Francisco Ganhão

Analytical BER and PER Performance of Frequency-Domain Diversity Combining, Multipacket Detection and Hybrid Schemes

Diversity Combining (DC) and Multipacket Detection (MPD) are efficient techniques that cope with packet errors due to severe propagation conditions and/or collisions. To evaluate their network performance on a network simulator, an accurate characterization of the Bit Error Rate (BER) and Packet Error Rate (PER) can successfully replace the behavior of the PHY layer. This choice is better in terms of computational time than implementing a full PHY layer to be jointly simulated with the upper layers. In this paper, an analytical model is proposed to compute the BER and PER of DC, MPD and hybrid techniques, considering a Single-Carrier with Frequency-Domain Equalization (SC-FDE) scenario. The paper also considers two frequency-domain detection methods: a simple linear receiver and a powerful iterative receiver. The proposed model is simple and versatile, since it can support nonhomogeneous transmitting powers, and different channel conditions concerning retransmissions and channel randomization techniques. Several simulations show that the proposed model provides accurate BER and PER results for a wide range of scenarios.

Analytical Performance Evaluation of SC-FDE Modulations with Packet Combining and Multipacket Detection Schemes

Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, leading to performance losses. Two different approaches are considered to cope with lost packets, a low-complexity packet combining ARQ scheme (Automatic Repeat reQuest)and a multi-packet detection scheme. These approaches are employed in an SC-FDE scheme (Single-Carrier with Frequency Domain Equalization). Suitable receiver structures are described, employing packet combining, multipacket detection and hybrid schemes. An accurate analytical tool is presented for predicting the performance of the different schemes.

Energy-Efficient QoS Provisioning in Demand Assigned Satellite NDMA Schemes

Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, leading to performance losses. Hybrid Automatic Retransmission reQuest (H-ARQ) and time diversity multipacket reception approaches, such as Network Diversity Multiple Access(NDMA), improve the system performance by requesting additional retransmissions and combining all the signals received together. However, the high round trip delay time associated to satellite networks introduces limitations in the number of retransmission requests that may be issued by the terminals to fulfill the Quality of Service (QoS) requirements. This paper considers the design of hybrid protocols combining H-ARQ and NDMA for satellite networks with demand-assigned traffic. The satellite NDMA (S-NDMA) protocol is presented and analytical models are proposed for its performance. Energy efficient QoS provisioning is also analyzed. The proposed systems performance is evaluated for a Low Earth Orbit (LEO) network with a Single-Carrier with Frequency Domain Equalization (SCFDE) scheme, and compared to H-NDMA. Results show that the proposed system is energy efficient and can provide enough QoS to support high demand services such as video telephony.

Performance Analysis of an Hybrid ARQ Adaptation of NDMA Schemes

Traditionally, an unsuccessful packet reception, either due to channel conditions or interference from multiple sources (collisions), is discarded and followed by a new reception of the same packet. Network diversity multiple access (NDMA) handles collisions by using time diversity multipacket reception: the base station forces terminals to transmit P copies of each packet when P terminals collide. This rigidity of having P copies is unsuitable for poor propagation conditions. It might be desirable to have more than P copies of a given packet, adopting a technique for single packet reception called hybrid-ARQ. Hybrid-ARQ effectively decreases the packet error rate. This paper proposes such mechanism for multi-packet reception, called hybrid-ARQ NDMA (H-NDMA), a gated slotted random access protocol, where the access mechanism forces the terminals involved in a collision with reception errors to transmit more than P times. Analytical models for the throughput, delay and energy per useful packet are proposed. The energy performance is analyzed for bounded average delay constraints. The proposed systems performance is evaluated for a single-carrier with frequency domain equalization (SC-FDE) scheme, and compared with the classical NDMA protocol. The comparison highlights that H- NDMA is scalable for an increasing number of terminals and network load.

Performance of Hybrid ARQ for Network Diversity Multiple Access Schemes

Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, leading to performance losses. Network Diversity Multiple Access (NDMA) handles collisions by combining a multipacket detection scheme with time diversity. In NDMA, the base station (BS) forces mobile terminals (MTs) to transmit J copies of each packet when J MTs collide. Diversity combining is limited to J copies of the packets, not allowing it to adapt to severe errors due to channel noise. This paper considers a multipacket detection scheme recently proposed, which reduces the packet error rate (PER) when more than J copies of the packets are available. In this paper, an Hybrid-ARQ NDMA access mechanism is proposed. The access mechanisms forces MTs with reception errors during a collision resolution epoch to transmit more than J times. Analytical models are proposed for the goodput and delay, considering Poisson traffic. The proposed systems performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) scheme, and compared to classical NDMA.

