**1. Introduction to SDR**

Software-defined radio (SDR) systems are those which can adapt to the future-proof solution and they cover both existing and emerging standards. An SDR has to possess elements of reconfigurability, intelligence and software programmable hardware [1]. As the functionality isdefinedinsoftware, anewtechnologycanbe easilyimplementedina software radiobymeans of a software upgrade. Channel equalization is an important subsystem in the software defined radio's receiver. For many years, modulation techniques have been extensively used for various

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

wireless applications, but the modern communication system requires data transmitted at a higher rate and larger bandwidth [2].

This chapter discusses an SDR system built using LabVIEW for a generic transceiver. SDR provides an alternative to systems such as the third-generation (3G) and the fourth-generation (4G) systems. There are two frequency bands where the software-defined radio might operate in the near future, that is, 54–862 MHz [very high-frequency (VHF) and ultra-high frequency (UHF) TV bands] and 3–10 GHz [ultra-wideband (UWB) radios]. A software-defined radio comprises a programmable communication system where functional changes can be made by merely updating the software. SDRs can be reconfigured and can talk and listen to multiple channels at the same time. Normally, high-performance digital signal processors (DSPs) are used to serve as the baseband processor. SDR systems can be used in ubiquitous network environments because of its flexibility and programmability [3]. The use of digital signals reduces hardware, noise and interference problems as compared to the analogue signal in transmission, which is one of the main advantages of digital transmission.

In this chapter, the software simulator of the SDR transceiver has been designed using LabVIEW and has been tested in real time using the universal software radio peripheral (USRP). Digital modulation schemes namely the frequency shift keying (FSK), phase shift keying (PSK) and quadrature amplitude modulation (QAM) are chosen to be the modulation schemes of the designed software-defined radio system due to its easy implementation and widespread usage in wireless communication equipment. Digital modulation techniques are considered to be very common technology for transmission and reception in current and future wireless communications, especially in the VHF and UHF frequency bands giving excellent bit error rate (BER) versus signal-to-noise ratio (SNR) ratio with high data rates. The role of modulation techniques in an SDR is very vital given that the modulation techniques describe the central part of any wireless technology. They can be reconfigured and can talk and listen to multiple channels at the same time. The role of modulation techniques in an SDR is very crucial since modulation techniques define the core part of any wireless technology. SDR's inherent flexibility must, however, be planned for in advance via hardware and software considerations, ultimately resulting in increased code portability, improved communications system life cycles and reduced costs. The main interest in any communication group is the sure sending of signals of info from a transmitter to a receiver [4]. The signals are transmitted via a guide who corrupts the signal. It is needful that the distorting effects of the channel and noise are minimized and that the information transmitted through the channel at any given time is maximized [5]. The channel is subject to various types of dissonance, twisting and interference. Also, some communication systems have limitations on transmitter power. All of this may lead to various types of errors. Consequently, we may need some form of error control encoding in order to recover the information reliably.

### **1.1. Related technologies of SDR**

In view of the fact that the field-programmable gate array (FPGA)'s prime function is to offer signal filtering and rate conversion from the analogue-to-digital converter (ADC) and to the system's digital-to analogue converter (DAC), its firmware can be customized to meet the particular needs of the user or just downloaded without modification, as a preconfigured file. Some of the USRP family support multi-radio cooperation using multiple-input, multiple output (MIMO) techniques. This is enabled by installing a MIMO interconnecting cable between two USRP devices [6].

To ensure reliable communication, forward error-correcting (FEC) codes are the main part of a communication system. FEC is a technique in which we add redundant bits to the transmitted data to help the receiver correct errors. There are two types of FEC codes: the convolutional codes and block codes. When we use block codes, they are defined by *n* and *k*, where *n* describes the total number of coded bits and *k* gives the number of input bits. In convolutional codes, the coding is applied to the entire data stream as one code word. In the year 1948, Shannon showed that arbitrarily reliable communication is only possible till the signal transmission rate does not exceed a certain limit which was termed as channel capacity [7]. After this different algebraic codes such as Golay codes, Bose-Chaud huri-Hocquenghem (BCH) codes and Reed-Solomon (RS) codes were created and used for error correction. The next series of codes originally referred as recurrent codes or convolutional codes were given which helped further to improve the error control coding [8]. The convolutional codes have efficient encoding and decoding algorithms and high performance over additive white Gaussian noise (AWGN) channels. Later on, concatenated-coding schemes were also given. Also, some weak points were there of convolutional codes during bursty transmissions which were later on reduced using Reed-Solomon codes by serially concatenating a convolutional code with an RS code. Development of turbo codes is the most recent discovery in the coding theory. Turbo codes show performance of near to Shannon limit with iterative decoding algorithms. Many iterative decoding algorithms came into existence such as Gallagher's low-parity density check (LDPC) codes [9]. Though these turbo codes exhibit excellent bit error performance but there are some problems associated with them such as these codes generate a certain number of low-weight code words which results in exhibition of an error 'floor' in the BER curve at high SNR. Also, the complexity of the soft-input, soft-output (SISO) decoder is such that low-cost decoders are unavailable for many commercial applications [10]. For these reasons, many applications still deploy RS codes because of its efficient decoder implementation and excellent error correction capabilities.

