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WO2006128973A1 - Recepteur, emetteur et procede de transmission a largeur de bande variable - Google Patents

Recepteur, emetteur et procede de transmission a largeur de bande variable Download PDF

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Publication number
WO2006128973A1
WO2006128973A1 PCT/FI2006/050227 FI2006050227W WO2006128973A1 WO 2006128973 A1 WO2006128973 A1 WO 2006128973A1 FI 2006050227 W FI2006050227 W FI 2006050227W WO 2006128973 A1 WO2006128973 A1 WO 2006128973A1
Authority
WO
WIPO (PCT)
Prior art keywords
filter
signal
filters
bandwidth
transmission
Prior art date
Application number
PCT/FI2006/050227
Other languages
English (en)
Inventor
Petri J. VÄISÄNEN
Olli Piirainen
Markku Vainikka
Original Assignee
Nokia Siemens Networks Oy
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.)
Filing date
Publication date
Priority claimed from FI20055284A external-priority patent/FI20055284A0/fi
Application filed by Nokia Siemens Networks Oy filed Critical Nokia Siemens Networks Oy
Publication of WO2006128973A1 publication Critical patent/WO2006128973A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
    • H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal
    • H04B1/1036—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H17/02—Frequency selective networks
    • H03H17/0248—Filters characterised by a particular frequency response or filtering method
    • H03H17/0264—Filter sets with mutual related characteristics
    • H03H17/0266—Filter banks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H2240/00—Indexing scheme relating to filter banks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
    • H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal
    • H04B2001/1054—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal by changing bandwidth

