A Reduced Complexity Ungerboeck Receiver for Quantized Wideband Massive SC-MIMO

Employing low resolution analog-to-digital converters in massive multiple-input multiple-output (MIMO) has many advantages in terms of total power consumption, cost and feasibility of such systems. However, such advantages come together with significant challenges in channel estimation and data detection due to the severe quantization noise present. In this study, we propose a novel iterative receiver for quantized uplink single carrier MIMO (SC-MIMO) utilizing an efficient message passing algorithm based on the Bussgang decomposition and Ungerboeck factorization, which avoids the use of a complex whitening filter. A reduced state sequence estimator with bidirectional decision feedback is also derived, achieving remarkable complexity reduction compared to the existing receivers for quantized SC-MIMO in the literature, without any requirement on the sparsity of the transmission channel. Moreover, the linear minimum mean-square-error (LMMSE) channel estimator for SC-MIMO under frequency-selective channel, which do not require any cyclic-prefix overhead, is also derived. We observe that the proposed receiver has significant performance gains with respect to the existing receivers in the literature under imperfect channel state information.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Performance Analysis of Quantized Uplink Massive MIMO-OFDM With Oversampling Under Adjacent Channel Interference

Massive multiple-input multiple-output (MIMO) systems have attracted much attention lately due to the many advantages they provide over single-antenna systems. Owing to the many antennas, low-cost implementation and low power consumption per antenna are desired. To that end, massive MIMO structures with low-resolution analog-to-digital converters (ADC) have been investigated in many studies. However, the effect of a strong interferer in the adjacent band on quantized massive MIMO systems have not been examined yet. In this study, we analyze the performance of uplink massive MIMO with low-resolution ADCs under frequency selective fading with orthogonal frequency division multiplexing (OFDM) in the perfect and imperfect receiver channel state information cases. We derive analytical expressions for the bit error rate and ergodic capacity. We show that the interfering band can be suppressed by increasing the number of antennas or the oversampling rate when a zero-forcing receiver is employed

Düşük Çözünürlüklü Nicemleyicilere Sahip Kitlesel Çok-Girdili Çok-Çıktılı Haberleşme Sistemleri

Low resolution analog-to-digital converters (ADC) attracted much attention for their use inmassivemultiple-inputmultiple-output (MIMO) systems due to their low power consumption and cost. In this thesis, we question whether large number of antennas present in massive MIMO is sufficient to provide an ultimate performance or additional sampling in time (temporal oversampling) will provide significant performance advantages. To begin with, we illustrate the benefits of oversampling in time for uplink massive MIMO systems with low-resolution ADCs in terms of symbol error rate (SER) and achievable rate for both single-carrier (SC) and multi-carrier modulation scenarios by deriving analytical bounds and with simulations. We also propose a sequantial linear minimum-mean-square error (LMMSE) based receiver as a low-complexity detector, which is much more feasible to implement compared to the zero-forcing (ZF) detector for temporally oversampled massive MIMO systems. We also examine and illustrate the benefits of temporal oversampling for quantized massive MIMO systems under adjacent channel interference caused by the non-linearity of the quantizers. According to the results that we obtain, it seems that temporal oversampling can be very beneficial and should always be considered for use in quantized massive MIMO. Finally, we examine whether a low-complexity MIMO detector, which can outperform the existing detectors of similar complexity, can be proposed even without resorting temporal oversampling. For that purpose, we propose a near optimal factor-graph based Ungerboeck type detector with bi-directional decision feedback, along with the derivation of LMMSE channel estimator for quantized wideband SC-MIMO systems. The proposed detector is shown to outperform a representative detector of comparable complexity from the literature in terms of SER and achievable rate per user performance metrics.Kitlesel çoklu-girdili çoklu-çıktılı (MIMO) sistemlerinde düşük çözünürlüğe sahip analogdan-sayısala-dönüştürücülerin (ADC) kullanımı sahip oldukları düşük maliyet ve güç tüketimlerinden ötürü ilgi uyandırmıştır. Bu tezde düşük çözünürlükteki ADC içeren kitlesel MIMO sistemlerinde var olan çok sayıda antene ek olarak zamanda aşırı örnekleme kullanılmasının önemli ölçüde avantaj sağlayıp sağlayamadığı sorgulanmaktadır. Başlangıç olarak tekli-taşıyıcılı ve bir-bitlik ADC kullanılan durumda aşırı örnekleme yönteminin SER ve erişilebilir oran başarımları açısından ciddi faydalar sağladığı hem analitik olarak elde edilen ifadeler ile hem de yapılan benzetimlerle gösterilmektedir. Bunun yanında kitlesel MIMO yapıları için aşırı örnekleme ile çalışan sıfır-zorlayıcı (ZF) alıcıya nazaran çok daha düşük karmaşıklığa sahip sıralı doğrusal en küçük karesel hata (LMMSE) tabanlı bir alıcı da önerilmektedir. Ayrıca nicemlemeli kitlesel MIMO yapıları için nicemleyicilerdeki doğrusalsızlık sonucunda ortaya çıkan yan bant girişiminin de aşırı örnekleme yöntemi ile bastırılabileceği yine bu çalışmada irdelenmektedir. Elde edilen bulgular, aşırı örnekleme tekniğinin nicemleme altında çalışan kitlesel MIMO yapılarında kullanımının her zaman değerlendirilmesi gerektiğini göstermektedir. Son olarak nicemleme altındaki kitlesel MIMO yapıları için aşırı örnekleme tekniği kullanılmadığı durumda literatürde var olan alıcılardan daha iyi başarım sağlayan bir alıcı önerilip önerilemeyeceği sorgulanmaktadır. Bu amaçla, nicemleme gürültüsü altında çalışan tekli-taşıyıcılı MIMO yapıları için çarpan çizge tabanlı ve çift yönlü karar geribildirimi yöntemini kullanan, düşük karmaşıklığa sahip Ungerboeck tipindeki bir alıcı, söz konusu yapılar için LMMSE tabanlı bir kanal kestirim algoritması ile birlikte önerilmektedir. Önerilen alıcının literatürde benzer karmaşıklığa sahip bir alıcıdan SER ve kullanıcı başına erişilebilir oran kriterleri açısından daha iyi başarım sağladığı gösterilmektedir.Ph.D. - Doctoral ProgramASELSANTÜBİTA