A Hybrid ARQ Scheme for Faster than Nyquist Signaling with Iterative Frequency-Domain Detection

FTN (Faster Than Nyquist) signaling allows capacity gains but requires substantially complex equalization schemes, even for an ideal AWGN (Additive White Gaussian Noise) channel. Extending conventional FTN receivers for severely time- dispersive channels is not an option, since the receiver complexity becomes prohibitively high. In this paper we address the design of a receiver for FTN signaling over severely time-dispersive channels. To cope with the severe ISI (Inter-Symbol Interference) associated to the combined effects of FTN signaling and the time-dispersive channel we consider an iterative FDE scheme (Frequency-Domain Equalization) combined with a HARQ (Hybrid Automatic Repeat reQuest) especially designed taking into account the characteristics of FTN signals. We also present a simple, yet accurate model for the performance evaluation, considering multiple retransmissions per block. Our performance results show that we can have significant throughput gains, while maintaining essentially the receiver complexity of conventional, Nyquist-rate signaling schemes, even for severely time-dispersive channels.

Analytical Evaluation of Iterative Packet Combining and Multipacket Detection Schemes for SC-FDE

Packet Combining (PC) and Multipacket Reception (MPR) techniques have great potential to deal with lost packets since both take full advantage of the signals associated to all failed transmission attempts. However, their performance evaluation in practical systems is difficult because lengthy simulations are needed to obtain the packet error rates for specific channel conditions. The paper presents an analytical tool to obtain the Bit Error Rate (BER) and Packet Error Rate (PER) performances for Packet Combining (PC), Multipacket Reception (MPR) and the hybrid of both schemes, based on Iterative Block Decision Feedback Equalization (IB-DFE) receivers for Single-Carrier with Frequency-Domain Equalization (SC-FDE). A set of simulation results show that the proposed analytical approach has accurate Bit Error Rate (BER) and Packet Error Rate (PER) results with a simple and relatively fast method.

A high throughput H-ARQ technique with Faster-than-Nyquist signaling

Current wireless communication systems rely on the assumptions of the Nyquist theorem. Faster-Than-Nyquist (FTN) assumes that a bandwidth below the Nyquist bandwidth can be used with minimum loss, however the existing receivers are too complex. Single Carrier with Frequency-Domain Equalization (SC-FDE) has been proposed to handle multipath dispersive broadband channels, however the uplink of SC-FDE can be severely affected by deep-fades and/or poor channel conditions. To cope with such difficulties Diversity Combining (DC) Hybrid ARQ is a viable technique, since it combines the several packet copies sent by a Mobile Terminal to create reliable packet symbols at the receiver. This paper proposes a simple SC-FDE Packet Error Rate analytical model using FTN signaling, based on the Iterative Block with Decision Feedback Equalization technique, which achieves a performance similar to Nyquist signaling.

SC-FDE femtocell energy saving using IB-DFE Interference Cancellation techniques

Femtocells were proposed as a solution to improve the performance in dense networks. They complement the macro base stations (eNB) with a dense set of low power micro base stations (HeNB). However, they also bring increased interference problems and consequently more collisions and lost packets. This paper considers the use of femtocells running the Single Carrier with Frequency Domain Equalization (SC-FDE) transmission technique. It evaluates the performance of an Iterative Block Decision-Feedback Equalizer (IB-DFE) receiver employing Interference Cancellation (IC) techniques in the downlink channel. Using the interference cancellation capability, it is possible to dynamically adjust the network deployment and reduce the network total energy consumption. This paper also proposes a HeNB control algorithm and evaluates the energy saving capabilities of the reception technique for different load levels. Results show that it is possible to turn off femtocells and still satisfy the users requirements, with significant energy saving.

A Soft-Handover Scheme for LEO Satellite Networks

Traditionally, Low Earth Orbit (LEO) satellite networks use hard handovers when a Mobile Terminal (MT) moves between the footprints of two satellites. Such approach introduces a transitory disconnection interval, which may limit the capacity to provide demanding real-time requirements. A soft- handover approach that applies distributed packet combining on a satellite diversity scenario is proposed in this paper. Considering inexpensive MT hardware and low transmission powers, the paper analyses the performance gains and the difficulties that are associated to different Doppler and time-of-arrival shifts when the MT signal is broadcast to two satellites during the short handover period where both satellites footprint overlap. A Single-Carrier with Frequency Domain Equalization (SC-FDE) transmission technique is considered in this paper. It is shown that it is possible to have an inter-satellite handover almost without quality of service (QoS) degradation for a Satellite Network Diversity Multiple Access (S-NDMA) scheme.