Definitions

  • the invention relates to transmission methods in telecommunication systems.
  • the invention relates to systems where transmission bandwidth varies between users or where users employ variable bandwidth transmission.
  • transmitted signals comprise time slots or frames, in which the signals are transmitted as pulses in finite lengths.
  • square pulse shapes cannot be transmitted over a band-limited channel, because square pulse shapes occupy an infinite bandwidth and inter-symbol interference will happen. Therefore, signals are filtered prior to the transmission to shape the spectrum of the signal.
  • a signal with a raised cosine (RC) spectrum is widely used in telecommunications systems for transmissions between a transmitter and receiver. This applies to wireless communication systems in particular.
  • the creation of the RC frequency response is usually split between a transmitter and a receiver.
  • both the transmitter and the receiver comprise a transmission filter and the combined response of the filters is of the RC shape.
  • variable bandwidth transmission means that each transmitter of the system may utilize a variable frequency band of the total bandwidth allocated to the system.
  • a receiver In a fully loaded system, a receiver must be able to receive at all times the entire bandwidth allocated to the system. This applies to base stations in cellular telecommunication systems in particular. The proportion of the total bandwidth allocated to each transmitter at each time instant is variable, however.
  • variable bandwidth transmission is a problem in transmitter and especially in receiver filters.
  • a prior art solution for adapting the filter response to the variable bandwidth transmission is to change the receiver filter's impulse response.
  • receivers operate continuously.
  • radio frequency (RF) parts and base band (BB) parts are typically separated. They are connected with each other through an RF-BB bus.
  • the receiver filtering is performed in radio frequency part. Changing the filter impulse response by changing the filter in real time receiver filter operation is difficult and could result undesired transition responses causing undesirable interference to adjacent channels or to adjacent timeslots. This may be the case even if the transmission bandwidth is known by the receiver.
  • the receiver may have also another problem if the transmission bandwidth is not known beforehand.
  • the used transmission bandwidth employed must be detected or estimated after the reception of a frame. The detection is performed by digital signal processing in the base band part. This would then require that the receiver be able to perform the receiver filtering after the actual transmission and detection of the transmission bandwidth.
  • An object of the invention is to provide an improved solution for variable bandwidth transmission.
  • a method for receiving a variable transmission bandwidth signal comprising: filtering the received signal with one or more filters of a square-root raised cosine filter bank, each filter having the same input signal, and configured to filter a subband, and adding up the output signals of the one or more filters of the filter bank to obtain a sum signal, the sum of the sub- bands of the one or more filters being equal to the transmission bandwidth of the received signal and the center frequencies of filters filtering adjacent sub- bands being orthogonal to each other.
  • a method for controlling transmission of a variable transmission bandwidth signal in a transmitter comprising: selecting the roll-off factor of the transmission filter of the transmitter on the basis of the bandwidth of the signal to be transmitted.
  • a receiver in a telecommunication system comprising: a square-root raised cosine filter bank, each filter of the filter bank having the same input signal, and configured to filter a subband, and an adder configured to add up the output signals of one or more filters of the filter bank to obtain a sum signal, the sum of the subbands of the one or more filters being equal to the transmission bandwidth of the received signal and the center frequencies of filters filtering adjacent subbands being orthogonal to each other.
  • a transmitter in a telecommunication system comprising a transmission filter, wherein the transmitter is configured to select the roll-off factor of the transmission filter on the basis of the bandwidth of the signal to be transmitted.
  • Embodiments of the invention may be utilized in a base station and a mobile station of a telecommunication system.
  • the invention provides several advantages.
  • the proposed structure will simplify the interface between radio frequency parts and base band parts (RF-BB) since the transmitter or receiver filter impulse responses do not have to change within real time operation. Thus, unwanted transition responses can be avoided.
  • the transmission bandwidth can be determined in the base band processing after the reception of a frame or a time slot.
  • the proposed structure enables blind transmission bandwidth detection in receiver base band processing. When the transmission bandwidth is detected, the sub-band signals can be combined.
  • variable transmission bandwidth base station receiver can be implemented with simple fixed transmission bandwidth subband filters.
  • the proposed square-root raised cosine filter bank can be implemented with computationally efficient polyphase structures with approximately the same complexity as one RRC receiver filter.
  • the embodiments of the invention enable efficient variable bandwidth transmission and performing other receiver functions on the narrower bandwidth sub-band signals.
  • Figure 1 shows an example of a telecommunication system
  • Figure 2 illustrates an example of a receiver
  • Figure 3 illustrates a root raised cosine impulse response
  • Figures 4A to 4C illustrate an example where a received signal is processed by two filters of a square-root raised cosine filter bank
  • Figure 5 illustrates a transmitter of an embodiment of the invention
  • Figure 6 illustrates the frequency response of a root raised cosine filter
  • Figure 7 illustrates a transmission filter structure of an embodiment of the invention
  • Figure 8 illustrates variable bandwidth multiple access transmission
  • Figure 9 illustrates an example of a filter structure
  • Figure 10 illustrates an embodiment of the invention in a flowchart.
  • the present invention is applicable to various telecommunication systems.
  • Typical examples of a system to which the invention can be applied are evolutions of the third generation cellular telecommunication systems, UMTS (Universal Mobile Telecommunications System).
  • UMTS Universal Mobile Telecommunications System
  • the invention is not limited to UMTS or any other cellular telecommunications system, as one skilled in the art is aware.
  • FIG. 1 examine an example of a data transmission system to which embodiments of the invention can be applied.
