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The popularity of handheld devices, which are usually powered by batteries, has made power saving an important and practical issue in recent years. Techniques of power saving for user devices using mobile communication systems such as WiMAX and LTE (Long-Term Evolution) are parts of the major focuses in the literature. In this paper, two revised schemes of the authors' previously proposed power saving schemes for IEEE 802.16 are proposed to be applied in LTE. The proposed schemes, namely LTE-LBPS-Aggr and LTE-LBPS-Merge, estimate the input load by traffic measurement and the channel capacity by channel quality indicator (CQI) reports, calculate the length of the sleep cycle, and notify related user equipments (UEs) of the next radio-on time for receiving data. The difference between LTE-LBPS-Aggr and LTE-LBPS-Merge lies in the grouping of UEs for sleep scheduling. LTE-LBPS-Aggr treats all UEs in a group, while LTE-LBPS-Merge allows multiple groups of UEs in sleep scheduling. The simulation study shows that in comparison with standard-based mechanisms, the proposed schemes can achieve better power saving efficiency at the cost of moderate increase on delays and the signaling overhead.

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By introduction of relay nodes, LTE-Advanced can provide enhanced coverage and capacity at cell edges and hot-spot areas. The authors have been researching the issue of power saving in mobile communications technology such as WiMax and Long Term Evolution (LTE) for some years. Based on the previous idea of load-based power saving, two strategies each with associated schemes to integrated relay nodes and user equipment in power saving are proposed in the paper. Simulation study shows the benefit of the proposed schemes in terms of better power saving than the standard-based scheme at the cost of moderately increased delay. Extended discussion about the impact of different load distribution among user equipments and the impact of a worse backhaul link on power saving is also presented in the paper.

Long-Term Evolution (LTE) is a 4G wireless broadband technology developed bythe Third Generation Partnership Project. Two duplex modes, namely, frequency division duplex and time division duplex (TDD), are defined in LTE for transmission in both downlink and uplink directions simultaneously. Power saving mechanisms for LTE-frequency division duplex were proposed in the authors' previous work. Applicability of the previously proposed mechanisms to LTE-TDD is investigated in this paper, and the idea of "virtual time" associated with the mapping mechanism from the virtual time domain to the actual time domain for different TDD configurations is proposed. With the help of the mapping mechanism, 3 revised power saving schemes are proposed to support real-time user equipments and nonreal-time user equipments in LTE-TDD. Simulation study demonstrates the effectiveness of the mapping mechanism as well as the benefit of the proposed schemes in power saving efficiency and real-time support in comparing with the standard-based mechanism.

LTE-Advanced (LTE-A) offloading is concerned about alleviating traffic congestion for the LTE-A network, which includes the core network and the radio access network (RAN). Due to the scarcity of the radio resource, offloading for the LTE-A RAN is more critical, for which an efficient way is to integrate Wi-Fi with LTE-A to form a heterogeneous RAN environment. An LTE-A UE (User Equipment) with the wi-fi interface can therefore access the Internet via an LTE-A base station of Evolved Node B (eNB) or a wi-fi Access Point (AP). In this paper, wireless network selection for UEs with delay-sensitive traffic in the heterogeneous RAN of LTE-A and wi-fi is addressed. Based on the queueing model of M/G/1, a novel network selection and offloading scheme, namely Delay-Sensitive Network Selection and Offloading (DSO), is proposed. The average system time at LTE-A eNBs and wi-fi APs calculated according to M/G/1 is used for network selection as well as offloading operations in DSO. The benefit of DSO in terms of satisfying the delay budget of UEs and load balancing is demonstrated by the simulation study.

Energy-saving for the LTE-A network with relay nodes in TDD mode is addressed in this paper, and integrated sleep scheduling schemes for relay nodes and user devices under a base station are designed. The authors' two previously proposed ideas, namely, Load-Based Power Saving (LBPS) and Virtual Time, are adopted in the design, and two strategies, namely, top-down and bottom-up each with three LBPS schemes are proposed. In the top-down strategy, the load as well as the channel quality on the backhaul link is first considered to determine the sleep pattern for all relay nodes, and then the sleep schedule for UEs under each relay node is determined accordingly. On the contrary, the load and the channel quality on the access links are first considered and then integrated into the sleep schedule on the backhaul link. Two associated mechanisms for the proposed LBPS schemes to operate in the virtual time domain are also proposed in the paper, i.e., calculation of the virtual subframe capacity and the mapping mechanisms from the virtual time to the actual time. The benefit of the proposed schemes in power saving over the standard-based scheme is demonstrated by the simulation study, and the bottom-up scheme of BU-Split outperforms the other schemes under equally distributed input load as well as the hotspot scenario. Discussion on the tradeoff of the processing overhead and the performance for the proposed schemes is presented in the paper.

In our previous work, the limitation of standard type I and II power saving in IEEE 802.16e was discussed, and the idea of load-based power saving (LBPS) was proposed for better power-saving efficiency. LBPS measures traffic load and adaptively generates proper sleep schedule for the current load. Three LBPS schemes have been proposed for mobile subscriber station (MSS) power saving. In this paper, base station (BS) power saving is taken into consideration, and our previously proposed LBPS schemes, are extended and revised to integrate both BS and MSS in sleep scheduling. Two strategies of integrated power saving, MSS first and BS first, each with associated LBPS schemes are proposed in the paper. A three-staged concept combining the proposed strategies is also presented to make the best of integrated power saving. A simulation study shows that the proposed schemes can effectively achieve high power-saving efficiency for both BS and MSS.