ERIC-1001
`Ericsson v IV
`Page 1 of 19
`
`

`
`US 7,269,127 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`2002/0122381 A1*
`2002/0122382 A1*
`2002/0181390 A1
`2002/0181509 A1
`2003/0043887 A1*
`
`9/2002 Wu et al.
`9/2002 Ma et al.
`12/2002 Mody et al.
`12/2002 Mody et al.
`3/2003 Hudson .... ..
`
`................. .. 370/208
`370/208
`370/208
`370/480
`.. 375/144
`
`
`
`OTHER PUBLICATIONS
`
`Vahid Tarokh, Hamid Jafarkhani, A. R. Calderbank, “Space-Time
`Block Codes from Orthogonal Designs,” IEEE Transaction on
`Inforn1ation Theory, Jul. 1999, pp. 1456-1467, vol. 45, No. 5.
`Vahid Tarokh, Hamid Jafarkhani, A. R. Calderbank, “Space-Time
`Block Coding for Wireless Communications: Performance Results,”
`IEEE Journal on Selected Areas in Communications, Mar. 1999, pp.
`451-460, vol. 17, No. 3.
`Ye (Geoffrey) Li, Nambirajan Seshadri, Sirikiat Ariyavisitakul,
`“Channel Estimation for OFDM Systems With Transmitter Diver-
`sity in Mobile Wireless Charmels,” IEEE Journal on Selected Areas
`in Communications, Mar. 1999, pp. 461-471, vol. 17, No. 3.
`
`Apurva N. Mody, Gordon L. Stuber, “Synchronization for MIMO
`OFDM Systems,” 2001, pp. 509-513, vol.
`1, Proceedings of
`GLOBECOM 2001, San Antonio.
`Apurva N. Mody, Gordon L. Stuber, “Parameter Estimation for
`OFDM With Transmit Receive Diversity,” 2001, Proceedings of
`VTC Rhodes, Greece.
`Apurva N. Mody, Gordon L. Stuber, “Eflicient Training and Syn-
`chronization Sequence Structures for MIMO OFDM,” 2001, Pro-
`ceedings of 6d‘ OFDM Workshop 2001, Paper 16, Hamburg, Ger-
`many.
`
`Timothy M. Schmidl, Donald C. Cox, “Robust Frequency and
`Timing Synchronization for ODFM,” IEEE Transactions on Com-
`munications, Dec. 1997, pp. 1613-1621, vol. 45, No. 12.
`Apurva N. Mody, Gordon L. Stuber, “Receiver Implementation for
`a MIMO OFDM System,” Nov. 2002, Proceedings of GLOBECOM
`2002, Taipei, Taiwan.
`
`* cited by examiner
`
`ERIC-1001 I Page 2 of 19
`
`ERIC-1001 / Page 2 of 19
`
`

`
`U.S. Patent
`
`Sep. 11,2007
`
`Sheet 1 of 7
`
`US 7,269,127 B2
`
`E
`
`mo»<._:oo_>_mo
`
`N5wsmm
`
`moE.5oos_m_o
`
`0
`
`’
`
`'
`
`mm
`
`-oNNLQN
`
`w_O._.<._Dn_O_>_
`
`ERIC-1001 I Page 3 of 19
`
`ERIC-1001 / Page 3 of 19
`
`
`
`

`
`U.S. Patent
`
`Sep. 11,2007
`
`Sheet 2 of 7
`
`US 7,269,127 B2
`
` ENCODER
`
`38
`
`18
`
`
`
`
`SYMBOL
`SPACE—T|ME
`CHANNEL
`ENCODER
`MAPPER
`PROCESSOR
`
`
`
`
`
`
`
`
`
`
`TRAINING
`SYMBOL
`INSERTER
`
`24
`
`MODULATOR
`
`22
`
`SERIAL TO
`PARALLEL
`
`so
`
`52
`
`IDFT
`
`CYCUC
`PREFIX
`INSERTER
`
`60
`
`54
`
`64
`
`26
`
`V
`
`PARALLEL
`DAC
`9 >
`T0 SERIAL - '5
`
`58
`
`55
`
`LOCAL
`OSCILLATOR
`
`62
`
`FIG. 3
`
`ERIC-1001 I Page 4 of 19
`
`ERIC-1001 / Page 4 of 19
`
`

`
`U.S. Patent
`
`Sep. 11,2007
`
`Sheet 3 of 7
`
`US 7,269,127 B2
`
`S1
`
`3Q+1
`
`5Q+2
`
`o
`
`'
`
`o
`
`'
`
`o
`
`'
`
`t
`
`520
`
`“T3
`
`S<q-m+1
`
`S(Q-1)o+2
`
`°
`
`'
`
`°
`
`Sou
`
`t+(0—1>Ts
`
`ERIC-1001 I Page 5 of 19
`
`ERIC-1001 / Page 5 of 19
`
`

`
`U.S. Patent
`
`Sep. 11,2007
`
`Sheet 4 of 7
`
`US 7,269,127 B2
`
`1?
