Data transmission method, base station, and subscriber terminal

Details Data transmission method, base station, and subscriber terminal Data transmission method, base station, and subscriber terminal

1996-04-19

1998-05-19

Olms, Douglas W.

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

H04B 7216

Patent

active

057545413

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a data transmission method in a CDMA cellular radio network having in each cell at least one base station which communicates on a specified traffic channel with the terminal equipments located within its area, the signal of the users being divided into bursts in the time domain.
CDMA (Code Division Multiple Access) is a multiple access method based on a spread spectrum technique, and it has been recently put into use in cellular radio systems in addition to previously used FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access). CDMA has many advantages over the prior methods, such as spectrum efficiency, simplicity of frequency planning, and traffic capacity.
In a CDMA method, a narrowband data signal of a user is multiplied to a relatively wide band of a traffic channel by a spreading code having a much wider band than the data signal. Traffic channel band widths used in known cellular network test systems include, e.g., 1.25 MHz, 10 MHz and 25 MHz. The multiplication spreads the data signal over the entire band to be used. All the users transmit simultaneously in the same frequency band, i.e. traffic channel. A different spreading code is used on each connection between a base station and a subscriber terminal, and the signals of the users can be distinguished from one another in the receivers on the basis of the spreading code of the connection.
Correlators in conventional CDMA receivers synchronize with a desired signal, which they recognize on the basis of the spreading code contained in the signal. In the receiver, the data signal is restored to the original band by multiplying it by the same spreading code as in the transmission step. Ideally, the signals that have been multiplied by some other spreading code in the transmission step do not correlate with the spreading code used in the receiver and are thus not restored to the narrow band. In view of the desired signal, they thus appear as noise. If possible, the spreading codes of the system are selected in such a way that the codes in each cell of the system do not correlate with one another, i.e. they are mutually orthogonal.
U.S. Pat. No. 4,901,307 describes a CDMA system in which a higher traffic capacity is achieved with the multiple access method concerned than with the earlier methods.
In both FDMA and TDMA multiple access methods, each user is assigned a specified traffic channel on which the other users cannot communicate. In FDMA, the channel is a specified narrow frequency band, and in TDMA, the channel is a specified time slot on a given frequency band. In principle, the traffic capacity of these systems can thus be simply defined as a sum of separate channels, either frequencies or time slots, available. If all the frequencies or time slots are busy, new users cannot be served until one of the existing users breaks the connection.
In a CDMA system, all the users transmit on the same, relatively wide frequency band. The traffic channel of each user is provided by a spreading code characteristic of the respective connection of each user on the basis of this code, the transmission of user is distinguished from the transmissions on the other connections, as described above. As there are usually a large number of spreading codes in use, the CDMA system does not have such an absolute limit for the capacity as the FDMA and TDMA systems have. CDMA is an `interference-restricted` system, in which the number of users is restricted by the amount of interference that they are allowed to cause to one another. Since in practice, the spreading codes of the users are not completely orthogonal, especially not as compared with the spreading codes used in a neighbouring cell, simultaneous users interfere with one another to some extent. This mutual interference is called multiple access interference. When the number of users increases, the interference they cause to one another increases also, and with a certain number of users the interference is so great as to weaken the

REFERENCES:
patent: 4574378 (1986-03-01), Kobayashi
patent: 4630261 (1986-12-01), Irvin
patent: 4630262 (1986-12-01), Callens et al.
patent: 4901307 (1990-02-01), Gilhousen et al.
patent: 4980886 (1990-12-01), Berstein
patent: 5101501 (1992-03-01), Gilhousen et al.
patent: 5109390 (1992-04-01), Gilhousen et al.
patent: 5319638 (1994-06-01), Lin
patent: 5347521 (1994-09-01), Zijerhand
patent: 5491801 (1996-02-01), Jain et al.
Kleinrock et al., "Packet Switching in Radio Channels: Part I-Carrier Sense Multiple-Access Modes and Their Throughtput-Delay Characteristics", IEE Transactions on Communications, vol. Com-23, No. 12, Dec. 1975, pp. 1400-1416.

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