IEEE 802.11ah and Bluetooth Low Energy (BLE) are candidates to become key technologies for many Internet of Things (IoT) applications. In this paper, 802.11ah and BLE technologies are evaluated and compared in a home automation scenario. The selected use case includes battery powered sensors, which generate traffic, and mains powered actuators, which consume traffic, connected through a central gateway. The performance is assessed in terms of service ratio, delay and activity factor of the transceivers. Results show that both technologies are suitable for the reference use case scenario. 802.11ah benefits from a higher throughput and lower delay jitter, whereas BLE sensors show lower activity factors and a longer battery lifetime is expected. The analysis is conducted for both fixed and variable traffic load. The performance of BLE results to be more sensitive to an increase of the traffic load with respect to 802.11ah. Eventually, the limitations of the current scenario are illustrated and alternative setups are discussed.

A key reference signal in 3GPP Long Term Evolution (LTE) Release 8 is the cell specific reference signal (CRS). For example, the LTE transmission mode 4 (TM4) uses the CRSs to derive the channel and the interference estimates, utilized in the demodulation process and for acquisition of channel state information (CSI). LTE networks may further operate using different CRS configurations. In a non-shifted CRS configuration the same time and frequency resources are used for CRS transmissions in all cells. In a shifted CRS configuration different cells transmit CRSs on resources that are shifted in frequency. The non-shifted configuration avoids that the CRSs interfere with data transmissions, but is also associated with a systematic CSI estimation error; especially noticeable at low traffic. Using the shifted configuration the CRSs interfere with data transmissions but the CSI estimation error is smaller. In this paper, the LTE downlink performance is evaluated in a heterogeneous network deployment using shifted and non-shifted CRS configurations. The network operation is optimized by means of adjusting the transmission rank selection and channel quality estimation for each CRS configuration. The results demonstrate that under such operational conditions, a non-shifted CRS configuration delivers the highest performance.

This paper focuses on energy saving techniques for LTE, and what overall energy savings they can achieve. The considered techniques are adaptive base station hardware, cell DTX, antenna muting, and adaptive sectorization. The paper discusses how these can be integrated and jointly save energy, and evaluates the energy savings as well as the quality of service impact by means of extensive system level evaluations of a radio access network. The system level simulations, which are carried out over 24 hours in a country-wide LTE network, indicate that these techniques together can provide energy savings in the order of 75% with only minor impact on quality of service.

The concept of antenna muting for reducing energy consumption in LTE is presented and system level evaluation results are provided. The results indicate that antenna muting can reduce the energy consumption with up to around 50% in a low load scenario without significantly affecting the user throughput. Results for 4TX, 2TX, and 1TX cell configurations are presented. The system level simulator used includes detailed models of UE pre-coder selection and feedback and we show in this paper that these algorithms performs well also when antennas are muted in a way that was not considered during the design of the algorithms. Antenna muting is a promising technique that operates on a rather short time scale in order to reduce the energy consumption of an LTE cell.

In order to quantify the energy savings in wireless networks, the power consumption of the entire system needs to be captured and an appropriate energy efficiency evaluation framework must be defined. In this paper, the necessary enhancements over existing performance evaluation frameworks are discussed, such that the energy efficiency of the entire network comprising component, node and network level contributions can be quantified. The most important addendums over existing frameworks include a sophisticated power model for various base station (BS) types, which maps the RF output power radiated at the antenna elements to the total supply power of a BS site. We also consider an approach to quantify the energy efficiency of large geographical areas by using the existing small scale deployment models along with long term traffic models. Finally, the proposed evaluation framework is applied to quantify the energy efficiency of the downlink of a 3GPP LTE radio access network.