`
`FIG.5
`
`space
`
`4:3
`‘/9
`/7459
`£’
`
`ERIC-1001 I Page 6 of 19
`
`ERIC-1001 / Page 6 of 19
`
`

`
`U.S. Patent
`
`Sep. 11,2007
`
`Sheet 5 of 7
`
`US 7,269,127 B2
`
`mm
`
`
`
`+11._oms_>w<591||v_
`
`8
`
`\+
`
`Z
`
`O.
`
`mm
`
`E
`
`_.<zzmpz<
`
`
`
`
`
`AullolllnlllmmE.o:m._.m<_.<o
`
`Az+9Un_
`
`MM
`
`B.U.E~
`
`am
`
`
`
`mm:»o:m»mm4m2<mmaanuuumwwlnuvN«M4om2>m
`
`
`
`oz;=<m»omoz<:zw
`
`
`
`4om2>mOZZEEH
`
`ERIC-1001 I Page 7 of 19
`
`ERIC-1001 / Page 7 of 19
`
`

`
`U.S. Patent
`
`Sep. 11,2007
`
`Sheet 6 of 7
`
`US 7,269,127 B2
`
`84
`
`\
`
`75
`
`78
`
`s1(NT/4)
`
`s1(NT/4)
`
`s1(NT/4)
`
`s1(NT/4)
`
`
`
`86-1
`
`86-2
`
`86-4
`
`86-5
`
`}
`
`88
`
`92
`
`‘
`
`I
`
`94
`
`FIG. 7
`
` S1‘
`
`98-1
`
`93-2 98-3 98-4
`
`S1‘
`S1‘
`(NT/8) (NTl8) (NT/8)
`
`F
`
`fl
`
`
`
`88 9° 92
`
`
`
`ERIC-1001 I Page 8 of 19
`
`ERIC-1001 / Page 8 of 19
`
`

`
`U.S. Patent
`
`Sep. 11,2007
`
`Sheet 7 of 7
`
`US 7,269,127 B2
`
`ANTENNA 1
`
`76
`
`10° \
`
`78
`
`s1(NT/4)
`
`s1(NT/4)
`
`-s1*(NT/4)
`
`s1(NT/4)
`
`
`
`104-1
`
`104-2
`
`104-4
`
`104-5
`
`I
`
`
`
`|
`
`106
`
`ERIC-1001 I Page 9 of 19
`
`ERIC-1001 / Page 9 of 19
`
`

`
`US 7,269,127 B2
`
`1
`PREAMBLE STRUCTURES FOR
`SINGLE-INPUT, SINGLE-OUTPUT (SISO)
`AND MULTI-INPUT, MULTI-OUTPUT
`(MIMO) COMMUNICATION SYSTEMS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application claims priority to co-pending U.S. pro-
`visional application entitled “Preamble Structures for SISO
`and MIMO OFDM Systems,” having Ser. No. 60/327,145,
`filed on Oct. 4, 2001, which is entirely incorporated herein
`by reference.
`This application is related to U.S. provisional application
`entitled “Efficient Training and Synchronization Sequence
`Structures for MIMO OFDM,” having Ser. No. 60/322,786,
`filed Sep. 17, 2001, which is entirely incorporated herein by
`reference.
`
`TECHNICAL FIELD OF THE INVENTION
`
`The present invention is generally related to communica-
`tion systems and, more particularly, to single-input, single-
`output (SISO) and multi-input, multi-output (MIMO) com-
`munication systems.
`
`BACKGROUND OF THE INVENTION
`
`Significant developments in communications have been
`made by the introduction of technologies that
`increase
`system operating efficiency (i.e., system “throughput”). One
`example of these technologies is the use of two or more
`transmit antennas and two or more receive antennas (i.e.,
`multiple antennas) in a wireless communication system.
