Evaluations of Digital Radio Techniques in Doppler Scenarios: HD Radio versus DAB, DAB+, T-DMB

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1 Evaluations of Digital Radio echniques in Doppler Scenarios: HD Radio versus DAB, DAB+, -DMB Jin Ren. School of Electronic and Information Engineering, orth China University of echnology, o.5 Jinyuanzhuang Road, Shijingshan District, Beijing, P.R, China Abstract: he advance of wireless communications brings in various schemes of wireless digital communication technology. Analog communication and broadcasting services convert into digital services in many countries. his paper develops simulation models to characterize the bit error rate (BER) performance of HDR (HD-Radio), digital audio broadcasting (DAB), DAB+, terrestrial digital multimedia broadcasting (-DMB) affected by Doppler spread. he IBOC (In-Band On-Channel) system has been developed to work in the same band with the conventional analog radio and broadcasting digital signal simultaneously. HDR (HD-Radio) standard of IBOC (In- Band-On-Channel) can use coherent demodulation using pilot sub-carriers. But DAB, DAB+ and -DMB standard of Eureka7 uses noncoherent demodulation by differential modulation. heoretically, coherent demodulation is better than non-coherent demodulation. o contribute to decision of digital radio standard and design of digital radio transmission network, the simulation results will give a help. Keywords: Digital audio broadcasting; DAB+; -DMB; HD Radio; IBOC. Introduction Digital radio broadcasting systems have come into the spotlight recently worldwide. Many digital radio broadcasting standards have been proposed recently, and the adoption of digital broadcasting is considered in many countries. But choosing most proper digital radio standard has become an important question for the successful deployment of the new radio service [-2]. In addition, to decide the national standard of digital radio broadcasting service, various considerations are required like economic efficiency, social influence, and technical suitability, etc. HD Radio is the trademark for ibiquity Digital Corporations in-band on-band (IBOC) digital radio system. While there are differences between amplitude modulation (AM) and frequency modulation (FM) band HD Radio systems, an HD Radio signal can be generally described as a digitally modulated RF signal that is transmitted around, under and alongside the present-day analog AM and FM signals. It should be noted that, strictly speaking, a hybrid HD Radio signal actually has components - an analog modulated component referred to here [3]. here digital signals are composed of multiple orthogonal frequency division multiplexed (OFDM) subcarriers, which are transmitted at a level to meet the specifications of the RF masks (AM and FM) as mandated in the United States by the Federal Communications Commission (FCC), and as specified in the digital radio broadcasting standard (RSC-5-A) of the ational Radio Systems Committee (RSC). Since the OFDM subcarriers of the HD Radio signals are contained with these masks, and are therefore considered to be contained within the allotted channel for a given station without allocating any additional spectrum, it is considered to be an in-band on-channel system. he FM HD Radio signal has more spectrum space available than the AM HD Radio signal, as the FM channel has been allocated greater bandwidth. herefore, the FM HD Radio signal can operate at a higher data rate than AM HD Radio signal. his greater data rate can be subdivided to allow additional audio channels to be transmitted on the frequency. he digital audio broadcasting (DAB) has recently become popular around the world, due to its ability to provide high quality reception additional features compared to the traditional AM/FM radio. It was developed in the 99s by the Eureka 47/ DAB project. In the meantime, the World DAB Forum have developed an upgrade of the Eureka 47 DAB system called DAB+ in order to improve the audio coding efficiency using the new coding schemes of MPEGHE AAC v2. Digital multimedia broadcasting (DMB) is one of the applications which have emerged from Eureka7 DAB system, Particularly in Korea, DMB focuses on the broadcasting of moving pictures and their reception in harsh conditions such as in places surrounded by high buildings and on highways where vehicles are moving at a very high speed. here are two kinds of DMB systems, satellite DMB and terrestrial DMB. he terrestrial DMB is called by -DMB in Korea [5-6]. Although the -DMB system is an improved version of the DAB system, should still be used in many parts of the -DMB system. he described sections of this paper are as follows: Section 2 introduces HDR standard, Section 3 is about DAB, DAB+, and -DMB. COFDM and Channel Model in Doppler Scenarios will be introduced in Section 4 and Section 5 respectively. In Section 6 implementation results of simulation will be reported. 