Network densification has led to a renewed emphasis on means to improveaggregate network throughputfor next-gen (High Efficiency) WLANs. The introduction of BSS color feature in support of enhanced spatial reuse sets IEEE 802.11ax apart from legacy WLAN. BSS color enables stations within a network to identify whether a transmission originates from an overlapped BSS and provides an option for mitigating the exposed node problem by allowing it to transmit (over the on-going OBSS transmission) albeit with reduced transmit power. As a result, distances between networks can be reduced, thereby improving the area spectral efficiency. To the best of our knowledge, this is the first work to develop an analytical model for IEEE 802.11ax spatial reuse that provides useful rules for optimizing network area throughput. We show that the spatial reuse gain is tightly linked to the interference range properties of each BSS in the network. Further, the analytical model predictions are validated and expanded via definitive ns-3 simulation results exploiting a recently concluded upgrade to 802.11 WLAN network stack (that implemented the necessary spatial reuse features).

We demonstrate a self-interference (SI) cancellation in cooperative multiple-input multiple-output (Co-MIMO) for full-duplex (FD) wireless communication systems by applying the block diagonalization used in multi-user MIMO. The proposed method's implementation uses a field-programmable gate array (FPGA) and software-defined radio (SDR). In the experiment, a total of 33 [dB] SI can cancel with two cooperative APs and two antennas per AP in the IEEE 802.11 system.

In this paper, we propose self-interference (SI) cancellation in cooperative multiple-input multiple-output (Co-MIMO) for full-duplex (FD) wireless communication systems. This proposal solves SI by applying the block diagonalization used in multi-user MIMO. Therefore, there is no need for a radio frequency (RF) canceller, which has a large hardware (HW) size and is difficult to extend to MIMO. Furthermore, we can achieve higher throughput by applying Co-MIMO, in which multiple access points (APs) work together to communicate. The proposed method's implementation uses field-programmable gate array (FPGA) and software-defined radio (SDR). In the experiment, a total of 33 [dB] SI can cancel with two cooperative APs and two antennas per AP in the IEEE 802.11 system.

IEEE 802.11ax partitions a regular 20MHz channel into smaller sub-channels called resource units to support simultaneous multiuser operation using orthogonal frequency division multiple access (OFDMA). Uplink OFDMA random access (UORA) in IEEE 802.11ax allows stations to transmit via a scheduled random access mechanism. UORA is initiated via a trigger frame which aside from serving as a synchronization mechanism, also informs stations which resource units are allowed for random access. Using the trigger frame information, the stations engage in an OFDMA backoff process to win access to a resource unit. Similar to slotted ALOHA, the maximum normalized throughput of UORA is only 37 percent due to high probability of collisions at high loads. To reduce collisions, we equip UORA with carrier sensing capability resulting in anewuplink hybrid UORA (H-UORA) OFDMA access mechanism. Unlike other multi-carrier CSMA methods previously proposed in literature, H-UORA is an easily implementable modification to current 802.11ax WLANs. We show that H-UORA can achieve a normalized throughput of at least 80 percent (which increases further depending on the buffering capabilities of the access point) using various numerical analysis and simulations.

Channel bonding in IEEE 802.11 wireless LANs is a technique whereby adjacent 20MHz channels are `bonded' to create a wider bandwidth channel that supports higher data rate transmissions. Although rate improvements due to channel bonding has been shown in sparse wireless LAN environments, its effectiveness in dense scenarios requires further exploration due to increased sensitivity to interference from overlapping co-channel basic service sets. With the newly finalized 802.11ax standard supporting enhanced spatial reuse feature, its impact on the expected gains from channel bonding needs careful analysis. In this work, we propose a new analytical framework that accurately models the performance of channel bonding as a function of both PHY and MAC parameters for a dense network scenario. A new channel bonding algorithm that is robust to overlapped co-channel interference is described, i.e. it preserves channel bonding gains by intelligently choosing the channel bonding bandwidth based on network conditions and parameters that are readily available to all stations, critically the modulation scheme chosen for packet transmission. The predicted gains of the proposed algorithm are verified via comprehensive simulations conducted with the open source network simulator ns-3.

