This letter proposes a simple tracking scheme for time-varying channels of IEEE 802.11 based MIMO-OFDM wireless LANs. The scheme combines a tentative channel estimate derived from a transmitted symbol replica with the channel estimate used to generate the replica. The propose scheme requires no prior knowledge on the statistics of the channel and instead uses a deductive approach to calculate weights to combine the channel estimates. The numerical results show the proposed scheme performs 1.0 dB CNR gain at FER of 10−2 over the conventional scheme for 3 × 3 MIMO and 64QAM when receiver velocity is 4 km/h.
We propose an interstitial coaxial antenna with a choke embedded in the outer conductor and with an arrowhead cap for microwave ablation therapy, operating at 2.45 GHz. The cap consists of ceramic and conductor. The heating is suppressed along both the direction in the tip side and the feeding side of the antenna because of the cap and the choke. In addition, a catheter is not required. We numerically clarify these advantages by analyzing the temperature distribution of a spherical breast tumor.
One of key technologies of 5G mobile networks is introducing small cells to supplement existing macrocells, and this results in heterogeneous networks. In this letter, we investigate criteria for cell association in heterogeneous networks, focusing on performance-oriented and fairness-oriented criteria. Through numerical evaluations, we reveal that employing the fairness-oriented criterion, i.e., maximizing the minimum throughput among users realizes both high throughput of whole networks and fair throughput sharing among users.
This letter proposes a power-controlled coded slotted ALOHA (PC-CSA) for reliable wireless networks. The proposed PC-CSA introduces the concept of the randomization of the transmission power control mechanism in CSA to achieve reliable packet receptions at base stations. We conduct computer simulations and confirm that the proposed PC-CSA can improve the packet loss rate under a predefined time constraint.
With an increasing demand for distributed systems storing big data, locally repairable codes (LRCs) have attracted attentions to recover lost data on failure nodes. An (r, t)-LRC has the property that each coordinate of codewords can be recovered from at most r other coordinates (repair set), and there are at least t disjoint repair sets for each coordinate, where r and t are called locality and availability, respectively. Wang, Zhang, and Lin recently have proposed a construction method of cyclic (r, t)-LRCs that can have high availability with a guaranteed lower bound on the minimum distance. However, due to the lack of flexibility in code design, it is impossible to modify code parameters while keeping the code performance. This letter presents a generalized construction of cyclic (r, t)-LRCs based on the trace function whose high-degree terms are truncated. It is shown that the proposed construction preserves the symbol-repairing performance and therefore provides better flexibility in code design.
Future 5th generation (5G) mobile system is required to accommodate a huge amount of mobile data traffic with different quality of services (QoS) in a large number of devices. To realize 5G system, a new waveform such as generalized frequency division multiplexing (GFDM) has been researched. In this paper, we propose a proportional fair (PF) scheduling method considering the delay budget of users for the coexistence system of GFDM and orthogonal frequency division multiplexing (OFDM). From computer simulation, we show that the proposed method can improve the average delay time for users of small delay budget without large degradation of system throughput.
Our recently proposed interference-aware channel segregation based dynamic channel assignment (IACS-DCA) forms a channel reuse pattern with low co-channel interference (CCI) in a distributed manner. It has been shown by numerical computation that IACS-DCA forms a stable channel reuse pattern. In this paper, we provide convergence analysis of IACS-DCA. The existence of convergent point of channel reuse pattern and the convergence performance of IACS-DCA are discussed.
In order to meet the diversifying demands, we propose the architecture of the software-based virtual EPON-OLT, where all of OLT functions except PHY-Layer are implemented as software running on an x86 server. The EPON-OLT requires not only high throughput, low latency but also accurate controls for the upstream transmission timing of ONUs. In order to satisfy these conditions, we introduced two methods for the virtual OLT: (1) Separation of D-Plane/C-Plane and (2) Smoothing RTT. Evaluation experiments show wire-speed throughput and low latency are achieved when the packet length is short, but simultaneously, a technical issue with long packet transmission.
This letter proposes a transport protocol for millimeter-wave (mm-wave) communications to shorten the time to resume communication after a mm-wave link is reconnected. The proposed method distinguishes whether a retransmission timeout occurs due to a mm-wave disconnection or network congestion. If a TCP sender detects a mm-wave disconnection, the sender keeps its retransmission timer to prevent the retransmission timer from increasing exponentially. We confirm the effectiveness of the proposed method using computer simulations.