WO2007145640A1 - Calcul de moyenne d'interférences dans le domaine temporel avec une diversité multi-utilisateurs dans des systèmes ofdma - Google Patents

Calcul de moyenne d'interférences dans le domaine temporel avec une diversité multi-utilisateurs dans des systèmes ofdma Download PDF

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Publication number
WO2007145640A1
WO2007145640A1 PCT/US2006/023823 US2006023823W WO2007145640A1 WO 2007145640 A1 WO2007145640 A1 WO 2007145640A1 US 2006023823 W US2006023823 W US 2006023823W WO 2007145640 A1 WO2007145640 A1 WO 2007145640A1
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WIPO (PCT)
Prior art keywords
tones
users
user
band
sub
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PCT/US2006/023823
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English (en)
Inventor
Djordje Tujkovic
Arogyaswami Paulraj
Original Assignee
Beceem Communications Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Priority to PCT/US2006/023823 priority Critical patent/WO2007145640A1/fr
Publication of WO2007145640A1 publication Critical patent/WO2007145640A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0452—Multi-user MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/12—Frequency diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0044—Arrangements for allocating sub-channels of the transmission path allocation of payload
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/02—Channels characterised by the type of signal
    • H04L5/023—Multiplexing of multicarrier modulation signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control

Definitions

  • the invention relates generally to digital communications. In particular it relates to interference averaging in orthogonal frequency-division multiple access (OFDMA) systems.
  • OFDMA orthogonal frequency-division multiple access
  • Wireless digital communications systems are poised to offer a cost- effective alternative to cable and DSL data services.
  • So called "WiMAX” technology based on the IEEE 802.16e air interface standard is a promising framework for broadband wireless applications. It has the potential to enable full internet and digital voice services for both fixed and mobile users.
  • the physical layer architecture for IEEE 802.16e OFDMA systems is based on orthogonal frequency-division multiplexing (OFDM) modulation. Since OFDM divides the total bandwidth into multiple narrowband sub-bands, the effects of frequency selective fading are reduced.
  • OFDM orthogonal frequency-division multiplexing
  • the OFDM system allows for a simple receiver structure while maintaining high link quality.
  • the technology also employs adaptive modulation and coding in both the downlink and the uplink to deal with variations in link quality. This enables WiMAX to offer multiple date rates at the physical layer which can be adapted dynamically based on the integrity of the air link.
  • spectral efficiency can be improved by allocating time - frequency resources based on throughput requirements, quality of service constraints and the channel qualities of each user.
  • a scheduler which optimizes resource allocation for multiple active users, becomes a key element in such a solution.
  • spectral efficiency decreases with an increasing number of active users because of intra-sector interference due to imperfect orthogonality of the downlinks.
  • CDMA code-division multiple access
  • the spectral efficiency instead increases with the number of active users. This effect is known as multiuser diversity.
  • Multiuser diversity in which sub-bands are allocated to users with the highest channel gains, can be quite effective for low-mobility users.
  • multiuser diversity mode is prone to errors due to the bursty nature of interference. This is a tradeoff of concentrating user transmissions within sub-bands.
  • an interferer's burst is in the same sub-band as that of a user, the user may experience a low signal-to-interference ratio on a large fraction of the tones in its burst.
  • Fig. 1 shows mobile users operating in sectors of a digital communications system.
  • Figs. 2A & 2B show examples of tone assignments in a frequency diversity allocation scheme.
  • Figs. 3A & 3B show examples of tone assignments in a multiuser frequency allocation scheme.
  • Figs. 4A & 4B show examples of tone assignments in a multiuser frequency allocation scheme with time domain interference averaging.
  • FIG. 5 shows a system block diagram for a transmitter incorporating time domain interference averaging.
  • Fig. 6 shows a flow chart for implementing an interference averaging, multiuser frequency allocation scheme.
  • wireless digital communications information is transmitted between base stations and users via radio signals that, in modern systems, lie approximately in the gigahertz frequency range.
  • the information can include digitized voice signals or any other type of digital information such as email or web page data.
  • digital data Prior to being sent over a radio link, digital data is mapped onto complex transmission symbols.
  • complex means containing real and imaginary parts, or both amplitude and phase components.
  • orthogonal frequency-division multiplexed (equivalently: orthogonal frequency-division multiple access, OFDMA) digital communications system
  • the range of frequencies over which symbols are transmitted i.e. the total system bandwidth
  • Individual symbols are sent by modulating tones within each bin.
  • the amount of time over which tones are modulated to send a symbol is a single time slot. Several time slots make up a burst of symbols and a long burst forms a frame.
  • an OFDMA system might use a total system bandwidth of 10 MHz. 0.78 MHz on each side is reserved for so-called "guard bands" in which no transmission is allowed.
  • the center 8.44 MHz is divided into 12 sub-bands, each of which is divided into 8 bins. Each bin is further divided into 9 tones. Therefore, in this example, there are a total of 864 tones available for time-frequency allocation.
  • the cardinality of the set of complex symbols that are used to modulate each tone could be 2, 4, 8, 16 or 64 (corresponding to 1 to 6 bits of information).
  • the symbol transmission time might be around 100 microseconds with a burst containing anywhere from 1 to about 50 symbols and a frame containing about 50 or more symbols.
  • the number of tones available in a given period of time determines the maximum information carrying capacity of the system. If, at a given time, all tones are being modulated with symbols, then the maximum amount of information that can be transmitted is being transmitted.