`Such systems are typically referred to as multi-input, multi-
`output (MIMO) communication systems. In contrast, tradi-
`tional wireless communication systems typically employ
`one transmit antenna and one receive antenna, and such
`systems are referred to accordingly as single-input, single-
`output (SISO) systems.
`In addition, traditional communication systems typically
`use one of two types of signal carrier systems. One such
`system uses only one carrier for the transmission of infor-
`mation and is known as a single carrier (SC) system. A
`system that uses multiple carriers to transmit information in
`parallel
`is known as a multi-carrier (MC) system. MC
`systems divide the existing bandwidth into a number of
`sub-charmel bandwidths and each bandwidth is modulated
`
`individually by a respective sub-carrier. The method of
`dividing the bandwidth into sub-channel bandwidths is
`referred to as frequency division multiplexing (FDM).
`Therefore, either SISO or MIMO communications may use
`a SC or an MC signal carrier system.
`In a MIMO communication system, signals are typically
`transmitted over a common path (i.e., channel) by multiple
`antennas. The signals are typically pre-processed to avoid
`interference from other signals in the common channel.
`There are several techniques that may be used to pre-process
`the signals in this regard, and some of these techniques may
`be combined to further improve system throughput. One
`such technique, known as space-time processing (STP),
`processes and combines “preamble structures” and “data
`structures” into groups referred to herein as “frame struc-
`tures.” Wireless communication systems typically transmit
`data, or information (e.g., voice, video, audio, text, etc.), as
`formatted data symbols (or information symbols), which are
`typically organized into groups referred to herein as data
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`
`structures. The preamble structure contains an overhead for
`providing synchronization and parameter estimation, allow-
`ing a receiver to decode signals received from a transmitter.
`In a MIMO communication system, multiple frame struc-
`tures are transmitted by a corresponding number of transmit
`antennas. The combination of the multiple frame structures
`is generally referred to space-time signal structures. Each
`frame structure generally includes a preamble structure
`followed by a data structure.
`Training symbols are typically added as prefixes to the
`data structures (e.g., at the beginning of frame structure) to
`enable training (i.e., time and frequency synchronization)
`between the transmitter and receiver of a MIMO commu-
`
`nication system. These training symbols can be referred to as
`preambles and are part of the preamble structures. Space-
`time signal structures are constructed using STP for training
`symbols and data symbols individually. Furthermore, pilot
`structures (or pilots) are symbols that are also constructed by
`STP and have the same structure as preambles. However,
`instead of being placed as a prefix to the data structure, the
`pilot structures are periodically arranged within groups of
`data symbols. Certain properties incorporated into space-
`time signal structures make it possible to recover the data
`structures by post-processing the space-time signal struc-
`tures with a receiver. Moreover, the formation and process-
`ing of space-time signal structures in a wireless communi-
`cation system may provide increased strength (i.e., gain) in
`the recovered signal, which typically enhances the perfor-
`mance of the communication system.
`Another technique that may be used to pre-process signals
`in a MIMO communication system is FDM as mentioned
`earlier. FDM involves dividing the frequency spectrum of a
`wireless communication system into sub-channels and trans-
`mitting modulated data, or information (i.e., formatted sig-
`nals for voice, video, audio,
`text, etc.), over these sub-
`channels at multiple signal carrier frequencies (“sub-carrier
`frequencies”).
`Communication systems involving orthogonal frequency
`division multiplexing (OFDM) have emerged as a popular
`form of FDM in which the sub-carrier frequencies are
`spaced apart by precise frequency differences. The applica-
`tion of the OFDM technology in a SISO communication
`system (i.e., a SISO OFDM system) provides the capability,
`among others, to efficiently transmit and receive relatively
`large amounts of information. The application of OFDM in
`a MIMO communication system (i.e., a MIMO OFDM
`system) increases the system’s capacity to transmit and
`receive information using approximately the same amount
`of bandwidth (i.e., transmission line capacity) as used in a
`SISO OFDM systems. A MIMO OFDM communication
`system also offers improved performance to overcome some
`of the difficulties experienced in other FDM communication
`systems, such as performance degradation due to multiple
`versions of a transmitted signal being received over various
`transmission paths (i.e., multi-path charmel interference).
