Modulation, Coding, and Receiver Design for Gigabit mmWave Communication

While wireless communication has become an ubiquitous part of our daily life and the world around us, it has not been able yet to deliver the multi-gigabit throughput required for applications like high-definition video transmission or cellular backhaul communication. The throughput limitation of current wireless systems is mainly the result of a shortage of spectrum and the problem of congestion. Recent advancements in circuit design allow the realization of analog frontends for mmWave frequencies between 30GHz and 300GHz, making abundant unused spectrum accessible. However, the transition to mmWave carrier frequencies and GHz bandwidths comes with new challenges for wireless receiver design. Large variations of the channel conditions and high symbol rates require flexible but power-efficient receiver designs. This thesis investigates receiver algorithms and architectures that enable multi-gigabit mmWave communication. Using a system-level approach, the design options between low-power time-domain and power-hungry frequency-domain signal processing are explored. The system discussion is started with an analysis of the problem of parameter synchronization in mmWave systems and its impact on system design. The proposed synchronization architecture extends known synchronization techniques to provide greater flexibility regarding the operating environments and for system efficiency optimization. For frequency-selective environments, versatile single-carrier frequency domain equalization (SC-FDE) offers not only excellent channel equalization, but also the possibility to integrate additional baseband tasks without overhead. Hence, the high initial complexity of SC-FDE needs to be put in perspective to the complexity savings in the other parts of the baseband. Furthermore, an extension to the SC-FDE architecture is proposed that allows an adaptation of the equalization complexity by switching between a cyclic-prefix mode and a reduced block length overlap-save mode based on the delay spread. Approaching the problem of complexity adaptation from time-domain, a high-speed hardware architecture for the delayed decision feedback sequence estimation (DDFSE) algorithm is presented. DDFSE uses decision feedback to reduce the complexity of the sequence estimation and allows to set the system performance between the performance of full maximum-likelihood detection and pure decision feedback equalization. An implementation of the DDFSE architecture is demonstrated as part of an all-digital IEEE802.11ad baseband ASIC manufactured in 40nm CMOS. A flexible architecture for wideband mmWave receivers based on complex sub-sampling is presented. Complex sub-sampling combines the design advantages of sub-sampling receivers with the flexibility of direct-conversion receivers using a single passive component and a digital compensation scheme. Feasibility of the architecture is proven with a 16Gb/s hardware demonstrator. The demonstrator is used to explore the potential gain of non-equidistant constellations for high-throughput mmWave links. Specifically crafted amplitude phase-shift keying (APSK) modulation achieve 1dB average mutual information (AMI) advantage over quadrature amplitude modulation (QAM) in simulation and on the testbed hardware. The AMI advantage of APSK can be leveraged for a practical transmission using Polar codes which are trained specifically for the constellation

Digital Synchronization for Symbol-spaced IEEE802.11ad Gigabit mmWave Systems

A complete digital synchronization architecture for an IEEE 802.11ad compliant 60 GHz receiver is presented. The characteristics of mmWave systems require a holistic view on the problem of parameter estimation, such that not each parameter is dealt with on its own, but in the context of the complete receiver architecture. To this end the proposed synchronization unit covers packet detection, frequency offset compensation, signal-to-interference-plus-noise (SINR) maximization, frame synchronization, and channel estimation. The presented architecture is especially suitable for low-complexity time domain receivers, which are the most power efficient systems for mmWave, but have high demands in terms of synchronization. A novel two step synchronization procedure takes the specific requirements of the employed equalization and detection stages into account, to maximize the overall system performance. Performance is further improved by a heuristic sampling phase alignment mechanism which search the best sampling phase in order to increase the effective SINR in finite length receivers

Energy-Proportional Single-Carrier Frequency Domain Equalization for mmWave Wireless Communication

mmWave wireless communication is proposed for high-throughput and high-density applications. Due to the large channel bandwidth, mmWave systems face a large variation in the observed delay spread. Many proposed single-carrier (SC) mmWave systems rely on cyclic-prefix (CP) frequency domain equalization (FDE) in order to deal with worst case channel conditions. A downside of CP-FDE receivers is their constant energy consumption independent of the actual channel conditions. The alternative overlap-save (OS) FDE receiver can adapt its complexity, but exhibits an inferior equalization performance. By proposing a hybrid FDE approach the receiver can adapt its complexity and therefor its power consumption dynamically to the given channel conditions. Using the structural similarity of overlap-save and cyclic-prefix FDE architectures the proposed hybrid receiver can switch between the two modes of operation with minimum required hardware overhead. It is shown that the proposed hybrid receiver can significantly reduce its complexity in benign channel conditions while still matching the equalization properties of a conventional CP-FDE receivers in very frequency selective environments

