WO2002007341A2 - Systeme de radiotelecommunication cellulaire - Google Patents

Systeme de radiotelecommunication cellulaire Download PDF

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Publication number
WO2002007341A2
WO2002007341A2 PCT/GB2001/003185 GB0103185W WO0207341A2 WO 2002007341 A2 WO2002007341 A2 WO 2002007341A2 GB 0103185 W GB0103185 W GB 0103185W WO 0207341 A2 WO0207341 A2 WO 0207341A2
Authority
WO
WIPO (PCT)
Prior art keywords
telecommunication system
cellular radio
radio telecommunication
signal
antennas
Prior art date
Application number
PCT/GB2001/003185
Other languages
English (en)
Other versions
WO2002007341A3 (fr
Inventor
Andrew Fogg
John Leslie Haine
Original Assignee
Ip.Access Ltd.
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 GB0017427A external-priority patent/GB0017427D0/en
Application filed by Ip.Access Ltd. filed Critical Ip.Access Ltd.
Priority to AU2001270832A priority Critical patent/AU2001270832A1/en
Publication of WO2002007341A2 publication Critical patent/WO2002007341A2/fr
Publication of WO2002007341A3 publication Critical patent/WO2002007341A3/fr

Links

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
    • H04B7/0667—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 of delayed versions of same signal
    • H04B7/0671—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 of delayed versions of same signal using different delays between antennas
    • 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
    • H04B7/0667—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 of delayed versions of same signal
    • H04B7/0676—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 of delayed versions of same signal using random or pseudo-random delays

