We propose a full rate space-time block code for 3+ T x antennas. The code is chosen to minimize the non-orhonormality that arises f r o m increasing the rate above the maximum allowed b y orthogonality. A linear decoding based on iterative interference cancellation b e t w e e n parts of the code approaches the m a x i m a l likelihood decoding performance.
Space-time block codes for providing transmit diversity in wireless communication systems are considered. Based on the principles of linearity and unitarity, a complete classification of linear codes is given in the case when the symbol constellations are complex, and the code is based on a square matrix or restriction of such by deleting columns (antennas). Maximal rate delay optimal codes are constructed within this category. The maximal rates allowed by linearity and unitarity fall off exponentially with the number of transmit antennas. Index Terms-Clifford algebras, multiple antennas, space-time block codes, transmit diversity. I. INTRODUCTION M ULTIANTENNA techniques have received a lot of attention in the scientific community after Foschini [1] and Telatar [2] showed that the capacity of the system increases linearly with the number of uncorrelated transmit and receive antennas. With a restricted number of receive antennas, a part of this capacity increase can be realized using transmit diversity. Within a short time, several schemes have been proposed for a number of wireless communication systems [3]-[6]. One implementation of transmit diversity, called space-time trellis coding, was developed by Tarokh, Seshadri, and Calderbank [4]. It performs well in slowly fading environments, but it has the drawback that decoding complexity grows exponentially with the number of antennas. Recently, the alternative multiantenna transmit diversity concept of space-time block coding 1 emerged in the work of Alamouti [5]. It was further developed and put into a theoretical framework by Tarokh, Jafarkhani, and Calderbank in [6]. The essential feature of these schemes is their inherent orthogonality. This guarantees that linear decoding provides the maximal likelihood result. Even in some systems with frequency-selective fading, orthogonality is almost preserved by the communication channel, as long as the ensuing intersymbol interference can be reliably equalized. This is the case, e.g.,
Abstract-Single-user, multiuser, and network MIMO performance is evaluated for downlink cellular networks with 12 antennas per site, sectorization, universal frequency reuse, scheduled packet-data, and a dense population of stationary users. Compared to a single-user MIMO baseline system with 3 sectors per site, network MIMO coordination is found to increase throughput by a factor of 1.8 with intra-site coordination among antennas belonging to the same cell site. Intra-site coordination performs almost as well as a highly sectorized system with 12 sectors per site. Increasing the coordination cluster size from 1 to 7 sites increases the throughput gain factor to 2.5.
The paper studies subchannel assignment in a two-hop OFDM relay system in which the transmitting nodes (source and relay) have access to channel information and interference-related information. We show that with L-superadditive relay (performance) functions a simple ranking of subchannels leads to the optimal assignment with a very low computational complexity. Numerical results quantify the benefit of subchannel assignment in a frequency-selective channel.
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