  • a tone modulated for one symbol transmission time is a convenient unit of data transmission capacity or resources available in the system.
  • Channel state information is used to schedule users.
  • the method for obtaining channel state information at the transmitter depends on the system architecture. For example in some systems receivers estimate channel state information based on their reception of a common pilot tone and feed the information back to the transmitter.
  • channel reciprocity allows the transmitter to use the channel state information estimated during reception for transmission.
  • amplitude information can be estimated from the opposite link, while it is more difficult to obtain accurate phase information due to difficulty in calibrating the difference in phase response between the transmitter and receiver chains.
  • Multiuser diversity can be used as an allocation strategy for maximizing the total data rate of an OFDMA system.
  • Multiuser diversity involves scheduling at any one time the user which can make the best use of the channel, i.e. the user with the best channel response or SNR.
  • Multiuser diversity yields an increase in the total throughput as a function of the number of users.
  • Fig. 1 shows mobile users operating in sectors of a digital communications system.
  • a first sector 105 contains base station or tower 115 and mobile user 125.
  • a second sector 110 contains base station or tower 120 and mobile user 130.
  • Jagged, dotted arrows indicate propagation channels between user 125 and tower 115, between user 130 and tower 120, and also between user 130 and tower 115.
  • Graphs of the signal-to-noise ratios (SNR) for these channels are provided as graphs 140, 155, and 135, respectively.
  • the graphs further show, as items 150, 160 and 145 sub-bands in use in the channels.
  • users are assigned sub-bands which offer them the best signal propagation characteristics; e.g. the best SNR.
  • users are either assigned different sub-bands or different burst times within the same sub-band to prevent interference.
  • users in different sectors are located near each other, as illustrated schematically in Fig. 1 , they may try to communicate with their respective base stations at the same time and in the same sub-band. This results in interference which is highly variable in amplitude.
  • Fig. 1 user 130 is in communication with tower 120 while user 125 is in communication with tower 115.
  • the propagation channel between user 130 and tower 115 also has, at least temporarily, high SNR as indicated in graph 135. Therefore user 125 is likely to experience strong interference from user 130 in the sub-band indicated by 150 in graph 140 which is the same as sub-band 145 in graph 135.
  • user 130 moves around the propagation channel between him and tower 115 may change suddenly, and therefore the amount of interference caused to user 125 may also change suddenly.
  • Interference between users within a preferred coherence bandwidth can be reduced by spreading out the users' transmission symbols randomly in time within the coherence bandwidth.
  • transmission symbols are dispersed randomly in time, the variance of interference between users' bursts in the same sub-band is reduced on average.
  • a scheduler assigns spectral resources to users.
  • Figs. 2, 3 and 4 illustrate three example spectral tone assignment schemes for frequency diversity, multiuser diversity, and multiuser diversity with interference averaging, respectively.
  • Multiuser diversity is preferable to frequency diversity when channel state information is available at the transmitter.
  • Multiuser diversity with interference averaging represents a further improvement in that the advantages of multiuser diversity are combined with the interference reduction available through interference averaging.
  • Figs. 2A & 2B show examples of tone assignments in a frequency diversity allocation scheme. This scheme avoids the problems of multiuser diversity just mentioned, but has other undesirable features.
  • Figs. 2A & 2B are schematic graphs of time - frequency resources, grouped into sub-bands "b - 1", "b", and "b + 1". Tones available during a time slot are indicated by rectangular areas such as 210. Tones used by a user are filled in; see, e.g. area 220 which represents a tone in use by user / in sector 1. Bursts lasting several symbol times are labeled at the top of each graph. In Fig.
  • Frequency diversity may be the best solution when no channel state information is available at the transmitter. However, if channel state information is available, it is more efficient to use multiuser diversity.
  • Figs. 3A & 3B show examples of tone assignments in a multiuser frequency allocation scheme. Similar to Figs. 2A & 2B, Figs. 3A & 3B are schematic graphs of time - frequency resources, grouped into sub-bands "b - 1", "b", and "b + 1". Tones are depicted as rectangular areas; hatched areas are tones in use by a user. Burst times lasting several symbols are indicated by double-ended arrows. [035] User / in sector 1 has been assigned sub-band "b” and a burst time as indicated in Fig. 3A. User/ in sector 2 has been assigned the same sub-band "b” and an overlapping burst time as indicated in Fig.
  • Figs. 4A & 4B show examples of tone assignments in a multiuser frequency allocation scheme with time domain interference averaging. Similar to Figs. 2A, 2B, 3A and 3B, Figs. 4A & 4B are schematic graphs of time - frequency resources, grouped into sub-bands "b - 1", "b", and "b + 1". Tones are depicted as rectangular areas; hatched areas are tones in use by a user. Burst times lasting several symbols are indicated by double-ended arrows. In each of Figs. 2A, 2B, 3A, 3B, 4A and 4B, tones that are not shown as being in use by either user / in sector 1 or user; in sector 2 are available for use by other users.
  • Figs. 4A & 4B users / and/ (located in sectors 1 and 2 respectively) have been assigned the same sub-band "b" in which they experience high SNR.
  • the tones of each user have been spread out into longer bursts. Transmission symbols have been assigned to tones within the burst on a pseudorandom basis. Many of the tones are left unused. There is a high probability that most of the time tones used by user /will not overlap with, and therefore will not interfere with, tones used by user/.