Definitions

  • This invention relates to cellular radio telecommunication systems.
  • any wireless system one of the primary limits on effective communications is multipath propagation.
  • an electromagnetic wave When an electromagnetic wave is emitted from an antenna into free space it undergoes reflection and diffraction from obstacles of all kinds, such as buildings, hills, vehicles, people, walls, and office furniture.
  • obstacles of all kinds such as buildings, hills, vehicles, people, walls, and office furniture.
  • the direct line of sight from the transmitter to the receiver is obstructed as well, so that the received signal is made up of several components with random amplitude and phase differences which depend on the different paths along which the signals travel.
  • the received signal is therefore dispersed in time, which causes inter-symbol interference with digital modulations.
  • the degree of dispersion is typically measured by the root-mean-square of the distribution in time of the received reflected signals, called the rms delay spread.
  • each received signal component is subject to a Doppler shift depending on the relative velocity between the terminal and its environment, resulting in a time-varying signal amplitude with very deep nulls.
  • the aggregate impairments caused by multipath are commonly known as multipath fading.
  • GSM Global System for Mobile Communications
  • multipath propagation is a primary cause of signal degradation.
  • the duration of a single transmitted GSM digital symbol is approximately 4 microseconds, yet the system has to operate in environments where the multipath delay spread can be of the order of 20 microseconds, or nearly 5 symbols.
  • GSM handsets and base stations always therefore incorporate means to compensate for the delay spread, known generically as a multipath equaliser.
  • a well-known method of countering multipath degradation is receive diversity.
  • a receiver is equipped with two or more antennas which are spatially separated. It is well known that if the antennas are in a multipath field but separated by at least one quarter of the operating wavelength ("space diversity"), then the fading envelopes of the signals -> received at the antennas are essentially un-correlated. The same is true if the signals are received at the same antenna but at different frequencies as long as the frequencies are sufficiently separated (“frequency diversity"). Thus even if one antenna is located at a point where the multipath components cancel, there is a high probability that at least one other antenna is not at such a point.
  • a significant benefit of diversity in cellular systems is the reduction of the effect of intra-system interference. Because the probability of the receiver experiencing a fade is significantly reduced by diversity, the transmitter power needed to obtain a desired minimum carrier to interference level over the cell can be reduced. Thus the interference caused in other, distant, cells operating at the same frequency is reduced. Applied throughout a cellular system, diversity can therefore increase system capacity. Space diversity is easy to achieve at the base station because there is no restriction on how far apart the antennas can be placed on the antenna tower. However it is difficult to achieve space diversity at the handset because the terminal itself has to be very small; and also its complexity, size, power consumption and cost will be increased if it is necessary to incorporate an additional receiver to process signals from the second antenna.
  • FH frequency hopping
  • the frequency used by a given timeslot in successive frames changes pseudo-randomly. If the signal received during the slot by the terminal (or by the BTS in the reverse direction) is at a frequency which is faded in one frame, it is relatively unlikely that it will also be faded at the frequency used in the next frame.
  • the forward error correction and interleaving means used in GSM can then often correct errors in the faded slot based on parity information in previous and following slots.
  • Frequency hopping also reduces the susceptibility of the system to co-channel interference because cells use different hopping sequences and therefore whilst co-channel interference may occur in one frame it is unlikely in succeeding frames. Frequency hopping is likely to be much less effective in combating multipath in an indoor environment, because the relative delay spread will be very short, which increases the correlation between fading at different channel frequencies.
  • DECT uses time division duplexing, in which the base station and handset transmit alternately in time on the same frequency.
  • the base station is equipped with at least two antennas and can select which is used for transmission or reception at any given instant. While the base station is receiving from the handset it determines which antenna provides the best reception. It then uses the same antenna to transmit signals back to the handset. Because both ends of the link operate at the same frequency and the radio link is reciprocal the same antenna will also give best performance for the other link direction.
  • transmit diversity is not applicable in the GSM system because the downlink (base - handset) and uplink (handset - base) are at different frequencies and their fading characteristics are therefore generally un-correlated.
  • PMR private mobile radio
  • the invention in particular, it is an object of the invention to improve the coverage provided by an indoor base station without having to increase its output power.
  • the invention thereby seeks to decrease the effect of interference from an external transmission at the same frequency on the performance of a handset covered by the indoor base station; and to reduce the interference caused by the indoor base station to handsets outside the building.
  • a cellular radio telecommunication system comprising a base station having at least two antennas, said antennas each arranged to transmit a downlink signal to one or more mobile subscriber units, wherein said base station is arranged so that signals transmitted from said antennas have a mutual time delay and phase difference, said phase difference changing from time-to-time.
  • phase difference between the at least two signals transmitted from the antennas changes periodically.
  • phase difference may change on a random or pseudo random basis.
  • the transmitted signals comprise a plurality of time slots, or bursts, and the phase difference changes at the beginning of each successive slot.
  • the phase difference may lie within the range of 0° to 360°.
  • the antennas are mutually spatially separated by distance sufficient to ensure that any multi-path fading in the transmitted signals as received by at least one mobile subscriber unit within the coverage of at least said two antennas is decorrelated.
  • the mutual time delay between the at least two signals transmitted from the antennas is within a predetermined maximum delay chosen such that a mobile subscriber unit including an equaliser can demodulate the aggregate signal received from the at least two antennas.
