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5.2-3>Paper ID < Amplitude-DQPSK Modulation for High-Data-Rate Terrestrial Digital Multimedia

Dae-Ken Kwon*, Hyoung-Nam Kim*, Member, IEEE, Hyoungsoo Lim**, Jong Soo Lim** *Dept. of Engineering, Pusan National University, Busan 609-735, Korea, E-mail:[email protected] ** Broadcasting System Research Group, ETRI, Daejeon 305-350, Korea

Im(x) Abstract - -DQPSK method is proposed Im(x) for a high-data-rate T-DMB system with the backward compatibility to existing receivers. Simulation results show that α β ββ the proposed A-DQPSK can be a good choice to achieve high- 1a a2 a3 data rate over other possible modulation schemes. Re(x) Re(x)

I. INTRODUCTION Terrestrial Digital Multimedia Broadcasting (T-DMB) service was launched in Korea to provide an effective solution (a) (b) for mobile broadcasting. The T-DMB system is based on the Fig. 1. Constellation diagrams. (a) DAPSK, (b) A-DQPSK. European Broadcasting (DAB) system known as Eureka-147 [1] which adopts Coded Orthogonal Binary Data DQPSK OFDM Symbol (conventional) Mapping x Generator Division (COFDM) and Differential Quadrature Phase Shift Keying (DQPSK). As well as audio services in Binary Data DASK (additional) Mapping DAB, T-DMB has provided services almost the same as (a) terrestrial DTV contents with the enhanced bit error immunity Binary Data DQPSK x OFDM Symbol obtained by additional Reed-Solomon coding and (conventional) Mapping Generator convolutional interleaving of MPEG-4 encoded video data [2]. Binary Data ASK Amplitude The quality of video service in T-DMB is originally VCD- (additional) Mapping pilot insertion like on 5-7 inch LCD display, and maximum picture ASK Modulation Block resolution is 352× 288 [3]. This resolution may be acceptable (b) in current services for handheld or small vehicle-equipped Fig. 2. T-DMB transmission system. (a) DAPSK, (b) A-DQPSK modulation. receivers. However, T-DMB service is expected to be channels where the channel coefficients are relatively constant extended to public transportation, such as buses, trains, and over at least two consecutive symbol intervals. In fast excursion ships, most of which are equipped with large-size channels caused by high-speed moving receivers, however, display. The data rate of the current T-DMB system is this condition does not hold. insufficient for an appropriate quality of video service on such As a good candidate for the modulation scheme of a high- large-size display. To solve this problem, the increase of the data-rate T-DMB system with the backward compatibility, we data rate of T-DMB has been recently considered. It is noted propose a novel modulation scheme of 16-Amplitude that the backward compatibility should be assured while the Differential Quadrature Phase Shift Keying (A-DQPSK) in transmission scheme would be modified for a high-data-rate which phase is modulated by DQPSK and amplitude is T-DMB system. modulated by amplitude shift keying (ASK). The proposed A typical way of increasing data rate is to increase the scheme of estimating channel spectral in each number of constellation points. One of the easiest ways is to individual OFDM symbol is robust for fast fading channels. use multilevel modulation techniques, like 16-Quadrature Amplitude Modulation (QAM). 16-QAM uses a coherent II. TRANSMISSION SYSTEM FOR HIGH-DATA-RATE T-DMB modulation technique which generally estimates a channel with the help of pilot symbols [4]-[5]. Since the T-DMB A-DQPSK and DAPSK constellations are shown in Fig. 1. system does not include any available pilot symbols except for (a) and (b), respectively. In the DAPSK constellation, the phase reference symbols [2], 16-QAM may not be amplitude factor which characterizes the distance between appropriate for the modulation scheme of a high-data-rate T- amplitude circles has been optimized in [6] to set a = 1.4. In DMB system. Another considerable modulation scheme is the A-DQPSK constellation, two parameters of α and β Differential Amplitude Phase Shift Keying (DAPSK) [6], [7] which affect the backward compatibility and the bit error rate which does not require any pilot symbols, channel estimation, in the enhanced data rate T-DMB system have been to be or equalization. This simple method works well in slow fading α = 1.5 , β = 1, through extensive simulations. To maintain compatibility with existing receivers, conventional T-DMB data is modulated by DQPSK and additional data by This work was supported in part by the Electronics and Research Institute (ETRI), Korea. amplitude modulation. Conventional T-DMB receivers can

0 0 10 10 DQPSK,v =10km/h DQPSK,v =200km/h DAPSK,v =10km/h -1 DAPSK,v =200km/h -1 10 A-DPSK,v =10km/h 10 A-DPSK,v =200km/h

