Ergodic Capacity of MIMO Correlated Channels in Multipath Fading Environment with known Channel State Information

In this paper we have evaluated the performance of Multiple Input Multiple Output (MIMO) channels in fading environment. Both cases of correlated and uncorrelated MIMO channels are considered under the condition when Channel State Information (CSI) is not known at transmitter and CSI is known at receiver side. We have compared the capacity of 2x2, 3x3 and 4x4 MIMO channels and have shown that capacity increases linearly with increase in the number of antennas at transmitter and receiver side. Increase in the channel capacity is observed because of the uncorrelated channel paths Correlation among the the signals is dependent on the antenna structure and properties and number of the scatterers in the environment. Antenna structure includes the number of elements, the inter-element distance, Angle of Arrival (AOA) and Direction of Arrival (DOA). Additionaly, Correlation increases with the number of scatterers, their distribution, location and degree of movement. Signals with same spatial signature received are considered correlated which reduces the channel capacity. In sum, correlation among the sub-channels causes the degradation in the spectral efficiency of MIMO channels.DOI:http://dx.doi.org/10.11591/ijece.v2i5.151

On the technical challenges of cognitive radio in TV white spaces

Cognitive Radio (CR) has been considered as a powerful technique to increase the spectral efficiency by enabling unlicensed users to access unused spectrum opportunistically. Cognitive Radio has two important paradigms to efficiently utilise spectrum which are spectrum sensing and spectrum database. In spectrum sensing unlicensed users sense the spectrum and to detect the availability of under-utilised channels before transmission and access the channels when idle or tolerable interference to primary user (PU) is guaranteed. For the later case i.e. database paradigm of CR unlicensed users can acquire the availability of channels through spectrum database before accessing the channels. In this work, spectrum sensing part of the CR has been focused. In cognitive radio SU should yield maximum throughput and guarantee maximum PU protection. Sensing-throughput tradeoff has been studied for both single cognitive radio and cooperative cognitive radio with different fusion strategies. In cooperative cognitive radio OR and Optimal fusion strategies yielded maxim throughput than the AND strategy. Thereafter, the problem of throughput has been compared for both half-duplex cognitive radio and full-duplex cognitive radio for a given target probability of detection. It was found that there is an optimal sensing time at which a CR yields maximum throughput for a given target probability of detection. Much of the initial discussion is based on half-duplex communication cognitive radio (HDC-CR) using HDC-SS scheme. It is of special interest to derive the PD, PFA mathematical expressions for full-duplex communication cognitive radio (FDC-CR) which uses full-duplex spectrum sensing scheme to do sensing and transmission at the same time. It was found that the FDC-CR yields higher throughput for SU than the HDC-CR since FDC-CR performs sensing and data transmission at the same time therefore it gets increased data transmission time for secondary user

Evaluating Cooperative Spectrum Sensing: A Hardware-in-the-Loop Approach

In this work, we present a hardware-in-the-loop evaluation of cooperative spectrum sensing using eigenvalue detection. Single-node spectrum sensing is unreliable as it is susceptible to hidden node problems. Therefore, multiple spatially distributed sensors collaboratively perform spectrum sensing to increase the spectrum sensing reliability. Cooperative spectrum sensing is an effective technique to reliably detect the absence or presence of a primary user (PU). Here, cooperative spectrum sensing is implemented on a wideband radio transceiver platform. The secondary users detect the presence or absence of PU signal over the 3GPP extended pedestrian A (EPA) channel model with a $5\,\mathrm{Hz}$ Doppler and varying levels of log-normal shadow fading

2x2 MIMO Prototype for BER and EVM Measurements in Metal Enclosure

In this work, we present a 2x2 near-field multi-input multiple-output (MIMO) prototype for bit-error-rate (BER) and error vector magnitude (EVM) measurements in a metal enclosure. The near-field MIMO prototype is developed using software-defined-radios (SDRs) for over-the-air transmission of QPSK modulated baseband waveforms. We check the near-field MIMO BER and EVM measurements in three different scenarios in a highly reflecting metal enclosure environment. In the first scenario, the line-of-sight (LOS) communication link is investigated when the mode-stirrer is stationary. In stationary channel conditions near-field MIMO BER and EVM measurements are performed. In the second scenario, BER and EVM measurements are performed in dynamic channel conditions when the mode-stirrer is set to move continuously. In the third scenario, LOS communication near-field MIMO BER and EVM measurements are performed in stationary channel conditions but now in the presence of MIMO interference. In three different scenarios, near-field MIMO BER and EVM measurements are investigated at different Tx USRP gain values and in the presence of varying levels of MIMO interference.Comment: 10 page

