a2) United States Patent
`US 7,221,680 B2
`(0) Patent No.:
`May22, 2007
`Vijayan etal.
`(45) Date of Patent:
`
`US007221680B2
`
`(54)
`
`(75)
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`(73)
`
`(*)
`
`(21)
`(22)
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`(65)
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`(60)
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`(51)
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`(52)
`(58)
`
`MULTIPLEXING AND TRANSMISSION OF
`MULTIPLE DATA STREAMSIN A WIRELESS
`MULTI-CARRIER COMMUNICATION
`SYSTEM
`
`Inventors: Rajiv Vijayan, San Diego, CA (US);
`Aamod Khandekar, San Diego, CA
`(US); Fuyun Ling, San Diego, CA
`(US); Gordon Kent Walker, Poway,
`CA (US); Ramaswamy Murali, San
`Diego, CA (US)
`QUALCOMM Incorporated, San
`Diego, CA (US)
`
`Assignee:
`
`Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 61 days.
`Appl. No.: 10/932,586
`Filed:
`Sep. 1, 2004
`
`Prior Publication Data
`
`US 2005/0058089 Al
`
`Mar. 17, 2005
`
`Related U.S. Application Data
`
`Provisional application No. 60/499,741, filed on Sep.
`2, 2003, provisional application No. 60/559,740, filed
`on Apr. 5, 2004.
`
`Int. Cl.
`
`(2006.01)
`HO4B 7/216
`US. Ch. ce cecenees 370/441; 370/335; 370/342
`Field of Classification Search................ 370/431,
`370/310.2, 335, 342, 441, 330, 208
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`9/2003 Merrill et al. we. 370/225
`6,618,353 B2*
`7/2002 Ehrmann-Patin et al.
`... 370/210
`2002/0085486 Al*
`5/2003 Branlundet al.
`........... 370/208
`2003/0086366 Al*
`2004/0266351 AL* 12/2004 Chuah et al. oo... 455/62
`
`* cited by examiner
`
`Primary Examiner—Chi Pham
`Assistant Examiner—Ronald Abelson
`
`(74) Attorney, Agent, or Firm—ThomasR.Rouse; Sandip S.
`Minhas; Albert J. Harnois, Jr.
`
`(57)
`
`ABSTRACT
`
`Techniques for multiplexing and transmitting multiple data
`streams are described. Transmission of the multiple data
`streams occurs in “super-frames”. Each super-frame has a
`predetermined time duration and is further divided into
`multiple (e.g., four) frames. Each data block for each data
`stream is outer encoded to generate a corresponding code
`block. Each code block is partitioned into multiple sub-
`blocks, and each data packet in each code block is inner
`encoded and modulated to generate modulation symbols for
`the packet. The multiple subblocks for each code block are
`transmitted in the multiple frames of the same super-frame,
`one subblock per frame. Each data stream is allocated a
`number of transmission units in each super-frame and is
`assigned specific transmission units to achieve eflicient
`packing. A wireless device can select and receive individual
`data streams.
