Performance Evaluation of Variable Bandwidth Channel Allocation Scheme in Multiple Subcarrier Multiple Access

Multiple Subcarrier Multiple Access (MSMA) enables concurrent sensor data streamings from multiple wireless and batteryless sensors using the principle of subcarrier backscatter used extensively in passive RFID. Since the interference cancellation performance of MSMA depends on the Signal to Interference plus Noise Ratio of each subcarrier, the choice of channel allocation scheme is essential. Since the channel allocation is a combinatorial problem, obtaining the true optimal allocation requires a vast amount of examinations which is impracticable in a system where we have tens of sensor RF tags. It is particularly true when we have variable distance and variable bandwidth sensor RF tags. This paper proposes a channel allocation scheme in the variable distance and variable bandwidth MSMA system based on a newly introduced performance index, total contamination power, to prioritize indecision cases. The performance of the proposal is evaluated with existing methods in terms of average communication capacity and system fairness using MATLAB Monte Carlo simulation to reveal its advantage. The accuracy of the simulation is also verified with the result obtained from the brute force method

Concurrent Backscatter Streaming from Batteryless and Wireless Sensor Tags with Multiple Subcarrier Multiple Access

This paper proposes a novel multiple access method that enables concurrent sensor data streaming from multiple batteryless, wireless sensor tags. The access method is a pseudo-FDMA scheme based on the subcarrier backscatter communication principle, which is widely employed in passive RFID and radar systems. Concurrency is realized by assigning a dedicated subcarrier to each sensor tag and letting all sensor tags backscatter simultaneously. Because of the nature of the subcarrier, which is produced by constant rate switching of antenna impedance without any channel filter in the sensor tag, the tag-to-reader link always exhibits harmonics. Thus, it is important to reject harmonics when concurrent data streaming is required. This paper proposes a harmonics rejecting receiver to allow simultaneous multiple subcarrier usage. This paper particularly focuses on analog sensor data streaming which minimizes the functional requirements on the sensor tag and frequency bandwidth. The harmonics rejection receiver is realized by carefully handling group delay and phase delay of the subcarrier envelope and the carrier signal to accurately produce replica of the harmonics by introducing Hilbert and inverse Hilbert transformations. A numerical simulator with Simulink and a hardware implementation with USRP and LabVIEW have been developed. Simulations and experiments reveal that even if the CIR before harmonics rejection is 0dB, the proposed receiver recovers the original sensor data with over 0.98 cross-correlation

普及型ソフトウェア無線を用いたモノパルススイッチングによる電波到来方向検知

著者らは無線通信機能がある携帯端末と複数の受信専用普及型ソフトウェア無線装置(SDR)を組み合わせることで通信相手が発する電波の到来方向を検知するシステムの実現を目指している．搬送波の位相情報を利用し到来方向を検知するためには，複数アンテナで電波を受信し，各アンテナと位相差検知回路の経路上の周波数変換器のクロック及び位相が同一である必要がある．しかし，普及型SDR装置を複数用いる場合，各SDR装置で生じる位相オフセットをキャンセルせねばならない．更に到来方向検知精度の劣化の原因となるマルチパスの対策も講じる必要がある．本論文では，2入力2出力スイッチをアンテナとSDR装置の間に挿入し，入力信号を切り替えて簡単な信号処理で位相オフセットをキャンセルできるモノパルススイッチングを提案し，その有効性を実験で検証し，到来方向検知誤差が3.0°以内で動作することを確認した．マルチパスの対策としては，複素モノパルスとモノパルススイッチングを組み合わせた複素モノパルススイッチングを提案する．複素モノパルス比の複素平面上の位置を確認することで，マルチパスの影響が大きいタイミングを検知・回避できることを実験により示した．The authors target the realization of AoA estimation system by plugging in two commercial off the shelf (COTS) software defined radio (SDR) modules on a mobile terminal. The simultaneous usage of two COTS SDRs suffers from the phase offset occurred in each SDR even after we synchronize the clock. To cancel the phase offset, we propose Monopulse Switching, which produces two sets of phase measurements with a double pole and double throw (DPDT) switch implemented between each antenna and SDR module, in this paper. A simple signal processing of the two sets IQ data cancels the phase offset. The AoA estimation accuracy of Monopulse Switching is evaluated both in wired and wireless environments to reveal we can achieve 3.0 degree accuracy. We also quantify the AoA accuracy degradation stemming from the inevitable multiphase and propose to apply a complex monopulse combined with Monopulse Switching to detect and eliminate the degraded measurements

Bridging UPnP and ZigBee with CoAP: protocol and its performance evaluation

ABSTRACT Incorporation of heterogeneous wireless sensor and actuator networks (WS&AN) is an essential challenge of web based Internet of Things (IoT) architectures. We propose to use UPnP and end-to-end HTTP communication using CoAP to bridge WS&AN and IoT system. UPnP enables automatic discovery of sensor devices which directly connect to a WS&AN via a gateway. Instead of translating WS&AN and UPnP protocols at the gateway, we propose to use CoAP in WS&AN. This provides flexible communications between sensor devices and applications. Drawback of this end-to-end Web based IoT information system is vulnerability to excessive traffics from sensor devices or from the applications because there is no authority to monitor and control traffics in the architecture. We examined the performance of our implementations to find that the transmit performance of a single sensor device could be limited by the serial communications of embedded transceiver. Excessive data requests from applications might also result in the packet loss and wasteful WS&AN congestion. If the traffic is confined within the performance limits, the implemented UPnP and ZigBee bridging using CoAP shows satisfactory performance. We can subscribe up to 16 sensor devices data with 500 msec using simple HTTP POST requests