Performance Analysis of an OFDM PHY Scheme with Zero Forcing Equalizer Using Software Defined Radio Platform and USRP

This study investigates the performance of a mobile communication system using a Correlated Double Ring (CDR) channel model, where both the transmitter and receiver are surrounded by scatterers and exhibit mobility, leading to time-varying channel conditions and Doppler effects. These effects introduce Inter-Carrier Interference (ICI) and Inter-Symbol Interference (ISI), which degrade signal integrity. To mitigate these impairments, Orthogonal Frequency Division Multiplexing (OFDM) combined with Zero Forcing (ZF) equalization is employed at the receiver. System performance is evaluated using Binary Phase Shift Keying (BPSK) modulation, with Bit Error Rate (BER) as the performance metric. At an AB/No of 10 dB, ZF equalization consistently reduces BER across various speeds: at 5 m/s from 0.1042 to 0.0545 (47.75% improvement), at 25 m/s from 0.1057 to 0.0548 (48.11%), and at 55 m/s from 0.1084 to 0.0544 (48.79%). These findings demonstrate the effectiveness of ZF equalization in mitigating Doppler-Induced degradation in high-mobility wireless channels.

We examine through numerical simulations the performance of three equalizers for CDMA downlink in which the channel is frequency-selective: the traditional RAKE receiver, and chip-spaced MMSE (minimum mean square error) and ZF (zero-forcing) equalizers. These simulation results provide an upper-bound on average BER performance for users near a single transmitting base-station, in which the channel is assumed static and known. We present results for two channel models: a random 4-path multipath channel with delay spread of 10 micro seconds, and an empirically derived random multipath channel generated by the commercial software package SMRCIM. We compare the cases of diversity obtained by two spatially separated antennas to two virtual channels obtained through oversampling a single antenna's received signal. This simulation study has yielded the expected result that spatial diversity is preferable to diversity obtained via oversampling. Furthermore, the MMSE always out-performs both RAKE and ZF equalizers.

Blind ZF equalization with controlled delay robust to order over estimation

Wireless network is one of the most important things in the development of telecommunication. However, the existing wireless technology has not been able to efficiently create a very high data rate because it was very sensitive to fading. Therefore, Orthogonal Frequency Division Multiplexing (OFDM) technology combined with MIMO (Multiple Input Multiple Output) transceiver system was used to gain more diversity and bandwidth efficiency. The propagation performed on the OFDM MIMO system was multipath propagation. To reduce Intersymbol Interference (ISI) was used Zero Forcing (ZF) equalizer which works by combining channel response and equalizer response itself to eliminate ISI. This study aims to determine the effect of Zero Forcing Equalizer on OFDM MIMO system using rayleigh fading channel and compared the result with OFDM MIMO STBC system. The research method used was simulation using MatLab R2015a. The simulation results showed that the performance of OFDM MIMO ZF system was worse than OFDM MIMO STBC system i.e BER vs EbNo simulation, eye diagram simulation, and constellation diagram simulation. The OFDM MIMO ZF system was required an Eb / No value more than 25 dB to achieve BER 10-4 while the OFDM MIMO STBC system only required an Eb / No value of 10.5 dB to achieve BER 10-4. The eye pattern generated by the OFDM MIMO ZF system was more closed and the dispersion of constellation signals away from the ideal point while OFDM MIMO STBC system displayed a more open eye pattern and the dispersion of its constellation signal closer to the ideal point. It indicated more ISI occurs in the OFDM MIMO ZF system than that in OFDM MIMO STBC system.

In telecommunication, Intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible. In this paper, we design a zero forcing equalizer, which is a type of linear equalizer used to mitigate the effects of ISI (Intersymbol Interference). The zero forcing equalizer does this by finding the inverse of the impulse response of the channel. The ISI can be studied using eye diagram, which overlays many samples of a signal and can give a graphical representation of the signal characteristics. In this paper the results have been shown with proper eye diagrams. In this paper we also investigate the bit error rate, which is used to estimate the performance characteristics of the zero forcing equalizer.

This work focuses on studying signal detection using three different equalization techniques, namely: Zero Forcing (ZF), Minimum Mean Square Error (MMSE) and Beam Forming (BF), for a 4×4 MIMO-system. Results show that ZF equalization is the simplest technique for signal detection, However, Beam Forming (BF) gives better Bit Error Rate (BER) performances at high Signal to Noise Ratio (SNR) values with some complexity in design. For more antennas at the base station, it is too complex to design the weight matrix for ZF, however, it is suitable for BF with the help of good quality digital signal processors. Performance of MIMO-system, with 8 antennas at the base station using BF equalization, is analysed to get BER values at different SNR. Results show a considerable improvement in BER for 8 antennas at the base station.