`
`35 Claims, 15 Drawing Sheets
`
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`U.S. Patent
`
`May 22, 2007
`
`Sheet 1 of 15
`
`US 7,221,680 B2
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`100
`—_
`
`
`
`ote
`1200
`“a “ig
`
`
`
`120n
`
`1109
`
`FIG. 1
`
`
`
`FIG. 2
`
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`U.S. Patent
`
`May 22, 2007
`
`Sheet 2 of 15
`
`US 7,221,680 B2
`
`Code Block
`
`eeeneneeeeeneenenneea
`eTnaeeeneente
`TTeee
`
`/ a
`
`—— One Super-Frame+}
`FIG. 3A
`
`Code Block1
`Code Block Nu
`
`_—___ One Super-Frame+
`FIG. 3B
`
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`U.S. Patent
`
`May22, 2007
`
`Sheet 3 of 15
`
`
`
`
`
`ewes8UO
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`
`US 7,221,680 B2
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`U.S. Patent
`
`May 22, 2007
`
`Sheet 4 of 15
`
`US 7,221,680 B2
`
`® E-
`
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`
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`
`
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`IPR2019-00958
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`U.S. Patent
`
`May22, 2007
`
`Sheet 5 of 15
`
`US 7,221,680 B2
`
`Time
`
`SeededOdOOD
`xxXXXXXOXXOXOXOX
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`U.S. Patent
`
`May22, 2007
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`Sheet 6 of 15
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`US 7,221,680 B2
`
` 009
`
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`spueqqns[FjOL N
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`U.S. Patent
`
`May 22, 2007
`
`Sheet 7 of 15
`
`US 7,221,680 B2
`
`KKKKKA_PLC 3
`SSK 16
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`8 7
`
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`FIG. 7A
`
`PLC 1
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`PLC 2
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`PLC 3
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`aom
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`INN
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`PENNS
`SSS
`
`symbol Period
`
`FIG. 7B
`
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`U.S. Patent
`
`May 22, 2007
`
`Sheet 8 of 15
`
`US 7,221,680 B2
`
`
`
`SubbandGroup
`
`
`
`OD1
`
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`—_: PLC4
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`
`
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`U.S. Patent
`
`May 22, 2007
`
`Sheet 9 of 15
`
`US 7,221,680 B2
`
`6
`
`a 5
`
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`
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`4
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`U.S. Patent
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`May 22, 2007
`
`Sheet 10 of 15
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`US 7,221,680 B2
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`Packet Interleaving across Code Blocks
`
`952
`me
`
`Packet 1 of all
`
`Packet2 ofall
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`Packet3 ofall
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`Packet 4 ofall
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`FIG. 9C
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`PLC 1
`PLC 2
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`Symbol Period
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`FIG. 9D
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`FIG. 9E
`
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`U.S. Patent
`
`May22, 2007
`
`Sheet 11 of 15
`
`US 7,221,680 B2
`
`1000
`xk
`
`1012
`
`Identify active PLCsfor
`the current super-frame
`
`least one code block for the PLC
`
`Processat least one data block
`for each active PLC to obtain at
`
`1014
`
`
`Allocate each active PLC with a
`
`
`specific numberof transmission
`units (or slots) based onits payload
`
`1016
`
`Assign specific transmission units
`in the current super-frame(e.g.,
`in a rectangular pattern or a zigzag
`
`1018
`
`1020
`
`Partition each code block into
`multiple subblocks, one subblock for
`each frameof the current super-frame
`
`1022
`
`Process (e.g., encode and modulate)
`the packets in each subblockto obtain
`modulation symbols for the subbiock
`
`1024
`
`segment) to each active PLC
`
`
`
`
`
`For each frame of the current super-
`frame, multiplex the data symbols
`in the subblock(s) to be sentin that
`
`frame for each active PLC onto the
`
`
`transmission units assigned to the PLC
`1026
`
`
`
`
`
`
`
`Form a composite symbol stream with
`the multiplexed data symbols forall active
`PLCs and overhead symbols for the PLCs
`
`
`
`FIG. 10
`
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`U.S. Patent
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`May22, 2007
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`Sheet 12 of 15
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`US 7,221,680 B2
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`
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`U.S. Patent
`
`May22, 2007
`
`Sheet 13 of 15
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`US 7,221,680 B2
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`U.S. Patent
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`May22, 2007
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`Sheet 14 of 15
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`US 7,221,680 B2
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`IPR2019-00958
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`U.S. Patent
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`May22, 2007
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`Sheet 15 of 15
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`US 7,221,680 B2
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`US 7,221,680 B2
`
`1
`MULTIPLEXING AND TRANSMISSION OF
`MULTIPLE DATA STREAMSIN A WIRELESS
`MULTI-CARRIER COMMUNICATION
`SYSTEM
`
`2
`There is therefore a need in the art for techniques to
`transmit multiple data streams in a multi-carrier system such
`that they can be received by wireless devices, with minimal
`power consumption.
`
`This application claims the benefit of provisional U.S.
`Application Ser. No. 60/499,741, entitled “A Method for
`Multiplexing
`and Transmitting Multiple Multimedia
`Streams to Mobile Terminals over Terrestrial Radio Links,”
`filed Sep. 2, 2003, and provisional U.S. Application Ser. No.
