This paper explores the potential benefits of combining the use of injection-locking techniques with GPS signals as a common clock source when applied to a low-cost Software Defined Radio (SDR) to improve the accuracy of coherent multiple receivers. Coherent systems impose severe requirements on the frequency stability of the signal source at the receiver. In this work, injection-locked oscillators are used as local clock receivers, which inherently synchronizes the SDR analog digital converter (ADCs) sampling times and keeps the local oscillator locked on to the GPS stimulus periodic signal. This paper illustrates the hardware modifications needed for to the injection locking oscillators of eight RTL-SDR radios and the theory behind it, and experimentally measures the degree of coherency in the frequency, phase and time synchronization to verify the proposed method. The coherency demonstrated in the results prove the feasibility of using beamforming, multiple input multiple output (MIMO) and RF transmitter geo-localization.
more »
« less
Hardware Implementation of an Underwater Acoustic Massive MIMO Transmitter
This paper presents the hardware implementation of a massive Multiple-Input Multiple-Output (MIMO) transmitter for underwater acoustic (UWA) communication capable of incorporating precoding or beamforming. The transmitter consists of baseband and passband processing modules implemented on an AMD-Xilinx All Programmable System-on-Chip (AP-SoC) architecture, frontend power amplifiers, and high-frequency transducers. While the number of channels can be easily scaled, the current hardware demonstrates a 16-channel transmitter at a carrier frequency of 115 kHz. Experiments in the lab and field show that passband beamforming and precoding are successfully transmitted through the 16 transducers. The receiver signal strengths, however, deviate largely from the free-space simulation of the beam patterns due to rich multipath reflections and imperfection in element spacing and omni-directionality of the transducers.
more »
« less
- PAR ID:
- 10660042
- Publisher / Repository:
- ACM
- Date Published:
- Page Range / eLocation ID:
- 1 to 5
- Format(s):
- Medium: X
- Location:
- Sibenik, Croatia
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Classical beamforming techniques rely on highly linear transmitters and receivers to allow phase-coherent combining at the transmitter and receiver. The transmitter uses eamforming to steer signal power towards the receiver, and the receiver uses beamforming to gather and coherently combine the signals from multiple receiver antennas. When the transmitters and receivers are instead constrained for power and cost reasons to be nonlinear one-bit devices, the potential advantages and performance metrics associated with beamforming are not as well understood. We define beamforming at the transmitter as a codebook design problem to maximize the minimum distance between codewords. We define beamforming at the receiver as the maximum likelihood detector of the transmitted codeword. We show that beamforming with one-bit transceivers is a constellation design problem, and that we can come within a few dB SNR of the capacity attained by linear transceivers.more » « less
-
null (Ed.)Spatial multiplexing, or multi-user MIMO, can improve the communication throughput by simultaneously supporting multiple spatially non-collocated data streams. Most multi-user MIMO TRXs at GHz are based on digital beamforming. However, as the data rate of each user approaches multi-Gb/s at mmWave, performing dynamic beamforming weights calculation in digital and high-speed digital-to-analog conversion faces a significant energy efficiency bottleneck for large-scale mmWave antenna arrays. Alternatively, hybrid beamforming can support a handful of concurrent data streams by combining analog beamforming with digital precoding. Although hybrid beamforming loses degrees-of-freedom compared to all-digital processing, it reduces digital computation complexity and the number of digital-to-analog conversion chains, resulting in greatly enhanced energy efficiency.more » « less
-
null (Ed.)Massive multi-user multiple-input multiple-output (MU-MIMO) wireless systems operating at millimeter-wave (mmWave) frequencies enable simultaneous wideband data transmission to a large number of users. In order to reduce the complexity of MU precoding in all-digital basestation architectures that equip each antenna element with a pair of data converters, we propose a two-stage precoding architecture which first generates a sparse precoding matrix in the beamspace domain, followed by an inverse fast Fourier transform that converts the result to the antenna domain. The sparse precoding matrix requires a small amount of multipliers and enables regular hardware architectures, which allows the design of hardware-efficient all-digital precoders. Simulation results demonstrate that our methods approach the error-rate performance of conventional Wiener filter precoding with more than 2x lower complexity.more » « less
-
Millimeter-wave large-scale antenna systems typically apply hybrid analog-digital precoders to reduce hardware complexity and power consumption. In this paper, we design hybrid precoders for physical-layer security under two types of channel knowledge. With full channel knowledge at transmitter, we provide sufficient conditions on the minimum number of RF chains needed to realize the performance of the fully digital precoding. Then, we design the hybrid precoder to maximize the secrecy rate. By maximizing the average projection between the fully digital precoder and the hybrid precoder, we propose a low-complexity closed-form hybrid precoder. We extend the conventional projected maximum ratio transmission scheme to realize the hybrid precoder. Moreover, we propose an iterative hybrid precoder design to maximize the secrecy rate.With partial channel knowledge at transmitter, we derive a secrecy outage probability upper-bound. The secrecy throughput maximization is converted into a sequence of secrecy outage probability minimization problems. Then, the hybrid precoder is designed to minimize the secrecy outage probability by an iterative hybrid precoder design. Performance results show the proposed hybrid precoders achieve performance close to that of the fully digital precoding at low and moderate signal-to-noise ratios (SNRs), and sometimes at high SNRs depending on the system parameters.more » « less
An official website of the United States government

