Browsing by Subject "MIMO"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Detection and channel estimation for channels with heavy interference.
    (2011-12) Yoon, Daejung
    Iterative decision-directed (DD) channel estimation (CE) and detection algorithms for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems are investigated. A main strength of the MIMO-OFDM is a potential capability to support high data rates. However, interference between MIMO antennas has been a serious obstacle to high data rate communication. Accurate channel state information (CSI) is critical to reduce antenna interference and improve throughput performance of the MIMO-OFDM communication systems. First, we develop soft-decision-driven sequential CE algorithms specific to turbo equalization for the MIMO communication. Two kinds of channel estimators are proposed: an optimal Kalman-based channel estimator geared to the pipelined turbo equalizer and a low-complexity estimator design for practical implementation. An effective strategy is established for the channel estimators dealing with different qualities of feedback decisions from the turbo equalizer. The proposed CE algorithms employ puncturing on observation samples to effectively deal with the inherent correlated error input that cannot easily be removed by the traditional innovations approach. Performance of the optimal estimator is excellent at compensating loss due to imperfect CSI; however, computational complexity of the MIMO CE becomes a challenge as the number of MIMO antenna links increases in practical systems. The proposed lowcomplexity algorithm resolves the MIMO channel estimation problem into a single-input single-output CE form to avoid heavy computation load associated with matrix operations. Also, in order to reduce packet losses due to the inherent correlated error, a novel packet recovery scheme is introduced that reprocesses failed packets by innovating on the inaccurate CSI. The recovery scheme detects erroneous OFDM-symbol locations by comparing extrinsic (EXT) information from the turbo equalizer. For the error correction, it applies additional turbo iterations to the erroneous OFDM symbols with the innovated CSI. In demonstrating the viability of the proposed schemes, a MIMO-OFDM communication system is constructed to comply with the IEEE 802.11n WLAN standard.
  • Thumbnail Image
    Item
    High Linearity Receiver In The Presence Of Blockers: Circuit Design And Layout Automation
    (2023-09) Poojary, Jitesh
    With Internet-of-Things (IoT) devices and smartphones getting connected to the 5G network, the number of inter-connected devices has grown exponentially. This interconnectivity between devices will continue for future communication networks such as 6G and beyond. As the number of connected devices sharing the frequency spectrum increases, desired radio signals between two devices get jammed by the interference from other connected devices. If the jammer signal power increases up to a certain threshold, the desired radio signal is completely blocked, and it cannot be decoded at the receiver end. Thus, it is important to reject the jammer/blockers at the receiver end to receive and decode the desired signals. There are two types of blockers depending on the frequency band of interest: inband and out-of-band blockers. Typically, out-of-band blockers are rejected using a spectral filter in the receiver. Spectral filters such as band pass filter, SAW filter, etc. have been an integral part of the receiver design since the 2G standard, and therefore, out-of-band blockers are not a major concern for future communication systems. Since the in-band blockers are located inside the frequency band of interest, the spectral filter cannot reject these blockers. Hence, in-band blockers are a major concern for future communication systems and they need to be filtered out using a different filter. This dissertation initially focuses on the design of spatially and spectrally passive MIMO receiver, which can reject both blocker types (in-band and out-of-band). The design involves use of spatial information from multiple antennas to create a spatial filter. This spatial filter can be used to filter out in-band blockers from the system. Additionally, the spatial filter and spectral filter in the MIMO receiver are created using passive techniques such as N-path mixers, resistors and capacitors, etc. This helps in improving the linearity of the MIMO receiver. Measured results of our 4-antenna MIMO receiver prototype achieved an in-band/in-beam B1dB of –10.6 dBm, which was 32 dB higher than other state-of-art designs. The performance of analog/RF circuits, such as the MIMO Receiver, depends on the careful layout design to reduce parasitics. Reducing parasitics, such as resistance and capacitance, leads to optimum design performance. Hence, there are many layout iterations to minimize the parasitic. This numerous iteration leads to a more extended design time for RF circuits. Analog circuits, instead of digital logic circuits, have non-standard test benches for simulating and verifying the design. Since digital logic circuits had standard test benches to verify functionality, it led to the automation of digital logic synthesis and layout. On the other hand, a layout engineer manually crafted analog circuit layouts due to different layout requirements and non-standard test benches. Moreover, the layout rules become more restrictive as semiconductor technology scales from bulk CMOS to advanced node FinFETs. With other analog/RF circuits, the layouts differ in placement and routing rules leading to longer design time. Thus, the other part of this dissertation focuses on layout automation of analog/RF circuits using the open-source tool ALIGN. ALIGN identifies common analog design primitives inside the hierarchy of top-level circuits to create a DRC clean layouts of primitives. Once the primitive layouts are created, and the design hierarchy is identified, ALIGN completes the placement and routing of the design block from bottom-to-top levels of the hierarchy. The measured result of the MIMO receiver with an ALIGN-generated layout showed a performance similar to the manually crafted layout. Thus, analog layout generation can be automated to reduce design time and improve productivity without reducing performance.
