Degrees-Of-Freedom in Multi-Cloud Based Sectored Cellular Networks.

This paper investigates the achievable per-user degrees-of-freedom (DoF) in multi-cloud based sectored hexagonal cellular networks (M-CRAN) at uplink. The network consists of N base stations (BS) and K ≤ N base band unit pools (BBUP), which function as independent cloud centers. The communication between BSs and BBUPs occurs by means of finite-capacity fronthaul links of capacities C F = µ F · 1 2 log ( 1 + P ) with P denoting transmit power. In the system model, BBUPs have limited processing capacity C BBU = µ BBU · 1 2 log ( 1 + P ) . We propose two different achievability schemes based on dividing the network into non-interfering parallelogram and hexagonal clusters, respectively. The minimum number of users in a cluster is determined by the ratio of BBUPs to BSs, r = K / N . Both of the parallelogram and hexagonal schemes are based on practically implementable beamforming and adapt the way of forming clusters to the sectorization of the cells. Proposed coding schemes improve the sum-rate over naive approaches that ignore cell sectorization, both at finite signal-to-noise ratio (SNR) and in the high-SNR limit. We derive a lower bound on per-user DoF which is a function of µ BBU , µ F , and r. We show that cut-set bound are attained for several cases, the achievability gap between lower and cut-set bounds decreases with the inverse of BBUP-BS ratio 1 r for µ F ≤ 2 M irrespective of µ BBU , and that per-user DoF achieved through hexagonal clustering can not exceed the per-user DoF of parallelogram clustering for any value of µ BBU and r as long as µ F ≤ 2 M . Since the achievability gap decreases with inverse of the BBUP-BS ratio for small and moderate fronthaul capacities, the cut-set bound is almost achieved even for small cluster sizes for this range of fronthaul capacities. For higher fronthaul capacities, the achievability gap is not always tight but decreases with processing capacity. However, the cut-set bound, e.g., at 5 M 6 , can be achieved with a moderate clustering size.

Polarization-time coding for PDL mitigation in long-haul PolMux OFDM systems.

In this paper, we present a numerical, theoretical and experimental study on the mitigation of Polarization Dependent Loss (PDL) with Polarization-Time (PT) codes in long-haul coherent optical fiber transmissions using Orthogonal Frequency Division Multiplexing (OFDM). First, we review the scheme of a polarization-multiplexed (PolMux) optical transmission and the 2 × 2 MIMO model of the optical channel with PDL. Second, we introduce the Space-Time (ST) codes originally designed for wireless Rayleigh fading channels, and evaluate their performance, as PT codes, in mitigating PDL through numerical simulations. The obtained behaviors and coding gains are different from those observed on the wireless channel. In particular, the Silver code performs better than the Golden code and the coding gains offered by PT codes and forward-error-correction (FEC) codes aggregate. We investigate the numerical results through a theoretical analysis based on the computation of an upper bound of the error probability of the optical channel with PDL. The derived upper bound yields a design criterion for optimal PDL-mitigating codes. Furthermore, a transmission experiment of PDL-mitigation in a 1,000 km optical fiber link with inline PDL validates the numerical and theoretical findings. The results are shown in terms of Q-factor distributions. The mean Q-factor is improved with PT coding and the variance is also narrowed.

Novel and recurrent mutations in the TAT gene in Tunisian families affected with Richner-Hanhart syndrome.

Tyrosinemia type II, also designated as oculocutaneous tyrosinemia or Richner-Hanhart syndrome (RHS), is a very rare autosomal recessive disorder. In the present study, we report clinical features and molecular genetic investigation of the tyrosine aminotransferase (TAT) gene in two young patients, both born to consanguineous unions between first-degree cousins. These two unrelated families originated from Northern and Southern Tunisia. The clinical diagnosis was based on the observation of several complications related to Richner-Hanhart syndrome: recurrent eye redness, tearing and burning pain, photophobia, bilateral pseudodendritic keratitis, an erythematous and painful focal palmo-plantar hyperkeratosis and a mild delay of mental development. The diagnosis was confirmed by biochemical analysis. Sequencing of the TAT gene revealed the presence of a previously reported missense mutation (c.452G>A, p.Cys151Tyr) in a Tunisian family, and a novel G duplication (c.869dupG, p.Trp291Leufs 6). Early diagnosis of RHS and protein-restricted diet are crucial to reduce the risk and the severity of long-term complications of hypertyrosinemia such as intellectual disability.