Waveforms and channel coding for 5G

Abstract. The fifth generation (5G) communication systems are required to perform significantly better than the existing fourth generation (4G) systems in data rate, capacity, coverage, latency, energy consumption and cost. Hence, 5G needs to achieve considerable enhancements in the areas of bandwidth, spectral, energy, and signaling efficiencies and cost per bit. The new radio access technology (RAT) of 5G physical layer needs to utilize an efficient waveform to meet the demands of 5G. Orthogonal frequency division multiplexing (OFDM) is considered as a baseline for up to 30 GHz. However, a major drawback of OFDM systems is their large peak to average power ratio (PAPR). Here in this thesis, a simple selective-mapping (SLM) technique using scrambling is proposed to reduce the PAPR of OFDM signals. This technique selects symbol sequences with high PAPR and scrambles them until a PAPR sequence below a specific threshold is generated. The computational complexity of the proposed scheme is considerably lower than that of the traditional SLM. Also, performance of the system is investigated through simulations and more than 4.5 dB PAPR reduction is achieved. In addition, performance of single carrier waveforms is analyzed in multiple-input multiple-output (MIMO) systems as an alternative to OFDM. Performance of a single carrier massive MIMO system is presented for both uplink and downlink with single user and multiple user cases and the effect of pre-coding on the PAPR is studied. A variety of channel configurations were investigated such as correlated channels, practical channels and the channels with errors in channel estimate. Furthermore, the candidate coding schemes are investigated for the new RAT in the 5G standard corresponding the activities in the third generation partnership project (3GPP). The schemes are evaluated in terms of block error rate (BLER), bit error rate (BER), computational complexity, and flexibility. These parameters comprise a suitable set to assess the performance of different services and applications. Turbo, low density parity check (LDPC), and polar codes are considered as the candidate schemes. These are investigated in terms of obtaining suitable rates, block lengths by proper design for a fair comparison. The simulations have been carried out in order to obtain BLER / BER performance for various code rates and block lengths, in additive white Gaussian noise (AWGN) channel. Although polar codes perform well at short block lengths, LDPC has a relatively good performance at all the block lengths and code rates. In addition, complexity of the LDPC codes is relatively low. Furthermore, BLER/BER performances of the coding schemes in Rayleigh fading channels are investigated and found that the fading channel performance follows a similar trend as the performance in the AWGN channel

Models of Control Channels in the LTE System

Dizertační práce se zabývá zpracováním signálu fyzických řídicích kanálů systému LTE a vyšetřováním bitové chybovosti při přenosu řídicí informace z vysílače do přijímače v závislosti na podmínkách příjmu. Práce je rozdělena do dvou hlavních částí. První část práce je zaměřena na simulaci přenosu řídicí informace LTE v základním pásmu. Jsou zde prezentovány vytvořené simulátory řídicích kanálů ve směru uplink i downlink. Simulace jsou provedeny pro všechny druhy nastavení systému a základní modely přenosového prostředí. Jsou zde popsány výsledky vlivu použití MIMO technologií na kvalitu příjmu řídicí informace především v únikových kanálech. Druhá část práce je zaměřena na možnost nasazení systému LTE ve sdíleném pásmu ISM (2.4 GHz). Jsou zde představeny základní koncepce použití, na jejichž základě je vytvořen scénář simulací. Kapitola dále popisuje tvorbu simulátoru koexistence LTE a systému Wi-Fi v přeneseném pásmu ISM 2.4GHz. Jsou zde uvedeny výsledky simulací koexistence LTE a rušivého systému Wi-Fi provedených dle vytvořeného scénáře. Výsledky simulací koexistence LTE a Wi-Fi jsou ověřeny měřením v laboratorních podmínkách. Toto porovnání je důležité z hlediska optimalizace simulátoru koexistence. Dle výsledků obou typů simulací a měření jsou stanovena provozní doporučení, která mají přispět k bezpečnému a spolehlivému vysílání a příjmu řídicích informací LTE i při nepříznivých podmínkách příjmu.The doctoral thesis is focused on a signal processing in the LTE physical control channels and performance analysis of control information transmission according to receiving conditions. The thesis is divided into two parts. The first part deals with simulation of the transmission of control information in baseband. The created simulators for uplink and downlink are presented. The simulations are performed for all possible system settings and various channel models. The MIMO influence on a quality of control information reception under fading channels is also presented. The second part of the thesis is focused on LTE utilization in shared channel ISM (2.4 GHz). The basic LTE application concept for ISM band is presented. This concept is fundamental to created simulation scenario. The chapter also presents the LTE and Wi-Fi coexistence simulator in 2.4 GHz ISM passband. The coexistence simulation are presented according to simulation scenario and the results are shown. The simulated coexistence analysis results are verified in laboratory environment. The comparison of the simulated and the measured coexistence analysis results is crucial for further optimization of the coexistence simulator. Recommendations for optimal and reliable operation of LTE are specified according to the simulated and the measured results. Recommendations should be useful to the reliable transmission of LTE control information in bad receiving conditions.

