Anders Wallén

Carrier aggregation for LTE-advanced: design challenges of terminals

Carrier aggregation is a key feature of 3GPP LTE that addresses the support of higher data rates and utilization of fragmented spectrum holdings. In this article, the relevant design challenges of terminals are discussed. The transmitter architectures are reviewed, and the minimum amount of power amplifier back-offs is evaluated. In addition, several receiver architectures are compared from the perspective of design tradeoff. The radio impairments affecting the receiver performance are analyzed and the simulation results are provided. The corresponding silicon implementation is presented together with the measurement results.

Reducing the Modem Complexity and Achieving Deep Coverage in LTE for Machine-Type Communications

The Internet of Things (IoT) has emerged as one of the focal points in the evolution of cellular networks, and has motivated the introduction of several features that facilitate Machine-Type Communications (MTC) in LTE networks. These features serve the MTC goals of reduced User Equipment (UE) modem cost and complexity, Coverage Enhancement (CE) to support UEs in remote radio locations, and an improved battery lifetime. In this paper, we discuss the features specified in LTE Release 12 and Release 13 for reducing the UE modem cost up to 81% compared to the least expensive broadband LTE UE modem. Further, we describe the techniques specified in Release 13 for the CE of physical channels that carry data or control information. We provide link-level simulation results for the CE performance over various physical channels in terms of their error rates and per-user throughput.

A Study of UE-to-UE Interference between TDD Systems

We study how UE-to-UE interference impacts the performance, considering transmitter out-of-band (OOB) emissions and receiver blocking characteristics for homogenous 20 MHz LTE systems. For co-existing TDD systems on different carrier frequencies within the same band, UE-to-UE interference may occur in certain situations. The impact of such interference is evaluated for a hotspot scenario and compared to a uniform user distribution scenario, and is found to be significantly worse. When the number of scheduled users in the aggressor cell is high (e.g. >; 2), then receiver blocking impact, rather than the OOB emission, dominates the interference performance in hotspot scenario. Consequently, guard bands cannot be used to mitigate the receiver blocking impacts.