Due to the reuse factor reduction, the same frequencies are reused in adjacent neighboring cells, which causes an attendant increase in co-channel interference (CCI). CCI has already become the limiting factor in the performance of orthogonal frequency division multiplexing (OFDM) based cellular systems. Joint maximum likelihood sequence estimation (JMLSE) based interference cancellation algorithms have been under intense research. However, despite the fact that the error probability of JMLSE is critical for analyzing the performance, to the best of our knowledge, the mathematical expression has not been derived for MQAM-OFDM yet. Direct computation of the error probability involves integrating a multi-dimensional Gaussian distribution that has no closed-form solution. Therefore, an alternative way is to upper and lower bound the error probability with computable quantities. In this paper, firstly, both the upper and the conventional lower error probability bounds of JMLSE are derived for MQAM-OFDM systems based on a genie-aided receiver. Secondly, in order to reduce the gap between the conventional lower bound and the simulation results, a tighter lower bound is derived by replacing the genie with a less generous one. Thirdly, those derived error probability bounds are generalized to the receiver diversity scheme. These error probability bounds are important new analytical results that can be used to provide rapid and accurate estimation of the BER performance over any MQAM scheme and an arbitrary number of interferers and receive antennas.

Over 100 Gbit/s/ch high-speed optical transmission is required to achieve the high capacity networks that can meet future demands. The coherent receiver, which is expected to yield high frequency utilization, is a promising means of achieving such high-speed transmission. However, it requires a high-speed Analog to Digital Converter (ADC) because the received signal bandwidth would be over several tens or hundreds of GHz. To solve this problem, we propose a band-divided receiver structure for wideband optical signals. In the receiver, received wideband signals are divided into a number of narrow band signals without any guard band. We develop a band-divided receiver prototype and evaluate it in an experiment. In addition, we develop a real-time OFDM demodulator on an FPGA board that implements 1.5 GS/s ADCs. We demonstrate that the band-divided receiver prototype with its real-time OFDM demodulator and 1.5 GS/s ADC can demodulate single polarization 12 Gbit/s OFDM signals in real-time.

This study demonstrates the ability of a portable X-band Doppler weather radar (XDR) to measure Doppler velocity (Vd). Existing portable X-band weather radars are housed in a container and hence have to be carried by a truck. Therefore they have limitations in their installation places. For installations at small areas where the existing X-band weather radars cannot be installed (e.g., rooftop area of small building), XDR is designed to be carried by a cart. Components of the outdoor unit (a parabolic antenna with a diameter of 1.2 m, magnetron transmitter, and radio frequency (RF) and intermediate frequency (IF) analog components) are housed in a compact body with a weight less than 300 kg. The radar operation, IF digital processing, and data storage are carried out by a desktop computer having a commercial IF digital receiver. In order to attain the required portability and reduced purchase and running costs, XDR uses a magnetron transmitter. Because XDR is the first that utilizes an IF digital receiver for the signal processing specific to magnetron transmitters (i.e., the phase correction of received signals due to the randomness of the transmitted pulse phase), Vd measured by XDR (hereafter VdXDR) was assessed. Using the dataset collected from 25 to 26 October 2009 at the Shigaraki MU Observatory (3451'N, 13606'E), the equivalent radar reflectivity factor (Ze) and VdXDR were assessed using Ze and Vd measured by a Micro Rain Radar and a L-band Doppler radar named LQ-7. The results using correlation coefficients and regression lines demonstrate that XDR measured Ze and Vd accurately. The results also show that IF digital receivers are useful for providing magnetron weather radars with the function of Vd measurement, and further suggest that a combination of IF digital receiver and magnetron transmitter contributes to future development of Doppler weather radars, because high cost performance is strongly required for a precipitation monitoring radar network.

Due to the reuse factor reduction, the attendant increase in co-channel interference (CCI) becomes the limiting factor in the performance of the orthogonal frequency division multiplexing (OFDM) based cellular systems. In the previous work, we proposed the least mean square-blind joint maximum likelihood sequence estimation (LMS-BJMLSE) algorithm, which is effective for CCI cancellation in OFDM systems with only one receive antenna. However, LMS-BJMLSE requires a long training sequence (TS) for channel estimation, which reduces the transmission efficiency. In this paper, we propose a subcarrier identification and interpolation algorithm, in which the subcarriers are divided into groups based on the coherence bandwidth, and the slowest converging subcarrier in each group is identified by exploiting the correlation between the mean-square error (MSE) produced by LMS and the mean-square deviation (MSD) of the desired channel estimate. The identified poor channel estimate is replaced by the interpolation result using the adjacent subcarriers' channel estimates. Simulation results demonstrate that the proposed algorithm can reduce the required training sequence dramatically for both the cases of single interference and dual interference. We also generalize LMS-BJMLSE from single antenna to receiver diversity, which is shown to provide a huge improvement.

