The present invention relates to a radio communication system and, more particularly, to a discontinuous transmission (DTX) bit processing method for an adaptive multirate modulation.

With the emergence of the information society, the focus of telecommunication services has shifted from low-speed voice communication services to multimedia services providing audio, video as well as voice communication. In order to support multimedia services that require high speed data transmission, it is critical to maximize the channel capacity by effectively utilizing the limited resources such as power and frequency bands.

For effective utilization of the limited resources, various modulation techniques have been developed. In the case of a wired network, channel characteristics are stable so that high efficiency QAM modulation/demodulation techniques are widely used. A radio network, generally, is not stable compared to the wired network, due to multipath transmission and fading according to a Doppler effect. A frequency shift keying (FSK) or a phase shift keying (PSK) modulation in which 1∼2 bits are transferred per 1Hz is often used. However, recently, with the development in modulation techniques, a multirate modulation scheme such as 16-QAM, 64-QAM, or the like is adopted even in the radio network.

The current and undergoing radio communication systems in the domestic and foreign countries are likely to adopt a fixed modulation scheme regardless of the channel state between the base station and the subscriber. Such a system has a problem in that a low rate modulation scheme is used even when a high rate modulation can be used in a good channel state, resulting in a failure to maximize the system capacity.

Also, the system adopting the fixed modulation scheme can not change the modulation rate such that the same low rate modulation is used even when the channel state is bad. Accordingly, the transmission quality is further degraded, and this causes the communication channel to break.

In order to solve the above problems, the 3^rd Generation Partnership Project (3GPP) standard conference has discussed a High speed Downlink Packet Access (HSDPA) on the basis of adaptive modulation.

In the quadrature phase shift keying (QPSK) modulation, a DTX bit can be allocated to one of In-Phase (I) and Quadrature (Q) axes in the IQ plane so that the transmission rate can be decreased by turning off the transmission power provided to the axis to which the DTX bit is allocated.

Since the discussion on HSDPA started, the multirate modulation scheme such as the QAM (Quadrature Amplitude Modulation) that generates four bits out of one symbol has been adopted for flexible modulation, in which the DTX bit allocation as in the QPSK is not adopted. In the HSDPA of the 3GPP standard, a multirate modulation such as 16-QAM or 64-QAM as well as QPSK, is used. In the case of the multirate modulation, a problem is how to process the DTX bits. In this regard, WO 02/065723 A1 to Mitsubishi has proposed a DTX bit processing method in which DTX bits are grouped into one symbol and then mapped onto the origin of an IQ plane.

FIG. 1A, FIG. 1B, FIG. 2A, and FIG. 2B illustrate the DTX bit processing method proposed by Mitsubishi. As shown in FIG. 1A, the empty region of a frame is allocated to a 4-bit DTX symbol and then the DTX symbol is mapped onto the origin of the IQ plane (see FIG. 1B). In FIG. 2A and FIG. 2B, the empty region of a frame is allocated to each 4 bit symbol to be transmitted by 2 bits so that only 4 symbol points of the IQ plane are used for transmission. Similar methods are proposed in EP 1 271 874 and EP 0 961 515.

The above DTX bit processing method has a drawback in that this method may not be compatible with the currently developing system since this method requires modification of the current multiplexing scheme. Also, it is very complicated to implement the algorithm in which DTX bits are grouped in one symbol so as to be mapped onto the origin or 2 bits are inserted into each data symbol so that the data symbols can be transmitted using only four symbol points on the IQ plane.

A DTX bit processing method for a multi rate modulation scheme, a DTX bit processing system, and a transmitter of a base station modem are provided according to claims 1, 5, and 6, respectively.

The mapping point is calculated by averaging the signal points in which the bits corresponding to the non-DTX bits of the symbol are identical with each other on the IQ plane. The mapping point is set in consideration of at least one of the number of the non-DTX bits, the number of the selected signal points, and the locations of the selected signal points on the IQ plane. The symbol is mapped onto an origin of the IQ plane, when all bits of the symbol are DTX bits.

The symbol is mapped onto a signal point in which the bits are identical with the bits comprised in the symbol on the IQ plane when the symbol has no DTX bit. The mapping point is set in consideration of plus and minus symbols of the signal points on the IQ plane. In some embodiments, the mapping point is set in consideration of at least one of the number of the non-DTX bits, the number of the selected signal points, and the locations of the selected signal points on the IQ plane.

In certain embodiments, the symbol is mapped onto an origin of the IQ Plane, when all bits of the symbol are DTX bits. The symbol is mapped onto a signal point of which the bits are identical with the bits comprised in the symbol on the IQ plane, when the symbol has no DTX bit. In one embodiment of the present invention, a DTX bit processing method reduces the transmission power consumption by mapping a symbol having DTX bits onto a predetermined signal point, on an IQ plane.

