3 research outputs found
Code diversity in multiple antenna wireless communication
The standard approach to the design of individual space-time codes is based
on optimizing diversity and coding gains. This geometric approach leads to
remarkable examples, such as perfect space-time block codes, for which the
complexity of Maximum Likelihood (ML) decoding is considerable. Code diversity
is an alternative and complementary approach where a small number of feedback
bits are used to select from a family of space-time codes. Different codes lead
to different induced channels at the receiver, where Channel State Information
(CSI) is used to instruct the transmitter how to choose the code. This method
of feedback provides gains associated with beamforming while minimizing the
number of feedback bits. It complements the standard approach to code design by
taking advantage of different (possibly equivalent) realizations of a
particular code design. Feedback can be combined with sub-optimal low
complexity decoding of the component codes to match ML decoding performance of
any individual code in the family. It can also be combined with ML decoding of
the component codes to improve performance beyond ML decoding performance of
any individual code. One method of implementing code diversity is the use of
feedback to adapt the phase of a transmitted signal as shown for 4 by 4
Quasi-Orthogonal Space-Time Block Code (QOSTBC) and multi-user detection using
the Alamouti code. Code diversity implemented by selecting from equivalent
variants is used to improve ML decoding performance of the Golden code. This
paper introduces a family of full rate circulant codes which can be linearly
decoded by fourier decomposition of circulant matrices within the code
diversity framework. A 3 by 3 circulant code is shown to outperform the
Alamouti code at the same transmission rate.Comment: 9 page
A Low Complexity Space-Time Block Codes Detection for Cell-Free Massive MIMO Systems
The new generation of telecommunication systems must provide acceptable data
rates and spectral efficiency for new applications. Recently massive MIMO has
been introduced as a key technique for the new generation of telecommunication
systems. Cell-free massive MIMO system is not segmented into cells. Each BS
antennas are distributed throughout the environment and each user is served by
all BSs, simultaneously.
In this paper, the performance of the multiuser cell-free massive MIMO-system
exploying space-time block codes in the uplink, and with linear decoders is
studied. An Inverse matrix approximation using Neumann series is proposed to
reduce the computational and hardware complexity of the decoding in the
receiver.
For this purpose, each user has two antennas, and also for improving the
diversity gain performance, space-time block codes are used in the uplink.
Then, Neumann series is used to approximate the inverse matrix in ZF and MMSE
decoders, and its performance is evaluated in terms of BER and spectral
efficiency.
In addition, we derive lower bound for throughput of ZF decoder.
The simulation results show that performance of the system , in terms of BER
and spectral efficiency, is better than the single-antenna users at the same
system. Also, the BER performance in a given system with the proposed method
will be close to the exact method.Comment: 5 pages, 4 figures, Accepted for ICEE202
Full-Rate, Full-Diversity, Finite Feedback Space-Time Schemes with Minimum Feedback and Transmission Duration
In this paper a MIMO quasi static block fading channel with finite N-ary
delay-free, noise-free feedback is considered. The transmitter uses a set of N
Space-Time Block Codes (STBCs), one corresponding to each of the N possible
feedback values, to encode and transmit information. The feedback function used
at the receiver and the N component STBCs used at the transmitter together
constitute a Finite Feedback Scheme (FFS). Although a number of FFSs are
available in the literature that provably achieve full-diversity, there is no
known universal criterion to determine whether a given arbitrary FFS achieves
full-diversity or not. Further, all known full-diversity FFSs for T<N_t where
N_t is the number of transmit antennas, have rate at the most 1. In this paper
a universal necessary condition for any FFS to achieve full-diversity is given,
using which the notion of Feedback-Transmission duration optimal (FT-Optimal)
FFSs - schemes that use minimum amount of feedback N given the transmission
duration T, and minimum transmission duration given the amount of feedback to
achieve full-diversity - is introduced. When there is no feedback (N=1) an
FT-optimal scheme consists of a single STBC with T=N_t, and the universal
necessary condition reduces to the well known necessary and sufficient
condition for an STBC to achieve full-diversity: every non-zero codeword
difference matrix of the STBC must be of rank N_t. Also, a sufficient condition
for full-diversity is given for the FFSs in which the component STBC with the
largest minimum Euclidean distance is chosen. Using this sufficient condition
full-rate (rate N_t) full-diversity FT-Optimal schemes are constructed for all
(N_t,T,N) with NT=N_t. These are the first full-rate full-diversity FFSs
reported in the literature for T<N_t. Simulation results show that the new
schemes have the best error performance among all known FFSs.Comment: 12 pages, 5 figures, 1 tabl