Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1997-01-24
1999-04-06
Vo, Nguyen
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
455440, 455456, 455562, H04Q 720
Patent
active
058930337
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase of international application PCT/FI96/00292, filed May 23, 1996.
BACKGROUND OF THE INVENTION
The invention relates to a cellular radio system comprising in each cell at least one base station communicating with terminal equipments located within its area, which base stations comprise means for measuring the direction angle and distance of each terminal equipment with respect to the base station, means for calculating the location of each terminal equipment in the coverage area of the base station on the basis of the direction angle and distance of the terminal equipment, and which terminal equipments comprise means for maintaining a list of nearby base stations, and means for measuring the signal strength from the base stations that are in the list kept by the terminal equipment, in order to determine the need for a handover.
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 earlier developed FDMA and TDMA methods. CDMA has several advantages over those earlier developed methods, for example spectral efficiency and the simplicity of frequency planning. An example of a known CDMA system is disclosed in the EIA/TIA Interim Standard: Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, TIA/EIA/IS-95, July 1993, EIA/TIA IS-95, which is incorporated herein by reference.
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 respective base station and a respective 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 respective receivers are synchronized with a desired signal, which they recognize on the basis of a spreading code. The data signal is restored in the respective 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 base stations to subscribers, 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.
In a typical mobile phone environment, the signals between a base station and a terminal equipment propagate along several paths between the transmitter and the receiver. This multipath propagation is
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A.F. Naguib, A. Paulraj: Performance of CDMA Cellular Networks with Base-Station Antenna Arrays; International Zurich Seminar on Digital Communications; Mar. 1994; pp. 87-100.
Jolma Petri
Keskitalo Ilkka
Laiho-Steffens Jaana
Muszynski Peter
Nokia Telecommunications: Oy
Vo Nguyen
LandOfFree
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