`In SISO and MIMO wireless communication systems,
`synchronization of data symbols is typically required in both
`the time domain and the frequency domain. Estimation of
`parameters such as noise variance and other charmel param-
`eters is also typically required. Thus, an efficient preamble
`structure for use in wireless communication systems should
`provide both synchronization and parameter estimation.
`Furthermore, an efficient preamble structure should possess
`a low peak-to-average power ratio (PAPR)
`(i.e., at or
`approaching unity) to facilitate efficient system operation.
`In their application to SISO and MIMO communication
`systems, however, various shortcomings have been identi-
`
`ERIC-1001 I Page 10 of 19
`
`ERIC-1001 / Page 10 of 19
`
`

`
`US 7,269,127 B2
`
`3
`fied in existing preamble structures. For example, the IEEE
`Standard 802.11a preamble structure includes a short
`sequence, which provides time synchronization and coarse
`frequency offset estimation, followed by a long sequence,
`which provides fine frequency and channel estimation.
`Although this preamble has application to SISO communi-
`cation systems,
`it is not directly applicable to a MIMO
`communication system to provide the above mentioned
`functions, without the need for significant modifications.
`Moreover, there is considerable redundancy in the IEEE
`Standard 802.11a preamble structure, which reduces the
`system throughput and hence the system efficiency.
`Therefore,
`there is a need for an efi‘icient preamble
`structure that provides time and frequency synchronization,
`estimation of parameters such as noise variance and channel
`parameters, and low PAPR when used with SISO and
`MIMO communication systems.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides a system for providing
`efficient preamble structures for use in single-input, single-
`output (SISO) and multi-input, multi-output (MIMO) com-
`munication systems. Briefly described, one embodiment of
`the present invention, among others, includes providing a
`communication system for transmitting space-time signal
`structures across a charmel. The space-time signal structures
`may be transmitted using a SISO communication system
`and/or a MIMO communication system. One such space-
`time signal structure includes at least one training symbol,
`each training symbol having a cyclic prefix and a training
`block. The length of N, samples of the training block is equal
`to a fraction of the length of N samples of a data block such
`that N,:N/I, where I is a positive integer. Furthermore, the
`length of G samples of the cyclic prefix is a fraction of the
`length N,. For example, G may be equal to N,/4, or 25% of
`NI. The training symbols provide coarse and fine time
`synchronization, coarse and fine frequency synchronization,
`channel estimation, and noise variance estimation.
`The present invention can also be viewed as providing a
`method for providing efiicient preamble structures for SISO
`and MIMO communication systems. In this regard, one
`embodiment of such a method, among others, can be broadly
`summarized by the following: providing a space-time signal
`structure having at least one training symbol, each training
`symbol having a cyclic prefix and a training block. The
`length of N, samples of the training block is equal to a
`fraction of the length of N samples of a data block, i.e.,
`N,:N/I. Furthermore, the length of G samples of the cyclic
`prefix is a fraction of the length of N,. For example, G may
`be equal to N,/4, or 25% of N]. The training symbols provide
`coarse and fine time synchronization, coarse and fine fre-
`quency synchronization, cha1mel estimation, and noise vari-
`ance estimation.
`
`Other systems, methods, features and advantages of the
`present invention will be or become apparent to one with
`skill in the art upon examination of the following drawings
`and detailed description. It is intended that all such addi-
`tional
`systems, methods,
`features, and advantages be
`included within this description, be within the scope of the
`present invention, and be protected by the accompanying
`claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Many aspects of the invention can be better understood
`with reference to the following drawings. Moreover, in the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`drawings, like reference numerals designate corresponding
`parts throughout the several views.
`FIG. 1 is a block diagram of an exemplary multi-input,
`multi-output (MIMO) communication system.
`FIG. 2 is a block diagram of an exemplary encoder with
`respect to the communication system depicted in FIG. 1.
`FIG. 3 is a block diagram of an exemplary modulator with
`respect to the communication system depicted in FIG. 1.
`FIG. 4 is a diagram illustrating exemplary signal trans-
`missions and associated signal sample matrices with respect
`to the communication system depicted in FIG. 1.
`FIG. 5 is a three-dimensional graphical illustration of a
`version of the receive sample matrix shown in FIG. 4 that is
`applicable to the MIMO communication system of FIG. 1
`when employing Orthogonal Frequency Division Multiplex-
`ing (OFDM).
