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
  • H04B7/10—Polarisation diversity; Directional diversity

Definitions

• the invention relates to a transmission method to be employed in a radio system comprising at least one transmitter and one receiver which em- ploy TDD duplexing when setting up a connection with each other, and in which signals propagated on different signal paths are received by means of antennas.
• signals between a base station and a mobile station propagate on several paths between a transmitter and a receiver.
• This multipath propagation is mainly caused by the signal being reflected from surrounding surfaces.
• the signals propagated on different paths are received by the receiver at different times on account of different transit delays.
• signal reception multipath propagation can be utilized in the same way as diversity.
• a multi-branch receiver structure is commonly employed in which each branch is synchronized to a signal component propagated on a different path.
• the signals of different receivers are combined in the receiver, preferably coherently or incoherently. A high quality signal can be generated by the combining manners.
• a commonly employed method in radio systems is Frequency Division Duplex (FDD) in which a signal is transmitted and received in different frequency bands.
• FDD Frequency Division Duplex
• the FDD method is employed in a radio system in conjunction with distributed antennas, downlink channel estimation is particularly problematic in advance. Since the downlink channel is unknown in the trans- mitter of a FDD base station, it is impossible for the base station to transmit a downlink signal as optimally as to receive an uplink signal. Of course, the problem becomes even more difficult when downlink traffic is heavier than uplink traffic. The aforementioned situation occurs when browsing through WWW (World Wide Web) pages, for instance.
• WWW World Wide Web
• the invention further relates to a radio system comprising at least one transmitter and one receiver which employ TDD duplexing when setting up a connection, said transmitter receiving signals propagated on different signal paths by means of antennas.
• the radio system of the invention is characterized in that it comprises transmission means which receive a signal from several polarization directions, measuring means which measure the signals received by the transmitter, which are combined into one signal on the basis of the measure- ment, and in which the transmission means polarize the signal and transmit the polarized signal to the receiver in several polarization directions on the basis of the measurement performed by the measuring means.
• the invention is particularly suited to radio systems employing TDD duplexing.
• the invention enables downlink and/or uplink channels to be estimated in advance.
• the method of the invention is particularly well suited to systems in which the data transmission need in the uplink and downlink directions is different.
• multipath components and antennas are combined in the transmitter.
• linear intersymbol interference is elimi- nated in the transmitter.
• Intersymbol interference refers to interference caused by crosstalk between successive symbols propagating in the multipath channel.
• the invention further enables transmission to occur in different polarization directions which are, if necessary, differently weighted.
• the polarization directions are weighted on the basis of the signals received from the above polarization directions.
• the signal is polarized in the transmitter and the receiver. Polarization enables extremely different channels to be generated.
• FIG. 2 shows a schematic block diagram of the transceiver employed in the radio system of the invention.
• Figure 1 displays a radio system comprising a base station 200 and a subscriber terminal 100 which in practise is a mobile telephone, for example.
• the subscriber terminal 100 and the base station 200 operate as transceivers.
• the subscriber terminal 100 comprises an antenna 101
• the base station 200 comprises a number of antennas 201.
• the subscriber terminal 100 can also comprise several antennas 101.
• the antennas 101, 201 oper- ate as transceiver antennas.
• FIG. 2 displays the schematic structure of the transceiver employed in the radio system of the invention.
• the transceiver comprises an antenna 201 which in practise operates as a transceiver antenna.
• the transceiver further comprises radio frequency components 112, 124, a modulator 123, a demodulator 113 and a control block 102.
• the control block 102 typically controls other transceiver blocks.
• the radio frequency components 112 transmit the radio frequency signal supplied from the antenna 201 to an intermediate frequency.
• the radio frequency components 112 are connected to the demodulator 113 which restores a broadband signal to a narrowband data signal, if a CDMA signal is involved.
• the invention is not, however, restricted to the CDMA system, but the system can be TDMA, for instance, or a combination of said systems.
• the transceiver further comprises a coder 122 and a decoder 114.
• the data signal is supplied from the demodulator 112 to the decoder 114 which decodes the data signal in a suitable manner.
• the signal supplied to the decoder 114 is convolution coded, for example.
• the operation of the decoder 114 can be based on the Viterbi algorithm, for example.
• the decoder 114 typically decodes the encryption and interleaving of the signal.
• the coder 122 receives a signal and transmits the encoded signal to the modulator 123.
• the coder 122 employs convolution coding, for instance.
• the coder 122 further encrypts the signal, for example.
• the coder 122 further interleaves the bits or bit groups of the signal.
• the convolution coded signal is supplied to the modulator 123 which in practise operates as a symbol modulator.
• the transceiver is of CDMA type
• the signal received from the modulator 123 is pseudonoise encoded to be a broadband spread spectrum signal.
• the spread spectrum signal is converted into a radio frequency signal in a known manner in the radio frequency components 124.
• the radio frequency components 124 transmit the signal to a radio path via the antenna 201.
• the transceiver further comprises measuring means 210 and transmission means 220.
• the measuring means 210 measure the signals received by the antenna 201.
• the transmission means 220 and the measuring means 210 are operatively connected with each other.
• the transmission means 220 transmit signals to the radio path on the basis of the measurement data obtained from the measuring means 210.
• the measuring means 210 can be located in the radio frequency components 112, for example.
• the transmission means 220 are in practise located in the radio frequency components 124, for example.
• a subscriber terminal 100 transmits the signal to a base station 200 which routes forward the received signal to a PSTN network, for example.
• the radio system employs the TDD (Time Division Duplex) method. In the TDD method, the uplink and downlink directions operate at the same frequency, time-divisionally separated. The advantages of the TDD method employed in the described radio system can be seen particularly in the downlink data transfer.
