In this paper, we evaluate the downlink performance of Transparent mode (T-mode) and Non-Transparent mode (NT-mode) in a two-hop cellular system based on IEEE 802.16j. In particular, we evaluate the performance in terms of the system capacity, optimal resource allocation, and outage probability using Monte Carlo simulation with various system parameters such as different Frequency Reuse Factors (FRFs) and the distance between Base Station (BS) and Relay Station (RS). To analyze the Signal to Interference and Noise Ratio (SINR) of the access and relay links, an SINR model is introduced for cellular multihop systems considering intra- and inter-cell interferences. Then, we present a method of optimal resource allocation for the Access Zone (AZ) and Relay Zone (RZ) to maximize the system capacity. Consequently, the simulation results provide an insight into choosing the appropriate RS position and optimal resource allocation. Through numerical examples, it is found that the FRFs of two and three are good choices to achieve the highest capacity with low outage in T- and NT-modes, respectively.

This letter proposes a wakeup-on-demand scheme based on the idea that a device should be awakened just when it has to receive a packet from a neighboring device. To prove this scheme, this letter proposes a mathematical model based on the busy cycle of M/G/1 queuing systems to obtain a battery lifetime of one-hop cluster-topology shaped W-WSN.

In dense femtocell networks (DFNs), one of the main issues is interference management since interference between femtocell access points (FAPs) reduces the system performance significantly. Further, FAPs serve different numbers of femtocell user equipments (FUEs), i.e., some FAPs have more than one FUE while others have one or no FUEs. Therefore, for DFNs, an intelligent channel assignment scheme is necessary considering both the number of FUEs connected to the same FAPs and interference mitigation to improve system performance. This paper proposes a two-stage dynamic channel assignment (TS-DCA) scheme for downlink DFNs based on orthogonal frequency division multiple access/frequency division duplex (OFDMA/FDD). In stage 1, using graph coloring algorithm, a femtocell gateway (FGW) first groups FUEs based on an interference graph that considers different numbers of FUEs per FAP. Then, in stage 2, the FGW dynamically assigns subchannels to FUE clusters according to the order of maximum capacity of FAP clusters. In addition, FAPs adaptively assign remaining subchannels in FUE clusters to their FUEs in other FUE clusters. Through simulations, we first find optimum parameters of the FUE clustering to maximize the system capacity and then evaluate system performance in terms of the mean FUE capacity, unsatisfied FUE probability, and mean FAP transmission energy consumption according to the different numbers of FUEs and FAPs with a given FUE traffic load.

In this letter, we propose a novel resource allocation scheme to enhance downlink system performance for orthogonal frequency division multiple access (OFDMA) and time division duplex (TDD) based femtocell networks. In the proposed scheme, the macro base station (mBS) and femto base stations (fBSs) service macro user equipments (mUEs) and femto user equipments (fUEs) in inner and outer zones in different periods to reduce interference substantially. Simulations show the proposed scheme outperforms femtocell networks with fractional frequency reuse (FFR) systems in terms of the system capacity and outage probability for mUEs and fUEs.

We present an adaptive power saving (APS) scheme to reduce downlink energy consumption of the transmit power in the cellular relay network (CRN). In the APS scheme, some cell topologies operating in 2-hop mode using relay stations (RSs) are converted to that of 3-hop mode and others are simultaneously converted to that of single-hop mode when the offered traffic load becomes very low, especially during night periods. By this means, we show the APS scheme outperforms the conventional CRN (CCRN) scheme in terms of energy consumption.

In this letter, we propose and analyze a cooperative transmission scheme (CTS) that uses transmission timing control for LTE enterprise femtocells. In our scheme, the user equipment (UE) can receive the desired signal from an adjacent fBS as well as its serving femtocell BS (fBS). Thus, UE achieves an improved signal to interference ratio (SIR) due to the synchronization of the two signals. Analysis and simulation results show that the proposed scheme can reduce the outage probability for enterprise femtocells compared to the conventional system. In particular, a significant performance improvement can be achieved for UEs located at cell edges.