Pekka Jänis

Interference-Aware Resource Allocation for Device-to-Device Radio Underlaying Cellular Networks

Future cellular networks such as IMT-Advanced are expected to allow underlaying direct Device-to-Device (D2D) communication for spectrally efficient support of e.g. rich multimedia local services. Enabling D2D links in a cellular network presents a challenge in radio resource management due to the potentially severe interference it may cause to the cellular network. We propose a practical and efficient scheme for generating local awareness of the interference between the cellular and D2D terminals at the base station, which then exploits the multiuser diversity inherent in the cellular network to minimize the interference. System simulations demonstrate that substantial gains in cellular and D2D performance can be obtained using the proposed scheme.

Device-to-Device Communication Underlaying Cellular Communications Systems

In this article we propose to facilitate local peer-to-peer communication by a Device-to-Device (D2D) radio that operates as an underlay network to an IMT-Advanced cellular network. It is expected that local services may utilize mobile peer-to-peer communication instead of central server based communication for rich multimedia services. The main challenge of the underlay radio in a multi-cell environment is to limit the interference to the cellular network while achieving a reasonable link budget for the D2D radio. We propose a novel power control mechanism for D2D connections that share cellular uplink resources. The mechanism limits the maximum D2D transmit power utilizing cellular power control information of the devices in D2D communication. Thereby it enables underlaying D2D communication even in interference-limited networks with full load and without degrading the performance of the cellular network. Secondly, we study a single cell scenario consisting of a device communicating with the base station and two devices that communicate with each other. The results demonstrate that the D2D radio, sharing the same resources as the cellular network, can provide higher capacity (sum rate) compared to pure cellular communication where all the data is transmitted through the base station.

Mode Selection for Device-To-Device Communication Underlaying an LTE-Advanced Network

Device-to-Device communication underlaying a cellular network enables local services with limited interference to the cellular network. In this paper we study the optimal selection of possible resource sharing modes with the cellular network in a single cell. Based on the learning from the single cell studies we propose a mode selection procedure for a multi-cell environment. Our evaluation results of the proposed procedure show that it enables a much more reliable device-to-device communication with limited interference to the cellular network compared to simpler mode selection procedures. A well performing and practical mode selection is critical to enable the adoption of underlay device-to-device communication in cellular networks.

Interference-avoiding MIMO schemes for device-to-device radio underlaying cellular networks

An underlaying direct Device-to-Device (D2D) communication mode in future cellular networks, such as IMT-Advanced, is expected to provide spectrally efficient and low latency support of e.g. rich multi-media local services. Enabling D2D links in a cellular network presents a challenge in transceiver design due to the potentially severe interference between the cellular network and D2D radios. In this paper we propose MIMO transmission schemes for cellular downlink that avoid generating interference to a D2D receiver operating on the same time-frequency resource. System simulations demonstrate that substantial gains in D2D SINR of up to 15 dB and around 10% total cell capacity gains can be obtained by using the proposed scheme.

Geodesical codebook design for precoded MIMO systems

We propose a numerical method for finding packings of multiple-input and multiple-output (MIMO) semi-unitary precoding matrices in Grassmannian manifolds with different metrics. The proposed expansion-compression algorithm (ECA) is practical, simple and produces efficient packings without the need for a sophisticated initialization. With chordal distance metric, the algorithm tends to converge into a degenerated point constellation, where two points contain identical as well as orthogonal columns and distance between them cannot increase further along geodesic. Therefore, we alternate between max-min and min-max clustering parts of ECA algorithm, where the latter prevents degenerated constellations. With Fubini-Study distance metric, the algorithm converges to best known packings without extra min-max processing.

Interference-Aware Radio Resource Management for Local Area Wireless Networks

Interference-aware multiple access is an enabler to cost-efficient and reliable high data-rate local area wireless access. In this paper, we propose an interference-aware radio resource management scheme where receivers inform about their throughput, interference, and signal levels by means of broadcast messages tied to data reception. In the proposed scheme, the conventional scheduler is extended to interference-aware operation where individual scheduling decisions are based on estimated change in system-level performance. The performance of the proposed scheme is evaluated in system simulations where it is compared to a conventional scheduler and a centralized scheduler (global optimum). The convergence of the proposed scheduler is analyzed and signaling overhead of an example implementation is characterized. The results demonstrate that the proposed scheme enables fair and efficient wireless access in challenging interference scenarios, for example, multiple networks deployed in the same geographical area and sharing a common band.

On the performance of flexible UL-DL switching point in TDD wireless networks

An advantage of Time Division Duplex (TDD) wireless networks over Frequency Division Duplex (FDD) is that the UL-DL switching point may be flexibly adapted to asymmetric traffic loads. This enables more efficient spectrum use, but on the other hand may lead to harmful cross-link interference between cells. As a result, the net gain (or loss) from flexible TDD depends on the traffic characteristics and network scenario. In this paper we address the problem in local area packet data networks where high fluctuation in short term traffic loads is expected. We show through analysis and system level simulations that in such a scenario a significant gain in effective user throughput (TP) may be achieved under low traffic loads. At high load the gain vanishes due to saturated queues implying full bandwidth usage. We also study the impact of interference-awareness at the scheduler. It is found out that the range of traffic loads over which there is gain from flexible TDD is significantly extended by interference-awareness as compared to a conventional scheduler.

Sparse equalization in high data rate WCDMA systems

Low computational complexity is among the most important criteria for receiver design in mobile communication systems such as WCDMA. Low complexity receivers are desirable especially in the downlink. In this paper we address the problem of complexity reduction of MMSE equalization. It is well known that for good performance the length of an equalizer should be at least twice the channel length. However, employing such a long filter is computationally very demanding. A novel method for selecting the filter coefficients for WCDMA receiver is proposed. This receiver is called sparse equalizer. It is shown via simulations to outperform both conventional RAKE and generalized RAKE (CRAKE) using the same filter length. Simulations are carried out in high speed downlink packet access (HSDPA) systems in ITU vehicular A and pedestrian A channels with multiple receive antennas.

MMSE equalizer and chip level inter-antenna interference canceler for HSDPA MIMO systems

In MIMO systems the interference from the same cell transmit (TX) antennas causes severe interference. Moreover, if the channel is frequency selective, also inter-chip interference is present. Canceling both inter-antenna and inter-chip interference is a challenging task, especially when the same codes are reused across the TX antennas. In this paper we propose a hybrid receiver combining minimum mean square error (MMSE) equalizer and chip level inter-antenna interference canceler. The performance is studied via simulations carried out in high speed downlink packet access (HSDPA) system with ITU channel

Low complexity space-time MMSE equalization in WCDMA systems

In this paper we propose a low complexity frequency-domain method for finding the minimum mean square error (MMSE) equalizer. Special properties of circulant matrices are exploited in the method. Simulations show that only a minor performance loss is experienced compared to time-domain processing. We also compare joint space-time processing to decoupled equalization and spatial combining. The complexity reduction due to the decoupled processing is evident, while the performance loss remains small. Consequently, the proposed low complexity frequency-domain method can also be used with multiple receive antennas with tolerable performance loss compared to joint space time equalization. Additionally, different MMSE equalizer definitions for multiple receive antennas are considered, and their performance is studied in simulation using estimated channels. Simulations are carried out in high data rate WCDMA system model