Digital signal processing techniques for peak-to-average power ratio mitigation in MIMO–OFDM systems

The focus of this thesis is to mitigate the very large peak-to-average transmit power ratios (PAPRs) inherent to conventional orthogonal frequency division multiplexing (OFDM) systems, particularly in the context of transmission over multi-input multi-output (MIMO) wireless broadband channels. This problem is important as a large PAPR generally needs an expensive radio frequency (RF) power amplifier at the transmitter due to the requirement for linear operation over a wide amplitude range and such a cost would be compounded when multiple transmit antennas are used. Advanced signal processing techniques which can reduce PAPR whilst retain the integrity of digital transmission therefore have considerable potential for application in emergent MIMO–OFDM wireless systems and form the technical contributions of this study. [Continues.

Performance analysis of multi-antenna and multi-user methods for 3G and beyond

Performance of cellular networks has become an issue with forecasted growing public demand for medium and high data rate services. Motivated by these expectations multi-antenna techniques such as transmit diversity (TD), channel-aware scheduling and multiple-input multiple-output (MIMO) transceivers have received a lot of enthusiasm within wireless communications community. We first focus on closed-loop (CL) TD and introduce extended mode 1 and 2 (e-mode 1 and 2) algorithms that are designed based on universal terrestrial radio access (UTRA) frequency division duplex (FDD) CL mode 1 and 2. We derive analytical performance results for e-mode 1 and 2 in terms of signal to noise ratio (SNR) gain, link capacity and bit error probability (BEP). We also consider the effect of feedback errors to the performance of closed-loop system. In the analysis of channel-aware scheduling we focus on on-off scheduling (OOS) where user's feedback consists of only a single bit. Performance results in both downlink and uplink clearly indicate that most of the achievable gain from channel-aware scheduling can be obtained with very scarce channel state information (CSI). Results also show that the design of feedback channel is of great importance because feedback errors may seriously degrade the system performance. The third topic of the thesis concentrates on MIMO techniques that can be implemented in UTRA FDD uplink without major revisions to the current air interface. We show that the UTRA FDD uplink coverage and capacity performance can be boosted by single-input multiple-output (SIMO) and MIMO transceivers. The information MIMO employing parallel multiplexing instead of transmit diversity shows its potential when extremely high user data rates are needed.Solukkoverkkojen suorituskyky on noussut tärkeään rooliin nopeiden datapalveluiden kasvuennusteiden myötä. Näiden kasvuodotusten perusteella moniantennitekniikat kuten lähetysdiversiteetti, kanavan huomioon ottava lähetyksen aikataulutus sekä useaa samanaikaista datavirtaa tukevat lähetinvastaanotinmenetelmät ovat saaneet osakseen paljon kiinnostusta langattoman tietoliikenteen tutkijayhteisössä. Tutkimuksessa keskitytään aluksi suljettua säätöä käyttäviin lähetysdiversiteettimenetelmiin, missä yhteydessä esitellään laajennetut moodien 1 ja 2 algoritmit, jotka on aiemmin kehitetty kolmannen sukupolven WCDMA järjestelmän suljetun säädön moodien 1 ja 2 pohjalta. Laajennetuille moodien 1 ja 2 algoritmeille johdetaan analyyttisiä suorituskykytuloksia käyttäen mittarina signaali-kohinasuhteen parannusta, linkin kapasiteettia sekä bittivirheiden todennäköisyyttä. Myös säätövirheiden vaikutusta järjestelmän suorituskykyyn tarkastellaan. Lähetyksen aikataulutuksen analyysi painottuu kytkettyyn aikataulutukseen, missä käyttäjän säätöinformaatio sisältyy yhteen bittiin. Sekä ylä- että alalinkin suorituskykytulokset osoittavat selvästi, että suurin osa mahdollisesta parannuksesta voidaan saavuttaa hyvin karkeaan kanavatilan informaatioon perustuen. Tulokset osoittavat myös, että säätökanavan suunnittelu on tärkeää, koska säätövirheet voivat vakavasti heikentää järjestelmän suorituskykyä. Kolmannessa aihealueessa keskitytään moniantennitekniikoihin, jotka voidaan toteuttaa WCDMA järjestelmän ylälinkissä ilman perustavanlaatuisia muutoksia nykyiseen ilmarajapintaan. Tutkimuksessa osoitetaan, että ylälinkin peittoa ja kapasiteettia voidaan parantaa tutkituilla moniantennitekniikoilla olipa lähettimessä yksi tai useampia antenneja. Menetelmä, jossa informaatio jaetaan useisiin rinnakkaisiin datavirtoihin sen sijaan että käytettäisiin vain yhtä datavirtaa, osoittautuu erityisen lupaavaksi kun tarvitaan hyvin nopeita tiedonsiirtoyhteyksiä.reviewe