Colin Sheldon

Four-channel spatial multiplexing over a millimeter-wave line-of-sight link

A scalable system architecture is proposed and demonstrated for spatial multiplexing over millimeter-wave line-of-sight communication links. This architecture provides increased data capacity without increasing the channel bandwidth. The modulation format is simple (BPSK or QPSK); this facilitates high-rate operation. The spatially multiplexed channels are separated at the receiver using broadband adaptive analog I/Q vector signal processing, a technique which should readily scale to data rates exceeding 10 Gb/s per channel. A control loop continuously tunes the channel separation electronics to correct for changes with time in either the propagation environment or the system components. Design and characterization of a four channel 60 GHz hardware prototype is presented.

Integrated Coherent Receivers for High-Linearity Microwave Photonic Links

In this paper, we present a coherent receiver based on an optical phase-locked loop (PLL) for linear phase demodulation. The receiver concept is demonstrated at low frequency. For high-frequency operation, monolithic and hybrid integrated versions of the receiver have been developed and experimentally verified in an analog link. The receiver has a bandwidth of 1.45 GHz. At 300 MHz, a spurious free dynamic range (SFDR) of 125 dB ldr Hz2/3 is measured.

Millimeter-Wave Spatial Multiplexing in an Indoor Environment

A unique feature of communication at millimeter (mm) wave carrier frequencies is that spatial multiplexing is available for multiple-input multiple-output (MIMO) links with moderate antenna spacing even without a rich scattering environment. In this paper, we investigate the potential for exploiting this observation for increasing the spectral efficiency of indoor 60 GHz links. We begin by establishing limits on the spatial degrees of freedom available for linear antenna arrays of constrained length. A system architecture designed to exploit the available degrees of freedom, including beamforming as well as spatial multiplexing, is proposed. We evaluate the link capacity achievable by the proposed architecture when operating in a simple indoor environment. The results illustrate the relationship between between the channel quality and the relative positions of the transmit and receive nodes. up to 10.2 Gbps. For wireless links to close this gap, new wireless architectures are required. With this motivation in mind, we investigate spatial mul- tiplexing as a means to increase spectral efficiency at mm- wave frequencies. We first consider the spatial degrees of freedom that are available in a mm-wave LOS environment given linear arrays of constrained size. We find that the physical dimensions of common consumer electronic devices are sufficient to permit spatial multiplexing of several data streams at 60 GHz. We then describe a system architecture that exploits the available spatial degrees of freedom. The architecture, originally proposed in (3), employs a two-level hierarchical design that decouples the tasks of beamsteering and multiplexing at the transmitter. The performance of the proposed architecture, as measured by link capacity, is sim- ulated assuming a simple indoor environment model. The results demonstrate that performance is dependent on the

A 60GHz line-of-sight 2x2 MIMO link operating at 1.2Gbps

We report first experimental results from a hardware prototype of a millimeter wave line-of-sight (LOS) 2times2 MIMO link. The proposed architecture uses antenna element spacing derived from the principles of diffraction limited optics to establish multiple parallel data channels. Operation at millimeter wave carrier frequencies reduces the antenna array size to reasonable dimensions. The proposed system architecture is scalable to larger one dimensional and two dimensional arrays supporting data rates >160 Gbps. This paper presents the design and characterization of a hardware prototype 2times2 LOS MIMO link operating at 1.2 Gbps.

Nonuniform Array Design for Robust Millimeter-Wave MIMO Links

Spatial multiplexing for millimeter (mm) wave line of sight (LOS) links potentially enables data rates of the order of 10-100 Gbps. Most prior work in this area has focused on uniform transmit and receive arrays, for which it is known that the spatial responses seen by different transmitters can be made orthogonal by choosing the antenna spacing appropriately as a function of range and wavelength. In this paper, we show that variations in range can cause significant degradation in performance for such uniformly spaced arrays optimized for a given range, due to the appearance of high correlations between the spatial responses for different transmitters (and hence rank deficiency in the MIMO channel matrix) as a function of range. We then demonstrate that optimized nonuniform arrays alleviate this problem by keeping correlations between spatial responses small over a significantly larger set of ranges than is possible with uniform spacing.

A 2.4 Gb/s millimeter-wave link using adaptive spatial multiplexing

A scalable system architecture is proposed and demonstrated for spatial multiplexing over millimeter-wave line-of-sight communication links. The architecture decouples spatial channel separation from demodulation, allowing the system bandwidth and data rates to scale up, while performing spatial processing on a time scale matched to the slow time variations of the spatiotemporal channel. The spatially multiplexed channels are separated at the receiver using broadband adaptive analog I/Q vector signal processing. A control loop continuously tunes the channel separation electronics to correct for changes with time in either the propagation environment or the system components. Design and characterization of a four-channel 60 GHz hardware prototype operating at 2.4 Gb/s is presented. This result is the highest data rate line-of-sight wireless link employing adaptive spatial multiplexing reported to date.

