Yeonwoo Lee

Interchannel Interference Avoidance in MIMO Transmission by Exploiting Spatial Information

Interchannel interference (ICI) is the key problem in wireless MIMO (multiple-input multiple-output) transmission. Numerous ICI reduction algorithms are reported in literature. It is common to these ICI reduction algorithms that they require considerable signal processing power. In this paper, a new approach is presented which avoids ICI and, thus, results in low complexity receivers whilst maintaining high spectral efficiency. It is demonstrated that this can be achieved for BPSK (binary phase shift keying) and QPSK (quadrature phase shift keying) modulation by compressing the symbols prior to transmission and by exploiting spatial information at the receiver. The V-BLAST (Vertical Bell Labs Layered Space-Time) algorithm and simple, low complexity MMSE (minimum mean squared error) and zero-forcing (ZF) detection without ICI reduction was used for comparison. It is shown that the new MIMO approach outperforms V-BLAST by about 6.5 dB at a signal-to-noise-ratio (SNR) of 15 dB while it outperforms direct MMSE detection by about 12 dB. In addition, it was found that the spectral efficiency compared to SISO (single-input single-output) is improved by a factor of 4 at about the same bit-error performance

Multi-carrier CDMA system with parallel interference cancellation for multipath fading channels

The multi-carrier CDMA technique is attractive in a wireless communication system. It can support a high rate data transmission with a high spectral efficiency. The MC-CDMA (multi-carrier code division multiple access) receiver which employs a multiple access interference (MAI) canceller is proposed and analyzed. The receiver first demodulates the received signal to produce the initial data and the channel estimates. Based on these channel estimations, the cancellation scheme essentially creates the replicas of the MAI and removes them for the second improved data decision. Using theoretical analysis and simulation, the performance of MC-CDMA with parallel interference cancellation (PIC) is investigated according to the mean square error (MSE) of the channel estimation. The result shows the considerably large improvement in performance, which is attained by the interference cancellation technique. But if channel estimation is not performed accurately, then the effect of interference cancellation may be significantly decreased.

Review on Sensor Cloud and Its Integration with Arduino Based Sensor Network

The expansion of embedded ICT infrastructure has resulted in the deployment of a wide range of embedded systems in our environment which indicate the need for reusable, manageable and flexible Wireless Sensor Network. Integration of WSN infrastructure with Cloud simplifies the system operation and maintenance as well as the cost and capable of providing services to multiple end users. The integration offers benefits whereby common processing, computational and analytical tasks can be hosted on cloud service and freeing the devices from running heavy applications, hence reducing power consumption and maximizing the lifetime of power units as well as the network itself. The sensor clouds are therefore gaining popularity for providing an open, flexible and a reconfigurable platform for many monitoring and controlling applications. This paper looks at the benefits and basic features of Senor Cloud Services and how Ethernet enabled Arduino microcontroller based sensor network can be integrated to send sensor data to them by looking at three popular cloud services.

TCP performance enhancement by implicit priority forwarding (IPF) packet buffering scheme for mobile IP based networks

The smooth handoff supported by the route optimization extension to the mobile IP standard protocol should support a packet buffering mechanism at the base station (BS), in order to reduce the degradation in TCP performance caused by packet losses within mobile network environments. The purpose of packet buffering at the BS is to recover the packets dropped during inter-subnetwork handoff by forwarding the packets buffered at the previous BS to the new BS. However, when the mobile host moves to a congested BS within a new foreign subnetwork, the buffered packets forwarded by the previous BS are likely to be dropped. This subsequently causes global synchronization to occur, resulting in the degradation of the wireless link in the congested BS, due to the increased congestion caused by the forwarded burst packets. Thus, in this paper, we propose an implicit priority forwarding (IPF) packet buffering scheme as a solution to this problem within mobile IP based networks. In the proposed IPF method, the previous BS implicitly marks the priority packets being used for inter-subnetwork handoff. Moreover, the proposed modified random early detection (M-RED) buffer at the new congested BS guarantees some degree of reliability to the priority packets. The simulation results show that the proposed IPF packet buffering scheme increases the wireless link utilization and, thus, it enhances the TCP throughput performance in the context of various inter-subnetwork handoff cases.

