Multiple antenna downlink: feedback reduction, interference suppression and relay transmission

Multiple input multiple output (MIMO), which uses multiple antennas at both the transmitters and the receivers, is an emerging technology that greatly improve the data rate of wireless systems. This dissertation focuses on the downlink of a cellular system, where a base station transmits data to multiple users. It proposes design solutions on how to combat the impairments in the system and improve the data rate or error rate performance with multiple antennas at the base station and/or the users. In the downlink, the scheduling decisions, which determine how to transmit data from the base station to the users, usually depend on users’ channel conditions, e.g., the gains or the coefficients of the channels. Reducing the system resource, e.g., transmission time or radio frequency band, used for feeding back the channel information from the downlink MIMO users, which works with scheduling algorithms and different MIMO transmitter and receiver configurations, has been recently recognized as an important design issue. The first part of this dissertation proposes a scheduling and feedback strategy that exploits multiuser diversity with significant reduction of the amount of resource for feedback of channel information. The second contribution of this dissertation studies the problem of interference suppression. Combatting interference from adjacent base stations that use the same radio frequency band (cochannel interference) requires signal processing techniques at the transmitters and/or the receivers. In particular, in orthogonal frequency division multiplexing (OFDM) systems, dealing with cochannel interference that is not synchronized in carrier frequency and propagation time poses challenges to the receiver design. This dissertation studies the design problem for suppressing the asynchronous cochannel interference at an OFDM receiver. In the third part of this dissertation, a technique for improving coverage for the downlink users under heavy signal attenuation is investigated. The basic idea is to use relays that are deployed at fixed locations in the downlink to receive and forward signals from the base station to mobile users. This dissertation studies the design of different signal processing components for the system where both the base station and the relay have multiple antennas.Electrical and Computer Engineerin

Analyze the FMCW Waveform Skin Return of Moving Objects in the Presence of Stationary Hidden Objects Using Numerical Models

In this paper, a high-performance antenna array system model is presented to analyze moving-object-skin-returns and track them in the presence of stationary objects using frequency modulated continuous wave (FMCW). The main features of the paper are bonding the aspects of antenna array and electromagnetic (EM) wave multi-skin-return modeling and simulation (M&S) with the aspects of algorithm and measurement/tracking system architecture. The M&S aspect models both phase and amplitude of the signal waveform from a transmitter to the signal processing in a receiver. In the algorithm aspect, a novel scheme for FMCW signal processing is introduced by combining time- and frequency-domain methods, including a vector moving target indication filter and a vector direct current canceller in time-domain, and a constant false alarm rate detector and a mono-pulse digital beamforming angle tracker in frequency-domain. In addition, unlike previous designs of using M × N fast Fourier transform (FFT) for an M × N array, only four FFTs are used, which tremendously save time and space in hardware. With the presented model, the detection of the moving-target-skin-return in stationary objects under a noisy environment is feasible. Therefore, to track long range and high-speed objects, the proposed technique is promising. Using a scenario having (1) a target with 17 dBm2 radar cross section (RCS) at about 40 km range with 5.936 Mach speed and 11.6 dB post processing signal to noise ratio, and (2) a strong stationary clutter with 37 dBm2 RCS located at the proximity of the target, it demonstrates that the root-mean-square errors of range, angle, and Doppler measurements are about 26 m, 0.68 degree, and 1100 Hz, respectively

Power spectrum optimization for interference mitigation via iterative function evaluation

