Benoit Pelletier

D2D neighbor discovery interference management for LTE systems

Direct Device-to-Device (D2D) communications in cellular systems has attracted a lot of interest for both commercial and public safety applications. To support D2D communications, a first step involving neighbor discovery is typically needed. This paper focuses on the study of neighbor discovery signal design aspects and interference management for D2D discovery under a typical LTE system deployment. System level results on detection rate and range comparing different interference management techniques are provided. The results indicate that practical interference management techniques have the potential to improve the performance of neighbor discovery for cell-edge devices significantly.

Group-Based Space-Time Multiuser Detection with User Sharing

To reduce the complexity of space-time multiuser detection, it has been proposed recently to exploit the spatial dimension by forming groups of users and apply the detection individually to each group. In this work we propose a new space-time receiver structure based on the group-optimal MMSE linear detector along with a new grouping algorithm that respects practical hardware limitations. Furthermore, an extension of the proposed structure which allows non-mutually exclusive grouping is presented. The simulation results show that the proposed reduced-complexity receiver structure provides a bit error rate (BER) performance close to the full linear MMSE multiuser detector.

Enhanced autonomous resource selection for LTE-based V2V communication

Vehicle-to-vehicle (V2V) communication has the potential to improve road safety significantly by providing connectivity between vehicles to exchange information messages. V2V has recently gained considerable attention in part due to the standardization work that has started for Long Term Evolution (LTE) under the Third Generation Partnership Project (3GPP). Efficient and reliable distributed allocation of time-frequency resources among different vehicle user equipments (VUEs) remains a challenge particularly in dense urban environments. In this work, a new autonomous resource selection scheme for urban V2V communication scenario is proposed. Specifically, the proposed scheme relies on resource partitioning based on VUE heading direction along with a sensing-based collision avoidance mechanism, which aims to alleviate the potential interference between VUEs due to resource collision and in-band emission (IBE). The performance of the two-stage autonomous resource selection scheme is evaluated by system-level simulations in urban scenarios, where the results show a significant performance gain in comparison to existing approaches.

Group optimal space-time MUD with beamforming

To improve the bandwidth efficiency of current and future generations of wireless cellular systems, several techniques exist such as beamforming (BF) and multiuser detection (MUD). To reduce the complexity of the MUD, it has been proposed to separate users within a cell into mutually exclusive groups and perform MUD independently in each group. Inter-group interference (IGI) is reduced by using beamforming. In this work, the group optimal MMSE linear receiver for BF based space-time multiuser detector (ST-MUD) receivers (BF-STMUD) is derived. The complexity of this structure is compared to that of the full ST-MUD. It is shown through computer simulations that with proper grouping, an important reduction in complexity can be achieved with almost insignificant loss of performance.

HARQ and AMC: Friends or Foes?

To ensure reliable communications in randomly varying and error-prone channels, wireless systems use adaptive modulation and coding (AMC) as well as hybrid ARQ (HARQ). In order to elucidate their compatibility and interaction, we compare the throughput provided by AMC, HARQ, and their combination (AMC-HARQ) under two operational conditions: in slow- and fast block-fading channels. Considering both incremental redundancy HARQ and repetition redundancy HARQ, we optimize the rate-decision regions for AMC/HARQ and compare them in terms of attainable throughput. Under a fairly general model of the channel variation and the decoding functions, we conclude that: 1) adding HARQ on top of AMC may be counterproductive in the high average signal-to-noise ratio regime for fast fading channels and 2) HARQ is useful for slow fading channels, but it provides moderate throughput gains. We provide explanations for these results which allow us to propose paths to improve AMC-HARQ systems.

A Combined PUSH/PULL Service Discovery Model for LTE Direct

LTE Device-to-device (D2D) discovery and communication has been considered a means to allow capacity offloading, range extension as well as commercial proximity services such as advertisement or social networking. Within this context, several service discovery approaches may be envisioned. In this paper, we study strategies which rely on a central function supporting service discovery between LTE UEs by push or pull mechanisms. We propose some simplified models to compare them in terms of control overhead and UE energy consumption. Then we propose and evaluate a new approach which combines both PUSH and PULL strategies and highlight the gain that can be achieved on service discovery performances.

Resource allocation schemes for D2D communications

Device-to-Device (D2D) communications in cellular systems have a lot of potential value for both commercial and public safety (PS) applications. In D2D communications, two or more devices exchange data using a direct communication link, i.e., without having to go through the network infrastructure. This paper focuses on the study of broadcast voice communication for PS and the resource allocation schemes for D2D communications. System-level simulation results on link budget for different resource allocation schemes are provided. The results indicate that the proposed centralized approach provides approximately 3-5 dB gains in link budget, leading to increased communication range.

Multistage MMSE PIC Space–Time Receiver With Non-Mutually Exclusive Grouping

The arrival of new data services for wireless mobile communications requires an efficient use of the available bandwidth. Interference-limited cellular systems based on code-division multiple access (CDMA) can benefit from multiuser detection (MUD) and beamforming with antenna array to reduce multiple-access interference. Group-based techniques have been proposed to reduce the complexity of space-time MUD and have been shown to provide a performance-complexity tradeoff between matched filtering and full MUD. In this paper, the intergroup interference, which is a limiting factor in group-based systems, is reduced using multistage parallel interference cancellation after group-based minimum mean square error (MMSE) linear filtering. In addition, the extra resources that are available at the receiver are exploited by sharing users among groups. The proposed receiver is shown to converge, as the number of stages increases, to the full space-time MMSE linear MUD filter. The results show that the new approach provides bit error rate (BER) performance close to the full MUD receiver at a fraction of the complexity.

SPC11-3: Group-Based Block Linear Successive Interference Cancellation For DS-CDMA

Mobile communication systems based on DS-CDMA suffer from multiple access interference (MAI), which limits the system capacity. Several techniques, such as beamforming with multiple antennas and multiuser detection (MUD), have proved to be effective to mitigate MAI. To reduce the complexity of MUD, it has been proposed to process users in smaller groups. The interference between group is then reduced using beamforming with smart antennas. In this paper, a new group-based block linear successive interference cancellation structure is developed. The structure is shown to provide BER performance close to the full space-time MUD at a lower computational cost.

Comparative study of uplink and downlink beamforming algorithms in UTRA/TDD

The arrival of new multi-media and Internet services to mobile cellular subscribers has led to the development of new techniques, such as antenna array or smart antennas (SA), to improve spectrum efficiency. SA provides a means for spatial filtering for separating users based on angular characteristics, a method also known as beamforming. In this contribution, the performance of various beamforming algorithms is studied for the uplink and downlink of an UTRA/TDD system under realistic deployment and channel models. The algorithms are evaluated in terms of improvement in signal to interference plus noise ratio (SINR) and coded bit error rate (BER) with a RAKE receiver structure and compared to a more complex space-time multiuser detection receiver. We consider three different beamforming algorithms, namely: switched beams (SB), dynamically phased arrays (DPA) and sample matrix inversion (SMI). The results indicate that on the uplink, SMI has the potential to perform better than both DPA and SB but DPA outperforms both SB and SMI on the downlink.