### **1.2. The benefits of multi-standard terminals**

A multi-standard terminal (MST) is a subscriber unit that is capable of operation with a variety of different mobile radio standards. Although it is not strictly necessary for such a terminal to be implemented using software-defined radio techniques, it is likely that this approach is the most economic in many cases [11].

### *1.2.1. Economies of scale*

wireless applications, but the modern communication system requires data transmitted at a

This chapter discusses an SDR system built using LabVIEW for a generic transceiver. SDR provides an alternative to systems such as the third-generation (3G) and the fourth-generation (4G) systems. There are two frequency bands where the software-defined radio might operate in the near future, that is, 54–862 MHz [very high-frequency (VHF) and ultra-high frequency (UHF) TV bands] and 3–10 GHz [ultra-wideband (UWB) radios]. A software-defined radio comprises a programmable communication system where functional changes can be made by merely updating the software. SDRs can be reconfigured and can talk and listen to multiple channels at the same time. Normally, high-performance digital signal processors (DSPs) are used to serve as the baseband processor. SDR systems can be used in ubiquitous network environments because of its flexibility and programmability [3]. The use of digital signals reduces hardware, noise and interference problems as compared to the analogue signal in

In this chapter, the software simulator of the SDR transceiver has been designed using LabVIEW and has been tested in real time using the universal software radio peripheral (USRP). Digital modulation schemes namely the frequency shift keying (FSK), phase shift keying (PSK) and quadrature amplitude modulation (QAM) are chosen to be the modulation schemes of the designed software-defined radio system due to its easy implementation and widespread usage in wireless communication equipment. Digital modulation techniques are considered to be very common technology for transmission and reception in current and future wireless communications, especially in the VHF and UHF frequency bands giving excellent bit error rate (BER) versus signal-to-noise ratio (SNR) ratio with high data rates. The role of modulation techniques in an SDR is very vital given that the modulation techniques describe the central part of any wireless technology. They can be reconfigured and can talk and listen to multiple channels at the same time. The role of modulation techniques in an SDR is very crucial since modulation techniques define the core part of any wireless technology. SDR's inherent flexibility must, however, be planned for in advance via hardware and software considerations, ultimately resulting in increased code portability, improved communications system life cycles and reduced costs. The main interest in any communication group is the sure sending of signals of info from a transmitter to a receiver [4]. The signals are transmitted via a guide who corrupts the signal. It is needful that the distorting effects of the channel and noise are minimized and that the information transmitted through the channel at any given time is maximized [5]. The channel is subject to various types of dissonance, twisting and interference. Also, some communication systems have limitations on transmitter power. All of this may lead to various types of errors. Consequently, we may need some form of error control encoding in

In view of the fact that the field-programmable gate array (FPGA)'s prime function is to offer signal filtering and rate conversion from the analogue-to-digital converter (ADC) and to the system's digital-to analogue converter (DAC), its firmware can be customized to meet the

transmission, which is one of the main advantages of digital transmission.

higher rate and larger bandwidth [2].

84 Field - Programmable Gate Array

order to recover the information reliably.

**1.1. Related technologies of SDR**

Even if terminal adaption over the air or via third-party software was not possible or was not permitted by, for example, regulatory bodies, the production benefits of a software-defined radio approach could well justify its existence. The wide range of new and existing standards in the cellular and mobile marketplace has resulted in the adoption of a diverse range of subscriber terminal (and base-station) architectures for the different systems deployed around the globe [12].

#### *1.2.2. Global roaming*

The present proliferation of mobile standards and the gradual migration to third-generation systems means that a large number of different network technologies will exist globally for some time to come. Indeed, even in the case of 3G systems, where a concerted effort was made by international standards bodies to ensure that a single global standard was produced, there are still significant regional differences, in particular between the US and European offerings (and also, potentially, China). With this background, it is clearly desirable to produce a terminal which is capable of operation on both legacy systems and the various competing 3G standards. Indeed, it could be argued that this is the only way in which 3G systems will be accepted by users, since the huge cost of a full-coverage network roll-out will discourage many operators from providing the same levels of coverage (at least initially) as their existing 2G systems enjoy. A user is unlikely to trade in his or her 2G terminal for one with perhaps better services, but significantly poorer basic voice coverage [13]. This is indeed what is happening in virtually all current 3G deployments. Software-defined radio architecture represents a very attractive solution to this problem.

