1 is generally used herein to denote inversion of a matrix and, exponent H is generally used herein to denote the Hermitian or conjugate transpose of a matrix in accordance with standard matrix notation.
• the optimal augmented pilot matrix P may be found by:
• Eq. (11) may be rewritten as
• Re ⁇ - ⁇ generally denotes the real part of a matrix
• any 2n t X m matrix P with orthogonal columns of the same norm ⁇ / t p may be considered an optimal matrix that minimizes Eq. (9) .
• the channel matrices H and G of a MIMO system such as the MIMO system 100 of FIG. 1 may be estimated in a widely- linear framework starting with step 402 of the process 400 illustrated in FIG. 4 as follows.
• step 412 The process 400 may end at step 414.
• the real-valued 2n t x 2n t matrix P may be determined (step 402) as follows.
• FIG. 6B A specific example of a three-level tree is shown in FIG. 6B.
• the matrix P is constructed in one aspect using the tree.
• the matrix P for a 2-input 2- output MIMO system may be determined as:
• the structured pilot matrix P constructed following the steps above satisfies the condition of Eq. (16), and hence may be considered as an optimal matrix. Furthermore, every element of the pilot matrix P has the same power p such that the equal power constraint for all transmitter ports is satisfied. [0067] With the above WL characterization of the underlying signal processing systems as disclosed herein, WL signal processing methods may be applied to thereby achieve the performance improvements over the SL system characterization .
• MMSE Minimum Mean-Sguare Error
• the present disclosure above describes a systematic approach for estimating the ordinary and conjugate system matrices simultaneously in the WL framework by transmitting a larger number (including twice the number) of pilot symbol vectors p than the number used for estimating only the system matrix H in the SL framework. While it is typical that m > n t for the SL system estimation, in various aspects the present disclosure uses m > 2n t for WL system estimation, where m denotes the number of pilot vectors or symbols that are systematically determined as described above.
• an estimation method such as the LS, MMSE, or any other estimation may be advantageously used to estimate the ordinary and conjugate system matrices of Eg. (1) in the widely-linear framework.
• FIG. 7 depicts a high-level block diagram of an example computing apparatus 700 suitable for implementing one or more aspects of the disclosure.
• Apparatus 700 comprises a processor 702 that is communicatively interconnected with various input/output devices 704 and a memory 706.
• the processor 702 may be any type of processor such as a general purpose central processing unit (“CPU") or a dedicated microprocessor such as an embedded microcontroller or a digital signal processor (“DSP”) .
• the input/output devices 704 may be any peripheral device operating under the control of the processor 702 and configured to input data into or output data from the apparatus 700, such as, for example, network adapters, data ports, and various user interface devices such as a keyboard, a keypad, a mouse, or a display.
• Memory 706 may be any type of memory suitable for storing electronic information, including data and instructions executable by the processor 702.
• Memory 706 may be implemented, for example, as one or more combinations of a random access memory (RAM) , read only memory (ROM) , flash memory, hard disk drive memory, compact-disk memory, optical memory, etc.
• apparatus 700 may also include an operating system, queue managers, device drivers, or one or more network protocols which may be stored, in one embodiment, in memory 706 and executed by the processor 702.
• the memory 706 may include non-transitory memory storing executable instructions and data, which instructions, upon execution by the processor 702, may configure apparatus 700 to perform the functionality in accordance with the various aspects and steps described above (e.g., one or more steps of process 400 of FIG. 4).
• the processor 702 may be configured, upon execution of the instructions, to communicate with and/or control the transmitter 110 of the MIMO system 100 (e.g., via a network) to cause the transmitter to transmit, over the communication channel 130, pilot symbol vector (s) p that are determined by the processor 702 in accordance with various aspects (or steps) described in the present disclosure.
• the processor 702 may also be configured to communicate with and/or control the receiver 120 of the MIMO system 100 (e.g., via a network) to receive measured output values y that are produced at the receiver 120 in response to the pilot symbol vector (s) p that are transmitted over the communication channel 130.
• apparatus 700 may be implemented using one or more application specific integrated circuits (ASICs) , field programmable gate arrays
• FPGAs field-programmable gate arrays

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• 2013
  • 2013-12-30 KR KR1020130167287A patent/KR101550110B1/ko active IP Right Grant
• 2014
  • 2014-11-25 WO PCT/EP2014/075464 patent/WO2015101445A1/en active Application Filing

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