`FIG. 6 illustrates exemplary data frames that may be
`implemented in the MIMO communication system depicted
`in FIG. 1.
`
`FIG. 7 illustrates an embodiment of a preamble structure
`that may-be implemented in a SISO communication system.
`FIG. 8 illustrates another embodiment of a preamble
`structure that may be implemented in a SISO communica-
`tion system.
`FIG. 9 illustrates an embodiment of a preamble structure
`that may be implemented in a MIMO communication sys-
`tem, e.g., the system depicted in FIG. 1.
`
`DETAILED DESCRIPTION
`
`The invention now will be described more fully with
`reference to the accompanying drawings. The invention
`may, however, be embodied in many different forms and
`should not be construed as limited to the embodiments set
`forth herein. Rather,
`these embodiments are intended to
`convey the scope of the invention to those skilled in the art.
`Furthermore, all “examples” given herein are intended to be
`non-limiting.
`FIG. 1 shows a block diagram of an exemplary multi-
`input, multi-output (MIMO) communication system 10. The
`exemplary MIMO communication system 10 and its sub-
`components will be described below to facilitate the descrip-
`tion of the present invention. In that regard, the exemplary
`MIMO communication system 10 may be implemented as a
`wireless system for the transmission and reception of data
`across a wireless channel 12. For example,
`the MIMO
`communication system 10 may be implemented as part of a
`wireless local area network (LAN) or metropolitan area
`network (MAN) system, a cellular telephone system, or
`another type of radio or microwave frequency system incor-
`porating one-way or two-way communications over a range
`of distances.
`
`The MIMO communication system 10 may transmit and
`receive signals at various frequencies. For example,
`the
`MIMO communication system 10 may transmit and receive
`signals in a frequency range from 2 to 11 GHz, such as in the
`unlicensed 5.8 GHz band, using a bandwidth of about 3 to
`6 MHz. Further, the MIMO communication system 10 may
`employ various signal modulation and demodulation tech-
`niques, such as single-carrier frequency domain equalization
`(SCFDE) or orthogonal frequency division multiplexing
`(OFDM), for example. However, throughout this descrip-
`tion, references will be made with respect to a MIMO
`OFDM communication system merely to facilitate the
`description of the invention.
`The MIMO communication system 10 may also be imple-
`mented as part of a communication system (not shown) that
`
`ERIC-1001 I Page 11 of 19
`
`ERIC-1001 / Page 11 of 19
`
`

`
`US 7,269,127 B2
`
`5
`includes an array of sub-charmel communication links,
`which convey one or more signals transmitted by one or
`more transmitting elements to one or more receiving ele-
`ments. The sub-channel communication links may include
`wires (e.g., in a wiring harness) or other forms of transmis-
`sion medium that span between a data source and a receiver
`within the communication system.
`The MIMO communication system 10 includes a trans-
`mitter 14 and a receiver 16. The transmitter 14 transmits
`
`signals across the channel 12 to the receiver 16. As depicted
`in FIG. 1,
`the transmitter 14 typically includes several
`components. In this regard, the transmitter 14 includes an
`encoder 18. The encoder 18 typically encodes data and/or
`other types of signals received, for example, from a data
`source 20. Such signals may alternatively be referred to
`collectively as “data,” “signals,” or “data signals.” The data
`source 20 may be a device, system, etc. that outputs such
`signals. The encoder 18 may also perform functions such as
`employing a channel code on data for transmission and
`forming sequence structures by STP techniques. Further, the
`encoder 18 may separate the signals from data source 20
`onto one or more signal paths, which are referred to as
`transmit diversity branches (TDBs) 22-1, 22-2,
`.
`.
`.
`, 22-Q,
`where Q is the number of transmit antennas from which the
`signals are transmitted. The encoder 18 typically facilitates
`the transmission of signals across the charmel 12 by bun-
`dling the signals into groups, which are typically referred to
`as space-time signal structures. Details of an exemplary
`space-time signal structure, with respect
`to the present
`invention, is discussed below with respect to FIG. 6.
`Further shown in FIG. 1, the transmitter 14 also includes
`one or more modulators 24-1, 24-2,
`.
`.
`.
