Investigating methods of incoherent detection of ultra-wideband signals

Master's thesis in the field of telecommunication engineering - system

Abstract

Investigation of methods of incoherent detection of broadband signals

With the emergence and expansion of the system Telecommunication systems with very narrow pulse width, very wide bandwidth, limited bandwidth and speed of existing electronic components, it is difficult to use many previously known incoherent detection structures, and designing a suitable receiver in such systems is of particular importance. In the field of radio, the design of simple and low-power receivers in ultra-wideband telecommunications (UWB [1]) without using complex channel estimation mechanisms that have acceptable performance is of great interest.

In this thesis, different types of incoherent detection of UWB signals have been investigated. In order to investigate these issues, first, the UWB system model has been introduced, and then the channel model used in the UWB system, which is based on two types of IEEE standards, has been studied, and their results have been analyzed using simulation. In the following, various methods of incoherent detection of UWB signals have been investigated and their efficiency has been compared and investigated using simulation. In the next part of the thesis, we proposed two types of multisymbol incoherent detection for pulse position modulation of UWB signals. In this method, we used the GLR method [2] to extract the incoherent detector of an observation block containing consecutive symbols. In this method, we do not need any information from the channel. Next, after extracting the GLR detector, in order to reduce the computational complexity of the detector, we used the SDR technique [3] to implement it. In the following, we improved the estimation of the received signal by assuming the thinness of the channel, and taking into account the new estimation of the received signal, we extracted the improved GLR detector. Then, in order to reduce its computational complexity, we used the SDR technique to implement it. The simulation results show the efficiency and performance of the proposed detectors. As we will see, when the number of symbols sent in an observation block increases, the efficiency of both proposed detectors will be close to the ideal Rake receiver.

Introduction

The emergence of telecommunication systems with very narrow pulse width and very wide bandwidth and the emergence of various applications for them, in recent years, has led to extensive research in There are various theoretical aspects and practical implementation of such systems. Ultra-wideband (UWB) systems have been used in military telecommunications, positioning and radar since about 20 years ago, and recently attention has been paid to consumer electronics and telecommunications. But with the increasing demand for the commercial application of this technique and with the efforts that started in the late 1990s, the license to use the frequency range of about 3-10 GHz was finally issued, under the condition of observing strict limits on the transmitted power ceiling. In fact, many wireless telecommunication systems use separate narrowband frequencies in order to avoid interference with each other. However, in order to prevent interference with other systems, they can be used for UWB systems, provided that strict limits on the transmitted power ceiling and the spectrum defined by the FCC are observed.

UWB systems have unique features compared to other telecommunication systems. Two unique features of UWB systems are very wide bandwidth and low duty cycle. A very wide bandwidth leads to the transmission of very narrow pulses that carry bits of information. In fact, UWB systems, instead of using very high power in separate frequency ranges, use low power signals in a very high frequency range. Therefore, sending UWB signals appeared as a noisy signal for other telecommunication systems. UWB systems can be used for indoor applications that require high data rates and in the short distance range of 1 to 10 meters.. Duty Cycle is defined as the ratio of the time a pulse is placed in a periodic period, which in UWB systems is very low and around 0.005.

1-1- Definition

The word UWB, despite its relatively general meaning before the 1990s, was applied to signals that have a bandwidth of at least 500 MHz. or their relative bandwidth (ratio of bandwidth to central frequency) is more than 20% [3]. The relative bandwidth is expressed as follows:

(1-1)

The cutoff frequencies are high and low. In the FCC report [3], the use of UWB is classified into three groups: 1. Measurement and telecommunication systems 2. Transmission radar systems 3. Image systems. Here is the spectral band corresponding to the first group in Figure (1-1). As you can see, the frequency spectrum allocated for UWB transmission is 1.3 to 10.6 GHz and the maximum power level allowed for UWB transmission is 41.3 dBm/MHz, this power level is lower than the noise power level for UWB telecommunication systems. They have unique features that distinguish UWB systems from other classical narrowband systems [1, 2, 5, 6, 14]. These features include:

1- The ability to use UWB systems along with other wireless systems. The FCC power limit requires UWB systems to be able to transmit pseudo-noise signals that will lead to a low probability of detection and interference for other systems (Figure 2-1).

2- They are able to compromise between distance and data rate. Suppose a pulse is sent to carry one bit of data, for long distances, in order to be acceptable, it can be high and high will lead to low data rate, in other words, it can be reduced for low distance and lead to high data rate. Therefore, the number of pulses per bit is used to send over long distances.

3- They have the ability to have a large capacity. Shannon's famous equation for capacity gives us insight into the advantages of UWB wireless systems. According to Shannon's law, the capacity of a channel is expressed as follows:

(1-2)

and they express the total signal power and noise power, respectively, and it is the channel bandwidth. The low transmit power level of UWB systems is useless for channel capacity, however, UWB systems compensate for the low signal-to-noise (SNR) effect due to their high bandwidth. Therefore, UWB systems are recommended for high capacity wireless communication [5]. style="direction: rtl;"> 

By

 Zakiyeh Atbaee

With the emergence and development of ultra wideband communication systems incorporating ultrashort pulses, the design of suitable receiver structures become one of the most significant problems in such system; since due to the limited bandwidth and speed of current electronic devices, most of the existing receiver structures cannot be used properly. In the field of radio communications, the design of simple and low power consumption receivers for ultra wideband (UWB) systems, which do not rely on complex channel estimation mechanisms, is of much interest.

In this thesis, noncoherent detection methods have been examined. In order to examine these problems, first the system model of UWB signals was produced, then the channel models of UWB systems based on IEEE standard have been studied and the simulation results of them have been shown and compared.