Differential data-aided channel estimation for up-link massive SIMO-OFDM

Pilot symbol assisted modulation (PSAM) is widely used to obtain the channel state information (CSI) needed for coherent demodulation. It allows the density of pilot symbols to be dynamically chosen depending on the channel conditions. However, the insertion of pilots reduces the spectral efficiency, more severely when the channel is highly time-variant and/or frequency-selective. In these cases a significant amount of pilots is required to properly track the channel variations in both time and frequency dimensions. Alternatively, non-coherent demodulation does not require any CSI for the demodulation independently of the channel conditions. For the particular case of up-link (UL) based on massive single input -multiple output (SIMO) combined with orthogonal frequency division multiplexing (OFDM), we propose to replace the traditional reference signals of PSAM by a new differentially-encoded data stream that can be non-coherently detected. The latter can be demodulated without the knowledge of the CSI and subsequently used for the channel estimation. We denote our proposal as hybrid demodulation scheme (HDS) because it exploits both the benefits of a coherent demodulation scheme (CDS) and a non-coherent demodulation scheme (NCDS) to increase the spectral efficiency. The mean squared error (MSE) of the channel estimation, bit error rate (BER), achieved throughput and complexity are analyzed to highlight the benefits of this differential data-aided channel estimation as compared to other approaches. We show that the channel estimation is almost as good as PSAM, while the BER performance and throughput are improved for different channel conditions with a very small complexity increase.This work has received funding from the European Union (EU) Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie ETN TeamUp5G, grant agreement No. 813391, and from the Spanish National Project TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE)

Doctor of Philosophy

dissertationMultiple-input and multiple-output (MIMO) technique has emerged as a key feature for future generations of wireless communication systems. It increases the channel capacity proportionate to the minimum number of transmit and receive antennas. This dissertation addresses the receiver design for high-rate MIMO communications in at fading environments. The emphasis of the thesis is on the cases where channel state information (CSI) is not available and thus, clever channel estimation algorithms have to be developed to bene t from the maximum available channel capacity. The thesis makes four distinct novel contributions. First, we note that the conventional MCMC-MIMO detector presented in the prior work may deteriorate as SNR increases. We suggest and show through computer simulations that this problem to a great extent can be solved by initializing the MCMC detector with regulated states which are found through linear detectors. We also introduce the novel concept of staged-MCMC in a turbo receiver, where we start the detection process at a lower complexity and increase complexity only if the data could not be correctly detected in the present stage of data detection. Second, we note that in high-rate MIMO communications, joint data detection and channel estimation poses new challenges when a turbo loop is used to improve the quality of the estimated channel and the detected data. Erroneous detected data may propagate in the turbo loop and, thus, degrade the performance of the receiver signi cantly. This is referred to as error propagation. We propose a novel receiver that decorrelates channel estimation and the detected data to avoid the detrimental e ect of error propagation. Third, the dissertation studies joint channel estimation and MIMO detection over a continuously time-varying channel and proposes a new dual-layer channel estimator to overcome the complexity of optimal channel estimators. The proposed dual-layer channel estimator reduces the complexity of the MIMO detector with optimal channel estimator by an order of magnitude at a cost of a negligible performance degradation, on the order of 0.1 to 0.2 dB. The fourth contribution of this dissertation is to note that the Wiener ltering techniques that are discussed in this dissertation and elsewhere in the literature assume that channel (time-varying) statistics are available. We propose a new method that estimates such statistics using the coarse channel estimates obtained through pilot symbols. The dissertation also makes an additional contribution revealing di erences between the MCMC-MIMO and LMMSE-MIMO detectors. We nd that under the realistic condition where CSI has to be estimated, hence the available channel estimate will be noisy, the MCMC-MIMO detector outperforms the LMMSE-MIMO detector with a signi cant margin

