Title

Basic Modulation Schemes In Digital Mobile Multimedia Broadcasting Systems

Abstract

Modulation is the mapping-superimposing process where the baseband bit stream message information is mapped to the radio carrier. Modulation and demodulation are paired with modulation being carried out at the transmitter, and the demodulation being carried out at the receiver. Most of the latest digital mobile multimedia broadcasting (DMMB) standards such as Digital Video Broadcasting, Handheld (DVB-H) and Terrestrial Digital Multimedia Broadcasting (T-DMB) [1-10] are using the orthogonal frequency-division multiplexing (OFDM) based techniques with various inner modulation schemes while the Advanced Television Systems Committee (ATSC) [11] is adopting the vestigial sideband (VSB) modulation approach. The selection of digital modulation schemes used in the digital mobile multimedia broadcasting system (DMMBS) has almost the same requirements as other digital communication systems. The consideration may include, but is not limited to the following: Nyquist theoretical minimum bandwidth, Shannon limit (Shannon-Hartley capacity), low bit error rate (BER), high power and bandwidth efficiency, high power efficiency, low out of band radiation, low sensitivity to multipath fading, constant envelope, low cost, ease of implementation, flexible and compatible to existing system and easy for future upgrade, and the regulation. Some of the above requirements conflict each others. The final decision always reflects a trade-off, a balance of these factors. For certain application, some factors may be paid more attention than others. In analog broadcasting and communication systems, the basic parameter is average signal power to average noise power ratio SNR or S/N, which is also called as the signal to noise ratio. For digital systems, the signal to noise ratio can be expressed in the form SNR = Eb/N0 = STb/N/W = S/R bN/W = S/N*Rb/W = S/N*ns where Eb is bit energy, W is bandwidth, S is signal power, Tb is bit time, Rb is bit rate, N0 is noise power spectral density, N is noise power, and çs is spectrum efficiency. The noise source can arise from a number of contributory factors in addition to the receiver thermal noise. This includes, but is not limited to: intermodulation performance, local oscillator phase noise, channel filter response, and quadrature imbalance, and their effects will sum in an RMS (root mean square) manner. Spectrum efficiency ns (also called as bandwidth efficiency nB) is one of the key attributes of the DMMB communication systems, which almost always operate in a crowded and valuable licensed radio frequency spectrum. Spectrum efficiency is used to measure in units of bits per second (bps) per bandwidth. ns = Rb/W = 1/WT b Log2 (M) bps/Hz (10.2) The capacity of a band-limited additive white Gaussian noise (AWGN) channel is governed by Shannon-Hartley theorem C = W Log2(1+average signal power/average noise power)=average signal power/average noise power*ln2(W→∞)(10.3) It is possible to transmit information over a channel at a rate R with an arbitrarily small error probability, if R = C. The rate limit is set by signal power (S), bandwidth (W) and noise power (N). Nyquist theoretical stated that the theoretical minimum bandwidth needed for the based band transmission of Rs symbols per second without ISI is Rs/2Hz. For M-ary system, relationship between bit rate Rb and symbol rate R s is Rs = Rb/log2M (10.4) The portable and mobile DMMBS needs to minimize the battery requirement; normally a nonlinear power amplifier is used. Nonlinear amplifier may degrade the bit error rate performance of some modulation schemes. Spectrum shaping and predistortion can be performed prior to up conversion and nonlinear application. Power efficiency, np, is a measure of how much received power is needed to achieve a specified BER. In digital modulation, the modulation is implemented in digital form and named as "Shifting &Keying." The basic digital modulation schemes are Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK). These systems represent the transmitted data signal by varying the amplitude, frequency or phase of a certain frequency carrier, respectively. There is another important type of modulation, hybrid modulation, which modulates more than one parameter. If the parameters are amplitude and phase then the modulation is the Quadrature Amplitude Modulation (QAM). The QAM is also called as QASK (Quadrature Amplitude Shift Keying) or APSK (Amplitude and Phase Shift Keying). The inner modulation schemes used in OFDM based DMMBS are very similar to the modulation schemes in other single carrier systems, which has been discussed thoroughly in many books [12-14]. Various digital modulation techniques have been used as modulation schemes in different DMMB standards [1-11]. The rest of the chapter will give introduction to various basic modulation schemes: BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), φ/4 DQPSK, 8PSK, 16QAM, 64QAM, 256QAM, 8VSB, and 16VSB. © 2009 Springer Science+Business Media, LLC.

Publication Date

12-1-2009

Publication Title

Mobile Multimedia Broadcasting Standards: Technology and Practice

Number of Pages

295-312

Document Type

Article; Book Chapter

Personal Identifier

scopus

DOI Link

https://doi.org/10.1007/978-0-387-78263-8_10

Socpus ID

84891988810 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/84891988810

This document is currently not available here.

Share

COinS