Olası 5G çoklu-taşıyıcı kiplemelerinin bant dışı emisyonları ve CFO dayanıklılıkları.

In this study, generalized frequency division multiplexing (GFDM) and windowed cyclic prefix circular offset quadrature amplitude modulation (WCP-COQAM), which are candidate physical layer modulation schemes for the 5G systems, are compared to orthogonal frequency division multiplexing (OFDM) in terms of out-of-band (OOB) radiation levels and carrier frequency offset (CFO) immunity. GFDM and WCP- COQAM are shown to be superior to OFDM with respect to OOB emissions in some studies in literature. However, we consider that these comparisons are made under unfair conditions since OOB reduction techniques are not also applied to OFDM and the spectral efficiencies of the three modulations are not equal. Establishing fair comparison grounds accordingly, the simulation results yielded no significant OOB emission performance difference between the three modulation types. Further simulations considering some parameters related to the transmitted signals such as error-vector magnitude or average power under the effects of amplifier nonlinearity or digital-to- analog converter also revealed no significant difference between the three modulation types under LTE spectral mask requirements. The three modulation types are also compared in terms of their carrier frequency offset (CFO) immunities. To achieve better CFO immunity, advanced pulse shaping methods defined for offset quadrature amplitude modulation OFDM (OQAM- OFDM) are also applied to WCP-COQAM. This is possible since the two modulations are also proved to be equivalent in terms of orthogonality, which is one of the main analytic contributions of this thesis. However, the error rate performance simulations under CFO for various channel conditions did not improve CFO immunity for WCP-COQAM or GFDM compared to OFDM.M.S. - Master of Scienc

Oversampling in One-Bit Quantized Massive MIMO Systems and Performance Analysis

Low-resolution analog-to-digital converters (ADCs) have attracted much attention lately for massive multiple-input multiple-output (MIMO) communication and systems with large bandwidth. Especially, 1-bit ADCs are suitable for such systems due to their low-power consumption and cast. In this paper, we illustrate the benefits of using faster than symbol rate (FTSR) sampling in an uplink massive MIMO system with 1-bit ADCs in terms of symbol error rate (SER). We show that the FTSR sampling provides about 5-dB signal-to-noise ratio (SNR) advantage in terms of SER and achievable rate with a linear zeroforcing-type receiver. We also develop analytical bounds on the SER and achievable rate performance of uplink massive MIMO structures with 1-bit quantization for the FTSR scenario for the whole SNR region. The proposed analytical hound holds not only for the FTSR case but also to yield more accurate results compared with some other analytical expressions in the literature. Our results establish a tradeoff between temporal oversampling and the number of receive antennas

Sequential Linear Detection in One-Bit Quantized Uplink Massive MIMO with Oversampling

Owing to their low power consumption and cost, employing 1-bit analog-to-digital converters (ADC) in massive multiple-input multiple-output (MIMO) systems has attracted significant attention, which resulted in such systems to be examined widely in the recent literature. In our previous studies, benefits of temporal oversampling in 1-bit quantized uplink massive MIMO systems is investigated by employing a high complexity zero-forcing (ZF) detector. In this study, we propose a sequential linear receiver as an alternative to the existing ZF receiver for the temporal oversampling case in literature. The complexity of the proposed receiver for temporally oversampled uplink massive MIMO with 1-bit ADC increases linearly with block length while the complexity of the existing ZF receiver grows with the cube of block length. Furthermore, significant reduction for the delay in the estimation of the transmitted data symbols is achieved with the proposed receiver

Comparison of New Multi-carrier Modulation Schemes under Amplifier Nonlinearity

OFDM is an essential part of the physical layer structure in 4G communication systems. Despite having many advantages compared to other modulation types, OFDM has the significant drawback of causing high out-of-band emissions (OOBE). This resulted in the consideration of alternative modulation schemes for the future communication standards. In this work, two of those alternatives, namely GFDM and WCP-COQAM are compared with OFDM under the efTects of digital-to- analog converter (DAC) and power-amplifier (PA) non-Iinearity taking into account the spectral mask requirements in the LTE standard. The performance metrics used in the comparisons are the error-vector magnitude (EVM), signal-to-intereference ratio (SIR) and average powers of the transmitted signals using the 3 modulation schemes. The results turned out to be such that there is no significant difference between the 3 modulation types in terms of the performance metrics taken into consideration