Abstract Power spectrum optimization is a well-known difficult nonconvex optimization problem for which only local optimality can typically be assured. This paper unifies several classes of local optimization methods and proposes efficient and new methods for power spectrum optimization by observing that methods for reaching the local optimal points can often be expressed in the form of an iterative function evaluation. This proposed new approach is based on the fact that the gradient of the objective function is zero at a local optimum, and that different manipulations of the optimality condition can then lead to different power update equations. As a practical application, this paper examines the benefit of dynamic power spectrum optimization for interference mitigation in a wireless backhaul network in which remote radio units are deployed to serve mobile users in areas with high data traffic demand. The remote radio units, called remote terminals (RT), are connected to access nodes (AN) via orthogonal frequency division multiple access (OFDMA) over a fixed bandwidth with one RT active in each frequency tone. The system performance is thus limited by internode interference solely, and no intranode interference. This paper shows that iterative function evaluation based methods provide a significant improvement in the overall network throughput in this setting as compared to a conventional network with fixed transmit power spectrum. The proposed methods have computationally fast convergence and can be implemented in a distributed fashion assuming reasonable amount of internode information exchange. Further, some of the proposed methods can be implemented asynchronously at each AN, which makes them amenable to practical utilization

Power spectrum optimization for interference mitigation via iterative function evaluation

Abstract—This paper proposes practical methods for and examines the benefit of dynamic power spectrum optimization for interference mitigation in wireless networks. The paper envisions a distributed antenna system, deployed as a means to increase the network capacity for areas with high data traffic demand. The network comprises several access nodes (AN), each serving a fixed set of remote radio units called remote terminals (RT). The RTs belonging to each AN are separated from each other using orthogonal frequency division multiple access (OFDMA) over a fixed bandwidth, where only one RT is active at each frequency tone. The system performance is thus limited by internode interference solely, and no intranode interference. This paper proposes methods for power spectrum optimization based on the idea of iterative function evaluation. The proposed methods provide a significant improvement of the overall network throughput, as compared to conventional wireless networks with fixed transmit power spectrum. The proposed methods are computationally feasible and fast in convergence. They can be implemented in a distributed fashion across all access nodes, with reasonable amount of internode information exchange. Some of the proposed methods can be further implemented asynchronously at each AN, which makes them amenable to practical utilization. I

Accumulatively Increasing Sensitivity of Ultrawide Instantaneous Bandwidth Digital Receiver with Fine Time and Frequency Resolution for Weak Signal Detection

It is always an interesting research topic for digital receiver (DRX) designers to develop a DRX with (1) ultrawide instantaneous bandwidth (IBW), (2) high sensitivity, (3) fine time-of-arrival-measurement resolution (TMR), and (4) fine frequency-measurement resolution (FMR) for weak signal detection. This is because designers always want their receivers to have the widest possible IBW to detect far away and/or weak signals. As the analog-to-digital converter (ADC) rate increasing, the modern DRX IBW increases continuously. To improve the signal detection based on blocking FFT (BFFT) method, this paper introduces the new concept of accumulatively increasing receiver sensitivity (AIRS) for DRX design. In AIRS, a very large number of frequency-bins can be used for a given IBW in the time-to-frequency transform (TTFT), and the DRX sensitivity is cumulatively increased, when more samples are available from high-speed ADC. Unlike traditional FFT-based TTFT, the AIRS can have both fine TMR and fine FMR simultaneously. It also inherits all the merits of the BFFT, which can be implemented in an embedded system. This study shows that AIRS-based DRX is more efficient than normal FFT-based DRX in terms of using time-domain samples. For example, with a probability of false alarm rate of 10−7, for N=220 frequency-bins with TMR = 50 nSec, FMR = 2.4414 KHz, IBW > 1 GHz and ADC rate at 2.56 GHz, AIRS-based DRX detects narrow-band signals at about −42 dB of input signal-to-noise ratio (Input-SNR), and just uses a little less than N/2 real-samples. However, FFT-based DRX have to use all N samples. Simulation results also show that AIRS-based DRX can detect frequency-modulated continuous wave signals with ±0.1, ±1, ±10 and ±100 MHz bandwidths at about −39.4, −35.1, −30.2, and −25.5 dB of Input-SNR using about 264.6 K, 104.7 K, 40.2 K and 18.3 K real-samples, respectively, in 220 frequency-bins for TTFT