49 research outputs found

    Design and Testbed Deployment of Frequency-Domain Equalization Full Duplex Radios

    Full text link
    Full-duplex (FD) wireless can significantly enhance spectrum efficiency but requires effective self-interference (SI) cancellers. RF SI cancellation (SIC) via frequency-domain equalization (FDE), where bandpass filters channelize the SI, is suited for integrated circuits (ICs). In this paper, we explore the limits and higher layer challenges associated with using such cancellers. We evaluate the performance of a custom FDE-based canceller using two testbeds; one with mobile FD radios and the other with upgraded, static FD radios in the PAWR COSMOS testbed. The latter is a lasting artifact for the research community, alongside a dataset containing baseband waveforms captured on the COSMOS FD radios, facilitating FD-related experimentation at the higher networking layers. We evaluate the performance of the FDE-based FD radios in both testbeds, with experiments showing 95 dB overall achieved SIC (52 dB from RF SIC) across 20 MHz bandwidth, and an average link-level FD rate gain of 1.87x. We also conduct experiments in (i) uplink-downlink networks with inter-user interference, and (ii) heterogeneous networks with half-duplex and FD users. The experimental FD gains in the two types of networks depend on the users' SNR values and the number of FD users, and are 1.14x-1.25x and 1.25x-1.73x, respectively, confirming previous analytical results.Comment: 13 pages, 22 figures. arXiv admin note: substantial text overlap with arXiv:1812.0112

    Real-time FPGA Implementation of a Digital Self-interference Canceller in an Inband Full-duplex Transceiver

    Get PDF
    Full-duplex is a communications engineering scheme that allows a single device to transmit and receive at the same time, using the same frequency for both tasks. Compared to traditionally used half-duplex, where the transmission and reception is divided temporally or spectrally, the spectral efficiency may theoretically be doubled in full-duplex operation. However, the technology suffers from a profound problem, namely the self-interference (SI) signal, which is the name given to the signal a node transmits and simultaneously also receives. Making the full-duplex technology feasible demands that the SI signal is mitigated with SI cancellers. Such cancellers reconstruct an estimate of the SI signal and subtract the estimate from the received signal, thus suppressing the SI. For the SI signal to be diminished as much as possible, canceller solutions should be deployed in both analog and digital domains. This thesis presents a digital real-time implementation of a novel nonlinear self-interference canceller, based on splines interpolation. This canceller utilizes a Hammerstein model to identify the SI signal, taking advantage of a FIR filter for the identification of the SI channel, and splines interpolation to model the nonlinear effects of the transceiver circuitry. The new canceller solution promises great reduction in computational complexity compared to traditional algorithms with little to no sacrifice in cancellation performance. The algorithm was implemented for a National Instruments USRP SDR device using LabVIEW Communications System Design Suite 2.0. The LabVIEW program provides the required connectivity to the USRP platform, as the SDR lacks a user interface. In addition, the functionality of the SDR is determined in LabVIEW, by creating code that is then run on the USRP, or more specifically, on the built-in FPGA of the device. The FPGA is where the SI canceller is executed, in order to ensure real-time operation. Even though the USRP device employs a high-end FPGA with plenty of resources, the canceller implementation needs to be simplified nonetheless, for example by approximating magnitudes of complex values and by decreasing the sample rate of the canceller. With the simplifications, the implementation utilizes only 34.9 % of available slices on the FPGA and only 34.6 % of the DSP units. Measurements with the canceller show that it is capable of SI cancellation of up to 48 dB, which is on par with state-of-the-art real-time SI cancellations in literature. Furthermore, it was demonstrated that the canceller is capable of bidirectional communication in various circumstances

    Low-resolution ADC receiver design, MIMO interference cancellation prototyping, and PHY secrecy analysis.

    Get PDF
    This dissertation studies three independent research topics in the general field of wireless communications. The first topic focuses on new receiver design with low-resolution analog-to-digital converters (ADC). In future massive multiple-input-multiple-output (MIMO) systems, multiple high-speed high-resolution ADCs will become a bottleneck for practical applications because of the hardware complexity and power consumption. One solution to this problem is to adopt low-cost low-precision ADCs instead. In Chapter II, MU-MIMO-OFDM systems only equipped with low-precision ADCs are considered. A new turbo receiver structure is proposed to improve the overall system performance. Meanwhile, ultra-low-cost communication devices can enable massive deployment of disposable wireless relays. In Chapter III, the feasibility of using a one-bit relay cluster to help a power-constrained transmitter for distant communication is investigated. Nonlinear estimators are applied to enable effective decoding. The second topic focuses prototyping and verification of a LTE and WiFi co-existence system, where the operation of LTE in unlicensed spectrum (LTE-U) is discussed. LTE-U extends the benefits of LTE and LTE Advanced to unlicensed spectrum, enabling mobile operators to offload data traffic onto unlicensed frequencies more efficiently and effectively. With LTE-U, operators can offer consumers a more robust and seamless mobile broadband experience with better coverage and higher download speeds. As the coexistence leads to considerable performance instability of both LTE and WiFi transmissions, the LTE and WiFi receivers with MIMO interference canceller are designed and prototyped to support the coexistence in Chapter IV. The third topic focuses on theoretical analysis of physical-layer secrecy with finite blocklength. Unlike upper layer security approaches, the physical-layer communication security can guarantee information-theoretic secrecy. Current studies on the physical-layer secrecy are all based on infinite blocklength. Nevertheless, these asymptotic studies are unrealistic and the finite blocklength effect is crucial for practical secrecy communication. In Chapter V, a practical analysis of secure lattice codes is provided

    Multiband OFDM for Cognitive Radio – A Way for Cyclostationary Detection and Interference Cancellation

    Get PDF
    With the tremendous growth in wireless technology there has been a shortage in the spectrum utilized for certain applications while some spectrum remains idle. To overcome this problem and for the efficient utilization of the spectrum cognitive radio is the suitable solution.Multiband OFDM can be easily modeled as cognitive radio, a technology that is employed for utilizing the available spectrum in the most efficient way. Since sensing of the free spectrum for detecting the arrival of the primary users is the foremost job of cognitive, here cyclostationary based spectrum sensing is carried out. Its performance is investigated using universal software defined radio peripheral (USRP) kit which is the hardware test bed for the cognitive radio system. Results are shown using Labview software. Further to mitigate the interference between the primary and cognitive users a modified intrusion elimination (AIC) algorithm had been proposed which in turn ensures the coexistence of both the users in the same wireless environment
    corecore