Man-Wai Kwan

Channel noise robust power optimized precoder for ISI channel with minimal complexity equalizer

A systematic method to design power optimized FIR precoder for a special class of ISI free noise robust precoder-equalizer structure is presented in this paper. The proposed equalizer has the lowest implementation complexity in theory, because the equalizer consists of a simple sampler only. It is also because of this simple equalizer, the proposed precoder-equalizer pair is robust to channel noise. The presented design method results in minimal power precoder with a given order such that the system achieve ISI free MMSE communication in ISI AWGN channel with a given SNR. Simulation results are presented to illustrate the performance of the proposed precoder-equalizer structure and compared it with that of the general linear precoder structure.

FIR zero-forcing equalizer for ISI MIMO channels using space-time modulated codes

Abstract-A systematic method for designing a finite-impulse response (FIR) zero-forcing equalizer (ZFE) of the space-time modulated code (STMC) system based on nonmaximally decimated filterbank is proposed. The physical channel considered is assumed to be multiple-input-multiple-output (MIMO) with intersymbol interference (ISI) and space-time correlated noise. STMC is a space-time block code (STBC) system. Most of the STMC systems require a long guard period to avoid interblock interference (IBI), but, with the proposed equalizer, the length of the guard period is greatly reduced. This can enhance the spectral efficiency of the STMC especially when the channel dispersion is large. The existence conditions for FIR ZFE of the STMC system were derived. These include the maximal code rate STMC for a given channel and the minimal filter order of the FIR ZFE. For a given STMC precoder, the equalizability of the system was verified. The solution of FIR ZFE of STMC was parameterized, which allows the design of optimal FIR ZFE through unconstrained optimization. It is further shown that FIR ZFE could be improved by adding a simple permutation in the system. Design examples and simulation results were presented to evaluate the proposed design method.

Minimal transmit redundancy FIR zero-forcing equalizer for space-time correlated noise ISI MIMO channel with space-time modulated code

A systematic method for designing FIR zero-forcing equalizer (ZFE) of space-time modulated coded (STMC) system based on non-maximally decimated filterbank is proposed. The physical channel considered is assumed to be MIMO with intersymbol interference (ISI) and span-time correlated noise. STMC is a space-time block code (STBC). Most of the STBC system required a Iong guard period to avoid inter-block interference but, with our designed equalizer, the guard period is not always necessary This can greatly enhance the spectral efficient of STMC especially when the channel dispersion is large. In our derivation, we first proposed some existence condition for the FIR ZFE of STMC. These include the maximal code rate STMC for given channel and the minimal required filter order. A verification method for the equalizability of given STMC precoder is also proposed. After that a parameterized solution of FIR ZFE of STMC is derived. Base on this parameterized result, the optimal FIR ZFE is obtained. By observing these results, we found that FIR ZFE can he further improved by adding a simple permutation in the system.

Iterative joint optimization of minimal transmit redundancy FIR zero-forcing precoder-equalizer system for MIMO-ISI channel

An iterative joint finite-impulse response (FIR) zero-forcing (ZF) precoder-equalizer optimization algorithm for multiple-input multiple-output intersymbol interference (MIMO-ISI) channel is proposed. The existing joint precoder-equalizer design algorithms for MIMO-ISI channels require a guard period, which is longer than or equal to the channel order to avoid the interblock interference (IBI). This longer guard period is a kind of unnecessary redundancy consuming the valuable channel bandwidth. Based on space-time-modulated codes (STMC), this paper proposes the first algorithm for jointly optimizing the FIR precoder and equalizer without the guard-period constraint. Hence, the precoder-equalizer pairs obtained can achieve minimal transmit redundancy ISI-free communications for complex-valued signals. This greatly enhances the spectral efficiency for wide-band communications. The proposed algorithm is performed in an iterative basis. Sufficient conditions and convergence analysis of this algorithm are presented. The resultant precoder and equalizer are proved to be a least-square (LS) optimal solution for each other. The simulation results show that substantial performance gain is obtained with the proposed joint optimization algorithm.