`, 24-Q that are
`configured to modulate signals for transmission over the
`channel 12. In this regard, the modulators 24 may employ
`various modulation techniques, such as SCFDE or OFDM.
`The modulators 24 are typically connected to the encoder 18
`by the TDBs 22. The transmitter 14 also includes one or
`more transmit antennas 26-1, 26-2,
`.
`.
`.
`, 26-Q connected
`respectively to the one or more modulators 24-1, 24-2, .
`.
`.
`, 24-Q. Thus, each TDB 22 directs signals from the encoder
`18 to a corresponding modulator 24, and the modulator 24
`modulates the signals for transmission by a respective
`transmit antenna 26. An embodiment of a space-time signal
`structure transmitted by the transmitter 14 is described
`below with reference to FIG. 6.
`
`As discussed above, the exemplary MIMO communica-
`tion system 10, shown in FIG. 1, also includes a receiver 16.
`The receiver 16 also typically includes several components.
`The receiver includes one or more receive antennas 28-1,
`28-2, .
`.
`.
`, 28-L, where L is the number of receive antennas
`used to receive the Q transmitted space-time signal struc-
`tures. With Q transmit antennas 26 and L receive antennas
`28, the MIMO communication system 10 can be referred to
`as a Q><L system. In a SISO communication system, the
`variables Q and L are both equal to one. In a MIMO system,
`Q and L are equal to a number greater than one and may be
`equal to each other or non-equal. For example, a 2x2 MIMO
`communication system comprises two transmit antennas,
`i.e., Q:2, and two receive antennas, i.e., L:2.
`The receive antennas 28-1, 28-2, .
`.
`.
`, 28-L are connected
`to one or more demodulators 30-1, 30-2,
`.
`.
`.
`, 30-L,
`respectively. The receive antennas 28 typically receive
`modulated signals, i.e., space-time signal structures, that are
`transmitted across the channel 12 from the transmit antennas
`
`26. The received signals are typically directed to the
`demodulators 30 from the respective receive antennas 28.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`The demodulators 30 demodulate signals that are received
`by the respective receive antennas 28.
`The receiver 16 also includes a decoder 32, which is
`connected to the demodulators 30-1, 30-2,
`.
`.
`.
`, 30-L via
`corresponding lines 31-1, 31-2, .
`.
`.
`, 31-L. The decoder 32
`typically combines and decodes the demodulated signals
`from the demodulators 30. In this regard, the decoder 32
`typically recovers the original signals that were provided by
`the data source 20. As depicted in FIG. 1, the original signals
`recovered by the decoder 32 may be transmitted to a
`connected data sink 34, which may include one or more
`devices configured to utilize or process the recovered sig-
`nals.
`the transmitter 14 of the MIMO
`As discussed above,
`communication system 10 includes one or more modulators
`24 that are connected to one or more transmit antennas 26,
`respectively. Further, the receiver 16 of the MIMO commu-
`nication system 10 includes one or more demodulators 30
`that are connected to one or more receive antennas 28,
`respectively. In this regard, the number of modulators 24 and
`respective transmit antennas 26 that are implemented in the
`transmitter 14 may be represented by a first variable, “Q.”
`Similarly, the number of demodulators 30 and respective
`receive antennas 28 that are implemented in the receiver 16
`may be represented by a second variable, “L.” In the
`exemplary MIMO communication system 10, the number Q
`of modulators 24 and respective transmit antennas 26 may
`be equivalent or non-equivalent to the number L of demodu-
`lators 30 and respective receive antennas 28. In this regard,
`the MIMO communication system 10 may be said to have
`“Q><L” transmit-receive diversity.
`FIG. 2 is a block diagram of an exemplary encoder 18 of
`the MIMO communication system 10 depicted in FIG. 1.
`The elements of the encoder 18 shown in FIG. 2 will be
`
`described below with respect to several elements that were
`described above for FIG. 1. The exemplary encoder 18
`includes a channel encoder 36. The charmel encoder 36
`
`typically converts data and/or other types of signals to
`channel encoded versions of the signals, which may also be
`referred to collectively as “charmel encoded data” or “chan-
`nel encoded signals.” These signals may be received by the
`channel encoder 36 from a data source 20, for example. The
`channel encoder 36 is typically configured to encode signals
`using an encoding scheme that can be recognized and
`decoded by the decoder 32 of the receiver 16. In the process
`of encoding signals, the channel encoder 36 typically adds
`parity to the signals so that the decoder 32 can detect errors
`in the received charmel encoded signals, which may occur,
`for example, due to environmental conditions that affect the
`channel 12 or noise inadvertently injected into the signals by
`the transmitter 14 and/or receiver 16.
