Opportunities and Challenges in OFDMA-Based Cellular Relay Networks: A Radio Resource Management Perspective

The opportunities and flexibility in relay networks and orthogonal frequency-division multiple access (OFDMA) make the combination a suitable candidate network and air-interface technology for providing reliable and ubiquitous high-data-r

Fairness-Adaptive Goodput-Based Resource Allocation in OFDMA Downlink with ARQ

We present a cross-layer resource-allocation (RA) scheme for the downlink in orthogonal frequency-division multiple-access (OFDMA) systems with fairness control among the users, where the resources to be allocated are power, bits per symbol, and subchannels. The use of subchannels, which are defined as group of subcarriers, leads to reducing the complexity of the bandwidth allocation compared with the commonly adopted subcarrier allocation. A goodput-based optimization function, which is derived by combining automatic repeat request (ARQ) and physical (PHY)-layer parameters, is used to perform RA for applications that demand error-free transmissions. Two transmission strategies are considered, with and without concatenation of subchannels, for which two different RA methods are developed, respectively. We also propose an algorithm that improves the complexity associated to both concatenation and nonconcatenation schemes, without appreciable performance loss.The work was supported by the GRE3N Project under Grant TEC2011-29006-C03-03.Publicad

Throughput analysis in wideband MIMO broadcast channels with partial feedback

It has been recently shown that opportunistic transmit beamforming using partial channel state information (CSI) achieves the same throughput scaling obtained from dirty paper coding for a broadcast channel with fixed number of transmit antennas and many receivers M. Sharif et al., (2005). In this paper, we study the generalization of this scheme to wideband broadcast channels. By using orthogonal frequency division multiplexing, an L-tap wideband channel can be decomposed to N parallel narrowband channels, where N is larger than L. Neighboring subchannels are therefore highly correlated, and it is intuitive to say that each group of neighboring subchannels (forming a cluster) can be characterized by one channel quality. We show in this paper that users need only feedback the best signal-to-noise-plus-interference ratio at the center of each cluster. Our results indicate that for cluster size of order ^N/_(L√(log K)), where K is the number of users, this feedback scheme maintains the same throughput scaling as when full CSI is known. Simulation results show that larger cluster sizes (N/(2L)) can also be implemented for a small throughput hit

Resource management in QoS-aware wireless cellular networks

2011 Summer.Includes bibliographical references.Emerging broadband wireless networks that support high speed packet data with heterogeneous quality of service (QoS) requirements demand more flexible and efficient use of the scarce spectral resource. Opportunistic scheduling exploits the time-varying, location-dependent channel conditions to achieve multiuser diversity. In this work, we study two types of resource allocation problems in QoS-aware wireless cellular networks. First, we develop a rigorous framework to study opportunistic scheduling in multiuser OFDM systems. We derive optimal opportunistic scheduling policies under three common QoS/fairness constraints for multiuser OFDM systems--temporal fairness, utilitarian fairness, and minimum-performance guarantees. To implement these optimal policies efficiently, we provide a modified Hungarian algorithm and a simple suboptimal algorithm. We then propose a generalized opportunistic scheduling framework that incorporates multiple mixed QoS/fairness constraints, including providing both lower and upper bound constraints. Next, taking input queues and channel memory into consideration, we reformulate the transmission scheduling problem as a new class of Markov decision processes (MDPs) with fairness constraints. We investigate the throughput maximization and the delay minimization problems in this context. We study two categories of fairness constraints, namely temporal fairness and utilitarian fairness. We consider two criteria: infinite horizon expected total discounted reward and expected average reward. We derive and prove explicit dynamic programming equations for the above constrained MDPs, and characterize optimal scheduling policies based on those equations. An attractive feature of our proposed schemes is that they can easily be extended to fit different objective functions and other fairness measures. Although we only focus on uplink scheduling, the scheme is equally applicable to the downlink case. Furthermore, we develop an efficient approximation method--temporal fair rollout--to reduce the computational cost