11,201 research outputs found
Subband decomposition techniques for adaptive channel equalisation
In this contribution, the convergence behaviour of the adaptive linear equaliser based on subband decomposition technique is investigated. Two different subband-based linear equalisers are employed, with the aim of improving the equaliser's convergence performance. Simulation results over three channel models having different spectral characteristic are presented. Computer simulations indicate that subband-based equalisers outperform the conventional fullband linear equaliser when channel exhibit severe spectral dynamic. Convergence rate of subband equalisers are governed by the slowest subband, whereby different convergence behaviour in each individual subband is observed. Finally, the complexity of fullband and subband equalisers is discussed
Implementation of the Trigonometric LMS Algorithm using Original Cordic Rotation
The LMS algorithm is one of the most successful adaptive filtering
algorithms. It uses the instantaneous value of the square of the error signal
as an estimate of the mean-square error (MSE). The LMS algorithm changes
(adapts) the filter tap weights so that the error signal is minimized in the
mean square sense. In Trigonometric LMS (TLMS) and Hyperbolic LMS (HLMS), two
new versions of LMS algorithms, same formulations are performed as in the LMS
algorithm with the exception that filter tap weights are now expressed using
trigonometric and hyperbolic formulations, in cases for TLMS and HLMS
respectively. Hence appears the CORDIC algorithm as it can efficiently perform
trigonometric, hyperbolic, linear and logarithmic functions. While
hardware-efficient algorithms often exist, the dominance of the software
systems has kept those algorithms out of the spotlight. Among these hardware-
efficient algorithms, CORDIC is an iterative solution for trigonometric and
other transcendental functions. Former researches worked on CORDIC algorithm to
observe the convergence behavior of Trigonometric LMS (TLMS) algorithm and
obtained a satisfactory result in the context of convergence performance of
TLMS algorithm. But revious researches directly used the CORDIC block output in
their simulation ignoring the internal step-by-step rotations of the CORDIC
processor. This gives rise to a need for verification of the convergence
performance of the TLMS algorithm to investigate if it actually performs
satisfactorily if implemented with step-by-step CORDIC rotation. This research
work has done this job. It focuses on the internal operations of the CORDIC
hardware, implements the Trigonometric LMS (TLMS) and Hyperbolic LMS (HLMS)
algorithms using actual CORDIC rotations. The obtained simulation results are
highly satisfactory and also it shows that convergence behavior of HLMS is much
better than TLMS.Comment: 12 pages, 5 figures, 1 table. Published in IJCNC;
http://airccse.org/journal/cnc/0710ijcnc08.pdf,
http://airccse.org/journal/ijc2010.htm
A Digital Predistortion Scheme Exploiting Degrees-of-Freedom for Massive MIMO Systems
The primary source of nonlinear distortion in wireless transmitters is the
power amplifier (PA). Conventional digital predistortion (DPD) schemes use
high-order polynomials to accurately approximate and compensate for the
nonlinearity of the PA. This is not practical for scaling to tens or hundreds
of PAs in massive multiple-input multiple-output (MIMO) systems. There is more
than one candidate precoding matrix in a massive MIMO system because of the
excess degrees-of-freedom (DoFs), and each precoding matrix requires a
different DPD polynomial order to compensate for the PA nonlinearity. This
paper proposes a low-order DPD method achieved by exploiting massive DoFs of
next-generation front ends. We propose a novel indirect learning structure
which adapts the channel and PA distortion iteratively by cascading adaptive
zero forcing precoding and DPD. Our solution uses a 3rd order polynomial to
achieve the same performance as the conventional DPD using an 11th order
polynomial for a 100x10 massive MIMO configuration. Experimental results show a
70% reduction in computational complexity, enabling ultra-low latency
communications.Comment: IEEE International Conference on Communications 201
- …