Timothy A. Thomas

Bio: Timothy A. Thomas is an academic researcher from Motorola. The author has contributed to research in topics: Communication channel & Orthogonal frequency-division multiplexing. The author has an hindex of 35, co-authored 97 publications receiving 5193 citations. Previous affiliations of Timothy A. Thomas include Nokia Networks & Nokia.

CSI Reference Signal Designs for Enabling Closed-Loop MIMO Feedback

Abstract: Obtaining reliable channel state information (CSI) in future wireless standards is critical for the operation of downlink closed-loop techniques such as SU-MIMO, MU-MIMO, and coordinated multipoint (CoMP). However, this CSI is difficult to obtain especially when considering the potentially strong interference from neighboring sectors/base stations on the downlink reference symbols (RSs, aka pilot symbols) used to obtain the CSI. This paper describes three possible CSI RS designs for enabling such closed- loop feedback in light of the strong interference environment and discusses some tradeoffs between the designs. First, two code-division multiplexing (CDM) designs are proposed where one has nine orthogonal sequences and the other has three orthogonal sequences. Next a new CSI-RS design is described which uses mutually unbiased bases (MUB) to provide a 6 dB quasi-orthogonal gain over neighboring cells. The MUB design is shown in system-level simulation to have performance close to a design with 9 orthogonal sequences while providing a finer frequency-domain sampling than the 9- orthogonal approach.

Experimental MIMO Comparisons of a 4-Element Uniform Linear Array to an Array of Two Cross Polarized Antennas at 3.5 GHz

Abstract: Motorola has developed a 20 MHz experimental widearea mobile multi-antenna system at 3.5 GHz for characterizing the spatial channel. With this system, simultaneous channel measurements were taken using both a uniform linear array (ULA) and an array of two cross-polarized (XP) antennas for locations near the Motorola Schaumburg campus. The ULA consists of eight vertically-polarized elements with half wavelength spacing between elements and the XP array consists of two XP panels spaced at two wavelengths where each XP panel consists of two co-located antennas with one antenna having a +45° polarization while the other has a -45° polarization. The receive array consists of eight vertically-polarized antennas in a uniform circular array with a radius of 2.62 wavelengths. This paper compares the antenna correlation and the downlink performance of a ULA (with both half wavelength and one wavelength spacings) and the XP array in a power-fair scenario with four transmit elements for each array type in each sector. Eigen beamforming (EBF) for TDD, DOA-beamforming for FDD, and single-user MIMO (SUMIMO) algorithms are compared.

PAPR reduction via a fixed frequency-domain weighting across multiple OFDM bauds

Abstract: The paper introduces a PAPR reduction technique for OFDM that uses the same PAPR reduction weights over multiple OFDM bauds. The PAPR reduction weights are applied on each subcarrier in the frequency domain and are designed to be either fixed over a group of subcarriers (in addition to multiple bauds) or parameterized by time taps. The advantage of these methods is to simplify channel estimation by not destroying the channel frequency correlation (for weights fixed over groups of subcarriers) or by increasing the effective length of the channel to be estimated (for the weights parameterized by time taps). Simulation results show up to a 6.0 dB decrease in PAPR where PAPR is measured over an OFDM baud.

Differential closed-loop transmission feedback in wireless communication systems

Abstract: A method and apparatus for providing channel feedback is provided herein. During operation a covariance matrix at time t (R) is calculated as a function of a received downlink signal. Matrix C t is also calculated and is based on a previous quantized covariance matrix (R q t-1 ), the covariance matrix (R) at time t, and a forgetting factor (γ) that is applied to R q t-1 . The C t is then used to create a DERC feedback message (signal or waveform) and may be transmitted with pilots on a proper feedback channel to a base unit. The base unit receives the feedback (C t ) as a DERC waveform on a proper feedback channel. The base unit uses non-coherent or coherent detection to detect the DERC values send by the remote unit and uses the DERC values with a previous quantized covariance matrix estimate, a forgetting factor, and a weighting value to compute a covariance matrix estimate to use for beamforming. The base unit then uses the covariance matrix estimate to determine appropriate channel beamforming weights, and instructs transmit beamforming circuitry to use the appropriate weights.

Title Improvements to the Uplink Channel Sounding Signaling for OFDMA

Abstract: Source(s) Frederick W. Vook Xiangyang (Jeff) Zhuang Kevin L. Baum Timothy A. Thomas Philippe Sartori Motorola Labs 1301 E. Algonquin Road Schaumburg, IL 60196 Zion Hadad Runcom Voice: +1-847-576-7939 Fred.Vook@motorola.com Re: IEEE P802.16-REVe/D5a-2004 Abstract Modifications to Uplink Channel Sounding methodology to optionally include DL channel coefficients. Purpose Adoption of proposed changes into P802.16e Notice

Internet of Things: A Survey on Enabling Technologies, Protocols, and Applications

Abstract: This paper provides an overview of the Internet of Things (IoT) with emphasis on enabling technologies, protocols, and application issues. The IoT is enabled by the latest developments in RFID, smart sensors, communication technologies, and Internet protocols. The basic premise is to have smart sensors collaborate directly without human involvement to deliver a new class of applications. The current revolution in Internet, mobile, and machine-to-machine (M2M) technologies can be seen as the first phase of the IoT. In the coming years, the IoT is expected to bridge diverse technologies to enable new applications by connecting physical objects together in support of intelligent decision making. This paper starts by providing a horizontal overview of the IoT. Then, we give an overview of some technical details that pertain to the IoT enabling technologies, protocols, and applications. Compared to other survey papers in the field, our objective is to provide a more thorough summary of the most relevant protocols and application issues to enable researchers and application developers to get up to speed quickly on how the different protocols fit together to deliver desired functionalities without having to go through RFCs and the standards specifications. We also provide an overview of some of the key IoT challenges presented in the recent literature and provide a summary of related research work. Moreover, we explore the relation between the IoT and other emerging technologies including big data analytics and cloud and fog computing. We also present the need for better horizontal integration among IoT services. Finally, we present detailed service use-cases to illustrate how the different protocols presented in the paper fit together to deliver desired IoT services.

