In current cellular networks, when a UE moves from the coverage area of one cell to another cell, a handover procedure needs to be performed. However, the baseline handover procedure used in 5G networks, as well as in the previous cellular network generations, is triggered by $\mathrm{L 3}$ measurements and involves a series of processes between the network and UE which result in a complete change of network configuration at the UE and reset of L1/L2 protocols. Therefore, the legacy L3 handover procedure leads to larger overhead and longer interruption time than beam switch mobility. To overcome this drawback, this paper highlights the latest progress made by 3GPP in the domain of mobility and handover. In doing that, we provide a comprehensive description of L1/L2 Triggered Mobility (LTM), the fundamental steps involved in LTM execution and LTM enhancements over the legacy L3 handover procedure. This scope of the paper is also complemented by a numerical simulation analysis which emphasizes LTM benefits, in terms of reduced handover interruption, downlink packet delay, and downlink packet drop rate at the UE.

One of the first key self-organizing features introduced in LTE was Automatic Neighbor Relations (ANR), a function for automatically generating relations between radio network entities that is needed for many features such as active-mode mobility, load balancing and dual connectivity. Given the benefits of ANR in LTE, we foresee that procedures for relations establishment will be an important integrated part of 5G systems as well. Moreover, the new emerging technology components of 5G such as massive beamforming expand the scope of relations beyond the neighbor relations of LTE. In this paper, we give an overview of key 5G radio access components, discuss the need for different types of identifiers and relations, and comment on the impact from the ultra-lean design principle of 5G. The paper also discusses some possible procedures for automatic relation establishment in consideration of the specific 5G aspects.

This paper presents the energy performance of a new radio access technology (RAT) component in 5G, here denoted as 5G-NX. The 5G-NX RAT encompasses massive beamforming and an ultra-lean design as two of its key technology components. The user throughput, resource utilization of the cells and daily average area power consumption are evaluated by means of system level simulations in an Asian city scenario, and the results are compared with a traditional LTE deployment using the same network layout. The simulation results indicate that the new 5G-NX system provides much better energy performance compared to LTE and this is primarily due to the ultra-lean design and the high beamforming gain that provides both longer and more efficient component sleep in the network. At expected traffic levels beyond 2020, 5G-NX is shown to decrease the network energy consumption by more than 50% while providing around 10 times more capacity.

To meet future demands on user experience and traffic volumes, mobile networks need to evolve towards providing higher capacities and data rates. In this paper we investigate the feasibility of incorporating higher frequency bands (15 GHz) and beamforming to support this evolution. We see that using user-specific beamforming, the challenging propagation conditions at higher frequencies are mitigated and outdoor-in coverage is often possible. In places where 15 GHz coverage is not satisfactory, swift fallback to a lower frequency band is essential. This is seamlessly provided by carrier aggregation with a 2.6 GHz band. Together these components provide a ten-fold increase in capacity over a reference system operating only at 2.6 GHz.

The focus of this paper is on the convergence of positioning technology between the WCDMA and the LTE cellular systems. The emerging possibility to use multi-RAT positioning nodes can be exploited to mitigate the lack of a high-precision indoor OTDOA positioning method in WCDMA, which today limits the coverage of self-learning databases for fingerprinting positioning in this cellular system. The problem at hand is solved by use of measured high precision OTDOA positions of opportunity from LTE.

Uplink co-ordinated multipoint reception (UL CoMP) has received attention recently, especially for LTE Advanced, due to its promise of increasing spectral efficiency. In this paper, UL CoMP for HSPA networks is considered. UL CoMP for HSPA may be deployed without changes to the standard, and may be applied also for legacy UEs. Comparisons and contrasts of CoMP with conventional soft/soft handover are discussed as well as practical receiver structures incorporating antenna selection within the pool of antennas available in a CoMP cell. Radio resource management issues are discussed including mobility, power control, load control, and scheduling. It is concluded that UL CoMP requires only minimal changes to these algorithms. In a practical scenario, gains in cell-edge throughput of at least 118% and 144% are demonstrated for CoMP-3 and CoMP-6, respectively, for the case of full buffer traffic. The gains are even larger for the case of short files uploads where the conventional network suffers from the inability to exploit soft/softer handover due to latencies involved in updating a UE's active set.

This paper proposes a low-complexity model for vertical antenna radiation patterns, e.g. for inclusion in system- level simulations. They can be seen as extensions to the horizontal radiation pattern model used in 3GPP simulation scenarios. The model is verified against and compared to predicted and measured data from real networks. The impact on system-level performance is also investigated. It is seen that using the proposed model, simulated geometry distributions and soft handover statistics closely matching those of real networks may be achieved. The analysis also concludes that many real networks have better cell isolation than what is modeled by the 3GPP antenna model. As a consequence, the horizontal radiation pattern model significantly under-estimates the system level performance in such networks. Furthermore, the proposed model is used to assess the LTE and HSPA system-level performance for realistic scenarios.

