HTC Corp., HTC America, Inc. - Ex. 1021, Page 1
`IPR2018-01555 and IPR2018-01581 (HTC and Apple v. INVT SPE)
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`

`4G LTE/LTE-Advanced
`for Mobile Broadband
`
`Erik Dahlman, Stefan Parkvall, and
`Johan Sköld
`
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`(cid:48)(cid:33)(cid:50)(cid:41)(cid:51)(cid:0)(cid:115)(cid:0)(cid:51)(cid:33)(cid:46)(cid:0)(cid:36)(cid:41)(cid:37)(cid:39)(cid:47)(cid:0)(cid:115)(cid:0)(cid:51)(cid:33)(cid:46)(cid:0)(cid:38)(cid:50)(cid:33)(cid:46)(cid:35)(cid:41)(cid:51)(cid:35)(cid:47)(cid:0)(cid:115)(cid:0)(cid:51)(cid:41)(cid:46)(cid:39)(cid:33)(cid:48)(cid:47)(cid:50)(cid:37)(cid:0)(cid:115)(cid:0)(cid:51)(cid:57)(cid:36)(cid:46)(cid:37)(cid:57)(cid:0)(cid:115)(cid:0)(cid:52)(cid:47)(cid:43)(cid:57)(cid:47)
`Academic Press is an imprint of Elsevier
`
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`Academic Press is an imprint of Elsevier
`The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK
`30 Corporate Drive, Suite 400, Burlington, MA 01803, USA
`
`First published 2011
`
`Copyright © 2011 Erik Dahlman, Stefan Parkvall & Johan Sköld. Published by Elsevier Ltd. All rights reserved
`
`The rights of Erik Dahlman, Stefan Parkvall & Johan Sköld to be identified as the authors of this work has been
`asserted in accordance with the Copyright, Designs and Patents Act 1988.
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`ISBN: 978-0-12-385489-6
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`36
`
`CHAPTER 3 OFDM Transmission
`
`Reference symbol
`
`Time
`
`FIGURE 3.12
`
`Time–frequency grid with known reference symbols.
`
`Single wideband carrier
`
`OFDM signal
`
`Sub-carrier experiencing
`very bad channel quality
`
`(a)
`
`FIGURE 3.13
`
`(b)
`
`(a) Transmission of single wideband carrier. (b) OFDM transmission over a
`frequency-selective channel.
`
`3.7 FREQUENCY DIVERSITY WITH OFDM: IMPORTANCE OF CHANNEL
`CODING
`As discussed in Section 2.3 in the previous chapter, a radio channel is always subject to some degree
`of frequency selectivity, implying that the channel quality will vary in the frequency domain. In the
`case of a single wideband carrier, such as a WCDMA carrier, each modulation symbol is transmitted
`over the entire signal bandwidth. Thus, in the case of the transmission of a single wideband carrier
`over a highly frequency-selective channel (see Figure 3.13a), each modulation symbol will be trans-
`mitted both over frequency bands with relatively good quality (relatively high signal strength) and fre-
`quency bands with low quality (low signal strength). Such transmission of information over multiple
`frequency bands with different instantaneous channel quality is also referred to as frequency diversity.
`On the other hand, in the case of OFDM transmission each modulation symbol is mainly confined
`to a relatively narrow bandwidth. Thus, for OFDM transmission over a frequency-selective channel,
`certain modulation symbols may be fully confined to a frequency band with very low instantaneous
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`3.8 Selection of Basic OFDM Parameters
`
`37
`
`Channel
`coding
`
`Frequency
`interleaving
`
`OFDM
`modulation
`
`b
`
`Information bit
`
`Channel coding
`
`c1 c2 c3 c4 ...
`
`Coded bits
`
`Frequency interleaving
`(mapping to sub-carriers)
`
`FIGURE 3.14
`
`Channel coding in combination with frequency-domain interleaving to provide frequency diversity in the case
`of OFDM transmission.
`
`signal strength, as illustrated in Figure 3.13b. Thus, the individual modulation symbols will typically
`not experience any substantial frequency diversity even if the channel is highly frequency selective
`over the overall OFDM transmission bandwidth. As a consequence, the basic error-rate performance
`of OFDM transmission over a frequency-selective channel is relatively poor and especially much
`worse than the basic error rate in the case of a single wideband carrier.
`However, in practice channel coding is used in most cases of digital communication and espe-
`cially in mobile communication. Channel coding implies that each bit of information to be transmit-
`ted is spread over several, often very many, code bits. If these coded bits are then, via modulation
`symbols, mapped to a set of OFDM subcarriers that are well distributed over the overall transmission
`bandwidth of the OFDM signal, as illustrated in Figure 3.14, each information bit will experience
`frequency diversity in the case of transmission over a radio channel that is frequency selective over
`the transmission bandwidth, despite the fact that the subcarriers, and thus also the code bits, will not
`experience any frequency diversity. Distributing the code bits in the frequency domain, as illustrated
`in Figure 3.14, is sometimes referred to as frequency interleaving. This is similar to the use of time-
`domain interleaving to benefit from channel coding in the case of fading that varies in time.
`Thus, in contrast to the transmission of a single wideband carrier, channel coding (combined with fre-
`quency interleaving) is an essential component in order for OFDM transmission to be able to benefit from
`frequency diversity on a frequency-selective channel. As channel coding is typically used in most cases of
`mobile communication this is not a very serious drawback, especially taking into account that a signifi-
`cant part of the available frequency diversity can be captured already with a relatively high code rate.
`
`3.8 SELECTION OF BASIC OFDM PARAMETERS
`If OFDM is to be used as the transmission scheme in a mobile-communication system, the following
`basic OFDM parameters need to be decided upon:
`● The subcarrier spacing Δf.
`● The number of subcarriers Nc, which, together with the subcarrier spacing, determines the overall
`transmission bandwidth of the OFDM signal.
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