Nassar Ksairi

Resource Allocation for Downlink Cellular OFDMA Systems—Part I: Optimal Allocation

In this pair of papers (Part I and Part II in this issue), we investigate the issue of power control and subcarrier assignment in a sectorized two-cell downlink OFDMA system impaired by multicell interference. As recommended for WiMAX, we assume that the first part of the available bandwidth is likely to be reused by different base stations (and is thus subject to multicell interference) and that the second part of the bandwidth is shared in an orthogonal way between the different base stations (and is thus protected from multicell interference). Although the problem of multicell resource allocation is nonconvex in this scenario, we provide in Part I the general form of the global solution. In particular, the optimal resource allocation turns out to be ¿binary¿ in the sense that, except for at most one pivot-user in each cell, any user receives data either in the reused bandwidth or in the protected bandwidth, but not in both. The determination of the optimal resource allocation essentially reduces to the determination of the latter pivot-position.

Near-Optimal Resource Allocation for Type-II HARQ Based OFDMA Networks Under Rate and Power Constraints

We address the problem of multiuser power and bandwidth allocation for a general class of OFDMA-based wireless networks that employ a Type-II hybrid automatic repeat request (HARQ) mechanism along with practical modulation and coding schemes (MCSs). This problem is formulated as minimizing the sum transmit power required to satisfy individual goodput constraints without exceeding maximum allowable per-link or per-node transmit power levels. We assume that the resource manager has only statistical knowledge of the channel state information (CSI) of the Rayleigh-distributed fast-fading links of the network. Using a tight approximation of the goodput, we propose an algorithm allowing computation of the corresponding optimal resource allocation. We finally provide an efficient selection of the different MCSs that can be coupled with the proposed resource allocation algorithm to significantly boost its performance.

Optimal resource allocation for Type-II-HARQ-based OFDMA ad hoc networks

We address the problem of multiuser power and bandwidth allocation for a general class of OFDMA-based wireless networks that employ a Type-II Hybrid Automatic Repeat reQuest (HARQ) transmission scheme. We assume that the resource manager has only statistical knowledge of the Channel State Information (CSI) of the Rayleigh-distributed fast-fading links forming the network. We then propose the optimal algorithm minimizing the total transmit power required to satisfy per-user goodput constraints when practical Coding and modulation Schemes (MCSs) are carried out.

Performance Analysis over Slow Fading Channels of a Half-Duplex Single-Relay Protocol: Decode or Quantize and Forward

In this work, a static relaying protocol, called Decode or Quantize and Forward (DoQF), is introduced for half duplex single-relay networks, and its performance is studied in the context of communications over slow fading wireless channels. The proposed protocol is inspired by the so-called Compress-and-Forward (CF) but only needs statistical Channel State Information at the Transmitter (CSIT). First, we analyze the behavior of the outage probability Po of the proposed protocol as the SNR p tends to infinity. In this case, we prove that ρ2Po converges to a constant ξ. We refer to this constant as the outage probability gain and we derive its closed-form expression for a general class of wireless channels that includes Rayleigh and Rice. We furthermore prove that the DoQF protocol has the best achievable outage gain in the wide class of half-duplex static relaying protocols and we minimize ξ w.r.t the power allocation to the source and the relay and the durations of the slots. Next, we focus on Rayleigh channels to derive the Diversity-Multiplexing Tradeoff (DMT) of the DoQF. Our results show that the DoQF achieves the 2 by 1 MISO DMT upper-bound for multiplexing gains r <; 0.25.

Outage performance analysis and optimization of OFDM-based relaying protocols

This paper is dedicated to studying the outage performance of half-duplex relaying protocols that convey data over slow-fading multipath channels using OFDM transmission. It also addresses the optimization of these protocols i.e., time and power allocation, with respect to this outage performance. In the context of communications in slow-fading scenarios, the outage probability Po is the relevant information-theoretic performance metric. However, it is generally hard to derive the expression of Po for all possible values of the Signal to Noise Ration (SNR) ρ, even for flat-fading channels. This is why we focus on the high SNR regime. It is known that when a single relay operates in this regime over flat-fading channels, ρ2Po usually converges to a constant that has been referred to in the literature as the “outage gain”. In this paper, we extend this result to the case of frequency-selective channels having L independent channel taps in their discrete-time base-band equivalent model. We show that for these channels ρ2LPo converges to a non-zero outage gain ξ that provides crucial information about the behavior of the outage probability. We compute ξ for three different relaying schemes: the non-orthogonal Decode-and-Forward (DF), the Decode-or-Quantize-and-Forward (DoQF) and the Compress-and-Forward (CF). We next show that the DoQF outperforms in terms of outage gain the other two protocols over frequency-selective channels as well as in flat-fading scenarios. Finally, we numerically compute the optimal time and power allocation that minimizes the derived outage gain of the considered protocols.

Optimal reuse factor and resource allocation for downlink OFDMA with multicell interference

In this paper we investigate the issue of power control and subcarrier assignment in an OFDMA downlink system impaired by multicell interference. As done in Wimax, we assume that a certain part of the available bandwidth is likely to be reused by different base stations (and is thus subject to multicell interference) and that an other part of the bandwidth is used by one base station only (and is thus ldquoprotectedrdquo from multicell interference). Questions are: (i) how many subcarriers should be assigned to a given user in the interference bandwidth, and how many in the protected bandwidth ? (ii) What power should be allocated to a given user in each of these bands ? (iii) What is the optimal frequency reuse factor ?

Resource allocation for the downlink of OFDMA cellular networks and optimization of the reuse factor

In this paper, we investigate the issue of power control and sub-carrier assignment in a downlink OFDMA system. We assume that a certain part of the available bandwidth is likely to be reused by the different base stations (and is thus subject to multicell interference) and that the other part of the bandwidth is shared in an orthogonal way between them (and is thus protected from multicell interference). Although this problem of multicell resource allocation is non-convex, we provide, in the limit of large number of users, the general form of its global solution. As a byproduct, we characterize the optimal value of the frequency reuse factor.

Optimal Resource Allocation for Type-II HARQ Based OFDMA Ad Hoc Networks under Individual Rate and PER Constraints

We address the problem of multiuser power and bandwidth allocation for Orthogonal Frequency Division Multiple Access (OFDMA) networks employing a Type-II Hybrid Automatic Repeat reQuest (HARQ) mechanism, practical Coding and Modulation Schemes (MCSs) and Bit Interleaved Coded Modulation (BICM). The problem is formulated as minimizing the sum power required to satisfy a goodput constraint for each link while its post-HARQ Packet Error Rate (PER) does not exceed a certain threshold. Assuming statistical Channel State Information (CSI), we propose a computationally-efficient algorithm to compute the corresponding optimal resource allocation. We finally provide a practical selection of the MCSs that significantly boosts the performance of the proposed resource allocation algorithm.

Optimal resource allocation for type-II HARQ based OFDMA ad hoc networks under individual rate and power constraints

We address multiuser power and bandwidth allocation for Orthogonal Frequency Division Multiple Access (OFDMA) networks employing a Type-II Hybrid Automatic Repeat reQuest (HARQ) mechanism, practical Coding and Modulation Schemes (MCSs) and Bit Interleaved Coded Modulation (BICM). The problem is formulated as minimizing the sum power required to satisfy a goodput constraint for each link while its transmit power does not exceed a certain level. Assuming statistical Channel State Information (CSI), we propose an algorithm to compute the corresponding optimal resource allocation and a practical selection of the MCSs that significantly boosts the proposed algorithm.

On the Outage Probability Optimization in MISO Rician Channels

We address the optimization issue of the outage probability in Rician block fading channels with