Activity-based uplink load estimation is considered for WCDMA. By taking the user activity explicitly into account, the method is suitable for a scenario where services with very different activity levels use the same RAB. Scenarios with different mixes of email and MMS (multimedia messaging service) traffic are considered. Simulations indicate that the method provides good accuracy in situations where methods without activity estimation may overestimate the uplink load with about 3 dB.

The capacity of a GSM system can be increased with fast power control. By sending four consecutive power control commands/measurement reports-instead of one-in the four bursts reserved for the slow associated control channel (SACCH), the system capacity can be increased by 10% for slow mobiles, and by 40% for fast mobiles. This gain is obtained with relatively small changes in the standard. The power control signaling is robust enough to handle low C/I situations. By simultaneously modifying its channel coding, the performance of the SACCH can be improved. This scheme will be part of Release 5 of the GSM/EDGE radio access network standard and is called enhanced power control.

With the use of the 8PSK modulation available in the GSM/EDGE radio access network (GERAN), adaptive multirate (AMR) voice can be supported with good speech quality using half-rate (HR) or even quarter-rate (QR) bearers. In this paper channel coding schemes for 8PSK HR are evaluated in terms of quality and capacity. System level simulations show that a capacity gain of 20% can be obtained with HR bearers as compared to the default full-rate bearers in a 1/3 reuse deployment. It is also shown that the introduction of QR bearers, together with an ideal adaptation mechanism, could lead to a capacity gain of up to about 90% in a 4/12 reuse pattern. However, dynamic system level simulations indicate that both measurement periods and intra-cell handover will limit the capacity gains estimated from the static system level simulations. The simulations also indicate that the maximum system capacity can not be increased by HR/QR adaptation.

With the now finalized standardization of the first phase of the EDGE concept and its introduction of 8PSK modulation to support higher data rates, GPRS has evolved into a third generation (3G) mobile communication system. Within its second phase, EDGE will evolve further into being capable of supporting real-time packet data and thereby providing the full range of 3G services. By adopting the UMTS quality of service (QoS) concept, together with the development of new radio bearers, support of real-time packet data is accomplished and the GSM/EDGE Radio Access Network (GERAN) is created. This paper describes and evaluates GERAN with the focus on IP multimedia and the alignment with the UMTS QoS model.

A general MMSE decision feedback equalizer (DFE) for multiple input-multiple output channels is presented. It is derived under the constraint of realizability, requiring finite smoothing lag and causal filters both in the forward and feedback link. The proposed DFE, which provides an optimal structure as well as optimal filter degrees, is obtained as an explicit solution in terms of the channel and noise description. A generalization of the scalar zero-forcing DFE is also presented. Conditions for the existence of such an equalizer are discussed. We argue that when no zero-forcing equalizer exists, poor near-far resistance of the corresponding optimal minimum mean square error DFE can be expected. A numerical example indicates the potential advantages of using a decision feedback equalizer with appropriate structure. The main improvements are obtained at moderate to high signal-to-noise ratios.

We investigate the use of an antenna array at the receiver in frequency-division multiple-access/time-division multiple-access systems to let several users share one communication channel within a cell. A decision-feedback equalizer (DFE) which simultaneously detects all incoming signals is compared to a set of DFEs, each detecting one signal and rejecting the remaining as interference. We also introduce the existence of a zero-forcing solution to the equalization problem as an indicator of near-far resistance of different detector structures. Near-far resistance guarantees good performance if the noise level is low. Simulations show that with an increased number of users in the cell, the incremental performance degradation is small for the multiuser detector. We have also applied the proposed algorithms to experimental measurements from a DCS-1800 antenna array testbed. The results from these confirm that reuse within a cell is indeed possible using either an eight-element array antenna or a two-branch diversity sector antenna. Multiuser detection will, in general, provide better performance than interference rejection, especially when the power levels of the users differ substantially. The difference in performance is of crucial importance when the available training sequences are short.

In wireless communication systems with antenna arrays the spatio-temporal channel can often be described by a low-rank model. By exploiting this information, corresponding low rank equalizers with reduced complexity can be designed. By applying such low rank equalizers to a set of uplink measurements, we demonstrate that the performance loss associated with the lower complexity is small.

During the last few years, the second generation mobile cellular telephone systems have become operational. One can foresee a dramatic increase in traffic demands, both concerning transmission quality and system capacity. We present a multivariable minimum mean square error (MMSE) DFE, which has the ability to operate on channels with different number of inputs and outputs. It is derived under the constraint of realizability and is calculated by solving a system of linear equations. The suggested DFE can be used for combined temporal and spatial equalization, as well as for narrowband, multiuser detection in systems with multiple antenna elements. The DFE may also serve as a multiuser detector in DS-CDMA systems. Simulations indicate that the DFE performs well as a multiuser detector. In a system with multiple antennas, it outperforms a corresponding detector for a single user in terms of the BER while doubling the capacity. If utilized for multiuser detection in CDMA, its performance is comparable to the best achievable performance of the decorrelating detector, and is attained at a substantially lower computational cost.