  • Figure 1 is a simplified block diagram describing the most important cellular telecommunication system parts at network element level. The structure and operation of the network elements are not described in detail, since they are commonly known.
  • the cellular telecommunication system may be divided into a core network (CN) 100, a radio access network (RAN) 102 and mobile stations (MS) 104A, 104B, 104C.
  • CN core network
  • RAN radio access network
  • MS mobile stations
  • the RAN 102 includes a base station system (BSS) 106, which includes a base station controller (BSC) 108 and base stations (BTS) 110, 112 and 114.
  • BSS base station system
  • BSC base station controller
  • BTS base stations
  • the structure of the core network 100 supports both circuit-switched connections and packet-switched connections.
  • a Mobile Services Switching Center MSC 116 is the center of the circuit-switched side of the core network 100.
  • the functions of the mobile services switching center 116 include: switching, paging, location registration of user equipment, handover management, collecting subscriber billing information, encryption parameter management, frequency allocation management and echo cancellation.
  • the number of mobile services switching centers 116 may vary: a small network operator may be provided with a single mobile services switching center 116, but larger core networks 100 may be provided with several.
  • Larger core networks 100 may comprise a separate Gateway Mobile Services Switching Center GMSC 118 handling the circuit-switched connections between the core network 100 and external networks 120.
  • the gateway mobile services switching centre 118 is located between the mobile services switching centres 116 and the external networks 120.
  • the external network 120 may be for instance a Public Land Mobile Network PLMN or a Public Switched Telephone Network PSTN.
  • a Serving GPRS Support Node SGSN 122 is the center of the packet-switched side of the core network 100.
  • the main task of the serving GPRS support node 122 is to transmit and receive packets with the user equipment 104A - 104C supporting packet-switched transmission using the base station system 106.
  • the serving GPRS support node 122 includes subscriber data and location information concerning the user equipment 104A - 104C.
  • a Gateway GPRS Support Node GGSN 124 is the corresponding part on the packet-switched side to the gateway GMSC 118 on the circuit- switched side.
  • the gateway GPRS support node 124 must be able to route the outgoing traffic from the core network 100 to external networks 126.
  • the Internet represents the external networks 126.
  • the base station system 106 is composed of a Base Station Controller BSC 108 and Base Transceiver Stations or Base Stations BTS 110, 112 and 114.
  • the base station controller 108 controls the base stations 110, 112 and 114.
  • the aim is to place the equipment implementing the radio path and the functions associated therewith in the base station 110, 112 and 114 and to place the control equipment in the base station controller 108.
  • the base station 110, 112 and 114 includes at least one transceiver implementing a carrier, or eight time slots, or eight physical channels.
  • one base station serves one cell, but such a solution is also possible, in which one base station 110, 112 or 114 serves several sectorized cells.
  • the base station 110, 112 and 114 has following functions: calculations of timing advance, measurements in the uplink direction, channel coding, encryption, decryption and frequency hopping, for example.
  • the mobile station or subscriber terminal 104A - 104C includes at least one transceiver that implements the radio connection to the radio access network 102 or to the base station system 106.
  • the mobile station 104A - 104C typically comprises an antenna, a processor controlling the operation of the device and a battery.
  • a band-limited signal is usually filtered so that inter symbol interference (ISI) may be avoided.
  • ISI inter symbol interference
  • RC raised cosine
  • H 10 ⁇ is widely used in telecommunications systems because it has good properties against ISI.
  • the equation for H rc ⁇ may be of the following format:
  • ⁇ is the roll-off factor that determines the excess bandwidth over the Nyquist frequency
  • T is the symbol period
  • ⁇ I2T is the Nyquist and at the same time the 3dB frequency.
  • the filtering operation is usually divided between the transmitter and the receiver.
  • f ⁇ ⁇ W, H rc ⁇ may be expressed as
  • variable transmission bandwidth receiver filtering is implemented with a square-root raised cosine filter bank (RRC-FB) having overall raised cosine power spectral characteristics.
  • RRC-FB square-root raised cosine filter bank
  • FIG. 2 illustrates an example of a receiver equipped with a square- root raised cosine filter bank.
  • the receiver of this example is a base station receiver configured to receive signals of several transmitters.
  • the receiver comprises a radio frequency part 200 and a base band part 202.
  • the radio frequency part comprises a square-root raised cosine filter bank 204.
  • the input signal of the square-root raised cosine filter bank 204 is the received signal r(t) 206.
  • the output signals 210a, 210b, 210c of the square-root raised cosine filter bank 204 are delivered to the base band part 202.
  • the received signal r(t) 206 may comprise signals of several transmitters.
  • the radio frequency part may comprise also other components, such as amplifiers, as one skilled in the art is aware.
  • the output signals 210a, 210b, 210c of the square-root raised cosine filter bank 204 are taken to an adder bank 212.
  • the output signals of the one or more filters of the filter band are added up to obtain one or more sum signals 214, 216.
  • Each sum signal corresponds to a signal of one transmitter.
  • one or more filters of the filter bank 204 are used to filter a signal of a transmitter and the output signals of these filters are added up in the adder bank 212.
  • the sum of the subbands of the one or more filters used to filter a signal of a transmitter is equal to the transmission bandwidth of the received signal of the transmitter.
  • the center frequencies of filters, i.e. sub- carriers of the exponentially modulated filter bank, used to filter a signal of a transmitter and filtering adjacent subbands, are orthogonal to each other.
  • the square-root raised cosine filter bank 204 comprises a set of filters 208A - 208C, each filter having a square-root raised cosine spectrum.
  • Each filter has an impulse response g ⁇ (t) , which may be of the following format:
  • N is the number of filters in the filter bank
  • j is the imaginary unit
  • ⁇ angular velocity of sub-carrier i
  • ⁇ is phase
  • h(t) is a root raised cosine low- pass prototype impulse response, illustrated by Figure 3.
  • the phase ⁇ is given by equation
  • the orthogonality of filters filtering adjacent subbands is determined by selecting the phase of the filters accordingly. For example, phases of filters filtering adjacent subbands may have a ⁇ /2 phase shift.