Advanced transmitter and receivers in future wireless networks

O objectivo desta dissertação é aprofundar o estudo de tecnologias que permitam atingir comunicações mais eficientes e fiáveis nas futuras redes sem fios. Uma das tecnologias estudadas nesta dissertação e que ainda não existem muitos estudos é o Complex Rotation Matrix (CRM). Esta tecnologia é bastante útil em sistemas que usem multi-portadoras como o Orthogonal Frequency Division Multiplexing (OFDM) pois permite dividir a informação pelas várias sub-portadoras. Caso este sistema use também a tecnologia MIMO ainda permitirá a divisão da informação por várias antenas. As constelações hierárquicas são outro dos temas abordados nesta dissertação e são um método eficiente de entregar o mesmo conteúdo a diferentes utilizadores. Esta técnica poderá ser bastante útil tanto em sistemas de uma portadora como multi-portadoras. O Single Carrier (SC) é outra das tecnologias abordadas nesta dissertação. Um dos standards em que poderia ser utilizado tanto o OFDM com o SC é no Digital Video Broadcasting – Satellite services to Handhelds (DVB-SH). Este esquema de comunicação tem com propósito a entrega de conteúdos multimédia aos terminais móveis via comunicação com estações base ou por satélite. O uso de o OFDM no downlink (DL) e do SC no uplink (UL) no mesmo standard/protocolo teria repercussões também ao nível dos terminais móveis pois permitiria uma melhor eficiência na duração das baterias. Os resultados obtidos nesta tese visam sobretudo o estudo do CRM, estimação de canal e constelações hierárquicas. Para a obtenção de resultados foram efectuadas simulações com o método de Monte Carlo e Turbo Códigos. Os simuladores foram desenvolvidos em Matlab.The main purpose of this dissertation is the study of technologies that allow achieving more reliable and efficient communications in wireless systems. One of the technologies studied in this dissertation and practically new is the Complex Rotation Matrix (CRM). This technology is useful in systems that use multi-carrier as the Orthogonal Frequency Division Multiplexing (OFDM). The hierarchical constellations are other theme approached in this dissertation and it purpose efficiently is to deliver the same content to different users. Another technology studied in this dissertation was the Single Carrier (SC) with Frequency Division Equalization. The SC is a well-know technology and is used in several telecommunications systems. The goal is the future wireless communications adopt the two technologies in the same system and use one of them depending of the situation. The Digital Video Broadcasting – Satellite services to Handhelds (DVB-SH) is one standard that can take advantage of the using of the OFDM and SC in the same system. The main goal of the DVB-SH is deliver multimedia content via satellite communications or communications with base stations to mobile terminals. The mobile terminals can achieve a more efficiency in their batteries whether in a standard/protocol that uses OFDM in DL and SC in UL. The results obtained with this thesis have the purpose to study the CRM, channel estimation and hierarchical constellation. The simulators were developed in Matlab platform and Turbo Codes are the codification used, channel estimation is also used and all the simulations were made with the Monte Carlo method

Study and implementation of a low complexity receiver using TCH codes

The use of coding in telecommunications systems reveals to be a technique with an essential contribution to the improvement of the recovery of transmitted signals. Depending on the circumstances to which a signal is subjected at transmission, by recurring to coding, it is possible to attenuate the unfavorable effects that result from this process, obtaining a signal with superior quality in comparison with a scenario where the presence of coding is absent. This study aims to test the feasibility of a high-rate wireless communications system using TCH codes being applied to an OFDM signal, subjected to noise components introduced by a wireless AWGN channel, considering a free path propagation model. Due to their correlation properties, the use of TCH codes reveals to be adequate since they allow the same codewords to be used to realize both error correction and channel estimation, mitigating the channels effects, leading to the realization of a receiver with lower complexity. With the intent of performing a qualitative analysis to this system, a simple simulation is executed in MATLAB where an OFDM signal is generated, being therefore applied various TCH codes and, through channel estimation, obtain the BER for their respective code lengths and, consequently, coding gains. The results were obtained for the modulation indexes of 16, 64 and 256-QAM. These demonstrate that the implementation of TCH codes is a viable option to reduce the rate of recovered errors, enabling the reception of a signal with better reliability, especially for higher code lengths and modulation indexes.O uso de codificação em sistemas de telecomunicações revela-se uma técnica com um contributo essencial na melhoria da recuperação de sinais transmitidos. Dependendo das circunstâncias às quais um sinal é submetido aquando a sua transmissão, com recurso à codificação, é possível atenuar os efeitos adversos resultantes deste processo, obtendo uma qualidade no sinal recebido superior face a um cenário com ausência da mesma. Este estudo tem como objetivo testar a exequibilidade de um sistema de comunicações sem fios para alto débito usando códigos TCH e aplicando-os a um sinal OFDM, sujeito a componentes de ruído introduzidos por um canal sem fios AWGN, considerando um modelo de propagação em espaço livre. Devido às propriedades de correlação destes códigos, a sua utilização revela-se adequada pois permite que as mesmas palavras de código sejam utilizadas para efetuar correção de erros, minimizando os efeitos do canal, possibilitando o desenvolvimento de um recetor com menor complexidade. Visando efetuar uma análise qualitativa do sistema, é realizada uma simulação simples em MATLAB onde é gerado um sinal OFDM ao qual são aplicados diversos códigos TCH, realizando estimação de canal com a finalidade de obter o BER para os diferentes comprimentos dos códigos e, consequentemente, ganhos de codificação relativos aos mesmos. Os resultados obtidos foram realizados para os índices de modulação 16, 64 e 256-QAM. Estes demonstram que o uso destes códigos é uma opção viável para reduzir os erros detetados, permitindo recuperar o sinal com maior fiabilidade, especialmente para comprimentos de código e índices de modulação elevados

