MAC isolation to realize effective management in public wireless LAN

This paper describes how to use medium access control (MAC) isolation to enhance management performance in public wireless LAN (PWLAN). To comply with the IEEE 802.11 standards, a scheme to implement MAC isolation in WLAN access points by re-designing the Distribution_Service component of the MAC state machine is proposed. A variable named dotl 1 Isolation is defined to determine whether the MAC level communication between wireless stations in the same BSS is permitted or not. Finally, a design solution based on MPC860 hardware and embedded Linux software for PWLAN access point is specified. The simulation results of MAC isolation for PWLAN show that the proposed scheme is feasible and effective.

MDL-based root-mean-squared delay spread estimation for MIMO OFDM systems

This paper studied the application of minimum description length (MDL) criterion for estimating root-mean-squared (RMS) delay spread (RDS) for MIMO OFDM systems. The analytic relationship between the powers and the correlation matrix of multipath components established the feasibility of the application of the MDL criterion to RDS estimation. The estimator presented both the estimate of instantaneous RDS and the estimates of noise variance, channel power and SNR of current channel with low computational complexity. Given the powers of the estimated multipath components, the MDL criterion was adopted to acquire the number of paths and the time delays of each path of current channel without making eigendecomposition of the correlation matrix normally required by MDL criterion, following which the noise variance and the power of each path can be estimated. The power delay profile (PDP) and RDS of the current channel were achieved. Simulation results showed that the proposed estimator was insensitive to variance of SNR and robust against frequency-selectivity.

A novel technique for wireless optical communications with lenslet array processor

A novel communication technique is proposed, which utilizes a set of mutually distinguishable optical patterns instead of convergent facula to transmit information. Then the capacity is increased by exploiting the optical spatial bandwidth resources. At last, we experimentally demonstrate the proposed communication technique based on four 8 × 8 spatial pattern signals by using lenslet array processor.

20 Mbps wireless communication demonstration using terahertz quantum devices

A wireless terahertz （THz） communication link is demonstrated, in which a THz quantum cascade laser and a THz quantum-well photo-detector （QWP） serve as the emitter and receiver, respectively. With the help of the well-matched THz QWP, the optical collection efficiency has greatly been improved. A data signal transmitted over 2.2 m with a low bit error rate （≤1 × 10^-8） and data rate as high as 20 Mbps is achieved, which are almost 1 order of magnitude higher than that previously reported.

Time domain dispersion of underwater optical wireless communication

A new method to count the expected value and variance of time dispersion is presented for time dispersion of underwater optical wireless communication.Instead of the typically used Gamma distribution,inverseGaussian distribution is suggested for underwater optical impulse response time waveform function.The expectation of this method is in good agreement with experimental data.Future works may include water absorption to the model.

Low power consumption high speed CMOS dual-modulus 15/16 prescaler for optical and wireless communications

Frequency synthesizer is an important part of optical and wireless communication system. Low power comsumption prescaler is one of the most critical unit of frequency synthesizer. For the frequency divider, it must be programmable for channel selection in multi-channel communication systems. A dual-modulus prescaler (DMP) is needed to provide variable division ratios. DMP is considered as a critical power dissipative block since it always operates at full speed. This paper introduces a high speed and low power complementary metal oxide semiconductor (CMOS) 15/16 DMP based on true single-phase-clock (TSPC) and transmission gates (TGs) cell. A conventional TSPC is optimized in terms of devices size, and it is resimulated. The TSPC is used in the synchronous and asynchronous counter. TGs are used in the control logic. The DMP circuit is implemented in 0.18 μm CMOS process. The simulation results are provided. The results show wide operating frequency range from 7.143 MHz to 4.76 GHz and it comsumes 3.625 mW under 1.8 V power supply voltage at 4.76 GHz.

Spread spectrum-based ultraviolet communication with experiments

We report experiments of ultraviolet （UV） communication based on spread-spectrum technique. Field measurements via online UV communication are conducted to compare the system performances with and without spectrum spreading. The results indicate that the spread-spectrum technique is capable of suppressing noise in UV atmospheric scattering channel and therefore improve the system performance evidently. Details of implementation are also provided to make the results useful for similar system design in research on optical wireless communications.

UWB monocycle pulse generation based on optical cross-polarization modulation

A novel all-optical method for ultra-wideband （UWB） monocycle pulses generation based on cross polarization modulation （CPM） effect in highly nonlinear photonic crystal fiber is proposed and demonstrated. Due to the CPM effect between the probe light and the pump pulse, a pair of polarity-reversed Gaussian pulses is produced. After proper differential delay, an UWB monocycle pulse with 84-ps width and the fractional bandwidth of 153% is generated after photodetection.

Indoor multi-robot intelligent coordination based on omni-directional visible light communication

Multi-robot coordination （MRC） is a key challenge for complex artificial intelligence systems, and conventional wireless-communication-based MRC mechanisms that cannot be deployed in radio-frequency-limited environ- ments. In this Letter, we present a promising solution that utilizes indoor omni-directional visible light communication （VLC） technology to realize efficient multi-robot intelligent coordination （MRIC）. The specific design is presented along with the implemental details of a practical MRIC experimental platform. The exper- imental results show that a 50 Mb/s on-off-keying-based omni-directional VLC can be realized with an effective distance of 2.3 m and a bit error rate of 〈10^-6 in the proposed MRIC platform.