`60/559,740, entitled “Multiplexing and Transmission of
`Multiple Data Streams in a Wireless Multi-Carrier Commu-
`nication System,”filed Apr. 5, 2004.
`
`BACKGROUND
`
`I. Field
`The present invention relates generally to communication,
`and more specifically to techniques for multiplexing and
`transmitting multiple data streams in a wireless multi-carrier
`communication system.
`II. Background
`A multi-carrier communication system utilizes multiple
`carriers for data transmission. These multiple carriers may
`be provided by orthogonal frequency division multiplexing
`(OFDM), some other multi-carrier modulation techniques,
`or some other construct. OFDM effectively partitions the
`overall system bandwidth into multiple orthogonal sub-
`bands. These subbandsare also referred to as tones, carriers,
`subcarriers, bins, and frequency channels. With OFDM,
`each subbandis associated with a respective subcarrier that
`may be modulated with data.
`A base station in a multi-carrier system may simulta-
`neously transmit multiple data streams for broadcast, mul-
`ticast, and/or unicast services. A data stream is a stream of
`data that may be of independent reception interest to a
`wireless device. A broadcast
`transmission is sent
`to all
`
`wireless devices within a designated coverage area, a mul-
`ticast transmission is sent to a group of wireless devices, and
`a unicast transmission is sent to a specific wireless device.
`For example, a base station may broadcast a numberof data
`streams for multimedia (e.g.,
`television) programs via a
`terrestrial radio link for reception by wireless devices. This
`system may employ a conventional multiplexing and trans-
`mission scheme suchas, for example, Digital Video Broad-
`casting-Terrestrial (DVB-T) or Integrated Services Digital
`Broadcasting-Terrestrial (SDB-T). Such a scheme would
`first multiplex all of the data streams to be transmitted onto
`a single high-rate composite stream and then process (e.g.,
`encode, modulate, and up-convert) the composite stream to
`generate a modulated signal for broadcast via the radio link.
`A wireless device within the coverage area of the base
`station may be interested in receiving only one or few
`specific data streams among the multiple data streams car-
`ried by the composite stream. The wireless device would
`need to process
`(e.g., down-convert, demodulate, and
`decode) a received signal to obtain a high-rate decoded data
`stream and then demultiplex this stream to obtain the one or
`few specific data streamsof interest. This type of processing
`may not be a problem for receiver units intended to be
`powered on all
`the time, such as those used in homes.
`However, many wireless devices are portable and powered
`by internal batteries. Continuous demodulation and decod-
`ing of the high-rate composite stream to recover just one or
`few data streamsof interest consumessignificant amounts of
`power. This can greatly shorten the “ON” time for the
`wireless devices, which is undesirable.
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`SUMMARY
`
`Techniques for multiplexing and transmitting multiple
`data streams in a mannerto facilitate power-efficient and
`robust reception of individual data streams by wireless
`devices are described herein. Each data stream is processed
`separately based on a coding and modulation scheme(e.g.,
`an outer code, an inner code, and a modulation scheme)
`selected for that stream to generate a corresponding data
`symbolstream. This allows the data streams to be individu-
`ally recovered by the wireless devices. Each data stream is
`also allocated certain amount of resources for transmission
`of that stream. The allocated resources are given in “trans-
`mission units” on a time-frequency plane, where each trans-
`mission unit corresponds to one subband in one symbol
`period and may be used to transmit one data symbol. The
`data symbols for each data stream are mappeddirectly onto
`the transmission units allocated to the stream. This allows
`
`the wireless devices to recover each data stream indepen-
`dently, without having to process the other data streams
`being transmitted simultaneously.
`In an embodiment,
`transmission of the multiple data
`streams occurs in “super-frames”, with each super-frame
`having predetermined time duration (e.g., on the order of a
`second or few seconds). Each super-frameis further divided
`into multiple (e.g., two, four, or some other number of)
`frames. For each data stream, each data block is processed
`(e.g., outer encoded) to generate a corresponding code
`block. Each code block is partitioned into multiple sub-
`blocks, and each subblock is further processed (e.g., inner
`encoded and modulated) to generate a corresponding sub-
`block of modulation symbols. Each code block is transmit-
`ted in one super-frame, and the multiple subblocks for the
`code block are transmitted in the multiple frames of the
`super-frame, one subblock per frame. The partitioning of
`each code block into multiple subblocks, the transmission of
`these subblocks over multiple frames, and the use of block
`coding across the subblocksof the code block provide robust
`reception performance in slowly time-varying fading chan-
`nels.
