Multiplex communications – Generalized orthogonal or special mathematical techniques – Quadrature carriers
Reexamination Certificate
1998-05-28
2001-07-24
Kizou, Hassan (Department: 2662)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Quadrature carriers
C370S207000, C370S209000, C370S335000
Reexamination Certificate
active
06266321
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to the transmission of parallel channels in a code division multiple access system. In particular, the invention relates to the transmission of two channels the data communications requirements of which differ from each other as regards e.g. the amount of data transmitted or data integrity.
2. Prior Art
In their operation, terminals, such as mobile phones, in cellular radio systems need to transmit both payload, or user, data and various control data which there are usually considerably less than user data or which have different quality requirements as regards the integrity of transmitted information. Control and user data are transferred in logically separate channels and it is known several methods for multiplexing those channels into a common physical radio-frequency channel. It is usual to arrange the information transmitted by a radio apparatus into frames in which the control data and user data are located in temporally separable frame components, i.e. multiplexed in the time domain. This kind of transmission method is poorly suited to so-called discontinuous transmission (DTX) if the transmission of control data has to be continuous because of the nature of said data. In discontinuous transmission, the transmission of user data is interrupted for the moments when there is no actual information to be sent (e.g., when the user of a mobile phone stops talking during a call). In code division multiple access (CDMA) systems, however, it is usually desirable to maintain the connection by always sending at least some control data; applying DTX requires pulse-type transmission within a frame.
In systems employing code division multiple access it is known to process control data and user data in two different code channels as shown in FIG.
1
. At the same time,
FIG. 1
also shows other known ways to combine different logic channels in one transmission. The arrangement according to
FIG. 1
is known e.g. from patent document FI 97837 which has the same applicant as this patent application. Line
10
represents a transmitted bit stream which is not very error critical but in which a maximum of 10
−3
bit error ratio (BER) is allowed, and line
11
represents an error critical bit stream in which the BER has to be smaller than 10
−6
. In order to achieve a better bit error ratio the bit stream of line
11
is Reed-Solomon coded in block
12
and interleaved in block
13
. Bit streams from lines
10
and
11
are combined in block
14
and certain tail bits are added to them in block
15
whereafter the resulting combined bit stream is convolution coded in block
16
. Line
18
, the bit stream of which is not error correction coded nor convolution coded, is then multiplexed in block
17
onto the same code channel. To achieve the desired symbol rate, symbol repetition in block
19
and interleaving in block
20
are used if necessary. Spreading is carried out in a coding element
21
using PN
1
code, whereafter the resulting symbol stream is taken to the I branch of a radio-frequency block
22
to produce a radio-frequency transmission together with the lower code channel, to be taken to an antenna
23
.
Frame control header (FCH) bits carrying information on the lower code channel are taken via line
24
to a coding block
25
and therefrom via symbol repetition
26
and interleaving
27
to block
28
where reference symbols
29
needed for synchronising the receiver as well as the power control (PC) symbols
30
are added to the symbol stream. A coding element
31
performs spreading using PN
2
code, which is different from the aforementioned PN
1
, whereafter the timing of the lower code channel with respect to the higher one is adjusted suitable by a delay element
32
before the symbol stream is taken to the Q branch of the radio-frequency block
22
to produce a radio-frequency transmission together with the higher code channel, to be taken to an antenna
23
. The delay generated by the delay element
32
may also be 0, in which case quadrature phase shift keying (QPSK) modulation is used.
In a radio apparatus according to
FIG. 1
, it is possible to use on the lower code channel, due to a lower bit rate, a lower power level than on the higher code channel, thus saving electric power. In small-sized cellular radio system terminals, power saving in transmission is advantageous both to lengthen the discharge time of the batteries and to limit the general noise level of the system. However, the arrangement according to
FIG. 1
is not optimal from the standpoint of using different power levels because of a power amplifier (not shown) in the radiofrequency block
21
and distortion occurring in it. RF amplifiers do not behave in a linear fashion when operated near the saturation region of the amplifier. Especially in the case of modulation methods with wide amplitude variation the intermodulation products generated in the amplifier should be reduced by operating the amplifier in a so-called backed-off mode, which means the amplifier input power must be decreased compared to the power that would drive the amplifier into saturation. The resulting decrease in output power is called the output back-off (OBO). The bigger the OBO, the poorer the amplifier's efficiency which is calculated as the ratio of RF power produced to DC power consumed. In the arrangement according to
FIG. 1
, the OBO is proportional to the power difference of the code channels so that decreasing the power level of the lower code channel with respect to the power level of the higher code channel increases the OBO.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a method and apparatus for transmitting two parallel logic channels using code division with an efficiency better than in the prior art.
The objects of the invention are achieved by using for the logic channels two spreading codes and in the radio-frequency part an IQ modulation method wherein the signal of the first branch is produced as the sum of the spread signals of the different channels, and the signal of the second branch is produced as the difference of the spread signals of the different channels.
SUMMARY OF THE INVENTION
The communications device according to the invention is characterised in that it comprises
first spreading means for spreading data related to a first channel using a first spreading code, and second spreading means for spreading said data related to the first channel using a second spreading code,
third spreading means for spreading data related to a second channel using said first spreading code, and fourth spreading means for spreading said data related to the second channel using said second spreading code,
means for changing the power level of said data related to the second channel with respect to the power level of data related to the first channel, and
combiner means to compile a transmission from spread data related to the first channel and spread data related to the second channel the gain of which has been changed.
The invention is also directed to a communications system in which at least one transmitter apparatus meets the characteristics listed above.
The invention is further directed to a transmission method characterised in that
data related to a first channel are spread in parallel using a first spreading code and a second spreading code,
data related to a second channel are spread in parallel using said first spreading code and said second spreading code,
the power level of said data related to the second channel is changed with respect to the power level of the data related to the first channel, and
a transmission is compiled from spread data related to the first channel and spread data related to the second channel the gain of which has been changed.
The method according to the invention for coding two channels uses two spreading codes such that the bit streams of both channels are spread separately using a first code and a second code. The first channel spread with the firs
Lilja Harri
Pehkonen Kari
Kizou Hassan
Mehra Inder Pal
Nokia Mobile Phones Ltd.
Perman & Green LLP
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