Mylene Pischella

Power control in distributed cooperative OFDMA cellular networks

This paper addresses downlink cooperation at a system level. Cooperation between base stations is an alternative to macrodiversity to provide QoS continuity in case of mobility. We propose a radio resource management strategy for the relay channel, made of relayed users identification, resource allocation and power control in an OFDMA-based system. Four scheduling methods are tested for power allocation in inter-cell interference environment: globally optimal, proportional fair, harmonic mean fair and max-min fair. Cooperation brings additional gain, both in terms of throughput and fairness, with all fair schedulers.

Optimal Power Allocation for the Two-Way Relay Channel with Data Rate Fairness

This letter studies data rate fairness on the two-way relay channel. It analytically determines the optimal power values at both nodes and at the relay, that lead to a maximization of the sum rate under the fairness constraint. Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying protocols are considered. For AF, the optimization problem is turned into a single-variable convex optimization problem. For DF, rate balancing between Multiple Access and broadcast phases must be performed prior to setting nodes powers. Both optimized protocols are compared with reference AF and DF in terms of data rates through numerical simulations.

Resource Allocation for QoS-Aware OFDMA Using Distributed Network Coordination

This paper considers resource allocation for downlink orthogonal frequency-division multiple access (OFDMA). We propose a subcarrier and power-allocation method that differentiates users per service type to fulfill the quality-of-service (QoS) requirements of each user. Network coordination improves the performance of users at the border of the cells and, thus, decreases the minimum sum power for users with guaranteed performance (GP). Best effort (BE) users are then scheduled to maximize their sum capacity. The proposed method only assumes causal coordination between base stations and can be seen as a generalized macro diversity scheme suited for distributed networks. Numerical results show that network coordination increases the ratio of satisfied GP users, as well as the average data rate of BE users.

Green Opportunistic and Efficient Resource Block Allocation Algorithm for LTE Uplink Networks

This work proposes a new radio resource allocation scheme for the green uplink Long-Term Evolution (LTE) networks. The proposed scheme aims at efficiently allocating the resource blocks (RBs) and the transmission power of the user equipment (UE). The allocation of RBs is based on the opportunistic and efficient RB allocation (OEA) algorithm, whose objective is to maximize the aggregate throughput while being subjected to single-carrier frequency-division multiple-access (SC-FDMA) constraints. An evolution of the algorithm, which is called quality-of-service (QoS)-based OEA, providing QoS differentiation, is also presented. It allocates a given maximum number of RBs to each UE, which is set according to the users QoS requirements. Once the allocation of RBs is completed, the allocation of the UE transmission power is performed. The transmission power considers the UE channel conditions over its whole allocated RBs. Its value is reduced as much as possible and adjusted such that the users required QoS satisfies throughput demand previously determined by the RB allocation. The proposed radio resource management algorithm has several interesting properties. It maximizes the aggregate throughput, decreases the ratio of inefficiently allocated RBs, cancels the RBs wastage, and increases the energy efficiency without affecting the users throughput. Furthermore, the OEA algorithms can be implemented in LTE hardware equipment devices on account of their low computational complexity.

Achieving a Frequency Reuse Factor of 1 in OFDMA Cellular Networks with Cooperative Communications

This paper addresses inter-cell interference mitigation techniques in OFDMA cellular networks. It compares the performance results obtained with partial frequency reuse in the outer cell and with a proposed cooperative scheme based on relaying of the users in the outer cell. The proposed scheme uses cooperative diversity via a relaying protocol between the source base station and the closest base station, therefore reducing inter-cell interference. Subcarrier and power allocation can be implemented in a distributed way in each base station. Numerical results show that the same average inter-cell interference is achieved with cooperation as with a frequency reuse factor of 3, whereas cooperation leads to a lower rejection probability and higher sum throughput at medium to high load.