`
`Each data stream may be “allocated” a variable number of
`transmission units in each super-frame depending on the
`stream’s payload in the super-frame,
`the availability of
`transmission units in the super-frame, and possibly other
`factors. Each data stream is also “assigned” specific trans-
`mission units within each super-frame using an assignment
`schemethat attempts to (1) pack the transmission units for
`all data streams as efficiently as possible, (2) reduce the
`transmission time for each data stream, (3) provide adequate
`time-diversity, and (4) minimize the amount of signaling to
`indicate the specific transmission units assigned to each data
`stream. Overhead signaling for various parameters of the
`data streams(e.g., the coding and modulation scheme used
`for each data stream,the specific transmission units assigned
`to each data stream, and so on) may be transmitted prior to
`each super-frame and may also be embedded within the data
`payload of each data stream. This allows a wireless device
`to determine the time-frequency location of each desired
`data stream in the upcoming super-frame. The wireless
`device may power on only when the desired data stream is
`transmitted, using the embedded overhead signaling, and
`thereby minimize power consumption.
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`3
`Various aspects and embodiments of the invention are
`described in further detail below.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`invention will
`The features and nature of the present
`become more apparent from the detailed description set
`forth below when taken in conjunction with the drawings in
`which like reference characters identify correspondingly
`throughout and wherein:
`FIG. 1 shows a wireless multi-carrier system;
`FIG. 2 shows an exemplary super-framestructure;
`FIGS. 3A and 3Billustrate transmission of one data block
`and multiple data blocks, respectively, on a physical layer
`channel (PLC) in a super-frame;
`FIG. 4 showsa framestructure in a time-frequency plane;
`FIG. 5A shows a burst-TDM (time division multiplex)
`scheme;
`FIG. 5B shows a cycled-TDM scheme;
`FIG. 5C shows a burst-TDM/FDM (frequency division
`multiplex) scheme;
`FIG. 6 shows an interlaced subband structure;
`FIG. 7A showsassignmentof slots to PLCs in rectangular
`patterns;
`FIG. 7B showsassignmentof slots to PLCs in “zigzag”
`segments;
`FIG. 7C shows assignmentof slots to two joint PLCs in
`rectangular patterns;
`FIG. 8 illustrates coding of a data block with an outer
`code;
`FIGS. 9A and 9B show assignmentof slots for one data
`block using one subband group and a maximum allowable
`numberof subband groups, respectively;
`FIG. 9C showsassignment of slots for six data blocks;
`FIGS. 9D and 9E show assignmentof slots to two joint
`PLCs with rectangular patterns stacked horizontally and
`vertically, respectively;
`FIG. 10 shows a process for broadcasting multiple data
`streams;
`FIG. 11 shows a block diagram of a basestation;
`FIG. 12 showsa block diagram of a wireless device;
`FIG. 13 showsa block diagram of a transmit (TX) data
`processor, a channelizer, and an OFDM modulator at the
`base station; and
`FIG. 14 showsa block diagram of a data stream processor
`for one data stream.
`
`DETAILED DESCRIPTION
`
`4
`the coverage area of the system. A wireless device may be
`fixed or mobile and may also be referred to as a user
`terminal, a mobile station, user equipment, or some other
`terminology. A wireless device mayalso be a portable unit
`such as a cellular phone, a handheld device, a wireless
`module, a personal digital assistant (PDA), and so on.
`Each base station 110 may broadcast multiple data
`streams simultaneously to wireless devices within its cov-
`erage area. These data streams may be for multimedia
`content such as video, audio, tele-text, data, video/audio
`clips, and so on. For example, a single multimedia (e.g.,
`television) program may be sent
`in three separate data
`streams for video, audio, and data. A single multimedia
`program mayalso have multiple audio data streams,e.g., for
`different languages. For simplicity, each data stream is sent
`on a separate physical layer channel (PLC). There is thus a
`one-to-one relationship between data streams and PLCs. A
`PLC mayalso be called a data channel, a traffic channel, or
`some other terminology.
