An Efficient Signaling for Multi-mode Transmission in Multi-user MIMO

In this paper the downlink of a multi-user MIMO (MUMIMO) system with multi-mode transmission is considered. We propose a low-complexity algorithm for selecting users and the corresponding number of data streams to each user, denoted as user transmission mode (UTM). The selection is only based on the average received signal-to-noise ratio (SNR) from the base station (BS) for each user. This reduces the overall amount of feedback for scheduling, as opposed to techniques that assume perfect instantaneous channel state information (CSI) from all users. Analytical average throughput approximations are derived for each user at different UTMs. Simulation results demonstrate that the proposed algorithm provides performance close to dirty paper coding (DPC) with considerably reduced feedback

Gray coding for multilevel constellations in Gaussian noise

The problem of finding the optimal labeling (bit-to-symbol mapping) of multilevel coherent phase shift keying (PSK), pulse amplitude modulation (PAM), and quadrature amplitude modulation (QAM) constellations with respect to minimizing the bit-error probability (BEP) over a Gaussian channel is addressed. We show that using the binary reflected Gray code (BRGC) to label the signal constellation results in the lowest possible BEP for high enough signal energy-to-noise ratios and analyze what is "high enough"in this sense. It turns out that the BRGC is optimal for PSK and PAM systems whenever the target BEP is at most a few percent, which covers most systems of practical interest. New and simple closed-form expressions are presented for the BEP of PSK, PAM, and QAM using the BRGC. \ua9 2007 IEEE

Methods for Compression of Feedback in Adaptive Multicarrier 4G Schemes

In this paper, several algorithms for compressing the feedback of channel quality information are presented and analyzed. These algorithms are developed for a proposed adaptive modulation scheme for future multi-carrier 4G mobile systems. These strategies compress the feedback data and, used together with opportunistic scheduling, drastically reduce the feedback data rate. Thus the adaptive modulation schemes become more suitable and efficient to be implemented in future mobile systems, increasing data throughput and overall system performance.This work has been partly funded by the Spanish government with projects MACAWI (TEC 2005-07477-c02-02), MAMBO2 (CCG06-UC3M-TIC-0698), and European COST Action 289 and is a result of work done within this European actio

On the performance of turbo codes and convolutional codes of low rate

Recently two new classes of low-rate codes have been presented. The first class is the super-orthogonal turbo codes (SOTCs) and the second is the maximum free distance (MFD) convolutional codes. In this paper we present an evaluation of the performance vs. arithmetic decoding complexity for these codes and compare them with the previously reported super-orthogonal convolutional codes (SOCCs). For all classes of codes, the arithmetic decoding complexity is estimated, and the error performance on the additive white Gaussian noise channel is simulated. The SOCCs offer performance comparable to that of the MFD codes. However, the existence of good SOCCs is restricted to a small number of rates while the MFD codes give high performance for a multitude of rates. For the parameters used in this investigation the SOTCs yield higher performance at lower arithmetic decoding complexity than the MFD code

On the performance of turbo codes and convolutional codes of low rate

Recently two new classes of low-rate codes have been presented. The first class is the super-orthogonal turbo codes (SOTCs) and the second is the maximum free distance (MFD) convolutional codes. In this paper we present an evaluation of the performance vs. arithmetic decoding complexity for these codes and compare them with the previously reported super-orthogonal convolutional codes (SOCCs). For all classes of codes, the arithmetic decoding complexity is estimated, and the error performance on the additive white Gaussian noise channel is simulated. The SOCCs offer performance comparable to that of the MFD codes. However, the existence of good SOCCs is restricted to a small number of rates while the MFD codes give high performance for a multitude of rates. For the parameters used in this investigation the SOTCs yield higher performance at lower arithmetic decoding complexity than the MFD code

Att mäta korruption

I denna uppsats genomförs en statistisk analys där fyra socialpolitiska teoriers förklaringskraft vad gäller förekomsten av korruption testas. Det huvudsakliga materialet utgörs av data från Quality of Government, Transparency International samt teorier från vetenskapliga artiklar. Uppsatsen är begränsad till EU-27-länderna för vilka data har sammanställts och redovisats i grafer. Teorierna testas mot ett korruptionsindex (CPI) och därefter följer en analys av respektive teori. Uppsatsen påvisar att det finns starka samband mellan samtliga teorier och korruptionsindex. Avslutningsvis konstateras att inga nya empiriska slutsatser kan dras, men att de uppmärksammade teoriernas validitet har stärkts. En diskussion om metodologiska överväganden och tillägg inför vidare forskning förs i slutet av uppsatsen

Utilizing Cross-Layer Information to Improve Performance in JPEG2000 Decoding

We focus on wireless multimedia communication and investigate how cross-layer information can be used to improve performance at the application layer, using JPEG2000 as an example. The cross-layer information is in the form of soft information from the physical layer. The soft information, which is supplied by a soft decision demodulator, yields reliability measures for the received bits and is fed into two soft input iterative JPEG2000 image decoders. When errors are detected with the error detecting mechanisms in JPEG2000, the decoders utilize the soft information to point out likely transmission errors. Hence, the decoders can correct errors and increase the image quality without making time-consuming retransmissions. We believe that the proposed decoding method utilizing soft information is suitable for a general IP-based network and that it keeps the principles of a layered structure of the protocol stack intact. Further, experimental results with images transmitted over a simulated wireless channel show that a simple decoding algorithm that utilizes soft information can give high gains in image quality compared to the standard hard-decision decoding