2. HD radio A logical channel is a signal path that conducts Layer 2 PDUs (Protocol Data Unit) in transfer frames into Layer with a specific grade of service, determined by service mode. Lay of the FM air interface provide logical channels to higher layer protocols [7]. ot all logical channels are used in every service mode. here are five primary logical channels that can be used with the Hybrid, Extended Hybrid, and All Digital waveforms. hey are denoted as P, P2, P3, P4, and PIDS. he PIDS channel transmits the Station Information Service (SIS) information. here are six secondary logical channels that are used only with the All-Digital waveform. hey are denoted as S, S2, S3, S4, S5, and SIDS. he bits in each logical channel are scrambled to randomize the time-domain data. he inputs to the scramblers are the active logical channels as selected by the service mode. Channel encoding improves system performance by increasing the robustness of the signal in the presence of channel impairments. his function uses convolutional encoding. he size of the logical channel vectors is increased in inverse proportion to the code rate. he encoding techniques are configurable by service mode. Diversity delay is also imposed on selected logical channels. At the output of the channel encoder, the logical channel vectors retain their identity. he interleaving techniques are tailored to very high frequency fading environment and are configurable by service mode. In this process, the logical channels lose their identity. he interleaver output is structured in a matrix format, each matrix consists of one or more logical channels and is associated with a particular portion of the transmitted spectrum. OFDM subcarrier mapping assigns interleaver partitions to frequency partitions. One row of each active interleaver matrix is processed every OFDM symbol to produce one output vector which is a frequency-domain representation of the signal. 3. DAB, DAB+, -DMB he source encoder for the DAB system is the MPEG Audio Layer II encoder with restrictions on some parameters and some additional protection against transmission errors. he MPEG II audio signal and the other data are the input services to DAB transmitter. Each service signal is coded individually at source level in the transmitter, error protected, and then time interleaved in the channel coder. Each service is independently error protected with a coding overhead ranging from about 25% to 3%, the amount of which depends on the Journal of Residuals Science & echnology, Vol. 3, o. 6, DEStech Publications, Inc. doi:.2783/issn /3/6/69

2 requirements of the broadcasters (transmitter coverage and reception quality). hen, the services are multiplexed in the Main Service Channel (MSC), according to a predetermined and adjustable multiplex configuration. Finally, Orthogonal Frequency Division Multiplexing (OFDM) is applied to the signal to shape the DAB signal which consists of a large number of sub-carriers. he OFDM signal generation involves the processes of Quadrature Phase Shift Keying (QPSK) mapping of the arrival bits, frequency interleaving, and differential modulation. When the signal is generated, it is defined in the frequency domain, and is then transformed into its time domain representation by Inverse Fast Fourier ransformer (IFF). Some of the ending samples of the IFF sequence are copied to the front of the symbol to add the cyclic prefix (CP). he CP is used to avoid inter symbol interference (ISI). he generated OFDM signal is amplified and sent to the RF block. he DAB system operates in four modes, and each mode has its specific characteristics, as shown in able I. he system uses five protection levels in each operation mode with respect to the desired application. Protection level one is suitable for a highly mobile receiver and level five for a fixed one. he cyclic prefix (CP). he CP is used to avoid inter symbol interference (ISI). he generated OFDM signal is amplified and sent to the RF block. he DAB system operates in four modes, and each mode has its specific characteristics. he system uses five protection levels in each operation mode with respect to the desired application. Protection level one is suitable for a highly mobile receiver and level five for a fixed one. Since different digital radio broadcasting methods have different audio codecs, channel coding, orthogonal frequency division multiplexing (OFDM) symbol features, and application frequency bands, the characteristics are highly different. DAB, DAB+, and -DMB audio are based on the Eureka7 standard. However, according to their broadcasting purposes, they have different parts. he DAB standard was initially designed to provide compact disk quality audio broadcasting service. herefore, simple and efficient transmission techniques are adopted, e.g., differential modulation and convolution coded OFDM (COFDM). In addition, since the standard was made in 995, a relatively old audio codec is used (masking-pattern adapted universal subband integrated coding and multiplexing). On the other hand, DAB+ was designed to provide higher quality audio broadcasting service. herefore, DAB+ uses the highly efficient advanced audio coding version 2, which is a state-of-the-art technology for an audio codec and concatenated channel coding (Reed and Solomon (RS) coding + convolutional coding) that is a more powerful channel coding scheme. he -DMB system is designed for real-time mobile multimedia services. herefore, MPEG video and bit-sliced arithmetic coding are adopted into the system. 