Shashika Biyanwilage

Selective sub-carrier relaying and power allocation for multi-relay-assisted cooperative OFDM systems

We investigate the relay selection, sub-carrier pairing and power allocation problems in a two-hop, multi-relay-assisted cooperative OFDM system with amplify-and-forward (AF) relays. We propose a sub optimal but more feasible approach to solve the power allocation problem with relay selection and sub-carrier pairing. The proposed method is based on selective sub-carrier relaying concept where the relays forward only a selected set of sub-carriers of the received OFDM symbol. Transmit power allocation is performed such that the end-to-end system capacity is maximized under individual power constraints at each node. The proposed technique outperforms the all sub-carrier relaying scheme when the relays are distributed between the source and the destination.

Power allocation in OFDM cognitive radio relay networks with outdated channel state information

In this paper, we study power allocation in OFDM cognitive radio CR relay networks. The objective of power allocation is to maximize the instantaneous capacity of the CR network. It is assumed that the available channel state information between the secondary and primary users is an outdated but correlated version of the actual instantaneous channel state information. Optimal power allocation schemes are developed for both decode-and-forward and amplify-and-forward relay assisted CR transmission, assuming that the primary users are subject to average interference constraints and the CR transmitters are subject to maximum transmit power constraint. In addition, suboptimal power allocation schemes with reduced complexity are also proposed. Performance of the proposed schemes is compared with uniform power allocation and numerical results confirm that the proposed power allocation schemes achieve significant capacity improvement in comparison to uniform power loading. Furthermore, the proposed suboptimal power allocation schemes can be used as less complex alternatives for optimal power allocation with some capacity degradation. Copyright

Power allocation in DF relay assisted OFDM cognitive radio networks with outdated CSI

In this paper, we investigate power allocation in decode-and-forward (DF) relay assisted OFDM cognitive radio (CR) networks. The objective is to maximize the instantaneous capacity of the CR system. Due to channel feedback delay, the available channel state information (CSI) between the secondary and primary users is considered as an outdated but correlated version of the actual instantaneous CSI. An optimal power allocation scheme is presented assuming that the primary users are subject to average interference constraints and the CR transmitters are subject to maximum transmit power constraint. In addition, a suboptimal scheme with reduced complexity is also proposed. Numerical results confirm that the proposed suboptimal power allocation scheme can be used as a less complex alternative for optimal power allocation with some degradation in capacity.

New power allocation methods for AF relay assisted OFDM cognitive radio networks with outdated CSI

In this paper, we investigate optimal and suboptimal power allocation schemes for amplify-and-forward (AF) relay assisted OFDM-based cognitive radio (CR) transmission. Due to channel feedback delay, the available channel state information (CSI) between the secondary and primary users is considered as an outdated but correlated version of the actual instantaneous CSI.We develop an optimal power allocation scheme to maximize the instantaneous capacity of the CR transmission assuming that the primary users are subject to average interference constraints, and the CR transmitters are subject to maximum transmit power constraint. A suboptimal scheme with reduced complexity has also been investigated and compared with the uniform loading algorithm. Numerical results confirm that the proposed optimal power loading scheme achieves on average, 60% capacity improvement than the uniform loading algorithm. Also the proposed suboptimal scheme outperforms the uniform loading approach and can be used as a less complex alternative for optimal power allocation with about 10% (on average) capacity degradation.

Power allocation in OFDM cognitive radio relay networks with average interference constraints

In this paper, we study power allocation in OFDM based cognitive radio (CR) relay networks when the fading statistics between cognitive and primary users are known at the CR transmitters. The objective of power allocation is to maximize the instantaneous capacity of the CR network. Optimal power allocation schemes are developed for both decode-and-forward (DF) and amplify-and-forward (AF) relay assisted CR transmission where the primary users are subject to average interference constraints and the CR transmitters are subject to maximum transmit power constraint. Performance of the proposed schemes is compared with uniform power allocation method and the numerical results confirm that the proposed optimal power allocation schemes achieve significant capacity improvement compared to uniform power loading.

Power allocation for nonregenerative OFDM relay links with outdated channel knowledge

This paper investigates the power allocation problem in a two-hop OFDM relay link with a nonregenarative relay where the available channel state information (CSI) is an outdated version of the actual instantaneous CSI. A power allocation method is proposed to maximize the expected capacity, assuming that the correlation between the outdated and instantaneous CSI is known. The performance is compared with that of the baseline method, where the power allocation is performed solely based on the outdated CSI. Results confirm that the proposed method outperforms the baseline method when the available CSI is highly outdated.

Resource allocation in OFDM-based cognitive radio networks with multiple AF relays

This paper investigates the relay selection and power allocation problems in OFDM-based cognitive radio networks with multiple amplify-and-forward relays. The objective is to maximize the total instantaneous capacity of the cognitive radio network while maintaining the interference introduced to the primary network below a given threshold and also maintaining the total transmit power below the individual power limitations at cognitive radio transmitters. The joint optimization problem is a mixed binary integer problem which is NP-hard. Thus, we divide the joint optimization problem into two subproblems, and solve the resource allocation problem suboptimally. Two suboptimal resource allocation methods are proposed and their performance is compared with the joint optimal resource allocation. Results show that near optimal performance can be obtained with less complex suboptimal approaches.

Interference minimization based power allocation for cognitive radio networks operating in TV white spaces

This paper investigates power allocation problems in OFDM-based cognitive radio (CR) networks operating in TV white space (TVWS). A new power allocation method is proposed to minimize the total interference introduced to the TV receivers while satisfying a minimum capacity threshold for secondary transmission. Performance of the proposed scheme is compared with other classical power loading methods such as water filling power allocation. The numerical results confirm that the proposed power allocation scheme achieves significant interference reduction compared to other power allocation methods.

RF interference to DVB-T reception from multiple LTE devices in adjacent bands

In this paper, we study the compatibility of operating multiple Long Term Evolution (LTE) mobile handheld devices in the digital dividend spectrum identified in Australia. European studies provide some valuable insights on the operation of mobile services in the digital dividend, the results however do not provide a direct comparison due to difference in the DVB-T transmission band plan, the DVB-T channel bandwidth and the preferred duplexing arrangement. The European studies also only take into consideration compatibility of operating single LTE handheld devices in adjacent bands. Thus our study is into the impact of multiple LTE transmission on the DVB-T reception in the boundary of the Australian digital dividend using Monte Carlo simulations.

Interference analysis in digital TV reception with LTE systems in adjacent bands in Australian context

Digital dividend spectrum, that is released after the digitalisation of analog TV broadcasting is harmonized internationally for the use of Long Term Evolution (LTE) technology. When LTE and digital television services operate in adjacent UHF bands, LTE transmitters can cause harmful interference to television reception. Thus in this paper, we study the compatibility of operating LTE services in the digital dividend spectrum identified in Australia based on the recently allocated band plan. We have used interference analysis method to calculate the minimum separation distance between LTE and DVB-T system and Monte Carlo Simulation for outage probability.