Optimal Power Allocation for Downlink Cooperative Cellular Networks

In cellular networks, base stations can cooperate in order to bring spatial diversity. Cooperative diversity enables to increase link capacity and signal to noise ratio. This paper presents source and relay base stations optimal power allocation in order to maximize the sum capacity over all relayed links. Average power allocation is solved by an iterative method which allocates relay and source powers separately, by convex optimization. Then source symbol powers are set with simple water-filling, in order to maximize the capacity. Simulation results show that sum capacity is highly increased by relaying under optimal power values. Relaying is especially efficient for user terminals who would have poor radio conditions without relaying. The paper also presents a simple method, based on path loss characterization, to determine the need for relaying. It can be used independently in the source base stations, which is particularly adapted for flat architectures.

Adaptive resource allocation and decoding strategy for underlay multi-carrier cooperative cognitive radio systems

This paper proposes a resource allocation and decoding strategy at the secondary system for underlay and interweave multi-carrier cooperative cognitive radio. The objective is to maximise the sum rate of both primary and secondary systems, taking into account the interference threshold constraint and the fact that the primary receiver always considers interference as noise. The decoding method at the secondary receivers is either Successive Interference Cancellation or treating interference as noise, depending on their channel gains. The rationale for this strategy is the extension of the Han–Kobayashi capacity-achieving strategy on the Gaussian interference channel to the studied cognitive scenario. The proposed resource allocation algorithm is composed of a subcarrier allocation procedure to avoid intercell interference between secondary cells and of an iterative power allocation algorithm that maximises the sum rate on the primary and secondary cells, respectively. The proposed algorithm achieves high data rate improvements for the secondary systems while maintaining a low degradation on the primary systems rate. It also benefits from multi-user diversity and is robust to the distance variations. Copyright

Distributed weighted sum throughput maximization in multi-cell wireless networks

This paper addresses the weighted sum throughput maximization problem on the interference channel. It proposes a sub-optimal algorithm that enables to perform a distributed power allocation, which performs well at any SINR regime. The sub-optimal method consists of two phases: first, identify the links that should be set to zero, and then, operate in the high SINR regime for the remaining links. In the single channel case, this simple, fully distributed algorithm is shown to perform almost as well as the centralized optimal algorithm. In the multi-channel case, the algorithm is more efficient than iterative water-filling in order to decrease the buffer size.

Comparison of distributed space and frequency interference alignment

This paper addresses multiple access in MIMO wireless networks. It compares two distributed interference alignment techniques, in space and in frequency, that both aim at removing interferences through orthogonalization. The theoretical advantages and drawbacks of each technique are highlighted. Then, the multiplexing gain and the computational complexity are analytically evaluated. It is shown that frequency interference alignment achieves a higher multiplexing gain than space interference alignment in realistic network conditions, and always requires a lower computational complexity. Finally, the performances of both algorithms with varying number of interfering links are assessed via numerical simulations. Space interference alignment fulfills complete interference suppression, and consequently provides the same spectral efficiency to all links, regardless of the number of interfering links. Frequency interference alignment is less efficient in terms of INR, and the spectral efficiency per link thus decreases when the number of links increases. Nevertheless, the spectral efficiency is always higher with frequency interference alignment than with space interference alignment.

Resource Block-Level Power Allocation in Asynchronous Multi-Carrier D2D Communications

This letter focuses on weighted sum rate maximization with filter bank multi-carrier (FBMC) and orthogonal frequency division multiplex (OFDM) multi-carrier modulations for asynchronous device-to-device (D2D) communications. The main difficulty in power allocation with asynchronous multi-carrier transmissions is that inter-channel interference (ICI) depends on subcarriers, whereas power values should be optimized with resource block (RB) granularity. In this letter, we show that the weighted sum rate maximization problem can be solved at RB level, while still considering ICI, and that the power allocation algorithm solving this problem is distributed and leads to its global optimum. Moreover, FBMC achieves higher data rates than OFDM, thanks to its lower ICI spread.