In this paper, we consider the problem of joint adaptive beamforming from multiple Access Points (APs), equipped with array antennas, to multiple single-antenna User Equipments (UEs). We derive an iterative algorithm for Multi-Cell Beam-Forming (MCBF) under per-cell power constraints and the constraint that a UE may receive data transmission from a single AP. The scheme is suitable for coordinated beamforming downlink transmission in a Coordinated Multi-Point (CoMP) cellular network. Simulation results indicate that as compared to uncoordinated transmission by means of a Grid of Beams (GoB) based Space Division Multiple Access (SDMA) scheme, MCBF offers much higher throughput for cell-edge UEs. For a single cluster of nine sectorized cells with four-element antenna arrays in an urban macro-cellular environment, MCBF obtains a 13 fold increase in 5 percentile user throughput at 2 bits/s/Hz/sector cell throughput as compared to GoB-SDMA.

The test environments for system level evaluations of IMT-A (International Mobile Telecommunications-Advanced) candidate technologies are analyzed. Compared to the evaluation criteria for previous IMT standards, the IMT-A test environments provide significantly more realistic settings for evaluating system-level performance. The models include line-of-sight probability in all scenarios, different groups of users in terms of propagation and speed, as well as indoor and outdoor deployments. This contribution scrutinizes the evaluation conditions and presents resulting performance for a basic Long-Term Evolution (LTE) candidate system. Each environment contains challenging characteristics. Examples include a mix of indoor and outdoor users, a mix of line-of-sight and non-line-of-sight conditions, and terminal speeds making accurate tracking of channel quality difficult. Together, these characteristics suggest that a radio transmission technology fulfilling the ITU IMT-A requirements is well suited for meeting a variety of challenges of real deployment scenarios.

Future cellular networks are expected to provide significantly higher capacity than today's systems. To support this higher capacity a denser deployment might be necessary. An alternative way is to deploy Multiple-Input-Multiple-Output (MIMO) base stations (BSs), called advanced BSs, so that the system capacity is improved without increasing the BSs density. This paper compares Single-Input-Single-Output (SISO) BS deployments with MIMO BS deployments from a cost perspective. We use a deployment methodology starting with a sparse density of BSs. By deploying additional BSs sequentially the number of BSs is increased until the traffic demand in the network area is supported. Providing equal service level, i.e., supporting the same traffic demand, by means of different deployment realizations enables a relevant comparison between the alternative single and multiple antenna systems. With the models and assumptions used here, results show that in order to support the same users' service level, the cost of deploying MIMO BSs is significantly less compared to increasing the density of SISO BSs. The cost gain is due to the reducing of the number of required BSs for the case of MIMO deployment.

Recently, several works have pointed out the negative impact of intercell interference variation on the performance of link adaptation in multi-cell single input single output (SISO) systems. However, the performance of adaptive precoder selection in multiple input multiple output (MIMO) cellular networks in the presence of interference variation is much less understood. In this paper we develop a simulation model for MIMO orthogonal frequency division multiple access (OFDMA) networks that allows us to study the impact of popular scheduling and power control algorithms on the time variation of the uplink interference power. We find that employing a time persistent proportional fair scheduler (which we term proportional fair in frequency, PFF, scheduler) together with an open loop power control scheme significantly reduces intercell interference variation and thereby it provides higher throughput than traditional schedulers that are primarily optimized for a single cell setting without taking into account the variation of the intercell interference power.

This paper outlines and evaluates a simplified interference model applicable in multi-cell multi-antenna radio network simulations. Based on the path-loss, the model classifies interferers as either strong or weak and the channels of strong interferers together with the channel of the desired signal are accurately modeled using a spatial channel model (SCM). The SCM assures that the spatial signature of the signals is accounted for in the evaluations. The channels of weak interferers are simply characterized by the path-loss and interference is modeled as additive white Gaussian noise (AWGN). The model is verified by means of simulations of a 57 sector OFDM/TDMA network and by comparing results achieved using the simplified model to results from simulations with full interference modeling, i.e., to the case when all interferers are accurately modeled. The verification results demonstrate that the simplified model with at least eight links accurately modeled provides a high modeling accuracy and results are comparable to results achieved with full interference modeling. Moreover, in the employed simulation tool this reduces the simulation time by up to a factor of four. The model may hence be used as a means to speed up simulations of multi-cell multi-antenna radio networks.

