In this paper, we present a vision beyond the conventional Long Term Evolution Fourth Generation (LTE-4G) evolution path and suggest that time division duplexing (TDD) could be a key enabler for a new heterogeneous network architecture with the potential to provide ubiquitous coverage and unprecedented spectral area efficiencies. This architecture is based on a cochannel deployment of macro base stations (BSs) with very large antenna arrays and a secondary tier of small cells (SCs) with a few antennas each. Both tiers employ a TDD protocol in a synchronized fashion. The resulting channel reciprocity enables not only the estimation of large-dimensional channels at the BSs, but also an implicit coordination between both tiers without the need to exchange user data or channel state information (CSI) over the backhaul. In particular, during the uplink (UL), the BSs and SCs can locally estimate the dominant interference sub-space. This knowledge can be leveraged for downlink (DL) precoding to reduce intra- and inter-tier interference. In other words, the BSs and SCs “sacrifice” some of their degrees of freedom for interference rejection. Our simulation results demonstrate that the proposed architecture and precoding scheme can achieve a very attractive rate region compared to several baseline scenarios. For example, with 100 antennas at each BS and four antennas at each SC, we observe an aggregate area throughput of 7.63 Gb/s/km2 (DL) and 8.93 Gb/s/km2 (UL) on a 20 MHz band shared by about 100 mobile devices.

Making smart use of excess antennas: Massive MIMO, small cells, and TDD

Understand the fundamentals of wireless and MIMO communication with this accessible and comprehensive text. Viewing the subject through an information theory lens, but also drawing on other perspectives, it provides a sound treatment of the key concepts underpinning contemporary wireless communication and MIMO, all the way to massive MIMO. Authoritative and insightful, it includes over 330 worked examples and 450 homework problems, with solutions and MATLAB code and data available online. Altogether, this is an excellent resource for instructors and graduate students, as well as an outstanding reference for researchers and practicing engineers.

Foundations of MIMO Communication

The present invention selects a space-time encoding mode to use when transmitting with spatial diversity based on the receive diversity associated with a receiver device and the quality of the transmission channels based on information fed back from the receiver device. The selectable space-time encoding modes are preferably space-time transmit diversity encoding and a version of BLAST-type encoding. Further, modulation modes, error encoding rates, or a combination thereof, may also be based on the quality of the transmission channels and the available diversity of the receiver device.

Adaptive modulation and coding

In general, linear complex-field encoding techniques are proposed For example, transmitter of a wireless communication system includes an encoder and a modulator. The encoder linearly encodes a data stream to produce an encoded data stream. The modulator to produce an output waveform in accordance with the encoded data stream for transmission through a wireless channel. The modulator generates the output waveform as a multicarrier waveform having a set of subcarriers, e.g., an Orthogonal Frequency Division Multiplexing (OFDM) waveform. The encoder linearly encodes the data stream so that the subcarriers carry different linear combinations of information symbols of the data stream.

Wireless communication system having linear encoder

In multi-cell OFDMA systems, inter-cell interference can severely degrade the system throughput, particularly for cell-edge users. To mitigate the inter-cell interference problem, interference coordination is a promising approach that effectively restricts and allocates certain resources among users in different cells to minimize the effect of inter-cell interference. However, most approaches are studied for static user distribution/traffic load and usually require a centralizer controller to solve a complicated optimization problem. In this paper, we propose an adaptive and distributed interference coordination algorithm that can achieve an efficient frequency reuse for a given user distribution and traffic load. The proposed algorithm only requires minimal coordination between base stations and does not need any a priori frequency planning. To enable reduction in system optimization, we classify the users into two groups, namely cell-interior and cell-edge user groups. With such user group differentiation, we can efficiently decompose a multi-cell optimization problem into distributed optimization problems, which is composed of solving single-cell resource allocation problem.

Adaptive interference coordination in multi-cell OFDMA systems

Coexistence of different access technologies, hierarchical cellular deployment, a wide variety of data services, requirements for transparent operation across different technologies, adaptivity to varying network conditions and mobility and quality of service (QoS) constraints introduce a number of challenges in the design of future generation systems and the specification of new air interfaces, such as efficiency and flexibility in the utilization of spectrum, dynamic resource allocation and exploitation of the multiuser diversity and reconfigurable interference management and inter-cell coordination. Three critical issues for the design of next generation systems are addressed: (i) duplexing, (ii) scheduling and resource allocation and (iii) interference and inter-cell coordination. A number of research directions are presented, which constitute promising potential candidates for next generation systems specification.

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Duplexing, resource allocation and inter-cell coordination: design recommendations for next generation wireless systems

Differential unitary space-time (DUST) communication is a technique for communicating via one or more antennas by encoding the transmitted data differentially using unitary matrices at the transmitter, and decoding differentially without knowing the channel coefficients at the receiver. Since channel knowledge is not required at the receiver, DUST is ideal for use on wireless links where channel tracking is undesirable or infeasible. Disclosed are a class of Cayley codes for DUST communication that can produce sets of unitary matrices that work with any number of antennas, and has efficient encoding and decoding at any rate. The codes are named for their generation via the Cayley transform, which maps the highly nonlinear Stiefel manifold of unitary matrices to the linear space of skew-Hermitian matrices. The Cayley codes can be decoded using either successive nulling/cancelling or sphere decoding.

Cayley-encodation of unitary matrices for differential communication

In a method of wireless transmission, space time matrices are used to spread the transmission of data over two or more transmit antennas and/or over two or more symbol intervals. Initially, blocks of data are encoded as symbols, each being a complex amplitude selected from a symbol constellation. A finite set of space-time matrices, referred to as “dispersion matrices,” is predetermined. In transmission, a group of symbols are transmitted concurrently. Each of the symbols to be transmitted is multiplied by a respective dispersion matrix. Thus, a composite matrix, proportional to a sum of dispersion matrices multiplied by their corresponding symbols, is modulated onto a carrier and transmitted. In reception, knowledge of the dispersion matrices is used to recover the transmitted symbols from the received signals corresponding to the composite matrix that was transmitted.

Method of multiple-antenna wireless communication using space-time codes

Embodiments of methods and apparatuses for characterizing an electrical power distribution system are disclosed. One method includes applying a plurality of test signals to a first plurality of test points of the electrical power distribution system, measuring a plurality of response signals at a second plurality of test points of the electrical distribution system, deriving a characterization matrix for the electrical power distribution system from the plurality of test signals and response signals, and characterizing the electrical power distribution system based on the derived characterization matrix.

Bertrand M Hochwald

Papers

Duplexing, resource allocation and inter-cell coordination: design recommendations for next generation wireless systems

Cayley-encodation of unitary matrices for differential communication

Method of multiple-antenna wireless communication using space-time codes

Characterization of electrical power distribution systems using characterization matrices

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