Author interview - Elsevier

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12 Δεκ 2013 (πριν από 3 χρόνια και 7 μήνες)

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Elsevier: You have included in this new edition 160 new pages on LTE, with total LTE content in
the book of 270 pages. Can you tell us briefly what are the key developments in LTE that you
have included in this new edition?


SP:

The LTE standard is now co
mplete. Compared to the first edition, which we wrote while the
LTE standard was maturing, the LTE coverage in the second edition has been expanded
significantly. I would say that the LTE part is to a large extent rewritten to capture the final
decisions a
nd details of LTE. In essence, the description now provides an additional level of
details compared to the first edition.

Furthermore, we also describe the background to
why

certain
decisions were made. We think that understanding the background to the des
ign choices made is
very useful in understanding LTE and this is also information that normally is not found in the
specifications.


One aspect distinguishing this book from other text on LTE is that we cover both FDD
and

TDD
in a common description. In th
e first edition, the focus was mainly on FDD as, at that stage, TDD
had not yet matured. One of the key features of LTE, not found in previous 3GPP standards, is
the supports of both FDD and TDD with a
single

radio
-
access scheme. As part of this, we
descri
be several interesting design aspects, for example how to support coexistence between LTE
and other TDD technologies with different frame structures.


TP: Can you explain why
such coexistence

is important?


SP:

Migration to a new radio
-
access technology i
s typically done gradually and several operators
will therefore operate LTE in parallel to other standards for quite some time, often in the same
frequency band, and avoiding interference between the different systems is therefore important.
Therefore, LTE
’s TDD mode has been designed to support efficient coexistence with for example
TD
-
SCMDA, currently deployed in China.


The support of both FDD and TDD is part of spectrum flexibility, one of the key
fetuses

of LTE.
This also includes support for different

bandwidths
. From a baseband perspective, supporting
different bandwidths is relatively straight forward, but it is challenging from an RF perspective.
Defining the RF requirements such as out
-
of
-
band emission etc for flexible spectrum allocations
required

3GPP to develop new generic principles. This is described in one of the new chapters.


TP: Could you elaborate on the structure of the book?


ED:

Similar to the HSPA part of the book, we have tried to use a “layered” approach, starting
with a “stand alone
” overall description of LTE in the first chapters of the LTE part. A reader
may start with these chapters to quickly get an overall understanding of what LTE is.


In the following chapters, we describe in detail the downlink and uplink physical layer of L
TE.
These two chapters, in total more than 100 pages, are completely new compared to the first
edition. Some of the aspects covered are frame structure (both FDD and TDD), reference signals,
control signaling, channel coding, multi
-
antenna transmission, an
d MBSFN transmission.


The following chapters, around 120 pages, describe the procedures a terminal use to access an
LTE network, for example cell search and random access. We also describe the procedures and
mechanism necessary for data transmission, for

example scheduling, rate adaptation, power
control and retransmission mechanisms.


Finally, there is a chapter devoted to the future
evolution

of LTE towards 4G and IMT
-
Advanced.



Elsevier:
You are all heavily involved in the standardization process. Wh
at key insights do you
give in the book that cannot be found in the standard?


SP:

A specification can be compared to a legal contract. It gives an unambiguous, water
-
proof
description of WHAT the signals should look like and WHAT the terminal should do in

certain
situations. If this was not the case, there would be a clear risk that terminals and base stations
from different vendors could not communicate. To avoid inconsistencies, the specification is also
written in a very compact way. For example, there
may just be an equation stating that a certain
signal shall be transmitted, but without any description of the purpose of the signal. Reading a
specification therefore requires some effort. After reading the spec, you would, if you are still
awake

, know
WHAT to transmit,
but
not

WHY and HOW. This is where our book becomes
important. Not only does it provide an easy
-
to
-
read description of the signals, procedures, and
mechanisms in LTE, it also tells you WHY a certain signal, channel or procedure is present

and
HOW is it used. After reading the book, you will have a good understanding on how LTE works
and why it is designed the way it is.


Elsevier: Why do you think network operators have adopted, and will adopt in the future, LTE?


ED:

There is today a v
ery large momentum behind both 3GPP standards such as LTE and HSPA
as the choice for mobile broadband.
All the major operators
in the world
have confirmed that they
have a long
-
term strategy to move to LTE

as the technology for their networks. Mobile syste
m
vendors such as Ericsson are announcing network products for LTE and also technology
platforms for mobile and laptop use. The reason is that LTE is seen as the natural choice for
future networks, since it is developed with high requirements on mobile bro
adband operation.


There is also a huge increase in use of mobile broadband through 3G networks, where HSPA the
technology of choice today. There are more than 60 million users of mobile broadband today,
some use HSPA over their mobile phone, wile other h
ave “dongles” connected to their laptops, or
an HSPA modem built into their laptop. You can today get a laptop at no cost and just pay for the
mobile broadband subscription, in the same way as you do for a mobile. This momentum for
mobile broadband across
the world spills off in an increased interest in LTE as the next
technology of choice for mobile broadband.


Elsevier: You have a chapter on other communication systems. What are the key differences of
LTE with some of these?


SP:

This chapter treats some
of the other 3G systems, which is useful as background.
For
example, a TD
-
SCDMA overview is part of this chapter and thus gives some background to some
of the requirements set on LTE TDD with respect to coexistence. Another example is 1x EV
-
DO,
a standard
used in the US and some other countries, with many basic principles being similar to
HSPA.


It is expected that LTE will become the dominant standard in the future, but some of these other
systems will be in operation for quite some time and it is therefor
e useful to have a brief
understanding of these as well.


Elsevier: Who do you think could benefit from the book and why?


ED:

Anybody who work in telecoms with mobile broadband and needs to be updated on the latest
technology developments will find a lot

of useful material in the book. It gives full
-
coverage
description of both HSPA, which is today’s mobile broadband technology of choice and LTE,
which is the next step. The descriptions of both HSPA and LTE are given with several levels of
detail, first a
s an overview description, then a more detailed description of the physical layer and
as the final step very detailed descriptions of procedures and mechanisms of LTE and HSPA.



Elsevier:
How do you see the development of IMT
-
Advanced playing out in the n
ext few
years?



ED:

ITU has recently issued a request for candidates for so
-
called IMT
-
Advanced radio access,
also often referred to as 4G radio access. If one looks at the requirements on IMT
-
Advanced one
can see that already the first release of LTE
a
ctually fulfills

most of these requirements implying
that 4G radio access is already here by means of LTE.


To further boost LTE capabilities and make it fully IMT
-
Advanced capable, 3GPP has recently
initiate work on the next release of LTE, often referre
d to as LTE
-
Advanced.


Within this second edition of the book we have captured also these discussions. What we have
captured is an overview of the targets of LTE
-
Advanced as agreed by 3GPP. These requirements
do not only correspond to the requirements on I
MT
-
Advanced but actually goes beyond that, We
also provide an overview of the different technology components that are being considered for
LTE
-
Advanced, such as even wider bandwidth and different types of inter
-
cell coordination
schemes and relaying funct
ionality that is currently being considered for LTE
-
Advanced. As far
as we know, this is the only book available that really discusses LTE
-
Advanced on a technical
level.