`FIG. 2 shows an exemplary super-frame structure that
`may be used for broadcast system 100. Data transmission
`occurs in units of super-frames 210. Each super-frame has a
`predetermined time duration, which may be selected based
`on various factors such as, for example, the desired statis-
`tical multiplexing for the data streams, the desired amount of
`time diversity, acquisition time for the data streams, buffer
`requirements for the wireless devices, and so on. A larger
`super-frame size provides more time diversity and better
`statistical multiplexing of the data streams being transmit-
`ted, so that less buffering may be required for individual data
`streams at the base station. However, a larger super-frame
`size also results in a longer acquisition time for a new data
`stream (e.g., at power-on or when switching between data
`streams), requires larger buffers at the wireless devices, and
`also has longer decoding latency or delay. A super-frame
`size of approximately one second mayprovide goodtradeoff
`between the various factors described above. However,
`other super-frame sizes (e.g., a quarter, a half, two, or four
`seconds) may also be used. Each super-frame is further
`divided into multiple equal-sized frames 220. For the
`embodiment shown in FIG. 2, each super-frame is divided
`into four frames.
`The data stream for each PLC is encoded and modulated
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`based on a coding and modulation schemeselected for that
`PLC. In general, a coding and modulation scheme comprises
`all of the different types of encoding and modulation to be
`performed on a data stream. For example, a coding and
`modulation scheme may comprise a particular coding
`scheme andaparticular modulation scheme. The coding
`50
`The word “exemplary” is used herein to mean “serving as
`scheme may comprise error detection coding (e.g., a cyclic
`an example, instance, or illustration.” Any embodiment or
`redundancy check (CRC)), forward error correction coding,
`design described herein as “exemplary”is not necessarily to
`and so on, or a combination thereof. The coding scheme may
`be construed as preferred or advantageous over other
`also indicate a particular code rate of a base code. In an
`embodiments or designs.
`embodimentthat is described below,the data stream for each
`The multiplexing and transmission techniques described
`PLCis encoded with a concatenated code comprised of an
`outer coder and an inner code andis further modulated based
`herein may be used for various wireless multi-carrier com-
`on a modulation scheme. As used herein, a “mode”refers to
`munication systems. These techniques may also be used for
`a combination of an inner code rate and a modulation
`broadcast, multicast, and unicast services. For clarity, these
`scheme.
`techniques are described for an exemplary multi-carrier
`FIG. 3A illustrates the transmission of a data block on a
`broadcast system.
`FIG. 1 shows a wireless multi-carrier broadcast system
`PLCin a super-frame. The data stream to be sent on the PLC
`100. System 100 includes a numberofbase stations 110 that
`is processed in data blocks. Each data block contains a
`are distributed throughout the system. A base station is
`particular number of information bits andis first encoded
`generally a fixed station and may also bereferred to as an
`using an outer code to obtain a corresponding code block.
`access point, a transmitter, or some other terminology.
`Each code block is partitioned into four subblocks, and the
`Neighboring base stations may broadcast the same or dif-
`bits in each subblockare further encoded using an inner code
`ferent content. Wireless devices 120 are located throughout
`and then mapped to modulation symbols, based on the mode
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`US 7,221,680 B2
`
`FIG. 2 showsa specific super-frame structure. In general,
`a super-frame maybe defined to be of any time duration and
`may be divided into any number of frames. Pilot and
`overhead information may also be sent in other manners
`different from the manner shown in FIG. 2. For example,
`overhead information may be sent on dedicated subbands
`using frequency division multiplexing (FDM).
`FIG. 4 shows the structure of one frame on a time-
`frequencyplane. The horizontal axis represents time, and the
`vertical axis represents frequency. Each frame has a prede-
`transmitted in the four frames of one super-frame. For each
`termined time duration, which is given in units of OFDM
`frame, N,, subblocks for the N,, code blocks are transmitted
`symbol periods (or simply, symbol periods). Each OFDM
`in a portion of the frame that has been allocated to the PLC.