`
`The exemplary encoder 18 depicted in FIG. 2 also
`includes a symbol mapper 38, which receives channel
`encoded signals from the channel encoder 36. The symbol
`mapper 38 is typically configured to map channel encoded
`signals into data blocks. This mapping may be done by
`grouping a predetermined number of bits of the data so that
`each group of bits constitutes a specific data block that is
`selected from a pre-determined symbol alphabet. In this
`regard, a symbol alphabet typically includes a finite set of
`values. For example, a symbol alphabet of a binary phase
`shift keying (BPSK) system typically comprises the values
`+1 and -1, and a symbol alphabet for a quadrature phase
`shift keying (QPSK) system typically comprises the values
`1+j, —1+j, 1—j, and —1—j. The symbol mapper 38 is also
`typically configured to structure a stream of data blocks into
`data structures, which will be discussed further below.
`
`ERIC-1001 I Page 12 of 19
`
`ERIC-1001 / Page 12 of 19
`
`

`
`US 7,269,127 B2
`
`7
`The exemplary encoder 18 also includes a space-time
`processor 40. The space-time processor 40 is typically
`configured to encode a stream of data blocks, received from
`the symbol mapper 38, through space-time processing to
`form the data block designated for different TDBs 22 such
`that the processed data blocks have properties that enhance
`the performance of the MIMO communication systems 10.
`The encoded data blocks are output from the space-time
`processor 40 over Q lines 42-1, 42-2, .
`.
`.
`, 42-Q, where Q
`represents the number of modulators 24 and respective
`transmit antennas 26 of the transmitter 14, as discussed
`above.
`
`the Q lines 42-1,
`illustrated in FIG. 2,
`As further
`42-2,
`.
`.
`.
`, 42-Q from the space-time processor 40 input
`respectively to Q adders 44-1, 44-2, .
`.
`.
`, 44-Q. The encoder
`18 also includes a pilot/training symbol inserter 46, which
`also has Q output lines 48-1, 48-2,
`.
`.
`.
`, 48-Q that input
`respectively to the Q adders 44-1, 44-2, .
`.
`.
`, 44-Q. The Q
`adders 44-1, 44-2, .
`.
`.
`, 44-Q combine, or mix, the inputs and
`provide an output to the Q TDBs 22-1, 22-2,
`.
`.
`.
`, 22-Q,
`which input
`respectively to the Q modulators 24-1,
`24-2, .
`.
`. 24-Q shown in FIG. 1. The pilot/training symbol
`inserter 46 typically provides pilot blocks and training
`blocks that are inserted into (or combined with) the data
`blocks by the adders 44.
`The term pilot blocks, as used in this description, refers to
`symbols provided by the pilot/training symbol inserter 46,
`which are inserted periodically into the data blocks. Typi-
`cally, pilot symbols may be inserted at any point in the data
`blocks. The term training blocks refers to one or more
`continuous sections of symbols provided by the pilot/train-
`ing symbol
`inserter 46. Training blocks are preferably
`inserted into preamble structures at the beginning of the
`frame structures and transmitted once per frame structure.
`However, training blocks may also be inserted in other parts
`of the signal structures, such as the middle or end of the
`frame structures. Preambles (or preamble structures) are
`symbol structures formed of training blocks inserted at the
`beginning of the frame.
`Pilot blocks are typically transmitted with data blocks to
`calibrate (i.e., synchronize) the receiver 16 to the transmitter
`14 on a small scale. This calibration, or synchronization,
`accounts for the time varying nature of the charmel 12, for
`example. Training symbols, however, are typically used to
`periodically calibrate the receiver 16 to the transmitter 14.
`The training symbols may be unique for each sub-charmel.
`Moreover, different sets of training symbols and/or pilot
`blocks may be provided by the pilot/training symbol inserter
`46, depending on the operating criteria of the communica-
`tion system 10, which may be determined by the user.
`FIG. 3 is a block diagram of an exemplary modulator 24
`from one of the modulators 24-1, 24-2,
`.
`.
`.