These and other embodiments of the present invention will also become readily apparent to those skilled in the art from the following detailed description of the embodiments having reference to the attached figures, the invention not being limited to any particular embodiments disclosed.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

FIG. 1A illustrates a conventional method for inserting DTX bits into symbols in accordance with one or more embodiments;

FIG. 1B illustrates how a symbol having DTX bits of FIG. 1A is mapped on an IQ plane in accordance with one or more embodiments;

FIG. 2A illustrates a conventional method for inserting DTX bits into symbols in accordance with one or more embodiments;

FIG. 2B illustrates how a symbol having DTX bits of FIG. 2A is mapped on an IQ plane in accordance with one or more embodiments;

FIG. 3 is a schematic view illustrating a transmitter of a base station modem adopting a DTX bit processing method in accordance with one embodiment of the present invention;

FIG. 4A is an exemplary constellation diagram of a 16-QAM in accordance with one embodiment;

FIG. 4B illustrates how a symbol having DTX bits is mapped on an IQ plane in accordance with one embodiment of the present invention; and

FIG. 5 is a flowchart illustrating a DTX bit processing method in accordance with one embodiment of the invention.

Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects in accordance with one or more embodiments of the system.

Referring to FIG. 3, a transmitter of a base station modem comprises a transport channel (TrCH) multiplexer 10 for multiplexing radio frames from all TrCHs into a composite transport channel (CCTrCH); a DTX insertion module 20 for inserting DTX bits into the radio frames of the CCTrCH; a physical channel segmentation module 30 for segmenting the CCTrCH into different physical channels (PhCHs); an interleaver 40 for interleaving the segments; and a PhCH mapping module 50 for mapping the segments onto the corresponding PhCHs.

FIG. 4A is a typical constellation diagram of a 16-QAM and FIG. 4B is a constellation diagram for illustrating how a symbol having DTX bits is mapped on an IQ plane in accordance with the present invention. As shown in FIG. 4A, 4 bits are allocated to determine a symbol in the 16-QAM (as a matter of course, 6 bits are to be allocated in the 64-QAM), for example. Accordingly, one to four DTX bits can be allocated to the symbol.

In the multirate modulation of MQAM, 'M' is the exponentiation value of 2. Accordingly, 1 to M DTX bits can be inserted into one symbol. DTX bits can be positioned in the symbol modulated by MQAM according to the number of DTX bits. In some embodiments, the symbol in which M bits are DTX bits is mapped onto the origin of the IQ plane and the symbol including DTX bit(s) less than M are mapped onto a predetermined signal point, on an IQ plane. The IQ plane is defined by averaging the vectors of the signal points. The bits corresponding to the non-DTX bits of the symbol are identical with each other, in consideration of the quadrants to which the signal points are located, for example.

Referring to FIG. 4B, when a symbol having, for example, a bit order of 1XX0 (X is DTX bit) is input, 4 signal points (e.g., 1000, 1010, 1100, and 1110) are selected on the IQ plane. The left most bit and the right most bit can be identical with each other. The vector values of the 4 signal points are averaged so as to obtain a mapping point (S). Accordingly, the symbol of 1xx0 is mapped onto the mapping point (S).

In the same manner, when, for example, a symbol of 1XXX is input, eight signal points (i.e., 1011, 1001, 1010, 1000, 1110, 1100, 1111, and 1101) of which the left-most bit is one and the others are DTX bits are selected and averaged for calculating the mapping point (S). The mapping point (S) for the symbol of 1xxx is defined in consideration of the number of the non-DTX bits, the number of the selected signal points, and the locations of the selected signal points on the IQ plane so as to distinguish it from the mapping point for the symbol of 1xx0. In certain embodiments, the symbol in which all the bits are DTX bits is mapped onto the origin of the IQ plane. For example, 16QAM is adopted in one embodiment.

FIG. 5 is a flowchart illustrating the DTX bit processing method in accordance with one embodiment of the present invention. In FIG. 5, when a 2^M bit QAM modulated signal is input to the DTX insertion module 20 from the TrCH multiplexer 10, the DTX insertion module 20 inserts DTX bits into the signal to be transmitted, if required. After passing through the DTX insertion module 20, the signal is segmented by the physical channel segmentation module 30, interleaved by the interleave 40 and then transmitted to the physical channel mapping module 50 (at step S106), for example.

The physical channel mapping module 50 determines whether or not there exists DTX bit(s) in the input signal (step S102). In some embodiments, if there is a DTX bit in the symbol, the physical channel mapping module 50 selects the signal points in which the bit(s) corresponding to the non-DTX bit(s) of the symbol is/are identical with each other on the IQ plane (step S103) and averages the vectors of the signal points on the basis of the I and Q axes of the IQ plane so as to define a mapping point (S) (step S104). In this case the mapping point (S) is defined in consideration of the number of the non-DTX bits, the number of the selected signal points, and the locations of the selected signal points on the IQ plane.

Subsequently, the physical channel mapping module 50 maps the symbols onto the mapping point (S) (step S105) and transmits the symbol in the power level associated with the mapping point (S) (step S106). The symbol in which all the bits are DTX bits is mapped onto the origin of the IQ plane.

In certain embodiments, in the DTX bit processing method, the symbol having the DTX bit(s) is mapped onto a mapping point which requires a low transmission power lever so that it is possible to minimize the transmission power consumption without modifying the typical modulation scheme for the HSDPA system.

Also, the DTX bit processing method of the present invention has an advantage in that the DTX bit processing algorithm can be simply implemented and easily applied to existing communication systems since this does not require any modification of the conventional modulation algorithm.

The embodiments described above are to be considered in all aspects as illustrative only and not restrictive in any manner. Thus, other exemplary embodiments, system architectures, platforms, and implementations that can support various aspects of the invention may be utilized without departing from the essential characteristics described herein. These and various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. The invention is defined by the claims.