35 research outputs found
Co-Channel Interference Cancellation in OFDM Networks using Coordinated Symbol Repetition and Soft Decision MLE CCI Canceler
In this paper, a new scheme of downlink co-channel interference (CCI)
cancellation in OFDM cellular networks is introduced for users at the
cell-edge. Coordinated symbol transmission between base stations (BS) is
operated where the same symbol is transmitted from different BS on different
sub-carriers. At the mobile station (MS) receiver, we introduce a soft decision
maximum likelihood CCI canceler and a modified maximum ratio combining (M-MRC)
to obtain an estimate of the transmitted symbols. Weights used in the combining
method are derived from the channels coefficients between the cooperated BS and
the MS. Simulations show that the proposed scheme works well under
frequency-selective channels and frequency non-selective channels. A gain of 9
dB and 6 dB in SIR is obtained under multipath fading and flat-fading channels,
respectively.Comment: 4 pages, 8 figures, IEEE International Conference on Signal
Processing and Communications, 2007. ICSPC 200
Parallel QRD-M encoder for multi-user MIMO systems
International audienceIn the context of multi-user precoding, the idea behind vector perturbation (VP) lies in adding an integer vector to the data vector such that the overall transmit power is reduced, where the performance at the users end is consequently improved. In the literature, several techniques have been proposed to nd a quasi-optimum perturbing vector, where this process was represented as an integer lattice search problem. In this paper, we propose a parallel QRD-M encoder (PQRDME) that, besides attaining a quasi-optimum diversity order, leads to tremendous reduction in the latency of the vector perturbation stage. Based on the set grouping, the proposed encoder transforms the full tree-search of the conventional QRDME into partial trees that can be pipelined to increase the encoding throughput. We evaluate the proposed algorithm under several scenarios with both perfect channel state information (PCSI) and imperfect CSI (ICSI) at the transmitter side, where simulation results show robust performance when compared to the optimum encoder
Complex Quadrature Spatial Modulation
In this paper, we propose a spatial modulation (SM) scheme referred to as
complex quadrature spatial modulation (CQSM). In contrast to quadrature spatial
modulation (QSM), CQSM transmits two complex signal constellation symbols on
the real and quadrature spatial dimensions at each channel use, increasing the
spectral efficiency. To this end, signal symbols transmitted at any given time
instant are drawn from two different modulation sets. The first modulation set
is any of the conventional QAM/PSK alphabets, while the second is a rotated
version of it. The optimal rotation angle is obtained through simulations for
several modulation schemes and analytically proven for the case of QPSK, where
both results coincide. Simulation results showed that CQSM outperformed QSM and
generalized SM (GSM) by approximately 5 and 4.5 dB, respectively, for the same
transmission rate. Its performance was similar to that of QSM; however, it
achieved higher transmission rates. It was additionally shown numerically and
analytically that CQSM outperformed QSM for a relatively large number of
transmit antennas.Comment: 11 pages, 3 tables, 11 figures. ETRI Journal, 201