Chandan Pradhan

Cost effective restoration of wireless connectivity in disaster hit areas using OpenBTS

In this paper, we have proposed a cost effective method for rapid restoration of wireless connectivity in disaster hit areas, which face large scale failure of wireless infrastructure. This method includes setting of a reconfigurable Base Transceiver Station (BTS) based on Software Defined Radio (SDR) technology. The setup covers the drawbacks of existing methods for establishing connectivity in disaster hit areas such as Ham radio. It also extends the connectivity to almost every individual in the area having a GSM handset at no additional cost. This low cost deployment will encourage government to implement such models in areas struck by major catastrophe. For demonstration, we have used OpenBTS along with Universal Software Radio Peripherals (USRP) N210, to set up the BTS infrastructure. We have also analyzed scaling up of the experimental system model to set up a Macrocell network in practical scenario.

Full-duplex transceiver for future cellular network: A smart antenna approach

In this paper, we propose a transceiver architecture for full-duplex (FD) eNodeB (eNB) and FD user equipment (UE) transceiver. For FD communication,.i.e., simultaneous in-band uplink and downlink operation, same subcarriers can be allocated to UE in both uplink and downlink. Hence, contrary to traditional LTE, we propose using single-carrier frequency division multiple accesses (SC-FDMA) for downlink along with the conventional method of using it for uplink. The use of multiple antennas at eNB and singular value decomposition (SVD) in the downlink allows multiple users (MU) to operate on the same set of subcarriers. In the uplink, successive interference cancellation with optimal ordering (SSIC-OO) algorithm is used to decouple signals of UEs operating in the same set of subcarriers. A smart antenna approach is adopted which prevents interference, in downlink of a UE, from uplink signals of other UEs sharing same subcarriers. The approach includes using multiple antennas at UEs to form directed beams towards eNode and nulls towards other UEs. The proposed architecture results in significant improvement of the overall spectrum efficiency per cell of the cellular network.

Full-duplex communication for future wireless networks

In this paper, we discuss a full-duplex (FD) communication scenario, where multiple FD user equipments (UEs) share same spectrum resources (or resource blocks) simultaneously. The FD eNodeB deploys digital precoding and successive interference cancellation with optimal ordering algorithm, to allow coexistence of multiple UEs in downlink and uplink, respectively. The sharing of same resource blocks, results in co-channel interference (CCI), in downlink of a UE, from uplink signals of other UEs. To mitigate the interference, a smart antenna approach is adopted. The approach includes using multiple antennas at UEs to form directed beams towards eNodeB and nulls towards other UEs. However, the approach fails when the UEs due to their mobility align themselves in the same direction with respect to the eNodeB (eNB). In this paper, we propose a dynamic resource block allocation (DRBA) algorithm for avoiding CCI due to mobility of UEs, sharing the spectrum resource, in a FD communication scenario. The proposed algorithm shows significant improvement of the quality of service (QoS) of the communication links.

Revamp of eNodeB for 5G networks: Detracting spectrum scarcity

This paper proposes the revamp of architecture of an eNodeB (eNB) for 5G cellular communication networks capable of opening up the crunched spectrum resources. We have developed a novel priority driven Resource Block (RB) handoff algorithm for Full-Duplex Multi-User MIMO communication, where the eNB creates beams for establishing communication links. The use of Full-Duplex operation enables simultaneous in-band uplink and downlink operation without sacrificing temporal resource in each link. Space-division multiple access (SDMA) technique has been used to dynamically create a beam towards the intended mobile users as well as track them through beam steering. The possibility of co-channel interference (CCI) due to mobility of users is eliminated by the introduction of RB handoff mechanism. This allows sharing of a RB or RBs by multiple users. In the proposed architecture, along with coexistence of multiple mobile UEs in same RBs diversity gain is introduced both in uplink and downlink. The work includes related simulations showing the conceptual validity of the proposed architecture to revamp. The proposed eNB model leads to improved QoS and a significant decrease in cellular spectrum requirement worth millions of dollars.