4. COFDM a Both HD radio and DAB consider an OFDM system in which complex data symbols n, k =,, -, are modulated onto orthogonal sub-carriers by means of an -point Inverse DF (IDF) to form an OFDM symbol with duration u. he OFDM symbol is further extended with a cyclic prefix of duration G and subsequently transmitted. We indicate with the sampling period, with G the number of samples within the guard interval so that = u and = G. G f he sub-carrier spacing is set to be s = u. he transmitted samples read as j2 π nq/ s ( q ) = ane q = G,,. () n= he samples s (q) are transmitted through the channel model. We indicate with q, q = G,,, the time variable and with i, i =,, + the delay variable so that the delay variable so the equivalent discrete time channel impulse response reads as duration, i.e. (, ) (, ) = ( ) δ ( ) h q i h q i i i indicates the delayed position of the time varying path ( ) L l l (2) hl q. he channel impulse response is assumed to be of finite he index l h q i = for i < and i > il. he receive samples r (q) are obtained via the convolution of the transmit samples with the channel impulse response and then corrupted by the additive white Gaussian noise (AWG) n(q) with two-sided 2.We obtain We then substitute () into (3) to write L l l (3) ( ) = ( ) ( ) + ( ) y q h q d q i n q l L j2π k( q i ) l ( ) (4) ( ) ( ) ( ) y q = h q s k e + n q j 2π kil H ( k, q ) = hl ( q ) e which upon defining the time-varying channel transfer function, becomes L j 2π kq y ( k ) = s ( k ) H ( k, q ) e + n( q ) (5) th he FF output at the k subcarrier can be expressed as j 2π kq y( k) = y( k) e k = (6) = s k H k + I k + k H( k) where I( k) L ( ) ( ) ( ) ( ) represents the average frequency domain channel response, defined as H( k) = H( k, q) (7) is ICI (inter-carrier interference) caused by the time-varying nature of the channel given as j2π qi ( k) I ( k ) s ( i) H ( i, q ) e q= = (8) i=, i k q= Journal of Residuals Science & echnology, Vol. 3, o. 6, DEStech Publications, Inc. doi:.2783/issn /3/6/69

3 and ( k) n demotes discrete Fourier transform of the white Gaussian noise ( q ) j2π qk n q e (9) q= ( ) = ( ) k he received signal after excluding the guard interval can be expressed in vector form as y = Hs + n () y = y(, ) y(, ), y( ), s (, ) (, ), ( ) = y y y, n = n (, ) n (, ), where n( ) and the time-varying channel matrix H is given by where the first and second indices of H(.,.) in () represent the discrete time and frequency variables, respectively. 5. Channel model in Doppler scenarios (,) (,) (,) j2π π (,) (,) (,) H H H j2 ( ) H H e H e H = j2π( ) j2π( )( ) H(, ) H(, ) e H(, ) e In wireless communication, htt (, ) is always modeled as a wide sense stationary uncorrelated scattering (WSSUS) process with L+ received path, such that L () ht (, t) = hl() tδt ( tl) (2) where t and τ h are time and delay respectively, () l t is the l th path gain and its power density spectrum P ( ) k f. he variance τ determines the average speed of variation in time, i.e. describes the influence of the Doppler effect on the waves arriving at delay time l. herefore Pk ( f) is also known as Doppler spectrum. A basic parameter is the maximum Doppler frequency f d v λ = (3) where v is the velocity of the receiver or surrounding objects and λ is the wavelength of the transmitted signal. In case that all waves are arriving from all directions at the receiving antenna with approximately the same power the real Doppler spectrum can be approximated by A P( k f ) = 2 f for f [ fd, fd] (4) fd his spectrum is also known as classical Jakes spectrum. It will be denoted Classical in able Simulation Results able is OFDM system standard parameter previous system. Simulation environment of the systems in this paper is used general multipath fading channel, given by able 2. Following, Fig. (a), Fig.2(a) and Fig3.(a) show BER performances for HDR-MP3. and Fig.(b), ]Fig.2(b) and Fig3.(b) show BER performances for DAB, DAB+, and -DMB respectively in multipath fading channel, i.e, AB- 2,AB and AB-7. When velocity is 6km/h,5km/h and 3km/h, so doppler shift frequency is 5.5Hz, 3.9Hz and 27.8Hz respectively. In Fig. (a), Fig.2(a) and Fig.3(a), the performance of P is better than P3, because the code rate of P is lower than P3. he code rate of P is 2/5, and P3 is /2. Interleaving depth of P3 (2 frame) is longer than P( frame), and if velocity is increased, the gap is expected to be decreased since P3 may obtain more diversity gain. able. System Parameters Parameters HDR(MP3) DAB DAB+ -DMB Guard Interval (us) FF (ms) (OFDM) Sym. duration (ms) FF size () # of Useful sub-carriers % of Pilot sub-carriers (%) Journal of Residuals Science & echnology, Vol. 3, o. 6, DEStech Publications, Inc. doi:.2783/issn /3/6/69