MMSE Equalizer for MIMO-ISI Channel With Shorten Guard Period

A finite-impulse-response minimum mean-square error equalizer (FIR-MMSEE) for block-based transmission over a multiple-input multiple-output (MIMO) intersymbol interference (ISI) channels is proposed in this correspondence. The proposed MMSE equalizer can avoid interblock interference (IBI) without requiring a guard period to be larger than or equal to the channel order. By reducing the number of redundant symbols in the transmitted signals, the spectral efficiency of the communication system with long channel dispersion can be greatly improved. We further investigated the parallel FIR-MMSEE equalization structure and proposed a group successive interference cancellation MMSE equalizer (GSIC-MMSEE). A group of elements in the output of the FIR-MMSEE will be used to successively cancel their own effect in the received signals after the signal detection in GSIC-MMSEE. Since the cancellation process eliminates some interference sources, the error performance of the subsequent equalization will be improved. Moreover, the interference cancellation is performed in a group-by-group basis. As a result, the computational complexity of the proposed equalizer can be controlled by adjusting the number of groups in the GSIC. Simulation results are presented to compare the performance of the proposed FIR-MMSEE and GSIC-MMSEE

Correlation-based adaptive filters for channel identification

A correlation-based recursive least-squares (CRLS) adaptive filter design is proposed. This algorithm is applied to the channel identification problem by minimizing the difference between the correlation functions of the received signal and of the designed filter output in the LS sense. The CRLS algorithm is shown to be much more robust to strong and instantaneous channel disturbance than the traditional RLS algorithm, especially when the disturbance is correlated with the input source signal. This is a common situation when echo cancellation is considered in communication systems with double-talk. The results of simulations to compare the channel identification performance of the CRLS and the traditional RLS algorithm for echo cancellation with double-talk are presented; they show the high robustness of the proposed CRLS algorithm.

Second-Order Statistics Based Minimal Transmit Redundancy Space-Time FIR Precoder-Blind Equalizer

A second-order statistics based minimal transmit redun- dancy space-time FIR precoder-blind equalizer is proposed. For most of the block based transmission system, like OFDM, a long guard period, which is longer than or equal to the channel order, is required to avoid inter-block interference. This guard period is a type of redundancy which consumes valuable bandwidth. With the precoder-equalizer structure, the blind equalizer that we have proposed can blindly equalize the received signal without the long guard period requirement. The simulation results show that the BER performance of the proposed blind equalizer is close to that of the least-squares optimal zero-forcing equalizer with channel state information. Moreover, the simulation results also show that good BER performance can be obtained by using a small amount of received data. The robustness of the algorithm towards channel order overestimation and different system delays were also illustrated in the simulation results.

Channel noise robust transmit power optimized linear precoder for ISI channel with minimal complexity equalizer

A special class of linear precoder-equalizer pair with equalizers formed by simple tapped delay lines is proposed. With this special equalizer structure, the equalizer of this system not only can enjoy the minimal implementation complexity, but also can avoid the noise amplification effect. Moreover, using nonmaximally decimated filterbank structure, this precoder-equalizer pair is proven to be able to guarantee intersymbol interference (ISI)-free communication by zero-forcing approach, even if spectral nulling exists in the physical channel. Another advantage of this system is that the length of the guard period introduced by the precoder can be any positive integer values, thus the guard period can be designed to maximize the spectral efficiency by selecting it to be as short as one symbol per block of transmitted signal. A systematic method for designing a minimal transmit power finite-impulse response (FIR) precoder under the proposed precoder-equalizer pair structure is presented. Under the ISI channel with independent additive white Gaussian noise, the design of this minimal transmit power FIR precoder is shown to be a minimum mean square error precoder design. Simulation results are presented to illustrate the performance of the proposed precoder-equalizer structure and that of the transmit power minimized precoder.

MMSE equalizer for MIMO-ISI channel with shortened guard period

An FIR MMSE equalizer (FIR-MMSEE) for block based transmission under the MIMO ISI channel is proposed in this paper. The proposed MMSE equalizer can get rid of the IBI problem without requiring a guard period which is not less than the channel order. By shortening the guard period, the bandwidth efficiency can be improved effectively especially for the channel with large dispersion. In addition, we further improve the BER performance of the FIR-MMSEE by propose a group successive interference cancellation MMSE equalizer (GSIC-MMSEE). In GSIC-MMSEE, a group of equalized outputs of the FIR-MMSEE is used to successively cancels their own effect in the received signals. This improves the error performance of the subsequent equalization. Moreover, because the interference cancellation is performed in group-by-group basis, the computation complexity can be controlled by adjusting the number of groups used. The performance of the FIR-MMSEE and GSIC-MMSEE was compared in the simulations.

Colored channel noise robust power optimized precoder for ISI channel with minimal complexity equalizer

A systematic method to design a power optimized FIR precoder for a special class of ISI free noise robust precoder-equalizer structure is presented in this paper. The proposed equalizer has the lowest implementation complexity in theory, because the equalizer consists of a simple sampler only. It is also because of this simple equalizer, the proposed precoder-equalizer pair is robust to channel noise. The presented design method results in a minimal power precoder with a given order such that the system achieve ISI free MMSE communication in ISI additive color noise channel with a given SNR. Simulation results are presented to illustrate the performance of the proposed precoder-equalizer structure and compared it with that of the general linear precoder structure.