  • the predetermined maximum delay equals the maximum allowable delay spread in accordance with GSM standards. By setting the predetermined maximum delay to be no larger than the maximum allowable delay spread specified in GSM standards the predetermined delay of the signals mimics the delay spread of a multiple path signal in a conventional GSM system that can be demodulated by a standard equaliser within a mobile subscriber unit.
  • the base station is arranged to generate a first downlink signal to be transmitted from a first one of the antennas and then taking this first downlink signal the base station introduces said time delay and phase difference to generate a second downlink signal that is transmitted from a second one of the antennas.
  • the downlink signals are phase shift key modulated.
  • the base station may be arranged to modify a digital baseband signal prior to modulation to thereby generate the phase difference at the time of modulation.
  • the baseband signal is differentially encoded and the base station arranged to modify the baseband signal by altering the voltage level of the encoded signal.
  • the downlink signal may be GMSK modulated.
  • the baseband signal may be EDGE encoded and said base station modifies said baseband signal by manipulating at least one symbol of said signal.
  • the auto-correlation function of the GSM signal is relatively narrow in time, so that two versions of the same GSM carrier which are sufficiently separated in time have low correlation. If both the signals are received at the same receiver, it is relatively unlikely that they will destructively interfere because they are not highly correlated.
  • the conventional equaliser of the GSM receiver will then optimally estimate the modulation signal from the combined signal which appears similar to a conventional GSM signal with multipath.
  • Figure 1 is an example block diagram of the base station transmitter scheme for GMSK modulation
  • Figure 2 shows the un-modified and modified GSM downlink burst structures for GMSK modulation
  • Figure 3 shows the un-modified and modified GSM downlink burst structures for EDGE modulation.
  • digital baseband circuits 101 generate the conventional GSM BTS data stream as described in GSM Specifications 05.04 and 05.02. This is differentially encoded by the encoder 102 whose output is the modulo-2 sum of the present and previous bit of the baseband data stream.
  • the differentially encoded binary stream is processed in items 103, 104, 105 106 and 107. First it is level shifted by 103 so that a binary 1 is translated to a negative level and a binary zero to an equal positive level.
  • the resulting bipolar signal is filtered by the Gaussian filter 104 which has impulse response defined in the above GSM Specification, and applied to the Voltage-Controlled Oscillator (VCO) 105 where it frequency modulates a carrier at the transmit frequency (with frequency hopping if appropriate) with a modulation index of 0.5.
  • VCO Voltage-Controlled Oscillator
  • PA Power Amplifier
  • a delayed version of the GSM signal with periodic phase shifts is generated.
  • a time delay Tl is inserted by digital delay line 108.
  • the signal is level-shifted as before by 109.
  • a random signal 115 generated by the Random Generator 116, is added to the level-shifted signal at a defined time. The timing and characteristics of the random signal are considered later.
  • the waveform is Gaussian filtered by 111; applied to the VCO 112; and finally amplified by the PA 113 and radiated by the antenna 114.
  • Figure 2 shows the signals in various parts of the system shown in Figure 1, derived from the GSM standards documents.
  • the signal 201 has 3 tail bits which are specified to be binary zeros as shown, followed by an inter-slot guard period of 8.25 bits.
  • the signal is specified to be all l's during this guard period, but this is arbitrary as the GSM handset is not required to demodulate these bits.
  • the differentially encoded data is shown as 202, and it can be seen that the transition from the tail bits to the guard bits is differentially encoded as a single binary 1, which will cause a -90° phase shift of the transmitted signal.
  • the delayed, differentially encoded signal is shown as 203 (assuming 2 symbols delay; and the level shifted signal as 204 (corresponding to the output of the block 109 in Figure 1).
  • the Random Signal 115 is as shown as 205 in Figure 2. For most of the time, the signal is zero, but during four bits of the guard period, during which the level shifted signal 205 is at +v, the random signal assumes a constant value -dv, where dv takes a value at random between 0 and v.
  • GMSK modulator uses a Gaussian filter and frequency modulator.
  • Most implementations of GMSK modulators use digital signal processing techniques to accurately synthesise the required phase without requiring a precise frequency modulator. It is however evident that the above method may be simply modified to cover any form of implementation of the modulator and the patent will cover these by extension.
  • another common implementation of the modulator contains a phase accumulator which digitally adds up phase increments indexed from a look-up table according to the current set of input symbols (four or five depending on the Gaussian filter aperture) and the sample phase.
  • the accumulator can also accept one-shot input from a phase offset register programmable from a micro-controller, this can be used to introduce random phase steps of any desired magnitude.
  • the current phase value in the accumulator is then used to look up sine and cosine sample values in a further lookup table, and these sample values converted into analogue form to produce the desired signal.
  • Figure 3 shows the burst structure for an EDGE modulated signal according to the above GSM standards.
  • EDGE uses 8-PSK modulation with a bit rate which is three times higher than conventional GSM. Each triplet of 3 bits maps to a symbol which has the same duration as the GSM GMSK symbol. EDGE does not apply differential encoding.
  • the signal 301 shows the bit sequence for the tail bits of the burst and the guard period for normal EDGE. It can be seen that instead of 8.25 l's the guard period consists of 24.75 l's. Because EDGE does not use differential encoding and the EDGE modulator provides means to rotate the carrier phase by any amount up to ⁇ 180°, the required phase shifts can be introduced by direct manipulation of just the first symbol (first three bits) of the guard period. Signals 302, 303, and 304 show the appropriate patterns required, taken directly from Figure 2 of GSM 05.04, for phase shifts of ⁇ 90° and 180° compared with the un-shifted carrier generated by 301. Again the phase offset applied can be periodic or selected pseudo-randomly.
  • the method can be generalised to three or more signals, where each signal has a different time delay and different phase sequence.

