Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

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Figure 2.1. Multi path propagation of the transmitted signal. The OFDM transmission scheme has the following key advantages: • Makes efficient use of the spectrum by allowing overlap. • By dividing the channel into narrowband flat fading subchannels, OFDM is more resistant to frequency selective fading than single carrier systems are. • Eliminates ISI and IFI through use of a cyclic prefix. • Using adequate channel coding and interleaving one can recover symbols lost due to the frequency selectivity of the channel. • Channel equalization becomes simpler than by using adaptive equalization techniques with single carrier systems. • In conjunction with differential modulation there is no need to implement a channel estimator. • Is less sensitive to sample timing offsets than single carrier systems are. • Provides good protection against co-channel interference and impulsive parasitic noise. In terms of drawbacks OFDM has the following characteristics: • The OFDM signal has a noise like amplitude with a very large dynamic range, therefore it requires RF power amplifiers with a high peak to average power ratio. • It is more sensitive to carrier frequency offset and drift than single carrier systems are due to leakage of the DFT [8]. 6
2.1.3 Reed-Solomon Codes 2.1.4 DVB-T Reed-Solomon codes (RS codes) are block-based error correcting codes and are very widely used in digital communications and storage. RS codes can detect and correct errors within blocks of data and are used in a lot of applications, for example: • Storage devices (including tape, compact, DVD, barcodes, etc) • Wireless or mobile communications (including cellular telephones, microwave links, etc) • Satellite communications • Digital television / DVB • High-speed modems such as ADSL, xDSL,etc The RS encoder takes a block of digital data and adds extra "redundant" bits. Errors occur during transmission or storage for a number of reasons (for example noise or interference, scratches on a CD, etc). The Reed-Solomon decoder processes each block and attempts to correct errors and recover the original data. DVB-H uses RS (255,191), were 191 is the number of information symbols input per block and 255 the number of symbols per block that the encoder outputs, the code rate can be varied. The term symbol may represent one bit or a number of bits. The number and type of errors that can be corrected depends on the characteristics of the Reed-Solomon code and is always half of the parity symbols. So in the DVB-H system it is possible to correct up to 32 errors in a codeword [9]. DVB-T is the terrestrial mode for Digital Video Broadcasting. DVB-T has been selected as the common standard for digital television in Europe and is the base platform for DVB-H, witch makes it possible to transmit IP-packages to handheld terminals. The standard for DVB-T was adopted in December 1995. In November 1998 the first DVB-T network became operational in the United Kingdom. Since 1998 DVB-T has been introduced in Europe, Australia, Singapore and Taiwan [6]. See figure 2.2 to see the spread of the different digital TV specifications. In DVB-T, each program is sent over a separate logical channel that is identified by a unique packet identifier. All users that have access to a specific service may receive any program on that logical channel. The control streams used with the packet identifiers such as the program and service information are transmitted repeatedly from the head end to the users [10]. 7
Page 1 and 2: Design of Antennas for Handheld DVB
Page 3 and 4: Acknowledgements This master thesis
Page 5 and 6: 4 DESIGN AND TESTING OF ANTENNA SOL
Page 7 and 8: Figure 5.2. Reference dipole antenn
Page 9 and 10: 1 Introduction The passed decade th
Page 11 and 12: 2 Background This chapter provides
Page 13: is simultaneously modulated into 10
Page 17 and 18: 2.1.5 DVB-H DVB-H is the latest dev
Page 19 and 20: 2.1.5.2 Time slicing A large proble
Page 21 and 22: figure 2.5). All three elements tog
Page 23 and 24: symbols or four 2K OFDM symbols. Th
Page 25 and 26: 2.2 Competing standards The DVB-H s
Page 27 and 28: 2.3 Antenna theory This section des
Page 29 and 30: Figure 2.9. Impedance bandwidth def
Page 31 and 32: unloaded quality factor (Q0) and th
Page 33 and 34: losses should be avoided in handhel
Page 35 and 36: 3.3 Loop Figure 3.1. Yagi-Uda anten
Page 37 and 38: PIFA Figure 3.2. Four different con
Page 39 and 40: The size of the antenna is another
Page 41 and 42: 4.4 PIFA To verify the balun a resi
Page 43 and 44: 4.5 Folded-Patch With the PIFA-ante
Page 45 and 46: Figure 4.9a. Folded-patch 2, front
Page 47 and 48: Figure 4.11. Loop antenna schematic
Page 49 and 50: Figure 4.15. Wire loop antenna retu
Page 51 and 52: using an H-field antenna together w
Page 53 and 54: antenna. The dimension of the anten
Page 55 and 56: The result of the return loss measu
Page 57 and 58: Figure 4.24. Return loss graph for
Page 59 and 60: The result of the measurement of th
Page 61 and 62: Figure 4.31. Return loss graph for
Page 63 and 64: frequency band, the first from 470
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Figure 5.6. Radiation pattern for R
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5.1.3 Measurement result In this ch
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Figure 5.10. Radiation pattern for
Page 71 and 72:
Page 73 and 74:
Table 5.4. Switched monopole 1, gai
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Power gain / dB 2 0 -2 -4 -6 -8 -10
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was received in all five channels.
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6.3 Control signal 6.4 Cost The swi
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not be possible, there will always
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There are many advantages with tuna
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8 References [1] Schiller, Jochen -
Page 89:
[29] Gardiol, Fred - Microstrip cir
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