#### *1.2.3. Upgrading the service*

A powerful benefit of a software-defined radio terminal, from the perspective of the network operator, is the ability to download new services to the terminal after it has been purchased and is operational on the network. At present, significant service upgrades require the purchase of a new terminal, with the required software built-in and this clearly discourages the adoption of these new services for a period. The launch of general packet radio service (GPRS) data services on the GSM network is a good example of this. With SDR handset architecture, services could be downloaded overnight, when the network is quiet, or from a website in the same manner as personal computer (PC) software upgrades are distributed [12]. There are clearly a number of logistical issues with this benefit (e.g., what to do about phones which are turned off at the time of the upgrade or what happens if a particular phone crashes with the new software, perhaps just prior to requiring the phone for an emergency call software which the phone user may not have wanted and so forth). Many of these problems have been solved by the PC industry and hence it is likely that this benefit will be realized in some manner with software-defined radios.

#### *1.2.4. Adaptive modulation and coding*

The ability to adapt key transmission parameters to the prevailing channel or traffic conditions is a further key benefit of a software-defined radio. It is possible, for example, to reduce the complexity of the modulation format, such as from 16-QAM (quadrature amplitude modulation) to quadrature phase-shift keying (QPSK) when channel conditions become poor, thereby improving noise immunity and decoding margin. It is also possible to adapt the channelcoding scheme to better cope with particular types of interference, rather than Gaussian noise, when moving from, say, a rural cell to an urban one [14]. Many parameters may be adapted dynamically, for example, burst structure, modulation type, data rate, channel and source coding, multiple-access schemes and so forth.

### **1.3. Operational requirements: various operational requirements for SDR are as stated below:**

## *1.3.1. Key requirements*

subscriber terminal (and base-station) architectures for the different systems deployed around

The present proliferation of mobile standards and the gradual migration to third-generation systems means that a large number of different network technologies will exist globally for some time to come. Indeed, even in the case of 3G systems, where a concerted effort was made by international standards bodies to ensure that a single global standard was produced, there are still significant regional differences, in particular between the US and European offerings (and also, potentially, China). With this background, it is clearly desirable to produce a terminal which is capable of operation on both legacy systems and the various competing 3G standards. Indeed, it could be argued that this is the only way in which 3G systems will be accepted by users, since the huge cost of a full-coverage network roll-out will discourage many operators from providing the same levels of coverage (at least initially) as their existing 2G systems enjoy. A user is unlikely to trade in his or her 2G terminal for one with perhaps better services, but significantly poorer basic voice coverage [13]. This is indeed what is happening in virtually all current 3G deployments. Software-defined radio architecture represents a very attractive

A powerful benefit of a software-defined radio terminal, from the perspective of the network operator, is the ability to download new services to the terminal after it has been purchased and is operational on the network. At present, significant service upgrades require the purchase of a new terminal, with the required software built-in and this clearly discourages the adoption of these new services for a period. The launch of general packet radio service (GPRS) data services on the GSM network is a good example of this. With SDR handset architecture, services could be downloaded overnight, when the network is quiet, or from a website in the same manner as personal computer (PC) software upgrades are distributed [12]. There are clearly a number of logistical issues with this benefit (e.g., what to do about phones which are turned off at the time of the upgrade or what happens if a particular phone crashes with the new software, perhaps just prior to requiring the phone for an emergency call software which the phone user may not have wanted and so forth). Many of these problems have been solved by the PC industry and hence it is likely that this benefit will be realized in

The ability to adapt key transmission parameters to the prevailing channel or traffic conditions is a further key benefit of a software-defined radio. It is possible, for example, to reduce the complexity of the modulation format, such as from 16-QAM (quadrature amplitude modulation) to quadrature phase-shift keying (QPSK) when channel conditions become poor, thereby improving noise immunity and decoding margin. It is also possible to adapt the channelcoding scheme to better cope with particular types of interference, rather than Gaussian noise,

the globe [12].

*1.2.2. Global roaming*

86 Field - Programmable Gate Array

solution to this problem.

*1.2.3. Upgrading the service*

some manner with software-defined radios.

*1.2.4. Adaptive modulation and coding*

The operational characteristics of an ideal multi-standard terminal include the following operations.

## *1.3.1.1. Software-definable operation*

As outlined earlier, the key to many of the advantages of a multi-standard terminal lies in its ability to be reconfigured either during manufacture, prior to purchase, following purchase (e.g., after-market software), in operation (e.g., adaptation of coding or modulation), or preferably all four. This impacts primarily upon the digital and baseband sections of the terminal and will require the use of reprogrammable hardware as well as programmable digital signal processors in a power and cost-effective implementation.

#### *1.3.1.2. Multi-band operation*

The ability to process signals corresponding to a wide range of frequency bands and channel bandwidths is a critical feature of an MST. This will impact heavily on the radio frequency (RF) segments of the terminal and it is this area which is arguably the main technology limitation on software-defined radio implementation at present [15] (although processor power consumption and cost are still both major issues for SDR).

#### *1.3.1.3. Multi-mode operation*

Many multi-mode software-defined radios already exist, although they are often not promoted as such (since the other features/benefits of software-defined radio techniques are not exploited). The ability to change mode and, consequently, modulation, coding, burst structure, compression algorithms and signalling protocols is clearly an essential feature of an MST.

### **1.4. Digital aspects of a software-defined radio**
