Academic literature on the topic 'Zero Forcing (ZF)'

University of Technology Sydney. Faculty of Engineering and Information Technology.<br>An ever-increasing data rate demand, mainly due to the proliferation of numerous smart devices, enterprises’ mission critical networks, and industry automation, has mounted tremendous pressure on today’s Wireless Local Area Networks (WLANs). Several avenues such as bandwidth, constellation density, the Multiple Input Multiple Output (MIMO) technique, etc., have been explored, e.g., IEEE802.11n/ac standards, to keep up with the demand. Future WLAN standard, e.g., IEEE802.11ax, with potential technologies such as uplink Multi-User (MU)-MIMO, full duplex transmission, etc., is anticipated by 2019. Having said that, there has been a strong emphasis on solving the technical issues with WLANs along with the addition of new frontiers in order to cope with the data rate demanded. One such appending decade-long issue is the inevitable Hidden Terminal (HT) problem in a distributive, decentralised and densely deployed WLANs, which fundamentally arises because of the transmission time overlaps between different transmitters operating at a particular frequency. The consequence is that it causes collisions of signals, which sharply reduces the system throughput. In the context of MU-MIMO based WLANs, several designs for a general network scenario, without the consideration of the HT problem, have been proposed, bringing efficiency by avoiding the collision of signals. However, a dedicated design, which could effectively address the HT problem in MU-MIMO WLANs and also become interoperable (with legacy standards) and feasible with existing hardware, is lacking to the best of our knowledge. In this thesis, we propose a solution for the HT problem which has three fundamental attributes. First, a) at the Physical (PHY) layer, the Zero-forcing (ZF) transmission strategy with fairness and throughput aware precoding is proposed, b) a hybrid scheduling scheme, combining the packet position-based First In First Out (FIFO) and channel quality-based scheme, namely the Best of the Two Choices, is designed, c) at the Medium Access Control (MAC) layer, Degrees-of-Freedom (DoF) based Transmission Opportunity (TXOP) for Access Points (APs) is developed which is backed by an extended Point Coordination Function (PCF), d) an explicit channel acquisition framework is proposed for ZF which has a reduced signaling time overhead of 98.6740 μs compared to IEEE802.11ac. e) performance evaluation methodologies are: i) hardware testbed results of the PHY strategy, which shows a received SNR gain of about 6 dB on average, and about 10 dB in comparison to the HT scenario, ii) simulation results of the MAC design, which shows a constant throughput gain of 4 − 5 times w.r.t. the popular Request to Send/Clear to Send (RTS/CTS) solution. Second, to address the interoperability issue, we purposefully use the standard frame format except for some required logical changes. Notably, the transition mechanism of our design, and for any MAC that uses standard frame formats, is investigated meticulously. The transition condition, transition steps and transition frame formats are detailed. Third, to address a practical constraint of an imperfect Channel State Information (CSI) at APs, a) we incorporate the Finite Rate Feedback (FRF) model in our solution. The effects on system parameters such as quantisation error bounds, throughput loss w.r.t. perfect CSI, etc., are discussed with closed-form analytical expressions, b) instead of an ideal ZF technique, a Relaxed ZF (RZF) framework is considered, in which the interference and power constraints of the optimisation problem are relaxed to the interference upper bound and to the maximum transmit power respectively. Our results lead to a distributive algorithm for calculating the optimal ZF precoding vector which suits the distributive, decentralised and uncoordinated nature of MU-MIMO WLANs.

Single Carrier Frequency Division Multiple Access (SC-FDMA) is a multiple access transmission scheme that has been adopted in the 4th generation 3GPP Long Term Evolution (LTE) of cellular systems. In fact, its relatively low peak-to-average power ratio (PAPR) makes it ideal for the uplink transmission where the transmit power efficiency is of paramount importance. Multiple access among users is made possible by assigning different users to different sets of non-overlapping subcarriers. With the current LTE specifications, if an SC-FDMA system is operating at its full capacity and a new user requests channel access, the system redistributes the subcarriers in such a way that it can accommodate all of the users. Having less subcarriers for transmission, every user has to increase its modulation order (for example from QPSK to 16QAM) in order to keep the same transmission rate. However, increasing the modulation order is not always possible in practice and may introduce considerable complexity to the system. The technique presented in this thesis report describes a new way of adding more users to an SC-FDMA system by assigning the same sets of subcarriers to different users. The main advantage of this technique is that it allows the system to accommodate more users than conventional SC-FDMA and this corresponds to increasing the spectral efficiency without requiring a higher modulation order or using more bandwidth. During this work, special attentions wee paid to the cases where two and three source signals are being transmitted on the same set of subcarriers, which leads respectively to doubling and tripling the spectral efficiency. Simulation results show that by using the proposed technique, it is possible to add more users to any SC-FDMA system without increasing the bandwidth or the modulation order while keeping the same performance in terms of bit error rate (BER) as the conventional SC-FDMA. This is realized by slightly increasing the energy per bit to noise power spectral density ratio (Eb/N0) at the transmitters.

No<br>In this work we present the work on the equalization algorithms to be used in future orthogonally multiplexed wavelets based multi signaling communication systems. The performance of ZF and MMSE algorithms has been analyzed using SISO and MIMO communication models. The transmitted electromagnetic waves were subjected through Rayleigh multipath fading channel with AWGN. The results showed that the performance of both of the above mentioned algorithms is the same in SISO channel but in MIMO environment MMSE has better performance.

No<br>We have studied the performance of multidimensional signaling techniques using wavelets based modulation within an orthogonally multiplexed communication system. The discrete wavelets transform and wavelet packet modulation techniques have been studied using Daubechies 2 and 8, Biothogonal1.5 and 3.1 and reverse Biorthognal 1.5 and 3.1 wavelets in the presence of Rayleigh multipath fading channels with AWGN. Results showed that DWT based systems outperform WPM systems both in terms of BER vs. SNR performance as well as processing. The performances of two different equalizations techniques, namely zero forcing (ZF) and minimum mean square error (MMSE), were also compared using DWT. When the channel is modeled using Rayleigh multipath fading, AWGN and ISI both techniques yield similar performance.

No<br>Study is presented into the performance of Fast Fourier Transform (FFT) and Discrete Wavelet Transform (DWT) and MIMO-DWT with transmit beamforming. Feedback loop has been used between the equalizer at the transmitter to the receiver which provided the channel state information which was then used to construct a steering matrix for the transmission sequence such that the received signals at the transmitter can be combined constructively in order to provide a reliable and improved system for next generation wireless systems. As convolution in time domain equals multiplication in frequency domain no such counterpart exist for the symbols in space, means linear convolution and Intersymbol Interference (ISI) generation so both zero forcing (ZF) and minimum mean squared error (MMSE) equalizations have been employed. The results show superior performance improvement and in addition allow keeping the processing, power and implementation cost at the transmitter which has less constraints and the results also show that both equalization algorithms perform alike in wavelets and the ISI is spread equally between different wavelet domains.