The Markov chain based model by Bianchi for IEEE802.11 distributed controlled access is a highly accurate analytical tool for estimating the system throughput when a single Basic Service Set (BSS) network operates in isolation. However, with the increase of wireless LAN access points being deployed on the same area, an environment with multiple BSS interfering with each other has become the default network scenario. The purpose of this work is to extend the single BSS Markov chain model into a multi-BSS model by incorporating the influence of STAs' interference range and carrier sense range to their own transmission and collision probabilities. We verify the proposed multi-BSS analytical model using the latest version of the ns-3 simulator which has recently supported accurate PHY abstractions for multi-BSS simulation. We show that the proposed model has a high accuracy (within 1%) independent of the multi-BSS network topology.

Currently, Global Positioning System (GPS) is widely used as a representative position estimation system. However, GPS suffers from poor position estimation accuracy in an indoor environment. Moreover, time synchronization between devices needs to be performed for position estimation which is a resource intensive process. In previous studies, an asynchronous protocol (i.e., no synchronization requirement) called Grid Search was proposed to handle this problem. However, this method also has high complexity and takes a lot of search time to estimate the position. In this paper, we propose a method to narrow the search range using intersecting chord under the condition that generated circles intersect with each other. The proposed position estimation method has low complexity but can achieve accuracy comparable to Grid Search, i.e., a maximum estimation error less than 2 meters with 80% of the trials are within 1 meter. In addition, the calculation time can be reduced up to 6 times compared to the Grid Search when the search range extends to 5 times.

Recently, 802.11ax has introduced uplink Orthogonal Frequency Division Multiple Access (UL OFDMA)-based random access transmission to provide uplink multiuser capability to stations (STA) with unknown buffer status. These STAs include those that are waking up from sleep and unassociated STAs trying to establish connection for the first time. Due to the absence of carrier sensing per resource unit, this procedure has a maximum efficiency of only about 37% for high number of STAs. The efficiency will decrease further without properly choosing the random access parameters. In this paper, we first build an analytical model of the performance of UL OFDMA random access transmission and verify it using simulations. In addition, we propose methods to optimize various random access parameters to maintain a system efficiency near the 37% limit. Simulation results show that our optimization methods can increase the throughput of UL OFDMA random access by as much as 39% when compared to randomly chosen parameters.

Image and video transmission is highly expected to proliferate with the wide spread of Wi-Fi devices and the introduction of multiple-input multiple-output (MIMO) systems. This paper proposes a novel precoder for video transmission in overloaded MIMO systems, which is based on an eigenbeam space division multiplexing (E-SDM) technique. This paper also proposes a low complexity postcoder, which detects some of data symbols by a linear approach and the others by a prevoting vector cancellation (PVC) approach. It is shown from simulation results that the proposed precoder and postcoder achieve 40 dB in peak signal-to-noise ratio while reducing the computational complexity by over 61 compared to the conventional PVC-based detection when received signal-to-noise ratio is higher than 10 dB.

Interleave division multiple access (IDMA) is a potential candidate for the future fifth generation (5G) systems. In this paper, we propose a novel architecture for IDMA system with low latency while maintaining low complexity. In the conventional architecture, the IDMA receiver sequentially processes deinterleaving, despreading, spreading and interleaving for multiuser detection. The proposed architecture, which is called the interleaved domain, can perform multi-user detection directly without deinterleaving the received frame. Because of this, the interleaving is no longer needed in the interference cancellation loop resulting in the decrease of latency by half and the increase of throughput by twice. In VLSI implementation results, the proposed architecture has reduced circuit area and power consumption by 53% and 58% compared to the conventional architecture on the same throughput condition.

This paper proposes a design of wireless communication system, particularly physical layer system (PHY) for Factory Automation (FA) system based on Wireless Local Area Network (WLAN) communication system. The designed PHY system is developed based on a fast and deterministic communication featuring a synchronous multi user round robin transmission protocol. Low overhead Packet Division Multiple Access (PDMA) scheme is utilized for Multi-user Downlink transmission, while the Frequency Division Multiple Access (FDMA) is employed for the uplink transmission. For efficient PHY implementation, several approaches on architectural aspects are also introduced. Implementation results show that the optimized design of transmitter and receiver have efficient logic resource while maintain required processing speed and error performance.

