No abstract

Abstract-Physical-layer network coding is a high-throughput technique for communicating over the two-way relay channel, which consists of two terminals that communicate exclusively via an intermediate relay. An exchange of messages begins with both terminals transmitting binary data sequences simultaneously to the relay. The relay determines the modulo-2 sum of the sequences, which it modulates and broadcasts to the terminals. Since each terminal knows the information it transmitted, it can determine the information transmitted by the other terminal by subtracting its own information from the broadcast signal. Prior work on the topic of physical-layer network coding has assumed that the signals transmitted by the two terminals arrive at the relay with perfectly aligned phases, permitting coherent reception. In this paper, we relax the assumption of aligned phases and consider noncoherent reception of binary continuous-phase frequency-shift keying signals. A derivation of the relay receiver is given for varying amounts of channel state information, and results are provided showing the error performance of the proposed system without an outer errorcorrecting code and with an outer turbo code.

Biometric recognition, or simply biometrics, is the use of biological attributes such as face, fingerprints or iris in order to recognize an individual in an automated manner. A key application of biometrics is authentication; i.e., using said biological attributes to provide access by verifying the claimed identity of an individual. This paper presents a framework for Biometrics-as-a-Service (BaaS) that performs biometric matching operations in the cloud, while relying on simple and ubiquitous consumer devices such as smartphones. Further, the framework promotes innovation by providing interfaces for a plurality of software developers to upload their matching algorithms to the cloud. When a biometric authentication request is submitted, the system uses a criteria to automatically select an appropriate matching algorithm. Every time a particular algorithm is selected, the corresponding developer is rendered a micropayment. This creates an innovative and competitive ecosystem that benefits both software developers and the consumers. As a case study, we have implemented the following: (a) an ocular recognition system using a mobile web interface providing user access to a biometric authentication service, and (b) a Linux-based virtual machine environment used by software developers for algorithm development and submission.

Abstract-Physical-layer network coding improves the throughput of the two-way relay channel by allowing multiple source terminals to transmit simultaneously to the relay. However, it is generally not feasible to align the phases of the multiple received signals at the relay, which motivates the exploration of noncoherent solutions. In this paper, turbo-coded orthogonal multi-tone frequency-shift keying (FSK) is considered for the two-way relay channel. In contrast with analog network coding, the system considered is an instance of digital network coding; i.e., the relay decodes the network codeword and forwards a re-encoded version. Crucial to noncoherent digital network coding is the implementation of the relay receiver, which is the primary focus of the paper. The relay receiver derived in this paper supports any modulation order that is a power of two, and features the iterative feedback of a priori information from the turbo channel decoder to the demodulator; i.e., it uses bit interleaved coded modulation with iterative decoding (BICM-ID). The performance of the receiver is investigated in Rayeligh fading channels through error-rate simulations and a capacity analysis. Results show that the BICM-ID receiver improves energy efficiency by 0.5-0.9 dB compared to a non-iterative receiver implementation.

Abstract-Digital network coding is a relaying technique that increases throughput in two-way relay networks. In contrast with analog network coding, which relays received analog signals plus noise, digital network coding relays digital codewords. The digital codewords are created by demodulation, channel decoding, and re-encoding at the relay. By using FSK and noncoherent reception, the relay may operate without knowledge of the phases of the signals transmitted by the two source terminals. In this paper, previous work on binary FSK is extended to multi-tone FSK, where the number of tones may be any power of 2. The relay receiver is formulated for any number of tones that is a power of two. Binary FSK is compared against quaternary FSK, which requires no expansion of bandwidth compared with binary FSK. The comparison is made using two metrics: the simulated bit-error rate (both with and without an outer turbo code), and the binary information rate between the sources and relay. The results illustrate that the energy-efficiency advantage of quaternary FSK on a point-to-point link is magnified when it is applied to digital network coding. I. INTRODUCTIONIn a two-way relay channel (TWRC), a pair of source terminals exchange information via a relay. The exchange is performed in two, three, or four time slots, depending on the protocol. When four time slots are used, the first two time slots are for the sources to communicate to the relay and the other two time slots are used for the relay to send each source its intended message. The time slots may be reduced from four to three by consolidating the last two time slots into one through the appropriate use of network coding; i.e., by having the relay broadcast the bitwise sum of the two received source packets. Using the physical-layer network coding (PNC) protocol, the first two slots are combined by having the two terminals transmit at the same time over a multiple-access channel (MAC) [1]. The relay receives the electromagnetic combination of both packets during the first slot, performs processing to compute the network coded information, and broadcasts the network codeword to the two terminals during the second slot.PNC may be implemented in one of two ways: (1) The relay amplifies and forwards the signal received from the sources, without performing demodulation and decoding [2], which is referred to as analog network coding (ANC), or (2) The relay demodulates and decodes the received signal, and then broadcasts its estimate of the network codeword [3], which is referred to as digital network coding (DNC). Under many channel conditions, DNC offers enhanced performance over ANC. The decoding operation at the relay helps DNC remove noise from the MAC phase, while the noise is amplified by the relay when ANC is used. To contrast with DNC, we refer to the three-slot protocol as link-layer network coding (LNC) in this paper.