Jose P. Gonzalez-Coma

Power minimization and QoS feasibility region in the multiuser MIMO broadcast channel with imperfect CSI

The aim of this work is to jointly achieve individual rate requirements and minimum total transmit power in a Multi User Multiple Input Multiple Output (MU-MIMO) Broadcast Channel (BC). Data streams are transmitted from a multi-antenna base station to several independent and non-cooperative multi-antenna users. Perfect Channel-State-Information (CSI) is known at the receivers and it is fed back to the transmitter, where partial CSI is used for the design of linear transmit filters. Employing a duality between Multiple Access Channel (MAC) and BC w.r.t. the average Mean Square Error (MSE) and identifying standard interference functions, we propose an algorithmic joint solution for the transmit filter design and the power allocation. Additionally, we describe the feasibility region in the average MMSE domain. This result allows for checking the convergence of the algorithm for given Quality of Service (QoS) constraints.

Power minimization in the multiuser downlink under user rate constraints and imperfect transmitter CSI

The aim of this work is to jointly achieve individual rate requirements and minimum total transmit power in the vector Broadcast Channel (BC). Data streams are transmitted from a multi-antenna base station to several non-cooperative single-antenna receivers having perfect Channel-State-Information (CSI). Partial CSI, e.g., obtained via feedback, is used for the design of linear transmit filters at the transmitter. Employing a duality between Multiple Access Channel (MAC) and BC rate regions and the so-called standard interference functions, we propose an algorithmic joint solution for the transmit filter design and the power allocation in this work.

Impact of transmit impairments on multiuser MIMO non-linear transceivers

This paper analyzes the impact of residual transmit impairments on the performance of multiuser Multiple-Input Multiple-Output (MIMO) systems. We focus on the uplink with Decision Feedback (DF) non-linear receivers and the downlink with Tomlinson-Harashima non-linear precoders. We show that transmit noise severely affects the performance of both non-linear transmission schemes, specially for the downlink with THP. Nevertheless, this degradation can be significantly alleviated when including the transmit noise into the transceiver design.

Evaluation of Analog Joint Source-Channel Coding Systems for Multiple Access Channels

We address the evaluation of low-complexity analog Joint Source Channel Coding (JSCC) methods for the transmission of discrete-time analog symbols over Multiple-Input Multiple-Output (MIMO) Multiple Access Channels (MAC). Analog JSCC is employed to encode the source information at each transmitter prior to be directly input to the MAC access scheme. Three channel access methods are considered to ensure the receiver is able to recover the user information: Code Division Multiple Access (CDMA), linear MMSE access codes and opportunistic access. CDMA allows the orthogonal transmission of the user data requiring only Channel State Information (CSI) at reception. On the other hand, linear MMSE access codes exploit CSI knowledge at transmission and exhibit better performance. Finally, opportunistic access also exploits CSI at transmission and allocates all MAC resources to the user with the strongest channel. This latter access scheme exhibits the best performance in terms of sum distortion although it may lead to unfair rate distributions among users.

QoS constrained power minimization in the MISO broadcast channel with imperfect CSI

In this paper we consider the design of linear precoders and receivers in a Multiple-Input Single-Output (MISO) Broadcast Channel (BC). We aim to minimize the transmit power while meeting a set of per-user Quality-of-Service (QoS) constraints expressed in terms of per-user average rate requirements. The Channel State Information (CSI) is assumed to be known perfectly at the receivers but only partially at the transmitter. To solve this problem we convert the QoS constraints into Minimum Mean Square Error (MMSE) constraints. We then leverage MSE duality between the BC and the Multiple Access Channel (MAC), as well as standard interference functions in the dual MAC, to perform power minimization by means of an Alternating Optimization (AO) algorithm. Problem feasibility is also studied to determine whether the QoS constraints can be met or not. Finally, we present an algorithm to balance the average rates and manage situations that may be unfeasible, or lead to an unacceptably high transmit power. HighlightsMISO BC under imperfect CSI and subject to QoS constraints is addressed.Average MMSE-based restrictions establishes lower bounds for the average rates.Optimum filters are found considering only statistical CSI.Average MSE feasible region is studied to ensure convergence to the optimum.

Design of MAC access schemes for analog joint source channel coding

We address the transmission of discrete-time analog samples over a block fading Multiple Access Channel (MAC). At each transmitter, the source information is first encoded using analog Joint Source Channel Coding (JSCC) and then input to a MAC access scheme. We consider three different access schemes: Code Division Multiple Access (CDMA), linear MMSE access codes and opportunistic communication. CDMA allows the orthogonal transmission of the user information requiring only Channel State Information (CSI) at reception. Linear MMSE access strategy exploits the CSI knowledge at transmission to obtain the optimal linear access codes that minimize the MSE at the output of a linear receiver. Finally, opportunistic access allocates all the transmit power to the user with the strongest channel. Although opportunistic is the optimal access strategy when the CSI is available at transmission, it can lead to an unfair allocation of the power and transmission rates of the users.

Average sum MSE minimization in the multi-user downlink with multiple power constraints

We consider a sum mean square error (SMSE) based transceiver design for the multi-user downlink with multiple linear transmit power constraints. Since the multi-antenna transmitter has only imperfect channel state information (CSI), the average SMSE is minimized via an alternating optimization (AO). For fixed equalizers, the average SMSE minimizing precoders are found via an uplink-downlink SMSE duality. The precoder update therewith transforms to an uplink max-min average SMSE problem, i.e., a minimum mean square error (MMSE) equalizer design and an outer worst-case noise search. This dual problem is optimally solved, e.g., by a gradient projection approach, and strong duality is shown.

Power minimization in the multiple stream MIMO Broadcast Channel with imperfect CSI

We address the design of linear precoders and receivers in a MIMO Broadcast Channel (BC) with perfect Channel State Information (CSI) at reception but partial CSI at the transmitter. Our aim is to minimize the transmit power subject to per-user rate constraints when multiple streams of data are sent to each user. We develop a gradient-projection algorithm to convert the per-user constraints into per-stream constraints. The MIMO BC linear precoders and receivers that minimize the transmit power are then obtained with an alternating optimization algorithm.

Feedback and power optimization in the multiuser downlink under QoS constraints

We consider the Multiple-Input Single-Output (MISO) Broadcast Channel (BC) with linear filters and perfect Channel State Information (CSI) at reception that is fed back to the transmitter via a limited feedback channel. Our goal is to jointly achieve per-user rate requirements by using minimum total transmit power. We develop a Lloyds algorithm to find both optimal quantizer and codebook by means of the duality between Multiple Access Channel (MAC) and BC w.r.t. the average Mean Square Error (MSE), and the properties of standard interference functions.

Performance of MIMO systems in measured indoor channels with transmitter noise

This study analyzes the impact of transmitter noise on the performance of multiple-input multiple-output (MIMO) systems with linear and nonlinear receivers and precoders. We show that the performance of MIMO linear and decision-feedback receivers is not significantly influenced by the presence of transmitter noise, which does not hold true in the case of MIMO systems with precoding. Nevertheless, we also show that this degradation can be greatly alleviated when the transmitter noise is considered in the MIMO precoder design. A MIMO testbed developed at the University of A Coruña has been employed for experimentally evaluating how much the transmitter noise impacts the system performance. Both the transmitter noise and the receiver noise covariance matrices have been estimated from a set of 260 indoor MIMO channel realizations. The impact of transmitter noise has been assessed in this realistic scenario.