• the radio system further comprises measuring means 210 and transmission means 220. In the solution of the figure the measuring means 210 and the transmission means 220 are operatively connected with the base station. When the subscriber terminal 100 transmits a signal to the base station 200, the signals propagate on different paths to the base station.
• the transmitted signal is reflected from possible obstacles on the radio path, whereby the base station 200 receives multipath components.
• Time delay and amplitude and phase changes occur between the multipath components.
• the amplitude changes are caused by multipath propagation which is largely dependent on the frequency employed. For example, the fadings of adjoining channels can be very different.
• the base station receives the multipath components preferably by means of the distributed antennas 201. From the antennas the signals are supplied to the measuring means 210 which weight the signals, if necessary.
• the different antennas 201 receive signals whose characteristics deviate from each other. Consequently, it is possible to weight the signals in a different manner. A strong signal is usually more weighted than a weak signal.
• the measuring means 210 combine the weighted signals. In the solution of the figure the measuring means 210 estimate the uplink channel.
• the measuring means 210 measure, for instance, delay, amplitude and phase from the signals received by the subscriber terminal 100 and the base station 200.
• the signals are received by combining multipath components received by several antenna branches or antennas.
• Measurement results obtained from the measuring means 210 are utilized in transmitting a signal to the subscriber terminal 100. It is possible to employ the measurement results since the uplink and downlink directions use the same frequency.
• the transmission means 220 transmit signals in such a manner as to enable the subscriber terminal 100 to receive preferably only one strong signal component by its antenna 101. It is possible to simplify the structure of the receiver 100 on account of the above mentioned.
• the invention enables the antenna beam formed by the distributed antennas together to be directed towards the subscriber terminal.
• the distributed antennas 201 direct their beams towards the subscriber terminal 100 on the basis of channel measurement, enabling the base station to receive an optimal signal.
• the subscriber terminal 100 can comprise several antennas 101.
• the subscriber terminal 100 can also comprise transmission means 220 and measuring means 210 which measure the downlink channel. In the above situation the subscriber terminal 100 transmits a signal to the base station 200 on the basis of the downlink channel estimate.
• the transmission means 220 regulate their transmission power on the basis of the measurement performed by the measuring means 210.
• the transmission power regulation results in a decreased need for power regulation signalling and fewer signalling errors. If the channel between the sub- scriber terminal 100 and the base station 200 is weak on account of fadings, the transmission power is not necessarily raised. In the above situation the transmission of the signal, a frame for example, is inhibited. Transmission power raised too high can cause interference in the radio system.
• the trans- mission means 220 also eliminate linear intersymbol interference from the signal to be transmitted on the basis of the signals received by the transmitter 200. The receiver 100 is able to receive a higher-quality signal owing to the interference elimination.
• the same frequency employed in the uplink and downlink channels allows the structure of receiver to be less complex.
• the transmitter can be of the Pre-RAKE type.
• a Pre-RAKE transmitter it is possible to combine the multipath components and antenna signals on the basis of the channel estimated by the receiver.
• the structure of the receiver is simplified in such a manner that elimination of the linear intersymbol interference is per- formed in the transmitter.
• the subscriber terminal 100 and the base station 200 preferably employ polarization transmission and polarization reception.
• the polarization is implemented by horizontal and vertical polarization.
• the use of different polarization directions allows different channels to be implemented at least in- doors.
• Polarization branches are made use of in the polarization transmission and reception.
• the measuring means 210 weight the signals supplied through the polarization branches in such a manner as to achieve the best possible signal/noise ratio.
• the different polarization directions can fade almost independently of each other in the channel between the base station and the sub- scriber terminal.
• the faded polarization components can be combined in the reception in the same manner as the multipath propagation signals.
• the measuring means 210 estimate the multipath components and signals supplied through the polarization branches.
• the transmission means 220 transmit their signal on the basis of the estimate of the measuring means 210.
• the signal can be transmitted and received in two different polarization directions, for instance.
• the transmitter antennas transmit the same data from each antenna.
• the method is extremely well suited to be employed in systems in which the last junction line of a fixed telephone network to a subscriber is replaced by a radio network, in other words in so-called WLL (Wireless Local Loop) applications.
• the subscriber terminal 100 is stationary or moves slowly in the WLL applications.
• the WLL technique allows the use of the SDMA (Space Division Multiple Access) technique.
• SDMA Space Division Multiple Access
• the users are distinguished by means of location. This is performed by regu- lating the receiver antenna beams in the base station in the desired directions in accordance with the mobile station locations.
• adaptive antenna arrays in other words phased antennas, are used in the radio system.
• the received signal is processed in such a manner as to enable the mobile stations to be monitored.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)
• Radio Transmission System (AREA)
• Radar Systems Or Details Thereof (AREA)
• Radio Relay Systems (AREA)
• Bidirectional Digital Transmission (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=8548411

Family Applications (1)

Country Status (7)

Families Citing this family (3)

Family Cites Families (5)

• 1997
  • 1997-03-17 FI FI971120A patent/FI103445B1/fi active
• 1998
  • 1998-03-13 CN CN 98803383 patent/CN1250561A/zh active Pending
  • 1998-03-13 WO PCT/FI1998/000226 patent/WO1998042085A2/en not_active Application Discontinuation
  • 1998-03-13 EP EP98909525A patent/EP0968575A2/en not_active Withdrawn
  • 1998-03-13 JP JP54016898A patent/JP2001516535A/ja active Pending
  • 1998-03-13 AU AU64029/98A patent/AU731614B2/en not_active Ceased
• 1999
  • 1999-09-16 NO NO994495A patent/NO994495L/no unknown

Non-Patent Citations (1)

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