  • FIGS 4A to 4C illustrate an example where a signal of a transmitter is processed by two filters of a square-root raised cosine filter bank.
  • the overall transmission bandwidth 2W used by a transmitter is obtained by summing two RRC responses with a bandwidth W.
  • the two RRC responses are denoted by
  • Figure 4A shows the power spectrum of an RRC filter.
  • Figure 4B illustrates an embodiment where two RRC filters with adjacent subbands of bandwidth W are used to filter the signal of a transmitter having a bandwidth of 2 W. If the center frequencies of two RCC filters are orthogonal to each other, the square sum of the two responses becomes flat as Figure 4C illustrates.
  • the RRC filter amplitude responses at the transition band near zero frequency may be defined in the following manner:
  • FIG. 10 illustrates an embodiment of the invention in a flowchart.
  • a signal is received.
  • a first time slot or a first frame of a signal is received, for example.
  • the bandwidth of the received signal is not known.
  • the signal is filtered with a number of filters of the filter bank 204.
  • the number of filters may be selected such that the total bandwidth of the filters is equal to the largest allowed bandwidth of a transmitted signal.
  • step 1020 the receiver detects the bandwidth of the received signal.
  • step 1030 the number of required filters of the filter bank 204 to cover the required bandwidth is determined.
  • the required number of filters is adjusted on the basis of the determination.
  • the already received and filtered time slot or frame is obtained by adding up the required outputs of filters.
  • step 1040 the reception of the signal continues utilizing the required number of filters, and adding the filter outputs in the adder 212 and performing equalization in equalizer 218.
  • Figure 5 illustrates a transmitter of an embodiment of the invention.
  • Input to the transmitter is the signal x fc (t)500 to be transmitted.
  • the signal is first modulated in a modulator 502 and channel coded in a coder 504. From the coder the signal is taken to a variable bandwidth transmission filter 506 having an impulse response % >rc (0 ⁇ From the filter, the signal is taken to an amplifier 508 and transmitted to a transmission channel. In the channel, noise is added to the signal.
  • the transmitter may further comprise a controller 510.
  • the controller 510 controls the operation of the transmitter.
  • the controller 510 may control the bandwidth of the filter 502 according to need.
  • the signal proceeds to the transmission channel 504, where noise is added 506 to the signal.
  • the controller is configured to select the roll-off factor of the transmission filter 506 on the basis of the signal to be transmitted.
  • the roll-off factor may be controlled on the basis of the bandwidth used in the transmission of the signal to be transmitted.
  • Figure 6 illustrates a frequency response of a root raised cosine filter.
  • the frequency response consists of unity gain at low frequencies L, the square root of the raised cosine function in the middle M 1 and total attenuation at high frequencies H.
  • the low frequency area L is determined as the area within which the attenuation of the signal is smaller than 3 db.
  • the width of the middle frequency areas at both ends of the response is defined by the roll off factor constant, which can be defined as the relation of the low frequency areas to the middle frequency area.
  • the roll-off factor is always between 0 and 1.
  • the controller is configured to select the transmission filter on the basis of the signal to be transmitted. By changing the number of sub-bands, the required bandwidth and roll-off factor may be obtained.
  • FIG. 7 illustrates an embodiment of the invention where the transmission filter is realized with a square-root raised cosine filter bank 700.
  • the filter bank comprises a set of filters 702A to 702C, each filter having the same input signal, and configured to filter a subband. The bandwidth of each filter is fixed.
  • the output signals of the filters are taken to an adder 704 which is configured to add up the output signals of one or more filters of the filter bank to obtain a sum signal 706.
  • the bandwidth of the sum of the subbands of the one or more filters is equal to the transmission bandwidth of the signal to be transmitted and the center frequencies of filters filtering adjacent subbands are orthogonal to each other.
  • Figure 8 illustrates the variable bandwidth multiple access transmission.
  • Figure 8 shows eight subbands 800 - 806 realized with eight filters of a filter bank 700. Assume that the bandwidth of each subband is W.
  • Four leftmost subbands 800 are used for the transmission of a first user. Thus, the bandwidth of the signal of the first user is AW.
  • the outputs of the four leftmost filters are summed in an adder 808 and a signal 812 of bandwidth 4W ⁇ s obtained.
  • the two subbands 802 are used in the transmission of a second user.
  • the bandwidth of the signal of the second user is 2W.
  • the outputs of the filters are summed in an adder 810 and a signal 814 of bandwidth 2 W is obtained.
  • Each of the subbands 804 and 806 is used in the transmission of a third and a fourth user.
  • the bandwidth of the signals of the third and a fourth user is W. Summation is not needed as only one filter is used.
  • the filters of the filter banks 212 and 700 are realized as a complex FIR (Finite Impulse Response) filter.
  • Figure 9 illustrates another embodiment, where the filters comprise a numerically controlled oscillator 900, whose output signal multiplies the signal 902 passing through the filter in the multiplier 904. The output signal of the numerically controlled oscillator
  • the 900 may be of format e j ⁇ ' t + ⁇ i .
  • the output signal of the multiplier 904 is taken to a FIR filter 906 with impulse response h(t).
  • the presented symbols correspond to equations 2 and 3 presented above.
  • the filters may also be realized as a muitirate filter system.
  • Embodiments of the invention may be implemented as a computer program.
  • the computer program may be stored on a computer program distribution medium readable by a computer or a processor.
  • the computer program medium may be, for example but not limited to, an electric, magnetic, optical, infrared or semiconductor system, device or transmission medium, may include at least one of the following media: a computer readable medium, a program storage medium, a record medium, a computer readable memory, a random access memory, an erasable programmable read-only memory, a computer readable software distribution package, a computer readable signal, a computer readable telecommunications signal, computer readable printed matter, and a computer readable compressed software package.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Mathematical Physics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Transmitters (AREA)