Layered Detection and Decoding in MIMO Wireless Systems

Iterative detection and decoding (IDD) in multiple-input multiple-output (MIMO) wireless systems is known to achieve near channel capacity. The high computational complexity of IDD, however, poses significant challenges for practical implementations (in terms of circuit area, latency, throughput, and power consumption). While the implementation of the involved detector and decoder circuits have received considerable attention in the literature, only little is known about the efficient combination of both blocks in an IDD architecture. In this paper, we propose a novel iterative receiver schedule, which simultaneously performs detection and decoding on the same code block. This novel IDD approach is referred to as layered detection and decoding (LDD) and achieves lower latency and better performance compared to conventional solutions. Moreover, LDD is able to automatically match the decoding effort to the wide range of different modulation schemes and code rates specified in modern MIMO wireless standards. To demonstrate the advantages of LDD, we present an extensive case study based on the characteristics of existing reference designs of a soft-input soft-output MMSE detector and an LDPC decoder

Fractionally Spaced Complex Sub-Nyquist Sampling for Multi-Gigabit 60 GHz Wireless Communication

A novel analog front-end architecture based on complex sub-Nyquist sampling for the intermediate frequency (IF) stage of a mmWave receiver is proposed. With this front-end, the use of a wideband hybrid coupler and two half-rate analog-to-digital converters (ADCs) allow for a flexible placement of the IF. It is shown that digital compensation of the impairments introduced by the non-ideal 90 degree hybrid coupler is required to use high modulation orders. Further a digital signal processing (DSP) architecture is presented which performs equalization of a fractionally spaced sub-sampled IF signal in frequency domain (FD) and integrates the compensation of the impairments with low overhead. Based on this DSP architecture a working 60GHz single-carrier link is demonstrated. Measurement results show the feasibility of 256QAM modulated transmission with a bandwidth of up to 1.8 GHz and a resulting raw data rate of 12.8 Gb/s using our frontend architecture with the digital FD compensation

A Parallelized Layered QC-LDPC Decoder for IEEE 802.11ad

We present a doubly parallelized layered quasi-cyclic low density parity-check decoder for the emerging IEEE 802.11ad multigigabit wireless standard. The decoding algorithm is equivalent to a nonparallelized layered decoder and, thus, retains its favorable convergence characteristics, which are known to be superior to those of flooding schedule based decoders. The proposed architecture was synthesized using a TSMC 40 nm CMOS technology, resulting in a cell area of 0.18 mm2 and a clock frequency of 850 MHz. At this clock frequency, the decoder achieves a coded throughput of 3.12 Gbps, thus meeting the throughput requirements when using both the mandatory BPSK modulation and the optional QPSK modulation

A 3.52 Gb/s mmWave Baseband with Delayed Decision Feedback Sequence Estimation in 40 nm

We present a digital baseband ASIC for 60 GHz single-carrier (SC) transmission that is optimized for communication scenarios in which most of the energy is concentrated in the first few channel taps. Such scenarios occur for example in office environments with strong reflections. Our circuit targets close-to-optimum maximum-likelihood performance under such conditions. To this end, we show for the first time how a reduced-state-sequence-estimation algorithm can be realized for the 1760 MHz bandwidth of the IEEE 802.11ad standard. The equalizer is complemented in the frontend by a synchronization unit for frequency offset compensation as well as a Golay-sequence based channel estimator and in the backend by an low density parity check (LDPC) decoder. In 40nm CMOS we achieve a measured data rate of up to 3.52 Gb/s using QPSK modulation

Layered detection and decoding in MIMO wireless systems

Iterative detection and decoding (IDD) in multiple-input multiple-output (MIMO) wireless systems is known to achieve near channel capacity. The high computational complexity of IDD, however, poses significant challenges for practical implementations (in terms of circuit area, latency, throughput, and power consumption). While the implementation of the involved detector and decoder circuits have received attention in the literature, only little is known about the efficient combination of both blocks in an IDD architecture. In this paper, we propose a novel iterative receiver schedule, which simultaneously performs detection and decoding on the same code block. This novel IDD approach is referred to as layered detection and decoding (LDD) and achieves lower latency and better performance compared to conventional solutions. Moreover, LDD is able to automatically match the decoding effort to the wide range of different modulation schemes and code rates specified in modern MIMO wireless standards. To demonstrate the efficiency of LDD, we present an extensive case study based on the characteristics of existing reference designs for a soft-input soft-output MMSE detector and an LDPC decoder

Robust Asynchronous Indoor Localization Using Led Lighting

We propose a low-cost system for indoor self-localization of mobile devices using modulated LED ceiling lamps that are fully autonomous and broadcast their identifiers without any synchronization. The proposed self-localization method is designed to handle this lack of synchronization as well as the possibility of blocked line-of-sight connections or severe attenuation in real-world environments. This robustness is achieved by applying a suitable Bayesian signal model and by taking into account the inherent sparsity in detecting the concurrently visible lamps. The proposed estimator of the location approximates optimal Bayesian estimation while maintaining low complexity. Simulation results confirm a significant gain in performance compared to a classical matched-filter approach