Europäisches Patentamt *EP001406421A2* (19) European Patent Office Office européen des brevets (11) EP 1 406 421 A2 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.7: H04L 27/34 07.04.2004 Bulletin 2004/15 (21) Application number: 03256098.9 (22) Date of filing: 29.09.2003 (84) Designated Contracting States: • Hayashi, Takahiro, c/o NTT DoCoMo Inc. AT BE BG CH CY CZ DE DK EE ES FI FR GB GR Tokyo 100-6150 (JP) HU IE IT LI LU MC NL PT RO SE SI SK TR • Futakata, Toshiyuki, c/o NTT DoCoMo Inc. Designated Extension States: Tokyo 100-6150 (JP) AL LT LV MK (74) Representative: (30) Priority: 03.10.2002 JP 2002291571 Luckhurst, Anthony Henry William MARKS & CLERK, (71) Applicant: NTT DoCoMo, Inc. 57-60 Lincoln’s Inn Fields Tokyo 100-6150 (JP) London WC2A 3LS (GB) (72) Inventors: • Moon, Sung Uk, NTT DoCoMo Inc. Tokyo 100-6150 (JP) (54) Data transmission using hierarchical modulation (57) A modulation device comprises a modulation ta having been subjected to hierarchical modulation us- unit (2) that modulates data in a hierarchical manner us- ing multiple types of modulation techniques, and a de- ing multiple types of modulation techniques, and a trans- modulation unit (6) that demodulates the hierarchical mission unit (3) that transmits the hierarchically modu- modulation data using a demodulation technique corre- lated data. A demodulation device comprises a receiv- sponding to a specific hierarchy of the hierarchical mod- ing unit (4) that receives the hierarchical modulation da- ulation data. EP 1 406 421 A2 Printed by Jouve, 75001 PARIS (FR) 1 EP 1 406 421 A2 2 Description with the above-described QPSK under the same trans- mission rate, the occupied band-width of 16-QAM is nar- BACKGROUND OF THE INVENTION rower than that of QPSK. This means that 16-QAM is more effective to realize high-speed digital data trans- [0001] The present invention generally relates to 5 mission. However, 16-QAM is easily influenced by fad- modulation and demodulation in digital data transmis- ing, which is the phenomenon of sharp fluctuation in in- sion, and more particularly to a modulation and demod- tensity level of a radio wave due to environmental ulation technique capable of dealing with multiple types change including time and the distance between the of modulation based on hierarchical modulation. transmitter and the receiver. The 16-QAM is mainly used [0002] In recent radio communications, digital modu- 10 for digital MCA (telecommunications business). lation techniques are employed in, for instance, cellular [0007] Since the above-described two modulation phone networks, BS television broadcast, and other dig- techniques, QPSK and 16-QAM, are used in digital mo- ital communication networks. Known modulation tech- bile telecommunications, hardware capable of dealing niques used in digital mobile communications include with these two modulation techniques is desirable. Such quadrature phase shift keying (QPSK) and quadrature 15 hardware is advantageous for both users and manufac- amplitude modulation (QAM). turers, reducing the cost of components and the space [0003] Quadrature phase shift keying (QPSK) is a for accommodating the hardware, while improving op- modulation technique that uses two carriers out of erability. From this standpoint, JPA 9-27426 proposes a phase by 90 degrees (that is, quarternary signal states), demodulation technique for demodulating both QAM allowing 2 bits/symbol transmission. FIG. 1 is a QPSK 20 modulation signals and QPSK modulation signals in one signal constellation, in which the in-phase component system. and the guadrature component of the QPSK modulation [0008] However, in spite of the existence of multiple signal are expressed in the phase plane defined by the modulation techniques used in digital telecommunica- I-axis (representing the real number) and the Q-axis tions, the transmission ability and the receiving ability (representing the imaginary number). The signal con- 25 are not always consistent with each other. If a receiver stellation is also called "signal diagram". In QPSK mod- is capable of dealing with only QPSK modulation sig- ulation, modulation signals with four different phases nals, 16-QAM modulation signals transmitted from a are arranged at the vertexes of a square. In other words, transmitter cannot be demodulated. To overcome this the transmission signal is represented by one of the four problem, a 16-QAM demodulator has to be furnished in phases. 