In code division multiple access (CDMA) systems transmitting over time-varying multipath channels, both intersymbol interference (ISI) and multiple access interference (MAI) arise. The conventional suboptimum receiver consisting of a bank of matched filters is often inefficient because interference is treated as noise. The optimum multi-user detector is too complex to be implemented at present. Four suboptimum detection techniques based on zero forcing (ZF) and minimum mean square error (MMSE) equalization with and without decision feedback (DF) are presented and compared. They combat both ISI and MAI. The computational complexity of all four equalizers is essentially the same and they are independent of the size of the data symbol alphabet. It is shown that all four equalizers considerably outperform the conventional receiver. The MMSE equalizers are superior to the corresponding ZF equalizers. Furthermore, the equalizers with DF perform better than the corresponding equalizers without DF. An algorithm termed channel sorting is introduced to reduce the impairing effect of error propagation on the equalizers with DF. >

Precoding for multiple-input multiple-output (MIMO) spatial multiplexing generally requires high feedback overhead and/or high-complexity processing. Simultaneous reduction in transmitter complexity and feedback overhead is proposed by imposing a diagonal structural constraint to precoding, i.e., power allocation. Minimum bit-error rate (MBER) is employed as the optimization criterion, and an approximate MBER (AMBER) power-allocation algorithm is proposed for a variety of receivers, including zero-forcing (ZF), successive interference cancellation (SIC), and ordered SIC (OSIC). While previously proposed precoding schemes either require ZF equalization for MBER, or use a minimum mean-squared error (MMSE) criterion, we provide a unified MBER solution to power allocation for ZF, SIC, and OSIC receiver structures. Improved error-rate performance is shown both analytically and by simulation. Simulation results also indicate that SIC and OSIC with AMBER power allocation offer superior performance over previously proposed MBER precoding with ZF equalization, as well as over MMSE precoding/decoding. Performance under noisy channels and power feedback is analyzed. A modified AMBER algorithm that mitigates error propagation in interference cancellation is developed. Compared with existing precoding methods, the proposed schemes significantly reduce both transmit processing complexity and feedback overhead, and improve error-rate performance

Multicarrier acoustic communication has enabled wireless underwater transmission at higher data rates. Several multicarrier modulation systems have been explored in the past for data transmission. Orthogonal frequency division multiplexing (OFDM) fights-off inter-symbol-interference due to orthogonality of the carriers. However, it is susceptible to time variations which introduces inter-carrier-interference. Being double selective, the underwater acoustic (UWA) channel is both time and frequency variant. Time variations and multipath fading makes it a complex channel to estimate. In this paper, we explore linear frequency domain equalization techniques available for radio OFDM systems and compare their performance for a shallow underwater acoustic channel. The underwater channel model used is based on Rician shadowed distribution with Doppler shifts. We compare the performance of a linear equalizer with pilot estimated channel against a zero-forcing equalizer where the channel is assumed to be known. Results collected through Monte Carlo simulations show that for a 128-subcarrier OFDM system and a transmitter-receiver separation of 800 m, a gain of almost 7dB is obtained at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> when a zero-forcing equalizer is used. Moreover, when the subcarriers are increased to 256, this gain almost doubles. In conclusion, the zero-forcing equalizer outperforms the LS equalizer for an underwater acoustic channel.

In this paper a 3D-deterministic channel model for UWB chipless RFID system is presented. The tag in this work will be modeled as a 3D object, with frequency dependent Radar Cross Section (RCS), embedded in the channel which has several incident and reflected multipath at various directions both from the reader-tag and the reader-reader environment effect. In this model all channel effects as multipath components, fading, frequency dependence, reflections, diffractions and polarization dependence will be considered. Moreover, a novel chipless RFID reader system model with Zero Forcing (ZF) based equalizer is proposed. The equalizer based system will increase the chipless tag identification distance by mitigating the aforementioned channel effect. The concept is tested using a deterministic channel from a ray-tracing model with a 8-bit frequency coded concept of a compact printable orientation independent chipless RFID tag. Furthermore, a 3D-Electromagnetic (EM) simulation tool is used to compute the Frequency Coding Response (FCR) and the RCS of the CFC-RFID tag. Simulation results show constructive guidelines for designing multi-tag UWB RFID communications and enhancing the channel estimation process of the chipless RFID tag systems.