Abstract

L'invention concerne des solutions destinées à la réception et à la transmission d'un signal à largeur de bande variable. L'invention concerne également un récepteur comprenant un banc de filtres en racine carrée de cosinus surélevé, chaque filtre du banc de filtres étant conçu pour filtrer une sous-bande, ainsi qu'un sommateur conçu pour additionner les signaux de sortie d'un ou plusieurs filtres du banc de filtres pour obtenir un signal de somme, la somme des sous-bandes du ou des filtres étant égale à la largeur de bande de transmission du signal reçu. L'invention concerne également un émetteur comprenant un filtre d'émission, le facteur de décroissance du filtre de transmission étant sélectionné sur la base de la largeur de bande du signal à émettre.
PCT/FI2006/050227 2005-06-03 2006-06-02 Recepteur, emetteur et procede de transmission a largeur de bande variable WO2006128973A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
FI20055284 2005-06-03
FI20055284A FI20055284A0 (fi) 2005-06-03 2005-06-03 Vastaanotin, lähetin ja vaihtuvan kaistanleveyden lähetysmenetelmä
US11/441,117 US20070005352A1 (en) 2005-06-03 2006-05-26 Receiver, transmitter and variable bandwidth transmission method
US11/441,117 2006-05-26

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Publication Number Publication Date
WO2006128973A1 true WO2006128973A1 (fr) 2006-12-07

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997004572A1 (fr) * 1995-07-14 1997-02-06 Telefonaktiebolaget Lm Ericsson (Publ) Mise en forme d'impulsions pour la modulation de porteuses multiples
EP0786890A2 (fr) * 1996-01-29 1997-07-30 Sony Corporation Allocation des ressources dans un système radio mobile multiporteur à plusieurs utilisateurs
US6246713B1 (en) * 1998-06-08 2001-06-12 Telefonaktiebolaget Lm Ericsson (Publ) Frequency-hopping in a bandwidth-on-demand system
US6252909B1 (en) * 1992-09-21 2001-06-26 Aware, Inc. Multi-carrier transmission system utilizing channels of different bandwidth
US20020142746A1 (en) * 2001-03-28 2002-10-03 Junsong Li Radio receiver having a dynamic bandwidth filter and method therefor
US20020177446A1 (en) * 2001-05-23 2002-11-28 Alex Bugeja System and method for providing variable transmission bandwidth over communications channels
EP1478148A1 (fr) * 2003-05-15 2004-11-17 Siemens Aktiengesellschaft Procédé de communication multiporteuse sans fil avec attribution dynamique d'un spectre de frequence et d'une pluralité de sous-bandes

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6252909B1 (en) * 1992-09-21 2001-06-26 Aware, Inc. Multi-carrier transmission system utilizing channels of different bandwidth
WO1997004572A1 (fr) * 1995-07-14 1997-02-06 Telefonaktiebolaget Lm Ericsson (Publ) Mise en forme d'impulsions pour la modulation de porteuses multiples
EP0786890A2 (fr) * 1996-01-29 1997-07-30 Sony Corporation Allocation des ressources dans un système radio mobile multiporteur à plusieurs utilisateurs
US6246713B1 (en) * 1998-06-08 2001-06-12 Telefonaktiebolaget Lm Ericsson (Publ) Frequency-hopping in a bandwidth-on-demand system
US20020142746A1 (en) * 2001-03-28 2002-10-03 Junsong Li Radio receiver having a dynamic bandwidth filter and method therefor
US20020177446A1 (en) * 2001-05-23 2002-11-28 Alex Bugeja System and method for providing variable transmission bandwidth over communications channels
EP1478148A1 (fr) * 2003-05-15 2004-11-17 Siemens Aktiengesellschaft Procédé de communication multiporteuse sans fil avec attribution dynamique d'un spectre de frequence et d'une pluralité de sous-bandes

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