`symbol period is the time duration to transmit one OFDM
`symbol (described below). The specific number of symbol
`Each data block may be encoded and modulated in
`periods per frame (N,,,,) is determined by the frame duration
`various manners. An exemplary concatenated coding
`and the symbol period duration, which in turn is determined
`scheme is described below. To simplify the allocation and
`by various parameters such as the overall system bandwidth,
`assignment of resources to the PLCs, each code block may
`the total number of subbands (N,,,), and the cyclic prefix
`be divided into four equal-sized subblocks that are then
`length (described below). In an embodiment, each frame has
`transmitted in the sameportion or location ofthe four frames
`a duration of 297 symbolperiods (or N,,=297). Each frame
`in one super-frame. In this case, the allocation of a super-
`also covers the N,,, total subbands, which are given indices
`frame to the PLCs is equivalent to the allocation of a frame
`of 1 through N,,,.
`to the PLCs. Hence, resources can be allocated to the PLCs
`With OFDM,one modulation symbol maybesent on each
`once every super-frame.
`subband in each symbolperiod, i.e., each transmission unit.
`Each PLC may betransmitted in a continuous or non-
`Ofthe N,,,, total subbands, N,,, subbands may be used for
`continuous manner, depending on the nature of the data
`data transmission and are referred to as “data” subbands,
`stream being carried by that PLC. Thus, a PLC may or may
`N_, subbands may be used for pilot and are referred to as
`“pilot” subbands, and the remaining N,,,, subbands may be
`not be transmitted in any given super-frame. For each
`super-frame, an “active” PLC is a PLC that is being trans-
`used as “guard” subbands (1.e., no data or pilot transmis-
`mitted in that super-frame. Each active PLC may carry one
`sion), where N,.,=N,+N,s0+Nes2- The number of “usable”
`or multiple data blocks in the super-frame.
`subbandsis equal to the numberof data and pilot subbands,
`or N,s,=Nas,tN,,5- In an embodiment, broadcast system
`Referring back to FIG. 2, each super-frame 210 is pre-
`100 utilizes an OFDMstructure having 4096 total subbands
`ceded by a pilot and overhead section 230. In an embodi-
`(N,,,=4096), 3500 data subbands (N,,,=3500), 500 pilot
`ment, section 230 includes (1) one or more pilot OFDM
`subbands (N,,,=500), and 96 guard subbands (N,,,=96).
`symbols used by the wireless devices for frame synchroni-
`Other OFDM structures with different numberofdata, pilot,
`zation, frequency acquisition, timing acquisition, channel
`usable, and total subbands mayalso be used. In each OFDM
`estimation, and so on, and (2) one or more overhead OFDM
`symbol period, N,,, data symbols may be sent on the N,,,
`symbols used to carry overhead signaling information for
`data subbands, N,,,,, pilot symbols may be sent on the N,,.,
`the associated (e.g.,
`immediately following) super-frame.
`pilot subbands,and N,,,, guard symbolsare sent on the N,.,,
`The overhead information indicates, for example, the spe-
`guard subbands. As used herein, a “data symbol” is a
`cific PLCs being transmitted in the associated super-frame,
`modulation symbol for data, a “pilot symbol” is a modula-
`the specific portion of the super-frame used to send the data
`tion symbolfor pilot, and a “guard symbol!”is a signal value
`block(s) for each PLC, the outer code rate and mode used for
`
`each PLC, and so on. The overhead OFDM symbol(s) of zero. The pilot symbols are knownapriori by the wireless
`carries overhead signaling for all PLCs sent in the super-
`devices. The N,,, data symbols in each OFDM symbol may
`frame. The transmission of the pilot and overhead informa-
`be for one or multiple PLCs.
