Bengt Lindoff

Machine-to-machine communication with long-term evolution with reduced device energy consumption

We present a method to reduce the device battery consumption to efficiently support battery-operated machine-to-machine (M2M) communication in 3GPP long-term evolution. The long-term evolution discontinuous reception (DRX) is a key mechanism in reducing the device energy consumption, and we discuss how the traffic behaviour of machines in the Internet of things scenarios differs from the typical cellular user of today, for whom the current DRX mechanism is optimised for. We list typical transactions in M2M scenarios and discuss how the DRX operation is affected. We continue by introducing a power consumption model for M2M devices. Our assumption is that the device transmits small amounts of data in the uplink with deterministic intervals. The model takes into account the energy consumption in the active and the nonactive periods of the communication, which alternate depending on the DRX configuration. We use the model with different parameter settings referring to potential future M2M devices and identify the parameters, which contribute most to the device energy consumption. The results indicate that making the current maximum DRX cycle length longer will lead to significant gains in the energy consumption of M2M devices compared with what is possible today. Our key contributions include the discussion of the DRX mechanism in the Internet of things scenarios and the realistic assumptions for the potential of trading the responsiveness of a device for energy consumption gain with very long DRX cycles. Copyright

Reducing energy consumption of LTE devices for machine-to-machine communication

We present a method to reduce the device battery consumption to efficiently support machine-to-machine (M2M) communication in LTE. We first introduce a model for calculating energy consumption of a LTE device. We assume that the M2M device transmits small amounts of data with deterministic intervals. Our model takes into account the energy consumption in active and nonactive periods which alternate depending on the configuration of discontinuous reception (DRX). We use the model with different parameter settings referring to potential future M2M devices. The results indicate that making the current maximum DRX cycle length longer would lead to significant gains in the energy consumption of M2M devices. Thus, our key contribution is to show the potential of trading the responsiveness of a device for energy consumption gain with very long DRX cycles.

Using a direct conversion receiver in EDGE terminals-a new DC offset compensation algorithm

The basic concept of EDGE (Enhanced Data rates for GSM and TDMA/136 evolution) is to provide higher data rate transmission, over 384 kbits/s, than in the GSM and TDMA/136 systems of today. In order to be able to reach such a high data rate within the GSM bandwidth a very good receiver design is required. Further, from a terminal perspective, the receiver design needs to be efficient from both a cost, current and size point of view. A direct conversion receiver fulfil these criteria. However, such an architecture gives rise to a DC offset that must be taken care of in order for good demodulation. A DC offset compensation algorithm based on joint estimation of the radio channel and the DC offset is presented, giving competitive receiver performance for the EDGE system.

Channel estimation for the W-CDMA system, performance and robustness analysis from a terminal perspective

Two different approaches for channel estimation for the wideband code division multiple access (W-CDMA) system are compared by means of simulations. As W-CDMA uses time-multiplexed pilots, there is a need for interpolating primary channel estimates obtained from using these pilot symbols. Both channel estimators are similar in that they linearly combine primary channel estimates to perform this interpolation. The first channel estimator uses simple linear interpolation and the second channel estimator uses a Wiener filter approach. The Wiener filter approach requires a knowledge of the Doppler spread and the signal-to-interference ratio (SIR). The channel estimators are compared in terms of the resulting bit-error rate (BER). This is done with respect to deviations in the SIR and Doppler spread as used for the design of the Wiener filter, from their nominal values. For the evaluation a Rayleigh fading channel, with three independent and equally strong paths, are assumed. No power control is used. On the one hand, for low velocities, the simulations indicate that the Wiener filter approach is quite robust against model errors in terms of SIR and Doppler spread. For high vehicular velocities, on the other hand, and in the presence of model errors, the interpolator performs well compared to the Wiener filter approach.

