Uplink

A low complexity user scheduling algorithm based on a novel adaptive Markov chain Monte Carlo (AMCMC) method is proposed to achieve the maximal sum capacity in an uplink multiple-input multiple-output (MIMO) multiuser system. Compared with the existing scheduling algorithms, our algorithm is not only more efficient but also converges to within 99% of the optimal capacity obtained by exhaustive search.

Massive multiple-input multiple-output (MIMO) promises improved spectral efficiency, coverage, and range, compared to conventional (small-scale) MIMO wireless systems. Unfortunately, these benefits come at the cost of significantly increased computational complexity, especially for systems with realistic antenna configurations. To reduce the complexity of data detection (in the uplink) and precoding (in the downlink) in massive MIMO systems, we propose to use conjugate gradient (CG) methods. While precoding using CG is rather straightforward, soft-output minimum mean-square error (MMSE) detection requires the computation of the post-equalization signal-to-interference-and-noise-ratio (SINR). To enable CG for soft-output detection, we propose a novel way of computing the SINR directly within the CG algorithm at low complexity. We investigate the performance/complexity trade-offs associated with CG-based soft-output detection and precoding, and we compare it to exact and approximate methods. Our results reveal that the proposed method outperforms existing algorithms for massive MIMO systems with realistic antenna configurations.

Cognitive radio (CR) has been considered a key technology to enhance overall spectrum utilization by opportunistic transmissions in CR transmitter-receiver link(s). However, CRs must form a cognitive radio network (CRN) so that the messages can be forwarded from source to destination, on top of a number of opportunistic links from co-existing multi-radio systems. Unfortunately, appropriate routing in CRN of coexisting

Relay enhanced networks are expected to fulfill the demanding coverage and capacity requirements in a cost-efficient way. Type 1 inband relaying is now being standardized as an integral part of 3GPP LTE-Advanced. This type of relay nodes supports a relaying mode where the relay link transmission is time-division multiplexed with the access link transmission, whereas macro users share the same resources with the relays. Hence, system performance depends strongly on the resource sharing strategy among and within the links. Besides, in order to fully exploit the benefits of relaying, the inter-cell interference, which is increased due to the presence of relay nodes, should be limited via a proper power control scheme on each link. Therefore, an optimization of both the resource sharing and power control strategy is required to enhance the overall performance of relay networks. In this paper, performance evaluation of two-step resource sharing and power control optimization is carried out within the LTE-Advanced uplink framework in urban and suburban scenarios. Furthermore, we propose a combination of scheduling based on the number of relay-served users and throughput throttling achieving max-min fairness. Results show that the proposed scheme achieves significant throughput gains and high system fairness.

In this paper, we present NB-TRACE, which is an energy-efficient network-wide voice broadcasting architecture for mobile ad hoc networks. In the NB-TRACE architecture, the network is organized into overlapping clusters through a distributed algorithm, where the clusterheads create a nonconnected dominating set. Channel access is regulated through a distributed TDMA scheme maintained by the clusterheads. The first group of packets of a broadcast session is broadcast through flooding, where each data rebroadcast is preceded by an acknowledgment to the upstream node. Nodes that do not get an acknowledgment for a predetermined time, except the clusterheads, cease to rebroadcast, which prunes the redundant retransmissions. The connected dominating set formed through this basic algorithm is broken in time due to node mobility. The network responds to the broken links through multiple mechanisms to ensure the maintenance of the connected dominating set. We compare NB-TRACE with four network layer broadcast routing algorithms (flooding, gossiping, counter-based broadcasting, and distance-based broadcasting) and three medium access control protocols (IEEE 802.11, SMAC, and MH-TRACE) through extensive ns-2 simulations. Our results show that NB-TRACE outperforms other network/MAC layer combinations in minimizing energy dissipation and optimizing spatial reuse, while producing competitive QoS performance