Signal Processing for Wireless Transceivers - Signal Processing Systems - page 168

1 Introduction and System Overview

More and more devices will be connected to the global ubiquitous information
network with the Wireless World Research Forum (WWRF) [ http://www.wireless-
world-research.org/ ] vision of seven trillion wireless devices serving seven billion
people by 2020. The diversity of the devices and services will increase. While the
demand of high data rates to provide multimedia services, like video transmission, is
increasing, the demand of low rate sensor information to enable location and context
awareness of the services is also increasing.
To enable the cost, energy and bandwidth efficient realization of the vision, the
transceiver and technology need to make major leaps. One of the key concerns
is the overall power and energy consumption of the devices and the whole net-
work infrastructure. The energy efficiency is major issue from battery and device
operation perspective, but also relates to the sustainable development when the
complete system is concerned. Therefore, in addition to more conventional target
of bandwidth efficiency and increasing the data rates, also the power and energy
efficiency of the evolving wireless systems is of major concern. The goal of this
chapter is to introduce the key aspects of the baseband (BB) and radio frequency
(RF) signal processing chains of wireless transmitters and receivers. Our emphasis
is on cellular type systems, but many of the principles can be applied in various
short range, wireless local area networks and other wireless applications.
The higher layers of the communication protocol stack of the Open System
Interconnect (OSI) model have conventionally been designed separate from the
physical layer. However, the current wireless systems are introducing more and
more crosslayer design and optimization. As an example, the evolving cellular
Third Generation (3G) Long Term Evolution (LTE) systems use so called channel
aware user scheduling and radio resource management (RRM) techniques. The
applied methodology capitalizes on signal processing tools and uses to some extent
similar approach as the physical layer signal processing. However, we do not cover
those either, but they are definitely important currently evolving fields of research
and development. Signal processing tools are applied in wireless devices also in
multimedia and application processing, data compression, etc. However, we do not
cover those aspects, but concentrate on the connectivity related problems on the
physical layer.
The typical transmitter (TX) and receiver (RX) functionalities are summarized
in Fig. 1 . The purpose of forward error control (FEC) coding and interleaving is to
protect the information from errors. Data modulation transforms the information bit
sequence into a complex multi-level symbol sequence with reduced sample rate and
bandwidth. The waveform generation block creates a discrete-time baseband signal
with specific spectral and time-domain characteristics suitable for transmission in
the used frequency band and radio propagation environment. The fundamental
classes of waveforms include linear and FSK-type single-carrier transmission,
multicarrier transmission, as well as spread-spectrum techniques. Multiplexing and
multiple-access functionalities are also closely related with waveform generation.