Small world wireless mesh networks

In this paper, the performance of a wireless mesh network (WMN) is improved by introducing a number of long links at strategic locations, based on the small world network concept, to shorten transmission delay. A Genetic Algorithm (GA) is used to determine the minimum number of long links and their locations such that the maximum number of hops of a given WMN with n nodes is minimized. In the optimization process, practical implementation aspects are considered. These include the radio interference likely to be introduced by the long links, and the possibility of traffic congestion at these links. It is envisaged that a long link will be equipped with a higher power transmitter and directional antenna

Adaptive array beam forming using a combined RLS-LMS algorithm

A new adaptive algorithm, called RLMS, which combines the use of recursive least square (RLS) and least mean square (LMS), is proposed for array beam forming. The convergence of the RLMS algorithm is analyzed, in terms of mean square error, in the presence of additive white Gaussian noise. Computer simulation results show that the convergence performance of RLMS is superior to either RLS or LMS operating on its own. Furthermore, the convergence of RLMS is quite insensitive to changes in either signal-to-noise ratio, or the initial value of the input correlation matrix for the RLS section, or the step size adopted for the LMS section

FPGA implementation of wideband IQ imbalance correction in OFDM receivers

This paper describes the implementation of a digital compensation scheme, called CSAD, for correcting the effects of wideband gain and phase imbalances in dual-branch OFDM receivers. The proposed scheme is implemented on a Xilinx Virtex-4 field programmable gate array (FPGA). The flexible architecture of the implementation makes it readily adaptable for different broadband applications, such as DVB-T/H, WLAN, and WiMAX. The proposed correction scheme is resilient against multipath fading and frequency offset. When applied to DVB-T, it is shown that an 11-bit arithmetic precision is sufficient to achieve the required BER of 2x10-4 at an SNR of 16.5 dB. Using this bit-precision, the implementation consumes 1686 Virtex-4 slices equivalent to about 42600 gates

Performance of RLMS algorithm in adaptive array beam forming

This paper examines the performance of an adaptive linear array employing the new RLMS algorithm, which consists of a recursive least square (RLS) section followed by a least mean square (LMS) section. The performance measures used are output and input signal-to-interference plus noise ratios (SINR), side lobe level (SLL), and SINRo as a function of the direction of arrival of the interfering signal. Computer simulation results show that the performance of RLMS is superior to either the RLS or LMS based on these measures, particularly when operating with low input SINR

A New LLMS Algorithm for Antenna Array Beamforming

A new adaptive algorithm, called LLMS, which employs an array image factor, AI, sandwiched in between two Least Mean Square (LMS) sections, is proposed for different applications of array beamforming. The convergence of LLMS algorithm is analyzed, in terms of mean square error, in the presence of Additive White Gaussian Noise (AWGN) for two different modes of operation; namely with either an external reference or self-referencing. Unlike earlier LMS based schemes, which make use of step size adaptation to enhance their performance, the proposed algorithm derives its overall error signal by feeding back the error signal from the second LMS stage to combine with that of the first LMS section.This results in LLMS being less sensitive to variations in input signal-to-noise ratio as well as the step sizes used. Computer simulation results show that the proposed LLMS algorithm is superior in convergence performance over the conventional LMS algorithm as well some of the more recent LMS based algorithms, such as constrained-stability LMS (CSLMS), and Modified Robust Variable Step Size LMS (MRVSS) algorithms. Also, the operation of LLMS remains stable even when its reference signal is corrupted by AWGN. It is also shown that LLMS performs well in the presence of Rayleigh fading

Analysis of the RLMS Adaptive Beamforming Algorithm Implemented with Finite Precision

This paper studies the influence of the use of finite wordlength on the operation of the RLMS adaptive beamformingalgorithm. The convergence behavior of RLMS, based on the minimum mean square error (MSE), is analyzed for operation with finite precision. Computer simulation results verify that a wordlength of nine bits is sufficient for the RLMS algorithm to achieve performance close to that provided by full precision. The performance measures used include residual MSE, rate of convergence, error vector magnitude (EVM), and beam pattern. Based on all these measures, it is shown that the RLMS algorithm outperforms other earlier algorithms, such as least mean square (LMS), recursive least square (RLS), modified robust variable step size (MRVSS) and constrained stability LMS (CSLMS)