A robust cell search algorithm for 3GPP LTE

Mobility handling and performance is of major importance for the 3GPP long term evolution (LTE) system. Therefore it is important for mobile devices to use reliable and robust algorithms for the cell search procedure, i.e. the procedure to detect neighbouring cells that can be used as potential handover candidates. We present a novel, low complexity, robust cell search scheme for LTE. The scheme uses a non-coherent approach and is therefore robust against Doppler spread and phase shifts due to sampling time instant mismatch, which makes it suitable for use in synchronized LTE TDD systems, as well as in high speed scenarios like high speed trains. This paper describes the theory behind the algorithm, and simulation results for LTE TDD showing its superior performance over coherent cell search algorithms are also presented.

Control Channel Design Trade-Offs for Ultra-Reliable and Low-Latency Communication System

Future generation of wireless networks, i.e. 5G, is envisioned to support several new use-cases demanding transmission reliability and latency that cannot be achieved by the current cellular networks such as long-term evolution (LTE). This paper looks at different design aspects of the control channel(s) to support ultra-reliable low-latency communication considering factory automation as an example scenario. In particular, we show that a fairly balanced design for both the uplink and the downlink control channels can be made given an appropriate selection of modulation, coding, diversity scheme, and time/frequency resources. By means of link-level simulations, we also show that the proposed control channel design supports a block-error rate of 10-9 under Rayleigh fading conditions at a signal-to-interference-plus-noise ratio comparable to that supported by current 4G systems (e.g. LTE). Furthermore, a radio frame structure is proposed to support the user plane end-to-end latency of 1 ms.

Enhanced DC estimation via sequence-specific frequency offset

A method for improving DC estimation over any particular training sequence is presented for use in direct conversion receivers. It is known that direct-conversion receivers suffer from a large DC-offset, which often cannot be adequately removed by a simple average of the received signal. To alleviate this problem, the DC offset can be jointly estimated with the channel over the training sequence in baseband. However, training sequences designed to facilitate channel estimation are not necessarily good for the estimation of DC offset. In the proposed method, an intentional frequency offset tailored to each training sequence is imposed at the radio front-end in order to improve the ability of estimating DC over that training sequence in digital baseband. We analyze the resulting DC estimation error and show analytically how the optimal frequency offset can be derived for each training sequence. Using the EDGE air interface, we demonstrate that significant gains can be achieved with this new method.

Evaluation of Inter-Frequency Quality Handover Criteria in E-UTRAN

In E-UTRAN multiple co-located carriers will typically be deployed requiring efficient inter-frequency (IF) handover procedures and algorithms for retaining service quality, better coverage and load balancing between the carriers. Five IF handover criteria using RSRP, RSRQ or combination thereof are investigated in synchronous and asynchronous E-UTRAN deployment scenarios. The results depict that an IF handover solely based on RSRP significantly increases number of handovers. Conversely the handover criterion based only on RSRQ reduces handovers but it slightly increases the packet loss rate. The overall best performance is achieved with the combined handover criterion, which uses both RSRP and RSRQ and thus guarantees that the received pilot strength as well as the signal quality stays within the desired limit after the handover.

Combining of power control commands during soft handover in WCDMA

This paper discusses the TPC detection performance in soft handover in WCDMA. A simple TPC commands combining method is evaluated and an improved TPC combining method is proposed. Results show that although the simple combining method fulfills the 3GPP requirements, it does not perform well from the system performance perspective. The proposed combining method significantly improves the system performance.

On selectivity filter design for 3G long-term evolution mobile terminals

Within 3GPP, the work of defining the long-term evolution (LTE) of 3G is ongoing. The fundamental targets of this evolution are to further improve the coverage and capacity, as well as increasing the data rates and reducing the latency. Another important aspect of 3G LTE is the possibility to use 3G LTE in existing GSM and WCDMA frequency bands, hence the mobile terminal selectivity filter has to be designed taking system coexistence into account. For 3G LTE, OFDM has been chosen for the down-link and a cyclic prefix is used to avoid inter symbol interference (ISI). This paper presents an adaptive selectivity filter design suitable for 3G LTE mobile terminals that utilizes the part of the cyclic prefix which is not needed to guarantee ISI free reception of the OFDM symbols to optimize the adjacent channel selectivity (ACS) for GSM interferers. Simulation results show that the above mentioned technique can improve the ACS by up to 20 dB in some scenarios compared to if a fixed selectivity filter is used.