Analysis and Design of Algorithms for the Improvement of Non-coherent Massive MIMO based on DMPSK for beyond 5G systems

Mención Internacional en el título de doctorNowadays, it is nearly impossible to think of a service that does not rely on wireless communications. By the end of 2022, mobile internet represented a 60% of the total global online traffic. There is an increasing trend both in the number of subscribers and in the traffic handled by each subscriber. Larger data rates, smaller extreme-to-extreme (E2E) delays and greater number of devices are current interests for the development of mobile communications. Furthermore, it is foreseen that these demands should also be fulfilled in scenarios with stringent conditions, such as very fast varying wireless communications channels (either in time or frequency) or scenarios with power constraints, mainly found when the equipment is battery powered. Since most of the wireless communications techniques and standards rely on the fact that the wireless channel is somehow characterized or estimated to be pre or post-compensated in transmission (TX) or reception (RX), there is a clear problem when the channels vary rapidly or the available power is constrained. To estimate the wireless channel and obtain the so-called channel state information (CSI), some of the available resources (either in time, frequency or any other dimension), are utilized by including known signals in the TX and RX typically known as pilots, thus avoiding their use for data transmission. If the channels vary rapidly, they must be estimated many times, which results in a very low data efficiency of the communications link. Also, in case the power is limited or the wireless link distance is large, the resulting signal-tointerference- plus-noise ratio (SINR) will be low, which is a parameter that is directly related to the quality of the channel estimation and the performance of the data reception. This problem is aggravated in massive multiple-input multiple-output (massive MIMO), which is a promising technique for future wireless communications since it can increase the data rates, increase the reliability and cope with a larger number of simultaneous devices. In massive MIMO, the base station (BS) is typically equipped with a large number of antennas that are coordinated. In these scenarios, the channels must be estimated for each antenna (or at least for each user), and thus, the aforementioned problem of channel estimation aggravates. In this context, algorithms and techniques for massive MIMO without CSI are of interest. This thesis main topic is non-coherent massive multiple-input multiple-output (NC-mMIMO) which relies on the use of differential M-ary phase shift keying (DMPSK) and the spatial diversity of the antenna arrays to be able to detect the useful transmitted data without CSI knowledge. On the one hand, hybrid schemes that combine the coherent and non-coherent schemes allowing to get the best of both worlds are proposed. These schemes are based on distributing the resources between non-coherent (NC) and coherent data, utilizing the NC data to estimate the channel without using pilots and use the estimated channel for the coherent data. On the other hand, new constellations and user allocation strategies for the multi-user scenario of NC-mMIMO are proposed. The new constellations are better than the ones in the literature and obtained using artificial intelligence techniques, more concretely evolutionary computation.This work has received funding from the European Union Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie ETN TeamUp5G, grant agreement No. 813391. The PhD student was the Early Stage Researcher (ESR) number 2 of the project. This work has also received funding from the Spanish National Project IRENE-EARTH (PID2020-115323RB-C33) (MINECO/AEI/FEDER, UE), which funded the work of some coauthors.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Luis Castedo Ribas.- Secretario: Matilde Pilar Sánchez Fernández.- Vocal: Eva Lagunas Targaron

Frame synchronization for PSAM in AWGN and Rayleigh fading channels

Pilot Symbol Assisted Modulation (PSAM) is a good method to compensate for the channel fading effect in wireless mobile communications. In PSAM, known pilot symbols are periodically inserted into the transmitted data symbol stream and the receiver uses these symbols to derive amplitude and phase reference. One aspect of this procedure, which has not received much attention yet, is the frame synchronization, i.e. the method used by the receiver to locate the time position of the pilot symbols. In this study, two novel non-coherent frame synchronization methods are introduced in which only the magnitude of received signal is used to obtain the timing of the pilot symbol. The methods are evaluated for both AWGN and frequency non-selective slow Rayleigh fading channels. One synchronization technique is derived by standard maximum likelihood (ML) estimation formulation, and the other is obtained by using maximum a Posteriori probability (MAP) with a threshold test. Signal processing in the receiver uses simplifying approximations that rely on relatively high signal-to-noise ratio (SNR) as consistent with the reception of 16-QAM. Computer simulation has been used to test the acquisition time performance and the probability of false acquisition. Several lengths and patterns of pilot symbol sequences were tested where every 10th symbol was a pilot symbol and all other symbols were randomly selected data symbols. When compared with the other published synchronizers, results from this study show better performance in both AWGN and fading channels. Significantly better performance is observed in the presence of receiver frequency offsets

On space-time trellis codes over rapid fading channels with channel estimation

Ph.DDOCTOR OF PHILOSOPH