A differential input non-coherent BPSK receiver for the UWB-IR communication, based on threshold detection, has been presented in this paper. The chip can recover BPSK modulated Gaussian monocycle pulses (GMP), along with its first derivative, at a data rate of 500 Mb/s. No clock reception is required, as the receiver recovers data based on the relative phase of the two simultaneously received inputs. While retrieving the data, it consumes a power of 63 mW from a supply voltage of 1.8 V. A shunt-peaked narrow band amplifier, matched to the input antenna, is used to amplify the received GMP. Wireless data have been successfully recovered using a pair of horn antennas at a distance of 6 cm. The chip, developed in a 180 nm CMOS technology, occupies a die area of 3.4 mm2. The receiver is suitable for the non-coherent (self-synchronized) UWB-IR communication.

As a future passive optical network (PON) system, the 10 Gigabit Ethernet PON (10G-EPON) has been standardized in IEEE 802.3av. As conventional Gigabit Ethernet PON (GE-PON) systems have already been widely deployed, 1G/10G co-existence technologies are strongly required for the next system. A gated voltage-controlled-oscillator (G-VCO)-based 10-Gb/s burst-mode clock and data recovery (CDR) circuit is presented for a 1G/10G co-existence PON system. It employs two new circuits to improve jitter transfer and provide tolerance to 1G/10G operation. An injection-controlled jitter-reduction circuit reduces output-clock jitter by 7 dB from 200-MHz input data jitter while keeping a short lock time of 20 ns. A frequency-variation compensation circuit reduces frequency mismatch among the three VCOs on the chip and offers large tolerance to consecutive identical digits. With the compensation, the proposed CDR circuit can employ multi VCOs, which provide tolerance to the 1G/10G co-existence situation. It achieves error-free (bit-error rate < 10-12) operation for 10-G bursts following bursts of other rates, obviously including 1G bursts. It also provides tolerance to a 256-bit sequence without a transition in the data, which is more than enough tolerance for 65-bit CIDs in the 64B/66B code of 10 Gigabit Ethernet.

We fabricated a p-i-n photodiode (PD) with an integrated microlens, and demonstrated its high performance capabilities including high speed (35 GHz), high responsivity (0.8 A/W), and large misalignment tolerance (26 µm), and an error-free 25-Gbit/s 10-km single-mode fiber transmission by using a 100-Gbit/s Ethernet quadplexer receiver module with the PDs.

The distribution of streaming multicast and real time audio/video applications in the Internet has been quickly increased in the Internet. Commonly, these applications rarely use congestion control and do not fairly share provided network capacity with TCP-based applications such as HTTP, FTP and emails. Therefore, Internet communities will be threatened by the increase of non-TCP-based applications that likely cause a significant increase of traffics congestion and starvation. This paper proposes a set of mechanisms, such as providing various data rates, background traffics, and various scenarios, to act friendly with TCP when sending multicast traffics. By using 8 scenarios of simulations, we use 6 layered multicast transmissions with background traffic Pareto with the shape factor 1.5 to evaluate performance metrics such as throughput, delay/latency, jitter, TCP friendliness, packet loss ratio, and convergence time. Our study shows that non TCP traffics behave fairly and respectful of the co-existent TCP-based applications that run on shared link transmissions even with background traffic. Another result shows that the simulation has low values on throughput, vary in jitter (0-10 ms), and packet loss ratio > 3%. It was also difficult to reach convergence time quickly when involving only non TCP traffics.

The need for efficient movement and precise location of robots in intelligent robot control systems within complex buildings is becoming increasingly important. This paper proposes an indoor positioning and communication platform using Fluorescent Light Communication (FLC) employing a newly developed nine-channel receiver, and discusses a new location estimation method using FLC, that involves a simulation model and coordinate calculation formulae. A series of experiments is performed. Distance errors of less than 25 cm are achieved. The enhanced FLC system yields benefits such as greater precision and ease of use.