The expected performance improvements of next-generation mobile radio access networks (RANs) can be achieved, e.g., by a flexible deployment of different types of radio access points (RAPs), such as intelligent relay nodes (RNs). To facilitate a cost-vs.-performance assessment of different deployment options, this paper presents a classification of different RAN cost components. Then, a method for deployment cost optimization is introduced which allows a comparison of the cost effectiveness of different RAN deployments by calculating optimum densities of different RAP types, based on a multi-dimensional iso-performance map. This method is first derived in theory and then demonstrated for two different deployment scenario examples.

In this paper, the impact of transmit antenna separations at the base station on the downlink in a cellular OFDM system with per antenna rate control (PARC) is investigated. For the minimum mean square error (MMSE) with successive interference cancellation (SIC) receiver, the highly correlated interference resulting from closely spaced antennas is more easily suppressed than the independent interference resulting from widely separated antenna installations assuming the same number of interfering source(s). In the region where the interference from co-located source is dominating, the larger the transmit antenna separation, the better performances by the MMSE-SIC receiver. But in the region where interference from other cells is dominating, no gain is found when enlarging the transmit antenna separation, since it will only increase the number of uncorrelated interference sources. This means that for cell edge users it is beneficial with base stations with closely separated antenna installation in order to maximize the cancellation of inter-cell interference since the gain by multi-stream transmission for these users are small anyway.

Future cellular networks are expected to provide significantly higher capacity than today's systems. This might require a denser access point deployment, with a potential increase in network deployment cost as a consequence. A promising way to reduce cost is a multi-hop deployment where wireless relay nodes (RN) are introduced to enhance capacity and coverage. In this paper, a deployment procedure for a static radio environment is considered, adding RNs incrementally as a complement to initially deployed macro base stations (BS). Different strategies of deploying BSs and RNs, providing equal service levels, are analyzed from a cost perspective. We develop a methodology that can determine and compare the most cost efficient deployment mixes of BSs and RNs. Further, we compare a deployment of macro BSs and relays with a deployment of macro BSs and micro BSs. Results show that relays are more cost efficient if the micro BS cost is between 10 and 15 % higher compared to the cost of an RN.

This paper presents and evaluates different multi-antenna deployments in an OFDM wireless system. Two downlink implementations, higher order sectorization (HOS) and downlink SDMA using fixed beams (FB), are considered. HOS with 3-, 6-, and 12-sector sites are compared with downlink FB SDMA in a 3-sector site where each sector is using up to four antennas. In the uplink we evaluate SDMA using multi-antenna MMSE receiver at base station. The simulation results indicate that in the downlink FB SDMA with four antennas per sector provides a cell throughput improvement of more than 100% compared to a 3-sector site equipped with a single antenna each. The gain can be further improved by using HOS at the expense of additional complexity. The uplink results show that SDMA allows to increase the throughput by up to a factor of two.

This paper discusses the requirements on future radio access and, based on the requirements, proposes a framework for such a system. The proposed system based on orthogonal frequency-division multiplexing supports very low latencies and data rates up to 100 Mb/s with wide area coverage and 1 Gb/s with local area coverage. Spectrum flexibility is identified as one main requirement for future systems, and the proposed framework can be deployed in a wide range of spectrum allocations with bandwidths ranging from 2.5 to 100 MHz. Multihop relaying, useful to extend the range for the high data rates, and multiple-antenna configurations are integral parts of the framework. A packet-centric approach is taken for the dataflow processing, implying that the scheduling mechanism and the retransmission protocol operate on complete packets rather than segments thereof, thus allowing for cross-layer optimization. Finally, numerical evaluations are provided, illustrating the feasibility of future very wideband radio access.