Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge

Coordinated Multi-Point (CoMP) is known to be a key technology for next generation mobile communications systems, as it allows to overcome the burden of inter-cell interference. Especially in the uplink, it is likely that interference exploitation schemes will be used in the near future, as they can be used with legacy terminals and require no or little changes in standardization. Major drawbacks, however, are the extent of additional backhaul infrastructure needed, and the sensitivity to imperfect channel knowledge. This paper jointly addresses both issues in a new framework incorporating a multitude of proposed theoretical uplink CoMP concepts, which are then put into perspective with practical CoMP algorithms. This comprehensive analysis provides new insight into the potential usage of uplink CoMP in next generation wireless communications systems.Comment: Submitted to IEEE Transactions on Wireless Communications in February 201

Transceiver design and interference alignment in wireless networks: complexity and solvability

University of Minnesota M.S. thesis. November 2013. Major: Mathematics. Advisor: Gennady Lyubeznik. 1 computer file (PDF); vi, 58 pages.This thesis aims to theoretically study a modern linear transceiver design strategy, namely interference alignment, in wireless networks. We consider an interference channel whereby each transmitter and receiver are equipped with multiple antennas. The basic problem is to design optimal linear transceivers (or beamformers) that can maximize the system throughput. The recent work [1] suggests that optimal beamformers should maximize the total degrees of freedom through the interference alignment equations. In this thesis, we first state the interference alignment equations and study the computational complexity of solving these equations. In particular, we prove that the problem of maximizing the total degrees of freedom for a given interference channel is NP-hard. Moreover, it is shown that even checking the achievability of a given tuple of degrees of freedom is NP-hard when each receiver is equipped with at least three antennas. Interestingly, the same problem becomes polynomial time solvable when each transmit/receive node is equipped with no more than two antennas.The second part of this thesis answers an open theoretical question about interference alignment on generic channels: What degrees of freedom tuples (d1, d2, ..., dK) are achievable through linear interference alignment for generic channels? We partially answer this question by establishing a general condition that must be satisfied by any degrees of freedom tuple (d1, d2, ..., dK) achievable through linear interference alignment. For a symmetric system with dk = d for all k, this condition implies that the total achievable DoF cannot grow linearly with K, and is in fact no more than K(M + N)/(K + 1), where M and N are the number of transmit and receive antennas, respectively. We also show that this bound is tight when the number of antennas at each transceiver is divisible by the number of data streams

Cooperative Communications with Partial Channel State Information in Mobile Radio Systems

Future 4G mobile radio cellular networks are considered OFDM-MIMO systems. Cooperative communication based on coordinated base stations is a very promising concept to perform inter-cell interference management. This thesis deals with the concept of cooperative communication from its information-theoretic background to its practical system design. The main focus is a practical design of the joint detection scheme in the uplink and the joint transmission scheme in the downlink with partial channel-state information (CSI), i.e., significant CSI and imperfect CSI.Zukünftige zellulare 4G-Mobilfunksysteme können als OFDM-MIMO-Systeme betrachtet werden. In solchen zukünftigen Mobilfunksystemen ist kooperative Kommunikation, basierend auf koordinierten Basisstationen, ein sehr vielversprechendes Konzept zum Interzellinterferenzmanagement. Die vorliegende Arbeit behandelt das Konzept der kooperativen Kommunikation vom informationstheoretischen Hintergrund bis hin zum praktischen Systemdesign. Der Schwerpunkt der vorliegenden Arbeit liegt auf dem praktischen Design kooperativer Kommunikationssysteme mit partieller Kanalkenntnis

Distributed base station processing in the uplink of cellular networks

This paper considers the problem of joint detection in the uplink of cellular multiaccess networks with base-station cooperation. Distributed multiuser detection algorithms with local passing among neighbor base stations are proposed and compared in terms of computational complexity required in the base stations, the amount of serial communications among them, error rate performance, and convergence speed. The algorithms based on the belief propagation algorithm result in complexity and delay per base station which do not grow as the network size increases. In addition, it is observed that these algorithms have near single user error rate performance for the fading channels considered. Thus it is illustrated that using the belief propagation algorithm, it is possible to use non-orthogonal signaling and still achieve near single user performance with moderate computational complexity and a limited amount of message passing between base stations of adjacent cells. © 2006 IEEE.6 page(s