The authors focus on the improvement of Visible Light Communication Identification (VLID) system that provides positioning information via LED light bulb, which is a part of Visible Light Communication (VLC) system. The conventional VLID system provides very low positioning estimation accuracy at room level. In our approach, neither additional infrastructure nor modification is required on the transmitter side. On the receiver side, 6-axis sensor is embedded to provide 3-axis of Azimuth and 3-axis of Tilt angulations information to perform positioning estimation. We verify the proposed system characteristics by making both empirical and numerical analysis, to confirm the effectiveness of proposed system. We define two words to justify the characteristic of the proposed system, which are Field-of-View (FOV: ψc) Limit and Sensitivity (RXS) Limit. Both FOV and Sensitivity Limits have crucial impact on positioning estimation accuracy. Intuitively, higher positioning accuracy can be achieved with smaller FOV configuration in any system that has FOV. Conversely, based on system characteristics of VLID, we propose a positioning estimation scheme, namely Switching Estimated Receiver Position (SwERP) yields high accuracy even with wide FOV configuration. Cumulative Distribution Function (CDF) of error distance and Root Mean Square of Error Distance (RMSED) between experimental positions and estimated receiver positions are used to indicate the system performance. We collected 440 samples from 3 receivers' FOV configurations altogether 1320 samples within the experimental area of 1200 mm5000 mm2050 mm. The results show that with the proposed scheme, the achievable RMSEDs are in the range of 298 and 463 mm under different FOV configurations, which attained the maximum accuracy improvement over 80% comparing to the one without positioning estimation scheme. The proposed system's achievable accuracy does not depend on transmitters' orientation; only one transmitter is required to perform positioning estimation.

In this paper, we propose a genetic algorithm (GA) based equalization approach for direct sequence ultra-wideband (DS-UWB) wireless communication systems, where the GA is combined with a RAKE receiver to combat the inter-symbol interference (ISI) due to the frequency selective nature of UWB channels for high data rate transmission. The proposed GA based equalizer outperforms significantly the RAKE and the RAKE-minimum mean square error (MMSE) receivers according to results obtained from intensive simulation work. The RAKE-GA receiver also provides bit-error-rate (BER) performance very close to that of the optimal RAKE-maximum likelihood detection (MLD) approach, while offering a much lower computational complexity.

In the conventional multi-input multi-output (MIMO) communication systems, most of the antenna selection methods considered are suitable only for spatially separated uni-polarized system under Rayleigh fading channel in non-line of sight (NLOS) condition. There have a few antenna selection schemes for the cross-polarized system in LOS condition and Ricean fading channel, and no antenna selection scheme for the MIMO channel with both LOS and NLOS. In the practical MIMO channel case, influence of LOS and NLOS conditions in the channel can vary from time to time according to the channel parameters and user movement in the system. Based on these influences and channel condition, uni-polarized system may outperform a cross-polarized. Thus, we should consider this kind of practical MIMO channel environment when developing the antenna selection scheme. Moreover, no research work has been done on reducing the complexity of antenna selection for this kind of practical MIMO channel environment. In this paper, reduced complexity in antenna selection is proposed to give the higher throughput in the practical MIMO channel environment. In the proposed scheme, suitable polarized antennas are selected based on the calculation of singular value decomposition (SVD) of channel matrix and then adaptive bit loading is applied. Simulation results show that throughput of the system can be improved under the constraint of target BER and total transmit power of the MIMO system.

TR-UWB (Transmitted Reference-Ultra Wide Band) systems have low system complexity since they transmit data with the corresponding reference signals and demodulate the data through correlation using these received signals. However, the BER (Bit Error Rate) performance in the conventional TR-UWB systems is sensitive to the SNR (Signal-to-Noise Ratio) of the reference templates used in the correlator. We propose an improved recursive transceiver structure that effectively minimizes the BER for TR-UWB systems by increasing the SNR of reference templates.

In this letter, a derivative constraint minimum output energy (MOE) receiver is proposed the offers enhanced robustness against carrier frequency offset (CFO). A theoretical analysis of the output signal-to-interference-plus-noise ratio (SINR) is presented to confirm its efficacy. Numerical results demonstrate that the proposed receiver basically offers the same performance as an optimal receiver with no CFO present.

