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.

Method and device for multi-user frequency-domain channel estimation

Abstract: The present invention is a technique of estimating the time and frequency response of at least one desired signal received by at least one antenna. The invention is an update formula for the time-invariant channel responses for multiple transmitting devices, called “Doppler channels”, that model the time-varying channel between each of the transmitting devices and each receiving device. Through use of the update formula, the time-varying channels of the multiple transmitting devices can be better tracked than with prior inventions.

Cooperative communications using multiple access points to improve data integrity

Abstract: A method ( 300, 400, 500, 600 ) of communicating with a subscriber station ( 102 ). Responsive to determining that a supplemental communication link with the subscriber station is desirable, at least a second access point ( 106, 108, 110, 112, 114, 116 ) can be identified to establish the supplemental communication link with the subscriber station. Information can be communicated to the second access point. The information can identify the subscriber station and a pilot zone in which downlink supplemental data is to be transmitted from the second access point to the subscriber station. Downlink supplemental data ( 150 ) also can be communicated to the second access point. The downlink supplemental data can improve integrity of data transmitted from a first access point ( 104 ) to the subscriber station when the downlink supplemental data is transmitted to the subscriber station from the second access point.

Method and system for codebook-based closed-loop mimo using common pilots and analog feedback

Abstract: A method and system that enables the usage of sounding-based feedback or analog feedback in a MIMO communication system with non-beamformed or broadcast pilot symbols is disclosed. The mobile station may employ a feedback channel to send a sounding waveform to a base station, a feedforward channel to receive from the base station codebook weights derived from the send sounding waveform, a receiver to receive communication from the base station, and a processor to detect beamformed data from the received communication and received codebook weights from the base station. The base station processes the sounding waveform to determine codebook weights on groups of subcarriers. Additionally, the base station transmits the beamformed payload and broadcast pilots to the mobile station.

Transmit diversity and transmit adaptive arrays for broadband mobile OFDM systems

Abstract: This paper explores the performance of several frequency-domain transmit array processing strategies for broadband mobile turbo-coded OFDM systems. We consider transmit adaptive array (TXAA) techniques (also known as maximal ratio transmission) with various assumptions on mobile- to-base channel response feedback in a two-transmit antenna OFDM system. We compare the performance of such techniques with the well-known Alamouti diversity scheme, which requires no channel response knowledge at the transmitter. The various techniques are compared with both simulated channels and with channel responses measured with an experimental broadband mobile MIMO-OFDM system. With perfect instantaneous feed- back of the matrix frequency response, the TXAA schemes have the expected 3 dB gain over the Alamouti scheme. However, if the transmit array cannot track the time and frequency selectiv- ity of the channel, the Alamouti method can in some cases out- perform the transmit adaptive array techniques.

Millimeterwave access architecture with rapid rerouting

Abstract: In accordance with the exemplary embodiments of the invention there is provided at least a method and apparatus to determine information comprising a direction and a strength of signaling associated with a mobile apparatus, where the apparatus is configured to connect with a cluster of more than one access point; retain the determined information of the signaling associated with the mobile apparatus; and communicate the information of at least the strength of the signaling towards the cluster of the more than one access point. Further, to determine with signaling received at a mobile apparatus from at least one access point information including a direction and strength of the signaling; retain the determined information of the signaling; use the retained information, identify the access point with the signaling having a strongest beam; and reroute communications with the apparatus towards the access point with the signaling having the strongest beam.

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.