30 the receiver, in addition to the QPSK demodulator, or [0004] Another type of QPSK modulation is pi/4-shift alternatively, a system proposed in JPA 9-275426 is re- QPSK, which is derived from the above-described quired. The former method causes the circuit scale and QPSK and used in personal digital cellular (PDC) the cost to increase because an extra demodulator has phones based on the second generation mobile com- to be added to the receiver. The latter method provides munications standard. With pi/4-shift QPSK, the phase 35 two independent signal paths, one functioning as a QAM of the carrier rotates by pi/4 per symbol, providing quar- demodulator when receiving a QAM modulation signal, ternary signal states. and the other functioning as a QPSK demodulator when [0005] In W-CDMA in FDD mode, which is one of the receiving a QPSK modulation signal. One of these two radio transmission protocols used in the third generation demodulation types is selected depending on the mod- cellular systems based on the International Mobile Tel- 40 ulation type of the received signal. Accordingly, it is es- ecommunications-2000 (IMT-2000) standard, BPSK sential to furnish the functions of a QAM demodulator (binary phase shift keying) is used for uplink data mod- and a QPSK demodulator in the circuit structure. ulation, while QPSK is used for downlink data modula- tion. In TDD mode, QPSK is employed for data modu- SUMMARY OF THE INVENTION lation on both uplink and downlink. 45 [0006] Another known modulation technique is [0009] The present invention is conceived to over- 16-QAM (quadrature amplitude modulation), which al- come the above-described problems, and it is an object lows 4 bits/symbol data transmission using a combina- of the invention to provide a modulation/demodulation tion of phase and amplitude of the carrier representing technique that allows received data to be demodulated one of sixteen (16) four-bit patterns. FIG. 2 is an exam- 50 according to the demodulation ability of the receiver ple of a 16-QAM signal constellation. With 16-QAM, four even if the demodulation ability on the receiving side is bits (16 patterns) of an input sequence are divided into not totally consistent with the modulation functions of four 2-bit patterns. The two carriers out of phase by 90 the transmission side apparatus. degrees are amplitude-modulated in the respective four [0010] To achieve the object, in one aspect of the in- signal states, and synthesized. The constellation plotted 55 vention, a modulation device is furnished with a hierar- after the amplitude modulation is shown in FIG. 2. The chical modulation function. To be more precise, the divisions on the I-axis and the Q-axis are -0.9487, modulation device comprises a modulation unit that -0.3162, 0.3162, and 0.9487. Comparing the 16-QAM modulates data in a hierarchical manner using multiple 2 3 EP 1 406 421 A2 4 types of modulation techniques, and a transmission unit modulation functions, the optimum demodulation type that transmits the hierarchically modulated data. is selected, taking into account the propagation environ- [0011] The modulation device further comprises a ment and other factors. Consequently, telecommunica- sampling pattern generating unit that generates a sam- tions can be maintained without undesirable disconnec- pling pattern for each of the modulation techniques. The 5 tion even if the propagation environment abruptly sampling pattern defines a sampling space for quantiz- changes. ing said data in accordance with each of said modulation techniques. In this case, the modulation unit modulates BRIEF DESCRIPTION OF THE DRAWINGS said data in the hierarchical manner using a digital signal sampled based on the sampling pattern. 10 [0019] [0012] The sampling pattern defines the sampling space of a carrier used in, for example, multi-phase FIG. 1 is an example of a QPSK signal constellation; phase shift keying or multi-value quadrature amplitude FIG. 2 is an example of a 16-QAM signal constella- modulation. tion; [0013] Preferably, the transmission unit transmits the 15 FIG. 3 illustrates the structure of the modulation and sampling pattern together with the hierarchically modu- demodulation device according to an embodiment lated data. of the invention; [0014] In another aspect of the invention, a demodu- FIG. 4 is a block diagram of the modulator included lation device that receives and demodulates hierarchi- in the modulation and demodulation device shown cal modulation data is provided. The demodulation de- 20 in FIG. 1; vice comprises a receiving unit that receives hierarchi- FIG. 5 is a block diagram of the demodulator includ- cal modulation data having been subjected to hierarchi- ed in the modulation and demodulation device cal modulation using multiple types of modulation tech- shown in FIG. 1; niques, and a demodulation unit that demodulates the FIG. 6 is a graph showing an example of hierarchi- hierarchical modulation data using a demodulation tech- 25 cal modulation carried out by the modulator shown nique corresponding to a specific hierarchy of the hier- in FIG. 4; archical modulation data. FIG. 7 is a table of a set of 16-QAM modulation sig- [0015] Preferably, the demodulation unit is furnished nals; with multiple types of demodulation techniques, and in FIG. 8 is a table of sampled transmission data mod- this case, the demodulation device further comprises a 30 ulated by 16-QAM; demodulation type selection unit that selects one of the FIG.