Cognitive base station design for efficient spectrum utilization in cellular network

This paper proposes the architecture of a cognitive base station for 4G cellular communication networks. We have developed a novel priority driven spectrum handoff technique for Multi-User MIMO communication, where the base station creates beams for establishing communication links. Adaptive beamforming methods along with DoA have been used to dynamically create a beam toward the intended receiver as well as track the users and steer the beam when users are mobile. The work is followed by related simulations which shows 5.4 dB gain over the traditional cellular architecture with respect to CCI. Our proposed algorithms lead to significant increase in overall capacity of the network. It also promises higher spectrum efficiency compared to the traditional cellular architecture.

Analysis of Full-Duplex Downlink Using Diversity Gain

In this paper, we carry out performance analysis of a multiuser full-duplex (FD) communication system. Multiple FD user equipments (UEs) share the same spectrum resources, simultaneously, at both the uplink and downlink. This results in co-channel interference (CCI) at the downlink of a UE from uplink signals of other UEs. This work proposes the use of diversity gain at the receiver to mitigate the effects of the CCI. For this an architecture for the FD eNodeB (eNB) and FD UE is proposed and corresponding downlink operation is described. Finally, the performance of the system is studied in terms of downlink capacity of a UE. It is shown that through the deployment of sufficient number of transmit and receive antennas at the eNB and UEs, respectively, significant improvement in performance can be achieved in the presence of CCI.

Modeling of ambient and ship noise in underwater ocean environment of the Bay of Bengal

In this paper, we model the ambient noise with and without ship noise data collected from the shallow waters of the Bay of Bengal. The wind speed and temperature were approximately constant for both the noise data. The ambient noise was collected using hydrophones at a depth of 5m and 15m from the surface, while the ambient noise added with ship noise data was collected using hydrophones at a depth of 3m and 5m. Statistical analysis of the ambient noise reveals that it follows Weibull distribution. Ambient noise along with ship noise is observed to exhibit Generalized Gaussian probability density function pdf. It is observed that both the noises collected near the surface exhibit higher variance compared to that collected at a deeper level in the ocean. The power spectral density analysis of the ambient noise with and without ship noise, at 5m hydrophone depth, shows the dominant frequency band to be up to 3KHz. Further, it is observed that though the power spectral density of both noises dominates over almost the same frequency range, these can be differentiated based on variations in their statistics.

Analysis of path loss mitigation through dynamic spectrum access: Software defined radio

In this paper, an analysis is carried out for a method to mitigate the path loss through the dynamic spectrum access (DSA) method. The path loss is a major component which determines the QoS of a wireless link. Its effect is complemented by the presence of obstruction between the transmitter and receiver. The future cellular network (5G) focuses on operating with the millimeter-wave (mmW). In higher frequency, path loss can play a significant role in degrading the link quality due to higher attenuation. In a scenario, where the operating environment is changing dynamically, sudden degradation of operating conditions or arrival of obstruction between transmitter and receiver may result in link failure. The method analyzed here includes dynamically allocating spectrum at a lower frequency band for a link suffering from high path loss. For the analysis, a wireless link was set up using Universal Software Radio Peripherals (USRPs). The received power is observed to increase by dynamically changing the operating frequency from 1.9 GHz to 830 MHz. Finally the utility of software defined radio (SDR) in the RF front end, to combat the path loss in the future cellular networks, is studied.

An Analytical Approach to Optimal Signal Design for Wireless Communication Channels

In this paper, we formulate an optimal signal design for time varying wireless communication channels. Wireless channels in a practical scenario suffer from impairments like fading due to multipath effects and time varying characteristics resulting in varying signal strength at the receiver. Decoding of the signal becomes unreliable when the received signal strength is lower than the noise power. To tackle this issue, we here take a control theory based approach to design optimal signal such that signal strength at the receiver is maximized. In this approach, the wireless channel is considered to be a linear system where the input to the system is the transmitted signal and output is the received signal at the receiver. We here analyze the influence of fading on the transmitted signal and formulate an optimal signal design for single input and single output (SISO) operation and multiple input and multiple output (MIMO) operation. We analytically prove that the optimal signal constitutes a stable state of a continuous time Hopfield neural network.