  • base stations When base stations are able to coordinate amongst themselves it becomes possible to improve upon pseudorandom tone assignment. For example, consider separate base stations communicating with users near the boundary between two sectors (see, e.g. Fig. 1).
  • the base stations can operate in several possible modes, for example: frequency diversity (see, e.g. Fig. 2); multiuser diversity without interference averaging (see, e.g. Fig. 3); multiuser diversity with pseudorandom interference averaging (see, e.g. Fig. 4); or, multiuser diversity with orthogonal time interleaving.
  • Multiuser diversity with orthogonal time interleaving means that rather than tones being distributed in a sub-band pseudorandomly within a burst, the tones are assigned in a pattern that is orthogonal to a tone assignment pattern used by another user.
  • Base stations that can coordinate tone assignment patterns can ensure that users sharing a sub-band use orthogonal patterns that do not interfere with one another.
  • Fig. 5 shows a system block diagram for a transmitter incorporating time domain interference averaging in a multiuser - diversity frequency allocation scheme.
  • block 510 represents part of the system where data is encoded in an error control coding scheme. Error control coding prevents data loss even when symbols are dropped or received incorrectly at a receiver.
  • Block 520 interleaving, is the part of the system in which encoded bits are interleaved so that complex symbols modulate non-consecutive bits from the encoded data stream.
  • Complex symbol mapping, block 530 is the part of the system in which data is assigned to complex transmission symbols.
  • Block 540, multiuser time - frequency scheduling is the part of the system that assigns complex transmission symbols to tones for wireless transmission.
  • Preferred coherence bandwidth selection block 560 is the part of the system that assigns preferred sub-bands to users.
  • the multiuser time - frequency scheduling block 540 uses information from block 560 to assign tones in an interference averaging scheme as described above especially in connection with Fig. 4.
  • complex symbols modulate tones in OFDM modulation block 550.
  • Fig. 6 shows a flow chart for implementing a multiuser - diversity frequency allocation scheme with interference averaging. The flow chart outlines major steps in a method for implementing interference averaging in multiuser - diversity frequency allocation. In step 610 a frequency sub-band and a burst transmission time for a first user communicating with a base station are designated.
  • step 620 data to be sent to the user is encoded in codewords comprising symbols.
  • step 630 the symbols are pseudorandomly distributed into tones within the frequency sub-band and the burst transmission time, such that interference is reduced between the first user and other users that have been allocated the same frequency sub-band and burst transmission time, but different tones on a pseudorandom basis.
  • assigning different tones on a pseudorandom basis includes the possibility that from time to time the same tone is assigned to more than one user.
  • the communication systems and methods described above include a method for wireless data transmission comprising designating a frequency sub- band and a burst transmission time for a first user communicating with a base station.
  • the method of an embodiment includes encoding data to be sent to the user into codewords comprising symbols.
  • the method of an embodiment includes pseudorandomly distributing the symbols into tones within the frequency sub-band and the burst transmission time, such that the variance of interference is reduced between the first user and other users that have been allocated the same frequency sub-band and burst transmission time, but different tones on a pseudorandom basis.
  • the communication systems and methods described above include a system for wireless data communication.
  • the system of an embodiment comprises an interleaving unit.
  • the system of an embodiment comprises a symbol mapper coupled to the interleaving unit.
  • the system of an embodiment comprises a scheduling unit coupled to the symbol mapper and configured to operate with preferred coherence bandwidth information to schedule tones for symbol transmission within a preferred coherence sub-band.
  • the system of an embodiment comprises a coding unit coupled to the interleaving unit.
  • the coding unit of an embodiment is configured to encode data using one or more error control coding schemes.
  • the symbol mapper of an embodiment is configured to assign received data to one or more complex transmission symbols.
  • the scheduling of tones of an embodiment includes pseudorandom scheduling.
  • the scheduling unit of an embodiment is configured to assign transmission symbols to the tones.
  • the transmission symbols of an embodiment are associated with communications data of a plurality of users.
  • the system of an embodiment being configured to assign transmission symbols to the tones includes use of information of one or more sub-bands assigned to each of a plurality of users.
  • the system of an embodiment includes a bandwidth selection device coupled to the scheduling unit.
  • the bandwidth selection device of an embodiment is configured to assigned one or more sub-bands to each of a plurality of users.
  • the communication systems and methods described above include a method for wireless data transmission comprising, in a digital communications system, pseudorandomly allocating tones within a frequency sub-band and a burst transmission time that is being used by more than one user simultaneously, such that the variance of interference between multiple users of the system is reduced on average.
  • the frequency sub-band of an embodiment is assigned to the more than one user simultaneously as a result of conflicts between multiuser diversity modes of two different base stations.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne la réduction d'une interférence entre une multiplicité d'utilisateurs qui opèrent selon une diversité multi-utilisateurs dans une bande passante de cohérence d'un système OFDMA par l'étalement aléatoire dans le temps de symboles de transmission dans la bande passante de cohérence. Lorsque les symboles de transmission sont aléatoirement dispersés, la variance de l'interférence entre utilisateurs d'une même sous-bande est réduite à la moyenne.
PCT/US2006/023823 2006-06-16 2006-06-16 Calcul de moyenne d'interférences dans le domaine temporel avec une diversité multi-utilisateurs dans des systèmes ofdma WO2007145640A1 (fr)