This paper proposes a 4×4 MU-MIMO channel emulator with automatic channel sounding feedback used for beam-forming and MU-MIMO precoding features of IEEE 802.11ac. The main contribution of this paper is the design of a MU-MIMO channel emulator capable of sending channel feedback automatically to the AP from the generated channel coefficients after a programmable time duration. This function helps to evaluate the precoding algorithms without channel estimation error and uses very minimal MAC features. The second contribution is the design of single path implementation with serial processing which plays an important role on reducing the hardware complexity. The design choice makes it possible to generate channel coefficients for very high sampling rate systems with little increase in complexity. In addition, single path implementation allows the addition of the feedback channel output with only few additional nonsequential elements which would otherwise double in a parallel implementation. To demonstrate the functionality of our MU-MIMO channel emulator, we present actual hardware emulator results of precoded receive signal constellation on oscilloscope.

In this paper, we present an efficient and high throughput hardware implementation of the RC4 algorithm. The main idea of the proposed architecture is the utilization of a tri-port RAM to reduce the memory resource and to increase throughput. The proposed design requires two clock cycles for generating one byte of ciphering key and uses only a block of 256 bytes RAM. These result in 50% increment of system throughput and three times reduction of RAM resource compared to the recent architectures. The proposed implementation supports variable key length from 8 to 128 bits and achieves 80 MB/s throughput at 160 MHz operating frequency. It aims to support the WEP security in the MAC layer of 600 Mbps 4×4 MIMO wireless LAN system based on IEEE 802.11n standard.

Tomlinson Harashima Precoding (THP) for Multi-User Multiple Input Multiple Output (MU-MIMO) system has been proposed as an effective way to achieve near capacity to the theoretical limit in MU-MIMO channels. In order to achieve better performance, other THP methods such as minimum mean square error (MMSE) THP and lattice reduction aided (LRA) THP are proposed. Those methods outperform the conventional THP, however, the computational complexity also increases. In this paper, we propose a modified THP by new approach using square root with less increase of computational complexity. Computer simulation shows that proposed method can achieve better trade-off between bit error rate and computational complexity than MMSE THP and LRA THP.

We propose a packet delayed lattice reduction aided MIMO detection for 802.11n system. Lattice reduction algorithms are iterative in nature that results in long latency. In high throughput systems like 802.11n, reduction of latency via parallelization causes high hardware complexity. Without parallelization, the receiver needs to buffer the incoming data until the lattice reduction finishes. Depending on the latency of the lattice reduction, this buffering may cause deep memory requirements as well as missed interframe space deadline requirement. In this paper, we resolve this problem by foregoing buffering of incoming data for the current packet and use the output of lattice reduction to the next packet after the computation is finished. We show that lattice aided MIMO detection can be delayed for as much as 15ms with negligible effect on performance.

We propose a new least squares based estimation algorithm for carrier frequency offset and frequency dependent I/Q imbalance compensation with very low complexity for direct conversion receivers. Compared to conventional algorithms, our proposed estimation has considerably lesser computation due to a reduced order least squares step. Simulation results show that the proposed algorithm has about 1.5dB better accuracy in CFO estimation compared to conventional algorithms and it can completely eliminate I/Q imbalance based on BER performance results. We also showed that the proposed algorithm needs only a minimum 3rdorder FIR filter to effectively remove an infinite impulse response modeled I/Q imbalance.

This paper introduces a novel algorithm for jointly estimating carrier frequency offset and I/Q imbalance for OFDM systems. The new algorithm is a closed form solution to obtain the frequency offset and I/Q imbalance parameters in the absence of noise. In the presence of noise, the proposed algorithm uses the least squares algorithm to accurately estimate the parameters. The proposed algorithm is thus very scalable in terms of complexity. While the target system is OFDM, the proposed algorithm applies to any system as long as two identical data blocks are received in the receiver. Simulation results show that given a suitable amount of CFO, the high estimation accuracy of the proposed algorithm makes its BER performance comparable to a system without CFO and I/Q imbalance.

This paper proposes a simple algorithm for joint estimation of carrier frequency offset and I/Q imbalance. The reduced complexity algorithm is derived from a closed form solution of the carrier frequency offset and I/Q imbalance parameters given two identical training blocks. The proposed algorithm also uses the least squares algorithm to give accurate estimate in the presence of noise. It was shown that for as little as 10 samples each from two identical OFDM symbols, the proposed algorithm can produce accurate estimate of CFO and I/Q imbalance. While the target system is OFDM, the proposed algorithm applies to any system as long as two identical data blocks are received in the receiver. Simulation results show that performance of the proposed algorithm that uses only 10 samples for complexity reduction is only ldB below a system without CFO nor I/Q imbalance degradation.