156 research outputs found
Cross-layer link adaptation for goodput optimization in MIMO BIC-OFDM systems
This work proposes a novel cross-layer link performance prediction (LPP) model and link adaptation (LA) strategy for soft-decoded multiple-input multiple-output (MIMO) bit-interleaved coded orthogonal frequency division multiplexing (BIC-OFDM) systems employing hybrid automatic repeat request (HARQ) protocols. The derived LPP, exploiting the concept of effective signal-to-noise ratio mapping (ESM) to model system performance over frequency-selective channels, does not only account for the actual channel state information at the transmitter and the adoption of practical modulation and coding schemes (MCSs), but also for the effect of the HARQ mechanism with bit-level combining at the receiver. Such method, named aggregated ESM, or αESM for short, exhibits an accurate performance prediction combined with a closed-form solution, enabling a flexible LA strategy, that selects at every protocol round the MCS maximizing the expected goodput (EGP), i.e., the number of correctly received bits per unit of time. The analytical expression of the EGP is derived capitalizing on the αESM and resorting to the renewal theory. Simulation results carried out in realistic wireless scenarios corroborate our theoretical claims and show the performance gain obtained by the proposed αESM-based LA strategy when compared with the best LA algorithms proposed so far for the same kind of systems
MIMO Systems
In recent years, it was realized that the MIMO communication systems seems to be inevitable in accelerated evolution of high data rates applications due to their potential to dramatically increase the spectral efficiency and simultaneously sending individual information to the corresponding users in wireless systems. This book, intends to provide highlights of the current research topics in the field of MIMO system, to offer a snapshot of the recent advances and major issues faced today by the researchers in the MIMO related areas. The book is written by specialists working in universities and research centers all over the world to cover the fundamental principles and main advanced topics on high data rates wireless communications systems over MIMO channels. Moreover, the book has the advantage of providing a collection of applications that are completely independent and self-contained; thus, the interested reader can choose any chapter and skip to another without losing continuity
Cooperative Transmission for Downlink Distributed Antenna in Time Division Duplex System
Multi-user distributed antenna system (MU-DAS) systems play the
essential role in improving throughput performance in wireless communications. This improvement can be achieved by exploiting the spatial
domain and without the need of additional power and bandwidth. In
this thesis, three main issues which are of importance to the data rate
transmission have been investigated.
Firstly, user clustering in MU-DAS downlink systems has been considered, where this technique can be effciently used to reduce the complexity and cost caused by radio frequency chains, associated with antennas while keeping most of the diversity advantages of the system.
The proposed user clustering algorithm which can select an optimal set
of antennas for transmission. The capacity achieved by the proposed
algorithm is almost same as the capacity of the optimum search method,
with much lower complexity.
Secondly, interference alignment in MU-DAS downlink systems has
been studied. The inter-cluster interference is uncoordinated and limits
the system performance. The inter-cluster interference should be eliminated or minimized carefully. The interference alignment is proposed to
consolidate the strong inter-cluster interference into smaller dimensions
of signal space at each user and use the remaining dimensions to transmit
the desired signals without any interference. The performance of single
cluster is better than the proposed algorithm due to the absence of intercluster interference in the single cluster. The numerical shows that the
proposed algorithm is more suitable in multi-cell DAS environment due
to the presence of inter-cell interference.
Finally, the impact of different user mobility on TDD downlink MUDAS has been studied. The downlink data transmission in time division
duplex (TDD) systems is optimized according to the channel state information (CSI) which is obtained at the uplink time slot. However, the
actual channel at downlink time slot may be different from the estimated
channel due to channel variation in mobility environment. Based on mobility state information (MSI), an autocorrelation based feedback interval
adjustment technique is proposed. The proposed technique adjusts the
CSI update interval and mitigates the performance degradation imposed
by the user mobility and the transmission delay. Cooperative clusters are
formed to maximize sum rate. In order to reduce the computational complexity, a channel gain based antenna selection and signal-to-interference
plus noise ratio (SINR) based user clustering are developed. A downlink
ergodic capacity is derived in single user clustering. The derived analytical expressions of the downlink ergodic capacity are verified by system
simulations. Numerical results show that the proposed scheme can improved sum rate over the non cooperative system and no MSI knowledge.
The proposed technique has good performance for a wide range of user
speed and suitable for future wireless communications systems
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