An Introduction to LDPC Codes

Over the last few years, the evolution of network and user handsets’ technologies, have challenged the telecom industry and the Internet ecosystem. Especially, the unprecedented progress of multimedia streaming services like YouTube, Vimeo and DailyMotion resulted in an impressive demand growth and a significant need of Quality of Service (QoS) (e.g., high data rate, low latency/jitter, etc.). Mainly, numerous difficulties are to be considered while delivering a specific service, such as a strict QoS, human-centric features, massive number of devices, heterogeneous devices and networks, and uncontrollable environments. Thenceforth, the concept of Quality of Experience (QoE) is gaining visibility, and tremendous research efforts have been spent on improving and/or delivering reliable and added-value services, at a high user experience. In this paper, we present the importance of QoE in wireless and mobile networks (4G, 5G, and beyond), by providing standard definitions and the most important measurement methods developed. Moreover, we exhibit notable enhancements and controlling approaches proposed by researchers to meet the user expectation in terms of service experience.

Quality of Experience for Streaming Services: Measurements, Challenges and Insights

In this paper, we provide mathematical frameworks to the analysis of amplify-and-forward dual-hop cooperative relaying protocols in the presence of Nakagami- $m$ fading and additive Gaussian noise at the relay, as well as additive Gaussian noise and symmetric alpha-stable interference at the destination. Quasi-static and fast-varying interference scenarios are investigated, which arise, e.g., when either the same or different interferers are active during the broadcast and relaying phases, respectively. A maximal ratio combining demodulator is studied, by assuming that the aggregate interference is either unknown (interference-oblivious) or can be estimated (interference-aware) at the destination. Closed-form expressions of the end-to-end moment generating function are provided, and the achievable diversity order is studied for different setups. The diversity order is shown to depend on the path-loss exponent of the interfering network. Under the assumption that the transmit-powers of cooperative and interfering networks are independent, it is proved that the interference-aware maximal ratio diversity combiner is capable of achieving second-order diversity only asymptotically, as the amplitude path-loss exponent tends to one.

End-to-End Error Probability and Diversity Analysis of AF-Based Dual-Hop Cooperative Relaying in a Poisson Field of Interferers at the Destination

In this letter, outage probability of dual-hop decode-and-forward (DF) relaying scheme is analyzed over mixed Rayleigh and generalized Gamma fading channels. Cooperation model considered in this work consists of a source, a relay and a destination. It is assumed that source-relay and relay-destination channels experience Rayleigh fading and generalized Gamma fading, respectively. Exact outage probability expression is derived and outage performance is illustrated for both direct transmission and DF relaying scheme.

Outage Probability Analysis of Dual-Hop Decode-and-Forward Relaying Over Mixed Rayleigh and Generalized Gamma Fading Channels

In this paper, the fixed-point implementation of adjustable fractional-delay filters using the Farrow structure is considered. Based on the observation that the sub-filters approximate differentiators, closed-form expressions for the L2-norm scaling values at the outputs of each sub-filter as well as at the inputs of each delay multiplier are derived. The scaling values can then be used to derive suitable word lengths by also considering the round-off noise analysis and optimization. Different approaches are proposed to derive suitable word lengths including one based on integer linear programming, which always gives an optimal allocation. Finally, a new approach for multiplierless implementation of the sub-filters in the Farrow structure is suggested. This is shown to reduce register complexity and, for most word lengths, require less number of adders and subtracters when compared to existing approaches.

On the Fixed-Point Implementation of Fractional-Delay Filters Based on the Farrow Structure

In this paper, a decode-and-forward cooperative interference-limited multiple relay network is considered. An efficient relay selection strategy and its performance analysis are proposed, where only the relay nodes are affected by multiple interferences. In the proposed relay selection scheme, the selected relay is not always used, depending on the power of interferences and the channel state information of all links, while the direct path between source and destination is always used. For analytical tractability the distribution of interference-limited channel is approximated as an exponential distribution with high accuracy. Analysis of cooperative networks with interference-limited relays can be performed using the approximate exponential distribution by the same methods which have been used without interferences. We derive the bit error probability and outage probability of the proposed opportunistic max-min relay selection (OMRS) scheme in independent non-identically distributed Rayleigh fading channels. Numerical results present the superiority of OMRS over the conventional relay selection scheme which always uses the selected relay path. The exactness of the approximate analysis for interference-limited relays is also shown in numerical results.

Opportunistic Decode-and-Forward Relaying with Interferences at Relays

Interpolation filters are widely used in symbol timing recovery systems to interpolate new sample values at arbitrary points between the existing discrete-time samples This paper presents an efficient way to implement polynomial interpolation filters based on the analysis of constraints which are used for optimization The proposed technique does not require two sub-filters in the well-known Farrow structure, which leads to a very efficient interpolator Implementation examples are included illustrating the efficiency of the proposed method

Efficient implementation of polynomial interpolation filters for full-digital receivers

To account for randomly distributed nodes in a wireless ad hoc network, the transmission capacity is defined as the number of successful transmissions taking place in the network per unit area under an outage constraint. In this paper, we analyze the transmission capacity for dual-hop relaying in a wireless ad hoc network in the presence of both cochannel interference and thermal noise, where interferers are spatially distributed following a Poisson distribution. Specifically, we first present the exact outage probability for amplify-and-forward and decode-and-forward protocols in a Poisson field of interferers without neglecting noise at all nodes. We then derive the transmission capacity of such networks, which determines the maximum allowable density of transmitting nodes for each relay strategy at a specified outage probability and data rate. Numerical results demonstrate that the dual-hop relaying is still beneficial in terms of the transmission capacity in wireless ad hoc Poisson networks.

/pdf/transmission-capacity-for-dual-hop-relaying-in-wireless-ad-1arref7awo.pdf

Transmission capacity for dual-hop relaying in wireless ad hoc networks

We propose a simple and robust carrier frequency recovery (CFR) scheme for DVB-S2 receivers. The proposed coarse CFR scheme employs a modified Mengali and Morelli (M&M) algorithm and recovers a coarse carrier frequency offset (CFO) accurately. After coarse CFR, a fine CFR scheme that employs a simple pilot block correlation algorithm recovers a residual CFO. The proposed scheme shows a bit error rate (BER) performance that is almost the same as the conventional scheme, and reduces the hardware complexity. In addition, when a normalized CFO is larger than 25%, the proposed scheme could achieve carrier synchronization (the conventional scheme might not achieve carrier synchronization).

A simple and robust carrier frequency recovery scheme for DVB-S2 systems

In relating the use of consumer-grade equipment, Carrier Synchronization is a difficult task for DVB-S2 receivers, which have to operate with a large initial Carrier Frequency Offset (CFO) yet needing to achieve relatively high estimation precisions. For these reasons, conventional Carrier Frequency Recovery schemes for DVB-S2 systems need significant hardware complexity. In contrast, this paper proposes a simple and robust CFR scheme for DVB-S2 systems that is able to reduce the hardware complexity without degrading the achievable performances.

http://icact.org/program/full_paper_counter.asp?full_path=/upload/2010/0282/20100282_finalpaper.pdf

Joon Tae Kim

Papers

Opportunistic Decode-and-Forward Relaying with Interferences at Relays

Efficient implementation of polynomial interpolation filters for full-digital receivers

Transmission capacity for dual-hop relaying in wireless ad hoc networks

A simple and robust carrier frequency recovery scheme for DVB-S2 systems

An alternative Carrier frequency Synchronization scheme for DVB-S2 systems