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Mobile Internet applications run on devices such as smartphones and tablets, and have dramatically changed the landscape of applicationgenerated network traffic. The potent combination of millions of such applications and the instant accessibility of high-speed Internet on mobile devices through 3G and now LTE technology has also changed how users themselves interact with the Internet. Specifically, the radio states in LTE such as RRC_Connected and RRC_Idle were designed with more traditional applications such as web browsing and FTP in mind. These traditional applications typically generated traffic only during Active (Connected) state, and once the user session ended, usually the traffic ended too, thus allowing the radio to move to Inactive (Idle) state. However, newer applications such as Facebook and Twitter generate a constant stream of autonomous and/or user generated traffic at all times, thus erasing the previously clear demarcation between Active and Inactive states. This means a given mobile device (or user equipment, in LTE parlance) often ends up moving between Connected and Idle states frequently to send mostly short bursts of data, draining device battery and causing excessive signaling overhead in LTE networks. This problem has grown and attracted the research community's attention to address the negative effects of frequent back and forth transitions between LTE radio states. In this article, we first explore the traffic characteristics of these emerging mobile Internet applications and how they differ from more traditional applications. We investigate their impact on LTE device power and air interface signaling. We then present a survey of state-of-the-art solutions proposed in literature to address the problems, and analyze their merits and demerits. Lastly, we discuss the solutions adopted by 3GPP including the latest developments in Release 11 to handle these issues, and present potential future research directions in this field.

3GPP has started to investigate feasibility of a low cost machine type communication (LC-MTC) terminal class in LTE networks in Release 12 aiming to be competitive with that of GSM/GPRS terminals targeting the same low-end MTC market with improved coverage. LC-MTC devices are expected to have limited power source. Since LTE technology is relatively more power hungry compared to GSM/GPRS, device power efficiency is one of the crucial requirements for LC-MTC over LTE networks. In this paper, we focus on exploring mechanisms to reduce power consumption for LC-MTC in LTE networks. Most of the current LTE power saving mechanisms are designed and optimized for human-to-human (H2H) communications which are not attractive for LC-MTC as traffic characteristics and service requirements for LC-MTC are expected to be largely different than those of H2H Communications. LC-MTC usually has very infrequent and small traffic burst mostly in UL. Therefore, one possible solution to maximize the power saving is to maximize the time with LTE radio turned off in between the traffic bursts. In this paper, we analyze the impact of turning off LTE radio without moving LC-MTC into Radio Resource Control (RRC) Idle and reducing the RRC Connected tail time (i.e., RRC Inactivity Timer). Our results show that turning LTE radio off after data transmission can achieve upto 95.28% reduction in power consumption compared to that in case of moving device to RRC Idle. Reducing RRC Connected tail time further improves the device power saving.

Discontinuous reception (DRX) is supported in 3GPP Long Term Evolution (LTE) to reduce power consumption of user equipments (UEs). Power conservation achieved via DRX can be further increased with a packet scheduler that takes DRX states into consideration. Thus, in addition to quality of service (QoS) and fairness factors, which have been the main focus so far in scheduler design, energy efficiency must also be considered in scheduling. In this paper, we introduce a DRX and QoS-aware uplink packet scheduling algorithm (DQEPS) for LTE networks. One of the main reasons of poor DRX utilization is the continuous uplink packet traffic generated by applications working in the background. Accordingly, we first lay out the cumulative distribution functions (CDF) of interpacket arrival durations constructed by inspecting uplink packet transmission for various applications. Then, we form metrics for each bearer using these CDFs along with the DRX states, QoS parameters, channel conditions, and the buffer status of the bearers. Using these metrics, we develop a scheduling algorithm for the uplink, which aims to maximize power conservation of DRX mechanism by scheduling packets in a way that tries to minimize ON duration, while meeting the QoS requirements. Performance evaluations indicate that DQEPS reduces power consumption significantly compared to the previously proposed methods for LTE.

Machine to Machine (M2M) communication is expected to be a major driver of growth in mobile communications for cellular networks such as LTE. Since LTE networks are primarily designed and optimized for human to human (H2H) communications, existing protocols and mechanisms are not very efficient for supporting M2M communication. Several modifications are needed to address the service requirements and traffic characteristics of M2M devices in these networks. Device power efficiency is one of the crucial requirements for M2M communication. We focus on solutions to decrease power consumption of M2M devices over 4G networks. M2M traffic characteristics are different from those of H2H traffic in terms of the size and the frequency of the generated data. One possible mechanism is to maximize the time that the M2M device is in low power state. In this paper, we evaluate the impact of extending the Paging Cycle and reducing the RRC Connected-to-Idle transition tail time on power savings. Our results show that for infrequent data transmission extending Paging Cycle reduces power consumption up to 79.3%. However, for frequent data transmission reducing Connected-to-Idle transition tail time is more effective and reduces power consumption by up to 76.2%.

Small Cells are under extensive investigation as a potential solution to meet the increasing capacity demand due to ever growing data traffic over cellular networks. The architecture of small cells is still under discussion, various architectures have been proposed based on potential use cases. One of the most important use cases is to deploy small cells on a different frequency than that of the macro cell to offload traffic. Small cell discovery in this type of inter-frequency scenario is an open research problem. Aggressive scanning mechanisms may result in faster discovery of small cells and higher user throughput as well as higher macro cell capacity due to potentially increased offloading opportunity. However, frequent scanning may also result in higher power consumption for the device. Therefore, a tradeoff between offloading opportunity and device power consumption seems inevitable in practice. In this paper, we analyze the trade-off between the offloading capacity and device power consumption due to inter-frequency scanning mechanism for small cell discovery. Our findings show that although increasing the frequency of inter-frequency scanning does result in increased power consumption due to scanning, it actually lowers the total power consumed by the device since it leads to offloading to small cells, where the device consumes less overall power due to better coverage.