4 Sampling rate (Msps) Sub-carrier spacing (Hz) Occupying BW (khz) Data symbol rate (ksps) Data rate (kbps) Spectral Efficiency In Fig. (a), performance of P is better than P3. P is 6.4dB, and P3 is 8.2dB by BER. Also P is 8.4dB and P3 is.3db by -6 BER. In Fig.2 (a), performance of P is better than P3. P is 5.2dB, and P3 is 6.7dB by BER. Also P is 8.3dB and P3 is 9.2dB -6 by BER. In Fig.3 (a), performance of P is better than P3. P is 7.2dB, and P3 is 7.5dB by BER. Also P is 8.2dB and P3 is dB by BER. he reason of P better than P3 is each other code rate. Code rate of P is 2/5, and P3 is /2. So P is excellent for error correction performance. Interleaving depth of P3 (2 frame) is longer than P ( frame). So if velocity increases, differences in performance decrease by time diversity. Path no. able 2. Channel Parameters AB-2 (Classical) AB (Classical) AB-7 (Classical) Attn Delay Doppler Delay Doppler Delay Doppler ( us ) ( Hz ) ( db ) ( us ) ( Hz ) ( db ) ( us ) ( Hz ) ( db) Attn Attn In Fig. (b), the performance of -DMB is best and DAB+ is better than DAB. -DMB is 2.2dB, DAB+ is 2.8dB and DAB is 3.8dB by BER. Also -DMB is 3.2dB, DAB+ is 4.3dB and DAB is 2dB -DMB by BER. In Fig. 2(b), the performance of -DMB is best and DAB+ is better than DAB. -DMB is.8db, DAB+ is 2.9dB and DAB is 4dB by BER. Also -DMB is 3dB, DAB+ is 4.2dB and DAB is 2dB -DMB by BER. In Fig. 3(b), the performance of -DMB is best and DAB+ is better than DAB. -DMB is 4dB, DAB+ is 5.dB and DAB is 8dB by BER. From all Figures, the performances of HDR-MP3 is better than DAB, DAB+ and DMB in different Doppler scenarios. Figure. (a) BER performance of HDR-MP3 for Ch. AB-2 Journal of Residuals Science & echnology, Vol. 3, o. 6, DEStech Publications, Inc. doi:.2783/issn /3/6/69

5 Figure. (b) BER performance of DAB, DAB+ and -DMB for Ch. AB-2 Figure 2. (a) BER performance of HDR-MP3 for Ch. AB Figure 2. (b) BER performance of DAB, DAB+ and -DMB for Ch. AB Figure 3. (a) BER performance of HDR-MP3 for Ch. AB-7 Figure 3. (b) BER performance of DAB, DAB+ and -DMB for Ch. AB 7. Conclusion Journal of Residuals Science & echnology, Vol. 3, o. 6, DEStech Publications, Inc. doi:.2783/issn /3/6/69

6 In this paper, we evaluate performances of digital radio technologies (HDR versus DAB, DAB+, and -DMB). echnically, HDR standard use coherent demodulation by pilot sub-carrier. DAB, DAB+ and -DMB standard of Eureka7 uses non-coherent demodulation by differential modulation. From the simulation results, it can be clearly seen that different system performances under various Doppler scenarios. he performance of HDR is better than DAB, DAB+ and -DMB. he reference data of simulation will be useful for experimental broadcasting. Acknowledgements his work was supported by 23 echnology Foundation for Selected Overseas Chinese Scholar (o ), Ministry of Personnel of Beijing and he Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry and raining program for Outstanding Young Scholars (o.485). 27 General Program of Science and echnology Development Project of Beijing Municipal Education Commission. References [] ESI E 3 4, Radio broadcasting systems: Digital audio broadcasting (DAB) to mobile, portable and fixed receivers, ESI, ech. Rep. Feb [2] ibiquity Digital, HD Radio. M air interface design description series, 2. [3] H.-L. Lou, D. Sinha and C.-E. W. Sundberg: Multistream transmission for hybrid IBOC-AM with embedded multi descriptive audio coding, IEEE rans. Brocas, 22, 48, 3, pp [4] R. F. Liebe and R. A. Surette, Combining digital and analog signals for US IBOC FM broadcasting, IEEE rans. Broadcasting, 22, 48, no.4, pp [5] Y.-. Lee, S.-R. Park, M.-S. Baek, J.-M. Kim, G. Kim, Y.-H. Lee, H. Lim, C.-H. Im, and S.-I Lee, Laboratory test results of digital ardio technologies: DAB, DAB+, -DMB audio and HD Radio, in Proc. AB BEC, 2, pp [6] M.-S. Baek, S. Park, G. Kim, Y.-H. Lee, H.-S. Lim, Y.-J. Song, C.-H.Im, and Y.-. Lee, Design and performance evaluation of digital radio measurement test beds for laboratory test: DAB, DAB+ and -DMB Audio, IEEE rans. Instrumentation Measurement, 23, 62, 2, pp [7] K. Ulovec and K. Milkulastik, Coexistence of digital and analog audio broadcasting in VHF-FM band-measurement, Radioelektronika, 28, pp Journal of Residuals Science & echnology, Vol. 3, o. 6, DEStech Publications, Inc. doi:.2783/issn /3/6/69