  • Thumbnail Image
    Item
    Low complexity MIMO detection algorithms and implementations
    (2014-12) Huai, Lian
    MIMO techniques use multiple antennas at both the transmitter and receiver sides to achieve diversity gain, multiplexing gain, or both. One of the key challenges in exploiting the potential of MIMO systems is to design high-throughput, low-complexity detection algorithms while achieving near-optimal performance. In this thesis, we design and optimize algorithms for MIMO detection and investigate the associated performance and FPGA implementation aspects.First, we study and optimize a detection algorithm developed by Shabany and Gulak for a K-Best based high throughput and low energy hard output MIMO detection and expand it to the complex domain. The new method uses simple lookup tables, and it is fully scalable for a wide range of K-values and constellation sizes. This technique reduces the computational complexity, without sacrificing performance and the complexity scales only sub-linearly with the constellation size. Second, we apply the bidirectional technique to trellis search and propose a high performance soft output bidirectional path preserving trellis search (PPTS) detector for MIMO systems. The comparative error analysis between single direction and bidirectional PPTS detectors is given. We demonstrate that the bidirectional PPTS detector can minimize the detection error. Next, we design a novel bidirectional processing algorithm for soft-output MIMO systems. It combines features from several types of fixed complexity tree search procedures. The proposed approach achieves a higher performance than previously proposed algorithms and has a comparable computational cost. Moreover, its parallel nature and fixed throughput characteristics make it attractive for very large scale integration (VLSI) implementation.Following that, we present a novel low-complexity hard output MIMO detection algorithm for LTE and WiFi applications. We provide a well-defined tradeoff between computational complexity and performance. The proposed algorithm uses a much smaller number of Euclidean distance (ED) calculations while attaining only a 0.5dB loss compared to maximum likelihood detection (MLD). A 3x3 MIMO system with a 16QAM detector architecture is designed, and the latency and hardware costs are estimated.Finally, we present a stochastic computing implementation of trigonometric and hyperbolic functions which can be used for QR decomposition and other wireless communications and signal processing applications.
  • Thumbnail Image
    Item
    MIMO Wireless Communications with limited feedback
    (2012-09) Ravindran, Niranjay
    In this dissertation, we investigate the effects of having imperfect channel state information due to limited training and feedback resources in multi-user systems with multiple antennas. We find that while the achievable rate is highly sensitive to the quality of channel training and feedback, the rate gap relative to the rate achievable with perfect channel information can be uniformly bounded for all values of signal-to-noise ratio, with proper design of the feedback link to acquire accurate channel information, that is, the multiplexing gain can be preserved. Further, when a large number of users are present in a system, we find the strong requirement for accurate channel information remains, contrary to many transmission strategies that are commonly proposed for this regime. We conclude that given a limited feedback budget, it is desirable to first use resources to acquire highly accurate channel information, and only then allocate resources to exploit multi-user diversity. We also obtain results characterizing the statistics of random subspace quantization, which we use to compute the reduction in feedback overhead possible when this form of quantization is used. Finally, we consider open-loop multi-hop ad hoc networks with multiple antennas and opportunistic routing, and investigate using multiple antennas to optimize the spatial reuse, per-hop length and per-hop rate to maximize end-to-end performance.