Landscapes

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

Abstract

L'invention concerne un système de radiotélécommunication cellulaire comprenant une station de base pourvue de deux antennes (107, 114) au moins. Chaque antenne est conçue pour transmettre un signal descendant à une ou plusieurs unités d'abonné mobiles. Lesdits signaux descendants que transmettent les antennes (107, 114) présentent entre eux une certain décalage temporel et une certaine différence de phase, laquelle différence de phase change de temps en temps. En raison de ces différences de phase, si les signaux reçus au niveau d'une station mobile sont en anti-phase sur un intervalle de temps donné du signal descendant, il est fort peu probable que lesdits signaux soient également en anti-phase au niveau de l'intervalle de temps correspondant dans les quelques trames suivantes.
PCT/GB2001/003185 2000-07-14 2001-07-16 Systeme de radiotelecommunication cellulaire WO2002007341A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001270832A AU2001270832A1 (en) 2000-07-14 2001-07-16 Cellular radio telecommunication system

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0017427A GB0017427D0 (en) 2000-07-14 2000-07-14 Cellular radio telecommunication system
GB0017427.6 2000-07-14
GB0114031.8 2001-06-08
GB0114031A GB2365281A (en) 2000-07-14 2001-06-08 Transmit diversity in an indoor gsm cellular system comprising a base station having at least two antennas having mutual time delay and phase difference

Publications (2)

Publication Number Publication Date
WO2002007341A2 true WO2002007341A2 (fr) 2002-01-24
WO2002007341A3 WO2002007341A3 (fr) 2002-05-30

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AU (1) AU2001270832A1 (fr)
WO (1) WO2002007341A2 (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2037592A3 (fr) * 2005-10-31 2010-03-03 Sharp Kabushiki Kaisha Transmetteur sans fil
EP2120365A3 (fr) * 2005-12-20 2010-07-07 Sharp Kabushiki Kaisha Procédé de contrôle de transmission, station de base, unité mobile et système de communication avec une diversité de temporisations
US8098763B2 (en) 2005-09-01 2012-01-17 Sharp Kabushiki Kaisha Wireless transmission device and wireless transmission method
US8165537B2 (en) 2005-12-26 2012-04-24 Sharp Kabushiki Kaisha Wireless transmitter and wireless transmission method
US8290527B2 (en) 2004-07-30 2012-10-16 Airvana, Corp. Power control in a local network node (LNN)
US8483304B2 (en) 2005-10-31 2013-07-09 Sharp Kabushiki Kaisha Radio transmitter, radio communication system, and radio transmission method
US8503342B2 (en) 2004-07-30 2013-08-06 Airvana Llc Signal transmission method from a local network node
US9876670B2 (en) 2004-07-30 2018-01-23 Commscope Technologies Llc Local network node

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US6034987A (en) * 1996-12-17 2000-03-07 Ericsson Inc. System for improving the quality of a received radio signal

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VIJITHA WEERACKODY: "CHARACTERISTICS OF A SIMULATED FAST FADING INDOOR RADIO CHANNEL" PERSONAL COMMUNICATION - FREEDOM THROUGH WIRELESS TECHNOLOGY. SECAUCUS, NJ., MAY 18 - 20, 1993, PROCEEDINGS OF THE VEHICULAR TECHNOLOGY CONFERENCE, NEW YORK, IEEE, US, vol. CONF. 43, 18 May 1993 (1993-05-18), pages 231-235, XP000393165 ISBN: 0-7803-1267-8 *

