Multiplex communications – Wide area network – Packet switching
Patent
1995-11-03
1996-10-29
Kizou, Hassan
Multiplex communications
Wide area network
Packet switching
370 951, 3701101, 379 59, 379 63, 455 331, 455 383, 455 541, H04B 7005
Patent
active
055703534
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a data transmission method in a CDMA cellular radio system, which comprises in each cell at least one base station communicating with mobile stations within its coverage area and in which system a the station adjusts the transmitting power of the mobile stations within its area by means of power control messages.
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.
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 users can be distinguished from one another in the receivers on the basis of the spreading code of each user.
Correlators provided in the receivers are synchronized with a desired signal, which they recognize on the basis of the spreading code. The data signal is restored in the receiver to the original band by multiplying it again by the same spreading code as during the transmitting stage. 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 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. CDMA differs from the conventional FDMA and TDMA in that the multipath propagation can be exploited in the reception of the signal. The receiver generally utilized in a CDMA system is a so-called rake receiver, which consists of one or more rake branches. Each branch is an independent receiver unit, the function of which is to compose and demodulate one received signal component. Each rake branch can be caused to synchronize with a signal component which has propagated along an individual path, and in a conventional CDMA receiver the signals of the receiver branches are preferably combined, either coherently or non-coherently, whereupon a signal of good quality is achieved.
To ensure the effective operation of the CDMA system, power control has to be used over the connection between a mobile station and a base station. The capacity of the base station can be maximized if it receives with the same signal strength from all mobile stations in its area. The mobile station can measure the strength of the signal it has received from the base station and adjust its transmitting power on the basis of this information. This type of power control method is called "open-loop power control". Furthermore, the base station measures the strength of the signal it has received from the mobile stations and transmits power control messages to the mobile stations which adjust their transmitting power on the basis of these messages. Such a power control method is called "closed-loop power control". These methods may be used simultaneously.
The power control messages required by the closed-loop power control from the base station to a mobile station may be transmitted in two ways to the mobile station. A certain part in the frame st
REFERENCES:
patent: 5056109 (1991-10-01), Gilhousen et al.
patent: 5093840 (1992-03-01), Shilling
patent: 5257283 (1993-10-01), Gilhousen et al.
patent: 5265119 (1993-11-01), Gilhousen et al.
patent: 5267262 (1993-11-01), Wheatley, III
patent: 5329547 (1994-07-01), Ling
patent: 5333175 (1994-07-01), Ariyavisitakul et al.
patent: 5383219 (1995-01-01), Wheatley, III et al.
patent: 5396516 (1995-03-01), Padovani et al.
patent: 5461639 (1995-10-01), Wheatley, III et al.
Frazen et al., "A Study of Code Division Multiple Access", Lund Institute of Technology, Dec. 5, 1992, pp. 23-34.
Lee, William C. Y., "Power Control in CDMA", Gateway to thge Future Technology in Motion, May 19-22, 1991 St. Louis, Mo., pp. 77-80.
Keskitalo Ilkka
Ojanpera Tero
Rikkinen Kari
Kizou Hassan
Nokia Mobile Phones Ltd.
Nokia Telecommunications Oy
LandOfFree
Method of transmitting and receiving power control messages in a does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of transmitting and receiving power control messages in a, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of transmitting and receiving power control messages in a will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1790741