Statistical Characterization of Wireless MIMO Channels in Mode-Stirred Enclosures

We present the statistical characterization of a 2x2 Multiple-Input Multiple-Output wireless link operated in a mode-stirred enclosure, with channel state information available only at the receiver (agnostic transmitter). Our wireless channel measurements are conducted in absence of line of sight and varying the inter-element spacing between the two antenna elements in both the transmit and receive array. The mode-stirred cavity is operated: i) at a low number of stirrer positions to create statistical inhomogeneity; ii) at two different loading conditions, empty and with absorbers, in order to mimic a wide range of realistic equipment level enclosures. Our results show that two parallel channels are obtained within the confined space at both the operating conditions. The statistical characterization of the wireless channel is presented in terms of coherence bandwidth, path loss, delay spread and Rician factor, and wideband channel capacity. It is found that the severe multipath fading supported by a highly reflecting environment creates unbalance between the two Multiple-Input Multiple-Output channels, even in presence of substantial losses. Furthermore, the channel capacity has a multi-modal distribution whose average and variance scale monotonically with the number of absorbers. Results are of interest in IoT devices, including wireless chip-to-chip and device-to-device communications, operating in highly reflective environments

Multi-path fading and interference mitigation with Reconfigurable Intelligent Surfaces

We exploit multi-path fading propagation to improve both the signal-to-interference-plus-noise-ratio and the stability of wireless communications within electromagnetic environments that support rich multipath propagation. Quasi-passive propagation control with multiple binary reconfigurable intelligent surfaces is adopted to control the stationary waves supported by a metallic cavity hosting a software-defined radio link. Results are demonstrated in terms of the error vector magnitude minimization of a quadrature phase-shift modulation scheme under no-line-of-sight conditions. It is found that the magnitude of fluctuation of received symbols is reduced to a stable constellation by increasing the number of individual surfaces, or elements, thus demonstrating channel hardening. By using a second software-defined radio device as a jammer, we demonstrate the ability of the RIS to mitigate the co-channel interference by channel hardening. Results are of particular interest in smart radio environments for mobile network architectures beyond 5G

Reconfigurable Intelligent Surface-assisted Classification of Modulations using Deep Learning

The fifth generating (5G) of wireless networks will be more adaptive and heterogeneous. Reconfigurable intelligent surface technology enables the 5G to work on multistrand waveforms. However, in such a dynamic network, the identification of specific modulation types is of paramount importance. We present a RIS-assisted digital classification method based on artificial intelligence. We train a convolutional neural network to classify digital modulations. The proposed method operates and learns features directly on the received signal without feature extraction. The features learned by the convolutional neural network are presented and analyzed. Furthermore, the robust features of the received signals at a specific SNR range are studied. The accuracy of the proposed classification method is found to be remarkable, particularly for low levels of SNR

Experimental Evaluation of Multi-operator RIS-assisted Links in Indoor Environment

In this work, we present reconfigurable intelligent surface (RIS)-assisted optimization of the multiple links in the same indoor environment. Multiple RISs from different operators can co-exists and handle independent robust communication links in the same indoor environment. We investigated the key performance metrics with the help of two simultaneously operating RIS-empowered robust communication links at different center frequencies in the same indoor environment. We found with the help of bit error rate (BER) and error vector magnitude (EVM) measurements that two operators can co-exist in the same RF environment without seriously impacting quality of service of users

Reconfigurable Intelligent Surface-Assisted Bluetooth Low Energy Link in Metal Enclosure

Reconfigurable intelligent surface (RIS) technology is at the forefront for its transformative role in future wireless communication systems such as wireless local area networks (WLAN), sixth-generation (6G) communication, and internet-of-things (IoT). This paper presents RIS-assisted Bluetooth low energy (BLE) communication links in neighbor discovery mode. We optimized the packet error rate (PER) performance of the BLE communication link in a highly reflecting metal enclosure environment. We used one RIS for the PER optimization of four BLE physical (PHY) modes. Then, we used two RISs simultaneously in a distributed and centralized manner to further optimize the PER of all BLE PHY modes. We found PER optimization using two RISs is better than the PER optimization using one RIS. Additionally, PER optimization using a centralized arrangement of RISs outperformed PER optimization using distributed arrangement. We found the coded BLE modes i.e., LE500K and LE125K show lower PER than the uncoded counterpart i.e., LE1M and LE2M. This is because uncoded BLE PHY modes have higher data rates than the coded BLE PHY modes. Because of additional channel power gains introduced by RIS-based passive beamforming, the PER of coded and uncoded BLE PHY modes is further reduced