-2 -2 10 10 BER BER

-3 -3 10 10 DAPSK, v=10km/h DAPSK, v=200km/h A-DPSK, v=10km/h A-DPSK, v=200km/h -4 -4 10 10 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40 SNRdB SNRdB Fig. 3. Comparison of the backward compatibility performance of DAPSK Fig. 4. Comparison of DAPSK and A-DQPSK in the high-data-rate T-DMB and A-DQPSK in the DQPSK demodulator. system. successfully demodulate A-DQPSK or DAPSK modulated modulation is severer than A-DQPSK. The reason is that the signal by regarding it as a DQPSK modulated signal. channel varies rapidly with the increase of vehicles speed Fig. 2 shows a high-data-rate T-DMB transmission system between two consecutive symbol intervals. This degrades the where amplitude modulated symbols are combined with the performance of the differential detection. The results mean conventional DQPSK symbols. In the DAPSK T-DMB system, that A-DQPSK is superior to other modulation schemes for DAPSK symbols in time domain is multiplied with DQPSK high-data-rate transmission. modulated symbols. In A-DQPSK, like the similar way to pilot symbol assisted modulation [4]-[5], amplitude pilots are IV. CONCLUSIONS inserted in the ASK modulation block. Whereas DQPSK We proposed an Amplitude-DQPSK modulation scheme for modulation used in the T-DMB prevents from inserting a high-data-rate T-DMB system and evaluated its performance known phase symbols, amplitude information can be used for comparing with DAPSK modulation. The backward data or known pilot transmission in the proposed scheme. compatibility to the DMB receiver was assured with less than Therefore, amplitude pilots make it possible to precisely 3-dB loss. A-DQPSK shows better BER performance than estimate channel amplitude response and the amplitude of the DAPSK, especially in mobile environment. The proposed received signal is equalized by using the estimated channel method may be considered as a good candidate for the coefficients. transmission scheme of a high-data-rate T-DMB system.

III. SIMULATION RESULTS REFERENCES Computer simulations were performed in order to verify the [1] ETSI, 2001., “ETSI EN 300 401, broadcast systems; Digital performance of the proposed A-DQPSK and DAPSK Audio Broadcasting (DAB) to mobile, portable and fixed receivers,” European Telecommunications Standards Institute, May 2001. modulation for a high-data-rate T-DMB system with the [2] ETSI, 2001., “ETSI TR 101 496-3, Digital Audio Broadcasting; backward compatibility. Simulation was performed in Guidelines and rules for implementation and operation; Part 3: Broadcast transmission mode I environment of DAB [1]. The carrier network”, European Telecommunications Standards Institute, May 2001. frequency is 200 MHz, and the is 1.536 MHz. The [3] Gwangsoon Lee, Sammo Cho, Kyu-Tae Yang, Young Kwon Hanhm, and Soo In Lee, “Development of terrestrial DMB transmission system frame duration is 96 ms and consists of 76 OFDM symbols. based on Eureka-147 DAB system,” IEEE Trans. Consumer Electronics, Each symbols composed of 1,536 sub-carriers with 1 kHz vol. 51, no. 1, pp. 63-68, Feb. 2005. carrier spacing. The channel profile used for our simulation [4] James K. Cavers, “An analysis of pilot symbol assisted modulation for channels,” IEEE Vehicular Technology Conf., vol. 2, pp. was COST 207 TU6 [8]. 894-898, Sept. 2002. Fig. 3 shows the BER performance using the conventional [5] Meng-Han Hsieh, Che-Ho Wei, “Channel estimation for OFDM systems T-DMB DQPSK demodulator for the vehicle speed of 10, 200 based on comb-type pilot arrangement in frequency selective fading channels”, IEEE Trans. Consumer Electronics, vol. 44, no. 1, pp. 217 – km/h. In terms of the backward compatibility, we can find that 225, Feb. 1998. the proposed high-data-rate modulation schemes degrade the [6] H. Rohling and V. Engels, “Differential amplitude phase shift keying BER performance by 3 dB for the vehicle speed of 10 km/h (DAPSK)—A new modulation method for DTVB,” in Proc. Int. Broadcasting Convention, Amsterdam, The Netherlands, 1995, pp. 102– and do not affect the performance for the vehicle speed of 200 108. km/h. [7] Der-Zheng Liu, Che-Ho Wei, ”DAPSK-OFDM transmissions for high Fig. 4 shows the BER performance of the A-DQPSK and date-rate digital ”, ISCAS Conf. vol. 2, pp. 417-420, May DAPSK on achieving high data rates. In mobile environment 2001. [8] COST 207 Report, Digital land mobile radio communications, near 200 km/h, the performances of DAPSK and A-DQPSK Commission of European Communities, Directorate General, are severely degraded by Inter sub-Carrier Interference (ICI). Telecommunications, Information Industries and Innovation, Luxemburg, However, the performance degradation of the DAPSK 1989.