In orthogonal frequency-division multiplexing (OFDM) systems, it is generally assumed that the channel response is static in an OFDM symbol period. However, the assumption does not hold in high-mobility environments. As a result, intercarrier interference (ICI) is induced and the system performance is degraded. A simple remedy for this problem is the application of the zero-forcing (ZF) and minimum mean square error (MMSE) equalizers. Unfortunately, the direct ZF method requires the inversion of an NxN ICI matrix, where N is the number of subcarriers. When N is large, the computational complexity can become prohibitively high. As for the direct MMSE method, in addition to an NxN matrix inverse, it requires an extra NxN matrix multiplication, making the required computational complexity higher compared to the direct ZF method. In this dissertation, we first propose a low-complexity ZF method to solve the problem in single-input-single-output (SISO) OFDM systems. The main idea is to explore the special structure inherent in the ICI matrix and to apply Newton's iteration for matrix inversion. With our formulation, fast Fourier transforms (FFTs) can be used in the iterative process, reducing the complexity from O(N^3) to O(Nlog_2 N) . Also, the required number of the iteration is typically one or two. We also analyze the convergence behavior of the proposed method and derive the theoretical output signal-to-interference-noise-ratio (SINR). For the MMSE method, we first reformulate the MMSE solution in a way that the extra matrix multiplication can be avoided. Similar to the ZF method, we then exploit the structure of the ICI matrix and apply Newton's iteration to reduce the complexity of the matrix inversion. For a multiple-input-multiple-output (MIMO) OFDM system, the required complexity of the ZF and MMSE methods becomes more intractable. We then manage to extend the proposed ZF and MMSE methods for SISO-OFDM systems to MIMO-OFDM systems. It turns out that the computational complexity can be reduced even more significantly. Simulation results show that the performance of the proposed methods is almost as good as that of the direct ZF and MMSE methods, while the required computational complexity is reduced dramatically. Finally, we explore the application of the proposed methods in mobility-induced ICI mitigation for OFDM multiple access (OFDMA) systems, and in carrier frequency offset (CFO) induced ICI mitigation for OFDMA uplink systems. As that in OFDM systems, the proposed methods can reduce the required computational complexity, effectively.

Publication in the conference proceedings of EUSIPCO, Viena, Austria, 2004

Rapidly growing demand for high data rates in wireless communication systems is the cause of the merging of Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques. MIMO-OFDM technique needs Radio Frequency (RF) front end in each antenna, which is not effective for large dimensional antenna size. Therefore, RF front end on the receiver side will be simplified using a single RF technique based on the Electrically Steerable Parasitic Array Radiator (ESPAR) antenna. In real life, a channel cannot be ideal. Therefore, before the signal is transmitted, that signal must be coded to minimized errors when the data transmission process. Convolutional code is a coding technique that can detect and correct error bit (error control coding) and that it is expected to reduce the quantity of Bit Error Rate (BER). In this research, a simulation is designed to analyze single RF performance on the MIMO-OFDM system using Vertical Bell Laboratories Space-Time (VBLAST) detection for convolutional code encoder and Viterbi decoder. The result simulation shows that the channel estimation technique works well on the MIMO-OFDM system using single RF, which is shown in the magnitude and phase curves against the subcarrier index between the theory channel and the estimated channel are at almost the same points. VBLAST-ZF detector performance is shown in the BER curve against SNR, where the difference BER value for SNR value 10 dB between the theory channel and the estimated channel is 0.001499. Channel coding technique using convolutional code encoder and Viterbi decoder with a rate of ½ works well on the MIMO-OFDM system using single RF which is shown in the BER curve against SNR, where BER value with coding technique is smaller than BER value without coding technique.

Analysis of Underwater Acoustic Communication System Using Equalization Technique for ISI Reduction

&lt;p&gt;In any communication system transmitter and receiver are used to transmit the signal via wired or wireless channel. In the transmitter, modulation is one of the processes to transmit the signal efficiently. Likewise, receiver contains demodulation to recover the original signal from the transmitter. In general, the communication system uses one modulation/demodulation process at a time. It cannot use different modulation/demodulation within a single system. To overcome this problem reconfiguration technique is implemented. It is the method using different modulation scheme at the same time. It will increase the efficiency of the communication system. QPSK and BPSK modulation technique is used to transmit and receive the signal.&lt;/p&gt;