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A general and flexible technique is proposed for sampling the complex envelope of a bandpass signal by using a nonuniformly interleaved two-channel analog-to-digital converter (TIADC). The signal is sampled directly without any demodulation operation, but the two sampling channels are not uniformly interleaved, since some TIADC timing offsets are rendered forbidden. The proposed complex envelope sampling scheme requires the implementation of two digital FIR filters and a discrete-time modulator. Quadrature sampling, a special case that assumes certain parameter relations, is investigated as an approximation technique. Computer simulations are presented and illustrate a -57dB mean-square error (MSE) can be achieved via quadrature approximation for sufficiently large filter orders.

The relentless growth of wireless applications and data traffic continues to accentuate the long felt need for decentralized, self-managed, and cooperative network architectures. Enlightened by the power of blockchain technology, we propose a blockchain radio access network (B-RAN) architecture and develop decentralized, secure, and efficient mechanisms to manage network access and authentication among inherently trustless network entities. We further identify promising advanced functions made possible by adopting blockchain for open radio access networks. Our test results demonstrate the benefits of the B-RAN architecture. We also present a number of challenges and future research directions.

A contraction analysis of risk-sensitive Riccati equations is proposed. When the state-space model is reachable and observable, a block-update implementation of the risk-sensitive filter is used to show that the N-fold composition of the Riccati map is strictly contractive with respect to the Thompson's part metric of positive definite matrices, when N is larger than the number of states. The range of values of the risk-sensitivity parameter for which the map remains contractive can be estimated a priori. It is also found that a second condition must be imposed on the risk-sensitivity parameter and on the initial error variance to ensure that the solution of the risk-sensitive Riccati equation remains positive definite at all times. The two conditions obtained can be viewed as extending to the multivariable case an earlier analysis of Whittle for the scalar case.

Switching noise generated by digital circuits can degrade analog circuit performance in mixed-signal integrated circuits (ICs). In an analog-to-digital converter (ADC), one major source of switching noise is digital output drivers. Traditional methods for mitigating this problem mostly have been to isolate the analog and digital circuits to minimize digital noise coupling into sensitive analog nodes. This paper presents two fully digital and adaptive algorithms, which find and cancel errors due to switching noise coupling at the output of an ADC without using noise sensors. To demonstrate the operation of these algorithms, a 12-bit, 40-MS/s pipelined ADC has been designed and fabricated in 0.18-μm CMOS process. The system consists of an ADC with its own output drivers, and eight other independent digital output drivers (noise buffers) that can be programmed to produce four different kinds of switching noise. The switching noise cancellation (SNC) algorithm estimates noise parameters and stores them in look-up tables. At the ADC output, the effects of switching noise are digitally removed to recover the input samples. Test results show that the ADC achieves a signal-to-noise-and-distortion-ratio (SNDR) of 64.9 dB with all of the noise-generating buffers off. With the noise buffers on, the worst case SNDR before and after SNC is 51.9 dB and 63.7 dB, respectively. © 1966-2012 IEEE.

This work studies the problem of neighbor discovery for device-to-device (D2D) communications of LTE user equipments (UEs) in a modern cellular network. By listening to cellular uplink transmissions, UEs can detect potential D2D partners through a neighbor discovery process compatible with the standard LTE network protocol. We focus on neighbor discovery utilizing sounding reference signal (SRS) channel, which can be accessed by peer UEs that are LTE-compliant. Under the constraint of unknown channel statistics during uplink hearing, we propose joint neighbor detection and D2D channel estimation for listening UEs using the framework of sparse channel recovery. Composite hypothesis testing methods are further developed to refine neighbor detection accuracy. We evaluate the performance of our neighbor discovery methods under various network parameters to facilitate practical design and implementation of D2D in 4G cellular networks. © 2012 IEEE.

In this paper, we consider robust optimization of amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay precoders in presence of deterministic imperfect channel state information (CSI), when the CSI uncertainty lies in a norm bounded region. Two widely used performance metrics, mutual information (MI) and mean square error (MSE), are adopted as design objectives. According to the philosophy of worst-case robustness, the robust optimization problems with respect to maximizing the worst-case MI and minimizing the worst-case MSE are formulated as maximin and minimax problems, respectively. Due to the fact that these two problems do not have a concave-convex or convex-concave structure, we cannot rely on the conventional saddle point theory to find the robust solutions. Nevertheless, by exploiting majorization theory, we show that the formulated maximin and minimax problems both admit saddle points. We further analytically characterize the saddle points, and provide closed-form solutions to robust relay precoder designs. Interestingly, we find that, under both MI and MSE metrics, the robust relay optimization leads to a channel-diagonalizing structure, meaning that eigenmode transmission is optimal from the worst-case robustness perspective. The proposed robust designs can improve the spectral efficiency and reliability of AF MIMO relaying against CSI uncertainties at the similar cost of computational complexity as the existing non-robust schemes. © 1991-2012 IEEE.