Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-01-15
2004-04-20
Phu, Phoung (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S146000, C375S150000
Reexamination Certificate
active
06724806
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a variable rate transmission method in radio communications, and more particularly to a variable rate transmission method and equipment for implementing it, which are applicable to direct spreading code division multiple access (DS-CDMA) in mobile communications.
BACKGROUND ART
In DS-CDMA, information data undergoes narrow-band carrier modulation (such as binary phase shift keying or quadrature phase shift keying), followed by spreading using a higher rate binary spreading code sequence, and by transmission. On a receiving side, the received signal is-multiplied by the same binary spreading code sequence as that used in the transmission to acquire the original narrow-band modulated signal, followed by demodulation to the original transmitted data.
In actual communications, however, the information rate is not always kept constant. For example, although voice communications is carried out at a rate of about 8 kbps, pauses in which no voice signal is present takes place frequently, and lowering the information rate in the pauses little degrades the voice quality. It is very important for the CDMA to reduce transmission power during a low information rate to minimize interference on other channels.
This is because the magnitude of interference determines the communication quality. Thus, implementation of the variable rate transmission method is important in the CDMA.
As one of the variable rate methods, intermittent transmission is known. It carries out, during a maximum information rate, continuous transmission, but reduces, at lower rates, the average transmission rate down to an information rate by decreasing the ratio of transmission intervals with maintaining the instantaneous transmission rate at the maximum, thereby trying to reduce the interference amount.
As for the intermittent transmission, refer to the following literature.
Reference 1: R. Padovani, R., “Reverse link performance of IS-95 based cellular systems”, IEEE Personal Communications, pp. 28-34, 3rd Quarter, 1994.
Reference 2: Y. Okumura and F. Adachi, “Variable rate data transmission with blind rate detection for coherent DS-CDMA mobile radio”, IEE Electron Lett. vol. 32, pp. 1865-1866, September 1996.
As another variable rate transmission method in the CDMA, continuous transmission is known which not only varies the instantaneous transmission rate of radio in response to variations in the information rate, but also controls the transmission power in response to the transmission rate.
The average interference amount can also be reduced in the continuous transmission as in the intermittent transmission because the transmission power is varied (in inverse proportion to) the transmission rate in the continuous transmission.
In the CDMA technology, the transmission power control is essential which controls the transmission power so that a received SIR (signal to interference ratio) measured on the receiving side matches a predetermined target SIR in response to results obtained by comparing the two values (refer to Japanese patent application laid-open No. 8-162972/1996 applied by the assignee of the present invention, for example). In this technique, the SIR of a received signal is measured slot by slot and compared with the target SIR, the slot being defined as a section in a received signal sandwiched by two successive pilot signals of a known pattern which are transmitted periodically. Then, a transmission control command is generated in response to the compared result, and is transmitted to the transmitting side to be reflected on the transmission power control. The transmission period of the transmission power control command is a slot interval, that is, the measuring interval.
The transmission power control cannot maintain constant reception quality if it uses the same target SIR for different rates when varying the transmission power in response to the transmission rate. Therefore, the conventional transmission power control that employs the target SIR cannot be applied without change to a transmitted signal whose transmission power is controlled in response to the transmission rate.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a transmitting method and receiving method and equipment for implementing the variable rate transmission method employing the foregoing continuous transmission scheme.
Another object of the present invention is to implement the transmission power control capable of achieving constant receiving quality on the receiving side regardless of rate variations when the transmission power is varied in response to the transmission rate (in inverse proportion to it, for example).
In order to accomplish the objects aforementioned, according to the invention claimed in claim
1
a variable rate transmission method comprising the steps of:
preparing a plurality of orthogonal codes whose lengths differ from each other and whose information rates are at least twice a maximum information rate, for one communication with one receiving side in which a rate of information to be transmitted changes, before the communication starts;
selecting, during the communication, in accordance with the changing rate of information to be transmitted, one of the prepared orthogonal codes;
multiplying a signal to be transmitted including the information by the selected orthogonal code; and
transmitting the signal to be transmitted which has been multiplied by the selected orthogonal code, without increasing transmission amount for transmitting information about the selected orthogonal code, during the communication,
wherein each of the plurality of orthogonal codes corresponds to each value that the rate of information to be transmitted assumes.
The method further includes continuously transmitting the signal which has been multiplexed by the selected orthogonal code, even if the selected orthogonal code has changed.
According to the invention as claimed in claim
2
, in the variable rate transmission method as claimed in claim
1
, where the step of preparing the orthogonal codes prepares orthogonal codes obtained by successively generating, using lower degree matrices under a predetermined rule, higher degree (2
N
×2
N
elements, where N is an integer equal to or greater than one) matrices with their row vectors orthogonal to each other, and by selecting one of row vectors of one of the matrices with a degree varying in accordance with each value that the rate of information to be transmitted assumes.
According to the invention as claimed in claim
3
, in the variable rate transmission method as claimed in claim
2
, where the step of preparing orthogonal codes prepares the orthogonal codes such that the orthogonal codes no not include both an orthogonal code corresponding to one of row vectors of a 2
k
×2
k
element matrix (k is an integer less than N), and an orthogonal code corresponding to any one of row vectors of any one of 2
J
×2
j
element matrices (j is an integer greater than k) which includes as its sub-vector, the one of the row vectors of the 2
k
×2
k
element matrix or a row vector obtained by inverting the one of the row vectors of the 2
k
×2
k
element matrix.
According to the invention claimed in claim
4
, in the variable rate transmission method as claimed in claim
1
, the signal is further multiplied by a spreading code sequence to be spectrum spread, and is transmitted at transmission power corresponding to the rate of information to be transmitted.
According to the invention as claimed in claim 5, the variable rate transmission method as claimed in claim
4
, further comprises the steps of:
inserting pilot symbols of a known pattern periodically into data symbols corresponding to the information to be transmitted; and
varying the rate on a frame by frame basis, the frame consisting of a plurality of slots defined by the pilot symbols.
According to the invention as claimed in claim
6
, the variable rate transmission method as claimed in claim
5
, further comprises the step of contro
Adachi Fumiyuki
Okumura Yukihiko
Brown & Raysman Millstein Felder & Steiner LLP
NTT Mobile Communications Network Inc.
Phu Phoung
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