This paper presents a multi-mode transmission technique that can increase the T-R distance of UCA OAM systems. The proposed technique uses dual polarized UCA antennas to increase the number of simultaneously transmitable modes at a specific T- R distance by exploiting the two basis of the polarized dipole antenna elements, and further extends the reaching distance of the multi-mode signals by using the inter-mode spreading between the OAM modes belonging to the same polarization domain. Simulation results show that the proposed scheme improves the T-R distances by at least 2 times as much as the conventional scheme in transmitting the same number of OAM modes with the same symbol error rate, and also that the proposed technique can transmit twice as many modes as the conventional method with the SNR loss of less than 3 dB at the same T-R distance.

This paper presents a cellular RF transmitter architecture based on a six-port modulator, and its application in an OFDM environment. This paper shows a possibility to apply RF transmitter based on six-port modulator to an OFDM environment, and also it shows that previous works which were limited to single-carrier transmission can be extended to multi-carrier transmission application. The proposed six-port modulator consists of three hybrid couplers, a Wilkinson power combiner, and CMOS Ron resistor banks, which can be favorably integrated into a 2.4 × 1.8 mm2chip area. It obviates the need for DACs and mixers, which are essential components in conventional RF transmitters. A prototype chip was fabricated using the TSMC 0.13 μm CMOS process. Its performance was evaluated and verified by transmitting OFDM signals following the 3GPP standard at 1.84 GHz carrier with 1.4 MHz bandwidth. The prototype chip achieved EVM of 16.1 % and 14.6 % for QPSK and 16-QAM transmissions, respectively. This is a report implementing a new RF transmitter based on a six-port modulator for multiple subcarriers in an OFDM environment, where I/Q signals have 8.3 equivalent number of bits resolutions, respectively.

This paper proposes a wireless ultra-wide area backhaul network consisting of fixed/mobile access points and a wireless backhaul switch with large scale array antenna for 5G mobile communication. We also consider a hybrid beamforming scheme for wireless ultra-wide area backhaul network. We designed an analog beamformer using the genetic algorithm for sum rate maximization, and conducted channel modeling for the proposed backhaul network by deterministic ray-tracing, which gives low path loss exponent of 3 due to the high position of wireless backhaul switch. In simulation results with zero-forcing (ZF) and maximum ratio transmission (MRT) precoding, we obtained the spectral efficiency over 900 bps/Hz with 99 downlink beams on 3 km radius cell, where 4 streams are supported per beam.

M-LWWF/M-LWDF scheduling schemes have attracted much interest due to their ability to both stabilize queues whenever possible and control delay through parameter selection. However, a good implementation of these schedulers would require a mechanism to minimize the required fraction of the bandwidth while satisfying its stability and delay requirements. To the best of our knowledge, previous works on these scheduling policies did not address the problem of minimizing the bandwidth utilization while satisfying delay constraints. In this paper, we explore the solution of this problem using a joint bandwidth and weight adaptation approach. We characterize the problem solution space for M-LWWF and M-LWDF scheduling, assuming time-varying traffic. We also show that, starting from any point in the solution space, simple dynamic bandwidth and weight updates can surely lead to the convergence to the optimal operation point in this space. Based on these characteristics, we propose a dynamic parameter adaptation algorithm that is able to track the time-varying optimal operation points for dynamic traffic and channel conditions. Simulation results show the efficiency of our proposed algorithm in tracking the optimal operation points in dynamic traffic and channel settings.

This paper designs a distributed Transmission Opportunity (TXOP) adaptation algorithm for IEEE802.11e Enhanced Distributed Channel Access (EDCA). Each node measures its throughput in a window and compares it with a target value. If the measured throughput is higher than the target value, the node reduces its TXOP, otherwise if the measured value is less than the target throughput, the node increases its TXOP. We show that the target throughput can be achieved in a globally stable manner.

In this paper, we propose a QoS tracking algorithm to support different QoS requirements to accommodate delay-sensitive and throughput-sensitive traffics in wireless mesh networks. The proposed scheme is carried out in a totally distributed manner by adjusting the minimum contention window size. Moreover, we investigate whether we can satisfy all QoS requirements in a stable manner through stability analysis. The simulation results show that the proposed algorithm can satisfy both average delay bound and minimum throughput requirements without sacrifice of total system efficiency.

Generalized processor sharing (GPS) service policy is a scheduling algorithm to allocate the bandwidth of a queueing system with multi-class input traffic. Simulating the GPS system in realistic traffic environments requires a large amount of time. Thus, fluid simulation is useful because it requires much less time. We analyze the bandwidth allocation for fluid simulation in GPS servers, in which the traffic into the server is treated as fluid. Three properties which characterize GPS servers with fluid input are discussed. We show that there exists a unique bandwidth allocation with the properties. It is shown that our previously proposed algorithm gives the unique bandwidth allocation and it is equivalent to the well-known Newton-Rapson method. In numerical study, the performance of finding the unique bandwidth allocation based on other known root finding methods is compared with that of our previous algorithm. We also investigate the impact of the length of the unit time on the accuracy of the performance measures.

In this paper, we propose a new connection admission control (CAC) algorithm accommodating various classes of traffic, which can easily be implemented in mobile WiMAX system. The proposed CAC algorithm has three characteristics: first, the variation of air capacity is taken into account by measuring the distribution of modulation and coding scheme (MCS) levels offline; second, we estimate the mean and variance of frame occupancy ratio of each QoS flow based on declared traffic descriptors; and third, the admission region is determined to satisfy the target overflow probability in the bufferless model. Through numerical analysis, we show that the accuracy of the proposed CAC is satisfactory.

We consider a bandwidth optimization problem in a Generalized Processor Sharing servers with multiple class queues to minimize the total bandwidth such that QoS requirements for each class queue are satisfied. In our previous paper [13], since it is difficult to obtain the performance such as the delay distribution mathematically with self-similar input traffic in a GPS server, we obtained an optimized bandwidth vector using a simulation-based optimization technique. However, the previous optimization algorithm requires rather long simulation time to solve the problem by using exterior penalty function methods. We propose a new bandwidth optimization algorithm based on bandwidth ratio adjustment without complex calculations. In numerical results, the required time to find the optimal bandwidth allocation in GPS servers is greatly reduced.

Bandwidth optimization is considered when several classes of Internet traffic are served in generalized processor sharing (GPS) servers. Internet traffic shows self-similar patterns that make it difficult to obtain analytical performance in GPS. Thus, for performance estimation of different classes of traffic, we use fluid simulation techniques that can reduce the simulation complexity, compared to packet-level simulation. Using the relationship between the guaranteed bandwidth vector and the corresponding performance, we propose a bandwidth optimization problem to minimize the total bandwidth such that performance requirements are satisfied. We use an exterior penalty function method to solve the optimization problem. However, a penalized objective function may have local minimum which is not a global minimum. Thus, we propose a new methodology to circumvent the limitation of the exterior penalty function method.