`tion in a time division multiplexed (TDM) mannerallows
`In general, any number of PLCs may be transmitted in
`the wireless devices to process this section with minimal ON
`each super-frame. For a given super-frame, each active PLC
`time. In addition, overhead information pertaining to each
`may carry one or multiple data blocks. In one embodiment,
`PLC’s transmission in the next super-frame may be embed-
`a specific mode and a specific outer code rate is used for each
`ded in one of the PLC’s transmitted data blocks in the
`active PLC, andall data blocks for the PLC are encoded and
`modulated in accordance with this outer code rate and mode
`to generate corresponding code blocks and subblocks of
`modulation symbols, respectively. In another embodiment,
`each data block may be encoded and modulated in accor-
`dance with a specific outer code rate and mode to generate
`a corresponding code block and subblocks of modulation
`symbols, respectively. In any case, each code block contains
`a specific number of data symbols, which is determined by
`the mode used for that code block.
`
`5
`selected for the PLC. The four subblocks of modulation
`
`symbols are then transmitted in the four frames of one
`super-frame, one subblock per frame. The transmission of
`each code block over four frames provides time diversity
`and robust reception performance in a slowly time-varying
`fading channel.
`FIG.3B illustrates the transmission of multiple (N,,) data
`blocks on a PLC in a super-frame. Each of the N,, data
`blocks is encoded separately using the outer code to obtain
`a corresponding code block. Each code block is further
`partitioned into four subblocks, which are inner encoded and
`modulated based on the modeselected for the PLC and then
`
`current super-frame. The embedded overhead information
`allows the wireless device to recover the PLC’s transmission
`
`in the next super-frame without having to check the over-
`head OFDM symbol(s) sent in that super-frame. Thus, the
`wireless devices may initially use the overhead OFDM
`symbols to determine the time-frequency location of each
`desired data stream, and may subsequently power on only
`during the time that the desired data stream is transmitted
`using the embedded overhead signaling. These signaling
`techniques may provide significant savings in power con-
`sumption and allow the wireless devices to receive content
`using standard batteries. Since the outer code rate and mode
`used for each PLC typically do not vary on a super-frame
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`6
`basis, the outer code rate and mode maybe sent on a separate
`control channel and do need not be sent in every super-
`frame.
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`Each active PLC in a given super-frame is allocated a
`specific amount of resources to transmit that PLC in the
`super-frame. The amount of resources allocated to each
`active PLC is dependent on (1) the numberof code blocks
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`US 7,221,680 B2
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`7
`to be sent on the PLC in the super-frame, (2) the number of
`data symbols in each code block, and (3) the numberof code
`blocks, along with the number of data symbols per code
`block, to be sent on other PLCs. Resources maybeallocated
`in various manners. Two exemplary allocation schemes are
`described below.
`FIG. 5A shows a burst-TDMallocation scheme. Forthis
`
`8
`of the resource allocation may be selected based on a
`tradeoff between packing efficiency and overhead signaling.
`In general, smaller granularity results in better packing
`efficiency but also requires more overhead signaling to
`indicate the resources allocated to each PLC. The inverse is
`
`generally true with larger granularity. The description below
`assumes the use of the burst-TDM/FDM scheme.
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`In an embodiment, the N,,,, usable subbands are divided
`scheme, each active PLC is allocated all N,,, data subbands
`into N,,. groups of usable subbands. One of the N,,. groups
`in one or more OFDM symbol periods. For the example
`shown in FIG. 5A, PLC 1 is allocated all data subbands in
`may then contain the pilot subbands. For the remaining
`symbol periods 1 through 3, PLC 2 is allocated all data
`groups, the number of data subbands in one group deter-
`
`subbands in symbolperiods 4 and 5, and PLC3is allocated mines the granularity of the resource allocation. The N,,,,
`usable subbands may be arranged into the N,,. groups in
`all data subbands in symbol periods 6 through 9. For this
`scheme, each OFDM symbolcontains data symbols for only
`various manners. In one subband grouping scheme, each
`group contains N,,, consecutive usable subbands, where
`one PLC. The bursts of OFDM symbols for different PLCs
`NisaNeg-Nepg: In another subband grouping scheme, each
`are time division multiplexed within a frame.
`If consecutive OFDM symbols are assigned to each active
`group contains N,,.
`usable subbands that are pseudo-ran-
`PLC, then the burst-TDM can minimize the transmiss