Developing Bipolar Transistors for Sub-mm-Wave Amplifiers and Next-Generation (300 GHz) Digital Circuits

Here we consider the prospects for continued improvement in InP HBTs, specifically the challenges faced in a further doubling of transistor and IC bandwidth. Our objective is an IC technology supporting 300 GHz digital clock rates, -600 GHz reactively-tuned amplifiers, and balanced cutoff frequencies in the 700-1000 GHz range. Such ICs would permit monolithic transceivers for 300 GHz and 600 GHz imaging systems, -250 GHz high-rate communications radios, chip sets for 300 Gb/s optical data transmission, and very high-resolution microwave mixed-signal ICs.

InP HBT digital ICs and MMICs in the 140-220 GHz band

Well-balanced InP HBTs now have /spl sim/450 GHz cutoff frequencies and /spl sim/4 V breakdown. With such devices, 150 GHz digital circuits (static dividers) and 175 GHz amplifiers have been demonstrated. We discuss device requirements (scaling laws and scaling limits) for realizing transistors and both digital and analog/RF circuits at sub-mm-wave frequencies; the most critical limitations are metal/semiconductor contact resistivities and dissipated power densities. Given present contact performance and thermal design, 200 GHz digital technologies and 300 GHz power amplifiers are now feasible and will soon be realized.

Telecommunications systems for the NASA Europa missions

The telecommunications systems for two NASA deep-space missions to Jupiters moon Europa are presented. One mission, Europa Clipper, is a Jovian orbiter with multiple Europa flybys; the other mission, Europa Lander, includes a Carrier and Relay Spacecraft (CRS), Deorbit Stage, Descent Stage (DS), and a Lander. Both missions are designed to communicate to Earth via the NASA Deep Space Network (DSN) and other ground stations. For Lander communications, both the CRS and Europa Clipper spacecraft are equipped with store-and-forward relay communication capability. The heart of each spacecrafts telecommunications system is the high-TRL Johns Hopkins University/Applied Physics Laboratory Frontier Radio, based on the Solar Probe Plus design. Other key telecommunnications hardware developments across the two missions include a 3-m dualband (X/Ka) high gain antenna (HGA), a GaN-based solid state power amplifier (SSPA) and slot-array HGA to enable the Lander communication system. All components must operate in a high-radiation environment and meet planetary protection requirements.

Maximizing data return for the Europa lander: A trade study in the application of CCSDS protocols

In support of NASA, Caltechs Jet Propulsion Laboratory and The Johns Hopkins Applied Physics Laboratory are studying concepts for two missions to explore Europa: a multiple flyby spacecraft and a surface lander. This paper analyzes the use of packetized, multi-hop, multi-path communications protocols for the Europa lander concept and assesses their potential for reducing power requirements while increasing data return. Analysis includes three protocols standardized by the Consultative Committee for Space Data Systems (CCSDS): the CCSDS File Delivery Protocol (CFDP), the Bundle Protocol (BP), and the Licklider Transmission Protocol (LTP). A spacecraft may implement a networking stack of one or more of these protocols, with each of these stacks exhibiting different strengths and weaknesses. We present heuristic and analytical methods for evaluating protocol performance including a priori computations of protocol overheads, Monte-Carlo analysis across bit error rates and packet sizes, and high fidelity simulations. Quantitative metrics such as retransmission efficiency, packet overhead, and end-to-end transaction duration characterize individual protocol options. Qualitative metrics such as cost of ownership, mission operations complexity, and computational processing load characterize the mission impacts of various networking stacks. We generate results using anticipated mission link characteristics, data volumes, and network geometries and provide recommendations relating to the value of software protocols and multi-protocol networking stacks. Results demonstrate that each candidate protocol combination can be tuned to within 15% of optimal performance over links of up to 10−4 bit error rate, although achieving this efficiency with solely CFDP incurs up to 800% greater computational processing load versus the other stacks. We conclude multiprotocol stacks separate concerns when optimizing performance for multiple stakeholders. A CFDP/BP/LTP networking stack solves a joint optimization problem where CFDP can be tuned for onboard data operations, BP can be used to provide standardized priority and store-and-forward operations, and LTP can be tuned for retransmission and acknowledgement. This approach enables efficient end-to-end communications for the Europa lander concept that maximizes data return with minimal power requirements.