Siyuan Zhou

Closed-form Output Statistics of MIMO Block-Fading Channels

The information that can be transmitted through a wireless channel, with multiple-antenna-equipped transmitter and receiver, is crucially influenced by the channel behavior as well as by the structure of the input signal. We characterize in closed form, the probability density function (pdf) of the output of multiple-input and multiple-output block-fading channels, for an arbitrary signal-to-noise ratio value. Our results provide compact expressions for such output statistics, paving the way to a more detailed analytical information-theoretic exploration of communications in presence of block fading. The analysis is carried out assuming two different structures for the input signal: 1) the independent identically distributed (i.i.d.) Gaussian distribution and 2) a product form that has been proved to be optimal for noncoherent communication, i.e., in absence of any channel state information. When the channel is fed by an i.i.d. Gaussian input, we assume the Gramian of the channel matrix to be unitarily invariant and derive the output statistics in both the noise- and interference-limited scenario, considering different fading distributions. When the product-form input is adopted, we provide the expressions of the output pdf as the relationship between the overall number of antennas and fading coherence length varies. We also highlight the relation between our newly derived expressions and the results already available in the literature, and, for some cases, we numerically compute the mutual information based on the proposed expression of the output statistics.

Ergodic Capacity Analysis of MIMO Relay Network Over Rayleigh-Rician Channels

We present an analytical characterization of the ergodic capacity for an amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network over asymmetric channels. In the two-hop system that we consider, the source-relay and relay-destination channels undergo Rayleigh and Rician fading, respectively. Considering arbitrary-rank means for the relay-destination channel, we first investigate the marginal distribution of an unordered eigenvalue of the cascaded AF channel, and we provide an analytical expression for the ergodic capacity of the system. The closed-form expressions that we derive are computationally efficient and validated by numerical simulation. Our results also show the impact of the signal-to-noise ratio and of the Rician factor on this asymmetric relay network.

Real-Time Scheduling for Content Broadcasting in LTE

Broadcasting capabilities are one of the most promising features of upcoming LTE-Advanced networks. However, the task of scheduling broadcasting sessions is far from trivial, since it affects the available resources of several contiguous cells as well as the amount of resources that can be devoted to unicast traffic. In this paper, we present a compact, convenient model for broadcasting in LTE, as well as a set of efficient algorithms to define broadcasting areas and to actually perform content scheduling. We study the performance of our algorithms in a realistic scenario, deriving interesting insights on the possible trade-offs between effectiveness and computational efficiency.

MIMO Relay Network with Precoding

We study the achievable rate in a MIMO, dual-hop, relay network where source and relay nodes may precode their input signals before transmission. Although an iterative expression for optimal precoders in this scenario is available in the literature, the corresponding achievable rate cannot be obtained analytically. We therefore propose approximate expressions for the precoding matrices and present semianalytical derivations of the achievable rate, which represent a significant progress toward closed-form expressions of this important metric. Beside being mathematically tractable, our expressions for the precoders provide data rates that are very close to the optimum and outperform existing approximate schemes. We apply our expressions to the analysis of the tradeoffs existing between achievable rate and nodes power consumption.

Outage probability of beamforming for multiuser MIMO relay networks with interference

We investigate the outage probability of a dual-hop MIMO system where amplify-and-forward relay and beamforming are used. A practically important case where proportional fair scheduling is implemented to schedule users transmissions and co-channel interference exists is considered in the analysis. Specifically, taking into account Rayleigh fading and the path-loss effect, we derive the lower bound and the asymptotic expressions of the outage probability in closed form, with arbitrary number of antennas and users. The proposed results are validated via Monte Carlo simulations.

Ergodic mutual information and its fluctuation in multi-level MIMO relay system

The help of relay devices is of paramount importance to overcome the impairments of channel randomness, especially in a rich scattering scenario with no line-of-sight communication path. Relaying strategies are gaining increasing attention due also to the eventual deployment of small-cells in future generations wireless networks, where short-range communication is inherently to be favored, to cope with path-loss and to jointly improve energy-efficiency of the links. MIMO is naturally combined with relaying in order to further increase the overall spatial degrees of freedom of the system. Since the early introduction of relay-aided transmission protocols, in the field of information theory lot of efforts has been devoted to the analytical characterization of the performance of such strategies, with a main focus on dual-hop, single relay systems. This work moves a step toward the characterization of multilevel MIMO relay channels, where data transmission takes place through an arbitrary number of hops. We leverage tools and results from the physics of disordered systems, and put them into the framework of finite-sized multiple-antenna systems.

A unifying analysis of error exponents for MIMO channels with application to multiple-scattering

Expressions for Gallagers Random Coding Error Exponent (RCEE) and the corresponding Expurgated Error Exponent (EEE) are derived in a unifying framework, as functions only of the squared singular values of the channel matrix. The results encompass spatially Kronecker-correlated Rayleigh channels (whose error exponents expressions are already present in the literature), line of sight MIMO systems, multiple-scattering channels, multi-hop amplify and forward MIMO channels with non-noisy relays and noisy destination. As an instance of application of our framework, we consider a multiple-scattering Rayleigh MIMO channels, with an arbitrary but finite number of scattering stages and channel state information (CSI) available at the receiver only. In this scenario, we evaluate closed-form expressions for both RCEE and EEE in terms of Meijers G functions.

Information densities for block-fading MIMO channels

This paper provides a characterization of the output and of the transition probability density function (pdf) of a MIMO block-fading channel, paving the way to its information-theoretic analysis. The information density, whose average in ergodic conditions gives the mutual information conveyed over the channel, is needed to characterize the channels with arbitrary behavior, as one in this case can neither resort to ergodicity nor to consequences of any law of large numbers. The information density expression is then provided under several assumptions on the channel model and also in the presence of multiple-antenna equipped interferers.

Output statistics of MIMO channels with general input distribution

The information that can be conveyed through a wireless channel, with multiple-antenna equipped transmitter and receiver, crucially depends on the channel behavior as well as on the input structure. In this paper, we derive analytical results, concerning the probability density function (pdf) of the output of a single-user, multiple-antenna communication. The analysis is carried out under the assumption of an optimized input structure, and assuming Gaussian noise and a Rayleigh block-fading channel. Our analysis therefore provides a quite general and compact expression for the conditional output pdf. We also highlight the relation between such an expression and the results already available in the literature for some specific input structures.