Access overload and signaling congestion are serious issues in machine-to-machine (M2M) networks. These issues can be caused by (i) external events triggering a large number of M2M devices to connect or disconnect all at once, (ii) recurring application events that are synchronized to the exact time (e.g., hour), and (iii) malfunctioning of M2M application or server. It is vital to control access overload and signaling congestion in order to prevent the network from a complete collapse. This paper investigates a few mechanisms to prevent this issue.

Discontinuous reception (DRX) brings power saving at user equipment (UE) at the cost of increased delay in 3GPP long term evolution (LTE) network. While configuring DRX parameters, a tradeoff between power saving and delay is inevitable in practice. For example, delay is crucial factor for delay sensitive applications such as online gaming, while power saving becomes the main concern for social networking applications. In this paper, we propose an algorithm to efficiently select DRX parameters to ensure a balanced tradeoff between these two conflicting performance parameters depending on application's delay requirement and UE power constraint. The proposed scheme is capable of optimizing one of these performance parameters while satisfying a specified level of guarantee for the other. Simulation results show that proposed algorithm is able to increase the power saving significantly by efficiently selecting the DRX parameters. For example, smart selection of DRX cycle for given inactivity timer increases the power saving by more than 40% depending on the delay requirement. Simulation results further show that proposed algorithm provides higher flexibility in DRX parameter selection by allowing a DRX parameter to be relaxed with the adjustment in other DRX parameter without any performance degradation.

The explosive number of applications now available on smart phone type of devices and the availability of high-speed mobile broadband connectivity through 4G networks such as LTE has only increased the challenges in improving battery life of these devices. In this paper, we illustrate the 4G power consumption issues through traffic traces and power measurements on LTE device over commercial LTE network. We analyzed the traces of various applications to understand the traffic characteristics. We also measured the power consumption of the various components of the device. This paper provides the cdf's of the packet size and packet inter-arrival times of background traffic of common applications (e.g., Skype, Google Talk, Twitter etc), and power consumption values and duration of low-power states which are crucial for the innovations and implementation of efficient power optimization mechanisms in LTE networks.

While the demand for battery capacity on mobile devices has grown with the increase in high-bandwidth multi-media rich applications, battery technology has not kept up with this demand. Therefore power optimization techniques are becoming increasingly important in wireless system design. Power optimization schemes are also important for interference management in wireless systems as interference resulting from aggressive spectral reuse and high power transmission severely limits system performance. Although power optimization plays a pivotal role in both interference management and energy utilization, little research addresses their joint interaction. In this paper, we develop energy-efficient power optimization schemes for interference-limited communications. Both circuit and transmit powers are considered and energy efficiency is emphasized over throughput. We note that the general power optimization problem in the presence of interference is intractable even when ideal user cooperation is assumed. We first study this problem for a simple two-user network with ideal user cooperation and then develop a practical non-cooperative power optimization scheme. Simulation results show that the proposed scheme improves not only energy efficiency but also spectral efficiency in an interference-limited cellular network.

Hop adaptive MAC-PDU (Protocol Data Unit) size optimization is proposed for Orthogonal Frequency Division Multiple Access (OFDMA) based wireless relay networks. Such optimization improves the end-to- end goodput via MAC-PDU size optimization. We provide design and evaluation for two hop cellular networks with fixed relays where the Base Station (BS) to Relay Station (RS) links are potentially robust and are Line of Sight (LOS). The proposal reduces the total overhead transmitted in the end-to-end path via transmitting longer length packets in the potentially robust BS-to-RS links. The link level simulations show that, the reductions in overhead that consists of header and tailer is 25% to 44%. The system level investigations in a multi-user environment with a total of 3 relays in the cell show an average end-to-end goodput gain of 13%.

Space-time trellis and space-time block codes harness the effects of spatial diversity by taking advantage of multiple independently fading transmit and receive antenna paths between the transmitter and receiver. In this paper, we present experimental studies primarily on the performance of four transmit antenna space-time block codes which, although promising in simulations, need to be investigated in real-world wireless channels. Simulations often inaccurately model the wireless channel impulse response and other impairments such as interference, signal fading, multipath, phase noise, etc. Experimental results reveal an improvement in reliability by use of space-time block codes as predicted in simulations. However, the theoretical diversity gains promised in the simulations cannot be fully realized because of what is believed to be interference generated by other RF sources on the same 2.4GHz WLAN band on which the experiments were conducted

The spatial channel models for antenna array communication systems have led to many theories of exploiting spatial diversity in wireless communications and more recently to space-time coding. For example, original space-time coding methods exploit a model that characterizes the spatial channel coefficients independent. Here we propose a space-time coding method that exploits a spatial channel model, which is based on the concentration of multipath signals or the direction of arrival (DOA). While we present this method for two dominant DOA channels, it can be easily extended for channels with more dominant DOAs. As with the original space-time coding methods, the proposed method does not require feedback from receiver to transmitter.