Transmission power control (TPC) is an important aspects of underlay transmission in the cognitive radio (CR) networks since it is able to avoid the extra interference from secondary transmission which can let the CR user coexist with the primary systems around. However, due to the different coverage of the primary signal and CR signal, combined with the complexity of the wireless communication, the scanning CR transmitter may not detect the existence of the primary systems. It will cause inaccurate TPC which will severely disrupt the primary service. In this letter, we propose a dynamic neighbor coordinated power control scheme that can avoid the misdetection of the primary signal and provide relatively accurate TPC related distance estimation. Simulation results show that the proposed scheme greatly reduces interference to the primary systems while enhancing overall CR network throughput.

Low noise terahertz (THz) receivers based on superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixers have been designed, fabricated and measured for applications in astronomy and cosmology. The NbN HEB mixer consists of a planar antenna and an NbN bridge connecting across the antenna's inner terminals on a high-resistivity Si substrate. To eliminate the influence of direct detection and instability of the local oscillation (LO) power, a wire grid has been used to change the input LO power for compensating the shift of bias current during Y-factor measurement. The double sideband (DSB) receiver noise temperatures at 4.2 K without corrections have been measured from 0.65 to 3.1 THz. The excess quantum noise factor β of about 4 has been obtained, which agrees well with the calculated value. Allan variance of the HEB has been characterized, and Allan time TA longer than 0.4 s is obtained. We also estimated the temperature resolution of the HEB from the Allan variance and obtained the minimum temperature resolution of 1.1 K using a Gunn oscillator with its multipliers at 0.65 THz as an LO source.

This paper proposes a novel system called the cyclic prefix reconstructable time domain synchronous orthogonal frequency division multiplexing ( CPR-TDS-OFDM ) system, which uses a new frame structure and restores the cyclicity of the received OFDM block with low complexity. Simulation results show that the CPR-TDS-OFDM system outperforms the conventional TDS-OFDM system in high-speed fading channels.

In this paper, a 10-Gb/s CMOS optical receiver analog front-end is designed and implemented in 0.13-µm CMOS technology. An optical receiver analog front-end includes a pre-amplifier and a post amplifier. To ensure 10-Gb/s operation, the effect of inherent photodiode parasitic capacitance should be suppressed. Thus, an advanced common-gate stage is exploited as the input stage of pre amplifier. To enhance the bandwidth without a passive inductor, a new post amplifier with active feedback and negative capacitance compensation techniques is proposed. A prototype chip has 98-dBΩ of trans-impedance gain (ZT), corresponding 40-dB input dynamic range (5-µA to 500-µA) and minimum allowable input current (5-µA). Also, the receiver achieves the bandwidth of 7.5-GHz for 0.25-pF photodiode parasitic capacitance, and the measured optical sensitivity equals -18-dBm for 10-12 bit error rate (BER).

Recent advanced technology makes digital circuits small and the number of digital functional blocks that can be integrated on a single chip is increasing rapidly. On the other hand, reduction in the size of analog circuits has been insufficient. This means that the analog circuit area is relatively large, and reducing analog circuit area can be effective to make a low cost radio receiver. In this paper, a new wireless receiver architecture that occupies small analog area is proposed, and measured results of the core analog blocks are described. To reduce the analog area, a balanced 3-phase analog system is adopted and the functions of analog baseband filters and VGAs are moved to the digital domain. The test chip consists of a 3-phase downconverter and a 3-phase ADC. There is no analog baseband filter on the chip and the analog filter is assumed to be replaced with a digital filter. The downconverter and ADC occupy 0.28 mm2. The measured results show the possibility that the requirements for IMT-2000 are fulfilled even with a small chip area.

Due to the importance of maintaining the orthogonality among subcarriers, the estimation of carrier frequency offset (CFO) is a crucial issue in orthogonal frequency division multiplexing (OFDM) systems. The CFO estimation becomes complicated in OFDM direct-conversion receivers (DCRs), where additional analog impairments such as I/Q imbalance and time-varying DC offset (TV-DCO) exist. In this paper, we propose a novel joint estimation method for CFO and I/Q imbalance in the presence of TV-DCO. By using the linear property of the TV-DCO and employing a periodic pilot sequence, the desired estimates can be obtained in closed-form. Simulation results confirm the validity of the proposed method.