On the Impact of Efficient Power Allocation in Pilot Based Channel Estimation Techniques for Multicarrier Systems

The use of pilot signals for the purpose of channel estimation in multicarrier systems does not only consume bandwidth but also signal power that could otherwise be invested in the information symbols to be transmitted. The aim of this paper is to investigate the issue of optimal transmitter power distribution between the pilot and information signals and evaluate its impact on the performance of multicarrier systems. It will be shown that the optimal power distribution is primarily influenced by the ratio of number of pilots to the total number of subcarriers used. An optimal pilot power allocation as a function of this ratio will be proposed for both MPSK and MQAM systems taking into account channel estimation errors

Performance analysis for hybrid wireless networks

A hybrid cellular and ad hoc network for high data rate wireless access is considered. An air-interface which uses TDD in combination with time division multiple access (TDMA) is assumed. Interference and resource reuse are important issues in hybrid networks. For this purpose analytical models for the reuse efficiency and a capacity bound of such a network are developed. These models are based on an exclusion range concept which is introduced to keep interference at an acceptable level. It is found that with this interference limiting measure, multi hop networks can benefit from a multi hop reuse gain compared to single hop networks. However, it is further found that this gain does not significantly increase for more than 5 hops. Furthermore, the pre-requisite for being able to exploit the multi hop reuse gain is a certain TS granularity. It was observed that with an increasing number of TS per frame, the mean and the variance of the number of supported hops increased almost linearly

A Distributed-Request-Based DiffServ CAC for Seamless Fast-Handoff in Mobile Internet

The next-generation wireless networks are evolving toward an IP-based network that can provide various multimedia services seamlessly. To establish such a wireless mobile Internet, the registration domain supporting fast handoff is integrated with the DiffServ mechanism. In this paper, a Distributed-request-based CDMA DiffServ call admission control (CAC) scheme is proposed for the evolving mobile Internet. Numerical examples show that the forced termination ratio of handoff calls is guaranteed to be much less than the blocking ratio of new calls for a seamless fast-handoff while proposed scheme provides quality of service guarantee for each service class efficiently.

Power-efficient and QoS-aware scheduling in Bluetooth scatternet for wireless PANs

In this paper, we propose a power-efficient and QoS (quality of service)-aware MAC (medium access control) scheduling algorithm for Bluetooth scatternet. If the inter-piconet scheduler in a bridge node between piconets operates simply by the round robin (RR) policy, a number of time slots may be wasted due to the guard time for piconet switching and the exchange of POLL-NULL packets. To overcome the link wastage problem in Bluetooth scatternet scheduling, several algorithms have been proposed. Although they can provide all of the links of a bridge node with fair service opportunities, they may cause waste of wireless resources since different Bluetooth devices may have various traffic characteristics. In addition, since Bluetooth devices are often required to operate under limited battery capacity, the number of unnecessary piconet switching has to be minimized for the power-efficient operation of a Bluetooth scatternet. Therefore, we propose a mechanism to support the power-efficient operation of a Bluetooth scatternet while guaranteeing various QoS requirements of Bluetooth devices. The proposed algorithm is compliant with the current Bluetooth specification, and we demonstrate its improved performance via simulations.

Resource Management for Fixed Relay Based Cellular Systems with Sectorization

Resource management for infrastructure-based two-hop fixed relay systems which are applicable to TDD-FH-OFDMA based cellular systems with sectorization is proposed in this paper. The severe interference problem caused by both inter-sector and inter-cell can be tackled by employing 6-sector directional antennas combined with the resource allocation. The simulation results demonstrate that at the outer-region of the cell, the high data rate service coverage can be extended.

Radio resource metric estimation for wireless CDMA communication systems maximising radio resource utilisation

In this paper, we propose a predictive resource metric region (RMR) based resource metric estimation method, which utilizes a resource metric mapping function (RMMF), both of which permit efficient inter-working between the physical layer and higher layers. The RMR can provide the acceptable resource region where QoS and acceptable link quality can be guaranteed with an achievable resource margin to be utilized in terms of capacity margin, the degree of confidence (DCL) of user, second-order statistics of Eb/Io. With predicted capacity margin and variance, DCL can deliver decision parameters with which an adaptive QoS based admission control can perform well taking capacity and resource availability into account in a dynamic and predictive manner.