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PCT/US2006/023823 WO2007145640A1 (fr) 2006-06-16 2006-06-16 Calcul de moyenne d'interférences dans le domaine temporel avec une diversité multi-utilisateurs dans des systèmes ofdma

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PCT/US2006/023823 WO2007145640A1 (fr) 2006-06-16 2006-06-16 Calcul de moyenne d'interférences dans le domaine temporel avec une diversité multi-utilisateurs dans des systèmes ofdma

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2136520A1 (fr) * 2008-06-20 2009-12-23 Nokia Siemens Networks Oy Procédé et dispositif de données de traitement et système de communication comprenant un tel dispositif
WO2013071660A1 (fr) * 2011-11-16 2013-05-23 中兴通讯股份有限公司 Procédé et appareil pour une réception en macro diversité

Citations (3)

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Publication number Priority date Publication date Assignee Title
US6490269B1 (en) * 1998-07-22 2002-12-03 Sony Corporation OFDM signal generation method and OFDM signal generation apparatus
US20040228267A1 (en) * 2003-05-12 2004-11-18 Avneesh Agrawal Fast frequency hopping with a code division multiplexed pilot in an OFDMA system
US6882618B1 (en) * 1999-09-07 2005-04-19 Sony Corporation Transmitting apparatus, receiving apparatus, communication system, transmission method, reception method, and communication method

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6490269B1 (en) * 1998-07-22 2002-12-03 Sony Corporation OFDM signal generation method and OFDM signal generation apparatus
US6882618B1 (en) * 1999-09-07 2005-04-19 Sony Corporation Transmitting apparatus, receiving apparatus, communication system, transmission method, reception method, and communication method
US20040228267A1 (en) * 2003-05-12 2004-11-18 Avneesh Agrawal Fast frequency hopping with a code division multiplexed pilot in an OFDMA system

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2136520A1 (fr) * 2008-06-20 2009-12-23 Nokia Siemens Networks Oy Procédé et dispositif de données de traitement et système de communication comprenant un tel dispositif
WO2009153284A1 (fr) * 2008-06-20 2009-12-23 Nokia Siemens Networks Oy Procédé et dispositif de traitement de données et système de communication comprenant un tel dispositif
CN102067541A (zh) * 2008-06-20 2011-05-18 诺基亚西门子通信公司 用于处理数据的方法和装置以及包括此装置的通信系统
US9264166B2 (en) 2008-06-20 2016-02-16 Nokia Siemens Networks Oy Method and device for processing data and communication system comprising such device
WO2013071660A1 (fr) * 2011-11-16 2013-05-23 中兴通讯股份有限公司 Procédé et appareil pour une réception en macro diversité

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