Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Patent
1997-01-24
1999-10-12
Vo, Nguyen
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
455434, H04B 138, H04M 100
Patent
active
059666706
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for transmitting a pilot signal in a cellular radio system, which comprises in each cell at least one base station communicating with mobile stations located within its area, and in which method the base stations transmit a data signal in the downlink transmission direction by using radiation patterns changing in time, and which base stations transmit a pilot signal to the mobile stations.
The present invention is applicable for use in a data transmission system applying any multiple access method, but especially in a cellular system utilizing code division multiple access. Code division multiple access (CDMA) is a multiple access method, which is based on the spread spectrum technique and which has been applied recently in cellular radio systems, in addition to the prior FDMA and TDMA methods. CDMA has several advantages over the prior methods, for example spectral efficiency and the simplicity of frequency planning. An example of a known CDMA system is disclosed in the broadband cellular radio standard EIA/TIA IS-95.
In the CDMA method, the narrow-band data signal of the user is multiplied to a relatively wide band by a spreading code having a considerably broader band than the data signal. In known test systems, bandwidths such as 1.25 MHz, 10 MHz and 25 MHz have been used. In connection with multiplying, the data signal spreads to the entire band to be used. All users transmit by using the same frequency band simultaneously. A separate spreading code is used over each connection between a base station and a mobile station, and the signals of the different users can be distinguished from one another in the receivers on the basis of the spreading code of each user.
Matched filters provided in the receivers are synchronized with a desired signal, which they recognize on the basis of a spreading code. The data signal is restored in the receiver to the original band by multiplying it again by the same spreading code that was used during the transmission. Signals multiplied by some other spreading code do not correlate, in an ideal case, and are not restored to the narrow band. They appear thus as noise with respect to the desired signal. The spreading codes of the system are preferably selected in such a way that they are mutually orthogonal, i.e. they do not correlate with each other.
In a CDMA cellular radio system, it is possible to use a so-called pilot channel in the transmission direction of a base station to subscriber equipments, i.e. in the downlink direction. A pilot channel is a signal which is transmitted with a specific spreading code and utilizing the same frequency band on which the actual traffic channels are situated, the pilot signal being distinguishable from them only on the basis of the spreading code. The pilot signal is a channel known and listened to by all subscriber equipments within the cell area, and it is used, for example, in power measurements and in the generation of a coherent phase reference. Each base station of the system transmits its own pilot signal on the basis of which the subscriber equipments can distinguish the transmissions of different base stations from each other.
U.S. Pat. No. 5,109,390, which is incorporated herein by reference, and the aforementioned IS-95 standard disclose a prior art CDMA cellular system utilizing a separate pilot channel that is transmitted to the same coverage area with the data signals.
In a typical mobile phone environment, the signals between a base station and a mobile station propagate along several paths between the transmitter and the receiver. This multipath propagation is mainly due to the reflections of the signal from the surrounding surfaces. Signals which have propagated along different paths arrive at the receiver at different times due to their different transmission delays. In the CDMA, the multipath propagation can be exploited in the reception of the signal in the same way as diversity. The receiver generally utilized in a CDMA system is a multibranch recei
REFERENCES:
patent: 5109390 (1992-04-01), Gilhousen et al.
patent: 5267261 (1993-11-01), Blakeney et al.
patent: 5576717 (1996-11-01), Searle et al.
patent: 5596333 (1997-01-01), Bruckert
patent: 5603089 (1997-02-01), Searle et al.
patent: 5708441 (1998-01-01), Kanai
TIA/EIA/IS-95, 1995, pp. 6-83 & 6-84, 6-95-6-98, 6-147-6-158, 6-197-6-202, 7-1 & 7-2, 7-21 & 7-22.
Naguib et al., "Performance of CDMA Cellular Networks With Base-Station Antenna Arrays," May 18, 1994, pp. 88-100.
Jolma Petri
Keskitalo Ilkka
Laiho-Steffens Jaana
Muszynski Peter
Nokia Telecommunications Oy
Vo Nguyen
LandOfFree
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