Spatially Sparse Precoding in Millimeter Wave MIMO Systems

Abstract: Millimeter wave (mmWave) signals experience orders-of-magnitude more pathloss than the microwave signals currently used in most wireless applications and all cellular systems. MmWave systems must therefore leverage large antenna arrays, made possible by the decrease in wavelength, to combat pathloss with beamforming gain. Beamforming with multiple data streams, known as precoding, can be used to further improve mmWave spectral efficiency. Both beamforming and precoding are done digitally at baseband in traditional multi-antenna systems. The high cost and power consumption of mixed-signal devices in mmWave systems, however, make analog processing in the RF domain more attractive. This hardware limitation restricts the feasible set of precoders and combiners that can be applied by practical mmWave transceivers. In this paper, we consider transmit precoding and receiver combining in mmWave systems with large antenna arrays. We exploit the spatial structure of mmWave channels to formulate the precoding/combining problem as a sparse reconstruction problem. Using the principle of basis pursuit, we develop algorithms that accurately approximate optimal unconstrained precoders and combiners such that they can be implemented in low-cost RF hardware. We present numerical results on the performance of the proposed algorithms and show that they allow mmWave systems to approach their unconstrained performance limits, even when transceiver hardware constraints are considered.

Millimeter-Wave Cellular Wireless Networks: Potentials and Challenges

Abstract: Millimeter-wave (mmW) frequencies between 30 and 300 GHz are a new frontier for cellular communication that offers the promise of orders of magnitude greater bandwidths combined with further gains via beamforming and spatial multiplexing from multielement antenna arrays. This paper surveys measurements and capacity studies to assess this technology with a focus on small cell deployments in urban environments. The conclusions are extremely encouraging; measurements in New York City at 28 and 73 GHz demonstrate that, even in an urban canyon environment, significant non-line-of-sight (NLOS) outdoor, street-level coverage is possible up to approximately 200 m from a potential low-power microcell or picocell base station. In addition, based on statistical channel models from these measurements, it is shown that mmW systems can offer more than an order of magnitude increase in capacity over current state-of-the-art 4G cellular networks at current cell densities. Cellular systems, however, will need to be significantly redesigned to fully achieve these gains. Specifically, the requirement of highly directional and adaptive transmissions, directional isolation between links, and significant possibilities of outage have strong implications on multiple access, channel structure, synchronization, and receiver design. To address these challenges, the paper discusses how various technologies including adaptive beamforming, multihop relaying, heterogeneous network architectures, and carrier aggregation can be leveraged in the mmW context.

MIMO Broadcast Channels With Finite-Rate Feedback

Abstract: Multiple transmit antennas in a downlink channel can provide tremendous capacity (i.e., multiplexing) gains, even when receivers have only single antennas. However, receiver and transmitter channel state information is generally required. In this correspondence, a system where each receiver has perfect channel knowledge, but the transmitter only receives quantized information regarding the channel instantiation is analyzed. The well-known zero-forcing transmission technique is considered, and simple expressions for the throughput degradation due to finite-rate feedback are derived. A key finding is that the feedback rate per mobile must be increased linearly with the signal-to-noise ratio (SNR) (in decibels) in order to achieve the full multiplexing gain. This is in sharp contrast to point-to-point multiple-input multiple-output (MIMO) systems, in which it is not necessary to increase the feedback rate as a function of the SNR

5G : A tutorial overview of standards, trials, challenges, deployment, and practice

Abstract: There is considerable pressure to define the key requirements of 5G, develop 5G standards, and perform technology trials as quickly as possible. Normally, these activities are best done in series but there is a desire to complete these tasks in parallel so that commercial deployments of 5G can begin by 2020. 5G will not be an incremental improvement over its predecessors; it aims to be a revolutionary leap forward in terms of data rates, latency, massive connectivity, network reliability, and energy efficiency. These capabilities are targeted at realizing high-speed connectivity, the Internet of Things, augmented virtual reality, the tactile internet, and so on. The requirements of 5G are expected to be met by new spectrum in the microwave bands (3.3-4.2 GHz), and utilizing large bandwidths available in mm-wave bands, increasing spatial degrees of freedom via large antenna arrays and 3-D MIMO, network densification, and new waveforms that provide scalability and flexibility to meet the varying demands of 5G services. Unlike the one size fits all 4G core networks, the 5G core network must be flexible and adaptable and is expected to simultaneously provide optimized support for the diverse 5G use case categories. In this paper, we provide an overview of 5G research, standardization trials, and deployment challenges. Due to the enormous scope of 5G systems, it is necessary to provide some direction in a tutorial article, and in this overview, the focus is largely user centric, rather than device centric. In addition to surveying the state of play in the area, we identify leading technologies, evaluating their strengths and weaknesses, and outline the key challenges ahead, with research test beds delivering promising performance but pre-commercial trials lagging behind the desired 5G targets.