Cited By (27)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9876670B2 (en) 2004-07-30 2018-01-23 Commscope Technologies Llc Local network node
US8503342B2 (en) 2004-07-30 2013-08-06 Airvana Llc Signal transmission method from a local network node
US8311570B2 (en) 2004-07-30 2012-11-13 Airvana Llc Method and system of setting transmitter power levels
US8290527B2 (en) 2004-07-30 2012-10-16 Airvana, Corp. Power control in a local network node (LNN)
US8116403B2 (en) 2005-09-01 2012-02-14 Sharp Kabushiki Kaisha Wireless transmission device and wireless transmission method
US8625717B2 (en) 2005-09-01 2014-01-07 Huawei Technologies Co., Ltd. Wireless transmission device and wireless transmission method
US8098763B2 (en) 2005-09-01 2012-01-17 Sharp Kabushiki Kaisha Wireless transmission device and wireless transmission method
US8170133B2 (en) 2005-09-01 2012-05-01 Sharp Kabushiki Kaisha Wireless transmission device and wireless transmission method
US8111743B2 (en) 2005-10-31 2012-02-07 Sharp Kabushiki Kaisha Wireless transmitter
US8107897B2 (en) 2005-10-31 2012-01-31 Sharp Kabushiki Kaisha Wireless transmitter
US8121184B2 (en) 2005-10-31 2012-02-21 Sharp Kabushiki Kaisha Wireless receiver
US8121559B2 (en) 2005-10-31 2012-02-21 Sharp Kabushiki Kaisha Wireless transmitter
EP2034624A3 (fr) * 2005-10-31 2010-03-10 Sharp Kabushiki Kaisha Emetteur sans fil
US9144058B2 (en) 2005-10-31 2015-09-22 Sharp Kabushiki Kaisha Multi-mode phase rotation apparatus that transmits CQI depending on the mode used
EP2034625A3 (fr) * 2005-10-31 2013-11-06 Huawei Technologies Co., Ltd. Emetteur sans fil
US8116708B2 (en) 2005-10-31 2012-02-14 Sharp Kabushiki Kaisha Wireless receiver
US8170512B2 (en) 2005-10-31 2012-05-01 Sharp Kabushiki Kaisha Wireless transmitter
US8483304B2 (en) 2005-10-31 2013-07-09 Sharp Kabushiki Kaisha Radio transmitter, radio communication system, and radio transmission method
EP2037592A3 (fr) * 2005-10-31 2010-03-03 Sharp Kabushiki Kaisha Transmetteur sans fil
EP2439861A3 (fr) * 2005-12-20 2012-04-18 Sharp Kabushiki Kaisha Appareil émetteur pour un système de communication avec antennes multiples
US8320849B2 (en) 2005-12-20 2012-11-27 Sharp Kabushiki Kaisha Transmitter for communications system
US8224263B2 (en) 2005-12-20 2012-07-17 Sharp Kabushiki Kaisha Transmitter for communications system
US8099063B2 (en) 2005-12-20 2012-01-17 Sharp Kabushiki Kaisha Transmitter for communications system
EP2120365A3 (fr) * 2005-12-20 2010-07-07 Sharp Kabushiki Kaisha Procédé de contrôle de transmission, station de base, unité mobile et système de communication avec une diversité de temporisations
US8116696B2 (en) 2005-12-20 2012-02-14 Sharp Kabushiki Kaisha Transmitter for communications system
EP2439860A3 (fr) * 2005-12-20 2012-04-18 Sharp Kabushiki Kaisha Procédé de transmission, station de base et station mobile pour un système de communication avec antennes multiples
US8165537B2 (en) 2005-12-26 2012-04-24 Sharp Kabushiki Kaisha Wireless transmitter and wireless transmission method

Also Published As

Publication number Publication date
WO2002007341A3 (fr) 2002-05-30
AU2001270832A1 (en) 2002-01-30

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