`, 24-Q of the
`communication system of FIG. 1. The exemplary modulator
`24 may be configured to modulate signals by various tech-
`niques, such as SCFDE or OFDM. The input to the modu-
`lator 24 is from a corresponding TDB 22, which was
`discussed above. As shown,
`the TDB 22 couples to a
`serial-to-parallel converter 50, which is one of several
`components of the modulator 24. The serial-to-parallel con-
`verter 50 converts the training blocks and data blocks from
`a serial format to a parallel format for further processing by
`other components of the modulator 24. Typically, the serial-
`to-parallel converter 50 converts a number of samples “N”
`of each of the data blocks from a serial format to a parallel
`format. The serial-to-parallel converter 50 also converts a
`number of samples “N,” of each of the training blocks from
`serial samples to parallel samples.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`The modulator 24 also includes an inverse discrete Fou-
`
`rier transform (IDFT) stage 52 that receives the parallel
`format of the training blocks and data blocks from the
`series-to-parallel converter 50. The IDFT stage 52 converts
`these blocks from the frequency domain to the time domain,
`as is known in the art. Typically, the IDFT stage 52 receives
`N samples for each data block and N, samples for each
`training block from the serial-to-parallel converter 50 and
`converts the samples in the frequency domain to N samples
`for each data block and N, samples for each training block
`in the time domain. The time domain samples from the IDFT
`stage 52 are input to a cyclic prefix inserter 54. The cyclic
`prefix inserter 54 inserts an additional number of samples
`“G” with each data block and training block to form data
`symbols and training symbols. The G samples are inserted
`into the data symbols and training symbols as guard inter-
`vals to reduce or eliminate inter-symbol interference (ISI) in
`the N or N, samples.
`The modulator 24 also includes a parallel-to-serial con-
`verter 56, which converts the G+N or G+N, samples
`received from the cyclic prefix inserter 54 from a parallel
`format to a serial format for further processing by other
`components of the modulator 24. The modulator 24 further
`includes a digital-to-analog converter (DAC) 58. The DAC
`58 converts the digital symbols to analog symbols and inputs
`the analog symbols to a mixer 60. A local oscillator 62
`generates carrier signals, which are also input to the mixer
`60. The mixer 60 mixes the analog symbols from the DAC
`58 with the carrier signals from the local oscillator 62 to
`generate up-converted versions of the signals for transmis-
`sion as radio-frequency (RF) signals. The mixer 60 inputs
`the up-converted signals to an amplifier 64 where the signals
`are amplified and then input to the transmit antenna 26,
`which transmits the signals across the charmel 12.
`FIG. 4 is a schematic diagram illustrating exemplary
`signal transmissions and associated signal sample matrices
`with respect to the modulator/demodulator configuration of
`the MIMO communication system 10 of FIG. 1. As shown
`in FIG. 4, the configuration includes one or more modulators
`24 and one or more demodulators 30. Each modulator 24 is
`
`connected to one or more respective transmit antennas 26,
`and each demodulator 30 is connected to one or more
`
`respective receive antennas 28, as discussed above with
`respect to FIG. 1. Also discussed above, the transmit anten-
`nas 26 are typically configured to transmit modulated signals
`across a charmel 12, and the receive antennas 28 are typi-
`cally configured to receive modulated signals via the chan-
`nel 12. In this regard, exemplary signal transmissions are
`depicted in FIG. 4, which will be discussed further below.
`Similar to the above discussion with respect to the MIMO
`communication system 10 of FIG. 1, the number of modu-
`lators 24 and respective transmit antennas 26 that are
`implemented in the modulator/demodulator configuration of
`FIG. 4 may be represented by the variable, “Q.” Accord-
`ingly, the number of demodulators 30 and respective receive
`antennas 28 in the arrangement of FIG. 4 may be represented
`by the variable, “L.” Thus the modulator/demodulator
`arrangement depicted in FIG. 4 may also be described as
`having “Q><L” transmit-receive diversity. Moreover,
`the
`variables, Q and L, may be equivalent or non-equivalent in
`various MIMO communication system configurations.
`Exemplary signal
`transmissions from the Q transmit
`antennas 26 across the channel 12 to the L receive antennas
`
`28 are depicted in FIG. 4. For example, the first receive
`antenna 28-1 receives each of the Q transmitted signals from
`the Q transmit antennas 26-1, 26-2,
`.
`.
`.
`, 26-Q. These Q